Application of a microassay method to study enzymatic hydrolysis of pretreated wheat straw

BACKGROUND: The conversion of lignocellulosic biomass to ethanol includes a disruptive pretreatment process followed by enzyme‐catalyzed hydrolysis of the cellulose and hemicellulose components to fermentable sugars. As the cost and hydrolytic efficiency of enzymes are major factors that restrict the commercialization of biomass conversion processes, significant efforts are made nowadays to improve the enzymatic mixtures and make the process cost‐effective. RESULTS: In this work, enzymatic microassays have been developed and validated to test new different enzymatic formulations on real lignocellulosic substrates. Homogeneous handsheets from steam pretreated wheat straw were elaborated to be used as substrate. The microassay was adapted to test both water‐insoluble solids and the whole slurry as substrates. Results in hydrolysis microassays were comparable with those obtained in standard flask assays using pretreated wheat straw. Moreover, using the enzymatic microassays, two novel preparations have been evaluated, demonstrating the ability of microassays to discriminate between different enzymatic mixtures. CONCLUSIONS: This enzymatic microassay represents a rapid method to test the performance of new selected cellulase enzymes on real pretreated lignocellulosic substrates. This microassay will enable evaluation of enzyme components separately, or optimized mixtures. Copyright © 2010 Society of Chemical Industry     

木质纤维素燃料乙醇生物转化预处理技术

由丰富的木质纤维素资源制备乙醇有利于缓解能源紧缺、减少环境污染、实现可持续发展.然而某些物理、化学因素阻碍了木质纤维素中纤维素和半纤维素的转化和利用.预处理引起物理和/或化学上的变化,主要目的是改变或去除各种结构和(或)化学障碍,增加纤维素酶解率和转化效果,是一系列纤维素乙醇转化技术中的关键和核心.本文就纤维素乙醇生物...     

Enhanced enzymatic hydrolysis of rice straw pretreated by alkali assisted with photocatalysis technology

BACKGROUND: The fermentable sugars in lignocellulose are derived from cellulose and hemicellulose, which are not readily accessible to enzymatic hydrolysis because of their biological resistance, so that pretreatment of lignocellulose is needed for this process. In this work, a novel lignocellulose pretreatment method using alkali solution assisted by photocatalysis was investigated. RESULTS: The reaction conditions of nano‐TiO₂ dosage and photocatalysis time were optimized at 2 g L^?1 and 1 h, respectively. After pretreatment under these conditions, cellulose in rice straw was increased from 37.5% to 71.5%, and lignin decreased from 18.5% to 9.0%. The results of X‐ray diffraction (XRD), Fourier transform infrared (FT‐IR) and scanning electron microscopy (SEM) analysis showed that the physical properties and microstructure of the straw were changed by this pretreatment, which favored the following enzymatic hydrolysis. The enzymatic hydrolysis rate of the straw pretreated using this technology was verified to be 73.96%, which was 2.56 times higher than that obtained with the alkali procedure. CONCLUSION: The proposed photocatalysis pretreatment technology was more efficient at degrading the lignin and hemicellulose in rice straw than alkali pretreatment, making it more readily available for the following enzymatic hydrolysis process. Copyright © 2009 Society of Chemical Industry     

Pretreatment of lignocellulosic biomass by autohydrolysis and aqueous ammonia percolation

A two-stage biomass pretreatment process-a combination of autohydrolysis and aqueous ammonia percolation-was experimentally studied as a method to remove and recover hemicellulose from lignocellulosic biomass. Hemicellulose was completely separated from the biomass after 1 hr of autohydrolysis at 200‡C. As reaction temperature and/or time of autohydrolysis was increased in the range of 170-200‡C and 1–2.5 hr, respectively, the amount of hemicellulose solubilization was increased ; however, more sugars were decomposed. Most of the extracted hemicellulose was recovered as xylose oligomer. Hemicellulose was found to inhibit the enzymatic hydrolysis of cellulose. When the biomass was consecutively pretreated with pure water at 180‡C for 30 min and with 10 wt% ammonia solution at 180‡C for 30 min, about 62% of the hemicellulose was extracted. The enzymatic digestibility of the pretreated biomass was as high as 95 %.     

