Method for pulp bleaching

Abstract

A process for pulp bleaching is disclosed wherein an amino acid phosphonic acid is used together with a bleaching agent, pH regulants and pH buffers for pulp treatment in an aqueous medium. The bleaching agent can be represented by oxidative and reductive bleaching agents. The oxidative bleach treatment is conducted in alkaline medium whereas the reductive treatment is conducted in mildly acid medium.

1 . A method for pulp bleaching comprising the steps of:
 providing an aqueous medium containing from 1% to 40% by weight of the pulp, expressed on the basis of the water in the aqueous medium (100%);   adding an amino acid alkyl phosphonic acid or a salt thereof having a formula selected from:
   A 1 —(B) y ;
 
   
       and
   A 2 —(B) y ;
 
 
       wherein A 1  and A 2  have the formula:
   A 1 =HOOC—A—NH 2 ;
 
 
       and
   A 2 =HOOC—C(NH 2 )(R)(R′)
 
 
       wherein B is an alkylphosphonic acid moiety having from 1 to 6 carbon atoms in the alkyl group and y is an integer of from 1 to 10; A is independently selected from C 2 -C 20  linear, branched, cyclic and aromatic hydrocarbon radicals, optionally substituted by one or more C 1 -C 12  linear, branched, cyclic and/or aromatic hydrocarbon groups, which radicals and/or which groups are optionally substituted by one or more OH, COOH and/or NH 2  moieties; R and R′ are independently selected from C 1 -C 20  linear, branched, cyclic and aromatic hydrocarbon radicals, optionally substituted by one or more C 1 -C 12  linear, branched, cyclic and/or aromatic groups, such as phenyl, NH 2 , NH—(C═NH)NH 2 , OH, SH, SCH 3 , NO 2 , CN, SO 3 H, halogen, CONH 2  and/or COOH, and one of R or R′ can be hydrogen;
 with the proviso of excluding: 
 compounds wherein R and/or R′ comprise electron rich moieties containing, at least, one lone pair of electrons, which moiety is directly attached to an aromatic moiety by a covalent bond; or aromatics wherein at least one of the carbon atoms has been substituted by a heteroatom; and compounds, in the event R is —C(Z)(R′″)(R″″) and R′, R″″ and R″″ are hydrogen wherein Z is an electron withdrawing group selected from NO 2 , CN, COOH, CONH 2 , SO 3 H, OH and halogen, and with the further proviso that when: 
 A 2  is L-lysine, at least one L-lysine amino radical carries 2 (two) alkyl phosphonic acid moieties; and when 
 A 2  is L-glutamic acid, the term glutamic acid phosphonate represents a combination of from 50-90% by weight pyrrolidone carboxylic acid N-methylene phosphonic acid and from 10-50% by weight of L-glutamic acid diphosphonic acid; 
 said aminoacid alkylphosphonic acid compound being added in a level of from 0.01% to 6% by weight, expressed on the level of the dry pulp (100%); 
 adding a bleaching agent, selected from oxidative bleaches and reducing bleaches, in an amount from 0.5% to 10% by weight, expressed on the basis of the dry pulp (100%), and bleaching additives selected from pH regulants and buffer components to conduct the oxidative bleaching treatment at a pH of from 8 to 13 and the reductive bleaching treatment at a pH of from 2 to 6.5; 
 and conducting a bleaching treatment at a temperature from 30° C. to 100° C. for a period of from 1 minutes to 8 hours. 
 
     
     
         2 . The method in accordance with  claim 1 , wherein the salt of the amino acid alkyl phosphonic acid is generated with a neutralizing agent selected from ammonia, alkali hydroxides, earth-alkali hydroxides and amines. 
     
     
         3 . The method in accordance with  claim 2 , wherein the neutralizing agent is selected from amines having the general formula
   (X) b [N(W)(H) 2-b ] z      
       wherein X is selected from C 1 -C 200000  linear, branched, cyclic or aromatic hydrocarbon radicals, optionally substituted by one or more C 1 -C 12  linear, branched, cyclic or aromatic groups which radicals and/or which groups are optionally substituted by OH, COOH, COOG, F, Br, Cl, I, OG, SO 3 H, SO 3 G and/or SG moieties; H; [V—N(H)] x —H ; [V—N(Y)]—V; [V—O] x —V; wherein V is selected from: C 2-50  linear, branched, cyclic or aromatic hydrocarbon radicals, optionally substituted by one or more C 1-12  linear, branched, cyclic or aromatic groups, which radicals and/or groups are optionally substituted by OH, COOH, COOR″, F/Br/Cl/I, OR″, SO 3 H, SO 3 R″ and/or SR″ moieties, wherein R″ is a C 1-12  linear, branched, cyclic or aromatic hydrocarbon radical, wherein G is selected from C1-C 200000  linear, branched, cyclic or aromatic hydrocarbon radicals, optionally substituted by one or more C 1 -C 12  linear, branched, cyclic or aromatic groups, which radicals and/or which groups are optionally substituted by OH, COOH, COOR″, F, Br, Cl, I, OR″, SO 3 H, SO 3 R″ and/or SR″ moieties; H; [V—N(H)] n —H; [V—N(Y)] n —V or [V—O] x —V; wherein Y is H, [V—N(H)] n —H or [V—N(H)] n —V and x is an integer from 1-50000, n is an integer from 0 to 50000; z is from 0-200000 whereby z is equal to or smaller than the number of carbon atoms in X, and b is 0 or 1; z=1 when b=0; and X is [V—N(H)] x —H or [V—N(Y)] n —V when z=0 and b=1. 
     
