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%。     

NaOH/H2O2预处理促进玉米秸秆酶解产糖工艺条件的研究

采用正交实验初步探讨了NaOH/HO2O2对经白腐菌Hyrophous sp.254处理15 d的玉米秸秆进行预处理的最佳条件.在NaOH/H2O2预处理过程中,NaOH浓度、H2O2体积分数、底物浓度及预处理时间均对秸秆的纤维素酶酶解效率存在一定影响.试验表明,NaOH/H2O2的最佳预处理条件:NaOH浓度为7g/L,H2O2体积分数为0.7%,底物浓度为50g/L,处理时间为24h.在优化的工艺条件下,玉米秸秆的还原糖产量达到了0.417 g/g,H2O2用量减少了30%,废水排放量减少了60%.     

酶酸联合水解玉米秸秆的实验研究

开发了一种通过酸酶联合水解处理玉米秸秆以得到可发酵单糖的工艺方法,进行了稀硫酸预处理玉米秸秆的研究。得到最佳的工艺条件,木糖收率达到84.90%。用纤维素酶水解酸处理过的玉米秸秆,考察了pH值、温度、时间对酶水解率的影响,结果表明:酶解温度为50℃,pH值为4.8,水解时间为60h时,酶水解率达到91.71%。该工艺达到了节能高效地转化玉米秸秆为可发酵单糖的目的。     

玉米秸秆的单独、混合糖化工艺试验研究

以玉米秸秆为原料,经稀酸预处理后对其进行糖化。经正交试验分析,纤维素、半纤维素混合糖化在酶浓度为50 U/g,纤维素酶与半纤维素酶比例为4∶3,温度为50℃的条件下,还原糖浓度最大,为7.235 mg/ml。由纤维素、半纤维素单独糖化和混合糖化对比试验可知,温度对还原糖浓度影响最大。     

超声波预处理对秸秆发酵的影响

以秸秆为研究对象,在37℃条件下对不同的超声波强度和工作时间预处理的秸秆进行为期50 d的厌氧发酵试验,分析发酵过程中产气效率、累计产气量、pH值、CH4浓度等参数变化,并对秸秆微观结构进行电镜扫描,研究超声波预处理对秸秆微观结构的破坏以及厌氧发酵产气特性影响。试验结果表明:超声波预处理能提高秸秆发酵累计产气量和产气效率,平均单位日产气量由未经预处理的4.54 ml/(g.d)提高到经超声波处理后的6.86 ml/(g.d),提高了51.10%;超声波预处理对秸秆发酵pH无显著影响;沼气中平均甲烷浓度由未经预处理的43.83%提高到处理后的47.86%;最佳超声波预处理功率为225 W,处理时间为30 min。     

预处理对秸秆废弃物沼气发酵的影响研究

研究了预处理对典型秸秆废弃物沼气发酵的影响。与豆秆和棉秆相比,木质素含量相对较低的玉米秆产气速率和沼气产率更高。碱处理缩短了产气高峰出现的时间,峰值也得到提高,这可能与预处理增加的可溶性组分的快速降解有关。经过几天的低产气期,又出现第二个小产气高峰。组分分析表明,碱处理去除大量木质素,纤维可及度得到提高,这是第二阶段产气得到加强的原因。最终,玉米秆、豆秆和棉秆的最高沼气产率分别达415,343 ml/g TS和298 ml/g TS,比未处理秸秆提高34%,54%和86%。结果表明,预处理豆秆和棉秆产气性能较好,可与玉米秆一样,作为沼气发酵的优良原料。     

稻草秸秆多酶水解条件研究

研究了稻草秸秆经过稀酸预处理后的酶水解条件,得到用于生产燃料乙醇的还原糖。试验结果表明:稻草秸秆经1%(w/w)的稀硫酸浸润,液固比(v/w)为5∶1,在121℃条件下处理60min后,每克稻草秸秆的初始水解还原糖得率达到0.187g。预处理后,在45℃,pH4.8,120r/min,48h条件下,采用酶的添加量最优配比(每克秸秆添加木聚糖酶217IU,纤维素酶5.13FPU,果胶酶25μ,β-葡聚糖酶500μ,淀粉酶150μ)时,水解产生的还原糖浓度达到最大值84.22g/L,原料水解率为41.19%。在酶水解糖化过程中,当MgSO4,Tween80的添加量分别为0.0001,0.005g时对纤维素酶有激活作用。     

碱性胍预处理水稻秸秆研究

以水稻秸秆为研究对象,采用有机强碱——胍进行预处理,考察了催化剂用量、预处理时间和温度对预处理效果的影响。以扫描电镜(SEM)、X-射线衍射仪(XRD)、红外光谱仪(FTIR)、热重分析仪(TG)对预处理前后样品进行了表征。结果表明:胍用量为3%、温度为60℃、时间为6 h是较适宜的预处理条件,催化剂用量是预处理水稻秸秆最关键的因素。SEM照片显示,预处理后秸秆表面呈现不规则的层片状皱褶、裂缝和孔洞;XRD表征显示,预处理后纤维素结晶度均提高;FTIR表征显示,胍对去除木质素和降解氢键作用明显;TG表征表明预处理前后水稻秸秆具有不同的热稳定特性。     

