Nitrogen transformation of 41 organic compounds during SCWO: A study on TN degradation rate, N-containing species distribution and molecular characteristics

Supercritical water oxidation (SCWO) of 41 N-containing compounds was examined under a stable temperature and pressure of 450 °C and 24 MPa, respectively, reaction time ranged from 0.5 to 6 min with 500% excess oxygen, resulted in the degradation rate constants of total organic carbon (kTOC) and total nitrogen (kTN) were 0.162–3.693 and 0.065–0.416 min−1, respectively. The N-containing products were primary N2, ammonium and nitrate. As for amino-group compounds, the main product was ammonia, while for nitro-group compounds, nitrate was the predominant. In terms of diazo and N-heterocyclic group compounds, the main products generally were nitrate and ammonium, respectively. Interestingly, 2-, 3- and 4-nitroaniline, containing both of nitro and amino group, would directly decompose into N2. The reaction pathways of acid orange 74 was proposed based on Fukui indices, which generally included denitrification, ring-open and mineralization. Density functional theory (DFT) method was applied to calculate the quantum properties of the 41 N-containing compounds in order to further examine the relationship between TN removal and molecular structural characteristics. The correlation result showed that among all the 17 molecular characteristics, F(+)n, F(-)n, F(0)n, and EHOMO achieved high correlation coefficients. [Display omitted] •SCWO of 41 N-containing compounds was investigated.•NO3− and NH4+ were the main N-containing product of nitro and amino compounds, respectively.•Nitroanilines, containing both of nitro and amino, largely decomposed into N2.•The reaction pathways of acid orange 74 was proposed.•Quantity parameters explained degradation behavior of TN.