Bioresource Technology 102 (2011) 9076–9082

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Bioresource Technology

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Dilute phosphoric acid-catalysed hydrolysis of municipal bio-waste woodshavings using autoclave parr reactor system

Angela M. Orozco a,⇑, Ala’a H. Al-Muhtaseb b,c,⇑, Ahmad B. Albadarin a, David Rooney a,Gavin M. Walker a, Mohammad N.M. Ahmad a

a School of Chemistry and Chemical Engineering, Queen’s University Belfast, Belfast BT9 5AG, Northern Ireland, UKb Department of Chemical Engineering, Faculty of Engineering, Al-Hussein Bin Talal University, P.O. Box 20, Ma’an, Jordanc Petroleum and Chemical Engineering Department, Faculty of Engineering, Sultan Qaboos University, P.O. Box 33, Al-khod 123, Oman

a r t i c l e i n f o

Article history:Received 4 April 2011Received in revised form 2 July 2011Accepted 5 July 2011Available online 18 July 2011

Keywords:Municipal bio-wasteWood shavingsDilute acid-catalysed hydrolysisPhosphoric acidXylose

0960-8524/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.biortech.2011.07.006

⇑ Corresponding authors at: Department of ChemEngineering, Al-Hussein Bin Talal University, P.O. BoMuhtaseb).

E-mail addresses: a.orozco@qub.ac.uk (A.M. Orozc(A.H. Al-Muhtaseb).

a b s t r a c t

The visibility of using municipal bio-waste, wood shavings, as a potential feedstock for ethanol productionwas investigated. Dilute acid hydrolysis of wood shavings with H3PO4 was undertaken in autoclave parrreactor. A combined severity factor (CSF) was used to integrate the effects of hydrolysis times, temperatureand acid concentration into a single variable. Xylose concentration reached a maximum value of 17 g/100 gdry mass corresponding to a yield of 100% at the best identified conditions of 2.5 wt.% H3PO4, 175 �C and10 min reaction time corresponding to a CSF of 1.9. However, for glucose, an average yield of 30% wasobtained at 5 wt.% H3PO4, 200 �C and 10 min. Xylose production increased with increasing temperatureand acid concentration, but its transformation to the degradation product furfural was also catalysed bythose factors. The maximum furfural formed was 3 g/100 g dry mass, corresponding to the 24% yield.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction or dilute sulphuric acid. The first advantage can be attributed to the

With increasing concern about global warming and dwindling oilsupplies, attention is turning to green processes that use sustainableand environmentally friendly feedstocks to produce renewableenergy such as fuel ethanol (Bartle and Abadi, 2010). A key factorin the economy of ethanol production is the choice of raw materialsas feedstocks. Although ethanol has been mainly produced fromsucrose-containing feedstocks and starchy materials, ethanol fromlignocellulosic material in the form of municipal solid waste areregarded more favourable due to the sustainable availability in largequantities, the avoidance of the conflict with production of foodproducts, carbon dioxide neutral sources, and substantially willreduce the amount of wastes that would otherwise exert pressureon municipal landfills (Chu et al., in press; Zhu et al., 2011).

To break down cellulose and hemicelluloses polymers in lignocellu-losic biomass to form individual sugar molecules which can be fer-mented into ethanol dilute or concentrated acid-catalysed hydrolysishas been widely employed (Lenihan et al., 2010; Ha et al., 2011). Thedilute acid hydrolysis of lignocelluloics materials is an attractive pro-cess due to the several advantages it offers over either concentrated

ll rights reserved.

