【作者】 贺黎明；

【导师】 陈晓春；

【作者基本信息】 北京化工大学 ， 工业催化， 2011， 博士

【摘要】 乙二醇是一种重要的化工原料,由于我国需求旺盛而产能不足,进口依赖度逐年增加。目前国内外乙二醇生产均采用以石油化工为基础的环氧乙烷直接水合法工艺,能耗和物耗等技术指标偏高,而我国属于贫油多煤国家,开发非石油路线合成乙二醇生产工艺具有原料优势。CO经草酸酯合成乙二醇由两步反应构成,第一步：CO偶联反应合成草酸酯工艺；第二步：草酸酯加氢合成乙二醇工艺。本论文分别对草酸酯合成催化剂的制备和草酸酯加氢催化剂的制备进行了研究,对催化剂进行了系统表征,考察了不同制备条件和不同工艺条件下的催化剂性能,具体研究工作如下：(1)草酸二乙酯(DEO)合成催化剂研究采用浸渍法制备了系列草酸二乙酯合成钯催化剂,对载体和催化剂进行了系统表征。研究结果表明,γ-氧化铝经过高温焙烧后,相应比表面、孔结构、晶型及表面酸性均发生改变。对于单金属Pd/a-Al2O3催化剂而言,钯呈蛋壳型分布,还原后催化剂活性组分以Pd。存在。对于双金属Pd-Fe/a-Al2O3催化剂而言,加入助剂铁后,钯分散度增加,还原后铁以FeO存在,载体、助剂和活性组分之间形成了“夹心”结构,活性组分分散性和稳定性有所提高。采用固定床反应器考察了催化剂制备条件和Cl-含量对催化性能的影响,发现α-Al2O3比α-Al2O3更适合作为催化剂载体；催化剂中Cl-含量对催化剂选择性有较大影响,讨论了副产物碳酸二乙酯的形成原因。反应工艺条件试验表明,在反应温度115-125℃,反应原料CO和草酸二乙酯配比为1.2-1.6,空速为2800-3600h-1的条件下,CO的转化率可达35%以上,草酸二乙酯选择性可达95%,Pd-Fe/α-Al2O3催化剂稳定性能良好。(2)草酸二乙酯加氢催化剂表征研究以四硅酸乙酯为硅源,硝酸铜为铜源,采用改进的溶胶-凝胶法制备了系列草酸二乙酯加氢Cu/SiO2催化剂,对还原前后的铜催化剂进行了系统表征,结果表明,催化剂铜含量和氨水溶液pH值对催化剂的比表面、孔结构、物相组成、铜价态、还原性能和分散性有较大的影响。在一定的铜含量范围内,催化剂前体中铜组分主要以层状硅酸铜的形式存在,即使在铜含量较高时,铜组分在载体中仍然有良好的分散性,催化剂有较大的比表面。Cu/SiO2催化剂经高温焙烧后,部分层状硅酸铜仍以层状形式存在,另一部分分解为CuO,且在载体上分散良好。铜含量低于37.8%的催化剂经焙烧存在两种铜组分：层状硅酸铜和高度分散的CuO；而铜含量高于37.8%的催化剂经焙烧后存在三种铜组分：层状硅酸铜、高度分散的CuO和颗粒较粗的CuO。催化剂经还原后,层状硅酸铜还原为一价铜,而CuO还原为金属铜。随着氨水溶液pH值的升高,硅胶中的羟基反应活性增强,因此较高的pH值有利于催化剂中层状硅酸铜的形成。作为对比,采用沉淀沉积法制备了Cu/SiO2催化剂并进行了相关表征,还原前沉淀沉积法催化剂中铜组分以CuO的形式存在,未发现层状硅酸铜的存在,因此这类催化剂比表面较低,还原后Cu物种主要以Cu0为主。(3)草酸二乙酯加氢催化剂性能评价对溶胶-凝胶法催化剂和沉淀沉积法催化剂进行了对比评价,研究结果表明,溶胶-凝胶法催化剂性能好于沉淀沉积法催化剂,究其原因是因为溶胶-凝胶法有助于层状硅酸铜的形成,导致焙烧后该类催化剂比表面积较大,还原后该类催化剂有适宜的Cu+/Cu0。实验考察了催化剂制备条件和反应条件对溶胶-凝胶法催化剂性能的影响,铜含量和氨水溶液pH值对催化剂性能有较大的影响,且有类似的变化规律。随着铜含量增加,草酸二乙酯转化率和乙二醇选择性呈现出先增加后减少的趋势,峰值出现在催化剂中铜含量37.8%处；催化性能随氨水溶液pH值的变化趋势与铜含量的变化趋势亦一致。焙烧温度和还原温度对催化性能也有重要的影响。至于反应条件对催化性能的影响,在优化工艺[温度220℃、压力2MPa、气体空速7000 h-1、n (H2):n(DEO)=70]条件下,草酸二乙酯的转化率可达96%,乙二醇的选择性为88%。实验研究了草酸二乙酯加氢铜催化剂失活的原因,催化剂主要失活原因是反应后催化剂中活性组分聚集长大和催化剂小孔被结焦物堵塞；进一步的催化作用机理分析表明,草酸二乙酯加氢催化性能与催化剂中Cu+和Cu0协同作用有关。更多还原

【Abstract】 Ethylene glycol is a valuable commercial chemical and the import for it increased year by year due to strong demand and limited production compacity in China. Currently the major method widely used for the industrial production of ethylene glycol is based on the direct hydrolysis of ethylene oxide obtained from oil as raw material. However this method is plagued by some problems such as the increased price of crude oil as a result of the long-term of shortage and high energy consumption for the distillation of the large amount of excess water etc. To deal with these problems, it is good choice to prepare ethylene glycol by alternative processes based on non-oil routes taking into account the advantages of sources of raw materials and the characteristics of oil-poor and coal-rich country. Synthesis of ethylene glycol from CO via oxalate ester is two-step process. The first one is oxalate ester synthesis by CO coupling and the second one is synthesis of ethylene glycol by hydrogenation of oxalate ester. In this thesis, some Pd/Al2O3 catalysts prepared for oxalate ester synthesis and Cu/SiO2 catalysts prepared for hydrogenation of oxalate ester were studied and characterized systematically. The