WO2024251935A1 - Method for producing bleached pulp, bleached pulp and use thereof - Google Patents

Abstract

The invention relates to a method for obtaining bleached pulp, to bleached pulp, and to the use thereof. The one-stage method for obtaining bleached pulp is based on the Acetosolv method using phosphoric acid as a catalyst.

Description

Process for the production of bleached pulp, bleached pulp, and their use

The invention relates to a process for producing bleached pulp, bleached pulp, and their use.

Pulp is an important raw material, for example for paper production. Pulp is produced in different regions from a variety of raw materials, mostly from wood that has been chopped into wood chips.

The wood chips are broken down using various methods. The so-called sulphate process is the dominant method, in which the raw material is broken down using caustic soda and sodium sulphide at pressures of 0.8 MPa to 1.0 MPa and temperatures of around 160 °C to 180 °C. The pulp obtained must then be bleached, which is a complex process. The regeneration of the digestion chemicals contained in the resulting black liquor is also complex in terms of energy requirements and the necessary, multi-stage plant technology. The sulphite process, which also represents the state of the art, includes some embodiments at temperatures of around 140 °C and increased pressures, mainly due to the base used and the pH value applied, which lead to pulp that is easier to bleach, but also require very complex and expensive chemical regeneration.

The Acetosolv process has been known since the 1920s. The digestion is carried out using acetic acid, catalyzed with hydrochloric or sulphuric acid at pressures of 0.8 MPa to 1.5 MPa and temperatures of 180 °C. It produces partially acetylated pulp, which is then bleached. Due to the aggressive conditions, defects such as corrosion on the equipment and product damage due to severe cellulose degradation occur. Therefore, the process has not yet been transferred to an industrial scale.

EP 0 325 890 A1 discloses a process for separating lignin from cellulosic masses or lignocelluloses which are exposed to ozone in the presence of a C 1-3 fatty acid and acetic acid, so that the solubility of the lignin in acetic acid is improved by an oxidative conversion.

DE 10 2016 225 827 B4 describes a two-stage digestion process for the chemical fractionation of lignocellulose, in which the lignocellulose is treated with steam or water in the first stage at a pressure of more than 1 bar and temperatures above 100 °C and is subsequently treated at more than 1 bar and above 80 °C with an extraction solution consisting of water and at least one lignin-dissolving organic solvent, such as aliphatic alcohols, and a catalyst, such as inorganic acids, in particular sulfuric acid. DE 3445 132 C2 discloses a process for digesting chopped wood and annual plants in acetic acid with small amounts of hydrochloric acid, whereby the pulp thus obtained has a kappa number of about 30. The pulp obtained can then be re-extracted and bleached in a further step with acetic acid and hydrogen peroxide.

WO 2011/073284 A1 discloses a process for extracting hemicelluloses and lignin from lignocellulose-containing biomass. In a first pre-hydrolysis step, the biomass is brought into contact with a digestion solution comprising 5 to 95% by weight of acetic acid at a temperature of 80 - 195°C. In a further step, the biomass pretreated in this way is subjected to an intermediate wash with acetic acid and in a subsequent digestion brought into contact with a digestion solution comprising 5 to 95% by weight of peroxyacetic acid at 50 - 95°C. The pulp obtained in this way has a kappa number in the range of 16 - 40 and a whiteness according to ISO 2470-1 in the range of 31 - 43.

The aim is therefore to provide a simplified, less complex process for the production of bleached pulp, which overcomes the above-mentioned disadvantages of the prior art and in particular enables the production of bleached pulp in an industrially scalable process with improved properties.

According to the invention, the object is achieved by a method and a bleached pulp according to the independent claims. Advantageous embodiments of the invention are specified in the dependent claims. Furthermore, the object is achieved by the use of the method and the bleached pulp.

The main claim of the invention relates to a process for producing bleached pulp comprising a modified acetosolv process. The modified acetosolv process is characterized in that the at least one catalyst is selected from oxygen acids of phosphorus with the oxidation number +5, phosphates and mixtures thereof; and that at least one oxidizing bleaching agent comprising hydrogen peroxide is added to the digestion solution; and that the process takes place at atmospheric pressure.

This advantageously avoids the defects, e.g. corrosion phenomena, of previously known catalysts such as hydrochloric or sulphuric acid and enables the industrial production of bleached pulp based on an acetosolve process. The process according to the invention also advantageously enables the digestion and Bleaching in one process step, in a one-stage process that can be carried out under atmospheric pressure.

