Selective Recovery of L-methionine Using Ion Exchange Membranes.

Permeation rates of L-methionine and acethyl-DL-methionine were measured through ion exchange membranes into sodium chloride solution, assuming that the former was produced from the latter using a immobilized enzyme reactor. Both were permeated through an anion exchange membrane. L-methionine was selectively recovered from a L-methionine and acethyl-DL-methionine mixture by Donnan dialysis using a cation exchange membrane under the various pH conditions, however its rate was smaller than that through anion exchange membrane.At low pH, the permeation of hydrogen ion was dominant while that of L-methionine was suppressed. The flux of L-methionine attained to a maximum at pH 2 and decreased with increasing pH. Its mechanism was discussed based on ion exchange equilibrium at the interface and mass transfer in the boundary layer and membrane.