A New Technology For Production Of Dodecene And Octadecene By Propene Oligomerization Over NiSO₄/γ-Al₂O₃ Catalyst

A new technology of producing dodecene and octadecene by propene oligomerization over NiSO4/γ-Al2O3 has been studied. Effects of reaction conditions, catalyst stability and regeneration methods of deactivated catalyst were investigated.The results showed that under mild reaction conditions, the selectivity of dodecene and octadecene were high. Reaction temperature and liquid hourly space velocity (LHSV) exerted strong influence on propene conversion and product selectivity. It was found that the conversion of propene was gradually increased with raising reaction temperature, but the effect of LHSV was reverse. The optimal reaction conditions were confirmed to be as follows: reaction pressure 2.0 MPa, LHSV 1.0h-1, reaction temperature 10℃ in first stage reactor and LHSV 0.5 h-1, reaction temperature 80 ℃ in the second. Under the optimal conditions, total conversion of propene was as high as 90%, and the selectivity of dodecene and octadecene were 49.1% and 9.3%, respectively.The effect of impurities in the propene on stability of the catalyst had been discussed. It was found that the stability of the catalyst were effected by various factors, especially by the trace amount of impurities like the H2O, CO and alkine.NiSO4/γ-Al2O3 catalyst showed promising stability on propene oligomerization. Propene conversion has been kept to be up to 90% for 812h during an on-stream running in first stage reactor and 2264h in the second. Upon prolonging the reaction time, the selectivity of dimmer in first stage reactor was increased slowly from 63% to 81%. However, the selectivity of tetramer and hexamer in second stage reactor was gradually decreased. The selectivity of tetramer could reach to 47% or even higher when raising reaction temperature. The selectivity of hexamer was maintained at a level of above 5%.Regeneration process of deactivated catalyst was investigated. A feasible regeneration method was determined. Deactivated catalyst can be regenerated by calcination in dry air at 500 ℃ for a couple of hours. Next, the calcined catalyst was impregnated a certain amount of (NH4)2SO4. Finally, it was calcined in dry nitrogen at 500℃ for 4h. The lost SO42- species on catalyst surface can be repaired by (NH4)2SO4. It has been found that activity, selectivity and stability of regenerated catalyst were almost the same as that of new catalyst.Direct connection of the two-stage reactor is an old technology with some disadvantages. To improve the performance of the old technology, a new method of using an independent propene separation equipment between the two stage reactor was proposed in this study. It was expected that the catalytic performance of the two reactors would be improved by such innovation.