稀酸预处理玉米秸秆条件优化的试验研究

采用稀硫酸对玉米秸秆进行预处理,采用DNS法测定玉米秸秆水解液中还原糖的含量,对水解温度、水解时间、稀硫酸质量分数、固液质量比4个因素进行单因素试验分析,再通过正交试验对预处理条件进行优化.试验结果表明,最佳预处理条件:水解温度为121℃,水解时间为1 h,稀硫酸质量分数为0.6%,固液质量比为10%.     

响应面法优化沼液预处理玉米秸秆条件的研究

为了确定沼液预处理玉米秸秆最优反应条件,选取沼液处理前后纤维素相对结晶度为评价指标,根据Box-Behnken试验设计原理,建立了纤维素相对结晶度与沼液用量、温度和时间之间的数学模型,并采用扫描电镜、X射线衍射法对处理前后玉米秸秆的结构特性进行分析。试验结果表明:回归方程决定系数R2为0.989 5;3个因素影响主次顺序为时间沼液用量温度,三者存在显著的交互作用;最佳处理条件为沼液用量48 m L,温度27℃,时间13 d,该条件下纤维素相对结晶度预测值为22.50%,实测值为21.88%,即沼液处理后玉米秸秆纤维素结晶度由60.82%降至47.51%,预测值与实测值相对误差为3%。沼液预处理后玉米秸秆表层被破坏,孔洞增加,有利于纤维素酶水解作用的进行。     

碱和双氧水预处理玉米秸秆的试验研究

研究了在5%NaOH中加入不同质量分数的双氧水时,对玉米秸秆的预处理效果;在预处理后的玉米秸秆中加入纤维素酶,考察此时酶解还原糖得率随预处理程度的变化;对浸泡时间、双氧水浓度、固液比3个因素进行单因素试验。试验结果表明,质量分数为2.5%的浓度下,糖得率最大;在2.5%H2O2浸泡24 h,固液比对酶解糖化几乎没有影响;当浸泡时间为24,72,96 h时,糖得率相差甚微。设计正交试验对预处理的条件进行优化,分析预处理玉米秸秆的各因素,以木质素去除率为基准参数,得到水解木质纤维素的适宜预处理条件:5%NaOH下加入质量分数为2.5%的双氧水,浸泡时间为72 h,固液比为1∶20。预处理后木质素的去除率为61.52%;加入纤维素酶酶解,还原糖得率为39.30%。     

榨糖收贮模式玉米秸秆蒸汽爆破预处理条件优化

使用蒸汽爆破法处理榨糖收贮玉米秸秆榨渣,观察不同蒸汽爆破压力和维压时间下纤维素、半纤维素、木质素（三大素）及纤维素酶水解得率的变化。榨渣三大素含量不同程度下降,半纤维素下降最多,其次是木质素,而纤维素下降最少。处理后进行的水解实验显示压力与维压时间的增加会导致纤维素水解酶得率有所提高,但压力增加对纤维素水解酶影响较小,维压时间对纤维素水解酶的影响较为突出。考虑经济成本的前提下选择1.2 MPa,10 min维压时间为最佳条件,其中纤维素含量为34.42%、半纤维素4.01%、木质素17.09%及纤维素酶水解得率为68.3%。     

玉米秸秆同步糖化共发酵工艺条件优化

以经过生物预处理后的玉米秸秆为原料,采用混合菌进行同步糖化发酵。以分光光度法测定发酵液中的乙醇含量,对发酵时间、发酵温度、接种比例、纤维素酶用量4个条件进行单因素试验分析,再通过正交试验对发酵条件进行优化。试验结果表明,最适发酵条件:发酵温度为36℃,发酵时间为96 h,接种比例为1∶1,纤维素酶用量为40 IU/g,乙醇产率为12.03%。     

玉米秸秆预处理对厌氧发酵制氢影响的研究

为提高玉米秸秆的产氢能力,实验研究了蒸汽爆破预处理、硫酸预处理、氢氧化钠预处理、盐酸预处理和酸化(碱化)气爆预处理5种预处理方法对玉米秸秆发酵产氢能力的影响。结果表明,预处理可以将秸秆中相当一部分纤维素和半纤维素水解生成还原糖,其中质量分数为0.8%的H2SO4酸化汽爆预处理对秸秆的水解效果最好。在固-液比1∶10、H2SO4质量分数0.8%、保持微沸状态30min的处理条件下,秸秆的糖含量达到最大值24.57%,最大氢气产量为141mL/g。     

