纤维素乙醇产业化的突破口——集成就地产酶工艺的多联产生物精炼

纤维素乙醇产业化在可再生资源利用、环境污染控制、农业产业链延伸、农村经济发展、农民就业等方面均可发挥重大作用。但由于生产成本仍然偏高,至今未能实现大规模的产业化。把集成了就地产酶过程的多联产生物精炼技术选择为实现纤维素乙醇大规模产业化的突破口,可以大幅度降低酶解产糖的用酶成本。同时,引进精炼概念,提高了纤维素乙醇生产与同类粮食和石油产品的经济竞争力。玉米芯生物精炼联产木糖产品-乙醇-木质素工艺技术,成功实现了纤维素乙醇工业化生产,最近正在合作开发秸秆生物精炼联产纸浆-乙醇-黄腐酸肥新技术,有望实现更大规模的工业生产。     

青霉生产木质纤维素降解酶系的研究进展

木质纤维素降解酶系的高效生产是实现植物生物质大规模生物炼制的重要支撑。就地生产木质纤维素降解酶,有助于降低其使用成本,提高技术经济效益。青霉是自然界常见的木质纤维素降解真菌,可以合成分泌种类多样、组分齐全的木质纤维素降解酶系,已被应用于纤维素酶制剂的工业生产。文中从就地生产降解酶,为木质纤维素生物炼制构建“糖平台”的角度,综述了青霉木质纤维素降解酶系的性质、菌株遗传改造及发酵工艺的研究进展。     

木质纤维素的自然生物转化系统及其过程特征与仿生利用

规模化和产业化开发利用木质纤维素类生物质面临着许多科学和技术上的挑战,这些挑战的核心是如何实现木质纤维素生物质的高效分离与有效转化。然而,在自然界中,不同生物系统分别进化出了其独特的木质纤维素降解与转化的生物过程机制,通过采用不同的策略与途径来克服生物质的抗降解屏障。综述了不同自然生物转化系统在降解生物质过程中的策略与过程特征,并着重分析了食木白蚁肠道消化系统在生物质降解过程中高效转化与利用的独特系统特点。向白蚁生物系统学习,利用自然生物系统的启迪及其相关基因与酶资源,结合生物仿生技术可望建立新型的生物质降解工艺,逐渐实现生物质的低能耗、低污染、高效率、全值化利用。     

木质纤维素生物转化产氢技术现状与发展趋势

氢能是一种清洁能源,利用木质纤维素类生物质生产氢气,在生产可再生绿色能源的同时,避免了木质纤维素资源未被充分利用而造成的环境污染和资源浪费,它的开发与应用对人类未来能源与经济发展具有十分重要意义。以下综述了木质纤维素生物转化产氢技术的研究现状,提出了木质纤维素生物转化产氢的总体构想与对产业发展方向的建议。     

木质纤维素资源化主要途径及半纤维素优先资源化利用策略

木质纤维生物质是地球上最丰富的可再生资源,可转化为能源、化学品和材料,开发木质纤维生物质有利于废弃物的高值化利用和缓解目前面临的环境污染等问题。木质纤维素主要包括纤维素、半纤维素和木质素,将其主要组分进行高效分离,是实现多元化、高值化生物精炼的基础。基于此,笔者简要总结了目前主要的木质纤维素资源化途径,如基于纤维素资源化、基于半纤维素资源化、基于木质素资源化、基于碳水化合物资源化以及全组分资源化的研究策略。依据半纤维素在植物细胞壁中承担的角色,结合前期的研究基础,提出半纤维素优先原位催化转化的木质纤维素生物炼制新策略,实现半纤维素的高选择性溶出和高效转化,保留结构完整的纤维素和木质素分级转化为小分子化学品和材料,最终实现资源生物量全利用,多元化产品联产的目的。     

燃料乙醇非粮化——我国发展纤维乙醇的挑战与对策

在分析国内外燃料乙醇发展状况的基础上阐述了以非粮原料木质纤维素生产燃料乙醇的重要性,着重论述了发展纤维素燃料乙醇所面临的发展机遇和技术挑战,同时对我国纤维乙醇的产业化发展提出了建议。     

