DE19620241A1 - Process for delignifying pulps and using a catalyst - Google Patents

Abstract

The invention refers to a method to delignify fibrous material comprising an aqueous suspension of fibers which has a consistency between 5 % - 40 %, with a peroxy compound that is used in amounts between 0.5 % - 10 % based on bone dry fibrous material, and with a metal complex of the general formula (1): [LnMnmXp]<z>Yq wherein Mn stands for manganese or iron, which can be present in oxidation state II, III, IV or V or in mixtures of these states; n and m are the integers 1-4; X is a coordinating ligand; p is an integer from 0 to 12; z is the charge of the complex and can be positive, neutral or negative; Y is a counter-ion or -molecule which depends on the charge of the complex; q is equal to z divided by the charge of Y; and L is a ligand and is represented by a macrocyclic organic molecule with general formula (2) wherein R<1>, R<2>, R<3> and R<4> can be either zero, H, alkyl, aryl or otherwise optionally substituted; D and D' are either N, NR, PR O, or S, wherein R can be substituted by H or alkyl or aryl or otherwise optionally substituted; t and t' are whole integers from 2 to 3, s is an integer between 2 and 4, u is an integer from 1 to 20, and v is 0 or 1; this metal complex is used at an amount of 0.0001 % - 0.1 % based on bone dry fibrous material, wherein the fibers are delignified at an initial pH-level between 7.5 and 13.5, at a reaction temperature between 20 DEG C and 130 DEG C, and with a reaction time between 15 and 360 minutes. Further, the invention relates to the use of a metal complex.

Description

The invention relates to a method for delignifying fibrous materials and the use of a catalyst in this process.

All lignin-containing fibers are referred to below as fiber materials either through the process of producing wood or the Cellulose production has been mechanically and / or chemically pretreated or the as chemically or mechanically untreated natural fibers this Procedures to be subjected. The fibers can also be multiple chemical and / or have undergone mechanical process stages, for example after pulping and a first delignifying treatment the outcrop.

Lignin-containing fibers from wood or from annual plants are said to be lignin should be exempted for most purposes. Furthermore the fibers should have a high degree of whiteness, preferably 90% ISO. This High degrees of whiteness are only achieved when lignin is largely eliminated the fiber or away from the fiber surface. With elementary chlorine and other bleaching chemicals containing chlorine could efficiently use lignin-containing fibers and delignified in a highly selective manner.

Now that chlorine and chlorine-containing chemicals have been used is avoided, oxygen and oxygen-containing chemicals are used Delignify these fibers. The reaction mechanisms of this Chemicals are far less selective, so delignification with is accompanied by greater damage to the cellulose. This is undesirable. It there is therefore a great need for procedures and thus for Chemicals that selectively break down the remaining lignin.

After the residual lignin has been removed as much as possible, in  The pulping chemicals used to bleach the fibers should lighten the highest possible degrees of whiteness. In these bleaching stages, still remaining or partially due to previous process stages resulting chromophoric groups are removed by oxidation. On Breakdown of fiber mass is quite undesirable here, among other things, to the Waste water from these bleaching stages does not become too organic strain. To the chlorine-free bleaching agents used for this purpose in the The pulp industry used includes hydrogen peroxide. Hydrogen peroxide is used primarily for environmental reasons. It is more expensive than bleaches containing chlorine and significantly less selective.

For these reasons, peroxide becomes as mild as possible Reaction conditions are used where fiber is lightened, but not be delignified. With more severe reaction conditions, for example increased temperature, increased use of chemicals and / or prolonged There is still a certain reduction in response time existing residual lignins, but this is accompanied by an enhanced Damage to the fiber and loss of yield. Is particularly undesirable that the unselective reaction of hydrogen peroxide strongly affects cellulose attacks so that the strength of the fibers is reduced.

