WO2011098599A1

WO2011098599A1 - Method for pulp bleaching

Info

Publication number: WO2011098599A1
Application number: PCT/EP2011/052129
Authority: WO
Inventors: Thierry Jules Guilmin; Patrick NOTTÉ
Original assignee: Dequest Ag
Priority date: 2010-02-12
Filing date: 2011-02-14
Publication date: 2011-08-18
Also published as: RU2012137954A; JP2013519801A; EP2534296A1; BR112012020292A2; CA2789180A1; US20130042986A1

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.

Description

Method for Pulp Bleaching

This invention pertains to a method of pulp bleaching wherein pulp is bleached in an aqueous medium by means of an oxidative or reducing bleaching agent in the presence of an amino acid alkyl phosphonic acid or a neutralized version thereof. In particular, the pulp is treated with an additive level of the bleaching agent in the presence of an additive level of a narrowly defined amino acid alkyl phosphonic acid at a temperature in the range from about 30 to 100°C for a period of 1 minute to 8 hours. The method was found to yield particularly beneficial results in the event the bleaching agent is an oxidative bleach whereby the treatment is applied at a pH in the range of from 8-13.

Pulp bleaching technology broadly has been around for a long time and has found considerable commercial application. Alkyl phosphonic acids have been used in the very domain with mitigated success. Actually, the most preferred phosphonic acid compounds for use in pulp bleaching technology is said to be diethylene triamino penta (methylene phosphonic acid) (DTPMP) . There was a considerable and standing desire to develop improved bleaching approaches.

US 2008/0115692 pertains to a method and compositions for improving properties of pulp produced in alkaline chemical pulping processes wherein at least one conventional phosphonate is used. Chinese patent application CN 2008- 10106832 relates to a method for preparing stabilizer composition for hydrogen peroxide used in paper pulp bleaching. The alkaline stabilizer composition containing EDTA, polyacrylic acid, nitrilotriacetic acid, hydroxyethylidene diphosphonic acid and sodium hydroxide can serve to reduce the decomposition of hydrogen peroxide to below 20%. The use of solutions of poly ( -hydroxyacrylic acid) salt and diethylene triamine penta-acetate having a pH of 3-8 as stabilizers in the hydrogen peroxide bleaching of fibre and paper pulp products is described in JP 1993-182234.

WO 2009/092738 and EP 2 082 991 pertain to the use of aqueous medium under substantial exclusion of metal ion interference. A selected phosphonic acid is used for the effective immobilization of metal ions. WO 99/46441 concerns a method for bleaching paper pulp with the aid of per oxidized oxidants consisting, inter alia, by pretreating the paper pulp under alkaline conditions by means of an aspartic acid chelating agent. US 5,759,440 describes a method for stabilizing an aqueous hydrogen peroxide solution by means of a pyrophosphate salt and an aminopolycarboxylic acid. The stabilized solution can be used for pulp bleaching.

WO 2008/086937 discloses a process for pulp bleaching comprising adding an amino phosphonate in combination with an oxidative bleaching agent. WO 00/68396 discloses a pulp bleaching agent, where the active ingredient is a XA protein type xylanase. US 4,372,811 disclose a process for pulp bleaching, where one or more aromatic diamines are added to inhibit degradation of carbohydrates in the pulp.

The search for novel technologies as e.g. shown by the art recitations has not yielded superior technologies capable of meeting expectations and desires. Indeed significant hurdles inclusive of active peroxide losses in oxidative pulp bleaching and effective heavy metal ion control remain obstacles, can be fairly expensive and can yield reduced performance. In addition, leading phosphonates currently used e.g. DTPMP tend to exhibit reduced bleaching activity at higher pH e.g. above 11 and contribute to undue peroxide decomposition .

It is a major object of this invention to generate superior pulp bleaching technology. It is another object of this invention to provide superior oxidative pulp bleaching technology characterized, in particular, by significantly reduced active peroxide losses. Still another object of this invention contemplates generating pulp bleaching technology with a significantly improved metal ion control and immobilization. Yet another object of this invention aims at securing pulp bleaching technology capable of yielding pulp products having markedly superior physical properties as compared to what can be achieved from using the art technology.

