Pretreatment of corn stover by soaking in aqueous ammonia at moderate temperatures

Soaking in aqueous ammonia at moderate temperatures was investigated as a method of pretreatment for enzymatic hydrolysis as well as simultaneous saccharification and cofermentation (SSCF) of corn stover. The method involves batch treatment of the feedstock with aqueous ammonia (15-30 wt%) at 40-90 degrees C for 6-24 h. The optimum treatment conditions were found to be 15 wt% of NH(3), 60 degrees C, 1:6 of solid-to-liquid ratio, and 12 h of treatment time. The treated corn stover retained 100% glucan and 85% of xylan, but removed 62% of lignin. The enzymatic digestibility of the glucan content increased from 17 to 85% with 15 FPU/g-glucan enzyme loading, whereas the digestibility of the xylan content increased to 78%. The treated corn stover was also subjected to SSCF test using Spezyme-CP and recombinant Escherichia coli (KO11). The SSCF of the soaking in aqueous ammonia treated corn stover resulted in an ethanol concentration of 19.2 g/L from 3% (w/v) glucan loading, which corresponds to 77% of the maximum theoretical yield based on glucan and xylan.     

Ammonia fiber expansion pretreatment and enzymatic hydrolysis on two different growth stages of reed canarygrass

Plant materials from the vegetative growth stage of reed canarygrass and the seed stage of reed canarygrass are pretreated by ammonia fiber expansion (AFEX) and enzymatically hydrolyzed using 15 filter paper units (FPU) cellulase/g glucan to evaluate glucose and xylose yields. Percent conversions of glucose and xylose, effects of temperature and ammonia loading, and hydrolysis profiles are analyzed to determine the most effective AFEX treatment condition for each of the selected materials. The controls used in this study were untreated samples of each biomass material. All pretreatment conditions tested enhanced enzyme digestibility and improved sugar conversions for reed canarygrass compared with their untreated counterparts. Based on 168 h hydrolysis results using 15 FPU Spezyme CP cellulase/g glucan the most effective AFEX treatment conditions were determined as: vegetative growth stage of reed canarygrass--100 degrees C, 60% moisture content, 1.2:1 kg ammonia/kg of dry matter (86% glucose and 78% xylose) and seed stage of reed canarygrass--100 degrees C, 60% moisture content, 0.8:1 kg ammonia/kg of dry matter (89% glucose and 81% xylose). Supplementation by commercial Multifect 720 xylanase along with cellulase further increased both glucose and xylose yields by 10-12% at the most effective AFEX conditions.     

Pretreatment of switchgrass by ammonia fiber explosion (AFEX)

The effects of ammonia fiber explosion (AFEX) pretreatment of switch grass using its major process variables are reported. The optimal pretreatment conditions for switchgrass were found to be near 100°C reactor temperature, and ammonia loading of 1:1 kg of ammonia: kg of dry matter with 80% moisture content (dry weight basis [dwb]) at 5 min residence time. Hydrolysis results of AFEX-treated and untreated samples showed 93% vs 16% glucan conversion, respectively. The ethanol yield of optimized AFEX-treated switchgrass was measured to be about 0.2 g ethanol/g dry biomass, which is 2.5 times more than that of the untreated sample.     

Pretreatment of corn stover using wet oxidation to enhance enzymatic digestibility

Corn stover is an abundant, promising raw material for fuel ethanol production. Although it has a high cellulose content, without pretreatment it resists enzymatic hydrolysis, like most lignocellulosic materials. Wet oxidation (water, oxygen, mild alkali or acid, elevated temperature and pressure) was investigated to enhance the enzymatic digestibility of corn stover. Six different combinations of reaction temperature, time, and pH were applied. The best conditions (60g/L of corn stover, 195°C, 15 min, 12 bar O₂, 2 g/L of Na₂CO₃) increased the enzymatic conversion of corn stover four times, compared to untreated material. Under these conditions 60% of hemicellulose and 30% of lignin were solubilized, whereas 90% of cellulose remained in the solid fraction. After 24-h hydrolysis at 50°C using 25 filter paper units (FPU)/g of dry matter (DM) biomass, the achieved conversion of cellulose to glucose was about 85%. Decreasing the hydrolysis temperature to 40°C increased hydrolysis time from 24 to 72 h. Decreasing the enzyme loading to 5 FPU/g of DM biomass slightly decreased the enzymatic conversion from 83.4 to 71%. Thus, enzyme loading can be reduced without significantly affecting the efficiency of hydrolysis, an important economical aspect.     

