Effects of Ethanol Pretreatment on Dissolution and Structural Changes of Lignin from Steam-exploded Wheat Straw

Pretreatment of steam-exploded wheat straw by ethanol has been used to dissolve lignin. Different pretreatment conditions were explored by varying reaction temperature, time, and the ratio of solid to liquid to determine that the rate of dissolution was approximately 51.6%. The examination of structural changes in L-P (lignin from ethanol pretreatment pulp) showed that the conjugated carbonyl/carboxyl of lignin was partly destroyed during ethanol pretreatment and alkali extraction process. The content of total hydroxyl groups was increased with increasing ethanol pretreatment. Higher intensities of the aromatic ring in L-P and L-L (lignin from black liquor) fractions compared to that of weak pretreatment conditions indicated that some extent of lignin condensation occurred during the ethanol pretreatment. The ratios of S/G in L-P were higher than in L-L and removal of the methoxyl groups happened during the ethanol pretreatment process, and this led to changes in proportions of lignin structural units.