EP0317921B1 - Bleaching agent additive - Google Patents

Abstract

An alkaline peroxide-containing bleaching agent (bleach) for chemical woodpulp, mechanical pulp and waste paper and/or their mixtures, which also contains, if desirable, waterglass and/or a complexing agent, contains as an additive a silicaceous ion exchanger modified with an alkali metal carbonate or an alkali metal hydrogen carbonate.

Description

The invention relates to an addition to an alkaline peroxide-containing bleaching agent for cellulose, wood pulp, waste paper and / or mixtures thereof, and to the use thereof in such a bleaching agent and to a bleaching process.

JP-A-59/145 300 relates to a bleaching detergent containing a type X zeolite and an H₂O₂ addition compound, namely sodium percarbonate. So it is not a (peroxide-free) bleach additive. While it is stated that the bleaching detergents are said to have excellent stability; however, this is only valid to a limited extent, since sodium percarbonate loses its active oxygen in a relatively short time.

JP-A-77 74 605 also relates to bleaching and cleaning agents which are reaction products of zeolites with H₂O₂. Again, there are no (peroxide-free) bleach additives as precursors to bleaching and cleaning agents. The bleaching and cleaning agent should also contain sodium carbonate, but only in a mixture with the H₂O₂ zeolite reaction product, so that the storage stability is relatively low.

DE-A-25 35 283 relates to bleaching or oxidizing water-insoluble silicates with cation exchange capacity, which additionally contain hydrogen peroxide. Again, it is not a peroxide-free bleach additive. The product is unstable because the hydrogen peroxide in the silicate decomposes during storage. The prior binding of H₂O₂ to the silicate cation exchanger is essential. Strong alkalis are required to activate the hydrogen peroxide, which lead to irreversible alkali yellowing and a high concentration of contaminants (high COD value), especially in the case of wood pulp.

The bleaching is said to reliably achieve high final whiteness contents with the least possible investment, with a minimum of running costs and, if possible, without any adverse side effects.

In principle, only a lignin-preserving bleach comes into consideration for the lightening of wood pulp, be it in the form of sanding, pressure sanding, refiner material, thermomechanical or chemical-thermomechanical material and waste paper in contrast to cellulose bleaching. Usually hydrogen peroxide (H₂O₂) is used as bleach. The lignin-removing bleach with oxygen and / or hydrogen peroxide is also used in the production of cellulose.

The lignins, lignin-like phenols and extract substances and their degradation products, which form chromophore systems as a result of the presence of conjugated double bonds and auxochromic groups, are essentially responsible for the brownish-yellow color of the wood materials. Increasing the white content without removing lignin requires specific destruction of the chromophoric systems, if possible without triggering substances, since a content of organic substances in the bleaching medium would increase the chemical oxygen demand (COD).

The processes involved in bleaching in lignin-preserving bleaching and their mechanisms are not yet precisely known.

Hydrogen peroxide breaks down according to two reaction mechanisms. In homolytic decay, which is given by the equation



H₂O₂ → 2 HO ̇ → H₂O + O₂ (1)



can be represented, the formation of hydroxide radicals takes place, which react in a chain reaction to the decay products water and oxygen. This inherently exothermic reaction is normally prevented by the high activation energy for the separation of the oxygen-oxygen bond in H₂O₂. However, it can be catalyzed in particular by heavy metals and their compounds, which are often contained in bleaching liquids. Homolytic decay can thus become the main reaction. However, this is not desirable since this course of the reaction gives rise to oxidative damage and bleaches only a little in the desired sense. In order to prevent this reaction, the presence of peroxide stabilizers and complexing agents was considered necessary during the bleaching process.

