EP0608687A1 - Process for improving the whiteness of chlorine-free bleached pulp - Google Patents
Process for improving the whiteness of chlorine-free bleached pulp Download PDFInfo
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- EP0608687A1 EP0608687A1 EP94100175A EP94100175A EP0608687A1 EP 0608687 A1 EP0608687 A1 EP 0608687A1 EP 94100175 A EP94100175 A EP 94100175A EP 94100175 A EP94100175 A EP 94100175A EP 0608687 A1 EP0608687 A1 EP 0608687A1
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- Prior art keywords
- chlorine
- pulp
- whiteness
- bleached
- cellulose
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/1026—Other features in bleaching processes
- D21C9/1042—Use of chelating agents
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- D—TEXTILES; PAPER
- D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
- D21C—PRODUCTION OF CELLULOSE BY REMOVING NON-CELLULOSE SUBSTANCES FROM CELLULOSE-CONTAINING MATERIALS; REGENERATION OF PULPING LIQUORS; APPARATUS THEREFOR
- D21C9/00—After-treatment of cellulose pulp, e.g. of wood pulp, or cotton linters ; Treatment of dilute or dewatered pulp or process improvement taking place after obtaining the raw cellulosic material and not provided for elsewhere
- D21C9/10—Bleaching ; Apparatus therefor
- D21C9/1084—Bleaching ; Apparatus therefor with reducing compounds
Definitions
- the invention relates to a process for increasing the whiteness of cellulose bleached without chlorine by treating the cellulose bleached without chlorine with an aqueous solution of a reducing agent.
- the unbleached pulp obtained from the production of wood pulp is generally very dark in color and is therefore unsuitable for many applications, in particular for the production of graphic papers, hygienic papers and special papers. Residues of lignin and lignin degradation products are responsible for the darkening, which change color due to their phenolic content during the pulp boiling and still adhere to the pulp fibers. In the case of the highest quality, so-called sulfate pulps, which are produced with the help of alkaline, sodium sulfide-containing lye, the darkening is particularly strong.
- Such sulfate pulps but also sulfite pulps and also sulfur-free pulps, are traditionally and most successfully bleached with chlorine, often in combination with chlorine dioxide and hypochlorite, since only chlorine is able to completely remove the dark lignin residues mentioned from the fiber without however, damage the fiber in any way and chemically break down the cellulose.
- the use of chlorine dioxide as a by-product in turn produces small amounts of free chlorine, which in turn provide organochlorine compounds in the bleaching waste water and in the pulp or paper. Therefore, the aim is to bleach cellulose without chlorine or oxidizing chlorine compounds.
- the object of the present invention is to provide an improved method for increasing the whiteness of cellulose bleached without chlorine.
- the object is achieved according to the invention with a method for increasing the whiteness of cellulose bleached without chlorine by treating the cellulose bleached without chlorine with an aqueous solution of a reducing agent if the treatment is carried out in the presence of complexing agents.
- the pulp is bleached essentially in two process stages. In the first stage of the process, pulp is subjected to chlorine-free bleaching using, for example, oxygen, ozone, hydrogen peroxide or water-soluble peroxides as the bleaching agent. If oxygen or hydrogen peroxide or peroxides are used as the bleaching agent, the pH is about 9 to 11. Sodium hydroxide solution is generally used to adjust the pH.
- the pH is about 2 to 4.
- the pulp can first be mixed with oxygen at temperatures of around 110 ° C in the alkaline pH range and then with ozone at a temperature of 40 ° C be bleached in the pH range of 2 to 6.
- the oxidative bleaching is usually followed by washing in order to separate the disruptive constituents from the pulp.
- Other combinations of oxidative bleaching are also possible.
- water glass is usually used as a stabilizer for hydrogen peroxide. By far the largest part of the water glass is removed from the cellulose fibers in the washing which is usually carried out after the oxidative bleaching. In this way, a maximum whiteness of 70% is achieved with commercially available cellulose.
- the chlorine-free bleached cellulose is treated with an aqueous solution of a reducing agent in the presence of complexing agents.
