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     

Enzymatic hydrolysis and fermentation of lime pretreated wheat straw to ethanol

BACKGROUND: The objective of this work is to develop an efficient pretreatment method that can help enzymes break down the complex carbohydrates present in wheat straw to sugars, and to then ferment of all these sugars to ethanol. RESULTS: The yield of sugars from wheat straw (8.6%, w/v) by lime pretreatment (100 mg g^?1 straw, 121 °C, 1 h) and enzymatic hydrolysis (45 °C, pH 5.0, 120 h) using a cocktail of three commercial enzyme preparations (cellulase, β‐glucosidase, and xylanase) at the dose level of 0.15 mL of each enzyme preparation g^?1 straw was 568 ± 13 mg g^?1 (82% yield). The concentration of ethanol from lime pretreated enzyme saccharified wheat straw (78 g) hydrolyzate by recombinant Escherichia coli strain FBR5 at pH 6.5 and 35 °C in 24 h was 22.5 ± 0.6 g L^?1 with a yield of 0.50 g g^?1 available sugars (0.29 g g^?1 straw). The ethanol concentration was 20.6 ± 0.4 g L^?1 with a yield of 0.26 g g^?1 straw in the case of simultaneous saccharification and fermentation by the E. coli strain at pH 6.0 and 35 °C in 72 h. CONCLUSION: The results are important in choosing a suitable pretreatment option for developing bioprocess technologies for conversion of wheat straw to fuel ethanol. Copyright © 2007 Society of Chemical Industry     

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     

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     

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     

A kinetic model for pretreated wheat straw saccharification by cellulase

A kinetic model for enzymatic hydrolysis of pretreated wheat straw able to describe the reaction process considering only macroscopic properties of enzyme and substrate would be useful in reactor design and scale-up. In this study Michaelis-Menten equations were used for different reaction schemes to fit experimental results obtained, working with enzyme loads between 5 and 44 i.u. g^?1 pretreated straw. Kinetic parameters were obtained by means of an optimization computer program.     

Kinetic studies of wheat straw hydrolysis using sulphuric acid

The kinetics of cellulose and hemicellulose hydrolysis of wheat straw was studied using both isothermal and non-isothermal techniques in a batch reactor. Reactions were carried out between 100 and 210°C and product sugars were analyzed using a Bio-Rad HPX-87P liquid chromatographic column. A simple first order series reaction model was used for both cellulose and hemicellulose hydrolysis reactions and kinetic parameters were obtained for the Arrhenius rate equations for three different sulphuric acid concentrations (0.5, 1.O and 1.5%). Activation energies remained constant with acid concentration but the pre-exponential factors showed an increase with acid concentration. To minimize the amount of experimental data required and to achieve a unique solution to the kinetic parameters, the technique of combining isothermal and non-isothermal reaction data was studied.     

Optimization of the enzymatic hydrolysis conditions of steam‐exploded wheat straw for maximum glucose and xylose recovery

BACKGROUND: The enzymatic hydrolysis of steam‐exploded wheat straw using commercial enzyme complexes has been studied. A cellulase enzyme complex (Accellerase 1500), along with specific xylanase complements (Accellerase‐XC and Accellerase‐XY) provided by Genencor, have been used to enhance glucose and xylose recovery. A systematic study with response surface methodology (RSM) was used to check the effect of the operating conditions: pH (4–5), temperature (50–60 °C) and enzyme/substrate ratio (0.1–0.5 mL g_cellulose^?1) on the enzymatic hydrolysis with Acellerase 1500 to maximize the sugar yield. Xylanases were used as complements to increase the release of xylose. RESULT: Statistical results from ANOVA analysis demonstrated that the enzymatic hydrolysis was clearly improved by temperature and enzyme/substrate ratio. The optimum conditions for higher glucose and xylose releases were obtained with the higher enzyme dosage ratio (0.5 mL g^?1_cellulose), 50 °C and pH 4. CONCLUSION: Model validation at optimum operating conditions showed good agreement between the experimental results and the predicted responses for a confidence level of 95%. The use of the xylanase complements, Accellerase‐XY (accessory xylanase enzyme complex) and Accellerase‐XC (accessory xylanase/cellulase enzyme complex), increases the conversion of hemicellulose. Accellerase‐XC supplementation was more effective, obtaining an increase in yields of glucose and xylose of 11.8% and 23.6%, respectively, using a dosage of 0.125 mL g^?1_cellulose. © 2012 Society of Chemical Industry     

