Detailed Insights into Lignin Stabilization and Carbohydrate Nature in H-transfer RCF: On the Role of Solvent Fractionation of Lignin Oil in Structural Profiling

05 December 2022, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Reductive Catalytic Fractionation (RCF) of lignocellulosic materials produces lignin oil rich in monomer products and high-quality cellulosic pulps. RCF lignin oil also contains lignin oligomers/polymers and hemicellulose-derived carbohydrates. The variety of components makes lignin oil a complex matrix for analytical methods. As a result, the signals are often convoluted and overlapped, making detecting and quantifying key intermediates challenging. Therefore, to investigate the mechanisms underlining lignin stabilization and elucidate the structural features of carbohydrates occurring in the RCF lignin oil, fractionation methods reducing the RCF lignin oil complexity are required. This report examines the solvent fractionation of RCF lignin oil as a facile method for producing lignin oil fractions for advanced characterization. We demonstrate solvent fractionation using small volumes of environmentally benign solvents (methanol, acetone, and ethyl acetate) to produce multigram lignin fractions comprising products in different molecular weight ranges. This feature allowed for determining structural heterogeneity across the entire molecular weight distribution of the RCF lignin oil via high-resolution HSQC NMR spectroscopy. This study provides detailed insight into the role of the hydrogenation catalyst (Raney Ni) in stabilizing lignin fragments and defining the structural features of hemicellulose-derived carbohydrates in lignin oil obtained by the H transfer RCF process.

Keywords

reductive catalytic fractionation
lignin-first
solvent fractionation
Raney Ni
lignin valorisation
carbohydrates

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