DE19510278A1 - Bleaching agent, useful esp. for recycled waste paper pulp prodn. - Google Patents

Abstract

A bleaching agent (I) contains: (a) dithionite salt(s), (b) water-soluble metal salt(s) of hydroxyalkane-sulphinic acid and/or condensation prod(s). of such salt(s) with ammonia, or a mixt. thereof, and (c) formamidine sulphinic acid (FAS) and/or a water-soluble salt thereof. Also claimed is a process for bleaching secondary fibre materials, in this case waste paper, by: (i) adding 0.05-2.5 wt.% of (I) (w.r.t. dry wt. of fibre) to the aq. pulp, and (ii) allowing it to act under suitable conditions until a sufficient degree of whiteness is obtd.

Description

The invention relates to a reductive bleach composition and its use in a method for lightening Secondary fiber from waste paper.

The paper industry is one of the industries that already long before the ever louder environmental discussion about a has a working recycling concept. On secondary fa sern mainly used the packaging industry fen. Waste paper was mainly used as corrugated material and liner is working. Crucial for the reuse of Altpa pier were purely economic aspects. Given one a whole range of factors, such as B. Problems with waste disposal care, overfilled landfills and increasing environmental awareness be in the population, recycled papers enjoy awake popularity. Favorable waste paper prices and a clear one lower energy requirements for the production of secondary fibers fabric compared to low-pressure wood sanding, TMP fabric (thermomechanical wood pulp) and cellulose left the share of secondary fiber for the production of newspaper printing, printing and writing paper as well as hygiene paper sen. Even well into the next millennium increasing share of secondary pulp for the production of Paper predicts.

Basic requirement for the production of graphic papers The availability of secondary pulp is made from waste paper sufficient whiteness. The lightening of secondary fiber succeeds with the usual techniques of flotation deinking and of washing deinking in combination with the various Bleaching process by adding bleaching chemicals.

A distinction is made between bleaching chemicals and oxidative ones  and reductive bleaches. To the oxidative bleaching agents include chlorine, chlorine dioxide and alkali hypochlorides as well as water fabric peroxide. Chlorine and its derivatives are losing more and more Importance because of their use in the formation of polluting organochlorine compounds leads. That's why today almost exclusively as an environmentally friendly alternative to hydrogen peroxide used. Hydrogen peroxide needed compared to the reductive bleaches have significantly longer reaction times. It must also be stabilized with alkalis and complexing agents become. Higher amounts of H₂O₂ can lead to fiber damage and are also not justifiable for cost reasons. Furthermore are Bulk colors and developed NCR dye oxidative with H₂O₂ not bleachable. As a rule, hydrogen peroxide is released during added to the flotation to compensate for the alkali yellowing through the sodium hydroxide solution required for fiber swelling is caused. In this way it takes place during the Flotationdeinkings a certain oxidative bleaching instead.

The reductive bleaching agents in use today Sodium dithionite (Na₂S₂O₄) and formamidine sulfinic acid (FAS; Thio urea dioxide; CH₄N₂O₂S), represented by the formula

Sodium dithionite, which is also commercially known as hydrosulfite  is the most used reductive in terms of quantity Bleach. The reason for this is its favorable price-performance ratio ratio, its ease of use, its environmental compatibility ness and its excellent bleaching effect, especially with Holzhal paper materials.

In addition to FAS, GB-PS 1 404 315 discloses the use of others reductive bleach for lignocellulose. This is what it is about are compounds of the formula (I)

[R₁R₂C (OH) SO₂] _n M (I)

wherein R₁ and R₂ are the same or different and each out are selected from a hydrogen atom and an alkyl group with less than 5 carbon atoms. M stands for a metal atom, such as Na, K or Zn, and n corresponds to the valence of M. Ammo is another suitable bleach niac condensation products of these compounds disclosed. A combined use of FAS and a compound of the formula (I) is not suggested. For the usability of Verbin of formula (I) for bleaching waste paper, in particular mass-colored paper and carbonless paper are available in the GB-PS 1 404 315 also no indication.

