烷基化反应混合物在Y型分子筛中吸附及反应失活机理的分子模拟

Simulation of Multi-Component Adsorption and Deactivation Mechanism of Alkylation Reaction in Zeolites

采用密度泛函法、蒙特卡罗方法以及分子动力学方法,系统研究了烷基化反应过程的反应物(异丁烷、丁烯)、产物(异辛烷)、副产物(代表组分C9H20、C12H26烷烃)在典型分子筛催化剂Y型分子筛中的吸附传质特性。研究得到了反应混合物组成及分子筛硅/铝摩尔比对分子筛吸附量的影响规律,探讨了烷基化反应高烷/烯比进料的分子尺度机理;获得了不同组分在分子筛内的扩散性质,并重点研究了分子筛中副产物(C12H26)吸附量对反应物受限扩散性质的影响规律。结果表明,烷基化反应过程中,随着副产物吸附量的增大,Y型分子筛催化剂活性位点可接近性与反应物自扩散系数显著降低是催化剂迅速失活的主要原因。

For the rapid deactivation of the zeolite catalysts in the alkylation process,the adsorption and mass transfer characteristics of typical reactants(isobutane,butene),products(isooctane),by-products(representative components C9H20 and C12H26)in zeolite Y were studied by density functional theory,Monte Carlo and molecular dynamics simulations.The effects of the composition of reaction mixture and the ratio of silicon to aluminium on the adsorption capacity of zeolite were studied,and the mechanism of feed with high ratio of isobutane to butene was revealed at the molecular scale.The diffusion properties of different components in zeolite were obtained,and the effects of by-products(C12H26)on confined diffusion of the reactants in zeolite were studied.The results show that the accessibility of the active sites and the diffusion coefficient of the reactants decrease significantly with the increase of the adsorbed by-products,which are the main reasons for the rapid deactivation of the zeolite catalysts.