On The Origin Of The Transesterification Reaction Route During Dimethyl Adipate Hydrogenolysis

Esters hydrogenolysis over CuZn catalysts was shown to be accompanied by transesterification lowering the yield of the desired alcohol. Here we investigate the origin of the transesterification activity by studying Cu, Zn and CuZn based catalysts in transesterification of dimethyl adipate (DMA) with hexane-1,6-diol (HDO). The experiments were performed at conditions relevant for hydrogenolysis, i.e. 210 degrees C and 10-70 bar of either N-2 or H-2 atmosphere. Although transterification was found to be catalysed by acid impurities present in DMA, the main formation of the transesterification products was due to the ZnO phase in the studied catalysts. In contrast, Cu or CuO phase were virtually inactive in transesterification. Moreover, it was shown that the reduced Cu-ZnO catalyst was stable under reaction conditions whereas its oxide form CuO-ZnO underwent leaching. The obtained catalytic data also evidenced that the transesterification products were important reaction intermediates in the formation of HDO.