木质素基酚类物质加氢脱氧制取芳烃的研究

发布时间：2018-05-03 02:16

本文选题：MoO_3 + 木质素　；参考：《中国科学技术大学》2017年硕士论文

【摘要】：为克服化石能源短缺及大量化石燃料消费引起的环境污染问题,人们正努力开发可替代化石能源的可再生能源与新能源。生物质是新能源中唯一可转化为碳氢液体燃料的可再生碳资源,已成为科技工作者的研究热点。木质素是由苯丙烷结构单体组成的天然高分子聚合物,在自然界中的含量仅次于纤维素,具有较高的能量密度。然而,木质素解聚得到的液体产物含氧量较高,较高的氧含量引起液体燃料具有热值低、化学性质不稳定、粘度大等缺点。因此必须对这类解聚液体产品进行加氢脱氧(hydrodeoxygenation,HDO)处理。基于此,本论文以MoO3为催化剂的主要构成组分,以芳烃为目标产物开展木质素解聚的酚类化合物的催化加氢脱氧反应特性研究。首先,以(NH4)6Mo7O24.4H2O为前驱体通过简单的焙烧方法制备了非负载型MoO3催化剂。以低温N2吸附、XRD、XPS和H2-TPR等技术对催化剂特性进行了表征,以苯酚等酚类物质的加氢脱氧反应对催化剂的催化活性进行了评价。重点考察了反应温度、反应时间、反应气组成等参数对苯酚转化率、目标产物苯选择性的影响,并就氧化钼催化加氢脱氧反应机制及催化剂的可重复使用性能进行了考察。实验结果表明,在340 ℃、0.5 MPa H2与3 MPa N2混合气氛的优化工况下,苯酚的转化率达到98.1%,产物苯的选择性达到99.5%。MoO3催化材料中的氧缺陷位是催化苯酚分子中CAR-OH键直接氢解生成芳烃苯的主要活性位。此外,MoO3重复使用三次后催化活性仍无明显下降。其次,以浸渍法、分步沉淀法与共沉淀法分别制备了 MoO3/SiO2催化剂。研究了不同方法制备的MoO3/SiO2催化剂作用下酚类模型化合物加氢脱氧反应特性,考察了负载量、反应温度等参数对反应物转化率、产物芳烃选择性的影响。反应温度为=340℃时,分步沉淀法制得的MoO3含量为80%时的MoO3/SiO2催化剂上愈创木酚加氢脱氧反应其转化率为98.5%,总的芳烃收率达到82.4%。分布沉淀法制得的催化剂催化活性高的本质原因在于该催化剂中Mo5+含量最高,这是酚类化合物加氢脱氧反应的关键活性位。反应后的催化剂上积炭量极少,表明具有的优异的抗积碳性能。最后,在酚类模型化合物研究的基础上,选取未负载的MoO3和分步沉淀法制得的MoO3/SiO2为催化剂开展了热解木质素(生物油重质组分)的加氢脱氧反应,实验结果表明MoO3/SiO2具有较好的催化活性,产物中芳烃类产物含量更高。
[Abstract]:In order to overcome the problem of environmental pollution caused by the shortage of fossil energy and the consumption of a large amount of fossil fuels, people are trying to develop renewable energy and new energy which can replace fossil energy. Biomass is the only renewable carbon resource that can be converted into hydrocarbon liquid fuel in new energy, which has become the research hotspot of science and technology workers. Lignin is a natural polymer composed of phenylpropane monomers, and its content in nature is second only to cellulose, which has a high energy density. However, the liquid products obtained by lignin depolymerization have higher oxygen content, and the higher oxygen content leads to the low calorific value, unstable chemical properties and high viscosity of liquid fuel. Therefore, hydrodeoxygenation (HDOO) must be carried out for these depolymerized liquid products. Based on this, the catalytic hydrogenation deoxidation of lignin depolymerized phenols was studied using MoO3 as the main component and aromatic hydrocarbons as the target product. Firstly, the unsupported MoO3 catalyst was prepared by a simple roasting method with NH _ 4N _ 6Mo _ 7O _ 24.4H _ 2O as the precursor. The characteristics of the catalyst were characterized by low temperature N2 adsorption XRDX XPS and H2-TPR, and the catalytic activity of the catalyst was evaluated by hydrodeoxidation of phenol and other phenols. The effects of reaction temperature, reaction time and composition of reaction gas on the conversion of phenol and benzene selectivity of the target product were investigated. The mechanism of molybdenum oxide catalytic hydrogenation deoxidation reaction and the reusability of the catalyst were also investigated. The experimental results show that under the optimum condition of 340C 0.5 MPa H2 and 3 MPa N2 mixed atmosphere, The conversion of phenol reaches 98.1, and the selectivity of benzene to oxygen defect in 99.5%.MoO3 catalyst is the main active site of direct hydrogenation of CAR-OH bond to aromatics benzene in phenol molecule. In addition, the catalytic activity of MoO3 was not significantly decreased after three times of repeated use. Secondly, MoO3/SiO2 catalysts were prepared by impregnation method, step precipitation method and co-precipitation method respectively. The hydrodeoxidation reaction characteristics of phenolic model compounds under the action of MoO3/SiO2 catalyst prepared by different methods were studied. The effects of loading amount and reaction temperature on the conversion of reactants and the selectivity of aromatic hydrocarbons were investigated. The conversion of guaiacol hydrodeoxidized over MoO3/SiO2 catalyst was 98.5 and the total yield of aromatics was 82.4% when the reaction temperature was 340C and the content of MoO3 prepared by step precipitation method was 80%. The essential reason for the high catalytic activity of the catalyst prepared by the distributed precipitation method is that the Mo5 content in the catalyst is the highest, which is the key active site for the hydrodeoxidation of phenolic compounds. The amount of carbon deposited on the catalyst after the reaction is very small, which indicates that the catalyst has excellent resistance to carbon deposition. Finally, based on the study of phenolic model compounds, the hydrogenation deoxidation of lignin (bio-oil heavy component) was carried out on the basis of unsupported MoO3 and MoO3/SiO2 prepared by step precipitation method. The experimental results show that MoO3/SiO2 has better catalytic activity and the aromatics in the product is higher.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;O625.1

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