Micro-structured packed bed reactors for solar photocatalysis: impacts of packing size and material on light harnessing.

The application of photochemistry in larger scales relies on studies in photoreactor engineering. This report investigates the structural parameters of externally irradiated micro-structured photochemical packed bed reactors (PBRs). It reports on the impacts of the size and material of spherical packings on the reactor ability to harness incoming photons. Tubular reactors were built from borosilicate glass tubes of two outer diameters (20 and 30 mm) packed with soda-lime glass spheres of three average diameters (1.0, 3.0 and 6.0 mm), alumina spheres (6.0 mm dia.), and polished iron spheres (5.0 mm dia.). The aqueous-phase oxidation of benzoic acid by oxygen radicals generated by UV-A irradiation of nitrite ions was used as a model homogeneous photochemical reaction. It was observed that increasing the D/dp ratio for the narrower reactors led to improved specific yields (3.0 mm = 1.050), suggesting that intensification is possible in these reactors. Lastly, it was found that glass spheres can be replaced by alumina spheres with considerably little loss in the light-collection efficiency (ca. 20%), indicating an attractive pathway for fixed-bed solar photocatalysis.