Dispersion-based membrane contactor

Figure 26.4 Dispersion creation and phase contacting in a dispersion-based membrane contactor.

The membrane in a contactor acts as a passive barrier and as a means of bringing two immiscible fluid phases (such as gas and hquid, or an aqueous hquid and an organic hquid, etc.) in contact with each other without dispersion. The phase interface is immobilized at the membrane pore surface, with the pore volume occupied by one of the two fluid phases that are in contact. Since it enables the phases to come in direct contact, the membrane contactor functions as a continuous-contact mass transfer device, such as a packed tower. However, there is no need to physically disperse one phase into the other, or to separate the phases after separation is completed. Several conventional chemical engineering separation processes that are based on mass exchange between phases (e.g., gas absorption, gas stripping, hquid-hquid extraction, etc.) can therefore be carried out in membrane contactors. 

Promising results are shown by recently developed integrated SLM-ELM [84, 85] systems. These techniques are known as supported liquid membrane with strip dispersion (SLMSD), pseudo-emulsion-based hollow fiber strip dispersion (PEHFSD), emulsion pertraction technology (EPP), and strip dispersion hybrid Hquid membrane (SDHLM). AH techniques are the same the organic phase (carrier, dissolved in diluent) and back extraction aqueous phase are emulsified before injection into the module and can be separated at the module outlet. The difference is only in the type of the SLM contactors hoUow fiber or flat sheet and in the Hquid membrane (carrier) composition. These techniques have been successfuUy demonstrated for the removal and recovery of metals from wastewaters. Nevertheless, the techniques stiU need to be tested in specific apphcations to evaluate the suitabUity of the technology for commercial use. 

S. Mukhopadhyay, Dispersion and emulsion based liquid membrane systems in hollow fiber contactor, in S.A. Ansari, A.K. Pandey, P.K. Mohapatra, A. Goswami (eds.), Proceedings of Theme Meeting on Membrane Separation for Fuel Cycle Applications, BARC, Mumbai, India, September 16-18, 2013, p. 11. 

Dispersion of either phase into the other in gas-liquid systems is undesirable. By having the pores filled with gas, the resistance to species transfer through the membrane pores is kept at a low level (Qi and Cussler, 1985a). For nondispersive operation, the liquid phase must not spontaneously wet the membrane pores. For porous hydrophobic membrane-based contactors, aqueous solutions are, therefore, preferred liquid phases for any non wetting liquid, the value of 0 is >90°. The surface tension of the liquid should be greater than the critical surface tension of the polymer, 7,-. However, dissolved substances, especially surface-active ones, in water can reduce the value of 7 and can lead... 

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