木质纤维生产燃料乙醇工艺的研究进展

利用丰富而廉价的木质纤维原料代替粮食生产燃料乙醇,对经济和社会的可持续发展有着重要的意义。以木质纤维为原料发酵生产燃料乙醇可分为4种工艺:分步糖水解化发酵法、同步糖化发酵法、同步糖化共发酵法和直接微生物转化法。介绍了以上4种工艺的研究进展,并对今后进一步研究提出了建议。     

纤维乙醇制乙烯的研究

采用改性HZSM-5催化剂对纤维乙醇脱水制乙烯进行研究,主要考察反应温度、底物加载量以及催化剂负荷性能等对乙烯产率的影响。结果发现：反应温度235℃、纤维乙醇质量分数为40%～95%乙醇质量空速不超过1.7 h-1时乙烯收率达98%以上。     

以玉米秸秆为原料同步糖化发酵生产燃料乙醇

以玉米秸秆为原料,经酸法预处理后,采用同步糖化发酵SSF工艺生产燃料乙醇。正交试验获得的最佳体系为:培养温度34℃、发酵pH值5.5、发酵的液固比8:1、当发酵108h后,乙醇浓度可达8.33g/L。该实验为纤维质燃料乙醇的产业化生产提供技术依据。     

加快我国纤维乙醇产业发展的建议

随着我国汽车保有量的不断增长,机动车尾气排放成为影响空气质量的重要因素之一。燃料乙醇具有绿色、环保、可再生的资源优势,能够促进燃烧、减少排放污染。本文从国家能源安全、粮食安全、农民增收和环境污染等多方面综述了发展纤维乙醇产业的重要性和必要性,同时结合当前纤维乙醇产业的发展现状对纤维乙醇产业政策提出了建议。     

常压甘油自催化预处理麦草浓醪发酵纤维素乙醇

目前纤维素乙醇成本偏高的根本原因在于没有达到淀粉质乙醇发酵水平的"三高"(高浓度、高转化率和高效率)指标,提高水解糖液浓度和避免发酵抑制物来实现浓醪发酵,是解决问题的关键。文中以常压甘油自催化预处理麦草为底物,尝试采用不同发酵策略,探讨其浓醪发酵产纤维素乙醇的可行性。在优化培养条件(15%底物浓度,加酶量30 FPU/g干底物,温度37℃,接种量10%)下同步糖化发酵72 h,纤维素乙醇产量为31.2 g/L,转化率为73%,发酵效率0.43 g/(L·h);采用半同步(预酶解24 h)糖化发酵72 h,纤维素乙醇浓度达到33.7 g/L,转化率为79%,发酵效率为0.47 g/(L·h),其中(半)同步糖化发酵中90%以上纤维素已被糖化水解用于发酵;采用分批补料式半同步糖化发酵,补料到基质浓度相当于30%,发酵72 h时纤维素乙醇产量达到51.2 g/L,转化率为62%,发酵效率为0.71 g/(L·h)。在所有浓醪发酵中乙酸不足3 g/L,无糠醛和羟甲基糠醛等发酵抑制物。以上结果表明,常压甘油自催化预处理木质纤维素基质适用于纤维素乙醇发酵;分批补料式半同步糖化发酵策略可用来进行浓醪纤维素乙醇发酵;未来工作中提高基质纯度和强化酶解产糖是浓醪纤维素乙醇达到"三高"指标的关键。     

