Modeling of slurry-type photocatalytic reactors containing core-shell particles for predicting transient behaviours based on Langmuir-Hinshelwood kinetics

Abstract

Governing equations were derived for photocatalytic batch reactors and CSTR (Continuously Stirred Tank Reactor) containing photocatalytic pellets to obtain numerical solutions of the concentration in bulk medium and intra-particle concentration based on Langmuir-Hinshelwood kinetics. Numerical solutions could be obtained by finite element method under proper initial and boundary conditions to solve coupled reaction-diffusion equations using partial and ordinary differential equations. Effects of Thiele modulus, Biot number, Langmuir—Hinshelwood parameter and photocatalyst loading were investigated by predicting the performance of batch reactor. Effects of residence time and initial reactant concentration were studied for CSTR. In addition to conventional morphologies of pellets such as sphere, cylinder and slab, mathematical modeling of core-shell particles was also conducted to study the effect of thickness of inert core. Although the performance of spherical pellets was the best, cylindrical pellets also showed good activity for removing reactant by photocatalytic decomposition. In core-shell spherical pellets, there was little effect of thickness of inert core on the reduction rate of reactant concentration and steady-state concentration in batch and CSTR, respectively, compared to core-shell cylindrical and slab-type particles. The cascade connection of photocatalytic CSTRs and fixed bed reactors with back mixing could be also analysed by finite element method. Experimental data about the removal of methylene blue using silica-titania core-shell particles in batch photocatalytic reactor were compared with numerical solutions to estimate reaction parameters.