Acid-Catalyzed Glycerol Pretreatment of Sugarcane Bagasse: Understanding the Properties of Lignin and Its Effects on Enzymatic Hydrolysis
Morteza Hassanpour, Mahsa Abbasabadi, Leigh Gebbie, Junior Te’o, Ian M. O’Hara, Zhanying Zhang
Abstract
In this study, lignin from acid-catalyzed glycerol (AG) pretreatment of sugarcane bagasse was recovered and characterized. Its effects on enzymatic hydrolysis and cellulase recycling were then investigated. Prior to lignin recovery, a two-step dilute acid and AG pretreatment was used to deconstruct sugarcane bagasse, which led to a glucan enzymatic digestibility of 99%, a glucose yield of 91%, and a xylose yield of 67%. Following enzymatic hydrolysis, lignin-rich residues were recovered by simple filtration at a lignin yield of 63% and a lignin purity of 90%. Two-dimensional heteronuclear single quantum correlation nuclear magnetic resonance analysis showed that glycerol had modified the bagasse lignin through α-etherification of β-aryl ethers and γ-esterification of hydroxycinnamic acids, generating a novel lignin structure. 31P NMR analysis showed that the recovered lignin had a high number of aliphatic hydroxyl groups suggesting that it is highly hydrophilic in nature. As a result, the AG lignin did not inhibit enzymatic hydrolysis of pretreated bagasse, and cellulases adsorbed onto lignin-rich solid residues were successfully recycled three times, leading to an average glucan digestibility of 93% (for a total of four batches) at an average cellulase dosage of only 4.1 FPU/g glucan. This study provides new and important information on AG pretreatment, which is critical toward the development of biorefinery processes based on this pretreatment.