天冠万吨纤维乙醇项目进入试运行

2008年5月8日，由河南天冠集团建设的1万t纤维乙醇一期产业化示范项目，进入试运行阶段。     

稀碱预处理棕榈残渣制备纤维乙醇

以棕榈残渣(Empty fruit bunch,EFB)为原料,通过预处理、酶解、发酵等过程制备纤维乙醇.首先对比了碱、碱/过氧化氢等预处理条件对棕榈残渣组成及酶解的影响,结果表明稀碱预处理效果较好.适宜的稀碱预处理条件为:NaOH浓度为1％,固液比为1∶10,在40℃浸泡24 h后于121℃下保温30 min,在该条件下,EFB的固体回收率为74.09％,纤维素、半纤维素和木质素的含量分别为44.08％、25.74％和13.89％.对该条件下预处理后的固体样品,以底物浓度5％、酶载量30 FPU/g底物酶解72 h,纤维素和半纤维素的酶解率分别达到84.44％和89.28％.进一步考察了酶载量和底物浓度对酶解的影响以及乙醇批式同步糖化发酵,当酶载量为30 FPU/g底物,底物浓度由5％增加至25％时,利用酿酒酵母Saccharomyces cerevisiae(接种量为5％,VIV)发酵72 h后乙醇的浓度分别为9.76 g/L和35.25 g/L,可分别达到理论得率的79.09％和56.96％.     

嗜热性乙醇发酵的研究进展

本文介绍了嗜热硫化氢梭菌,布氏嗜热厌氧细菌、乙醇嗜热厌氧杆菌,热纤梭菌等嗜热乙醇苗的生长特性以及嗜热性乙醇发酵过程中与终产物形成相关的酶学特性和代谢调控机理,最后讨论了几种提高乙醇产量的技术。     

木薯纤维素乙醇发酵的纤维素酶成本评价

木薯中的纤维素成分约占木薯干重的10％(W/W).文中以木薯燃料乙醇生产的木薯纤维素酒渣为原料,从纤维素酶成本角度评估了三种利用木薯纤维素组分发酵生产乙醇的方法,包括木薯纤维素酒渣的直接糖化和乙醇发酵、木薯纤维素酒渣预处理后的糖化与乙醇发酵、木薯乙醇发酵中同步淀粉与纤维素糖化以及乙醇发酵.结果表明,前两种方法的纤维素利用效率不高,酶成本分别达到13602、11659元/吨乙醇.第三种方法,即在木薯乙醇发酵过程同时加入糖化酶和纤维素酶,进行同步淀粉与纤维素糖化,进而进行乙醇发酵,木薯纤维素乙醇的收益最高.发酵结束时的乙醇浓度从101.5g/L提高到107.0g/L,纤维素酶成本为3 589元/吨乙醇.此方法利用木薯纤维素与木薯淀粉同时进行,不会带来额外的设备及操作投入,酶成本低于产品乙醇价格,可实现盈利,因此第三种方法为木薯纤维用于乙醇发酵的最适方法,本研究结果将为木薯乙醇产业深度利用木薯纤维提供依据.     

Chemical characteristics and ethanol fermentation of the cellulose component in autohydrolyzed bagasse

The chemical characteristics, enzymatic saccharification, and ethanol fermentation of autohydrolyzed lignocellulosic material that was exposed to steam explosion were investigated using bagasse as the sample. The effects of the steam explosion on the change in pH, organic acids production, degrees of polymerization and crystallinity of the cellulose component, and the amount of extractive components in the autohydrolyzated bagasse were examined. The steam explosion decreased the degree of polymerzation up to about 700 but increased the degree of crystallinity and the micelle width of the cellulose component in the bagasse. The steam explosion, at a pressure of 2.55 MPa for 3 mins, was the most effective for the delignification of bagasse. 40 g/L of glucose and 20 g/L of xylose were produced from 100 g/L of the autohydrolyzed bagasse by the enzymatic saccharification using mixed cellulases, acucelase and meicelase. The maximum ethanol concentration, 20 g/L, was obtained from the enzymatic hydrolyzate of 100 g/L of the autohydrolyzed bagasse by the ethanol fermentation usingPichia stipitis CBS 5773; the ethanol yield from sugars was 0.33 g/g sugars.     

