1. Part (I)
Introduction to Membrane Technology in Drinking & Industrial Water Production

5. ? ? ? What is a membrane? A membrane is...
Membrane Separations
What is a membrane? ? ? ?
A membrane is...
...a physical barrier (no necessarily solid) that gives, or at least helps, the separation of the components in a mixture.

6. Membrane Separations
The sorting demon...

7. - In 1998, these sales were over 5000 million €.
Membrane Separations
- Membrane processes are not based in thermodynamic equilibrium but based in the different transport rate of each species through the membrane.
- The membrane market is still growing. In the decade, the sales related to membrane products and systems doubled.
- In 1998, these sales were over 5000 million €.

8. Membrane Separations

9. Membrane Separations
Advantages
 Energy savings. The energy consumption is very low as there is no phase change.
 Low temperature operation. Almost all processes proceed at room temperature, thus they can deal with compounds that are not resistant at high temperatures.
 Recovery. Both the concentrate and the permeate could be recovered to use.
 Water reuse. When applied to recover water, they avoid the transport of large water volumes and permit the reduction of the Chemical Oxygen Demand (COD) loading in sewage plants.

10.  Compact operation. Which permits to save space .
Membrane Separations
Advantages
 Compact operation. Which permits to save space .
 Easy scale-up. Because usually they are designed in modules, which can be easily connected.
 Automatic operation. The most of the membrane plants are managed by expert systems.
 Tailored systems. In many cases, the membranes and systems can be specifically designed according the problem.

11. Membrane Separations
Disadvantages
 High cost. Membranes (and associated systems) are costly, but for low selective separations.
 Lack of selectivity. In many cases, the separation factors are still insufficient.
 Low fluxes. The permeat flowrate available are still too low for some applications.
 Sensitive to chemical attack. Many materials can be damaged by acids, oxidants or organic solvents.
 Lack of mechanical resistance. Many materials do not withstand abrasion, vibrations, high temperatures or pressures.

12. • Microfiltration (MF).
Membrane Separations
- The membrane operations more widely used are those based in applying a pressure difference between both sides of the membrane.
• Microfiltration (MF).
• Ultrafiltration (UF).
• Nanofiltration (NF).
• Reverse osmosis (RO).
- Although similar in appearance, the involved mechanisms in the separation can be very very different.

13. low molecular weight compounds
Membrane Separations
Hemoglobin
(7 nm)
Pseudomonas
Diminuta
(280 nm)
Starch
(10000 nm)
Na+
(0,4 nm)
H2O
(0,2 nm)
Glucose
(1 nm)
Influenza Virus
(100 nm)
Staphylococcus
(1000 nm)
Salts and
low molecular weight compounds
Microfiltration
Ultrafiltration
Cells,
bacteria
and polymers
Nanofiltration
Virus and
proteins
Emulsions
and colloids
Vitamins
and sugars
Reverse Osmosis
0.1 1 10
100
1000
10000
Pore diameter (nm)
Name of the membrane process in function of the particle size.

14. Membrane Separations
More examples.

15. Membrane Separations
... and more.

16. • Electrodialysis (ED). • Liquid membranes. • Pervaporation.
Membrane Separations
- There are other separation operations where a membrane is the responsible of the la selective separation of the compounds:
• Dialysis.
• Gas permeation (GP).
• Electrodialysis (ED).
• Liquid membranes.
• Pervaporation.
- In others, the membrane is not directly responsible for the separation but it actively participates:
• Membrane extraction.
• Membrane distillation.
• Osmotic distillation.

17. Membrane Separations
Dead-end
Cross-flow
Type of filtration.

18. Simple scheme of a membrane module.
Membrane Separations
CA,f, CB,f
CA,r, CB,r
Feed
Retentate
(Concentrate)
Membrane
Permeate
(Filtrate)
CA,p, CB,p
Simple scheme of a membrane module.

19. Membrane Separations
- Synthetic membranes are solid barriers that allow preferentially to pass specific compounds due to some driving force. +
(Very) Simple scheme for some mechanisms of selective separation on a porous membrane.