废纸亚临界水解制备还原糖的动力学研究

还原糖是生物质资源制备乙醇的中间体。为了证实亚临界水解废纸制备还原糖工艺的可行性,研究了在280～320℃,0.25～10 min内废纸亚临界水解为还原糖的水解动力学,构建了一级反应动力学模型,对废纸水解为还原糖的数据进行了动力学拟合。研究结果表明,废纸水解为还原糖的活化能为90.45 kJ/mol,而还原糖水解为其他物质的活化能为106.53 kJ/mol,前者的活化能低于后者,且前者的水解速率常数高于后者,有利于还原糖的积累,故此工艺可行;在310℃,2 min时,废纸水解为还原糖的得率高达46.32%。     

碱性双氧水预处理玉米秸秆性质研究

使用碱性双氧水对玉米秸秆进行预处理,可以有效提高秸秆的酶解效果。实验表明,最优预处理参数为使用分别占秸秆质量16%的 H₂O₂和25.6% 的NaOH,于40℃下预处理秸秆24 h。对经不同预处理剂处理后的秸秆进行酶解,发现NaOH及碱性双氧水预处理秸秆的酶解还原糖产量为7.48 g/L和8.26 g/L,而经H₂O及H₂O₂预处理秸秆的还原糖产量仅为1.35 g/L和1.59 g/L。通过木质纤维素含量及SEM分析发现,氢氧化钠主要作用为溶解秸秆中的木质素及半纤维素,而双氧水的存在则会破坏秸秆表面结构。计算秸秆预处理前后质量损失发现,双氧水的存在不能显著提高秸秆预处理后的质量损失,但会氧化分解被氢氧化钠溶解的大分子物质,对此过程机理及产物还需进行深入的研究。     

麦草碱性沸石催化制浆及其酶水解

采用过氧化氢进行预浸渍,以固体沸石A和B为催化剂,研究麦草氧碱法制浆对其酶水解的影响。结果表明,当制浆黑液中乙酰丙酸和甲酸的浓度分别达5.1442,6.7096mg/ml时,采用固体沸石A和B蒸煮成浆的水解得率分别为18.38%和23.16%。AMF分析表明,与表面物理结构相比,成浆纤维化学结构的改变对酶水解的影响更大。     

稻草“两步法”酸水解制备乙酰丙酸的研究

以稻草为原料,采用"两步法"稀酸水解制备乙酰丙酸,考察了反应时间、反应温度、固液比(质量比,下同)、酸的质量分数对还原糖转化率和乙酰丙酸收率的影响。研究结果表明,酸水解制糖的较佳反应条件:反应时间为35 min,反应温度为220℃,固液比为1∶15,酸质量分数为6%时,还原糖转化率为28.45%。生成乙酰丙酸的较佳反应条件:反应时间为40 min,反应温度为250℃时,乙酰丙酸的收率为34.14%。用IR对产品进行结构表征,证明其结构正确。     

Optimization of acidic hydrolysis conditions of rice husk for fermentable sugar production

Lignocellulosic biomass (LSB) is the most abundantly available renewable source in the world. Rice husk (RH) is also one of the LSB. In this study, the optimization of dilute acid hydrolysis conditions of RH by using one-factor-at-a-time method was performed. The optimum hydrolysis conditions of RH were determined as 131.04°C, 1:10.28 (w/v) of solid:liquid ratio, 1.47% (w/v) of acid ratio and 24.05 min, which yielded as 25.52 g/L of fermentable sugar concentration. Furthermore, the chemical composition of hydrolysate was also examined and the levels of phenolics, 5-hydroxymethylfurfural (HMF), acetate, glucose, and fructose+xylose were found as 0.89, 0, 3.27, 2.10, and 13.80 g/L, respectively. Accordingly, RH can be utilized as a favorable feedstock for the production of value-added products.     

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。     

Pretreatment of rye straw with aqueous ammonia for conversion to fermentable sugars as a potential substrates in biotechnological processes

Alkaline pretreatment causes the disruptions in the lignin structure and breaks the linkage between lignin and the other carbohydrate fractions in lignocellulosic biomass. The aim of the current study was to investigate the possibility of rye straw hydrolysis with 2% aqueous ammonia for 0–8 h, at 60 °C and 90 °C, under atmospheric pressure. The study investigated how rye straw hydrolysis with aqueous ammonia at low concentration and relatively low temperatures affect such parameters as total and volatile solids (TS & VS), chemical oxygen demand (COD) and pH at low concentration. The experimental results indicated that the concentration of reducing sugars and volatile fatty acids (VFA) in rye straw after 8 h hydrolysis with ammonia were about 1.3 and 5.2 times higher at 60 °C, respectively and 1.8 and 5.2 times higher at 90 °C, respectively compared to samples in which water hydrolysis of rye straw. The percentage content of glucose in the hydrolysates ranged between 17.98% and 50.98% in water and 21.62%–41.75% in 2% aqueous ammonia. SEM and FTIR analysis of rye straw after 8 h hydrolysis confirmed the positive effect of 2% aqueous ammonia on changes in the material structure.     

