木质素氧化降解研究进展

木质素是当今世界上含量第二丰富的可再生高聚物.氧化降解是木质素价值增值过程中一种非常有前景的方法,它能提供高度官能化的单体和低聚物产品作为其他价值增值过程的起始原料,为代替化石燃料在化工和制药行业中的应用提供了一种可能.主要对木质素及其模型化合物的氧化改性方法进行了综述,包括生物催化、仿生催化、有机金属催化、电化学催化氧化及其他几种催化氧化法,并简单讨论了氧化降解过程的反应机理,为今后木质素的氧化价值增值研究提供一定的参考.     

木质素的结构研究与应用

木质素是自然界中最丰富的可再生芳香族聚合物,可制备生物燃料和高附加值化学品。在以石油为基础的现代能源与化工行业中,木质素作为替代原料展现出良好的应用前景。要实现木质素的利用,必须首先充分了解木质素的组成与结构特征。然而,由于木质素来源的多样化和结构的复杂性给了解木质素的组成结构带来巨大的困难。本文以揭示木质素的化学组成为出发点,分析比较了应用于木质素结构研究的分离提取、转化以及分析测试等方法与技术,重点阐述了木质素结构研究最新进展,包括木质素的组成单体及其连接方式、生物合成过程、模型化合物的反应和木质化理论体系等,概述了木质素及其衍生物在聚合物材料、树脂、炭纤维、活性炭和高附加值化学品制备等领域的应用,展望了木质素的结构研究与应用的发展方向并提出了需要解决的相关难点问题。     

丹参木质素及其单体含量的测定

本文建立了一种准确、快速的检测丹参中木质素及其单体含量的方法.采用Klason法和紫外分光光度法分别对丹参根和茎中酸不溶性木质素(Klason木质素)和酸溶性木质素含量进行了测定;运用硫代酸解法并结合气相色谱-质谱法(GC-MS)分别对丹参根和茎中各木质素单体组成进行了分析.结果显示,总木质素在丹参根和茎中的含量分别为...     

路易斯酸/硫醇体系在木质素降解中的应用

在Lewis酸AlCl_3和亲核试剂EtSH的协同作用下,实现了木质素模型化合物中C—O键的断裂及产物中C—S键的形成,生成硫功能化的芳香二硫缩醛单体和苯酚类化合物.我们成功地将该体系应用于氧化的松木木质素降解中,反应后,氧化松木木质素的相对分子质量明显下降.本文为木质素降解增值得到硫功能化芳香族化合物提供了一种可行的方法.     

微波辅助高效降解木质素转化酚类化合物的研究进展

木质素作为自然界中丰富的可再生芳香族聚合物,可用于生产高附价值的酚类化合物,木质素降解已引起了各界越来越广泛的兴趣,为了高效降解木质素以获得酚类化合物更高得率,各种技术被广泛运用在木质素降解的研究中,其中微波辅助高效降解技术因更具优势而备受关注,微波降解木质素具有环境友好、高效快速、节能省电、易控制、安全、选择性强等特点。为了解微波辅助高效降解木质素转化酚类化合物的现状,并预测未来发展方向,本文在综述其研究进展的基础上,着重回顾了微波辅助高效降解技术的机理、特点及优势,考察了微波辅助条件下不同催化剂高效降解木质素的效果,介绍了微波辅助高效降解与其他物质偶联降解木质素的方法以及效果,同时综述了降解产物的分离检测方法、特点以及优势与应用前景,最后以此为依据,展望微波辅助高效降解木质素转化绿色化学品研究的未来发展方向。     

