Application of a Novel CO2 DC Thermal Plasma Torch Submerged in Aqueous Solution for Treatment of Dissolved Carboxylic Acid

Abstract

A novel direct current (DC) plasma torch, operating with a gas mixture consisting of carbon dioxide and hydrocarbon (methane), has been adapted and used for the first time for treatment of a solution containing dissolved carboxylic acid. Compared with conventional DC thermal plasma torches, this novel torch has high plasma enthalpy, high thermal conductivity, low cost and often readily available operating gas (CO 2 ) and long electrode life-time. Performance of this CO 2 /CH 4 DC thermal plasma torch submerged in aqueous solution was investigated for decomposition of dissolved organic contaminants. Sebacic acid was selected as a representative of organic pollutants in wastewater of chemical process industries. Effect of different operational conditions including treatment time, initial solution pH, and the reactor pressure as well as the role of oxidizing agents such as (H 2 O 2 ) were investigated on decomposition rate of sebacic acid and its intermediate products. It was shown that the submerged CO 2 /CH 4 DC thermal plasma could decompose carboxylic acid. The highest decomposition rate was obtained at neutral solution pH. Adding H 2 O 2 could significantly enhance the decomposition rate due to synergetic effect of ultraviolet radiation (UV) absorption and hydrogen peroxide oxidation. Photo-oxidation was also proposed as the decomposition mechanism with the novel CO 2 / CH 4 plasma torch based on its high level of UV. This work shows the ability of this novel plasma torch for treatment of organic acids in liquids and solutions and therefore offers a new application for the CO 2 /CH 4 thermal plasma in wastewater treatment.

Reduction of an Ilmenite Concentrate by Using a Novel CO2/CH4 Thermal Plasma Torch

“…The CO 2 /CH 4 mixture's chemical equilibrium has been calculated. CO 2 is an oxidative agent, which can result from the following decomposition reaction [27]:…”

“…The presence of CH 4 in the plasma gas mixture causes the deposition of a stream of positive carbon ions on the negatively charged cathode's surface. This carbon deposit protects the electrode from erosion and extends its life [27]. The reaction between CO 2 and CH 4 can generate carbon monoxide (CO) and hydrogen (H 2 ) as soon as the temperature rises.…”