FAS is used to bleach mass-colored waste paper and through writing papers used. It is also suitable for bleaching of low-wood and wood-free waste paper types. DE-OS 15 46 252 describes a process for bleaching wood pulp with low cellulose content. For this purpose, FAS suggested. Furthermore, FAS is proposed if necessary in combination with sodium disulfite (Na₂S₂O₅) and a poly use phosphate.

US Pat. No. 3,481,828 discloses a process for bleaching Wood pulp known, a combination of bleaching agents 0.2-1% FAS and 1-5% ZnSO₄ is suggested.

EP-A-0 247 387 relates to a process for bleaching in the mass of colored paper and carbonless paper. 0.05-2.5% by weight of FAS is used as the bleaching agent. At a comparison with dithionite is found that the latter often even called the compound due to its degradation products loss of whiteness.

From DE-PS 33 09 956 a method for bleaching Pa pier raw materials, such as. B. waste paper, known. FAS becomes here used in a concentration of 0.05-3 wt .-%. The Bleaching step with FAS can be another bleaching step with Per oxide, dithionite or FAS downstream or a bleaching step be connected upstream with peroxide or dithionite. The simultaneous  Use a combination of FAS and other bleaching agents tel is not disclosed.

FAS offers the bleaching of wood-containing DF waste paper grades Experience has shown that there are no advantages over hydrosulfite Lich its bleaching effect. However, it is significantly more expensive. Wuh urea is released after decomposition of the FAS. this leads to nitrogen enrichment in the process water. Dependent on of the municipal ordinances arise from the heightened Nitrogen freight in the wastewater additional wastewater costs. In serious cases can be the excessive nitrogen load in the Ab water even lead to the withdrawal of the production license.

The invention has for its object a reductive Bleaching agent for bleaching secondary fibers Waste paper, especially mass-colored paper and Carbonless papers and wood-poor or wood-free To provide waste paper, the bleaching effect of which which is comparable to formamidine sulfinic acid, whose However, nitrogen content compared to FAS is significantly reduced. In addition, a bleach is to be provided that is strong Wood-containing waste paper bleaches better than hydrosulfite or FAS.

The object of the invention is achieved by providing a reductive bleaching agent comprising, as reducing agent, a synergistically acting mixture of components (a), (b) and optionally (c), where
Component (a) comprises a dithionite salt, especially sodium or zinc dithionite;
Component (b) comprises at least one water-soluble metal salt of a hydroxyalkanesulfinic acid and / or a condensation product of this metal salt with ammonia, or a mixture thereof; and
Component (c) formamidine sulfinic acid (FAS) and / or a water-soluble metal salt, in particular a Na, K, or Zn salt thereof.

It has now surprisingly been found that the bleaching agent  The addition of dithionite (hydrosulfite) and / or FAS of water-soluble metal salts of hydroxyalkanesulfinic acids, preferably of hydroxyalkanesulfinates or of ammonia cone densification products of hydroxyalkanesulfinates, who increased that can. This fact is all the more surprising than that Bleaching action of hydroxyalkanesulfinates, such as. B. of sodium hydroxymethanesulfinate, alkali hydroxyethanesulfinate, alkali benzaldehyde sulfoxylate (alkali 1-hydroxy-1-phenyl-methane sulfinate) and the ammonia condensation products of Sodium hydroxymethanesulfinates, among the usual Bleaching conditions are significantly worse than that Bleaching effect of hydrosulfite or FAS.

The invention particularly relates to bleaches type described in the introduction, which are characterized in that the water-soluble metal salt of hydroxylated sulfinic acid a sulfinate of the formula (II)

is what
R₁ and R₂ are the same or different and represent a hydrogen atom, an alkyl group with fewer than five carbons such. B. methyl, ethyl, i- and n-propyl and i-, n- and t-butyl, or a phenyl radical;
x represents a number from 0 to 6,
n represents 1 or 2; and
M represents an alkali or alkaline earth metal atom.