催化一步转化木质素单体为苯酚:建立木质素到高附加值化学品的通道（英文）

木质素是地球上产量最大的芳香类有机高分子,其有效转化利用在近年来备受关注.催化降解木质素制备酚类单体在过去十年取得了长足进步,目前已开发出氢解、水解、热解、氧化、光解等一系列方法.通过加氢脱氧法可以将木质素的降解产物转化为烃类燃料,但该过程耗氢量大,并且芳香环在加氢气氛下被破坏.另一个可能的应用是将木质素衍生物进一步转化为高附加值的芳香族化合物,但解聚产物成分复杂,成为木质素高效转化为单一高附加值化学品的瓶颈.在加氢条件下,木质素解聚产物主要为酚类混合物,多在羟基临位带有一至两个甲氧基,并在对位带有C2或C3的取代基(多为烷基).针对这一结构特点,我们设计了新反应路径,通过分别去除甲氧基和烷基得到苯酚.该过程保留了苯酚的基本结构而将其他取代基去除,原理上可以有效的将木质素降解的混合物转化为单一产物苯酚.通过催化剂的筛选和优化,Pt/C催化剂对脱甲氧基显示出最好的活性和选择性,在400°C,常压下脱除效率80%.在流动气氛下连续工作4 h,Pt/C催化剂无失活迹象.H-ZSM-5为最有效的脱烷基催化剂,最优效率83%左右.H-ZSM-5在反应过程中逐渐失活.通过热重差热及红外光谱分析,失活主要原因为积碳.在400°C空气中煅烧后,催化剂可以再生.通过简单的物理混合,Pt/C和H-ZSM-5一步将木质素单体转化为60%的苯酚,显示了该方法直接转化木质素到高附加值苯酚的巨大潜力.这是同时将木质素中甲氧基、烷基选择性脱除的首例报道.经过估算,从原生木质素出发,通过加氢解聚,耦合本文开发的一步脱甲氧基、烷基路径,可将木质素转化为约25%的苯酚.木质素中的甲氧基、烷基将分别转化为甲醇和烯烃,提高了木质素碳资源的利用效率.     

钌碳耦合碱还原催化降解三倍体毛白杨

化石资源的过度消耗及因此产生的环境问题驱动了生物质资源各组分转化为燃料、化学品及材料的研究发展.木质素是自然界最丰富的可再生芳香碳氢资源,也是生物质中最难以实现高值化利用的组分.将木质素催化降解生成苯酚类单体化合物是其高值化利用的关键,因此开发新型催化体系对于提高当前生物精炼产业经济效益具有重要意义.本文利用钌碳耦合碱...     

木质素酶及其化学模拟的研究进展

木质素酶（包括木质素过氧化物酶和锰木质素过氧化物酶）及其模拟物对木质素的催化降解是绿色化学的一个重要研究课题。本文综述了近年来有关木质素酶的分子结构，活性中心结构、催化木质降解机理及模型物的研究进展。     

开环聚合接枝改性木质素

作为自然界储量丰富的生物质资源之一,木质素尚未得到充分利用,成为掣肘生物化工发展的挑战。利用木质素丰富的功能基团进行接枝聚合改性,已成为木质素高值化利用的一个重要途径。开环聚合是一种温和、高效的聚合方法,可以将脂肪族聚酯链段引入到木质素中,提高材料的溶解性、相容性和可降解性,拓展木质素的应用范围。本文关注多催化条件下丙交酯、己内酯等环状单体通过开环聚合对木质素进行接枝改性的研究进展,同时对木质素改性材料的性能、应用以及发展前景进行了探讨。     

麦草碱木质素的微波辅助液化降解

研究了微波辅助条件下液化剂、催化剂、反应温度和反应时间对麦草碱木质素进行液化降解制备生物油收率的影响,并利用红外光谱(FT-IR)、气相色谱质谱联用仪(GC-MS)和核磁共振氢谱(1H-NMR)对产物进行表征。结果表明,微波辅助下以甲醇为液化剂,硫酸铁为催化剂液化降解碱木质素可以显著缩短液化反应时间,在160℃相对较低液化温度下反应5 min,生物油的收率达到55.22%。液化降解后的木质素残渣结构变化少,表明木质素降解产物的重新聚合的几率低,碱木质素反应原料可以回收再利用以提高原料利用率。生物油主要为单酚类物质,其中,S型、G型和H型单体的含量分别为57.72%、25.28%和8.98%。核磁共振氢谱中β-O-4键和C-C键质子峰的存在说明生物油中含有部分的二聚体和低聚体酚类化合物。     

