渗透汽化法在无水乙醇生产中的应用研究

介绍了渗透汽化法在无水乙醇生产中的应用情况，讨论了亲水性膜与亲乙醇性膜的研制以及膜组件的设计，认为在膜组件的设计过程中必须综合考虑进料水分含量、进料温度、进料流率和透过侧压力等操作条件对渗透汽化膜性能的影响。同时介绍了渗透汽化法在乙醇连续发酵过程中的应用，认为这种工艺有利于加快发酵速度，提高乙醇的产率。指出了高性能膜的研制以及膜组件的改进将会使渗透汽化法在燃料乙醇生产中得到更加广泛的应用．     

混合固态发酵降解甘蔗渣产糖产乙醇研究

以碱处理甘蔗渣为原料,比较里氏木霉(Trichoderma reesei CICC40359)和斜卧青霉(Penicillium decumbens LSM-1)单菌和混菌固态发酵及转化乙醇效果,研究发酵过程菌体生长、产酶产糖和乙醇转化情况。结果表明:混菌发酵效果优于单菌,在接种量8%,发酵温度30℃,混菌固态发酵(SSF)72h后总糖和还原糖产量最大值为20.21 g/L和12.47 g/L;β-葡萄糖苷酶活力和菌体生物量在144 h后分别达到0.48 IU/m L和0.21 g/g DM;对发酵3 d后底物(包括生成糖、合成酶及未降解基质)接种酵母进行乙醇同步糖化发酵,乙醇浓度在发酵24 h时达到5.83 g/L,发酵效率达到理论值的40.84%。利用多菌混合固态发酵转化底物产乙醇能避免传统乙醇生产过程高成本纤维素酶的应用,为纤维乙醇生产提供一条经济有效的新途径。     

美、日利用纤维素生物质原料制燃料乙醇的技术开发

介绍了近年来美、日两国有关纤维素制乙醇技术的发展规划，以及相关技术研究开发的进程和所取得的成就。特别是，纤维素不能采用传统的发酵菌种直接发酵生产乙醇，采用硫酸水解法先把纤维素分解为低聚糖再发酵的工艺，采用纤维酶糖化纤维素的工艺都存在着产量低成本高的缺点有待改进。采用基因工程培育的具有纤维素酶基因的新酵种已引起世界各国研究者的关注。凝集性酵母在纤维素制乙醇的工业生产中已获得成功。     

酵母菌复合培养物对木质纤维素稀酸水解液原位脱毒乙醇发酵

为了解决木质纤维素稀酸水解产物中发酵抑制剂对微生物的抑制作用以及木糖的乙醇发酵问题,该研究用本实验室开发的能高效代谢葡萄糖产乙醇并代谢糠醛和5-羟甲基糠醛的2株酵母菌种Saccharomyces cerevisiae Y5和Ismtchenkia/orientalis Y4分别与Pichia.stipitis CBS6054组成2个复合菌种,用复合菌种对木质纤维素稀酸水解产物进行原位脱毒乙醇发酵.结果证明,复合菌种S.cerevisiae Y5,P.stipitis CBS6054显示出了很好的代谢稀酸水解液中的葡萄糖和木糖产乙醇并快速代谢糠醛和5-羟甲基糠醛的能力,乙醇产率为0.43g/g(达到理论值的85.1%).该复合培养物可作为木质纤维索稀酸水解产物不需任何脱毒处理直接进行乙醇发酵的复合菌种.     

生物质合成气发酵生产乙醇技术的研究进展

20世纪70年代以来，开发低成本、可再生的能源已成为各国的研究热点。以生物质为原料生产的燃料乙醇是一种很有应用潜力的能源。文章简要讨论了生物质合成气发酵生产乙醇的技术途径．分析了该技术的优点、工艺过程、生产成本和市场化进程，特别介绍了美国BRI公司和密西西比乙醇公司（ME）在生物质合成气发酵生产乙醇方面所做的工作；同时，指出了我国发展生物质合成气发酵技术的必要性和应用前景。     

微生物选育技术在生物燃料乙醇生产中的应用

随着全球性能源危机、粮食危机和环境危机的到来,燃料乙醇作为汽油的替代品日益受到关注.应用微生物发酵技术将甘蔗、玉米、木薯和纤维类废弃物等转化为燃料乙醇,已成为解决世界能源危机的一条理想途径.通过对环境中各种微生物进行筛选分离和育种,可以得到转化能力较强的高效菌株,将这些高效菌株应用于燃料乙醇生产中,能够有效提高燃料乙醇的生产效率.文章对微生物选育技术在燃料乙醇生产中的应用进行了总结与展望.     

