Decomposition of nitrobenzene in supercritical water

This work was conducted to extend the understanding of the reaction kinetics and mechanisms of nitrogen containing compounds in SCW. The main objectives were to investigate the reaction kinetics and pathways for the decomposition of nitrobenzene in SCW, and the fate of nitrogen upon the decomposition. The experimental conditions included the temperature range from 440 to 550 degrees C and the supercritical water density range from 0.09 to 0.23 g ml(-1). A continuous flow stirred tank reactor system and a batch reactor system were used for the decomposition experiments without and with oxygen, respectively. In the absence of oxygen, nitrobenzene decomposed in SCW to form primarily benzene and nitrite. The decomposition kinetics had an activation energy of 68.0 +/- 9.0 kJ mol(-1). Nitrobenzene concentration showed a weak effect on the decomposition kinetics whereas the density of SCW had no effect. Additional decomposition products such as carbon monoxide and carbon dioxide suggested the occurrence of oxidation driven possibly by the nitro-group as well as SCW. The oxidative role of the nitro-group was supported by the observation of the reduction of nitrite to nitrogen gas. The decomposition rate was substantially enhanced in the presence of oxygen. The oxidation yielded a number of aromatic reaction products including aniline, phenol, 2-(2-pyridinyl)-benzonitrile, and dibenzofuran. The nitrogen in the decomposed nitrobenzene appeared to form mainly nitrogen gas even in the oxidative environments.