HYDROTHERMAL DECOMPOSITION AND OXIDATION OF P-NITROANILINE IN SUPERCRITICAL WATER

The decomposition kinetics and nitrogen speciation of p-nitroaniline ( pNA) were investigated at supercritical water conditions in the absenc e/presence of oxygen. A tubular flow reactor system was used at the te mperature ranges 385-440 degrees C and 380-420 degrees C for hydrother mal (oxygen absent) and oxidation experiments, respectively, The destr uction of pNA significantly occurred in the absence of oxygen, The hyd rothermal decomposition rate had an activation energy of (1.59 +/- 0.2 5) x 10(5) J/mol and was first-order with pNA. The formation of oxygen (O-2,), carbon monoxide (GO), carbon dioxide (CO2,), and nitrogen (N- 2,) indicated that the nitro group in the decomposed pNA drove oxidati on in the absence of oxygen. Appreciable quantity of ammonia and trace s of nitrite and nitrate were formed. Oxygen enhanced the pNA destruct ion, although its effect did not show explicitly in the oxidation rate expression. The activation energy of the oxidation was (1.28 +/- 0.35 ) x 10(5) J/mol. Also, in the presence of oxygen, ammonia was formed o nly in trace quantities. The reduction of ammonia level was attributab le to the potential ammonia oxidation by the nitro group of the decomp osed pNA. It follows from this result that nitro group-containing comp ounds may be cooxidized with other nitrogen containing substances to r educe the production of ammonia, nitrite and nitrate in supercritical water oxidation processes, (C) 1997 Elsevier Science B.V.