Catalytic organosolv fractionation of willow wood and wheat straw as pretreatment for enzymatic cellulose hydrolysis

BACKGROUND: Ethanol‐based organosolv fractionation of lignocellulosic biomass is an effective pretreatment technology for enzymatic cellulose hydrolysis to produce sugars and lignin within a biorefinery. This study focuses on the catalytic effect of H₂SO₄, HCl, and MgCl₂ on organosolv pretreatment of willow wood and wheat straw. RESULTS: The use of catalysts improved fractionation of both feedstocks. The maximum enzymatic cellulose digestibility obtained was 87% for willow wood (using 0.01 mol L^?1 H₂SO₄ as catalyst) and 99% for wheat straw (0.02 mol L^?1 HCl). Non‐catalytic organosolv fractionation at identical conditions resulted in 74% (willow wood) and 44% (wheat straw) glucose yield by enzymatic hydrolysis. Application of catalysts in organosolv pretreatment was particularly effective for wheat straw. The influence of the acid catalysts was found to be primarily due to their effect on the pH of the organosolv liquor. Acid catalysts particularly promoted xylan hydrolysis. MgCl₂ was less effective than the acid catalysts, but it seemed to more selectively improve delignification of willow wood. CONCLUSION: Application of catalysts in organosolv pretreatment of willow wood and wheat straw was found to substantially improve fractionation and enzymatic digestibility. The use of catalysts can contribute to achieving maximum utilization of lignocellulosic biomass in organosolv‐based biorefineries. Copyright © 2011 Society of Chemical Industry     

New lignocellulose pretreatments using cellulose solvents: a review

Non‐food lignocellulosic biomass is the most abundant renewable bioresource as a collectable, transportable, and storable chemical energy that is far from fully utilized. The goal of biomass pretreatment is to improve the enzymatic digestibility of pretreated lignocellulosic biomass. Many substrate factors, such as substrate accessibility, lignin content, particle size and so on, contribute to its recalcitrance. Cellulose accessibility to hydrolytic enzymes is believed to be the most important substrate characteristic limiting enzymatic hydrolysis. Cellulose solvents effectively break linkages among cellulose, hemicellulose and lignin, and also dissolve highly‐ordered hydrogen bonds in cellulose fibers accompanied with great increases in substrate accessibility. Here the history and recent advances in cellulose solvent‐based biomass pretreatment are reviewed and perspectives provided for addressing remaining challenges. The use of cellulose solvents, new and existing, provides opportunities for emerging biorefineries to produce a few precursors (e.g. monosaccharides, oligosaccharides, and lignin) for the production of low‐value biofuels and value‐added biochemicals. © 2012 Society of Chemical Industry     

Comparison of atmospheric aqueous glycerol and steam explosion pretreatments of wheat straw for enhanced enzymatic hydrolysis

BACKGROUND: The oversupply of cheap glycerol by the oleochemicals industry together with problems occurring in low‐boiling‐point organosolv pretreatments, has generated an interest in the use of glycerol in the organosolv pretreatment of lignocellulosic biomass. Atmospheric aqueous glycerol autocatalytic organosolv pretreatment (AAGAOP) is a promising strategy that can effectively enhance enzymatic hydrolysis of lignocellulosic biomass. As a cost‐effective technique, steam explosion pretreatment (SEP) is being adopted in industrial applications. Accordingly, work has been carried out to investigate how AAGAOP enhanced enzymatic hydrolysis of lignocellulosic biomass compares with the SEP method. RESULTS: Under controlled laboratory conditions, based on ≥ 90% cellulose recovery, AAGAOP removed ≥ 60% hemicellulose and ≥ 60% lignin from wheat straw while SEP led to ～80% hemicellulose and 10% lignin removal. Enzymatic hydrolysis yields of AAGAOP and SEP reached ～90% and ～70%, respectively. Physical‐chemical structural characterization by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FT‐IR), helped explain the above results. The two methods gave priority to dissociating the guaiacyl lignin and had a relatively small effect on syringyl units. However, AAGAOP exhibited a superior performance. CONCLUSION: The two methods enhanced the enzymatic hydrolysis of lignocellulosic biomass by removing and/or altering physical‐chemical structural impediments. The AAGAOP technique, with some special advantages, was more effective than SEP in enhancing the recovery and enzymatic digestibility of cellulose. Copyright © 2008 Society of Chemical Industry     

