Maleic anhydride hydrogenation over Pd/Al2O3 catalyst under supercritical CO2 medium

Hydrogenation of maleic anhydride (MA) to either γ-butyrolactone (GBL) or succinic anhydride (SAH) over simple Pd/Al2O3 impregnated catalyst in supercritical CO2 medium has been studied at different temperatures and pressures. A comparison of the supercritical CO2 medium reaction with the conventional hydrogenation in the presence of commonly employed organic solvents is also described. The use of various co-solvents for CO2 has also been investigated. Selectivities different from traditional liquid phase reactions are observed under supercritical conditions. A 100% MA conversion with more than 80% selectivity to γ-butyrolactone could be obtained at 473 K and at a pressure of 2.1 MPa H2 and 12 MPa CO2. Temperature is found to be critical in obtaining the desired high γ-butyrolactone selectivity. Catalyst deactivation is observed after extended number of recycle experiments, which resulted in a lower butyrolactone selectivity. The lactone selectivity, however, could be improved by increasing the H2 partial pressure or by increasing the reaction temperature. Hydrogenation of maleic anhydride under supercritical CO2 as solvent is found to be promising for the selective hydrogenation of low vapor pressure solid compounds without employing environmentally harmful organic solvents.