Phenol oxidation in supercritical water

Abstract

Phenol oxidation in supercritical water were carried out by batch and continuous systems. New reactor system was designed for batch experiments, and individual parameter effect on reaction rate was determined separately. In batch experiments, oxygen was used as an oxidant, and hydrogen peroxide was used in continuous experiments. According to the batch work, oxidation rate was dependent on temperature, and concentration of water, phenol and oxygen. However, reaction rate was not dependent on system pressure. As the ratio of oxygen concentration to phenol concentration increases, the reaction rate increases asymptotically. In case that the oxygen concentration was greater than 300%, oxygen content does not affect on reaction rate anymore. Water has a significant effect on reaction rate, and oxidation rate was increased as water concentration increases. Various reaction mechanism, in which water can affect reaction rate, was considered, and this consideration suggested that the water participates in the reaction as a reactant to generate active radicals. The global reaction order was 1.38±0.24 for water and that of phenol was 1. The effect of oxygen on reaction rate was expressed as a Langmuir type equation with the ratio of oxygen to phenol concentration as a variable, whose constant was 2.75±1.14. The corresponding activation energy was 23.9±2.1 kcal/mol, which was larger than that of gas phase reaction ,but smaller than that of liquid phase reaction. In continuous experiment, the global reaction order of phenol was 0.808, and those of water and hydrogen peroxide were 0.140 and 0.134. The activation energy was 20.4 kcal/mol over experimental temperature range. However, the study on the effect of each parameter pointed out that oxidation rate was dependent on temperature, the concentration of hydrogen peroxide, and phenol, but not dependent on the water concentration. As the ratio of initial hydrogen peroxide concentration to phenol concentration increases, th...