DEPARTMENT OF CHEMICAL ENGINEERING

By A.V. Baloyi

Subject : Chemical Process Design

Project : Methane Oxidation to Acetic Acid

ABSTRACT

The main objective of this project is to produce acetic acid from

methane. This project will show the industrialization or

commercializing of this process by using Unisim design software.

The objective of the development of new acetic acid processes has

been to reduce raw material consumption, energy requirements, and

investment costs. Significant cost advantages resulted from the

use of carbon monoxide and of low-priced methanol as feedstock’s.

At present, industrial processes for the production of acetic

acid are dominated by methanol carbonylation. The kinetic reactor

has therefore been efficient for the operation. Material and

energy balances were constructed effectively using the data

generated from the simulated unit operations. The

commercialization the production acetic acid from methane

oxidation it is a success. The production occurs in three major

steps. In the process another method is introduced to maximize

the production without any loss of the raw material. The

carbonylation stage makes sure that no byproducts are discharged

everything is converted to acetic acid.

The scope of work covered in the project includes:

Designing a simulation of the plant using UniSIM1

Constructing a process flow diagram of the entire process

Calculating mass and energy balances

Equipment design and sizing

Project investment and costs

Carry out HAZOP study on the process

Table of Contents

Abstract 1

1. Introduction 3

2. Literature Review 4

2.1 Theoretical Background 4-5

2.2 Experimental 6-8

3. Technical 9

3.1 Process Flow Diagram 9

3.2 Material and Energy Balance 10-11

3.3 Process Description 12-13

2

3.4 Design and Description of

each Unit

14

4. Hazards & Safety

Considerations

20

5. Economic Analysis 21-22

6. Conclusions and

Recommendations

23

7. References 24

8. Appendix 25-28

3

1. INTRODUCTION

Acetic acid is an important commodity used in chemical

industries, with about 9 million tons of world demands per year.

The primary use of this chemical is in the manufacture of

assorted acetate esters, fungicide, organic compounds, organic

solvents and the preparation of pharmaceuticals, cellulose

acetate that is important in making film and plastic wares,

perfumes and synthetic fiber. Methane is the most abundant

reactive trace gas in the atmosphere and arises from both natural

and anthropogenic sources. It is a valuable gas and is usable at

a wide range of concentrations, down to 5%. The main objective of

this process is to produce acetic acid from methane. Methane

oxidation to acetic acid catalyzed by Pd2+ cations in the

presence of oxygen is the objective of this project but for total

conversion other methods will be used because the are some

byproduct in the reaction, which is methanol. This project will

show the industrialization or commercializing of this process by

using Unisim design software. This method it inverted in the lab

by Mark Zerella, Argyris Kahros and Alexis T.Bell

The conversion of methane to acetic acid is currently carried out

in a three-step process. Methane is rst reformed in afi

4

heterogeneously catalyzed process that is energy and capital-

intensive to produce synthesis gas, a mixture of CO and H2. The

CO and H2 then react at high pressure in a second step to produce

methanol, and nally, in the third step, acetic acid is producedfi

by homogeneous-phase carbonylation of methanol. This process is

also carried in three major stapes. The present method to the

liquid phase oxidation of methane with an oxidant in a strong

acid in the presence of a catalyst comprising palladium combined

with a promoter. However, this process displayed a serious

drawback. During the reaction particles of palladium black were

formed due to the reduction of Pd (II) to Pd. This invention

comprises a process for the production of acetic acid, or

derivatives such as methyl acetate and acetyl sulphate, from

methane, by contacting a methane-containing feed with an oxidant

in the presence of a palladium- containing catalyst, a promoter,

and an acid selected from concentrated sulfuric acid and fuming

sulfuric acid.

2. LITERATURE REVIEW

2.1. Theoretical Background

This invention relates in general to an improved process for the

production of acetic acid or a derivative thereof by liquid phase

5

oxidation of methane. In particular the present invention relates

to the liquid phase oxidation of methane with an oxidant in a

strong acid in the presence of a catalyst comprising palladium

combined with a promoter. The primary process route used today

for production of acetic acid is by catalytic reaction of

methanol and carbon monoxide. Such a process, typically termed

“carbonylation”, is described in a number of patents and

publications. Rhodium, palladium or iridium-containing catalysts

have been found especially useful for conducting this reaction.

