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
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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
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[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)