- reducing agents for the bleaching of cellulose bleached completely chlorine-free there are primarily the reducing agents which are already known as agents for bleaching wood pulp in the field of paper manufacture.
- these are salts of dithionic acid, in particular sodium dithionite (Na2S2O 4) and zinc dithionite (ZnS2O4), which are either used directly as a substance or in aqueous solution or in the pulp mill by known methods, for example from sodium boranate and sulfur dioxide or sodium sulfite or sodium bisulfite can be produced.
- Na2S2O4 sodium dithionite
- ZnS2O4 zinc dithionite
- you can also formamidine sulfinic acid (CH4N2O2S), also known as thiourea dioxide, or use their alkali salts.
- Sodium sulfite and sodium bisulfite or sulfur-free reducing agents such as sodium boranate are also effective.
- Sodium dithionite is preferably used.
- the reducing agents are used in amounts of 0.1 to 1.5% by weight, based on dry cellulose.
- complexing agents are, for example, nitrilotriacetic acid, ethylenediaminetetraacetic acid, ethylenediamine, propylenediamine, Hydroxypropylendiaminessigklare, Hydroxyethanoldiphosphonklare, diethylenetriaminetetraacetic acid, Diethylentriamintetramethylenphosphonklare, Hydroxyethyleniminodiessigklare, hydroxyethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid, diethanolglycine, ethanol glycine, citric acid, glucoheptonic acid, tartaric acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic ), Ethylenediaminetetra- (methylenephosphonic acid) and / or diethylenetriaminepenta- (m
- Biodegradable complexing agents are used with particular advantage.
- Suitable products of this type are, for example, ⁇ -alanine-N, N-diacetic acid, isoserinediacetic acid, aspartic diacetic acid, mixtures of the acids mentioned or the alkali metal or ammonium salts of these acids.
- the production ⁇ -alanine-diacetic acid and its alkali metal or ammonium salts are known, for example, from EP-A-0 356 972.
- the alkali metal or ammonium salts of the acids mentioned are prepared by neutralizing the acids with, for example, sodium hydroxide solution, potassium hydroxide solution, ammonia or amines such as methylamine, dimethylamine, trimethylamine, ethylene diamine, triethylamine, ethanolamine, diethanolamine, triethanolamine or morpholine or mixtures of the bases mentioned.
- the complexing agents are usually used in the reductive treatment of the pulp in amounts of 0.1 to 0.5, preferably 0.2 to 0.4% by weight, based on dry pulp.
- the treatment of the pulp according to the invention is carried out in an aqueous suspension of pulp at a pulp concentration of 3 to 25, preferably 3 to 5,% by weight.
- the use of complexing agents in the reductive treatment of cellulose bleached without chlorine leads to an increase in the whiteness of the cellulose compared to a reductive treatment of cellulose bleached without chlorine in the absence of complexing agents.
- the paper whiteness is determined by producing paper sheets with a basis weight of 400 g / m 2 on a Rapid-Köthen sheet former, then drying the sheets at 90 ° C. for 25 minutes and the whiteness with an Elrepho photometer at a wavelength of 457 nm determined as a percentage reflectance.
- 100 g of a needle sulfate pulp suspension made of chlorine-free bleached needle sulfate pulp with a whiteness of 71.4% and a consistency of 4% by weight are filled into a bag made of polyethylene, in each case based on dry needle sulfate pulp, with 0.12% by weight .-% ⁇ -Alanine diacetic acid in the form of the sodium salt and 1 wt .-% sodium dithionite.
- the pH of the sulfate pulp suspension is 6.
- the bag is then closed and the contents are homogenized by intensive kneading. After mixing, the bag is immersed for one hour in a water bath that has a temperature of 60 ° C. After that - how described above - the whiteness determined on paper sheets. It was 76.3%.
- Example 1 was repeated with the only exception that the reductive aftertreatment of the chlorine-free bleached needle sulfate pulp was carried out in the absence of the sodium salt of ⁇ -alaninediacetic acid.
- the whiteness of the paper sheets thus obtainable was 75.4%.
