Isolation and fractionation of lignosulfonates by amine extraction and ultrafiltration: A comparative study

Spent sulfite liquors (SSLs) were fractionated by two common separation techniques: amine extraction and ultrafiltration. The lignin fractions obtained were characterized with respect to their elemental composition, functional groups and molecular weight distribution. The results of size exclusion chromatography indicate a broad molecular weight distribution of the lignosulfonates (LS). Irrespective of the separation technique used, a small LS fraction with high molecular mass and low degree of sulfonation was obtained, while most of the lignosulfonates have much lower molar masses and a much higher degree of sulfonation. Both separation methods offer the opportunity to extract high-purity LS fractions; however, compared to amine extraction, ultrafiltration provides additional information about the molecular weight distribution of the SSL components without application of other analytical techniques.