Reactor design of oxidative species generation for process intensification of photolytic ozonation

Abstract

The experimental and theoretical productions of oxygen, ozone, and hydrogen peroxide are accounted for during a photolytic ozonation (PO) process, with the aim of selecting a suitable reactor maximizing the interaction between ozone and radiation. In this process, ozone (O₃) reacts with water (H₂O) to produce oxygen (O₂) and hydrogen peroxide (H₂O₂). Additionally, ozone reacts with hydrogen peroxide, leading to the formation of the ozonide radical anion (O₃^•-), oxygen (O₂), and protons (H⁺). An ozonide radical trapping test was conducted using Sulfamethoxazole (SMX) as a model contaminant. To analyze the presence of ozonide, ascorbic acid was supplied to the cylindrical reactor. The oxidation processes for radical detection lasted for 90 min. The inhibition of SMX oxidation confirmed the presence of the ozonide radical. Experimental measurements are firstly evaluated to estimate kinetic constants using in-line sensors and permanganometry method, which are subsequently connected in a proposed reaction model applied to three different reactor geometries (e.g. parallel plates, serpentine, cylindrical). Species distribution is considered in the fluid dynamics of these configurations in terms of water inlet velocity at Reynolds numbers of 6.4, 12.8, 25.6, and 102.4. It is found that experimental data for oxidant productions are appropriately fitted by theoretical models, confirming the validity of the proposed model kinetic constants. Likewise, the kinetic reaction model can be simplified into two main reactions, with the major products being H₂O₂, O₂, and O₃^•-. While ozone concentrations increase at higher Reynolds numbers, hydrogen peroxide and oxygen exhibited linear growth over time, and O₃^•- production showed nonlinear behavior. The cylindrical reactor design demonstrates optimal reaction efficiency, combining effective mixing and continuous operation at significant cost savings due to reduced energy requirements, making it suitable for applications involving oxidant production using radiation and ozone. To this concern, the significance of O₃^•- generation, flow regime and reactor geometry are determining factors to maximize the oxidant concentrations.