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二氧化碳间接合成有机醇酯多相催化体系研究
李凤姣
学位类型博士
导师李会泉
2016-07
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业化学工艺
关键词二氧化碳 甲醇 乙二醇 碳酸二乙酯 脂肪酸甲酯
摘要

CO2清洁合成有机醇酯是CO2化学利用的研究热点。但是,由于CO2分子的热力学稳定性与动力学惰性,CO2直接合成路线通常存在合成效率低、反应条件苛刻、产物收率低等缺点。值得注意的是,CO2能与高能化合物环氧乙烷高效合成碳酸乙烯酯,还能与氨气、乙醇有效合成氨基甲酸乙酯,也能经生物固碳等途径大量制备脂肪酸甘油三酯。因此,以上述三种CO2碳氧载体进一步转化制备有机醇酯,是实现CO2间接合成高价值有机醇酯的有效途径。本文针对上述三种CO2碳氧载体的酯基转化过程,重点开展了碳酸乙烯酯加氢联产甲醇与乙二醇、氨基甲酸乙酯与乙醇醇解合成碳酸二乙酯以及脂肪酸甘油三酯与甲醇酯交换合成脂肪酸甲酯的高效多相催化体系研究,系统深入进行了反应热力学、催化剂表征、催化剂构效关系、催化剂稳定性、催化机理和反应条件影响等研究工作。主要研究内容和结论如下:(1)针对碳酸乙烯酯加氢联产甲醇与乙二醇过程,首先通过热力学计算揭示了该反应为热力学有利的放热反应,然后以三种不同介孔硅分子筛KIT-6、MCM-41和SBA-15为载体,采用蒸氨法成功制备了Cu/KIT-6、Cu/MCM-41和Cu/SBA-15催化剂,研究了载体对负载铜基催化剂的织构性质和催化活性的影响。催化剂表征结果表明不同比例的Cu0和Cu+物种共同存在于上述三种催化剂中,其中Cu0由CuO还原得到,Cu+由层状硅酸铜还原得到。催化剂评价结果发现Cu/SBA-15表现出更优异的催化性能,主要归因于其具有较高的铜分散度和合适的Cu0/Cu+比例。以Cu/SBA-15为催化剂,在优化条件下,碳酸乙烯酯转化率达100%,甲醇收率和乙二醇收率分别达62.3%、94.7%。Cu/SBA-15的稳定性考察结果发现,其活性随着循环次数增加而逐渐下降,原因主要归结于Cu/SBA-15结构中Cu和Cu2O颗粒的团聚长大。(2)针对碳酸乙烯酯加氢联产甲醇与乙二醇过程,进一步以硅溶胶为硅源经蒸氨法可控制备了不同铜负载量2%~30%Cu/SiO2-AE催化剂,系统研究了铜负载量对Cu/SiO2-AE催化剂的织构性质和催化活性的影响。催化剂系统表征分析结果证明了2%~30%Cu/SiO2-AE催化剂同时含有不同比例的Cu0和Cu+成分,两者分别来源于CuO的还原和层状硅酸铜的还原。催化性能评价结果表明铜负载量适中的10%Cu/SiO2-AE催化剂具有较优的催化活性,关键原因在于Cu0与Cu+物种的协同催化作用及其含有合适的Cu+/(Cu0+Cu+)比例。以10%Cu/SiO2-AE为催化剂,在优化条件下,碳酸乙烯酯转化率达100%,甲醇收率和乙二醇收率分别提高到70.8%、98.0%。提出了Cu0促进氢气解离、Cu+吸附在碳酸乙烯酯的羰基上的催化机理。10%Cu/SiO2-AE的稳定性考察结果发现,Cu和Cu2O颗粒的团聚长大是10%Cu/SiO2-AE催化剂在循环过程中催化活性下降的主要原因。(3)针对氨基甲酸乙酯与乙醇醇解合成碳酸二乙酯过程,采用以碳酸钠为沉淀剂的沉淀法发展了高效固体碱催化剂MgO-SC-450。该催化剂具有245 m2 g-1的高比表面积、纳米薄片状形貌和丰富的中等强度碱性位。MgO-SC-450表现出优异的活性与选择性,在200 oC条件下的TOF值为3522 mgDEC gcat-1 h-1,在优化条件下,氨基甲酸乙酯转化率达62.9%,碳酸二乙酯收率和选择性分别高达58.0%和92.1%。催化剂构效关系研究表明,丰富的中等强度碱性位是MgO-SC-450起高效催化作用的关键因素。MgO-SC-450还具有良好的重复使用性和结构稳定性。准原位红外实验结果表明氨基甲酸乙酯能被MgO活化,并且乙醇被解离成亲核性强的乙氧基。理论计算研究结果证实了氨基甲酸乙酯与乙醇共吸附于MgO表面上的双分子共活化机理。 (4)针对脂肪酸甘油三酯与甲醇酯交换合成脂肪酸甲酯过程,以来源广、成本低的电石渣大宗工业固体废弃物为钙基固体碱催化剂原料,采用简便易行的热活化法,发展了低成本高活性的电石渣钙基催化剂CS-650,实现了远优于商品CaO的催化活性。催化剂构效关系研究结果表明CS-650活性优异的关键在于其具有丰富的强碱性位。以CS-650为催化剂,在优化条件下,脂肪酸甲酯收率达91.3%,相应的TOF值为182.6 gFAME gcat-1 h-1。对CS-650催化剂的稳定性和反应前后结构变化进行了研究,结果发现催化剂在循环过程中活性下降到80.1%,归因于循环过程中形成了活性低于CS-650的甘油钙新结构。

其他摘要

Clean synthesis of organic alcohols and esters derived from carbon dioxide is a hot research topic of chemical utilization of carbon dioxide. However, direct transformation of CO2 to organic alcohols and esters usually suffers from the problems of low reaction efficiency, harsh reaction conditions and low product yields due to the thermodynamic stability and dynamics inertia of CO2 molecular. It is worth noting that CO2 can react with epoxide to highly efficiently synthesize ethylene carbonate. CO2 can also react with ammonia and ethanol to easily produce ethyl carbamate. In addition, a large volume of fatty acid triglyceride can be achieved via biological carbon sequestration of CO2. Therefore, ethylene carbonate, ethyl carbamate and fatty acid triglycerides can be used as CO2 carrier to further produce high-valued organic alcohols and esters. With the aim of the transformation of the ester group of the three