Membrane contactors pores entrance

A membrane is usually seen as a selective barrier that is able to be permeated by some species present into a feed while rejecting the others. This concept is the basis of all traditional membrane operations, such as microfiltration, ultrafiltration, nanofil-tration, reverse osmosis, pervaporation, gas separation. On the contrary, membrane contactors do not allow the achievement of a separation of species thanks to the selectivity of the membrane, and they use microporous membranes only as a mean for keeping in contact two phases. The interface is established at the pore mouths and the transport of species from/to a phase occurs by simple diffusion through the membrane pores. In order to work with a constant interfacial area, it is important to carefully control the operating pressures of the two phases. Usually, the phase that does not penetrate into the pores must be kept at higher pressure than the other phase (Figure 20.1a and b). When the membrane is hydrophobic, polar phases can not go into the pores, whereas, if it is hydrophilic, the nonpolar/gas phase remains blocked at the pores entrance [1, 2]. 

Membrane contactors (MCs) are another interesting emerging membrane technology for desalination. MCs are devices that bring two phases (gas/liquid, liquid/liquid or liquid/gas/liquid) into contact at the entrance of pores (Fig. 2.1). MCs are today most commonly employed in the production of ultrapure water, wastewater treatments and water purification, as well as being used to control the concentration of several non-volatile solutes in aqueous solutions, such as salt and sugar in fruit juices and blood treatments. 

Membrane contactors are devices in which a microporous hydrophobic membrane acts as a barrier between two phases, permitting gas/liquid or liq-uid/liquid mass transfer of the components without dispersion of one phase into the other. The hydrophobic character of the membrane prevents penetration of the aqueous solution into the pores and the transport occurs at the pore entrance. 

In liquid/liquid systems, one of the two phases is able to wet the manbrane and fills the membrane pores. The other liquid is located at the other side of the membrane and an interface between two immiscible liquids is created at the entrance of each pore. Bey et al. [133] prepared PVDF hollow fibers using DMF as solvent and a mixture of water and PVP (K-17) as pore-forming additives, which were applied as contactors for the removal of As(V). The effect of BF composition and flowrate on fiber morphology and properties was examined. The MC performance was enhanced by working with thinner membranes, which was obtained by increasing the BF flowrate. A removal of about 70% in 6 h of operation was obtained working with a solution with arsenic 100 ppm as feed. 

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