Methods for treating lignocellulosic materials

A method of producing a high purity lignin from a biomass, comprising:

• (i) removing an acidic hemicellulose sugar stream from the biomass, thereby obtaining a lignin-containing remainder;
• wherein the lignin-containing remainder comprises lignin and cellulose;
• (ii) providing a two-phase lignin extraction solution comprising water and a limited-solubility solvent, wherein the limited-solubility solvent is a ketone comprising 4 to 8 carbon atoms and having a solubility in water of no more than 30 weight percent at 20° C., wherein the two phases of the lignin extraction solution are an organic liquid phase and an aqueous liquid phase;
• (iii) combining the lignin-containing remainder with the two-phase lignin extraction solution at a temperature of between 160° C. to 200° C. and a pressure of between 1 megaPascal and 10 megaPascal to produce a lignin extract and a cellulosic remainder, wherein the lignin extract comprises the lignin and the organic liquid phase, and wherein the cellulosic remainder comprises the cellulose and the aqueous liquid phase;
• and
• (iv) separating the lignin extract from the cellulosic remainder.