measurement of bioreactor k l a l.
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Measurement of Bioreactor K L a. Motivations. 2. Good example of mass transfer at gas-liquid interface 3. Experience modeling in both semi-empirical and factorial methods. Biotech/pharmaceutical industry employing more Chemical Engineers Process Engineering Validation Management

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motivations
Motivations

2. Good example of mass transfer at gas-liquid interface

3. Experience modeling in both semi-empirical and factorial methods

  • Biotech/pharmaceutical industry employing more Chemical Engineers
      • Process Engineering
      • Validation
      • Management
      • Pilot testing
      • Scale-up
types of products
Types of Products
  • Natural Products
    • Drugs
      • Penicillin is early example
      • Taxol
      • Mupricin
      • Cyclosporin A, etc.
    • Foods
      • Fermented beverages
      • Fermented dairy products
types of products4
Types of Products
  • Transgenic Products
    • Gene for a therapeutic protein inserted in foreign expression system
      • Factor IX
      • a-1-antitrypsin
      • EPO
      • Antibodies
      • antithrombin III
      • tissue plasminogen activator (TPA)
      • Interferons, etc.
expression systems
Expression Systems
  • Bacterial Cells
  • Fungal Cells
  • Plant Cells
  • Insect Cells
  • Mammalian Cells
types of bioreactors fermenter often depends on shear sensitivity
Types of Bioreactors (fermenter)(often depends on shear sensitivity)
  • Stirred tank
    • Aerobic or Anaerobic (air-sparged if aerobic)
    • Most common for bacterial cells
  • Bubble or airlift column
    • Good for shear-sensitive cells
  • Fixed bed systems
    • Trickle beds, hollow membrane fiber (mammalian cells), etc.
why is k l a important
Why is KLa Important?
  • Dissolved oxygen is an important substrate in aerobic fermentations. Since oxygen is sparingly soluble in water, it may be the growth-limiting substrate in these fermentations. For bacteria and yeast cultures, the critical oxygen concentration is about 10% to 50% of the saturated DO (dissolved oxygen concentration).
equation for transport
Equation for Transport

Oxygen transfer is usually limited by the liquid film surrounding the gas bubbles:

where mO2 is the rate of oxygen transfer per volume of bioreactor (mass O2/ L3 t), kL is the oxygen transport coefficient, [=]L/t, a is the gas-liquid interfacial area per volume of reactor [=] L2/L3, kLa is the volumetric oxygen transfer coefficient [=]1/t, C* is saturated DO (dissolved oxygen) concentration [=] m/L3 (approx. 7 mg/l at 25 deg. C and 1 atm.), CL is the actual DO concentration in the liquid [=] m/L3

terms affecting rate
Terms affecting rate
  • KLa
    • What we are trying to determine and correlate with mixing speed and aeration rate
    • Two quantities multiplied together
      • Liquid side (essentially overall mass transfer coefficient)
      • Total area of bubbles in bioreactor
      • Can’t be separated
terms affecting rate14
Terms affecting rate
  • C* (saturation oxygen concentration; max solubility of the gas in liquid)

- Constant at a given T and P

- Available in tables (see on-line lab manual)

  • CL (C(t)) the oxygen concentration at a given time during the run; what we measure

- {C*- CL} = “driving force”

terms affecting rate15
Terms affecting rate
  • KL -mass transfer coefficient
  • a- interfacial area for mass transfer
probe response rate needed to get real c l t value
Probe response rate needed to get “real” CL(t) value
  • Gaseous oxygen dissolves in water at bubble interface and disperses in the bioreactor
  • Dissolved O2 crosses probe membrane at tip.
  • O2 in probe is sensed and sent to meter

1

2

3

Time constant =1/kLa

Time constant =1/kp

Fast