Preferably one of the radicals R₁ and R₂ is methyl or Phenyl and the other residue for a hydrogen atom or both R₁ and R₂ are hydrogen. M stands out advantageously for an alkali metal atom, preferably for Na trium or potassium.

Such bleaches are particularly preferred, their hydroxy  alkanesulfinic acid salt component is selected from: sodium hydroxymethanesulfinate, sodium hydroxyethanesulfinate, potassium hy droxymethanesulfinate, potassium hydroxyethanesulfinate, sodium 1-hy droxy-1-phenyl methanesulfinate, potassium 1-hydroxy-1-phenyl methanesulfinate or the ammonia condensation product of Na triumhydroxymethanesulfinate; or mixtures thereof.

In the above formula (II) x is preferably 2 when R₁ and R₂ represent a hydrogen atom; otherwise x preferably takes the value 0.

In the above-mentioned bleaching agents according to the invention a preferred embodiment each of the three reduction mit tel components (a), (b) and (c) in a proportion of about 5 to contain about 90%. In these agents according to the invention a particularly advantageous synergistic bleaching effect observe. For example, components (a), (b) and (c) in a weight ratio of about 1 to 4: 1: 1 to 4, such as B. of about 1: 1: 1, 2, 3 or 4. The Ge weight ratio can also z. B. 2, 3 or 4: 1: 1 gene.

According to a further preferred embodiment, this comprises agents according to the invention only the above components (a) and (b), each of the components in a proportion of 2 to 98% can be included. The proportion by weight is preferably component (a) in the range from 98 to 50% by weight and com component (b) in the range of 2 to 50 wt .-%. Particularly preferred is a weight ratio of these components (a) and (b) in Range from approximately 1: 1 to 3: 1, in particular approximately 1: 1 to 2: 1, such as B. 1: 1, 1.5: 1 or 2: 1. Also with this component com combination is a surprisingly synergistic effect respect, think highly of.

The choice of a suitable weight ratio of the above Reduk Detergent components depend on the respective quality of the waste paper to be bleached. This is affected, for example flows from the lignin content or the proportion of mass-colored paper  in the waste paper to be treated. Based on the teaching However, the present invention does not prepare the person skilled in the art nerlei difficulties, the reducing agent according to the invention mix on the respective recovered paper quality opti times to set.

Through the combination of reducing agents according to the invention can the bleach costs with the same bleaching effect and same dosage when lightening mass-colored paper and carbonless papers and wood-poor or wood-free Papers are cut because of hydrosulfite and the commercial available hydroxyalkanesulfinates are significantly cheaper are as FAS. Hydrosulfite and the hydroxyalkane also help sulfinate to minimize the nitrogen pollution of the process water ren.

Sam used in connection with the present invention The term waste paper includes mass-colored papers writing papers, newspapers, magazines and computer papers etc. a. The bleach formulations according to the invention proper are suitable both for the bleaching of heavily wood-containing Altpa types of paper and for bleaching from low-wood to wood-free Waste paper types.

The bleach mixture according to the invention is advantageously used treated with a dedusting agent. This dust removal medium consists of a biodegradable ester oil and a biodegradable quaternary amine. As organic Logically degradable quaternary amines are preferably used Imidazolium derivatives, preferably 1-methyl-2-norstearyl-3- stearic acid amidoethyl methosulfate.

The biodegradable ester oil is preferably used Beet oil transesterification products. The dedusting agent is not used only for dedusting the powder mixture. It also improves Lich its flow behavior and it has a stabilizing effect. Known Dithionites are hygroscopic substances and decompose yourself in the presence of moisture. By oiling the Effect of hygroscopy suppressed. The amount added  Dedusting agents range from 0.1 to 1.5 % By weight, based on the total weight of the bleach.