The term "percent" or "%" as used throughout this application stands, unless defined differently, for "percent by weight" or "% by weight". The terms "phosphonic acid" and "phosphonate" are also used interchangeably depending, of course, upon medium prevailing alkalinity/acidity conditions. The term "ppm" stands for "parts per million". The terms "phosphonic acid" and "phosphonate" are used interchangeably depending upon medium prevailing alkalinity/acidity conditions. The terms "pulp" and "pulp consistency" are used interchangeably. Unless defined differently, pH values are measured at 25 °C on the reaction medium as such. The term amino acid stands for amino acids in their D, L and DL forms as well as mixtures of the D and L forms. The term "aromatic" hydrocarbon radical or moiety preferably includes aryl and heteroaryl groups.

The above and other objects can now be met by using a novel bleaching arrangement whereby the bleaching treatment is carried out in the presence of an amino acid alkyl phosphonic acid. In more detail the inventive method herein concerns pulp bleaching comprising the steps of:

-treating 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 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;

-adding an amino acid alkyl phosphonic acid or a salt, i.e. a neutralized version, thereof having a formula selected from: A¹-(B)_y; and

A²- (B)_y; wherein A¹ and A² have the formula:

A¹ = HOOC-A-NH₂; and

A² = HOOC-C (NH₂) (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 C2-C20 linear, branched, cyclic and aromatic hydrocarbon radicals, optionally substituted by one or more C₁-C₁2 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 NH₂ moieties; R and R^' are independently selected from C₁-C₂₀ linear, branched, cyclic and aromatic hydrocarbon radicals, optionally substituted by one or more C1-C12 linear, branched, cyclic and/or aromatic groups, NH₂ and/or COOH, and one of R or R' can be hydrogen; whereby the neutralizing agent to obtain the salt is preferably selected from ammonia, alkali hydroxide, earth- alkali hydroxide and amine whereby the amine preferably has the general formula

(X)_b[N(W) (H)₂-b]_z wherein X is selected from C1-C2₀₀₀₀₀ linear, branched, cyclic or aromatic hydrocarbon radicals, optionally substituted by one or more C₁-C₁₂ linear, branched, cyclic or aromatic groups which radicals and/or which groups are optionally substituted by OH, COOH, COOG, F, Br, CI, I, OG, S0₃H, S0₃G and/or SG moieties; H; [V-N(H)]_X-H ; [V-N(Y)]_n-V; [V-0]_x-V; wherein V is selected from: C₂-50 linear, branched, cyclic or aromatic hydrocarbon radicals, optionally substituted by one or more Ci- ₁₂ linear, branched, cyclic or aromatic groups, which radicals and/or groups are optionally substituted by OH, COOH, COOR' ' , F/Br/Cl/I, OR'', S0₃H, S0₃R' ' and/or SR" moieties, wherein R" is a Ci-₁₂ linear, branched, cyclic or aromatic hydrocarbon radical, wherein G is selected from C1-C200000 linear, branched, cyclic or aromatic hydrocarbon radicals, optionally substituted by one or more C1-C₁₂ linear, branched, cyclic or aromatic groups, which radicals and/or which groups are optionally substituted by OH, COOH, COOR'', F, Br, CI, I, OR", SO3H, SO₃R" and/or SR" moieties; H; [V-N(H)]_n-H; [V- N(Y)]_n-V or [V-0]_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=l when b=0; and X is [V-N(H)]_X-H or [V-N(Y)]_n-V when z=0 and b=l; with the proviso of excluding: compounds wherein R and/or R^' are 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 O₂, CN, COOH, SO₃H, OH and halogen, and with the further proviso that when:

A is L-lysine, at least one L-lysine amino radical carries 2 (two) alkyl phosphonic acid moieties; and when

A² 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, expressed on the basis of the reaction products; said amino acid alkyl phosphonic acid compound being added in a level of from 0.01% to 6% by weight, expressed on the level of the dry pulp (100%); said bleaching treatment being conducted at a temperature from 30°C to 100°C for a period of from 1 minutes to 8 hours. A first essential amino acid alkyl phosphonic acid for use in the method of this invention can be represented by the formula : A¹-(B)_Y wherein A¹ has the formula

