Deep Eutectic Solvent Aqueous Solutions as Efficient Media for the Solubilization of Hardwood Xylans

• Published in: ChemSusChem Vol. 11; no. 4; pp. 753 - 762
• Main Authors: Morais, Eduarda S., Mendonça, Patrícia V., Coelho, Jorge F. J., Freire, Mara G., Freire, Carmen S. R., Coutinho, João A. P., Silvestre, Armando J. D.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 22-02-2018
• Subjects: Acetic Acid; Aqueous solutions; Biorefineries; biorefinery; Choline; deep eutectic solvents; Eucalyptus; Eucalyptus - chemistry; extraction; green solvents; Lignocellulose; Plant Extracts; Response surface methodology; Solubility; Solubilization; Solvents; Solvents - chemistry; Temperature; Temperature effects; Urea; Water - chemistry; Wood - chemistry; xylans; Xylans - chemistry; Xylans - isolation & purification; biorefinery; xylans; extraction; deep eutectic solvents; green solvents
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.201702007

This work contributes to the development of integrated lignocellulosic‐based biorefineries by the pioneering exploitation of hardwood xylans by solubilization and extraction in deep eutectic solvents (DES). DES formed by choline chloride and urea or acetic acid were initially evaluated as solvents for commercial xylan as a model compound. The effects of temperature, molar ratio, and concentration of the DES aqueous solutions were evaluated and optimized by using a response surface methodology. The results obtained demonstrated the potential of these solvents, with 328.23 g L−1 of xylan solubilization using 66.7 wt % DES in water at 80 °C. Furthermore, xylans could be recovered by precipitation from the DES aqueous media in yields above 90 %. The detailed characterization of the xylans recovered after solubilization in aqueous DES demonstrated that 4‐O‐methyl groups were eliminated from the 4‐O‐methylglucuronic acids moieties and uronic acids (15 %) were cleaved from the xylan backbone during this process. The similar Mw values of both pristine and recovered xylans confirmed the success of the reported procedure. DES recovery in four additional extraction cycles was also demonstrated. Finally, the successful extraction of xylans from Eucalyptus globulus wood by using aqueous solutions of DES was demonstrated.
New media provides the solution: Deep eutectic solvents formed by choline chloride and urea in aqueous solutions display excellent ability to solubilize hardwood xylans and show great potential for the extraction of these polysaccharides from hardwoods in an integrated biorefinery context.