木质素:一种有潜力的生物质基催化剂来源

木质素是自然界中储量丰富的唯一含芳环生物质可再生资源,但复杂的结构使其难以高效利用,目前大部分被废弃。除通过氧化还原等过程可将其转化为石油化工产品的替代品外,木质素结构中丰富的含氧官能团及制浆过程引入的硫元素等均可提供有效位点,为其作为催化剂基质提供了丰富的可行性。本文从木质素资源的来源和结构分析出发,根据不同催化反应的机理和制备催化剂过程中的结构改性类型,综述了具有不同结构特征的木质素基催化剂分别在生物质平台化合物水解等酸碱催化反应、电催化反应和负载金属纳米粒子催化氧化还原反应等过程中的应用,讨论了木质素类型、制备或活化改性条件对催化材料性能的影响,也指出了当前木质素基催化剂的开发研究难点和未来发展方向。     

木质素活化及在木材胶粘剂中的应用进展

木质素是相对分子量较高的天然聚合物,由于具有苯酚结构利于制备木材胶粘剂,但是木质素本身反应活性低,一般都将其活化后再利用.而且,除了以往利用最多的造纸工业产生的木质素外,研究发现木材经过褐腐菌降解后残留主要成分是结构部分发生变化的木质素,这种可再生生物质资源以其自身的结构特点在合成胶粘剂上也有很大的优势,本文结合木质素胶粘剂应用中的问题,重点概述了活化木质素的各种方法及褐腐木质素在木材胶粘剂中的应用.     

Selectively transform lignin into value-added chemicals

Selective transformation of lignin into value-added chemicals is of strategic significance. Phenols, aldehydes, carboxylic acids, alkanes and arenes can be harvested from lignin with high selectivity under appropriate reaction condition.     

Chemical synthesis of beta-O-4 type artificial lignin

An artificial lignin polymer containing only the beta-O-4 substructure was synthesized. The procedure consists of two key steps: 1) polycondensation of a brominated monomer by aromatic Williamson reaction; and 2) subsequent reduction of the carbonyl polymer. 13C-NMR and HMQC spectra of the polymer were consistent with beta-O-4 substructures in milled wood lignin isolated from Japanese fir wood. The weight average degree of polymerization (DP(w)) ranged from 19.5 to 30.6, which is comparable to enzymatically synthesized artificial lignin from p-hydroxycinnamyl alcohols (dehydrogenation polymer, DHP) and some isolated lignins. Using this new lignin model polymer, it will now be possible to reinvestigate the properties and reactivity of the main lignin structure in terms of its polymeric character.     

Lignin: Applications and Ways of Utilization (Review)

The main applications and ways of utilization of industrial lignins, which are a large-tonnage waste from pulp and hydrolysis plants, are considered. The first group of methods includes nonthermal methods of lignin processing with preservation of the natural polymeric structure of lignin. The second group of methods includes thermal methods for lignin processing with the formation of low- and high-molecular-mass compounds and combustible gas. The largest-tonnage application fields of lignins are building, mining, metallurgical, oil-extracting, and agro industries, and also water treatment.     

Highly Selective Oxidation and Depolymerization of α,γ‐Diol‐Protected Lignin

Lignin oxidation offers a potential sustainable pathway to oxygenated aromatic molecules. However, current methods that use real lignin tend to have low selectivity and a yield that is limited by lignin degradation during its extraction. We developed stoichiometric and catalytic oxidation methods using 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) as oxidant/catalyst to selectively deprotect the acetal and oxidize the α‐OH into a ketone. The oxidized lignin was then depolymerized using a formic acid/sodium formate system to produce aromatic monomers with a 36 mol % (in the case of stoichiometric oxidation) and 31 mol % (in the case of catalytic oxidation) yield (based on the original Klason lignin). The selectivity to a single product reached 80 % (syringyl propane dione, and 10–13 % to guaiacyl propane dione). These high yields of monomers and unprecedented selectivity are attributed to the preservation of the lignin structure by the acetal.     