The desired reaction of the hydrogen peroxide is dissociation in water according to the equation



H₂O + H₂O₂ ⇄ HO₂⁻ + H₃O⁺ (2)



The equilibrium constant of this reaction is 1.78 x 10⁻¹² at room temperature. Of importance here is the perhydroxide anion (HO₂⁻), which is generally regarded as a bleaching reagent. A concentration can be increased by increasing the H₂O₂ concentration or by adding alkali and removing the acid. The latter is carried out generally and one speaks of the activation of the hydrogen peroxide.

In the lignin-removing bleaching with H₂O₂ in an alkaline environment, not only the perhydroxide anions but also the HO ̇ radicals according to equation (1) and other peroxide radicals can form without the use of stabilizers made of hydrogen peroxide being able to lead. Here in particular are traces Effective from heavy metals, so it is important to eliminate them.

The bleaching technology requirements can therefore be summarized as follows:

1. Activation of the bleach with alkali

The right ratio between hydrogen peroxide and alkali is very important, this ratio being temperature-dependent. In both the lignin-preserving and the lignin-removing bleaches, the amount of alkali must be matched to the amount of hydrogen peroxide used. The pollution of the circulating water also depends on this. For wood pulp bleach stabilized with water glass and deinking, an initial pH value of 10.5 to 11 is usually set. The whiteness maxima are shifted with increasing amounts of hydrogen peroxide to higher alkali inputs (primarily sodium hydroxide). It was previously believed that peroxide bleaching was not sufficiently activated at low alkali hydroxide concentrations.

2. Stabilization of the hydrogen peroxide

To prevent the formation of hydroxide radicals according to equation (1), various stabilizers have already been used.

(a) Water glass

The chemistry of the stabilization of hydrogen peroxide by water glass in alkaline solution has not yet been clarified. The reason for this is probably the very difficult colloidal chemical processes. The water glass probably also binds heavy metals. Furthermore, the stabilization with water glass in connection with magnesium ions important for wood pulp bleaching. In addition to its stabilizing effect, the water glass also acts as an alkali dispenser and buffer substance as well as a wetting and dispersing agent. It can also be used inexpensively.

Because of some disadvantages, which will be discussed in more detail below, there has been no lack of efforts to replace or supplement the water glass with other substances.

(b) complexing agent

The attempt to reduce the use of water glass has led to the use of complexing agents. As a rule, compounds complexing heavy metals are used for this. Among the inorganic chelating agents, the polyphosphates, mainly sodium tripolyphosphate, are important. The organic complexing agents are mainly the polyhydroxycarboxylic acids (e.g. gluconic acid), the aminopolycarboxylic acids (e.g. nitrilotriacetic acid = NTA, ethylenediaminetetraacetic acid = EDTA, diethylenetriamineopentaacetic acid = DTPA) and polyphosphonic acids (ATMP, EDMP, DTPMP).

Compared to the free heavy metal ions, complexed heavy metal ions are no longer able to catalytically decompose hydrogen peroxide according to equation (1).

The adverse effects of today's necessary bleaching conditions on the bleaching process and the papermaking process can be summarized as follows:

1. Effect of alkali

The most important chemical in wood pulp and waste paper bleaching, as well as for good ink detachment and thus for the highest possible lightening of the fiber materials the sodium hydroxide. This effect is counteracted by a partially irreversible yellowing of the alkali, depending on the treatment conditions.

There is also a substantially linear function of the dependence of the COD on the NaOH concentration, i.e. with increasing NaOH concentration, the content of organic substances in the bleaching medium increases. A high COD load causes an increased consumption of hydrogen peroxide and reduces the strength properties of the fiber materials. Furthermore, a high COD load acts as a "disruptive substance" due to unwanted interactions with cationic auxiliaries, the effectiveness of which is impaired. Production disruptions can also occur due to increased deposits.

2. Effects of water glass

Since water glass reacts alkaline, there are basically the adverse effects mentioned for alkali. There may also be production disruptions, e.g. in the presence of alkaline earth ions are caused by the precipitation of alkaline earth silicates. Furthermore, the hydrolytic reactions of the water glass lead to the formation of deposits on pipelines, cells, suction rolls, sieves, calenders, etc., and finally the action of retention aids and flocculants is impaired, which leads to a poorer efficiency and an increased consumption of these chemicals.

