碳基固体酸催化纤维素热解制备左旋葡聚糖和左旋葡萄糖酮

将纤维素快速热解转化为高价值的左旋葡聚糖和左旋葡萄糖酮是国内外研究热点之一。通过制备及表征碳基固体酸,并优化纤维素催化热解的实验条件,在350℃下,Fe₃O₄/C₇₀₀-H₃PO₄与纤维素以1∶3的比例混合,可以显著提高热解过程中左旋葡聚糖[40.7%（质量）]和左旋葡萄糖酮[13.5%（质量）]的产率,分别比纯纤维素热解提高了2倍和22倍。该研究对纤维素的定向高值化转化具有指导意义。     

左旋葡聚糖溶剂热转化为高值化学品的研究进展

木质纤维素热解是一种高效生物质利用途径,其衍生产物左旋葡聚糖(LGA)是纤维素热解产物中最主要的初级产物,其产率可高达80%,将LGA高效转化为其他平台化学品可实现其高值化利用。首先综述了纤维素热解制备LGA的研究进展,对比反应器类型和反应条件对LGA产率的影响,生物质预处理工艺将进一步提升工业化规模制备LGA。然后概述了LGA在不同条件下转化为左旋葡萄糖酮、葡萄糖和呋喃类化合物的最新研究进展。发现在LGA溶剂热催化转化为左旋葡萄糖酮的过程中,催化剂Br?nsted酸性位点及原位移除反应生成的水分有助于提升左旋葡萄糖酮的产率,最优条件下左旋葡萄糖酮的最大产率可接近60%,开发合适的催化剂及溶剂体系有助于进一步提高左旋葡萄糖酮产率。通过酸水解作用,LGA转化为葡萄糖的产率及选择性均可达近100%,且催化剂能够长时间稳定运行,该方法提供了一个由纤维素间接生产葡萄糖的方法。最后,总结了催化剂理化特性及溶剂条件对LGA生成呋喃类和酸酯类化合物的影响规律,发现葡萄糖间接转化机制可促进LGA高效转化为此类化学品。     

催化热解生物质生成左旋葡聚糖酮的研究进展

左旋葡聚糖酮（LGO）在有机合成领域有巨大的应用价值,快速热解生物质制取左旋葡聚糖酮是生物质能开发与利用的研究热点。目前LGO的应用主要受到其产量的限制：一是没有较好的化学合成方法,二是常规热解生物质得到的产物中左旋葡聚糖酮的含量极低,使得LGO难以大量生产。催化热解可以显著提高左旋葡聚糖酮的产率,目前用于催化热解生物质制取左旋葡聚糖酮的各类催化剂,包括液体酸、固体酸、金属氯化物、离子液体等均取得了一定的成果,但效果差异明显,因此分析了不同催化剂间的优势与劣势,并对以后的工作进行了展望。     

纤维素快速热解反应气体的在线催化裂解

通过浸渍法制备MHZSM-5(M Fe,Zr,Co)催化剂,采用激光粒度分析仪、比表面积及孔径分析仪和X射线衍射仪(XRD)对催化剂的性质进行表征,并在立式两段加热炉上进行纤维素快速热解蒸汽的在线催化实验。对不同催化剂条件下的产物分布特性及生物油组成特性进行分析,结果表明,随着催化剂的引入,液相产率从52.06%最大下降至23.63%,气相产率从42.39%最大提高至70.84%,CoHZSM-5对于热解蒸汽的催化气化效果最为明显;纤维素快速热解生物油中以1,6-脱水-β-D-吡喃葡萄糖(左旋葡聚糖)为主,引入催化剂对纤维素热解蒸汽进行在线催化重整后,产物中芳烃类物质显著增加,以FeHZSM-5和ZrHZSM-5效果最佳;HZSM-5催化下生物油中左旋葡聚糖的含量提高至63.78%;催化后热解油中乙酸及丙酸含量均减少,但降低幅度有限。综合催化剂对产率及组分的影响效果来看,FeHZSM-5和ZrHZSM-5对纤维素快速热解蒸汽的催化调控作用较为显著。     

