Continuous Flow Hydroxylation of Benzene to Phenol in a Photocatalytic Millistructured Flat-Plate Reactor

Phenol can be produced from benzene via photocatalytic hydroxylation. A continuous flow flat-plate reactor emerges as a promising option, as it allows for a large irradiation window and a short photon penetration depth. In this work, TiO2 (Degussa P25) was applied as a photocatalyst. The use of smectite clays and a 3D-printed casting template was the key to the uniform immobilization of photocatalysts over the glass window surface. Acetonitrile was selected as a carrier solvent for benzene since the fluid dynamics exhibited an efficient mixing with the aqueous H2O2 flow solution. Furthermore, the response surface methodology was employed to examine the effects of residence time, temperature, and light power. Our flat-plate reactor produced a high photocatalytic space-time yield of 1.2 × 10–11 mol/W s, which is about 1–2 orders of magnitude higher than the reported batch setups. The transport phenomena equation was also formulated to elucidate the kinetics of the photocatalytic reaction, giving the adsorption constant and the intrinsic kinetic constant to be 0.0535 m3/mol and 8.21 × 10–6 mol/(m2·s), respectively.