Membrane photoreactors

Besides, the membrane photoreactors allow operation in continuous systems [39] in which the reaction of interest and the separation of the product(s) simultaneously occur, avoiding in some cases the formation of by-products. 

The ultrafiltration or microfiltration membrane used in the described submerged membrane photoreactors showed high fluxes and a good removal efficiency of organic molecules, nevertheless, they are not able to reject compounds with low molecular weight. 

Membrane distillation - photocatalysis To solve the problem of membrane fouling observed in the pressure-driven membrane photoreactor, Mozia et al. [90] studied a new type of PMR in which photocatalysis was combined with a direct contact membrane distillation (DCMD). MD can be used for the preparation of ultrapure water or for the separation and concentration of organic matter, acids and salt solutions. In the M D the feed volatile components are separated by means of a porous hydrophobic membrane thanks to a vapor-pressure difference that acts as driving force and then they are condensed in cold distillate (distilled water), whereas the nonvolatile compounds were retained on the feed side. 

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. 

By means of TOC analyzes carried out during photodegradation experiments in closed and continuous membrane photoreactors it was observed that some oxidation products pass through the membrane. Therefore, further investigation is in progress to analyze this aspect. 

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. 

The submerged membrane photoreactor was more advantageous in terms of permeate flux, with values almost twice those measured with the flat-sheet membranes. Nevertheless, the UF membranes used in the submerged system were not able to reject the drug and its degradation products [94],... 

In particular, our research is addressed to the simultaneous one-step production and separation of phenol by selective oxidation of benzene in a membrane photoreactor using Ti02 as catalyst and a membrane contactor for the separation process. 

The membrane photoreactor under investigation consists of an external lamp placed on a batch reactor containing the aqueous solution with the catalyst in suspension by means of a peristaltic pump the solution is withdrawn from the... 

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. 

MoUnari R, Caruso A, Argurio P and Poerio T (2008), Degradation of the drugs Gemfibrozil and Tamoxifen in pressurized and de-pressurized membrane photoreactors using suspended polycrystalline TiOj as catalyst , / Membr Sci, 319, 54-63. 

Chin S S, Lim T M, Chiang K and Fane A G (2007a), Hybrid low-pressure submerged membrane photoreactor for the removal of bisphenol A , Desalination, 202,253-261. 

Closed and continuous procedures were used to investigate the behavior of pressurized membrane photoreactors. The obtained data of the closed membrane system showed a complete photodegradation of GEM and TAM, with an abatement of 99% after 20 min and a mineralization higher than 90% after approximately 120 min. 

However, the submerged membrane photoreactor offered more advantages in terms of permeate flux than those obtained operating with pressurized module. 

In this context, the possibility of using a membrane photoreactor for organic synthesis, developing a hybrid system in which the photocatalytic reaction and the separation of the product of interest occurs in one step will be highlighted. 

At present the scientific literature is lacking in modeling membrane photoreactors because the coupling between photocatalysis and membranes is a relatively new subject of study. 

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. 

A thorough analysis of the economics of membrane photoreactors can hardly be found in published data because the research is still mainly at laboratory and pilot scale. A pilot scale plant (Photo-Cat ) has been implemented in full scale by Purifies ES Inc. (Canada) company which in 2010 was awarded contracts at the W.R. Grace Superfund Site in Concord, Massachusetts (USA) and at an elementary school in Ontario (Canada). 

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