The Cation Exchanger

1
The Cation Exchanger

• CHEE 450 Design Project
• David Grant
• Cynthia Mukoro
• Jenna Smith
• Vehniah Tjong

2
Overview

• Purpose of cation exchangers
• Principles of ion exchange chromatography
• Design considerations
• Vessel sizing
• Cost analysis
• Alternative options

3
The Cation Exchanger

• Purpose
• Separates insulin precursor produced in reactor
• What happens?
• The supernatant carrying the insulin precursor
  passes through the cation exchanger to remove
  impurities
• Elution of the insulin precursor then follows to
  extract the precursor from the resin
• A wash stream is passed through the column to
  remove any residual impurities
• Product continues for further purification in the
  diafilter

4
Principles Behind Cation Exchange Chromatography

• How does it work?
• Ion-exchange chromatography revolves around the
  separation of molecules (ions, polar molecules,
  etc.) on the basis of a difference in charge
• Specifically, cation exchange chromatography is
  useful for the separation of positively charged
  species in solution
• Two phases
• Stationary phase consists of a resin or gel
  matrix of covalently bound negatively charged
  groups
• Mobile phase composed of a buffered aqueous
  solution of counter-ions (positively charged
  molecules) that is in equilibrium with the total
  charge of the resin

5
Principles Behind Cation Exchange Chromatography

• Once the insulin precursor is selectively bound
  to the negative stationary phase, it is eluted by
  an decreasing pH gradient
• This introduces a competitive environment for
  which the insulin precursor may bind and thus
  causes its elution from the vessel.
• Commercial examples of resins with strong binding
  properties
• CM Sephadexcarboxymethyl group with sodium
  counter-ion
• SP Sephadexsulphopropyl group with sodium
  counter-ion

6
Design Considerations

• Pressure drop Ergun equation
• Flow characteristics Reynolds number
• Laminar Flow

where
7
Design Considerations

• Eluant
• pH below the pI of insulin precursor
• Sample buffers
• Malonic acid (pKa 2.88)
• Citric acid (pKa 3.13)
• Residence time

8
Vessel Sizing
9
Cost Considerations

• Capital Costs
• Want a small exchanger to minimize unit cost
• Have an efficient exchanger
• Resin Cost
• Recycling resins costs 60 less than new ones
• Operating Costs
• Operation at low pressure
• Minimize pressure drop (short unit with fast
  flow)

10
Cost Analysis

• Resin Cost 390,000 per vessel
• Capital cost 250,000 per vessel
• Operating costs approx. 40,000/yr
• Total capital cost approx. 1.4 million

11
Alternative Options

• High Performance Liquid Chromatography
• Consists of a reservoir containing a mobile
  phase, a pump, an injector, a separation column
  and a detector
• Compounds separated by injecting sample mixture
  into column
• Different components pass through column at
  different rates due to differences in their
  partitioning behavior between the mobile and
  liquid phases

12
Alternative Options

• Gel Filtration
• Separation is based on size
• Stationary phase consists of porous beads with a
  well defined range of pore sizes
• The stationary phase has a fractionation range
• It has moderate resolution and relatively low
  capacity for loaded proteins

13
Alternative Options

• Membrane Chromatography
• Uses microfilters with absorption properties
• Increased flow rates compared to normal column
  chromatography
• Increases yield, productivity and decreases
  capital cost
• Easy to scale up while retaining characteristics
  and performance

14
Questions