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Fermentable sugars from biopolymers of bagasse
Resources and Conseruation, 15 (1987)291-298 Elsevier Science Publishers B.V., Amsterdam -
291
Printed
in The Netherlands
Short Communication
Fermentable Sugars from Biopolymers of Bagasse
K. RAMACHANDRAN,
K. DAS*
Chemical Engineering Department, Indian Institute of Technology and D.K. SHARMA Center of Energy Studies, Indian Institute of Technology, Hauz Khas, New Delhi-110016 (India) (Received December
15,1986; accepted in revised form March 3, 1987)
INTRODUCTION
Ethanol can replace oil as a fuel and its use would help in the conservation of the meagre oil reserves. Some convenient and cost-effective processes for the production of ethanol from biopolymers available in agricultural wastes Agrowastes have been subjected to two-stage acid have been developed [l-5]. hydrolysis to extract fermentable sugars from biopolymers such as hemicellulose and cellulose. Suitability of acid or enzymatic processes for the recovery of fermentable sugars has been studied by other workers [ 6,7]. Fermentable sugars obtained from acid hydrolysis of biomass can easily be digested to ethanol. In the present work, a two-stage process for the hydrolysis of biomass using aqueous HCI has been developed to selectively extract xylose and glucose from bagasse. The interesting feature of the process is that it operates under ambient pressure conditions and thus avoids the constraints of working under high pressures. HCl was chosen as the catalyst because of its easy recovery. This also allowed the use of promoters which could improve the yields of hydrolysis. HCl can be recovered through distillation and part of it can also be neutralized with lime. The CaCl, thus obtained can be used as a promoter for the hydrolysis of biopolymers. Selective production of xylose and glucose allows their separate fermentation to alcohol, whereby xylose can also be utilized properly. *To whom all correspondence
0166-3097/87/$03.50
should be addressed.
0 1987 Elsevier Science Publishers
B.V.
292
MATERIALS AND METHODS
Prehydrolysis
of bagasse
Bagasse was crushed to 40-60 BSS (417-495 pm) mesh size and dried. The bagasse powder was impregnated with 18% HCl and the impregnated bagasse was used for prehydrolysis. Reaction was allowed to proceed for 180 min at 35, 45,55,65 and 75°C. Aliquots were withdrawn at regular intervals of time for determination of xylose, glucose and furfural formed. For the experiments where CaCl, was used as a promoter for bagasse, this reagent was dissolved in the 18% HCl and the reaction took place under similar conditions. Hydrolysis of bagasse residue The bagasse residue obtained from the prehydrolysis was washed with water and dried. The residue was then taken in the reactor which contained 35% HCl. Hydrolysis was allowed to proceed for 180 min, and aliquots were withdrawn at regular intervals for determination of glucose. For the experiments where CaCl, was used as a promoter for bagasse residue, this reagent was dissolved in the 35% HCl and the reaction took place under similar conditions. Agitation for the prehydrolysis and hydrolysis experiments was provided by a magnetic stirrer. Composition
of bagasse and assays
The composition of bagasse and the assay procedures furfural were as reported in our earlier works [ l-41.
for xylose, glucose and
RESULTS AND DISCUSSION
The fact that the bioi>olymer hemicellulose is more easily hydrolysed under milder conditions, when cellulose remains unhydrolysed, makes it possible to hydrolyse only the hemicellulose fraction from biomass. In the present work, 18% HCl was used for the hydrolysis of biomass in the first stage at moderate temperatures from 35 to 90°C. The residual biomass was rich in cellulose, as cellulose does not get hydrolysed under these relatively mild conditions. The residual biomass was subjected to hydrolysis by 35% HCl at 35’ C. The lower temperature of 35°C was selected on the premise that the degradation of the sugars formed is minimum at lower temperatures. Bagasse, an agricultural residue, was selected for the studies.
293
Y g
12
-z' 7 2-s 3 2 t LY I+ '2 z
0
c
20
LO
60
80 TIME
100
120
140
160
imnl
Fig. 1. Xylose yield from prehydrolysis
Fig. 2. Xylose yield from prehydrolysis on potential sugars.
of bagasse at different
x
AT
3S'C
??
