Influence of Steaming Pressure on Steam Explosion Pretreatment of Lespedeza stalks (Lespedeza cyrtobotrya). II. Characteristics of Degraded Lignin

摘要

Lignin fractions obtained by steam explosion pretreatment and subsequent alkaline ethanol solution post-treatment from Lespedeza cyrtobotrya stalks were studied in terms of chemical characteristics, to reflect the influence of elevating steam pressure from 15 to 25 kg/m(2). Because of the remarkable selectivity with respect to lignin, the post-treatment with 60% ethanol solution Containing 1% NaOH yielded 8.3, 1.3.0, 16.0, 16.4, and 17.8% lignin fractions from the samples steam-exploded at 15, 17.5, 20, 22.5, and 25 kg/m(2) for 4 min, respectively, comparing to 7.7% lignin removal from the raw material. Steam explosion pretreatment, not only obviously cleaved the linkage between carbohydrates and lignin resulting in the significantly decrease of the associated hemicelluloses in lignin fractions, but also broke the beta-O-4 bond between lignins to some degrees. In particular, slightly more guaiacyl moieties than syringyl units were affected.