Chromium-free catalysts for selective vapor phase hydrogenation of maleic anhydride to gamma-butyrolactone

The replacement of chromite catalysts in the selective vapor phase hydrogenation of maleic anhydride (MA) to gamma-butyrolactone (GBL), useful intermediate in the production of chlorine-free solvents, was investigated. In order to avoid the interferences related to physical dishomogeneity 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, with maximum values when the Al-content was about 17% (as atomic ratio) and the Cu/Zn ratio fell between 0.5 and 1.0. Furthermore, better carbon balances were observed for these last catalysts, which may be attributed to lower light hydrocarbon synthesis and tar formation.