Steam pretreatment of H(2)SO(4)-impregnated Salix for the production of bioethanol

In the bioconversion of lignocellulosic materials to ethanol, pretreatment of the material prior to enzymatic hydrolysis is essential to obtain high overall yields of sugar and ethanol. In this study, steam pretreatment of fast-growing Salix impregnated with sulfuric acid has been investigated by varying the temperature (180-210 degrees C), the residence time (4, 8 or 12 min), and the acid concentration (0.25% or 0.5% (w/w) H(2)SO(4)). High sugar recoveries were obtained after pretreatment, and the highest yields of glucose and xylose after the subsequent enzymatic hydrolysis step were 92% and 86% of the theoretical, respectively, based on the glucan and xylan contents of the raw material. The most favorable pretreatment conditions regarding the overall sugar yield were 200 degrees C for either 4 or 8 min using 0.5% sulfuric acid, both resulting in a total of 55.6g glucose and xylose per 100g dry raw material. Simultaneous saccharification and fermentation experiments were performed on the pretreated slurries at an initial water-insoluble content of 5%, using ordinary baker's yeast. An overall theoretical ethanol yield of 79%, based on the glucan and mannan content in the raw material, was obtained.     

Enhancement of the enzymatic digestibility of sugarcane bagasse by steam pretreatment impregnated with hydrogen peroxide

Sugarcane bagasse was subjected to steam pretreatment impregnated with hydrogen peroxide. Analyses were performed using 2³ factorial designs and enzymatic hydrolysis was performed at two different solid concentrations and with washed and unwashed material to evaluate the importance of this step for obtaining high cellulose conversion. Similar cellulose conversion were obtained at different conditions of pretreatment and hydrolysis. When the cellulose was hydrolyzed using the pretreated material in the most severe conditions of the experimental design (210°C, 15 min and 1.0% hydrogen peroxide), and using 2% (w/w) water‐insoluble solids (WIS), and 15 FPU/g WIS, the cellulose conversion was 86.9%. In contrast, at a milder pretreatment condition (190°C, 15 min and 0.2% hydrogen peroxide) and industrially more realistic conditions of hydrolysis (10% WIS and 10 FPU/g WIS), the cellulose conversion reached 82.2%. The step of washing the pretreated material was very important to obtain high concentrations of fermentable sugars. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 2012     

Combined sugar yields for dilute sulfuric acid pretreatment of corn stover followed by enzymatic hydrolysis of the remaining solids

A number of previous studies determined dilute acid pretreatment conditions that maximize xylose yields from pretreatment or glucose yields from subsequent digestion of the pretreated cellulose, but our emphasis was on identifying conditions to realize the highest yields of both sugars from both stages. Thus, individual xylose and glucose yields are reported as a percentage of the total potential yield of both sugars over a range of sulfuric acid concentrations of 0.22%, 0.49% and 0.98% w/w at 140, 160, 180 and 200 degrees C. Up to 15% of the total potential sugar in the substrate could be released as glucose during pretreatment and between 15% and 90+% of the xylose remaining in the solid residue could be recovered in subsequent enzymatic hydrolysis, depending on the enzyme loading. Glucose yields increased from as high as 56% of total maximum potential glucose plus xylose for just enzymatic digestion to 60% when glucose released in pretreatment was included. Xylose yields similarly increased from as high as 34% of total potential sugars for pretreatment alone to between 35% and 37% when credit was taken for xylose released in digestion. Yields were shown to be much lower if no acid was used. Conditions that maximized individual sugar yields were often not the same as those that maximized total sugar yields, demonstrating the importance of clearly defining pretreatment goals when optimizing the process. Overall, up to about 92.5% of the total sugars originally available in the corn stover used could be recovered for coupled dilute acid pretreatment and enzymatic hydrolysis. These results also suggest that enhanced hemicellulase activity could further improve xylose yields, particularly for low cellulase loadings.     