The approach for the direct synthesis of acetic acid from methane

has been reported by Periana et al., who describe the oxidation

of methane to acetic acid catalyzed by Pd2+ cations in 96 wt%

sulfuric acid.

The only other products observed are methyl bisulfate and carbon

dioxide. Whereas the selectivity to the liquid-phase products is

reported to be as high at 90%, Pd2+ is observed to precipitate

from solution as Pd-black, causing the reaction to stop.

According to the invention, acetic acid is produced from methane

by contacting the methane, in a feed comprising methane and

optionally other components, With an oxygen containing gas in the

presence of a palladium-containing catalyst, a promoter, and an

acid selected from concentrated sulfuric acid and fuming sulfuric

acid. The inclusion of a promoter, for example a copper (II)

6

salt, increases the rate of acetic acid formation from methane by

more than a factor of five as compared With the Periana et al.

Work and, in addition, inhibits the precipitation of Pd black, it

reduced the production of the sulfur products and carbon dioxide.

The methane that is introduced into the process may be an

essentially pure methane stream, a methane stream that contains

various impurities, or a stream that contains methane as one of

several components, for example, a methane containing stream that

emanates from a chemical process unit, a natural gas stream, a

methane-containing stream produced by a gas generator, a methane-

containing off-gas, a biogenic methane stream, and the like. The

methane feed to the process may also contain other materials that

may be oxidized under the process conditions to form acetic acid.

Methanol, dimethyl ether, methyl acetate and methyl bisul fate

may also be fed to the process. The palladium-containing catalyst

may be any palladium containing material that possesses the

necessary catalytic activity for this reaction. Preferred

palladium-containing catalysts are palladium salts such as

palladium (II) and palladium (IV) sulfates, chlorides, nitrates,

acetates, acety lacetonates, amines, oxides, and ligand-modified

palladium systems, for example systems containing ligands such as

phosphines, nitriles, and amines. Promoters suitable for use in

the process of this invention include materials that have a

7

demonstrated REDOX couple with palladium, such as salts of

copper, silver, gold, vanadium, niobium, tantalum, iron,

chromates, and organic sys tems such as hydroquinone or

anthraquinone complexes with such metals. Preferred promoters for

the process are salts of copper and iron, most preferably cupric

salts. Other preferred promoters include cupric and cuprous

nitrate, sulfate, phosphate, acetate, acetylacetonate, and oxide,

ferric chloride and ferric sulfate.

For metals that have multiple valences, e.g. copper and iron, the

promoter can be introduced as a salt of the lower valence which

becomes oxidized in situ When in contact With the oxygen-

containing gas or With H2SO4 or S03. In addition to its primary

function, the promoter may also serve to catalyze regeneration of

the acid. Additionally, a salt of platinum or mercury may be

included in the process, to assist in conversion of methane to

methanol and/or methyl bisulfate, which may then be converted to

acetic acid by the Catalyst/promote

8

2.2. Experimental

2.2.1. Method 1

The effects of CH4 and O2 partial pressures were explored to

determine the in uence of these variables on the yields offl

acetic acid and methyl bisulfate, the selectivity of methane

conversion to these products, and the retention of Pd2+ in

solution. Unless speci ed otherwise, all reactions were carriedfi

out in 96 wt% H2SO4 containing 20 mM of PdSO4 at 453 K. The

initial partial pressures of CH4 and O2 were chosen to avoid

compositions that would result in an explosive mixture during any

part of the reaction. The results of these experiments are given

in Tables 1 shows that for an initial CH4 partial pressure of 200

psi, the yield of acetic acid rose from 65.7 to 181 mM as the

initial partial pressure of O2 increased from 0 to 125 psi. Over

the same range of O2 partial pressures, the yield of methyl

bisulfate increased from 2.5 to 4.8 mM, whereas the production of

methanesulfonic acid increased from 3.0 to 29.4 mM. The are other

two sulfur-containing byproducts, sulfoacetic acid and methane

disulfonic acid.

9

Figure 1: method 1 results

2.2.2. Method 2 (preferred method)

In this example CH4 and 02 Were reacted at 180° C. in a high

pressure, glass-lined autoclave containing catalytic amounts of

PdSO4 and CuCl2 added to concentrated sulfuric acid (96% W/W).