ical Engineering, Faculty ofx 20, Ma’an, Jordan (A.H. Al-

o), a.almuhtaseb@ahu.edu.jo

lower levels of corrosion associated with diluting the acid streams. Inaddition it is known that sulphuric acid is more corrosive to stainlesssteel (316) when compared to phosphoric acid. Furthermore phos-phate salts, obtained by the neutralisation of the phosphoric acid postreaction, are often used as buffers in fermentation processes. One canalso include as an advantage the fact that the residue liquor from thesystem would be rich in phosphate which is a major component in fer-tilizers (Hu et al., 2010). The interest in the use of H3PO4 acid is thatafter neutralization with NaOH, will yields sodium phosphate whichwill remain in the hydrolysates and subsequently used as nutrient bymicroorganisms in down-stream fermentation media etc. Therefore,filtration is not needed with the consequent advantage: improve theeconomics of the process (avoid the filtration to remove the saltsand decrease the amount of nutrient needed for fermentation) andis friendly with the environment (the salt formed is not a waste)(Gámez et al., 2006). However, in a low concentrated acid process,the reaction should be carried out at high temperature and pressure,otherwise poor yields of glucose from cellulose will result in thehydrolysis step thereby impacting on overall ethanol yield. Near-quantitative yields of glucose from cellulose may be obtained byusing high concentrations acid in the hydrolysis process yieldinghigher quantities of ethanol however different vessels with suitablemetallurgy and a suitable acid recovery process will be required(Iranmahboob et al., 2002; Vazquez et al., 2007).

Lignocellulosic materials such as forest products (hardwood andsoftwood) and their residues are renewable resources of energy.

Table 1Main components of wood shavings.

Component Weight%(g/100 gdry mass)

Cellulose 27.8Hemicellulose 16.0Xylan 15.3Arabanan 0.7Klason lignin 29.5Ashes 1Water 9.7

Carbon 46.5Hydrogen 5.5Nitrogen 0.1Oxygen 47.9

A.M. Orozco et al. / Bioresource Technology 102 (2011) 9076–9082 9077

Typically, wood is composed of 40–50% cellulose, 25–30% hemicellulose and 20–30% lignin (Sjöstrom and Alen, 1996). Recent reportsestimated that up to 10.5 million tonnes of wood enters the wastestream each year in the UK. A very large proportion of this materialcomes from the construction and demolition sector. It has been esti-mated that utilizing two million tonnes of this material could gener-ate 2600 GWh of electricity each year and save 1.15 million tonnes ofCO2. Nguyen et al. (1999) converted tree chips obtained from soft-wood forest thinnings to ethanol via a two-stage dilute acid hydroly-sis followed by yeast fermentation. Recovery yields of 50% forglucose and 70–98% for other sugars were obtained. Iranmahboobet al. (2002) investigated sugar recovery rates from mixed woodchips originating from a variety of sources. Their results indicatedthat the use of sulphuric acid at moderate concentrations (26% byweight) corresponds to overall conversion efficiency of mixed woodchip cellulose to dextrose in the range of 78–82%. In their study onthe acid hydrolysis of olive tree biomass Romero et al. (2010) foundthat a small fraction of hemicelluloses was instantaneously hydroly-sed regardless of the acid concentration used. Only 80.6% of thehemicellulose produces reducing sugars as a consequence of hydro-lysis process and 17.2% yields glucose. The temperature and the acidconcentration had an important influence on the maximum amountof fibres that can be hydrolysed. Hu et al. (2010) found that dilute sul-phuric acid hydrolysis can convert hot-water sugar maple woodhemicellulose extract to monomeric sugars. The resulting hydroly-zate is rich in monomeric sugars, especially in xylose. After a certainprocess of centrifuge–neutralization–centrifuge and membrane fil-tration, those solid and fermentation inhibitors can be nearly elimi-nated and then the hydrolyzate can be used as fermentable media toyield bio-ethanol and other valuable products. Cho et al. (2011)investigated the feasibility of ethanol production from the construc-tion and demolition wood waste using concentrated sulphuric acidhydrolysis, they found that ethanol yield efficiency were 84.7–90.7%.