Phosphates means the salts and esters of orthophosphoric acid H3PO4, such as primary, secondary and tertiary phosphates. Primary phosphates are also called dihydrogen phosphates, e.g. sodium dihydrogen phosphate NaH2PÜ4. Secondary phosphates are also called hydrogen phosphates, e.g. disodium hydrogen phosphate Na2HPU4. A tertiary phosphate is, for example, sodium phosphate NasPO4.

The digestion solution in the Acetosolv process comprises an aqueous acetic acid to which at least one catalyst and at least one oxidizing bleaching agent are added.

Atmospheric pressure refers to the prevailing air pressure at any location on earth where the procedure is carried out, e.g. the mean air pressure of the atmosphere at sea level, which is 101,325 Pa by default.

In preferred embodiments, the process for producing bleached pulp comprises the following steps: a) providing mechanically comminuted cellulose-containing plant components, b) adding the mechanically comminuted cellulose-containing plant components to a digestion solution comprising aqueous acetic acid, c) adding at least one catalyst and at least one oxidizing bleaching agent comprising hydrogen peroxide, d) heating the digestion solution with the mechanically comminuted cellulose-containing plant components, characterized in that the at least one catalyst is selected from oxygen acids of phosphorus with the oxidation number +5, phosphates, and mixtures thereof, and that the process takes place at atmospheric pressure.

This advantageously achieves the digestion and bleaching in one process step - step d) - and provides a one-step process for the production of bleached pulp, which does not require complicated plant technology, works at atmospheric pressure and thus shows improvements in terms of energy requirements and the hazard potential of the chemicals used. Furthermore, this enables the production of in-situ functionalized pulp, which opens up further application possibilities in the sense of a cellulose monomaterial. Furthermore, the digestion solution, catalyst and bleaching agent used enable a universal delignification capacity. The process also has the advantage of Yields of bleached pulp in the range of 40% to 60% based on wood as the cellulose-containing plant components used and 50% to 80% based on non-wood plants as the cellulose-containing plant components used are achieved, whereby the yield refers to the percentage of the mass of the pulping material, ie the bleached pulp, of the mass of the cellulose-containing plant components used, in each case based on the dry mass. A further advantage is that such a process can be used as a starting material for a large number of possible cellulose-containing plant components. A further advantage is that energy can be saved by means of the process according to the invention due to the low process temperatures. An in-situ functionalized pulp within the meaning of the invention means a pulp that undergoes esterification of the hydroxyl groups during delignification, so that a degree of substitution (abbreviated DS value) or degree of acetylation in the range of 0.1 to 0.9 is achieved. Such pulps can advantageously be adapted to the later function/application of the pulps through partial derivatization during production. A cellulose monomaterial within the meaning of the invention means that in the application case the product consists of only one material, which is cellulose-based, and does not contain any foreign components, e.g. plastics.

In embodiments, steps b) and c) can be carried out sequentially or simultaneously. In further embodiments, step d) takes place after step c) or simultaneously with step c).

Preferably, steps b), c) and d) are carried out simultaneously.

This advantageously makes it possible to produce bleached pulp in a one-step process. The pulp produced in this way also advantageously has a kappa number in the range of 1 - 15 according to DIN 54357 and a whiteness of 45 - 95% according to DIN 3145-1. The pulp produced in this way can also be used directly - i.e. without further process steps - for example in the production of paper, chemical pulp, regenerated cellulose fibers, cellulose derivatives and/or barrier films. In further embodiments, it is advantageous if the cellulose-containing plant components are comminuted in such a way that they have a homogeneous size distribution. A homogeneous size distribution means that 80% of the comminuted cellulose-containing plant components have a size in the range of 15 mm x 10 mm x 3 mm to 40 mm x 30 mm x 4 mm (length x width x thickness).

Cellulose-containing plant components include wood, annual plants, grasses, biogenic residues and/or waste wood.

Wood means hardwood, such as beech or aspen, and softwood, such as spruce or pine. Annual plants mean plants that require a growing season from the germination of the seed to the development of the entire plant, the formation of the flower and fertilization until the fruit of the new seed is ripe, e.g. hemp. Grasses means sweet grasses, e.g. Miscanthus.

Biogenic residues refer to wood residues that arise during the felling of wood, during the treatment and processing of wood, but also other plant, harvest and processing residues that arise as residues in agriculture, such as straw, harvest residues from root crops such as potatoes or beets.

