A review on direct carboxylation of glycerol waste to glycerol carbonate and its applications

Concern over global warming, energy demand and the economic impact of exploiting fuel reserves have driven the commercial interest and action to produce biodiesel as the substitute for fossil fuel. Biodiesel produced via the transesterification reaction of triglyceride with methanol is known to be a promising renewable and clean energy. However, increase in the biodiesel production leads to undesirable generation of glycerol waste, considering that 1 kg of glycerol can be generated as by-product from every 10 kg of biodiesel production. Utilising and upgrading of glycerol waste into high-value chemical can reduce the waste volume and increase the market value of the glycerol itself and the sustainability of the biodiesel production towards achieving circular economy. Direct carboxylation of glycerol waste is an emerging alternative to utilise and convert the abundance and easily available waste into glycerol carbonate (GC). GC has various applications as solvent, additives and chemical intermediate. It has properties such as high boiling and melting point, low volatility and biodegradable. This review aims to reveal the impact of both homo- and heterogeneous catalysts employed and their impact on glycerol conversion and selectivity to GC. Also, the impact of dehydrating agents, solvents and other reaction conditions is thoroughly discussed, aiming to provide insights into further development of the carboxylation of glycerol to GC. The use and application of GC are also reviewed.