So far, hydrogen peroxide has hardly been used as a delignifying agent, because the reaction mechanisms of hydrogen peroxide are not suitable for this are the strongly condensed under sufficiently mild reaction conditions to break down phenolic components of the residual lignin. Individual procedures, who also propose hydrogen peroxide to delignify pulp, allow approximately 30% of the residual lignin to be broken down.

Previously known methods, for example in WO 94/00234 described, which catalyze the reactions of an oxidizing agent, describe the separate addition of metal and ligand and the treatment of the pulp fibers at a pH of 3.7 at -0 to 98 ° C Reaction temperature. However, this procedure occurs in an acidic environment to considerable degradation of the cellulose.  

To make the whitening effect of hydrogen peroxide as effective as possible have long been sought catalysts that the numerous suppress unselective side reactions and thereby more Hydrogen peroxide available for removing chromophoric groups do. For this purpose, substances were repeatedly used that for example for the bleaching or lightening application in Detergents were used. The results from the field of However, detergents are hardly on the pulp and paper industry transferable because in the industrial process of pulp production in addition to Bleaching fibers contain a variety of other chemicals in the process water be carried along. In addition, the textile fibers are not lignin fibers. So far, numerous studies have not done so led to the bleaching results of the hydrogen peroxide stage by addition of catalysts have been improved.

Due to the change of chlorine-containing chemicals The process control in the The pulp industry has changed significantly and there is a particularly great need of chemicals or processes that make it possible to use fibers with a considerable residual lignin content, for example after pulping or continue to low after a first oxygen level To delignify residual lignin contents in order to get a chlorine-free to high whiteness to achieve bleached pulp with good strength properties.

It is therefore an object of the invention to provide a method for improved, selective Delignification of pulps using chlorine-free chemicals to provide.

It is very surprising that transition metal-containing catalysts that promote the lightening or bleaching effect of peroxides in detergents, enable extraordinarily improved delignification of fibers, the degradation of the lignin is extremely selective.

The catalysts are used in the process according to the invention  those in European patent applications EP 0 458 397 A2, EP 0 458 398 A2, EP 0 544 490 A1 and in WO 95/30681 and priority-based DE OS 44 16 438 are described and hereby expressly included in the present description of the invention at least as far as the detailed description of the metal Concerns complexes. These are single or multi-core metal complexes with the general formula

[L _n Mn _m X _p ] ^z Y _q

where Mn is manganese or iron, which in oxidation states II, III, IV or V or mixtures of these stages may be present; n and m are Numbers from 1 to 4; X represents a coordinating ligand; p is one Number from 0 to 12, Y is a counter ion or molecule, which depends on the charge z depends on the complex and which can be positive, neutral or negative; q is equal to z divided by the charge Y; and L is a ligand and will by a macrocyclic organic molecule with the following general Formula shown:

wherein R¹, R², R³ and R⁴ can each be either zero, H or alkyl or aryl or optionally substituted, D and D ′ are each either N, NR, PR O or S, where R is either H or alkyl or aryl or optional may be substituted, t and t 'are each integers from 2 to 3, s is a number between 2 and 4, u is a number from 1 to 20, v is 0 or 1.

