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XIV. SUGAR AGROINDUSTRY DIVERSIFICATION

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CO-GENERATION IN THE SUGAR INDUSTRY

Mario Muñoz

INTRODUCTION Co-generation has had sustainable evolution and development in sugar mills in Guatemala; this impulse has sprouted due to the secondary generation of a subproduct that came from being a waste product to being biomass in abundant quantities, with an exploitable heat value that converted it into a good fuel: Bagasse. With the burning of bagasse as a fuel in the boilers, steam production was produced and maintained, especially since it provides the necessary energy to move most of the equipment in a sugar mill, as well as for being used in all sugar production processes. As a result of the need to increase such steam production, co-generating sugar mills have been developing their technology; so they went from one-stage turbines to multistage turbines; the former are used as simple power transmitters to equipment such as mills, whereas the latter are connected to electric power generators. With this change, sugar mills became electric power co-generators, since they are producing steam for electric power generation and are then using the surplus energy from such steam for the processes involved in the production of sugar, all of this from a single fuel source. , Co-generation has grown even more, by taking advantage of the improvement in the country’s laws. The new laws have promoted and liberated the generation, transportation, and distribution of electrical power. This also gave the sugar mills an incentive to increase the quantity of sugarcane they were milling, in order to optimize the consumption of steam in the factories and to raise their electric power availability through more efficient turbogenerators with larger capacities. The processes associated to co-generation in sugar mills illustrated in this chapter, are conceptually the same or very similar. However, each co-generating sugar mill has a different arrangement; each sugar mill has its own way of managing its operations, from the management and treatment of the bagasse itself, going through the generation of steam and electric power, to the use of the steam that comes out from the sugar factory. The energy balances from each process and each co-generator are different.

Industrial-Mechanical Engineer, Energy Efficiency Professional from CENGICAÑA. www.cengicana.org

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Currently, resources have begun to limit co-generation. However, in the country’s electrical power market, the demand for more cleaned electrical power surpasses the offer; and therefore, sugar mills are facing two challenges: First, investing and growing in the electrical power generation market together with other fuels, such as mineral coal. Second, optimizing and improving their co-generation processes by improving their internal energy efficiency and the use of the bagasse as fuel efficiency. This section presents a brief summary of the history of the development of co-generators, the efficiency indexes, the benefits, and the processes involved in this form of energy management.

BACKGROUND Some industries, like sugar mills in Guatemala, have been generating their own electrical power for a little over 70 years, with the purpose of satisfying their internal energy needs for the production of sugar. Initially, the generation of electrical power was for local use only, and it was limited to satisfying the kinetic energy demands of the juice extraction equipment, such as shredders and mills, whose main moving force was the steam produced by boilers. The second fundamental energy demand was made by the factory processes, known as treatment, processing, and cooking of the juice and syrups, such as evaporation, heating, and crystallization. To meet this second energy demand, the so called “exhaust” steam was used; that is, steam that has already given part of its energy in a first process (i.e. moving a turbine) but it still has enough energy at a lower pressure and temperature to still be used in other processes. This, to some, is the definition of co-generation. The reason for this statement comes from the fact that the source of the exhaust steam was the discharge of the extraction equipment that used the kinetic energy found in the main steam for a first phase. This means that the main steam used by the juice extraction equipment, is the same that is later used in the sugar production process, except with less energy, lower pressure, and lower temperature. Such energy is almost depleted by the extraction equipment, and whatever remains in the exhaust steam is the doubled used energy. Co-generating sugar mills have been investing in larger turbines connected to the electric power generators due to the increase in the amount of milled sugarcane. This brought about, not only a growth in the size of the factories but an optimization in the sugar production process, as well. Electrical power was thus produced and during harvest season, the sugar mills were able to disconnect themselves from the national electrical power network. This is

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translated into significant energy savings for the country. The turbines also discharge exhaust steam, and therefore, the availability of the thermal energy needed within the factory for sugar production, was maintained. The next step taken by some co-generating sugar mills has been the change from steam power to electrical power for the equipment used in the juice extraction processes (shredders and mills). As a result, the use of energy is much more efficient for the main steam flow, since the previously used to move the shredders and mills, is now exclusively used to move turbogenerators. These, in turn, produce electrical power, making the whole operation of extraction and other much more efficient processes. With this strategy, sugar mills have been able to co-generate, at the same time, and sequentially, main energy and exhaust energy, both thermal and electrical. The production of these forms of energy has been attained with the burning of a single fuel in the boilers, the bagasse. Bagasse is a sub-product of the sugarcane milling. It comes from the cane in the form of fiber that can not be used in the extraction of sugar. Along history, sugar mills have made tremendous efforts to efficiently burn bagasse so as to obtain ever more surpluses and so, produce more electrical energy. Those who have reached this goal, generate all the thermal and electrical energy they need for themselves, and sell part of the excess to the national electrical network. This has allowed sugar mills to contribute to the country’s ever increasing electrical power demand. Additionally, co-generation in sugar mills has represented a positive factor to the environment. The argument is that the use of a “non-fossil” fuel has decreased the amount of green house gases discharged into the air.

BASIC CONCEPT There isn’t just one definition for co-generation. Various authors consider it a technique while others say it is a process or system. From an energy point of view, co-generation is defined as follows: Co-generation is a technique employed for the sequential production of energy, generally thermal and electrical, from a single source of energy. However, co-generation can be viewed as an integral process and not as a technique: It is a process by which a heat discharge from a process is converted into an energy source for another later conversion process.

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In co-generation systems (Figure 1), primary processes and secondary processes of energy use, are given simultaneously and sequentially; the energy that is transformed can be electrical, mechanical, or thermal, in nature. This last one usually comes in the form of heat, even though the concept can also apply to cold. All these types of energy are always produced from the combustion of a single fuel.

Figure 1. Co-generation system with simultaneous and sequential production of

thermal and electrical energy The basic idea in co-generation is to raise the overall yield by integrating two energetic systems, generally, electric with thermal power. As a result, the combined system gives more efficiency and lower costs than developing the operation of each energy resource, separately. Types of Co-Generation If the energy at first produced, is used but it releases heat that will later be used as process heat, then it is called a head process or topping. If the heat discharge from an industrial process is used in a second process to generate energy, then we have a tail or bottoming configuration.

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Head Co-Generation Cycle: In this cycle, electrical energy is produced first; steam turbines, gas turbines, or diesel engines are used to generate the electrical energy and then the heat given off is used in some later industrial process. Examples of processes using this discharge heat include evaporators and cooker, or any other equipment using thermal energy. It is the most widely used system in the sugar industry. If steam turbines are used, then both, the exhaust gases from the boilers as well as the steam discharged by the turbines, become sources of heat for other processes. Tail Cycle Co-generation: This is a thermal cycle. Its goal is to recover heat from an industrial process so as to produce electrical energy with it later. This type of cycle requires steam at a specific pressure and termperature, for an adequate operation of turbogenerators that generate electrical energy. This process is not useful in co-generating sugar mills. Necessary Characteristics for Co-generation In principle, any process with an important heat and electricity demand is a possible co-generator. However, in general terms, it can be established that potential generators must meet some of the following characteristics: Produce important heat surpluses, either from the hot gases coming from

the boiler combustion, or as low pressure exhaust steam coming from the turbine discharge.

To have a very cheap fuel, with continuous supply, stable and uniform. In fact, the higher the difference between the price of the fuel and the price of electricity, the greater the financial or economic benefit from implementing a co-generation system.

The industrial process involved must be continuous; otherwise, the co-produced energy would be lost.

CO-GENERATION IN THE SUGAR INDUSTRY Co-generation in the sugar industry is subject for a legal framework, supported by the General Law of Electricity. Legal Framework1 The General Law of Electricity of Guatemala establishes that the generation of electricity is a free market that requires no previous authorization from the

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State. Article 8 of the same legal body establishes that the installation of electrical power generation centrals is open to anyone. The generation, transportation, and distribution process of electrical energy in Guatemala had been regulated by the Law of the National Electrification Institute [INDE, for its acronym in Spanish] Legistlative Decree Number 1287 from March 27, 1959. It established the mechanisms to go into the electricity business, and it was the Executive Council, the organism in charge of proposing the fares to be charged. This institution was created as a de-centralized State entity with operating autonomy, legal status, private funds, and full capacity to acquire rights and contract obligations within its competency realm. The electrical energy business had been managed by way of the State (through INDE, Empresa Elécrica de Guatemala [EEGSA, for its acronym in Spanish], and municipal electrical energy enterprises); the Guatemalan Constitution has established for many years (article No. 129) that private sector can participate in the production of electricity. In the last years, the national economy has experimented a series of changes, framed within the globalization process and the structural adjustment propelled by the international financial organisms, which has promoted economic modernization. This aspect has been manifested by a higher liberalization towards the international market and a restructuring of the State, in terms of higher participation of private agents and under the outline of a free market. The idea that the State has to relegate (subsidize) the productive activities that the private sector cannot fulfill has become fundamental. It has motivated an order, which in the case of the electrical sub-sector has materialized in the form of concrete legal proposals. It is directly allowing a free market in this sub-sector. Within the electrical energy sub-sector framework briefly outlined above, the free market process began. The first step was to name a Multi-sector Committee that would take care of proposing integral solutions to the problems produced by the upcoming General Law of Electricity. Some of the most important conclusions produced by the Committee were: a) Create a free market for the electrical energy sub-sector. b) Establish the necessary mechanisms, so that the participating agents would

do so without political interference. c) Guarantee that the agents participating in any of the operations of the

service (generation, transmission, distribution, and marketing) do so in conditions of equality.

d) Revise the legislation and structure of the public enterprises of the sub-sector.

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e) Guarantee the rational use of renewable and non-renewable natural resources.

f) Promote the use of alternative sources of energy for the generation of electricity.

g) Revise the energy distribution structure and promote competition and reconversion of the companies in charge of distribution, as well as to promote participations of new companies.

h) Establish the mechanisms for the sale of stocks and any other process that allows the optimization of resources owned by the Guatemalan Electric Company [EEGSA, for its acronym in Spanish].

i) All the electric companies will have autonomy to manage the production, acquisition, and distribution of electricity.

j) Make the necessary changes to the existing legislation, so that each company can set their own prices.

Law to Promote the Development of New and Renewable Sources of Energy: The General Law of Electricity constitutes the framework for every activity dedicated to any part of the process (generation, transmission, distribution, and marketing). It is important to point out that where the process of co-generation itself is concerned, there is the existence of this law (Law-Decree No. 20-86). It has as its fundamental purpose, to promote the exploitation for new and renewable sources of energy, non-conventional sources and new sources of energy in the country. It establishes incentives and legal advantages for the activities involving one or more of the following fields: Research, experimenting, education, training, promoting, diffusing, production, and the manufacturing of specific equipment. The use of new and renewable resources of energy and the marketing of products obtained from theses activities, are defined as “those such as solar radiation, wind, ocean tides, water, geothermal, biomass, and any other energy source that is not nuclear or that is produced by hydrocarbons and its derivates” (Article 7). Flow of Energy in Co-Generation In a typical co-generation plant, the main production of steam is made in the boilers. A water tube boiler constantly receives hot condensates from the evaporation process; the evaporators produce the condensate after using the exhaust steam and they return it to the boiler again. The condensate evaporates only if it receives heat transfer by radiation and convection supplied by the combustion of bagasse. Simultaneously, bagasse (fuel) will not burn unless there’s enough ventilation with air from the atmosphere flowing into the burner. Most modern facilities nowadays pre-heat the air flowing into the combustion chamber with the chimney gases from the boiler. This maintains an adequate turbulence and a bagasse bed that favors complete combustion.

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Bagasse is a fuel obtained from the extraction process of sugarcane, meaning that the efficiency in the boiler will depend on the stability of the milling and the industrial processes. Two other energy flows generated from the boiler: On the one side, we have the steam produced that will later be used by the turbines; and on the other, the energy lost in the chimney gases, which represent the entropy in this process and which are expelled into the atmosphere. Even though, the boiler gases are sometimes used to pre-heat the condensates and the combustion air, they still carry with them an energy surplus that will not be completely used. The turbogenerator uses all the energy contained in the steam when it converts its enthalpy into electrical energy. This electrical energy is used to cover the demand from the industrial process, the boiler needs, and the turbine itself. The electrical energy surplus leaves the system towards the national electric network and the exhaust steam from the turbine, with less pressure and temperature, goes into the industrial process again to be reused, and then, condensated so it can go back to the boiler and begin the cycle again. Figure 2 illustrates the flow of the necessary energy inputs for the co-generation of thermal and electrical energy.

Figure 2. Flow of energy in a co-generating sugar mill

Offer and Demand in the Energy Market In practice, the amount of energy that can be produced and co-produced by each sugar mill varies according the capacity of each one has. This has been an incentive for growth and for investments in the future. At first, sugar mills

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fixed their interests in the possibility of increasing their energy production purely for self-consumption, thinking to limit their investments in order to make their processes more efficient and to increase their in-factory electricity availability. Nowadays, the focus is on growing as electrical energy suppliers. Figure 3 shows how generation has grown in the co-generating sugar mills in the last ten harvesting seasons. They have been favored by the new laws and by the general increase in the energy demand in the country.

 

Figure 3. Generation growth of sugar mill co-generators Bagasse is considered biomass, acording to the statistics report of the Wholesale Market Manager of Guatemala [AMM for its acronym in Spanish]; the internal electrical energy generation of the country at the end of 2010 was of 7,913.91 GW; around 11.8 per cent of this energy was co-produced from biomass. Figure 4, shows the annual contribution made to the electrical energy need of the country by the sugar mills through co-generation in the year 2010.

