Activity and selectivity of nickel-exchanged silica-alumina catalysts for the oligomerization of propene and 1-butene into distillate-range products

The oligomerization of propene and 1-butene into Cl10+ or distillate-range products has been studied using Ni(II)-exchanged silica-alumina catalysts in a fixed-bed flow-reactor. The reaction temperature was varied between 40 and 350 degreesC, and pressures between 0.75 and 4.5 MPa were applied. As reported previously for the oligomerization of ethene, two temperature regions of high catalyst activity were also found with propene and 1-butene. At low temperature (+/-120 degreesC), mainly selective nickel-catalyzed oligomerization was observed, with the oligomers formed consisting of integral multiples of the monomer (true oligomerization). In this temperature region, the reactivity of the alkenes was found to decrease with increasing chain length (ethene much greater than propene > 1-butene). As the reaction temperature is raised, acid-catalyzed oligomerization contributes increasingly to the product spectrum, and this is evidenced by the formation of products composed of non-integral multiples of the monomer (hetero-oligomerization). The mass percentage of C10+ product which can be obtained in a straight run at low temperature (+/-120degreesC), high pressure (3.5 MPa) and a MHSV = 2h(-1), varied as follows: similar to35% from ethene, similar to25% from propene and similar to 10% from 1-butene. However, more than 50% distillate-range products can be obtained from 1-butene at temperatures >220 degreesC. Diesel fractions with satisfactory cetane numbers were obtained only from ethene as feedstock. Low reaction temperatures and high space velocities have a beneficial influence on the cetane number of the final product. (C) 2003 Elsevier Science B.V. All rights reserved.