The complexes according to the invention with the following ligands have proven to be particularly suitable for delignification:
Bis-azamacrocycles, in which two molecules of the general formulas I to V are each linked via one of their residues R¹ to R⁴ or R⁵ by means of a bridge member of the structure -T- or -A- (OA) _h between the two nitrogen atoms, where stands for an integer from 1 to 19 and the radicals R⁵ may additionally have the meaning of R¹ to R⁴;
T is a C₂ to C₈ alkylene group and
A is a C₂ to C₄ alkylene group;
R to R⁴ represent hydrogen, C₁- to C₆₀-alkyl, which can be interrupted by up to 19 non-adjacent oxygen atoms and can additionally carry up to 5 hydroxyl groups, C₁- to C₃₀-alkyl, phenyl or benzyl, the aromatic nucleus in each case by up can be substituted to three C₁ to C₄ alkyl groups, C₁ to C₄ alkoxy groups, halogen atoms, hydroxyl groups, sulfo groups or carboxyl groups, or groupings of the formula - (CH₂) _l -COOH, - (CH₂) _l -SO₃H, - (CH₂) _l -PO₃H₂ or - (CH₂) _l -OH, where l is an integer from 1 to 4 and the acid groups mentioned can also be in salt form,
R⁵ stands for groupings of the formula - (CH₂) _l -COOH, - (CH₂) _l -SO₃H, - (CH₂) _l -PO₃H₂ or - (CH₂) _l -OH or for an oxygen atom interrupted by 1 to 19 not adjacent and / or C₂ to C₆₀-alkyl carrying 1 to 5 hydroxyl groups, where l each represents an integer from 1 to 4 and the acid groups mentioned can also be present in salt form,
R⁶ stands for hydrogen, C₁- to C₆₀-alkyl, which is interrupted by up to 19 non-adjacent oxygen atoms and can additionally carry up to 5 hydroxyl groups, phenyl or benzyl, the aromatic nucleus each having up to three C₁ to C bis-alkyl groups, C₁ to C₄-alkoxy groups, halogen atoms, hydroxyl groups, sulfo groups or carboxyl groups can be substituted, or groups of the formula - (CH₂) _r -COOH, - (CH₂) _r -SO₃H, - (CH₂) _r -PO₃H₂ or - (CH₂) _r -OH , where r is an integer from 0 to 4 and the acid groups mentioned can also be in salt form,
Q is a group consisting of 1 to 3 carbon atoms with 1 or 2 carbonyl groups and methylene groups as the remaining elements,
s denotes the number 2 or 3,
w denotes the number 3 or 4,
g is independently 0 or 1

Another ligand that works well is 1,2-bis (4,7-dimethyl-1,4,7-triaza-1, cyclononyl) ethane.

An example of a particularly suitable manganese complex is

[(Ethylene bridge (Me₂TACN) ₂Mn ^III Mn ^IV (µ-O) ₂ (µ-OAc)] ²⁺ (ClO₄) ⁻₂

Me stands for methyl group and TACN stands for triazacyclononane.

With these metal complexes, which in concentrations from 0.0001 to 0.1% based on the amount of oven-dried fibers used, Surprisingly, however, the delignification of fibers with the The inventive method compared to the known, only brightening P level can be increased by up to approx. 220%, the cellulose only is slightly degraded. It is particularly striking that this Rates of increase with rather low residual lignin contents can be achieved where experience has shown that it is particularly difficult to degrade, highly condensed and thus there are few reactive lignin structures.

This enormous delignification is achieved by the in claim 1 specified process conditions are observed.

The method according to the invention is based on a wide variety of fiber types applicable, so to mechanically and / or chemically pretreated fibers including waste paper fibers but also on untreated natural fibers.  

Hydrogen peroxide or hydrogen peroxide can be used as the peroxy compound releasing compounds, but also organic or inorganic Peroxyacids or their salts, for example peracetic acid, Peroxymonosulfuric acid or percarboxylic acids and their salts used will. In a delignification stage, mixtures of different Peroxy compounds are used. So that is a vote on special process requirements possible.

The method according to the invention is in a wide range of consistency applicable (consistency is equal to the proportion of dry fiber mass on Total weight). The consistency can be between 3 and 40% however preferably between 10 and 15% consistency.

In order to achieve an optimal delignification effect, between 0.5 and 10%, but preferably between 1 and 6% of a peroxy compound are used, each based on the oven-dry to be delignified (otro) fiber mass.

The method according to the invention shows excellent Delignification results if between 0.001 and 0.05% of the Metal complex based on oven-dry fiber mass can be used.

The residual lignin is broken down very efficiently when the pH value begins the reaction is above 10, preferably above 11.

