Advances and Developments in Strategies to Improve Strains of <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> and Processes to Obtain the Lignocellulosic Ethanol−A Review

The conversion of biomass into ethanol using fast, cheap, and efficient methodologies to disintegrate and hydrolyse the lignocellulosic biomass is the major challenge of the production of the second-generation ethanol. This revision describes the most relevant advances on the conversion process of lignocellulose materials into ethanol, development of new xylose-fermenting strains of Saccharomyces cerevisiae using classical and modern genetic tools and strategies, elucidation of the expression of some complex industrial phenotypes, tolerance mechanisms of S. cerevisiae to lignocellulosic inhibitors, monitoring and strategies to improve fermentation processes. In the last decade, numerous engineered pentose-fermenting yeasts have been developed using molecular biology tools. The increase in the tolerance of S. cerevisiae to inhibitors is still an important issue to be exploited. As the industrial systems of ethanol production operate under non-sterile conditions, microbial subpopulations are generated, depending on the operational conditions and the levels of contaminants. Among the most critical requirements for production of the second-generation ethanol is the reduction in the levels of toxic by-products of the lignocellulosic hydrolysates and the production of low-cost and efficient cellulosic enzymes. A number of procedures have been established for the conversion of lignocellulosic materials into ethanol, but none of them are completely satisfactory when process time, costs, and efficiency are considered.     

Pretreatment of lignocellulosic agricultural waste for delignification,rapid hydrolysis,and enhanced biogas production: A review

Lignocellulosic biomass can play a pivotal role in achieving the goal of sustainable development of a predominantly agrarian country like India. The abundant availability of lignocellulosic materials makes it more suitable to go for the energization of this waste material. Lignocellulosic agriculture waste is essentially renewable and carbon-neutral source of energy. It has the potential to minimize greenhouse gas emissions by adopting proper biomass to energy conversion routes like biochemical conversion to mitigate climate change. Pretreatment of lignocellulosic biomass is a compulsory step for delignification before hydrolysis and subsequent AD or fermentation process to facilitate enhanced biofuel (biogas/bioethanol) generation. The most studied pretreatment methods of lignocellulosic agricultural biomass in the past 10 years including acid, alkali, ionic liquid, microwave, ultrasonication, steam explosion, liquid hot water, ammonia-based, biological, and electrohydrolysis pretreatments methods are discussed in this review paper. The criteria to measure pretreatment efficiency, different pretreatment processes parameters, and their pros and cons are also discussed. The alkaline pretreatment method is most promising in the delignification of lignocellulosic agricultural biomass residues like rice straw. This review may impart help to the prospective researchers in understanding rubrics of different pretreatment processes for further research work in the area of pretreatment.     

New methods of heterogeneous catalysis for lignocellulosic biomass conversion to chemicals

This review deals with the use of solid catalysts for the enhancement of the efficiency and the development of a new generation of environmentally friendly, energy and resource efficient processes for the deep processing of lignocellulosic biomass to desired chemicals. The oxidative delignification of wood with hydrogen peroxide in the presence of the suspended TiO₂ catalyst, the oxidation of wood with molecular oxygen in the presence of copper catalysts, the acidcatalyzed conversion of cellulose to glucose and levulinic acid, and the thermal conversion of lignin to fuel additives on solid acid catalysts are analyzed. New integrated processes based on the heterogeneous catalytic oxidation are suitable for the complex processing of lignocellulosic biomass to produce valuable chemicals and engine fuel components without the use of toxic and corrosion-active reagents.     

