Hydrothermal Degradation of Glycerol by Electrolysis in Subcritical Water

Biodiesel has become an attractive fuel recently, because it is renewable, non-toxic, biodegradable, environmentally friendly, etc. With the increase in the production of biodiesel, the problem of disposing crude glycerol, which is produced as main by-product from biodiesel process such as transesterification, has been raised. Therefore, we have been developing a new green technology-Hydrothermal electrolysisby which crude glycerol inside the biodiesel wastewater can be converted into more value added products such as lactic acid and formic acid under high-temperature and high-pressure conditions. In this study, hydrothermal electrolysis reactions of model biodiesel wastewater was investigated by varying operating parameters such as electrolysis time, applied current value and alkali concentration, etc. We tried to understand the effects of these parameters on the decomposition of glycerol and clarify possible reaction mechanisms. We carried out experiments by applying current and without any current then compared the product distribution obtained by hydrothermal electrolysis with hydrothermal degradation. The experiments were carried out by using both continuous and batch type reactors equipped with titanium and iridium electrodes, a current supplier, an electric heating device, a temperature control unit and a pressure gauge. At the end of the experiments, liquid products were analyzed by high performance liquid chromatography and gas chromatography with flame ionization detector. For the identification of gas products, gas chromatography with thermal conductivity detector was used. Total organic carbon was monitored by using TOC analyzer.