基于离子液体再生的纤维素热解特性

利用离子液体1-丁基-3-甲基咪唑氯([Bmim]Cl)溶解PH-101微晶纤维素,通过不同的再生方法获得两种再生的纤维素,并利用XRD确定其结晶度,场发射扫描电镜(SEM)获得其形貌特征,热重(TG)分析表征其热稳定性.采用Py-GC/MS 对不同结晶度纤维素进行快速热解,并对热解挥发分进行在线分析,观察结晶度对纤维素热解特性的影响.研究表明左旋葡聚糖产率随结晶度降低而减少,而小分子产物随结晶度降低而增多.     

基于PY-GC/MS的生物质组分间相互作用的热解实验

为研究生物质三组分间热裂解过程中的相互作用,利用热裂解-气相色谱/质谱联用仪（PY-GC/MS）联用的方法,对纤维素、木聚糖（半纤维素的模化物）和木质素进行单独热裂解及两两组分混合热裂解实验。单组分实验结果表明,在热解温度600℃、热解时间10s条件下纤维素的热解产物主要以左旋葡聚糖为主,木聚糖以乙酸和糠醛为主,而木质素主要以酚类物质为主。组分混合热裂解实验结果表明,纤维素促进了木聚糖热裂解生成更多的乙酸和糠醛,而木聚糖和木质素对纤维素热解生成左旋葡聚糖具有强烈的抑制作用;纤维素和木聚糖的存在大大促进了木质素热裂解生成酚类物质,而木质素抑制了木聚糖热裂解生成乙酸和糠醛。此外,研究还发现混合组分热解的相互作用受到热解温度和停留时间的影响。     

四种金属氯化物对纤维素快速热解的影响(Ⅰ) Py-GC/MS实验

通过浸渍的方式在纤维素上负载了四种金属氯化物(KCl、CaCl2、FeCl3和ZnCl2),采用Py-GC/MS装置对其进行快速热解并对热解气在线分析,考察各金属氯化物及其负载量对纤维素热解产物的影响。结果表明,负载金属氯化物能够显著降低纤维素的热解温度,其中负载CaCl2和FeCl3会抑制纤维素热解形成挥发性产物,而负载KCl和ZnCl2则不会。纯纤维素快速热解主要得到了以左旋葡聚糖为主的脱水糖以及一定量的呋喃类产物,和以羟基乙醛为主的小分子醛酮类产物。负载金属氯化物后都抑制了左旋葡聚糖的生成,其中KCl和CaCl2主要促进了纤维素解聚后脱水形成呋喃类产物,以及吡喃环开裂形成醛、酮、酸等小分子产物;FeCl3和ZnCl2则主要是促进纤维素解聚后形成脱水糖以及呋喃类产物。     

基于苯甲酰化的纤维素热解过程中典型脱水糖的定量分析

在固定床中对纤维素进行低温热解实验,采用苯甲酰化的方法,对收集的3种典型的脱水糖进行了深入研究。实验结果表明,基于苯甲酰化的HPLC-UV检测方法是一种快速、有效的糖类物质检测分析方法,满足纤维素热解产物中脱水糖的定量分析研究。纤维二聚糖和纤维三聚糖主要是通过纤维素随机断链形成的,而并非来源于左旋葡聚糖的二次聚合反应。聚合度越高的脱水糖在热解过程中更倾向于进一步反应形成其他产物。     

基于苯甲酰化的纤维素热解过程中典型脱水糖的定量分析

在固定床中对纤维素进行低温热解实验,采用苯甲酰化的方法,对收集的3种典型的脱水糖进行了深入研究。实验结果表明,基于苯甲酰化的HPLC-UV检测方法是一种快速、有效的糖类物质检测分析方法,满足纤维素热解产物中脱水糖的定量分析研究。纤维二聚糖和纤维三聚糖主要是通过纤维素随机断链形成的,而并非来源于左旋葡聚糖的二次聚合反应。聚合度越高的脱水糖在热解过程中更倾向于进一步反应形成其他产物。     

