NORMACAT PROJECT Normalized Tests using a Closed-Loop Reactor for the Performance Evaluation of Commercial Photocatalytic Medias for Indoor Air Aplications
Résumé
Since research found that poor indoor air quality (IAQ) can significantly affect peoples health, comfort, satisfaction and productivity, the reduction of indoor air pollutants by air cleaning/purification devices have received a considerable interest [1]. A new substantial market for removing various indoors contaminants from residences and offices is settled. So far, between the numerous techniques available, photocatalytic oxidation (PCO) technology has shown to be well suited for the purification of indoor air [2-3]. Besides that PCO is still under development, nowadays in the market, numerous PCO cleaners are commercially available and promoted. However, there is limited information available regarding their performance and there are no standard methods for testing the VOCs removal efficiency from PCO air cleaning devices. The evaluation of the performance of the photocatalytic filters used in these air cleaning systems is the key issue of this study. Different TiO2-supported catalysts, from commercial air cleaning devices, based on photocatalytic technology for indoor air treatment, were tested in a new experimental close-loop reactor (Figure 1). The photocatalytic efficiency of the TiO2 catalysts immobilized on various supports (organic cellulose, glass fibers, quartz fibers and active carbon) were evaluated at realistic conditions: low VOCs concentrations (ppbv levels) and high airflow rates (m3h-1 range), equivalent to those encountered in HVAC (heating, ventilation and air conditions) systems. The filters were evaluated in terms of conversion, mineralization (CO2) and by-products formation. For this purpose, robust sensitive analytical methods were also developed: for the conversion of the initial VOCs, a chromatograph equipped 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 equipped with a plasma emission detector (GC-PED) and for the on-line formaldehyde and acetaldehyde detection at low concentrations a gas chromatograph equipped with a pulsed discharge photoionization detector (GC-PDID) was used. According to the results of this work, if the photocatalytic efficiency of the catalyst was measured only by taking into account the VOC removal capacity, all the filters were considered highly effective. Our results showed that the mineralization (CO2) of the target pollutants and the formation of reaction intermediates have to be considered in order to obtain a relevant evaluation of the photocatalytic activity of the filters.