Catalytic valorization of hardwood for enhanced xylose-hydrolysate recovery and cellulose enzymatic efficiency via synergistic effect of Fe3+ and acetic acid

Kaixuan Huang; Lalitendu Das; Jianming Guo; Yong Xu

doi:10.1186/s13068-019-1587-4

Catalytic valorization of hardwood for enhanced xylose-hydrolysate recovery and cellulose enzymatic efficiency via synergistic effect of Fe³⁺ and acetic acid

Biotechnol Biofuels. 2019 Oct 17:12:248. doi: 10.1186/s13068-019-1587-4. eCollection 2019.

Authors

Kaixuan Huang^{1

2}, Lalitendu Das^{3

4}, Jianming Guo^{1

2}, Yong Xu^{1

2}

Affiliations

¹ 1Key Laboratory of Forestry Genetics & Biotechnology (Nanjing Forestry University), Ministry of Education, Nanjing, 210037 People's Republic of China.
² 2Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, Jiangsu Province Key Laboratory of Green Biomass-based Fuels and Chemicals, College of Chemical Engineering, Nanjing Forestry University, Nanjing, 210037 People's Republic of China.
³ 3Joint BioEnergy Institute, 5885 Hollis Street, Emeryville, CA 94608 USA.
⁴ 4Biomass Science and Conversion Technology, Sandia National Laboratories, 7011 East Avenue, Livermore, CA 94551 USA.

Abstract

Background: Poplars are considered suitable dedicated energy crops, with abundant cellulose and hemicellulose, and huge surplus biomass potential in China. Xylan, the major hemicellulosic component, contributes to the structural stability of wood and represents a tremendous quantity of biobased chemicals for fuel production. Monomeric xylose conversion to value-added chemicals such as furfural, xylitol, and xylonic acid could greatly improve the economics of pulp-paper industry and biorefinery. Acetic acid (HAc) is used as a friendly and recyclable selective catalyst amenable to xylan degradation and xylooligosaccharides production from lignocellulosic materials. However, HAc catalyst usually works much feebly at inert woods than agricultural straws. In this study, effects of different iron species in HAc media on poplar xylan degradation were systematically compared, and a preferable Fe³⁺-assisted HAc hydrolysis process was proposed for comparable xylose-hydrolysate recovery (XHR) and enzymatic saccharification of cellulose.

Results: In presence of 6.5% HAc with 0.17-0.25 wt% Fe³⁺, xylose yield ranged between 72.5 and 73.9%. Additionally, pretreatment was effective in poplar delignification, with a lignin yield falling between 38.6 and 42.5%. Under similar conditions, saccharification efficiency varied between 60.3 and 65.9%. Starting with 100 g poplar biomass, a total amount of 12.7-12.8 g of xylose and 18.8-22.8 g of glucose were harvested from liquid streams during the whole process of Fe³⁺-HAc hydrolysis coupled with enzymatic saccharification. Furthermore, the enhancement mechanism of Fe³⁺ coupled with HAc was investigated after proof-of-concept experiments. Beechwood xylan and xylose were treated under the same condition as poplar sawdust fractionation, giving understanding of the effect of catalysts on the hydrolysis pathway from wood xylan to xylose and furfural by Fe³⁺-HAc.

Conclusions: The Fe³⁺-assisted HAc hydrolysis process was demonstrated as an effective approach to the wood xylose and other monosaccharides production. Synergistic effect of Lewis acid site and aqueous acetic acid provided a promising strategy for catalytic valorization of poplar biomass.

Keywords: Acetic acid catalysis; Enzymatic saccharification of cellulose; Fe3+-assisted hydrolysis; Poplar; Xylose-hydrolysate recovery.