Therefore, it can be concluded that wood wastes dumped inlandfill sites could be used as a raw material feedstock for the pro-duction of bioethanol. To the best of our knowledge, there are noreports about acid hydrolysis of wood shavings within municipalbio-waste. Therefore the aim of this work was to investigate diluteacid hydrolysis of waste cellulosic biomass (wood shavings) withphosphoric acid using autoclave parr reactor. Process parametersinvestigated include variation in reaction temperature (135–200 �C) and acid catalyst concentration (2.5–10% w/v). The concen-tration levels of the monomers, (mainly xylose and glucose) werestudied. The main degradation products (e.g. acetic acid, furfuraland HMF) were also measured throughout to investigate its effecton sugar yield. The results of this study may benefit governmentand private sectors that are interested in the production of biofuelfrom waste materials. The kinetics of the acid hydrolysis for sugarformation, which can be used for the optimization of a pilot scalereactor, will be addressed in the second paper of this work.

2. Methods

2.1. Experimental aim

For the purposes of this research work the conditions to be var-ied were temperature and acid concentration. The raw materialwas hydrolysed at 135, 150, 175 and 200 �C using phosphoric acidat 2.5%, 5%, 7.5% and 10% (w/w) acid concentrations. The raw mate-rial substrate being studied was wood shavings.

2.2. Wood shavings

Wood shavings from pine trees used as animal bedding werepurchased from a local store. The main components of wood shav-ings are shown in Table 1 and its calorific value is 18.68 MJ/kg.

2.3. Analytical methods

2.3.1. Sample preparationWood shaving samples were chopped in small pieces and then

left in an oven (Genlab, UK) at 45 �C until dry. Samples were thenmilled at size 1 mm in a hammer mill (IKA Werke MF 10) accordingto the method ASTM E1751-95 for both compositional analysis andacid hydrolysis reactions.

2.3.2. Cellulose and hemicellulose analysisThree 0.3 g samples were weighed into three test tubes and to

each is added 3 ml of 85% sulphuric acid that has been cooled to15 �C. The samples were stirred thoroughly before being placedin a water bath at 30 �C. This temperature was maintained for2 h, stirring the samples every 10 min. After a total time of 2 hthe mixture was washed from the vial into an Erlenmeyer flaskand made up to 89.11 g with distilled water. The dilute solutionwas autoclaved at 1.5 bar steam pressure and 121 �C for 1 h. Atthe end of this time the sample was cooled and vacuum filteredto remove un-reacted lignin. The filtrate was then syringedthrough a 0.45 lm filter, before being analysed by HPLC. With100% conversion assumed the composition of glucose is recognizedas cellulose and that of xylose, arabinose and mannose can be rec-ognized as hemicellulose.

2.3.3. Other analysesHaving hydrolysed the cellulose and hemicellulose components

of the biomass the composition of lignin can be determined quiteeasily. The process of vacuum filtering the samples results in theseparation of the hydrolysate with the remaining solid depositing.This deposit is made up of mainly lignin and ash components. Theglass filter crucibles which had been used in the vacuum filter weredried over night in an oven at 110 �C before having their weight re-corded. They were then placed in a muffle furnace at 550 �C for 3 hto burn off the remaining organic deposits. The weight was thenrecorded again. The proportion of acid-insoluble residue mainlylignin can be calculated using Eq. (1) as per the Standard TestMethod for Determination of Acid-Insoluble Residue in Biomass –E1721-95:

Percentage of lignin ¼ W2 �W3

W1 � T110� 100 ð1Þ

Where W1, weight of wood shavings sample (g); W2, weight offilter crucible after ignition in muffle furnace – ash sample (g); W3,weight of filter crucible after vacuum filtration – lignin and ash (g);T110, received sample conversion factor.

