Thermal stability of glycerol containing compounds from the biodiesel production chain

Abstract

Glycerol is a by-product from transesterification for biodiesel production. Due to the presence of hydroxyl groups (–OH), glycerol is pointed as a possible dehydrating agent for the production of anhydrous ethanol which, in turn, can be used as a methanol-substitute reagent in the transesterification. For that, glycerol must be purified by specific purification procedures, which are defined depending on the contaminant to be removed. In the case of thermal processes, as distillation, glycerol containing impurities from the biodiesel production must be thermally resistant to allow its reuse. The effect of some contaminants that can be found in glycerol was thus evaluated in terms of thermal stability of glycerol. Differential scanning calorimetry and thermogravimetry were used as tools to avail the thermal stability of several binary compositions of glycerol with a contaminant. Glycerol containing 5% sodium hydroxide or 5% sodium methoxide or 10% sodium ethoxide or sulfuric acid in any composition (up to 4.75%) exhibited a notable degradation. Therefore, it is required that the neutralization and further purifying steps ensure the removal of such contaminants or even to avoid the contact of glycerol with some dangerous compounds, as strong acids. On the other hand, the evaluated salts (sodium chloride and sodium sulfate) and water caused a change on the mixture boiling point, but no degradation was detected. Glycerol remained stable even containing high amount of ethanol or water (up to 30%), which confirms that such components can be removed from glycerol by thermal processes as distillation without its degradation. Graphical abstract: [Figure not available: see fulltext.]