Simultaneous saccharification and fermentation of cellulose: effect of β-d-glucosidase activity and ethanol inhibition of cellulases

Compared with saccharification in the absence of yeast, simultaneous saccharification and fermentation (SSF) using Trichoderma cellulases and Saccharomyces cerevisiae enhanced cellulose hydrolysis rates by 13–30%. The optimum temperature for SSF was 35°C. The requirement for β-d-glucosidase (β-d-glucoside glucohydrolase, EC 3.2.1.21) in SSF was lower than for saccharification: maximal ethanol production was attained when the ratio of the activity of β-d-glucosidase to filter paper activity was ～1.0. Ethanol inhibited cellulases uncompetitively, with an inhibition constant of 30.5 gl ^?1, but its effect was less severe than that of an equivalent concentration of cellobiose or glucose. No irreversible denaturation of cellulases [1,4-(1,3;1,4)-β-d-glucan 4-glucanohydrolase, EC 3.2.1.4] by ethanol was observed.     

响应面法优化耐高温酵母生产高浓度乙醇

利用耐高温酵母GXASY-10菌株对木薯粉同步糖化(SSF)法生产高浓度乙醇的发酵条件进行了优化。在单因素实验的基础上,首先应用Plackett-Burman试验设计筛选影响酒精高温高浓度发酵的重要参数,采用最陡爬坡实验逼近最大酒精生产区域后,利用Box-Behnken设计确定重要参数的最佳水平。筛选结果表明,影响酒精产量的重要参数是液化时间、糖化酶用量和初始木薯粉(底物)浓度。最佳工艺条件为:液化时间为35min,糖化酶添加量为1.21AGU/g底物,底物浓度为37.62%。20L发酵罐在此条件下(发酵温度37℃,转速100r/min)经过48h发酵,酒精浓度可达16.07%(V/W)。优化条件与初始条件相比较,酒精浓度提高了33%。     

Study of the enzymatic hydrolysis of cellulose for production of fuel ethanol by the simultaneous saccharification and fermentation process

The biochemical conversion of cellulosic biomass to ethanol, a promising alternative fuel, can be carried out efficiently and economically using the simultaneous saccharification and fermentation (SSF) process. The SSF integrates the enzymatic hydrolysis of cellulose to glucose, catalyzed by the synergistic action of cellulase and beta-glucosidase, with the fermentative synthesis of ethanol. Because the enzymatic step determines the ethanol. Because the enzymatic step determines the availability of glucose to the ethanologenic fermentation, the kinetic of cellulose hydrolysis by cellulase and beta-glucosidase and the susceptibility of the two enzymes to inhibition by hydrolysis and fermentation products are of significant importance to the SSF performance and were investigated under realistic SSF conditions. A previously developed SSF mathematical model was used to conceptualize the depolymerization of cellulose. The model was regressed to the collected data to determine the values of the enzyme parameters and was found to satisfactorily predict the kinetics of cellulose hydrolysis. Cellobiose and glucose were identified as the strongest inhibitors of cellulase and beta-glucosidase, respectively. Experimental and modeling results are presented in light of the impact of enzymatic hydrolysis on fuel ethanol production. (c) 1993 Wiley & Sons, Inc.     

白腐真菌Pleurotus sajor-caju预处理对红麻秸秆发酵乙醇的影响

为研究微生物法预处理对红麻秸秆中木质素的降解及后续的红麻纤维素酶促糖化和发酵效率的影响,将白腐真菌Pleurotus sajor-caju接种在红麻秸秆培养基上固态培养,对红麻秸秆进行预处理。经P. sajor-caju培养25~35 d后,有效转化红麻秸秆中的木质素,转化率最高可达50.20％,并提高红麻纤维素的酶促水解效率,糖化率达69.33％~78.64％,与对照组相比提高了3.5~4.1倍。以微生物法预处理后的红麻秸秆样品为底物的同步糖化发酵实验表明,发酵72 h,发酵液中乙醇浓度达到18.35~     

戊糖和己糖共发酵生产燃料乙醇条件研究

利用嗜鞣管囊酵母P-01对木糖和葡萄糖共发酵生产燃料乙醇的条件进行了试验研究,结果表明,木糖和葡萄糖混合液生产燃料乙醇的最佳条件为发酵液的pH值5.5、30℃、摇床转速120 r/min、接种量10%、发酵液初始糖浓度6%、葡萄糖与木糖之比为2、发酵周期为84h。在最佳发酵条件下,发酵醪液中的燃料乙醇浓度为2.101%,糖醇转化率为35%。     

