生物油模型化合物—香兰素在碳化钼基催化剂上加氢脱氧反应的研究

发布时间：2018-05-27 13:36

本文选题：生物质 + 香兰素　；参考：《浙江大学》2015年硕士论文

【摘要】：随着全球工业化的进程,能源问题是人类在实现可持续发展过程中必须面对的首要问题。目前,随着传统化石燃料储备量下降、消耗增加、环境恶化等一系列问题的出现,寻找清洁可再生能源已成为全球关注的重要课题。其中,生物质能作为一种可再生能源,具有蕴藏量大、分布广、能在短期内循环再生等优点,其开发利用也逐渐成为各国政府和学者解决能源问题的主要研究方向。在生物质的众多处理手段中,通过高温快速热裂解制备生物油的方法,不仅有望替代传统的化石燃料,同时还可为化工生产提供大量原材料,因而具有重要的研究价值和战略意义。然而,生物油因含氧量高而导致酸性强、粘度大、挥发性差、不稳定、热值低等缺点,这极大地限制了其应用范围和产业化进程。因此,研究生物油的催化转化是生物质资源高效利用的重要内容。香兰素是生物质木质素热解种的一种典型含氧化合物,研究香兰素的催化转化对于生物基化学品的转化研究具有重要的理论和实验指导意义。加氢脱氧作为生物质催化转化的方法之一,因具有“原子经济效益”而优于脱羰和脱羧反应,并在提高生物油品质方面优于催化裂解反应。根据文献报道,M02C因具有类贵金属的价层电子结构,在许多涉氢反应中表现出和贵金属相类似的催化性能,对加氢、脱氢和异构化等反应均具有良好的催化活性。此外,M02C基催化剂在选择性、稳定性、抗烧结能力和不易中毒方面都表现出优于贵金属催化剂的特性,并且M02C合成原料易得,制备成本低,是Pt、Pd等贵金属催化剂的理想替代品。本论文以得到香兰素选择性加氢脱氧为目标对一系列碳化钼催化剂的合成、表征、活性评价及反应机理进行研究,研究结果如下： (1)以活性炭为载体,通过“碳热氢还原”法制备的碳化钼基催化剂比表面积较大、颗粒较小、分散均匀,制得的催化剂物相取决于碳热还原温度,而负载量则主要影响催化剂的粒径、孔径及分布情况。在绿色溶剂水中,以活性炭为载体的碳化钼基催化剂催化香兰素加氢脱氧的最优反应条件为：20.0%Mo2C/AC为催化剂,在120℃、1.OMPa的初始氢压下反应3h。另在重复再生使用多次后,催化剂活性保持。本方法制备的高分散的M02C/AC催化剂具有高效的加氢脱氧催化活性,具有潜在的工业应用前景。 (2)根据原料及产物香兰醇的浓度随时间的变化曲线,得出在碳化钼基催化剂上香兰素的加氢脱氧反应机理是以香兰醇为中间产物的连续一级加氢反应。其中,反应第一步和第二步的反应速率常数分别为0.49h-1和0.43h-1,香兰醇加氢脱水生成4-甲基-2-甲氧基苯酚的步骤表现为该反应的速控步。 (3)掺杂A1203到碳化钼催化剂中能在一定程度上增加催化剂的酸性,但是会降低催化剂的比表面积及活性位点分散度,进而导致催化剂活性降低。向反应体系中添加质子酸能增加溶液中的原料和中间产物活化率,这在一定程度上导致直接被催化剂表面活化的原料量下降,进而导致原料转化率降低,但同时也提高了最终产物2-甲氧基-4-甲基苯酚的选择性。向反应体系中添加较强酸性物质或具有孔结构的酸性物质,会与催化剂对原料形成竞争吸附,表现为催化剂活性降低。结果表明,催化剂活性受载体比表面积、活性位点分布情况、载体酸性强弱、溶液酸性强弱等综合因素的影响。 (4)通过对不同炭载体上的负载型碳化钼催化剂的系统研究,成功应用于生物油模型化合物分子—天然香兰素的加氢脱氧,并在温和的反应条件下、水相溶液中表现出优异的催化活性。该系列的碳化钼基催化剂作为加氢脱氧反应廉价高效的催化剂,有望替代贵金属催化剂,成为生物质化学品催化转化及生物油催化提质的新型催化体系。
[Abstract]:With the process of global industrialization, the problem of energy is the primary problem that human beings must face in the process of sustainable development. At present, with the emergence of a series of problems, such as the decline in the reserve of fossil fuels, the increase of consumption, and the deterioration of the environment, the search for clean renewable energy has become an important issue in the world. As a renewable energy, it has the advantages of large reserves, wide distribution and recycling in a short period of time. Its development and utilization has gradually become the main research direction for governments and scholars to solve the energy problem. In many ways of treating biomass, the method of preparing bio oil by rapid thermal cracking through high temperature and rapid thermal decomposition is not only expected to replace the traditional one. Fossil fuels, which can also provide a large amount of raw materials for chemical production, have important research value and strategic significance. However, bio oil is highly acidic, viscous, volatile, unstable, and low calorific value because of high oxygen content, which greatly restricts its application and industrialization process. Therefore, the study of the catalysis of bio oil is very important. Transformation is an important content of efficient utilization of biomass resources. Vanillin is a typical oxygenated compound of biomass lignin pyrolysis. The study of the catalytic conversion of vanillin has important theoretical and experimental significance for the transformation of biological based chemicals. Hydrodeoxidation is one of the methods for biomass catalytic conversion. "Atomic economic benefit" is superior to decarbonylation and decarboxylation and is superior to catalytic cracking reaction in improving the quality of bio oil. According to the literature, M02C shows a similar catalytic performance with precious metals in many hydrogen related reactions due to the valence layer electronic structure of precious metals, and is good for hydrogenation, dehydrogenation and isomerization. In addition, the M02C based catalyst is superior to the noble metal catalyst in selectivity, stability, sinter resistance and intoxication, and the M02C synthesis material is easy to be obtained and the preparation cost is low. It is an ideal substitute for Pt, Pd and other noble metal catalysts.