玉米秸秆的渗滤式稀酸预处理

对玉米秸秆的渗滤式稀酸预处理进行了考察,通过对温度、酸浓度、渗滤速度、液固比等影响因素的实验分析,得到了优化的工艺条件:反应温度170℃,硫酸浓度0.25%,液固比为10:1,渗滤速度150mL/min,70%水解液排出后,渗滤速度降为100mL/min。水解液中木糖浓度达到22g/L,糖得率达到约80%。经过稀酸预处理后的玉米秸秆进行酶水解,纤维素转化率达到80%。     

黑曲霉AS0006预处理玉米秸秆产沼气研究

为了提高玉米秸秆与牛粪混合发酵的产气效率,文章对黑曲霉AS0006预处理后的玉米秸秆进行了研究,考察了不同预处理时间的玉米秸秆在混合厌氧发酵过程中的日产气量、累积产气量、TS和VS去除率以及木质纤维素去除率等发酵特性的变化情况。研究结果表明:黑曲霉AS0006对木质纤维素有较强的降解能力,玉米秸秆经黑曲霉AS0006预处理28 d后,纤维素、半纤维素和木质素的降解率分别为26.86%,11.93%和25.09%;经过黑曲霉AS0006预处理的玉米秸秆与牛粪混合发酵可以提高日产气量并缩短厌氧发酵周期,其中,预处理21 d后的玉米秸秆的产气高峰最大,为523.4 mL/d;经过黑曲霉AS0006预处理的玉米秸秆与牛粪混合发酵后, TS和VS去除率以及木质纤维素去除率均比未经预处理的玉米秸秆高。     

玉米秸秆热解反应动力学的研究

利用热重分析法(TG)对粒径为0.28~0.60mm的玉米秸秆在5、10、20、30℃/min 4种不同升温速率下的热解反应动力学进行了研究。结果表明,秸秆的热解过程分为4个阶段,主要反应阶段在287~400℃之间,随着升温速率的增加,主要反应区间略有增加。Ozawa法计算出的玉米秸秆活化能(E)值在153~160 kJ/mol范围内,KAS法得出的玉米秸秆活化能集中在147~157 kJ/mol之间。用微分法Achar方程、积分法Coats-Redfern方程,将41种常用的固体反应动力学机理函数一一代入,再根据热分析动力学三因子求算的比较法得出玉米秸秆热解过程符合Mampel Power法则,并给出机理函数的微分形式和积分形式,反应级数为2,本研究为生物质热解装置的设计及参数优化提供了科学依据。     

变温调控对玉米秸秆同步糖化条件的影响

文章采用树干毕赤酵母和酿酒酵母的混合菌种对玉米秸秆进行变温发酵。首先对温度、接种量、纤维素酶用量、摇床转速、混合比例、发酵时间6个条件进行单因素试验分析,然后通过正交试验对发酵条件进行优化。结果表明,变温发酵的最优条件为41℃先发酵24h后,35℃再发酵48h,接种量为10%,树干毕赤酵母∶酿酒酵母为2:1,发酵时间为72h,纤维素酶用量为30IU/g,摇床转速为120r/min,在此条件下,乙醇产率为0.1252g/g。     

CaO催化热解玉米秸秆实验研究

在管式加热炉中对玉米秸秆进行了热解实验研究,实验结果表明添加CaO后,气体中CO、H2、CH4含量均有增加,尤其是H含量增加最为明显,产气热值相对于纯玉米秸秆热解提高了17·9%。     

Impact of dilute acid pretreatment on the structure of bagasse for bioethanol production