HOOC-A-NH2 wherein A is independently selected from C2-C2₀ linear, branched, cyclic and aromatic hydrocarbon radicals, optionally substituted by one or more C₁-C₁2 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 N¾ moieties. In a preferred execution, A is represented by a C2-C1 linear hydrocarbon chain, optionally, and preferably, substituted by 1 to 3 N¾ moieties. The selection of any number of carbon atoms in the hydrocarbon chain can constitute a desirable execution depending upon the choice of additional optional groups and/or optional moieties. The actual determination of preferred combinations is a routine measure, well known in the domain of the technology. A second essential amino acid alkyl phosphonic acid for use in the method of this invention can be represented by the formula :

( B ) y wherein A² has the formula

HOOC-C (NH₂) (R) (R ) wherein R and R^' are independently selected from C1-C20 linear, branched, cyclic and aromatic hydrocarbon radicals, optionally substituted by one or more C₁-C₁2 linear, branched, cyclic and/or aromatic hydrocarbon groups, which radicals and/or groups are optionally substituted by one or more OH, N¾ and/or COOH moieties, and one of R or R' can be hydrogen.

In a preferred execution of the method herein, the amino acid in the phosphonate inhibitor A² can be represented by D,L- alanine wherein y is 2, L-alanine wherein y is 2, L-lysine wherein y is in the range of from 2 to 4, L-phenylalanine wherein y is 2, L-arginine wherein y is in the range of from 2-6, 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.

It was found that the L-glutamic acid alkylene phosphonic acid compound as such is, because of insufficient performance and stability, not suitable for use in the method of this invention. Depending upon the formation reaction conditions, the L-glutamic acid alkylene phosphonic acid resulting from the methylenephosphonation of L-glutamic acid can be represented by a substantially binary mixture containing, based on the mixture (100%), a majority of a mono-methylene phosphonic acid derived from a carboxylic acid substituted pyrrolidone and a relatively smaller level of a dimethylene phosphonic acid glutamic acid compound. It was found that, in one beneficial embodiment the reaction product frequently contains from 50 % to 90 % of the pyrrolidone carboxylic acid N-methylene phosphonic acid scale inhibitor and from 10 % to 50 % of the L-glutamic acid bis (alkylene phosphonic acid) compound. The sum of the diphosphonate and monophosphonate inhibitors formed during the reaction frequently exceeds 80 %, based on the glutamic acid starting material. The binary mixture can also be prepared by admixing the individual, separately prepared, phosphonic acid compounds. In another preferred execution, the L-lysine carrying one alkylene phosphonic acid group attached to amino radical (s) represents not more than 20 molar % of the sum of the L-lysine carrying one and two alkylene phosphonic acid groups attached to amino radical (s) . In another preferred execution, the L-lysine alkylene phosphonic acid is represented by a mixture of L- lysine carrying two alkylene phosphonic acid groups attached to (individual) amino radical (s) (lysine di) and L-lysine carrying four alkylene phosphonic acid groups (lysine tetra) whereby the weight ratio of lysine tetra to lysine di is in the range of from 9 : 1 to 1 : 1, even more preferred 7 : 2 to 4 : 2.

Preferred aminoacids in the A phosphonate inhibitors include 7-aminoheptanoic acid, wherein x is 2, 6-aminohexanoic acid, wherein x is 2, 5-aminopentanoic acid, wherein x is 2, 4-amino butyric acid, wherein x is 2 and β-alanine wherein x is 2. Preferred aminoacids in the phosphonate inhibitors A¹ can be prepared beneficially starting from lactams or other conventionally known materials; 7-aminoheptanoic acid can be used instead of 2-azacyclooctanone to make the corresponding diphosphonate . The preferred aminoacid starting materials are illustrated in the examples hereinafter. In short, a mixture of stoichiometric proportions of the starting material aminoacid (1 mole), phosphorous acid (2 moles), aqueous hydrochloric acid (1.2 moles) is heated under stirring to 100 °C, the formaldehyde (2 moles) is then gradually added over a period of 120-140 minutes at a temperature in the range of from 100-120 °C. The reaction mixture is thereafter kept at 105-115 °C for an additional 60-100 minutes. It is understood that the stoichiometric proportions of the starting materials can be varied to meet the desired degree of phosphonic acid substitution by reaction with the available N-H functions.