木质纤维原料组分分离的研究

从木质纤维原料预处理对微生物转化的必要性和回收利用半纤维素、木质素意义两个方面分析了木质纤维原料组分分离的必要性。木质纤维原料组分分离意味着木质纤维原料的精制,不是把木质纤维原料仅作为纤维素单一资源看待,而是把它视为一种多组分物料,将木质纤维原料精制成为具有一定纯度的各种组分,并分别加工成有价值的产品,这也是生物量全利用对于木质纤维原料预处理提出的新要求,赋予新的哲理思想。根据生物量全利用的要求,提出了木质纤维原料组分分离技术的新定性评价标准。根据利用汽爆和乙醇萃取法联合对麦草组分分离的研究结果,可提出一条经济可行的麦草组分分离的工艺过程,半纤维素和木质素回收率分别达到了80%和75%,纤维素酶解率达90%以上。     

NaOH/AQ预处理对玉米秸秆脱木质素及酶解性能的影响

对玉米秸秆进行氢氧化钠/蒽醌（NaOH/AQ）去木质化预处理,考察了预处理温度、时间和NaOH用量对玉米秸秆脱木质素程度的影响,并探讨了脱木质素程度对提高预处理后物料酶解性能的影响。L₉（3⁴）正交试验得出较适宜预处理工艺条件为：温度160℃,时间60 min,NaOH用量（以绝干原料质量计）2.8%;其他条件为AQ用量0.05%,固液比1：5（g：mL）,此时木质素脱除率为75%,酶解后聚糖转化率达到73.79%。随着物料脱木质素程度的提高,其酶解效率相应增加;当木质素脱除率达到一定程度后,预处理后的聚糖转化率达到最大值,继续提高木质素脱除率,聚糖转化率反而降低。响应面优化的酶水解工艺条件为纤维素酶用量30 FPU/g,β-葡萄糖苷酶10 IU/g,反应时间72 h,温度50℃,底物质量分数2.5%,此时还原糖得率为85.62%。对酶解液进行HPLC分析,酶解液中的葡萄糖质量浓度为14.83 g/L,木糖质量浓度为4.83 g/L。XRD分析显示,预处理前后纤维素的晶型没有变化,而结晶度由31.40%提高至46.91%,表明物料中木质素和半纤维素发生了不同程度的溶出。     

稻草秸秆3种预处理方法的比较

底物w(纤维素)和w(半纤维素)是木质纤维素转化为乙醇、乳酸和其他化学品最为重要的因素。为了提高底物w(纤维素)、w(半纤维素)和糖化得率,该文采用稀硫酸、氢氧化钠和氢氧化钠联合过氧乙酸等3种化学方法对稻草秸秆进行了预处理。结果表明,用ρ(NaOH)=20 g/L的碱液于85℃与ρ(过氧乙酸)=60 g/L酸液于75℃联合处理秸秆时,秸秆w(纤维素)从41.5%上升到81.5%,w(半纤维素)下降为13.7%,纤维素酶酶解48 h葡萄糖质量浓度达37.7 g/L,木糖质量浓度为12.8 g/L;用ρ(NaOH)=20 g/L碱液于121℃处理秸秆时,秸秆w(纤维素)为66.3%,w(半纤维素)为20.2%,酶解60 h后葡萄糖质量浓度为33.5 g/L,72 h木糖质量浓度为15.1 g/L。     