利用固体磷酸催化热解纤维素制备左旋葡萄糖酮

以SBA-15为载体制备了固体磷酸,将其和纤维素机械混合后进行快速热解制备左旋葡萄糖酮（LGO）。通过Py-GC/MS（快速热解-气相色谱/质谱联用）实验,考察了催化热解温度、催化剂/纤维素比例对纤维素热解生成LGO以及其他产物的影响。实验结果表明,固体磷酸能够抑制纤维素热解形成左旋葡萄糖（LG）等产物,并大幅促进LGO的生成,从而高选择性地获得以LGO为主的热解产物。在热解温度为350℃以及催化剂/纤维素比例为1/1的条件下,可获得最高的LGO产率与相对含量,相对峰面积值高达68.6%。此外固体磷酸还能促进LG脱水形成LGO。     

Pyrolysis products of untreated and flame retardant-treated α-cellulose and levoglucosan

A typical gas chromatogram of the volatile pyrolysis products of untreated α-cellulose contains 39 peaks; however, mass spectral data indicate that at least 59 compounds, with molecular weights less than about 150, are present. A total of 37 compounds have been identified, 13 of which have not been previously reported. Most of the newly identified compounds contain a benzene ring, indicating that these compounds may be products of reactions between initial volatiles. A comparison of the products generated in the temperature range of 330°–440°C indicates that the formation of pyrolysis products is essential independent of temperature. Comparisons of the chromatograms obtained for untreated levoglucosan and cellulose indicate that most of the decomposition of cellulose probably forms levoglucosan which then decomposes to yield the observed pyrolysis products. In addition, the products of flame retardant-treated levoglucosan are essentially the same as those of cellulose with the same retardant treatment. This suggests that the retardants act on the levoglucosan formed in the decomposition of the cellulose rather than on the cellulose directly.     

Production of levoglucosan and glucose from pyrolysis of cellulosic materials

Vacuum pyrolysis of cellulose within the temperature range of 300–500°C provides a tar fraction containing mainly levoglucosan and glucose condensation products. It was found that pyrolysis proceeds at a much faster rate at the higher temperatures without detrimental effect on the yields. At 400°C the reaction was essentially complete within 3 min yielding a tar that contained 39% levoglucosan and, upon mild acid hydrolysis, gave 49% D-glucose. The yields could be further improved by washing or treatment of cellulosic substrates with acids. Cotton hydrocellulose provided up to 58% levoglucosan or 77% D-glucose. This is the highest yield determined by unequivocal methods. Commonly available cellulosic materials such as wood and newsprint give very poor yields of levoglucosan. However, the yields could be improved substantially by acid washing or prehydrolysis to the extent that pyrolysis of these substrates may become an attractive industrial process. The data in this report provide the technical basis for such a process and resolve the existing controversies on the reported yields.     

A study on the mechanism research on cellulose pyrolysis under catalysis of metallic salts

Experimental research on cellulose pyrolysis under catalysis of metallic salts was done on a thermobalance and a rapid pyrolysis system. Thermogravimetric analysis showed that K⁺ catalyzed the formation of active cellulose strongly and decreased the activation energy of cellulose pyrolysis. Experimental results indicated that K⁺ would promote the formation of char and restrain the production of bio-oil largely. Fe²⁺ had a similar catalysis effect on cellulose pyrolysis with K⁺. Fe²⁺ particularly catalyzed the formation of small molecule gaseous product while K⁺ the formation of char. The addition of K⁺ or Fe²⁺ resulted in a reduction of levoglucosan formation, and enhanced the production of hydroxyacetaldehyde and other small molecule components. Levoglucosan and hydroxyacetaldehyde were formed by the decomposition of active cellulose in a parallel mode. The secondary cracking of levoglucosan would also produce hydroxyacetaldehyde. A modified cellulose pyrolysis mechanism model was proposed based on the B-S model.     