Figure 4. Electrical energy production in Guatemala in 2010 (% of the total of

GW)

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PROCESSES Co-Generation Cycles The co-generation processes or cycles that use steam turbines and are more widely used in the sugar industry are those of condensation and counterpressure. The first is the most conventional, the second is the most efficient and modern, but it needs steam at higher pressure and temperature (i.e. >600 psig y 700 °F). Besides these two processes, there is a third one currently in the demonstration and experimentation phase: It is the combined cycle with the gasification of bagasse. There is no documentation proving the use of this process in Guatemala. Counterpressure cycle: These processes get their name because of the steam turbine that moves the generator of electrical energy. The steam that enters a counterpressure turbine, whether it be high pressure or low pressure steam, transforms its enthalpy into kinetic energy, transmitting it into an electrical energy generator. The steam in the turbine slowly loses pressure and temperature with every stage in the turbine it passes. These machines are so efficient that steam never reaches the exhaust, that is to say, its pressure and temperature are exhausted in the turbine; the steam is extracted by other means, most frequently vacuum pumps. The steam then passes on to a condensator, where it cools down and condensates; then it is driven to the beginning of the cycle to be turned into the steam that goes into the turbine again therefore, constituting a closed cycle. However, co-generation doesn’t exist in this disposition; therefore steam extractions are placed at each of the stages in the turbine so that the different pressures and temperatures of this steam can be used in the industrial processes. Steam in the turbine gives off enthalpy and produces work, which is used to generate electrical energy, which in turn is used for the industrial plant’s equipment and to be sold to the national electric network. This type of cycle has an advantage for an industrial process not requiring exhaust steam. If this is the case, extractions from the turbines can be closed and all the steam can go to condensation; in this way everything is focused on generating electrical energy, by means, the turbine can be a dual cycle turbine co-generating both, during and and after harvest season. Figure 5 illustrates the most commonplace co-generation cycles.

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Figure 5. Industrial plant operating with both co-generation cycles

Production of Thermal Energy Primary thermal energy is part of the main line steam; water is heated, evaporated, and generally taken to a superheated temperature, with pressure and temperature surpluses; this steam is geared toward the turbines, where it gives up enthalpy and makes its work. Fuels Used: One of the basic conditions for co-generation is that only one type of fuel must be present in the following processes: generation, delivery, and utilization of energy, both thermal and electrical. In the case of the co-generators from the Guatemalan Sugar Agroindustry, bagasse is the most often and widely used. Bagasse constitutes the surpluss biomass from the milling of sugarcane. Bagasse is a fibrous cellulose compound with a dry biomass heating value of 19,868.51 KJ/kg and a wet biomass (51%) heating value of 7,887.50 KJ/kg. Table 1 shows the typical chemical composition of cane bagasse. Table 1. Typical components of bagasse

Compuesto % Carbon 23.52

Hydrogen 3.47 Oxigen 22.03 Ashes 1.49

Humidity (water) 49.5

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Sugarcane bagasse has three fundamental physical characteristics: 1) Humidity content: This is the most important property in terms of its

energy yield in the production of main-line steam. This depends mostly on the type of mills and the way the juice extraction is carried out. Usually, the humidity range of bagasse is between 49 and 52 percent. This means that for a fuel mass unit burned in the boilers, approximately half is bagasse and the other half is water.

2) Ash content: The percentage of ash fluctuates between 0.75 and 4 percent. The amount of ash depends on the type of soil, age, burning, hoisting, harvesting and washing of the sugarcane before it is milled. Components will vary according to the type of soil, fertilizers, varieties, climate, etc.

3) Granulometry: The shape, type and arrangement of the fiber depend on the degree of preparation that sugarcane has during the juice extraction process; the number of blade sets, pithers, shredders and mills. Thus, the smaller the bagasse particle, the lower its weight; and therefore, the time it takes the particle to fall from the furnace’s entrance to the grill is longer. Hence, a smaller size particle ensures better combustion.

Figure 6 shows the development in the use of bagasse as a fuel. Co-generating sugar mills have gradually made technological changes in their plants, substituting fossil fuels (such as Fuel Oil No. 6 or bunker C) for bagasse. Co-generators have practically doubled their consumption of bagasse in the last ten harvest seasons. This has brought about an increase in total energy generation and they have substituted fossil fuels for a cleaner and cheaper fuel.

Figure 6. Generation of energy by co-generators exclusively from bagasse

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Main-line steam production: The fuel coming from the milling of the cane or from the stock warehouses is fed to the boilers by conveyor belts; once there, it is either automatically or manually fed into the boiler furnaces. Boilers are water tube steam generators. They take the thermal energy from the combustion of bagasse and transfer it to the water inside the tubes, through convection and conduction on the pipe walls, until it reaches a boiling and superheating temperature. The furnace in the boiler then continues to absorb energy in the form of vaporization latent heat; therefore the supply of water to the boiler must be continuous and constant during operation. The steam produced is led to the turbine facility through the piping system. The most important factors to take into account for an adequate and efficient production of steam in the boilers are: Automatic gauging of the pressure is a factor that must be designed

correctly. The gauging circuits must be able to balance the fuel-air ratio fed to the boilers as well as the gases produced and extracted from the furnace, so that the operation settings remain constant.

The humidity in the bagasse is a variable that directly affects the combustion. If it is too high, the heat produced by the fuel will first have to evaporate the water contained in the bagasse before burning and gasifying the fiber. The amount of humidity will depend on the imbibition water used during the extraction of the juice and on the operating conditions of the mills. A balance must be found so that resources and operations can be optimized in order to obtain the greatest possible yield in the extraction processes and in the generation of the steam.

Excess air. An efficient steam production process is in which, the excess in the combustion air is strictly controlled. An excess in air will ensure the transformation of all the carbon dioxide that will leave in the chimney gases. On the contrary, a lack of excess air will prevent the fuel from fully burning, producing carbon monoxide (CO), and carbonous particles. This increases the losses due to the fuel that didn’t burn completely and therefore the amount of ashes in the draining systems, the ashtrays and the chimneys as well. Too much air allows the production of NOX and it lowers gas temperatures.

The amount of ash produced. The ashes produced during combustion are mostly composed of sand from the fields, which doesn’t burn and immediately passes to the “non-burned” form the boiler. The lightest ashes and sand fly together with the combustion gases to the chimney; they cause wear, due to abrasion wherever they pass, especially in the areas where gases have a maximum velocity.

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The operation. Best operating practices of a water tube boiler include an adequate chemical control of the feedwater, an opportune cleaning of the soot that adheres to the transference pipes, and a fast and efficient cleaning of the furnace and grill.

Furnance design. The furnace must have an easy to clean grill; it should be well sealed, with adequate and well distributed air entries; it should have bagasse feeders that measure the amount of bagasse going in, as well as to shred it properly, and to assure an efficient combustion, nozzles producing the right amount of turbulence.

Monitoring: The operation variables of the boiler, such as the feedwater, pressure, temperature, efficiency, steam flow, etcetera, should be constantly monitored by means of an adequate gauging system; it should have an alarm system responding to the allowed operating values.

Process steam production: Exhaust steam is not produced directly in the boilers. This steam generally has a pressure between 15-25 psig; it is the main line steam that has already given away most of its energy in the turbines; it comes out of them almost exhausted of energy, and it is led towards the industrial process, thus becoming a process steam. The amount of exhaust steam is the same as the amount of steam produced in the boilers, except with less pressure and temperature. This steam is precisely the number one reason for a co-generation process. Usually, the industrial process is the one that determines the amount of steam and the pressure needed; the production of electricity through co-generation is intimately linked to this need. In other words, if the industrial process decreases or comes to a stop, electricity co-generation process must also decrease; and therefore the primary thermal energy produced in the boilers. Otherwise, the exhaust steam would have to be spread out into the atmosphere, losing it forever. Generation of electricity Electricity is produced by turbogenerators; superheated main-line steam coming from the boilers that goes into the turbines. Here, the thermal energy is transformed into mechanical work: The turbine rotates at high speeds while attached to an electric generator, hence producing an electric current. This current is transformed and driven to the equipments that use electricity for the production of sugar and for the generation of electrical energy. The electricity surpluses are given to the national electrical network so it can be distributed by other companies. Transformation of mechanical energy to electrical energy: A turbine is a high speed rotating machine. It needs a moving force to make it rotate; the energy needed to make it rotate is provided by the steam, produced in the

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boilers. It is led to the turbine through steel pipes and admitted in it, by means of admission valves, that automatically control the flow of steam according to the regulation of electrical charge required. The steam inside the turbine goes through a nozzle plate in charge of evenly distributing the steam throughout the first stage vane of the turbine. It does this successively throughout all the stages of the turbine, losing part of its pressure, temperature and speed, as it goes from stage to stage. The turbine is connected to an electrical generator, therefore the latter spins together with the turbine. In some cases, a motorreducer will be placed between the turbine and the generator. The work done by the steam on the turbine is manifested as a high speed rotation mechanical energy; the generator rotor spins inside a fixed stator around it and due to the effect of the magnetic field produced between them, a high voltage electric current, is established. Use of electricity: The electric current that flows from the generator is led to transformers that raise or low the voltage of the current, depending on the posterior use. Low voltage energy is sent to the different industrial processes in order to cover all the internal electricity needs of the plant, such as lighting, air conditioning, power to move mechanical and electrical equipment, as well as all electronic control systems. High voltage electricity, generally between 69,000 to 230,000 Volts at 60 Hz, is sincronized with the national network and sold as surplus. Parallel to this, the exhaust steam discharged by the turbine is constantly flowing towards the industrial process, that is how the co-generation cycle ends and keeps going.

Figure 7. Electricity sales and consumption of co-generating sugar mills

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Figure 7 shows the increase in electricity produced by co-generating sugar mills, as well as the consumption within the mills; part of the reason for the latter, is the electrification of the milling tandems. This consumption represents an improvement that can be monitored through efficient usage of energy efficiency indexes.

EFFICIENCY INDEXES The energy efficiency of a co-generating central in a sugar mill, is measured by the steam consumption, the production (generation) surplus and the steam production. These indexes are expressed as:

Specific process steam consumption (Kgv) per ton of milled sugarcane (Tc). If the consumption of process steam is decreased, the surpluses in fuel increase and the range of operation schedules for the co-generating plant broadens.

Steam consumption = Kgv / Tc

Specific production index of surplus electricity, expressed in KWh of

surplus electricity (internal consumption not taken into account) per milled sugarcane ton (Tc). The higher the surplus of electricity, the greater the revenue due to the increase in volume sold to the national electric network.

Production surplus = KWh/Tc

Steam production index; it represents the kg of steam generated in the

boiler for every kg of bagasse used as fuel.

Steam genetarion with bagasse = Kgs / Kgb

It represents the yield of the co-generating process cycle; less bagasse consumption means a higher fuel surplus and a better use of resources. COSTS In order to keep track of the co-generating costs, the cost of fuel-bagasse must first be established; its cost corresponds to the energy consumed in the extraction process. Operating costs must be added (personnel and maintenance), as well as the costs for chemical supplies for the water treatment

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and electricity costs pertaining to the functioning of the equipment in the co-generating plant. In order to determine the costs of co-generation, a differentiation and distribution of the costs associated with each of the different processes must first take place: The cost of producing electricity The cost of producing sugar and of all the electricity consumed during the

process The cost of the exhaust steam used in the industrial process. Second, the way to assign the fuel is defined, which is attributed to each energy consumer in the process. This allocation should be based, as much as possible, according to the available enthalpy head, that is to say that energy should be weighed according to its ability to produce work at the specific point of demand.

GLOSSARY Biomass: Mass integrated by a diversity of bio-components with combustibility characteristics. For the present document, it refers to the mass subject to combustion in sugar mills, based on, sugarcane bagasse. Electric power: For a generator, power is the measure of the plant’s capacity to produce electric energy. It is the amount of electricity available at the plant for its clients. For a consumer, it is the measure of the amount of electricity it needs to operate or the amount of electricity demanded by its supplier. Electrical energy: It refers to the energy resulting from the existence of a potential difference between two points; this difference allows establishing current between both points. Shredders and mills: Equipment that prepares, shreds, and extracts juice and bagasse from sugarcane. Harvest season: Period of the year in which sugarcane is harvested, transported, milled, and processed to produce sugar. Boiler: Steam generator that uses heat produced by the burning of a fuel in order to produce steam at specific pressures and temperatures.

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Turbine: Rotating machine in which steam is used in order to transform thermal energy to mechanical energy. If it is coupled to a generator, electrical energy is produced at the same time. The combination of these two machines is called: a TURBO-GENERATOR. Water-tube boiler: Boiler that uses a large amount of pipes in which water circulates; heat is transferred to the circulating water through the pipe walls and steam is thus produced. Main-line steam: Steam produced in the water-tube boilers for later use, exclusively by turbines. Exhaust steam: Steam that is discharged in the last stage of the turbines, for which energy can be used in subsequent industrial processes. AMM: [For the acronym it represents in Spanish] Guatemalan Wholesale Market Manager. It is the entity in charge of coordinating transactions between the agents in the electrical energy sector in Guatemala.

BIBLIOGRAPHY

1. Administrador del Mercado Mayorista. 2011. Informe Estadístico 2010. Guatemala. 32 p.

2. Agüero, C.; Pisa, J.; Andina, R. 2006. Consideraciones sobre el

aprovechamiento racional del bagazo de caña como combustible. Perú. 8 p. 3. Batres, Luis. 2008. Beneficios económicos de instalar una planta

cogeneradora de energía en Guatemala. España. 89 p. 4. Castillo, Leonidas. 2010. Resultados zafra 2009-2010. Presentación de la

Asociación de cogeneradores independientes. Guatemala, CENGICAÑA. 5. Hugot, E. 1964. Manual para Ingenios Azucareros. USA. 6. Kenneth Wark, Jr. 1996. Termodinámica. Quinta Edición. Editorial

McGRAW-HILL. pp. 783-787.

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7. Logan, Christel. 2008. Régimen jurídico aplicable a la actividad de generación de energía eléctrica en el ordenamiento jurídico guatemalteco. Guatemala. 134 p.

8. Spiewak, Scott A. 1987. Cogeneration & Small power production manual.

USA. The Fairmont Press, INC. 642 p. 9. Vargas, Luis; La Fuente, Fernando. 2000. Cogeneración en Chile.

