Sodium-Carbonate-Assisted Supercritical Water Oxidation of Chlorinated Waste

Abstract

Supercritical water oxidation (SCWO) is emerging as a promising technology for the destruction of organic wastes. However, corrosion is a severe problem for chlorinated wastes because of the formation of hydrochloric acid. Recently, it was proposed that the addition of Na 2 CO 3 significantly reduces the corrosion. This work examines the effect of Na 2 CO 3 on the oxidation kinetics of phenol and 2-chlorophenol in supercritical water. The kinetics data in the absence of Na 2 CO 3 are verified to conform to the literature data. New data in the presence of Na 2 CO 3 show that the oxidation is highly enhanced, which may be due to a combination of the catalytic effects of Na 2 CO 3 and removal of HCl by Na 2 CO 3 . If all other kinetic parameters are unchanged, the activation energy of 2-chlorophenol decomposition decreases from 11.5 kcal/mol without Na 2 CO 3 to 2.44 kcal/mol with Na 2 CO 3 . Similarly, a reduction from 10.4 to 7.5 kcal/mol is observed for phenol. Also, Na 2 CO 3 plays a key role in reducing corrosion on the reactor walls by first neutralizing the acid and then providing a large surface area for adsorption of the precipitated corrosive compounds. Because Na 2 CO 3 is insoluble in supercritical water, it precipitates as fine particles with a large surface area. A new reactor design is proposed for obtaining fine Na 2 CO 3 particles based on the supercritical anti-solvent method; these fine particles provide a surface area that is several orders of magnitude larger than that of the reactor walls.