一步催化转化纤维素制备化学品的研究进展

高效利用纤维素制备燃料及化学品对人类的可持续发展具有重要的意义。通过化学转化,可以将纤维素转化为一系列的小分子有机物,作为平台化合物制取生物质基液体燃料或材料。本文综述了利用化学方法直接转化纤维素制备小分子化学品（5-羟甲基糠醛、乳酸、乙二醇、山梨醇和异山梨醇）的研究进展,并对后续研究进行了展望。     

纤维素催化氢解制取多元醇的研究进展

化石资源日益减少和使用化石资源带来的气候与环境问题促使人们将目光转向可再生的生物质资源。由生物质资源制备高附加值的化学品已成为国内外的研究热点。通过催化氢解将纤维素转化为多元醇化学品是一种可行的手段。本文总结了由纤维素氢解制备多元醇的最新研究进展,重点介绍了纤维素转化为山梨醇/甘露醇、异山梨醇和小分子多元醇（丙二醇和乙二醇）的催化剂体系以及可能的转化途径。最后分析了该领域存在的问题和今后的研究趋势。     

生物质到生物燃料—费托合成催化剂的研究进展

费托合成反应是煤、甲烷和生物质等非油基碳资源转化制高品质液体燃料或化学品的重要途径。以生物质基合成气为原料,利用传统的Fe、Co催化剂制备生物燃料引起普遍关注。本文简要总结了近年来高性能Fe基和Co基费托合成催化剂的发展,以及近年来新型材料和核壳结构的双功能催化剂在费托合成中的应用。重点关注了生物质合成气方面的应用,比较了Fe、Co催化剂在该应用中的特点。虽然Co基催化剂较Fe基催化剂有更好的活性,但在BTL（Biomass-To-Liquid）过程中需要考虑多种因素,Fe基催化剂可能更具优势,开发廉价高性能的Fe基催化剂可能成为BTL-FT催化剂的发展方向。     

生物质催化热裂解技术的研究进展

生物质催化裂解是生物质热化学转化的一种重要途径。综述了生物质催化热裂解技术使用的反应器、催化剂类型,以及催化热裂解过程中热裂解温度、吹扫气、升温速率、生物质原料等条件的影响,展望了生物质催化热裂解技术的发展趋势。     

半纤维素侧链降解酶——α-葡萄糖醛酸酶的研究进展

半纤维素是自然界中最丰富的可再生资源之一,将半纤维素降解为单糖并转化为燃料或化学品一直是科学界研究的热点。半纤维素是由木糖基主链以及α-葡萄糖醛酸等侧链共同组成的异质多聚体。α-葡萄糖醛酸酶是半纤维素完全降解过程中的关键酶之一,能够水解4-O-甲基葡萄糖醛酸与木糖之间的α-1,2-糖苷键。本文综述了α-葡萄糖醛酸酶的分类、催化机制及晶体结构、酶学性质和基因克隆表达等方面的研究进展,同时对该研究进行了展望。     

木质纤维素类生物质热解转化研究进展

综述了木质纤维素类生物质热解技术的研究进展,总结了不同生物质原料的热解机理,分析了产物的组成和性质,研究了产物的调控、改性和应用。指出未来的研究方向应该集中在以下几方面：技术改进,致力于改进生物质热解技术,提高能源转化效率和产物选择性;产品多样化,除了生物质热解产生的主要能源产品,如生物炭、生物油和生物气,还应着眼于开发高价值的化学品和材料,包括生物基化学品、特殊化学品和高性能材料;集成系统,应尝试将生物质热解与其他能源转化技术相结合,形成多能源联供系统,与生物质发酵、光催化、电解和储能等技术集成,以提高整体能源系统的效率和可持续性。     

响应面法优化生物质基固体酸催化剂的制备

以获取生物质基固体酸催化剂制备的最佳工艺条件为目的,利用生物质玉米秸秆为原料,设计碳化时间、碳化温度、磺化时间、磺化温度四因素三水平Box-Behnken试验,通过催化剂催化水解玉米秸秆所得还原糖得率进行表征,采用响应面法确定玉米秸秆碳基固体酸催化剂的最佳制备工艺。结果表明,实验数据建立的二次多项式数学模型显著性极高(P0.0001),相关系数R2=0.9981,预测值与实验值具有很好的拟合度。通过二次回归模型得到玉米秸秆基固体酸催化剂制备的最佳工艺条件为:碳化温度548.78℃、碳化时间13.67 h、磺化温度120.82℃、磺化时间6.83 h。在此条件下获得的生物质碳基固体酸催化剂催化水解玉米秸秆所得还原糖的得率为7.978%,预测值为7.983%,二者相差0.005%;比其他固体酸催化剂催化水解纤维素所得还原糖得率可提高65%,说明用此模型来优化玉米秸秆基固体酸催化剂的制备工艺是可行的。     

双相体系果糖催化转化为5-羟甲基糠醛研究

以水-1,4-二氧六环为双相体系,催化果糖制取5-羟甲基糠醛,研究催化剂种类、反应时间、反应温度、水相体积、原料与催化剂比例、催化剂循环使用等不同因素对果糖制取5-羟甲基糠醛的影响.结果表明:当采用NaHSO4为催化剂、反应温度为140℃、反应时间为1 h时,5-羟甲基糠醛产率达到最高值,为83％.进一步探究以葡萄糖、...     

