| abstract |
In the process for the chlorine-free bleaching of pulps by means of ozone, a pulp suspension is brought into contact with an ozone-containing gas, with vigorous stirring or mixing, at a temperature of 15 - 80 degree C, preferably 40 - 70 degree C, and at a pH of 1 - 8, preferably 2 - 3. The ozone-containing gas contains 20 - 300 g/m3, preferably 50 - 150 g/m3, of ozone. A maximum of 2% by mass, preferably 0.05 - 0.5% by mass, of ozone is used, based on bone-dry pulp. In order to make this process suitable for a pulp suspension in the medium consistency (MC) range, that is to say for a pulp suspension at a consistency of 5 - 20% by mass, especially 7 - 15% by mass, according to the invention the ozone-containing gas is introduced into the pulp suspension at a pressure of 1.1 - 15 bar, preferably 1.1 - 10 bar. The process can also be carried out once or many times in a multi-stage bleaching process. |