2.3.3.1. Moisture analysis. Moisture content of a sample of woodshavings was measured by weighing out a recorded amount ofsample and placing it in an oven at 110 �C until the dry weight

9078 A.M. Orozco et al. / Bioresource Technology 102 (2011) 9076–9082

of the sample is constant over a 2 h period. The sample was thencooled and its weight was recorded. Moisture content was deter-mined according to the following equation:

M:C ¼ 1� dryweightinitialweight

ð2Þ

2.3.3.2. Ash analysis. The ash content was calculated by dividing theweight of the filter crucible, after it has been ignited in the mufflefurnace W2, by the initial weight of the sample W1 times the con-version factor T110.

2.4. Sugar analysis

2.4.1. Sample preparationThe hydrolysates were filtered through a filtering crucible. The

pH was measured and recorded using a pH meter ‘4330 Jenway’and an electrode ‘Philips Harris’, the pH was adjusted to approxi-mately 4.0 with Calcium Hydroxide, Ca(OH)2. Samples were centri-fuged at 13,000 rpm for 15 min in a Micro Centaur MSE centrifuge,and after, the sample was filtered with a cellulose nitrate mem-brane filter ‘Whatman’ of 0.45 lm pore size and 25 mm diameter.The samples were kept in the fridge at 4 �C.

2.4.2. HPLC with refractive index detectorA HPLC with refractive index detector ‘Agilent Technologies

1200 Series’ was used with a ‘Bio-Rad Aminex HPX-87H’ columnfor analysis of sugars and decomposition products respectively.Samples were run at 40 �C and eluted at 0.6 mL/min with 5 mMH2SO4. When using this column the peaks for xylose, mannoseand galactose eluted together. As the technique used could not dif-ferentiate between them it was not possible to quantify the concen-trations of each of these species. Herein we will group theses threesugars together and refer to them as xylose throughout. The peakarea was calculated using the software ChemStation for LC systems.The sugars produced in the hydrolysis reactions were identifiedusing the retention times of standards sugars such as D-Xylose (AlfaAesar), D-Galactose (Sigma), L-Arabinose (Sigma), D-Mannose (AlfaAesar), D-Glucose (BDH AnalaR) and, D-Cellobiose (Sigma) and cor-relations coefficients for each standard was R2 > 0.99.

2.4.3. Combined severity factor (CSF)A calculated CSF (Eq. (3)) was used to integrate the effects of

reaction time, temperature and acid concentration into a singlevariable (Lloyd and Wyman, 2005):

CSF ¼ log t: exp½ðTH � TRÞ=14:75f �g � pH ð3Þ

Where t is the reaction time in minutes, TH the reaction temper-ature in �C, TR is the reference temperature, and pH is the acidity ofthe aqueous solution in terms of acid concentration.

2.5. Experimental procedure

2.5.1. Autoclave Parr reactorA 1 L continuously stirred pilot batch reactor (Parr reactor) was

employed for the experimental programme. The reactor operatesat a temperature range of �10 to 350 �C up to 130 bar pressure.

Operating conditions were modulated by a 4843 controller unit.The total contents of the reactor constitute 700 g of which 5%(w/w) will be the raw material wood shavings. The wood shavingsamples were dried and milled to 16 mesh or 1 mm diameter par-ticles. The remaining 95% (w/w) content of the reactor was madeup of the dilute acid concentration. The acid concentration wasnot initially added to the reactor but instead is delivered throughthe acid reservoir during the initialization of the reaction. For acid

