1. Membrane Technology

2. Membrane Nomenclature
Retentate (residue)
Feed
Permeate
Stage Cut = Permeate Flow / Feed Flow

3. Membrane Barrier Applications
Polymer Pros
Inexpensive
Flexible
Lightweight compared to glass and metal
Polymer Cons
Insufficient barrier properties
I study polymers for their end uses as barrier materials. Food, electronics, and pharmaceuticals all have a need to be packaged in a material that does not allow oxygen to permeate though it. Historically, glass and metal have been used, but polymers are favored as barrier materials for packaging applications because they are inexpensive, flexible, and lighter weight. However, common polymer packaging have insufficient barrier properties.

4. Solution-Diffusion Model
Upstream pressure
pfeed
Downstream pressure
pperm JA
But before I go into how to improve the barrier properties, what is permeability and Barrer that I’ve been talking about? They can be best described by the solution-diffusion model which is a three step process for describing gas transport. First, the gas molecules sorb into the upstream surface of the film, followed by the diffusion of the gas through the film. The final step is the desorbing from the downstream surface.
The flow or flux of the gas through the film is defined as the permeability times the pressure difference divided by the film thickness. Permeability is a polymer property and is the product of the diffusion and solubility coefficients. The diffusion coefficient describes how fast the gas moves through the polymer and the solubility coefficient describes the attraction between the gas and polymer.
The unit for permeability is Barrer which contains the units for flux in volume per area per time, length, and pressure.
Component A
Component B
Wijmans, J.G., Baker, R.W. Journal of Membrane Science 107, 1-21, (1995)

5. Solution Diffusion Mechanism (Permeability = Solubility * Diffusivity)
Solute “dissolves” in polymer ( Solubility ) and moves through the polymer chain gaps (Diffusivity).
Solute
Dense Membrane Film

6. Pore Diffusion Mechanism
Porous Membrane

7. Solute moves through polymer channels via diffusive jump (Diffusivity)
PTMSP

8. Membrane Polymers

9. Relative Permeation Rates Through Polysulfone
H2O, H2, He, H2S
CO2, O2
Ar, CO, N2, CH4
Fast
Medium
Slow

10. Permeability – Selectivity Plot (glassy polymer)

11. Permeability – Selectivity Plot (rubbery polymer)

12. Experimental Test Unit

13. Membrane Example O2 21mol % N2 79 mol % O2 rich P= 1 atm T = 25 C
Q = 100 scfm 1 2
Silicone rubber membrane
Case 1: a O2 / N2 = 3.2
P O2 = 500 Barrer = 5 X 10-8 cm3 (STP) cm / ( cm2 sec cm Hg)
Case 2: a O2 / N2 = 10.0
P O2 = 1 Barrer = 1 X cm3 (STP) cm / ( cm2 sec cm Hg)
Membrane film thickness (L) = 1000 A
Find: Downstream concentrations and membrane area required

14. Membrane Example Results
P = 1 Barrer
Area = 315,000 ft2
O2 purity = 72 %
a = 3.2
P = 500 Barrers
Area = 630 ft2
O2 purity = 43 %

15. Hollow Fiber Membranes

16. Hollow Fiber Membrane Cross-section
Zoom in

17. Hollow Fiber Membrane Microstructure
Outer wall
Anisotropic: has pore size gradient

18. Typical Hollow Fiber Spinning Process
Purge valve
Mass flow controller
Steel Mixing
Vessel
Nitrogen Cylinder
Spinneret
AIR GAP
*spinning can still be done at room temperature with this setup.
*emphasize that the clad undergoes phase separation either in the air gap or in the quench bath
*UT fibers: micron OD; micron ID
*UT spinneret OD = 3600 microns, ID = 3000 microns
*surface/volume ratio for polysulfone dialyzer = 6000, with about 60% of the module volume occupied by fibers
Metering Pump
Quench Bath
Take-up drum
Explosion-proof oven

19. Hollow Fiber Spinning

20. Membrane Module Designs
Retentate (residue)
Permeate
Tube side feed

21. Hollow Fiber Module Hollow fiber form Bioseparations Gas separations
Dialysis
Virus removal
Gas separations
Water purification
ABOVE: Hollow fiber membrane module used in the hemodialysis process

22. Hollow Fiber Module

23. Spiral Wound Module

24. Module Performance VariablesID OD
Fiber Properties
QO2 Permeance
a Selectivity (QO2/QN2)
L Length
N Number
OD Outer diameter
ID Inner diameter
Operating Conditions
Pfeed Feed pressure
g Pressure ratio (Pshell/Plumen)
Co, cross, or counter

25. Membrane Simulation 1 2 3 n D C B A Fiber Skin Retentate Feed R1 R2 R3Rn 1 2 3 n
Permeate D C B A
Fiber Skin PD PC PB PA
Coker, D.T., Freeman, B.D., Fleming, G.K. “Modeling Multi-component
Gas Separation Using Hollow-Fiber Membrane Contactors,” AIChE J.,
44(6), 1289 (1998).

26. Membrane Simulation Example 1
Calculate the purity of H2 in the permeate stream of a hydrotreater membrane unit (which separates H2 from a mixture of CH4,C2H4, C2H6, and C3H8 ) as a function of hydrogen recovery in the permeate of two cases:
A) Feed pressure = 79.0 bar , permeate pressure = 7.9 bar
B) Feed pressure = bar, permeate pressure = 42.4 bar.
Data:
Feed composition (mol %) Permeance (GPU) H CH
C2H
C2H
C3H
Feedrate = 1000 SCFM, Operating temperature = 60 C, Fiber count = 50,000

27. Membrane Simulation Example 2
One option for recovering CO2 from coal fired power plant flue gas is a multi-stage membrane system.
Determine the required area for each stage of the following membrane system.
Determine the compressor horsepower requirements of the system.
1.8 X 106 SCFM total flow of flue gas at 115 F and 16 psia
Feed - 13 volume percent CO2, volume percent N2
Two stage unit: PF = 500 psia, Pp = 35 psia
P CO2 = 200 GPU, P N2 = 5 GPU

28. Nitrogen Separation Applications
Oil Well, Pressure Control
Inert Atmosphere
Military Fuel Tank Protection

29. Hydrogen Separation Applications
Hydrogen removal in refineries,
ammonia plants, and olefin units.

30. Ethylene Plant Application
Feed
PERMEATE
RESIDUE
Caustic Scrubber
FURNACE
MEMBRANE
HYDROGEN
LIQUIDS
COOLING
Sieve
Dryer
Light Hydrocarbons
Heavier Hydrocarbons 5

31. CO2 Separation Applications
CO2 removal in natural gas
CO2 removal in synthetic natural gas

32. CO2 Recovery - Amine Unit vs Membrane System

33. Hybrid System Composed of Both an Amine and
Membrane System for CO2 Processing
Sales Gas
Amine Contactor
Membrane Unit
Acid Gas
Feed
Acid Gas
Amine Stripper
Compressor

34. Reverse Osmosis Dense Film Liquid Feed PHigh Water Product PLow Water
PHigh – PLow > Osmotic Pressure

35. Concentration Polarization Reverse Osmosis Application
Dense Film
Liquid Feed
PHigh
Water Product
PLow
Water
Salt
PHigh – PLow > Osmotic Pressure ????

36. Ceramic Membranes

37. Ceramic Membranes