Characterization of fractional cuts of co-solvent enhanced lignocellulosic fractionation lignin isolated by sequential precipitation

Abstract

Lignin valorization is significantly hindered by the intrinsic heterogeneity of its complex structures and variability of biomass feedstocks. Fractionation of lignin can overcome these challenges by producing functionally distinct lignin cuts that can be further tailored to end products. Herein, lignin was extracted and depolymerized from poplar by the co-solvent enhanced lignocellulosic fractionation method with renewable THF to obtain CELF lignin. Several solvents were screened to separate soluble and insoluble fractions from the parent CELF lignin. The ethanol soluble portion was then fractionated into different molecular weight cuts via sequential precipitation of the lignin by reducing the concentration of THF. The physicochemical structures of different CELF lignin cuts were elucidated by GPC and NMR techniques. These results suggest that CELF lignin cuts with lower molecular weight contain progressively higher phenolic and carboxylic acid OH groups, which can be more suitable as green antioxidants than the parent lignin.

Determination of hydroxyl groups in biorefinery resources via quantitative 31P NMR spectroscopy

“…In the early 2000s, Ragauskas's group introduced NHND as a promising alternative IS in 31 P NMR analysis of lignin owing to its ability to be fully baseline resolved from lignin-derived resonances 98 . His group has applied 31 P NMR using this IS to diverse areas including the characterization of transgetic and pretreated biomass [99][100][101] . In addition, Argyropoulos's group carried out extensive studies to elucidate the spin-lattice relaxation times and solvent effects on the 31 P NMR chemical shifts and arrived at the now universally used relaxation additive (chromium acetylacetonate) and the mixture of pyridine and CDCl 3 at the ratio of 1.6:1 as the solvent 15,20 .…”

Biomass Fractionation and Lignin Fractionation towards Lignin Valorization

“…[100] Suitable lignin fractions with low molecular weight contained progressively higher phenolic and carboxylic acid À OH groups were acquired by similar methods. [114] Recently, γ-valerolactone (GVL) has aroused the interest of researchers due to its good stability, low toxicity, biodegradability, and recyclability. Wang et al fractionated enzymatic hydrolysis lignin (EHL) into three parts only by using a GVL/ water mixture; they subsequently reused GVL for lignin fractionation and found that the obtained fractions presented low M w dispersity and structural heterogeneity.…”

“…Three different aqueous solvents (ethanol, acetone, and propylene glycol monomethyl ether) were used to dissolve kraft lignin, and precipitated lignin fractions with constant quality and high purity were obtained by tuning the amount of water added into the system . Suitable lignin fractions with low molecular weight contained progressively higher phenolic and carboxylic acid −OH groups were acquired by similar methods …”

Effects of CELF Pretreatment Severity on Lignin Structure and the Lignin-Based Polyurethane Properties

“…This high degree of lignin tunability opens a broad range of potential pathways for upgrading lignin such as biopolymers, carbon substrates, antioxidants, resins, and hydrocarbon fuels (Ragauskas et al, 2006(Ragauskas et al, , 2014. While structural characterization of CELF lignin resulting from reaction conditions identified for achieving optimal total sugar recovery or high furfural yields have been reported previously (Meng et al, 2018(Meng et al, , 2019bWang et al, 2018), a systematic study focused on elucidating the impact of pretreatment temperature, reaction time, and acid loading on lignin structure is needed to understand the potential spectrum of chemical moieties and inter-unit components that would be available to serve future lignin valorization efforts. Herein, the correlation between CELF pretreatment severity and resultant CELF lignin characteristics from hardwood poplar was established quantitatively by using 31 P nuclear magnetic resonance (NMR), heteronuclear Single Quantum Coherence (HSQC) NMR, gel permeation chromatography (GPC), thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC).…”