Membrane modules

1
Membrane modules

• Stirred cell module
• Uses flat sheet membrane element
• Flat sheet tangential flow (TF) module
• Uses flat sheet membrane element
• Spiral wound membrane module
• Uses flat sheet membrane element
• Tubular membrane module
• Uses tubular membrane element
• Hollow fibre membrane module
• Uses hollow fibre membrane element

2
Stirred cell

• Useful for small scale and research applications
• Used for UF and MF
• Provide uniform conditions near the membrane
  surface
• Useful for small-scale process development work

3
Flat sheet tangential flow

• Design is similar to plate and frame filter press
  
• Easily disassembled for cleaning and replacement
  of defective membranes
• Can be used to filter suspended solids and
  viscous fluids
• Relatively low packing density
• Used for UF, MF and NF
• Design calculations based on empirical
  correlations

4
Spiral wound membrane module

• The spiral wound membrane envelope)
• Feed flowing around the envelope
• Permeate collected inside envelope
• Design calculations are empirical
• High membrane packing density
• Low cost
• Unable to handle suspended solids
• Difficulty to clean
• Used for NF and UF

5
Tubular membrane module

• Several tubular membranes arranged as in a shell
  and tube type heat exchanger
• Feed stream enters the tube lumen
• Permeate passes through tube wall collected on
  shell side
• Retentate collected at other end of tubes
• Low fouling, easy cleaning, easy handling of
  suspended solids and viscous fluids and high
  transmembrane pressures
• High capital cost, low packing density, high
  pumping costs, and limited achievable
  concentrations
• Used for all types of pressure driven separations

6
Hollow fibre membrane module

• Similar in design to the tubular membrane i.e.
  shell and tube configuration.
• Advantages Low pumping power, very high packing
  density, and ability to achieve high
  concentrations in the retentate
• Disadvantages Fragility of the fibres, inability
  to handle suspended solids Used for UF, MF and
  dialysis

7
Ultrafiltration

• Used for
• Concentration of solutes by removal of solvent
• Purification of solvent by removal of solute
• Fractionation of solutes
• Separates solutes with molar mass within the
  range of 5 kDa to 500 kDa
• Pore diameter 1 to 20 nm
• Ultrafiltration membranes are anisotropic,
• Advantages
• High throughput of product
• Low process cost
• Ease of scale-up
• Application
• Fractionation of proteins and nucleic acids
• Concentration of macromolecules
• Desalting, i.e. removal or salts and other low
  molecular weight compounds from solution of
  macromolecules
• Removal of cells and cell debris from
  fermentation broth
• Virus removal from therapeutic products

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Ultrafiltration models
Pore flow model
Resistance model
Osmotic pressure model
9
Ultrafiltration models
Concentration polarization model
Gel polarization model
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Mass transfer coefficient
k ( mass transfer coefficient) D / ?b

• Dimensionless correlations are used for
  determining mass transfer coefficient
• Correlations are based on heat-mass transfer
  analogy
• General form is Sh a Reb Scc

For fully developed laminar flow Graetz-Leveque
correlation
For turbulent flow (Re gt 2000) the
Dittus-Boelter correlation
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Solute transmission through membranes
Intrinsic rejection and sieving coefficient
Apparent rejection and sieving coefficient
? lt 1
Classical theory of rejection
? ? 1
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Solute transmission through membranes
Modern theory of solute transmission
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Solute fractionation

• Solute fractionation refers to separation of one
  solute from another
• For fractionation of a binary mixture of solutes,
  it is desirable to achieve maximum transmission
  of the solute desirable in the permeate and
  minimum transmission of the solute desirable in
  the retentate
• Efficiency of solute fractionation for a binary
  mixture is expressed in terms of the selectivity
  (?)