茂金属催化的丙烯气相聚合过程的单颗粒传质与传热模型

摘要

在分析负载茂金属催化的丙烯气相聚合过程中催化剂颗粒破碎行为基础上,提出了该过程聚丙烯颗粒内部传质与传热物理模型,耦合丙烯聚合本征反应建立了丙烯气相聚合过程的单颗粒模型:改进的多粒模型.采用上述模型得到了丙烯气相聚合过程中聚丙烯颗粒内部的单体浓度、平均温度、颗粒内部的温度梯度以及催化剂活性中心浓度等的变化规律.模拟结果表明,聚丙烯颗粒内部的温度及催化剂浓度变化较小,而颗粒内部的传质阻力对聚合影响较大.另外,模拟结果也表明负载茂金属催化剂颗粒在聚合过程是一个由外到里的逐层破裂过程.%Based on the analysis of the catalyst fragmentation during the polymerization, a physical model used to describe the mass and heat transport behaviors of the gas-phase propylene polymerization catalyzed by a silica-supported metallocene catalyst was proposed. Furthermore, a modified multigrain model (MMGM) was obtained by coupling the physical model proposed with the intrinsic reaction of the propylene polymerization.Accordingly, the variation rules of the monomer concentration, mean temperature, temperature gradient and catalyst concentration, etc. in the polymer particles were obtained based on the MMGM. The simulation results show that both the catalyst concentration change and temperature gradient in the polymer particles are very small and the intrapartiele mass transport resistance has a great effect on the polymerization. In addition, the simulation results also show that the silica-supported metallocene catalyst fragmentation happens according to the shell-by-shell way from the surface to the centre oftbe catalyst during the polymerization.