The oligomerisation of propene over nickel oxide silica alumina

Master Thesis


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University of Cape Town

A synthesis techniQue was developed for the preparation of a nickel oxide sil ica alumina catalyst. The propene oligomerisation activity and the selectivity of the catalysts prepared by homogeneous decomposition deposition (HDD) were investigated and compared with nickel oxide silica alumina catalysts prepared by the techniQues of impregnation (IMP) and co-precipitation (SG). Amongst others. the effect of the nickel content. reacti6n temperature and pressure, and water content of the feed, on the activity and selectivity. were investigated. Also investigated were the lifetime of the various catalysts and, in the case of HDD type catalysts. the ability to oligomerise high molecular weight hydrocarbons (Cb). Nickel oxide silica alumina prepared by the HDD method is more active for the propene oligomerisation than catalysts prepared by the IMP and SG methods. The product spectrum in the case of IMP and HDD type catalysts are similar, with a propene dimer (Cb) being the main product. In the case of SG type catalysts. however. a shift to heavier products was observed, i.e., propene dimer (Cb) and trimer (Cq) were formed in eQual Quantities. It is proposed that the increase in activity of HDD type catalysts was due to a large extent of metal dispersion and distribution and a stronger interaction between the metal and the support. It is also proposed that the metal is readily accessible to the reactant molecules. The activity and selectivity of catalysts prepared by the HDD method were independent of the nickel content. This was not the case for IMP and SG type catalysts. both of which showed decreasing activity with increasing nickel content when the nickel content was increased beyond 5 wt%. The lifetimes of the various catalysts were also examined. From the results obtained. over the first 10 h. the lifetime of HOD type catalysts was superior to that of the other catalysts studied. The activity and selectivity of the various catalysts were sensitive to the reaction conditions. Thus moving into the vapour phase. by either increasing the temperature at a fixed pressure or decreasing the pressure at a fixed temperature. was in each case acCompanied by a shift to heavier products and a decrease in activity.

Bibliography: pages 129-132.