In another preferred execution herein, the amino acid phosphonate for use in the method of this invention can be represented by selected combinations of the amino acid polyphosphonates in combination with a polyphosphonic acid selected from the group of: (a) amino (poly) alkylene polyphosphonic acids 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. Actually preferred are: aminoalkylene polyphosphonic acids having from 1 to 12 carbon atoms in the alkylene moiety; hydroxyalkylene phosphonic acids containing from 2 to 12 carbon atoms in the alkylene moiety and two phosphonic acid groups; whereas phosphono alkane polycarboxylic acids have a straight chain alkane configuration having from 4 to 8 carbon atoms and wherein the molar ratio of phosphonic acid radical to carboxylic acid radical is in the range of from 1 : 2 to 1 : 4. Particularly preferred are polyphosphonic acids having from 2 to 8 phosphonic acid groups. Individually preferred species were found to include the following: aminotri (methylene phosphonic acid) and its N-oxide; 1-hydroxyethylene ( 1 , 1-diphosphonic acid) ; ethylenediamine tetra (methylene phosphonic acid) ; diethylene triamine penta (methylenephosphonic acid) ; hexamethylene diamine tetra (methylene phosphonic acid) ; hydroxyethyl aminobis (methylene phosphonic acid); N,N'-bis(3- aminopropyl ) -ethylenediamine hexa (methylene phosphonic acid); and butane-2-phosphono-l , 2 , 4-tricarboxylic acid. The weight ratio of amino acid phosphonate to phosphonic acid is in the range of from 98 : 2 to 25 : 75, preferably from 90 : 10 to 50 : 50. A² can be represented by -amino acids including specific natural amino acids such as e.g. occurring in animal species. Amino acids generally are the building blocks of proteins. There are over forty known amino acids about twenty of which are actually contained in e.g. animal tissue. Amino acids can be made by hydrolysis starting from proteins, by enzymatic fermentation and/or by chemical synthesis. This domain of the technology is eminently well known and all the individual technologies are abundantly documented in the literature. Suitable amino acids can be used in their D, D,L, and L forms as well as mixtures of the D and L forms. Preferred a-amino acids for use in the phosphonate inhibitors include: D,L- alanine; L-alanine; L-phenylalanine ; L-lysine; L-arginine; L- methionine; L-cysteine; L-threonine ; and L-glutamic acid. Specific amino acids are excluded as follows:

1. oi-aminoacids wherein R and/or R^' comprise electron rich moieties directly attached to an aromatic moiety. As an example, the reaction of L-tyrosine (1 eq.) (R= p-OH-Phenyl- CH₂; R^'= H) with H₃PO₃ (2 eq.) and formaldehyde (2.2 eq.) in the presence of HC1 (1.5 moles) between 108 and 112 °C does not lead to the corresponding bis (methylene phosphonic acid) . Indeed, ³¹P NMR analysis only shows signals for the starting phosphorous acid with traces of phosphoric acid. A water insoluble product is obtained; it is believed to be due to the reaction of formaldehyde with tyrosine resulting in the formation of methylene bridges between aromatic moieties; 2. -aminoacids wherein R and/or R^' comprise aromatics wherein at least one carbon atom has been substituted by a heteroatom. For example, the reaction of L-tryptophan (1 eq.) with H₃PO₃ (2 eq.) and formaldehyde (2.2 eq.) in the presence of HC1 (2.5 moles) between 107 and 111 °C does not lead to the corresponding bis (methylene phosphonic acid) . ³¹P NMR analysis only shows signals for the starting phosphorous acid with traces of phosphoric acid. A water insoluble product is obtained; it is believed to be due to the reaction of formaldehyde with tryptophan resulting in the formation of methylene bridges between aromatic moieties; and

