Patent ID: 7976582

Claim:
A method of bleaching a cellulose material comprising the following steps: treating the cellulose material with an non-buffered aqueous solution having an initial pH from 8 to 11, the aqueous solution comprising: (i) a preformed transition metal catalyst having a concentration from 0.1 to 100 micromolar, wherein the preformed transition metal catalyst is a mononuclear or dinuclear complex of a Mn(III) or Mn(IV) transition metal catalyst, and the ligand of the transition metal catalyst is of formula (I): p is 3; R is independently selected from: hydrogen, C1-C6-alkyl, CH 2 CH 2 OH, and CH 2 COOH, or one of R is linked to the N of another Q via an ethylene bridge; R1, R2, R3, and R4 are independently selected from: H, C1-C4-alkyl, and C1-C4-alkylhydroxy, and (ii) from 5 to 1500 mM of hydrogen peroxide; and maintaining the pH of the aqueous solution within an operating window such that the initial pH does not decrease by more than 1.5 pH units during the treating step, wherein maintaining the pH comprises a process selected from the group consisting of: (a) pretreating the cellulose material, wherein the cellulose material is treated with NaOH at a pH from 11 to 12 for between 2 and 120 min at a temperature in the range from 50 to 110° C. in the absence of the preformed transition metal catalyst; lowering the pH to the range from 9 to 11; and then adding the non-buffered aqueous solution to treat the cellulose material for between 2 and 60 min at 50 to 110° C.; (b) adjusting the pH of the non-buffered aqueous solution in the presence of NaOH and an organic sequestrant selected from an aminophosphonate sequestrant or a carboxylate sequestrant to a pH in the range from 10 to 11; to treat the cellulose material; and (c) adding aqueous NaOH during the treating step to maintain the pH within the operating window.