Kinetic Approach of the Photocatalytic Oxidation of Dichloromethane in a Coated Mesh Reactor

ALFANO, ORLANDO M.; CLAUDIO PASSALIA; RODOLFO J. BRANDI; TIBALDO, MARÍA

Praga

Conferencia; 5th European Conference on Environmental Applications of Advanced Oxidation Processes (EAAOP5); 2017

Univeristy of Chemistry and Technology

Dichloromethane (DCM) is one of the most typical indoor air pollutants; it is usually found in concentrations several times larger than outdoors [1] and is classified as a potential carcinogenic to humans. DCM was selected as a target pollutant for the evaluation of a coated mesh photocatalytic reactor for air purification.A kinetic approach was performed in a laboratory scale, one-pass, continuous reactor [2] by modification of the main operating variables: flow rate, inlet DCM concentration and incident radiation level. The surface that supports the catalyst within the reactor is a commercial 304 stainless steel mesh. It was treated to strengthen its corrosion resistance and then coated with titanium dioxide (Aeroxide P25). The reactor is made in acrylic and the radiation source is composed by two sets of actinic UV lamps (Sylvania F15W T12). DCM concentrations in the feeding air stream were determined by gas chromatography; radiation levels were experimentally determined by a portable spectrophotometer (Ocean Optics USB4000-UV-VIS).In order to obtain kinetic data, an analysis of the influence of the total flowrate on the global reaction rate was  performed. The global reaction rate was calculated as indicated in the figure, where Q is the volumetric air flow rate and Acat is the nominal catalytic area of the mesh. As can be seen, a kinetic control regime is achieved at a flow rate of 1 L/min. The next experimental essays were performed at a flow rate of 1 L/min, in the absence of external mass transfer limitations. Under the studied conditions, the maximum quantum efficiency, R /ea,s , is 4.17%. The Langmuir-Hinshelwood type models have been widely shown to be valid to represent heterogeneous photocatalytic reaction rates [3]. A LH type expression with an explicit dependence on the absorbed radiation (ea,s ) was proposed and its parameters were obtained by an optimization mehod. In addition, the dependence of the reaction rate with the ea,s is between the two theoretical limiting cases of order 1 and 0.5, with a fitted value of 0.716. The high reaction rate values obtained are promising for reactor scaling-up.