Product concentration by ultrafiltration

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Product concentration by ultrafiltration

• Concentration involves the removal of solvent
  (i.e. water) from macromolecule solutions. A
  concentration process is used for
• Increasing the macromolecule concentration for
  facilitating bioseparation steps such as salt and
  solvent induced precipitation
• Increasing or adjusting the concentration of a
  therapeutic macromolecule in a formulation (eg.
  vaccine, monoclonal antibody, therapeutic enzyme)
• Pre-treating macromolecule solutions for
  polishing steps such as crystallization and
  freeze drying
• Increasing macromolecule concentration for
  facilitating detection and analysis

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Small-scale product concentration Vacuum
evaporation Dialysis against PEG Dialysis against
sucrose Centrifugal ultrafiltration Stirred cell
ultrafiltration
Large-scale product concentration Tangential
flow ultrafiltration
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Solute retention requirement
A good concentrating membrane should give greater
than 99 retention MWCO can be used as a guideline
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Concentration processes

• Continuous increase in macromolecule
  concentration in the feed in batch process
• Non-uniformity in the feed concentration during
  operation results in several operational and
  design limitations
• In constant TMP batch operation permeate flux
  declines with time
• Increased membrane fouling may result from
  increase in concentration
• At high concentrations, macromolecules tend to
  form gels
• There is an upper limit in terms of product
  concentration beyond which it is not possible to
  rely on ultrafiltration for concentration.
• It is desirable to operate below the limiting TMP
  
• Constant flux ultrafiltration is rarely used for
  concentration
• Techniques used for permeate flux enhancement
  have been found to be useful in concentration
  processes

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Modules used in concentration processes

• Desirable characteristics
• Low hold-up volume on the feed side
• Ability to handle viscous feed
• Ability to provide high membrane wall shear rate
  (or mass transfer coefficient)
• Laboratory scale
• Centrifugal ultrafilter
• Stirred cell
• Large scale
• Flat sheet tangential flow
• Hollow fibre

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Batch concentration
Limitations Large dedicated feed tank
required Batch operation
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Fed-batch operation
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Continuous concentration
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Multi-stage continuous concentration
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Partial recycle mode
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Concentration Applications

• Concentration of blood proteins eg. albumin,
  immunoglobulins
• Processing of milk products eg. cheese, milk
  concentrate
• Concentration of milk proteins eg. casein,
  ?-lactalbumin, ?-lactoglobulin
• Concentration of vegetable proteins eg. soy
  proteins, gluten
• Concentration of animal enzymes eg. amylases,
  lipases, proteases
• Concentration of plant enzymes eg. papain,
  bromelain, pectinase
• Concentration of microbial enzymes eg.
  cellulases, hemicellulases, proteases

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Diafiltration
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Membrane modules used for diafiltration

• Laboratory scale
• Centrifugal ultrafilter
• Stirred cell
• Large scale
• Flat sheet tangential flow
• Hollow fibre
• Tubular
• Spiral wound

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Diafiltration by suction
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Batch diafiltration
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Continuous diafiltration
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Diafiltration Applications

• Removal of precipitating salts (eg. ammonium
  sulfate, sodium chloride) from protein solutions
• Removal of precipitating solvents (eg. ethanol,
  acetone) from protein solutions
• Removal of peptide fragments from protein
  solutions
• Buffer exchange before and after chromatographic
  separation
• Removal of toxic metabolites from blood (i.e.
  hemodiafiltration)
• Formulation of proteins in appropriate buffer
• Removal of inhibitors from enzyme solutions

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Clarification

• Removal of particulate matter from macromolecular
  solutions.
• Applications
• Sterile filtration of therapeutic protein
  solutions before dispensing into vials
• Sterile filtration of therapeutic protein
  solutions prior to parenteral administration
• Removal of cell debris after cell disruption
• Separation of cells from extracellularly secreted
  proteins
• Continuous removal of protein products from
  bioreactors

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Particle transmission through UF membrane
Macromolecule transmission through UF membrane in
clarification
- Ideally 100 - Low concentration polarization -
Low fouling due to macromolecule
NF Number of particles per unit volume of
feed NP Number of particles per unit volume of
permeate
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Modules used in clarification processes

• Desirable characteristics
• Low hold-up volume on the feed side
• Ability to provide high membrane wall shear rate
  (or mass transfer coefficient)
• Laboratory scale
• Centrifugal ultrafilter
• Syringe filter
• Stirred cell
• Large scale
• In-line cartridge filter
• Flat sheet tangential flow
• Hollow fibre

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Dead-end clarification
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Dead-end clarification with dilution
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Cross-flow clarification