3. Effect of hardness agents

Since calcium carbonate is used in large quantities as a filler and coating pigment in the paper industry, carbonate hardnesses of 100 ° dH and above occur in the paper mills depending on the closed circuit. The Ca⁺² ions dissolved in the circulating water impair the bleaching effect of the Hydrogen peroxide, since they consume both water glass and complexing agents so that they can no longer form heavy metals, which leads to the undesirable peroxide decomposition according to equation (1). If the complexing agent is in a substoichiometric ratio with respect to polyvalent metal ions, carbonates and insoluble salts of the complexing agents with the hardness formers of the water can precipitate. These precipitations can lead to considerable production disruptions.

The invention has for its object to reduce or even avoid the use of alkalis, water glass and / or complexing agents in the bleaching of pulp, wood pulp, waste paper and / or their mixtures, and even avoid them, and still products with comparable or even higher whiteness to obtain.

The invention thus relates to an additive to an alkaline, peroxide-containing bleach for cellulose, wood pulp, waste paper and / or mixtures thereof, which may also contain water glass and / or a complexing agent, which is characterized in that it is a water-insoluble material modified with an alkali metal carbonate or alkali metal bicarbonate represents inorganic silicate ion exchanger.

By adding the modified silicate ion exchanger, bleaching with hydrogen peroxide without addition or only with small additions of alkali hydroxide, i.e. in the neutral to weakly alkaline pH range and without addition or only with small additions of water glass and without, can be carried out, contrary to the previous knowledge Achieve addition or only with small amounts of complexing agents, the fiber products obtained having high degrees of whiteness. Furthermore, by adding the modified ion exchanger, in addition to the lower water cycle load (COD load), a cycle relief by adsorption of Contaminants. However, when using the modified silicate ion exchangers in combination with alkali, water glass or complexing agents, which can be used in smaller quantities than previously, better bleaching results are obtained than with the products mentioned.

• 1. Aktivierung des Wasserstoffperoxids auch im neutralen bzw. schwach alkalischen pH-Bereich, was aufgrund der Gleichung (2) an sich nicht vorhersehbar war;
• 2. Bevorzugter Ionenaustausch bzw. Adsorption von zersetzend wirkenden Schwermetallionen, wodurch eine Verwendung von Komplexbildnern und/oder Wasserglas nicht mehr bzw. nur in geringerer Konzentration als bisher erforderlich ist.
• 3. Absorption von organischen "Störstoffen", die das Bleichergebnis nachteilig beeinflussen.

Based on the investigations to date, the modified functions of the silicate ion exchangers can be attributed to the following functions in hydrogen peroxide bleaching:

• 1. Activation of the hydrogen peroxide also in the neutral or weakly alkaline pH range, which was not predictable per se due to equation (2);
• 2. Preferred ion exchange or adsorption of decomposing heavy metal ions, whereby the use of complexing agents and / or water glass is no longer required or only in a lower concentration than previously.
• 3. Absorption of organic "contaminants" that adversely affect the bleaching result.

• 1. Vermeidung einer irreversiblen Alkalivergilbung;
• 2. Vermeidung von hohen CSB-Frachten und deren Folgereaktionen, wie z.B. erhöhter Verbrauch an Wasserstoffperoxid, Festigkeitseinbußen, Wirksamkeitsbeeinträchtigung kationischer chemischer Hilfsmittel, Produktionsstörungen durch Ablagerungen;
• 3. Vermeidung der Wirksamkeitsbeeinträchtigung von Retentions-und Flockungsmittel durch Wasserglas;
• 4. Verhinderung von Kieselsäure-Ausfällungen aus dem Wasserglas an Saugwalzen, Sieben usw.;
• 5. Vermeidung von Ausfällungen von unlöslichen Salzen von Härtebildnern mit Komplexbildnern.