Long‐term lime pretreatment of poplar wood

Long‐term lime pretreatment has proven to increase digestibility of many herbaceous lignocellulose sources; but until this work, its effects had not been evaluated on wood, whose lignin content is higher, and therefore, more recalcitrant to enzymatic hydrolysis. In this study, the mild conditions of long‐term lime pretreatment (1‐atm pressure, temperatures ranging from 25 to 75°C, and reaction times between 1 and 12 weeks, with and without air) were systematically applied to poplar wood available in two batches with different lignin contents. These batches were designated as low‐lignin biomass (LLB) with lignin content of 21.4% and high‐lignin biomass (HLB) with lignin content of 29.1%. Full factorial designs resulted in 79 samples of pretreated poplar that were analyzed for lignin and carbohydrates pretreatment yields, and enzymatic digestibility (15 FPU/g glucan in raw biomass cellulose loading). After aerated lime pretreatment at 65°C for 4 weeks, and subsequent enzymatic hydrolysis, an overall yield of 0.76 g glucan + xylan recovered per gram glucan + xylan in raw biomass was obtained. This is equivalent to an increased poplar wood digestibility of 7.5‐fold compared with untreated biomass. Different batches of the feedstock resulted in different lignin and carbohydrates pretreatment yields; however, overall yields of carbohydrates (combining pretreatment and enzymatic hydrolysis) were similar. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Evaluation of enzymatic hydrolysis of wheat straw pretreated by atmospheric glycerol autocatalysis

BACKGROUND: Because ethanol organosolv pulping requires high pressure and is highly volatile, an atmospheric autocatalytic glycerol organosolv pretreatment process has been investigated. Enzymatic hydrolysis of wheat straw pretreated using this method was evaluated to explore a novel, economically competitive and environmentally friendly pretreatment technology for bioconversion of lignocellulosic biomass. The method also provides economical utilization of industrial glycerol, helping to cope with the challenge of the excess production of glycerol and to further defray the cost of biodiesel production. RESULTS: With preliminary optimization of the parameters in the pretreatment process, pretreatment performed at 240 °C for 4 h with the glycerol addition of 15 g g^?1 dry feedstock and wash at 80 °C led to high recovery of cellulose (95%) and good removal of lignin (>70%), which formed, respectively, 80% and 10% of the pulp. The enzymatic hydrolysis of the pretreated wheat straw yielded 90% of theoretically achievable sugar after 24 h and 92% after 48 h. CONCLUSION: Atmospheric autocatalytic glycerol organosolv pretreatment removed significant amounts of hemicellulose and lignin without affecting good cellulose recovery. The proposed novel strategy increased the susceptible of wheat straw to enzyme attack and led to enzymatic hydrolysis that was comparable with that achieved using ethanol organosolv pretreatment. Copyright © 2007 Society of Chemical Industry     

表面活性剂耦合离子液体对稻秆酶解糖化的影响

酶解糖化是木质纤维素材料制备生物质乙醇的关键环节,因此提高稻秆等木质纤维素材料的酶解糖化效率具有重要意义。以稻秆为原料,采用表面活性剂耦合离子液体为预处理方法,考察预处理温度、时间、表面活性剂的添加比例对稻秆酶解的影响。结果表明,预处理温度为110℃、时间为60 min、表面活性剂添加比例为1%,稻秆的酶解效果最佳,与单独离子液体处理的稻秆相比,纤维转化率可提高8%～15%。同时分别通过稻秆成分分析、FTIR、XRD、SEM等对预处理前后的稻秆结构进行表征,证实预处理后酶解效率提高的合理性。     