Dilute acid pretreatment is a commonly used pretreatment method in the course of producing bioethanol from lignocellulosics and the structure variation of the lignocellulosics is highly related to the pretreatment process. To understand the impact of dilute acid pretreatment on the structure of bagasse, four different pretreatment conditions by varying heating time are considered where the bagasse and the pretreated materials are examined using a variety of analysis methods. The obtained results indicate that the thermogravimetric analysis (TGA) is able to provide a useful insight into the recognition of lignocellulosic structure. Specifically, the peak of the TGA of the pretreated materials moves toward the low temperature region, revealing that the lignocellulosic structure is loosened. However, the characteristic of crystal structure of cellulose remains in the pretreated materials. Increasing heating time enhances the pretreatment procedure; as a result, the average particle size of the investigated materials increases with heating time. This swelling behavior may be attributed to the enlarged holes inside the particles in that the surface area decreases with increasing heating time. In addition, when the heating time is increased to a certain extent (e.g. 15 min), some fragments are found at the surface and they tend to peel off from the surface. It follows that the dilute acid pretreatments have a significant effect on the bagasse structure. Copyright © 2009 John Wiley & Sons, Ltd.     

Optimizing thermomechanical pretreatment conditions to enhance enzymatic hydrolysis of wheat straw by response surface methodology

Wheat straw was pretreated with a thermomechanical process developed in our laboratory to improve the enzymatic hydrolysis extent of potentially fermentable sugars. This process involves subjecting the lignocellulosic biomass for a short time to saturated steam pressure, followed by an instantaneous decompression to vacuum at 5 kPa. Increasing of the heat induced by saturated steam result in intensive vapour formation in the capillary porous structure of the plant material and the subsequent release of the pressure to vacuum allows fixing the expanded structure. Response surface methodology (RSM) based on central composite design was used to optimize three independent variables of the pretreatment process: processing pressure (300-700 kPa), initial moisture contents of wheat straw (10-40%) and processing time (3-62 min). The process was optimised for hydrolysis yield and initial hydrolysis rate obtained by enzymatic hydrolysis on the pretreated solids by Celluclast (1.5 L). The analysis of variance (ANOVA) revealed that, among the process variables, processing pressure and processing time have the most significant effect on the hydrolysis yield and on initial rate of hydrolysis whereas initial moisture content observed significantly lower effect on the two responses. The predicted hydrolysis yield and in a lesser extent the predicted initial rate of hydrolysis agreed satisfactorily with the experimental values with R² of 96% and 86% respectively.     

稀酸处理对秸秆厌氧发酵产氢的影响

以稻草秸秆为纤维素原料,先利用稀硫酸对其进行预处理,再利用活性污泥进行厌氧发酵产氢。试验研究了压力、温度、硫酸浓度、加压时间、固液比以及原料粒度对预处理结果的影响,并根据产氢量优化了预处理条件。试验结果表明:在硫酸浓度为0.7%、处理压力为0.1MPa、加压时间为60min、固液比为1∶12,秸秆原料过60目筛的情况下预处理效果最好,此时每克秸秆产氢量为113ml,秸秆中半纤维素、纤维素的利用率为87.47%,秸秆的有效利用率为52.38%。     

微波辅助NaOH预处理提高油菜秸秆酶解效率的研究

为提高油菜秸秆的酶解效率,试验借助于常压微波加热技术辅助NaOH预处理,并对处理条件进行了优化。结果表明,与未处理比较,经微波预处理的油菜秸秆致密结构明显破坏,利于被纤维素酶水解。微波辅助预处理的最优化条件:微波功率600 W,时间5 min,NaOH 0.1 mol/L,温度80℃,经预处理后的油菜秸秆酶解率可达28.09%,较未处理前增加2.75倍,显著提高了酶解效果。     

Optimisation of dilute alkaline pretreatment for enzymatic saccharification of wheat straw

