Characterization of dissolved lignins in two-stage organosolv delignification of wheat straw

Wheat straw was pre-treated with 0.5 N NaOH at 75 degrees C for 2 h and then post-delignified by 1.0 N H2SO4 catalyzed in ethanol-water (60/40, v/v) system at 75 degrees 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 C-13-NMR spectroscopy. The chemical composition of the four lignin fractions are reported.