Optimization of dilute-acid pretreatment of corn stover using a high-solids percolation reactor

We have previously demonstrated that pretreatment of corn stover with dilute sulfuric acid can achieve high digestibility and efficient recovery of hemicellulose sugars with high yield and concentration. Further improvement of this process was sought in this work. A modification was made in the operation of the percolation reactor that the reactor is preheated under atmospheric pressure to remove moisture that causes autohydrolysis. This eliminated sugar decomposition during the preheating stage and led to a considerable improvement in overall sugar yield. In addition, liquid throughput was minimized to the extent that only one reactor void volume of liquid was collected. This was done to attain a high xylose concentration in the hydrolyzate. The optimum reaction and operating conditions were identified wherein near quantitative enzymatic digestibilities are obtained with enzyme loading of 15 FPU/g glucan. With a reduced enzyme loading of 5 FPU/g glucan, the enzymatic digestibility was decreased, but still reached a level of 92%. Decomposition of carbohydrates was extremely low as indicated by the measured glucan and xylan mass closures (recovered sugar plus unreacted) which were 98% and 94%, respectively. The data obtained in this work indicate that the digestibility is related to the extent of xylan removal.     

Pretreatment of corn stover by low-liquid ammonia recycle percolation process

A pretreatment method using aqueous ammonia was investigated with the intent of minimizing the liquid throughput. This process uses a flow-through packed column reactor (or percolation reactor). In comparison to the ammonia recycle percolation (ARP) process developed previously in our laboratory, this process significantly reduces the liquid throughput to one reactor void volume in packed bed (2.0–4.7 mL of liquid/g of corn stover) and, thus, is termed low-liquid ARP (LLARP). In addition to attaining short residence time and reduced energy input, this process achieves 59–70% of lignin removal and 48–57% of xylan retention. With optimum operation of the LLARP to corn stover, enzymatic digestibilities of 95, 90 and 86% were achieved with 60, 15, and 7.5 filter paper units/g of glucan, respectively. In the simultaneous saccharification and fermentation test of the LLARP samples using Saccharomyces cerevisiae (NREL-D₅A), an ethanol yield of 84% of the theoretical maximum was achieved with 6% (w/v) glucan loading. In the simultaneous saccharification and cofermentation (SSCF) test using recombinant Escherichia coli (KO11), both the glucan and xylan in the solid were effectively utilized, giving an overall ethanol yield of 109% of the theoretical maximum based on glucan, a clear indication that the xylan content was converted into ethanol. The xylooligomers existing in the LLARP effluent were not effectively hydrolyzed by cellulase enzyme, achieving only 60% of digestibility. SSCF of the treated corn stover was severely hampered when the substrate was supplemented with the LLARP effluent, giving only 56% the overall yield of ethanol. The effluent appears to significantly inhibit cellulase and microbial activities.     

Optimizing ammonia processing conditions to enhance susceptibility of legumes to fiber hydrolysis

A warm-season legume, Florigraze rhizoma peanut (FRP), was used as the source of fiber to produce sugars. FRP was subjected to several ammonia-processing conditions using temperature, biomass moisture content, and ammonia loading as process variables during a 5-min treatment. A cellulase loading of 2 FPU/g DM and 24 h incubation were used to produce the sugars. Total sugar yield was 3.34-fold higher in the optimal treatment (1.5 g ammonia/g DM-60%-90°C) compared to untreated and was 65.3% of theoretical. Cellulose and hemicellulose conversions increased from 30 and 15.5% in untreated FRP to 78 and 34% in treated FRP.     

Effects of temperature and moisture on dilute-acid steam explosion pretreatment of corn stover and cellulase enzyme digestibility

