Deep eutectic solvents (DESs) have emerged as a promising class of solvents for lignin dissolution, which could significantly expand the application potential of lignin. In this study, over forty ChCl-based DESs of three major types were synthesized and subjected to investigate the solubilisation of two industrial lignins in DES. The results showed that higher HBD content, shorter carbon chain length in the HBD, and fewer functional groups favored lignin solubilization. DESs containing carboxyl groups were found to be more favorable for breaking β-O-4 bonds and solubilizing lignin. Additionally, high temperature and appropriate water content were observed to promote lignin solubilization. The pretreatment of poplar and maize straw with ChC/FA(1:3), ChC/LA(1:3), ChC/Gly(1:3), ChC/EG(1:3), ChC/Urea(1:3), and ChC/TEOA(1:3) showed good solubilization of lignin, with ChCl/FA(1:3) being particularly effective in solubilizing poplar lignin and maize straw lignin, achieving lignin solubilization of 82% and 57%, respectively. Overall, these findings suggest that DESs have great potential as solvents for lignin dissolution.

Cellulose aerogels based on crosslinking of cellulose with 1,4-butanediol diglycidyl ether (BDE) were homogeneously synthesized in NaOH/urea aqueous solution followed by freeze-drying. In the NaOH/urea aqueous solution, cellulose existed in a sodium alkoxide form that could react with the epoxide groups of BDE. The rheological behavior of the cellulose/NaOH/urea aqueous solution showed that the crosslinking reaction occurred immediately once the BDE was added to the cellulose/NaOH/urea aqueous solution at room temperature. The X-ray diffraction (XRD) characterization identified a transition from the crystalline structure of cellulose to an amorphous state of cellulose aerogels with increasing amount of BDE. Elemental analysis revealed the variation in carbon and oxygen elemental percentages in cellulose aerogels caused by the reaction between cellulose and BDE. The porous network of aerogels was observed by scanning electron microscopy (SEM) and the pore size of the aerogels increased as a function of BDE. The water adsorbent ability of aerogels was up to 41 g g⁻¹—even after 30 squeezing–adsorption cycles, the water adsorbent ability was still 37 g g⁻¹.

Lignocellulosic biorefineries have received considerable attention for the purpose of producing high-value chemicals and materials. Levulinic acid (LA) is an important biomass-derived platform chemical that is produced from sugar-based biomass. Unfortunately, the catalysts reported thus far have shortcomings, such as expensive starting materials, complicated synthesis or purification operations, and a low LA yield under harsh reaction conditions. Herein, we develop a novel dual-functional catalyst, HScCl₄, by combining Brønsted acid (HCl) and Lewis acid (ScCl₃) sites. The as-prepared HScCl₄ catalyst shows high efficiency and high selectivity for converting 5-hydroxymethylfurfural (HMF) to LA in a biphasic system consisting of methyl isobutyl ketone (MIBK) and water. The density functional theory (DFT) results show that the synergistic catalytic effect, originating from the Brønsted and Lewis acidic sites of HScCl₄, significantly decreases the energy barriers of reactants and intermediates, thus facilitating the conversion of HMF to LA. Moreover, the efficient separation of LA in the water-MIBK biphasic system by extracting LA to the MIBK phase minimizes the side reactions of LA and thus the formation of humins while significantly improving the LA yield. The conversion of HMF and the selectivity for LA are 100 and 95.6% at 120 °C for 35 min, respectively. The free energy (ΔG) and activation energy (E_a) of the reaction are −30 kcal mol^–1 and 13.7 kJ mol^–1, respectively. The developed process provides a green, sustainable, and efficient pathway to produce LA from biomass-derived HMF under mild conditions.

Brønsted-Lewis acidic ionic liquids (ILs) were applied to catalyze cellobiose to prepare levulinic acid (LA) in one pot under hydrothermal conditions. Under the optimum conditions, the highest LA yield of 67.51% was obtained when low [HO₃S-(CH₂)₃-mim]Cl-FeCl₃ (molar fraction of FeCl₃ x = 0.60) was used. This indicated the Brønsted-Lewis acidic ILs played an active role in the conversion of cellobiose to LA. The catalytic mechanism of ILs had been established, disclosing that the Brønsted-Lewis acidic ILs had the catalytic synergistic effect originating from its double acid sites. During the reaction process, the Lewis acid sites improved the isomerization of glucose to fructose, then the Brønsted and Lewis acid sites simultaneously enhanced the dehydration of fructose to produce hydroxymethylfurfural (HMF), which was propitious to the synthesize LA with high yield. In addition, LA could be easily extracted by methyl isobutyl ketone (MIBK), and the ILs could retain its basic activity after 5 cycles. The solid residues were characterized using SEM, FT-IR and TG-DTG spectroscopy. It was the conclusion that a large amount of humins were produced during the cellobiose conversion process. In this reaction, the ILs not only overcomes the problems of the conventional catalyst, but also completes the reaction-separation integration and the recycling of the catalyst. This paper provided an important theoretical basis for the application of ILs in the field of biomass.