Liquid membrane

Introduction about liquid membranes.
Types of liquid membrane and mechanism of seperation.

1. Liquid Membrane Presented By : Group 2 Krushan Patel 1402004 Harsh Painter 1402016 Anand Patel 1402032 Kathan Shukla 1402036 Manish Patel 1402040 Chintan Gadhetharia 1402018

2. Introduction Types of Membranes : [3]

3. Liquid Membrane A material for the preparation of a membrane need to be solid only. A liquid may also act as a separation barrier between two phases or mediums where the transport occurs by the ‘Solution – diffusion mechanism ’. [3] [6]

4. Types of Liquid Membrane : (1). Immobilized liquid membrane (ILM) (2). Emulsion liquid membrane (ELM)

5. (1). Immobilized liquid membrane (ILM) : Also Called as Supported liquid membrane(SLM) Made by immersing a thin porous film of suitable solid substance with a liquid. Molecules diffuse through the liquid in the pores. Membrane thickness is 20 -150 µm [3]

6. (2) . Emulsion liquid membrane (ELM) : An ELM is a liquid droplet which contains number of very small globules [Droplet - size about 0.5-10 µm] of another liquid within it, suspended in a liquid medium. [3]

7. Separation mechanism with example of phenol recovery from aqueous solution by NaOH+oil emulsion.

8. The liquid membranes illustrated here are only used in some specific applications because of the rather low selectivities which is the differences in solubility and diffusivity. Far higher selectivities can be obtained by adding a carrier molecule to the liquid (membrane) which has a high affinity for one of the solutes in phase 1. The carrier accelerates the transport of this specific component. This type of transport is called 'carrier-mediated‘ transport or facilitated transport. [1]

9. carrier-mediated transport / facilitated transport When a carrier is present inside the membrane with the ability to complex with a specific solute the flux of that solute may be enhanced. Carrier may be dissolved in the liquid - carrier is mobile. Carrier can be bound chemically (covalently) or physically to a solid polymer - Carrier is fixed and has a very restricted mobility. [1]

10. Comparison of diffusivities : System Mechanism D(cm 2 /s) Mobile carrier system The carrier-solute complex diffuses across the membrane. 10 -5 – 10 -7 Gel system The carrier-solute complex diffuses across the membrane. 10 -6 – 10 -8 Fixed carrier The solute jumps from one site to the other. > 10 -7 [1]

11. Types of transport mechanism in liquid membrane : (1) . Passive diffusion : Passive diffusion dueto concentration gradient . [2]

12. (2). Facilitated transport : The liquid membrane phase contains a carrier agent that chemically combines with the feed solute to be transported . [2]

13. (3). Coupled transport : The carrier agent couples the flow of two species. Because of this coupling, one of the species can be moved against its concentration gradient, provided the concentration gradient of the second coupled species is sufficiently large. [2]

14. Liquid Membrane development Liquid membranes consist of three main components : support membrane ,organic solvent and carrier. Support Membrane : Because a free liquid film is not very stable, the function of the porous support membrane is to act as a framework. The surface porosity and overall porosity of such support materials should be high in order to obtain an optimal flux. The membrane should be as thin as possible because the flux is inversely proportional to the membrane thickness.

15. Preparation technique Materials Stretching Polypropylene polytetrafluoroethylene Phase inversion Polypropylene polyethylene Materials used for support membrane : [1]

16. Choice of Organic Solvent : The organic liquid must be a solvent for both the carrier and the carrier-solute complex. Another important factor is the viscosity of the organic phase. On increasing the carrier concentration, two effects are counteracting. ↑ CC → ↑ Entering flux ↑ CC → ↑ Viscosity → ↓ diffusion coefficient → ↓ diffusion flux [1]

17. Some solvents used in Liquid Membrane : Solvents Viscosity (T=298 K) g.cm -1 .s -1 o-dichlorobenzene 0.013 1-octanol 0.076 dibutylphthalate 0.154 o- nitrophenyl octyl ether 0.128 o-nitro diphenylether 0.161 [1]

18. It is essential for the solubility of the organic phase in the aqueous phase to be as low as possible. Even if the solubility meets this requirement, after a finite period of time process will become unstable. Emulsification of organic phase [1]

19. One approach to solve these problems is by gelantion of the liquid membrane phase. This means that the liquid film has the properties of a highly swollen crosslinked polymer (a 'gel') rather than that of a liquid. Although the diffusion coefficient will be lower in a gel phase compared to the liquid but the stability of the layer will have been improved. Polymers which are useful in this process are : poly vinyl chloride(PVC), poly acrylonitrile (PAN) and poly methylmethacrylate (PMMA). [1]

20. Choice of carrier : High selectivities are obtained if the carrier is very specific to one solute. Here are some class of carrier molecules mentioned : oximes (tertiary), amines, crown ethers, cobalt complexes. [1]

21. Applications Removal of specific ions - cations (cadmium, copper, nickel, lead) -anions (nitrate, chromate) Removal of gases -oxygen/nitrogen separation -removal of H 2 S, C0 2 , S0 2 , CO, NH 3 Separation of organic liquids Removal of phenol [1]

22. Advantages Uphill Transport Characteristic High Interfacial Area per Unit Volume Low Solvent Loss Low possibilities of concentration polarization [5]

23. Disadvantages SLM Instability of liquid film. Resistance due to membrane itself. ELM Anything effecting emulsion stability must be controlled, i.e. ionic strengths, pH, etc. If, for any reason, the membrane does not remain intact during operation, the separation achieved to that point is destroyed. In order to recover the receiving phase we have to broke down the emulsion. Since in order to make stable emulsion we have to work against the ease of breaking it back down. [5] [4]

24. References Marcel Mulder , “Basic Principles of Membrane Technology”, second edition, kluwer , pp. 339-357,1997. Richard W. baker, “Membrane technology and applications”, second edition, wiley , pp. 425-426,2004. Binay K. dutta , “Principal of mass transfer and separation process “, PHI learning pvt . Ltd., pp. 785-786, 2007 http://www.separationprocesses.com/Membrane/MT_Chp07d.htm https://www.hindawi.com/journals/jchem/2013/618236/ https://www.researchgate.net/publication/258396267_Supported_Liquid_Membrane_Principle_and_Its_Practices_A_Short_Review

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