20. • Pore size and structure
Membrane Separations
- The separation ability of a synthetic material depends on its physical, chemical properties.
• Pore size and structure
• Design
• Chemical characteristics
• Electrical charge

21. - Porous membranes give separation due to...
Membrane Separations
- The membranes can be roughly divided in two main groups: porous and non porous.
- Porous membranes give separation due to...
• size
• shape
• charge
...of the species.
- Non porous membranes give separation due to...
• selective adsorption
• diffusion
...of the species.

22. Main parameters. - Rejection, R, if there is just one component (RO)
Membrane Separations
Main parameters.
- Rejection, R, if there is just one component (RO)
- Separation factor
- Enrichment factor
for two or more component

23. Main parameters. - In RO, often we use the Recovery (Y)
Membrane Separations
Main parameters.
- In RO, often we use the Recovery (Y)
Qp: Permeate flowrate (m3/s)
Qf: Feed flowrate (m3/s)

24. Membrane Separations
Main parameters.
- Passive transport in membranes. The permeate flux is proportional to a given driving force (some difference in a property).
Driving forces:
 Pressure (total o partial)
 Concentration
 Electric Potential

25. Membrane processes and driving force.
Membrane Separations
Main parameters.
Membrane processes and driving force.

26. Main parameters. - Permeate flux.
Membrane Separations
Main parameters.
- Permeate flux.
In MF and UF, porous membrane model is assumed, where the a stream freely flows through the pore. Then, the transport law follows the Hagen-Poiseuille equation.
Jw: Solvent flux (m3/s·m2)
Qw: Solvent flowrate (m3/s)
Am: Membrane area (m2)
r: Pore radius (m)
d: Membrane thickness (m)
: Porosity
: Viscosity (Pa ·s)
: Tortuosity
P: Hydraulic pressure difference (Pa)

27. Membrane Separations
Main parameters.
- The above model is good for cylindrical pores. However, if the membrane is rather formed by a aggregated particles, then the Kozeny-Carman relation works much better.
JW: Solvent flux (m3/s·m2)
QW: Solvent flowrate (m3/s)
S: Particle surface area (m2/m3)
K: Kozeny-Carman constant
d: Membrane thickness (m)
Am: Membrane area (m2)
: Viscosity (Pa ·s)

28. Formation of the polarisation layer.
Membrane Separations
- In the operations governed by the pressure, a phenomenon called concentration polarisation appears, which must be carefully controlled. This is due to the solute accumulation neighbouring the membrane surface.
Feed
Polarisation layer
membrane
Permeate
Formation of the polarisation layer.

29. - Concentration polarisation.
Membrane Separations
- Concentration polarisation.
(It is not fouling!!!)

30. - Fouling: Irreversible reduction of the flux throughout the time.
Membrane Separations
- Fouling: Irreversible reduction of the flux throughout the time.
• Pore size reduction by irreversible adsorption of compounds.
• Pore plugging.
• Formation of a gel layer over the membrane surface (cake).

31. • Structure: symmetric, asymmetric
Membrane Separations
- Membrane can be classified in several ways, but always there are arbitrary classifications.
• Structure: symmetric, asymmetric
• Configuration: flat, tubular, hollow fiber
• Material: organic, inorganic
• Surface charge: positive, negative, neutral
• ...and even other divisions and subdivisions

32. - Integral: the layers are continuous.
Membrane Separations
- Structure:
• Symmetric. Also called homogeneous. A cross section shows a uniform porous structure.
• Asymmetric. In a cross section, one can see two different structures, a thin dense layer and below a porous support layer.
- Integral: the layers are continuous.
- Composites: the active layer (thickness μm) is supported over a highly porous layer ( μm), sometimes both layers are of different materials.

33. Membrane Separations
Symmetric UF membrane of 0.45 m made of cellulose acetate (Millipore).

34. Membrane Separations
Surface
Cross section
Symmetric ceramic membrane of 0.2 m made of alumina (Al2O3) (AnoporeTM).

35. Asymmetric ceramic membrane made of -Al2O3 (Membralox).
Membrane Separations
Asymmetric ceramic membrane made of -Al2O3 (Membralox).

36. UF integral asymmetric membrane made of polypropylene.
Membrane Separations
UF integral asymmetric membrane made of polypropylene.