纤维素制取乙醇技术

以纤维素为原料生产燃料乙醇由于其原料来源广泛及环保效益良好而被认为是最有前景的生产燃料乙醇的方法之一。以纤维素为原料生产乙醇主要包括水解和发酵两个转化过程。本文介绍了纤维素生产燃料乙醇的原理及工艺过程,同时讨论了各工艺过程需要解决的关键技术问题,分析了过程的经济性,最后介绍了国内外的应用现状,展望了纤维素生产燃料乙醇的产业化前景。     

纤维素制取乙醇技术

以纤维素为原料生产燃料乙醇由于其原料来源广泛及环保效益良好而被认为是最有前景的生产燃料乙醇的方法之一.以纤维素为原料生产乙醇主要包括水解和发酵两个转化过程.本文介绍了纤维素生产燃料乙醇的原理及工艺过程,同时讨论了各工艺过程需要解决的关键技术问题,分析了过程的经济性,最后介绍了国内外的应用现状,展望了纤维素生产燃料乙醇的产业化前景.     

Environmentally friendly fuel briquettes and pellets based on renewable lignocellulosic raw material and recycling thereof

This paper presents data regarding developments in the field of renewable energy sources based on lignocellulosic raw material, which can continuously provide a wide range of energy services. Data regarding reserves of nonhydrocarbon raw materials are presented: Russian forests represent 25% of the world timber reserves (perennial lignocellulosic materials), while fields and croplands represent 9% of the annual plants growing in the world. Processing of renewable lignocellulosic raw materials and biomass into fuel pellets and briquettes is capable of providing reliable supply of heating, electricity, and transport energy without green-house gas emissions and affecting the climate (in compliance with the Kyoto Protocol). The features of catalytic biomass gasification, which can be used to design the combined processes of biomass processing with simultaneous obtaining of fuel gas or synthesis gas, as well as nanoporous carbon materials, are discussed.     

碳纳米管担载纳米Ir催化生物质基乙酰丙酸合成γ-戊内酯

以碳纳米管(CNTs)担载Ir纳米粒子为催化剂进行生物质基平台化合物乙酰丙酸(LA)选择加氢制备γ-戊内酯(GVL)的研究,并利用X射线衍射、X射线光电子能谱和透射电镜表征了使用前后的Ir/CNT催化剂,探讨了影响LA催化加氢制GVL反应性能的因素和该反应的可能路径.结果表明,与Ru,Rh和Pd等传统铂族金属相比,Ir/CNT催化剂不但可在温和条件下(50℃,2.0 MPa,H₂)实现LA至GVL的完全转化,且可对多类直接源于生物质水解的含等量LA/甲酸的“真实”体系实现GVL的高效选择合成.     

An economic and environmental comparison of a biochemical and a thermochemical lignocellulosic ethanol conversion processes

With the world’s focus on rapidly deploying second generation biofuels technologies, there exists today a good deal of interest in how yields, economics, and environmental impacts of the various conversion processes of lignocellulosic biomass to transportation fuels compare. Although there is a good deal of information regarding these conversion processes, this information is typically very difficult to use on a comparison basis because different underlying assumptions, such as feedstock costs, plant size, co-product credits or assumed state of technology, have been utilized. In this study, a rigorous comparison of different biomass to transportation fuels conversion processes was performed with standard underlying economic and environmental assumptions so that exact comparisons can be made. This study looked at promising second-generation conversion processes utilizing biochemical and thermochemical gasification technologies on both a current and an achievable state of technology in 2012. The fundamental finding of this study is that although the biochemical and thermochemical processes to ethanol analyzed have their individual strengths and weaknesses, the two processes have very comparable yields, economics, and environmental impacts. Hence, this study concludes that based on this analysis there is not a distinct economic or environmental impact difference between biochemical and thermochemical gasification processes for second generation ethanol production.     

Protection Strategies Enable Selective Conversion of Biomass

Selective and economic conversion of lignocellulosic biomass components to bio‐based fuels and chemicals is the major goal of biorefineries, but low yields and selectivity for fuel precursors such as sugars, furanics, and lignin‐derived monomers pose significant disadvantages in process economics. In this Minireview we summarize the existing protection strategies used in biomass chemocatalytic conversion processes and focus the discussions on the mechanisms, challenges, and opportunities of each strategy. We introduce a concept of using analogous methods to manipulate biomass catalytic conversion pathways during the upgrading of carbohydrates to fuels and chemicals. This Minireview may provide new insights into the development of selective biorefining processes from a different perspective, expanding the options for selective conversion of biomass to fuels and chemicals.     

