【作者】 刘定华；

【导师】 钟秦； 刘晓勤；

【作者基本信息】 南京理工大学 ， 化学工程与技术， 2010， 博士

【摘要】 碳酸二甲酯(Dimethyl Carbonate, DMC)是近来受到高度关注的绿色化工产品,羰基合成DMC原料廉价、工艺简单、无污染,是最有前途的工业化方法。CuCl是该法中具有较好羰化活性的催化剂,但存在稳定性差、腐蚀性强及催化剂分离困难等不足,阻碍了其迅速发展,因此,改善与提高催化剂的性能已成为该工艺研发的热点与关键。CuBr2用作催化剂的特点是稳定性与溶解性好,Br-氧化性低,腐蚀性小,但需要克服Cu(Ⅱ)活性较差的不足。考虑到金属配合物具有独特的晶体结构和配合键特性,本文研究CuBr2配合物的羰化性能,包括配合物的制备及表征、热力学分析与机理探讨、过程模拟等方面。首先,根据铜络合能力较强的特点,制备了季铵盐、季鳞盐与CuBr2形成的配合物。具有一定电子效应、空间结构的配体,由于配体上正电荷被屏蔽的程度提高,使得络合到CuBr2中的R4N+(R4P+)与Br-离子键对Br-的修饰,改善CuBr2中Br-的活化度,有利于CO、O2及甲醇的插入,形成活性中间体,提高羰化活性。季铵盐修饰的性能优于季鳞盐,这与氮比磷屏蔽程度大的特性相一致,其中以(C3H7)4NBr的活性为最好。N—甲基咪唑及2,2—联吡啶直接与Cu(Ⅱ)结合,形成稳定的配合物,其羰化活性改善有限。其次,通过FTIR、XRD、EA、ICP-AES及XPS分析,(C3H7)4NBr与CuBr2形成的配合物结构有[Cu2Br6]2-,而不是常见的[CuX4]2-,铜的价态没有变化,结构式是[(C3H7)4N]2Cu2Br6。以乙醇为溶剂,配体与CuBr2摩尔比为2：1,在353K下回流1h,干燥得到配合物,制备收率为59.2%。该配合物的活性高于CuBr2,与CuCl相当,甲醇的转化率为27.4%,DMC的选择性为98.3%。再者,对反应过程进行的热力学分析,揭示出反应自发进行的趋势明显。同时,依据铜配合物活性中心Cu(Ⅱ)价态不变的特征,提出了反应机理不同于前人的氧化还原历程,而是通过双聚结构[Cu2Br6]2-中链接配体的变化,使得替换或络合到Cu2+周围的甲醇、CO及O2活化分子很容易经过桥联反应得到DMC。在此研究基础上,有目的研究了酸碱环境、脱水剂和第二金属助剂的影响,筛选得到由具有脱水性能的弱碱K2CO3、协同助剂ZnBr2和铜配合物组成的复合催化剂,正交实验得到的优化配方,使得甲醇的转化率提高到44.9%,DMC的选择性达到95.1%。最后,针对复合催化剂,研究了工艺条件、催化剂循环及气相连续过程的影响,在温度363～378K、压力2.8～3.5 MPa、时间4～6h下,当催化剂浓度0.31g·mL-1、二甲基乙酰胺溶剂量0.30mL·mL-1时,甲醇的转化率为58.1%,DMC的选择性为93.5%；当原料O2控制在20%以下,气速为15～18L·h-1,CO的选择性为95%。ASPEN全流程模拟了过程的可行性及可靠性,为工业化应用提供了重要的技术依据。更多还原

【Abstract】 Dimethyl carbonate (DMC) is a green chemical attracted high attention. The carbonylation of methanol to DMC is highly promising for industrial application due to the inexpensive substrates, simple process, and low pollution. The catalyst CuCl is widely used for the liquid phase carbonylation of methanol to DMC; however, the application of CuCl is hindered by the shortcomings of low stability, strong corrosiveness, and difficult separation of reaction mixture. As a result, the improvement of catalytic performance becomes a hot research topic. We choose CuBr2 instead of CuCl as research direction because of the better stability and solubility as well as lower corrosiveness of CuBr2 than CuCl, while the catalytic activity of Cu(II) is relatively low. Taking account of the special crystalline structure and coordination property of metal complexes, we employed transition metal complexes as catalysts and systematically investigated their catalytic performance, which includes the preparation and characterization of complexes, thermodynamics, mechanism, and process simulation.Firstly, we choose quaternary ammonium salts and phosphonium salts as ligands to form complexes with CuBr2. Interaction between R4N+ or (R4P+) in ligand and Br" have been changed to enhance the activation degree of Br- in CuBr2, which are favorable for the generation of reaction intermediates and the insertion of CO, O2 and methanol, and subsequently enhance the reaction activity. The effect of ligand quaternary ammonium salts is obvious than phosphonium salts, which is consistent with the shield extent of nitrogen and phosphor atoms. Among them, the ligand (C3H7)4NBr in quaternary ammonium salts showed the best promoting effect. N-methyl-imidazole and 2,2-bipyridine can react with CuBr2 to form stable copper complexes, which is not beneficial to the addition of reactant molecules. Hence, the promotion effects are worse than those of (C3H7)4NBr and (C6H5)4PBr.Secondly, on the basis of the results of FTIR, XRD, EA, ICP-AES, and XPS, the structure of copper complexes is [Cu2Br6]2-rather than the common structure [CuX4]2-. The chemical formula of copper complexes is [(C3H7)4N]2Cu2Br6. The optimal preparation conditions were the molar ratio of CuBr2 to (C3H7)4NBr 1:2, ethanol as solvent, the temperature of 353 K, the reaction time of 1～1.5 h, and dried in low-temperature vacuum system. The complexes catalyst can be obtained with the yield of 59.2%. The catalytic performance of the complexes is higher than that of CuBr2, and is almost equivalent to that of CuCl catalyst. Methanol conversion and DMC selectivity are 27.4% and 98.3%, respectively. Thirdly, thermodynamic analysis to the process of liquid phase oxidative carbonylation of methanol to DMC was obtained under certain reaction conditions, which reveals that the tendency to spontaneous reaction is evident. The reaction mechanism was also proposed according to the fact that the constant valence state of Cu(II) in the reaction. DMC was produced from the reaction of methanol, CO, and O2 activated by Cu2+through the variation of ligand in [Cu2Br6], rather than via the conventional oxidation-reduction pathway. The effects of acidic or basic environment, dehydration agents, and metal additives were also investigated. The optimal composition of composite catalysts was obtained by orthogonal experiments and consisted of K2CO3, ZnBr2, and copper complexes. Under the optimal conditions, the methanol conversion can reach 44.9% with DMC selectivity of 95.1%.Finally, on the catalysis of the complex catalysts, we evaluated the effects of process conditions, recycling of catalysts, and gas continuous process on catalytic activity. Under the conditions of reaction temperature 363～378 K, reaction pressure 2.8-3.5 MPa, reaction time 4-6 h, gas velocity 15～18 L·h-1, total catalysts concentration 0.31 g·mL-1, and solvent dimethylacetamide volume 0.30 mL·mL-1, the methanol conversion and DMC selectivity can reach 58.1% and 93.5%, respectively. When the concentration of raw materials O2 is controlled below 20%, CO selectivity could reach 95%. We investigated the feasibility and reliability of the whole carbonylation process by ASPEN process simulation. The results may provide important technical supports for potential industrial applications.更多还原