Reactions were carried out for 4 h, after which an equal volume

of Water Was added to the product solution in order to hydrolyze

any anhydrides. Reaction products were analyzed by 1H NMR. More

specially, using a 50 mL glass autoclave liner, 0.0121 g (20 mM)

of PdSO4, and 0.0081 g (20 mM) of CuCl2 Were dissolved in 3 mL

(5.67 g) of 96% sulfuric acid. A small Teflon-coated stir bar Was

10

added prior to sealing the autoclave. The reactor was purged With

Ar and then pressurized With 400 psig of CH4 and 30 psig of O2.

Figure 2: lab results

11

2.3. Carbonylation of methanol to acetic acid

Novel acetic acid processes and catalysts have been introduced,

commercialized, and improved continuously sincethe1950s.The

objective of the development of new acetic acid processes has

been to reduce raw material consumption, energy requirements, and

investment costs. Significant cost advantages resulted from the

use of carbon monoxide and of low-priced methanol as feedstock’s.

At present, industrial processes for the production of acetic

acid are dominated by methanol carbonylation.

The carbonylation of methanol is catalyzed by Group VIII

transition metal complexes, especially by rhodium, iridium,

cobalt, and nickel. All methanol carbonylation processes need

iodine compounds as essential co-catalysts, the reaction

proceeding via methyl iodide, which alkylates the transition

metal involved. Apart from acetic acid, the carbonylation of

methanol also gives rise to the formation of methyl acetate, . In

some carbonylation processes methyl acetate is also used as a

solvent. The determination of reaction rate parameters,

equilibrium constants, CO solubility and rate constant, can give

rise to develop a reaction rate expression that could be used to

design and to scale up the process. So can the study of the

determined parameters in the reaction modeling and simulation by

commercial simulators such as HYSYS.Plant. Because of the lack of12

information on homogeneous catalysts in this field, this study

focuses on the kinetics of the homogeneous Rh-catalyzed methanol

carbonylation (CH3I: promoter; water content: ~ 11 wt. %) using

experimental tests and applying theoretical methods such as ab

initio method with the help of Gaussian-98 program. In the

following section, the experimental apparatus of the research are

discussed. Then, the kinetics, modeling and simulation of the

carbonylation of methanol are developed

13

3. TECHNICAL

3.1. Process Flow diagram

14

Figure 3; flow diagram from unisim

15

3.2 Material and Energy Balance

3.1.1 Overall Mass Balance

16

3.2.2 Energy Balance

17

3.3 Process Description

The design models a process based on a three-part system

containing the following systems: The methane oxidation reactor,

flash distillation system and the carbonylation reactor.

The reaction requires high pressure and temperatures, from the

lab report it required 1800C and 400Psi of pressure. A compressor

and heater were introduced to system. The system consists of a

kinetic reactor containing palladium sulphate as catalyst. The

reactor feed is 900 kmol of methane and 1490 kmol of air. The

methane to oxygen ration is 0.3. The methane conversion is 100%

(calculated value). The reaction is highly exothermic and

therefore water will be used as a cooling medium, which would

then be used as a steam utility.

A separator was introduced to remove the excess of air to make

the flash distillation column to converge faster. The product

where cooled down to -500C for the separator. The liquid products

were transferred to the flash distillation column where only the

two components had to be separated, methanol the byproduct and

acetic acid the required product. They feed at temperature of -

500C and pressure of 1atm.Them boiling points where very low,

high pressure and low temperatures were used at the flash

distillation column. The top came out methanol and bottom was

acetic acid.

18

Realizing that a lot of methanol is produced another method was

found to convert methanol to acetic acid. This method was

introduced to maximize production of acetic acid to make sure no

raw material goes to waste. The new reaction was called

carbonylation of methanol. Carbonylation of methanol is when

methanol reacts with carbon monoxide to produce acetic acid. It

is a homogenous reaction where rhodium is used as catalyst. A

packed bed reactor was used for this reaction. The 98kmol of was

converted to acetic acid (97.37% conversion). The reaction occurs

in 20MPa and temperature of 2510c. A compressor was introduced

to system. the reaction was endothermic no cooler was required .