Abstract
Description
Die Erfindung betrifft ein Verfahren zur Erhöhung der Weiße von chlorfrei gebleichtem Zellstoff durch Behandlung des chlorfrei gebleichten Zellstoffs mit einer wäßrigen Lösung eines Reduktionsmittels.The invention relates to a process for increasing the whiteness of cellulose bleached without chlorine by treating the cellulose bleached without chlorine with an aqueous solution of a reducing agent.
Der bei der Herstellung von Zellstoff aus Holz erhaltene ungebleichte Zellstoff ist in der Regel sehr dunkel gefärbt und deshalb für viele Anwendungen, insbesondere für die Herstellung von graphischen Papieren, Hygienepapieren und Spezialpapieren, ungeeignet. Verantwortlich für die Dunkelfärbung sind Reste von Lignin und Ligninabbauprodukten, die sich aufgrund ihrer phenolischen Anteile bei der Zellstoffkochung verfärben und noch an den Zellstoffasern haften. Bei den hochwertigsten, sogenannten Sulfatzellstoffen, die mit Hilfe von alkalischer, Natriumsulfid enthaltender Lauge hergestellt werden, ist die Dunkelfärbung besonders stark. Solche Sulfatzellstoffe, aber auch Sulfitzellstoffe und auch schwefelfrei hergestellte Zellstoffe, werden traditionsgemäß und am erfolgreichsten mit Chlor gebleicht, häufig auch in Kombination mit Chlordioxid und Hypochlorit, da nur Chlor in der Lage ist, die erwähnten dunklen Ligninreste vollständig von der Faser zu entfernen, ohne jedoch die Faser in irgendeiner Weise zu schädigen und die Cellulose chemisch abzubauen.The unbleached pulp obtained from the production of wood pulp is generally very dark in color and is therefore unsuitable for many applications, in particular for the production of graphic papers, hygienic papers and special papers. Residues of lignin and lignin degradation products are responsible for the darkening, which change color due to their phenolic content during the pulp boiling and still adhere to the pulp fibers. In the case of the highest quality, so-called sulfate pulps, which are produced with the help of alkaline, sodium sulfide-containing lye, the darkening is particularly strong. Such sulfate pulps, but also sulfite pulps and also sulfur-free pulps, are traditionally and most successfully bleached with chlorine, often in combination with chlorine dioxide and hypochlorite, since only chlorine is able to completely remove the dark lignin residues mentioned from the fiber without however, damage the fiber in any way and chemically break down the cellulose.
In jüngster Zeit ist jedoch die Verwendung von Chlor bei der Bleiche aus Gründen des Umweltschutzes stark zurückgegangen, weil einerseits eine Entsorgung der Bleichlaugen, die biologisch nicht abbaubare chlororganische Kohlenwasserstoffe enthalten, nicht ohne Umweltprobleme möglich ist, und andererseits die Papiere, die mit Chlor gebleichten Zellstoff enthalten, noch geringe Reste von chlororganischen Verbindungen aufweisen. Man versucht deshalb, Chlor in der Bleiche von Sulfatzellstoff durch Chlordioxid zu ersetzen, doch bekommt man damit nicht ganz die mit Chlor erzielbare Weiße und das Chlordioxid greift außerdem oxidativ den Zellstoff an und vermindert dadurch seine Qualität. Erschwerend kommt hinzu, daß beim Einsatz von Chlordioxid als Nebenprodukt wiederum geringe Mengen freies Chlor entstehen, die ihrerseits wieder für chlororganische Verbindungen im Bleichereiabwasser und im Zellstoff bzw. Papier sorgen. Daher strebt man eine Zellstoffbleiche ohne Chlor oder oxidierende Chlorverbindungen an.Recently, however, the use of chlorine in bleaching has declined sharply for reasons of environmental protection because, on the one hand, it is not possible to dispose of the bleaching liquors, which contain biodegradable chloroorganic hydrocarbons, without environmental problems, and on the other hand, the paper, the chlorine-bleached pulp contain, still have small residues of organochlorine compounds. An attempt is therefore made to replace chlorine in the bleaching of sulfate pulp with chlorine dioxide, but this does not quite achieve the whiteness which can be achieved with chlorine and the chlorine dioxide also oxidatively attacks the pulp and thereby reduces its quality. To make matters worse, the use of chlorine dioxide as a by-product in turn produces small amounts of free chlorine, which in turn provide organochlorine compounds in the bleaching waste water and in the pulp or paper. Therefore, the aim is to bleach cellulose without chlorine or oxidizing chlorine compounds.
