Electrical discharges directly in liquid glycerol for the production of hydrogen

Summary form only given. Glycerol is generated in large amounts during the transesterification of both bioethanol and biodiesel. Specifically, with every 100 lbs of biodiesel produced by the transesterification of vegetable oils or animal fats, 10 lbs of crude glycerol are generated. Thus, the tremendous growth of the biodiesel industry created a glycerol surplus that has resulted in a dramatic 10-fold decrease in crude glycerol prices over the past two years.This study investigates the possibility of converting liquid glycerol (C₃H₈O₃) into a hydrogen-rich gas by pulsed high-voltage electrical discharges. Due to the difficulties associated with the breakdown on non-conductive liquids, experiments were conducted with the addition of sodium chloride at 25 kV and a pulse repetition frequency of 55 Hz. Streamer-like plasma was formed at the tip of a nickelchromium high-voltage electrode in a point-to-plane-electrode geometry. Gas chromatography measurements reveal that pulsed electrical discharges dissociate glycerol primarily into hydrogen, CO, and CO₂. Viscosity measurements show that a 3 h plasma treatment reduces the viscosity of glycerol by ~20%. FTIR analysis of the treated liquid reveals only the presence of the -C=C-Cband which is formed by the dehydration of the glycerol molecule. Optical emission spectroscopy measurements indicate that plasma dissociates glycerol into OH, H₂, H, CH, and C₂ excited species. This implies that chemical reactions inside the liquid glycerol plasma are driven by high temperature cracking in addition to electron collisions. A chemical reaction scheme for the decomposition of glycerol is proposed.