Characterization of Dissolved Lignins in Two-Stage Organosolv Delignification of Wheat Straw

Abstract

Wheat straw was pre-treated with 0.5 N NaOH at 75°C for 2 h and then post-delignified by 1.0 N H₂SO₄ catalyzed in ethanol-water (60/40, v/v) system at 75°C for 2 h (Alkaline Pretreatment) or pre-hydrolyzed with 1.0 N H₂SO₄ for partial release of hemicelluloses at reflux temperature for 2 h and then post-delignified in organosolv process (Acidic Pretreatment) through two-stage, respectively. Alkaline pretreatment yielded a higher release of lignin (51.2%) as compared to acidic pretreatment, in which 23.0% lignin was dissolved. On the other hand, acidic pretreatment appeared to be more effect on the rate of the organosolv delignification during the following stage. The isolated alkali lignin LA, acid-soluble lignin and organosolv lignin fractions were characterized by UV, IR and ¹³C-NMR spectroscopy. The chemical composition of the four lignin fractions are reported.