Conversion of Glycerol into Bio-Fuel Additives over Heterogeneous Catalysts

Abstract

Biodiesel is produced from vegetable oils and animal fats, by transesterification of triglycerides and esterification of free fatty acids with methanol or ethanol, in presence of acid or basic catalysts. The glycerol is a by-product in the biodiesel production. For every 9 kg of biodiesel produced, about 1 kg of a crude glycerol is formed. Due to the increase of biodiesel production, an increase of glycerol production has been observed. Therefore, it is imperative to find new applications for the excess of glycerol produced from biodiesel. A possibility is to transform glycerol into fuel additives, by different reactions (etherification, esterification and acetalisation). Traditionally, strong homogeneous acid catalysts, e.g sulphuric acid, have been used in these acid reactions. Heterogeneous catalysts have some advantages over homogeneous ones. They can be separated from reaction mixture, are reusable, do less harm to the environment and have not corrosion or disposal of effluent problems. This present review focuses on solid acid catalysts as potential heterogeneous catalysts for glycerol conversion (by esterification, etherification and acetalisation) into biofuel additives, replacing homogenous ones.