AT
L5'1
'
AT
55'1
0
AT
65'1
of bagasse at different
temperatures
temperatures
with 18% HCI.
with 18% HCl, based
Prehydrolysis of bagasse Bagasse was subjected to prehydrolysis with HCl and the effect of temperature on xylose yields was studied. Figures 1 and 2 show xylose yields on the basis of dry weight of bagasse as well as on the basis of potential sugar at 35,
294
TABLE 1 Xylose yield from prehydrolysis Time (min)
5 15
of bagasse at 35 ’C
Xylose yield ( % ) (based on dry wt. of bagasse)
Xylose yield ( %) (based on potential
without agitation
with agitation
without agitation
8.1 10.5
9.0 11.5
12.46
15.75
16.15
23.06
sugar) with agitation
30
12.3
15.5
18.92
36.00
45
18.6
17.3
28.60
27.50
60 90
11.4
15.0
17.50
23.50
9.9
8.0
15.25
27.50
120
6.6
6.0
10.50
23.50
180
6.6
6.0
10.20
23.50
45, 55, 65, 75 and 90°C respectively. Xylose yields increased with time up to the first 45 min of the reaction and then started dropping at higher temperatures. The maximum yield of xylose was obtained at 35” C, as 18.6% (Table 1) on the basis of dry weight of bagasse. Xylose yield on the basis of potential sugar was found to be 28.6%. The yield was found to decrease with increasing prehydrolysis temperature from 35 to 90’ C (Fig. 1) . This shows that the xylose (formed) decomposes at a higher hydrolysis temperature. Yields of furfural under the prehydrolysis conditions studied were low (Table 2). This was due to the fact that dehydration of xylose to furfural takes place at higher temperatures. Furfural formation [ 8,9] is high at temperatures above 190” C. Thus, by keeping the prehydrolysis temperature low, the formation of furfural in the reaction products can be reduced considerably. Prolonged reaction time of 120 min yields about 6.5% furfural (Table 2). Steam treatment of xylose formed TABLE 2 Furfural yield from the prehydrolysis Time (min)
of bagasse at 35 “C
Furfural yield ( % ) (based on dry wt. of bagasse)
5
1.0
15
2.0
30 45 60
3.0 4.6 4.8
90
4.5
120 180
6.5 6.0
295
TABLE 3 Glucose yield from the hydrolysis Time (min)
5 15 30 45 60 90 120 180
of the bagasse residue after prehydrolysis
Glucose yield ( % ) (based on dry wt. of bagasse )
Glucose yield ( % ) (based on potential sugar)
without agitation
with agitation
without agitation
with agitation
8.4 10.5 11.4 15.0 13.5 9.0 6.9 6.0
8.4 12.9 17.7 16.2 15.3 nd nd nd
19.53 24.10 26.50 35.00 31.30 20.90 16.04 13.95
19.53 30.00 41.16 37.67 35.60 nd nd nd
nd= not determined.