Potencialidad y desafíos. Revista Chilena de Energía. Volumen 430. pp. 1-4.

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PRODUCTION OF ETHANOL

Rodolfo Espinosa y Claudia Ovando

INTRODUCTION

Ethanol or ethyl alcohol is a natural hydrocarbon, with general formula C2H5OH, which in chemical nomenclature is a derivate of ethane (C2H6). It is industrially produced by the fermentation process of glucose, a monomeric carbohydrate present in sucrose and other polymeric compounds, such as starch and cellulose. The intermediate or final syrups produced in sugar mills are rich in glucose or in sucrose. They can be converted into a mix of glucose/fructose by means of acid hydrolysis. These, in turn, can be transformed into ethanol by means of catalyzed glycolysis reactions with enzymes produced by microorganisms such as the yeast Saccharomyces cereviseae. The industrial production process of ethanol consists of three perfectly well defined stages: 1) Biochemical reactions which are a product of the metabolism of the microorganisms used to the effect; they transform fermentable sugars into ethyl alcohol, as a main product, and into other metabolic or residual byproducts, that depend on the purity of the raw material used, and on the environmental conditions in which the reaction takes place. 2) The separation of the desired product (ethanol) from the rest of the compounds present in the fermented mash and the concentration of the product, in order to reduce its volume for its later handling. The most widely used method to achieve this is distillation – separation of components due to their relative volatility, its different boiling and condensation temperatures, and other unit operations such as extraction, adsorption, etc. 3) The treatment, disposition, and best use of the byproducts separated during distillation. This last stage has recently gained vital importance in the better use of resources and environmental protection.

Rodolfo Espinosa, Ph.D., is a Chemical Engineer and Industrial Research Program Leader at

CENGICAÑA. www.cengicana.org; Claudia Ovando is Chemical Engineer, M.Sc. Head of Laboratory Processes, Bio Etanol, S.A. (Group Pantaleon) www.pantaleon.com

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Figure 1. Production of ethanol Ethanol, as a product of fermentation has been used for over 40 centuries, mainly as an intoxicating drink. Other uses have been found for it in the last 200 years, such as industrial and medicinal uses. In the last 40 years yet another use for it has been found, as motor fuel, mostly due to the high prices of petroleum. Uses of ethanol: Intoxicating drink

Solvent for perfume industry and others

Medicine (antiseptic at 85%)

Industrial reactant

Fuel

Fuel for 4 stroke engines

Others

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Figure 2. Alcohols and their reactions

BRIEF HISTORY The production of ethanol in Guatemala probably began in the pre-columbian era with the manufacturing of intoxicating drinks from corn, possibly, and fruit, within the family home environment. During the colonial period, thanks to the import of sugarcane, panela, was eventually used as raw material and its production became regulated for tax purposes during the mid XIX century. This brought about a handcrafted distillery industry with wooden fermentation

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tanks and copper stills installed on the outskirts of the Income Revenue Service of each of the departments of Guatemala, for better tax control. During the mid XXth century, panela, and virgin syrups (concentrated juice at 45-60 Brix) producers, together with alchohol producers, got together to install a production and aging central facility in Santa Lucía Cotzumalguapa, with a more industrial than traditional infrastructure. Trapiches and sugar mills back then were the raw material suppliers (virgin syrup for “potable” alcohol and molasses for industrial alcohol (Circa, 1960)). The Guatemalan annual production in those years was approximately 5 million liters of ethanol, mostly for consumption as alcoholic beverages. Production increased during the next two decades up to 15 million liters, then to 30 million liters per year. Ultimately, it reached 40 million liters per year and two other distilleries emerged, one of them annexed, for the first time, to a sugar mill. Nowadays, sugarcane is harvested in 230,000 hectares of flatlands in the south coast and some small regions of the east and northeast of Guatemala. The average yield is 100 ton of cane/hectare. Twenty million tons of cane is annually milled with an average yield of 0.1 ton of sugar / ton of milled sugarcane. With the quantity of sugarcane actually cultivated in Guatemala, it could be possible to produce annually, between 360 million gallons of ethanol, if if sugar wasn’t produced; and 55 millions of gallons if only the molasses was processed. The current installed capacity to produce ethanol from molasses is approximately 40 million gallons a year in five distilleries adjacent to sugar mills. The annual consumption of gasoline in Guatemala, which is all imported, is 150 million gallons. If the necessary legislation existed, anhydrous ethanol mixed with gasoline to a 10% proportion would be able to substitute the MTBE (methyl-ter butyl-ether) that is incorporated into gasoline as an antiknocking agent, without making any modification to the vehicles already in circulation. The current production of ethanol from molasses is enough for such a substitution without affecting the sugar production in any way. Any surplus in the production of ethanol could be exported as a means of generating foreign currency capital, as is already done with present sugar exports.

DISTILLERY ANNEXED TO A SUGAR MILL With the increase of oil prices and its by-products (i.e. gasoline), the production of steam inside a distillery became non- cost effective. Steam is used as the main heat source in the distillation process and its production depended mostly on Bunker C. At the same time, co-generation of electricity within the sugar

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mills made the installation of annexed distilleries very attractive. This way, the exhaust steam from the turbines can be used, the distance syrups have to be transported can be minimized, the process water condensates can be used and it counts with the sugar mill’s infrastructure to provide other services for the distillery. The main disadvantage, though, is that the distillery’s production is partially subject to the sugarcane harvest season (zafra) . However, with the rise of coal-fed boilers being implemented in the main sugar mills, production season can be considerably extended. It is important to note that such annexing has brought with it a cultural transition in how distilleries are operated, since some technical terms used in the production of sugar have a different meaning for the operators in the distilleries, and viceversa; what is relevant for the former, is not relevant for the later.

Pantaleon Group Courtesy

Figure 3. Ethanol distillery annexed to a sugar mill Main sections of the ethanol production process Raw material preparation; fermentation, distillery; molasses vinasses (slop)

management and services.

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Figure 4. Diagram of a typical process in a distillery

APPLIED PROCESSES Raw material Sugarcane mill produce juice with 13% of sugars; it is filtered and concentrated through evaporation to obtain syrup with 65% of sugars (saccharose, fructose, glucose, and others). This syrup or “meladura” is subjected to an evaporation/crystallization process , then separation of the cristals ( table sugar ) by consecutive centrifuging of syrups A and B. The final syrup, or syrup C, better known as molasses, has an average content of 50% of fermentable sugars (typically 33% saccharose, 9% glucose, and 8% fructose). The production of molasses is of 0.03 ton/ ton of milled cane, that is, 0.24 ton of molasses/ ton of sugar produced.

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Figure 5. Syrup production process in a sugar mill

Such molasses currently constitutes the raw material for the production of ethyl alcohol or ethanol. However, the latter could be produced using any fraction of the sugar production process as its raw material: juice, concentrated juice, syrup A or syrup B, depending on the economic factors and the market of both products. Obviously, the operation conditions and yields in production will vary depending on the raw material used.

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Figure 6 shows the general classification of carbohydrates, among which we can find sugars. It is necessary to note that not all sugars can be transformed into alcohol by means of glycolysis, which, as its name indicates, originates from the glucose mollecule. The sugar contained in cane juice and in concentrated juices or syrups, is mainly sucrose. It has to be converted to glucose by means of acid hydrolysis (pH 4.5) and catalyzed artificially or naturally with hydrolase. Hydrolase is produced by yeast (Saccharomyces sp.) and it is separated and industrially concentrated, so it can be applied as a catalyzer in the reaction called “sucrose inversion”, in the production of “inverted syrup” or High Test Molasses (HTM), with a high glucose content (not crystallizable).

Figure 6. Classification of carbohydrates The following expressions are used in the production of ethanol from the derivatives of sugarcane: Fermentable sugars: Sugars that can be transformed or directly degradated

by microorganisms. Reducing sugars: Sugars that reduce the Fehling reactant. Not all reducing sugars are fermentable. Not all fermentable sugars are reducing. However, most fermentable sugars are reducing (approx. 98%). Sucrose is not fermentable, as such, and it isn’t reducing either, but when it

is hydrolyzed, it is turned into glucose and fructose, which are both fermentable and reducing.

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Figure 7. Structure of saccharose Source: www.perafan.com

For distillery operators, glucose content is the most important thing. The total of reducing sugars is an indicator that comes very close to the content of fermentable sugars. Saccharose as such is not fermentable, but when it becomes hydrolyzed the glucose-fructose complex is equivalent to two available molecules of glucose for its conversion to ethanol and carbon dioxide. The brix value in fermentation, even though, it is an easily and quick indicator that can be obtained, it is a measure of total solids, not of the fementable sugars in the molasses mixture. Futhermore, such content of solids and fermentable sugars varies constantly, from day to day and even from hour to hour; depending on a series of factors, such as the origin and variety of sugarcane used, how far along the harvest season is, the sugar mill’s efficiency rate, the storage conditions of the mixture, etc. Therefore, the use of brix as a parameter to characterize and predict fermentation results is inaccurate, as well as, the determination of the reducing sugars; and both methods are now unused, since high precision liquid chromatography (HPLC) is available. It offers fast, precise results of saccharose, glucose, fructose, organic acids and ethanol, as separate fractions. Figure 8 shows the variations in the sugar content with respect to Brix in some molasses samples.

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Figure 8. Relationship in sugar concentration and Brix degrees

Microbiology The production of alcohol is a multidisciplinary process based on chemistry, biochemistry, and microbiology. In the past, the production of alcohol was considered an artform, and it wasn’t until 150 years ago that the science of alcohol fermentation was described. Treating the process with full knowledge on its scientific basis it is possible to reduce the number of microbiological and engineering problems, thus obtaining better operation results and a better use of the raw materials (Ingledew, ATB). Having knowledge of the microbiological aspects of alcohol fermentation is fundamental, since the main players in the reaction are yeasts and the other competing microorganisms (bacterial contamination). Yeast is a type of unicellular fungus (eumycete). It is generally reproduced through budding. Being unicellular microorganisms, they grow and reproduce faster than filamentous fungi in proportion to their weight; they are better equipped to carry out chemical changes since they have a greater surface area in proportion to their volume. They are easily differentiated from most bacteria due to their relatively large size (Pelczar, 1982). They differ in size and shape; they can measure anywhere from 1-5 microns in diameter. The most widely used yeast in the regular alcohol fermentation processes is the Saccharomyces cereviseae strain (bread leavening yeast).

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Figure 9. Saccharomyces cereviseae stock. Alcohol is produced by the metabolization of glucose ( Glycolysis ) by the yeast. In aerobic conditions (with the presence of air), the reproduction of yeast is stimulated, whereas fermentation occurs in anaerobic conditions (absence of air); both reactions start out the same way and their common branch is glycolysis (successive reactions for the conversion of glucose into energy by enzyme reactions). During this conversion of glucose, byproducts like ethyl acohol, carbon dioxide and in a lesser degree, glycerol and some organic acids, are produced. Some of the enzymes that participate in fermentation are diastase, invertase or hydrolase, and zimase; this last one is responsible for directing the biochemical reaction that converts glucose into ethanol.

Figure 10. Saccharomyces cereviseae metabolism in the production of ETOH

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Fermentation Fermentation fundamentals: Transformation/degradation reaction of organic matter catalyzed by enzymes, inside or outside the cell, in a controlled way or not, to produce cell protoplasma, desired or not metabolites, microorganism reproduction in the presence or absence of air. The sugar contained in the dilluted syrups to the desired concentration is mainly converted into ethyl alcohol by fermentation; as stated before, fermentation is a series of reactions catalyzed by enzymes produced by microorganisms (yeast, Saccharomyces sp) following the biochemical route of glycolysis. Such route describes the reactions that would happen if the substrate were a pure glucose solution. But when the substrate is a molasses solution or a mid-syrup solution from sugarcane, that besides fermentable sugars, they contain an ample variety of compounds (more than 200 have been identified) then, they can react under the environmental conditions of the fermentation process, allowing other byproducts; some of these subproducts are: Methanol, cetones, aldehydes, organic acids (pyruvic, succinic, acetic) and higher alcohols with more than three carbons in their composition (propanol, butanol, pentanol, etc.). This group of alcohols, very closely related to each other, and with very similar physical-chemical qualities, are collectively known as “fusel oil” due to their oily appearance and because of their low affinity with water. For preliminary calculation purposes and for in-plant yield estimations, the basic reaction to be used is the following:

Figure 11. Production of ethanol (basic reaction)

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The real yield is much lower due to the formation of other compounds, as it was described in the previous paragraph; besides, yeast cells are also formed at the expense of glucose. Yield optimization depends then, on the quality of the raw material, the process adopted and the operating conditions of such process. In general, it is important to note that: Yeast reproduces more in the presence of air (respiration) and when nutrients are

present (nitrogen, phosphorus, and trace elements). In the absence of air (fermentation) and with limited nutrients (which limit the

formation of DNA and RNA), yeast reproduces on a lesser extent, and it produces alcohol as part of its survival metabolism, as well as other compounds.

Exposing yeast to high concentrations of ethanol and CO2 for long periods of time, reduce its viability.

A massive inoculum has a higher possibility of reaching the desired efficiency in the process in a non-aseptic culture, that is , in competition with bacterial contamination.

The chosen species of microorganism (S.sp.) will react according to the environmental conditions surrounding it (i.e. pH, temperature, relative substrate concentration, and rheology).

Glycolysis, for the production of ethanol, is an exothermic reaction; thus, the heat generated inside the reactor must, somehow, be removed in order to keep the internal temperature as close as possible to the optimum temperature, favoring the chosen yeast species (i.e. 33°C).

Figure 12. Activity in the fermentator

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Figure 13 shows the progress of the biochemical reactions in the conversion of sugars into ethanol and yeast cell mass. Under normal conditions, these reactions can be completed in periods from 24 to 60 hours, depending on the initial concentration of fermentable sugars and the size of inoculum . It is important to note, though, that the variables that characterize fermentation vary with respect to time at different rates (different slopes) clearly defining three stages: 1) Adaptation or “lag” period of the yeast inoculum to the initial conditions

and auto-adjustment to the proper environment. This occurs at an industrial level in the reactor called the “Propagator,” under aerobic and the most aseptic conditions possible.