Carbonylation of methanol

Kinetics of reaction

CO+CH3OH K⃗CH3COOH

−r=KeqC

Kmethane=2.5×1010exp(9.2×104 /RT )

19

There is only one reaction in the reactor which carbonylation of

methanol to acetic acid and methanol. The E and A for the

arrinhius equation were found in one of references of the

research. All the assumptions were in UNIFAC and 97.3% conversion

was achieved

Catalyst

The production of acetic acid by the Monsanto process utilizes a

rhodium catalyst and operates at a pressure of 30 to 60

atmospheres and at temperatures of 150 to 200°C. During the

methanol carbonylation, methyl iodide is generated by the

reaction of added methanol with hydrogen iodide. The infrared

spectroscopic studies have shown that the major rhodium catalyst

species present is [Rh (CO)2I2]

20

3.3 Design and Description of each Unit

3.4.1 Mixer

Function: A mixer is used to manipulate a heterogeneous physical

system, with the intent to make it more homogeneous.

Figure 4 mixer

A mixer was introduced to the system to combine the in feed

streams to so they can be heated and compressed for reactor.

3.4.2 Heater

21

Figure 5 heater

From the lab results the reaction required a high pressures and

temperatures. The mixed feed was heated to 1800c and 400Psi of

pressure that was the feed to the reactor. The energy required

was 1.17e7 kj/hr

3.4.3 Methane oxidation reactor

Function: A reactor is a vessel in which chemical reactions take

place. Conditions of operation are based on the nature of the

reaction system and its behavior as a function of temperature,

pressure, catalyst properties, and other factors.

Kinetics of the reaction

CH4+O2 K⃗eqCH3COOH+CH 2OH

−r=KmethaneC

Kmethane=1.07×1022exp(1.7×105/RT )

22

There is only one reaction in the reactor which is methane

oxidation to acetic acid and methanol. The E and A for the

arrinhius equation were found in one of references of the

research. All the assumptions were in UNIFAC and 100% conversion

was achieved.

Catalyst

Palladium catalyzed cross-coupling reactions have revolutionized

the way in which molecules are constructed. The field of cross-

coupling has grown to include numerous strategies for C-C, C-N,

and C-O bond formation. While a range of palladium catalysts have

been developed for each transformation, it is often difficult to

determine which catalyst is best for your desired cross-coupling

application. This reaction between CH4 and 02 is reacted at 180°

C. in a high pressure, catalytic amounts of PdSO4 and CuCl2

added to concentrated sulfuric acid (96% W/W).

23

3.4.4 Cooler

Function: A cooler is a heat removal devices used to cool the working fluid.

Figure 6 cooler

The product stream was at high temperatures and pressure. It

required to be cooled for separation. It was cooled from 4000c to

-500c at that temperature air is still in gaseous phase. The

pressure was also decreased from 2809 kPa to 1atm. It required

energy of 4.5e7kj/hr

3.4.5 Separator

24

Function: A separator is used to separate dispersed liquid in a

gas stream. It is important that the dimension of the separator

is large enough so that liquid can settle in the bottom of the

tank.

Figure 7 separator

The separator was the first stage of separation where excess of

air is removed from the main product. The excess of was emitted

to atmosphere where it still safe for the environment. The

emissions contained high amounts of nitrogen.

3.4.6 Distillation column

Function: A distillation column is used to separate different

components in a fluid, by using their difference in boiling

point.

The design

25

Figure 8 distillation column

The column has 10 stages and the feed stage is no 5. It is full

reflux and the operational pressures are between 1000kPa and

1015kPa.

Worksheet (Distillation Column)

26

Figure 9 worksheet

The worksheet results show that methanol exits at the top and

acetic acid at the bottom. The UNIFAC models it is advantageous

because the VLE can be predicted for a large number of systems

without introducing new model parameters that must be fitted to

experimental VLE data. The binary coefficients of acetic acid

were displayed by the UNIFAC only. The first batch of acetic acid

is produced and the methanol continues to produce the second

batch.

27

3.4.7 Compressor

Function: A compressor converts power into kinetic energy to

increase the pressure of gases. Compressors are used for high

operation from 200 kPa - 400MPa.

Figure 10; compressor

The compressor was installed because of the knowledge that was

obtain from research that carbonylation occurs in at high

pressures. The compressor was compressing the methanol so the

inlet of the reactor can have high pressures.

