Ethylenediamine pretreatment changes cellulose allomorph and lignin structure of lignocellulose at ambient pressure.

Lei Qin,Bing-Zhi Li,Wen-Chao Li,Jia-Qing Zhu,Jing-Nan Liang,Ying-Jin Yuan

doi:10.1186/s13068-015-0359-z

Abstract

BackgroundPretreatment of lignocellulosic biomass is essential to increase the cellulase accessibility for bioconversion of lignocelluloses by breaking down the biomass recalcitrance. In this work, a novel pretreatment method using ethylenediamine (EDA) was presented as a simple process to achieve high enzymatic digestibility of corn stover (CS) by heating the biomass–EDA mixture with high solid-to-liquid ratio at ambient pressure. The effect of EDA pretreatment on lignocellulose was further studied.ResultsHigh enzymatic digestibility of CS was achieved at broad pretreatment temperature range (40–180 °C) during EDA pretreatment. Herein, X-ray diffractogram analysis indicated that cellulose I changed to cellulose III and amorphous cellulose after EDA pretreatment, and cellulose III content increased along with the decrease of drying temperature and the increase of EDA loading. Lignin degradation was also affected by drying temperature and EDA loading. Images from scanning electron microscope and transmission electron microscope indicated that lignin coalesced and deposited on the biomass surface during EDA pretreatment, which led to the delamination of cell wall. HSQC NMR analysis showed that ester bonds of p-coumarate and ferulate units in lignin were partially ammonolyzed and ether bonds linking the phenolic monomers were broken during pretreatment. In addition, EDA-pretreated CS exhibited good fermentability for simultaneous saccharification and co-fermentation process.ConclusionsEDA pretreatment improves the enzymatic digestibility of lignocellulosic biomass significantly, and the improvement was caused by the transformation of cellulose allomorph, lignin degradation and relocalization in EDA pretreatment.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0359-z) contains supplementary material, which is available to authorized users.

Highlights

Pretreatment of lignocellulosic biomass is essential to increase the cellulase accessibility for bioconver‐ sion of lignocelluloses by breaking down the biomass recalcitrance
Dry method was crucial to increase EDA pretreatment efficiency Cellulose allomorphs after the separation of EDA and cellulose were affected by the dry methods [17]
Glucan recoveries were above 98 % after all the separation methods, which is different from the EDA/salts dissolution effect of cellulose [10, 11]

Summary

Introduction

Pretreatment of lignocellulosic biomass is essential to increase the cellulase accessibility for bioconver‐ sion of lignocelluloses by breaking down the biomass recalcitrance. The effect of EDA pretreat‐ ment on lignocellulose was further studied. Cellulose and hemicellulose, accounting to more than half of total mass in lignocellulose, can be hydrolyzed to fermentable hexose (glucose) and pentose EDA was coupled with ionic liquid or organic solvent to remove lignin [12]. Upon removing EDA by washing with polar/non-aqueous solvents (e.g., ethanol) or drying under vacuum, the hydrogen bonds reform between cellulose molecules, and the crystal form of cellulose converts to cellulose IIII [17]. It was reported that the enzymatic saccharification rate of cellulose IIII was much higher than cellulose I [19]

Methods

Results

Discussion

Conclusion