2) Exponential growth period. Under optimum conditions, yeast reproduces and develops its metabolic activity at a constant rate increase . Such activity is used in the “pre-fermentator”; this is a piece of equipment in charge of performing the transition between the aerobic and the anaerobic stages.

3) Stabilization and death period. It takes place in the main fermentator with the initial inoculum in its exponential phase and with maximum substrate volume. Metabolic activity gradually decreases; as the available substrate concentration decreases, the metabolite concentration increases until the source of energy and nutrients is exhausted, causing the death or inhibition of the microorganisms.

Figure 13. Progress of the fermentation reaction

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Figure 14 shows all three stages:

Figure 14. Fermentation sequence

Batch fermentation: It is also known as discontinuous fermentation. A fixed volume of molasses solution is fed into a tank reactor or fermenter, together with the necessary nutrients and the necessary yeast inoculum to start the reaction. The inoculum is previously prepared from a pure yeast stock in a laboratory, and then propagated in incremental fractions until it reaches between 5 and 10 percent of the total volume. Some distilleries have opted for buying the inoculum already reproduced in the form of fresh or dried commercial yeast and just adding it directly into any of the final stages previous to the fermenter. With this, contamination risks are avoided and financial investment in the reproduction/propagation equipment is saved. After the necessary time period for the exhaustion of all the sugar has passed by and it has obtained the maximum ethanol concentration, the batch is taken as finished, and the totality of the volume in the fermentator is transferred to the distillation process.

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Figure 15. Batch fermentation

Batch fermentation with yeast recycle: In this case, after the initial batch is done, a fraction of the yeast present is separated by centrifugation, then washed with clean water and submitted to a low pH treatment (2.5-3.5), in order to force the cells to naturally protect themselves by strenghtening their cell wall and making themselves more resistant and supposedly healthier. The yeast cream, treated like that, constitutes the inoculum for the next batch, meaning that, less sugar would be use in the formation of yeast protoplasm, leaving the rest available for the formation of ethanol, and thus increasing the fermentation yield. The supernatant after centrifugation, which contains the alcohol of the entire batch, is transferred to the distillation process. This process is repeated successively until the yeast cream is no longer in optimum conditions, and a new cycle begins. This variant in the fermentation process is no longer used in Guatemala because it requires more energy, more input and materials, more control and it did not show significant savings or gain.

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Figure 16. Batch fermentation with yeast reusage (Melle-Boinot) Continuous fermentation: In this kind of process, a continuous flow of the molasses solution is fed into the reactor, while a similar flow of fermented must is removed from it in a continuous fashion; this establishes a steady state inside the reactor where the cell mass, ethanol and sugar concentration are constant and in equilibrium. Since the concentration of sugars cannot be allowed to decrease to its minimum for the yeast’s sake, the fermented mash is sent to a second stage of sugar depletion and maximum ethanol production; after this, the must is sent to the distillation process. When observing the kinetic curves of the production of ethanol, it becomes apparent that there are two well defined stages that suggest the adequate design of the volume of the reactors for both stages. Continuous fementation requires even more control, and the bacterial contamination risks are higher since it is not economically viable to sterilize the molasses solution previous to its inoculation. When this type of fermentation is used, it must be understood that the fermentation is meant to be continuous but not perpetual.

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Figure 17. Continuous fermentation

Discontinuous fermentation with continuous pre-fermentation: This is a variant of the previous process where the kinetics of alcohol fermentation is used at a maximum level. Yeast is propagated once and fed into the pre-fermentator, so it can develop its logarithmic cell growth and production rate of ethanol. Feeding the syrup or molasses solution is done in a continuous manner. When the volume is complete and the culture has been kept in its optimum exponential conditions, part of it (80%) is transferred to the final fermentator as inoculum , at the same time that this is being filled up. The 20% that remains in the pre-fermentator is used as inoculum for the fermentable culture medium that is continuously fed into it, in preparation for the subsequent fermentator, and so on. This allows the fermentation curves to be kept optimized; it also shortens the total fermentation cycle since fermentation also occurs during the filling and emptying of the fermenters.

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Figure 18. Batch fermentation with continuous pre-fermentation

Other important general considerations are: The lower the initial concentration of fermentable sugars, the higher the

reaction velocity and the greater the yield: R= ΔP / ΔS, but the lower the volume of product obtained.

The higher the concentration of fermentable sugars and total solids, the

slower the reaction and the lower the yield, but the higher the concentration of product P in the final must and the higher the productivity: P = R / Δt, up to a certain limit for each species, as can be appreciated in Figure 19.

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Even though values of up to 16 percent alcohol in the final must have been reported (obtained at bench scale after 120 hours), for practical purposes at an industrial level, 11 percent of the volume can be obtained in a 48 hour cycle, with an efficiency of up to 88 percent (Eff = R real x 100 / R stoichiometrical).

Figure 19. Fermentation curves

Distillation

Distillation fundamentals: Distillation is a physical process for the separation of two or more compounds with different molecular weight from the solution by virtue of, their relative volatility and the difference in their boiling points. All compounds have, among their physical properties, a corresponding boiling and condensation point under different pressure conditions and that are specific to each compound. When a heat is applied to a solution or mixture of compounds, the boiling point of each is reached, one at a time and each one volatilizes, thus separating it in the form of gas or vapor from the other or others still in their liquid phase. This is done at industrial scale using pieces of equipment called distillation columns, designed to contain both phases.

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Figure 20. Separation of two components through distillation

In a continuous column, the heat is applied at the bottom and the solution to be distilled is fed through the top or middle of the column. In this way, the vapors at the bottom have to go up and while they do so, they are enriched with the compound that is to be separated when they come in contact with the liquid being fed. The vertical column has horizontal trays that provide surface contact between the vapor and liquid to promote mass transfer. The liquid that comes down, transfer the content of the product being separated into the rising vapors, without reaching its own boiling point. The more volatile fractions that reach the higher part of the column have to turn back to the liquid phase in order to be adequately recovered and managed. This is achieved by cooling the product down in heat exchangers called condensers. In distilling two or more components, as it is the case of ethanol from sugarcane by-products, akin fractions of the solution can be separated by parcial condensers. The desired product, free of its similar undesired components, is recirculated to the highest tray to enrich the liquid phase and henceforth become extracted from the column as a final product. Not all the individual fractions can be separated in a single distillation column, first, because for large production volumes, a single column would be difficult and impractical to be built , for structural reasons; and also

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because all the products resulting from fermentation are very similar and akin to each other; therefore the liquid and gaseous portions that are in equilibrium in each tray are really a mix of various components; hence, other thermodynamic conditions are necessary in order to separate them, and in some cases, even other and different unit operations are necessary, such as extraction, adsorption, decanting, etc.

Figure 21. Multi-component distillation column Figure 22 illustrates a typical contemporary distillation arrangement. In it, the heat source, low pressure steam, no longer comes into direct contact with the fermented mash being distilled. Instead, it transfers its heat to the liquid at the bottom of the column in a re-boiler. The vapors that are formed in this exchange are the ones that rise throughout the column, so they can be enriched with ethanol. The volume of the vinasse (distilling slops or stillage) at the bottom of the column is in this manner reduced, and the clean condensed steam can return to the boiler, and so contribute to the energy and water savings of the sugar mill. This arrangement also shows the use of cooling water in a cascade arrangement so as to attain the necessary minimum temperature gradients for the condensation of the volatile fractions. On the other hand, the primary vapors that are to be condensed, can be used as a heat source for a re-boiler, part of another distillation column set up next to it.

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Figure 22. General distillation diagram

Figure 23. Combination of refluxes and reboilers Distillation of the fermented must: The fermented must, with analcoholic content between 8 and 11 percent, passes through a distillation process, in order to separate ethanol from cogeneric compounds, thanks to its relative volatility. The necessary heat is provided by the residual steam coming from the sugar mill. Azeotropic distillation allows an alcohol concentration of 95.5 percent.

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Figure 24. Multicomponent fractions in the distillation of alcohol

Azeotrope is the chemical term used for two liquids at a specific concentration that vaporize together, and at the same time, because they boil at the same temperature. Ethanol and water cannot separate from each other, when the mixture reaches 95.5 G.L (that is , 95.5 % Ethanol and 4.5 % water, by volume), since they form an azeotrope at that concentration, and therefore vaporize together. The 4.5 percent of water remaining must be removed through some dehydration process, such as adsorption, by means of a molecular sieve if the final product is to be used as a fuel (MFG, motor fuel grade). The residue left behind by distillation is known as vinasse (stillage); depending on the alcohol percent in the fermented mash and how much it can be recirculated into the process, anywhere between 2.5 and 10 L of vinasse per liter of ethanol, is produced. A commonplace practice is to dispose of the vinasse in the sugarcane fields through irrigation to return the nutrients back to the soil. Depending upon the desired product(s) quality, the arrangements of the columns vary from one distillery to another. Some modern distilleries are able to produce a variety of products, even simultaneously, though this implies a greater financial investment for a higher number of columns, and a much more complicated operation.

Some typical arrangements are illustrated in the following paragraphs:

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Barbet Distillation: It is the most widely used column combination for the production of heavy rums and spirits. The first column (beer or stripper column) separates everything that isn’t water, glycerol and solids into vapor; the former elements go to the bottom of the column as vinasse (stillage). The light components mixture goes on to the top of this column and then into the second column (purifying or “heads” column), where the compounds more volatile than ethanol (methanol, adehydes, ketones and volatile acids), evaporate; ethanol remains in a mixture with water and heavy alcohols (fusel oil) in liquid form; this mixture is removed from the bottom of the column so as to feed the third column (concentrating or rectifying column). In this last column, the fusel oil is extracted by the first third of the column; the water (flegm) is extracted from the bottom and the ethanol and its remaining cogenerics are recovered as the final distilled product from.

Figure 25. Barbet distillation

Extractive distillation: This is a variation of the previous arrangement. In it, the purifying column is substituted by an extractive distillation column. That is, a column in which the operations of distilling and extraction are combined and take place simultaneously. Thanks to a phenomenon discovered in the middle of the XXth century, both the light cogenerates as well as the heavy ones, when combined, have a relative volatility higher than the ethanol solution – water, when it is close to 14 percent of the volume. The water at the bottom of the third column is used to dilute the recovered solution from the first column, favoring the necessary conditions to extract alcohol from the mixture; then take

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it to the bottom of the column so it can be fed into the rectification column, where it is easily separated as binary distillation.

Figure 26. Extractive distillation

Purification and ethanol recovery: In order to obtain alcohol with the least possible amount of cogenerates (names for this vary from region to region, they are colloquial and are not official: high grade, neutral, extra-neutral, super-fine, etc.), additional columns are added to the basic arrangement of extractive distillation; in order to: a) recover alcohol from the volatile fractions, and b) to eliminate any trace of cogenerics that could still be in the rectified alcohol; the latter is usually achieved through the optimization of the temperature profiles in the rectifying column.

Figure 27. High grade alcohol

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Dehydration: Under positive pressure conditions, there is a maximum value for the alcohol concentration in water (between 95.5 and 96.5%) in ethanol-water distillation, depending on the atmospheric pressure of the site. So the product of azeotropic distillation is “hydrated” ethanol. Alcohol with water cannot be used as a fuel for obvious reasons. However, it is possible to “dehydrate” alcohol by other industrially used procedures, such as: Use of vacuum pressure in the column so as to lower the boiling point of

ethanol, and thus displacing the azeotrope to a concentration of 99.5 percent v/v. Add a third component which when mixed with water has a different

boiling point than the original mix, therefore displacing the azeotrope also. Additionally, the third component has more affinity to water than ethanol, and it extracts the water from the original mix, forming a new mixture of water/solvent that is later distilled to recover the third component for further use.

Make the mix go through resins with high affinity with water and with

enough contact area so as to adsorb it. When the gaps in the resin (molecular sieve) become saturated with water, the latter becomes desorbed by means of steam heat forced into the column containing the resin.

Nanomembranes with a very small pore (at a molecular level) that they

function as sieves, which only allows the water molecules to pass them through, since it is significantly smaller than the ethanol molecule.

The first two methods have both fallen into disuse, and the fourth is not commercially available yet.

Figure 28. Dehydrated alcohol

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Products and Quality The final product of the alcohol production process through sugar fermentation and distillation of the fermented mash is ethyl alcohol (ethanol). The classification of the types of alcohol obtained from distillation processes, is based on the composition and concentration of the alcohol and byproducts produced and on plant design. Some plants are designed exclusively to produce hydrated alcohol, characterized by having the maximum obtainable water concentration due to the azeotrope. Others have additional processes so as to eliminate the water not removed during azeotropic distillation, and thus producing dehydrated alcohol. Then, according to the degree of purifying or rectification applied, different product qualities or compositions can be obtained. Hydrated alcohol: There is a wide range of specifications for hydrated alcohol, and they usually vary from client to client. It can be characterized according to its final purpose (i.e. potable alcohol) and some minimum requirements, such as the alcohol content, the oxidation period, the amount of methanol and higher alcohols allowed, esters, ketones, and other cogeneric products. It is important to make a sensory evaluation of the product, such as a taste, aroma and visual inspection analysis when evaluating a product, not just chromatography and physical-chemical analysis. It can be observed that quality requirements for hydrated alcohol are more demanding than one used for fuel; the reason is that hydrated alcohol is usually used in drinks, perfumes or pharmaceuticals, where it is a requirement that other components do not interfere with the properties of the desired product. Common types of hydrated alcohol Raw alcohol: A non-rectified alcohol, usually between 92 and 95 percent v/v of alcohol; also called crude alcohol. Its smell, taste and cogeneric products depend on the raw material it came from. It is usually sold as raw material for later rectification and refining. Industrial alcohol: It contains at least 95 percent v/v of ethanol; it may have some degree of rectification, however, its characteristics are not enough to consider it as potable. It is mainly destined for the chemical (dye solvent, paints, and resins) and pharmaceutical industries. It has a high aldehyde, ester and fusel alcohol (higher alcohols) content, a strong and unpleasant smell. It is also called semi-rectified alcohol, second degree alcohol or REN type alcohol.

