Preparing a modified and promoted homogeneous titanium catalyst for ethylene dimerization to butene-۱

Ethylene dimerization is a significant process among the other petrochemical processes due to the production of alpha olefins as the most widely used industrial intermediate. Titanium tetra butoxide/tetrahydrofuran/triethyl aluminum is the main homogeneous catalyst complex in this process. On the other hand, the formation of polymer or oligomerization side reactions are the salient obstacles in the ethylene dimerization process. The effect of various promoters from the group of halo hydrocarbons, along with different modifiers from the group of esters and silane compounds had been investigated to conquer the barriers mentioned above. The reaction conversion, selectivity, and polymer production were the remarkable parameters that were evaluated to study the components’ impacts. The results indicated that the addition of promoters through reaction with Triethyl aluminum (TEA) (co-catalyst) increased the reaction speed and thus increased the conversion of the reaction to ۸۸.۲۶% and reduced the reaction time to ۶۰ min. Among the promoters, the reaction conversion and selectivity of dichloromethane were ۸۸.۲۶% and ۷۸.۴۵%, higher than that of dibromopropane (۴۸.۵۲% and ۳۹.۵۲%), but a higher amount of polymer was produced by dichloromethane. Moreover, Esters strongly decreased the catalyst activity, resulting in a decrease in the conversion to under ۲۵%. On the other hand, silanes showed a significant effect on the control of the polymer chains in Ziegler-Natta homogeneous catalysts. Dicyclopentyldimethoxysilane (DCPDS) modifier brought about an increase of ۱.۵% in ethylene conversion and a ۶% increase in the ۱-butene selectivity. At the same time, the polymer formation also prevented a significant amount so the amount of polymer decreased to about ۲.۱ mg. DCPDS modifier performed better than the Cyclohexylmethyldimethoxysilane (CHMDS) donor.

Keywords:

Butene-۱ , Homogeneous catalyst , Dimerization , Ethylene conversion , promotor