The reaction temperature can vary depending on the particular Fiber raw material can be selected in a wide range. Between 20 ° C and 130 ° C, but preferably between 40 ° C and 110 ° C delignify most fibers. The is particularly preferred Temperature range between 50 ° C and 98 ° C, because here under mild Conditions are delignified very selectively, and this at relatively short Response times.

The reaction time can, depending on the reaction temperature  also chosen in a wide range, between 5 and 240 minutes will. However, a reaction time of 30 to 150 minutes is preferred. Delignification is particularly widespread if the method has a Period of 45 to 120 minutes is applied. These response times are shorter than with normal P-levels.

The metal complexes used according to the invention for delignification not only improve the effect of a simple peroxide step they increase also the delignification of an oxygen level with the addition of peroxide is carried out. Will be bleached with the addition of oxygen achieves particularly good results when an overpressure between 0.15 and 1.5 MPa is applied. A reaction pressure of is particularly preferred 0.2 to 0.9 MPa is applied.

The complexation of heavy metal ions has an advantageous effect. DTPA, DTPMPA or poly-α-hydroxyacrylic acid are preferably used, which are stable even at higher pH values. In addition or alternatively, water glass and / or magnesium sulfate can be used will.

The method according to the invention is described below with some Described exemplary embodiments:

For the investigations on the catalyzed delignification stages with peroxy - and possibly also with oxygen-containing chemicals, spruce kraft pulp with the following technological data was used for Examples 1 to 3:
Kappa number: 19.3
Whiteness: 29.3% ISO
Viscosity: 1 020 mg / l
in addition, the same spruce kraft pulp was used for Examples 4 to 7 after an oxygen step:
Kappa number: 10.1
Whiteness: 34.1% ISO
Viscosity: 901 mg / l.

An ASAM softwood pulp with the following properties was used for embodiment 8:
Kappa number: 26.7
Whiteness: 45.4% ISO
Viscosity: 1237 mg / l.

The process according to the invention was carried out in polyethylene bags tempered water bath in batches of 10 g otro (oven-dry cellulose) carried out. The chemicals were mixed in such a way that first an aqueous solution of the additives and the catalyst was mixed in. In a second step, the pH value required for the reaction was determined NaOH adjusted. The third step was for the trial required amount of hydrogen peroxide added. After that the The pH of each sample was measured and then placed in a PE bag transferred, which was fixed in the appropriately tempered water bath.

Unless otherwise stated, all tests were carried out at 10% consistency carried out. Unless otherwise stated, data in "%" refer to on the amount of oven dry fibers. The analyzes were made after following standards:

The Kappa number was determined according to Zellcheming IV / 37/80, the Microkappa number determined according to TAPPI regulation UM 246. The viscosity of the Pulp was made in copper ethylenediamine solution according to the Zellcheming protocol IV / 36/61 determined. The whiteness was measured with an Elrepho 2000 (Fa. Datacolor) measured according to SCA regulation 11:75.

Each embodiment has a table with the same number, the the respective test conditions, especially the one used  Catalyst and related results.

Embodiment 1

The data for this example are shown in Table 1, in particular the catalyst used is described as a footnote. There were Experiments with and without catalyst with different Temperatures (50 ° C and 90 ° C) carried out. In these trials no other additives used.

By using the catalyst, rates of increase in the Delignification of 70% at 50 ° C or 52% at 90 ° C reaction temperature be achieved. The amount of hydrogen peroxide used was in the Try each completely and very efficiently implemented. Remarkably, that the catalyzed P stage (test P2) compared to the uncatalyzed P level (trial P3) not only improved delignification but moreover results in approximately the same viscosity. The resulting deriving improved selectivity (same viscosity at lower Residual lignin content) indicates because of the correlation between viscosity and Strength properties to a small damage and thus improved Strength properties of the fibers after a P level. To the correlation between loss of viscosity (DP degradation) and loss of strength see: GURNAGUL et al: "The effect of cellulose degradation on the strength of wood pulp fibers "(Nordic Pulp and Paper Research Journal 7, (3) 1992, p. 152-154.