In this paper, the synthesis, characterization, activity evaluation and reaction mechanism of a series of molybdenum carbide catalysts for selective hydrodeoxidation of vanillin are studied. The results are as follows:
(1) the carbonized molybdenum based catalysts prepared by the "carbon thermo hydrogen reduction" method are larger than the surface area, the particles are smaller and the dispersion is uniform. The prepared catalyst phase depends on the carbon thermal reduction temperature, while the load is mainly affected by the particle size, pore size and distribution of the catalyst. In green solvent water, the carbon as the carrier carbon is used in the green solvent water. The optimum reaction conditions for the hydrogenation of vanillin catalyzed by molybdenum based catalysts are as follows: 20.0%Mo2C/AC is the catalyst, and the activity of the catalyst is maintained after the initial hydrogen pressure of 1.OMPa under the initial hydrogen pressure at 120, and the activity of the catalyst is maintained. The highly dispersed M02C/AC catalyst prepared by this method has the potential of high catalytic activity for dehydrogenation and deoxidation. Industrial application prospects.
(2) according to the change curve of the concentration of vanillin with the time, the hydrogenation dehydrogenation reaction mechanism of Vanillin on the Mo based catalyst is a continuous first order hydrogenation reaction with vanillol as the intermediate product. The reaction rate of the first and second steps is 0.49h-1 and 0.43h-1 respectively, and the hydrodehydration of vanillol is hydrodehydrated. The step of producing 4- methyl -2- methoxy phenol is the fast control step of the reaction.
(3) doping A1203 to molybdenum carbide can increase the acidity of the catalyst to a certain extent, but it will reduce the specific surface area of the catalyst and the dispersion of the active site, and lead to the reduction of the activity of the catalyst. The amount of raw material activated by the catalyst is decreased, and the conversion of raw material is reduced, but the selectivity of the final product 2- methoxy -4- methyl phenol is also increased. The addition of strong acidic substance or acid material with pore structure to the reaction system will form a competitive adsorption with the catalyst for the raw material, showing the activity drop of the catalyst. The results showed that the activity of catalyst was influenced by the specific surface area, the distribution of active sites, the acidity of carriers, the acidity of solution and so on.
(4) through the systematic study of the supported molybdenum carbide catalyst on different carbon carriers, it has been successfully applied to the hydrodeoxy deoxidization of the molecule natural vanillin in the bio oil model compound, and shows excellent catalytic activity in the aqueous solution under mild reaction conditions. The series of molybdenum carbonized catalysts are cheap and high in the hydrogenation deoxidization reaction. The catalyst is expected to replace the noble metal catalyst and become a new catalytic system for catalytic conversion of biomass chemicals and catalytic upgrading of bio oil.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE665;O621.251

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