Oxidation of Aroclor 1248 in supercritical water: A global kinetic study

Supercritical water oxidation of extracted contaminants is the second step of a two-stage supercritical fluid technology proposed to remediate soils a nd sediments contaminated with polychlorinated biphenyls (PCBs) and/or poly aromatic hydrocarbons. In connection with the second step, the supercritica l water oxidation rate of Aroclor 1248 (A1248), a mixture of similar to 76 PCB congeners, is investigated at 25.3 MPa and temperatures of 723, 748, 77 3, and 823 K. The reactions are conducted in an isothermal, isobaric plug-f low tubular reactor, and GC/ECD, GC/ FID, GC/TCD, and GC/MS chromatographic methods are employed for product analysis. Experiments are conducted at a nominal A1248 feed concentration of 5.75 x 10(-5) mol/L (reaction condition s) using a methanol solution of 5.245 g/L (5245 ppm) and H2O2 as an initial oxidant (providing similar to 20 mol % excess of O-2). Molar global conver sion of A1248 varies from 36.06% (for residence time equal to 6.29 s at 723 K) to 99.95% (54.4 s at 823 K). The overall conversion follows apparent se cond order, and the rate constant calculated from the data leads to Arrheni us parameters of frequency factor A = 10(17.0+/-0.1) s(-1) (mol/L)(-1) and energy of activation E-a = 186 +/- 2 kJ/mol (44.43 +/- 0.51 kcal/mol). The congener specific analysis indicates a buildup of intermediate congener byp roducts, which also undergo oxidation decomposition. The identified reactio n products are mainly biphenyl, low-chlorinated PCB congeners such as 2-chl orobiphenyl and 2,2'-dichlorobiphenyl, CO, and CO2.