Corn stover is emerging as a viable feedstock for producing bioethanol from renewable resources. Dilute-acid pretreatment of corn stover can solubilize a significant portion of the hemicellulosic component and enhance the enzymatic digestibility of the remaining cellulose for fermentation into ethanol. In this study, dilute H₂SO₄ pretreatment of corn stover was performed in a steam explosion reactor at 160°C, 180°C, and 190°C, approx 1 wt% H₂SO₄, and 70-s to 840-s residence times. The combined severity (Log₁₀ [R _o ] - pH), an expression relating pH, temperature, and residence time of pretreatment, ranged from 1.8 to 2.4. Soluble xylose yields varied from 63 to 77% of theoretical from pretreatments of corn stover at 160 and 180°C. However, yields >90% of theoretical were found with dilute-acid pretreatments at 190°C. A narrower range of higher combined severities was required for pretreatment to obtain high soluble xylose yields when the moisture content of the acid-impregnated feedstock was increased from 55 to 63 wt%. Simultaneous saccharification and fermentation (SSF) of washed solids from corn stover pretreated at 190°C, using an enzyme loading of 15 filter paper units (FPU)/g of cellulose, gave ethanol yields in excess of 85%. Similar SSF ethanol yields were found using washed solid residues from 160 and 180°C pretreatments at similar combined severities but required a higher enzyme loading of approx 25 FPU/g of cellulose.     

Enzymatic hydrolysis of high-moisture corn fiber pretreated by afex and recovery and recycling of the enzyme complex

Corn fiber is a grain-processing residue containing significant amounts of cellulose, hemicellulose, and starch, which is collected in facilities where fuel ethanol is currently manufactured. Preliminary research has shown that corn fiber (30% moisture dry weight basis [dwb]) responds well to ammonia-fiber explosion (AFEX) pretreatment. However, an important AFEX pretreatment variable that has not been adequately explored for corn fiber is sample moisture. In the present investigation, we determined the best AFEX operating conditions for pretreatment of corn fiber at high moisture content (150% moisture dwb). The optimized AFEX treatment conditions are defined in terms of the moisture content, particle size, ammonia to biomass ratio, temperature, and residence time using the response of the pretreated biomass to enzymatic hydrolysis as an indicator. Approximate optimal-pretreatment conditions for unground corn fiber containing 150% (dwb) moisture were found to be: temperature, 90?C; ammonia: dry corn fiber mass ratio, 1:1; and residence time 30 min (average reactor pressure under these conditions was 200 pounds per square inch [psig]). Enzymatic hydrolysis of the treated corn fiber was performed with three different enzyme combinations. More than 80% of the theoretical sugar yield was obtained during enzymatic hydrolysis using the best enzyme combination after pretreatment of corn fiber under the optimized conditions previously described. A simple process for enzyme recovery and reuse to hydrolyze multiple portions of AFEX-treated corn fiber by one portion of enzyme preparation is demonstrated. Using this process, five batches of fresh substrate (at a concentration of 5% w/v) were successfully hydrolyzed by repeated recovery and reuse of one portion of enzyme preparation, with the addition of a small portion of fresh enzyme in each subsequent recycling step.     

Pretreatment of corn stover by soaking in aqueous ammonia

Soaking in aqueous ammonia (SAA) was investigated as a pretreatment method for corn stover. In this method, the feedstock was soaked in aqueous ammonia over an extended period (10–60 d) at room temperature. It was done without agitation at atmospheric pressure. SAA treatment removed 55–74% of the lignin, but retained nearly 100% of the glucan and 85% of the xylan. The xylan remaining in the corn stover after SAA treatment was hydrolyzed along with the glucan by xylanase present in the Spezyme CP enzyme. In the simultaneous saccharification and fermentation (SSF) test of SAA-treated corn stover, using S. cerevisiae (D₅A), an ethanol yield of 73% of theoretical maximum was obtained on the basis of the glucan content in the treated corn stover. The accumulation of xylose in the SSF appears to inhibit the cellulase activity on glucan hydrolysis, which limits the yield of ethanol. In the simultaneous saccharification and co-fermentation (SSCF) test, using recombinant E. coli (KO11), both the glucan and xylose were effectively utilized, resulting in on overall ethanol yield of 77% based on the glucan and xylan content of the substrate. When the SSCF process is used, the fact that the xylan fraction is retained during pretreatment is a desirable feature since the overall bioconversion can be carried out in a single step without separate recovery of xylose from the pretreatment liquid.     