Effect of water extraction on sugars recovery from steam exploded olive tree pruning

Biomass of olive tree pruning can be considered a suitable raw material for the production of ethanol due to its high content of potentially fermentable carbohydrates. However its high extractives content could cause condensation reactions between extractives and acid insoluble lignin during pretreatment, hindering the enzymatic hydrolysis of pretreated material. In this work, the effect of extractives removal before steam explosion of olive tree pruning was evaluated. The objectives are to recover as much glucose as possible in the extraction stage and to avoid the condensation reactions. The effect of temperature and time of water extracted material on sugars recovery was studied using a response surface method according to a central composite design. Extractive removal previous to steam explosion resulted in 20% more total sugars recovery in comparison to a material without water extraction stage.     

Optimization of ammonia fiber expansion (AFEX) pretreatment and enzymatic hydrolysis of Miscanthus x giganteus to fermentable sugars

Miscanthus x giganteus is a tall perennial grass whose suitability as an energy crop is presently being appraised. There is very little information on the effect of pretreatment and enzymatic saccharification of Miscanthus to produce fermentable sugars. This paper reports sugar yields during enzymatic hydrolysis from ammonia fiber expansion (AFEX) pretreated Miscanthus. Pretreatment conditions including temperature, moisture, ammonia loading, residence time, and enzyme loadings are varied to maximize hydrolysis yields. In addition, further treatments such as soaking the biomass prior to AFEX as well as washing the pretreated material were also attempted to improve sugar yields. The optimal AFEX conditions determined were 160 degrees C, 2:1 (w/w) ammonia to biomass loading, 233% moisture (dry weight basis), and 5 min reaction time for water-soaked Miscanthus. Approximately 96% glucan and 81% xylan conversions were achieved after 168 h enzymatic hydrolysis at 1% glucan loading using 15 FPU/(g of glucan) of cellulase and 64 p-NPGU/(g of glucan) of beta-glucosidase along with xylanase and tween-80 supplementation. A mass balance for the AFEX pretreatment and enzymatic hydrolysis process is presented.     

Thermo-mechanical extrusion pretreatment for conversion of soybean hulls to fermentable sugars

Thermo-mechanical extrusion pretreatment for lignocellulosic biomass was investigated using soybean hulls as the substrate. The enzyme cocktail used to hydrolyze pretreated soybean hulls to fermentable sugars was optimized using response surface methodology (RSM). Structural changes in substrate and sugar yields from thermo-mechanical processing were compared with two traditional pretreatment methods that utilized dilute acid (1% sulfuric acid) and alkali (1% sodium hydroxide). Extrusion processing parameters (barrel temperature, in-barrel moisture, screw speed) and processing aids (starch, ethylene glycol) were studied with respect to reducing sugar and glucose yields. The conditions resulting in the highest cellulose to glucose conversion (95%) were screw speed 350 rpm, maximum barrel temperature 80 °C and in-barrel moisture content 40% wb. Compared with untreated soybean hulls, glucose yield from enzymatic hydrolysis of soybean hulls increased by 69.6%, 128.7% and 132.2%, respectively, when pretreated with dilute acid, alkali and extrusion.     

Effect of washing on yield in one- and two-step steam pretreatment of softwood for production of ethanol

Two-step steam pretreatment of softwood on laboratory scale has previously been shown to result in higher yields than one-step steam pretreatment. In this study, these results are verified on a larger scale. In an industrial process filtration and washing of the material between the two pretreatment steps are difficult without release of pressure. A worst case without filtration or washing was thus investigated to determine the influence of poor washing on the yield of sugars and the formation of byproducts. Steam pretreatment with SO(2) impregnation was investigated using three different procedures. One-step steam pretreatment was performed at 215 degrees C for 5 min. Two different kinds of two-step steam pretreatment were performed at 190 degrees C for 2 min in the first step and at 210 degrees C for 5 min in the second step. In one case the slurry obtained after the first pretreatment step was separated into a liquid and a solid phase, where the water-insoluble solid material was washed with water and then used for pretreatment in the second step. In the other case of two-step steam pretreatment, neither separation nor washing was performed. The pretreated material was evaluated using both enzymatic hydrolysis and fed-batch simultaneous saccharification and fermentation. Both two-step steam pretreatment process configurations investigated resulted in higher yields of ethanol (300 L/ton) than one-step steam pretreatment (227 L/ton). Separation and washing of the material between the pretreatment steps in the two-step steam pretreatment process did not improve the overall sugar yield, although the formation of sugar degradation products was reduced.     