生物转化能源草制取纤维素乙醇的研究进展

随着化石燃料的日益枯竭和环境污染的日益加剧,寻找一种绿色能源以代替化石能源成为当今世界迫在眉睫的任务。清洁燃料当中的生物乙醇具有车用价值,可作为化石能源的替代品而受到研究学者的广泛关注。而草本能源植物的生物转化被认为是生物质能源产业化发展的最有效途径之一。能源草作为木质纤维素原料之一,由于其具有生长快,产量高,抗性强等优势而备受瞩目。详细论述了近期国内外以能源草为底物进行纤维素乙醇的生物转化研究进展,从纤维素原料预处理到乙醇发酵工艺等各方面的进展及存在的问题,并对木质纤维素制取生物质能源的生物转化效率,以及全纤维素组分的多级利用进行了简单阐述,以期找出一条产业化生产纤维素乙醇的最优生产模式。     

微生物降解利用木质纤维素的协同作用

木质纤维素复杂的结构组成,是制约高效降解利用这一资源、发展生物炼制的瓶颈。微生物的多酶(菌)体系可有效降解木质纤维素。除好氧微生物的游离酶协同系统之外,主要存在于厌氧细菌中的纤维小体也是有序、高效的协同降解纤维素的复合体系。近年来,在天然纤维小体研究的基础上,研究者们成功设计、构建了人工纤维小体,加深了对这一复合体系的组成单元的理性认识。另外,菌群共培养技术利用各组成菌株代谢途径的协同作用实现了木质纤维素的高效降解。最后,引入异源纤维素酶,可改造现有工程菌株的代谢网络,提高工程菌发酵生产终产物的能力。这些技术有利于实现一步转化生产乙醇的联合生物工艺,有助于提高生物炼制的产率、降低生产成本。     

木质纤维素生物炼制的研究进展

木质纤维素是一种广泛存在的可再生生物质资源,主要由纤维素、半纤维素和木质素组成。如何更有效地综合利用木质纤维素是当前面临的世界性难题。本文中,笔者梳理了木质纤维素生物化学法转化生产以燃料乙醇为代表的生物基产品,特别是转化过程中关键技术环节的研究现状及难点,深入探讨了木质素的生物转化利用趋势,并综述了合成生物学在这些领域的研究趋势和最新成果。本文力图描绘出木质纤维素生物炼制研究全景,为后续研究提供潜在思路。     

大力推动纤维素乙醇产业化发展--访山东大学生命科学学院院长曲音波教授

《生物产业技术》：全世界各主要国家都在大力推动研发纤维素乙醇,从纤维素乙醇产业化进程看,我国纤维素乙醇产业化处于一个什么样的位置,目前发展情况如何？曲音波：纤维素乙醇研发工作在全世界都受到重视,即使像美国那样粮食和土地资源非常丰富的国家,也十分重视利用植物纤维原料生产乙醇的工作。     

Oil Palm Biomass Biorefinery for Sustainable Production of Renewable Materials

Oil palm biomass is widely known for its potential as a renewable resource for various value‐added products due to its lignocellulosic content and availability. Oil palm biomass biorefinery is an industry that comes with sociopolitical benefits through job opportunities, as well as potential environmental benefits. Many studies have been conducted on the technological advancements of oil‐palm biomass‐derived renewable materials, which are discussed comprehensively in this review. Recent technological developments have made it possible to bring new and innovative technologies to commercialization, such as compost, biocharcoal, biocomposites, and bioplastics.     

