环管反应器中聚丙烯颗粒内部的质量与热量传递模型

Intraparticle Mass and Heat Transport Model of Polypropylene in a Loop Reactor

针对环管反应器中Ziegler-Natta催化剂催化的聚丙烯颗粒增长过程,采用多层模型建立了聚丙烯颗粒内部的质量与热量传递预测模型。通过模型模拟得到聚丙烯颗粒内部的丙烯单体浓度梯度和温度梯度。此外,通过模型分析了聚丙烯颗粒的增长规律。结果表明,环管反应器中的聚丙烯颗粒内部的单体浓度梯度明显,该浓度梯度值随扩散系数的增大而减小,随催化剂初始粒径减小而减小;相比于浓度梯度而言,聚丙烯颗粒内部的温度梯度并不明显,温度值随聚合进行而增加,温度梯度则随催化剂初始粒径的增加而增加;不同大小的催化剂颗粒增长得到的聚丙烯颗粒的增长倍数不同。

In the present study, the multilayer model （MLM） was used to describe the intraparticle mass and heat transport phenomena of polypropylene produced by propylene polymerization with the Ziegler-Natta catalyst in a loop reactor. Accordingly, the monomer concentration gradient and temperature gradient in the polymer particles and the rule of polymer particle growth were obtained based on the MLM. The results show that the intraparticle monomer concentration gradient is obvious, while the intraparticle temperature gradient is not so evident. Moreover, the simulated intraparticle monomer concentration gradient decreases with the increase of the value of the diffusion coefficient and decreases with the decrease of the original catalyst particle size. In addition, the intraparticle temperature increases with the increase of the polymerization time and the intraparticle temperature gradient increases with the increase of the catalyst original particle size. The results also show that the growth multiple of the polypropylene particle changes with the change of the original particle diameter of the catalyst.