Flameless supercritical water incineration of polycyclic aromatic hydrocarbons

Among the environmental chemical groups, polycyclic aromatic hydrocarbons (PAH) comprise the largest group of carcinogens. Flameless supercritical water incineration is an emerging technology which has attracted attention for the oxidation of organic compounds in environmental samples. The oxidation reactions occur in a aqueous fluid phase under conditions that exceed the critical point of water (T_c = 374°C, P_c = 21.9 MPa). PAH are known to be relatively resistant to combustion. In this paper PAH have been combusted in a supercritical water oxidation batch reactor to determine the combustion processes in relation to such condensed molecular species. The PAH investigated were naphthalene, biphenyl, fluorene, phenanthrene, pyrene and a mixture of all the PAH. The influence of temperature, pressure, sub-critical and supercritical conditions and reaction time were investigated in relation to the destruction of the PAH. The PAH were reacted in the water phase, adsorbed to solid sand samples and as simulated contaminated soil. It was found that up to 99.9wt% destruction of the PAH occurred at supercritical conditions. The main gases produced from the degradation of PAH, were CO, CO₂ and H₂. At sub-critical temperature and pressure conditions the degradation of the PAH required, longer reaction times or higher concentrations of the oxidant.