     
         4 . The method in accordance with  claim 1  wherein the aminoacid Al in the aminoacid alkylphosphonic acid is selected from:
 D,L-alanine wherein y is 2; 
 L-alanine wherein y is 2; 
 L-phenylalanine wherein y is 2; 
 L-lysine wherein y is in the range from 2 to 4; 
 L-arginine wherein y is in the range from 2 to 6; 
 L-threonine wherein y is 2; 
 L-methionine wherein y is 2; 
 L-cysteine wherein y is 2; and 
 L-glutamic acid wherein y is 1 to 2; and 
 from moieties A in the aminoacid phosphonic acid A 1  selected from C 2 -C 16  linear hydrocarbon radicals substituted by 1 to 3 NH 2  moieties. 
 
     
     
         5 . The method in accordance with  claim 4  wherein the amino acid phosphonic acid is selected from:
 7-aminoheptanoic acid; 
 6-aminohexanoic acid; 
 5-aminopentanoic acid; 
 4-aminobutyric acid; and 
 β-alanine; 
 whereby y is 2 in each of such species. 
 
     
     
         6 . The method in accordance with  claim 1 , wherein the amino acid alkyl phosphonic acid is made in the presence of not more than 0.4% of hydrohalogenic acid, expressed in relation to the phosphorous acid component (100%) by reacting:
 (a) phosphorous acid;   (b) an amino acid of formula A 1  or A 2 ; and   (c) formaldehyde:   in reactant ratios of (a):(b) of from 0.05:1 to 2:1; (c):(b) of from 0.05:1 to 5:1; and (c):(a) of from 5:1 to 0.25:1;   wherein (a) and (c) stand for the number of moles to be used and (b) represents the number of moles multiplied by the number of N—H functions in the amine, in the presence of an acid catalyst having a pKa equal or inferior to 3.1, said catalyst being homogeneous with respect to the reaction medium and being used in reactant ratios as follows:   (b):(d) of from 40:1 to 1:5;   wherein (d) stands for the number of moles of catalyst multiplied by the number of available protons per mole of catalyst.   
     
     
         7 . The method in accordance with  claim 1 , wherein, in addition to the amino acid alkyl phosphonic acid, a polyphosphonic acid is added, said polyphosphonic acid being selected from the group of
 (a) aminopolyalkylene polyphosphonic acid 5 wherein the alkylene moiety contains from 1 to 20 carbon atoms;   (b) hydroxyalkylene polyphosphonic acids wherein the alkylene moiety contains from 2 to 50 carbon atoms; and   (c) phosphono alkane polycarboxylic acids wherein the alkane moiety is in straight chain configuration containing from 3 to 12 carbon atoms;   in a weight ratio of amino acid alkyl phosphonic acid to polyphosphonic acid in the range of from 98:2 to 25:75.   
     
     
         8 . The method in accordance with  claim 1 , wherein the bleaching treatment is conducted at a temperature of from 40 to 90° C. for a period of from 8 minutes to 6 hours. 
     
     
         9 . The method in accordance with  claim 1 , wherein the pulp represents from 3 to 30% by weight. 
     
     
         10 . The method in accordance with  claim 1  wherein the bleaching agent is an oxidative bleach selected from hydrogen peroxide, oxygen, peroxide reinforced oxygen, chlorine dioxide, ozone and peracids, said bleaching agent being added at a level from 1% to 6% by weight, said aqueous medium having a pH of from 8 to 12. 
     
     
         11 . The method in accordance with  claim 10  wherein the oxidative bleaching is conducted at a pH of from 8-12 regulated with the aid of magnesium hydroxide, silicate buffer and/or Epsom salt. 
     
     
         12 . The method in accordance with  claim 10  wherein the oxidative bleaching is conducted at a pH in the range of from 8.5-10.5. 
     
     
         13 . The method in accordance with  claim 1 , wherein the bleaching agent is a reducing bleaching agent selected from the group of dithionite, formamidine sulfinic acid and boronhydride. 
     
     
         14 . The method in accordance with  claim 13  wherein the reductive bleaching is conducted at a pH of from 4-6.5.