Research On MgCl₂/SiO₂ Complex Support Catalyst For Ethylene Gas Phase Polymerization

Ziegler-Natta catalyst is widely used in polyethylene industry due to its easy preparation and low sensitivity to impurity. Now, the aim of research and development of Ziegler-Natta catalyst is not only on high activity, but also on its high performance and morphology structure. Both support and drying-molding process play important role in the preparation process of Ziegler-Natta catalyst. They are important aspects of researching Ziegler-Natta catalyst, and internal electron donor is another important aspect. In this paper, we prepared Ziegler-Natta catalyst of MgCl₂/SiO₂ complex support by spray-drying technology. In the preparation process, internal electron donor occured a weak chemical reaction with SiO₂ support so as to bind some active components. By the effect of internal electron donor, on the one hand, the load of active component was enhanced and activity of the catalyst was increased. On the other hand, the bulk density of polymer was enhanced because the active components entered the tiny hole of the SiO₂ support.The effects of different kinds of components, catalyst preparation conditions and electron donors on the performance of the catalyst were investigated during the preparation process. From the experiment results we know that the optimal catalyst component are when the SiO₂/MgCl₂ molar ratio is 0.5, Ti/Mg molar ratio is 0.5, Donor/Ti molar ratio is 0.6. When the flow of spray-drying carrier gas is 15L/s, temperature of its inlet and outlet respectively are 150℃and 70℃, spray-drying reaches the best effect. Polymerization activity of the catalyst can reach 12385g·PE/g·Cat and is higher than that of UCAT-J catalyst. As activity of the catalyst intensively releases in the earlier stage of polymerization process, the catalyst is very suitable for the condensation state operation in gas fluidized-bed polyethylene process.