SFGP 2007-An adsorption and photocatalysis study of ethyl hexanoate
Résumé
Titanium dioxide photocatalysis is an emerging and very promising technology to reduce odorous industrial pollution. Using an adsorbent could offer an interesting way to enhance the pollutants photodecomposition rate. Our project deals with industrial emissions that contain a high concentration of esters such as ethyl hexanoate (EH) which has a very low olfactory detection threshold and it is very unpleasant both in industrial indoor air and in outer emission. Photocatalysis is performed here within a mixed flow reactor involving two fibrous media. The first one is a media coated with TiO2, SiO2 and zeolite and the second one is a mixture of TiO2, SiO2 and activated carbon (AC). A three-level full factorial design of experiments is performed with TiO2 – zeolite media. It permits us to determine the impact of two main parameters on adsorption and photocatalysis phenomena; moisture inflow (from 0 to 15 g.m-3) and pollutant concentration (from 50 to 150 mg/m3). Adsorption capacity ranges between 4 to 37 mg EH/g of media. It decreases while humidity increases due to competitive adsorption of water and pollutants on photocatalyst sites. Moreover the EH conversion rate increases when inlet concentration decreases. An optimal relative humidity can be deduced to reach an optimal conversion rate for a fixed inlet concentration. Conversion rate values of 24, 39 and 25 % are observed at respective humidity values of 0, 7.5 and 15 g.m-3 for a 100 mg/m-3 inlet concentration. The designs of the experiment are descriptive and predictive for adsorption capacity and degradation rates. With TiO2 – AC media, experiments are carried out at 15 g.m-3 of humidity and 100 mg/m3 of EH inlet concentration. As expected, a high-grade adsorbent media leads to a higher adsorption capacity compared with TiO2 – zeolite media (130 instead of 4 mg EH/g of media). Nevertheless, even if adsorption capacity is higher, conversion rate decreases (23 % instead of 46 %). Thus, in our experimental conditions, a very high content of adsorbent in the photocatalyst media does not improve the global degradation efficiency probably due to the lack of desorption of pollutants from AC.