concentrations 2.5%, 5% and 7.5% (w/w) this was made by prepar-ing a 70 g sample made up of the 85% phosphoric acid required toachieve the desired acid concentration for the reaction and dis-tilled water. The remaining distilled water required to achieve thisdilution was mixed with the wood shavings and charged to theParr reactor vessel. The sample tube was then fitted with a gauzemesh to restrict the solid sample from blocking it. The reactorwas secured tightly by 6 bolts to maintain the operating pressurewithin the vessel during the reaction. The vessel was then attachedwith the heating jacket and the agitator impellor was connected tobegin mixing. The sample line and acid reservoir were boltedtightly to the reactor. The nitrogen line was then attached to theacid reservoir. Finally the thermocouple which provides feedbackto the 4843 controller was inserted and the temperature setpointwas entered. The 4843 controller then ramped up the jacket heat-ing to achieve and maintain the required operating temperatureset point. Depending on the whether the temperature output re-quired is 135, 150, 175 or 200 �C this took between 30 and60 min to reach the desired temperature. The impellor was initi-ated at the same point as the jacket heating element and remainedconstant for all experiments at the 4843 controller maximum RPMrate of 632. This was to ensure that by the time the reaction com-mences the dispersion of wood shavings will be constant through-out the vessel. Once the desired temperature set point was atsteady state the reaction was commence.

2.5.2. Reaction procedureTo initialise the reaction the phosphoric acid must be delivered

to the reaction vessel from the acid reservoir. The reservoir wasfirst pressurised by opening the nitrogen valve, thus pressurisingit to 20 bar. The acid inlet valve was then opened, causing a pres-sure differential between the reservoir and the reaction vesselwhich allowed the acid to be delivered to the vessel. The pressuregauge of the vessel was monitored for any increase in pressure,once this was observed it indicated that all the acid had been deliv-ered. At this point the inlet valve was closed and the stop watchstarted simultaneously. Sampling occurred at time intervals of 2,4, 8, 15, 30, 45, 60, 75 and 90 min. A sample tube was secured tothe sample line; the sample outlet valve was opened allowing amaximum of 5 ml of solution to be collected. The sample tubewas cooled using cold water to further reduce the reaction rateof the solution by rapid cooling and then cleared using compressedair to prevent contamination from subsequent samples. Sampleswere sealed and placed in ice reduce impact of further reaction.Although contamination of the solution by wood shavings particleswas severely reduced by the presence of gauze mesh it was noteliminated, therefore purification by vacuum and syringe filtrationwas performed prior to HPLC analysis.

3. Results and discussion

3.1. Effect of temperature and acid concentration

Diluted acid hydrolysis of wood shavings was carried out atphosphoric acid concentration range of 2.5–10 wt.% and tempera-tures between 150–200 �C.

3.1.1. Xylose formationFig. 1 illustrates a plot of xylose production (yield and concen-

tration) versus severity factor with variation in both acid concen-tration and reaction temperature. The experimental dataillustrate the complex inter-relationship between severity factor,reaction temperature and acid concentration. Xylose concentrationreached a maximum value of 17 g/100 g dry mass corresponding toa yield of 100% at the best identified conditions of 2.5 wt.% H3PO4

Fig. 1. Effect of temperature and H3PO4 concentration on xylose formation on the dilute acid hydrolysis of wood shavings over a range of combined severity factors.

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concentration at 150 �C in 80 min reaction time and severity factorof 2.1; 2.5 wt.% H3PO4 concentration at 175 �C in 10 min reactiontime and severity factor of 1.9 wt.% and 7.5 wt.% H3PO4 concentra-tion at 135 �C in 120 min and severity factor of 2.06 (Fig. 1). Similarresults were reported by Yat et al. (2008) for balsam (softwood)70%, 80% for basswood and 85% for aspen (hardwood). For aspen(hardwood) and balsam (softwood), Jensen et al. (2010) reporteda maximum xylose yield of 12.9% and 4.4%, respectively. Guoet al. (2008) reported a xylose yield between 70% and 75% from sil-vergrass. Redding et al. (2011) reported 83% yield of xylose fromcoastal Bermuda grass.