Waste wood means used wood of waste wood classes A1 and A2 according to the German Waste Wood Ordinance (AltholzV), which has already been put to a use and is available as waste or secondary raw material, such as beams from roof trusses.

In embodiments, it is advantageous if the weight ratio of the cellulose-containing plant components to the digestion solution is in the range of 1:1 to 1:14.

In embodiments, the reaction temperature of the digestion solution is 80 °C to 120 °C.

In preferred embodiments, heating in step d) is carried out with constant mixing until the boiling point of the digestion solution is reached. This can advantageously improve the digestion and bleaching, so that the recovery of the bleached pulp becomes more efficient.

In further preferred embodiments, the oxygen acids of phosphorus with the oxidation number +5 are H3PO4 and/or polyphosphoric acids of the formula H _n +2PnO3n+i with n = 3 to 8.

This advantageously avoids known deficiencies of previous catalysts, such as corrosion phenomena. The catalysts according to the invention also advantageously enable the economic production of bleached pulp in an atmospheric pressure process. The oxygen acids of phosphorus mentioned also advantageously enable the stabilization of the peroxides and minimize the hydrolysis of the carbohydrates.

In preferred embodiments, the digestion solution is an aqueous acetic acid having a concentration in the range of 50 wt.% to 95 wt.%.

This has the advantage of saving on the chemicals used, digestion solution, catalyst and bleach, and on energy costs. Another advantage is that it can minimize corrosion on the systems.

It is advantageous to choose the concentration of the aqueous acetic acid depending on the lignification of the cellulose-containing plant components used and the further processing of the pulp produced. In principle, it is advantageous for more lignified For cellulose-containing plant components, choose aqueous acetic acid in a higher concentration.

In further embodiments, the digestion solution is an aqueous acetic acid with a concentration in the range of 70 wt.% to 75 wt.%. This is advantageous when biogenic residues are used as cellulose-containing plant components.

In further preferred embodiments, 0.05 wt.% to 1 wt.% of the at least one catalyst and 1 wt.% to 10 wt.% of the at least one bleaching agent are added, each based on the amount of the digestion solution in step c).

This advantageously means that the digestion and bleaching are efficiently achieved in one process step - step c) - in a single-stage process. Another advantage is that economical process times are achieved.

In further embodiments, the digestion solution has a pH in the range of 1 to 4, preferably in the range of 2 to 3.

In further preferred embodiments, the mechanically comminuted cellulose-containing plant components are impregnated with the digestion solution, the at least one catalyst and/or the at least one oxidizing bleaching agent after step a) and before step b).

This advantageously improves the digestion and bleaching, so that the process times can be reduced.

Impregnation in the sense of the invention means that the mechanically comminuted cellulose-containing plant components are brought into contact with the digestion solution, the at least one catalyst and/or the at least one bleaching agent. In embodiments, the impregnation is carried out by dipping, soaking or spraying.

In preferred embodiments, the process comprises at least one further step, wherein the at least one further step is washing the resulting bleached pulp, sorting the washed bleached pulp, and/or circulating the resulting mixture.

The digestion solution, the at least one catalyst and the bleaching agent are advantageously removed by washing. In embodiments, washing is carried out with water or an alkaline wash. An alkaline wash means washing with an alkaline solution with a pH value greater than 7. Another advantage of sorting is that the coarse material is separated and the pulp obtained is divided into different further processing steps. In some embodiments, the pulp obtained is sorted based on particle size. Insufficiently digested components, so-called coarse materials, can thus be sorted out, which can be subjected to a further digestion step if necessary.

Circulating the resulting mixture of mechanically comminuted cellulose-containing plant components, digestion solution, at least one catalyst and at least one bleaching agent intensifies the digestion and bleaching. In other embodiments, the circulation is carried out by stirring.

In further preferred embodiments, the resulting mixture is circulated for a period of 1.5 to 8 hours.

This advantageously improves the duration and uniformity of the digestion and bleaching.

If the mechanically comminuted cellulose-containing plant components are impregnated after step a) and before step b) with the digestion solution, the at least one catalyst and/or the at least one bleaching agent, the circulation times can be in the lower range, e.g. 1 to 4 hours. If no impregnation takes place, the circulation times can be in the upper range, e.g. 4 to 8 hours.

In preferred embodiments, the bleached pulp obtained is washed with a sodium hydroxide solution.

This advantageously achieves a neutralization of the cooking acid.

