Synthesis of glycerol carbonates by transesterification of glycerol in a continuous system using supported hydrotalcites as catalysts

MgAl hydrotalcites have been grown onto alpha- and gamma-Al2O3 and characterized by XR diffraction, N-2 and CO2 adsorption. XRD patterns show the crystallization of hydrotalcites as nanometric crystals. On the calcined supported materials, the thermal desorption of CO2 evidences the presence of relatively strong basic sites which are absent on the pure supports. The samples supported by alpha-Al2O3 exhibit a higher basic strength than those supported on gamma-Al2O3. After rehydration, the total number of sites changes only little, but the original sites, presumed to be of Lewis type are converted to stronger Bronsted sites. The synthesis of glycerol carbonate and dicarbonate has been performed by transesterification of glycerol by diethyl carbonate in a green, efficient and selective process catalyzed by these hydrotalcites supported on alpha- and gamma-Al2O3. The control of grain size of the support allows to operate in a flow reactor, then to evaluate the extent of deactivation as a function of time on stream at full conversion of glycerol. Stable catalysts are obtained when a-Al2O3 is the support. (C) 2011 Elsevier B.V. All rights reserved.