The effect of severity factor in xylose formation is shown inFig. 1. Xylose formation increased with the increasing severity fac-tor. Xylose degradation was not observed below a reaction temper-ature of 135 �C however this decomposition was more severe whenthe temperature was increased. When the temperature was 200 �Cand the H3PO4 concentration was 10 wt.%, the xylose formed wasvery low, which is attributed to the high severity leading to rapiddecomposition. From the severity data it was also found that theyield of xylose formation increases when the acid concentrationdecreases with the greatest xylose was generated at the lowestacid concentrations and temperatures, demonstrating once again

Fig. 2. Effect of temperature and H3PO4 concentration on glucose formation on the di

that hemicelluloses are very easy hydrolysable. The data indicatethat ‘‘milder’’ reaction conditions provide the higher yields, albeitat longer reaction times.

At the highest acid concentration (10 wt.%) a very low concen-tration of xylose was detected, maximum obtained was 6 g/100 gdry mass. As previously explained this is attributed to the balancebetween production and degradation with degradation dominatingat high severities such as those obtained at low pH and higher tem-peratures. Similar results were reported by Téllez-Luis et al. (2002)Bustos et al. (2003), Hu et al. (2010) and Lee and Jeffries (2011).

3.1.2. Glucose formationThe maximum yield for glucose production was an average of

10 g/100 g dry mass corresponding to 33% of the glucose available(maximum estimated glucose at 36 g/100 g dry mass) was ob-tained at the best identified conditions of 5 wt.% H3PO4 concentra-tion, 200 �C in 10 min reaction time and severity factor of 2.9(Fig. 2). The low yield for glucose is likely due to its crystallinestructure. Low glucose yields were expected as the main goal of di-lute acid hydrolysis was to breakdown the hemicelluloses (Jensenet al., 2010). It is expected that the glucose formed here was mainlydue to the glucan presence in the hemicelluloses (Vazquez et al.,

lute acid hydrolysis of wood shavings over a range of combined severity factors.

9080 A.M. Orozco et al. / Bioresource Technology 102 (2011) 9076–9082

2007). Similar to xylose, glucose degradation was observed at thehighest temperature and concentration. It would appear that lowseverities were insufficient to break the bonds between the glucosemolecules in the strong structure of cellulose. Similar results werereported by Jensen et al. (2010) who found 42.3% and 2.8% for as-pen (hardwood) and balsam (softwood), also by Yat et al. (2008)who found 11% to 13% yield when using dilute sulphuric acid(0.25–1.0%) for timber and switch grass, and by Guo et al. (2008)who reported a value of 10% for silvergrass.

Glucose concentration increased with the increase in severityfactor (Fig. 2). It can be seen that at 200 �C the generation of glu-cose was always higher than at the other temperatures. Glucosedegradation to HMF was observed at 200 �C at a very high rate.There was no effect on the glucose formation when the acid con-centration was increased, but there was a difference in glucosedegradation, where it increased with an increase in acid concentra-tion. Glucose degradation was not as severe with temperature andacid concentration as xylose during the time. Degradation only oc-curred when the reaction conditions were severe as 10 wt.% H3PO4

concentration and/or temperature of 200 �C.

3.1.3. Total sugars formationThe maximum yield for the total sugars formation was an aver-

age of 22 g/100 g dry mass corresponding to 40% of the total sugars

0

10

20

30

40

50

0

5

10

15

20

25

0 20 40 60 80 100 120

Yiel

d (%

)

Tota

l Sug

ars

(g/1

00 g

dry

mas

s)

Time (min)

Fig. 3. Effect of temperature on total sugar formation on the dilute acid hydrolysisof wood shavings at 2.5 wt.% H3PO4.

Fig. 4. Effect of temperature and H3PO4 concentration on acetic acid formation on the

available at the following conditions of 2.5 wt.% H3PO4 concentra-tion, 150 �C and 60 min reaction time; 2.5 wt.% H3PO4 concentra-tion, 175 �C and 10 min reaction time (Fig. 3). Despite almost allhemicellulose being converted to its monomer, the low yield isdue to the maximum sugar of each monomer being obtained at dif-ferent times and also sugar degradation was catalysed by both,temperature and acid concentration. In Fig. 3 the effect of temper-ature on the total sugar formation is clearly seen. The higher thetemperature the more sugars are formed, in contrast with the low-er the acid concentration the higher the temperature (figure is notshown here). As mentioned previously, sugars were degradedquicker according to the severity of the reaction conditions, espe-cially xylose.

