Pretreatment of jerusalem artichoke stalk with modified hydroxylammonium ionic liquids for 2,3-butanediol production

Abstract

Lignocellulose is the most abundant biomass for sustainable production of biofuels and chemicals, and the pretreatment is essential for efficient saccharification. In this work, the low-cost hydroxylammonium ionic liquids (HILs) with different base-acid molar ratios (BAMRs) were prepared to pretreat non-crop biomass, Jerusalem artichoke stalk (JAS), and the effect of HIL structure on pretreatment performance was evaluated via lignin removal, saccharification, solvent recycling, and structural changes of JAS and regenerated lignin. With BAMR increasing, the lignin removal and saccharification yield increased, while polysaccharide recovery changed a little. When JAS was pretreated at 160 °C for 6 h using ethanolammonium acetate (EOAA) with BAMR varied from 1 to 5 (EOAA(5:1)), the lignin removal increased from 52.3 to 80.7%, glucose yield increased from 81.1 to 93.2%, and glucose yield was still 90% in the fifth use of EOAA(5:1). The spectra of FT-IR and 2D-HSQC NMR indicated that JAS lignin was mainly composed of syringyl (S) and guaiacyl (G) units and a trace amount of p-hydroxyphenyl (H) unit. During the pretreatment, the connection between lignin and hemicellulose was disrupted. The predominant structure (β-O-4, β-β, and β-5) was well preserved in the regenerated lignin, while the S/G ratio was decreased from 3.12 to 2.78. Finally, microbial production of 2,3-butanediol (2,3-BD) and acetoin from JAS residue was carried out, and 92.3 g/L 2,3-BD and 14.4 g/L acetoin were obtained after 78 h of fermentation. This work could contribute to the improvement of lignocellulose digestibility and the production of bio-based chemicals from lignocellulosic biomass.