37. RO composite membranes.
Membrane Separations
Cellulose acetate
Polyamide
RO composite membranes.

38. - Configuration and modules
Membrane Separations
- Configuration and modules
• Configuration: geometric form given to the synthetic membranes.
• Module: name of the devices supporting one or several membranes (housing).
The module seals and isolates the different streams. The geometry and specific fluid movement through the confined space characterises each module. The type of flux, the transport mechanism and the membrane surface phenomena depend on the module design.

39. - The active layer is a flat. - Synthesised as a continuous layer.
Membrane Separations
- Configuration:
• Flat.
- The active layer is a flat.
- Synthesised as a continuous layer.
- Later, one can select a desired geometry (rectangle, circle,...) to be placed in the module.
- Used in two kind of modules: plate-and-frame and spiral wound.
- High surface area/volume ratio.

40. Plate-and-Frame Membrane System.
Membrane Separations
Plate-and-Frame Membrane System.
Consists of layers of membranes separated by corrugated structural sheets, alternating layers with feed material flowing in and retentate flowing out in one direction, while permeate flows out in the other direction.

41. Membrane Separations
Spiral-wound module.

42. Membrane Separations
Spiral-wound module.

43. - Usually the active layer is inside.
Membrane Separations
- Configuration:
• Tubular.
- It is like a tube.
- Usually the active layer is inside.
- The permeate crosses the membrane layer to the outside (this is, the feed flows inside).
- Low surface are/volume ratio.
- Several lengths and diameter (>10 mm).
- Modules grouping one or various membranes.

44. Different types of tubular modules.
Membrane Separations
Different types of tubular modules.

45. Membrane Separations
Hollow fiber module.

46. Hank of polyamide hollow fiber for RO (DuPont).
Membrane Separations
Hank of polyamide hollow fiber for RO (DuPont).

47. Cross section of hollow fiber (Monsanto). Comparison with a clip.
Membrane Separations
Cross section of hollow fiber (Monsanto). Comparison with a clip.

48. Hollow fiber cross section of polyamide for RO (DuPont).
Membrane Separations
Hollow fiber cross section of polyamide for RO (DuPont).

49. Hollow fiber made of polysulfone (  1 mm) for UF (detail).
Membrane Separations
Hollow fiber made of polysulfone (  1 mm) for UF (detail).

50. Hollow fiber cross section of   1 mm (Monsanto).
Membrane Separations
Hollow fiber cross section of   1 mm (Monsanto).

51. Hollow fiber surface of polypropylene (Celgard).
Membrane Separations
Hollow fiber surface of polypropylene (Celgard).

52. Hollow fiber ceramic membranes (CEPAration).
Membrane Separations
Hollow fiber ceramic membranes (CEPAration).

53. - Comparison between modular configurations.
Membrane Separations
- Comparison between modular configurations.

54. - Comparison between modular configurations.
Membrane Separations
- Comparison between modular configurations.

55. - Made of polymers or polymer blends. - Low cost.
Membrane Separations
- Material:
• Organic.
- Made of polymers or polymer blends.
- Low cost.
- Problems with their mechanical, chemical resistance.
Temperature
pH, Solvents
Pressure

56. Polypropylene with 0.2 m pores (Accurel).
Membrane Separations
Polypropylene with 0.2 m pores (Accurel).

57. Polytetrafluoroetylene with 0.2 m pores.
Membrane Separations
Polytetrafluoroetylene with 0.2 m pores.

58. Polytetrafluoroetylene with 0.2 m pores.
Membrane Separations
Polytetrafluoroetylene with 0.2 m pores.

59. • Dialysis - Applied since the 70’s. - Low industrial interest.
Membrane Technology
• Dialysis
- Applied since the 70’s.
- Low industrial interest.
- Ions & species of low MW (<100 Da).
- Ionic Membranes (just like ED).
- Driving Force: concentration gradient.
Slow and low selective.

60. • Dialysis - Artificial kidney.
Membrane Technology
• Dialysis
- Artificial kidney.
- NaOH recovery in textile effluents, alcohol removal from beer, salts removal (pharmaceutical industry).