超临界甲醇中复合金属氧化物催化木质纤维生物质转化为液体燃料：反应温度的影响

以类水滑石为前驱体,制备2种Cu基复合金属氧化物(CMO)催化剂。X射线衍射分析(XRD)显示,Ni的加入可降低CMO的结晶度,使得晶粒变小,有利于金属的分散。在超临界甲醇(sc-MeOH)介质中,考察2种催化剂对木质纤维生物质液化反应的催化性能。在无催化剂时,生物质液化的液体产物以酸类和呋喃类为主。加入催化剂后,产物以酮类和醇类为主,表明CMO可有效促进生物质催化液化转化为液体燃料。探讨反应温度对液化反应产物组成与分布的影响,结果显示甲醇的临界温度是生物质氢解的关键,当反应温度高于甲醇的临界温度(239℃)时,CMO能有效催化裂解甲醇,为生物质组分的氢解提供氢当量。温度越高甲醇裂解提供的氢当量越多,生物质液化产物中作为液体燃料的组分随温度的升高逐渐增加。     

1,3-二磺酸根咪唑四氯化铝盐催化葡萄糖脱水制备5-羟甲基糠醛

1,3-二磺酸根咪唑四氯化铝盐{[Dsim]AlCl₄}作为一种新型的磺酸根咪唑盐,同时具有布朗斯特酸和路易斯酸性质。本文合成了1,3-二磺酸根咪唑四氯化铝盐,并将其用于催化葡萄糖转化为5-羟甲基糠醛（5-HMF）的反应。研究表明：反应温度、反应时间和催化剂用量对催化葡萄糖转化为5-HMF这一反应起着重要的影响,提高反应温度能够缩短反应时间,进一步延长反应时间,5-HMF的产率反而减少。在最优化的条件下（140℃,30 min）,5-HMF的产率可达52.1%。此外,动力学分析揭示了{[Dsim]AlCl₄}在DMSO中催化葡萄糖转化为5-HMF的反应为二级反应,并计算出其活化能为138 kJ•mol^-1。本研究对咪唑金属盐催化转化葡萄糖制备5-HMF具有一定的指导意义。     

A new future for carbohydrate fuel cells

The development of renewable energy sources to reduce our dependence on limiting fossil fuel reserves continues to be a critical research initiative. Utilizing the abundant high energy content of carbohydrates contained in biomass (cellulose and hemicellulose) must be considered to be an important contribution to our overall energy budget. Carbohydrate-derived furan-based liquid fuels and especially ethanol are becoming important added components forming gasoline blends to lower overall fossil fuel use. Alternate renewable energy processes that more efficiently use the carbohydrate energy content are desirable and would lower the overall carbohydrate input requirement for energy production. Recently, new catalysts have shown the feasibility of efficiently transporting the 24 electrons in glucose to fuel cell electrodes making possible the direct conversion of the stored energy in carbohydrates into electricity with the benign formation of carbonate and water as products. The conversion of glycerol, a byproduct of biodiesel production, into three-carbon carbohydrates provides another opportunity to produce electricity from an abundant carbohydrate source. New developments in catalyst systems promise to make carbohydrate fuel cells an important part of future energy strategies.     

纤维素类碳水化合物转化为糠醛的研究进展

糠醛是一种用于制备高附加价值液体燃料和其他精细化学品的重要的生物质平台化合物。通常,木质纤维素中的半纤维素在水介质中经酸催化剂作用解聚得到五碳糖后进一步脱水可转化为糠醛,该工艺技术已趋于成熟并用于工业化生产。纤维素在水或一般的双相反应体系中解聚为六碳糖后脱水通常生成5-羟甲基糠醛与乙酰丙酸,而难以甚至不能转化为糠醛。最近的一些文献报道了纤维素类碳水化合物在特定的反应介质中经酸催化剂作用后可转化为糠醛,且提出了不同的反应历程。基于当前研究背景,本文针对纤维素类碳水化合物转化为糠醛的反应特点,综述了已有报道中纤维素类碳水化合物转化为糠醛的反应机理、反应路径和反应体系的特点及反应介质对该反应的影响。最后,对未来纤维素类碳水化合物转化为糠醛的研究方向和发展前景进行了展望。     

