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

Abstract

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 industrialscale 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.

One-step topological preparation of carbon doped and coated TiO2 hollow nanocubes for synergistically enhanced visible photodegradation activity

“…To date, there have been a signicant amount of studies devoted to improving the visible light utilization of TiO 2 by semiconductor coupling, 3,4 metal and non-metal ion doping 5,6 and surface sensitized modication. 7,8 Although semiconductor coupling can effectively utilize heterojunction effects to speed up the separation rate of photo-generated electron-hole pairs and improve photocatalytic activity, photoactivity strongly depends on heterojunction structures and energy conversion efficiencies are too low for industrial applications.…”

TiO2 Solar Photocatalytic Reactor Systems: Selection of Reactor Design for Scale-up and Commercialization—Analytical Review

“…Falling film reactor is a variation of the flat plate collector where the surface of reactor is left open to the atmosphere [60]. Falling film reactor is a non-concentrating reactor employing both direct and diffuse solar radiations.…”

“…Laminar flow conditions prevail resulting in film thickness of 1 mm [63]. Eliminating reactor cover has two advantages: (1) Purging reaction solution with air/oxygen is unnecessary since oxygen is exchanged rapidly between air and water [61]; (2) Falling film reactors have higher optical efficiency, elimination of transmissive losses due to cover material and thickness [60]. Thin-film fixed-bed reactor (TFFBRs) is a falling film reactor having TiO 2 immobilized on the reactor surface.…”

“…Despite the extensive research on photocatalytic oxidation using TiO 2 , pilot and demonstration plants through the last four decades are still countable [1], [57][58][59][60][61][62][63][64][65][66] as shown in Table 1. Different reactor configurations have been used to degrade various types of pollutants using solar light or artificial light simulating sunlight.…”

Green Photochemical Processes and Technologies for Research & Development, Scale‐up and Chemical Production

“…22 In contrast to the early 'flask in the sun' approach, modern solar reactors are now available that enable technical applications on large scales. 23 In the 1990'ies, Scharf and co-workers were the first to use concentrated sunlight for the solar manufacturing of selected fine chemicals. 24 Following this pioneering work, a number of laboratory-to large-scale solarchemical reactions in sunlight using different concentrating and non-concentrating solar reactors (Fig.…”