Studies on dimerization of 1-butene in ionic liquid system

The dimerization of 1-butene has attracted much attention because C₈ olefins are widely used in chemical industry, such as in the manufacture of linear low-density polyethylene comonomers, special detergents, synthetic lubricating oils, etc. The dimerization of 1-butene catalyzed by transition metal (such as nickel, zirconium, and cobalt) compounds was systematically studied using 1-butyl-3-methyl-imidazolium chloride ionic liquid as solvent. The conversion of 1-butene and the selectivity for C₈ olefins could be enhanced by adjusting the composition of the catalyst. Among the transition metal compounds, the nickelous chloride exhibited the best catalytic performance for 1-butene dimerization, the conversion of 1-butene was up to 95.6% and the selectivity for C₈ olefins was 85.8%. Zirconium chloride was active for the dimerization reaction, while the selectivity for C₈ olefins was low. The catalytic activity of cobalt compounds was low. The other transition metal compounds tested in this work could not catalyze 1-butene dimerization in ionic liquid. Accordingly, 1-butene could be dimerized effectively in ionic liquid under mild conditions no need of organic solvent and strict oxygen-free and water-free conditions, the good solubility of nickel compounds and the poor solubility of olefins in polar and non-coordinating ionic liquid make it possible to separate the products from solvent by decantation.