Modeling of Pretreatment Condition of Extrusion-Pretreated Prairie Cordgrass and Corn Stover with Poly (Oxyethylen)20 Sorbitan Monolaurate

Extrusion processing has shown potential to be used as a pretreatment method for second-generation bioethanol production. Furthermore, surfactants have been shown to reduce enzyme deactivation and increase the efficiency of hydrolysis. Therefore, a sequential pretreatment technique was developed for corn stover (CS) and prairie cordgrass (PCG) in which a single screw extruder was used for the first pretreatment according to a previously optimized condition using 70?C180?°C for feed, barrel, and die zones with 65?C155?rpm screw speed. The second pretreatment was optimized in this study at 45?C55?°C, 1?C4?h, 0.15?C0.6?g Tween 20/g glucan according to response surface methodology. Optimization of surfactant pretreatment facilitated the estimation of interaction and higher-order effects for major factors involved in surfactant treatment (temperature, time, surfactant loading). Using 8.6?FPU/g glucan cellulase, the optimum conditions found by fitting appropriate quadratic models to the data increased glucose and xylose yield by 27.5 and 33?% for CS and by 21.5 and 27?% for PCG, respectively. Tween 20 concentrations and pretreatment temperature were the most significant factors affecting sugar yield (p value <0.05). Studies of SDS concentration at and beyond critical micelle concentration (5.2?C100?mM) demonstrated a decrease in sugar yield compared to control.     

Effects of Low Moisture Anhydrous Ammonia (LMAA) Pretreatment at Controlled Ammoniation Temperatures on Enzymatic Hydrolysis of Corn Stover

Corn stover was treated using low-moisture anhydrous ammonia (LMAA) at controlled ammoniation temperature. Moisturized corn stover (50 % moisture) was contacted with anhydrous ammonia (0.1 g NH₃/g-biomass) in a batch reactor at various temperatures (ambient to 150 °C). After ammoniation at elevated and controlled temperature, ammoniated corn stover was pretreated at various temperatures (60–150 °C) for 72–144 h. Change in composition was marginal at low pretreatment temperature but was relatively severe with pretreatment at high temperature (130–150 °C). The latter resulted in low enzymatic digestibility. It was also observed that extreme levels (either high or low) of residual ammonia affected enzymatic digestibility, while residual ammonia improved by 1.0–1.5 %. The LMAA method enhanced enzymatic digestibility compared to untreated corn stover (29.8 %). The highest glucan and xylan digestibility (84.1 and 73.6 %, respectively) was obtained under the optimal LMAA conditions (i.e., ammoniation at 70 °C for 20 min, followed by pretreatment at 90 °C for 48 h).     

Hydrolyzabilities of Different Corn Stover Fractions After Aqueous Ammonia Pretreatment

The effect of aqueous ammonia pretreatment on the hydrolysis of different corn stover fractions (rind, husk, leaf, and pith) by xylanase (XYL) with cellulases (CELs) was evaluated. The aqueous ammonia pretreatment had excellent delignification ability (above 66 %) for different corn stover fractions. The corn rind exhibited the lowest susceptibility to aqueous ammonia pretreatment. The pretreated rind showed the lowest hydrolyzability by CEL and XYL, which was supported by a high content of crystalline cellulose in the hydrolyzed residues of rind, as confirmed by X-ray diffraction (XRD). With the addition of 1 mg XYL/g dry matter, a high glucose yield (above 90 %) could be obtained from the pretreated rind by CEL. The results revealed that a high hydrolyzate yield of corn rind after aqueous ammonia pretreatment could be obtained with 1 mg xylanase/g dry matter, showing that aqueous ammonia pretreatment and xylanase addition to cellulases have great potential for the efficient hydrolysis of corn stover without previous fractionation.     

Maximum Saccharification of Cellulose Complex by an Enzyme Cocktail Supplemented with Cellulase from Newly Isolated <Emphasis Type="BoldItalic">Aspergillus fumigatus</Emphasis> ECU0811

Either the natural biodegradation process or the industrial hydrolytic process requires synergistic interactions between various cellulases. However, it is sometimes impeded by low hydrolytic rate of existing cellulases and the lack of accessory enzymes. Herein, the ability of a commercial cellulase (Spezyme CP, from Genencor) to degrade steam explosion-pretreated corn stover was significantly improved. Firstly, a fungal cellulase producer, Aspergillus fumigatus ECU0811, was isolated from hundreds of soil samples. A 96-deep-well microscale-based platform was developed here to reduce the labor-intensive screening work and proved to be consistent with macroscale screening work. After optimization of fermentation, 3% corn cob could induce A. fumigatus ECU0811 to yield the highest cellulase production. Based on the high activities of β-glucosidase and xylanase by A. fumigatus ECU0811, 0.91 and 125 U/mg protein, respectively, an enzyme cocktail was composed with a fixed dosage of Spezyme CP (CPCel) at 14.2 filter paper units (FPU)/g glucan and varied dosages of A. fumigatus cellulase (AFCel). Consequently, the glucan-to-glucose conversion of corn stover was increased from 25.6% in the presence of CPCel at a dosage of 14.2 FPU/g glucan to 99.5% in the presence of the enzyme cocktail (14.2 FPU CPCel plus 1.21 FPU AFCel per gram of glucan). On the other side, it reduced the total protein amount of CPCel by as much as tenfold, which extremely improved the hydrolytic rate of Spezyme CP and reduced its dosage.     