from bagasse, at temperatures above 190°C would result in the production of larger amounts of furfural. Hydrolysis temperature may be raised above 190’ C if furfural is the desired product. Hydrolysis of the bagasse residue The bagasse residue obtained after prehydrolysis was rich in cellulose and lignin. This was subjected to hydrolysis with 35% HCl at 35°C. Lignin is not attacked under these conditions, and only the cellulose part gets hydrolysed to glucose. Table 3 shows the yields of glucose obtained. Glucose yields were found to increase with time up to 45 min and after that the yields started dropping. The drop in yields could be due to the decomposition of sugars formed. About 15% yield of glucose was obtained after 45 min. The glucose yield on potential sugar basis was found to be maximum (about 35% ) at this time. This shows that reasonable glucose yields are obtainable at lower temperatures and under atmospheric pressure. Attempts were made to further improve the yields of fermentable sugars by using promoters and through agitation of the reactants. Effect of promoters Earlier studies [lo] have shown that the use of ZnCl,, SnCl,, AlCl, and CaCl, promotes the hydrolysis of biomass. In the present studies, CaClz was used as a promoter in both the prehydrolysis and the hydrolysis of bagasse. CaCl, can be obtained by neutralization of HCl with lime after hydrolysis. The yields of hemicellulose and cellulose hydrolysis were found to improve through the addition of CaCl, as a promoter. There was a 3% improvement in the yield
296
of xylose by addition of CaCl, in the prehydrolysis of bagasse for 45 min at 35°C using 18% HCl, over the blank experiment. Addition of the same proportion of CaCl, in the hydrolysis of prehydrolysed bagasse residue (containing mainly cellulose and lignin) resulted in 3.5% improvement in the yields of glucose in comparison with the control experiment without CaCl, at 35’ C using 35% HCl after 45 min reaction time. Higher amounts of CaCl, were not tried, because of cost reasons. Further attempts, using ZnCl, and SnCl, as promoters in the hydrolysis of hemicellulose and cellulose, are currently underway. Effect of agitation Agitation was found to have a significant effect on the hydrolysis of both hemicellulose and cellulose present in bagasse. Table 1 shows that with agitation the xylose yields increase up to 36% after 30 min of reaction at 35°C in comparison with 28.6% in the blank experiment after 45 min under similar conditions. Similarly, the glucose yields also increased from 15.0% after 45 min to 41% within 30 min through agitation under similar conditions (Table 3). This showed that in the absence of agitation, hydrolysis does not go to completion. The hydrolysis follows the diffusion-controlled mechanism of a firstorder reaction. With agitation hydrolysis goes to completion with yields of high fermentable sugars in a shorter time. The rate constants are about 5-20 times greater than those without agitation [ 10,111. Complete hydrolysis can be effected within 10 min at 50” C and within 45 min at 30°C. Integrated process Earlier it had been reported [ l-51 that particle size, solid-liquid ratio, lignin content, and pretreatment affect the hydrolysis yield of fermentable sugars from biomass. Recently, the fermentation of xylose to ethanol has also been achieved in good yield [ 1,4,6]. The fermentable sugars, xylose and glucose, obtained from this two-stage acid process could be fermented to ethanol. In the present process, furfural formation is not so signifcant. In fact, furfural has been reported to poison the yeast [ 11. Furfural can be removed from the fermentable sugars through extraction with tetraiin, isoamyl alcohol, or toluene. But toluene is poisonous to yeast and hence the use of isoamyl alcohol for the [ 41. extraction of furfural has been recommended The residual bagasse obtained after the prehydrolysis followed by hydrolysis contains mainly lignin. Lignin can be hydrocracked or hydropyrolysed to get value-added aromatic chemicals. Thus, this affords a three-step integrated process for the extraction of alcohols and aromatic chemicals and fuels from agrowastes. Figure 3 shows the flow scheme of this process. The process allows the utilization of every component of biomass effectively. The process employs milder conditions for the production of ethanol, a clean fuel, from agrowastes. This two-stage acid hydrolysis process is better than the enzymatic hydrolysis process in many ways. The process takes 45 min for prehydrolysis and about the same time for hydrolysis. Thus, in total 90 min is required for the hydrol-
pq-.Jzg_Fg Fig. 3. Flow scheme of the integrated process for the production
of ethanol from agricultural wastes.
ysis of bagasse biopolymers as against more than 24 h for the enzymatic hydrolysis at the same temperature, that is, between 35 and 45°C. The recovery of HCl is easier than that of the enzyme, but HCl is a corrosive material. In fact, Teflon reactors can be used at these temperatures to handle HCl. The main advantage of the two-stage process is that it allows the recovery of xylose and glucose separately. Thus, this makes it possible to ferment xylose and glucose separately to get ethanol. In the enzymatic hydrolysis, a mixture of xylose and glucose is obtained, which is not as convenient for fermenting to ethanol.
