Solar Photocatalytic Reactor Designs

Most of the reactor designs tested for the photooxidation of organic pollutants by solar radiation are Ti02 slurry reactors. The implementation of solar photocatalytic reactors has occurred concurrently with advances in thedesign of solar thermal collectors, given the important characteristics shared by these units. There are, however, specific constraints for the design of solar photocatalytic reactors. 

The main advantages and drawbacks of concentrating and non-concentrating solar photocatalytic are summarized in Table 2.3. 

Non-concentrating reactors involve negligible optical losses due to the reflective surfaces therefore, these reactors can benefit from both direct and diffuse sun irradiation. In fact, non-concentrating reactors can continue their operation under cloudy conditions when only diffuse solar light is available. Furthermore, under clear sky conditions, they can take advantage of the diffuse sun iiTadiation component, close to 50% of the total available UV light (Alfano et al., 2000). 

Finally, non-concentrating reactors tend to be more efficient than concentrating units given that at high-energy flux densities the reaction rate depends on a fraction of 

---

This chapter reviews some of the main topics involved in the design and modeling of solar photocatalytic reactors, with particular emphasis on the authors research experience. Solar photons are source of energy that initiates photocatalytic degradation. Thus, proper consideration of radiative processes is key to address this subject. The determination of the directional and spectral characteristics of solar UV radiation, the interaction of the catalyst with radiation inside reaction spaces, the optical design of solar collectors, and the optical properties of the materials involved are all subjects where these concepts are necessary. Therefore, developments in this area should be solidly grounded on the fields of solar collector optics and radiative transfer, besides the more traditional chemical engineering aspects involved. This requires a multidisciplinary approach. 

Although different solar photoreactors have been developed in the last 20 years, each one with its own advantages and limitations, there is still room for new designs and innovative ideas. Nowadays, CPC appear as one of the most promising alternatives among solar photocatalytic reactors. The concepts of nonimaging optics, with its emphasis in efficient energy collection can also be a very useful in future developments. 

Braham, R. J. Harris, A. T. Review of Major Design and Scale-up Considerations for Solar Photocatalytic Reactors. Ind. Eng. Chem. Res., 2009, 48, 8890-8905. 

Compound parabolic collectors (CPCs) belong to the most promising photocatalytic solar reactors which combine the advantages of parabolic trough concentrator and non-concentrating system [178]. CPCs are low-concentration static collectors with reflective surface and can be designed for any given reactor shape (see Fig. 7.3a) [182]. The CPC reflectors are usually made from polished aluminum... 

---