【作者】 陈英；

【导师】 赵新强；

【作者基本信息】 河北工业大学 ， 化学工艺， 2005， 硕士

【摘要】 首先制备了氧化锌一氧化铅(ZnO-PbO)催化剂,并对其在碳酸丙烯酯(PC)与甲醇酯交换合成碳酸二甲酯(DMC)反应中的催化性能进行了研究。其次,探讨了反应-萃取技术对KOH和ZnO-PbO催化剂上PC和甲醇酯交换合成DMC反应的促进作用。采用共沉淀法制备了ZnO-PbO催化剂。首先探讨了前驱体、沉淀剂、Zn/Pb重量比和焙烧温度等制备条件对ZnO-PbO催化剂性能的影响,得出如下最佳制备条件:Pb(CH3COO)2·3H2O和Zn(NO3) 2·6H2O为前驱体、Zn/Pb质量比为3. 5、 摩尔比为3:1的NaOH-Na2CO3的混合溶液作沉淀剂、焙烧温度为500℃。然后优化了ZnO-PbO催化剂上PC与甲醇酯交换合成DMC的反应条件:反应温度110℃、反应时间2h、甲醇与PC摩尔比为8. 4,催化剂占体系的重量百分率为3. 0%。在此条件下,PC转化率达到63. 8%,DMC收率为62. 4%,选择性为97. 8%。XRD分析结果显示ZnO、PbO及适量Pb3O4的协同作用促进了ZnO-PbO催化活性的提高。CO2·TPD分析表明ZnO-PbO催化剂的活性与其表面的碱量及碱强度有关。此外还考察了催化剂重复使用效果,并对其失活原因进行了分析。将反应-萃取技术应用于PC和甲醇酯交换合成DMC反应过程,既可提高反应的平衡转化率,又可避免DMC-甲醇共沸物的形成。对于以KOH为催化剂的均相反应,当以正辛烷为主萃取剂、邻苯二甲酸二辛酯(DOP)为助萃取剂,萃取相与反应相体积比为2. 8,正辛烷与DOP体积比为0. 7,催化剂占体系的重量百分率为3. 0%,反应温度为50℃,反应时间为3h时,DMC的分配系数为1. 07,DMC与甲醇的分离系数为7. 8,PC转化率达到85. 3%,DMC的收率为64. 8%,选择性为76. 0%。与未加萃取剂时相比,DMC收率提高了47. 6%,选择性提高了26. 7%。对于以ZnO-PbO为催化剂的非均相反应,当以正十二烷为主萃取剂、邻二甲苯为助萃取剂、邻二甲苯与正十二烷体积比为0. 4,萃取相和反应相体积比为0. 3,催化剂占体系的重量百分率为2. 7%,反应温度为100℃,反应时间2h时,PC转化率达到67. 7%,DMC的收率为66. 0%,选择性为97. 5%。与不加萃取剂时相比,DMC收率提高17. 0%,而选择性变化不大。可见,反应-萃取技术对PC与甲醇酯交换合成DMC反应具有较好的促进作用。更多还原

【Abstract】 Zinc-lead double oxide (ZnO-PbO ) was prepared and its catalytic performance on synthesis of dimethyl carbonate (DMC) by transesterification of propylene carbonate (PC) and methanol was studied. And then reactive extraction technique was incorporated in the reaction of synthesizing DMC by transesterification of PC and methanol.ZnO-PbO was prepared by coprecipitation method firstly. The dependence of its properties on the preparation conditions, such as precursors of Zn and Pb, precipitators, weight ratio of Zn to Pb, and calcination temperature, was investigated. The optimal preparation conditions are as follows: Zn(NO3)2-6H2O and Pb(OAc)2-3H2O as the precursors, (NaOH:Na2CO3 = 3:l) as the precipitator, weight ratio of Zn to Pb being 3.5, and calcination temperature of 500°C. Then the effect of reaction conditions on the performance of ZnO-PbO catalyst in the transesterification reaction was studied. Under the following reaction conditions: reaction temperature of 110℃, reaction time of 2h, molar ratio of methanol to PC being 8.4, and catalyst amount of 3.0% (wt), the conversion of PC reached 63.8%, and the yield and the selectivity of DMC were 62.4% and 97.8%, respectively. XRD analysis result shows that the synergetic effect of ZnO, PbO, and suitable amount of Pb3O4 promotes the increase of the catalytic activity of ZnO-PbO. CO2-TPD measurement shows that the catalytic activity of ZnO-PbO can relate with the basic strength and the alkali amount of the alkali sites on the surface of the sample. In addition, the reuse of the catalyst was examined and the reason for deactivation was also analyzed.Incorporation of the transesterification of PC and methanol with reactive extraction technique can not only increase the equilibrium conversion but also avoid the formation of DMC-methanol azeotrope.At first, a series of alkanes were tested as the extractants in the homogeneous reaction system catalyzed by KOH. The result shows that n-octane is a feasible extractant and di-n-octyl phthalate (DOP) is the accessory extractant. The volumetric ratio of extract phase to reaction phase is 2.8 and the volumetric ratio of the main extratant and the accessory extractant is 0.7. Under the conditions of reaction temperature 100℃, reaction time 3h, and the weight percentageof the catalyst in the reaction system 3.0%, the distribution coefficient of DMC is 1.07, DMC yield is 64.8 %, and the selectivity is 76.0%. Comparing with the reaction without extractant, DMC yield increases by 47.6% and the selectivity increases by 26.7%.Reactive extraction technique has been incorporated in the heterogeneous reaction system catalyzed by ZnO-PbO. The result shows that n-dodecane is a feasible extractant and o-xylene is the accessory extractant. The optimal volumetric ratio of the accessory extractant and the main extratant is 0.4 and the volumetric ratio of extract phase to reaction phase is 0.3. Under the conditions of reaction temperature 100℃, reaction time 2h, and the weight percentage of the catalyst in the reaction system 2.7%, DMC yield is 66.0%, and the selectivity is 97.5%. Comparing with the reaction without extractant, DMC yield increases by 17.0% and the selectivity keeps almost constant.It is obvious that the reaction of synthesizing DMC by transesterification of PC and methanol can be promoted preferably by the reactive extraction technique.更多还原