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。     

合成气和培养基组分对C.autoethanogenum发酵产乙醇的影响研究

以合成气发酵菌株Clostridium autoethanogenum DSM10061为研究对象,研究改良DSM培养基640,添加玉米浆、焦油含量和产物浓度对合成气发酵的影响.结果表明:玉米浆浓度为0.175g/L时利于合成气乙醇发酵.适量的焦油有利于乙醇的生成,抑制乙酸的产生.低浓度的乙醇和乙酸能促进对应产物乙酸和乙醇的生成,但随着浓度的升高,乙醇和乙酸均会严重抑制产物的生成.     

生物质合成气发酵生产乙醇的工艺分析

介绍了生物质合成气发酵制备乙醇的工艺过程。采用Aspen plus软件对工艺过程建立模型,模拟计算乙醇的产量。针对影响乙醇产量的主要参数进行了灵敏度分析,结果表明:气化过程中氧气与干生物质质量比对乙醇产量影响显著,且比值为0.4时,乙醇产量最大;而气化过程中过多蒸汽的加入会降低乙醇产量;发酵过程中CO和H2转化率的提高有利于乙醇产量的增加。     

乙醇型发酵与丁酸型发酵产氢机理及能力分析

氢气是一种新型清洁能源，方便快捷的制氢方法正日益受到重视，产氢－产酸发酵过程中氢气产生的主要途径为乙醇型发酵过程和丁酸型发酵过程，在对这两种发酵类型产氢机理及能力的理论研究及对比试验中，发现乙醇型发酵途径发酵产氢能力要优于丁酸型发酵过程（平均为25％－40％），并且该文将pH值和氧化还原电位（ORP）作为综合环境因子考察，通过与发酵过程产氢量指标相配合分析，认为乙醇型发酵过程是一种较佳的有机物生物发酵制氢途径。     

我国生物质能源现代化应用前景展望(二)——生物质制备液体燃料的转化途径

利用可再生生物质资源转化制备液体燃料已成为全球关注的热点。常见的生物质能源原料主要有草本植物、木本植物、微藻和脂肪类生物质资源,丰富的生物质资源为生物质液体燃料的生产提供了广泛的原料来源,也为生物质能源的多样性发展提供了坚实的物质基础。不同的生物质原料种类和转化方式可生产出性能各异的多种液体燃料,主要包括醇类燃料(乙醇、丁醇等)、烃类燃料和生物柴油等,由此构建出生物质转化制备液体燃料的转化途径网络。醇类燃料的生物质转化途径主要包括生物质直接发酵、生物质合成气发酵、生物质合成气化学合成等;烃类燃料的生物质转化途径主要有生物质液化加氢、微藻热化学途径、生物质合成气费托合成、生物质发酵脂肪酸加氢及油脂类加氢途径等;生物柴油的转化途径主要有油脂酯交换和微藻萃取酯交换。在这些液体燃料的转化途径中,只有生物质发酵制乙醇途径和油脂酯交换途径基本实现了商业化应用,其他大部分转化途径仍处于开发阶段。     

乙醇发酵重组大肠杆菌的构建——运动发酵单胞菌pdc基因在大肠杆菌中的高效表达

为了使大肠杆菌代谢葡萄糖和木糖产乙醇,将运动发酵单胞菌乙醇发酵途径中的关键酶基因丙酮酸脱羧酶基因与质粒载体pGM-T连接转化至大肠杆菌TOP10中。丙酮酸脱羧酶基因在T7启动子的启动下得到了高效表达。构建的重组大肠杆菌不但能利用葡萄糖也能利用木糖产乙醇,在葡萄糖和木糖同时存在时,优先利用葡萄糖。     

Fe对产氢发酵细菌发酵途径及产氢能力影响

经过对20株产氢发酵细菌的静态发酵试验，结果发现加入Fe的培养液中细菌发酵由原来的丁酸型发酵过程向乙醇型发酵过程转化；在有机物发酵产氢的两个主要途径中，Fe为必要成分之一，其参与促进酶促反应的进行。在相似培养条件下，单质Fe与Fe^2 均可诱导细菌代谢向乙醇型发酵转化，其中单质Fe的作用能力优于Fe^2 ；在细菌代谢过程中，单质Fe具有提高细菌发酵产氢能力的作用。     

