煤和生物质共热解过程中半焦的作用机制研究

How to achieve directional conversion of H and O in order to obtained high yield and high quality pyrolysis oil during co-pyrolysis of coal and biomass is a challenging academic research topic. Char, one of the main intermediate product in pyrolysis reaction system, will undoubtedly plays an important role in the migration of the main elements and product distribution in the process of co-pyrolysis. However, seldom study had investigated the role of char during co-pyrolysis. In this project, the co-pyrolysis experiment of coal and biomass was carried out in a free fall reactor. The in situ char generated during co-pyrolysis is taken as the research object. The formation mechanism of char during co-pyrolysis was analyzed, and the relationship between the char reaction to its components, structure was clarified. Through studying product distribution and product properties of coal and biomass co-pyrolysis, the mechanism of char on the intermediate pyrolysis product in secondary reaction and on the directional migration of H and O were discussed. At last, electron paramagnetic resonance was applied to study the rule of free radical change during co-pyrolysis. The effect of char on the formation and transfer of free tadicals in secondary reaction processes was claried and then the formation mechanism of high quality tar was revealed. The project will provide a theoretical basis for building directional transformation theory and technology system for fast co-pyrolysis of coal and biomass to prepare oil.

在煤和生物质共热解过程中，如何实现H和O的定向转化获取高产率和高品质的热解油是极具挑战性的学术研究课题。半焦作为热解反应体系中的主要中间产物之一，其对共热解过程中主要元素的迁移和产品分布无疑具有重要作用。但目前鲜有研究将半焦作为煤和生物质共热解的研究主体。本项目拟在自由落下床开展生物质和煤的快速共热解实验，以煤和生物质共热解产生的原位半焦为主要研究对象，分析共热解过程中半焦的形成机制，阐明半焦反应性与其组分、结构的关系；研究煤和生物质共热解产物分布和产物性质，明确半焦对热解中间产物的二次反应的作用机理及其对H和O定向迁移的影响机制；借助电子顺磁共振波谱研究煤和生物质共热解过程中自由基变化规律，阐明半焦对二次反应过程中自由基形成、转移的影响，揭示煤和生物质共热解高品质焦油形成机理。本项目将为生物质和煤快速共热解制油的高效、定向转化的理论和技术体系的构建提供理论依据。

生物质是唯一可直接转换为清洁液体燃料的可再生资源，生物质与煤共热解制油技术的发展对于缓解我国能源危机、实现经济和社会的可持续发展具有重要意义。本项目通过开展不同工况条件下生物质和煤的热解/共热解实验，研究了生物质和煤的热解/共热解特性。通过跟踪气体、液体和固体产品的组成和结构的变化，结合元素分析、GC-MS、1H-NMR、FTIR等表征分析数据，揭示了热解工艺条件和热解产物之间的关系，阐明了共热解过程中半焦的作用机制。发现在生物质和煤在共热解过程中，随生物质混合比的增加，半焦产率减少，液体和气体产率增加。热解初始阶段，煤和生物质都裂解产生大量自由基，生物质作为外部氢源，起到了一定的供氢作用，有利于焦油产率的提高。较明显的协同效应发生在相对较高的生物质混合比条件下。同时考察了热解过程中产生的原位半焦对热解油生成和提质的作用，发现热解过程中半焦床层的存在有利于焦油产率的增加。在半焦-挥发分的相互作用过程中，半焦具有脱氧作用，同时能促进焦油中多环芳烃裂解，使所得焦油中氧含量降低，单环芳烃化合物含量增加，实现了热解油的提质。本项目将为煤和生物质共热解的规模化应用提供重要基础。