Ethanol production from alkaline peroxide pretreated enzymatically saccharified wheat straw

Wheat straw used in this study contained 44.24 +/- 0.28% cellulose and 25.23 +/- 0.11% hemicellulose. Alkaline H(2)O(2) pretreatment and enzymatic saccharification were evaluated for conversion of wheat straw cellulose and hemicellulose to fermentable sugars. The maximum yield of monomeric sugars from wheat straw (8.6%, w/v) by alkaline peroxide pretreatment (2.15% H(2)O(2), v/v; pH 11.5; 35 degrees C; 24 h) and enzymatic saccharification (45 degrees C, pH 5.0, 120 h) by three commercial enzyme preparations (cellulase, beta-glucosidase, and xylanase) using 0.16 mL of each enzyme preparation per g of straw was 672 +/- 4 mg/g (96.7% yield). During the pretreatment, no measurable quantities of furfural and hydroxymethyl furfural were produced. The concentration of ethanol (per L) from alkaline peroxide pretreated enzyme saccharified wheat straw (66.0 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 37 degrees C in 48 h was 18.9 +/- 0.9 g with a yield of 0.46 g per g of available sugars (0.29 g/g straw). The ethanol concentration (per L) was 15.1 +/- 0.1 g with a yield of 0.23 g/g of straw in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 37 degrees C in 48 h.     

Enzymatic digestion of alkaline‐sulfite pretreated sugar cane bagasse and its correlation with the chemical and structural changes occurring during the pretreatment step

Sugar cane bagasse is recalcitrant to enzymatic digestion, which hinders the efficient conversion of its polysaccharides into fermentable sugars. Alkaline‐sulfite pretreatment was used to overcome the sugar cane bagasse recalcitrance. Chemical and structural changes that occurred during the pretreatment were correlated with the efficiency of the enzymatic digestion of the polysaccharides. The first 30 min of pretreatment, which removed approximately half of the initial lignin and 30% of hemicellulose seemed responsible for a significant enhancement of the cellulose conversion level, which reached 64%. After the first 30 min of pretreatment, delignification increased slightly, and hemicellulose removal was not enhanced; however, acid groups continued to be introduced into the residual lignin. Water retention values were 145% to the untreated bagasse and 210% to the bagasse pretreated for 120 min and fiber widths increased from 10.4 to 30 μm, respectively. These changes were responsible for an additional increase in the efficiency of enzymatic hydrolysis of the cellulose, which reached 92% with the 120 min pretreated sample. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:890–895, 2013     

玉米秸秆分批补料获得高还原糖浓度酶解液的条件优化

木质纤维素高浓度还原糖水解液的获得是纤维乙醇产业化发展的方向。在发酵工业领域,分批补料法是实现这一目标的重要研究途径。本研究采用分批补料法对获得高浓度玉米秸秆酶解还原糖的条件进行了优化。以稀硫酸预处理的玉米秸秆为原料,考察了液固比、补加量与补加时间对分批补料糖化的影响。结果表明,秸秆高浓度酶解液条件的初始物料为20％ (重量/体积),木聚糖酶220 U/g (底物),纤维素酶6 FPU/g (底物),果胶酶50 U/g (底物),在24 h、48 h后分批补加8％预处理后的物料,同时添加与补料量相应的木聚糖酶20 U/g (底物),纤维素酶2 FPU/g (底物),72 h后,最终糖化结果与非补料法相比,还原糖浓度从48.5 g/L提高到138.5 g/L,原料的酶解率最终达到理论值的62.5％。试验结果表明补料法可以显著提高秸秆水解液还原糖浓度。     