两株高效代谢木质纤维素稀酸水解物产乙醇的酵母特性及耐毒研究

对实验室筛选出的两株高效代谢木质纤维素稀酸水解液产乙醇的酵母菌Y1(Candida tropicalis)和Y4(Issatchenkiaorientalis)的乙醇发酵特性及耐毒能力进行研究。以未经任何脱毒处理的木质纤维素稀酸水解液为发酵底物进行乙醇发酵(原位脱毒乙醇发酵)。结果表明:Y1和Y4均能在24h内将水解液中所有的葡萄糖消耗完,乙醇产率分别为0.49g/g和0.45g/g,分别达到理论值的96.1%和86.0%。在含有不同浓度梯度的糠醛及5-羟甲基糠醛的模拟水解液中,Y1和Y4能耐受的最高糠醛浓度均为5.0g/L及最高的5-羟甲基糠醛浓度均大于7.0g/L,当两种抑制剂等量混合时,两株菌能耐受的最高浓度为4.0g/L,两株菌均有较好的乙醇发酵及耐毒能力。该研究结果为木质纤维素水解液的原位脱毒发酵生产然料乙醇奠定了基础。     

酵母乙醇发酵动力学模型研究

文章研究了Saccharomyces cerevisiae BY4742以葡萄糖为底物的发酵动力学。根据最优化影响因素实验的结果,利用Logistic方程、Leudeking-Piret方程和类Luedeking-Piret方程,分别建立了酵母乙醇发酵的菌体生长模型、产物形成模型以及底物消耗模型,利用软件拟合并得到模型的参数估值。结果表明,乙醇的合成与酵母菌的生长速率及菌体积累量均有关,根据细胞生长速率与产物形成速率是否偶联进行动力学分类,其属于部分偶联型。底物消耗模型和产物形成模型拟合度R2分别达到了0.983与0.900,可用于描述利用Saccharomyces cerevisiae BY4742菌株的葡萄糖发酵制乙醇过程。     

酿酒酵母代谢有机酸对乙醇发酵的影响

发酵过程中酵母代谢产生的有机酸会影响发酵效率。以葡萄糖为底物,在自动发酵罐中进行了酿酒酵母间歇乙醇发酵实验,研究了发酵过程中酵母的主要代谢副产物中有机酸的种类及其对乙醇发酵的影响。结果表明,发酵过程中酵母代谢的主要有机酸是琥珀酸、乳酸和乙酸。3种酸的总量随温度(25~40℃)升高或p H增大(3~6)呈上升趋势,最大值可达5.78 g/L,占产物的23.3%。通过外源投加有机酸实验发现,3种代谢有机酸对酵母抑制作用的大小并不完全由其酸性决定,还与其进入细胞的难易程度等相关。通过外源投加有机酸实验结合发酵过程中去除有机酸实验可以确定,对乙醇发酵的影响由大到小依次为乙酸、琥珀酸和乳酸,且三者之间对乙醇发酵无明显的协同抑制效应。乙酸是发酵过程中产生主要抑制作用的代谢有机酸,2 g/L的乙酸可引起菌体浓度明显下降,4 g/L的乙酸即可引起乙醇得率下降86.7%。     

