Novel chromatographic process for the recovery and purification of hydroxy acids from alkaline spent pulping liquors

Abstract

In this study, an efficient sequential chromatographic process for recovering hydroxy acids (HAs) from soda and kraft black liquors (BLs) has been developed. Lignin and pulping chemicals are also recovered and can be recycled back to the pulping process. A weak cation exchange resin in Na+ form separates lignin from BL. Up to 95% lignin yield was obtained, with over 50% yield for HAs as Na salts. A cellulose-based resin is used to separate HAs from NaOH. Complete separation, and thus 100% yield for HAs and NaOH, was achieved. The HAs in soda BL are liberated by ion exchange. In case of kraft BL, the solution is acidified with H2SO4 and subjected to ion exchange and ion exclusion chromatography to recover the remaining pulping chemicals. It was found that fouling, which limits the efficiency of membrane-based processing of BLs, is avoided with the appropriate choice of chromatographic separation materials.