catalytic performance was investigated under different preparation conditions and reaction conditions. The specific research work is as follows:(1) Pd/Al2O3 catalysts for diethyl oxalate (DEO) synthesisA series of Pd/Al2O3 catalysts were prepared by the impregnation method. Some supports and catalyst samples were characterized by nitrogen physisorption, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Temperature programmed reduction(TPR), Scanning electron microscopy (SEM) and Transmission electron microscopy(TEM). The results show that, after calcinations at high temperature, the corresponding specific surface area, pore structure, crystal type and surface acidity of y-alumina were changed. For pure Pd/a-Al2O3 catalysts, the active species for the reaction was zero valent palladium with egg-shelled distribution in the support. For the bimetallic Pd-Fe/a-Al2O3 catalyst, the promoter existed in the form of FeO, resulting in the formation of a "sandwich" typed catalyst which could improve the catalytic activity and stability. Some catalysts in terms of their activity and selectivity were evaluated in a laboratory fixed bed reactor. Superior catalytic performance of Pd/α-Al2O3 catalyst over Pd/y-Al2O3 catalyst was ascribed to the support effect. It was found that the effect of [Cl-] content in the palladium based catalyst on the catalytic selectivity and the reseaon for the formation of diethyl carbonate as by-product was disscussed. The Pd-Fe/α-Al2O3 sample for diethyl oxalate synthesis showed good performance and stability with CO conversion 35% and DEO selectivity 95% over Pd/y-Al2O3 catalyst under the optimal reaction conditions with reaction temperature ranged froml 15～125℃, molar ratio of reactants CO to DEO ranged from 1.2 to 1.6 and gas space velocity ranged from 2800-3600h-1(2) Characterization of Cu/SiO2 catalysts for diethyl oxalate hydrogenationA series of Cu/SiO2 catalysts for diethyl oxalate hydrogenation were prepared by an improved sol-gel method with tetraethoxysilane(TEOS) used as silica source and copper nitrate as copper source. Some catalyst samples before and after reduction were characterized systematically. It was found that the copper content and pH value of ammonia solution had a great impact on the specific surface area, pore structure, phase composition, copper oxidation state, reducibility and dispersion. In a certain range of copper content, the copper species in catalyst precursor appeared mainly in the form of copper phyllosilicate with finely dispersed in the support even at elevated copper loading, resulting in the catalyst with higher specific surface area. Copper phyllosilicate in the Cu/SiO2 catalyst precursor undergoes partial decomposition during calcination, resulting in well dispersed CuO particles and intact copper phyllosilicate. In the calcined sol-gel-derived catalyst samples with a copper loading lower than 37.8 wt%, there were two copper species:copper phyllosilicate and well-dispersed CuO whereas in the high copper content (> 