Research on solid-state fermentation on rice chaff with a microbial consortium

A microbial consortium of Trichoderma reesei AS3.3711, Aspergillus niger 3.316 and Saccharomyces cerevisiaes AS2.399 was constructed to decomposed rice chaff on the basis of the characters of each microorganism and the mechanism of cellulases. In this experiment, rice chaff was pretreated before fermentation with NaOH so that the lignin structure of rice chaff was degraded and hemicellulose was dissolved partly, which remove the protection of lignin and hemicellulose on cellulose and demolish its special crystal structure. After pretreatment, rice chaff can be degraded more easily with the microbial consortium. The optimal technical paths and technological methods were achieved for intenerating rice chaff with the microbial consortium perfectly through orthogonal experiment. According to the technological methods, some experiments were done at 30 degrees C with pH 4.5. It was found that the highest filter paper enzyme activity (FPA) was 5.64 U/g and the ratio of cellulose degradation (RCD) was 28.05%.     

Study of the Topological Structure of Bamboo <Emphasis Type="Italic">Bambusa</Emphasis> sp. Lignin Macromolecules

The topological structure of macromolecules of Pepper lignin isolated from bamboo stems is studied. The molecular properties of dilute lignin solutions in dimethylformamide are investigated by the methods of high-velocity sedimentation, translational diffusion, and viscometry. The molecular mass of fractions, the scaling coefficients of the Kuhn–Mark–Houwink equation, and the Tsvetkov–Klenin hydrodynamic invariant are determined. It is first shown that the lignin of bamboo stems belongs to the universal class of chaotically branched polymers, and the degree of branching of macromolecules is estimated.     

Evaluation and Characterization of Forage Sorghum as Feedstock for Fermentable Sugar Production

Sorghum is a tropical grass grown primarily in semiarid and drier parts of the world, especially areas too dry for corn. Sorghum production also leaves about 58 million tons of by-products composed mainly of cellulose, hemicellulose, and lignin. The low lignin content of some forage sorghums such as brown midrib makes them more digestible for ethanol production. Successful use of biomass for biofuel production depends on not only pretreatment methods and efficient processing conditions but also physical and chemical properties of the biomass. In this study, four varieties of forage sorghum (stems and leaves) were characterized and evaluated as feedstock for fermentable sugar production. Fourier transform infrared spectroscopy and X-ray diffraction were used to determine changes in structure and chemical composition of forage sorghum before and after pretreatment and the enzymatic hydrolysis process. Forage sorghums with a low syringyl/guaiacyl ratio in their lignin structure were easy to hydrolyze after pretreatment despite the initial lignin content. Enzymatic hydrolysis was also more effective for forage sorghums with a low crystallinity index and easily transformed crystalline cellulose to amorphous cellulose, despite initial cellulose content. Up to 72% hexose yield and 94% pentose yield were obtained using modified steam explosion with 2% sulfuric acid at 140 °C for 30 min and enzymatic hydrolysis with cellulase (15 filter per unit (FPU)/g cellulose) and β-glucosidase (50 cellobiose units (CBU)/g cellulose).     

The nature of lignin from steam explosion/enzymatic hydrolysis of softwood

Effective utilization of the lignin by-product is a prerequisite to the commercial viability of ethanol production from softwood wastes using a steam explosion (SE)/enzymatic hydrolysis (EH)/fermentation process. Changes in the chemical composition of Douglas fir wood on SO₂-catalyzed SE followed by EH were assessed using conventional analytical methods and new halogen-probetechniques. A significant solubilization of hemicelluloses was observed in the SE stage, the severity of which affected subsequent fermentation of cellulose and sorption of enzymes. SE of softwood resulted in dramatic changes in the chemical structure of lignin in the residual material involving chemical reactions via the benzyl cation. This leads to a more condensed lignin with partly blocked α-reaction centres. Possible uses for this lignin are discussed.