The complete or partial omission of alkali hydroxide, water glass or complexing agent results in the following advantages:

• 1. Avoidance of irreversible alkali yellowing;
• 2. Avoidance of high COD loads and their subsequent reactions, such as, for example, increased consumption of hydrogen peroxide, loss of strength, impairment of effectiveness of cationic chemical auxiliaries, production disturbances due to deposits;
• 3. Avoidance of the effectiveness of retention and flocculants through water glass;
• 4. Prevention of silica precipitation from the water glass on suction rolls, screens, etc .;
• 5. Avoiding the precipitation of insoluble salts of hardening agents with complexing agents.

In the bleach additive according to the invention, the silicate ion exchanger is preferably modified by coating it with 1 to 70, in particular with 5 to 50,% by weight, based on the total additive, of alkali carbonate or alkali metal bicarbonate.

Preferably the silicate ion exchanger (i.e. the non-carbonate or bicarbonate component) has a BET surface area of at least 30 m² / g and a cation exchange capacity of at least 30 meq / 100 g.

The silicate ion exchanger is preferably a smectitic clay mineral, an attapulgite or a natural or synthetic zeolite (preferred average diameter 2 to 6 µm). The clay mineral used is preferably a mineral from the montmorillonite-beidellite series, in particular bentonite, hectorite, saponite or Nontronite or an acid activated mineral from the montmorillonite-beidellite range. Acid-activated bentonite is particularly preferably used.

Acid activation leads to an increase in the specific surface area, which improves the sorption capacity of the silicate ion exchanger.

The invention also relates to the use of the bleaching agent additive defined above in a bleaching agent for cellulose, wood pulp, waste paper and / or mixtures thereof which contains hydrogen peroxide and optionally water glass, alkali metal hydroxide and / or a complexing agent.

The bleaching agent preferably contains 20 to 300, in particular 30 to 200 g of additive per mole of hydrogen peroxide.

The invention further relates to a method for bleaching pulp, wood pulp, waste paper and / or mixtures thereof, the substances to be bleached being treated with a hydrogen peroxide and optionally with a bleaching agent containing alkali hydroxide, water glass and / or a complexing agent; this process is characterized in that the treatment with a bleaching agent as defined above is carried out at a pH of from 7.0 to 12.0, in particular from 7.5 to 9.0.

The bleaching can therefore be carried out in a weakly alkaline medium, thereby reducing the difficulties which occur when adding a large amount of alkali or water glass.

