The selective gas phase hydrogenation of 1-butyne, 1-butene-3-yne, 1,3-butadiene and of an industrial C4-feed stream has been examined in a flow system employing a Cu/SiO2 catalyst. The variations in product distributions with temperature, hydrogen partial pressure and C4-reactant partial pressure have been determined together with the kinetics and activation energies. No butane formation was observed for all experiments, proving the Cu/SiO2 catalyst to be highly selective for the formation of alkenes. Butene isomerisation was found to be negligible for all reactions. Catalyst deactivation, as a result of the build-up of oligomeric material on the catalyst surface was particularly pronounced for the C4-alkynes but could be minimised by applying elevated temperatures and increased hydrogen partial pressures. Orders of reaction with respect to hydrogen (1.1-1.5), 2-butene (zero) and the C4-reactants (zero) indicate that the strengths of adsorption decrease in the sequence: alkyne > dialkene > alkene ≥ hydrogen. Apparent activation energies for the formation of 1-butene were measured 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 were selectively hydrogenated while 1,3-butadiene was found to be inert. Thus the catalyst can be used for the selective removal of alkynes from industrial C4-streams.
- Alkyne hydrogenation