Acid-Catalyzed Glycerol Pretreatment of Sugarcane Bagasse: Understanding the Properties of Lignin and Its Effects on Enzymatic Hydrolysis

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.

Toward a Fundamental Understanding of the Role of Lignin in the Biorefinery Process

“…Acid-catalyzed glycerol (AG) pretreatment of sugarcane bagasse was investigated and it was found that glycerol had modified the bagasse lignin through α-etherification of β-aryl ethers and γ-esterification of hydroxycinnamic acids. The obtained lignin was highly hydrophilic, and it did not inhibit the enzymatic hydrolysis of pretreated bagasse (Hassanpour et al, 2020). By comparing liquid-hot-water (LHW) pretreatment with acid-free ethanolwater (EW) pretreatment, it was found that the nonproductive adsorption between EW pretreatment-induced lignin and cellulases was significantly weakened due to the advantages of suppressing the deposition of lignin condensates (Shi et al, 2018).…”

Recent advances in understanding the effects of lignin structural characteristics on enzymatic hydrolysis

“…After, respectively, adding 2 g/L of two lignins, the glucan conversion of cellulose was increased from 28.0% to 37.4% and 31.3%. Hassanpour et al [ 108 ] prepared the acid–glycerol (AG) pretreated sugarcane bagasse and dilute acid pretreated sugarcane bagasse and recovered the lignin from enzymatic hydrolysis residual of AG pretreated sugarcane bagasse. After adding lignin produced from AG pretreated process to the two substrates, lignin did not inhibit the enzymatic hydrolysis efficiency of AG pretreated sugarcane bagasse, but increased the enzymatic hydrolysis efficiency of dilute acid pretreated sugarcane bagasse from 33 to 38%.…”

The Food–Materials Nexus: Next Generation Bioplastics and Advanced Materials from Agri‐Food Residues

“…[ 312 ] Alternatively, lignin can be isolated from 2) a lignin‐rich residue by enzymatic digestion of residual polysaccharides or solubilization in organic solvents and subsequent precipitation by acidification from the concentrated residue. [ 313 ]…”

“…[312] Higher lignin yields have been achieved via acid-catalyzed glycerol treatment, enabling the recovery of 63% of the initial lignin in SCB at a high purity of 90%. [313] Lignin solutions can be transformed into nano-and microparticles by aerosolization or solvent exchange routes. [316] The size of lignin particles can be controlled by the processing conditions, [317] and their surface chemistry can be tailored by selecting the lignin source material.…”