木质素催化解聚的研究进展

木质素是一种芳环结构来源丰富且价格低廉的可再生资源。从木质素出发催化解聚制备单酚类高附加值精细化学品和芳香烃烷烃等高品位生物燃料,可以部分替代以化石燃料为原料的生产过程,是生物质资源全组分高效综合利用的重要组成部分。在木质素催化解聚方法中,催化氢解可以直接将木质素转化为低氧含量的液体燃料,在生物燃料利用方面展现出巨大的潜力。本文详细总结了木质素的催化解聚方法,从催化剂类型、溶剂种类、反应机理及催化剂循环使用性等方面介绍了国内外的主要研究进展,着重阐述了木质素催化氢解方法。最后总结了当前木质素催化解聚过程中存在的难题,并对未来的技术发展提出了建议和展望。     

化学法降解木质素为酚类化合物的研究进展

木质素是一种具有潜在巨大应用前景的可再生资源,其降解的酚类化合物产物是可替代部分仅依靠石油能源为主要来源的化工原料,故可缓解一定的石油能源压力。主要从化学法降解木质素的方法和防止降解物重聚两个角度综述木质素降解的研究现状,总结木质素降解存在的主要问题及对其未来的发展提出了展望。     

Study on the catalytic degradation of sodium lignosulfonate to aromatic aldehydes over nano-CuO: Process optimization and reaction kinetics

As one of the few renewable aromatic resources, the research of depolymerization of lignin into high-value chemicals has attracted extensive attention in recent years. Catalytic wet aerobic oxidation (CWAO) is an effective technology to convert lignin like sodium lignosulfonate (SL), a lignin derivative, into aromatic aldehydes such as vanillin and syringaldehyde. However, how to improve the yield of aromatic aldehyde and conversion efficiency is still a challenge, and many operating conditions that significantly affect the yield of these aromatic compounds have rarely been investigated systematically. In this work, we adopted the stirred tank reactor (STR) for the CWAO process with nano-CuO as catalyst to achieve the conversion of SL into vanillin and syringaldehyde. The effect of operating conditions including reaction time, oxygen partial pressure, reaction temperature, SL concentration, rotational speed, catalyst amount, and NaOH concentration on the yield of single phenolic compound was systematically investigated. The results revealed that all these operating conditions exhibit a significant effect on the aromatic aldehyde yield. Therefore, they should be regulated in an optimal value to obtain high yield of these aldehydes. More importantly, the reaction kinetics of the lignin oxidation was explored. This work could provide basic data for the optimization and design of industrial operation of lignin oxidation.     

木质素氢解反应溶剂与催化剂研究进展

木质素是由三种苯丙烷单元随机键合形成的复杂大分子物质,是自然界中唯一可直接提供芳环的可再生能源。以木质素为原料制取高品位液体燃料和高附加值化学品,特别是木质素氢解是国内外关注的热门研究领域之一。梳理了近年木质素催化氢解研究进展,针对木质素氢解过程中溶剂体系（水溶剂以及醇类溶剂）和催化剂体系（均相催化剂以及非均相金属催化剂）对木质素氢解效率、产物分布的影响机理,做了较全面的概述和分析。最后,针对木质素催化氢解领域目前尚存在的问题提出建议,期望为木质素高值化利用相关研究提供参考。     

Energetic analysis of gasification of biomass by partial oxidation in supercritical water

Partial oxidation gasification in supercritical water could produce fuel gases (such as H2, CO and CH4) and signif-icantly reduce the energy consumption. In this work, an energetic model was developed ...     

