High Purity Softwood Lignin Obtained by an Eco-Friendly Organosolv Process

Organosolv processes provide access to less degraded and higher purity lignins. However, these are rarely applied to softwood species with high lignin contents and complex condensed structures. We are presenting here the results of an optimized organosolv process, allowing for a high extraction yield of organosolv lignin from black spruce (Picea mariana), while preserving a good solid cellulose recovery. Optimized conditions are 70% ethanol liquor with a ratio of 1:10 (wood:liquor) and 5% FeCl3.6H2O as catalyst, treated in a Parr reactor for 90 min at 180 °C. The cellulosic pulp was then extracted with pure ethanol to recover the 2nd lignin. This 2nd lignin was darker in colour and denser than the 1st lignin obtained by precipitation from residual liquor. The other lignin properties were almost identical. The total lignin recovery averaged at 74% (with a purity of 97%), the highest result for lignin recovery from softwoods published so far.