【作者】 张震；

【导师】 马新宾；

【作者基本信息】 天津大学 ， 化学工艺， 2007， 博士

【摘要】 碳酸二乙酯(DEC)作为一种“绿色化学品”是一种可以用于替代光气的重要化工中间体,特别是近年来发现DEC可以作为汽油、柴油的含氧添加剂,取代MTBE的使用,有着广泛的应用前景。本研究对乙醇气相直接氧化羰基合成碳酸二乙酯的活性炭负载Wacker型催化剂体系进行探讨。助剂对乙醇氧化羰基合成碳酸二乙酯催化剂影响的研究表明,KCl助剂表现出较佳的助催化性能。XRD以及XPS表征分析表明,加入KCl助剂后,催化剂活性组分由γ-Cu2(OH)3Cl部分转变为Cu(OH)Cl。碱式氯化铜晶型结构分析结合反应活性评价表明,Cu(OH)Cl在DEC合成中更具催化活性。通过Cu组分ESR表征以及Pd组分XPS解叠分析,解释了过程中所采用的Wacker型催化剂Pd-Cu间电子传递促进反应进行的原理,并指出由于Cl流失所造成的电子传递循环的中断,Pd0的不断产生是催化剂失活的主要原因。催化剂表面基团的DRIFT分析表明,反应过程中主、副产物的生成提高了催化剂表面基团极性,造成催化剂催化反应活性下降。CuCl2-PdCl2-KCl-NaOH催化剂的原位升温XRD研究表明,采用温度热处理的手段可以有效调变催化剂活性组分碱式氯化铜的晶型结构。其中,523 K热处理的催化剂由于促进了Cu(OH)Cl晶型的产生,催化剂的催化反应活性较佳。活性炭载体经等离子体表面改性研究表明,O2等离子体气氛处理有利于活性炭表面的羰基以及酚羟基的形成,H2等离子体气氛处理的活性炭有利于活性炭表面内酯基的形成,而活性炭表面羧基基团含量对等离子体气氛种类不敏感。活性炭载体预处理的研究表明,预处理后的活性炭载体表面含氧基团的含量增加,促进了铜组分向载体上的负载以及分散。催化体系的准原位XPS、XRD以及原位漫反射红外光谱分析表明,反应过程中存在乙醇解离吸附、一氧化碳化学吸附、一氧化碳插入等过程,而氧气主要以气相方式参与反应。催化剂活性组分除Pd-Cu电子传递促进反应进行外,Cl元素同时参与了反应循环。得出Wacker型催化剂催化氧化羰基合成碳酸二乙酯的反应历程。更多还原

【Abstract】 Oxidative carbonylation of ethanol for preparation of diethyl carbonate (DEC) offers prospects for a“green chemistry”replacement of phosgene for polymer production and other processes. Over past years, diethyl carbonate has been found to be a substitute for methyl tert-butyl ether (MTBE), which is used as an oxygen-containing fuel additive. Wacker type catalysts for the (gas-phase) oxidative carbonylation of ethanol to diethyl carbonate have been discussed and present in this dissertation.We report on the effect of promoters on catalytic activities in the oxidative carbonylation of ethanol to diethyl carbonate and the results have shown that KCl is the best promoter. Additionally, KCl favors crystalline Cu(OH)Cl formation, which plays a decisive role in the DEC synthesis. An electron transfer effect of Pd-Cu in the Wacker type catalyst has been proved by ESR analysis of copper species and XPS analysis of palladium species. We have also presented evidence that deactivation of catalysts can be ascribed to the leaching of Cl species that is a possible intermediate in electron transfer between Pd and Cu, which leads to the formation of a large amount of Pd0. DRIFT analysis of surface functional groups on the Wacker type catalyst indicates that the presence of main product and by products result in an increase in polar groups on the surfaces of the catalysts, which causes a decrease in the catalytic activities.In-situ XRD studies on the CuCl2-PdCl2-KCl-NaOH catalyst shows that thermal pretreatment on the catalyst significantly alters the structures catalyst crystal. A optimal thermal pretreated temperature has been obtained at 523 K, which favors the formation of Cu(OH)Cl.Modifications of surface groups on the activated carbon via different type of plasma have been discussed. O2 plasma is found to be favored for the formation of hydroxyl groups, while H2 plasma improves the production of lactone groups. However, surface group of carboxyl is not sensitive to the type of plasmas. In addition, pretreatment of activated carbon provides increased amount of oxygen containing group on the activated carbon surfaces and enhances the dispersion of Cu species on the supports.Quasi in-situ XPS, XRD and in-situ DRIFT investigations on the catalytic system indicate that the reaction involves a multiple steps in the oxidative carbonylation of ethanol to diethyl carbonate, e.g., dissociative adsorption of ethanol; chemisorption of CO, and the insertion of CO. Oxygen is involved in the reaction as a gas phase. Chloride species plays a significant role in the cycle of reaction and besides, Pd-Cu electron transfer process in the catalyst promots the reaction, Basen on these experimental results, a reaction course of oxidative carbonylation of ethanol to diethyl carbonate over Wacker type catalyst has been proposed..更多还原