(71g) Screening of the Deep Eutectic Solvents with Controllable ?-O-4 Linkage in Lignocellulose Pretreatment for Various Biomaterial Manufacture

Deep eutectic solvents (DES) are emerging as novel green solvents for lignocellulose pretreatment and lignin extraction owing to their outstanding characteristic of chemical and thermal stability, easy preparation, and recyclability¹. The cleave of β-O-4 linkages occurs in the extracting lignin in DES. However, β-O-4 linkage is important for the lignin-based biomaterials, the content of β-O-4 linkages correlates significantly with the tensile strength and elastic modulus of lignin carbon fibers². The lignin cleaved more β-O-4 linkage could be prepared the lignin nanoparticle with superior uniformity and greater stability³. Although there has been extensive research on the separation of lignocellulosic biomass using DES, DES is diverse and its structure and regulation of lignin properties are not clear, it is still a challenge to rapidly and effectively select the appropriate DES for lignocellulosic pretreatment and obtain the controllable β-O-4 linkage lignin.

Conductor-like Screening Model for Real Solvents (COSMO-RS), has emerged as a valuable and fast tool to predict and screen ionic liquids for biomass dissolution and DES for gas separation, and liquid-liquid extraction⁴. Herein, we combine the COSMO-RS calculation and experiment verification to find the effect of DES on lignin properties (β−O−4 linkages, and β−5 bond), predict and design the DES for pretreating hardwood to get the lignin with the controllable β-O-4 linkages content. 260 DES, composting of 13 hydrogen bond acceptors (HBA), 20 hydrogen bond donors (HBD), and 4 lignin models that the minimal lignin dimers with β−O−4 linkages were chosen to predict the activity coefficients (γ). Based on the γ prediction, we synthesized 9 representative DES for lignin pretreatment and characterizations. The result shows that the smaller the γ, the stronger the destructive power of β−O−4 and β−5; HBDs play a major role in the lignin dissolution and extraction, and HBAs may have synergistic effects due to the little effect on the γ. Multivariate analysis of the calculation γ and experimental β−O−4 linkages content, β−5 bond content revealed that HG-β-O-4 lignin model occupies the main part of the β-O-4 bond of wood lignocellulosic, followed by SS-β-O-4 and SG-β-O-4, GG-β-O-4 is almost negligible. The prescreen DES1 and DES2 pretreated lignin have higher (47%) and lower β-O-4 linkages content (0%) respectively. These two DES were chosen to pretreatment the hardwood to obtain the lignin and prepare the carbon fiber and lignin nanoparticles. Lignin regenerated from DES1 has low β-O-4 content (0%), and the lignin nanoparticles have smaller sizes and higher zeta potential under the same conditions. Lignin regenerated from DES2 has higher β-O-4 content (47%), and the carbon fiber has better mechanical performance. This work not only provides a new paradigm to predict the lignin properties and design the DES with the ability to achieve controllable tailor the β-O-4 linkage of lignin by COSMO-RS calculation, but also broadens the applications of lignin with different β-O-4 contents for the various biomaterial manufacture.

1. Cheng, J. Y.; Huang, C.; Zhan, Y. N.; Liu, X. Z.; Wang, J.; Meng, X. Z.; Yoo, C. G.; Fang, G. G.; Ragauskas, A. J., A high-solid DES pretreatment using never-dried biomass as the starting material: towards high-quality lignin fractionation. Green Chem 2023, 25 (4), 1571-1581.
2. Li, Q.; Hu, C.; Li, M. J.; Truong, P.; Li, J. H.; Lin, H. S.; Naik, M. T.; Xiang, S. S.; Jackson, B. E.; Kuo, W.; Wu, W. H.; Pu, Y. Q.; Ragauskas, A. J.; Yuan, J. S., Enhancing the multi-functional properties of renewable lignin carbon fibers defining the structure-property relationship using different biomass feedstocks. Green Chem 2021, 23 (10), 3725-3739.
3. Liu, Z. H.; Hao, N. J.; Shinde, S.; Olson, M. L.; Bhagia, S.; Dunlap, J. R.; Kao, K. C.; Kang, X. F.; Ragauskas, A. J.; Yuan, J. S., Codesign of Combinatorial Organosolv Pretreatment (COP) and Lignin Nanoparticles (LNPs) in Biorefineries. Acs Sustainable Chemistry & Engineering 2019, 7 (2), 2634-2647.
4. Palomar, J.; Lemus, J.; Navarro, P.; Moya, C.; Santiago, R.; Hospital-Benito, D.; Hernández, E., Process Simulation and Optimization on Ionic Liquids. Chem Rev 2024, 124 (4), 1649-1737.