Abstract
► Comparison between two types of reactors (cylindrical and planar) on VOCs photocatalytic degradation. ► Influence of the mass transfer step on the reactor performance. ► All the by-products were identified.
An investigation of isovaleraldehyde (ISOV) photocatalytic oxidation was conducted at initial concentrations ranging from 25 to 150mg/m3 and different relative humidities (5–90% RH) in order to characterize the process performances close to indoor air conditions. Experiments were carried out in two different reactors: cylinder and flat-plate photoreactor (planar reactor) at different air gap (20–60mm) and gas residence times (0.67–5.0s). A plug flow reactor system was developed in order to perform kinetic studies of (i) isovaleraldehyde removal, (ii) selectivity of CO2, (iii) by-products formation and removal. It appears that ISOV removal efficiencies increased with lower inlet concentrations, lower air gap and higher gas residence times.
In small amounts, the presence of water vapor has a promoting effect on the degradation due to the formation of OH radicals.
Evaluating different kinetic models by least squares analysis, it was shown that the Langmuir-Hinshelwood (L-H) model could give a good correlation with the experimental results. Thus, the effect of ISOV gas-phase concentration, air gap and light intensity on chemical conversion rates is discussed.
A kinetic model based on Langmuir-Hinshelwood (L-H) approach and taking into account the mass transfer step was developed. This allows us to determine L-H constants regardless of the transfer aspect. This last is estimated by semi-empirical correlation. The separation between the mass transfer and the chemical reaction steps is obtained. The effect of UV light intensity is also considered.