VAPOR-PHASE HYDROGENATION OF MALEIC-ANHYDRIDE TO GAMMA-BUTYROLACTONE .3. REACTION PATHWAY AND NEW CATALYST COMPOSITIONS

The reactivities of the main products observed in the vapour phase hyd rogenation of maleic anhydride (MA) were investigated separately, usin g a multicomponent catalyst (Cu/Zn/Mg/Cr=40:5:5:50, atomic ratio %), o btained by reduction of a non-stoichiometric spinel-type precursor. Te trahydrofuran (THF) reacted only at high temperature forming small amo unts of ethanol (EtOH), while gamma-butyrolactone (GBL) gave rise, wit h high conversion, to overhydrogenation [to butyric acid (BuA) or n-bu tanol (BuOH)] and/or hydrogenolysis [mainly to EtOH. Furthermore, the formation in the catalytic tests with BuA and BuOH of n-butanal (notwi thstanding the high H-2/organic ratio), suggested it as the main inter mediate in the hydrogenolysis reaction. Therefore, a new reaction sche me is proposed, evidencing the key role of GEL as the ''intersection'' of two possible reaction pathways, giving rise to THF or unwanted and low-cost by-products. Because of the increasing restrictions on the u se of Cr-containing catalysts, the research was extended to include an investigation of the reactivity of Al-containing catalysts, also prep ared by reduction of spinel-type precursors. These catalysts, in parti cular those with low copper contents, gave rise to high productions of GEL, favouring also the formation of THF and reducing the amounts of unwanted and low-cost by-products. It was shown that a Cu/Zn/Al=25:25: 50 (atomic ratio %) composition may represent a useful compromise, all owing good yields in GEL to be obtained at lower reaction temperatures .