生物质超临界水部分氧化气化的能量过程分析(英文)

Partial oxidation gasification in supercritical water could produce fuel gases (such as H2, CO and CH4) and signif-icantly reduce the energy consumption. In this work, an energetic model was developed to analyze the partial oxidative gasification of biomass (glucose and lignin) in supercritical water and the related key factors on which gasification under autothermal condition depended upon. The results indicated that the oxidant equiva-lent ratio (ER) should be over 0.3 as the concern about energy balance but less than 0.6 as the concern about fuel gas production. Feedstocks such as glucose and lignin also had different energy recovery efficiency. For ma-terials which can be efficiently gasified, the partial oxidation might be a way for energy based on the combustion of fuel gases. Aromatic materials such as lignin and coal are more potential since partial oxidation could produce similar amount of fuel gases as direct gasification and offer additional energy. Energy recovered pays a key role to achieve an autothermal process. Keeping heat exchanger efficiency above 80%and heat transfer coefficient below 15 kJ·s?1 is necessary to maintain the autothermal status. The results also indicated that the biomass loading should be above 15%but under 20%for an autothermal gasification, since the increase of biomass loading could improve the energy supplied but decrease the efficiency of gasification and gaseous yields. In general, some specific conditions exist among different materials.     

木质素制备生物液体燃料进展

木质素中含有丰富的芳环结构,可以作为可持续再生的原料用于生产高值能源及化工品。但由于木质素结构复杂,现阶段用于制备生物液体燃料仍处于探索阶段。本文首先介绍了木质素通过催化热解、催化氢解、催化氧化3种解聚方式制备生物液体燃料的进展,分析了当前解聚产物存在低碳原子数、高氧含量的不足而导致其难以投入生产使用的现状,指出应通过C—C偶联方法（包括羟醛缩合、烷基化反应、寡聚反应以及Diels-Alder 反应）增加产物碳原子数、使用加氢脱氧（hydrodeoxygenation, HDO）工艺以降低产物氧含量,从而实现由木质素制备高密度生物液体燃料。最后对当前木质素制备高密度燃料所面临的挑战以及未来研究趋势进行了总结与展望,指出构建高效催化体系,耦合解聚、C—C偶联和HDO过程,将是该领域未来研究重点。     

木质素的催化加氢转化

木质素是来源于木质纤维素的一种重要的可再生生物质资源,可用于制备化学品和燃料。由于木质素本身结构的复杂性和稳定性使其难以有效利用。目前大量的制浆和造纸工业的木质素没有得到有效利用,大部分用于燃烧供能,并且造成了一定程度的环境污染。为了保护环境、实现可持续发展,催化转化木质素制备高附加值化学品成为了研究的热点。木质素转化的研究众多,但是进展依然相对缓慢。目前主要的转化方法包括碱催化解聚、酸催化解聚、热化学转化、加氢处理解聚、氧化解聚等。由于加氢处理解聚木质素可以获得低聚木质素、酚类等有价值的化学品和制备烃类燃料,是目前研究的热点和最有效的方法之一。但是,催化剂失活和解聚产物产率不高等依然是需要进一步解决的问题。基于此,梳理了近年来木质素加氢处理主要的催化体系和相关结果,提出了尚待解决的问题,以期为今后建立有效的木质素解聚体系并实现其高值化利用的相关研究提供参考。     

Alkaline Partial Wet Oxidation of Lignin for the Production of Carboxylic Acids

The production of carboxylic acids by partial wet oxidation of alkali lignin was studied experimentally. The factors influencing the different types of products, their yields and concentrations were investigated. Formic, acetic, succinic, oxalic, and glutaconic acid were the main identified products. Both the temperature and oxygen partial pressure are shown to have direct effects on the product yields whereas the lignin concentration has an indirect effect. At low lignin concentrations, the yield of products was relatively high. However, at higher concentrations, the yield decreased. By measuring the lignin molecular weight distributions, it is shown that this decrease is linked to repolymerization/condensation reactions of lignin fragments which compete with oxidative lignin depolymerization.     

