Effective extraction of larch holocellulose with alkaline deep eutectic solvent and production of furan chemicals with the coordination of temperature-controlled polyoxometalates and metal salt in biphasic system

Abstract

This study focused on extracting holocellulose from Changbai larch waste, which is rich in hexose and beneficial for furan chemicals production. Various alkaline deep eutectic solvents (DESs) was applied in the extraction of holocellulose. DES composed of lysine (Lys) and 2-aminoethanol (MEA) with strong alkalinity had a superior ability to remove lignin, and the purity of holocellulose could reach 82.7 %. Consequently, a double-acid system formed by a temperature-controlled polyoxometalates catalyst (Ch_nH_3-nPW₁₂, n = 1, 2, 3,) prepared by choline chloride (ChCl) and phosphotungstic acid (H₃PW₁₂O₄₀) and different metal salts were used in the hydrolysis of holocellulose to 5-hydroxymethylfurfural (HMF) and 2-furaldehyde (FF) in a two-phase system of water and organic solvent. The yields of HMF and FF reached 43.5 % and 78.2 %, respectively, when ChH₂PW₁₂ and AlCl₃ were employed under the conditions of 10 mL water/methyl isobutyl ketone (MIBK) (1:9, V:V), 9 h, and 150 °C. ChH₂PW₁₂is easy to recycle and can be used up to 5 times. This study offers a novel strategy to retain as much hemicellulose as possible to achieve holocellulose by alkaline DESs, and the one-pot process by the coordination of polyoxometalates and metal salt provides a simultaneous production of high-value furan chemicals from larch waste.