61. • Dialysis Looks not very important...?. Membrane and module markets
Membrane Technology
• Dialysis
Looks not very important...?.
Membrane and module markets

62. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED)
- First applications back at 30’s.
- Ion Separations.
- Ionic Membranes (non porous).
- Driving Force: gradient in electrical potential.
- Potential: 1-2 V.
- Flat configuration.
- Hundreds of anionic and cationic membranes placed alternatively.
- Orthogonal electrical field.

63. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED)

64. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED)

65. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED)
- Ionic Membranes (non porous).
- Based on polystyrene or polypropylene with sulfonic and quaternary amine groups.
- Thickness: mm.
- ED with reverse polarization (EDR).
- ED at high temperature (60ºC).
- ED with electrolysis.

66. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED) j+
VC c+in
VC c+out
- Required membrane area
 Mass balance (in equivalents)
 Charge flow
i: electric current density (A/m2)
Am: membrane surface (m2)
combining
η: global electrical efficiency (~0.5 commercial equipment)
j: cation flow (eq/m2 s)
F: Faraday constant (96500 C/eq)
N: number cells in the equipment
z: cation charge (eq/mol)

67. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED)
- Then the required energy, E (J), is
UC: potential gradient in a cell (V)
RC: total resistance in a cell () as
then
P: required Power (J/s)

68. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED)
Where, the required specific energy, (J/m3), is
La cell resistance can be estimated from a model based on series of resistances where the resistances to transport are considered through two membranes and the compartments concentrate and diluted.

69. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED)
- How to determine operational i?
 Cation Transport
Limit boundary  
cCM+
cC+ - +
cD+
If cDM+ = 0
cDM+
concentrate
diluted
Usually: i = 0.8ilim
Cationic Membrane
t: transport number
D: diffusion coefficient

70. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED)
- Intensity Evolution versus applied potential
i (A/m2)
ilim
Ohmic zone
U (V)
Resistance rise
Ionic water splitting

71. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED)
- Fields of application:
Water desalination.
- Competing to RO.
- Economically more interesting at very high or very salt concentrations.
- Other fields of application:
Food Industry.
Treatment of heavy metal polluted water.

72. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED)
- Examples:
 Production of drinking water from salty water.
 Water softening.
 Nitrate removal.
 Lactose demineralization.
 Acid removal in fruit juice.
 Tartrate removal from wines.
 Heavy metal recovery.
 Production of chlorine and sodium hydroxide.

73. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED)
electrolytic Cell for the production of chlorine and sodium hydroxide with cationic membrane.

74. • Electrodialysis (ED)
Membrane Technology
• Electrodialysis (ED)
Electrolytic cell for the production of sulfuric acid and sodium hydroxide with bipolar membrane.

75. Hydrogen fuel cell with a cationic membrane.
Membrane Technology
• Electrodialysis (ED)
Anode H2
2H++ 2e-
Cathode
O2 + 4e- + 4H+
2H2O
Global
2H2 + O2
2H2O
Hydrogen fuel cell with a cationic membrane.

76. • Pervaporation - Discovered 1917. - Only operation with phase change.
Membrane Technology
• Pervaporation
- Discovered
- Only operation with phase change.
- Non-Porous Membranes.
- Mechanism solution-diffusion.
- Driving force: difference in partial pressure.
Vacuum (<40 mm Hg), dilution (inert gas, N2) or temperature difference.

77. General Pervaporation system.
Membrane Technology
• Pervaporation
Retentate
Pervaporat. module
Feed
Condenser
Heater
Permeate condensate
Vacuum pump
General Pervaporation system.

78. • Pervaporation - Industrial applications.
Membrane Technology
• Pervaporation
- Industrial applications.
- Alternative to distillation when thermodynamic limitations.
 Low energy costs.
 Low investment costs.
 Better selectivity, without thermodynamic limitations.
 Clean and closed operation.
 No process wastes.
 Compact and scalable units.

79. • Pervaporation - Drawbacks:  Scarce Membrane market.
Membrane Technology
• Pervaporation
- Drawbacks:
 Scarce Membrane market.
 Low permeate flows.
 Limited applications:
- Organic substances dehydratation.
- Recovery of volatile compounds at low concentrations.
- Separation of azeotropic mixtures.