Embodiment 2

In the experiments PS to P8, an acid wash of the Pulp carried out. The reaction conditions were: consistency 3%, pH 2.0, reaction temperature 70 ° C, reaction time 30 minutes. The Results are shown in Tab. 2. The acid pretreatment (A)  effectively removes heavy metal ions, mainly with the pulp be entered. This makes the delingification otherwise unchanged reaction conditions compared to the embodiment 1 significantly improved.

It is noteworthy here that the lignin content is approximately the same (Kappa number 12.7 and 12.8) in experiments P6 and P7 the use of the Catalyst significantly improved viscosity results. Here too improved strength properties of the pulp are therefore to be expected.

In all experiments P1 to P8 it is noticeable that the catalyst is used at most approximately the same increases in whiteness as the uncatalyzed use of hydrogen peroxide. Most attempts fail however, the whiteness is worse.

Aside from the fact that chemicals that bleach or whiten Promote effect of peroxy chemicals, usually no contribution to The degradation of lignin would also contribute to the catalysts examined here usual standard experiments on the use of hydrogen peroxide, which are based on limit the analysis of whiteness than for the pulp and Paper industry has been unsuitably discarded.

Embodiment 3

Tab. 3 shows the influence of increasing amounts of catalyst on the Delignification. Again, kraft pulp becomes acidic after washing used. Up to an amount of catalyst of 0.006% based on otro pulp shows an increase in delignification performance. over 0.006% catalyst is no further increase in delignification performance noticeable. The catalyst used is given in Table 3.

With increasing catalyst use, the residual peroxide content decreases sharply, without causing a better delignification or an increase in the  Whiteness leads. Since maximum degradation of the residual lignin is desired, the amount of catalyst used for the subsequent experiments 0.006% set.

Embodiment 4

In experiments P15 to P18, the effect of the complexing agent DTPMPA (Diethylenetriaminepentamethylenephosphoric acid) using one with a Oxygen level and an acid wash of pre-treated pulp examined. Regardless of the use of the complexing agent, it can be seen that despite the lower initial kappa number, the delignification with doubled peroxide use can be further increased. The kappa number when using the catalyst is based on the delignification performance the uncatalyzed P stage by 83% lower. Despite this substantial Lignin degradation shows that the test result of P15 is much higher Viscosity on than the trial P16. The higher whiteness of the catalyzed P level is probably primarily due to the lower residual lignin content, since with kappa numbers below 10 a reduction in the kappa number always with one high whiteness increase.

The addition of the complexing agent causes higher residual peroxide contents in the Liquor, it noticeable that in the presence of the catalyst Hydrogen peroxide is implemented far more efficiently than in the simple P level.

Embodiment 5

Tab. 5 shows that the same starting pulp as in the previous example was used. There were two different catalysts K1 and K2 tested. The catalysts used in each case and the corresponding ones Ligands are described in Tab. 5. The use of DTPA continues (Diethylenetriaminepentaacetic acid) and DTPMPA, each in the presence of 0.5%  Magnesium sulfate based on otro pulp, examined.

In comparison to the simple P-stage (tests P21 and P24) much higher delignification performance. As special the catalyst K1 proves to be suitable, as compared to the simple one P level provides 100% better delignification performance. He also points compared to the catalyst K2 higher and thus better viscosities of the Pulp fibers. Finally, K1 causes the higher than K2 Whiteness increases. Basically, however, both catalysts are for the proposed intended use.

Embodiment 6

This series of experiments shows the delignification depending on the Reaction time. Most of the remaining lignin is within the first 15 Minutes. Up to the maximum response time of 60 minutes takes place in the presence of the catalyst, further lignin degradation takes place, which eventually is 120% above the delignification performance of the simple P-level.

