摘要
在室温条件下用氧化钙催化碳酸丙烯酯 (PC)和甲醇的酯交换反应 ,高收率、高选择性地合成了碳酸二甲酯 (DMC) .在假设羟丙基甲基碳酸酯 (HPMC)是反应中间产物的基础上 ,计算了甲醇、PC和HPMC的电荷分布 ,并推论出可能的副反应PC的聚合 .通过考察反应温度对DMC选择性和收率的影响 ,证明了关于中间体HPMC和副反应PC聚合的假设 .考察了加料顺序、反应温度对DMC生成速率的影响 。
Dimethyl carbonate (DMC) is an important precursor of polycarbonate resins as well as a useful carbonylation and methylation agent. Because of the moderate reaction conditions and the use of CO_2 as raw material, preparation of DMC by transesterification of cyclic carbonate with methanol has gained increasing attention in recent years. In the present paper, CaO , which shows excellent catalytic activity, was used as a solid base catalyst for the rudimental investigation of its catalytic behavior for synthesis of DMC from propylene carbonate (PC) and methanol and the mechanism of this reaction over CaO. CaO was prepared from CaCO_3 calcined at 900 ℃ in N_2 atmosphere. The reaction was carried out in a flask (250 ml) equipped with a reflux condenser, water bath and magnetic stirring. The reaction products were analyzed by GC after centrifugal separation of the solid catalyst from the solution. On the basis of the assumption that hydroxylpropyl methyl carbonate (HPMC) was the intermediate of this reaction, the charge distribution of PC, methanol and HPMC was calculated and the possible reactions were proposed. There were both consecutive reactions and competitive reactions. The first step of consecutive reaction, the transesterification of PC with methanol, was slow; whereas the second step, the transesterification of HPMC with methanol, was fast, with a slow side reaction of PC polymerization competing with it. The result of the effect of temperature on DMC selectivity was consistent with the assumption of HPMC as an intermediate and the inference of possible reaction. Further investigation of the effect of addition sequence on reaction rate elucidates that the main function of the catalyst is to activate MeOH other than PC and the H-bond between PC and MeOH can activate PC to some extent. From the result of the effect of temperature on reaction rate, it is found that the reaction rate is controlled by both the activation of methanol and its reaction with PC. Based on the results illustrated above, the mechanis
出处
《催化学报》
SCIE
CAS
CSCD
北大核心
2003年第1期52-56,共5页
基金
中国石油天然气总公司资助项目 (KF 2 0 0 2 0 1)
关键词
合成
氧化钙
碳酸丙烯酯
甲醇
酯交换
碳酸二甲酯
催化剂
calcium oxide, propylene carbonate, methanol, transesterification, dimethyl carbonate