Als interessantes Bleichmittel hat sich bisher Ozon erwiesen, doch ist dieses aggressive Produkt sehr teuer und greift aufgrund seiner hohen Oxidationskraft auch in hohem Maße die Cellulose an. Deshalb versucht man, das im Zellstoff noch vorhandene dunkel gefärbte restliche Lignin mit weniger wirksamen, aber auch weniger faserschädigenden und umweltfreundlicheren Chemikalien, wie Sauerstoff und Wasserstoffperoxid zu bleichen. Dies gelingt mit leidlichem Erfolg bei dem sogenannten Sulfitzellstoff, ist aber auch hier für die meisten Zwecke nicht recht befriedigend. Völlig unzureichend ist dagegen die Bleiche von Sulfatzellstoff mit Sauerstoff und Peroxid. Die so gebleichten Zellstoffe haben eine Weiße von maximal ca. 70 %, während ein guter, mit Chlor gebleichter Sulfatzellstoff normalerweise eine Weiße bis ca. 95 % aufweist. Eine Weiße von 70 % oder darunter ist für viele Einsatzzwecke von Zellstoff nicht akzeptabel.So far, ozone has proven to be an interesting bleach, but this aggressive product is very expensive and, due to its high oxidizing power, also attacks cellulose to a high degree. For this reason, attempts are made to bleach the dark-colored residual lignin still present in the pulp with less effective, but also less fiber-damaging and environmentally friendly chemicals, such as oxygen and hydrogen peroxide. This succeeds with reasonable success with the so-called sulfite pulp, but is also not quite satisfactory here for most purposes. On the other hand, the bleaching of sulfate pulp with oxygen and peroxide is completely inadequate. The pulps bleached in this way have a maximum whiteness of approximately 70%, while a good sulfate pulp bleached with chlorine normally has a whiteness of approximately 95%. A whiteness of 70% or below is not acceptable for many uses of pulp.
Aus Tappi Journal, Vol. 67, Nr. 8, 76 bis 80 (1984), ist bekannt, daß oxidativ gebleichter Kraftzellstoff zur Erhöhung der Weiße mit Natriumdithionit nachbehandelt wird.From Tappi Journal, Vol. 67, No. 8, 76 to 80 (1984), it is known that oxidatively bleached kraft pulp is aftertreated with sodium dithionite to increase the whiteness.
Der vorliegenden Erfindung liegt die Aufgabe zugrunde, ein verbessertes Verfahren zur Erhöhung der Weiße von chlorfrei gebleichten Zellstoffen zur Verfügung zu stellen.The object of the present invention is to provide an improved method for increasing the whiteness of cellulose bleached without chlorine.