两株高效代谢木质纤维素稀酸水解物产乙醇的酵母特性及耐毒研究

对实验室筛选出的两株高效代谢木质纤维素稀酸水解液产乙醇的酵母菌Y1(Candida tropicalis)和Y4(Issatchenkiaorientalis)的乙醇发酵特性及耐毒能力进行了的研究。以未经任何脱毒处理的木质纤维素稀酸水解液为发酵底物进行乙醇发酵(原位脱毒乙醇发酵)。结果表明,Y1和Y4均能在24h内将水解液中所有的葡萄糖消耗完,乙醇产率分别为0.49g/g和0.45g/g,分别达到了理论值的96.1%和86.0%。在含有不同浓度梯度的糠醛及5-羟甲基糠醛的模拟水解液中,Y1和Y4能耐受的最高糠醛浓度均为5.0g/L,最高的5-羟甲基糠醛浓度均大于7.0g/L,当两种抑制剂等量混合时,两株菌能耐受的最高浓度为4.0g/L。两株菌均有较好的乙醇发酵及耐毒能力。该研究结果为木质纤维素水解液的原位脱毒发酵生产然料乙醇奠定了基础。     

Covalent immobilization of enzymes and yeast: Towards a continuous simultaneous saccharification and fermentation process for cellulosic ethanol

The immobilization of enzymes and yeast cells is a key factor for establishing a continuous process of cellulosic ethanol production, which can combine the benefits of a separated hydrolysis and fermentation process and a simultaneous saccharification and fermentation process. This paper investigates the use of cellulase enzyme and yeast cell immobilization under a flow regime of ethanol production from soluble substrates such as cellobiose and carboxymethyl cellulose. The immobilization was achieved by incubating enzymes and yeast cells on polystyrene surfaces which had been treated by nitrogen ion implantation. The saccharification by immobilized enzymes and the fermentation by immobilized yeast cells were conducted in two separate vessels connected by a pump. During the experiments, glucose concentrations were always maintained at low levels which potentially reduce product inhibition effects on the enzymes. Covalent immobilization of enzymes and yeast cells on the plasma treated polymer reduces loss by shear flow induced detachment. The potential for continuous flow production of ethanol and the influence of daughter yeast cells in the circulating flow on the immobilized enzyme activity are discussed.     

双菌比较优化稻草“液化”发酵产乙醇的研究

利用稻草液化产物为底物,分别采用酿酒酵母和休哈塔假丝酵母发酵生产乙醇,对影响发酵阶段的各因素进行优化,选取最佳菌种完成秸秆到乙醇的转化。结果表明,液化产物经酶解后葡萄糖浓度可达69.5mg/mL,是发酵制备乙醇的良好底物。优化发酵后,酿酒酵母更适合做液化产物的发酵菌种。适宜的发酵条件:初始葡萄糖浓度60~65 mg/mL,温度30℃,pH=6.0,装液量80 mL,接种量10%,发酵时间36 h,在此条件下乙醇得率可达49.3%,能达到理论得率的96.1%,转化率最高为0.27 g/g(乙醇/液化产物)。     

Ethanologens vs. acetogens: Environmental impacts of two ethanol fermentation pathways

Bioconversion production of ethanol from cellulosic feedstock is generally proposed to use direct fermentation of sugars to ethanol. Another potential route for ethanol production is fermentation of sugars to acetic acid followed by hydrogenation to convert the acetic acid into ethanol. The advantage of the acetogen pathway is an increased ethanol yield; however, using an acetogen requires the additional hydrogenation, which could substantially affect the life cycle global warming potential of the process. Assuming a poplar feedstock, a cradle to grave Life cycle assessment (LCA) is used to evaluate the environmental impacts of an acetogen based fermentation pathway. An LCA of a fermentation pathway that uses ethanologen fermentation is developed for comparison. It is found that the ethanologen and acetogen pathways have Global Warming Potentials (GWP) that are 92% and 46% lower than the GWP of gasoline, respectively. When the absolute GWP reduction compared to gasoline is calculated using a unit of land basis, the benefit of the higher ethanol yield using the acetogen is observed as the two pathways achieve similar GWP savings. The higher ethanol yield in the acetogen process plays a crucial role in choosing a lignocellulosic ethanol production method if land is a limited resource.     

