Supercritical water oxidation (SCWO) for the removal of N − containing heterocyclic hydrocarbon wastes. Part I: process enhancement by addition of isopropyl alcohol

The present work investigates the destruction of nitrogen-containing heterocyclic hydrocarbons frequently encountered in hazardous wastes by supercritical water oxidation (SCWO), with focus on the process enhancement using isopropyl alcohol (IPA) as co-fuel. 1,8-Diazabicyclo[5.4.0] undec-7-ene (DBU) was selected for SCWO in a continuous plug flow reactor, under a range of temperatures (400–525 °C), oxidant ratios nSR (0.8–2.0) and IPA/DBU ratios (0.5–3.5). Experimental results were presented in terms of total organic carbon (TOC) removal %, and nitrogenous products yield %. Based on GC-MS analysis, a free radical reaction mechanism for SCWO of DBU was proposed. Results showed that temperature was the predominant factor to influence the rate of DBU oxidation, while oxidant ratio (nSR) significantly affected the N speciation in the exit stream. IPA addition had a significant impact on shifting recalcitrant aqueous ammonia NH4+ in the liquid stream to gaseous nitrogen. It also increased TOC removal % (DBU + IPA) due to the increased free radicals produced by IPA oxidation.