3. oi-aminoacids wherein 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 N0₂, CN, COOH, S0₃H, OH and halogen. As an example, the reaction of L-aspartic acid (1 eq.) (Z=COOH) with H3PO3 (2 eq.) and formaldehyde (2.2 eq.) in the presence of HC1 (1.5 moles) between 110 and 115 °C leads to a complex product mixture including: fumaric acid; imino- bis (methylene phosphonic acid) ; aminotri (methylene phosphonic acid) (ATMP) and L-aspartic acid bis (methylene phosphonic acid) . The latter product has been shown by ³¹P NMR to decompose under the reaction conditions into fumaric acid and imino bis (methylene phosphonic acid) which is itself converted into ATMP. In another example, the reaction of L-serine (1 eq.) (Z=OH) with H₃PO₃ (2 eq.) and formaldehyde (2.2 eq.) in the presence of HC1 (1.5 moles) between 107 and 112 °C leads to a complex product mixture including amino tri (methylene phosphonic acid) (ATMP) and phosphorous acid. ³¹P NMR does not show signals corresponding to the L-serine mono- or di- phosphonates . It is believed that the L-serine phosphonates are unstable and decompose, under the reaction conditions, ultimately leading to ATMP. Specific -aminoacids not suitable for use within the claimed technology are: tyrosine; tryptophan; asparagine; aspartic acid; and serine.

The amino acid alkylphosphonates for use in the inventive method can be prepared by reacting one or more of the available N-H functions of the amino acid with phosphorous acid and formaldehyde, in the presence of hydrochloric acid, in aqueous medium having a pH of generally less than 4 by heating that reaction mixture, at a temperature of usually greater than 70 °C for a sufficient time to complete the reaction. This kind of reaction is conventional and well-known in the domain of the technology and examples of the novel phosphonate compounds have been synthesized, as described below, via the hydrochloric acid route.

In a preferred method, the aminoacid phosphonates can be made under substantial exclusion of hydrohalogenic acid and corresponding by-products and intermediates. Specifically, the aminoacid phosphonates can be manufactured in presence of not more than 0.4 %, preferably less than 2000 ppm, of hydrohalogenic acid, expressed in relation to the phosphorous acid component (100 %) by reacting: (a) phosphorous acid;

(b) an aminoacid; and

(c) a formaldehyde: in reactant ratios of (a) : (b) of from 0.05 : 1 to 2 (c) : (b) of from 0.05 : 1 to 5 : 1; and (c) : (a) of from 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. The aminoacid phosphonates formed can be recovered in a manner known per se. The reaction can also be conducted similarly to the homogeneous catalyst parameter selection in the presence of a heterogeneous catalyst selected from e.g. solid acidic metal oxides as such or deposited onto a carrier; cation exchange resins carrying sulfonic or carboxylic Broensted acid groups; acid catalysts derived from the interaction of a solid support having a lone pair of electrons onto which is deposited an organic Broensted catalyst; the interaction of such support onto which is deposited a compound having a Lewis acid site; heterogeneous solids functionalized by chemical Broensted grafting and heterogeneous phosphorus and silicon containing polyacids.

Pulp is a dry fibrous material prepared by chemically or mechanically separating fibers from wood, fiber crops or waste paper. There are a number of different processes which can be used to separate wood fibers. These processes are very well known in the domain of the technology. The pulp designation can relate to the process used, e.g. known species are: mechanical pulp; thermomechanical pulp; chemithermomechanical pulp; chemical pulp; and recycled pulp, also known as deinked pulp. The pulp so available can be bleached to produce e.g. a white paper product. One objective of bleaching is to improve the brightness and the cleanliness of the pulp product. The bleaching agent can be selected from oxidative bleaches and reductive bleaches which bleaches are used in a level of from 0.5 to 10%, preferably from 1 to 6%, in particular from 2 to 5%, expressed on the basis of the dry pulp (100%) . Well known examples of bleaching agents suitable for use herein include dithionite, boronhydride, chlorine dioxide, peroxomonosulferic acid (H₂SO₅) , formamidine sulfinic acid, activated acid peroxide e.g. molybdate peroxide; oxygen, peroxide reinforced oxygen, hydrogen peroxide, peracids such as peracetic acid and ozone. In general, the oxidative bleaching agent shall not react with the aminoacid phosphonate. Chlorine and hypochlorite can react with the amino acid phosphonate and can not be used in the oxidative bleaching step herein. The oxidative bleaching treatment is generally conducted at a pH in the range of from 8-13, preferably 8-12, in particular 8.5- 10.5. The reductive bleaching treatment is generally carried out at a pH in the range of from 2-6.5, preferably 3-6.5, in particular 4-6.5. The bleaching step requires, evidently, the presence of suitable pH regulants, buffer components and optionally additives conventional and well known in the domain of the technology. The pH can during the oxidative approach be established with the aid of alkaline materials, in particular alkaline hydroxides including sodium and potassium hydroxide, alkaline earth hydroxides including magnesium and calcium hydroxide, silica buffers and also MgS0₄.7H₂0, Epsom salt. The use of regulant combinations of magnesium hydroxides and magnesium salts was found to be beneficial in that it can deliver better alkalinity reserve, compared to e.g. alkali hydroxide alone, under comparable level conditions. As an example, the pH can be adjusted during the oxidative bleaching with the aid of sodium hydroxide whereas sulfuric acid can be used for pH control preparatory to the reductive bleaching step . The pulp is used during the bleaching treatment in a level of from 1 to 40%, preferably from 3 to 30%, in one particular execution from 4 to 25% expressed on the basis of the aqueous medium. These ranges are fairly standard in the relevant technical domain. These ranges can be, and frequently are, slightly different depending upon which bleaching step, oxidative or reductive, is used. The pulp consistency is usually higher for the oxidative bleaching step than for the reducing bleaching step although the respective levels are within the ranges recited herein.