发酵五碳糖和六碳糖产乙醇染色体整合大肠杆菌的构建

为了保证外源基因表达的稳定性,减少发酵副产物的生成,根据同源重组原理,将大肠杆菌丙酮酸甲酸裂解酶pfl基因两侧的基因片段作为同源片断,构建了带有运动发酵单胞菌丙酮酸脱羧酶基因pdc和乙醇脱氢酶基因adhB的整合重组质粒PA-pfl,用化学法转入大肠杆菌TOP10的感受态细胞,将经过氨苄青霉素筛选得到的重组子进行PCR扩增,证明pdc和adhB基因整合到了大肠杆菌的染色体基因组丙酮酸甲酸裂解酶基因pfl位点上.乙醇发酵结果表明,重组菌E.coli TOP10-pfl不但能稳定地利用葡萄糖产乙醇,也能稳定地利用木糖产乙醇,在大肠杆菌中建立了一条新的代谢糖生成乙醇的途径.     

重组酿酒酵母发酵木糖产乙醇的研究进展

木糖发酵是利用木质纤维素原料制取乙醇商业化生产的基础和关键,但传统的乙醇生产菌株酿酒酵母(Saccharomyces cerevisiae)不能利用木糖,因而无法满足商业生产的需求.人们利用各种基因工程手段对S. cerevisiae实施基因改造,包括对木糖运输途径的改造,木糖代谢途径的引入,增强其对发酵抑制剂的耐受性等方面都得到广泛研究,各重组菌的木糖发酵能力有了不同程度的改善,但是仍然未能用于商业化生产.酿酒酵母的木糖代谢工程有待于进一步深入研究.     

纤维乙醇及渗透汽化原位分离技术研究进展

生物乙醇特别是纤维乙醇是未来化石燃料的重要替代品之一。原位分离发酵技术是近年来兴起的一种新型发酵技术,可使菌体密度较分批培养有显著的提高,最终提高特定产物的生产率。分批发酵过程中产生的乙醇会抑制菌体生长,开发一种解除乙醇抑制作用的发酵方法有助于获得高密度的菌体,从而提高乙醇的产量。近年来渗透汽化膜技术迅速发展,逐步成为乙醇发酵原位分离的理想方法。本文就纤维乙醇、原位分离以及渗透汽化技术涉及的膜材料、耦合技术等研究应用现状进行阐述,并对其研究应用前景进行了展望。     

A visionary and conceptual macroalgae-based third-generation bioethanol (TGB) biorefinery in Sabah,Malaysia as an underlay for renewable and sustainable development

Several biofuel candidates were proposed to displace fossil fuels in order to eliminate the vulnerability of energy sector. Biodiesel and bioethanol produced from terrestrial plants have attracted the attention of the world as potential substitute. However, due to food vs. fuel competition as well as land consumption of these biofuel, they have brought much controversy and debate on their sustainability. In this respect, cultivation of macroalgae such as seaweed at sea water which does not expend arable land and fertilizers provides a possible solution for this energy issue. Carbohydrates derived from seaweeds contain hexose sugars which are suitable materials for fermentation to produce ethanol. Therefore, it is possible to produce fuel ethanol from seaweeds. The potential and prospective of seaweeds to play the role as a sustainable energy provider are demonstrated in this paper. This study offers a conceivable picture of macroalgae-based third-generation bioethanol biorefinery to stimulate the initiation of the exploration in the related field.     

Full chain energy analysis of fuel ethanol from cane molasses in Thailand

An analysis of energy performance and supply potential was performed to evaluate molasses utilization for fuel ethanol in Thailand. The Thai government recently has set up a production target of 1.925 million litres a day of sugar-based ethanol. The molasses-based ethanol (MoE) system involves three main segments: sugar cane cultivation, molasses generation, and ethanol conversion. Negative net energy value found for MoE is a consequence of not utilizing system co-products (e.g. stillage and cane trash) for energy. Taking into account only fossil fuel or petroleum inputs in the production cycle, the energy analysis provides results in favour of ethanol. A positive net energy of 5.95 MJ/L which corresponds to 39% energy gain shows that MoE is efficient as far as its potential to replace fossil fuels is concerned. Another encouraging result is that each MJ of petroleum inputs can produce 6.12 MJ of ethanol fuel. Regarding supply potential, if only the surplus molasses is utilized for ethanol, a shift of 8–10% sugar cane produce to fuel ethanol from its current use in sugar industry could be a probable solution.     

