Supercritical water oxidation of thiodiglycol

Abstract

The total organic carbon (TOC) disappearance kinetics of the model organic sulfur heteroatom, thiodiglycol [TDG, (HOC2H4)(2)S], was investigated in an isothermal continuous tubular reactor under supercritical water oxidation (SCWO) conditions. The experiments were conducted at a temperature of 397-617 degrees C and a fixed pressure of 25 MPa, with a residence time that ranged from 9 s to 40 s. The initial TOC concentrations of TDG were varied from 1.75 mmol/L to 21.04 mmol/L and the oxygen concentrations were varied from 110% to 440% of the stoichiometric requirement. All the TOC conversions were > 90% under the above experimental conditions. The major sulfur-containing products of the reaction were sulfuric acid and hydrogen sulfide, whereas the carbon-containing products included carbon monoxide, methane, and carbon dioxide. By taking into account the dependence of the oxidant and TOC concentration on the reaction rate, a global TOC disappearance rates expression was regressed from the data of 58 experiments, to a 95% confidence level. The resulting activation energy was determined to be 41.53 +/- 1.65 kJ/mol, and the pre-exponential factor was (1.64 +/- 0.55) x 10(2) L-1.12 mmol(-0.12) s(-1). The reaction orders for the TOC and the oxidant were 1.02 +/- 0.01 and 0.10 +/- 0.01, respectively.