水热预处理工艺参数对玉米秸秆组分与酶解效率的影响

采用间歇式水热预处理方法,考察了不同水热预处理温度和处理时间对玉米秸秆主要成分变化的影响以及水热预处理后的纤维素酶解效率。在180～220℃,10～25 min范围内,随温度升高和时间延长预处理后半纤维素移除率和纤维素损失率也随之增大,但木质素质量并未减少反而有所增加。在210℃,25 min时得到最大半纤维素移除率为86.0%。以半纤维素移除率、木质素移除率和纤维素损失率为因变量,处理温度和处理时间为自变量通过多元线性回归分析或二次方程(多元线性回归方程拟合度不佳时)拟合分别获得回归模型。模型显示处理温度和处理时间对三者均具有显著影响。分析敏感性显示处理温度对三种因变量的影响均大于处理时间。经210℃,20 min处理后,纤维素酶解率最高为76.2%,继续提高处理温度和延长处理时间半纤维素移除率提高,但纤维素酶解率下降。     

木质纤维素预处理技术研究进展

木质纤维素转化燃料乙醇一般需要经过原料预处理、酶水解和发酵过程。由于木质纤维原料化学结构复杂、直接酶解效率非常低,一般在酶水解之前需要进行适当的预处理以打破其致密结构,增加纤维表面积,提高后续纤维素酶的可及性。预处理程度直接影响纤维底物后续酶水解的效果。本文在木质纤维素常用预处理技术分析的基础上,重点讨论了3种相对高效的预处理技术：微波辅助离子液体预处理、两阶段深度共熔溶剂（DES）预处理和氯化铁预处理技术,分析了它们的优势、不足及发展现状。文中指出微波辅助离子液体预处理可有效解构木质素和半纤维素,破坏纤维素结晶区域,利于后续酶解,但微波加热过程会使离子液体分解和部分底物碳化。两阶段DES预处理可有效提高酶水解效率,但是预处理后原料中残留的DES可能会对后续反应中纤维素酶和微生物产生抑制作用。氯化铁预处理可有效破坏木质素与碳水化合物间的结合键,脱除底物中的半纤维素,而对木质素和纤维素降解较少,具有很好的发展前景。由于单一预处理技术的局限性,寻求低成本高效的联合预处理技术将是未来重点发展的方向。     

碳酸钠预处理对麦草酶水解糖化的影响

麦草是一种具有很大潜力的制取生物乙醇的可再生木质纤维素原料。文章探讨了碳酸钠预处理预浸时间、保温时间、碳酸钠用量对麦草化学成分及酶水解效率的影响。结果表明,延长碳酸钠预处理保温时间对木质素脱除无明显影响,但浆料得率和酶水解总糖转化率有所下降;合理的预浸时间为30 min,继续延长预浸时间对预处理浆料酶水解总糖转化率无促进作用;增加预处理Na2CO3用量有助于促进木质素的脱除,大部分碳水化合物保留在浆料中。在8% Na2CO3(Na2O计)用量下,麦草于80℃预浸30 min后升温至130℃,不保温所得到的浆料在纤维素酶用量为20 FPU/g(对纤维素)时,其总糖转化率为60%。     

Peracetic acid pretreatment of sugarcane bagasse for enzymatic hydrolysis: a continued work

Previous work has shown that the enzymatic hydrolysis of sugarcane bagasse could be greatly enhanced by peracetic acid (PAA) pretreatment. There are several factors affecting the enzymatic digestibility of the biomass, including lignin and hemicelluloses content, cellulose crystallinity, acetyl group content, accessible surface area and so on. The objective of this work is to analyze the mechanism of the enhancement of enzymatic digestibility caused by PAA pretreatment. Delignification resulted in an increase of the surface area and reduction of the irreversible absorption of cellulase, which helped to increase the enzymatic digestibility. The Fourier transform infrared (FTIR) spectrum showed that the absorption peaks of aromatic skeletal vibrations were weakened or disappeared after PAA pretreatment. However, the infrared crystallization index (N.O'KI) was increased. X‐ray diffraction (XRD) analysis indicated that the crystallinity of PAA‐treated samples was increased owing to the partial removal of amorphous lignin and hemicelluloses and probable physical change of cellulose. The effect of acetyl group content on enzymatic digestibility is negligible compared with the degree of delignification and crystallinity. The results indicate that enhancement of enzymatic digestibility of sugarcane bagasse by PAA pretreatment is achieved mainly by delignification and an increase in the surface area and exposure of cellulose fibers. Copyright © 2008 Society of Chemical Industry     

