Ziegler-Natta催化剂催化丙烯聚合的动力学OA

This study investigated the propylene polymerization behaviors using particulate Ziegler-Natta(Z-N)catalyst(Cat-P)and slurry Z-N catalysts(Cat-M1 and Cat-M2)derived from Cat-P with different dispersion media.The results demonstrated that Cat-P exhibited the fastest activation,the highest catalytic activity and yielded polypropylene(PP)with the highest isotacticity and the lowest fine powder content(0.6%,mass fraction).In contrast,the slurry catalyst Cat-M1 showed the lowest catalytic activity and produced PP with the highest fine powder content(10.7%)and the lowest isotacticity.The slurry catalyst Cat-M2,prepared by modifying the viscosity and surface tension of dispersion medium M1,exhibited higher catalytic activity,improved isotacticity,and reduced fine powder content compared to Cat-M1.The study elucidated that the dispersion medium with high viscosity and surface tension impeded the diffusion of co-catalyst,external donor,and propylene monomer into the catalyst particles.Diffusion control slowed the formation of highly stereospecific active sites,while also leading to insufficient monomer supply locally,which in turn facilitated the deactivation of some active sites via further reduction by alkylaluminum.Consequently,Cat-M1 exhibited lower initial activity,decreased isotacticity,and increased fine powder generation during the early polymerization stage.The particulate Cat-P and modified Cat-M2 catalysts allowed for rapid initiation and polymerization at the Ti active sites.The rapidly growing polymer chains effectively exerted a"guard effect"to protect the active sites from deactivation.This work clarified the diffusion-controlled effects during the activation and chain propagation of heterogeneous Z-N catalysts,providing a theoretical basis for the stable control of industrial olefin polymerization.