Bipolar membrane-based process for the recycle of p-toluenesulfonic acid in D-(-)-p-hydroxyphenylglycine production

A bipolar membrane-based process was proposed to regenerate sodium p-toluenesulfonate (or sodium 4-methylbenzenesulfonate) in the production of D-(-)-p-hydroxyphenylglycine (or R- α-amino-4-hydroxy-benzeneacetic acid). The conversion of pure sodium p-toluenesulfonate solution and actual feed solution that contains small amount of R-α-amino-4-hydroxy-benzeneacetic acid besides sodium p-toluenesulfonate was compared and a new processing route was proposed. The removal ratio of Na+ was typically around 80% with an average current efficiency of 20-50%.