80. Membrane Technology
• Pervaporation.
- Do not mistake with a distillation where a membrane is just separating phases.
- Three steps mechanisms:
 Selective absorption on the membrane.
 Dissolution at the membrane.
 Diffusion through the membrane.

81. Pi = Si (ci, cj)· Di (ci, cj)
Membrane Technology
• Pervaporation
- The membrane is active in this process.
- The permeability coefficient (P) of a compound depends on the solubility (S) and the diffusivity (D), in the polymeric phase, of the crossing compound
Pi = Si (ci, cj)· Di (ci, cj)
- Simplificated transport equation:
Ji: flux of component i
d: membrane thickness
xi: molarfraction in liquid
i: activity coefficient
pio: vapour pressure
yi: molar fraction at permeate
pp: pressure at permeate side

82. • Pervaporation - Main membrane parameters: - Separation factors
Membrane Technology
• Pervaporation
- Main membrane parameters:
- Separation factors
- Enrichment factors

83. Membrane Technology
• Pervaporation
1.0
azeotrope
0.8
Phase equilibria
0.6
Ehtanol at permeate (vapour)
pervaporation
0.4
pseudoazeotrope
0.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
Ethanol at feed (liquid)
Pervaporation process of an ethanol/water mixture with a PVA membrane.

84. Membrane Technology
• Pervaporation
Intermediat tank
Condenser
Pervap. unit
Feed
Ethanol >90% w/w
Permeate
Boiler
Water
Distillation column
Ethanol >99.95% w/w
Ethanol 20-80% w/w
Ethanol 15% w/w
Plant for production of ethanol from sugar (Bethéniville, France).
Combination of distillation and pervaporation for the production of pure ethanol.

85. Organic solvents to apply pervaporation.
Membrane Technology
• Pervaporation
Dehydration of organic solvents.
Organic solvents to apply pervaporation.
 Hydrophilic membranes: PVA, PAN...

86. • Pervaporation - Organic compounds recovery.
Membrane Technology
• Pervaporation
- Organic compounds recovery.
 For volatile compounds.
 Economically competitive.
 Hydrophobic membranes: PDMS and derivatives.
- Azeotrope breaking of organic compounds.
 Studied at lab scale.
 Low selectivity.

87. Lab scale separations reported.
Membrane Technology
• Pervaporation
Lab scale separations reported.

88. Membrane Technology
• Pervaporation
Pure cyclohexane
Solvent
Pervaporation unit C o l u m n 1 C o l u m n 2
Pure benzene
Feed
Hybrid process: extractive distillation and pervaporation for the production of pure benzene and cyclohexane .

89. • Gas permeation - Since 50’s. - Membranes: porous and no porous.
Membrane Technology
• Gas permeation
- Since 50’s.
- Membranes: porous and no porous.
- Several possible mechanisms for gas transport:
X Viscous Flow.
 Knudsen Flow.
 Solution-diffusion.
- The last two are selective.

90. Membrane Technology
• Gas Permeation
- Knudsen Flow (porous membranes). When the porous diameter is on the range of the average free space of the molecule (kinetic theory for gases).
Transport equation
Knudsen diffusivity
Enrichment
: porosity
d: membrane thickness
: tortuosity
R: gas constant
T: temperature
P: transmembrane P
r: porus radi
M: MW

91. • Gas permeation Solution-diffusion (non-porous membranes).
Membrane Technology
• Gas permeation
Solution-diffusion (non-porous membranes).
Pi = Si· Di
The selectivity is referred to the separation factors of the compounds to be separated
There are “slow” and “fast gases” for a determined membrane.

92. • Gas permeation - Driving force: partial pressure gradient.
Membrane Technology
• Gas permeation
- Driving force: partial pressure gradient.
- Working pressure: up to 100 bar.
- Non-porous polymeric membranes:
PDMS, CA, PS, PES i PI
- Ceramic Membranes (small pores for Knudsen).
- Metallic membranes (Pd and Ag alloys).

93. • Gas permeation - Asymmetric membranes.
Membrane Technology
• Gas permeation
- Asymmetric membranes.
- Thin polymer on a structural porous material.
- Preferred configuration Hollow Fiber or Spiral, others like flat or tubular also possible.
- Applied in petrochemistry.
 Purification of H2, CO2, CH4 and gaseous hydrocarbons of difficult distillation.
 Nitrogen purification.

