Preparation And Optimization Of SiO₂/MgCl₂?Ethoxide Type?Bi-supported Ziegler-natta Polyethylene Catalyst

Polyethylene is one of the most widely applied synthetic resin At present,the production of polyethylene with Ziegler-Natta catalysts accounts for about half of global polyethylene production,which is closely related to the discovery of efficient Ti-Mg catalysts.The magnesium sources used for catalysts include anhydrous MgCl2,RMgX,Mg(OH)2,Mg(OEt)2 and so on,among which the Mg(OEt)2-based Ziegler-Natta catalyst was industrialized due to its high activity.However,it is difficult to control the particle morphology of the catalysts.In this study,silica gel was impregnated with Mg(OEt)2 in solvent,and then the SiO2/MgCl2(ethoxide type)bi-supported Ziegler-Natta catalyst was prepared by reacting with TiCl4.The preparation method of the catalyst was novel and simple,and the catalyst showed good particle morphology and high polymerization activity.The main work is to optimize the preparation conditions of the catalysts,and the contents including:(1)300 ?,450 ? and 600 ? were chosen for thermal activation temperature of silica gel,respectively;(2)The catalyst precursors with different magnesium loading were reacting with TiCl4;(3)Changing the Ti/Mg.molar ratio.The effects of preparation conditions on the catalysts were analysed by polymerization.The results showed that 600 ? calcination temperature of silica was more conducive to the formation of active ?-MgCl2 carrier.Under this condition,the obtained catalyst showed the highest activities of homo-and co-polymerization,good hydrogen response and the copolymer had the highest incorporation of comonomer.By comparing the catalysts obtained from different magnesium loading contents with each other,the catalyst with 15 wt%of magnesium toading showed the best performance of polymerization and good hydrogen response,due to its highest surface area and the most formation of ?-MgCl2.By changing Ti/Mg molar ratios,the catalyst obtained from 2.25 of Ti/Mg molar ratio had larger surface area and more ?-MgCl2,which could effectively improve the activities of homo-and co-polymerization,and the copolymer had the highest incorporation of 1-hexene.