Physico-chemical pretreatment of lignocellulosic biomass is critical in removing substrate-specific barriers to cellulolytic enzyme attack. Alkaline pretreatment successfully delignifies biomass by disrupting the ester bonds cross-linking lignin and xylan, resulting in cellulose and hemicellulose enriched fractions. Here we report the use of dilute alkaline (NaOH) pretreatment followed by enzyme saccharifications of wheat straw to produce fermentable sugars. Specifically, we have assessed the impacts of varying pretreatment parameters (temperature, time and alkalinity) on enzymatic digestion of residual solid materials. Following pretreatment, recoverable solids and lignin contents were found to be inversely proportional to the severity of the pretreatment process. Elevating temperature and alkaline strengths maximised hemicellulose and lignin solubilisation and enhanced enzymatic saccharifications. Pretreating wheat straw with 2% NaOH for 30 min at 121 °C improved enzyme saccharification 6.3-fold when compared to control samples. Similarly, a 4.9-fold increase in total sugar yields from samples treated with 2% NaOH at 60 °C for 90min, confirmed the importance of alkali inclusion. A combination of three commercial enzyme preparations (cellulase, ??-glucosidase and xylanase) was found to maximise monomeric sugar release, particularly for substrates with higher xylan contents. In essence, the combined enzyme activities increased total sugar release 1.65-fold and effectively reduced cellulase enzyme loadings 3-fold. Prehydrolysate liquors contained 4-fold more total phenolics compared to enzyme saccharification mixtures. Harsher pretreatment conditions provide saccharified hydrolysates with reduced phenolic content and greater fermentation potential.     

Insights into biological delignification of rice straw by Trametes hirsuta and Myrothecium roridum and comparison of saccharification yields with dilute acid pretreatment

Rice straw is the most abundant agricultural residue on a global scale and is widely available as feedstock for cellulosic fuel production. However, it is highly recalcitrant to biochemical deconstruction and also generates inhibitors that affect enzymatic saccharification. Rice straw from eastern Arkansas was subjected to dilute acid pretreatment (160 °C, 48 min and 1.0% sulfuric acid) and solid-state fermentation with two lignocellulolytic fungi, Trametes hirsuta and Myrothecium roridum, and their saccharification efficacies were compared. T. hirsuta and M. roridum were tested separately; pretreatment of rice straw with either strain for seven days resulted in 19 and 70% enrichment of its holocellulose content, respectively. However, liquid chromatography analysis of the alkali extracts showed significant differences in cell wall degradation by T. hirsuta and M. roridum. T. hirsuta removed 15% more phenolic compounds and 38% more glucan than M. roridum, while M. roridum removed 77% more xylan than T. hirsuta. Fungal and dilute acid pretreated biomass was then hydrolyzed using Accellerase^® 1500, a saccharification cocktail. Saccharification efficiency of M. roridum was 37% higher than that of dilute acid pretreatment of rice straw, requiring 8% lower enzyme loading and 50% shorter enzymatic hydrolysis duration. Alkali extraction of fungal pretreated biomass also yielded 10–15 g kg⁻¹ of acid precipitable polymeric lignin (APPL), which is a valuable co-product for biorefineries. In comparison to dilute acid pretreatment, fungal pretreatment could be a cost-effective alternative for the degradation of recalcitrant biomass, such as rice straw.     

Identification of new critical points for logistics model in cumulative methane yield curves after co-digestion of apple pulp and chicken manure with sulphuric acid pretreatment and a new modelling study

In this study, anaerobic co-digestion of apple pulp (AP) with high carbon content and chicken manure (CM) with high nitrogen content was evaluated with regard to sulphuric acid pretreatment conditions in the concentration range of 1%-6% v/v. The best mixing ratio of CM:AP was determined as 3:1 w/w under untreated conditions for which the methane yield was 255.88 ± 11.55 mL/g VS (volatile solid). Sulphuric acid pretreatments were applied to this mixture ratio. The highest methane yield after pretreatment was 466.01 ± 10.85 mL/g VS in the reactor, where the sulphuric acid pretreatment concentration was 3.0% v/v. Control of acid pretreatment results were achieved by analysis of lignocellulosic degradation and increase in soluble chemical oxygen demand. The highest cellulose, hemicellulose and lignin degradation after pretreatment were 27.5% ± 1.4%, 35.9% ± 2.9% and 14% ± 1.5% w/w, respectively. The cumulative methane yields (CMY) were analysed by the modified logistic model, modified Bertalanffy model (MBM), modified Gompertz model (MGM) and modified Holling model (MHM). The MBM and MGM were found to fit the experimental data better than other models. The MHM has not previously been applied to CMY. In addition to the kinetic studies, new critical points for CMYs were identified in the logistics model (lm). The importance and critical properties of these points with regard to CMY are introduced. The differences and superior properties of these critical points compared to other modelling methods are discussed.