Delignification of cellulosic raw materials using acetic acid, nitric acid and ozone

A process for the delignification of lignocellulose-containing raw materials utilizing in a first stage a weight ratio of the lignocellulose-containing raw material to a pulping solution containing aqueous monocarboxylic acid of between 0.08:1 to 0.5:1, with a water content in the pulping solution of 5 to 50% by weight, a temperature of between 140.degree. and 230.degree. C. under a pressure of 3 to 30 bar and with a residence time of between 0.5 and 8 hours, followed by a subsequent extraction or washing treatment, said process being further characterized by treatment of the thus-obtained monocarboxylic acid-moist pulp with a pulping solution having a composition corresponding to the pulping solution used in the first stage, with addition of nitric acid at a weight proportion of 0.5 to 5.0% by weight / atro of the raw material at a temperature of 60.degree. to 140.degree. C. and under a pressure of 1 to 6 bar and a residence time of 0.1 to 6 hours, and subsequent washing or extraction with water or with the pulping solution in a second stage and thereafter in a third stage effecting treatment of the resulting monocarboxylic acid-moist pulp in a consistency range of 3 to 60% by weight in a liquid phase corresponding to the composition of the pulping solution of the first stage with an ozone-containing gas under a pressure of 1 to 12 bar and at a temperature of 15.degree. to 50.degree. C. with an amount of ozone of 0.1 up to 2.5% by weight based on the atro weight of the raw material to produce a pulp with a lignin content of less than 1% by weight;

• said monocarboxylic acid comprising a C.sub.1 -C.sub.4 aliphatic monocarboxylic acid or a mixture thereof.