The bleaching agent according to the invention can be used as a powder mixture Reducing agent components or as a combination of the components are available in form that can be dosed independently of one another.

The invention also relates to a method for bleaching of secondary fibers using the above Bleach. The bleach mixture according to the invention is using conventional reductive bleaching techniques used. The dosage amount is 0.05 to 2.5 wt .-% before adds 0.1 to 1.0 wt .-%, based on the amount of fiber (atro = on a dry basis).

The bleaching takes place in a temperature range from 20 to 100 ° C, preferably at 40 to 70 ° C. With disperger bleaching higher temperatures may occur in the short term, which Accelerate the bleaching effect significantly. The pH of the pulp before the bleach addition is between 7.5 and 11.0, be preferably between 8.0 and 10.0. After bleaching, the pH is Value between 6.0 and 8.0, preferably between 6.5 and 7.5. The consistency can be between 2 and 20% by weight, based on the Total weight of the pulp.

The following exemplary embodiments serve the further purpose clarification of the invention. The specified degrees of whiteness are determined according to ISO brightness R457. The hydroxymethanesulfinate is used as a dihydrate. The other hydroxyalkanesulfinates are used in anhydrous form.

example 1

Waste paper with no flotation is removed from the twin-wire press taken and diluted to 8 percent consistency. The deink fabric with a wood content of less than 10% and a share of approx. 32% Carbonless paper has a base whiteness of 72.0 points, the pH was 8.0. This deinked substance is included under various amounts of formamidine sulfinic acid, hydrosulfite, natri  umhydroxymethanesulfinate and mixtures of these three bleaches reagents treated. The bleaching chemicals become strong diluted sodium hydroxide solution, the weight ratio of NaOH to bleaching chemical was 1: 2.38.

The temperature during the bleaching test is 90 ° C. Fabric, the bleaching time is two hours.

The results of the test series can be seen in Table 1 and Fig. 1.

Example 2

Bulk colored paper with a wood content of approx. 5% is flotation-friendly and removed from the twin-wire press. The deinked substance with an initial pH of 7.9 will open a fabric density of 4% diluted and one hour with the in Table 2 bleach formulations described. The temperature in the fabric was 65 ° C during bleaching. The results are summarized in Table 2.

Table 2

Example 3

Waste paper with a wood content of less than 10% is in a flotation dinking plant with a production capacity of 220 tonnes of paper stock (atro) according to the usual tech niken thinks. The bleach is dosed directly after Twin-wire press just before the disperger. The paper stock be after the twin-wire press, a fabric density of 25% sits The pH value is 7. The temperature in the disperser is brief at 90 ° C. The paper stock then migrates through the Bleach tube. The dwell time in the bleaching tube is approximately 25 minutes Immediately after the Disperger and on the Variocleaner, the on the bleach tube is connected, fabric samples can be taken become.

During a test lasting several days, the bleaching became effect of FAS with a mixture of FAS: hydrosulfite: na triumhydroxymethanesulfinate = 4: 1: 1 examined.

The amount of bleach was 0.33% dry The amount of bleach to NaOH was reduced to 1: 0.5 parts by weight poses.

The test results are described in Table 3.  

Table 3

The indicated degrees of whiteness are average values
The whiteness determination (ISO Brightness R457) is carried out with Elre pho 2000

Example 4

Waste paper consisting of 50% newspapers and 50% magazines with a wood content of more than 60% is in a flotati onseinking plant with a capacity of 110 tonnes per day deinked secondary fiber. The paper stock after the twin wire press is diluted to 4.5% consistency with circulating water and then stayed reductive. Unbleached deinked fabric with a consistency of 4.5% is atro. 0.4% each Bleach reductively bleached. The temperature is 70 ° C, the pH of the stock suspension before adding bleach is 7.8. The bleaching time is one hour. The pale medium is dissolved in very dilute sodium hydroxide solution. The Ver ratio of bleach to NaOH is 1: 0.4 parts by weight. Hydrosulfite, FAS, Na-hydroxymethanesul are used as bleaching agents use finate and K-hydroxyethanesulfinate or their mixtures det. The results are summarized in Table 4.