Optimization of organic acid pretreatment of wheat straw

The objective of this study was to determine the effectiveness of different organic acids (maleic, succinic, and oxalic acid) on enzymatic hydrolysis and fermentation yields of wheat straw. It was also aimed to optimize the process conditions (temperature, acid concentration, and pretreatment time) by using response surface methodology (RSM). In line with this objective, the wheat straw samples were pretreated at three different temperatures (170, 190, and 210°C), acid concentrations (1%, 3%, and 5%) and pretreatment time (10, 20, and 30 min). The findings show that at extreme pretreatment conditions, xylose was solubilized in liquid phase, causing an increase in cellulose and lignin content of biomass. Enzymatic hydrolysis experiments revealed that maleic and oxalic acids were quite effective at achieving high sugar yields (>90%) from wheat straw. In contrast, the highest sugar yields were 50–60%, when the samples were pretreated with succinic acid, indicating that succinic acid was not as effective. The optimum process conditions for maleic acid were, 210°C, 1.08% acid concentration, and 19.8 min; for succinic acid 210°C, 5% acid concentration, and 30 min; for oxalic acid 210°C, 3.6% acid concentration, and 16.3 min. The ethanol yields obtained at optimum conditions were 80, 79, and 59% for maleic, oxalic and succinic acid, respectively. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1487–1493, 2016     

沙柳原料高浓度底物酶解发酵乙醇工艺

为了提高沙柳生物转化过程的经济可行性,考察了沙柳原料经过蒸爆、超微粉碎+稀酸、超微粉碎+稀碱预处理后高浓度底物补料酶解的效果,并对其高浓度水解糖液进行了乙醇发酵。结果表明:蒸爆处理法水解效果最好,通过补料酶解,底物质量分数可以达到30%,酶解液中总糖质量浓度达到132 g/L,葡萄糖质量浓度105 g/L;超微粉碎+稀酸预处理原料底物质量分数可以达到22%,酶解液中总糖质量浓度达到123 g/L,葡萄糖质量浓度73 g/L;超微粉碎+稀碱预处理原料底物质量分数可以达到22%,酶解液中总糖质量浓度133 g/L,葡萄糖质量浓度77 g/L。3种预处理使沙柳原料的酶解糖液都可以较好地被酿酒酵母利用发酵产乙醇,蒸爆处理原料的酶解糖液乙醇发酵效果最好,乙醇质量浓度达到47 g/L。     

Efficient conversion of sugarcane stalks into ethanol employing low temperature alkali pretreatment method

An alternative route for bio-ethanol production from sugarcane stalks (juice and bagasse) featuring a previously reported low temperature alkali pretreatment method was evaluated. Test-tube scale pretreatment-saccharification experiments were carried out to determine optimal LTA pretreatment conditions for sugarcane bagasse with regard to the efficiency of enzymatic hydrolysis of the cellulose. Free fermentable sugars and bagasse recovered from 2 kg of sugarcane stalks were jointly converted into ethanol via separate enzymatic hydrolysis and fermentation (SHF). Results showed that 98% of the cellulose present in the optimally pretreated bagasse was hydrolyzed into glucose after 72-h enzymatic saccharification using commercially available cellulase and β-glucosidase preparations at relatively low enzyme loading. The fermentable sugars in the mixture of the sugar juice and the bagasse hydrolysate were readily converted into 193.5 mL of ethanol by Saccharomyces cerevisiae within 12h, achieving 88% of the theoretical yield from the sugars and cellulose.     

Dilute acid pretreatment, enzymatic saccharification, and fermentation of rice hulls to ethanol

Rice hulls, a complex lignocellulosic material with high lignin (15.38 +/- 0.2%) and ash (18.71 +/- 0.01%) content, contain 35.62 +/- 0.12% cellulose and 11.96 +/- 0.73% hemicellulose and has the potential to serve as a low-cost feedstock for production of ethanol. Dilute H2SO4 pretreatments at varied temperature (120-190 degrees C) and enzymatic saccharification (45 degrees C, pH 5.0) were evaluated for conversion of rice hull cellulose and hemicellulose to monomeric sugars. The maximum yield of monomeric sugars from rice hulls (15%, w/v) by dilute H2SO4 (1.0%, v/v) pretreatment and enzymatic saccharification (45 degrees C, pH 5.0, 72 h) using cellulase, beta-glucosidase, xylanase, esterase, and Tween 20 was 287 +/- 3 mg/g (60% yield based on total carbohydrate content). Under this condition, no furfural and hydroxymethyl furfural were produced. The yield of ethanol per L by the mixed sugar utilizing recombinant Escherichia colistrain FBR 5 from rice hull hydrolyzate containing 43.6 +/- 3.0 g fermentable sugars (glucose, 18.2 +/- 1.4 g; xylose, 21.4 +/- 1.1 g; arabinose, 2.4 +/- 0.3 g; galactose, 1.6 +/- 0.2 g) was 18.7 +/- 0.6 g (0.43 +/- 0.02 g/g sugars obtained; 0.13 +/- 0.01 g/g rice hulls) at pH 6.5 and 35 degrees C. Detoxification of the acid- and enzyme-treated rice hull hydrolyzate by overliming (pH 10.5, 90 degrees C, 30 min) reduced the time required for maximum ethanol production (17 +/- 0.2 g from 42.0 +/- 0.7 g sugars per L) by the E. coli strain from 64 to 39 h in the case of separate hydrolysis and fermentation and increased the maximum ethanol yield (per L) from 7.1 +/- 2.3 g in 140 h to 9.1 +/- 0.7 g in 112 h in the case of simultaneous saccharification and fermentation.     

