Organosolv extraction of softwood combined with lignin-to-liquid-solvolysis as a semi-continuous percolation reactor

As part of a concept for a continuous biorefining process, a fractionation procedure for lignocellulosic biomass based on flow-through organosolv lignin solubilisation has been developed and tested. Lignin is removed from the biomass in a continuous flow-through system, producing a dissolved lignin fraction and a residual fibre fraction rich in cellulose. A solvent system comprising ethanol, water and sulfuric or formic acid as catalyst is tested over a 413–468 K temperature range. Process conditions that are suitable for fractionation of softwood from Norway spruce are determined using an experimental design. The best conditions give yields up to 86% of the initially determined lignin mass, leaving a clean fibre residue that corresponds to 67% of the initial cellulose mass. The produced lignin fraction can be converted by formic acid assisted solvolysis to a liquid comprising mostly methoxy-phenols at nearly 90% mass yield. The results show that the continuous flow fractionation of lignocellulosic biomass is a promising route for biorefinery processing. - Highlights: • Semi-continuous organosolv fractionation of biomass providing lignin yields of ≤86% based on lignin mass in feedstock. • Optimal fractionation and lignin recovery with solvent ratio 63:37 EtOH:H₂O (mass ratio) and [6.00 mol m⁻³] H₂SO₄, at 448 K. • Formic acid assisted solvolytic thermochemical conversion of lignin to bio-oil (LtL) providing conversion yields of ∼90%.