亚硫酸氢钠预处理对杨木浆料化学成分及酶解糖化的影响

研究了亚硫酸氢钠预处理对杨木浆料化学成分及酶水解效率的影响。增加预处理试剂亚硫酸氢钠用量可以脱除更多的木质素和半纤维素,随着试剂用量的增加葡聚糖、木聚糖和总糖的酶水解得率呈现先升高后降低,然后又升高的规律。当预处理试剂用量为4％时,木质素脱除率为28．7％,酶水解总糖转化率为55．2％;继续增加试剂用量至16％时,对酶水解糖的得率无明显促进作用,反而由于高聚糖降解较多导致得率下降;当试剂用量超过20％时,酶水解糖的得率又有所上升。亚硫酸氢钠用量为24％时,木质素脱除率为61．6％,总糖的转化率达到最大,在纤维素酶用量40FPU／g时,葡聚糖、木聚糖和总糖的转化率分别为59．7％、64．6％和66．2％。     

氨预处理对大豆秸秆纤维素酶解产糖影响的研究

为了提高大豆秸秆酶解产糖能力, 以利于从大豆秸秆中提取生物降解性塑料的原料 ?? 乳酸, 对大豆秸秆纤维素预处理过程的影响因素进行了探索,对预处理前后大豆秸秆的物理结构变化、化学成分变化及预处理条件对大豆秸秆酶水解产糖的影响进行了研究。研究结果表明,粉碎结合氨处理对大豆秸秆酶水解影响较大,较适宜的预处理条件为大豆秸秆粉碎至 140 目,10%氨水处理 24h。经过预处理后大豆秸秆纤维素含量提高 70.27%, 半纤维素含量下降 41.45%, 木质素含量下降 30.16%, 有利于大豆秸秆酶解产糖。     

Ethanosolv pretreatment of barley straw with iron(III) chloride for enzymatic saccharification

BACKGROUND: Barley straw is a potential lignocellulosic biomass for the production of bioethanol because of its high cellulose and hemicelluloses content. Ethanosolv pretreatment catalyzed with inorganic acids has some undesirable effects, and thus, inorganic salts, such as FeCl₃, were studied as the catalyst in order to enhance enzymatic digestibility. RESULTS: The addition of 0.1 mol L^?1 FeCl₃ (Iron(III) chloride) had a particularly strong effect on the enzymatic digestibility, reaching a value as high as 89%, with cellulose recovery as high as 90% after the ethanosolv pretreatment. The enzymatic digestibility was 89% and 55% after the addition of 0.1 mol L^?1 FeCl₃ and H₂SO₄ (adjusted to the same pH), respectively. The enzymatic hydrolysis rate was significantly accelerated as the ethanosolv temperature increased, reaching the highest enzymatic digestibility of 89% after 72 h at 170 °C. The concentrations of HMF(5‐hydroxy‐2‐ methyl furfural) and furfural were 0.011 and 0.148 g L^?1 in the hydrolysate during FeCl₃‐ethanosolv treatment, which were lower than the concentrations quantified during H₂SO₄‐ethanosolv treatment. After the pretreatment, 88.5% of FeCl₃ was removed through the filtration process. CONCLUSION: The addition of several inorganic salts significantly accelerated enzymatic digestibility in the ethanosolv. FeCl₃ had a particularly strong effect on enzymatic digestibility and cellulose recovery. The formation of HMF and furfural and the remaining amount of FeCl₃ were investigated, and FeCl₃ had no effect on the subsequent processes after pretreatment. Copyright © 2010 Society of Chemical Industry