Continuous photocatalytic reactor: Critical review on the design and performance

Photocatalysis is considered as one of the most promising advanced oxidation processes due to its ability to completely degrade contaminants to safer end product or intermediate compounds, ability to handle a wide range of contaminants, negligible requirement of post-processing, disposability of spent stream, and mild temperature and pressure conditions. The popularity of continuous flow photocatalytic reactors has grown over the last decade. The main advantages are scalability, continuous reaction monitoring, and efficiency. Because of its excellent photocatalytic activity, chemical and biological stability, corrosion resistance, and TiO 2 is considered the most versatile photocatalytic semiconductor for wastewater treatment. Here we attempt to demonstrate the development, application, and challenges in the design of continuous photocatalytic reactors, as well as their established and potential solutions, and classify them according to the containment-type, catalyst, geometry, and light source (UV-Vis, sunlight, LED, etc.). The effect of several factors on degradation efficacy is investigated, including catalyst dose, containment concentration, pH range, flow rate, and light source. Since reaction kinetics, flow rate and flow behaviour inside the reactor are significant factors in the design of a continuous photocatalytic reactor, we conduct a comparative study on rate constant and dimensionless parameters such as Reynolds number and Damkohler number. Suitability of continuous photocatalytic reactor as a sustainable green chemical process for environmental applications. • Comparison of the different continuous-type photocatalytic reactors is presented. • Design and scale up issues of continuous photocatalytic reactors is described. • In depth analysis of the reactor geometry and flow configuration on performance.