木质素解聚和液相催化降解研究进展

木质纤维生物质作为地球上最丰富的可再生资源, 不仅储量巨大而且在利用过程中具有碳平衡的显著优势, 已逐渐成为最具发展前景的可再生能源之一。木质纤维中的木质素是自然界最大且唯一的可再生芳香族化合物原料, 在生物质燃料转化, 尤其是解聚生产苯系化工产品等领域具有极为重要的作用和意义。本文在简述木质素化学结构的基础上, 综述了近年来木质素高温热解聚, 生物酶解聚, 催化热解聚, 光催化解聚和溶剂热解聚等解聚方法, 深入分析了液相催化过程中酸、碱催化体系, 加氢和氧化催化体系的机理及优缺点, 总结了现阶段木质素解聚方法中存在的问题, 并对未来的发展方向进行了展望。     

Hydrotreating and hydrothermal treatment of alkaline lignin as technological valorization options for future biorefinery concepts: a review

Lignin has the potential to be a sustainable resource for producing biobased chemicals (e.g. phenols, aromatic hydrocarbons, vanillin) for multiple applications. However, given its heterogeneous and rigid structure, its efficient conversion to value‐added products remains one of the most important limiting factors for the successful viability of the biobased economy. Hydrotreating and hydrothermal treatment (including liquefaction, gasification and wet oxidation) are promising technologies that can convert lignin into biobased products. This review article provides a literature overview of how key process parameters of hydrotreating and hydrothermal treatment (operating conditions, catalysts, solvents, type of starting lignin) may influence the conversion of alkaline lignin into valuable chemical products. It was observed that low selectivity to products (and subsequent required separation and purification) and char formation are the main hurdles for effective conversion of alkaline lignin. However, experimental work in alternative catalytic systems, solvents and hydrogen sources has shown that promising opportunities exist to overcome these drawbacks. Certain catalysts (e.g. Ru/Al₂O₃) have been found to improve selectivity and the use of alcohol solvents (especially methanol or ethanol) as a hydrogen source has been found to improve product yields and reduce char formation at lower working temperatures and pressures. © 2016 Society of Chemical Industry     

木质素光催化氧化的产物分析及机理浅析

使用GC(气相色谱)-MS(质谱)联用仪对木质素光催化氧化的产物进行分析,从中检出了香兰素、愈创木基丙酮、愈创木基乙酸、1-羟基-3-愈创木基丙酮等具有较高价值的化合物。在木质素的光催化氧化降解反应中,氧化降解和交联并存,两者是一对竞争反应。木质素的氧化可以经愈创木基丙酮和1-羟基-3-愈创木基丙酮、愈创木基乙醇、愈创木基乙酸而获得香兰素,然后继续氧化成分子量更小的化合物,直至变成水和CO2。愈创木基乙醇的氧化是氧化过程的控制反应。氧化与交联的并存,使得反应过程中木质素的平均分子量呈现出先增大后减小的趋势,相应地分子量分布是先变窄后变宽,而峰值分子量则持续增加。同时交联反应的存在也降低了木质素氧化生成小分子产物的效率,而且反应时间越长,小分子化合物产率越低。     

Integrated chemo- and biocatalytic processes: a new fashion toward renewable chemicals production from lignocellulosic biomass

Concerns over climate change and environmental pollution resulting from petroleum refining has spurred the exploitation of green replacements for producing chemicals and fuels. Valorization of lignocellulosic biomass into chemicals represents a promising alternative to petroleum refining. Biological and chemical catalysis are two leading routes for lignocellulose variolization, but strategies relying simply on biological or chemical conversion have shown limitations. Integrating biocatalysts with chemocatalysts could leverage the inherent strengths of both while circumventing their respective disadvantages, benefiting product yield and selectivity, and reducing cost and waste generation. This review focuses on the coupled chemocatalytic and biocatalytic synthesis of renewable chemicals from polysaccharides and their derived platform chemicals. In addition, strategies for producing value-added products from lignin via integrated chemical depolymerization and biological conversion are highlighted. The techno-economics of integrating chemocatalysts and biocatalysts in producing chemicals in the context of biorefinery are also discussed. Finally, perspectives on designing integrated chemical and biological catalysis for renewable chemicals production are provided. © 2022 Society of Chemical Industry (SCI).     

