Characterization of a titanium-aluminium catalyst with n-butoxy ligands in the process of ethylene polymerization
The course of ethylene polymerization in the presence of a catalytic system comprising (n-BuO)4Ti+Et2AlCl has been investigated. The effect of monomer and catalyst concentration and of composition of the catalytic system, Expressem as the Al/Ti molar ratio, on the yield of polymerization and on the process of titanium reduction has been investigated. By kinetic method the concentration of active centres (no*) and rate constant of elementary reaction of chain propagation (kp) has been determined. The obtained values have been compared with analogous data from the literature for other catalytic systems. The (n-BuO)4Ti+Et2AlCl catalytic system is characterized by a relatively low value of no* and a high value of kp, what results in the formation of polyethylene with a high molecular mass. It has been found that the reaction of catalytic system deactivation is of first order in relation to active centres concentration. The value of rate constant of the deactivation reaction has been also determined — it is equal to kd =(4.32±0.1)·10-5s-1. This value is independent on the monomer concentration and on the presence of hydrogen in the polymerization medium. The reasons of a high stability of the catalytic system under study have also been explained.
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