Supercritical water oxidation (SCWO) has been shown to be an effective method for the treatment of industrial wastes. Organic compounds containing nitrogen are very usual in industrial wastes, and therefore, it is necessary to study the oxidation behavior of such compounds in order to improve the applicability of this technology to wastewaters and sludges. In this paper, oxidation parameters of several nitrogen-containing compounds in supercritical water such as aniline, acetonitrile, pyridine, and the intermediate stable compound ammonia are studied, using 2-propanol as auxiliary fuel. SCWO of feedstreams containing 2-propanol and the nitrogenous compound was carried out using a pilot-plant scale, based on a continuous-flow reactor system. Results show that for these compounds suitable conditions for SCWO are the following:  reaction temperature in the range 600−700 °C; stoichiometric amount of oxygen at residence time of 40 s. In these conditions, compound concentration in the effluent is below detection limits, TOC removal is greater than 99.97%, and N removal is greater than 97%.

Supercritical water oxidation (SCWO) provides high destruction efficiencies for a wide variety of hazardous wastes at low reactor residence times. This paper studies the feasibility of the SCWO process for the treatment of the esterification wastewater from the poly(ethylene terephthalate) (PET) industry, for which the major contaminant product is ethylene glycol. Both the feed and the liquid-phase product were analyzed in terms of total organic carbon (TOC) to determine the efficiency of the process. Effluent from the PET industry contained 16000 mg/L TOC, equivalent to 4 wt % ethylene glycol. Experiments were carried out in a pilot plant equipped with a pressure shell and a cooled-wall reactor. The effects of temperature and oxidant concentration on removal efficiency were investigated. Tests were performed in the range of 550−750 °C at a pressure of 23 × 106 Pa. Results showed elimination efficiencies of up to 99.9% at 630 °C and residence times of less than 50 s. The scale-up of this plant has been simulated using the software Aspen Plus.

The unique physical-chemical properties of water above its critical point (374.2°C and 22.1 MPa) makes supercritical water (SCW) an effective reaction medium for oxidation of organic compounds. Gases and many organic compounds are miscible in SCW, so reaction between oxygen and waste is carried out without interface transport constraints. Supercritical water oxidation (SCWO) can give high destruction efficiencies for a wide variety of hazardous wastes, at low reactor residence times. To study the SCWO, experiments were carried out in a pilot plant equipped with a pressure shell and cooled wall reactor. Effect of operation variables: oxidant excess, reaction temperature and residence time, is studied in order to optimise the contaminant removal efficiency. Aqueous solutions of isopropyl alcohol were used as feed. No effect of air excess and residence time higher than 1 minute on removal efficiency was found, so exclusive dependence of temperature is concluded. Whereas temperature is above 650°C, reactor can work in a wide range of operation conditions with destruction efficiency over 99%. In addition, operation at optimal conditions is reported, using 10%(w) isopropyl alcohol – 1%(w) aniline as feed. Removal efficiencies higher than 99.9% and nitrite-nitrate concentrations less than 10 ppm were obtained.