A further aspect of the invention relates to a product obtainable by the process according to the invention.

The product obtained by the process according to the invention can advantageously be used as a starting material for the production of paper, chemical pulp, regenerated cellulose fibers, cellulose derivatives and/or barrier films.

A further aspect of the invention relates to a bleached pulp having a kappa number according to DIN 54357 in the range of 1 to 15, a whiteness in the range of 45% to 95% according to DIN 3145-1, a content of hemicelluloses in the range of 3% to 25% and a degree of acetylation of 0.1 to 0.9. Such a pulp is advantageously suitable for further processing into paper, chemical pulp, regenerated cellulose fibers, cellulose derivatives and/or barrier films. It is also advantageous if such a pulp is functionalized in-situ, ie partially acetylated, for example.

A bleached pulp in the sense of the invention comprises a fibrous mass containing cellulose, cellulose derivatives, hemicelluloses and residual lignin.

Chemical pulp means high-purity cellulose with a cellulose content of at least 90% a-cellulose, which serves as a starting material for cellulose deformation and derivatization and for the production of cellulose regenerates, also known as regenerated cellulose fibers.

Cellulose regenerated fibers are fibers made from natural, renewable raw materials that are produced through chemical processes, such as viscose, modal or lyocell fibers.

Cellulose derivatives are chemical derivatives of cellulose, obtained by modifying or substituting the hydroxy groups of the anhydroglucose units (AGU), e.g. by methylation, ethylation, acetylation, nitration. Well-known cellulose derivatives are, for example, cellulose ethers or cellulose esters.

Barrier films refer to dense papers that form a barrier against air, oxygen, aromas and fats, which can be in the form of individual transparent barrier films or as barrier coatings.

The kappa number indicates the residual lignin content of the pulp obtained, which is determined according to DIN 54357.

The whiteness refers to the spectral reflection factor at a wavelength of 457 nm and is determined according to DIN 53145-1.

Hemicelluloses are polysaccharides made up of a variety of possible monomers, such as hexoses and pentoses. Examples of hemicelluloses are xylan and mannan, whose content can be determined from the mass difference between holocellulose and cellulose.

The degree of acetylation refers to the degree of substitution (abbreviated DS) of the bleached pulp. The degree of substitution is understood as the number of hydroxy groups that are esterified with acetyl groups on average per anhydroglucose unit (AGU) of the cellulose.

In preferred embodiments, the bleached pulp has a dewatering resistance of 85 SR after 6,000 revolutions of PFI refining according to DIN EN ISO 5264-2.

SR means the degree of freeness of the bleached pulp, which is determined as Schopper-Riegler degree (SR) according to DIN EN ISO 5267-1. In further preferred embodiments, the bleached pulp has a DP range of 300 to 1,200, preferably from 450 to 1,000 and particularly preferably from 550 to 800, an α-cellulose content in the range of > 80 wt.%, preferably > 90 wt.% and particularly preferably ≤ 95 wt.%, a hemicellulose content in the range of < 20%, preferably ≤ 10 wt.% and particularly preferably of a maximum of 5 wt.%, and a kappa number below 5, preferably below 3 and particularly preferably below 1.5.

Such pulp is advantageously suitable for the production of the above-mentioned types of regenerated cellulose fibres and cellulose derivatives.

DP range means the average degree of polymerization of the pulp, which is usually determined using aqueous copper(II) ammonium hydroxide (Cuoxam) solutions according to, for example, TS 3852 - Method for determining the viscosity of cotton and regenerated cellulose fibers/fibers in copper ammonium hydroxide (Cuoxam) solution or using aqueous copper(II) ethylenediamine hydroxide (Cuen) solution according to DIN EN 60450.

A bleached pulp with a DP of around 1,000 can be used advantageously as a raw material for the production of cellulose triacetate or textile CA fibers (acetate fibers), with a DP of around 800 as a raw material for the production of sustainable viscose or modal fibers and with a DP of around 600 as a raw material for the production of lyocell fibers.

In further preferred embodiments, the bleached pulp has metal contents of < 10 ppm for the sum of all heavy metals from the group iron, copper, manganese, chromium and/or nickel, < 200 ppm for alkaline earth metals magnesium and/or calcium, < 100 ppm for alkali metals sodium and/or potassium. Such a pulp is advantageously suitable as chemical pulp for the production of cellulose regenerates or cellulose derivatives.

