Copolymerization of Ethylene and Propylene Using 4th Generation Ziegler- Natta Catalyst: Influence of Cocatalyst, External Electron Donor and Hydrogen
Copolymerization of ethylene and propylene was investigated using a 4th generation phthalate Ziegler-Natta catalyst in normal hexane in a Buchi reactor. The effects of different mole fractions of [Al]/[Ti], [Si]/[Al] and various amounts of hydrogen on productivity and weight percent of ethylene on the product, were studied. In the copolymerization reactions, tri-isobutyl aluminum (TiBAl) was used as cocatalyst instead of triethyl aluminum (TEAl) because TiBAl produced a more amorphous copolymer. In molar ratio [TiBAl]/[Ti] = 480 the catalyst activity was at maximum and ethylene content in this ratio was at minimum. Cyclohexyl-methyldimethoxy silane was used as external donor. In molar ratio [Si]/[TiBAl] = 0.05, the copolymer showed more amorphous behavior. In this molar ratio, the external donor decreased the productivity of the catalyst and a further increase of external donor concentration increased the productivity. Hydrogen increased the productivity of the catalyst and decreased the ethylene content of the copolymer in low concentration. In high concentration, however, hydrogen decreased the productivity and increased the ethylene content of the copolymer. Hydrogen as a chain transfer agent decreased the viscosity average molecular weight.
کلیدواژه ها [English]
copolymerization, Ziegler-Natta catalyst, external electron donor, slurry polymerization, cocatalyst