Patent ID: 7396434

Claim:
A method for producing pulp and lignin from lignocellulosic material, the pulp comprising cellulose, the method comprising: contacting the lignocellulosic material with an aqueous acid solution to impregnate the lignocellulosic material, the aqueous acid solution comprising from about 10% to about 40% by weight of the acid and further comprising ammonium hydroxide; heating the lignocellulosic material to a temperature that is at or above the boiling point of the aqueous acid solution to distill off the aqueous acid solution, without substantially degrading the cellulose or lignin in the lignocellulosic material; contacting the lignocellulosic material with an aqueous alkaline solution under heat to solubilize lignin in the alkaline solution, leaving a black liquor; removing the pulp from the black liquor; adding sufficient acid to the black liquor to precipitate the lignin; and removing the lignin from the liquor.