Decomposition of high molecular weight carboxylic acid in aqueous solution by submerged thermal plasma

Abstract

Submerged thermal plasma has been used to decompose an aqueous solution containing high molecular weight carboxylic acid. Carboxylic acids should be removed from chemical processes because it forms a significant amount of pollutants in wastewater and process liquors. Sebacic acid, which is representative of a high molecular weight carboxylic acid, is selected to study the feasibility of large organic compound decomposition by submerged thermal plasma. Sebacic acid decomposition in thermal plasma is investigated thermodynamically by using the equilibrium composition of mixture. Kinetic behavior of sebacic acid decomposition by submerged thermal plasma is described using a kinetic model with time-dependent rate constant. The experimental decomposition process is also studied with different plasma gases (oxygen and air). Different sodium hydroxide concentrations are employed to investigate the effect of pH variation on conversion rates. IC/MS (Ion Chromatography/Mass Spectrometry) is presented as a quantitative analytical technique for carboxylic acids. Intermediate products are also quantified and identified by IC/MS and TOC (Total Organic Carbon) analyzer. It is shown that submerged thermal plasma can decompose sebacic acid and decreases its concentration to less than 17% of its initial concentration after 30min treatment. The main decomposition product is CO2 which can be found in solution in form of dissolved inorganic carbon and other products including lower molecular weight dicarboxylic acids. Reaction mechanism of sebacic acid decomposition is also formulated based on the identified products. This work therefore shows the ability of submerged thermal plasma to decompose large organic compounds in aqueous solutions and demonstrates that this technology can be promising for liquid and solution treatment.