3.4.8 Mixer 2

28

Figure 11 mixer

The mixer is there to combine both the reactants so they could

feed to the reactor. The feed to the reactor is at a pressure of

20MPa and temperature of 2510C .

4. HAZARDS AND SAFETY CONSIDERATIONS

Hazards Identification

Very hazardous in case of skin contact, of eye contact , of ingestion, of inhalation.

Hazardous in case of skin contact (corrosive, permeator), ofeye contact (corrosive).

Liquid or spray mist may produce tissue damage particularly on mucous membranes of eyes, mouth and respiratory tract.

Inhalation of the spray mist may produce severe irritation of respiratory tract, characterized by coughing, choking, orshortness of breath.

Reacts with metals to produce flammable hydrogen gas.

First Aid Measures

Eye Contact: immediately flush eyes with plenty of water forat least 15 minutes.

29

Skin Contact: immediately flush skin with plenty of water for at least 15 minutes while removing contaminated clothingand shoes. Cover the irritated skin with an emollient.

Inhalation: remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen.

Ingestion: Do not induce vomiting unless directed to do so by medical personnel.

Fire Fighting Measures

Dry chemical powder. Alcohol foam. Water spray or fog

Accidental Release Measures (Spillage)

Absorb with dry earth, sand or other non-combustible material.

Absorb with an inert material and put in an appropriate waste disposal.

Use water spray curtain to divert vapor drift. Neutralize the residue with a dilute solution of sodium

carbonate.

Handling and Storage

Keep away from heat. Keep away from sources of ignition. Do not ingest. Do not breathe gas/fumes/ vapor/spray. Store in a segregated and approved area.

30

5. ECONOMIC ANALYSIS

Chemical plants are built to make profit, and an estimate of the

investment required and the cost of production, are needed before

the profitability of a project can be assessed. In the economic

analysis of a chemical plant, the costs for the plant are divided

into investment cost and operating cost.

The fixed capital investment is the total cost of the plant ready

for start-up. The fixed capital investment can be subdivided into

manufacturing fixed-capital also known as direct cost, and

nonmanufacturing fixed capital or indirect cost. The working

capital for an industrial plant consist of the total amount of

money invested in raw materials and supplies carried in stock,

cash for monthly payment of operating expenses, accounts payable,

and taxes payable, etc.

The total capital investment (TCI) is the sum of the fixed

capital investment end the working capital. The ratio of working

capital to total capital investment used by most chemical plants

is 10-20 percent of the total capital investment. In our analysis

the working capital was estimated to be 15 percent of the total

capital cost.

Estimation of Total Capital Investment

31

Estimation of Total Product Cost

32

S. No. DescriptionDirect Costs

1 Purchased Equipm ent R 88 000,002 Purchased Equipm ent Installation R 30 000,003 Instrum entation and Controls R 54 700,004 Piping R 39 990,005 Electrical Equipm ent and M aterials R 36 499,006 Buildings (Including services) R 59 999,007 Yard Im provem ents R 10 141,008 Service Facilities R 21 500,009 Land R 525 000,00

Total Direct Costs (D) R 865 829,00Indirect Costs

10 Engineering and Supervision R 68 000,0011 Construction Expenses R 54 600,0012 Contractors Fee R 46 533,00

Total Indirect Costs (I) R 169 133,00Fixed Capital Investm ent (FCI), D + I R 1 034 962,00W orking Capital (W C), 15% R 155 244,30Total Capital Investm ent (TCI) R 1 190 206,30

Cost in R.

33

S. No. DescriptionM anufacturing CostsDirect Production Costs

1 Raw M aterials R 42 114,002 Operating Labor R 229 588,003 Operating Supervision R 120 411,004 Power and Utilities R 52 000,005 M aintenance and Repairs R 21 899,006 Operating Supplies R 18 577,007 Laboratory Charges R 38 999,008 Patents & Royalties R 0,009 Catalysts and Solvents R 0,00

Total Direct Production Costs R 523 588,00Fixed Charges

10 Depreciation R 80 000,0011 Taxes R 58 000,0012 Insurance R 515 011,0013 Rent R 0,00

Total Fixed Charges R 653 011,00Plant Overhead Costs

14 Plant Overhead Costs R 205 161,00Total Plant Overhead Costs R 205 161,00Total M anufacturing Costs (M ) R 1 381 760,00General Expenses

15 Adm inistrative Expenses R 6 500,0016 Distribution & M arketing Expenses R 8 500,0017 Research & Developm ent R 0,0018 Financing (Interest) R 0,00

Total General Expenses (G) R 15 000,00Total Product Cost, M + G R 1 396 760,00

Cost in R.