Fungal glycoside hydrolases for saccharification of lignocellulose: outlook for new discoveries fueled by genomics and functional studies

Genome sequencing of a variety of fungi is a major initiative currently supported by the Department of Energy’s Joint Genome Institute. Encoded within the genomes of many fungi are upwards of 200+ enzymes called glycoside hydrolases (GHs). GHs are known for their ability to hydrolyze the polysaccharide components of lignocellulosic biomass. Production of ethanol and “next generation” biofuels from lignocellulosic biomass represents a sustainable route to biofuels production. However, this process has to become more economical before large scale operations are put into place. Identifying and characterizing GHs with improved properties for biomass degradation is a key factor for the development of cost effective processes to convert biomass to fuels and chemicals. With the recent explosion in the number of GH encoding genes discovered by fungal genome sequencing projects, it has become apparent that improvements in GH gene annotation processes have to be developed. This will enable more informed and efficient decision making with regard to selection and utilization of these important enzymes in bioprocess that produce fuels and chemicals from lignocellulosic feedstocks.     

The study of model systems subjected to sub- and supercritical water hydrolysis for the production of fermentable sugars

Bioenergy obtained from lignocellulosic biomass is considered the most efficient way to achieve sustainable development in the future. However, there still are challenges in the cellulose conversion to hexoses, which could be used as raw material for the bioenergy production. Sub- and supercritical water hydrolysis have been researched as emergent technologies to obtain simple sugars from lignocellulosic biomass; however, the reaction pathways and kinetics of the hydrolysis of cellulose into oligomers and monomers, and their degradation under sub- and supercritical conditions, are not completely understood yet. Thus, this review provides an overview of the state-of-the-art on hydrolysis with sub- and supercritical water of model systems, cellulose and starch, in the context of elucidating the reaction pathways and kinetic behavior of the biomass hydrolysis to produce suitable fermentation substrates for the production of second generation bioethanol and other biofuels.     

Determination of Organic Group Parameters: (AOCI,AOBr, AOS) in Water by Means of Ion-Chromatographic Detection. Pyrohydrolysis and Absorption

Abstract

In recent years methods have been developed to determine organic halogen at the μg/1 level in water samples by adsorbing these compounds on active carbon and by detecting the inorganic halides formed after conversion of the adsorbates by pyrohydrolysis. Applying these techniques the analysis of the so-called group parameter “Adsorbable Organic Halogen (AOX)” is performed.

The distinction of each of the halogens in the group parameter AOX and the determination of the parameter “adsorbable organic sulfur compounds (AOS)” can be realized using ion-chromatography for the detection of the anions, obtained after pyrohydrolysis of the adsorbed organic compounds.

Further investigations have shown good adsorption capacity of a newly developed nearly chlorine- and sulfur-free active carbon for organic model substances. This report presents the examinations concerning pyrohydrolysis of the organic solutes and absorption of the formed inorganic species.

The conditions for complete conversion of the model substances and high recovery rates in inorganic anions have been proved successfully. The optimization of the pyrohydrolysis apparatus and of the combustion conditions have been performed and proved with good results.     

Mathematical modeling of cellulose conversion to ethanol by the simultaneous saccharification and fermentation process

Ethanol, a promising alternative fuel, can be produced by the simultaneous saccharification and fermentation (SSF) of lignocellulosic biomass, which combines the enzymatic hydrolysis of cellulose to glucose and the fermentation of glucose to ethanol by yeast in a single step.

A mathematical model that depicts the kinetics of SSF has been developed based on considerations of the quality of the substrate and enzyme, and the substrate-enzyme-microorganism interactions. Critical experimentation has been performed in conjunction with multiresponse nonlinear regression analysis to determine key model parameters regarding cell growth and ethanol production. The model will be used for rational SSF optimization and scale-up.

