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 probl em for chlorinated wastes because of the formation of hydrochloric acid. Re cently, it was proposed that the addition of Na2CO3 significantly reduces t he corrosion. This work examines the effect of Na2CO3 on the oxidation kine tics of phenol and 2-chlorophenol in supercritical water. The kinetics data in the absence of Na2CO3 are verified to conform to the literature data. N ew data in the presence of Na2CO3 show that the oxidation is highly enhance d, 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, t he activation energy of 2-chlorophenol decomposition decreases from 11.5 kc al/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 a cid and then providing a large surface area for adsorption of the precipita ted corrosive compounds. Because Na2CO3 is insoluble in supercritical water , it precipitates as fine particles with a large surface area. A new reacto r design is proposed for obtaining fine Na2CO3 particles based on the super critical anti-solvent method; these fine particles provide a surface area t hat is several orders of magnitude larger than that of the reactor walls.