Process for extracting lignin from lignocellulosic material using an aqueous organic solvent and an acid neutralizing agent

A process for extracting lignin from lignocellulosic material to recover reactive lignin and to yield high quality cellulosic pulp, which comprises the steps of:

• (a) impregnating lignocellulosic material with a liquor which comprises an aqueous organic solvent, capable of solvating lignin, and an acid neutralizing agent;
• (b) cooking the lignocellulosic material in its liquor by heating the liquor with the impregnated lignocellulosic material submerged therein from a temperature of about 150.degree. C. through a temperature range of 150.degree.-175.degree. C. to a selected maximum temperature in the maximum temperature range of 200.degree. C. to 280.degree. C. and then cooling the liquor with material submerged therein to a temperature of less than about 150.degree. C.;
• (c) maximizing reactive lignin solvation while suppressing cellulose degradation during step (b) by:
• i. controlling the amount of neutralizing agent in step (a) and controlling the time at which the liquor with the impregnated resin is within the temperature range of 150.degree.-175.degree. C. to a range of 4-10 minutes to achieve a pH for step (b) of from 6.0 to 8.0 in the liquor before heating above 175.degree. C. in step (b), and
• ii. controlling the time at which the liquor is at the selected maximum temperature during step (b) in inverse relation to the selected maximum temperature so that the time at which the liquor is held at the selected maximum temperature of 200.degree. C. is at least about 25-30 minutes and for correspondingly lesser times at selected maximum temperatures greater than 200.degree. C. by rapidly cooling the liquor from the selected maximum temperature to said temperature of less than about 150.degree. C. to terminate step (b);
• and
• (d) recovering reactive lignin and high quality cellulose pulp from the cooled liquor.