Methods and apparatus for separating alkali metal ions from alkali salts of glycerine to thereby form clean glycerine. These methods are enabled by the use of alkali ion conductive membranes in electrolytic cells that are chemically stable in low pH conditions. The alkali ion conductive membrane preferably includes a chemically stable ionic-selective polymer membrane. A layered composite of a chemically stable ionic-selective polymer and a cation-conductive ceramic membrane is disclosed.