PHOTOCATALYTIC MICROREACTOR FOR INTRINSIC KINETIC ASSESSMENT

SILVIA MERCEDES ZACARIAS; AGUSTINA MANASSERO; MARÍA LUCILA SATUF; CLAUDIO BERLI

Praga

Congreso; 5th European Conference of Environmental Applications of Advanced Oxidation Processes; 2017

University of Chemistry and Technology, Prague, Czech Republic (UCT Prague)

Intrinsic kinetic parameters useful for the design, optimization and comparison of photocatalytic devices, are difficult to obtain in conventional reactors. Carefully planned experiments must be carried out, along with complex models, to take into account the influence of radiation, mass transfer and fluid dynamics on the reaction rate. In turn, microreactors provide an excellent platform for photocatalytic kinetic studies because of the advantages of the microscale: laminar flow, short molecular diffusion distances, uniform irradiation, large surface to volume ratio, and accurate control of operation variables [1,2]. In this work, a simple method for obtaining kinetic parameters for first order reactions is developed. The degradation of the pollutant 4-chlorophenol (4-CP) is evaluated in a photocatalytic microreactor under different flow rates and constant UV illumination. The microreactor consists of a rectangular reaction chamber of 5.8 cm  2 cm  200 m (reactor volume VR=232 L). The top layer of the reactor is a borosilicate glass plate coated with TiO2, which act as a window. The TiO2 film was obtained by the dip-coating technique from a suspension of 150 g/L of AEROXIDE TiO2 P 25 (Evonik, Germany). The thickness of the film, evaluated by SEM images, was 500 nm. Illumination was provided by a set of 4 UV lamps (Philips TL 8 W Actinic BL), with maximum emission at 365 nm. The resulting irradiation flux at the reactor window was 1.21 mW/cm2. A solution of 20 mg/L of 4-CP was pumped into the reactor by a syringe pump at flow rates (Q) ranging from 20 to 300 L/min. The concentration of 4-CP was determined by HPLC. The microreactor is mathematically modeled as a Hele-Shaw cell, considering first-order kinetics. In the limit of negligible mass transfer limitations: , where k is the kinetic constant, and Cin and Cout represent the inlet and outlet concentration of 4-CP, respectively. From the slope of the plot Q vs 1/ln(Cin/Cout), in the linear range (Q below 170 L/min), the value of the kinetic constant can be calculated. Following these simple steps, first-order kinetic constants of different chemical compounds can be obtained. Additionaly, it represents a reliable methodology to evaluate the performance of different catalytic films for a given reaction.