Recovery of lignin from black liquor by acid precipitation and solvent extraction and the evaluation of antioxidant activity

The pulp and paper industry generate black liquor containing 10-50% lignin. It is estimated that approximately 60-70 million tons of lignin are produced annually. Thus, it represents an abundant renewable polyphenolic material for producing resins, additives, biofuels, and value-added chemicals. In this study, lignin in black liquor was precipitated by sulfuric acid to obtain lignin powder, followed by solvent (i.e., acetone, ethanol, DMSO) extraction. At a solid:liquid ratio of 10:1, lignin powder was completely dissolved in DMSO, but partially dissolved in acetone and ethanol. The antioxidant activity of the extracted lignins was tested by 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical scavenging assay. Results showed that DMSO-extracted lignin showed very high antioxidant activity (IC50 = 367.54 ug/mL). This result indicates that black liquor from pulp and paper industry is good source for the recovery of antioxidant lignin for further biotechnological application.