Solar photocatalytic gas-phase degradation of n-decane—a comparative study using cellulose acetate monoliths coated with P25 or sol-gel TiO2 films

Abstract

Cellulose acetate monoliths (CAM) were used as the substrate for the deposition of TiO2 films to produce honeycombed photoactive structures to fill a tubular photoreactor equipped with a compound parabolic collector. By using such a setup, an efficient single-pass gas-phase conversion was achieved in the degradation of n-decane, a model volatile organic compound. The CAM three-dimensional, gas-permeable transparent structure with a rugged surface enables a good adhesion of the catalytic coating. It also provides a rigid structure for packing the tubular photoreactor, and maximizing the illuminated catalyst surface. The efficiency of the photocatalytic oxidation (PCO) process on n-decane degradation was evaluated under different operating conditions, such as feeding concentration (73 and 146 ppm), gas stream flow rate (73, 150, and 300 mL min(-1)), relative humidity (3 and 25 %), and UV irradiance (18.9, 29.1, and 38.4 WUV m(-2)). The results show that n-decane degradation by neat photolysis is negligible, but mineralization efficiencies of 86 and 82 % were achieved with P25-CAM and SG-CAM, respectively, for parent pollutant conversions above 95 %, under steady-state conditions. A mass transfer model, considering the mass balance to the plug-flow packed photoreactor, and PCO reaction given by a Langmuir-Hinshelwood bimolecular non-competitive two types of sites equation, was able to predict well the PCO kinetics under steady-state conditions, considering all the operational parameters tested. Overall, the performance of P25-CAM was superior taking into account mineralization efficiency, cost of preparation, surface roughness, and robustness of the deposited film.

Evaluation of a solar/UV annular pilot scale reactor for 24h continuous photocatalytic oxidation of n-decane

“…This means that the excess of photons (in high irradiance conditions) favours the production of hydroxyl radicals in enough amount to mineralize all the pollutant molecules entering the reactor. Notwithstanding, by-products such as alkanes carboxylic acids or aldehydes [18,19] are, most likely, being formed and released to the atmosphere as final products of n-decane PCO during the above mentioned days. It is also worth noting that the PCO of n-decane over the photocatalytic films did not evidence any catalyst deactivation or support deterioration during the experiment periods.…”

“…In this case, the production of reaction intermediates may justify this behaviour. In our previous works an n-decane PCO mechanism was already proposed, based on the intermediates that were identified [18,19]. Briefly, n-decane oxidation initiates with a homolytic cleavage into radicals by a hydroxyl radical attack and, according to the identified intermediates, four paths can be followed: (1) radical recombination generating new alkane hydrocarbons such as n-hexane, n-octane, or 2,6-dimethyloctane; (2) hydrogen abstraction reactions leading to the formation of alkanes and alkenes; (3) reaction with adsorbed O 2 producing highly reactive superoxide alkyl-derived radicals; (4) oxidation by hydroxyl radicals forming alcohols.…”

“…Considering the above-mentioned research studies as well as the lab-scale fix-bed data reported in our previous works [17][18][19], a new versatile pilot-scale, single-pass, continuous-flow fixed-bed annular photoreactor based on an optimized compound parabolic collector (CPC) to capture both direct and diffuse UV natural solar radiation was designed and manufactured. Hereupon, the photocatalytic reactor was employed in PCO experiments of pure-targeted VOCs over TiO 2 -based photocatalytic films coated on cellulose acetate monolithic (CAM) structures under solar or artificial radiation.…”