Simultaneous glucose and xylose utilization for improved ethanol production from lignocellulosic biomass through SSFF with encapsulated yeast

Simultaneous glucose and xylose uptake was investigated for ethanol production using the simultaneous saccharification, filtration and fermentation (SSFF) process with pretreated wheat straw as a xylose-rich lignocellulosic biomass. A genetically engineered strain of Saccharomyces cerevisiae (T0936) with the ability to ferment xylose was used for the fermentations. SSFF was compared with a conventional method of simultaneous saccharification and fermentation (SSF) for glucose and xylose uptake, ethanol production, and cell viability on 10% and 12% suspended solids (SS) basis. With 10% SS, an ethanol yield of 90% of the theoretical level was obtained during SSFF with 80% xylose uptake while only 53% ethanol yield was observed during the SSF process. Increasing the solid load to 12% resulted in an ethanol yield of 77% of the theoretical value and 36% xylose uptake during SSFF while only 27% ethanol yield and no xylose uptake was observed during the corresponding SSF process. The SSFF process preserved the viability of the genetically engineered yeast throughout the fermentation, even when reused for 2 consecutive cultivations. The results show that the SSFF process does not only enhance effective cell performance but also facilitates simultaneous glucose and xylose utilization, which is important for broad range of biomass utilization for lignocellulosic ethanol production.     

Fuels and chemicals from biomass

Increasing energy consumption, coupled with decreased petroleum supplies, has made development of alternate energy sources a pressing national problem. One of the alternatives presently being examined is obtaining fuels from biomass. Biomass, which is a form of stored solar energy (sunlight having been converted by photosynthesis to cellulosic materials) is an abundant, renewable, domestically available energy resource. Although techniques of converting cellulosic materials in biomass to sugars and then to alcohol have been available for over one hundred years, it is only recently that the efficiency of this type of process has been improved to the point where the economics look potentially attractive. A major processing step responsible for this improvement is the conversion of cellulose to glucose in high yield. While the yield of sugars from cellulose was on the order of 50% previously, this has been improved to 90% or greater by a process in which cellulosic material is solvent-pretreated to make it readily accessible to hydrolysis to sugars by either acid or enzyme. This approach to hydrolysis, together with the fermentation of the resulting sugars to alcohol, is known as the Purdue Process. This process is discussed in the context of prior work done in this field.     

Feedstock analysis sensitivity for estimating ethanol production potential in switchgrass and energycane biomass

Efficient ethanol production from lignocellulosic biomass requires highly degradable feedstock; therefore, there is a similarity between forage crop production for ruminant animals and ethanol production from lignocellulosic biomass. Feed value analysis techniques may be used to estimate lignocellulosic biomass quality. Because lignin and its derivatives in cell walls are major compounds interrupting biomass degradation, fiber analysis and in vitro incubation tests were conducted with switchgrass (Panicum virgatum) and energycane (Saccharum spp.) biomass collected at 100 and 120 g lignin (acid detergent lignin) kg^?1 DM (dry matter). Mean NDF (neutral detergent fiber) in switchgrass was consistently greater than that of energy cane regardless of lignin levels, while ADF (acid detergent fiber) did not differ. Mean of energycane in vitro true digestibility and digestible neutral detergent fiber were greater than those of switchgrass. The ADF and ruminal fermentation rate averaged by lignin levels differed, while most of the analysis results did not. Based on ADF and NDF concentrations, switchgrass contained a greater concentration of hemicellulose than energycane, while cellulose concentration was similar. Fermentability of energycane was consistently greater than that of switchgrass. Fermentation gas volume was positively correlated with cellulosic biomass degradation for ethanol production. Consequently, fermentation gas kinetic parameters obtained from biomass fermentation with rumen fluid or with yeast indicate that the fermentable pool size is the parameter most closely correlated to ethanol production potential across the species. Results obtained from feed value analyses demonstrate fermentation variability and meaningful relationships between fermentation gas parameters and ethanol production. Thus, the ruminal fermentation process is useful as a screening tool for ethanol production potential of biofuel feedstock. Copyright © 2015 John Wiley & Sons, Ltd.     