Non-catalytic conversion of wheat straw,walnut shell and almond shell into hydrogen rich gas in supercritical water media

Agricultural wastes as lignocellulosic biomasses are known as the major resources of bioenergy. These valuable resources can be converted into useful environmental friendly fuels and chemicals. Wheat straw, walnut shell and almond shell are the main agricultural wastes in Kurdistan province, Iran. This study investigates the hydrogen-rich gas production via gasification of these biomasses in supercritical water media. Experiments were performed first, in the base case condition using a stainless steel batch micro reactor system. Then, the effect of reaction time on the total gas yield and yield of hydrogen, were investigated. It was seen that the total gas yields and gasification efficiencies increased by increasing the reaction time to 30 min and then the total gas yield was approximately remained constant. Among three used feed stocks, wheat straw with higher amount of cellulose and lower amount of lignin had the highest total gas and hydrogen yields in shorter reaction times. The maximum hydrogen yields of 7.25, 4.1 and 4.63 mmol per gram of wheat straw, almond shell and walnut shell occurred at 10, 15 and 20 min of reaction time, respectively.     

Effect of cellulose, lignin, alkali and alkaline earth metallic species on biomass pyrolysis and gasification

Fundamental pyrolysis/gasification characteristics of natural biomass and acid-washed biomass without alkali and alkaline earth metals (AAEM) were investigated by a thermogravimetric analyzer (TGA) and a fixed-bed reactor. In these experiments, six types of biomass were used and the contents of cellulose, lignin and AAEM species in the biomass were measured. It was observed that the characteristic of biomass pyrolysis and gasification was dependent on its components and AAEM species on the basis of TGA experiments. During biomass pyrolysis, the tar and gas yields increased with the growth of cellulose content, but the char yield decreased. There were two reactions indicating two major decomposition mechanisms. The first stage of decomposition showed rapid mass decrease due to the volatilization of cellulose, while the second stage became slow attributed to the lignin decomposition. The higher the cellulose content, the faster the pyrolysis rate. In contrast, the pyrolysis rate of biomass with higher lignin content became slower. In addition, the rises of cellulose content elevated the peak temperature of gasification and prolonged the gasification time. Meanwhile, the effect of AAEM species on gasification behavior was studied by comparing unwashed and acid-washed biomass. AAEM species increased the peak gasification value, whereas decreased initial gasification temperature. It revealed that the activity of biomass gasification was attributed to the interaction between AAEM-cellulose/lignin.     

Coal liquefaction in lignin-derived liquids under low severity conditions

It is found that lignin-derived liquids when reacted with coal under mild reaction conditions (375 °C and 2.17 × 10⁶ − 3.55 × 10⁶ N m⁻¹) enhance the rate of coal depolymerization. Up to 30% enhancement in coal conversion rate is achieved using lignin-derived liquids. The influence of time of reaction and temperature on the degree of reaction was investigated. The lignin liquid-assisted coal depolymerization products (liquid) are observed to contain a significant amount of the desirable pentane-soluble fraction. Influence of the time of storage of lignin-derived liquids on coal conversion was also determined. Also reported are data on elemental analyses of the solid and liquid products. The liquid product analyses using n.m.r. and s.e.c. techniques are also presented. Based upon the experimental data collected, it is hypothesized that enhancement in coal depolymerization rate can be explained by a reaction pathway involving intermediates formed from lignin-derived lignin liquids. A mathematical model describing the reaction chemistry has been developed. Computed rate constants are also reported. The analysis indicates that the lignin-derived intermediates are short-lived as compared to the time needed for complete coal depolymerization.     

Phenol-enriched hydroxy depolymerized lignin by microwave alkali catalysis to prepare high-adhesive biomass composites

Lignin, a by-product produced during pulping and papermaking, is a phenol-rich compound with excellent prospect to be used as a substitute for phenol in phenolic resin adhesive. Phenol-enriched hydroxy depolymerized lignin by microwave alkali catalysis is an effective method to prepare high-adhesive biomass composite. This study investigated the microwave digestion of lignin under different conditions of the alkali catalysis (sodium hydroxide) concentration, power, reaction time, and reaction temperature. The results show that on the condition of sodium hydroxide concentration of 0.3 mol/L, temperature of 170 °C, and time of 20 min, the highest phenolic hydroxy content obtained by depolymerization of lignin is 21.68%. SEM shows that the depolymerized lignin has no original basic constituent units and lignin-based phenolic resin has dense uniform pine needle units. Therefore, it has a high bonding strength of 1.934 MPa. The bonding strength and phenol content obtained by the microwave depolymerization method are much higher than those of other modification methods.     