37.8 wt%) catalysts the copper species were composed of copper phyllosilicate, well-dispersed CuO, and some of copper oxide agglomerates. Reduction of calcined Cu/SiO2 catalyst sample could lead to Cu+ and Cu0 species, originating from reduction of copper phyllosilicate and CuO respectively. As for the impact of pH value of the ammonia solution, it was found that higher pH value favored the formation of copper phyllosilicate in the catalyst because the silica sol formed during the hydrolysis of TEOS became very reactive at elevated pH value of ammonia soulution. For comparison purpose, some Cu/SiO2 catalyst samples prepared by the deposition precipitation method were characterized, in which the copper species appeared in the form of CuO without copper phyllosilicate, leading to the lower specific surface area and presence of Cu0 in the catalyst sample after reduction process.(3) Evaluation of Cu/SiO2 catalyst for diethyl oxalate hydrogenation to ethylene glycolThe Cu/SiO2 samples prepared by sol-gel method and deposition precipitation method were evaluated focusing on the effect of preparation method on the catalytic properties. The experiment results show that the Cu/SiO2 catalyst prepared by the sol-gel method was superior in catalytic performance to the Cu/SiO2 catalyst prepared by the deposition precipitation method, which could be explained by the existence of finely dispersed copper phyllosilicate in the sol-gel derived catalyst precursor resulting in the reduced catalyst with higher copper surface area and the suitable Cu+/Cu0 ratio. At the same time, the effect of preparation conditions and reaction conditions on catalytic performance was investigated in hydrogenation of diethyl oxalate to ethylene glycol. It is found that the catalytic performance was heavily dependent on copper loading and the pH value of ammonia solution, which was understandable considering that the effect of copper loading and pH value on the catalyst structure. With the rise in copper loading, the diethyl oxalate conversion and ethylene glycol selectivity increased, reaching a maximum at a copper loading of 37.8 wt%, followed by a drop with further rise in copper loading. The same trend was found for the effect of the pH value on the catalytic performance. In addition, the calcination temperature and reduction temperature also played an important role in the catalytic performance. As for the effect of reaction conditions on the catalytic performance, it was found that under optimum reaction conditions[temperature=220℃, pressure=2.0MPa, GHSV=7000h-1, n (H2) :n(DEO)= 70], conversion of diethyl oxalate was 96%, and selectivity of ethylene glycol was 88%. On the other hand, it was suggested that the main reasons for catalyst deactivation were coke polymer formation and the sintering of the Cu0 phase. Catalytic mechanism for hydrogenation of diethyl oxalate was analyzed. In hydrogenation of diethyl oxalate to ethylene glycol, the catalytic performance is related with synergy effect between Cu0 and Cu+更多还原