NEW REACTOR SYSTEM FOR SUPERCRITICAL WATER OXIDATION AND ITS APPLICATION ON PHENOL DESTRUCTION

A new reactor system for supercritical water oxidation which can treat reaction variables independently was developed. With this system, phe nol oxidation experiments were carried out at temperatures 380-440 deg rees C and pressures 190-270 atm. Reaction time was varied from 12 to 120 s, and corresponding conversion was 11-99%. The initial phenol con centration was below 8.8 mM based on reaction volume. The initial oxyg en concentration ranged from 100 to 1750% of the stoichiometrically re quired amount for complete oxidation of phenol. According to the resul ts of kinetic experiments, oxidation rate was dependent on temperature and concentration of water, oxygen and phenol. However, the oxidation rate was not dependent on the pressure itself. As the ratio of oxygen concentration to phenol concentration increases, the reaction rate in creases asymptotically In the case where oxygen concentration was grea ter than 300%, the oxygen content did not affect the reaction rate any more. Water has a significant effect on the reaction rate, and oxidat ion rate increased as water concentration increased. Various reaction mechanisms in which water can affect the reaction rate were considered , and this consideration suggested that the water participates in the reaction as a reactant to generate active radicals. The global reactio n order was 1.38 +/- 0.24 for water and 1 for phenol. The effect of ox ygen on reaction rate was expressed as a Langmuir-type equation with t he ratio of oxygen to phenol concentration as a variable, whose consta nt was 2.89 +/- 1.43. The corresponding activation energy was 23.8 +/- 2.2 kcal/mol, and this was larger than that of a gas-phase reaction, but smaller than that of a liquid-phase reaction. A previously suggest ed reaction model and equation were used to predict phenol conversion. The multi-step reaction model suggested by Tufano cannot predict the conversion well, but it seems to explain the effects of each parameter qualitatively. The equation proposed by Gopalan and Savage predicts c onversion fairly well when the concentration of oxygen is adjusted to 300% of the stoichiometrically required amount. (C) 1997 Elsevier Scie nce Ltd.