Ultrafiltration Membranes:

1
Ultrafiltration Membranes
Synthesis and Permeability Studies.

• 10.467 Experiment 14
• Ismael Gomez and Derric Tay
• 12 Dec. 2006

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Presentation overview

• Introduction
• In-house membrane production
• Membrane testing results
• in-house-produced membranes
• commercial membranes
• Conclusions

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Introduction

• Ultrafiltration and polymers
• uses of ultrafiltration
• polyethersulfone (PES) as a material for
  membranes
• membrane structure
• thin filtration layer
• porous support layer

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Membrane formation

• unsteady-state phase separation
• exchange of water and NMP
• based on insolubility of PESin water
• when mixed, NMP diffuses outwater diffuses in
  and precipitates PES

NMP
PES
Figures are taken from the lab 14 manual.
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Industrial production ofPES membranes

• continuous process
• thin film of PES on a rolling conveyer belt of
  Mylar support
• support sheet enters water at 30 degrees
• membrane sheet formed as support passes through
  water
• membrane then dried in warm air oven and rolled up

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In-house production method

• simulating a near-continuous sheet
• PES syrup spread onto glass plate
• doctor bar to spread syrup evenly
• plate slid into a water bath of controlled
  temperature

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In-house production method(cont.)
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Conditions that affect structure

• casting temperature
• diffusion properties of water, NMP
• controlled by water bath temperature
• compositions of solutions
• organic syrup composition 16 PES dissolved in
  NMP
• water tap water

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Conditions that affect structure(cont.)

• What do they affect?
• filter layer thickness
• membrane permeability
• susceptibility to fouling

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Imperfections of thein-house method

• problems with this production method
• unevenness
• membrane folding on itself (may cause pockets of
  unreacted monomer)
• fold seams becoming tears
• boundary effects

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Permeability

• J p ?P
• Where
• J Permeate Flux Permeate Flow Rate/Area
• p Permeability Coefficient
• ?P Pressure Difference
• Pressure difference increases Flux
  increases
• Permeability decreases Flux
  decreases

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Experimental Setup
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Permeability Testing(Lab-Made Membranes)
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Permeability Testing(Commercial Membrane)
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Membrane Comparison

• Membrane Permeability
  Coefficient
• 10 C Lab-made 6.9E-3
• Commercial 4.6E-3
• 40 C Lab-made 2.8E-3

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Filtration Testing(Commercial Membrane)
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Fouling

• -Accumulation of large molecules on membrane
  surface
• Hemoglobin impermeable, blocks Vitamin B12
• Dextran impermeable, blocks yellow dye

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Pore Size

• Commercial Membrane
• Hemoglobin, 55 Å, does not permeate through
  membrane
• Vitamin B12, 12 Å, does permeate through membrane
• Expected Pore Size 12 Å -55
  Å
• Lab-Made Membranes
• 40 C Smaller Pores More
  selective
• 10 C Larger Pores Less
  selective

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Conclusion

• Casting temperature affects pore size, and
  therefore permeability
• Large molecules become stuck in membrane, causing
  fouling

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Thank you!

• Any questions?