The current technology for catalytic oxidation of aqueous organic contaminants at elevated temperature and pressure works well at operating conditions of 265 °F and 70 psia with effluent TOCs (total organic carbon) of less than 0.5 ppm. However, it does not perform well at the reduced temperature, i.e., sub-water-boiling temperature (200 °F), and the reduced pressure such as ambient pressure (14.7 psia) as indicated by the effluent TOCs approximately the same as feed TOC.
There are two factors that may lead to the reduced organic oxidation rate. One is the decreased oxygen solubility by more than 6 times at the reduced pressure, and the other factor is decreased catalytic activity at reduced temperature. The reduced oxygen solubility in the aqueous solution will have a negative impact on the oxygen diffusion rate into the catalyst’s inside pores, where the oxidation reaction occurs. Therefore, a catalyst structure that facilitates mass transfer of oxygen reactant or oxidation products inside pores will enhance an overall organic oxidation rate.
A new bimodal catalyst pore structure was developed to increase the organic oxidation rate. The bimodal pore structure includes micropores in 1-10 nm and macropores of l00-1000 nm. The macro pores provide rapid mass transfer of oxygen reactant into the interstices that lead to the micropores where the reaction takes place, and also provide quick diffusion of oxidation products outwards of the micropores. It is expected that by implementing the bimodal pore structure, the internal effectiveness factor (ratio of actual reaction rate/reaction rate when entire interior surface is exposed to the external surface conditions) can be dramatically improved as the active reaction sites will be made accessible to oxygen reactant, and more reaction products will be removed efficiently from the catalyst sites.