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Extra-neutral alcohol: Alcohol with at least 96-96.2 percent v/v, destined for the production of light liquours, such as vodka and gin; on a lesser scale, it is also used in fine perfume production and in some pharmaceuticals. It is soft and odorless; it passes rigorous organoleptic tests, usually carried out by expert tasters. It contains almost no adehydes, dry residues or fusel alcohols. Neutral and extra-neutral alcohols are rectified; the amount of times it is rectified depends on the amount of impurities present in the wines and fermented mashes they come from or on the process design. They are also called extra-fine alcohols. When dehydrated, it becomes an absolute alcohol (99.9%). Table 1 shows an example of how the quality and the reaction time to permanganate of the product increases as the amount of cogenerics decreases; these same specifications vary depending on the sales region (Europe, United States of America, Japan, etc.) and the client’s requirements. The main properties were included; however, depending of its final destination or the desired purity, more parameters may be needed for evaluation; in some cases, even the color might need evaluation through specific wave lengths or the aroma, according to expert tasters. Table 1. Types of alcohol according to their properties

Properties Units Raw Industrial

(REN)

Neutral (potable or

fine)

Extra- neutral

(extra-fine) Degree of alcohol @20°C

% v/v 94-95.2 95-96 96 min 96-96.2 min

Acidity as acetic acid

mg/100 mL 3 max 2 max 1.5 max 0.5 max

Volatile material mg/100 mL 4 max 4 max 1 max 1 max Methanol mg/100 mL 35 max 5 max 1.5 max 1 max Ésters mg/100 mL 10 max 6 max 2.1-4 0.2 – 1 max Aldehydes mg/100 mL 3 max 5 max 1.1 - 6 0.2- 1 max ISO propanol mg/100 mL 1 max 1 max 0.5 max 0.5 max Higher alcohols ( fusel oil)

mg/100 mL 20 max 10 max 0.5 max 0.5 max

Permanganate time at 15°C

minutes 1 min 5 min 25 mínimum 36-50

Aspect Without particles in suspension

Without particles in suspensión

Without particles in suspension

Without particles in suspensión

Color Clear transparent

Clear Transparent

Clear transparent

Clear Transparent

Odor Characteristic Characteristic

Neutral without trace of other materials

Neutral without trace of other materials

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Dehydrated alcohol: It is the alcohol on which the remaining water after rectification has been removed. This is usually done by means of molecular sieving or with extractive distillation (benzene /hexane), although the latter is almost no longer used. Its main use of the dehydrated alcohol is on fuel ignited engines and for its compatibility when mixed with gasoline. It is commonly known as motor fuel grade ( MFG) ethanol, anhydrous ethanol, and anhydrous ethyl-alcohol. When it is prepared with a denaturalizer it is called denatured fuel ethanol. A denaturalizer is a substance added to fuel and industrial ethanol which makes it unsuitable for human intake but suitable for automobile or industrial use. Denatured alcohol has different specifications to those of plain fuel alcohol since the proportions of its components change. The international standards that govern the quality of fuel alcohol are mainly concentrated in three regions: Brazil, USA, and the European Union. Brazilian standards (NBR) are given by the Brazilian Association of Thechnical Standards [ABNT for its acronym in Portuguese], the American standards by the American Society for Testing and Materials (ASTM) and the European standards by the European Committee for Standardization [CEN for its acronym in French], although some standards exist for specific clients with exclusive uses. Despite the differences in each of the standards, the quality requirements are similar; this has brought actions since 2006 between the governments of Brazil and the USA, as well as a committee representing the European Union, to unify the quality standards in order to significantly increase the market viability of the product. On December 2007, members of this team published the first results of the pertaining discussions, negotiations, and recommendations for the different standardizing bodies (TTF, 2007). However, as long as there isn’t a unified standardization document, producers will seek to comply with the requirements of their main clients and local regulations. That is why, it is important to know the standards and, above all, its meaning for each quality requirement. Even though Guatemala still hasn’t commercialized fuel alcohol or gasoline, and fuel alcohol mixtures within the country, there is an important alcohol production that exported to other countries. For that reason, it is imperative to know the importance of each requirement application for its consequent effect on the motors equipment. Table 2 shows the most commonly utilized specifications for fuel alcohol.

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Table 2. Fuel alcohol specifications (Silva, 2007)

Requirement Unit Brazil ASTM Europe Method or norm Density (20°C) kg/m3 max 791.5 NBR 5992/ Alcoholic degree at 20°C

% m/m %v/v

min/min 99.3* / 99.6

ASTM D 4052

Ethanol content at 20°C

% m/m %v/v

min/min 92.1**

98.7** ASTM D 5001/ EC*2870/200 METHOD B/ASTM D 4052

Water % m/m %v/v

max/max 0.7 0.1

0.3 ASTM E 203/ PR EN 15489

Total acidity as acetic acid

mg/l %m/m

max/max 30 56 0.007

56 0.007

NBR 9866/ASTM D 1613-06/PREN 15488

Electric conductivity

mS/m max 500 NBR 10547

pH 6.5-9.0 ASTM D 6423 Copper mg/kg max 0.07 0.1 0.1 NBR 10893/ASTM D

1688ª/PREN 15492 Chlorides mg/kg

Mg/l max/max 40

32

20 ASTM D 7319-7/ASTM 7328-07E1/PREN 5484/15492

Washed gums

mg/100 ml

max 5 ASTM D 381

Aspect clear clear clear ASTM D 4176-07/ VISUAL

Methanol %v/v %m/m

max 0.5 1

ASTM D 5501/EC/2870/2000/EN 1601/EN 13132

Higher alcohols (C3-C5)

%m/m max 2 EC/2870/2000 EN 1601/EN 13132

Sulphur mg/kg max 30 10 ASTM D 2622/D3120 ASTM D 5453/D6468/PREN 15485/15486

Non-volatile materials

mg/l max 100 ASTM D 1353-03/EC/2870/2000, METHOD II

*Densimetry, **Gas chromatography. ASTM- American Society of Testing Materials, NBR-Associação Brasileira de Normas Técnicas, EC-European Community, EN-European Norms, prEN-Draft method

Note: all specifications include these requirements; in fact, there are some that include other characteristics such as the phosphorous, nitrogen, benzene, cyclohexane, lead, sulfate and sodium content, among others. It also depends on the client and the specific use for the product. Byproducts Vinasse: As it was previously said, the residue from distillation is known as vinasse or stillage, and depending on how much of it can be returned and recycled into the process, 3 to 14 L of vinasse is produced for every liter of

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ethanol. Common practice tries to dispose of the vinasse in the irrigation of the sugarcane fields, so as to return nutrients into the soil. Vinasse is no longer considered a waste but a valuable byproduct. It carries with it usable heat, minerals, organic compounds, protein and vitamines contained in the yeast. It can be recovered and used as animal feed, as a fertilizer full of mineral and organic salts for the sugarcane fields, as a substrate for the production of methane due to the residual carbohydrates, and other biodegradable compounds by means of anaerobic fermentation for fuel used in the sugar mill or in the distillery. Likewise, the water in it can be recovered through evaporation or filtration, and the residual solids can be managed as compost and even as solid fuel. Depending on the specific conditions of each company and their technical-economical analysis, any combination of the above mentioned processes can be applied, so as to obtain the best benefit out of the ethanol byproduct, both economically and for the environment.

Figure 29. Vinasse treatment and disposition options Carbon Dioxide: During fermentation, a quantity of carbon dioxide, CO2, approximately equal to the mass of ethanol generated by the metabolism of yeast, is produced. The evolution of CO2 within the fermentator causes turbulence, producing natural stirring as a benefit, since mechanical stirring is therefore, no longer needed. The main use given to carbon dioxide, industrially, is as a preservant in carbonated drinks and for the production of dry ice. It is profitable only when

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these industries are located close to the distilleries. It is also an inhibitor for undesired fermentations that occur during the storing of molasses or syrups; in such cases, molasses are sometimes kept under a CO2 atmosphere, on the top of the content in the storage tank. It is important to consider that it is also a greenhouse gas, and because of this, the research is being done on its recovery and uses so as to decrease its effect on the atmosphere. Cogenerics Fusel oils or Higher alcohols: Sugar products also contain aminoacids; yeasts assimilate the radical nitrogen in the synthesis of new aminoacid compounds, such as proteins and enzymes. Among these aminoacids present in the juices and syrups, leucine, isoleucine, valine, etc, can be mentioned. Which when deprived of the radical containing nitrogen, they give alcohols as a product of the reaction, causing the formation of aliphatic higher alcohols with the general formula CnH2n+1OH (n from 3 to 8). They have high molecular weight, and it is due to their viscuous appearance, that their mixture is called fusel oil. The name fusel oil comes from the German word fousel which means “evil spirits”. Among the main higher alcohols found in fuel alcohol are: propanol, isopropanol, butanol, isobutanol, amyl and isoamyl alcohol, these last two, generally in a higher proportion than the others. As an example of the conversion reactions from aminoacids in alcohols, the following global reactions are presented:

leucine + water -----------------------> isoamyl alcohol

(CH3)2.CH.CH2.CH(NH2).COOH + H2O----> (CH3)2.CH.CH2.CH2OH + NH3 + CO2

isoleucine + water --------------------> amyl alcohol

CH3 (CH2)3.CH (NH2).COOH + H2O --->CH3. (CH2)3. CH2OH + NH3 + CO2

valine + water ------------------------> n-butyl alcohol

(CH3) 2.CH.CH(NH2).COOH + H2O ----> (CH3)2.CH.CH2OH + NH3 + CO2

alfa-amino butyl alcohol + water -----> n-propyl alcohol

CH3.CH2.CH (NH2).COOH + H2O ------> CH3.CH2.CH2OH + NH3 + CO2

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The production of the higher alcohol mixture or fusel oil reaches average values between 0.4 and 0.6 percent of the total alcohol production.

The amount of fusel oil obtained in a distillery will depend mainly on the conditions of fermentation and on the fusel extraction tray selection system, for the rectifying column and concentrating of heads. Composition of the fusel oil: The typical composition of the fusel oil obtained in distilleries that process sugarcane juices or syrups, is shown in the following table. Table 3. Typical composition of fusel oils

Compound Chemical formula Concentration (%v/v)

Acetaldehyde C2H4O 0.003

Propanol CH3CH2CH2OH 0.060

Ethyl acetate C4H8O2 0.008

Iso-butanol C4H10O 0.076

n-butanol CH3(CH2)2CH2OH 0.025

3-pentanol C5H12O 0.002

Isoamyl Alcohol (CH3)2CHCH2CH2OH 63.53

n- amyl C5H12O 0.186

2,4 dimetyl 3 pentanol C7H16O 0.001

Furfural C5H4O2 0.008

n-amyl acetate C7H14O2 0.583

Uses of fusel oil: Due to the low production of fusel oil in distilleries, it is economically unviable to use it by ways of separating the cogenerates it contains. This is the reason why it is usually disposed of as waste or used as fuel in the distillery or sugar mill boilers. However, it can serve as raw material for the production of acetates using esterification reactions. Other materials Besides molasses, ethanol production requires other materials, such as nutrients, chemicals, process water, cooling water, electricity and steam. Some of these materials can be obtained at a nominal price as byproducts from the sugar mill, while others must be specifically obtain for the distillery. These materials will depend on the equipment, technology, and process available.

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Table 4. Energy and other materials required in distilleries DIST 1 DIST 2 DIST 3 DIST 4 DIST 5 KATZEN LITERATURE ** Steam, Kg / Liter of Alcohol *

3 4.2 3.5 5.5 4.8 2.28- 5.21 4.8

EE KW / Liter of Alcohol

0.033 0.2 0.15 0.15 0.03 0.03

L Alcohol / t molasses 49FS

252 262 260 264 261 267

H2SO4 lb / L Alcohol

0.004 0.006 0.008 0.01 0.0038

UREA, lb / L Alcohol

0.004 0.008 0.0015

H3PO4 lb / L Alcohol

0.0025 0.0015

Yeast lb / L Alcohol

0.0015 0.02 0.005 0.008 0.0025

* Depending on the arrangement of the columns and on the final product design ** Peters & Timmerhaus. IRAS Statement of Capabilities.

BIBLIOGRAPHY 1. Aiba, S.; Humphrey, A.; Millis, N. 1975. Biochemical Engineering. 2nd

Edition, Academic press, London , UK. 2. Borzani, W.; Almeida e Lima, V.; Aquarone, E. 1975. Biotecnología –

Enghaniaria Bioquímica. Edgard Blucker Ltda. 3. Espinosa, R. 1984. The alcoholic Fermentation of molasses- practical

aspects. Doctoral dissertation, Century University, New Mexico. 4. Duarte, P.; Vânya, Marcia. 2006. Especificaciones de la calidad del etanol

carburante y del gasohol (mezcla de dasolina y etanol) y normas técnicas para la infrastructura. Naciones Unidas, Comisión Económica para América Latina y El Caribe-CEPAL. LC/MEX/L.71/Rev.1. pp. 3-7.

5. Ingledew, W. M. 2009. The Alcohol Textbook, 5th Edition. Ethanol

Technology Institute. Nothingham,University press. 6. Normas: ASTM D 891-95, 2004; ASTM D 4052-96, 1996; ASTM D 4806-

6 c, 2006; ASTM D 5798-06, 2006; ASTM D 5501, 2004; ASTM D 1613, 2006; ASTM D 6423-99, 2004; ASTM D 4176, 2004.

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7. Paturau, J. M. 1982. Byproducts of the Cane Sugar Industry. Elsevier Scientific Publishing Co. New York.

