Separation and Structural Characteristics of Lignin in the Prehydrolysis Liquor of Whangee Dissolving Pulp

Separation and structural characterization of lignin are essential for value-added utilization of hemicelluloses and lignin in the prehydrolysis liquor (PHL) of a kraft-based Whangee (a genus of bamboo) dissolving pulp production. In this work, lignin in the PHL was separated by acidification treatment (AT) and rotary vacuum evaporation treatment (RVET), and the separated crude lignin was then compared and characterized. The crude lignin separated by RVET could be justified as p-hydroxyphenyl (H) syringyl (S)-guaiacyl (G) lignin, and a conjugated carbonyl was also found in it. The crude lignin separated by AT was mainly composed of S lignin that had beta-1, beta-5, beta-O-4, and beta-beta bonds. Thermogravimetric analysis (TGA) showed that the maximum thermal decomposition temperatures and the final carbon residues of crude lignin separated by RVET and AT were 520 degrees C, 5.26%, and 470 degrees C, 27.92%, respectively. Moreover, of the five kinds of sugar (arabinose, galactose, glucose, xylose and mannose) in the PHL, only galactose and glucose were decreased after AT, while all five kinds were decreased after RVET.