Optimizing dilute acid hydrolysis of hemicellulose in a nitrogen-rich cellulosic material--dairy manure

Effective dilute acid hydrolysis of dairy manure which contains roughly 12% hemicellulose on a dry matter basis can produce a variety of mono-sugars such as arabinose, xylose and galactose, as well as to further benefit utilization of cellulose in the manure. To enhance the effectiveness of this dilute acid hydrolysis, the effect of manure nitrogen content was studied because some reactions such as the browning reaction between amino acids and reducing sugars and acid-base reactions involving ammonia and acid interfere with the hydrolysis. Two dairy manure samples were used to study this nitrogen effect; the original manure and the pretreated manure derived from a solid/liquid separation pretreatment. The pretreated manure had a total nitrogen content of 1.3% dry matter (DM) while the original dairy manure had twice that amount with a total nitrogen content of 2.6% DM. Results found that the optimal conditions for hydrolysis of manure hemicellulose were 2 h reaction time, 1% sulfuric acid concentration, 135 degrees C, and 10% sample concentration using the pretreated dairy manure as raw material. Under these conditions the corresponding sugar yield from hemicellulose was 111% and sugar concentration in the solution reached 16.5 g/l. At the same time, the hydrolyzed solid had 43% DM of cellulose, which was much higher than both the original manure containing 22% and the pretreated manure with 32%.     

Ethanol production from rice straw using optimized aqueous-ammonia soaking pretreatment and simultaneous saccharification and fermentation processes

Rice straw was pretreated using aqueous-ammonia solution at moderate temperatures to enable production of the maximum amount of fermentable sugars from enzymatic hydrolysis. The effects of various operating variables including pretreatment temperature, pretreatment time, the concentration of ammonia and the solid-to-liquid ratio on the degree of lignin removal and the enzymatic digestibility were optimized using response surface methodology. The optimal reaction conditions, which resulted in an enzymatic digestibility of 71.1%, were found to be 69 °C, 10 h and an ammonia concentration of 21% (w/w). The effects of different commercial cellulases and the additional effect of a non-cellulolytic enzyme, xylanase, were also evaluated. Additionally, simultaneous saccharification and fermentation was conducted with rice straw to assess the ethanol production yield and productivity.     

Hydrolysis of nonstarch carbohydrates of wheat-starch effluent for ethanol production

A (polysaccharide-rich) waste stream derived from a combined starch and ethanol factory was investigated regarding hydrolysis of the nonstarch carbohydrates for ethanol production. The material was characterized and processed to yield the maximum amount of sugars. The starch fraction was hydrolyzed with amylolytic enzymes, and the resulting fibrous material was separated by filtration. This material, denoted starch-free fibers (SFF), was subjected to heat treatment followed by enzymatic hydrolysis to recover the other major carbohydrate components, namely, cellulose and hemicellulose, in monomeric form. Heat treatment in a microwave oven efficiently solubilized a fraction of these polysaccharides and made the material more accessible to the cellulolytic and hemicellulolytic enzymes used in the subsequent enzymatic hydrolysis. The maximum sugar yield after enzymatic hydrolysis, achieved with pretreatment at 170 degrees C for 40 min, was 34.1 g per 100 g SFF, comprising 12.8 g glucose, 13.9 g xylose and 7.4 g arabinose, corresponding to 66%, 71% and 51% of the theoretical, respectively.     

