Photosensitized reactions in an annular continuous photoreactor

Abstract

The process of energy emission by a lamp of finite spatial dimensions is considered, and a general expression for the local volumetric rate of energy absorption (L.V.R.E.A.) is given under the assumptions of no reflection and of negligible scattering and emission phenomena in the absorbing medium. When a reaction is occurring in the absorbing medium, L.V.R.E.A. can be easily computed if the reaction is a photosensitized one. In this case profiles of L.V.R.E.A., computed in an annular photoreactor solving the equations which govern rigorously the phenomenon, can differ in a relevant way from those computed assuming a radial model for the emission by the same lamp, the difference being mainly dependent, for a given radial geometry, on the reactor length and on the value of the optical thickness of the absorbing medium. Photosensitized reactions of order 0 and 1 with respect to the reactant concentration were studied for different values of the optical thickness, of Damkoheler and Peclet numbers. In particular the effects of variations of Pe number on the conversion were taken into consideration and the results were explained on the basis of physical and mathematical arguments.