LIQUIDLIQUID EXTRACTION

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LIQUID-LIQUID EXTRACTION

• Separate inhibitory fermentation products such as
  ethanol, acetone-butanol

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Liquid extractant

• Non toxic
• Selective
• Inexpensive
• Immiscible with fermentation broth
• High distribution coefficient

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EXTRACTION
Y1
Y2
Y3
L
H
X2
X0
X1

• Distribution coefficient KD YL/XH
• YL and XH are concentrations of the solute in
  light and heavy phase, respectively.
• -Also extraction of a compound from one phase to
  the other is based on solubility differences.
• Mass balance on the extracted solute
• H(X0-X1)LY1
• X1X0-(L/H)Y1
• KD Y1/X1 so
• X1X0-(LKD/H)X1
• X1/X0 1/1(LKD/H) 1/(1E)
• E LKD/H is the extraction factor.
• Assume KD is constant, solvents are immiscible
  and L0L1L, H0H1H.

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For a multistage countercurrent operation

• R E(Eª-1)/(E-1)
• R is the rejection time which is the weight ratio
  of the solute leaving in the light phase to that
  leaving in the heavy phase a is the number of
  equilibrium stages.
• The fraction of solute extracted
• extraction 1-1/(R1)
• The rejection ratio
• R Eª(E-1)/(Eª-1)
• When the solute enters the system in the light
  phase. a is the number of stage.

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Extraction

• -Antibiotics are extracted from fermentation
  broth by using amylacetate and isoamylacetate
  with continuous centrifugal Podbielniak
  extractors.
• -Penicillin soluble in organic phase at low pHs
  and soluble in aqueous phase at high pHs. So
  Penicillin is extracted between organic and
  aqueous phase by shifting pH.
• -Some products can be weak acids and bases, since
  they are not ionized are soluble in organic phase
  so pH conditions are selected that the extracted
  compound is neutral and soluble in organic phase.
• -If fermentation broth contains more that one
  component (ß) selectivity becomes an important
  parameter.
• ßijKi/Kj
• Higher the ßij value is, the easier the
  separation of i from j.

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Extraction

• Separation of similar compounds by extraction is
  difficult.
• The extraction of ionized species is known as
  dissociation extraction.
• Many fermentation products are unstable and
  because of the residence time of the product in
  the pH-adjusted broth is too long, there are seen
  some problems. The rapid rotation of Podbielniak
  extractor produces a centrifugal field that
  rapidly drives the two fluids countercurrent each
  other.

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Example 11.2

• Penicillin is extracted from a fermentation broth
  using isoamylacetate as the organic solvent in a
  continuous countercurrent cascade extraction
  unit. The flow rates of organic (L) and aqueous
  (H) phases are L10L/min and H100L/min,
  respectively. The distribution coefficient of
  penicillin between organic and aqueous phases at
  pH 3 is KDYL/XH50. If the penicillin
  concentration in the feed stream is 20g/l,
  determine the number of stages required to
  reduce the penicillin concentration to 0.1g/l in
  the effluent of the extraction unit.

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Solution

• E LKD/H(10)(50)/(100)5
• Xa/X00.1/20510-³
• Using figure we obtain a4 if a Podbialniak
  centrifugal extractor were used, it would have to
  correspond to four ideal stage.

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