     

Cellulosic Ethanol Production Using Waste Wheat Stillage after Microwave-Assisted Hydrotropic Pretreatment

One of the key elements influencing the efficiency of cellulosic ethanol production is the effective pretreatment of lignocellulosic biomass. The aim of the study was to evaluate the effect of microwave-assisted pretreatment of wheat stillage in the presence of sodium cumene sulphonate (NaCS) hydrotrope used for the production of second-generation bioethanol. As a result of microwave pretreatment, the composition of the wheat stillage biomass changed significantly when compared with the raw material used, before treatment. Microwave-assisted pretreatment with NaCS effectively reduced the lignin content and hemicellulose, making cellulose the dominant component of biomass, which accounted for 42.91 ± 0.10%. In post pretreatment, changes in biomass composition were also visible on FTIR spectra. The peaks of functional groups and bonds characteristic of lignins (C–O vibration in the syringyl ring, asymmetric bending in CH₃, and aromatic skeleton C–C stretching) decreased. The pretreatment of the analyzed lignocellulosic raw material with NaCS resulted in the complete conversion of glucose to ethanol after 48 h of the process, with yield (in relation to the theoretical one) of above 91%. The highest observed concentration of ethanol, 23.57 ± 0.10 g/L, indicated the high effectiveness of the method used for the pretreatment of wheat stillage that did not require additional nutrient supplementation.     

Chemical Activation of Lignocellulosic Precursors and Residues: What Else to Consider?

This paper provides the basis for understanding the preparation and properties of an old, but advanced material: activated carbon. The activated carbons discussed herein are obtained from “green” precursors: biomass residues. Accordingly, the present study starts analyzing the components of biomass residues, such as cellulose, hemicellulose, and lignin, and the features that make them suitable raw materials for preparing activated carbons. The physicochemical transformations of these components during their heat treatment that lead to the development of a carbonized material, a biochar, are also considered. The influence of the chemical activation experimental conditions on the yield and porosity development of the final activated carbons are revised as well, and compared with those for physical activation, highlighting the physicochemical interactions between the activating agents and the lignocellulosic components. This review incorporates a comprehensive discussion about the surface chemistry that can be developed as a result of chemical activation and compiles some results related to the mechanical properties and conformation of activated carbons, scarcely analyzed in most published papers. Finally, economic, and environmental issues involved in the large-scale preparation of activated carbons by chemical activation of lignocellulosic precursors are commented on as well.     

The Role Played by Ionic Liquids in Carbohydrates Conversion into 5-Hydroxymethylfurfural: A Recent Overview

Obtaining industrially relevant products from abundant, cheap, renewable, and low-impacting sources such as lignocellulosic biomass, is a key step in reducing consumption of raw fossil materials and, consequently, the environmental footprint of such processes. In this regard, a molecule that is similar to 5-hydroxymethylfurfural (5-HMF) plays a pivotal role, since it can be produced from lignocellulosic biomass and gives synthetic access to a broad range of industrially important products and polymers. Recently, ionic liquids (ILs) have emerged as suitable solvents for the conversion of biomass and carbohydrates into 5-HMF. Herein, we provide a bird’s-eye view on recent achievements about the use of ILs for the obtainment of 5-HMF, covering works that were published over the last five years. In particular, we first examine reactions involving homogeneous catalysis as well as task-specific ionic liquids. Then, an overview of the literature addressing the use of heterogeneous catalysts, including enzymes, is presented. Whenever possible, the role of ILs and catalysts driving the formation of 5-HMF is discussed, also comparing with the same reactions that are performed in conventional solvents.     

