Research In Ethylene Oligomerization/in Situ Copolymerization With Catalysts Immobilized Onto Molecular Sieves

This thesis focuses on the research in ethylene oligomerization and in situ copolymerization in the confined geometry, i.e. homogenous catalysts immobilized onto molecular sieves, in comparison with ethylene polymerization behavior using homogenous catalysts. We primarily explored the similarities and differences between the two catalytic systems. Experimental results showed that there are potential commercial applications for catalysts immobilized onto molecular sieves. Main contents of the research work are listed below:Two kinds of bis(imino)-pyridyl complexes possessing methyl alone and methyl plus halogen resp. catalyzed by MAO-modified SiO₂ with molecular sieves as absorbing reagent. Corresponding iron complexes by reacting bis(imino)-pyridyl complexes with FeCl₂·4H₂O were synthesized thereafter. Ethylene oligomerization activity under atmospheric pressure reached 2.89×10⁷ g/molFe·h with iron-based complexes as catalyst and MAO the co-catalyst. The oligomer distribution can be regulated by changing the structure of complexes.Iron-based LTM catalysts are firstly immobilized onto mesoporous molecular sieves (MCM-41 and SBA-15) and exhibited higher oligomerization activities than their homogenous counterparts above 70℃. In addition to its high temperature performance the molecular sieve-immobilized catalyst possessed relatively high selectivities for low molar-massα-olefins compared to the homogeneous catalyst.Iron-based LTM catalyst C₂₅H₁₇Cl₂N₃·FeCl₂ and metallocene catalyst Et(Ind)₂ZrCl₂ are firstly immobilized onto mesoporous molecular sieves (spherical MCM-41) and LLDPE is formed within the confined geometry of the pores of molecular sieve by in situ copolymerization. The dual-functional catalytic system showed easily controlled smoother kinetics process and the polymeric morphology of LLDPE was greatly improved. Compared with the homogenous catalyst systems, LLDPE prepared this way has obvious advantages such as higher molecular weights, lower melting temperatures, and higher branching degrees.