Extraction plus ion exchange processing of a brine stream

A process for recovering a liquid polymerization reaction diluent having a low salt content from a mixture containing said diluent along with an alkali-metal salt and water, said process comprising the following steps performed in the sequence set forth below:

• (a) extracting essentially all of said diluent from said mixture in an extraction column employing an extractant material so as to produce an extract mixture predominantly containing said diluent and said extractant material and further containing said alkali-metal salt and water;
• (b) converting a substantial portion of said alkali-metal salt in said extract mixture to an alkali-metal hydroxide in the presence of an ion exchange resin so as to produce an exchange mixture predominantly containing said diluent and said extractant material and also containing said alkali-metal hydroxide and water;
• (c) removing essentially all of the water and converting at least a first portion of said alkali-metal hydroxide contained in said exchange mixture to an alkali-metal salt of aminocarboxylic acid in a first fractional distillation column;
• (d) removing essentially all of the extractant material and converting essentially all of the remaining alkali-metal hydroxide in said exchange mixture to an alkali-metal salt of aminocarboxylic acid in a second fractional distillation column;
• and
• (e) recovering said diluent having a low salt content from said second fractional distillation column.