8. Prescott, S.; Dunn, C. 1967. Industrial Microbiology, McGraw- Hill, co. 9. Peters, M.; Timmerhaus, K. 1980. Plant Design and Economics for

Chemical Engineers, McGraw –Hill, N.Y. 10. Reynolds, R. 2002. Fuel Specification and Fuel Property Issues and Their

Potential Impact on the Use of Ethanol as a Transportation Fuel. Downstream Alternatives Inc. Phase III Project Deliverable Report. Oak Ridge National Laboratory, Ethanol Project. pp. 2-2/2.

11. Silva Junior, J. F. 2007. Market specification and Methods for Fuel Ethanol.

Simposium on BioFuels: Measurements and Standars to Facilitate the Transition to a Global Commodity. US National Institute of Standards and Technology (NIST), Brazil's National Institute of Metrology (INMETRO). UNICA/IETHA. June 26-29, 2007. Pp.

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COPRODUCER PERSPECTIVES ON SUGARCANE

Mario Muñoz

INTRODUCTION Traditionally, the Sugar Industry bases its production on three main products: Sugar, electricity, and alcohol. The markets for these three products show demands with a certain variation, which at specific times may show uncertainty and less revenue than the one foreseen by the producers. Among the most important factors affecting production, generation, demand, and consumption of these products are: Government policies such as subsidies or taxes, both of the producing countries as well as of the buying companies; local climate effects and environmental conservation regulations; the entrance of countries with emerging economies into the market; the need to substitute non-renewable materials, such as petroleoum and its byproducts; the rise and search for biofuels and biodegradable raw materials; and in general, the growth in economies in an evermore globalized world. All of this forces the sugar producers to find alternatives for new co-products that can be developed either as by-products of the products still in progress within the process or from their waste and residual sub-products. The range of possibilities is great; however, its commercial success will depend on the degree of development of the technologies applied and on the added value of said products. That is, if products with high added values can be produced, even though this implies that high priced products will be sold in low volumes, or, if on the contrary, they are sold at lower prices but in higher volumes; either way, producing these co-products is full of challenges not only technological but in marketing as well. Throughout the sugar production process, there are several stages where “products still in progress” can be extracted; they would constitute the raw material for other co-products and by-products, sometimes, with well differentiated fabrication methods, and in some others with adjoining chemical processes; the integration of these processes is known as a bio-refinery. The first product usually not used is the harvest residue; this is due to the burning that takes place in the sugarcane fields. When the sugarcane is harvested “in green” (without burning the fields prior to cutting the cane), a large amount of biomass is left behind in the fileds; it could be used as animal

  Industrial-Mechanical engineer, Professional in the Energy Efficiency Industrial Research Program of CENGICAÑA. www.cengicana.org  

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feed, as fuel for the boilers, as fertilizer, as a medium for growing mushrooms, as a paper pulp generator, etc. Another important by-product is the bagasse that comes out from the milled sugarcane; because of its high heat value, it is usually used as fuel for boilers; however, it could also be used for the production of a variety of products such as concrete aggregates, construction boards, animal feed, pulps and papers and it can even be used as absorbent material during on-land oil spills. The syrups and juices not used for sugar production are fundamentally the raw material for the production of alcohol; alcohol, in turn, is used in fine chemical applications to make other compounds and a number of chemical substances in the pharmaceutical and food industries. Bio-refineries can process sugary products to produce sweeteners and the likes to make chemical products with a variety of applications in all kinds of industries. Finally, residues from the sugar process, such as vinasse, mud cakes left from the filters, and the ashes leftover from the boilers also have a possible participation in the markets of important industries, such as the production of biogas, fodders and puzzolanic aggregates. The technologies used to produce all of these products go from elementary and conventional all the way to experimental; again, it will be the market the one that marks the plausibility and development of these technologies at a given moment. What is for sure, in a rapidly changing and demanding world where the demands are many and the raw materials are limited, sugar mills will be forced to develop technologies and alternative co-products to face the everchanging future. There is an ample range of processes and products, and this allows a modern sugar producing factory some flexibility. However, it will all depend on its size, its potential and its persperctives on the market in which these co-products will develop. Figure 1 illustrates some of the pathways in which some of the co-product in the sugar industry can develop. Coproducts A co-product is derived form the main materials in a production process (raw material, labor, and indirect costs) where two or more products are obtained simultaneously; they are considered of equal importance with respect to the total production, whether it be for the needs they cover or for their commercial value. Subproduct (byproduct) or derivative A byproduct is derived from the materials in a production process (raw material, labor and indirect costs) where two or more different products are obtained simultaneously or successively, and according to their commercial value, they are considered of lesser importance with respect to the main products.

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A large number of products and byproducts can be derived from sugar; their production depends on the final value of the main coproducts and the size of the market to which they belong. Table 1 shows, in a general manner, a miscellaneous variety of final co-products obtained from sugarcane, their characteristics and common markets.

Figure 1. Possible products and co-products in a bio-refinery based on sugarcane Table 1. Miscellaneous products from sugarcane (Cabello, 2002)

Product Characteristics Use and market Bagasse Alternative fuel Fire logs

Pleurotus mushroom Culinary delicacy Restaurants Maple type syrup Sweets and baking Industrial

Sugar and “panela” Minidose, cubes, etc. Airlines Caramel color Food and drinks Drinks and canned goods Hydrocoloids Food and pharmaceuticals Medicine

Candy Different types General use Camic flavoring Autolyzed yeasts Cold meats and soups

Veterinary products Probiotics Cattle, pork Typical drinks Local folk products Tourism

Alcohol specifics Cleaning gel Household and others Dry ice Alternative refrigeration Fishing, milk, ice cream

APPLICATIONS FOR CO-PRODUCTS A co-product has more or less added value depending on whether it can be sold in bulk (at a lower price), than when it is sold in retail at higher prices; when the latter happens, sugar products go on to being fine chemistry substances. Table

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2 shows the products that are commercialized in bulk and are carbohydrates; saccharose occupies second place after cellulose, and it easily exceeds the combined production of all the other carbohydrates.

Table 2. Annual production of carbohydrate products

Carbohydrate products Annual production (millons of tons)

Cellulose < 130Saccharose ~ 124

Starch ~ 25Glucose ~ 6Cellulose ~ 5

Gums < 1

It is estimated that only 1.7 percent of the annual saccharose production is destined for “non” food uses. Sugarcane and its co-products are open to possibilities in the following areas: Fine chemistry products Pharmaceutical products Polymers (biodegradable plastics) Construction and structural materials Fermentation or enzyme substrate for the production of chemical products New food products and sweeteners Co-generation of energy Fuels such as bio-diesel and ethanol DIVERSIFICATION OF THE COPRODUCTS The coproducts and derivatives of sugarcane can participate in different markets, according to the technology used in their production, from the raw material and other materials used throughout all the stages of the sugar production process. It is said that they are used in an elementary way when their application is direct and without added value due to process; they can also be processed with conventional industrial procedures, where the products have very distinct and known technologies and markets. A third and fourth markets are represented by complex and latest technologies, where the processing of raw materials is complex, of high added value but sometimes limited use, and in some cases still in the developing or experimental phase. In Table 3, the different raw materials coming from the different phases of sugar production can be appreciated; to the right, the technologies and frequent uses of derivative co-products are shown.

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Table 3. Sugarcane coproduct diversification according to technology (ICIDCA, 2000)

Raw Material Technology (Products/Processes)

Uses Elemental Conventional Complex Updated

Leaves and tips Direct use Edible mushrooms Food, feed

Densification Soil additives

Silage with clarifier muds

Animal feed

Bagasse Mixed with molasses Increased digestibility Paper and pulp Paper and cardboards Animal feed, Industry

Compacted Molded panel

products

Macrocrystaline cellulose Fuels, Industry, farmaceuticals

Furfural Lignin compounds Industrial, veterinary use

Xylitol Furanic compounds Industrial, farmaceutical

Marrow* Mixed with molasses Increased digestibility Animal feed

Low grade juices and

syrups

Alcohol Glucose, fructose Yeast by-products Potable, Industrial, farmaceutical

Recovered yeast Citric, lactic acids Hormones, enzymes Animal feed, Industrial, agricultural

Rum, liquor Fodder yeast Pest control Human consumption, Food, agriculture

Carbon gas, dry ice Lysine Reactive alcohol Industry, Food, laboratories

Deshydration Dextrane, Xantane Drinks Industry, Human consumption

Alcohol Alcohol Phytosterols Potable, Industrial, cosmétics

Molasses Mixed with bagasse or

marrow

Recovered yeast Glucose, fructose Animal feed

Nutritional blocks Rum, liquor Cítrico, láctico Anima feedl, human consumption

Carbon gas, dry ice Fodder yeast Industrial, Food

Dehydration Lysine Industrial

Dextrane, Xantane Industrial

Alcohol Industrial

Clarifier muds Direct use Composting Waxes, oil Heavy weight alcohols Fertilizer, Industrial, farmaceutical

Sundried Fertilizer

Ash Mixed with clarifier

muds

Fertilizer

Residuals Lagoon treatment Fertilizer

Vinasse Field irrigation Lagoon treatment Fodder yeast Fertilizer, irrigation

Biogas Environmental protection

Concentration / Incineration Environmental protection

Marrow: Sugarcane pith, cane core after the fiber has been taken away

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CO-PRODUCT AND BY-PRODUCT DESCRIPTION The by-products of sugarcane can be analyzed according to the raw material they are produced from. The manufacturing process of cane sugar is divided into several steps, where transforming the cane into sugar gives way to “products in progress” and from which other co-products and by-products can be extracted. Depending on the manufacturing stage, the most commonplace products in progress in the sugar industry are: Residue from the harvest Bagasse Syrups, juices, and molasses Clarifier muds from the filters Vinasse Figure 2 illustrates different scenarios for which a sugarcane by-product can become industrialized; this will depend on its manufacturing costs and its market value (price).

Figure 2. Economic indexes for the selection of a co-product deriving from

sugarcane (Almazán, 1998) Co-products derived from the harvest residue These are the products deriving from the biomass left behind in the cane fields after the sugarcane has been cut and lifted; they are basically made up of leaves,

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tips, hearts, and straw. The amount and the quality will depend on the way the harvest is done (by burning or in green, by hand or mechanized) and the physical and chemical characteristics will vary according to the sugarcane variety, the soil and how the plant is treated before harvest. Figure 3 shows the commercial and technological possibilities residues left in the field after harvest.

Figure 3. Alternatives for the use of agricultural residue of sugarcane The following is a summary of some of the specific, alternative and non-conventional applications of the harvest residue. Forage: They (hearts, tips, leaves, and straw) can be used as cattle feed, although it is generally necessary to previously mix them with molasses, urea and mineral salts to complete the feed. Lactic acid production: Results from studies prove that harvest residue (leaves and tips) can be used as cheap raw material for the production (by fermentation) of lactic acid. The harvest residue when cane is cut in green has a water content of approximately 75 percent and a total nutritional content with sugars, nitrogen, phosphorous, potassium, calcium and magnesium. These nutrients are necessary for microorganism growth, which suggests that both harvest residue and sub-products can be employed as cheap substrates for fermentation (Serna, 2007).

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Biogas: The production of biogas using biodigestors to treat crushed sugarcane stems and the residual biomass left behind in the cane fields after harvest has proven to be feasible. These products increase the quantity and quality of the biogas production coming from the mixture of cow manure (Pound, 1981). Bagasse co-products (ICIDCA, 2000) Bagasse, according to the previous concepts, is a co-product whose high heat value is used to produce thermal and electrical energy in sugar mills; commercially, it also represents an important source of income for the factories. However, as biomass, bagasse can be transformed into a series of co-products and by-products through different technologies, representing alternatives to the current method of electrical power generation. Bagasse, a lignocellulosic residue from the cane stalks obtained at the outlet of the last mill, constitutes a heterogeneous set of particles of different size. From a physical point of view, bagasse is made up of: Bagasse fiber, soluble solids, insoluble solids and water. Chemically, it is made up of cellulose, hemicellulose and lignin, as main natural polymers. Refer to Table 4.

Table 4. Physical composition of bagasse

Fraction Range %

Fiber 55-60 Heart (core) 30-35 Fine particles, soils and solubles 10-15

In the following paragraphs you some specific applications for the use of bagasse to produce alternative non-conventional products, are described. Concentrate for animal feed: Protein concentrates have been produced with the Saccharomyces cerevisiae and Candida utilis yeasts as protein sources for bovine and caprine herds; this is done by the biotechnological use of bagasse. The bagasse is submitted to hydrolysis with diluted sulphuric acid (6% v/v) in a liquid/solid relation of 30/70, and subjected to 4 hours of reflux boiling; from the sugarcane bagacillo, soluble reducing sugars are obtained; they serve as a culture medium for the yeasts, which are non-toxic to animals. The C. utilis surpassed the S. cerevisiae in the production of biomass (single cell protein) by 48%, for the same reducing sugar concentration from the concentrated hydrolyzed acid from the bagacillo. Statistical analysis showed that the C. utilis is the best yeast for this bioprocess. The high lysine and treonine content, as well as a

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balanced aminoacid content, suggests a potential use for these protein concentrates as complements to cereal diets, since the latter is deficient in aminoacids. (Ferrer, 2004) Pulp and paper: The ever decreasing availability of fibrous materials for the paper industry and its by-products, and the renewable nature of bagasse (sugarcane), has stimulated its use in the pulp and conglomerate products industry during the last decades. Bagasse pulps present a combination of properties and resistance that allow them to incorporate into paper paste. They can be used to make newspaper and printing paper, as well as a variety of high quality cardboards; if the process of the pulps is alkaline, it can also be used to produce finer type of paper, such as bond (white) paper, card, and tissue paper. If the pulps have elevated chemical purities (alpha pastes), then, they are used for the production of the fibre and threads used in rayon. Absorbent pulps are a special type of pulp designed for the quick absorption of liquids, making them the ideal raw material for the diaper and sanitary napkin industry. The use of bagasse in the paper industry will depend on the cost and characteristics of the bagasse itself; to that, it is important to acknowledge the costs added by transportation, processing and storage of the bagasse (ICIDCA, 2000). Figure 4 shows one of the commonplace processes used in the production of paper from bagasse.