• 1. Allgemeine Versuchsdurchführungen
  • 1.1 Holzstoffbleiche
    50 g atro Holzschliff wurden bei 25 Gew.-% Stoffdichte unter Luftausschluß mit den Bleichchemikalien versetzt. Nach Einstellung der Stoffdichte auf 20 Gew.-% und Homogenisierung wurde 2 Stunden auf dem Wasserbad unter gelegentlicher Durchmischung bei einer Badtemperatur von 70°C gebleicht. Der gebleichte Holzstoff wurde mit destilliertem Wasser auf etwa 0,5 bis 1 Gew.-% verdünnt, desintegriert, in einer Labornutsche abgesaugt und im Blattbildner getrocknet. Die Weißgradbestimmung der gebildeten Blätter erfolgte im Elrephomat^(R) (Remission R bei 457 nm).
  • 1.2 Altpapierbleiche/Flotationsdeinking
    Das Altpapier (Tageszeitungen oder Tageszeitungen/Illustrierte 50 : 50) wurde bei 60°C 144 Stunden wärmegealtert und anschließend mindestens 24 Stunden bei 23°C und 50 % rel. Luftfeuchte klimatisiert. Nach Zusatz der Bleich- und Flotationschemikalien wurde das Altpapier in mit Ca(OH)₂ bzw. CaCl₂ auf eine definierte Härte gebrachtem Wasser bei 4 Gew.-% Stoffdichte und 40°C 5 Minuten bei einer Rotordrehzahl von 3000 min⁻¹ desintegriert. Nach einer 90minütigen Reaktionsphase bei 40°C wurde bei einer Stoffdichte von 3,5 Gew.-% erneut für 2 Minuten aufgeschlagen. Anschließend wurde auf 0,8 Gew.% Stoffdichte verdünnt, in eine Labor-Flotationszelle übergeführt und bei einer Luftzufuhr von 60 Liter/h und einer Rührgeschwindigkeit von 1200 min⁻¹ 15 Minuten flotiert. Nach Einstellung des pH-Wertes der Gutstoffsuspension auf 5 wurden auf Porzellanfilternutschen Probeblätter gebildet, die bei etwa 90°C getrocknet und klimatisiert wurden. Die Weißemessung (R 457) erfolgte wie oben im Elrepho^(R) bzw. Elrephomat^(R).
  • 1.3 Zellstoffbleiche
    Für die Anwendung z.B. in Zeitungsdruckpapier und in anderen Druckpapieren sowie in manchen Verpackungsstoffen reicht es aus, wenn der Sulfitzellstoff bei Weißgraden von 60 bis 75 eine mittlere Reinheit aufweist. Dieses Ziel wird mit einer einstufigen Peroxidbleiche erreicht. Neben der einfachen Handhabung ist der Vorteil des Peroxid-Bleichverfahrens darin zu sehen, daß die Ausbeute sehr hoch bleibt.
    50 g atro Zellstoff wurden bei 12 Gew.-% Stoffdichte unter Luftausschluß mit den Bleichchemikalien und dem Ionenaustauscher (SAB mit wechselnden Mengen Natriumcarbonat; vgl. Tabelle 7) versetzt. Nach Homogenisierung wurde 2 Stunden auf dem Wasserbad unter gelegentlicher Durchmischung bei einer Badtemperatur von 70°C gebleicht. Der gebleichte Zellstoff wurde mit destilliertem Wasser auf etwa 0,5 bis 1 Gew.-% verdünnt, desintegriert, in einer Labornutsche abgesaugt und im Blattbildner getrocknet. Die Weißgradbestimmung der gebildeten Blätter erfolgte im Elrephomat^(R) (R 457).
