Catalytic liquid phase oxidation of aqueous phenol solutions in a trickle-bed reactor

Aqueous-phase deep oxidation at comparatively low temperatures and pressures made possible by the use of heterogeneous catalysts is a promising technique for the destruction of organic water pollutants. Catalytic liquid-phase oxidation of aqueous phenol solutions was investigated in an isothermal trickle-bed reactor at T = 403-423 K and oxygen partial pressure of 7 bar. The results obtained in the presence of a catalyst composed of supported copper, zinc, and cobalt oxides show that during the reaction course only small amounts of aromatic and aliphatic hydrocarbons are accumulated in the liquid phase, thus resulting to a constant pH value of the aqueous solution along the axial reactor coordinate. In the off-gas, no carbon monoxide was detected at any operating conditions. Process simulating using one-dimensional axial dispersion and plug-flow models demonstrates that efficiency of the catalyst bed for phenol removal is influenced by the mass-transfer rate of oxygen from the gas phase to the bulk liquid phase, and by resistance due to a surface reaction step. It is believed that partial wetting of catalyst particles in a trickle-bed reactor increases phenol conversion to intermediates and CO2 as the main reaction product, through the formation of a larger number of active sites on the catalyst surface. Finally, it has been observed that at the given operating conditions metal oxide phases are leached into the aqueous solution. (C) 1997 Elsevier Science Ltd.