Valorisation of glycerol by condensation with acetone over silica-included heteropolyacids

The acetalisation of glycerol was studied using heteropolyacids, immobilized in silica, as catalysts, at 70 °C. The main product of glycerol acetalisation was solketal. The tungstophosphoric (PW), molybdophosphoric (PMo), tungstosilisic (SiW) and molybdosilisic (SiMo) acids were immobilized in silica by sol–gel method.It was observed that the catalytic activity decreases in the series: PW_S > SiW_S > PMo_S > SiMo_S. All catalysts exhibited good values of selectivity to solketal (about 98% near complete conversion). The effect of different parameters, such as catalyst loading, molar ratio of glycerol to acetone and temperature on the glycerol acetalisation, over PW_S catalyst, was studied. Catalytic stability of the PW_S, SiW_S, PMo_S and SiMo_S catalysts was evaluated by performing consecutive batch runs with the same catalyst sample. After the third batch, it was observed a stabilisation of the initial activity.