Enzymatic hydrolysis from carbohydrates of barley straw pretreated by ionic liquids

BACKGROUND: Lignocellulosic biomass offers many potential advantages in comparison with the traditionally used sugars or starchy biomass since it is very widely available and does not compete with food and feed production. The abundance and high carbohydrates content of barley straw make it a good candidate for bioethanol production in Europe. Since biomass must be pretreated before enzymatic hydrolysis to improve the digestibility of both the cellulose and the hemicellulose biomass, the use of ionic liquids (IL) has been proposed as an environment‐friendly pretreatment of biomass. RESULTS: Different pretreatment conditions were investigated to determine the effects of the experimental conditions (temperature and time) on the enzymatic digestibility of pretreated material. The pretreatment of barley straw with 1‐ethyl‐3‐methyl imidazolium acetate treatment resulted in up to a 9‐fold increase in the cellulose conversion and a 13‐fold increase in the xylan conversion when compared with the untreated barley straw. CONCLUSION: Ionic liquid pretreatment of barley straw at 110°C for 30 min, followed by enzymatic hydrolysis, leads to a sugar yield of 53.5 g per 100 g raw material. It is then ready available for conversion into ethanol and is equivalent to more than 86% from potential sugars. The increase in saccharification was possible due to rupture of the lignin–hemicellulose linkages by treatment with 1‐ethyl‐3‐methyl imidazolium acetate. © 2012 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。     

Study on enzymatic hydrolysis of steam exploded straw by using shaking ball

A novel method of enzymatic hydrolysis was developed in this paper to produce a high conversion yield and hydrolysis rate. A comparison was described by using three methods of enzymatic hydrolysis and adsorption of steam exploded straw (SEWS): shaking ball in the regime, shaking with stirrer bed, and static state. The most adequate filter-paper activity, speed and reaction time were 3.6 × 10^-7 mol/(smL), 150 r/min and 24 h, respectively, with the reducing sugar yield of 0.43. The results showed that the method of shaking ball produced the highest adsorption, conversion yields and hydrolysis rate of the enzyme. This might be due to the continuous frequency increase of enzyme adsorption and desorption on the substrate surface as well as the relieved end-product inhibition. The morphological variation of SEWS was characterized by environmental scanning electron microscopy (ESEM).     

Study on enzymatic hydrolysis of steam exploded straw by using shaking ball

A novel method of enzymatic hydrolysis was developed in this paper to produce a high conversion yield and hydrolysis rate. A comparison was described by using three methods of enzymatic hydrolysis and adsorption of steam exploded straw (SEWS): shaking ball in the regime, shaking with stirrer bed, and static state. The most adequate filter-paper activity, speed and reaction time were 3.6 × 10⁻²⁷ mol/(s·mL), 150 r/min and 24 h, respectively, with the reducing sugar yield of 0.43. The results showed that the method of shaking ball produced the highest adsorption, conversion yields and hydrolysis rate of the enzyme. This might be due to the continuous frequency increase of enzyme adsorption and desorption on the substrate surface as well as the relieved end-product inhibition. The morphological variation of SEWS was characterized by environmental scanning electron microscopy (ESEM). __________ Translated from Journal of Beijing University of Chemical Technology, 2006, 33(6): 26-30 [译自: 北京化工大学学报]     

Production of fermentable sugars from enzymatic hydrolysis of pretreated municipal solid waste after autoclave process

A ligno-cellulosic concentrate from municipal solid waste (MSW) obtained after an autoclave separation process was investigated for its potential as a feedstock to produce fermentable sugars for ethanol production. A maximum enzymatic hydrolysis conversion of 53% of the cellulose and hemi-cellulose was found using a particle size range of 150–300 μm hydrolyzed in a 100 ml buffer solution containing 6 wt% lingo-cellulosic MSW concentrate with 90 mg cellulase at pH 4.8 held at 40 °C for 12 h. The hydrolysis rate leveled off at longer hydrolysis time and with increased substrate concentration and was related to enzymatic access to substrate. Lower hydrolysis rate at smaller particle size indicates that the grinding process may change the surface chemistry or morphology of the fibers making them less available for enzyme access. A drop in the hydrolysis rate was observed for the particles above 300 μm associate with the longer diffusion time for the enzyme into the fiber particles. The findings indicate that 152 L of ethanol could be obtained from a ton of lingo-cellulosic concentrate from MSW.     