above-mentioned CO2 carrier, this dissertation mainly focused on developing heterogeneous catalytic systems for the hydrogenation of ethylene carbonate to co-produce methanol and ethylene glycol, ethanolysis of ethyl carbamate to synthesize diethyl carbonate, and transesterification of fatty acid triglycerides with methanol to synthesize fatty acid methyl esters. Systematic and in-depth investigations such as the thermodynamics calculation, characterization of catalysts, relationship between catalyst structure and activity, catalyst reusability, catalytic mechanism, and reaction conditions were carried out. The main research contents and conclusions are as follows: (1) Thermodynamics calculation of the hydrogenation of ethylene carbonate to co-produce methanol and ethylene glycol was firstly carried out, which revealed that this reaction was a thermodynamic favorable exothermic reaction. Then, three copper-based catalysts Cu/KIT-6, Cu/MCM-41 and Cu/SBA-15 were successfully prepared by ammonia evaporation method using three ordered mesoporous silicas KIT-6, MCM-41 and SBA-15 as supports. The species of Cu0 and Cu+ with varied ratio were found to co-exist on the catalyst surfaces after reduction, which were verified to originate from CuO and copper phyllosilicate, respectively. The catalytic performances of the three as-prepared copper-based catalysts revealed that among the three catalysts, Cu/SBA-15 exhibited a better catalytic activity. It was found that high copper dispersion and suitable Cu0/Cu+ ratio were responsible for the excellent activity of Cu/SBA-15. Under the optimized condition, the conversion of ethylene carbonate reached 100%, and the yields of methanol and ethylene glycol reached 62.3% and 94.7%, respectively. The reusability of Cu/SBA-15 showed that, the gradually decreasing catalytic activity of Cu/SBA-15 during recycling experiments was probably ascribed to the agglomeration of Cu and Cu2O particles. (2) A series of 2%~30%Cu/SiO2-AE catalysts with different copper loadings were controllably prepared using silica sol as the silica source by ammonia evaporation method. The as-prepared 2%~30%Cu/SiO2-AE catalysts were also used in the hydrogenation of ethylene carbonate to co-produce methanol and ethylene glycol. The effects of copper loading on the catalyst properties and catalytic activities of Cu/SiO2-AE catalysts were systematically investigated. The systematic catalyst characterization results demonstrated that different proportions of Cu0 and Cu+ species co-existed in the Cu/SiO2-AE catalysts, which derived respectively from the reduction of CuO and copper phyllosilicate. Catalytic performance evaluation results showed that the 10%Cu/SiO2-AE catalyst with moderate copper loading exhibited better catalytic activity,mainly attributing to the synergetic effect of Cu0 and Cu+ species and the suitable proportion of Cu+/(Cu0+Cu+). Under the optimized condition, the conversion of ethylene carbonate reached 100%, and methanol yield and ethylene glycol