丙烯液相本体聚合过程Polymers Plus建模与分析

Steady-State Modeling of Commercial Liquid Phase Bulk Polypropylene Process with Polymers Plus

依据聚合反应机理,采用ASPEN公司的PolymersPlus为软件平台,对Hypol工艺的丙烯液相本体聚合过程进行建模与流程模拟。聚合体系的物性以及相平衡采用含链扰动的统计流体理论(PC-SAFT)方法计算,参考文献值并结合工业装置的操作数据对丙烯聚合反应机理及其动力学参数进行修正。模拟分析表明,催化剂的氢活化速率常数、催化剂自失活速率常数以及链增长速率常数对单体转化率影响较大;氢气的链转移常数、活性中心向单体的链转移常数以及链增长速率常数对聚合度影响较大;催化体系的多活性中心导致相对分子质量分布加宽,对相对分子质量分布曲线进行解耦得到催化剂的活性位个数为6;反应器温度的变化不仅影响产量,同时也影响产品的相对分子质量。

A comprehensive model for liquid phase bulk propylene polymerization was developed by using polymers plus of ASPEN. The perturbed-chain statistical associating fluid theory equation of state (PC-SAFT) was applied to predict thermodynamic properties and phase equilibrium of propylene, hydrogen, and polypropylene in propylene bulk polymerization. Ziegler-Natta catalyst was characterized by assuming existence of six catalytic site types, and data from gel permeation chromatography (GPC) was deconvoluted to determine mass-average molecular mass and relative amounts of polymer produced at each site type. The model was validated by using plant data from production of two polypropylene grades. The model could accurately predict polymer production rate, relative molecular mass, and polydispersity index. Conversion of polymerization was sensitive to catalytic site activation by hydrogen, spontaneous catalytic site deactivation and chain propagation. The degree of polymerization was sensitive to chain transfer to hydrogen, chain transfer to monomer and chain propagation. Temperature in reactor affected not only productivity but also degree of polymerization because of sensitivity of reaction activation energy and phase equilibrium to temperature.