Hydrogen-rich syngas fermentation for bioethanol production using Sacharomyces cerevisiea

Bioethanol is an eco-friendly biofuel due to its merit that makes it a top-tier fuel. The present study emphasized on bioethanol production from hydrogen-rich syngas through fermentation using Sacharomyces cerevisiea. Syngas fermentation was performed in a tar free fermenter using a syngas mixture of 13.05% H₂, 22.92% CO, 7.9% CO₂, and 1.13% CH₄, by volume. In the fermentation process, effects of various parameters including syngas impurity, temperature, pH, colony forming unit, total organic carbon and syngas composition were investigated. The yield of bioethanol was identified by Gas chromatography-Mass spectrometry analysis and further, it was confirmed by Nuclear magnetic resonance (¹H) analysis. From GC-MS results, it is revealed that the concentration of bioethanol using Saccharomyces cerevisiae was 30.56 mmol from 1 L of syngas. Thus, hydrogen-rich syngas is suited for bioethanol production through syngas fermentation using Saccharomyces cerevisiae. This research may contribute to affordable and environment-friendly bioethanol-based energy to decrease the dependency on fossil fuels.     

木质纤维素制取燃料乙醇菌种的研究

目前,随着石油资源的日益枯竭,寻求一种廉价的、清洁的、可再生的新型能源成为各国能源领域科研人员的一项重要任务.乙醇作为一种工业燃料,具有许多优点,利用生物质制取燃料乙醇技术,越来越受到人们的广泛关注.文章报道了国内外近年来利用木质纤维素稀酸水解液制取燃料乙醇的菌种的研究现状,主要包括木质纤维素稀酸水解液乙醇发酵的酵母菌、细菌及基因重组菌的菌种构建等.     

Use of waste for heat,electricity and transport—Challenges when performing energy system analysis

This paper presents a comparative energy system analysis of different technologies utilising organic waste for heat and power production as well as fuel for transport. Technologies included in the analysis are second-generation biofuel production, gasification, fermentation (biogas production) and improved incineration. It is argued that energy technologies should be assessed together with the energy systems of which they form part and influence. The energy system analysis is performed by use of the EnergyPLAN model, which simulates the Danish energy system hour by hour. The analysis shows that most fossil fuel is saved by gasifying the organic waste and using the syngas for combined heat and power production. On the other hand, least greenhouse gases are emitted if biogas is produced from organic waste and used for combined heat and power production; assuming that the use of organic waste for biogas production facilitates the use of manure for biogas production. The technology which provides the cheapest CO₂ reduction is gasification of waste with the subsequent conversion of gas into transport fuel.     

Integrated fossil fuel and solar thermal systems for hydrogen production and CO2 mitigation

In most current fossil-based hydrogen production methods, the thermal energy required by the endothermic processes of hydrogen production cycles is supplied by the combustion of a portion of the same fossil fuel feedstock. This increases the fossil fuel consumption and greenhouse gas emissions. This paper analyzes the thermodynamics of several typical fossil fuel-based hydrogen production methods such as steam methane reforming, coal gasification, methane dissociation, and off-gas reforming, to quantify the potential savings of fossil fuels and CO₂ emissions associated with the thermal energy requirement. Then matching the heat quality and quantity by solar thermal energy for different processes is examined. It is concluded that steam generation and superheating by solar energy for the supply of gaseous reactants to the hydrogen production cycles is particularly attractive due to the engineering maturity and simplicity. It is also concluded that steam-methane reforming may have fewer engineering challenges because of its single-phase reaction, if the endothermic reaction enthalpy of syngas production step (CO and H₂) of coal gasification and steam methane reforming is provided by solar thermal energy. Various solar thermal energy based reactors are discussed for different types of production cycles as well.     

