Kinetic Investigation Of Highly Selective Ethylene Trimerization Into 1-hexene Over Phillips M-based Catalyst System

1-Hexene is an important comonomer for the production of high-performance polyolefins. Recently chromium based catalyst system is playing an important role for highly-selective ethylene trimerization into 1-hexene with high selectivity up to 90%. Thus, it has become one of the hot research topics in this field. However, this catalyst technology is blockaded by Chevron Phillips Company. For independent intellectual property right in this field, it is necessary to further study on the kinetic of this catalyst system.In this work, the kinetics of the ethylene trimerization into 1-hexene over M/ligand/alkyl metal compounds/halide catalyst system (the Phillips ethylene trimerization catalyst system) was systematically studied. Firstly, after investigating the promotion effects of different halides, it was found that the catalyst system with tetrachloromethane presented the highest activity followed by halide A while the latter showed better 1-hexene selectivity. And the general performance of the system with halide A is better than that with 1,1,2,2-tetrabromoethane. Thus, the subsequent kinetic study of ethylene trimerization was focused on the M/ligand/cocatalyst/halide A catalyst system. It was found that among the different alkyl metal cocatalysts, triethylaluminum showed the best performance. The catalytic activity firstly increased with the increasing of the amounts of alkyl aluminum, halide and ligand, then decreased with the further increasing the amounts of the three compounds. The optimal conditions are as follows:the molar ratio of M/ligand/cocatalyst /halide A is 1:5:140:15 with the reaction temperature of 95℃. Combined the methods of Aspen Plus software and the classical kinetic model for kinetic simulation, it is found that the ethylene trimerization reaction is first order to the concentration of chromium species and second order to the ethylene pressure, and the activation energy of this reaction at the optical conditions is 85.3 kJ/mol. The obtained kinetic equation is R= 4.95×1016×exp(-(?))(Cca)1.09(Ce)1.95 The results provide much deeper mechanistic understanding on the ethylene trimerization process.