Membrane photoreactor configurations

The aim of our experimental studies was to show the possibility to use the PMRs for the degradation of organic pollutants, in particular drugs, in water, considering different reacting system configurations of membrane photoreactors and investigating the effects of some parameters on the efficiency of the process. 

Particular attention is addressed to the permeate flux and to this purpose some preliminary experiments were realized on a different configuration of membrane photoreactor with a submerged membrane module located separately from the photoreactor. Bubbled oxygen on the membrane surface has the roles to reduce the catalyst deposition, to increase the flux through the membrane and to facilitate the photocatalytic reaction. 

Various configurations of membrane photoreactors described can be chosen to influence the performance of the photocatalytic systems and possible solutions can be found to solve some problems such as the control of the catalyst activity and the fouling, the selectivity and the rejection of the membrane. 

Generally, the radiant energy balance must be added to the usual equations of mass, heat and momentum balance. Various approaches exist to obtain the hybrid photocatalysis-membrane systems and each of them requires modeling a specific configuration of the membrane photoreactor. Also, the characteristics of the membranes and their influence on reactivity must be taken into account. 

Depending on the photocatalytic reaction involved and on the type of membrane module used, the kinetic model changes, and consequently modeling a membrane photoreactor requires knowledge of the kinetic equations of the catalyst, the membrane and the reactor configuration. 

The obtained results have shown that the configuration where the recirculation tank was irradiated and the catalyst was used in suspension appeared to be the most interesting for industrial applications [73]. Moreover, it was observed that the degradation rate was higher when an immersed lamp was used compared to a system with an external lamp [81]. Therefore, actually the studies in progress are realized in the system described elsewhere [39] consisting of a Pyrex annular photoreactor with a 125-W medium-pressure Hg lamp axially positioned inside the reactor. The separation module containing the flat-sheet membrane was connected to the photoreactor in a recirculation loop. 

The photocatalytic reaction in PMRs with suspended photocatalyst might be conducted in (a) a feed tank, (b) a membrane module or (c) an additional reservoir (photoreactor) located between the feed tank and the membrane module. In some cases the reaction is conducted in both the membrane module and the feed tank. The above mentioned configurations are the most popular ones however, one might find modifications of these solutions. In the PMRs with suspended photocatalyst, the Ught source must be positioned above or inside the element of the membrane installation in which the photocatalytic degradation is carried out. Schematic diagrams of the most common configurations are presented in Fig. 6.31. 

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