CaAl-layered double hydroxides as active catalysts the transesterification of glycerol to glycerol carbonate

Several hydrocalumite-type materials (CaAl-LDHs) were prepared by precipitation using nitrate or chloride salts with and without ultrasound, and aged hydrothermally in autoclave or by refiuxing with and without microwaves. These samples were tested as catalysts for the transesterification of glycerol with dimethyl carbonate to glycerol carbonate. After 3 h of reaction, all catalysts showed high glycerol conversion (70-84%) and moderate selectivity values to glycerol carbonate (52-65%) accompanied by the formation of low amounts of glycidol (7-15%). These results are very interesting taking into account the low specific surface area of these catalysts (7-25 m(2)/g). No significant catalytic differences were observed between the catalysts. This can be due to the similar surface and basic characteristics observed for all of them. By increasing the reaction time, an increase of conversion was observed arriving practically to total conversion after 24 h of reaction, with selectivity to glycerol carbonate in the range 65-75%. Several catalytic reuses favoured the decarboxylation of glycerol carbonate resulting in the formation of higher amounts of glycidol (30%) but still maintaining high selectivity values to glycerol carbonate (70%). (C) 2016 Elsevier B.V. All rights reserved.