Enhanced Enzymatic Hydrolysis of Lignocellulose by Optimizing Enzyme Complexes

To enhance the conversion of the cellulose and hemicellulose, the corncob pretreated by aqueous ammonia soaking was hydrolyzed by enzyme complexes. The saturation limit for cellulase (Spezyme CP) was determined as 15 mg protein/g glucan (50 filter paper unit (FPU)/g glucan). The accessory enzymes (β-glucosidase, xylanase, and pectinase) were supplemented to hydrolyze cellobiose (cellulase-inhibiting product), hemicellulose, and pectin (the component covering the fiber surfaces), respectively. It was found that β-glucosidase (Novozyme 188) loading of 1.45 mg protein/g glucan [30 cellobiase units (CBU)/g glucan] was enough to eliminate the cellobiose inhibitor, and 2.9 mg protein/g glucan (60 CBU/g glucan) was the saturation limit. The supplementation of xylanase and pectinase can increase the conversion of cellulose and hemicellulose significantly. The yields of glucose and xylose enhanced with the increasing enzyme loading, but the increasing trend became low at high loading. Compared with xylanase, pectinase was more effective to promote the hydrolysis of cellulose and hemicellulose. The supplementation of pectinase with 0.12 mg protein/g glucan could increase the yields of glucose and xylose by 7.5% and 29.3%, respectively.     

Potential of Agricultural Residues and Hay for Bioethanol Production

Production of bioethanol from agricultural residues and hays (wheat, barley, and triticale straws, and barley, triticale, pearl millet, and sweet sorghum hays) through a series of chemical pretreatment, enzymatic hydrolysis, and fermentation processes was investigated in this study. Composition analysis suggested that the agricultural straws and hays studied contained approximately 28.62-38.58% glucan, 11.19-20.78% xylan, and 22.01-27.57% lignin, making them good candidates for bioethanol production. Chemical pretreatment with sulfuric acid or sodium hydroxide at concentrations of 0.5, 1.0, and 2.0% indicated that concentration and treatment agent play a significant role during pretreatment. After 2.0% sulfuric acid pretreatment at 121 degrees C/15 psi for 60 min, 78.10-81.27% of the xylan in untreated feedstocks was solubilized, while 75.09-84.52% of the lignin was reduced after 2.0% sodium hydroxide pretreatment under similar conditions. Enzymatic hydrolysis of chemically pretreated (2.0% NaOH or H2SO4) solids with Celluclast 1.5 L-Novozym 188 (cellobiase) enzyme combination resulted in equal or higher glucan and xylan conversion than with Spezyme(R) CP- xylanase combination. The glucan and xylan conversions during hydrolysis with Celluclast 1.5 L-cellobiase at 40 FPU/g glucan were 78.09 to 100.36% and 74.03 to 84.89%, respectively. Increasing the enzyme loading from 40 to 60 FPU/g glucan did not significantly increase sugar yield. The ethanol yield after fermentation of the hydrolyzate from different feedstocks with Saccharomyces cerevisiae ranged from 0.27 to 0.34 g/g glucose or 52.00-65.82% of the theoretical maximum ethanol yield.     

Production of Cellulase from Kraft Paper Mill Sludge by Trichoderma Reesei Rut C-30

