Catalysts and conditions for the highly efficient, selective and stable heterogeneous oligomerisation of ethylene

Abstract

The oligomerisation of ethylene into products in the C-4-C-20 range over heterogeneous nickel catalysts in a fixed-bed reactor at low temperature and high pressure (LT-HP) is reported. The catalysts were obtained by Ni (II) exchange or impregnation of two differently prepared amorphous and mesoporous silica-alumina supports. A plot of catalytic activity versus temperature at 35 bar and MHSV=2 produces a volcano-type curve with a maximum around 120 degrees C. Experiments performed under the LT-HP reaction conditions, viz. 120 degrees C, 35 bar and MHSV=2, give an ethylene conversion level of 99% and a 97% selectivity to products with an even number of carbon atoms. The product spectrum (C-n distribution) was dependent on the type of catalyst used, with the percentage of the C10+ oligomers lying in the range 23-41% by mass. Of practical significance, these types of catalyst were found to be extremely stable in use showing no detectable drop in conversion after 108 days on stream under the LT-HP reaction conditions employed.