Die Aufgabe wird erfindungsgemäß gelöst mit einem Verfahren zur Erhöhung der Weiße von chlorfrei gebleichtem Zellstoff durch Behandlung des chlorfrei gebleichten Zellstoffs mit einer wäßrigen Lösung eines Reduktionsmittels, wenn die Behandlung in Gegenwart von Komplexbildnern vorgenommen wird. Die Bleiche des Zellstoffs erfolgt im wesentlichen in zwei Verfahrensstufen. In der ersten Stufe des Verfahrens wird Zellstoff einer chlorfreien Bleiche unterworfen, indem man als Bleichmittel z.B. Sauerstoff, Ozon, Wasserstoffperoxid oder wasserlösliche Peroxide verwendet. Wenn man als Bleichmittel Sauerstoff oder Wasserstoffperoxid bzw. Peroxide verwendet, arbeitet man bei pH-Werten von etwa 9 bis 11. Zur Einstellung des pH-Wertes wird in aller Regel Natronlauge verwendet. Sofern man die oxidative Bleiche mit Ozon als Bleichmittel durchführt, beträgt der pH-Wert etwa 2 bis 4. Der Zellstoff kann zunächst mit Sauerstoff bei Temperaturen von etwa 110°C im alkalischen pH-Bereich und anschließend mit Ozon bei einer Temperatur von 40°C in dem pH-Bereich von 2 bis 6 gebleicht werden. An die oxidative Bleiche schließt sich üblicherweise eine Wäsche an, um die störenden Bestandteile vom Zellstoff abzutrennen. Auch andere Kombinationen der oxidativen Bleiche sind möglich. Beim Einsatz von Wasserstoffperoxid verwendet man üblicherweise Wasserglas als Stabilisator für Wasserstoffperoxid. Der weitaus größte Teil des Wasserglases wird bei der Wäsche, die im Anschluß an die oxidative Bleiche üblicherweise durchgeführt wird, von den Cellulosefasern entfernt. Man erreicht auf diese Weise bei handelsüblichen Zellstoffen eine Weiße von maximal 70 %.The object is achieved according to the invention with a method for increasing the whiteness of cellulose bleached without chlorine by treating the cellulose bleached without chlorine with an aqueous solution of a reducing agent if the treatment is carried out in the presence of complexing agents. The pulp is bleached essentially in two process stages. In the first stage of the process, pulp is subjected to chlorine-free bleaching using, for example, oxygen, ozone, hydrogen peroxide or water-soluble peroxides as the bleaching agent. If oxygen or hydrogen peroxide or peroxides are used as the bleaching agent, the pH is about 9 to 11. Sodium hydroxide solution is generally used to adjust the pH. If the oxidative bleaching is carried out with ozone as a bleaching agent, the pH is about 2 to 4. The pulp can first be mixed with oxygen at temperatures of around 110 ° C in the alkaline pH range and then with ozone at a temperature of 40 ° C be bleached in the pH range of 2 to 6. The oxidative bleaching is usually followed by washing in order to separate the disruptive constituents from the pulp. Other combinations of oxidative bleaching are also possible. When using hydrogen peroxide, water glass is usually used as a stabilizer for hydrogen peroxide. By far the largest part of the water glass is removed from the cellulose fibers in the washing which is usually carried out after the oxidative bleaching. In this way, a maximum whiteness of 70% is achieved with commercially available cellulose.
In der zweiten Stufe des erfindungsgemäßen Verfahrens werden die chlorfrei gebleichten Zellstoffe in Gegenwart von Komplexbildnern mit einer wäßrigen Lösung eines Reduktionsmittels behandelt.In the second stage of the process according to the invention, the chlorine-free bleached cellulose is treated with an aqueous solution of a reducing agent in the presence of complexing agents.
Als Reduktionsmittel für die Bleiche von völlig chlorfrei gebleichtem Zellstoff kommen in erster Linie die Reduktionsmittel in Frage, die bereits als Mittel zur Holzstoffbleiche im Bereich der Papierherstellung bekannt sind. In erster Linie handelt es sich dabei um Salze der dithionigen Säure, insbesondere um Natriumdithionit (Na₂S₂O4) und Zinkdithionit (ZnS₂O₄), die entweder direkt als Substanz bzw. in wäßriger Lösung eingesetzt werden oder aber in der Zellstoffabrik nach bekannten Methoden, z.B. aus Natriumboranat und Schwefeldioxid bzw. Natriumsulfit oder Natriumbisulfit hergestellt werden. Man kann aber auch Formamidinsulfinsäure (CH₄N₂O₂S), auch als Thioharnstoffdioxid bekannt, oder deren Alkalisalze verwenden. Wirksam sind auch Natriumsulfit und Natriumbisulfit oder auch schwefelfreie Reduktionsmittel wie z.B. Natriumboranat. Technisch am interessantesten ist allerdings die Verwendung von Salzen des Dithionits, unabhängig von ihrer Herstellungsweise. Vorzugsweise verwendet man Natriumdithionit. Die Reduktionsmittel werden in Mengen von 0,1 bis 1,5 Gew.-%, bezogen auf trockenen Zellstoff, eingesetzt.As reducing agents for the bleaching of cellulose bleached completely chlorine-free, there are primarily the reducing agents which are already known as agents for bleaching wood pulp in the field of paper manufacture. Primarily, these are salts of dithionic acid, in particular sodium dithionite (Na₂S₂O 4) and zinc dithionite (ZnS₂O₄), which are either used directly as a substance or in aqueous solution or in the pulp mill by known methods, for example from sodium boranate and sulfur dioxide or sodium sulfite or sodium bisulfite can be produced. But you can also formamidine sulfinic acid (CH₄N₂O₂S), also known as thiourea dioxide, or use their alkali salts. Sodium sulfite and sodium bisulfite or sulfur-free reducing agents such as sodium boranate are also effective. The most technically interesting, however, is the use of salts of dithionite, regardless of their method of production. Sodium dithionite is preferably used. The reducing agents are used in amounts of 0.1 to 1.5% by weight, based on dry cellulose.