Enzymatic routes to hydrogen and organic acids production from banana waste fermentation by autochthonous bacteria: Optimization of pH and temperature

The Central Composite Rotational Design (CCRD) was employed to find the optimum pH (5.09–7.91) and temperature (27.1–46,9 °C) for hydrogen production in banana waste (BW) fermentation by autochthonous microbial biomass. The P and Rm ranged between 6.06 and 62.43 mL H₂ and 1.13–12.56 mL H₂.h^?1, respectively. The temperature 37 °C and pH 7.0 were the optimum conditions for P (70.19 mL H₂) and Rm (12.43 mL H₂.h^?1) as predicted by the mathematical model. Fructose and glucose are the primary alternative carbon sources in banana waste-fed batch reactors. The high concentration of lactic acid and H₂ production was associated to Lactobacillus (52–81%) and Clostridium (14–35%). However, the most important finding was about butyric acid (HBu). This acid is the better indicator of hydrogen production than acetic acid (HAc). The pH effected carbohydrates fermentation and organic acids production. The genes encoding the enzymes related to galactose, sucrose, fructose, arabinose and xylose metabolism were predominant.     

Chemical composition and response to dilute-acid pretreatment and enzymatic saccharification of alfalfa,reed canarygrass,and switchgrass

Alfalfa stems, reed canarygrass, and switchgrass; perennial herbaceous species that have potential as biomass energy crops in temperate regions; were evaluated for their bioconversion potential as energy crops. Each forage species was harvested at two or three maturity stages and analyzed for carbohydrates, lignin, protein, lipid, organic acids, and mineral composition. The biomass samples were also evaluated for sugar yields following pretreatment with dilute sulfuric followed by enzymatic saccharification using a commercial cellulase preparation. Total carbohydrate content of the plants varied from 518 to 655 g kg⁻¹ dry matter (DM) and cellulose concentration from 209 to 322 g kg⁻¹ DM. Carbohydrate and lignin contents were lower for samples from early maturity samples compared to samples from late maturity harvests. Several important trends were observed in regards to the efficiency of sugar recovery following treatments with dilute acid and cellulase. First, a significant amount of the available carbohydrates were in the form of soluble sugars and storage carbohydrates (4.3–16.3% wt/wt). Recovery of soluble sugars following dilute acid pretreatment was problematic, especially that of fructose. Fructose was found to be extremely labile to the dilute acid pretreatments. Second, the efficiency at which available glucose was recovered was inversely correlated to maturity and lignin content. However, total glucose yields were higher for the later maturities because of higher cellulose contents compared to the earlier maturity samples. Finally, cell wall polysaccharides, as determined by the widely applied detergent fiber system were found to be inaccurate. The detergent fiber method consistently over-estimated cellulose and hemicellulose and underestimated lignin by substantial amounts.     

Solid acid mediated hydrolysis of biomass for producing biofuels

Solid acid catalysts, which have favorable characteristics such as efficient activity, high selectivity, long catalyst life and ease in recovery and reuse, have great potential for efficiently transforming lignocellulosic biomass into biofuels and can replace many conventional liquid acids for hydrolysis and pretreatment. This work briefly introduces conventional biomass pretreatment and hydrolysis techniques, and reviews in detail the characteristics of biomass hydrolysis for five types of solid acid catalysts grouped as H-form zeolites, transition-metal oxides, cation-exchange resins, supported solid acids and heteropoly compounds. Carbonaceous solid acid (CSA) catalysts are considered as the most promising catalyst for cellulose hydrolysis, since they provide good access of reactants to the acidic sites of SO₃H groups. High glucose yields of up to 75% with 80% selectivity have been achieved at 150 °C for 24 h with CSA. However, separation of CSA from un-hydrolyzed cellulose residues after hydrolysis needs further research since these catalysts have similar physical and chemical properties to the residues. Use of functionalized CSA catalysts that contain paramagnetic groups is one method to improve CSA separation and reuse. Suggestions are given for promoting catalytic efficiency for each kind of solid acid catalysts. Methods to promote reactions or increase selectivities such as microwave, ultrasonication and nanotechnology are introduced. Finally, we highlight a recent strategy that exploits acid-functionalized paramagnetic nanoparticles suitable for cellulose hydrolysis, and address new opportunities for the use of solid acid catalysts.     

