【作者】 李向科；

【导师】 吕惠生；

【作者基本信息】 天津大学 ， 化学工艺， 2007， 硕士

【摘要】 在煤炭、石油、天然气等化石资源日趋枯竭的今天,纤维素作为一种主要的生物质资源,越来越受到人们的重视。乙酰丙酸用途广泛,被誉为“绿色平台化合物”。本课题以亚临界H₂O-CO₂体系为反应介质,考察了纤维素降解制备乙酰丙酸的工艺条件,建立了乙酰丙酸的高效液相色谱（HPLC）定量分析方法,研究了反应速率与产物收率的关系,并结合纤维素热裂解反应,探讨了亚临界H₂O-CO₂体系中纤维素制备乙酰丙酸的反应机理。本研究以纤维素降解制备乙酰丙酸的质量收率为目标,确定了亚临界H₂O-CO₂体系中纤维素降解制备乙酰丙酸的适宜工艺条件:纤维素与水投料的质量比为1:0.0135,反应温度为290℃,CO₂加入量为7.5%,反应压力17.2MPa,反应时间为15min,乙酰丙酸的质量收率为34.99%,达到理论质量收率的49%。研究中用N₂代替CO₂考察了反应压力对实验的影响。实验结果表明:增大反应压力有助于乙酰丙酸收率的提高;亚临界水中加入CO₂一方面增大了反应压力,另一方面也提高了体系的酸性,从而促进了纤维素的降解,提高了乙酰丙酸的收率。通过对纤维素热裂解产物与水热降解产物的GC-MS定性分析得出:纤维素的水热降解是一个包括水解、热裂解和脱水等多种反应的复杂过程。反应可以分为以下几个阶段:纤维素→1,6-脱水-β-D-吡喃葡萄糖→5-羟甲基糠醛→乙酰丙酸。对乙酰丙酸生成过程的反应机理进行分析后,得出了亚临界H₂O-CO₂体系中纤维素降解的反应网络图。反应速率的研究结果表明:在温度250℃～310℃、CO₂加入量7.5%、压力17.2MPa的实验条件下,反应可以认为是一级反应,表观活化能Ea为141.52kJ/mol,指前因子A为3.73×10¹¹min^-1,反应速率与产物收率关联式为:更多还原

【Abstract】 Nowadays, the fossil resource is severely exhausted. The biomass is a kind of renewable resource, and is being studied by more and more people. The decomposition of cellulose, which is the largest kind of biomass, to levulinic acid which is called“green platform chemical”is going to be studied in this paper.In this study, subcritical H₂O-CO₂ system was used as the reaction media. The technologcial conditions for preparation of levulinic acid were studied. The quantitative analysis method of levulinic acid by HPLC was established. The relationship between reaction rate and product yield was studied. Combined with the pyrolysis of cellulose, the mechanism of cellulose hydrothermal decomposition was discussed.The mass yield of levulinic acid was used as the research target. The optimum technologcial conditions were determined: mass feed ratio of water and cellulose 1:0.0135, temperature 290℃, CO₂ molar fraction 7.5%, pressure 17.2MPa and time 15min. Under above conditions, the mass yield of levulinic acid was up to 34.99%, and accounted for 49% of theory mass yield （71.4%）.Another experiment was set by substituting N₂ for CO₂. And the results showed that high pressure was helpful for the improvement of mass yield of levulinic acid. The addition of CO₂ to subcritical water could increase the pressure; on the other hand, it could enhance the acidity of the system. This promoted the decomposition of cellulose, and improved the mass yield of levulinic acid.Through the qualitative analysis of products in cellulose pyrolysis and hydrothermal decomposition by GC-MS, it could be concluded that the hydrothermal decomposition of cellulose was a complex process which included hydrolysis, pyrolysis, dehydration, and so on. The reaction contains several stages: cellulose→levoglucosan→5-hydroxymethyl-furaldehyde→levulinic acid. After the mechanism for the preparation of levulinic acid was analyzed, the networks for the decomposition of cellulose under subcritical H₂O-CO₂ conditions werre obtained.The research of reaction rate showed that the system was a first-order reaction under the conditions which were 250℃～310℃, 7.5%CO₂, and 17.2MPa. The apparent activation energy of the reaction （E_a） is 141.52kJ/mol. The relationship between reaction rate and product yield is as follows:更多还原