3.1.4. Total inhibitorsFigs. 4–6 show acetic acid, furfural and HMF formation, respec-

tively. Acetic acid does not seem to be affected by temperature oracid concentration; it is formed quickly until it reaches a constantvalue of about 2.0 g/100 g dry mass average. Furfural formationwas clearly affected by the severity factor and temperature, thehigher the severity factor and temperature the higher the furfuralformation and consequently degradation. The effect of acid concen-tration also increased with the temperature. When the temperaturewas fixed above 150 �C and the acid concentration increased, thefurfural formed also increased, being more prominent at higher tem-peratures. The maximum furfural formed was an average of 3.0 g/100 g dry mass, corresponding to the 26% yield (maximum obtain-able furfural was 12.65 g/100 g dry mass). This maximum yieldwas obtained at the best identified conditions of 2.5 wt.% H3PO4 con-centration, 175 �C and 60 min reaction time; 5.0 wt.% H3PO4 concen-tration, 200 �C and 10 min reaction time; 7.5 wt.% H3PO4

concentration, 200 �C and 5 min reaction time; 10 wt.% H3PO4 con-centration, 175 �C and 30 min reaction time (not all figures areshown here). Similar results were reported by Téllez-Luis et al.(2002), Bustos et al. (2003), Hu et al. (2010) and Lee and Jeffries(2011).

HMF formation was affected by the temperature of the reaction,the higher the temperature, the higher the amount of HMF formedbut this too underwent degradation. Here the acid concentrationdoesn’t seem to have a strong effect on the HMF formation whenthe temperature is fixed but it has an effect on the HMF degradation.The degradation of HMF to levulinic acid was also affected by thetemperature and acid concentration mainly for the temperatures

dilute acid hydrolysis of wood shavings over a range of combined severity factors.

Fig. 5. Effect of temperature and H3PO4 concentration on furfural formation on the dilute acid hydrolysis of wood shavings over a range of combined severity factors.

Fig. 6. Effect of temperature and H3PO4 concentration on HMF formation on the dilute acid hydrolysis of wood shavings over a range of combined severity factors.

A.M. Orozco et al. / Bioresource Technology 102 (2011) 9076–9082 9081

175–200 �C and the acid concentrations 5.0 wt.% and 10 wt.%. Simi-lar results were reported by Lee and Jeffries (2011).

4. Conclusions

The dilute acid hydrolysis of wood shavings using phosphoricacid gave a good performance for sugar production. This wasmainly a combination of xylose, mannose and galactose whicheluted together. Excellent yield was achieved (100%) at the bestidentified conditions of 2.5 wt.% H3PO4 concentration, 175 �C in10 min reaction time. However, for glucose, an average yield of30% was obtained at 5 wt.% H3PO4 concentration, 200 �C and10 min reaction time. Xylose production increased with increasingtemperature and acid concentration in a very short time. Glucosewas very difficult to hydrolyse, with almost all the glucose pro-duced coming from the glucan present in the hemicelluloses. Thespecies reported here all, with the exception of acetic acid, showeda maximum yield at a given severity. The value for the grouped xy-lose sugars was approximately 2 while that for glucose wasapproximately 3. It can be concluded that the xylose sugars are

easier to produce than glucose using the methods reported hereand that when the severity is increased to produce glucose this re-sults in xylose deactivation. In taking all the investigated experi-mental parameters into account, it can be concluded that‘‘milder’’ reaction conditions (low acid concentration and temper-ature) within our system can provide xylose yields approaching100%, albeit at longer reaction times.

Acknowledgements

The authors are very grateful for the support of QUESTOR re-search centre at Queen’s University Belfast, UK.

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