纤维素热解机理研究进展:以中间态纤维素为核心的纤维素演变

摘要

纤维素热解的机理研究对于生物质能的热利用至关重要,能够有效指导工业实际应用.基于著名的Broido-Shafizadeh模型,纤维素热解被分为两步,首先转变为活性的熔融态中间体(中间态纤维素),然后通过解聚和开环生成左旋葡聚糖、5-羟甲基糠醛、羟基乙醛等重要的化工原料.在这两步转变中,主要涉及低温段氢键网络的断裂、中间态纤维素的生成,以及高温段的解聚和吡喃环开环反应.本文从这3个部分对前人的研究进行了综述,着重介绍了中间态纤维素的生成和表征,综述了纤维素热解几个研究方向:结晶度和结晶形态对热解的影响、纤维素解聚反应方式、吡喃环开环方式等,详细阐述了二次反应对纤维素热解的影响,并提出了部分解决方案.关于纤维素热解依然存在诸多未知和争论,需要进一步的实验研究和理论计算对其进行揭示.%Research of cellulose pyrolysis mechanism is crucial for thermal utilization of biomass and provides guidance for industrial application.Based on the famous Broido-Shafizadeh model, the pyrolysis of cellulose is divided into two steps.First, cellulose turns into an active molten state named intermediate cellulose, and then subsequently generates levoglucosan, 5-hydroxymethylfurfural, glycolaldehyde and other valuable chemical feedstock.In the two steps, the collapse of hydrogen bonds network and the generation of intermediate cellulose at low temperature, the depolymerization reaction and ring cleavage are mainly involved.Focusing on these studies, this work reviews the effects of the degree of crystallinity and different crystallization morphology on cellulose pyrolysis, the depolymerization path of cellulose and the cleavage reaction of pyran rings, especially the generation and characterization of intermediate cellulose.It also introduces the effects of secondary reactions during pyrolysis in detail and proposes some solutions.There are still many unknown and debates on cellulose pyrolysis mechanism, and a deeper understanding of it through experiments and simulations is impending.