Bench-scale supercritical and near-supercritical water oxidation assays to treat Propylene Oxide-Styrene Monomer (POSM) wastewater

Abstract

Supercritical Water Oxidation is a promising technology to deal with the phenolic-benzoic nature of the wastewater from Propylene Oxide-Styrene Monomer processes. To assess its feasibility to meet discharge regulations for a continuous process, lab-scale assays were conducted with real wastewater. After a screening to maximize Chemical Oxygen Demand (COD) removal efficiency, a supercritical, four-hour duration test was run at 550 °C, 235 bar g, with 50% excess oxygen and residence time of 120 seconds. Though a successful COD degradation of 99.97 ± 0.01% was achieved, salt scaling and corrosion occurred. The key findings are that to redissolve salts and avoid corrosion, focus must be on the supercritical to subcritical transition location. Near-supercritical oxidation was also tested as a cost-effective alternative to avoid scaling. Residence times up to 192 min were required at 300 °C, 165 bar g and 40% excess oxygen to achieve similar degradation obtained to supercritical conditions.