• 2. Ergebnisse
  • 2.1 Holzstoffbleiche (Tabelle 1)
    Die Beispiele 1 bis 32 zeigen die Ergebnisse der Holzstoffbleichversuche, ausgedrückt als R 457-Werte, die den Weißeunterschied zwischen gebleichtem Stoff und Ausgangsstoff beschreiben.
    Als Ionenaustauscher wurde ein Zeolith A-Typ, modifiziert mit 5 % Na₂CO₃, verwendet.
    • 2.1.1 Versuche ohne DTPA (Nr. 1-11)
      Versuch 1 dokumentiert den Weißgradverlust gegenüber dem Ausgangsstoff durch Alkalivergilbung. Versuche 2-8 zeigen die Ergebnisse bei Einsatz von Wasserglas, dem erfindungsgemäßen modifizierten Ionenaustauscher und Gemischen beider; als besonders günstig erwiesen sich also Kombinationen wie in Versuch 7 oder vor allem in Versuch 8. Die Versuche 1 bis 8 wurden unter Zusatz von 0,5 % NaOH durchgeführt, so daß sich der pH-Wert stets bei 10 bis 12 einstellte. Ein geringer NaOH-Zusatz ist häufig zweckmäßig, wenn es sich um einen sauer reagierenden Holzstoff handelt. Ohne NaOH-Zusatz (Versuche 9 bis 11; pH-Wert 8-9) werden die Vorteile des erfindungsgemäßen modifizierten Ionenaustauschers besonders deutlich. Bei den Holzstoffproben nach den Versuchen 9 bis 11 konnte keine nachträgliche Alkalivergilbung festgestellt werden, während die Proben nach den Versuchen 1 bis 8 eine Alkalivergilbung zeigten. Das Filtrat der Proben 1 bis 9 zeigte CSB-Werte von 800 bis 1100 mg/Liter, das Filtrat der Proben 9 bis 11 CSB-Werte von nur 600 bis 800 mg/Liter
    • 2.1.2 Versuche mit DTPA (Nr. 12 - 32)
      Die Versuche 12 bis 23 wurden im stark alkalischen Bereich durchgeführt. Wiederum lieferten die besten Ergebnisse ein Gemisch von wenig Wasserglas mit dem erfindungsgemäßen modifizierten Ionenaustauscher (Nr. 20 bis 22). Im schwach alkalischen Bereich - ohne Zusatz von NaOH - erbrachte der erfindungsgemäße modifizierte Ionenaustauscher bessere Resultate als Wasserglas, die auch durch Wasserglaszumischung nicht mehr zu steigern waren (Versuche 31, 32,).
  • 2.2 Altpapierbleiche (Tabellen 2 bis 6)
    Tabelle 2 (Versuche 1 bis 14) zeigt die Abhängigkeit des Flotationsdeinking-Ergebnisses von der Wasserhärte und dem Wasserstoffperoxid-Stabilisator. Unabhängig vom Altpapierstoff - nur Zeitungen (Z) oder Zeitungen/Illustrierte 1/1 (Z/I) - lag das Ergebnis mit dem erfindungemäßen modifizierten Ionenaustauscher (säureaktivierter Bentonit, modifiziert mit 25 % Na₂CO₃), stets über dem mit Wasserglas erhaltenen Ergebnis.
    Bei den in Tabelle 3 angegebenen Versuchen 15 bis 22 wurden dem Altpapierstoff (Zeitungen/Illustrierte 1/1) bei 100° dH Schwermetallionen (Cu²⁺, Fe³⁺, Mn²⁺, Cd²⁺) zudosiert. Wiederum lieferte, bei gleicher Einsatzmenge,. der erfindungsgemäße Ionenaustauscher bessere Ergebnisse als ein Zusatz von Wasserglas.