Raw plant-based biorefinery: A new paradigm shift towards biotechnological approach to sustainable manufacturing of HMF

Unlike petrorefinery, biorefinery uses carbon-based biomaterials, such as plant feedstocks, as the major feeding input materials in chemical manufacturing. To date, petroleum-based resources have been used for the production of wide spectrums of chemical products. However, petrorefinery is currently associated with a variety of issues, i.e., concerns over adverse impacts on the environment and human society. As an alternative technology, the sustainable biorefinery is a matter of great importance in industrial chemical manufacturing due primarily to its sustainability. As carbon-based resources, plants are paramount biomaterials for biorefinery process required in sustainable chemical manufacturing. In particular, raw plant-based biorefinery is a breakthrough technology for chemical manufacturing due mainly to its sustainable benefits. Nowadays, numerous biorefinery technologies have been developed for the production of industrially valuable chemicals. HMF, a versatile platform chemical, can be produced by dehydrating hexose sugars using raw plant feedstocks such as inulin-rich, starch-rich, and lignocellulosic plants and now, it is generally recognized as a chemical feedstock for future chemical manufacturing and bioenergy production. In this review article, this emerging hybrid technology is discussed in relation to the production of HMF from raw plant feedstocks mentioned above. In addition, the plant candidates useful for biorefinery processing of raw plant feedstocks are introduced and bioengineering strategy for their genetic modification is together described to provide current knowledge on sustainable biorefinery.     

Biorefinery: Toward an industrial metabolism

Fossil fuel reserves are running out, global warming is becoming a reality, waste recycling is becoming ever more costly and problematic, and unrelenting population growth will require more and more energy and consumer products. There is now an alternative to the 100% oil economy; it is a renewable resource based on agroresources by using the whole plant. Production and development of these new products are based on biorefinery concept. Each constituent of the plant can be extracted and functionalized in order to produce non-food and food fractions, intermediate agro-industrial products and synthons. Three major industrial domains can be concerned: molecules, materials and energy. Molecules can be used as solvent surfactants or chemical intermediates in substitution of petrol derivatives. Fibers can be valorized in materials like composites. Sugars and oils are currently used to produce biofuels like bioethanol or biodiesel, but second-generation biofuels will use lignocellulosic biomass as raw material. Lipids can be used to produce a large diversity of products like solvent, lubricants, pastes or surfactants. Industrial biorefinery will be linked to the creation of new processes based on the twelve principles of green chemistry (clean processes, atom economy, renewable feedstocks…). Biotechnology, especially white biotechnology, will take a major part into these new processes with biotransformations (enzymology, micro-organisms…) and fermentation. The substitution of oil products by biobased products will develop a new bioeconomy and new industrial processes respecting the sustainable development concept. Industrial biorefinery can be developed on the principle that any residues of one can then be exploited as raw material by others in an industrial metabolism.     

Comparison of different pretreatment methods for lignocellulosic materials. Part II: Influence of pretreatment on the properties of rye straw lignin

Several processes have been suggested to convert various types of lignocellulosic biomass into lignin products and saccharides. This paper evaluates the suitability of an organosolv process, a process using soda, a hydrothermal process and a process developed in this work, called the “Aquasolve process” for inclusion into a lignocellulosic biorefinery concept. Part II of this paper investigates the influence of the different pretreatment processes on the properties of rye straw lignin and evaluates their ability to produce high recoveries of high quality lignin.Specifications for high quality lignin products are defined and the isolated lignin fractions are analysed by Klason lignin, carbohydrate and ash content, elemental analysis, thermo-gravimetric analysis, ³¹P NMR, and size exclusion chromatography. The organosolv process shows the largest lignin recovery, followed by the soda and Aquasolve processes. Lignin products from the soda process, the Aquasolve process and with reservation the organosolv process show interesting properties for polymer applications.     

