CHROMIUM-FREE CATALYSTS FOR SELECTIVE VAPOR-PHASE HYDROGENATION OF MALEIC-ANHYDRIDE TO GAMMA-BUTYROLACTONE

The replacement of chromite catalysts in the selective vapor phase hyd rogenation of maleic anhydride (MA) to gamma-butyrolactone (GBL), usef ul intermediate in the production of chlorine-free solvents, was inves tigated. In order to avoid the interferences related to physical disho mogeneity of the precursors, Cu/Zn/M catalysts (38:38:24, atomic ratio percent, where M = Cr, Al or Ga) obtained by thermal decomposition of hydrotalcite-type anionic clays were used. The Al-containing catalyst exhibited better performances than the Cr-containing catalyst, while with gallium no significant differences in comparison to aluminum were observed, capable of justifying the significantly higher cost. Cu/Zn/ Al catalysts showed complete MA conversion and high yields in GEL, wit h maximum values when the Al-content was about 17% (as atomic ratio) a nd the Cu/Zn ratio fell between 0.5 and 1.0. Furthermore, better carbo n balances were observed for these last catalysts, which may be attrib uted to lower light hydrocarbon synthesis and tar formation.