Flameless oxidation of chlorinated wastes in supercritical water using sodium carbonate as the oxidation stimulant

Oxidation of decachlorobiphenyl (10-CB) in supercritical water was studied in the presence of Na2CO3, which was used as catalyst. In situ observations of the 10-CB oxidation process were carried out with a diamond anvil cell (DAC) coupled with optical and Fourier transform IR microscopes. Tests of destruction of 10-CB were conducted in a larger batch reactor at 450 degreesC and 30 MPa. Experiments were performed at different oxygen excesses ranging between -36% and +225% of the theoretical value and at two reaction times, 600 and 1200 s, in the batch reactor. At the highest excess O-2 of 225% a destruction rate of only 99.2% of 10-CB was achieved for non-catalytic oxidation. Adding 2.5 mol % Na2CO3 in the DAC significantly enhanced the dissolution rate of 10-CB, and complete dissolution was achieved at 434 degreesC and 125 MPa with 69.5% theoretical O-2. Addition of Na2CO3 stimulated the supercritical water oxidation process taking place in a homogenous phase. Complete destruction was achieved at moderate excess oxygen of 159.5%. The presence of sodium carbonate reduced corrosion of the reactor by neutralizing the main oxidation product of hydrochloric acid and providing fine Na2CO3 particles on the wall of the reactor for protection. Destruction rates of 10-CB were determined, a possible oxidation process proposed, and a sequence of corrosion reactions suggested.