Simulation of CO2 photoreduction in a twin reactor by multiphysics models

[Display omitted] •A 2D axisymmetric multiphysics model was built for CO2 photoreduction in a twin reactor.•The model was based on the turbulent bubbly flow, transport of dilute phase and radiation in the participating medium.•The effects of variables, such as size of bubble, gas volume rate, bubble entrance size and photocatalyst loading were investigated.•The predicted CH3OH yields matched the experimental data. The production of solar fuels through CO2 photoreduction is a promising process to control CO2 emissions and provide alternative renewable fuels. Recently, a twin photoreactor design has been used to enhance CO2 conversion efficiency. However, the reaction mechanisms and operating conditions are not well understood. Therefore, the purpose of this work is to understand the CO2 photoreduction mechanisms in the twin photoreactor by using multiphysics modelling (COMSOL 5.2a). A 2D axisymmetric model was built and the predicted yield of CH3OH matched the experimental values very well under different molar ratios of CO to CO2. Moreover, the effects of operating parameters, including bubble size, gas volume rate, bubble entrance size and photocatalyst loading, were investigated. The CO2 photoreduction in the liquid phase was shown to be a mass-transfer controlled process, and the flow properties significantly influenced the CO2 photoreduction. It was found that the bubbly circulation flow structure, interfacial area between gas and liquid, and surface area of the catalyst are critical for the CH3OH yield. This study can provide the theoretical guidance for process optimization and reactor design.