Process for the chlorine-free bleaching of cellulosic materials with ozone

A process for the chlorine free bleaching of pulps in an aqueous suspension which comprises:

• (a) forming said suspension with a consistency of 3 to 20 mass percent;
• (b) introducing into said suspension an ozone-containing gas having an ozone content of 20 to 300 g/m.sup.3 in an amount corresponding to at most 2 mass percent ozone calculated on dry pulps of said suspension during vigorous agitation in a high shear mixer of the suspension to react with the suspension forming a reaction mixture;
• (c) maintaining a pressure of said ozone-containing gas at a pressure of 1.1 to 15 bar during introduction into the suspension;
• (d) transferring the suspension of the ozone-containing gas from the high shear mixer to a tube reactor and continuing the reaction of the suspension and the ozone-containing gas, while maintaining the pressure of the ozone-containing gas at 1.1 to 15 bar;
• and
• (e) controlling reaction conditions during contact of the ozone-containing gas with the suspension during steps (b), (c) and (d) to maintain a reaction temperature of 15.degree. to 80.degree. C., a pH of 1 to 8, and a volume ratio of gas:liquid in said reaction mixture of 1:2.5 to 1:6.