Integrated lignocellulosic value chains in a growing bioeconomy: Status quo and perspectives

Lignocellulose is the most abundant biomass on Earth, with an estimated 181.5 billion tonnes produced annually. Of the 8.2 billion tonnes that are currently used, about 7 billion tonnes are produced from dedicated agricultural, grass and forest land and another 1.2 billion tonnes stem from agricultural residues. Economic and environmentally efficient pathways for production and utilization of lignocellulose for chemical products and energy are needed to expand the bioeconomy. This opinion paper arose from the research network “Lignocellulose as new resource platform for novel materials and products” funded by the German federal state of Baden‐Württemberg and summarizes original research presented in this special issue. It first discusses how the supply of lignocellulosic biomass can be organized sustainably and suggests that perennial biomass crops (PBC) are likely to play an important role in future regional biomass supply to European lignocellulosic biorefineries. Dedicated PBC production has the advantage of delivering biomass with reliable quantity and quality. The tailoring of PBC quality through crop breeding and management can support the integration of lignocellulosic value chains. Two biorefinery concepts using lignocellulosic biomass are then compared and discussed: the syngas biorefinery and the lignocellulosic biorefinery. Syngas biorefineries are less sensitive to biomass qualities and are technically relatively advanced, but require high investments and large‐scale facilities to be economically feasible. Lignocellulosic biorefineries require multiple processing steps to separate the recalcitrant lignin from cellulose and hemicellulose and convert the intermediates into valuable products. The refining processes for high‐quality lignin and hemicellulose fractions still need to be further developed. A concept of a modular lignocellulosic biorefinery is presented that could be flexibly adapted for a range of feedstock and products by combining appropriate technologies either at the same location or in a decentralized form.     

Integrating Separation and Conversion—Conversion of Biorefinery Process Streams to Biobased Chemicals and Fuels

The concept of the integrated biorefinery is critical to developing a robust biorefining industry in the USA. Within this model, the biorefinery will produce fuel as a high-volume output addressing domestic energy needs and biobased chemical products (high-value organics) as an output providing necessary economic support for fuel production. This paper will overview recent developments within two aspects of the integrated biorefinery—the fractionation of biomass into individual process streams and the subsequent conversion of lignin into chemical products. Solvent-based separation of switchgrass, poplar, and mixed feedstocks is being developed as a biorefinery “front end” and will be described as a function of fractionation conditions. Control over the properties and structure of the individual biomass components (carbohydrates and lignin) can be observed by adjusting the fractionation process. Subsequent conversion of the lignin isolated from this fractionation leads to low molecular weight aromatics from selective chemical oxidation. Together, processes such as these provide examples of foundational technology that will contribute to a robust domestic biorefining industry.     

Improved bioconversion of lignocellulosic biomass by Saccharomyces cerevisiae engineered for tolerance to acetic acid

Lignocellulosic biomass has considerable potential for the production of fuels and chemicals as a promising alternative to conventional fossil fuels. However, the bioconversion of lignocellulosic biomass to desired products must be improved to reach economic viability. One of the main technical hurdles is the presence of inhibitors in biomass hydrolysates, which hampers the bioconversion efficiency by biorefinery microbial platforms such as Saccharomyces cerevisiae in terms of both production yields and rates. In particular, acetic acid, a major inhibitor derived from lignocellulosic biomass, severely restrains the performance of engineered xylose‐utilizing S. cerevisiae strains, resulting in decreased cell growth, xylose utilization rate, and product yield. In this study, the robustness of XUSE, one of the best xylose‐utilizing strains, was improved for the efficient conversion of lignocellulosic biomass into bioethanol under the inhibitory condition of acetic acid stress. Through adaptive laboratory evolution, we successfully developed the evolved strain XUSAE57, which efficiently converted xylose to ethanol with high yields of 0.43–0.50 g ethanol/g xylose even under 2–5 g/L of acetic stress. XUSAE57 not only achieved twofold higher ethanol yields but also improved the xylose utilization rate by more than twofold compared to those of XUSE in the presence of 4 g/L of acetic acid. During fermentation of lignocellulosic hydrolysate, XUSAE57 simultaneously converted glucose and xylose with the highest ethanol yield reported to date (0.49 g ethanol/g sugars). This study demonstrates that the bioconversion of lignocellulosic biomass by an engineered strain could be significantly improved through adaptive laboratory evolution for acetate tolerance, which could help realize the development of an economically feasible lignocellulosic biorefinery to produce fuels and chemicals.     