Als Komplexbildner können sämtliche Verbindungen verwendet werden, die in der Lage sind, Schwermetallionen wie Calcium-, Eisen-, Nickel-, Cobalt- und Manganionen zu komplexieren. Bekannte Komplexbildner sind beispielsweise Nitrilotriessigsäure, Ethylendiamintetraessigsäure, Ethylendiamintetramethylenphosphonsäure, Propylendiamintetraessigsäure, Hydroxypropylendiaminessigsäure, Hydroxyethanoldiphosphonsäure, Diethylentriamintetraessigsäure, Diethylentriamintetramethylenphosphonsäure, Hydroxyethyleniminodiessigsäure, Hydroxyethylendiamintriessigsäure, Diethylentriaminpentaessigsäure, Diethanolglycin, Ethanolglycin, Citronensäure, Glucoheptonsäure, Weinsäure, 1-Hydroxyethyliden-1,1-diphosphonsäure, Aminotri-(methylenphosphonsäure), Ethylendiamintetra-(methylenphosphonsäure) und/oder Diethylentriaminpenta-(methylenphosphonsäure). Mit besonderem Vorteil werden biologisch abbaubare Komplexbildner eingesetzt. Geeignete Produkte dieser Art sind beispielsweise β-Alanin-N,N-diessigsäure, Isoserindiessigsäure, Asparagindiessigsäure, Mischungen der genannten Säuren oder die Alkalimetall- oder Ammoniumsalze dieser Säuren. Die Herstellung von β-Alanin-diessigsäure und ihren Alkalimetall- oder Ammoniumsalzen ist beispielsweise aus der EP-A-0 356 972 bekannt. Die Alkalimetall- oder Ammoniumsalze der genannten Säuren werden durch Neutralisieren der Säuren mit beispielsweise Natronlauge, Kalilauge, Ammoniak oder Aminen wie Methylamin, Dimethylamin, Trimethylamin, Ethylendiamin, Triethylamin, Ethanolamin, Diethanolamin, Triethanolamin oder Morpholin bzw. Mischungen der genannten Basen hergestellt. Die Komplexbildner werden bei der reduktiven Behandlung des Zellstoffs üblicherweise in Mengen von 0,1 bis 0,5, vorzugsweise von 0,2 bis 0,4 Gew.-%, bezogen auf trockenen Zellstoff, eingesetzt.All compounds capable of complexing heavy metal ions such as calcium, iron, nickel, cobalt and manganese ions can be used as complexing agents. Known complexing agents are, for example, nitrilotriacetic acid, ethylenediaminetetraacetic acid, ethylenediamine, propylenediamine, Hydroxypropylendiaminessigsäure, Hydroxyethanoldiphosphonsäure, diethylenetriaminetetraacetic acid, Diethylentriamintetramethylenphosphonsäure, Hydroxyethyleniminodiessigsäure, hydroxyethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid, diethanolglycine, ethanol glycine, citric acid, glucoheptonic acid, tartaric acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic ), Ethylenediaminetetra- (methylenephosphonic acid) and / or diethylenetriaminepenta- (methylenephosphonic acid). Biodegradable complexing agents are used with particular advantage. Suitable products of this type are, for example, β-alanine-N, N-diacetic acid, isoserinediacetic acid, aspartic diacetic acid, mixtures of the acids mentioned or the alkali metal or ammonium salts of these acids. The production β-alanine-diacetic acid and its alkali metal or ammonium salts are known, for example, from EP-A-0 356 972. The alkali metal or ammonium salts of the acids mentioned are prepared by neutralizing the acids with, for example, sodium hydroxide solution, potassium hydroxide solution, ammonia or amines such as methylamine, dimethylamine, trimethylamine, ethylene diamine, triethylamine, ethanolamine, diethanolamine, triethanolamine or morpholine or mixtures of the bases mentioned. The complexing agents are usually used in the reductive treatment of the pulp in amounts of 0.1 to 0.5, preferably 0.2 to 0.4% by weight, based on dry pulp.
