Solvent extraction: effect of pH
Step 1
Contacting the fermentation broth with immiscible organic solvent
such as MIBK.
The pH is adjusted just prior to mixing with the
organic solvent. The product has a carboxyl group that makes it
water soluble when ionized. When the -COOH is not ionized, the
product prefers to be in an non-polar organic solvent. Assume that
pK=5. Within roughly one pH unit, the concentration of product will
depend on satisfying the distribution coefficient. Remember that
when pH = pK, the compound is one-half ionized, but the solvent
can get part of it as the equilibrium supplies more.