Two stage pulp bleaching process - by ozone bleaching of acidified pulp at high consistency, diluting to lower consistency, and making alkaline for peroxy bleaching

摘要

Pulp bleaching process comprises (a) bleaching the pulp with ozone at an acid pH and a consistency of ca. 20-45%, (b) reducing the consistency of the acid ozone-treated pulp by the addn. of water without raising the pH to 7 or more, and allowing the pulp to stand in this state for at least 10; and (c) adding sufficient alkali to raise the pH over 7 so as to cause peroxy bleaching of the pulp without adding peroxy type chemical bleaching agents. By introducing stage (b), the peroxy functions formed in the system during the acid ozone treatment are not destroyed, so that alkaline peroxy type bleaching can be carried out subsequently without the addn. of further chemical agents.