异丁烷-丁烯烷基化体系基元反应网络研究

ELUCIDATION OF ELEMENTARY REACTION NETWORK FOR ISOBUTANE-BUTENE ALKYLATION SYSTEM

利用分子模拟方法,对异丁烷-丁烯烷基化反应体系中C4和C8碳正离子可能进行的各类基元反应进行了研究。结果表明,对于C4碳正离子而言,2种伯丁基碳正离子的能量明显较高,而仲丁基碳正离子和叔丁基碳正离子的能量分别比伯正丁基碳正离子低71.94 kJ/mol和125.99 kJ/mol;对于C8碳正离子而言,所有的伯碳正离子在结构优化时,均自发地异构成了相应的C8仲碳正离子或叔碳正离子。这表明异丁烷-丁烯烷基化反应体系中C4和C8伯碳正离子不可能存在,或者说存在几率很低。依据量子化学计算结果,确定了异丁烷-丁烯烷基化反应体系中可能存在的碳正离子中间体,依据碳正离子反应假设,确定了12种烯烃质子化反应、29种碳正离子异构化反应、32种碳正离子与丁烯的加成反应、30种碳正离子与异丁烷之间的负氢离子转移反应和18种碳正离子脱附反应。在此基础之上,构建了涉及60个物种和121个基元反应的具有较强预测能力的基元反应网络。

Density functional theory-based ab-initio quantum method was selected to optimize the structure of butyl and octyl carbeniums. Calculation results showed that primary butyl carbenium was less stable than secondary and tertiary butyl carbenium, and the energy of secondary and tertiary butyl carbenium were 71.94 kJ/mol and 125.99 kJ/mol lower than that of primary butyl carbenium respectively. As for octyl carbeniums, it was proved that all primary octyl carbenium spontaneously turned into corresponding secondary or tertiary octyl carbenium while being optimized, which indicated that there was no or very low probability for primary carbenium to exist in isobutane-butene system. Based on these quantum results, possible carbenium intermediates were chosen, and according to the carbenium mechanism＇, all main possible elementary reactions were designed, which consisted of 12 olefin protonation reactions, 29 isomerization reactions, 32 addition of carbenium to various butenes, 30 hydride transfer reactions and 18 deproponation of carbeniums. As a result, a powerful elementary reaction network has been established for isobutane-butene alkylation system.