Paper mill sludge is a solid waste material generated from pulping and papermaking operations. Because of high glucan content and its well-dispersed structure, paper mill sludges are well suited for bioconversion into value-added products. It also has high ash content originated from inorganic additives used in papermaking, which causes hindrance to bioconversion. In this study, paper mill sludges from Kraft process were de-ashed by a centrifugal cleaner and successive treatment by sulfuric acid and sodium hydroxide, and used as a substrate for cellulase production. The treated sludge was the only carbon source for cellulase production, and predominantly inorganic nutrients were used as the nitrogen source for this bioprocess. The cellulase enzyme produced from the de-ashed sludge exhibited cellulase activity of 8 filter paper unit (FPU)/mL, close to that obtainable from pure cellulosic substrates. The yield of cellulase enzyme was 307 FPU/g glucan of de-ashed sludge. Specific activity was 8.0 FPU/mg protein. In activity tests conducted against the corn stover and α-cellulose, the xylanse activity was found to be higher than that of a commercial cellulase. Relatively high xylan content in the sludge appears to have induced high xylanase production. Simultaneous saccharification and fermentation (SSF) was performed using partially de-ashed sludge as the feedstock for ethanol production using Sacharomyces cerevisiae and the cellulase produced in-house from the sludge. With 6% (w/v) glucan feed, ethanol yield of 72% of theoretical maximum and 24.4 g/L ethanol concentration were achieved. These results were identical to those of the SSF using commercial cellulases.     

Oxidative lime pretreatment of high-lignin biomass

Lime (Ca[OH]₂) and oxygen (O₂) were used to enhance the enzymatic digestibility of two kinds of high-lignin biomass: poplar wood and newspaper. The recommended pretreatment conditions for poplar wood are 150°C, 6 h, 0.1 g of Ca(OH)₂/g of dry biomass, 9 mL of water/g of dry biomass, 14.0 bar absolute oxygen, and a particle size of −10 mesh. Under these conditions, the 3-d reducing sugar yield of poplar wood using a cellulase loading of 5 filter paper units (FPU)/g of raw dry biomass increased from 62 to 565 mg of eq. glucose/g of raw dry biomass, and the 3-d total sugar (glucose + xylose) conversion increased from 6 to 77% of raw total sugars. At high cellulase loadings (e.g., 75 FPU/g of raw dry biomass), the 3-d total sugar conversion reached 97%. In a trial run with newspaper, using conditions of 140°C, 3 h, 0.3 g of Ca(OH)₂/g of dry biomass, 16 mL of water/g of dry biomass, and 7.1 bar absolute oxygen, the 3-d reducing sugar yield using a cellulase loading of 5 FPU/g of raw dry biomass increased from 240 to 565 mg of eq. glucose/g of raw dry biomass. A material balance study on poplar wood shows that oxidative lime pretreatment solubilized 38% of total biomass, including 78% of lignin and 49% of xylan; no glucan was removed. Ash increased because calcium was incorporated into biomass during the pretreatment. After oxidative lime pretreatment, about 21% of added lime could be recovered by CO₂ carbonation.     

Conversion of aqueous ammonia-treated corn stover to lactic acid by simultaneous saccharification and cofermentation

Treatment of corn stover with aqueous ammonia removes most of the structural lignin, whereas retaining the majority of the carbohydrates in the solids. After treatment, both the cellulose and hemicellulose in corn stover become highly susceptible to enzymatic digestion. In this study, corn stover treated by aqueous ammonia was investigated as the substrate for lactic acid production by simultaneous saccharification and cofermentation (SSCF). A commercial cellulase (Spezyme-CP) and Lactobacillus pentosus American Type Culture Collection (ATCC) 8041 (Spanish Type Culture Collection [CECT]-4023) were used for hydrolysis and fermentation, respectively. In batch SSCF operation, the carbohydrates in the treated corn stover were converted to lactic acid with high yields, the maximum lactic acid yield reaching 92% of the stoichiometric maximum based on total fermentable carbohydrates (glucose, xylose, and arabinose). A small amount of acetic acid was also produced from pentoses through the phosphoketolase pathway. Among the major process variables for batch SSCF, enzyme loading and the amount of yeast extract were found to be the key factors affecting lactic acid production. Further tests on nutrients indicated that corn steep liquor could be substituted for yeast extract as a nitrogen source to achieve the same lactic acid yield. Fed-batch operation of the SSCF was beneficial in raising the concentration of lactic acid to a maximum value of 75.0 g/L.     

Optimization of steam pretreatment of SO2-impregnated corn stover for fuel ethanol production

In this study, corn stover with a dry matter content of 20% was impregnated with SO₂ and then steam pretreated for various times at various temperatures. The pretreatment was evaluated by enzymatic hydrolysis of the solid material and analysis of the sugar content in the liquid. The maximum overall yield of glucose, 89% of the theoretical based on the glucan in the raw material, was achieved when the corn stover was pretreated at 200°C for 10 min. The maximum overall yield of xylose, 78%, was obtained with pretreatment at 190°C for 5 min.