Photocatalytic oxidation of trimethylamine and isovaleraldehyde in an annular reactor: Influence of the mass transfer and the relative humidity

This study presents an experimental investigation of the photodegradation of two volatiles organic compounds (VOCs): Trimethylamine (TMA) and isovaleraldehyde (ISOV).Experiments were performed by using an annular plug-flow reactor. The influence of the inlet concentration, flowrate and relative humidity (RH) on the conversion rate has been studied for the two VOCs. The increase of inlet concentration leads to a lower conversion rate due to the availability of the active sites. The flowrate increase also induces a lower degradation rate due to the shorter residence time. A kinetic model based on the Langmuir–Hinshelwood (L–H) approach and taking into account the mass transfer step was developed. This allows us to determine the adsorption and kinetic degradation constants with no influence of mass transfer.This latter could be estimated by a semi-empirical correlation.In small amounts, the presence of water vapor has a promoting effect on the degradation due to the formation of OH radicals. When the RH increases, the competition between water molecules and VOCs toward the active sites becomes predominant and the degradation rate decreases. A bimolecular L–H model, including mass transfer step, was developed. A good agreement with the experimental results was observed. Moreover by derivating the equation model, the optimum RH values could be estimated for the two pollutants. These RH values are equal to 40% for isovaleraldehyde and 25% for trimethylamine.

► L–H approach to model the mass-transfer step on photocatalytic continuous reactor.
► Adsorption and kinetic constants depends only on the catalyst and the pollutant.
► Bimolecular L–H model to approach the effect of the relative humidity.