yield were further increased to 70.8% and 98.0%, respectively. A plausible catalytic mechanism that Cu0 promoted the dissociation of H2 and Cu+ adsorbed on the carbonyl group of ethylene carbonate was proposed. The catalyst reusability result showed that the catalytic activity of 10%Cu/SiO2-AE catalyst gradually declined along with recycling experiments. The agglomeration of Cu and Cu2O particles was responsible for the decreasing catalytic activity of 10%Cu/SiO2-AE catalyst during recycling experiments.(3) An efficient catalyst MgO-SC-450 was prepared using sodium carbonate as the precipitant and applied in the ethanolysis of ethyl carbamate (EC) to synthesize diethyl carbonate (DEC). Catalyst characterization results revealed that MgO-SC-450 possessed a high specific surface area of 245 m2 g-1, nanosheet morphology and a larger amount of appropriate medium basic sites. MgO-SC-450 exhibited higher activity and selectivity with a TOF of 3522 mgDEC gcat-1 h-1 obtained at 200 oC. Under the optimized reaction condition, an excellent DEC yield of 58.0% with a high DEC selectivity of 92.1% and EC conversion of 62.9% were achieved over MgO-SC-450 catalyst. The structure and surface basicity of the different MgO catalysts showed that more abundant medium basic sites were favorable for MgO-SC-450 to obtain much superior catalytic activity. Moreover, the catalytic activity and structure properties of MgO-SC-450 could be essentially retained during recycling experiments. Quasi in situ FT-IR experiments were carried out to elucidate the adsorption behaviors of reactants. It was found that EC could be effectively activated and ethanol could be dissociated to a strong nucleophilic ethoxy group by MgO. In addition, the theoretical calculation results proved that EC and ethanol co-adsorbed on the MgO surface, and ethanol could be dissociated to ethoxy group. (4) A highly efficient waste carbide slag based catalyst CS-650 was developed using widely available and low-cost waste carbide slag as the solid calcium-based catalyst materials by facile thermal activation. The as-prepared CS-650 was employed in the transesterification of fatty acid triglyceride with methanol to synthesize fatty acid methyl esters (FAME). It was found that the catalytic activity of CS-650 was much higher than commercial CaO. The relationship between the surface basicity and activity indicated that stronger basicity of catalyst was responsible for the higher activity of CS-650. Under the optimized condition, 91.3% FAME yield with TOF of 182.6 gFAME gcat-1 h-1 were achieved over CS-650. In addition, the reusability and structure changes of CS-650 showed that the formation of calcium glyceroxide resulted in the decreasing activity of CS-650 to 80.1% along with recycling experiments. 

语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/22893
专题研究所(批量导入)
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李凤姣. 二氧化碳间接合成有机醇酯多相催化体系研究[D]. 北京. 中国科学院研究生院,2016.
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