Valorization of hydrolysis lignin from a spruce-based biorefinery by applying γ-valerolactone treatment

Hydrolysis lignin, i.e., the hydrolysis residue of cellulosic ethanol plants, was extracted with the green solvent gamma-valerolactone (GVL). Treatments at 170-210 C were performed with either non-acidified GVL/water mixtures (NA-GVL) or with mixtures containing sulfuric acid (SA-GVL). SA-GVL treatment at 210 C resulted in the highest lignin solubilization (64% (w/w) of initial content), and 76% of the solubilized mass was regenerated by water induced precipitation. Regenerated lignins were characterized through compositional analysis with sulfuric acid, as well as using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), high-performance size-exclusion chromatography (HPSEC), solid-state cross-polarization/magic angle spinning C-13 nuclear magnetic resonance (CP/MAS C-13 NMR) spectroscopy, H-1-C-13 heteronuclear single-quantum coherence NMR (HSQC NMR), and Fourier-transform infrared (FTIR) spectroscopy. The characterization revealed that the main difference between regenerated lignins was their molecular weight. Molecular weight averages increased with treatment temperature, and they were higher and had broader distribution for SA-GVL lignins than for NA-GVL lignins.

Automated summary

In this study, hydrolysis lignin was extracted using the green solvent gamma-valerolactone (GVL), and it was found that mixtures containing sulfuric acid resulted in higher solubilization and regeneration rates. Characterization of the regenerated lignins revealed that treatment temperature had a significant impact on molecular weight, with SA-GVL lignins exhibiting higher and broader distribution of molecular weight.