Water‐density effects on phenol oxidation in supercritical water

Abstract

Supercritical water oxidation SCWO experiments were performed in a tubular flow reactor at 420 ᎐ 465ЊC and 141᎐ 241 bar. Phenol was the organic reactant. Both pure ( ) water and a helium 1r3 by mol ᎐ water mixture ser®ed as reaction media. Adding helium to the reaction medium permitted ®ariation of the water concentration and system pressure independently. By decoupling the water concentration from the system pressure, it was shown that the rate of phenol disappearance during SCWO is influenced by the water concentration and not the system pressure. The experiments consistently re®ealed that adding helium, and thereby decreasing the water concentration at a fixed system pressure, increased the phenol con®ersion. In addition, experiments showed that lowering the water concentration using pure water as the sol®ent also increased the ( phenol con®ersion. The results suggest that dilution with helium and perhaps other ) inert gases may be a new way to control SCWO reaction rates.

Application of Dielectric Barrier Discharge Reactor Immersed in Wastewater to the Oxidative Degradation of Organic Contaminant

“…The use of various advanced oxidation processes (AOPs) including supercritical water oxidation [1], electrochemical method [2], direct ozonation [3], electron-beam irradiation [4], ultrasonification [5], photocatalytic oxidation [6] and pulsed electrical discharge [7,8] to remove organic contaminants from wastewater has been an active field of research and development. In addition, there have been many studies on the combination of an AOP process with another to improve the removal of the organic contaminants [7,[9][10][11].…”

Effect of Water Density on Methanol Oxidation Kinetics in Supercritical Water

“…Since over 99.5% of the molar mass in the reactor was water during these experiments, we assumed that the system physical properties could be taken to be those of pure water. The experimental apparatus, procedure, and gas chromatographic method for gas analysis are discussed fully in a previous article on phenol SCWO …”

“…The experimental apparatus, procedure, and gas chromatographic method for gas analysis are discussed fully in a previous article on phenol SCWO. 3 We used a gas chromatograph with flame ionization detection to determine the methanol concentration in the reactor effluent. The injection port and oven temperatures were set at 165 and 125 °C, respectively.…”

“…Previous SCWO research − has demonstrated that the oxidation rate can be sensitive to the water density (or concentration), with all other process variables held constant. For example, the phenol oxidation rate in SCW at 420 °C is inhibited by increasing water density at low densities but accelerated by water at high densities. , Phenol oxidation chemistry was too complex to allow definitive identification of the fundamental chemical or physical processes responsible for this behavior.…”

“…Previous SCWO research [3][4][5][6] has demonstrated that the oxidation rate can be sensitive to the water density (or concentration), with all other process variables held constant. For example, the phenol oxidation rate in SCW at 420 °C is inhibited by increasing water density at low densities but accelerated by water at high densities.…”