Nanoengineered ligninolytic enzymes for sustainable lignocellulose biorefinery

Lignin is a key structural component of lignocellulosic biomass with immense potential to replace non-renewable and environmentally unfriendly fossil resources. Structural recalcitrance, heterogeneity, and multifaceted composition of lignin are the major impediments to its gainful biotransformation to a spectrum of bio-based products, biomaterials, and specialty chemicals. In contrast to physicochemical methods, harnessing the biocatalytic potential of the robust ligninolytic armory is considered a greener and more sustainable way for lignin biorefinery. Immobilization of ligninolytic enzymes on different nanoengineered support matrices resulted in designing nanobiocatalytic system with intensified catalytic performance and long-term stability for efficient lignocellulosic biomass valorization. Enzyme incorporation on magnetic nanostructures additionally facilitates facile separation, recovery, and reusability of magnetic nanobiocatalysts. Therefore, developing and implementing immobilized ligninolytic enzyme-based nanoengineered biocatalytic systems constitutes a prodigious and eco-sustainable option to catalyze the deconstruction of lignocellulosic biomass. The multi-enzyme nano-biocatalytic system offers the advantage of direct substrate conversion into the product in a single step owing to its concurrent biocatalytic attributes. This opinion article spotlights current achievements and state-of-the-art developments in engineering ligninolytic enzymes to create a novel biocatalytic system to create greener and sustainable lignocellulose biorefineries ranging from the production of biomaterials to bioenergy.     

凝结相中功能性碳材料和碳纳米复合物催化转化生物质制备可再生化学品(英文)

The production of chemicals from lignocellulosic biomass provides opportunities to synthesize chemicals with new functionalities and grow a more sustainable chemical industry. However, new challenges emerge as research transitions from petrochemistry to biorenewable chemistry. Compared to petrochemisty, the selective conversion of biomass-derived carbohydrates requires most catalytic reactions to take place at low temperatures ( 300 °C) and in the condensed phase to prevent reactants and products from degrading. The stability of heterogeneous catalysts in liquid water above the normal boiling point represents one of the major challenges to overcome. Herein, we review some of the latest advances in the field with an emphasis on the role of carbon materials and carbon nanohybrids in addressing this challenge.     

Potential of Mangrove-Associated Endophytic Fungi for Production of Carbohydrolases with High Saccharification Efficiency

The endophytic fungi represent a potential source of microorganisms for enzyme production. However, there have been only few studies exploiting their potential for the production of enzymes of industrial interest, such as the (hemi)cellulolytic enzymatic cocktail required in the hydrolysis of lignocellulosic biomass. Here, a collection of endophytic fungi isolated from mangrove tropical forests was evaluated for the production of carbohydrolases and performance on the hydrolysis of cellulose. For that, 41 endophytic strains were initially screened using a plate assay containing crystalline cellulose as the sole carbon source and the selected strains were cultivated under solid-state fermentation for endoglucanase, β-glucosidase, and xylanase enzyme quantification. The hydrolysis of a cellulosic material with the enzymes from endophytic strains of the Aspergillus genus resulted in glucose and conversion values more than twofold higher than the reference strains (Aspergillus niger F12 and Trichoderma reesei Rut-C30). Particularly, the enzymes from strains A. niger 56 (3) and A. awamori 82 (4) showed a distinguished saccharification performance, reaching cellulose conversion values of about 35% after 24 h. Linking hydrolysis performance to the screening steps played an important role towards finding potential fungal strains for producing enzymatic cocktails with high saccharification efficiency. These results indicate the potential of mangrove-associated endophytic fungi for production of carbohydrolases with efficient performance in the hydrolysis of biomass, thus contributing to the implementation of future biorefineries.     

生物质半纤维素稀酸水解反应*

半纤维素是木质纤维素类生物质中第二大组分,半纤维素的高效、低成本转化是实现木质纤维素类生物质转化工艺实用化的一个技术关键。稀酸水解技术被广泛应用于水解生物质半纤维素,其对半纤维素糖的转化率高,得到的糖可进一步发酵生产燃料乙醇等。半纤维素还可直接水解制低聚糖等功能性食品和糠醛等化工产品。本文综述了半纤维素稀酸水解反应的研究进展。介绍了半纤维素的基本结构特征,解析了稀酸催化半纤维素水解的反应机理及反应网络,评述了半纤维素水解过程中反应条件等对目标产物的影响,并总结了半纤维素稀酸水解动力学模型。在此基础上,对今后半纤维素稀酸水解反应的研究方向与水解产物的利用进行了展望。