Comparative LCA studies of simulated HMF biorefineries from maize and miscanthus as an example of first- and second-generation biomass as a tool for process development

5-Hydroxymethylfurfural (HMF) is a versatile platform chemical for a fossil free, bio-based chemical industry. HMF can be produced by using fructose as a feedstock. Using edible, first-generation biomass to produce chemicals has been questioned in terms of potential competition with food supply. Second-generation biomass like miscanthus could be an alternative. However, there is a lack of information if second-generation lignocellulosic biomass is a more sustainable feedstock to produce HMF. Therefore, a life cycle assessment was performed in this study to determine the environmental impacts of HMF production from miscanthus and to compare it with HMF from high-fructose corn syrup (HFCS). HFCS from either Hungary or Baden-Württemberg (Germany) was considered. Compared to the HFCS biorefineries the miscanthus concept is producing less emissions in all impact categories studied, except land occupation. Overall, the production and usage of second-generation biomass could be especially beneficial in areas where the use of N fertilizers is restricted. Besides, conclusions for the further development of the on-farm biorefinery concept were elaborated. For this purpose, process simulations from a previous study were used. Results of the previous study in terms of TEA and the current LCA study in terms of environmental sustainability indicate that the lignin depolymerization unit in the miscanthus biorefinery has to be improved. The scenario without lignin depolymerization performs better in all impact categories. The authors recommend to not further convert the lignin to products like phenol and other aromatic compounds. The results of the contribution analyses show that the major impact in the HMF production is caused by the auxiliary materials in the separation units and the required heat. Further technical development should focus on efficient heat as well as solvent use and solvent recovery. At this point further optimizations will lead to reduced emissions and costs at the same time.     

Screening of carbon sources for beta-glucosidase production by Aspergillus saccharolyticus

The fungus Aspergillus saccharolyticus was found to produce a culture broth rich in beta-glucosidase activity, an enzyme which plays an essential role for efficient and complete hydrolysis of lignocellulosic biomass. Direct application of fungal fermentation broths produced on-site in a biorefinery may be an integral part of a biorefinery for lowering the cost associated with the use of commercial enzymes for saccharification of biomass. Utilization of low value slip streams from the biorefinery as substrates for such an on-site enzyme production would be ideal to reduce costs. In order to understand which carbon sources that support growth and trigger A. saccharolyticus to produce beta-glucosidases, carbon sources, ranging from monomer sugars to complex lignocellulosic biomasses, including pretreated and hydrolyzed corn stover fractions, were investigated as substrates and inducers of enzyme production. A convenient micro titer plate experimental setup was developed that facilitated a fast screening for beta-glucosidase activity on the different carbon sources. The greatest beta-glucosidase activity was found when A. saccharolyticus was cultivated on media containing xylose, xylan, wheat bran, and pretreated corn stover. In a refinery, beta-glucosidase production by A. saccharolyticus could with success be based on the biomass hemicelluloses and their degradation products which cannot be converted by conventional yeast.     

Mixed Feedstock Approach to Lignocellulosic Ethanol Production—Prospects and Limitations

Lignocellulosic ethanol is a promising alternative to fossil-derived fuels because lignocellulosic biomass is abundant, cheap and its use is environmentally friendly. However, the high costs of feedstock supply and the expensive processing requirements of lignocellulosic biomass hinder the development of the lignocellulosic biorefinery. Lignocellulosic ethanol production so far, has been based mainly on single feedstocks while the use of mixed feedstocks has been poorly explored. Previous studies from alternative applications of mixed lignocellulosic biomass (MLB) have shown that their use can bring about significant cost savings when compared to single feedstocks. Although laboratory-scale evaluations have demonstrated that mixed feedstocks give comparable or even higher ethanol yields compared to single feedstocks, more empirical studies are needed to establish the possibility of achieving significant cost savings in terms of pre-biorefinery logistics. In this review, some potential benefits of the use of MLB for ethanol production are highlighted. Some anticipated limitations of this approach have been identified and ways to surmount them have been suggested. The outlook for ethanol production from MLB is promising provided that revolutionary measures are taken to ensure the sustainability of the industry.