Separation using supported liquid membranes

Di Luccio M, Smith BD, Kida T, Borges CP, and Alves TLM. Separation of fructose from a mixture of sugars using supported liquid membranes. J. Membr. Sci. 2000 174 217-224. 

M., ViUora, G. (2007). Integrated reaction/separation processes for the kinetic resolution of rac-l-phenylethanol using supported liquid membranes based on ionic liquids. Chem. Eng. Process., 46, 818-24. 

Bara JE, Gabriel CJ, Carlisle TK, Camper DE, FinoteUo A, Gin DL, Noble RD (2009) Gas separations in fluoroalkyl-functionalized room-temperature ionic liquids using supported liquid membranes. Chem Eng J 147 43-50... 

El-Said, N., Rahman, N.A., Borai, E.H., Modification in Purex process using supported liquid membrane separation of cerium(III) via oxidation to cerium(IV) from fission products from nitrate medium by SLM, J. Membr. Sci. 198, 23, 2002. 

Mohapatra, P.K., Bhattacharyya, A., Manchanda, V.K., Selective separation of radio-cesium from acidic solutions using supported liquid membrane containing chlorinated cobalt dicarbollide (CDD) in phenyltrifluoromethyl sulphone (PTMS), J. Hazard. Mater. 181, 679, 2010. 

The removal of actinides from reprocessing acidic waste solutions is advantageous in terms of minimizing the radioactive discharge to the natural environment. The separation of plutonium using supported liquid membranes was extensively studied, as well as U(V1) and Pu(lV) selective transport over fission products and minor actinide contaminants (Lakshmi et al. 2004 Sriram et al. 2000 Kedari et al. 1999). 

The enantiomer separation with the use of membranes is a promising technique, more convenient than traditional methods, due to its high processing capacity, continuous operation mode and low energy consumption allowing its use in a large scale enantiomer separation processes. Supported liquid membranes show high chiral selectivity, however they are not stable on the contrary, solid membranes with immobilized chiral carrier polymer are stable and therefore able to a durable enantiomer separation [100]. 

As described above, the application of classical liquid- liquid extractions often results in extreme flow ratios. To avoid this, a completely symmetrical system has been developed at Akzo Nobel in the early 1990s [64, 65]. In this system, a supported liquid-membrane separates two miscible chiral liquids containing opposite chiral selectors (Fig. 5-13). When the two liquids flow countercurrently, any desired degree of separation can be achieved. As a result of the system being symmetrical, the racemic mixture to be separated must be added in the middle. Due to the fact that enantioselectivity usually is more pronounced in a nonaqueous environment, organic liquids are used as the chiral liquids and the membrane liquid is aqueous. In this case the chiral selector molecules are lipophilic in order to avoid transport across the liquid membrane. 

ILs, on the other hand, are uniquely suited for use as solvents for gas separations. Since they are non-volatile, they cannot evaporate to cause contamination of the gas stream. This is important when selective solvents are used in conventional absorbers, or when they are used in supported liquid membranes. For conventional absorbers, the ability to separate one gas from another depends entirely on the relative solubilities (ratio of Henry s law constants) of the gases. In addition, ILs are particularly promising for supported liquid membranes, because they have the potential to be incredibly stable. Supported liquid membranes that incorporate conventional liquids eventually deteriorate because the liquid slowly evaporates. Moreover, this finite evaporation rate limits how thin one can make the membrane. This... 

The solubilities of the various gases in [BMIM][PFg] suggests that this IL should be an excellent candidate for a wide variety of industrially important gas separations. There is also the possibility of performing higher-temperature gas separations, thanks to the high thermal stability of the ILs. For supported liquid membranes this would require the use of ceramic or metallic membranes rather than polymeric ones. Both water vapor and CO2 should be removed easily from natural gas since the ratios of Henry s law constants at 25 °C are -9950 and 32, respectively. It should be possible to scrub CO2 from stack gases composed of N2 and O2. Since we know of no measurements of H2S, SO, or NO solubility in [BMIM][PFg], we do not loiow if it would be possible to remove these contaminants as well. Nonetheless, there appears to be ample opportunity for use of ILs for gas separations on the basis of the widely varying gas solubilities measured thus far. 

These types of separators consist of a solid matrix and a liquid phase, which is retained in the microporous structure by capillary forces. To be effective for batteries, the liquid in the microporous separator, which generally contains an organic phase, must be insoluble in the electrolyte, chemically stable, and still provide adequate ionic conductivity. Several types of polymers, such as polypropylene, polysulfone, poly(tetrafluoroethylene), and cellulose acetate, have been used for porous substrates for supported-liquid membranes. The PVdF coated polyolefin-based microporous membranes used in gel—polymer lithium-ion battery fall into this category. Gel polymer... 

The use of liquid membranes in analytical applications has increased in the last 20 years. As is described extensively elsewhere (Chapter 15), a liquid membrane consists of a water-immiscible organic solvent that includes a solvent extraction extractant, often with a diluent and phase modifier, impregnated in a microporous hydrophobic polymeric support and placed between two aqueous phases. One of these aqueous phases (donor phase) contains the analyte to be transported through the membrane to the second (acceptor) phase. The possibility of incorporating different specific reagents in the liquid membranes allows the separation of the analyte from the matrix to be improved and thus to achieve higher selectivity. 

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. 

Partitioning of components between two immiscible or partially miscible phases is the basis of classical solvent extraction widely used in numerous separations of industrial interest. Extraction is mostly realized in systems with dispergation of one phase into the second phase. Dispergation could be one origin of problems in many systems of interest, like entrainment of organic solvent into aqueous raffinate, formation of stable, difficult-to-separate emulsions, and so on. To solve these problems new ways of contacting of liquids have been developed. An idea to perform separations in three-phase systems with a liquid membrane is relatively new. The first papers on supported liquid membranes (SLM) appeared in 1967 [1, 2] and the first patent on emulsion liquid membrane was issued in 1968 [3], If two miscible fluids are separated by a liquid, which is immiscible with them, but enables a mass transport between the fluids, a liquid membrane (LM) is formed. A liquid membrane enables transport of components between two fluids at different rates and in this way to perform separation. When all three phases are liquid this process is called pertraction (PT). In most processes with liquids membrane contact of phases is realized without dispergation of phases. 

Li, S.-J., Chen, H.-L. and Zhang, L. (2009) Recovery of fumaric acid by hollow-fiber supported liquid membrane with strip dispersion using N7301 as carrier. Separation and Purification Technology, doi 10.1016/j. seppur.2008.12.004. 

Tsai, C.Y., Chen, Y.F., Chen, W.C., Yang, F.R., Chen, J.H. and Lin, J.C. (2005) Separation of gallium and arsenic in wafer grinding extraction solution using a supported liquid membrane that contains PC88A as a carrier. Journal of Environmental Science and Health Part A-Toxic/Hazardous Substances e[ Environmental Engineering, 40, 477. 

---