Supercritical Water Gasification of Lactose as a Model Compound for Valorization of Dairy Industry Effluents

The dairy industry effluents, including whey waste and milk-based residues, are enriched in lactose and minor amounts of glucose that could potentially be converted to biofuels and biochemicals. Lactose was used in this work as a model compound of dairy effluents for gasification in supercritical water using a continuous flow tubular reactor. Four parameters impacting supercritical water gasification were studied, namely, temperature (550–700 °C), residence time (30–75 s), feed concentration (4–10 wt %), and catalyst concentration (0.2–0.8 wt %). The best total gas yields, carbon gasification efficiency, H2 yields, and other major gases (CO2 and CH4) were obtained at 700 °C using a feed concentration of 4 wt % lactose and a residence time of 60 s at fixed pressure of 25 MPa. Furthermore, catalytic lactose gasification involving 0.8 wt % Na2CO3 resulted in maximum H2 yield (22.4 mol/mol) compared to those obtained by 0.8 wt % K2CO3 (21.5 mol/mol) and noncatalytic gasification (16 mol/mol).