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The objective of this article is to find the optimal design of rectangular microchannel reactors, in terms of reactor dimensions and materials, in order to increase the photocatalytic activity. Microchannel reactors with immobilized titanium dioxide (TiO2) as photocatalyst have been designed, fabricated, and tested. The photocatalytic degradation of salicylic acid is investigated as a function of microchannel size, materials that constitute the reactor, contaminant concentration and flow rate. All the reactors exhibit the same behavior. Higher degradation is observed for low pollutant concentrations and flow rates. The nature of the constituent element of the reactor has practically no influence on the photocatalytic process. The degradation performance is affected by the microchannel dimensions. The reactor with the largest channel width and length, and the lowest channel height displays the highest photocatalytic activity. For an optimal design of the rectangular microchannel reactors a relation between the degradation ratio X and the dimensions of the microchannel is reported. A linear relationship between X and wL/h2 (L: length, w: width, h: height of the channel) is found experimentally. The product wL emphasizes the uniform irradiance over the entire catalyst surface and confirms that the bottom of the channel covered with TiO2 is photoactivated. The term in 1/h2 is necessary to take into account the mass transfer limitation.

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