| abstract |
In the process for chlorine-free bleaching of pulps by means of ozone, a pulp suspension is contacted at a temperature of 15 - 80 DEG C, preferably 40 - 70 DEG C, and at a pH of 1-8, preferably 2-3, with an ozone-containing gas, while vigorously stirring or mixing. The ozone-containing gas contains 20-300 g/m<3>, preferably 50-150 g/m<3>, of ozone. At most 2% by mass, preferably 0.05 - 0.5% by mass, of ozone is used relative to absolutely dry pulp. In order to make this process suitable for a pulp suspension in the medium consistency (MC) range, i.e. for a pulp suspension having a stock consistency of 3 - 20% by mass, preferably 5 - 20% by mass and especially 7 - 15% by mass, the ozone-containing gas is introduced according to the invention under a pressure of 1 - 15 bar, preferably 1.1 - 10 bar, into the pulp suspension. The process can also be carried out in a multi-stage bleaching process once or several times. <IMAGE> |