Nondispersive membrane extraction

Extraction (Nondispersive Membrane Extraction) and Model Equation.124... 

Nondispersive solvent extraction is a novel configuration of the conventional solvent extraction process. The term nondispersive solvent extraction arises from the fact that instead of producing a drop dispersion of one phase in the other, the phases are contacted using porous membrane modules. The module membrane separates two of the immiscible phases, one of which impregnates the membrane, thus bringing the liquid-liquid interface to one side of the membrane. This process differs from the supported liquid membrane in that the liquid impregnating the membrane is also the bulk phase at one side of the porous membrane, thus reducing the number of liquid-liquid interfaces between the bulk phases to just one. 

All the novel separation techniques discussed in this chapter offer some advantages over conventional solvent extraction for particular types of feed, such as dilute solutions and the separation of biomolecules. Some of them, such as the emulsion liquid membrane and nondispersive solvent extraction, have been investigated at pilot plant scale and have shown good potential for industrial application. However, despite their advantages, many industries are slow to take up novel approaches to solvent extraction unless substantial economic advantages can be gained. Nevertheless, in the future it is probable that some of these techniques will be taken up at full scale in industry. 

As a part of our comprehensive programme on membrane technology, we evaluated nondispersive solvent extraction (NDSX) with a hydrophobic microporous hollow fiber contactor (HFC) for the separation and removal of actinides [1,10-12]. As the separation and recovery of actinides from different sources is paramount to radiotoxicity, there is a constant need for advances in the field. Among recently developed technologies, membrane extraction using microporous hollow fibers is particularly... 

Let us present some examples. The systems presented by the term membrane-based (or nondispersive) solvent extraction describe, as a rule, dynamic LM processes in which the equilibrium-based solvent extraction (forward and back) are only local processes taking place on the immiscible phases interfaces (on the surface of membrane support). The term pertrac-tion or perstraction [2] spread over the supported and emulsion LMs, which is not accurate, because the SLM and ELM are steady state processes. 

Membrane-based or nondispersive solvent extraction systems... 

Inclusion of this technique to the BOHLM has to be explained. Solvent extraction or partition of the solute between two immiscible phases is an equilibrium-based separation process. So, the membrane-based or nondispersive solvent extraction process has to be equilibrium based also. Liquid membrane separation is a rate process and the separation occurs due to a chemical potential gradient, not by equilibrium between phases [114]. According to these definitions, many authors who refer to their works as membrane-based or nondispersive solvent extraction processes are not correct. 

The authors of very many works on so-caUed membrane-based or nondispersive solvent extraction could not prove that the process reaches equilibrium. Therefore, we cannot confirm the processes, published in these works, as membrane-based solvent extraction, but can confirm them as liquid membrane processes. Liquid membrane separations are dynamic nonequilibrium processes, in which only local equilibrium at immiscible phases interface may be suggested. 

R. Basu, P. Prasad, and K. K. Sirkar, Nondispersive membrane solvent back extraction of phenol, AIChEJ., 36,450-460 (1990). 

Consider microporous membrane-based solvent extraction using a hydrophilic porous membrane whose pores are filled with the organic solvent used to extract a product, species i, from an aqueous feed solution. The aqueous-phase pressure is maintained equal to or higher than the organic-phase pressure to maintain the aqueous-organic interface for nondispersive solvent extraction conditions. 

Mass Ti ansfer The rate of mass transfer in a liquid-liquid extraction system implemented in a nondispersive membrane contactor is analyzed in the manner followed in conventional contactor analysis. The overall organic phase-based mass transfer coefficient Kio of a species i being extracted (or back extracted) from an aqueous solution into a solvent wetting the pores of a hydrophobic membrane is described via the resistances-in-series model ... 

Pabby AK, Melgosa A, Haddad R, Sastre AM. HoUow fiber membrane-based nondispersive extraction of silver(I) from alkaline cyanide media using I, IX 79. In Proceedings of the ISEC 2002, Cape Town, South Africa, 2002 699-705. 

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