Elucidation of the interaction among cellulose,xylan, and lignin in steam gasification of woody biomass

The reaction mechanism for gas and tar evolution in the steam gasification of cellulose, lignin, xylan, and real biomass (pulverized eucalyptus) was investigated with a continuous cross‐flow moving bed type differential reactor, in which tar and gases can be fractionated according to reaction time. In the steam gasification of real biomass, the evolution rates of water‐soluble tar (derived from cellulose and hemicelluloses) and water‐insoluble tar (derived from lignin) decrease with increasing reaction time. It was found that the evolution of water‐soluble tar occurs earlier than in the gasification of pure cellulose, indicating an interaction of the three components. The predicted yield of water‐insoluble tar is substantially less than that of real biomass. This implies that the evolution of tar from the lignin component of biomass is enhanced, compared with pure lignin gasification, by other components. The gas evolution rate from real biomass is similar to that predicted by the superposition of cellulose, lignin, and xylan. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

Characteristics of lignin from flax shives as affected by extraction conditions

Lignin, a polyphenolic molecule, is a major constituent of flax shives. This polyphenolic molecular structure renders lignin a potential source of a variety of commercially viable products such as fine chemicals. This work compares the performance of different lignin isolation methods. Lignin from flax shive was isolated using both conventional alkaline extraction method and a novel experimental pressurized low polarity water (PLPW) extraction process. The lignin yields and chemical composition of the lignin fractions were determined. The conventional alkali treatment with 1.25 M NaOH, heated at 80 °C for 5 h, extracted 92 g lignin per kg flax shives, while lignin yields from the PLPW extracts ranged from 27 to 241 g lignin per kg flax shives. The purity and monomeric composition of the lignins obtained from the different extraction conditions was assessed via UV spectroscopy and alkaline nitrobenzene oxidation. Lignin obtained from conventional alkali treatment with 1.25 M NaOH, heated at 80 °C for 5 h was of low purity and exhibited the lowest yields of nitrobenzene oxidation products. With respect to alkali assisted PLPW extractions, temperature created an opposing effect on lignin yield and nitrobenzene oxidation products. More lignin was extracted as temperature increased, yet the yield of nitrobenzene oxidation products decreased. The low yield of nitrobenzene oxidation products may be attributed to either the formation of condensed structures or the selective dissolution of condensed structures of lignin during the pressurized alkaline high temperature treatment. Analytical pyrolysis, using pyroprobe GC-MS, was used to investigate the molecular composition of the lignin samples. The total yield of pyrolysis lignin products was 13.3, 64.7, and 30.5% for the 1.25 M NaOH extracted lignin, alkaline assisted PLPW extracted lignin, and the unprocessed flax shives, respectively. Key lignin derived compounds such as guaiacol, 4-vinyl guaiacol, 4-methyl guaiacol, syringol, eugenol, isoeugenol, catechol, homocatechol, and vanillin were detected in all of the samples.     

Study on Lignin–Glyoxal Reaction by MALDI-TOF and CP-MAS 13C-NMR

Abstract

Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) mass spectrometry was used to elucidate lignin–glyoxal reactions. The reaction of glyoxal with a low molecular weight lignin involves a number of different reactions; in particular lignin depolymerization and recombination through condensation reactions with glyoxal to form glyoxalene bridges linking both lignin units and mainly fractions of lignin units derived from degradation during depolymerization. The reactive hydroxyglyoxalated lignin is the one species still available for co-reaction for use in wood adhesives. The reactions described increase the viscosity of the lignin as the reaction proceeds towards higher molecular mass species and the condensed species grow in relative proportions. NMR analysis confirmed the existence of functional groups pertaining to structures that are formed from glyoxalation of the lignin observed by some results obtained by MALDI-TOF. MALDI-TOF mass spectrometry appears to be a suitable method for examining lignin–glyoxal reactions.