| abstract |
We propose a process for bleaching cellulose without the use of chlorine, with an ozone shift in the cellulose suspension, at a temperature of 15 to 80 C, preferably 40-70 C and at a pH of 1-8, preferably 2-3, with an ozone-containing gas shift, with vigorous stirring. The ozone-containing gas contains 20-300 g / m, preferably 50-150 g / m ozone. A maximum of 2% by weight, preferably 0.05-0.5% by weight of ozone, based on absolutely dry cellulose is added. That this process is suitable for medium-consistency cellulose suspensions (sk) -field, i. for a cellulose suspension with a density of 3-20% by weight, preferably 5-20% by weight, in particular 7-15% by weight, ozone-containing gas is introduced at a pressure of 1-15 bar, preferably 1.1-10 bar, into the cellulose suspension. The process can also be performed in a multi-stage bleaching process one or more times (Figure la). |