Delignification of lignocellulosic material with an alkaline liquor in the presence of a cyclic keto compound

A process for the delignification of lignocellulosic material comprising the steps of

• 1. treating the lignocellulosic material in a closed reaction vessel with an alkaline pulping liquor containing from 0.001% to 10.0% by weight based on the lignocellulosic material, of a cyclic keto compound selected from the group consisting of naphthoquinone, anthraquinone, anthrone, phenanthrenequinone, the alkyl, alkoxy and amino derivatives of said quinones, 6,11-dioxo-1H-anthra-[1,2-c]pyrazole, anthraquinone-1,2-naphthacridone, 7,12-dioxo-7,12-dihydroanthra[1,2-b]pyrazine 1,2-benzanthraquinone and 10-methylene anthrone, the treatment taking place at a maximum temperature in the range of from 150.degree. C. to 200.degree. C. for a period of 0.5 to 480 minutes, and
• 2. displacing the pulping liquor from the lignocellulosic material with water or an aqueous liquor inert to the lignocellulosic material to obtain a delignified cellulosic material.