Review of Major Design and Scale-up Considerations for Solar Photocatalytic Reactors

Photocatalytic processes are applicable in wastewater treatment, energy production, chemical synthesis, and greenhouse gas mitigation and thus have the potential to address both the consumption of nonrenewable fossil fuels and global warming, two of the greatest problems facing humankind. The ability to achieve these outcomes using only solar energy as an input is particularly attractive. However, the implementation of most photocatalytic processes at an effective scale requires the use of a photoreactor, a device which brings photons, a photocatalyst and reactants into contact, as well as collecting the reaction products. In this work, we review the state-of-the-art in solar photoreactor design and assess those systems which are most applicable for industrial-scale implementation. Designs for parabolic trough, compound parabolic, inclined plate, double skin sheet, rotating disk, water bell, fiber optic, and fixed/fluidized bed photoreactors are qualitatively discussed and compared. Compound parabolic photoreactors are most suited to near term applications at pilot-scale (>1000 L/day) due to their advantageous light collecting properties and well-known design methodology. Double-skin sheet photoreactors are also suited to near term applications; however, significantly less is known about. their design and performance discrepancies between Studies in the literature have been reported. Compared to other photoreactor designs, the significantly simplified design and low material cost of inclined plate photoreactors makes them particularly suitable for use in economically and logistically challenged areas where the volumes to be treated are small (< 100 L/day). Fluidized bed photoreactors are highly efficient. but More research is needed into their design and operation for effective use with solar radiation. The other photoreactor designs reviewed are unlikely to see wide use due to, variously, high mechanical complexity, poor efficiency, and/or susceptibility to environmental conditions but May find limited use in specialized applications, e.g. in instances where it is advantageous to separate the light gathering and photocatalytic components of the photoreactor.