Figure 4. Manufacturing process of newspaper from sugarcane bagasse

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Celluloses: Carboxymethylcellulose and microcrystaline cellulose can also be produced from sugarcane bagasse. Carboxymethylcellulose is used as detergent, thickener and glue in the tobacco and rayon industries; it is also used to glue threads in the textile industry. Microcrystaline cellulose, due to its chemical purity, posseses properties that make it suitable for the manufacture of creams, cosmetics, detergents and as an excipient in the pharmaceutical industry. Filter aids and filter media: Bagasse has proven to be feasible, in combination with other wooden fibers, in the production of filter aids. These have several uses: Filters for rum and beer, for sugary syrups, for vinegars, wines, pharmaceutical products, papers for laboratories, and for paints and varnishes. Pharmaceuticals: Pharmaceuticals for gastrointestinal disorders are developed from lignin (due to its absorbing capacity). It has been proven to be capable of bonding nitrates, cancerogenous substances, bile salts, nitrosamines and mineral salts in the gastrointestinal tract. Panel products: These are panel sheets and boards made with bagasse particles aglomerated with organic glue under specific temperature and pressure conditions. The furniture business is the largest consumer of these sheets, especially in the form of mdf and the likes. If the glue is in the form of cement, then the bagasse sheets can be used for the building of houses and schools. Additionally, if the conglomerates include plaster, then they can be used as sheetrock for ceilings. Furfural: This is an aldehyde by-product from the pentosans found together with cellulose in many of the plant tissues. It constitutes the main element of furans. Their chemical properties make it a very versatile product with a high reactivity for organic compound synthesis. Its main applications are industrial products such as polymers and pesticides. They derive from the following chemical reaction:

C5H8O4 + H2O ----------C5H10O5----------C5H4O2 + 3H2O

Xylan Xylose Furfural

In practice, clos to 25 tons of bagasse are necessary to produce one ton of furfural. Figure 5 shows a diagram description of the products that can be derived from it.

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Figure 5. Applications for furfural (Gravitis, 1999)

Activated carbon: Bagasse can be treated through pyrolysis (chemical decomposition of organic material and all types of material, except metals and glass, by heating in the absence of oxygen) in order to obtain activated carbon. The final product is used as an adsorbent in decoloration, chemical protection, residual water treatment and chemical product purification processes. Hydrolysis of bagasse: Hydrolysized bagacillo (unfolding of the molecule of certain organic compounds in bagasse through the action of water) is a product obtained by its treatment with steam; the goal is to increase its digestibility so it can be employed as animal feed, especially for cattle and poultry. Source of silica: Depending of the type of soil and the time when the sugarcane is cut, the ashes from bagasse taken from the boilers can be a rich source of silica. Some studies reveal silica gel has applications as an adsorbent, as material for ceramics, cement, concrete additive, catalizer, cosmetics, paints and coatings. The treatment consists in drying, filtering and heating the ashes of bagasse in a furnace with oxygen; later, it is treated with hydrochloric acid. Table 5 shows, in the right hand column, the components in bagasse ash after this treatment. (Worathanakul, 2009)

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Table 5. Production of silica (SiO2) from the ashes of bagasse

Component Mass %

Raw Material Heating

3 h Treatment with

acid SiO2 19.417 29.849 89.037 K2O 35.036 23.99 2.134 P2O5 12.428 12.043 1.687 SO3 10.969 13.242 0.33 CaO 14.482 13.307 2.549

Mn2O3 1.236 1.303 0.153 Fe2O3 1.884 1.812 1.969 Al2O3 0.973 1.262 0.791 Otros 0.809 0.594 0.791

Hydrocarbon removal: Bagasse and clarifier muds as soil bio-remedies have been used as texturizers and rectifiers when petroleum, diesel and gasoline spills occur. Clarifier muds, besides working as rectifiers, present the advantage of being able to contribute microorganisms to the soil with the capacity to bio-transform toxic waste. (García, 2011) Puzzolanic aggregates: The introduction of substitute materials for Portland cement, such as puzzolans, allows for the possibility of productively using a waste material, of which there are generally large amounts in sugar mills, such as bagasse. Certain criteria have been applied for the packaging of particles in the manufacturing of binary, ternary and multicomponent mixtures for the tailoring of pastes, mortars, and concrete. When formulating a mixture of particles where a binder will hold them together, it is important to pack them as densely as possible to achieve the best aglomerate possible. This will minimize the amount of binder (glue) necessary since the spaces between the aggregates will be reduced to a minimum. There is an economic benefit to this, as well as an improvement in the final product (concrete, mortar or paste) for less contraction, and therefore more strength will be obtained. (Martínez, 2003) Co-products from juices, syrups and molasses (ICIDCA, 2000) Sugar products from sugarcane are the ones that are exhausted in the sugar factories and where sugar is extracted from. Yet there are good amounts of sweetening agents and by-products that can be extracted from syrups, or from molasses that are best left for other purposes besides sugar, generally, for the production of alcohols (rums and ethanol). However, as an alternative to sugar, there are other co-products that can be extracted or derived from the cane

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syrups. The following is a list of products and applications of those juices and syrups. Amylase: Enzyme product of bacterial origin. It participates in the degradation of starch. The final result is a mixture of glucose, maltose and low molecular weight dextrins. Amylase provides a valuable solution to the problems involving the improvement of products such as starch, paper, alcohols, beers, textiles, and detergents. Dextranase: It is an endoenzyme used to degrade the high weight dextrans, with the purpose of reducing the sugar losses and the deformation of sugar crystals, resulting in the increase of viscosity in the massecuites. Cellulose: The fundamental use of these enzymes is the degradation of cellulose. It is frequently used in the processing of cereals, beer, fruit extracts, and treatment of residuals. Xylanase: The fundamental use of this complex enzyme is the degradation of Xylane. Its main application is in the production of Xylytol, a substitute of sugar for diabetics. Yeasts: Yeasts are unicellular microorganisms used for industrial and commercial purposes. They are used as a food suplement for human consumption and for animal feed. Yeasts have the advantage of being able to metabolyze a large quantity of substrates; they grow at great speeds and their biomass is easily separated. The Saccharomyces yeast is used in the alcohol, bread, and beer industries. Torula yeast is a valuable fodder due to its high protein content. Invertase is the yeast produced enzyme used in the inversion of syrups because it hydrolizes saccharose. Dehydrated syrup: This is a hygroscopic powder with a brown-redish color and pleasant flavor. It is designed to feed pigs and birds in their first growing baby stage, substituting the use of cereals. Direct use: Syrups are obtained from the concentration and exhaustion of saccharose in sugarcane juice. Depending on the stage of the process, they can be high syrups, virgin syrups, inverted syrups, syrup A, syrup B, and final molasses. These syrups are good alternatives for cattle feed, especially when combined with bagasse and urea. Figure 6 shows a comparison of the calorie yield per hectare between several co-products and some grains used as animal feed. The greatest yield corresponds to sugarcane.

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Figure 6. Annual calorie yield per hectare in mega-calories Lysine: It is an aminoacid that cannot be synthesized by animals. Therefore, it must be incorporated externally. A lack of lysine in the diet obstructs the sexual system and causes muscular exhaustion and other pathological phaenomena. This product is utilized for the enrichment of cereals for human consumption and in the pharmaceutical industry. Citric acid: It is a chemical product obtained from final syrups by fermentation. Most of the citric acid is used in the food industry as anacidulate, emulsifier, fat, and oil stabilizer to enhance flavor. It is also used in the pharmaceutical industry. Co-products of alcohol Alcohol is a by-product of sugarcane. It also constitutes the raw material for other sub-products through the many ways there are for its transformation. Among them, the production of ethylene or acetaldehyde and its by-products, permitting the growth of the industry called alco-chemistry. Alcohol (C2H5OH) is a colorless, transparent, volatile, ether smelling and pungent tasting liquid. It is used in the distilling industry with different grades of purity. It is commercialized in both hydrated and dehydrated form. It is obtained by the bio-chemical synthesis of fermenting juices, syrups and sugarcane molasses. Alcohol can be used as an alternative fuel, as an antiseptic, solvent, and preserving agent in the manufacturing of: gums, resinol, soaps, escence oils, perfumes, pharmaceuticals, waxes, and alcoholic beverages.

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The chemistry of alcohol combines two successful technologies: Alcoholic fermentation and alcohol catalytic processes. Many of the biology based products can be obtained from ethanol by the chemical pathway of alcohol. The production of ethylene opens a door for the production of bio-plastics. Ethylene is a forerunner to certain plastics, for example PE, PVC, PVA and polyestyrene; it is sold worldwide by millions of metric tons.

The rise in oil (petroleum) prices and the environmental protection laws have given rise to a considerable increase in the demand of alcohol, both as a fuel and as an antiknock alternative to metyl tert-butyl ether (MTBE). Due to Brazil’s decisive role as an exporter of both sugar and alcohol, any change in its strategy for the use of sugarcane, has direct consequences on the availability of both products (sugar, alcohol) in the market. Hence, two aspects in the Central American region require attention. On the one hand, the main market for this type of alcohol is the United States of America; thus, the future of possible exports to that market will depend largely on the subsidies to the national production of alcohol made from corn and other local (US) raw materials. On the other hand, small countries with immediate access to the sea have considerable limitations when it comes to the treatment of residue, since the direct irrigation of the cane fields mainly used in Brazil is not really viable when there are area limitations; and industrial treatment of the residue has a very high investment cost.

The following are applications and co-products extracted from alcohol.

Rum and eau-de-vie(“aguardiente”): Eau-de-vie, also called firewater is defined as non-rectified alcohol, embiagating beverage obtained from the distilling of sugarcane by-products after fermentation and used for human consumption. The production of distilled beverages from sugarcane (aguardiente, rum, vodka, etc.) is one of the most lucrative alternatives, despite the high taxes commonly applied to this type of product, as long as the marketing regulations in such a competitive market. The right design related to quality, presentation and price is essential for the success of a product in this sort of activity. Tires: Tires can also be made from sugarcane. Synthetic rubber for tires can be made from butadiene; it can be obtained by the catalytic conversion of alcohol. Its process was developed in Russia in the XX century. There is currently a high demand for biomaterials in the automotive industry.

The process begins with the oxidation of ethanol; acetaldehyde is produced. It is an important intermediate chemical product for the production of other products, such as acetic acid, peroxyacetic acid, anhydride acetic, butanol, crotonaldehyde, pentaerithritol, cloral, pyridine, and acetic acid esters. This way, ethanol can reach, through chemistry, different markets such as: agricultural, food, packaging, construction, coatings, inks, cosmetics, and

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pharmaceutical products. Ethyl esters are another type of products deriving from ethanol. Ethyl tert-butyl ether (ETBE) is an oxygenating additive for gasoline that can susbstitute methyl tert-butyl ether (MTBE). On the other hand, diethylether can also be obtained from ethanol. Here the deal is with an important solvent for the chemical industry, used in the production of cellulose plastics, as for example, cellulose acetate. Figure 7 shows how several chemical co-products can be extracted from ethanol acetaldehyde .

Biobutanol: It is an alcohol that offers several advantages. It can be transported in already existing gasoducts; it is less corrosive; it can be mixed with gasoline or used by itself only in internal combustion engines; and it gives off more energy per gallon than ethanol. Until the mid XXth century, it was produced form fermented sugars such as corn glucose. However, low yields, high recovery costs and an increase in the availability or petroleum after World War II gave margin to the fermentation and the production systems of Biobutanol. This process used the Clostridium bacteria to carry out the critical task of fermentation. Such processes usually involve four separate and consecutive preparation stages: Pre-treatment, hydrolysis, fermentation and recovery. Biobutanol is a colorless and tasteless liquid with a slight odor. Other names for it are buthyl-alcohol and wood alcohol. It is produced from natural gas, but it can also be derived from raw biomatter sources.

Figure 7. Acetaldehyde ethanol and its by-products (ICIDCA, 2000)

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Methanol: It is a raw material for many of the by-products in the chemical industry. It is used to produce folmaldehyde, acetic acid and a variety of intermediate chemical products. These by-products are used in the manufacturing of innumerable products used in our daily lives, such as: Resins, adhesives, paints, inks, foams, silicones, plastic bottles, polyester, dissolvents and liquid windshield cleaner. Methanol is also widely considered as a potential hydrogen carrier for many of the future applications of fuel cells. Methanol is among the four chemical products most widely used in the world. (Mohan, 2007) Other by-products (ICIDCA, 2000) Dextrane: It is a polymer of glucose. Its use is limited to toothpaste, pharmaceutical products, paints and adhesives. Xanthan gum: It is a polysaccharide viscosifying agent. It has applications in many industries, such as the food and petroleum industries. Sorbitol: It is a hexacyclic alcohol obtained form the hydrogenation of dextrose. Due to its energy value and since it is less sweet than sugar; it is used in the manufacturing of food with low calories content for diabetics. Glycerol: Used in the synthesis of resins and gums in the manufacturing of explosives, cellophanes, toothpastes, cosmetics, pharmaceutical products and food preservants. Hydrogen: It is considered the fuel of the future, especially since it has water as its residue after its energy release reaction with oxygen. There are different ways of producing it; the reformulation of hydrocarbons and the separation of the water molecule through electrolysis is the industrial method most widely used; the reformulation of ethanol and the use of microorganisms are still being studied. The possibility of reformulating ethanol for the production of hydrogen is an alternative in sugarcane and corn producing countries, making its direct use or the use of fuel cells possible. A recent study on the energy released by hydrogen fuel cells produced the reformulation of ethanol, besides using the solid residue for the production of biogas; the latter supplies the necessary fuel for the distillation and ethanol reformulation processes. The production of microbiological hydrogen directly from solar energy by anaerobic bacteria, green bacteria and cianobacteria or blue algae, is currently under research. Co-products from sugar (GODSHALL, 2011) In the sugar factory of the future (bio-refinery), strategic alliances between production, commercialization and other associates, the use of new technologies and the development of new chemical products, will be enough to produce an

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ample range of low, medium and high value products. The sugar factory of the future integrates the production of sugar, ethanol, electrical power (through bagasse and harvest residue), bioplastics and chemical products. Australia, Brazil, and India are well on their way to produce energy through the gasification of bagasse. An efficient bio-refinery integrates and recycles mass and energy flow with the purpose of supplying the maximum efficiency at the lowest cost; integration in agriculture, as well allows the residue to be reused in the sugar plantations so the CO2 produced can be recycled through photosynthesis. Figure 8 shows a diagram of an efficient bio-refinery.

