(649a) Novel Dihydrogen-Bonding Deep Eutectic Solvents: Pretreatment of Rice Straw for Butanol Fermentation Featuring Enzyme Recycling and High Solvent Yield

Novel dihydrogen-bonding deep eutectic solvents:
pretreatment of rice straw for butanol fermentation featuring enzyme recycling
and high solvent yield

Guochao Xu, Wanru Xing, Hao Li, Ye Ni

¹ The Key Laboratory of Industrial Biotechnology,
Ministry of Education, School of Biotechnology, Jiangnan University, Wuxi
214122, Jiangsu, People¡¯s Republic of China

* Corresponding author: guochaoxu@jiangnan.edu.cn; yni@jiangna.edu.cn.

The
demand for non-renewable energy sources such as oil, gas and coal is ever
increasing in modern society. Our known fossil fuel deposits will be depleted
in 40-50 years at current consumption rate. Butanol, is one of the most
promising biofuels, possessing superiorities such as higher hydrophobicity and
energy density, lower corrosivity, and easier miscibility with gasoline in
comparison to ethanol [1]. Besides that,
butanol is an important organic solvent and chemical reagent with widespread
applications in paint, plastics and organic synthesis . Biobutanol, produced
from lignocellulosic biomass by solventogenic clostridia or Escherichia coli and Saccharomyces cerevisiae engineered with
heterogeneously solventogenic pathways, is regarded as a promising alternative
to chemical synthesis of butanol, concerning the exhausted fossil fuels and
environmental pollution [2]. Rice straw (RS) is
the most abundant lignocellulosic biomass in China with an annual production
ranging between 180 and 270 million tons [3], which could be potentially transformed into
biofuels. Traditionally, RS is burnt in the field to enhance soil fertility, whereas
has caused serious air pollution. The main components of RS are cellulose,
hemicellulose and lignin. Among them, cellulose and hemicellulose are main
sources of fermentable sugars, consisting 66% to 75% dry weight of
lignocellulosic raw materials [4], while the
lignin content is lower than other feedstocks such as wheat straw [5]. Therefore, conversion of cheap RS into biofuels
is a promising strategy to alleviate current energy crisis and environmental
pollution.

In this study, a novel deep
eutectic solvent (DES), foraceline, was prepared with choline chloride and double
hydrogen bond donors (formic acid and acetic acid). By combining foraceline and
sodium carbonate (1%), a two-stage pretreatment method was developed and
applied in RS pretreatment to improve the biodegradability of lignocellulose.
The highest glucose and total sugar of 37.3 g∙L^¨C1 and 42.8 g∙L^¨C1
were obtained after hydrolysis of 24 h using 50 FPU∙g¨C1   total solid of cellulase. The
cellulase attached to RS was reutilized for five continuous cycles in which enzyme
loading was reduced from 50 FPU∙g¨C1  
total solid (Cycle I) to 30 FPU∙g¨C1   total solid (Cycle V), resulting
in total sugar of 41.3¨C42.6 g∙L^¨C1 for each cycle. RS hydrolysates
(Cycle I and V) was utilized in butanol fermentation by Clostridium saccharobutylicum DSM 13864, achieving butanol titer
and yield of 9.5g∙L^¨C1 and 0.25 g∙g‒1   total sugar,
similar to those of glucose medium. This study
demonstrated the feasibility of this newly developed biomass pretreatment by
dihydrogen bonding DES featuring cellulase recycling and high butanol yield.

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[2] Ezeji, T. C.; Qureshi, N.; Blaschek, H. P.
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[3] Lei, Z.; Chen, J; Zhang Z.; Sugiura, N. Bioresour. Technol., 2010, 101, 4343¨C4348.

[4] Lippert, K.; Galinski, E. A. Appl. Microbiol. Biotechnol., 1992, 37, 61¨C65.

[5] Buranov, A. U.; Mazza, G. Ind. Crop. Prod., 2008, 28, 237¨C259.