Lignin concentration and fractionation from ethanol organosolv liquors by ultra- and nanofiltration

Biorefineries, especially lignocellulosic feedstock biorefineries may play a major role for sustainable production in the future. In the presented work, findings of four separate studies were combined. These experimental and process simulation works included one study regarding the production of organosolv liquors to investigate lignin and carbohydrate solubilization and the precipitation of lignins, a process simulation of the whole organosolv process to investigate possibilities for process integration, energy and chemicals savings, a third study investigating the nanofiltration behavior of organosolv liquors, which were approximated with synthetic solutions of kraft lignin and glucose, and a study on lignin fractionation by membrane processes. The focus lies on the possibilities of concentrating the organosolv liquor by nanofiltration for lignin separation and production. Ethanol organosolv liquor with a lignin concentration of 9.1 g/L and a total monomeric sugar concentration of 61.8 mg/L was produced by ethanol organosolv treatment at 180 °C. The synthetic liquors, which resembled these conditions the most, had concentrations of 1.1 wt% lignin and 0.02 wt% glucose. With the model liquor, a lignin rejection of ca. 99 % was reached. In the process simulation, which was based on earlier results, a lignin rejection of 90 % was used. This would mean a much lower “loss” of lignin to the permeate and a higher lignin yield in the precipitation step, while chemicals demand could be reduced for up to 78 %. The results show, that membrane preconcentration and precipitation is a viable combination of unit operations for a lignocellulose biorefinery process. •Solutions of organosolv and Kraft lignin were filtrated by nano- and ultrafiltration.•Lignin concentration had a significant influence on transmembrane flux.•Membrane soaking in ethanol had no significant effect on lignin rejection.•The majority of the organosolv lignin had a molecular weight below 1000 Da.