利用酵母生物转化植物纤维为乙醇的研究进展

地球上每年可形成大量价格低廉的可再生植物纤维资源。利用可再生资源生物转化生成乙醇,使得乙醇作为替代能源成为可能。利用酵母发酵生成乙醇因具有工业应用前景,是目前研究的热点之一。本着重介绍了植物纤维水解液中有毒物质对酵母菌种发酵的影响、水解液的脱毒处理及菌种的驯化等方面的进展。     

High solid simultaneous saccharification and fermentation of wet oxidized corn stover to ethanol

In this study ethanol was produced from corn stover pretreated by alkaline and acidic wet oxidation (WO) (195 degrees C, 15 min, 12 bar oxygen) followed by nonisothermal simultaneous saccharification and fermentation (SSF). In the first step of the SSF, small amounts of cellulases were added at 50 degrees C, the optimal temperature of enzymes, in order to obtain better mixing condition due to some liquefaction. In the second step more cellulases were added in combination with dried baker's yeast (Saccharomyces cerevisiae) at 30 degrees C. The phenols (0.4-0.5 g/L) and carboxylic acids (4.6-5.9 g/L) were present in the hemicellulose rich hydrolyzate at subinhibitory levels, thus no detoxification was needed prior to SSF of the whole slurry. Based on the cellulose available in the WO corn stover 83% of the theoretical ethanol yield was obtained under optimized SSF conditions. This was achieved with a substrate concentration of 12% dry matter (DM) acidic WO corn stover at 30 FPU/g DM (43.5 FPU/g cellulose) enzyme loading. Even with 20 and 15 FPU/g DM (corresponding to 29 and 22 FPU/g cellulose) enzyme loading, ethanol yields of 76 and 73%, respectively, were obtained. After 120 h of SSF the highest ethanol concentration of 52 g/L (6 vol.%) was achieved, which exceeds the technical and economical limit of the industrial-scale alcohol distillation. The SSF results showed that the cellulose in pretreated corn stover can be efficiently fermented to ethanol with up to 15% DM concentration. A further increase of substrate concentration reduced the ethanol yield significant as a result of insufficient mass transfer. It was also shown that the fermentation could be followed with an easy monitoring system based on the weight loss of the produced CO2.     

Modeling bacterial contamination of fuel ethanol fermentation

The emergence of antibiotic‐resistant bacteria may limit the effectiveness of antibiotics to treat bacterial contamination in fuel ethanol plants, and therefore, new antibacterial intervention methods and tools to test their application are needed. Using shake‐flask cultures of Saccharomyces cerevisiae grown on saccharified corn mash and strains of lactic acid bacteria isolated from a dry‐grind ethanol facility, a simple model to simulate bacterial contamination and infection was developed. Challenging the model with 10⁸ CFU/mL Lactobacillus fermentum decreased ethanol yield by 27% and increased residual glucose from 6.2 to 45.5 g/L. The magnitude of the effect was proportional to the initial bacterial load, with 10⁵ CFU/mL L. fermentum still producing an 8% decrease in ethanol and a 3.2‐fold increase in residual glucose. Infection was also dependent on the bacterial species used to challenge the fermentation, as neither L. delbrueckii ATCC 4797 nor L. amylovorus 0315‐7B produced a significant decrease in ethanol when inoculated at a density of 10⁸ CFU/mL. In the shake‐flask model, treatment with 2 µg/mL virginiamycin mitigated the infection when challenged with a susceptible strain of L. fermentum (MIC for virginiamycin ≤2 ppm), but treatment was ineffective at treating infection by a resistant strain of L. fermentum (MIC = 16 ppm). The model may find application in developing new antibacterial agents and management practices for use in controlling contamination in the fuel ethanol industry. Biotechnol. Bioeng. 2009;103: 117–122. Published 2008 Wiley Periodicals, Inc.