Design of Photocatalytic Reactors Made Easy by Considering the Photons as Immaterial Reactants

G. CAMERA-RODA, F. SANTARELLI Y C.MARTIN

Barcelona, España

Congreso; SPEA3 3rd European Meeting on Solar Chemistry and Photocatalysis: Environmental Applications; 2004

Reactant conversion, product yield, selectivity and effectiveness factors are direct and sound indexes used in chemical reaction engineering to describe different performances of the reaction process. Also in photocatalytic reactions some attempts have been made to consider indices, that might help in reactor design and in assessing the reactor performances, but their definition is often rather complicated and their use is sometimes cumbersome. Some of the difficulties encountered when dealing with a photocatalytic reactor, particularly in the case of solar photocatalytic reactors, can be summarised as follows: -the radiant energy must be absorbed in order that the reaction take place, so that its intensity decreases inside the reactor. On the other hand, from the point of view of a good exploitation of the reactor volume, it should advisable that the radiant energy could be evenly available inside the reactor. -The radiant energy is transported in a very different way with respect to material compounds. -The kinetics of the reaction appears not to be linear with respect to the intensity of the radiant energy. In this paper these aspects are taken into account, and an attempt is made to use indexes of comprehensible definition, possibly with a clear meaning. Indeed, if the photons are considered as "immaterial" reactants, then some descriptors of the performances which are analogue to those commonly used for conventional reactants can be defined. The use of such descriptors allow to derive some simple rules that can be followed in order to optimise the reactor and to council between opposite requirements. The methodology is illustrated for some simple cases without loss of generality, in fact the method can be applied for different geometries of the reactor and different optical properties of the photocatalyst is dispersed. The same approach can be extended also to photosynthetic systems.