A further aspect of the invention relates to barrier films produced from a product of the process according to the invention or from a bleached pulp according to the invention, characterized in that the barrier films are slightly air-permeable according to Bendtsen in accordance with ISO 5636-3 and/or have a barrier against fat and flavors with a kit value > 12 according to TAPPI T-559.

Such barrier films are advantageously suitable as dense papers, whereby the barrier to grease is determined according to TAPPI T-559. Such barrier films are also advantageous as they have low air permeability according to Bendtsen in accordance with ISO 5636-3. Low air permeability in the sense of the invention means values below 0.38 pm/Pa s according to Bendtsen in accordance with ISO 5636-3. Greaseproof in the sense of the invention means a kit value > 12 according to TAPPI T- 559.

A further aspect of the invention relates to the use of the product of the process according to the invention and/or the bleached pulp according to the invention for the production of paper, chemical pulp, regenerated cellulose fibers, cellulose derivatives and/or barrier films.

Advantageously, a large number of products can thus be produced from the product of the process according to the invention and/or the bleached pulp according to the invention.

A further aspect of the invention relates to the use of oxygen acids of phosphorus with the oxidation number +5, phosphates and mixtures thereof as catalyst in a process for producing bleached pulp from cellulose-containing plant components, preferably wood, annual plants, grasses, biogenic residues and/or waste wood.

This advantageously overcomes the shortcomings of known catalysts, such as corrosion phenomena, and enables the industrial production of bleached pulp using acetic acid as a digestion solution.

For the realization of the invention, it is also expedient to combine the above-described inventive embodiments, embodiments and features of the claims with one another.

implementation examples

The invention will be explained in more detail below using an exemplary embodiment. The exemplary embodiment is intended to describe the invention without limiting it.

The invention is explained in more detail with the aid of drawings.

Fig. 1 is a flow diagram of an embodiment of the process according to the invention for obtaining bleached pulp, and

Fig. 2 is a flow diagram of another embodiment of the process according to the invention. Figure 1 shows an embodiment of a method for obtaining bleached pulp, wherein the entire process takes place at atmospheric pressure and the digestion and bleaching take place in one process step. According to Figure 1, in a step a), mechanically shredded cellulose-containing plant components, for example wood, annual plants, grasses, agricultural residues and/or waste wood, are provided. It is advantageous if the cellulose-containing plant components are in the form of wood chips. In a step b), these are added to a digestion solution, an acetic acid with a concentration of 70% by weight. It can also be advantageous if the shredded cellulose-containing plant components are impregnated with the digestion solution before step b), for example by spraying. In embodiments, impregnation of the cellulose-containing plant components with the catalyst and the bleaching agent can also be advantageous, for example before steps b) and/or c). This improves the digestion and bleaching, which can lead to a reduction in the overall process time. In a step c), phosphoric acid H3PO4 is added as a catalyst and hydrogen peroxide as a bleaching agent, with 0.5% by weight of phosphoric acid and 5% by weight of hydrogen peroxide being added, each based on the mass of the digestion solution. In a step d), the resulting mixture of cellulose-containing plant components, digestion solution, catalyst and bleaching agent is heated to the boiling point, in this example up to 104 °C, and constantly mixed. In embodiments, a phosphate, e.g. sodium hydrogen phosphate, can be added as a catalyst in step c), which forms phosphoric acid in the acetic acid digestion solution. Steps b), c) and d) can be carried out one after the other or simultaneously.

The bleached pulp thus obtained can be subjected to further known process steps for further processing into paper or fibers.

Figure 2 shows a further embodiment of the method according to the invention, wherein steps a) to d) are carried out according to Figure 1. Heating of the digestion solution (step d)) is followed by circulation of the mixture obtained or is carried out simultaneously for a period of 1.5 hours to 8 hours. The bleached pulp thus obtained can be washed in a subsequent step in order to remove the residues of the digestion solution, the catalyst and the bleaching agent. The washing can be carried out with water or an alkaline wash with a sodium hydroxide solution. The washed, bleached pulp is then sorted. Sorting can be carried out on the basis of particle size, so that any insufficiently digested pulp can be subjected to further digestion. The washed, bleached pulp thus sorted can be used in known processes for producing paper, chemical pulp, regenerated cellulose fibres, cellulose derivatives and/or barrier films.