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.     

Effect of sodium sulfite on acid pretreatment of wheat straw with respect to its final conversion to ethanol

A pretreatment process that combines dilute acid and sodium sulfite has been applied to wheat straw to study the effect of temperature (120–180 °C) and sodium sulfite concentration (0–3%) on the yield of glucose in subsequent enzymatic hydrolysis and ethanol production by fermentation. The results were compared with both dilute acid pretreatment (without Na₂SO₃ addition) and hot water pretreatment. Formation of furfural and hydroxymethylfurural, which can inhibit ethanol-producing microorganisms, were measured and the ethanol yield in a subsequent fermentation was evaluated. The results indicate that a combination of 180 °C, 30 min, 1% H₂SO₄ and 2.4% Na₂SO₃ during pretreatment produced the highest ethanol yield; 17.3 g/100 g dry weight of initial biomass, which corresponds to 75% of the theoretical yield from glucose. 28 mg of furan inhibitors (sum of furfural and hydroxymethylfurfural) per gram dry weight of initial wheat straw were generated under this condition. Increasing sulfite loading up to 2.4% decreased inhibitor formation, leading to increased delignification and preservation of cellulose from dissolution. On the other hand, an elevated temperature in combination with low pH reduced the amount of solid phase after pretreatment, increased the level of inhibitors and reduced the concentration of ethanol produced by fermentation.     

Enzymatic saccharification of dilute acid pretreated saline crops for fermentable sugar production

Four saline crops [athel (Tamarix aphylla L), eucalyptus (Eucalyptus camaldulensis), Jose Tall Wheatgrass (Agropyron elongatum), and Creeping Wild Ryegrass (Leymus triticoides)] that are used in farms for salt uptake from soil and drainage irrigation water have the potential for fuel ethanol production because they don’t take a large number of arable lands. Dilute sulfuric acid pretreatment and enzymatic hydrolysis were conducted to select the optimum pretreatment conditions and the best saline crop for further enzymatic hydrolysis research. The optimum dilute acid pretreatment conditions included T = 165 °C, t = 8 min, and sulfuric acid concentration = 1.4% (w/w). Creeping Wild Ryegrass was decided to be the best saline crop. Solid loading, cellulase and β-glucosidase concentrations had significant effects on the enzymatic hydrolysis of dilute acid pretreated Creeping Wild Ryegrass. Glucose concentration increased by 36 mg/mL and enzymatic digestibility decreased by 20% when the solid loading increased from 4 to 12%. With 8% solid loading, enzymatic digestibility increased by over 30% with the increase of cellulase concentration from 5 to 15 FPU/g-cellulose. Under given cellulase concentration of 15 FPU/g-cellulose, 60% increase of enzymatic digestibility of pretreated Creeping Wild Ryegrass was obtained with the increase of β-glucosidase concentration up to 15 CBU/g-cellulose. With a high solid loading of 10%, fed-batch operation generated 12% and 18% higher enzymatic digestibility and glucose concentration, respectively, than batch process.     

Optimizing peracetic acid pretreatment conditions for improved simultaneous saccharification and co-fermentation (SSCF) of sugar cane bagasse to ethanol fuel

The use of several lignocellulosic materials for ethanol fuel production has been studied exhaustively in the U.S.A.. Strong environmental legislation has been driving efforts by enterprises, state agencies, and universities to make ethanol from biomass economically viable. Production costs for ethanol from biomass have been decreasing year by year as a consequence of this massive effort. Pretreatment, enzyme recovery, and development of efficient microorganisms are some promising areas of study for reducing process costs.Sugar cane bagasse constitutes the most important lignocellulosic material to be considered in Brazil as new technology such as the production of ethanol fuel. At present, most bagasse is burned, and because of its moisture content, has a low value fuel. Ethanol production would result in a value-added product. The bagasse is available at the sugar mill site at no additional cost because harvesting, transportation and storage costs are borne by the sugar production.The present paper presents an alternative pretreatment with low energy input where biomass is treated in a silo type system without need for expensive capitalization. Experimentally, ground sugar cane bagasse is placed in plastic bags and a peracetic acid solution is added to the biomass at concentrations of 0, 6, 9, 15, 21, 30, and 60% w/w of peracetic acid based on oven dried biomass. The ratio of solution to wood is 6:1; a seven day storage period had been used. Tests using hydrolyzing enzymes as an indicator for SSCF have been performed to evaluate the pretreatment efficiency.As an auxiliary method, a series of pre-pretreatments using stoichiometric amounts of sodium hydroxide and ammonium hydroxide based on 4-methyl-glucuronic acid and acetate content in the sugar cane bagasse have been performed before addition of peracetic acid. The alkaline solutions are added to the raw bagasse in a ratio of 17:1 solution to biomass and mixed for 24 hours at room temperature. Biomass is filtered and washed to a neutral pH before the peracetic acid addition.According to enzymatic hydrolysis results, peracetic acid is a powerful chemical for improving enzymatic digestibility in sugar cane bagasse with no need for using high temperatures. Basic pre-pretreatments are helpful in reducing peracetic acid requirements in the pretreatment.