核交换法对禾草类木质素结构的研究

本文采用核交换法对麦草粉、Nkny－HCHO－AQ（SFP－AQ）浆、NaOH—Na2SO3一AQ（ASP—AQ）浆和NaOH—AQ（AP—AQ）浆中残余木质素的化学结构特性进行了研究。通过核交换法结合硝基苯氧化反应，测定麦草原本木质素和浆中残余本质素的各类型酚核的数量。结果表明麦草原本木质素主要由25．35mol％非缩聚G单元，17．60mol％非缩聚S单元和57．05mol％缩聚G单元所组成。与AP—AQ浆相比，SFP浆含有较少的DPM结构单元，这可能是SFP浆漂白性能好的原因之一。     

酶解木质素在SBR胶料中的应用

试验研究酶解木质素在SBR胶料中的应用,并与防老剂RD和D进行对比。结果表明,在SBR胶料中加入木质素,胶料的MH增大,t90延长,硫化速率减小;木质素与防老剂D并用能够提高其抗氧化作用;硫化胶的物理性能、耐热氧老化性能和耐水抽出性均与防老剂RD硫化胶相近。     

亚硫酸氢镁预处理麦秆废液中同步分离木质素磺酸盐和低聚木糖的方法研究

分别采用有机溶剂萃取法、超滤法、大孔树脂吸附法、离子交换法分离提取亚硫酸氢镁预处理麦秆废液中的木质素磺酸盐和低聚木糖。研究结果表明超滤法不能达到分离目的,有机溶剂沉淀和大孔树脂吸附可实现木质素磺酸镁的纯化,采用D380离子交换树脂进行离子交换层析可将废液中低聚木糖和木质素磺酸镁完全分离,回收所得低聚木糖和木质素磺酸盐纯度分别可达63.95%和91.28%。因此,D380树脂固定床离子交换法是一种简单有效的提取废液中高附加值产品的方法,可实现亚硫酸氢镁预处理麦秆废液的高值化利用,具有强劲的市场应用潜力。     

Structural characterization of residual lignins isolated with cyanamide-activated hydrogen peroxide from various organosolvs pretreated wheat straw

The posttreatment of various organosolvs pretreated wheat straw with cyanamide-activated hydrogen peroxide was studied. About 44–80% of the total residual lignin and 38–85% of the total residual hemicelluloses were released or degraded during the posttreatment with 1.8% H₂O₂–0.18% cyanamide at 50°C under pH 10.0 for 4 h from different aqueous organic acids or alcohols pretreated straw. The seven degraded residual lignin preparations were subjected to a comprehensive physicochemical and structural characterization by UV, FTIR, and ¹H and ¹³NMR spectroscopy, and GPC. The nitrobenzene oxidation method was also applied to the in situ lignins. It was found that the seven residual lignin preparations contained large amounts of noncondensed syringyl and guaiacyl units, together with fewer noncondensed p-hydroxyphenyl units, esterified p-coumaric acid, and mainly etherified ferulic acid. All of the lignin fractions are free of associated polysaccharides and had molecular-average weights ranging between 2980 and 3820 g mol⁻¹. Analysis of these low molecular weight degradation products revealed an oxidation of residual lignin had occurred. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Optimization of selective acidolysis pretreatment for the valorization of wheat straw by a combined chemical and enzymatic process

The cover image is based on the Original Article Optimization of selective acidolysis pretreatment for the valorization of wheat straw by a combined chemical and enzymatic process by Yong Xu, Jianming Guo, Shizhong Zhang et al., https://doi.org/10.1002/jctb.6251 .

     

盐酸水解玉米秸秆木聚糖的动力学研究

对稀盐酸水解秸秆半纤维素生成木糖水解液过程进行动力学研究。分别测定了不同温度下,不同水解时间水解液中木糖质量浓度以及其降解产物糠醛的质量浓度。利用Saeman模型拟合木糖生成过程。实验表明,该模型能够较好地描述木糖生成过程以及其降解产物糠醛的产生过程。通过曲线拟和确定了不同水解温度下木糖的生成速率以及分解速率常数,同时利用Arrhenius方程确定木糖生成活化能Ea为116 kJ/mol。综合比较不同温度下水解液中的木糖以及糠醛质量浓度,确定使用质量分数为2%的稀盐酸于120℃下水解60 min为最佳水解条件。其水解液中木糖质量浓度可达20.99 g/L,糠醛质量浓度可维持在1.46 g/L以下。