Studies on Ligninsulfonic Acid (X)

Abstract

Isolation of ligninsulfonic acid (LSH) with precipitating its dicyclohexylamine (DCHA) salt from sulfite spent liquor (SSL) was studied.When water solution of mineral acid salt of DCHA was added, SSL was so much diluted that yield of LSH was very low, because solubility of mineral acid salt of DCHA was very poor.If DCHA was added to SSL directly after removing of calcium sulfate by addition of sulfuric acid, good yield of LSH was obtained. Moreover, concentration of SSL was the higher, yield of LSH was the better.For example, when 1.5 equivalent DCHA per sulfonic residue of LSH was added to concentrated SSL (LSH content: 31%), yield of LSH was about 80% and fractionation by molecular weight was recognized between precipitated LSH and remaining LSH.Changing to Na-LS from LSH·DCHA and recovery of DCHA from LSH·DCHA were easily accomplished by steam distilating after addition of equivalent NaOH.