STANDARDIZATION METHODS FOR THE PERFORMANCE EVALUATION OF PHOTOCATALYTIC MEDIAS FOR INDOOR AIR APLICATIONS
Résumé
The Photocatalytic Oxidation (PCO) seems to be a promising technique for commercial air cleaning applications1. However besides the numerous scientific publications2,3 there are still potential drawbacks inherent with this technology, like the risk of dangerous by-products generations by incomplete reactions. The absence of standard methodologies in order to evaluate the real performance of the process are the main issues that need to be addressed to ensure successful applications. In order to better understand the photocatalytic process in indoor air treatments the Normacat Project was established by two french laboratories (IRCELYON, IPREM) and several industrials. It has as main objectives the development of: i) new experimental approaches, tools and test benches to measure the efficiencies of photocatalytic media under typical indoor air conditions, ii) new photocatalytic materials iii) and to give recommendations to improve materials and systems. The photocatalytic performance of PCO medias were study using two different test benches: a photoreactor designed according to the standard ISO 22197 at realistic low VOCs concentrations (<20 ppbv) and a new experimental close-loop reactor using high air velocities (m s-1 range), equivalent to those encountered in HVAC (heating, ventilation and air conditions) systems. Robust sensitive analytical methods were also developed: for the conversion of the initial VOCs, a chromatograph equiped with a pulsed photoionization detector (GC-PID), for the quantification and identification of the reaction by-products an automated thermal desorption technique coupled with gas chromatography-mass spectrometry (ATD-GC-MS), for the analysis of CO, CO2 at ppbv levels a gas chromatograph equiped with a plasma emission detector (GC-PED) and for the on-line formaldehyde and acetaldehyde detection at low levels a gas chromatograph equiped with a pulsed discharge helium photoionization detector (GC-PDHID). A representative VOC mixture found in buildings (Toluene, n-Heptane, Acetone, Acetaldehyde and Formaldehyde) was used as target pollutants at typical indoor air levels. The influence of the different supports (organic cellulose, glass fibers, quartz fibers, ceramic foam and active carbon) on the photocatalytic activity used by commercial PCO air cleanear systems was studied and evaluated in terms of conversion, mineralization (CO2) and by-products formation. The effects of different parameters (humidity level, residence time, inlet concentrations UV lamps, radiation intensity) will be also discussed.