Chromatographic fractionation of complex mixtures of hydroxy carboxylic acids

Abstract

An efficient sequential chromatographic process for the production of pure individual hydroxy acids (HAs) or simple mixtures of these HAs from black liquor (BL)-based HA mixtures was developed. The method enabled the production of 99 wt% pure isosaccharinic, glycolic, lactic, and 2-hydroxybutanoic acids at high yields (57–96% for the batch process). Such separation has not been achieved before this study, and was attributed to the differences in hydrophobicity and acid strength, and intramolecular lactonization of the isosaccharinic acids. Hydrophobicity differences are utilized when polymeric adsorbents (e.g. Sepabeads SP-207 and Amberchrom CG300M) are employed as separation materials, while acid strength differences and intramolecular lactonization are utilized when strong anion exchange resins (e.g. Dowex 1X8) in SO42− form are used as separation materials. This study demonstrated that HAs can be efficiently and selectively recovered from BLs. In addition, these findings can be applied also for the separation of other carboxylic acids.