REFERENCES Singh, A., Das, K. and Sharma, D.K., 1984. Production of furfural, xylose, fermentable sugars and ethanol from agricultural wastes. J. Chem. Technol. Biotechnol., 24: 51-61. Singh, A., Das, K. and Sharma, D.K., 1984. Integrated process for production of furfural, xylose, glucose and ethanol by two step acid hydrolysis. Ind. Eng. Chem., Prod. Res. Dev., 23: 257-261. Singh, A., Das, K. and Sharma, D.K., 1984. Acid hydrolysis of agricultural wastes to reducing sugars. Int. J. Agric. Wastes, 9: 131-145. Sharma, D.K., Das, K. and Singh, A., 1985. Production of value added fuels and chemical feedstocks from biomass through chemical and biochemical treatments. Chem. Age India, 35: 919-921. Sharma, D.K., Das, K. and Raj, V., 1986. Two stage acid hydrolysis of bagasse under atmospheric pressure conditions. Accepted for presentation at the 1987 TAPPI Pulping Conference, Washington, DC, November l-5. Grethlein, H.K., 1978. A comparison of the economics of acid and enzymatic hydrolysis of newsprint. Biotechnol. Bioeng., 20: 503-525. Beck, M.J. and Stickland, R.C., 1984. Production of ethanol by bioconversion of wood sugars from two stage dilute acid hydrolysis of hard woods. Biomass, 6: 101-l 10.
8 9 10
11
Sharma, D.K. and Sahgal, P.N., 1983. Elevated temperature hydrolysis of rice husk with pressurized water in a semi-batch process. Cellulose Chem. Technol., 17: 655-658. Sharma, D.K. and Sahgal, P.N., 1982. Production of furfural from agricultural wastes by using pressurised water in a batch reactor. J. Chem. Technol. Biotechnol., 32: 666-668. Goldstein, IS., Helena, P., Pittman, J.L., Strouse, B.A. and Searingelli, P., 1983. The hydrolysis of cellulose with superconcentrated hydrochloric acid. In: Proc. Vth Symp. on Biotechnology for Fuels and Chemicals, Gatlingburg, Tennessee, 1983. Ramachandran, K., 1983. Biomass conversion to reducing sugars and furfural. M. Tech. Thesis, Indian Institute of Technology, New Delhi.
291
Printed
in The Netherlands
Short Communication
Fermentable Sugars from Biopolymers of Bagasse
K. RAMACHANDRAN,
K. DAS*
Chemical Engineering Department, Indian Institute of Technology and D.K. SHARMA Center of Energy Studies, Indian Institute of Technology, Hauz Khas, New Delhi-110016 (India) (Received December
15,1986; accepted in revised form March 3, 1987)
INTRODUCTION
Ethanol can replace oil as a fuel and its use would help in the conservation of the meagre oil reserves. Some convenient and cost-effective processes for the production of ethanol from biopolymers available in agricultural wastes Agrowastes have been subjected to two-stage acid have been developed [l-5]. hydrolysis to extract fermentable sugars from biopolymers such as hemicellulose and cellulose. Suitability of acid or enzymatic processes for the recovery of fermentable sugars has been studied by other workers [ 6,7]. Fermentable sugars obtained from acid hydrolysis of biomass can easily be digested to ethanol. In the present work, a two-stage process for the hydrolysis of biomass using aqueous HCI has been developed to selectively extract xylose and glucose from bagasse. The interesting feature of the process is that it operates under ambient pressure conditions and thus avoids the constraints of working under high pressures. HCl was chosen as the catalyst because of its easy recovery. This also allowed the use of promoters which could improve the yields of hydrolysis. HCl can be recovered through distillation and part of it can also be neutralized with lime. The CaCl, thus obtained can be used as a promoter for the hydrolysis of biopolymers. Selective production of xylose and glucose allows their separate fermentation to alcohol, whereby xylose can also be utilized properly. *To whom all correspondence
0166-3097/87/$03.50
should be addressed.
0 1987 Elsevier Science Publishers
B.V.