Die erfindungsgemäße Behandlung des Zellstoffs wird in einer wäßrigen Anschlämmung von Zellstoff bei einer Zellstoffkonzentration von 3 bis 25, vorzugsweise von 3 bis 5 Gew.-% durchgeführt. Man kann dabei beispielsweise so vorgehen, daß man den partiell gebleichten Zellstoff zunächst mit einer wäßrigen Lösung eines Komplexbildners vermischt oder den Komplexbildner zu einer Aufschlämmung des Zellstoffs in Wasser zuführt. Man kann jedoch auch so vorgehen, daß man zu einem Zellstoffbrei eine wäßrige Lösung zufügt, die ein Reduktionsmittel und einen Komplexbildner oder eine Mischung mehrerer Komplexbildner enthält. Die Mitverwendung von Komplexbildnern bei der reduktiven Behandlung von chlorfrei gebleichtem Zellstoff führt zu einer Erhöhung der Weiße des Zellstoffs gegenüber einer reduktiven Behandlung von chlorfrei gebleichtem Zellstoff in Abwesenheit von Komplexbildnern.The treatment of the pulp according to the invention is carried out in an aqueous suspension of pulp at a pulp concentration of 3 to 25, preferably 3 to 5,% by weight. One can proceed, for example, by first mixing the partially bleached cellulose with an aqueous solution of a complexing agent or by feeding the complexing agent into a slurry of the cellulose in water. However, one can also proceed by adding an aqueous solution to a pulp slurry which contains a reducing agent and a complexing agent or a mixture of several complexing agents. The use of complexing agents in the reductive treatment of cellulose bleached without chlorine leads to an increase in the whiteness of the cellulose compared to a reductive treatment of cellulose bleached without chlorine in the absence of complexing agents.
Die Papierweiße wird bestimmt, indem man auf einem Rapid-Köthen-Blatt-Bildner Papierblätter mit einem Flächengewicht von 400 g/m² herstellt, die Blätter dann 25 Minuten bei 90°C trocknet und die Weiße mit einem Elrepho-Photometer bei einer Wellenlänge von 457 nm als Prozent Remissionsgrad ermittelt.The paper whiteness is determined by producing paper sheets with a basis weight of 400 g / m 2 on a Rapid-Köthen sheet former, then drying the sheets at 90 ° C. for 25 minutes and the whiteness with an Elrepho photometer at a wavelength of 457 nm determined as a percentage reflectance.
100 g einer Nadel-Sulfatzellstoffsuspension aus chlorfrei gebleichtem Nadel-Sulfatzellstoff mit einer Weiße von 71,4 % von einer Stoffdichte von 4 Gew.-% werden in einen Beutel aus Polyethylen gefüllt, jeweils bezogen auf trockenen Nadel-Sulfatzellstoff, mit 0,12 Gew.-% β-Alanindiessigsäure in Form des Natriumsalzes und 1 Gew.-% Natriumdithionit versetzt. Der pH-Wert der Sulfatzellstoffsuspension beträgt 6. Der Beutel wird dann verschlossen und der Inhalt durch intensives Kneten homogenisiert. Nach dem Durchmischen taucht man den Beutel eine Stunde in ein Wasserbad ein, das eine Temperatur von 60°C hat. Danach wird - wie oben beschrieben - die Weiße an Papierblättern bestimmt. Sie betrug 76,3 %.100 g of a needle sulfate pulp suspension made of chlorine-free bleached needle sulfate pulp with a whiteness of 71.4% and a consistency of 4% by weight are filled into a bag made of polyethylene, in each case based on dry needle sulfate pulp, with 0.12% by weight .-% β-Alanine diacetic acid in the form of the sodium salt and 1 wt .-% sodium dithionite. The pH of the sulfate pulp suspension is 6. The bag is then closed and the contents are homogenized by intensive kneading. After mixing, the bag is immersed for one hour in a water bath that has a temperature of 60 ° C. After that - how described above - the whiteness determined on paper sheets. It was 76.3%.
