An Overview of Photoreactors and Computational Modeling for the Intensification of Photocatalytic Processes in the Gas-Phase: State-of-Art

TLDR: In this paper, a comprehensive review of the photoreactors for gas-phase reaction focusing on process intensification and recent computer simulations is provided, in which the state-of-the-art of photocatalytic air treatment providing examples such as the VOCs oxidation and NOx degradation.

Abstract: This article provides a comprehensive review of the photoreactors for gas-phase reaction focusing on process intensification and recent computer simulations. This review selected two photocatalytic gas-phase reactions, namely the oxidation of volatile organic compounds (VOCs) and the degradation of nitrogen oxides (NOx). It was also discussed two photocatalytic gas-phase reactions’ importance from a scientific and social perspective. Therefore, heterogeneous photocatalysis was applied, and it excelled itself as a promising technology for gas-phase reaction applications. However, despite the numerous advances in photocatalytic processes in recent times, there are still several challenges in their development for this technology to achieve high performance. Mass transfer and low quantum efficiency (photon transfer) are some of these challenges becoming a significant concern for the design of new photoreactors or the improvement of existing ones. Different types of photocatalytic reactors have already been designed, examined, and simulated, seeking to maximize the pollutant-catalyst contact (enhancing mass transfer) and to maximize the lighting efficiency throughout the catalyst surface (enhancing photon transfer). The process intensification has been highlighted in the development of photoreactors to ensure the improvement in mass and photons transfer. Here, we will address the monolithic photoreactors, photocatalytic membrane reactors, and photo-microreactors, in which each photoreactor has its advantages and drawbacks. CFD-based models, combined with the design of the photoreactors, are essential since they can successfully predict the performance of various geometric configurations and identify the limitations to the photon and the mass transfer with only validated virtual prototypes. From this perspective, this review presents the state-of-art of photocatalytic air treatment providing examples such as the VOCs oxidation and NOx degradation. Furthermore, this review also reports a literature exam of three different types of photoreactor designs presenting their advantages and limitations regarding the mass and the photons transfer focusing on photocatalytic process intensification. Also, it is presented a discussion of the recent applications of photocatalytic reactor modeling using computational fluid dynamics (CFD) for the gaseous pollutant degradation.