292
MATERIALS AND METHODS
Prehydrolysis
of bagasse
Bagasse was crushed to 40-60 BSS (417-495 pm) mesh size and dried. The bagasse powder was impregnated with 18% HCl and the impregnated bagasse was used for prehydrolysis. Reaction was allowed to proceed for 180 min at 35, 45,55,65 and 75°C. Aliquots were withdrawn at regular intervals of time for determination of xylose, glucose and furfural formed. For the experiments where CaCl, was used as a promoter for bagasse, this reagent was dissolved in the 18% HCl and the reaction took place under similar conditions. Hydrolysis of bagasse residue The bagasse residue obtained from the prehydrolysis was washed with water and dried. The residue was then taken in the reactor which contained 35% HCl. Hydrolysis was allowed to proceed for 180 min, and aliquots were withdrawn at regular intervals for determination of glucose. For the experiments where CaCl, was used as a promoter for bagasse residue, this reagent was dissolved in the 35% HCl and the reaction took place under similar conditions. Agitation for the prehydrolysis and hydrolysis experiments was provided by a magnetic stirrer. Composition
of bagasse and assays
The composition of bagasse and the assay procedures furfural were as reported in our earlier works [ l-41.
for xylose, glucose and
RESULTS AND DISCUSSION
The fact that the bioi>olymer hemicellulose is more easily hydrolysed under milder conditions, when cellulose remains unhydrolysed, makes it possible to hydrolyse only the hemicellulose fraction from biomass. In the present work, 18% HCl was used for the hydrolysis of biomass in the first stage at moderate temperatures from 35 to 90°C. The residual biomass was rich in cellulose, as cellulose does not get hydrolysed under these relatively mild conditions. The residual biomass was subjected to hydrolysis by 35% HCl at 35’ C. The lower temperature of 35°C was selected on the premise that the degradation of the sugars formed is minimum at lower temperatures. Bagasse, an agricultural residue, was selected for the studies.
293
Y g
12
-z' 7 2-s 3 2 t LY I+ '2 z
0
c
20
LO
60
80 TIME
100
120
140
160
imnl
Fig. 1. Xylose yield from prehydrolysis
Fig. 2. Xylose yield from prehydrolysis on potential sugars.
of bagasse at different
x
AT
3S'C
??
AT
L5'1
'
AT
55'1
0
AT
65'1
of bagasse at different
temperatures
temperatures
with 18% HCI.
with 18% HCl, based
Prehydrolysis of bagasse Bagasse was subjected to prehydrolysis with HCl and the effect of temperature on xylose yields was studied. Figures 1 and 2 show xylose yields on the basis of dry weight of bagasse as well as on the basis of potential sugar at 35,
294
TABLE 1 Xylose yield from prehydrolysis Time (min)
5 15
of bagasse at 35 ’C
Xylose yield ( % ) (based on dry wt. of bagasse)
Xylose yield ( %) (based on potential
without agitation
with agitation
without agitation
8.1 10.5
9.0 11.5
12.46
15.75
16.15
23.06
sugar) with agitation
30
12.3
15.5
18.92
36.00
45
18.6
17.3
28.60
27.50
60 90
11.4
15.0
17.50
23.50
9.9
8.0
15.25
27.50
120
6.6
6.0
10.50
23.50
180
6.6
6.0
10.20
23.50
45, 55, 65, 75 and 90°C respectively. Xylose yields increased with time up to the first 45 min of the reaction and then started dropping at higher temperatures. The maximum yield of xylose was obtained at 35” C, as 18.6% (Table 1) on the basis of dry weight of bagasse. Xylose yield on the basis of potential sugar was found to be 28.6%. The yield was found to decrease with increasing prehydrolysis temperature from 35 to 90’ C (Fig. 1) . This shows that the xylose (formed) decomposes at a higher hydrolysis temperature. Yields of furfural under the prehydrolysis conditions studied were low (Table 2). This was due to the fact that dehydration of xylose to furfural takes place at higher temperatures. Furfural formation [ 8,9] is high at temperatures above 190” C. Thus, by keeping the prehydrolysis temperature low, the formation of furfural in the reaction products can be reduced considerably. Prolonged reaction time of 120 min yields about 6.5% furfural (Table 2). Steam treatment of xylose formed TABLE 2 Furfural yield from the prehydrolysis Time (min)
of bagasse at 35 “C
Furfural yield ( % ) (based on dry wt. of bagasse)
5
1.0
15
2.0
30 45 60
3.0 4.6 4.8
90
4.5
120 180
6.5 6.0
295
TABLE 3 Glucose yield from the hydrolysis Time (min)
5 15 30 45 60 90 120 180
of the bagasse residue after prehydrolysis
Glucose yield ( % ) (based on dry wt. of bagasse )
Glucose yield ( % ) (based on potential sugar)
without agitation
with agitation
without agitation
with agitation
8.4 10.5 11.4 15.0 13.5 9.0 6.9 6.0
8.4 12.9 17.7 16.2 15.3 nd nd nd
19.53 24.10 26.50 35.00 31.30 20.90 16.04 13.95
19.53 30.00 41.16 37.67 35.60 nd nd nd
nd= not determined.