Beispiel 1 wurde mit der einzigen Ausnahme wiederholt, daß man die reduktive Nachbehandlung des chlorfrei gebleichten Nadel-Sulfatzellstoffs in Abwesenheit des Natriumsalzes von β-Alanindiessigsäure durchführte. Die Weiße der so erhältlichen Papierblätter betrug 75,4 %.Example 1 was repeated with the only exception that the reductive aftertreatment of the chlorine-free bleached needle sulfate pulp was carried out in the absence of the sodium salt of β-alaninediacetic acid. The whiteness of the paper sheets thus obtainable was 75.4%.
Claims (4)
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE4301802 | 1993-01-23 | ||
| DE19934301802 DE4301802A1 (en) | 1993-01-23 | 1993-01-23 | Process for increasing the whiteness of cellulose bleached without chlorine |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| EP0608687A1 true EP0608687A1 (en) | 1994-08-03 |
Family
ID=6478793
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP94100175A Withdrawn EP0608687A1 (en) | 1993-01-23 | 1994-01-07 | Process for improving the whiteness of chlorine-free bleached pulp |
Country Status (2)
| Country | Link |
|---|---|
| EP (1) | EP0608687A1 (en) |
| DE (1) | DE4301802A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| USH1690H (en) * | 1995-07-20 | 1997-11-04 | Nye; Jeffrey | Process for bleaching kraft pulp |
| US6998015B2 (en) * | 1998-10-28 | 2006-02-14 | Pulp And Paper Research Institute Of Canada | Method for reducing alkaline darkening of mechanical pulp containing a calcium carbonate filler |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4340043A1 (en) * | 1993-11-24 | 1995-06-01 | Henkel Kgaa | Use of nitrogen-containing complexing agents in wood pulp bleaching |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3531563A1 (en) * | 1985-09-04 | 1987-03-05 | Benckiser Knapsack Gmbh | WOOD FABRICS |
| DE4128084A1 (en) * | 1991-08-24 | 1993-02-25 | Basf Ag | Beta-alanine-N,N-di:acetic acid, alkali or ammonium salt complex former in paper mfr. - useful for biodegradable alkaline earth and heavy metal ion complexant in bleaching mechanical wood pulp and printed waste paper de inking |
-
1993
- 1993-01-23 DE DE19934301802 patent/DE4301802A1/en not_active Withdrawn
-
1994
- 1994-01-07 EP EP94100175A patent/EP0608687A1/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3531563A1 (en) * | 1985-09-04 | 1987-03-05 | Benckiser Knapsack Gmbh | WOOD FABRICS |
| DE4128084A1 (en) * | 1991-08-24 | 1993-02-25 | Basf Ag | Beta-alanine-N,N-di:acetic acid, alkali or ammonium salt complex former in paper mfr. - useful for biodegradable alkaline earth and heavy metal ion complexant in bleaching mechanical wood pulp and printed waste paper de inking |
Non-Patent Citations (1)
| Title |
|---|
| LIEBERGOTT N. ET AL.: "Bleaching a softwood kraft pulp without chlorine compounds.", TAPPI JOURNAL, vol. 67, no. 8, August 1984 (1984-08-01), ATLANTA US, pages 76 - 80 * |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| USH1690H (en) * | 1995-07-20 | 1997-11-04 | Nye; Jeffrey | Process for bleaching kraft pulp |
| US6998015B2 (en) * | 1998-10-28 | 2006-02-14 | Pulp And Paper Research Institute Of Canada | Method for reducing alkaline darkening of mechanical pulp containing a calcium carbonate filler |
Also Published As
| Publication number | Publication date |
|---|---|
| DE4301802A1 (en) | 1994-07-28 |
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