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

Biotechnology for Biofuels, Oct 2015

Background Pretreatment 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. Results High 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. Conclusions EDA 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.

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

Qin et al. Biotechnol Biofuels Ethylenediamine pretreatment changes cellulose allomorph and lignin structure of lignocellulose at ambient pressure Lei Qin 0 2 3 Wen‑Chao Li 0 2 3 Jia‑Qing Zhu 0 2 3 Jing‑Nan Liang 1 Bing‑Zhi Li 0 2 3 YingJ‑in Yuan 0 2 3 0 SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineering and Technology, Tianjin University , Weijin Road 92, Nankai District, Tianjin 300072 , People's Republic of China 1 Institute of Microbiology Chinese Acad‐ emy of Sciences , No.1 West Beichen Road, Chaoyang District, Beijing 100101 , People's Republic of China 2 SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), School of Chemical Engineer‐ ing and Technology, Tianjin University , Weijin Road 92, Nankai District, Tianjin 300072 , People's Republic of China 3 Key Laboratory of Systems Bioengineering (Ministry of Education), Tianjin University , Weijin Road 92, Nankai District, Tianjin 300072, People's Repub‐ lic of China Background: Pretreatment 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. Results: High 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. Conclusions: EDA 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. Biomass; Pretreatment; Cellulose; Hydrolysis; Lignin; Ethylenediamine - Lignocellulosic biomass is an abundant resource to produce fermentable sugars and consequent ethanol or other chemical products. The transformation of lignocellulose is beneficial to sustainable energy and environment. Cellulose and hemicellulose, accounting to more than half of total mass in lignocellulose, can be hydrolyzed to fermentable hexose (glucose) and pentose (xylose and arabinose) by specific enzymes, respectively [1]. However, the enzymatic digestibility of lignocellulose is low due to the structural recalcitrance [2]. Pretreatment is aimed to enhance cellulose conversion by deconstructing biomass structure and thus increasing the accessibility of enzymes and water to the components [3]. Alkaline pretreatments increases enzyme accessibility by degrading lignin and breaking linkage of lignin–carbohydrates [4], in which ammonia pretreatment is widely applied due to the recoverability of ammonia. Ammonia pretreatment employed either aqueous ammonia or liquid ammonia (ammonia fiber expansion, AFEX) [5–7]. Other amines have also been considered effective in pretreatment, such as N-methylmorpholine-N-oxide © 2015 Qin et al. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/ zero/1.0/) applies to the data made available in this article, unless otherwise stated. [8], n-butylamine and ethylenediamine (EDA) [9]. EDA/ salts system was used to dissolve cellulose [10, 11]. EDA was also coupled with ionic liquid or organic solvent to remove lignin [12]. Besides, EDA has been widely used in changing cellulose allomorph as well as ammonia. Cellulose Iα and cellulose Iβ are the predominant allomorphic forms of cellulose found in microb (...truncated)


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Lei Qin, Wen-Chao Li, Jia-Qing Zhu, Jing-Nan Liang, Bing-Zhi Li, Ying-Jin Yuan. Ethylenediamine pretreatment changes cellulose allomorph and lignin structure of lignocellulose at ambient pressure, Biotechnology for Biofuels, 2015, pp. 174, 8, DOI: 10.1186/s13068-015-0359-z