Processing of glycerol under sub and supercritical water conditions

Converting glycerol, a by-product from biodiesel production into useful products and energy could contribute to a positive life cycle for the biodiesel process. One kg of glycerol is produced for every 10 kg of biodiesel and has the potential to be used as a source of H2, syngas or CH4 by an appropriate conversion process. Catalytic Supercritical Water Gasification (CSCWG) processing of crude glycerol solutions is one such viable option. Above its critical point [>221 barg, >374 °C], the properties of water, such as the low relative permittivity and high ionic product make it capable of dissolving non-polar organic compounds, allowing for high reactivity, and the ability to act as an acid/base catalyst. In this work, the degradation of glycerol by CSCWG at temperatures [400–550 °C] and pressures [170–270 barg] was investigated using a packed bed reactor (PBR) containing a Fe2O3 + Cr2O3 catalyst. Glycerol feed concentrations were between 2 and 30 wt% at flow rates from [10–65 ml/min], which gave weight hourly space velocities (WHSV) of [38–125 h−1]. The results indicated that high temperature and low feed concentration tended to increase the gas yield and selectivity toward H2 production with some char (