from bagasse, at temperatures above 190°C would result in the production of larger amounts of furfural. Hydrolysis temperature may be raised above 190’ C if furfural is the desired product. Hydrolysis of the bagasse residue The bagasse residue obtained after prehydrolysis was rich in cellulose and lignin. This was subjected to hydrolysis with 35% HCl at 35°C. Lignin is not attacked under these conditions, and only the cellulose part gets hydrolysed to glucose. Table 3 shows the yields of glucose obtained. Glucose yields were found to increase with time up to 45 min and after that the yields started dropping. The drop in yields could be due to the decomposition of sugars formed. About 15% yield of glucose was obtained after 45 min. The glucose yield on potential sugar basis was found to be maximum (about 35% ) at this time. This shows that reasonable glucose yields are obtainable at lower temperatures and under atmospheric pressure. Attempts were made to further improve the yields of fermentable sugars by using promoters and through agitation of the reactants. Effect of promoters Earlier studies [lo] have shown that the use of ZnCl,, SnCl,, AlCl, and CaCl, promotes the hydrolysis of biomass. In the present studies, CaClz was used as a promoter in both the prehydrolysis and the hydrolysis of bagasse. CaCl, can be obtained by neutralization of HCl with lime after hydrolysis. The yields of hemicellulose and cellulose hydrolysis were found to improve through the addition of CaCl, as a promoter. There was a 3% improvement in the yield
296
of xylose by addition of CaCl, in the prehydrolysis of bagasse for 45 min at 35°C using 18% HCl, over the blank experiment. Addition of the same proportion of CaCl, in the hydrolysis of prehydrolysed bagasse residue (containing mainly cellulose and lignin) resulted in 3.5% improvement in the yields of glucose in comparison with the control experiment without CaCl, at 35’ C using 35% HCl after 45 min reaction time. Higher amounts of CaCl, were not tried, because of cost reasons. Further attempts, using ZnCl, and SnCl, as promoters in the hydrolysis of hemicellulose and cellulose, are currently underway. Effect of agitation Agitation was found to have a significant effect on the hydrolysis of both hemicellulose and cellulose present in bagasse. Table 1 shows that with agitation the xylose yields increase up to 36% after 30 min of reaction at 35°C in comparison with 28.6% in the blank experiment after 45 min under similar conditions. Similarly, the glucose yields also increased from 15.0% after 45 min to 41% within 30 min through agitation under similar conditions (Table 3). This showed that in the absence of agitation, hydrolysis does not go to completion. The hydrolysis follows the diffusion-controlled mechanism of a firstorder reaction. With agitation hydrolysis goes to completion with yields of high fermentable sugars in a shorter time. The rate constants are about 5-20 times greater than those without agitation [ 10,111. Complete hydrolysis can be effected within 10 min at 50” C and within 45 min at 30°C. Integrated process Earlier it had been reported [ l-51 that particle size, solid-liquid ratio, lignin content, and pretreatment affect the hydrolysis yield of fermentable sugars from biomass. Recently, the fermentation of xylose to ethanol has also been achieved in good yield [ 1,4,6]. The fermentable sugars, xylose and glucose, obtained from this two-stage acid process could be fermented to ethanol. In the present process, furfural formation is not so signifcant. In fact, furfural has been reported to poison the yeast [ 11. Furfural can be removed from the fermentable sugars through extraction with tetraiin, isoamyl alcohol, or toluene. But toluene is poisonous to yeast and hence the use of isoamyl alcohol for the [ 41. extraction of furfural has been recommended The residual bagasse obtained after the prehydrolysis followed by hydrolysis contains mainly lignin. Lignin can be hydrocracked or hydropyrolysed to get value-added aromatic chemicals. Thus, this affords a three-step integrated process for the extraction of alcohols and aromatic chemicals and fuels from agrowastes. Figure 3 shows the flow scheme of this process. The process allows the utilization of every component of biomass effectively. The process employs milder conditions for the production of ethanol, a clean fuel, from agrowastes. This two-stage acid hydrolysis process is better than the enzymatic hydrolysis process in many ways. The process takes 45 min for prehydrolysis and about the same time for hydrolysis. Thus, in total 90 min is required for the hydrol-
pq-.Jzg_Fg Fig. 3. Flow scheme of the integrated process for the production
of ethanol from agricultural wastes.
