Sodium-carbonate-assisted supercritical water oxidation of chlorinated waste

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 Na2CO3 significantly reduces the corrosion. This work examines the effect of Na2CO3 on the oxidation kinetics of phenol and 2-chlorophenol in supercritical water. The kinetics data in the absence of Na2CO3 are verified to conform to the literature data. New data in the presence of Na2CO3 show that the oxidation is highly enhanced, which may be due to a combination of the catalytic effects of Na2CO3 and removal of HCl by Na2CO3. If all other kinetic parameters are unchanged, the activation energy of 2-chlorophenol decomposition decreases from 11.5 kcal/mol without Na2CO3 to 2.44 kcal/mol with Na2CO3. Similarly, a reduction from 10.4 to 7.5 kcal/mol is observed for phenol. Also, Na2CO3 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 Na2CO3 is insoluble in supercritical water, it precipitates as fine particles with a large surface area. A new reactor design is proposed for obtaining fine Na2CO3 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.