Table 4

Example 5

Deinktstoff from a flotation deinking plant with one Wood content below 10% is at a consistency of 8% 90 ° C for two hours with various bleaches treated.

The pH value of the deinked substance was before the bleach was added at 8.0. In order to increase the bleaching effect of formamidic acid, the pH was raised to 9.0 with 0.1N NaOH.

The results are summarized in Table 5

Table 5

Claims (14)

1. bleach, characterized by a mixture of:

• (a) at least one dithionite salt;
• (b) at least one water-soluble metal salt of a hydroxyalkanesulfinic acid and / or a condensation product of this metal salt with ammonia, or a mixture thereof; and if necessary
• (c) formamidine sulfinic acid and / or a water-soluble metal salt thereof.

2. Bleaching agent according to claim 1, characterized in that the water-soluble metal salt of hydroxyalkanesulfinic acid is a sulfinate of the formula is what
R₁ and R₂ are the same or different and represent a hydrogen atom, an alkyl group having less than five carbon atoms or a phenyl radical;
x represents a number from 0 to 6; and
n represents 1 or 2; and
M represents an alkali or alkaline earth metal atom. 3. Bleaching agent according to claim 2, characterized in that one of the radicals R₁ and R₂ for methyl or phenyl and other radical represents a hydrogen atom; or both radicals R₁ and R₂ represent a hydrogen atom.   4. Bleaching agent according to claim 2 or 3, characterized net that M for an alkali metal atom, preferably for Na trium or potassium, and n represents 1. 5. Bleaching agent according to claim 4, characterized in that the hydroxyalkanesulfinic acid salt sodium hydroxymethanesulfi nat, sodium hydroxyethanesulfinate, potassium hydroxymethanesul finate, potassium hydroxyethanesulfinate, sodium 1-hydroxy-1 phenyl methanesulfinate, potassium 1-hydroxy-1-phenyl methane sulfinate or an ammonia condensation product from Natri umhydroxymethanesulfinate. 6. Bleaching agent according to one of claims 1 to 5, characterized characterized in that each of the three components (a), (b) and (c) in a proportion of 5 to 90%, based on the total weight of the agent, or each of the components (a) and (b) in a proportion of 2 to 98% each, based on the total weight of the agent. 7. Bleaching agent according to claim 6, characterized in that components (a), (b) and (c) in a weight ratio Ratio of (1 to 4): 1: (0 to 4) contains. 8. Bleaching agent according to one of claims 1 to 7, characterized characterized in that, based on the total weight of the By means of 0.1-1.5% by weight of a dedusting agent holds. 9. Bleaching agent according to claim 8, characterized in that the dustproofing agent is a biodegradable ester oil and comprises a biodegradable quaternary amine. 10. Bleaching agent according to claims 1-9, characterized in that it as a powder mixture of the three reducing agent compo or as a combination of the three components in independent dependent form is available. 11. Process for bleaching secondary fibers, thereby  characterized in that an aqueous waste paper pulp, based on the dry weight of the fiber, 0.05 to 2.5% by weight of a bleaching agent according to one of claims 1 to 10 adds and act under suitable conditions leaves until sufficient whiteness is reached. 12. The method according to claim 11, characterized in that the pulp fiber density is 2 to 20% by weight. 13. The method according to claim 11 or 12, characterized in net that the bleach at a temperature in the range of 20 to 100 ° C, preferably 40 to 70 ° C, performed becomes. 14. The method according to any one of claims 11 to 13, characterized ge indicates the pH of the pulp before bleach added at 7.5 to 11 and after bleaching at 6 to 8 lies.