Conversion of fossil and biomass fuels to electric power and transportation fuels by high efficiency integrated plasma fuel cell (IPFC) energy cycle

The IPFC is a high efficiency energy cycle, which converts fossil and biomass fuel to electricity and co-product hydrogen and liquid transportation fuels (gasoline and diesel). The cycle consists of two basic units, a hydrogen plasma black reactor (HPBR) which converts the carbonaceous fuel feedstock to elemental carbon and hydrogen and CO gas. The carbon is used as fuel in a direct carbon fuel cell (DCFC), which generates electricity, a small part of which is used to power the plasma reactor. The gases are cleaned and water gas shifted for either hydrogen or syngas formation. The hydrogen is separated for production or the syngas is catalytically converted in a Fischer–Tropsch (F–T) reactor to gasoline and/or diesel fuel. Based on the demonstrated efficiencies of each of the component reactors, the overall IPFC thermal efficiency for electricity and hydrogen or transportation fuel is estimated to vary from 70 to 90% depending on the feedstock and the co-product gas or liquid fuel produced. The CO₂ emissions are proportionately reduced and are in concentrated streams directly ready for sequestration. Preliminary cost estimates indicate that IPFC is highly competitive with respect to conventional integrated combined cycle plants (NGCC and IGCC) for production of electricity and hydrogen and transportation fuels.     

Detailed kinetic modelling of non-catalytic ethanol reforming for SOFC applications

Ethanol is a particularly attractive alternative fuel for automotive and stationary applications. Due to its high hydrogen content, ethanol can also be utilized for hydrogen production in SOFC systems. The present study assesses the potential of non-catalytic ethanol reforming using a detailed chemical kinetic approach. A recently developed comprehensive detailed mechanism for ethanol oxidation, pyrolysis and combustion is implemented and validated against data from ethanol reformers. Comparisons between computations and experimental major and intermediate species data are shown to be satisfactory. Chemical aspects of the fuel reforming process are thoroughly investigated through rate-of-production and sensitivity analyses with particular emphasis on syngas and potential carbonaceous deposit formation. An assessment of ethanol as a primary fuel versus conventional fuels with similar hydrogen content is also numerically performed. It is shown that ethanol features higher conversion efficiency to syngas than methane. Soot precursor chemistry is shown to be largely dependant both on fuel and reactor operating conditions. Finally, the work demonstrates the limitations of the thermodynamic equilibrium approach.     

Analysis of syngas production rate in empty fruit bunch steam gasification with varying control factors

Biomass gasification is a prevailing approach for mitigating irreversible fossil fuel depletion. In this study, palm empty fruit bunch (EFB) was steam-gasified in a fixed-bed, batch-fed gasifier, and the effect of four control factors—namely torrefaction temperature for EFB pretreatment, gasification temperature, carrier-gas flow rate, and steam flow rate—on syngas production were investigated. The results showed that steam flow rate is the least influential control factor, with no effect on syngas composition or yield. The gasification temperature of biomass significantly affects the composition of syngas generated during steam gasification, and the H₂/CO ratio increases by approximately 50% with an increase in temperature ranging from 680 °C to 780 °C. The higher H₂/CO ratio at a lower gasification temperature increased the energy density of the combustible constituents of the syngas by 3.43%.     

Process engineering evaluation of ethanol production from wood through bioprocessing and chemical catalysis

Ethanol produced from lignocellulosic biomass through a number of conversion pathways presents a more viable alternative to fossil fuels because non-food feedstocks are used. The approaches for ethanol production from biomass, such as wood, can be classified into three general pathways: hydrolysis fermentation (hydrolysis followed by fermentation of the sugars), gasification biosynthesis (gasification followed by biosynthesis to ethanol), and gasification chemical synthesis (gasification followed by catalytic synthesis to ethanol). To compare performance of the three pathways, a black-box system model was utilized with relevant assumptions to analyze their mass and energy conversion efficiencies. Their processing times were also estimated. A comprehensive comparison of the modeling results showed that from a process engineering standpoint, the feasibility of the biomass refining pathways ordered from high to low is gasification chemical synthesis, hydrolysis fermentation, then gasification biosynthesis. Calculations of a performance index, a singular number incorporating the major input and output and processing time of a pathway that was defined, also supported this order.