Studies On Ethylene Oligomerization With Novel Catalysts

α-olefins such as 1-hexene and 1-octene are important chemical feedstocks, and the key to producing it via ethylene oligomerization is the development of the high effective catalysts. In this paper, a series of nickel, iron, trinal and quadplex chromium, supported chromium-based complexes were synthesized and systemic investigated.Nickel-based catalysts: First of all, five kinds amount to fifteen acetyl pyridy nickel-based complexes were synthesized, and the influences of the steric bulk of ortho-substituents, the variety of ortho-substituents, p-substituents, m-substituents, alkyl-substituents and single or double substituents on the catalytic performance were studied in the presence of aniline ligand. The results show that 2-acetyl-6(2-methyl phenyl imino)ethyl pyridyl nickel-based complexes exhibited higher catalytic activity andα-olefins selectivity. In addition, the reaction temperature, catalyst and reaction time were studied and optimized on the productivity of ligand. Finally, various reaction parameters such as reaction temperature, reaction pressure, molar ratio of aluminum to nickel, the concentration of precatalyst and reaction time on the catalytic activity and the selectivity ofα-olefin were investigated. Under the conditions of 60℃, 2.0 MPa, 30 minute, the molar ratio of aluminum to nickel of 1500 and the concentration of nickel of 20μmol/L, the catalyst gives a high catalytic activity of 1.95×107 g/mol Ni?h, a selectivity of 1-hexene up to 20.0 wt% and 1-octene 19.1 wt%.Iron-based catalysts: Chloro-2-acetyl-6(2-methyl phenyl imino)ethyl pyridyl ironl-based complexes were synthesized. The effects of reaction temperature, molar ratio of aluminum to iron and reaction pressure on the catalytic activity and the selectivity ofα-olefin were investigated. Under the condition of 60℃, 4.0 MPa,30 minute, the molar ratio of aluminum to iron of 1500 and the concentration of iron of 20μmol/L. The catalyst system yields 1-octene in selectivity up to 18.5 wt%, 1-hexene up to 20.6 wt%, catalytic activity in excess of 2.70×107 g/mol Fe?h could be achieved.Trinal chromium-based catalysts: Twelve P∩N∩P / P∩N∩R∩N∩P ligands were synthesized. Ethylene oligomerization was carried out in the presence of ligands, Cr(acac)3 and MAO, and the effects of steric bulk of ligands were also studied. The results reveal that the catalyst system with j, k, l ligands show high catalytic activity and 1-octene selectivity. Subsequently, the effects of reaction temperature, molar ratio of aluminum to chromium and reaction pressure on the catalytic activity and the selectivity of 1-octene were investigated. Under the condition of chromium of 190μmol/L, the molar ratio of aluminum to ligand to chromium of 350: 2:1, 30 minute, 50℃and 4.0MPa, the catalytic activity is 3.42×106g/mol Cr?h, the selectivity of 1-octene is 73.3 wt%.Quadplex chromium-based catalysts: In order to improve the selectivity of 1-octene, an accelerant was added into the catalyst system which is composed of Cr(acac)3, ligand 1 and cocatalyst, and the effects of accelerant, cocatalyst, molar ratio of ligand to chromium, molar ratio of aluminum to chromium, reaction temperature and reaction pressure were investigated. The results demonstrate that an increased activity and 1-octene selectivity were observed in the presence of hexachloroethane and MAO. Under the condition of chromium of 100μmol/L, molar ratio of chromium to ligand to MAO to hexachloroethane of 1:1:300:1.5, 30min, 50℃and 5.0 MPa, the catalytic activity is 4.5×106 g/mol Cr?h, the selectivity of 1-octene is 79.3 wt%. Quadplex chromium-based complexes supported on SiO2: In order to prevent the polymer from pasting on the reactor and reduce the amount of the cocatalyst, quadplex chromium-based complexes supported on SiO2 which was modified by MAO were prepared and characterized. Upon the effects of reaction condition on supported amount of chromium and aluminum, we supposed the mechanism of supporting. Furthermore, reaction parameters were studied, as well as the kinetics. Finally, comparing with homogeneous catalysts, the polymer by-products were characterized by thermal analysis, as well as the molecular weight and molecular distribution. Under the condition of chromium of 480μmol/L, molar ratio of chromium to ligand to MAO to hexachloroethane of 1:1:100:1.5, 30 minute, 40℃and 4.0 MPa, the catalytic activity is up to 1.9×106 g/mol Cr?h, the selectivity of 1-octene is 81.4 wt%. The results show that the apparent configuration of the polymers were remarkably improved by using the homogeneous catalysts supported on SiO2. Moreover, the compact polyethylene, the configuration of which is similar to SiO2 was obtained.