Autohydrolysis Pretreatment of Mixed Softwood to Produce Value Prior to Combustion

Autohydrolysis is a hot water pretreatment to extract soluble components from wood that can be used prior to converting the woody residuals into paper, wood products, fuel, or other goods. In this study, mixed softwood chips were autohydrolyzed in hot water at 150, 160, 170, and 180 °C for 1 and 2 h residence times. The objective was to understand the tradeoff between the extraction of fermentable sugar and the residual solid total energy of combustion quantitatively. This process strategy will be referred to as “value prior to combustion”. High-performance liquid chromatography was used to determine chemical compositions (sugars and byproducts such as acetic acid, furfural, and hydroxymethylfurfural) of the extracted liquid and residuals; a bomb calorimeter was used to measure the heating value of original wood and solid residue. As the autohydrolysis temperature increased, material balances of the system indicated higher volatile byproducts loss. More hemicelluloses were solubilized by the hot water extraction process at higher temperatures and longer residence times, and a greater degree of sugar degradation was also observed. The maximum sugar yield was determined to occur at conditions of 170 °C for 2 h, during which 13 g of sugar was recovered from the extract out of 100 g of oven-dried wood. The heating value of the solid residues after extraction was greater than the original wood. The total energy content of the solid residual after extraction ranged from 85 to 98 % of the original energy content of the feed with higher temperatures reducing the total energy content.     

Comparative study on chemical pretreatment methods for improving enzymatic digestibility of crofton weed stem

In order to utilize and control the invasive weed, crofton weed (Eupatorium adenophorum Spreng), a potential pathway was proposed by using it as a feedstock for production of fermentable sugars. Three chemical pretreatment methods were used for improving enzymatic saccharification of the weed stem. Mild H2SO4 pretreatment could obtain a relatively high yield of sugars in the pretreatment (32.89%, based on initial holocellulose), however, it led to only a slight enhancement of enzymatic digestibility. NaOH pretreatment could obtain a higher enzymatic conversion ratio of cellulose compared with H2SO4 pretreatment. Peracetic acid (PAA) pretreatment seemed to be the most effective for improving enzymatic saccharification of the weed stem in the three chemical pretreatment methods under the same conditions. The conversion ratio of cellulose in the sample pretreated by PAA under the "optimal" condition was increased to 50% by cellulase loading of 80 FPU/g cellulose for 72 h incubation. A number of empirical quadratic models were successfully developed according to the experimental data to predict the yield of sugar and degree of delignification.     

Effect of dilute acid pretreatment on the saccharification and fermentation of rye straw

This research shows the effect of dilute acid pretreatment with various sulfuric acid concentrations (0.5–2.0% [wt/vol]) on enzymatic saccharification and fermentation yield of rye straw. After pretreatment, solids of rye straw were suspended in Na citrate buffer or post-pretreatment liquids (prehydrolysates) containing sugars liberated after hemicellulose hydrolysis. Saccharification was conducted using enzymes dosage of 15 or 25 FPU/g cellulose. Cellulose saccharification rate after rye straw pretreatment was enhanced by performing enzymatic hydrolysis in sodium citrate buffer in comparison with hemicellulose prehydrolysate. The maximum cellulose saccharification rate (69%) was reached in sodium citrate buffer (biomass pretreated with 2.0% [wt/vol] H₂SO₄). Lignocellulosic complex of rye straw after pretreatment was subjected to separate hydrolysis and fermentation (SHF) or separate hydrolysis and co-fermentation (SHCF). The SHF processes conducted in the sodium citrate buffer using monoculture of Saccharomyces cerevisiae (Ethanol Red) were more efficient compared to hemicellulose prehydrolysate in respect with ethanol yields. Maximum fermentation efficiency of SHF processes obtained after rye straw pretreatment at 1.5% [wt/vol] H₂SO₄ and saccharification using enzymes dosage of 25 FPU/g in sodium citrate buffer, achieving 40.6% of theoretical yield. However, SHCF process using cocultures of pentose-fermenting yeast, after pretreatment of raw material at 1.5% [wt/vol] H₂SO₄ and hydrolysis using enzymes dosage of 25 FPU/g, resulted in the highest ethanol yield among studied methods, achieving 9.4 g/L of ethanol, corresponding to 55% of theoretical yield.