Electrochemical conversion of enriched crude glycerol: Effect of operating parameters

Abstract

The enrichment of crude glycerol (29.8 wt.%) from a biodiesel production plant and its subsequent electrochemical conversion under a galvanostatic mode to added-value compounds was successfully performed at a laboratory scale. The optimal solvent-extraction based enrichment of the crude glycerol, after the acid pre-treatment to remove most free fatty acids and salts, was found using n-propanol:pre-treated crude glycerol at volume ratio of 2, attaining 97.9% glycerol. The effects of the initial glycerol solution pH (1, 7 or 11), type of electrode (platinum (Pt), titanium-coated ruthenium oxide (Ti/RuO2) or stainless steel (SS)) and applied current density (0.08–0.27 A/cm2) were explored. Using a galvanostatic mode, the enriched crude glycerol could be converted to added-value products, such as ethylene glycol, acetol, glycidol, acrolein, 1,2-propanediol (PD) and 1,3-PD. A Pt electrode, initial glycerol solution pH of 1 and current density of 0.14 A/cm2 were found to be optimal giving a complete conversion of 0.3 M glycerol within 14 h with a total product yield of 68.7%. However, each specific product had a different optimal applied current density and electrolysis time. Finally, a simplified diagram showing the possible major reaction pathways of glycerol conversion by this electrochemical conversion over a Pt electrode was presented.