Design and evaluation of co-currently illuminated two-phase bubbly flow photochemical reactors

Current two-phase flow photochemical reactors are lacking energy efficiency required for industrial applica-bility. As an alternative, co-currently illuminated bubbly flow photochemical reactors are proposed. These have the advantage of running at higher absorbance values, thereby wasting less photons, improving cost efficiency, and decreasing gas holdup by separating gas and liquid residence time in the reactor. A mathematical model was used in the study in combination with photosensitized reactions, which yielded three coupled differential equations and four non-dimensional groups governing the reactor performance. A parameter study yielded an optimal operating point at a quantum photon balance (& phi;tot & rho;) of 1, an absorbance (AS) of at least 1, a chemical quenching parameter (& kappa;A) of less than 0.1, and a sensitizer stability ratio (& phi;S/fS) of less than 1. Optimal absorbance was determined via the use of a ray tracing study, yielding a theoretical optimal absorbance of 1.75 using 7 & mu;M of rose bengal. The modelling results are experimentally validated, and the model was shown to be suitable across a wide range of operating conditions. Optimal absorbance was experimentally evaluated to match the modelling results, higher absorbance values lead to more local absorbance, throttling reactor performance. With high reagent concentrations, the reaction was found to be liquid side mass transfer limited. Guidelines are presented to design this novel type of reactor and ways to improve the reactor performance in scaled up versions. The reactor was compared against the current state-of-the-art reactors, yielding an improvement PSTY by 4.5 times and an increased reagent/sensitizer ratio by 100 times, both drastically decreasing operational cost of the reactor.