Performance of continuous stirred-tank reactors connected in series as a photocatalytic reactor system

Film-diffusion resistance significantly reduces the decomposition of organic compounds over an immobilized photocatalyst in the vicinity. To overcome this problem, the performance of a photocatalytic system consisting of five continuous stirred-tank reactors (CSTRs) in series was investigated. Each reactor was a square-shaped container with a glass plate immobilized with a film of TiO2 photocatalyst at the bottom. Two 4-W blacklight blue-fluorescent lamps fixed above the container provided UV light. A 10-ppm aqueous solution of 2,4-dinitrophenol (DNP) supplied continuously to the reactor was stirred by an impellor fixed to a shaft with a wind propeller at its upper end. The change in the DNP concentration in each reactor with increasing flow rate agreed with the result calculated by a mathematical model, constructed for the photocatalytic system, which included a mass-transfer coefficient expressed in terms of rotational speed. Hence, this model was used to simulate the performance of the reactor system. At sufficiently high rotational speeds, the conversion of DNP at the exit of the fifth CSTR was substantially higher than that at the exit of a single CSTR with the same liquid volume, and was close to the calculated value for a plug-flow reactor without film-diffusion resistance. At low rotational speeds, however, the DNP concentration remained remarkably high because of large film-diffusion resistance, demonstrating that the photocatalytic reaction requires sufficient liquid mixing to enhance the reaction rate. Thus, the system of five CSTRs in series is effective as a photocatalytic reactor system. (C) 2015 Elsevier B.V. All rights reserved.