    Der pH-Wert des Flotationsmediums lag bei 9 bis 12. Die Flotation wurde wie unter 1.2 beschrieben, durchgeführt.
    Die Tabelle 4 zeigt die Ergebnisse der Versuche 23 bis 29. Die Versuche 23, 24 und 29 wurden unter Verwendung von Zeitungen, Illustrierten 1/1 nur mit Wasserglas, nur mit modifiziertem, sauer aktiviertem Bentonit bzw. nur mit dem organischen Komplexbildner DTPA durchgeführt. Die Versuche 25 bis 28 zeigen einen Wirkungssynergismus Ionenaustauscher/DTPA, so daß selbst bei Ersatz von 90 % DTPA durch den erfindungsgemäßen Ionenaustauscher (Versuch 25) kein Wirkungsverlust eintrat.
    Bei den in Tabelle 5 angegebenen Versuchen 30 bis 34 wurde Wasserglas stufenwiese durch den erfindungsgemäßen Ionenaustauscher (säureaktivierter Bentonit = SAB) ersetzt, wobei deutliche Weißgradsteigerungen festgestellt wurden.
    Die Ergebnisse der Versuche 35 bis 40 zeigen, daß eine Dosierung von 1,5 Gew.-% Ionenaustauscher dem Einsatz von 3 Gew.-% Wasserglas als äquivalent angesehen werden kann Versuche 35, 38). Eine weitere Verbesserung brachte hier die Reduzierung der NaOH-Konzentration (Versuch 39).
    Bei den in Tabelle 6 angegebenen Versuchen 41 bis 56 wurden bei einem Altpapier-Einsatz in Form von Zeitungen (Versuche 41 bis 48) die Wasserhärte, die NaOH-Konzentration und die Menge des eingesetzten Ionenaustauschers variiert. Als Ionenaustauscher wurde (SAB) verwendet, der mit 25 % Na₂O₃ bzw. 25 % NaHCO₃ modifiziert war. Bei 100° dH erbrachten 2 % erfindungsgemäßer Ionenaustauscher mit 1 % NaOH dasselbe Ergebnis wie 3 % Ionenaustauscher und 2 % NaOH. Beide Versuche (42 und 43) lagen besser als der Vergleichsversuch (41) mit Wasserglas.
    Durch die Reduzierung der Wasserhärte wurden erwartungsgemäß die Weißgrade verbessert (Versuche 44 bis 48). Das beste Ergebnis dieser Reihe wurde mit dem erfindungsgemäßen Ionenaustauscher, modifiziert mit 25 % NaHCO₃ und Einstellung des pH-Wertes auf 7,5 erzielt (Versuch 48).
    Bei den Versuchen 49 bis 56 wurde Altpapier in Form eines 50/50-Gemisches von Zeitungen und Illustrierten verwendet. Die Wasserhärte betrug 20° dH. Variiert wurde der Einsatz von Wasserglas, Ionenaustauscher (hier auf Zeolithbasis, mit NaHCO₃ modifiziert), DTPA und NaOH.
    Bemerkenswerterweise konnte das Ergebnis des Standardversuches 50 (3 % Wasserglas, 0,3 % DTPA, 2 % NaOH) im Versuch 52 (3 % Ionenaustauscher, kein DTPA, keine NaOH) erreicht werden.
  • 2.3 Zellstoffbleiche (Tabelle 7)
    Aus den Untersuchungsergebnissen geht hervor, daß ein Ersatz des Wasserglases durch den modifizierten anorganischen Ionenaustauscher Weißgradgewinne ergibt.

