【作者】 范明慧；

【导师】 李全新；

【作者基本信息】 中国科学技术大学 ， 物理化学， 2014， 博士

【摘要】 木质素是木质纤维素生物质的主要成分之一。从分子角度看,木质素是一种无定型的、结构复杂的三维网状芳香类天然高聚物,它是自然界中唯一能提供大宗可再生芳香基化合物的天然资源。受环境保护和石油资源短缺压力的影响,如何将木质素高效利用已经成为研究热点课题之一。木质素通过催化转化可制备石化工业中重要的基础原料,如苯、甲苯、二甲苯、乙苯、异丙苯等高值芳香族化工产品,而目前这些芳香族化合物的生产几乎全部依赖石油或煤等不可再生资源。本论文探索研究了利用木质素催化转化制备高附加值的芳香族化合物,主要结果如下：1.木质素催化转化制取三苯的研究考察了不同孔径和酸度的HZSM-5、HY和MCM-22催化剂,优选了木质素催化裂解制备三苯BTX(苯、甲苯、二甲苯)的HZSM-5催化剂。同时详细研究了木质素催化裂解的反应过程及其反应条件影响(包括反应温度、载气流速、催化剂/木质素配比)。木质素催化裂解产物主要由苯、甲苯和二甲苯构成,不同反应条件对产物分布影响极大：BTX的选择性随着反应温度的升高而增加,但过高的反应温度也增强了二次裂解反应,使得大于600℃时BTX的产率明显下降；催化剂用量的增加有利于提高BTX的芳香选择性,但过量的催化剂使得木质素裂解油在催化剂上进一步裂解生成烷烃、烯烃类产物,从而降低了BTX的产率。实验表明,当裂解温度为550℃、载气流速为300ml/min.催化剂与木质素的质量配比等于2时,木质素催化裂解得到的BTX芳香选择性达到79.8C-mol%, BTX碳产率为25.3%C-mol%。详细分析了木质素热裂解和催化裂解过程,发现二者最大的区别在于：与热裂解相比,催化裂解过程得到的BTX收率明显增加。木质素热裂解主要是大分子聚合物解聚生成小分子含化氧合物；催化裂解过程主要分两步：一是通过热裂解过程形成大量中间含氧化合物,二是中间含氧化合物在催化剂上进一步经过脱羧基、脱羰基、脱水反应形成BTX或其他碳氢化合物。2.木质素催化转化制备乙苯研究以木质素为原料定向制备乙苯可为石化工业提供重要的基础产品。本论文通过木质素定向催化制苯与苯烷基化的有机耦合,探索研究了木质素定向催化转化制乙苯的反应过程。利用优选Re-Y/HZSM-5(25)复合催化剂,将木质素定向催化转化为苯,在优化的反应条件下获得了苯的选择性和产率分别为83.2C-mol%和22.7C-mol%；同时利用HZSM-5(25)催化剂和烷基化试剂乙醇进行烷基化反应制备乙苯,在烷基化温度350℃C、油醇比为1、载气(N2)流速为150ml/min的优化反应条件下,产物中乙苯的选择性达到62.5C-mol%;烷基化过程的副产物主要是二乙苯和甲苯。利用产物分析并结合催化剂表征,详细分析了木质素定向催化制苯与苯烷基化过程的反应通道。3.木质素催化转化制异丙苯初步研究利用苯和烷基化试剂(乙醇和异丙醇)作为木质素催化裂解模型化合物,初步研究了苯烷基化转化为异丙苯的反应过程。采用HZSM-5(50)催化剂和300℃C反应温度时,苯的转化率为27.5%,醇几乎完全转化,乙苯和异丙苯的选择性约为75.4C-mol%;提高反应温度显著增加了苯的转化率,同时也导致副产物(包括甲苯、二乙苯、正丙苯、丁苯)的大量形成；当烷基化温度低至280℃C时,有机产物中乙苯和异丙苯的总芳香选择性可达91.7C-mol%。初步探讨了苯烷基化转化为异丙苯的反应过程和机理。更多还原

【Abstract】 Lignin constitutes one of major components of lignocellulosic biomass. It was revealed that lignin is a three dimensional amorphous polymer and lignin is the only nature renewable resource which can provide large quantities of aromatic compounds. In the recent years, there is considerable interest in the production of chemicals and bio-fuels from lignin through pyrolysis, catalytic pyrolysis, hydrogenationm reduction, gasification, biochemical conversion and so on. Benzene, Toluene, and xylenes (BTX) together with ethylbenzene and cumene are are important aromatic platform compounds. By now the production of these aromatic platforms are based on non-renewable resources such as oil or coal. Our research is foucs on how to use lignin to produce high value-added aromatic compounds.1. Production of BTX through catalytic depolymerization of ligninIn present work, we investigated catalysts with different pore size and acidity. The transformation of lignin into benzene, toluene, and xylenes was studied over the HZSM-5, HY and MCM-22catalysts, and the HZSM-5catalyst showed the highest carbon yield of BTX. The reaction conditions strongly impacts the distribution of the products:The aromatic selectivities of BTX increased by rising the reaction temperature, but the BYX yield decreased when the reaction temperature reaches over600℃due to the second cracking of organics liquid. It was found that the BTX selectivity showed a positive dependence on the catalyst/lignin ratio, however, the BTX yield showed a slight decrease, which accounts for an increase in yield of gas products and a decrease in liquid yield.. The carbon yield of BTX reached about25.3C-mol%and the aromatic selectivities of BTX reached about79.8C-mol%over HZSM-5catalyst under T=550℃,f(N2)=300cm3min-1, and catalyst/lignin ratio of2. Catalyst plays an important role in the process of depolymerization and the ultimate organic liquid has a very low yield of BTX without the addition of catalyst The main components of lignin pyrolysis products are small molecular oxygen containing compounds. Formation of BTX through catalytic cracking of lignin proceeded through lignin depolymerizaton followed by the dehydration, decarboxylation and decarbonylation process. 2. Directional synthesis of ethylbenzene through catalytic transformation of ligninThis work explored the production of ethylbenzene from lignin through the directional catalytic depolymerization of lignin into the aromatic monomers followed by the selective alkylation of the aromatic monomers. For the first step, the aromatics selectivity of benzene derived from the catalytic depolymerizationof lignin over the composite catalyst of Re-Y/HZSM-5(25) at600℃. The lignin-derived oil contains83.2C-mol%benzene.For the alkylation of the aromatic monomers in the second step, the selectivity of ethylbenzene was about62.5C-mol%at T=35O℃, feed: EtOH=1:1(in mol ratio), WHSV=1.0.oover the HZSM-5(25) catalyst. The main by-products include di-ethylbenzene and toluene. Increase of benzene content in the reactants is useful to restrain the generation of diethylbenzene, and decrease the reaction temperature can effectively restrain the formation of toluene3. Exploration the production of cumene from ligninUse benzene, ethanol, isopropanol as model compounds to produce ethylbenzene and cumene. As the selective production of ethylene and propylene from bio-oil can be achieved, this study laid a foundation to future research——All raw materials derived from biomass. The aromatics selectivity of ethylbenzene and cumene reached about75.4C-mol%over HZSM-5(50) catalyst and the conversion of alcohols (ethanol and isopropano) in our test range near100%Rise the reaction temperature can largely enhance the conversion of benzene but can also increase the formation of by-products (toluene, diethylbenzene, propylbenzene). When alkylation temperature is280℃, the total aromatics selectivity of ethylbenzene and cumene can reach91.7C-mol%。This dissertation studies preliminarily the mechanism and reaction pathway of alkylation of benzene to cumene.更多还原