SELECTIVE HYDROGENATION OF C-4-ALKYNES OVER A COPPER ON SILICA CATALYST

The selective gas phase hydrogenation of 1-butyne, 1-butene-3-yne, 1,3 -butadiene and of an industrial C-4-feed stream has been examined in a flow system employing a Cu/SiO2 catalyst. The variations in product d istributions with temperature, hydrogen partial pressure and C-4-react ant partial pressure have been determined together with the kinetics a nd activation energies. No butane formation was observed for all exper iments, proving the Cu/SiO2 catalyst to be highly selective for the fo rmation of alkenes. Butene isomerisation was found to be negligible fo r all reactions. Catalyst deactivation, as a result of the build-up of oligomeric material on the catalyst surface was particularly pronounc ed for the C-4-alkynes but could be minimised by applying elevated tem peratures and increased hydrogen partial pressures. Orders of reaction with respect to hydrogen (1.1-1.5), 2-butene (zero) and the C-4-react ants (zero) indicate that the strengths of adsorption decrease in the sequence: alkyne > dialkene > alkene greater than or equal to hydrogen . Apparent activation energies for the formation of 1-butene were meas ured as 69 kJ/mol (1-butyne), 62 kJ/mol (1-butene-3-yne) and 63 kJ/mol (1,3-butadiene). In competitive hydrogenation reactions the alkynes w ere selectively hydrogenated while 1,3-butadiene was found to be inert . Thus the catalyst can be used for the selective removal of alkynes f rom industrial C-4-streams.