Second generation biofuels: Thermochemistry of glucose and fructose

The energetic conversion of biomass into syngas or biogas is a more and more important topic. In the framework of these studies, improved understanding of glucose and fructose thermal decomposition and oxidation appears crucial. For this task, thermodynamic data are needed to make possible, for instance, the building of a detailed chemical kinetic model of glucose and fructose reactivity at high temperature. A semitheoretical protocol, presented elsewhere, is used for the estimation of the thermodynamic data of glucose and fructose in the gas phase. Five isomers of glucose and five isomers of fructose are considered and the lowest-energy conformers are found to be β-d-glucopyranose for glucose and β-d-fructopyranose for fructose. The data for all 10 isomers are provided in the CHEMKIN-NASA format.     

Multi-scale complexities of solid acid catalysts in the catalytic fast pyrolysis of biomass for bio-oil production – A review

Despite remarkable progress in catalytic fast pyrolysis, bio-oil production is far from commercialization because of multi-scale challenges, and major constraints lie with catalysts. This review aims to introduce major constraints of acid catalysts and simultaneously to find out possible solutions for the production of fuel-grade bio-oil in biomass catalytic fast pyrolysis. The catalytic activities of several materials which act as acid catalysts and the impacts of Bronsted and Lewis acid site on the formation of aromatic hydrocarbons are discussed. Considering the complexity of catalytic fast pyrolysis of biomass with acid catalysts, in-depth understandings of cracking, deoxygenation, carbon-carbon coupling, and aromatization for both in-situ and ex-situ configurations are emphasized. The limitation of diffusion along with coke formation, active site poisoning, thermal/hydrothermal deactivation, sintering, and low aromatics in bio-oil are process complexities with solid acid catalysts. The economic viability of large-scale bio-oil production demands progress in catalyst modification or/and developing new catalysts. The potential of different catalyst modification strategies for an adequate amount of acid sites and pore size confinement is discussed. By critically evaluating the challenges and potential of catalyst modification techniques, multi-functional catalysts may be an effective approach for selective conversion of biomass to bio-oil and chemicals through catalytic fast pyrolysis. This review offers a scientific reference for the research and development of catalytic fast pyrolysis of biomass.     

Nickel hydroxide deposited indium tin oxide electrodes as electrocatalysts for direct oxidation of carbohydrates in alkaline medium

In this work, the direct electrochemical oxidation of carbohydrates using nickel hydroxide modified indium tin oxide (ITO) electrodes in alkaline medium is demonstrated; suggesting the feasibility of using carbohydrates as a novel fuel in alkaline fuel cells applications. The chosen monosaccharides are namely glucose and fructose; disaccharides such as sucrose and lactose; and sugar acid like ascorbic acid for this study. ITO electrodes are chemically modified using a hexagonal lyotropic liquid crystalline phase template electrodeposition of nickel. Structural morphology, growth, orientation and electrochemical behaviour of Ni deposits are characterized using SEM, XRD, XPS and cyclic voltammetry (CV), respectively. Further electrochemical potential cycling process in alkaline medium is employed to convert these Ni deposits into corresponding nickel hydroxide modified electrodes. These electrodes are used as novel platform to perform the electrocatalytic oxidation of various carbohydrates in alkaline medium. It was found that bare and Ni coated ITO electrodes are inactive towards carbohydrates oxidation. The heterogeneous rate constant values are determined and calculated to be two orders of magnitude higher in the case of template method when compared to non-template technique. The observed effect is attributed to the synergistic effect of higher surface area of these deposits and catalytic ability of Ni(II)/Ni(III) redox couple.     

Influence of impregnation with lactic acid on sugar yields from steam pretreatment of sugarcane bagasse and spruce, for bioethanol production

Lignocellulosic biomass can be utilized to produce ethanol, a promising alternative energy source produced through fermentation of sugars. However, in order to achieve high sugar and ethanol yields, the lignocellulosic material must be pretreated before the enzymatic hydrolysis and fermentation. Dilute acid pretreatment, using SO₂, is one of the most promising methods of pretreatment for softwood and agricultural residues. However, handling the high acidity of the slurry obtained from pretreatment and difficulty in recycling/degradation of the impregnating agent are some of the drawbacks of the dilute acid processes. In the present study the influence of utilization of a weak organic acid (lactic acid), as impregnating agent, on the sugar yield from pretreatment, with and without addition of SO₂, was investigated. The efficiency of pretreatment was assessed by enzymatic hydrolysis of the slurry obtained by pretreatment, using sugarcane bagasse and spruce, stored for one and two months in the presence of lactic acid separately, as feedstocks. Pretreatment of bagasse after storage with 0.5% lactic acid resulted in an overall glucose yield, i.e. after enzymatic hydrolysis, of 79% of theoretical based on the amount available in the raw material. This was as good as pretreatment using SO₂ as impregnating agent. However, storage of spruce with lactic acid before pretreatment, with and without addition of SO₂, was not efficient and resulted in lower sugar yields than pretreatment using SO₂ only.