Patent ID: 7285181

Claim:
A method of bleaching and brightness stabilization of a lignocellulosic pulp comprising: i) bleaching the lignocellulosic pulp, in an aqueous medium with a water-soluble phosphine or phosphonium compound of formula (A): wherein t is zero or 1; when t=0, R 4 R 5 PY 2 is absent and R 3 is bonded to the P of the R 1 R 2 PY 1 group; when t=1, R 5 is absent such that there is a P—P bond, or R 5 is an alkylene group (CH 2 ) s (s=1 to 12) interrupted by 0 to 6 oxygen (O) atoms or secondary amino (NR′) groups, and/or substituted by a zero to 2s number of a hydroxyl, alkyl, aryl, thio, thioether, amino, ester, amide, carboxyl and/or carboxylate groups, or a phenylene group substituted by a zero to 4 number of a hydroxyl, alkyl, aryl, thio, thioether, amino, ester, amide, carboxyl, carboxylate, and/or sulfonate groups; m is an integer of 0 to 5 and y is an integer of 1 or more, and n and z are integers of 0 or more such that yn=zm; when y=1, and n=z=m=0, then X is absent; R 1 , R 2 and R 3 , or R 1 , R 2 , R 3 , R 4 and R 5 groups are collectively selected such that said compound of formula (A) has an overall solubility of at least 0.01 g/L; R 1 , R 2 and R 3 , or R 1 , R 2 , R 3 and R 4 are independently selected from hydrogen, optionally substituted linear or branched alkyl groups, or optionally substituted aryl groups, the optional substitution being the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties; and Y 1 and Y 2 are independently absent or a carboxylate moiety; or when X is present, X is an inorganic or organic anion, and the value of m is ≦5; the total charge of yn=zm; and Y 1 is a hydroxymethyl group (CH 2 OH); R 1 , R 2 and R 3 , or R 1 , R 2 , R 3 , R 4 and Y 2 are independently selected from hydrogen, boron trifluoride (BF 3 ), optionally substituted linear or branched alkyl groups, or optionally substituted aryl groups, the optional substitution being the presence of substituents selected from ether, amino, hydroxy, ester, thioether, amide, carbonyl, carboxyl, and carboxylate moieties; and ii) stabilizing the brightness in the resulting bleached lignocellulosic pulp with said compound of formula A of said bleaching in step i).