Effect of Tetrahydrofuran on the Solubilization and Depolymerization of Cellulose in a Biphasic System.

The dissolution of cellulose from biomass is a crucial but complicated issue for maximizing the utilization of biomass resources to produce valuable chemicals, because of the extreme insolubility of cellulose. A biphasic NaCl-H ₂ O-tetrahydrofuran (THF) system was studied, in which most of the pure microcrystalline cellulose (M-cellulose, 96.6 % conversion at 220 °C) and that contained in actual biomass were converted. Nearly half of the O6-H⋅⋅⋅O3 intermolecular hydrogen bonds could be broken by THF in the H ₂ O-THF co-solvent system, whereas the cleavage of O2-H⋅⋅⋅O6 intramolecular hydrogen bonds by H ₂ O was significantly inhibited. In the NaCl-H ₂ O-THF system, THF could significantly promote the effects of both H ₂ O and NaCl on the disruption of O2-H⋅⋅⋅O6 and O3-H⋅⋅⋅O5 intramolecular hydrogen bonds, respectively. In addition, THF could protect and transfer the cellulose-derived products to the organic phase by forming hydrogen bonds between the oxygen atom in THF and the hydrogen atom of C4-OH in the glucose or aldehyde group in 5-hydroxymethylfurfural (HMF), which can lead more NaCl to combine with the -OH of M-cellulose and further disrupt hydrogen bonding in M-cellulose, thereby improving the yield of small molecular weight products (especially HMF) and further promoting the dissolution of cellulose. As a cheap and reusable system, NaCl-H ₂ O-THF system may be a promising approach for the dissolution and further conversion of cellulose in lignocellulosic biomass without any enzymes, ionic liquids, or conventional catalysts.
(© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)