Figure 8. Diagram of an efficient bio-refinery Sucralose: It was discovered in 1976 by Tate & Lyle researchers when three chlorine atoms were added to the saccharose molecule; they noticed they had created a substance 600 times sweeter than saccharose, with the same taste as saccharose, but it would not decompose in the human body. Evidence showed the compound is safe for human comsumption. In 1991, Canada became the first country to approve its use in food. In 1998, sucralose was approved by the FDA for its use in the United States; it is now used in at least 28 countries. The McNeil Specialty Products Company in New Brunswick, New Jersey, sells sucralose under the Splenda brand. Olestra: It is a substitute for saccharose based fat. It was developed by Procter & Gamble in the 1970’s. It was approved for human consumption by the FDA in January 1996 after three years of research and evidence. To make it, saccharose is made to react with fatty acids to produce a polyester of liquid saccharose. Olestra is sold by P&G under the Olean brand. Olestra has similar

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properties to liquid vegetable oil, but without the calories. It is currently being used to prepare salty appetizers, in particular for French fries, in a merger between Frito-Lay and P&G. Fructo-oligosaccharides: They represent an interesting study case in the development of a new product; it falls some place between the category of food additives and neutraceutics. They are also known as FOS, and commercially they are known as Neosugar and Meijioligo. FOS is a new healthy food developed through the fermentation or enzymatic transformation of saccharose. It is extremely popular in Japan, although it has also raised interest in Europe and North America. It is said that FOS is good for “abdominal health” in the sense that it promotes the growth of bifidobacteria in the intestine, and they supposedly give many other benefits to the body. Its sweetness ranges between 30 and 80 percent than that of saccharose, depending on its composition. It is sold in the form of syrup or in a powder; it generally contains a certain proportion of saccharose and fructose, together with another three oligosaccharides: Kestose, nitrose, and fructofuransonil nistose. Some of their most promising uses include the protection of pork from E. coli infenction and porcine odor control. Sucralphate: It is a complex aluminum hydroxide, saccharose sulphate used as medicine for ulcers in humans and animals. It is not absorbed by the body and it has its own characteristics in the fight agains ulcers; it acts as an “ulcer bandage”, actively aiding in healing. Polysucrose: It is a copolymer of saccharose and epiclorohydrine. It is used to make density gradients for cellular separation and as a diagnostics agent. It also has some potential as a nutraceutic or as a food additive. Patents in the United States have promoted it as ingredient in sports’ drinks, and in India, as an iron supplement. Sucrose esters: These can take many forms because they have eight available hydroxyl to react with numerous fatty acid groups. This flexibility means that many products and functionalities can be adapted depending on the fraction of the fatty acid used. Saccharose esters have many applications in food and non-food products, especially as surfactants and emulsifiers; they have evergrowing uses in pharmaceutical products, cosmetics, detergents, and food products. They are easily biodegradable, non toxic and soft for the skin. Isobutyrate acetate: This (SAIB) is the one with the highest volume of use, both in food and industrially. It is used in automotive paints, as a clouding and stabilizing agent in beverages, in nail polish and in hair spray, among other uses.

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Detergents with a saccharose base: Biodegradable non-ionic detergents with antibacterial properties can be made from saccharose esters; it is a small but emerging market. Derisa Corp., in Argentina, commercializes a saccharose based detergent called Sucrotex; some are also manufactured in the Philipines. Europe has shown a significant interest in these types of products. Thermal sucrose-oligosaccharide caramel: Researches from the University of Montana developed sucrose thermal-oligosaccharide (STOC) by means of the controlled pyrolysis of saccharose. Amorphous saccharose is heated with citric acid to produce fructoglucan. This functions as a dietary supplement to increase the growth in poultry and it can be applied as a possible non-calorie agent in foods. These researchers have also experimented with the reaction of other carbohydrates from saccharose to manufacture other products. For example, a controlled thermal reaction between sucrose and ciclodextrine produces fructose cyclodextrin compounds with the ability to improve the solubility of inclusion complexes, and as flavor and vitamin carriers in processed foods, these can have applications as flavor and vitamin carriers in food. Epoxies: Doctor Nozar Sachinvala, a scientific researcher form the South Regional Research Center for the FDA in New Orleans, has discovered a series of sucrose epoxies that are neither mutagenic nor cytotoxic, they can adhere metal to metal, metal to glass, and fiber to fiber. The big sucrose based adhesive producers are trying to introduce them into the textile, housing insulation, and other construction materials industries. Hydrogels (sucrogels): Compounds made in a two stage processs. Their properties can be manipulated on a wide scale by adjusting the reticulation relation and initial monomer concentration. These products are super-porous and they have a potential use in the controlled release of pharmaceuticals. They can be made in any size, shape and form, with the required properties. They have many industrial applications. Biodegradable plastic (bioplastic): An area that creates a lot of enthusiasm for environmental preservation using “green chemistry” is the production of natural biodegradable plastics using microorganisms. Several species of bacteria produce biodegradable plastics by storing polymers within their cells. Between 50 and 60 percent of the microorganism’s body weight can be bioplastics, and in some cases even up to 90 percent. Bioplastics are expensive, but they have the advantage of being able to be processed in the same equipment used to manufacture conventional plastics. Research is being done to design bacteria capable of producing polyhydroxyalkanoates (PHA) and other polymers. Fermentation has benefited from the recent events in

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biotechnology. These results allow for new developments with microorganisms. As a consequence, the performance of the process can be significantly improved. Some examples of fermentative production chemical substances are biodegradable plastics such as Polyhydroxybutyrate (PHB), a completely renewable biopolymer obtained from sugarcane. Sugar is the substrate for fermentation, a process that allows the microorganism to accumulate the polymer. Cells are harvested at the end of the fermentation and the polymer is recovered from the biomass. Production of copolymers is also possible. Their biodegradability allows for special applications, such as special containers for plant growing that degrade, after the seed has been planted. Research is still ongoing to genetically modify plants that will be able to produce bioplastics instead of these microorganisms. Thus, we can assume that in the future sugarcane will be used to produce a wide range of products: Sweetners, biofuels, bioenergy, bioplastics, and other chemical products. Table 6 shows the perspectives from these points of view. Table 6. Development perspectives of co-products. (Langeveld, 2010)

Product Raw Material Market

Size Market Price

Sharing Potential

Production Size

Impact for Producers

Application Potential

Development Perspectives

Pharmaceutical Select crops Very small

Very high

Very large

Very low Very low Very poor

General Chemistry

Starch, sugar, crops, proteins

Very large

Low Modest Very low Very low Poor to modest

Fine Chemistry

Oils, Straws, Sugar, Proteins, crops

Very small

From average to good

Low Low Modest Very limited

Modest to good

Solvents

Oils, Straws, Sugar, Proteins, crops

Small Low Very Low

Very low Very lowVery limited

Very poor

Surfactants Various Small Low Modest Low Low Very limited

Poor

Lubricants Oils Very small

Low Modest to high

Low Low good Modest to good

Polymers Starch and sugar

Very large

Very Low

Low Modest Very LowVery limited

Very limited

Fibers Lignocellulose, fats, crops

Modest Low Low Modest Low Good Modest to good

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Co-products and By-products of Clarifier Muds Wax: Wax, oil, and resine make up the three fractions of the raw wax found in clarifier muds. Refined wax is used in shoe and floor waxes, cosmetics, dyes, emulsions for fruit, etc. Phytosterols: Oil from the clarifier muds is a product obtained from the refining of waxes and it represents a source of phytosterols. The mixture of phytosterols has a wide usage in the pharmaceutical industry to obtain hormones such as progesterone, pregnenolone, testosterone and their derivates. Hydrocarbon removers: In the event of an oil-spill with hydrocarbons such as petroleum, diesel or gasoline, bagasse and clarifier muds can be used as as soil bioremedy for they are able to texturize and absorb the spill. Clarifier muds not only work as rectifiers but they also gives microorganisms to the soil, biotransforming toxic materials. (García, 2011) Co-products and By-products of Vinasse Vinasse for fertirrigation: Vinasse is the residue left over by the alcohol industry. It is applied to the sugarcane fields mainly because it constitutes a source of potassium and other nutrients, besides providing carbohydrates that are easily assimilated and benefit microbial growth. Decomposition of the straw depends mainly on the activity of microorganisms, which are mainly responsible for the mineralization and recycling of nutrients to the soil. An increase in the production of CO2 can be considered as a result of the mineralization of straw, due to an increase in microbial activity. The addition of vinasse stimulates the production of CO2 and the activity of cellulose in the straw (Sanomiya, 2006). A more feasible and immediate alternative would be fertirrigation, where vinasse would be mixed in, with the residual liquids from the sugar mill during harvest season, and then it can be applied after no more than five days, of the retention time. Biogas: Vinasse is fundamental for the production of energy; it constitutes the raw material for the production of biogas. Among its main characteristics, it has low pH, high temperature, high biological oxygen demand (BOD), high chemical oxygen demand (QOD), and it also possess an important nutrient content. In order to take advantage of the potential of its physical-chemical characteristics, vinasse is subjected to an anaerobic digestion process through which methane gas is produced and captured. Then, in specially equipped chambers in the biodigestors, the methane gas is piped up towards the

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industrial plant, where it is used as a fuel for the boilers that produce the steam necessary for the plant’s operation. Needless to say, it is a source of renewable energy or bioenergy. BIBLIOGRAPHY 1. Almazán, O.; González, Gálvez, L. 1998. The Sugar Cane, its byproducts

and coproducts. Asociación de Técnicos Azucareros de Cuba. 12 p. 2. Alriksson, B. et al. 2009. Cellulase production from spent lignocellulose

hydrolysates by recombinant aspergillus niger. 10 p. 3. Broderick, G. A.; Radlo, W. J. 2004. Effect of molasses supplementation on

the production of lactating dairy cows fed diets based on alfalfa and corn silage. 13 p.

4. Brossard, L. E.; Penedo, M. Pirolisis al vacío del bagazo de la caña de azúcar. 10 p.

5. Cabello, A. 2002. La producción de derivados de la caña de azúcar en Cuba,

situación actual y perspectiva. pp. 12 6. Craig, K.; Overend R. 1995. Biomass power systems, where are we, where

are we going, and how do we get there? 19 p. 7. Ferrer, J.; Davalillo, Y.; Chandler, C.; Páez, G.; Mármol, Z.; Ramones, E.

2004. Producción de proteína microbiana a partir de los desechos del procesamiento de la caña de azúcar (bagacillo). 59 p.

8. García, C.; Bueno, V. Estudio toxicológico de un producto derivado de la

caña de azúcar. 11 p. 9. García, R. 2011. Uso de cachaza y bagazo de caña de azúcar en la remoción

de hidrocarburos en suelo contaminado. 10. Godshall, M. A. Future directions for the sugar industry. 8 p. 11. Gravitis, J.; Suzuki, M. 1993. Biomass refinery a way to produce value

added products and base for agricultural zero emissions system. 14 p.

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12. ICIDCA. 2000. Manual de los derivados de la caña de azúcar. MINAZ, La Habana, Cuba, tercera edición. 458 p.

13. Jeffries, T. W.; Schartman, R. Bioconversion of secondary fiber fines

ethanol using counter current enzymatic saccharification and cofermentation.

14. Kodera, K. 2007. Analysis of allocation methods of bioethanol LCA. 55 p. 15. Langeveld, J. W.; Dixon, A. J.; Jaworski, J. F. 2010. Development

perspectives of the biobased economy: A review. pp. 141-151. 16. Martínez, L.; Quintana, R.; Martirena, J. F. Aglomerante puzolánico

formado por cal y ceniza de paja de caña de azúcar: la influencia granulométrica de sus componentes en la actividad aglomerante. 15 p.

17. Médoc, J.; Guerrin, F.; Courdier, R. Paillat, J. A multi modelling approach

to help agricultural stakeholders design animal wastes management strategies in the reunion island. 6 p.

18. Meneses B. 2008. www.Sugarjournal.com. La Producción de Biogás con Vinaza una Alternativa Factible para Contribuir al Desarrollo de la Bioenergía. pp. 17-18.

19. Mohan, P. 2006. Liquid energy from cane in India. India. 6 p. 20. Murillo, F.; Araujo, C.; Bonfá, A.; Porto, W. 2011. Chemistry based on

renewable rawmaterials: Perspectives for a sugar cane based biorrefinery. 8 p.

21. Paturau, J. M. Usos Alternativos de la caña de azúcar y sus derivados en las

agroindustrias. 22 p. 22. Perdigón, S. M. La vinaza de jugos de caña energética y su aplicación en los

suelos cañeros. 11 p. 23. Pound, B.; Preston, T.R. 1981. Biogas production from mixtures of cattle

slurry and pressed sugar cane stalk, with and without urea. pp 11. 24. Sanomiya, L.; Assis, L.; De Oliveira, J. Nahas, E. Mineralización de la paja

de caña de azúcar en suelo adicionado con vinaza, subproducto de la industria del alcohol de caña de azúcar y fertilizante. 8 p.

431

25. Serna, L. S.; Rodríguez, A. 2007. Lactic acid fermentative production using waste from the harvest of green sugar cane as a substrate. 6 p.

26. Worathanakul, P.; Payubnop, W.; Muangpet, A. 2009. Characterization for

posttreatment effect of bagasse ash for silica extraction. 3 p.

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