The inventive bleaching treatment is conducted for a period of from 1 minute to 8 hours, preferably from 8 minutes to 6 hours, in particular from 20 minutes to 2 hours at a temperature of from 30 to 100°C, preferably from 40 to 90 °C, in particular from 45 to 80°C. In the process of the invention the sequence of adding the amino acid alkyl phosphonic acid component and the bleaching agent is not fixed. In a preferred embodiment the amino acid alkyl phosphonic acid component is added first. In a further embodiment both components are simultaneously added. Of course it is also possible to add the pulp to the components.

The method herein generally has been practiced extensively for a long time. A summary description can serve as a brief reminder of the known state of the art. The bleaching method herein can embody multiple variations whereby the most common approaches embody single or multiple subsequent stages. As an example, a one-stage bleaching process comprises adding the pulp and the chelant before the pulp thickener followed by a steam mixer where the bleaching agent, frequently a bleach solution, is added. The bleaching can occur in a bleach tower followed by neutralizing before transferring the bleached pulp to the paper machine. As an example of another approach, a two-stage bleaching process is arranged whereby an oxidative bleaching step is followed by a reductive bleaching step. Actually, the oxidative step can be identical to the one-stage process above up to the neutralizing stage. At that time, the reductive bleach is added together with the bleached pulp originating from the first stage, and possibly additional chelant, into a second bleaching tower, e.g. an up flow tower. The bleached pulp is usually kept in a stock chest and can from there be transferred to the paper machine, possibly via a pulp thickener to generate the right pulp consistency. These technologies are well known and any method variation is standard practice.

The potential benefits attached to the application of the technology of this invention is illustrated with the aid of comparative showings as follows.

Performance of the amino acid phosphonates have been compared with traditional products used for the stabilization of the oxidative bleach used in conditions similar to the paper making processes. Products used in this comparison are the diethylene triamino penta- (methylene carboxylic acid) (DTPA) ; diethylene triamino penta- (methylene phosphonic acid) (Dequest^® 2066) and the lysine tetra- (methylene phosphonic acid) ethanolamine salt (Lysine tetraphph) .

A test is conducted as follows: In a three neck flask equipped with a mechanical stirrer, a constant pressure dropping funnel and a tubing connected to a volumetric measuring devise are placed 0.2 g of the test product; 6g of a 32%w/w magnesium hydroxide aqueous slurry; 3g of sodium silicate and lOg of a 1% iron sulfate hepta hydrate in water. Demineralized water is added up to a total weight of 150g. The mixture is heated to 60°C under stirring before addition of 16.7g of a 42% aqueous hydrogen peroxide solution. Volumes of oxygen gas formed after addition of the hydrogen peroxide are recorded on a time basis. Table 1 gives the experimental results where time is expressed in minutes (min) and oxygen volumes in milliliters (ml) .