In the experiments without a catalyst, a high proportion of the hydrogen peroxide used unused in the bleaching solution, while in The presence of the catalyst already over 80% of the chemical used consumed within the first 15 minutes.

The course of the delignification reaction thus differs significantly from the development of bleach. During the delignification after approx. 45 Minutes comes to a standstill both with and without a catalyst the whiteness increase slowly but continuously.

Embodiment 7

The associated table 7 shows the influence of the alkali use or the initial  pH value on the delignification performance and the whiteness development as well as the viscosity. This increases both with and without the use of a catalyst Residual lignin degradation with increasing use of NaOH. However, the increase extremely low in the simple P stage (tests P37 to P40), while the delignification performance in the presence of the catalyst of 42.6% increases to 64.4%. Already at an initial pH of 10.4 (experiment P33) is the delignification compared to the reference test without Catalyst significantly improved. However, an initial pH is particularly efficient, which is over 11. With an initial pH value of 11.8 (P36) at extremely low temperatures of residual lignin degradation compared to Reference trial (P40) intensified by 217%.

The increase in whiteness is correspondingly steeper. The viscosity is in experiments P33 to P36, especially considering the low Kappa numbers, surprisingly stable, are even slightly above the values in the end the simple P level. It can therefore be expected that the Strength properties of using the catalyst delignified pulps show better results than those without Addition of the catalyst were delignified.

Embodiment 8

Here a softwood ASAM pulp is made after a simple one Complexing agent delignified. EDTA (0.4% Ethylenediaminetetraacetic acid based on otro pulp) at pH 4.5, 70 ° C Reaction temperature and at 3% consistency over a reaction time of 30 minutes.

The subsequent delignification took place through the combined use of oxygen and hydrogen peroxide (surgical stage). The following were Reaction conditions selected: 1.5% NaOH, 0.1% MgSO₄, 90 ° C, 140 Minutes response time (including heating up time), 10% consistency, 800 g otro Pulp per attempt. Other additives were described as in Table 8  used. The experiments were carried out in an electrically heated 15 l Rotary cooker performed.

Without using the catalyst, a kappa number of 12 was achieved in the OP stage reached. With the addition of the catalyst and the use of 0.1% DTPMPA Kappa numbers of 7 and whiteness of over 85 were obtained on otro pulp reached. The use of DTPA or water glass led to similar ones Delignification services, but resulted in a lower Whiteness increase. The pulp delignified with the catalyst insert has high viscosities, which are between 1033 and 1074.

The extraordinarily high delignification performance in the surgical stage (trial OP50: 73% based on the original pulp) could only be used for particularly severe reaction conditions, not without high losses in viscosity and was not technically feasible because the fiber damage is too strong and therefore not for further use was acceptable.

It is surprising and not yet known from the prior art that the delignifying effect of peroxide is more than doubled if the catalysts described above are used. Of the gentle degradation of the remaining lignin enables Application of the method according to the invention is likely to achieve this of high final whiteness (90% ISO). In addition, the so delignified and then bleached pulps due to gentle and selective Process higher viscosities and are thus stronger than the fibers after known chlorine-free processes were treated.

Claims (23)

1. Process for delignifying fibrous materials

• - An aqueous suspension of fibers with a consistency of 5 to 40% with
• - A peroxy compound, which is used with 0.5 to 10% based on the oven-dry fiber mass, and with
• a metal complex of the general formula: [L _n Mn _m X _p ] ^z Y _q where Mn is manganese or iron, which may be in the oxidation states II, III, IV or V or mixtures of these stages; n and m are numbers from 1 to 4; X represents a coordinating ligand; p is a number from 0 to 12; z is the charge of the complex and can be positive, zero or negative; Y is a counter ion or molecule that depends on the charge of the complex; q is equal to z divided by the charge Y; and L is a ligand and is represented by a macrocyclic organic molecule with the following general formula: where R¹, R², R³ and R⁴ can each be either zero, H or alkyl or aryl or can be optionally substituted, D and D 'are each either N, NR, PR, O or S, where R is either H or alkyl or aryl or may optionally be substituted, t and t 'are each integers from 2 to 3, s is a number from 2 to 4, u is a number from 1 to 20, v is 0 or 1;
  this metal complex is used with 0.0001 to 0.1%, based on the oven-dry fiber mass, for delignifying fiber materials, whereby