94. • Gas permeation - Some examples:
Membrane Technology
• Gas permeation
- Some examples:
 Enrichment, recovery and dehydration of N2.
 H2 recovery in residual flows of proceses, purge o natural gas.
 Adjust of the ratio H2/CO synthesis gas.
 Acid gas removal (CO2, H2S) from natural gas.
 Helium recovery from natural gas and other sources.
 VOC removal from process flow.

95. Unitat de isomerització
Membrane Technology
• Gas permeation
Residuals gases
Gas permeation
to fuel-gas
Hydrogen
Recycle of n-C4
Unitat de isomerització
n-Butane
Isobutane
Recycle
H2 (96%)
A typical PRISM® Separator (Airproducts)
Hydrogen recovery in a butane isomeration plant.

96. • Liquid Membranes - A liquid barrier between to phases.
Membrane Technology
• Liquid Membranes
- A liquid barrier between to phases.
- Not yet industrial uses.
- Driving force: chemical potential, concentration.
- Two configurations:
 Emulsion (ELM).
 Supported Liquid Membranes (SLM).

97. • Liquid Membranes Possible configuration for LM. Membrane Technology
Organic liquid + surfactant (membrane)
Possible configuration for LM.
Aqueous phase
Emulsion liquid Mem.
Receiving phase
Porous Support
Organic liquid impregnated into the pores
SLM

98. • Liquid Membranes - Advantages: - Drawbacks:
Membrane Technology
• Liquid Membranes
- Advantages:
 High flows due to the transport velocity in liquids.
 Selective separations due to the presence of specific reagents.
 Pumping effect (against the gradient) due to the carrier equilibrium.
 Small quantities of solvent lets to the application of expensive solvents.
- Drawbacks:
 Low stability of emulsions in ELM.
 Leaching out of organic phase from the pores of a SLM .

99. M: selectively separated
Membrane Technology
• Liquid Membranes
Ag+ M + B MB
M: selectively separated
diphenyl-18-crown-6
B: selective carrier N MB M M O B P
Liquid Membrane
Facilitated Transport in Liquid Membrane.

100. • Liquid Membranes - ELM: low practical interest
Membrane Technology
• Liquid Membranes
- ELM: low practical interest
- SLM: lab scale and few applications restricted high added value compounds.
- Hydrophobic Membranes (PE, PP ...).
- Hollow fibers.
- Potential applications:
 Selective removal and concentration of cations in solution.
 Selective separation of gases.
 Recovery of acid or basic compounds.
 Organic compound separation in complex mixtures.

101. • Other Techniques - Membrane distillation.
Membrane Technology
• Other Techniques
- Membrane distillation.
 A hydrophobic membrane separates two aqueous phases.
 The volatile compounds cross the membrane and condensate.
 The hydrophobic membrane avoids the aqueous phases to get into the membrane.
 The driving force in the temperature gradient.

102. • Other techniques - Membrane distillation.
Membrane Technology
• Other techniques
- Membrane distillation.
 Driven by the phase equilibrium in both sides of the membrane.
 The membrane acts just like a physical barrier.
 Some applications:
 Water demineralization.
 Inorganic acid or salt concentration.
 Ethanol extraction at the fermentation.

103. • Other techniques - Osmotic distillation.
Membrane Technology
• Other techniques
- Osmotic distillation.
 Similar to membrane distillation.
 Both phases at the same temperature.
 The partial pressure gradient due to the osmotic pressure is the driving force.
 The osmotic pressure is risen by adding appropriate compounds to the receiving phase.
 Attractive to the food industry provided it maintains the temperature.
 Alcohol removal from wine and beer.
 Fruit juice enrichment.

104. • Other techniques - Membrane extraction.
Membrane Technology
• Other techniques
- Membrane extraction.
 The membrane acts as a barrier to separate immiscible phases.
 It has to assure immiscibility between phases.
 Hollow Fiber membranes have high area.
 It makes possible to avoid the separation at decanting of the phases at the end.
 Lab scale research.