Table 1- Volumes of oxygen emissions during the 120 min experiment .

Example 1 Comparative Ex. 1 Comparative

Ex.2

ime Oxygen volumes Oxygen volumes (ml) Oxygen volumes (min) (ml ) for Lysine for Dequest 2066 (ml) for DTPA tetraphph

0 0 0 0

2 5 15 5

4 25 60 40

6 45 100 85

8 70 145 130

10 100 195 185

12 125 255 240

14 160 315 295

16 180 370 355

18 200 420 410

20 225 475 475

22 255 530 530

24 280 580 585

26 305 635 640

28 335 685 685

30 360 735 735

32 385 780 780

34 420 825 830

36 435 870 870 38 460 910 915

40 485 955 965

60 750 1310 1315

75 875 1515 1500

90 1015 1665 1655

120 1220 1910 1845

The volume of oxygen gas formed after addition of the hydrogen peroxide is significantly by reduced in the inventive method.

Claims

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:

A¹-(B)_y; and A²-(B)_y; wherein A¹ and A² have the formula:

A¹ = HOOC-A-NH₂; and

A² = HOOC-C (NH₂) (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 C₂ - C₂0 linear, branched, cyclic and aromatic hydrocarbon radicals, optionally substituted by one or more C₁ - C₁₂ 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 NH₂ moieties; R and R^' are independently selected from C₁ - C₂0 linear, branched, cyclic and aromatic hydrocarbon radicals, optionally substituted by one or more C₁ - C₁₂ linear, branched, cyclic and/or aromatic groups, such as phenyl, N¾, H- (C=NH)NH₂, OH, SH, SCH₃, N0₂, CN, S0₃H, halogen, CONH₂ 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 N0₂, CN, COOH, CONH₂, SO3H, OH and halogen, and with the further proviso that when:

A is L-lysine, at least one L-lysine amino radical carries 2 (two) alkyl phosphonic acid moieties; and when A² 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%) ;

-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 amine has the general formula (X)_b[N(W) (H)₂__b]_z wherein X is selected from C₁-C200000 linear, branched, cyclic or aromatic hydrocarbon radicals, optionally substituted by one or more C1-C₁2 linear, branched, cyclic or aromatic groups which radicals and/or which groups are optionally substituted by OH, COOH, COOG, F, Br, Cl, I, OG, S0₃H, S0₃G and/or SG moieties; H; [V-N(H)]_X-H ; [V-N(Y)]_n-V; [V-0]_x-V; wherein V is selected from: C2-50 linear, branched, cyclic or aromatic hydrocarbon radicals, optionally substituted by one or more Ci- ₁2 linear, branched, cyclic or aromatic groups, which radicals and/or groups are optionally substituted by OH, COOH, COOR' ' , F/Br/Cl/I, OR'', S0₃H, S0₃R' ' and/or SR' ' moieties, wherein R' ' is a Ci-₁2 linear, branched, cyclic or aromatic hydrocarbon radical, wherein G is selected from Ci-C2ooooo linear, branched, cyclic or aromatic hydrocarbon radicals, optionally substituted by one or more C₁-C₁2 linear, branched, cyclic or aromatic groups, which radicals and/or which groups are optionally substituted by OH, COOH, COOR'', F, Br, Cl, I, OR", SO₃H, SO₃R" and/or SR" moieties; H; [V-N(H)]_n-H; [V- N(Y)]_n-V or [V-0]_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=l when b=0; and X is [V-N(H)]_X-H or [V-N(Y)]_n-V when z=0 and b=l;

4. The method in accordance with any one of Claims 1 to

3 wherein the aminoacid A¹ 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 A¹ selected from C2-C16 linear hydrocarbon radicals substituted by 1 to 3 N¾ 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 any one of claims 1 to

5, 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 A¹ or A²; 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 any one of Claims 1 to

6 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 any one of Claims 1 to

7 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 any one of Claims 1 to

8 wherein the pulp represents from 3 to 30% by weight.

10. The method in accordance with any one of Claims 1 to 9 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 or 11 wherein the oxidative bleaching is conducted at a pH in the range of from 8.5-10.5.

13. The method in accordance with any one of Claims 1 to

9 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.