生物质预处理技术及其对热解产物的影响综述

总结了国内外各种生物质预处理技术及其对热解产物的影响的研究现状,分析了不同预处理方法的优势及存在的问题,指出微波干燥预处理是一种快捷的生物质干燥方式;脱灰预处理能加快生物质热解速率,并实现糖类组分的富集;而烘焙预处理则能提高生物油的热值。同时介绍了一些新型生物质预处理技术,如离子液体预处理可以减少裂解反应时间,使生物质油产率得到提升;而水热预处理则能使生物油中糖含量（主要是左旋葡聚糖）显著增加。并指出了今后的研究方向为：努力提高各种预处理方法的效率并降低预处理技术的成本;进一步改善现有预处理方法甚至发现新的预处理方法;通过学科交叉探索新的物理化学生物预处理技术;期望原料的预处理可以增加生物油中某些有特殊价值物质的含量或同时得到具有较高利用价值的气液固热解产物。     

Value-added products from waste: Slow pyrolysis of used polyethylene-lined paper coffee cup waste

The objectives of this study were to examine how to recycle cup waste efficiently and effectively and to determine if cup waste can be converted into liquid, solid, and gas value-added products by slow pyrolysis. The characteristics and potential utilizations of the pyrolysis products were investigated. The study included the effects of temperature, heating rate, and different feedstocks. The yield of pyrolysis oil derived from cup waste increased from 42% at 400°C to 47% at 600°C, while the yield of char decreased from 26% at 400°C to approximately 20% at 600°C. Acetic acid and levoglucosan were identified as the main components of the pyrolysis oil. The char obtained at 500°C was physically activated at 900°C for 3 h with CO₂. The adsorption capacity of the activated char was investigated with model compounds, such as methyl orange, methylene blue, ibuprofen, and acetaminophen. The results showed that the adsorption capacity of the activated char was similar to that of commercial activated carbon produced from peat. The higher heating value of the produced gas stream calculated at 400°C was 19.59 MJ/Nm³. Also, conventional slow pyrolysis (CSP) and microwave-assisted pyrolysis (MAP) technologies were compared to determine the differences in terms of products yields, composition and characteristics of the pyrolysis oil, and their potential applications. The CSP yields higher liquid products than MAP. Also, the pyrolysis oil obtained from the CSP had significantly more levoglucosan and acetic acid compared to that of the MAP.     

Origin of furanic compounds in thermal degradation of cellulosic insulating paper

The chemical components of cellulosic insulation (i.e., Kraft paper, cellulose, lignin, pentosans) used in electrical transformers were aged in transformer oil to determine the relative yield of furanic degradation products. The results show that the pentosans component of the paper give, by far, the highest yield of 2-furfural followed by cellulose, levoglucosan, and lignin. However, the pentosans did not produce any detectable quantities of either 5-hydroxymethyl-2-furfuraldehyde or 2-furfurol, both of which are known to be produced by the degradation of Kraft paper. α-Cellulose was found to give 3 times as much 2-furfural as levoglucosan, which is a degradation product of cellulose, suggesting another pathway to 2-furfural production from cellulose than exclusively through the commonly quoted mechanism in which levoglucosan is the intermediate. It was also found that the production of 2-furfural from levoglucosan appears to be accelerated by acidic conditions in oxidized oil. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2541–2547, 1998     

Saccharification of douglas-fir wood by a combination of prehydrolysis and pyrolysis

A process has been investigated for the saccharification of wood, involving prehydrolysis, lignocellulose pyrolysis, and tar hydrolysis. In this process, ground wood was first prehydrolyzed to remove the more readily hydrolyzable hemicelluloses. The residual lignocellulose was then pyrolyzed rapidly to provide a tar containing levoglucosan and its condensation products. The tar was hydrolyzed to convert these products to glucose. Laboratory experiments have shown that this process can convert a common softwood such as Douglas-fir to 14% char and 42% hexoses. This amounts to a 59% recovery of the hexoses: 32% from prehydrolysis and 27% from pyrolysis. The prehydrolysis served not only to remove hemicelluloses, but also to increase the yield of glucose from pyrolysis and subsequent tar hydrolysis. It has been shown that this enhancement is due to the removal of inorganic ash and the catalytic effect of trace amounts of acid remaining in the lignocellulose.