ysis of bagasse biopolymers as against more than 24 h for the enzymatic hydrolysis at the same temperature, that is, between 35 and 45°C. The recovery of HCl is easier than that of the enzyme, but HCl is a corrosive material. In fact, Teflon reactors can be used at these temperatures to handle HCl. The main advantage of the two-stage process is that it allows the recovery of xylose and glucose separately. Thus, this makes it possible to ferment xylose and glucose separately to get ethanol. In the enzymatic hydrolysis, a mixture of xylose and glucose is obtained, which is not as convenient for fermenting to ethanol.
REFERENCES Singh, A., Das, K. and Sharma, D.K., 1984. Production of furfural, xylose, fermentable sugars and ethanol from agricultural wastes. J. Chem. Technol. Biotechnol., 24: 51-61. Singh, A., Das, K. and Sharma, D.K., 1984. Integrated process for production of furfural, xylose, glucose and ethanol by two step acid hydrolysis. Ind. Eng. Chem., Prod. Res. Dev., 23: 257-261. Singh, A., Das, K. and Sharma, D.K., 1984. Acid hydrolysis of agricultural wastes to reducing sugars. Int. J. Agric. Wastes, 9: 131-145. Sharma, D.K., Das, K. and Singh, A., 1985. Production of value added fuels and chemical feedstocks from biomass through chemical and biochemical treatments. Chem. Age India, 35: 919-921. Sharma, D.K., Das, K. and Raj, V., 1986. Two stage acid hydrolysis of bagasse under atmospheric pressure conditions. Accepted for presentation at the 1987 TAPPI Pulping Conference, Washington, DC, November l-5. Grethlein, H.K., 1978. A comparison of the economics of acid and enzymatic hydrolysis of newsprint. Biotechnol. Bioeng., 20: 503-525. Beck, M.J. and Stickland, R.C., 1984. Production of ethanol by bioconversion of wood sugars from two stage dilute acid hydrolysis of hard woods. Biomass, 6: 101-l 10.
8 9 10
11
Sharma, D.K. and Sahgal, P.N., 1983. Elevated temperature hydrolysis of rice husk with pressurized water in a semi-batch process. Cellulose Chem. Technol., 17: 655-658. Sharma, D.K. and Sahgal, P.N., 1982. Production of furfural from agricultural wastes by using pressurised water in a batch reactor. J. Chem. Technol. Biotechnol., 32: 666-668. Goldstein, IS., Helena, P., Pittman, J.L., Strouse, B.A. and Searingelli, P., 1983. The hydrolysis of cellulose with superconcentrated hydrochloric acid. In: Proc. Vth Symp. on Biotechnology for Fuels and Chemicals, Gatlingburg, Tennessee, 1983. Ramachandran, K., 1983. Biomass conversion to reducing sugars and furfural. M. Tech. Thesis, Indian Institute of Technology, New Delhi.