the fibers at an initial pH between 7.5 and 13.5 at a reaction temperature between 20 and 130 ° C and one Reaction time between 15 and 240 minutes delignified will. 2. The method according to claim 1, characterized in that fibrous materials Are cellulose fibers or natural fibers. 3. The method according to claim 1, characterized in that as Peroxy compound releasing hydrogen peroxide or hydrogen peroxide Connections is used. 4. The method according to claim 1, characterized in that as Peroxy compound inorganic or organic peroxy acids or their Salts are used. 5. The method according to any one of the preceding claims, characterized characterized in that mixtures of different peroxy compounds be used. 6. The method according to claim 1, characterized in that the Delignification carried out at a consistency between 3 and 40% becomes. 7. The method according to claim 6, characterized in that the Delignification with a consistency between 10 and 15% is carried out.   8. The method according to claim 1, characterized in that for Delignify between 0.5 and 10% of a peroxy compound be used. 9. The method according to claim 8, characterized in that for Delignify between 1 and 6% of a peroxy compound used will. 10. The method according to claim 1, characterized in that for Delignification between 0.001 and 0.06% of the manganese catalyst, based on otro pulp. 11. The method according to claim 1, characterized in that the pH is over 10 at the beginning of the delignification. 12. The method according to claim 1, characterized in that the pH is above 11 at the beginning of the delignification. 13. The method according to claim 1, characterized in that the Reaction temperature is between 40 and 110 ° C. 14. The method according to claim 13, characterized in that the Reaction temperature is between 50 and 98 ° C. 15. The method according to claim 1, characterized in that the Reaction time is between 30 and 150 minutes. 16. The method according to claim 15, characterized in that the Response time is between 45 and 120 minutes. 17. The method according to claim 1, characterized in that the Delignification at a pressure between 0.15 and 1.5 MPa is carried out.   18. The method according to claim 17, characterized in that the Delignification at a pressure between 0.2 and 0.9 MPa is carried out. 19. The method according to claim 1, 17 or 18, characterized in that the delignification is carried out in the presence of oxygen. 20. The method according to any one of the preceding claims, characterized characterized in that organic complexing agents, water glass and / or Magnesium sulfate must be added before delignification. 21. The method according to claim 20, characterized in that DTPA, and / or DTPMPA can be added before delignification. 22. Use of a manganese complex with the general formula [L _n Mn _m X _p ] ^z Y _q where Mn means manganese or iron, which may be in the oxidation states II, III, IV or V or mixtures of these stages; n and m are numbers from 1 to 4; X represents a coordinating ligand; p is a number from 0 to 12: z is the charge of the complex and can be positive zero or negative: Y is a counter ion or molecule, which depends on the charge of the complex; q is equal to z divided by the charge Y; and L is a ligand and is represented by a macrocyclic organic molecule with the following general formula: where R¹, R², R³ and R⁴ can either be zero, H or alkyl or aryl or can be optionally substituted, D and D 'are each either N, NR PR O or S, where R is either H or alkyl or aryl or may optionally be substituted, t and t ′ are each integers from 2 to 3, s is a number from 2 to 4, u is a number from 1 to 20, v is 0 or 1,
wherein the complex is used with 0.0001 to 0.1% based on the oven-dry fiber mass, in a method according to one or more of claims 1 to 21 for delignifying fibrous materials.