Synthesis of ethylene trimerization catalyst and tandem catalysis for preparing linear-lowdensity polyethylene

Abstract

The selective trimerization of ethylene was investigated using catalytic systems con-taining potentially tetradentate trianionic triethoxyamine. Cyclopentadienyl-arene titanatrane catalysts activated by methylaluminoxane cocatalyst were studied for the trimerization of ethylene. The introduction of electron-rich multidentate ligands to the catalysts` active sites resulted in good productivity and selectivity for ethylene trimerization. The catalysts showed selective ethylene trimerization (over 92 wt%) with good 1-hexene productivity (over 25 $kgC_6/mmolTi.h$). Small amounts of polyethylene byproduct were also produced. Various amounts of methylaluminoxane were tested and methods of its introduction to the system were varied. It has been shown that pre-alkylation of catalyst with methylaluminoxane increases the productivity of ethylene trimerization. The effects of reaction temperature and pressure on 1-hexene productivity and selectivity were also studied. The rate of ethylene conversion was approximately first order with respect to ethylene concentration. 1-Hexene was produced under moderate conditions, allowing energy savings to be gained through lower temperature reactions.

Tandem catalysis systems with trimerization catalyst and polymerization catalyst were investigated to synthesize linear low-density polyethylene(LLDPE) from ethylene without comonomer like 1-hexene in a single reactor. Cyclopentadienyl-arene titanatrane catalyst was used for selective ethylene trimerization. Metallocene catalyst like bis(indenyl)zirconium dichloride catalyst and constrained-geometry catalyst(CGC) like half metallocene complex constructed with thiophene-fused cyclopentadienyl/tetrahydroquinaldine were used as po-lymerization catalyst. Two steps of temperature change from $15^circ C$ to $70^circ C$ is the optimum condition for synthesizing LLDPE with single ethylene feeding. For the solvent, toluene can be the best solvent for homogeneous polymerization; cyclohexane can...