Improving reactor fluid dynamics enhances styrene degradation by advanced oxidation processes

Abstract

Styrene, being one of the volatile organic compounds (VOCs), presents a notable environmental risk. This study primarily addresses the mitigation of styrene emissions from waste air streams through advanced oxidation processes. Nonetheless, the development and experimentation of novel photoreactors can incur substantial costs and time commitments. Nevertheless, mathematical modelling can substantially reduce both expenses and reaction times. By experimental analysis, this research aims at comparing two designs of the first step of styrene treatment (dry photolytic reactor (UV185/UV254/O3)) in a two-step pilot plant unit. The new design differed in fluid geometry while maintaining identical dimensions and irradiation field in the photolytic reactor. Increasing the mean residence time of gas inside the reactor increased styrene removal efficiency by 25% at both flow rates, 100 and 150 m3·h−1. The experimental results were effectively explained by mathematical modelling, highlighting its invaluable role in designing new photoreactors. Based on our modeling, we added a baffle to the center of the photolytic reactor to further increase the residence time, thereby enhancing even more the photoreactor. The model with the baffle should completely remove 50ppmv of styrene from a gas stream at a 100 m3·h−1 flow rate already in the first step of the pilot unit. When comparing the cost-effectiveness of the three designs by calculating their electrical energy per order (EEO) values, we found that Design D (the new design with the baffle) reduces styrene emissions by 90% at approximately one quarter of the cost of Design A (original design). Precisely, treatment of air containing 50 ppmv of styrene utilizing Design D would cost 0.0012 € per each cubic meter. This study clearly demonstrates that fluid dynamics have a greater impact on the performance of advanced oxidation processes in air than photoreactor geometry and also the importance of mathematical modelling for reactor design.