6. CONCLUSSION AND RECOMMENDATIONS

The commercialization the production acetic acid from methane

oxidation it is a success. The production occurs in three major

steps. In the process another method is introduced to maximize

the production without any loss of the raw material. The

carbonylation stage makes sure that no byproducts are discharged

everything is converted to acetic acid. The yield of acetic acid,

the primary product of methane oxidation, increases with

increasing O2/CH4 ratio for a xed CH4 partial pressure and withfi

increasing total reactant pressure for a xed O2/CH4 ratio.fi

Using the Pd/Cu/O2 mixture, the effect of reaction conditions is

evaluated with the aim of maximizing the acetic acid yield. The

increase in acetic acid yield as a consequence of increasing

O2/CH4 ratio is accompanied by only a modest loss in selectivity

to oxygen containing organic products, and the increase in total

pressure of CH4 and O2 at a xed O2/CH4 ratio results in afi

slight rise in the yield of acetic acid. This study leads to an

efficient and simultaneous estimation of the effects of pressure,

temperature, and the thermodynamic restrictions on kinetic

investigation of the homogeneously rhodium catalyzed

carbonylation process. The kinetic reactor has therefore been

efficient for the operation. Material and energy balances were

constructed effectively using the data generated from the

simulated unit operations.

34

35

7. REFERENCES

1. Mohammadrezaei, Ali Reza; Jafari Nasr, Mohammad Reza. Iran.

J. Chem. Chem. Eng. Vol. 31, No. 1, 2012

2. Paulik F.E., Roth J.F., Novel Catalysts for the LowPressure

Carbonylation of Methanol to Acetic Acid,Chem. Commun, 1578a

(1968).

3. . Mark Zerella, ArgyrisKahros, Alexis T.Bell. Methane

oxidation to acetic acid catalyzed by Pd2+ cations in the

presence of oxygen ∗. 2005

4. WANG Ye*, AN DongLi & ZHANG QingHong. Catalytic selective

oxidation or oxidative functionalization of methane and

ethane to organic oxygenates. Vol.53 No.2: 337–350.2010

5. Roy A. Periana, Marina Del Rey. process for converting

methane to acetic acid. us 7,368,598 b2 .2008.\

6. Abdulwahab GIWA. methyl acetate reactive distillation

process modeling, simulation and optimization using aspen

plus. vol. 8, no. 5, 2013

7. Christophe M. Thomas*, Georg Su¨ss-Fink. Ligand effects in

the rhodium-catalyzed carbonylation of methanol. 2003 8. Lødeng, R.: “A Kinetic Model for Methane Directly to Methanol”, Ph.D. Thesis, NTNU,

1991

9. Meyers, R.A.: “Handbook of Petrochemicals Production Processes”, RR Donneley, USA,2005

10. Olah, G.A., Goeppert, A. and Prakash, G.K.: Beyond Oil and Gas: The Methanol Economy, Wiley-VCH, Darmstad, 2006

36

11. Peters, M.S., Timmerhaus, K.D. and West, RE.: Plant Design and Economics for Chemical Engineers”, 5th ed., McGraw-Hill, New York, 2003

12. Sinnot, R. and Towler, G.: Chemical Engineering Design, 5th ed., Elsevier Ltd., UK, 2009

13. Smith, R.: “Chemical Process Design and Integration”, John Wiley and Sons Ltd., Chippenham, 2005

14. Tijm, P.J.A., Waller, F. J. and Brown, D.M.: Methanol technology developments for the new millnium. Applied Catalysis A: General, 221, 275-282, 2001

15. Trimm, D.L. and Wainwright, M.S.: “Steam Reforming and Methanol Synthesis”, Catalysis today, 6, 261-278, 1996

37

8. APPENDIX

Simulation Parameters

8.1 Stream 1

8.2 Oxygen stream

38

8.3 Mixed stream

8.4 Reactor stream

39

8.5 Prod stream

8.6 Separator stream

40

8.7 Products

41

42