Efficient Separation of Lignin from Mild Alkaline Hydrolysate of Bagasse by Selective Adsorbent Resin

Abstract

Amongst industrial lignins, such as alkaline and kraft lignins, lignin from hemicellulose pre-treatment liquor is gaining considerable interest because of its various properties. To explore application potential, a lignin sample that was selectively adsorbed by XAD-16N resin from mild alkaline extracts of sugarcane bagasse waste was identified by structural analysis. Trace amounts of hemicellulose were found in the adsorbates that exhibited lignin carbohydrate complexes (LCCs) structure. Prominent NMR signals indicated β-O-4ʹ, β-5ʹ, β-βʹ, and β-1ʹ structures in the side chain, and aromatic signals corresponded to major bagasse lignin units: p-coumarate and ferulate. The quantity of benzyl ether (BE) was 3.33 per 100 Ar-units, which was considerably higher than that of hydrolysate obtained from hydrothermal pretreatments. The content of various hydroxyl groups of mild alkaline lignin obtained by resin adsorption was higher than that of lignin isolated by other methods. Moreover, the adsorbed lignin was relatively pure, and its thermal stability was superior to that of the centrifuged lignin. These results revealed new characteristics of lignin and LCC structures obtained via mild alkaline pretreatment and resin adsorption.