Process development and pilot-scale validation of γ-valerolactone pretreatment for softwood biorefining

Developing effective fractionation methods remains challenging in biorefining. γ-Valerolactone (GVL) is a promising green solvent, yet its application in softwood biorefineries is still underexplored. In this study, GVL pretreatment for softwood biorefining was assessed at laboratory and pilot scales. The effects of temperature (170–210 °C), time (20–60 min), and GVL-to-water ratios (20:80 – 80:20 %) on the biorefining of spruce sawdust were initially investigated through lab-scale experiments using a 1-L reactor. A GVL/water solution at a 40:60 ratio, assisted by 0.4 g of sulfuric acid per 100 g of biomass, enabled the solubilization of up to 81.4 % of lignin and nearly the entire hemicellulosic fraction, while effectively preserving cellulose, which was subsequently saccharified with over 90 % conversion. Lignin was regenerated from the liquors and characterized using pyrolysis-gas chromatography/mass spectrometry, high-performance size-exclusion chromatography, Fourier-transform infrared spectroscopy, and ¹H-¹³C heteronuclear single-quantum coherence nuclear magnetic resonance spectroscopy. The biorefinery concept was successfully scaled up and validated at pilot scale in a 50-L reactor, where enzymatic saccharification of the resulting cellulosic pulp produced hydrolysates that, upon fermentation, yielded 231.4 g of ethanol per kilogram of pulp. Lignin regenerated from the pilot-scale pretreatment liquors (118.9 g per kilogram of raw sawdust) and the lignin-rich saccharification residue (182.7 g/kg) were subjected to hydrothermal liquefaction, and the resulting biocrudes were characterized to assess their potential for biofuel formulation. The study showed the suitability of GVL for spruce biorefining to achieve high recovery of digestible cellulose, lignin and hemicelluloses fractions, that are subsequently valuable for chemicals and fuels production.