Ion exchange equilibria under pressure



Previous work on the ionization equilibria of weak acids and bases at high pressures suggested that compression should favor the transfer of protons from a weakly acidic resin to a weakly basic one in a mixed bed system, and that the resulting increase of ionization should extract cations and anions from the surrounding solution. In agreement with this idea it has now been observed that the equilibrium concentration of a solution of sodium chloride around a mixture of De-Acidite M and Zeo-Karb 226 resins is almost halved when the pressure is raised from 1 to 3,000 atm. The change is completely reversible.

The measurements indicate that the proton transfer process involves a contraction of about 15 cc. mole−1, which is remarkably close to the analogous contraction [15 to 18 cc. mole−1] that occurs when a proton is transferred from a free carboxylic acid to an amine in solution.