K/KCC-1催化碳酸二甲酯和乙醇酯交换合成碳酸甲乙酯

Synthesis of methyl ethyl carbonate by transesterification of dimethyl carbonate and ethanol catalyzed by K/KCC-1

以水热合成法制备的树突纤维状二氧化硅(KCC-1)为载体、乙酸钾为前驱体,采用等体积浸渍法制备了不同K理论负载量(x,x为K与Si物质的量的比值,分别为0.3、0.5、0.7、0.9、1.1)的固体碱催化剂(x K/KCC-1)。采用XRD、FTIR、BET、CO_(2)-TPD和SEM对x K/KCC-1进行了表征,评价了其对碳酸二甲酯(DMC)和乙醇进行酯交换反应合成碳酸甲乙酯(EMC)的催化性能。结果表明,x K/KCC-1具有2种碱性位,分别是由K_(2)SiO_(3)提供的弱碱性位和由K_(2)CO_(3)提供的中强碱性位,且随着K理论负载量的增加,弱碱性位点逐渐下降,中强碱性位点逐渐增强,催化剂的反应活性增强。K理论负载量≤0.9的x K/KCC-1仍保持KCC-1的树突纤维结构,使反应物分子能够较好地扩散到活性位点上,0.9K/KCC-1具有最高的催化活性。在反应温度为80℃、反应时间为5 h、乙醇与DMC(4.494 g)的物质的量比为4∶1、0.9K/KCC-1用量为DMC质量的5%的最佳反应条件下,DMC的转化率为91.0%,EMC的选择性为95.5%,且其具有良好的循环稳定性,重复使用5次后,DMC的转化率为86.7%,EMC的选择性为95.2%。

Solid base catalysts(xK/KCC-1)with different K theoretical loading(x,x is the molar ratio of K to Si,x=0.3,0.5,0.7,0.9,1.1)were synthesized by equi-volumetic impregnation method using dendrite fibrous silica(KCC-1)prepared from hydrothermal synthesis as support and potassium acetate as precursor,and characterized by XRD,FTIR,BET,CO_(2)-TPD and SEM.xK/KCC-1 samples were then evaluated for their catalytic performance on the synthesis of methyl ethyl carbonate(EMC)via transesterification of dimethyl carbonate(DMC)and ethanol.The results indicated that xK/KCC-1 had two types of basic sites,the weak basic sites provided by K_(2)SiO_(3) and the medium strong basic sites provided by K_(2)CO_(3).With the increase in K theoretical loading,the weak basic sites gradually decreased,while the medium strong basic sites gradually increased,thus enhancing the reaction activity of transesterification.xK/KCC-1 with K theoretical loading≤0.9 still maintained the dendritic fiber structure of KCC-1,allowing reactant molecules to diffuse well to the active sites.0.9K/KCC-1 exhibited the highest catalytic activity.Under the optimal reaction conditions of reaction temperature 80℃,reaction time 5 h,molar ratio of ethanol to DMC(4.494 g)4∶1,and 0.9K/KCC-1 dosage 5%of DMC mass,the conversion rate of DMC was 91.0%,and the EMC selectivity was 95.5%.Furthermore,0.9K/KCC-1 showed good cyclic stability,with a DMC conversion of 86.7%and an EMC selectivity of 95.2%after 5 recycles.