Supercritical water oxidation of acrylic acid production wastewater

Abstract

Supercritical water oxidation (SCWO) of wastewater from an acrylic acid manufacturing plant has been studied on a continuous flow experimental system, whose reactor was made of Hastelloy C-276. Experimental conditions included a reaction temperature (T) ranging from 673 to 773 K, a residence time (t) ranging from 72.7 to 339 s, a constant pressure (P) of 25 MPa and a fixed oxidation coefficient (α) of 2.0. Experimental results indicated that reaction temperature and residence time had significant influences on the oxidation reaction, and increasing the two operation parameters could improve both degradation of chemical oxygen demand (COD) and ammonia nitrogen (NH3‒N). The COD removal efficiency could reach up to 98.73% at 25 MPa, 773 K and 180.1 s, whereas the destruction efficiency of NH3‒N was only 43.71%. We further carried out a kinetic analysis considering the induction period through free radical chain mechanism. It confirms that the power-law rate equation for COD removal was 345 exp(−52200/RT)[COD]1.98[O2]0.17 and for NH3‒N removal was 500 exp(−64492.19/RT)[NH3‒N]1.87[O2]0.03. Moreover, the induction time formulations for COD and NH3‒N were suspected to be exp(38250/RT)/173 and exp(55690/RT)/15231, respectively. Correspondingly, induction time changed from 2.22 to 5.38 s for COD and 0.38 to 1.38 s for NH3‒N. Owing to the catalysis of reactor inner wall surface, more than 97% COD removal was achieved in all samples.