Counter-flow silica-titania reactor for the simultaneous treatment of air and water contaminated with VOCs

The photocatalytic oxidation of VOCs was investigated using a novel countercurrent flow reactor designed to enable the treatment of toluene present in the gas and the aqueous phases simultaneously. The reactor was packed with silica-titania composites commingled with plastic pall rings. Using this mixed packing style was advantageous as it resulted in a higher UV penetration throughout the reactor. The average UV intensity in the reactor was determined to be 220 μW/g irradiated TiO₂. It was found that under dry conditions, the STCs had a high adsorption capacity for toluene; however, this adsorption was completely hindered by the wetting of the STCs when the two phases were flowing simultaneously. The destruction of toluene in the aqueous phase was determined to follow a linear trend as a function of the contaminant concentration. In the presence of both phases, toluene destruction was only observed under conditions in which the solution was initially supersaturated with respect to the gas phase. Under these conditions, the net destruction of toluene in the system reached a maximum of 68%. For the most part, the destruction occurred in the aqueous phase, and it was observed that high gas phase flowrates could be detrimental to the toluene destruction in the two phase reactor. The operating conditions in the system could be optimized to achieve improved destruction in the presence of both phases compared to the aqueous phase only.