Ethylene Oligomerization To α-Olefins Catalyzed By Late-Transition-Metal Catalysts

Linear α-olefms are used widely in many areas as co-monomer for the production of linear low-density polyethylene (LLDPE), politicizes and synthetic lubricant etc. α-olefins are produced mainly by ethylene oligomerization in the world except in China. The increasing demands for α-olefins need us pay more attention on ethylene oligomerization.As a core technology of ethylene oligomerization, catalysts have attracted much attention academically and commercially. In recent years, the late-transition-metal catalyst, especially Fe(II)-based complexes have been found with high activities and selectivity for oligomerization of ethylene to linear α-olefms.3 kinds of novel Fe(II)-based complexes were synthesized, {2,6-bis[l-(2-methyl-4 -methoxylphenylimino)ethyl]pyridine iron(II)chloride} (1), {2,6-bis[l- (2,4-dimethylphenyl -imino)ethyl]pyridine iron(II) chloride} (2), (2,6-bis[l-(2-methyl -4-brone -phenylimino)ethyl] -pyridine iron(II) chloride} (4), by using standard Schlenk techniques, with exceptionally high activities of 2.8×108g/ (mol-h) (1), 2.9×108g./ (mol-h) (2), 5.1×108g/ (mol-h) (4)) respectively for oligomerization of ethylene and high selectivity for linear a-olefins as well.It was found that the structure of catalyst was the main factor of tuning the catalytic activity and the molecular weight distribution of the oligomer. Iron-based catalysts showed higher catalytic activity than cobalt-based catalysts over more than 10 times. With the electronic withdrawing of the substituents on the bis(imino)pyridyl group increasing, the catalytic activity increased and the molecular weight of the oligomer decreased. The effects of reaction conditions were also studied, such as reaction temperature, ethylene pressure, the molar ratio of aluminum to iron, the concentration of catalysts. The kinetics behaviors of ethylene oligomerization by novel iron-based catalysts were investigated. The apparent kinetic parameters were determined.