In a further embodiment, the method according to the invention is carried out in such a way that the steps b) adding the mechanically comminuted cellulose-containing plant components to a digestion solution comprising aqueous acetic acid, c) adding at least one catalyst and at least one bleaching agent comprising hydrogen peroxide and d) heating the digestion solution with the mechanically comminuted cellulose-containing plant components are carried out simultaneously. The following Table 1 shows the parameters of the individual process steps of WO 2011/073284 A1 and the properties of the resulting pulp in each case in comparison to the method according to the invention.

Table 1:

Claims

patent claims 1. A process for producing bleached pulp comprising a modified Acetosolv process, characterized in that the at least one catalyst is selected from oxygen acids of phosphorus with the oxidation number +5, phosphates and mixtures thereof; and that at least one oxidizing bleaching agent, comprising hydrogen peroxide, is added to the digestion solution, and that the process takes place at atmospheric pressure. 2. Process for producing bleached pulp, comprising the following steps: a) providing mechanically comminuted cellulose-containing plant components, b) adding the mechanically comminuted cellulose-containing plant components to a digestion solution comprising aqueous acetic acid, c) adding at least one catalyst and at least one bleaching agent comprising hydrogen peroxide, d) heating the digestion solution with the mechanically comminuted cellulose-containing plant components, characterized in that the at least one catalyst is selected from oxygen acids of phosphorus with the oxidation number +5, phosphates and mixtures thereof, and that the process takes place at atmospheric pressure. 3. Process according to claim 1 or 2, characterized in that the heating in step d) is carried out with constant mixing up to the boiling point of the digestion solution. 4. Method according to one of claims 1 to 3, characterized in that the Oxygen acids of phosphorus with the oxidation number +5 H3PO4 and/or Polyphosphoric acids of the formula H _n +2PnO3n+i with n = 3 to 8. 5. Method according to one of claims 1 to 4, characterized in that the The digestion solution is an aqueous acetic acid with a concentration in the range of 50 wt.% to 95 wt.%. 6. Process according to one of claims 1 to 5, characterized in that 0.05 wt.% to 1 wt.% of the at least one catalyst and 1 wt.% to 10 wt.% of the at least one oxidizing bleaching agent, each based on the amount of the digestion solution in step c). 7. Process according to one of claims 1 to 6, characterized in that the mechanically comminuted cellulose-containing plant components are impregnated with the digestion solution, the at least one catalyst and/or the at least one oxidizing bleaching agent after step a) and before step b). 8. Process according to one of claims 1 to 7, characterized in that the process comprises at least one further step, wherein the at least one further step is washing the bleached pulp obtained, sorting the washed bleached pulp, and/or circulating the resulting mixture. 9. Process according to claim 8, characterized in that the circulation of the resulting mixture takes place for a period of 1.5 to 8 hours. 10. Process according to claim 8, characterized in that the washing of the bleached pulp obtained is carried out with a sodium hydroxide solution. 11. Product obtainable by the process according to any one of claims 1 to 10. 12. Bleached pulp having a kappa number according to DIN 54357 in the range of 1 to 15, a whiteness in the range of 45% to 95% according to DIN 3145-1, a hemicellulose content in the range of 3% to 25% and a degree of acetylation of 0.1 to 0.9. 13. Bleached pulp according to claim 12, characterized in that the pulp has a dewatering resistance of 85 SR after 6,000 revolutions of PFI refining according to DIN EN ISO 5264-2. 14. Bleached pulp according to one of claims 12 or 13, characterized in that the pulp has a DP range of 300 to 1,200, preferably from 450 to 1,000 and particularly preferably from 550 to 800, an a-cellulose content in the range of >80% by weight, preferably >90% by weight and particularly preferably >95% by weight, a hemicellulose content in the range of <20%, preferably <10% by weight and particularly preferably of a maximum of 5% by weight, and a kappa number below 5, preferably below 3 and particularly preferably below 1.5. 15. Barrier films made from a product according to claim 11 or from a bleached pulp according to one of claims 12 or 13, characterized in that they have low are permeable to air according to Bendtsen in accordance with ISO 5636-3 and/or have a barrier against fat and flavours with a kit value > 12 according to TAPPI T-559. 16. Use of the product according to claim 11 and/or the bleached pulp according to claim 12 or 13 for the production of paper, chemical pulp, regenerated cellulose fibers, cellulose derivatives and/or barrier films. 17. Use of oxygen acids of phosphorus with the oxidation number +5, phosphates and mixtures thereof as a catalyst in a process for producing bleached pulp from cellulose-containing plant components, preferably wood, annual plants, grasses, biogenic residues and/or waste wood.