Developments in biobutanol production: New insights

Biobutanol will become an attractive, economic and sustainable fuel as petroleum oil leads towards expensive fuel due to diminishing oil reserves and an increase of green house gases in the atmosphere. The major challenges in biobutanol production are low butanol titer, availability of compatible feedstocks, and product inhibition. These hurdles are being resolved using several genetic engineering techniques, metabolic engineering strategies, and promising integrated continuous fermentation processes with efficient product recovery techniques (like gas stripping). Adequate success in utilizing renewable and cost-effective cellulosic materials as feedstocks has opened up novel grounds for the advancement in economic biobutanol production. In this direction, Clostridium beijerinckii is being explored as promising strain to produce biobutanol from cellulosic materials. Moreover, high biobutanol titer is being focused through genetic modifications of Clostridia and non-Clostridia organisms (e.g., Escherichia coli, Saccharomyces cerevisiae, Pseudomonas putida, and Bacillus subtilis) in both aerobic and anaerobic fermentation. Further, application of various novel genetic tools and genome sequencing of hyper-butanol-producing Clostridial organism will enhance the scope of genetic engineering for biobutanol production. Therefore, consolidation of academic and industrial research towards economic synthesis of biobutanol illustrates the possibility of substantial breakthrough in future. In this review, we focus on (i) selection of suitable bacterial strain (ii) availability of cheaper biomass to produce butanol (iii) metabolic engineering strategies of various microorganisms (iv) attempts at process development and (v) biobutanol recovery techniques that provide future direction of economical biobutanol fermentation.     

Ultrasonic vibration-assisted pelleting for cellulosic biofuel manufacturing: Investigation on power consumption

Cellulosic ethanol produced from cellulosic biomass is an alternative to petroleum-based transportation fuels. Raw cellulosic biomass has low density, causing high costs in their storage, transportation, and handling. Ultrasonic vibration-assisted (UV-A) pelleting can increase the density of cellulosic biomass. Effects of UV-A pelleting variables on pellet quality (density, durability, stability, and strength) and sugar yield have been reported. However, power consumption in UV-A pelleting has not been fully investigated. This paper presents an experimental investigation on power consumption in UV-A pelleting of wheat straw. Effects of input variables (biomass moisture content, biomass particle size, pelleting pressure, and ultrasonic power) on power consumption are investigated. Results show that power consumption in UV-A pelleting increases as moisture content and particle size decrease, and as pelleting pressure and ultrasonic power increase.     

Pretreatment and hydrolysis of cellulosic agricultural wastes with a cellulase-producing Streptomyces for bioethanol production

Production of reducing sugar by hydrolysis of corncob material with Streptomyces sp. cellulase and ethanol fermentation of cellulosic hydrolysate was investigated. Cultures of Streptomyces sp. T3-1 improved reducing sugar yields with the production of CMCase, Avicelase and ??-glucosidase activity of 3.8, 3.9 and 3.8 IU/ml, respectively. CMCase, Avicelase, and ??-glucosidase produced by the Streptomyces sp. T3-1 favored the conversion of cellulose to glucose. It was recognized that the synergistic interaction of endoglucanase, exoglucanase and ??-glucosidase resulted in efficient hydrolysis of cellulosic substrate. After 5 d of incubation, the overall reducing sugar yield reached 53.1 g/100 g dried substrate. Further fermentation of cellulosic hydrolysate containing 40.5 g/l glucose was performed using Saccharomyces cerevisiae BCRC 21812, 14.6 g/l biomass and 24.6 g/l ethanol was obtained within 3 d. The results have significant implications and future applications regarding to production of fuel ethanol from agricultural cellulosic waste.     

植物纤维原料发酵生产燃料乙醇研究进展

综述了以植物纤维素为原料生产燃料乙醇的4种不同工艺,包括:分段水解与发酵(SHF)、同步糖化和发酵(SSF)、同步糖化共发酵(SSCF)和联合生物加工工艺(CBP),并比较了它们的成熟程度以及优缺点。简述了纤维乙醇在国内外的发展现状,同时提出了我国今后一段时间内发展纤维乙醇的策略。