The invention is illustrated by the examples below.

• 1. General experiments
  • 1.1 pulp bleach
    50 g of dry wood pulp were mixed with the bleaching chemicals at 25% by weight consistency in the absence of air. After the consistency had been set to 20% by weight and homogenization was carried out for 2 hours on a water bath with occasional mixing at a bath temperature of 70 ° C. The bleached pulp was diluted to about 0.5 to 1% by weight with distilled water, disintegrated, suctioned off in a laboratory suction filter and dried in the sheet former. The whiteness of the sheets formed was determined in Elrephomat ^(R) (remission R at 457 nm).
  • 1.2 Waste paper bleaching / flotation thinking
    The waste paper (daily newspapers or daily newspapers / magazines 50:50) was heat-aged at 60 ° C for 144 hours and then at least 24 hours at 23 ° C and 50% rel. Air-conditioned humidity. After adding the bleaching and flotation chemicals, the waste paper was disintegrated in water brought to a defined hardness with Ca (OH) ₂ or CaCl₂ at 4% by weight consistency and 40 ° C for 5 minutes at a rotor speed of 3000 min⁻¹. After a 90-minute reaction phase at 40 ° C., the mixture was pitched again for 2 minutes at a consistency of 3.5% by weight. The mixture was then diluted to 0.8% by weight consistency, transferred to a laboratory flotation cell and floated for 15 minutes with an air supply of 60 liters / h and a stirring speed of 1200 min -1. After adjusting the pH of the accept material suspension to 5, test sheets were formed on porcelain suction filters, which were dried at about 90 ° C. and air-conditioned. The white measurement (R 457) was carried out as above in the Elrepho ^(R) or Elrephomat ^(R) .
  • 1.3 pulp bleaching
    For use, for example, in newsprint paper and in other printing papers as well as in some packaging materials, it is sufficient if the sulfite pulp has a medium purity at whitenesses of 60 to 75. This goal is achieved with one-step peroxide bleaching. In addition to the simple handling, the advantage of the peroxide bleaching process is that the yield remains very high.
    50 g of dry cellulose were added to the bleaching chemicals and the ion exchanger (SAB with varying amounts of sodium carbonate; see Table 7) at 12% by weight consistency. After homogenization was 2 hours bleached on a water bath with occasional mixing at a bath temperature of 70 ° C. The bleached pulp was diluted to about 0.5 to 1% by weight with distilled water, disintegrated, suctioned off in a laboratory suction filter and dried in the sheet former. The whiteness of the leaves formed was determined in Elrephomat ^(R) (R 457).
• 2. Results
  • 2.1 pulp bleach (table 1)
    Examples 1 to 32 show the results of the pulp bleaching tests, expressed as R 457 values, which describe the difference in whiteness between the bleached fabric and the starting fabric.
    A zeolite A type, modified with 5% Na₂CO₃, was used as the ion exchanger.
    • 2.1.1 Experiments without DTPA (No. 1-11)
      Experiment 1 documents the loss of whiteness compared to the starting material due to alkali yellowing. Experiments 2-8 show the results when using water glass, the modified ion exchanger according to the invention and mixtures of both; Combinations such as in Experiment 7 or especially in Experiment 8 were found to be particularly favorable. Experiments 1 to 8 were carried out with the addition of 0.5% NaOH, so that the pH was always between 10 and 12. A small addition of NaOH is often advisable if the pulp is acidic. Without the addition of NaOH (tests 9 to 11; pH 8-9), the advantages of the modified ion exchanger according to the invention are particularly clear. No subsequent alkali yellowing was found in the wood pulp samples after experiments 9 to 11, while the samples after experiments 1 to 8 showed an alkali yellowing. The filtrate of samples 1 to 9 showed COD values of 800 to 1100 mg / liter, the filtrate of samples 9 to 11 COD values of only 600 to 800 mg / liter
    • 2.1.2 Trials with DTPA (No. 12 - 32)
      Experiments 12 to 23 were carried out in the strongly alkaline range. Again, the best results were obtained by mixing a little water glass with the modified ion exchanger according to the invention (No. 20 to 22). In the weakly alkaline range - without the addition of NaOH - the modified ion exchanger according to the invention produced better results than water glass, which could no longer be increased even by adding water glass (experiments 31, 32,).
  • 2.2 Waste paper bleaching (Tables 2 to 6)
    Table 2 (experiments 1 to 14) shows the dependence of the flotation deinking result on the water hardness and the hydrogen peroxide stabilizer. Regardless of the waste paper - only newspapers (Z) or newspapers / magazines 1/1 (Z / I) - the result with the modified ion exchanger according to the invention (acid-activated bentonite, modified with 25% Na₂CO₃) was always above the result obtained with water glass.
    In experiments 15 to 22 given in Table 3, the waste paper stock (newspapers / magazines 1/1) was added 100 ° dH heavy metal ions (Cu²⁺, Fe³⁺, Mn²⁺, Cd²⁺) metered. Again delivered, with the same amount used. the ion exchanger according to the invention has better results than the addition of water glass.
    The pH of the flotation medium was 9 to 12. The flotation was carried out as described under 1.2.
    Table 4 shows the results of experiments 23 to 29. Experiments 23, 24 and 29 were carried out using newspapers, magazines 1/1 only with water glass, only with modified, acid-activated bentonite or only with the organic complexing agent DTPA. Experiments 25 to 28 show an action synergism ion exchanger / DTPA, so that even when 90% DTPA was replaced by the ion exchanger according to the invention (experiment 25) there was no loss of activity.
    In experiments 30 to 34 shown in Table 5, water glass was replaced by the ion exchanger according to the invention (acid-activated bentonite = SAB), with marked increases in whiteness being found.
    The results of experiments 35 to 40 show that a dosage of 1.5% by weight of ion exchanger can be regarded as equivalent to the use of 3% by weight of water glass (experiments 35, 38). A further improvement here was the reduction in the NaOH concentration (experiment 39).
    In experiments 41 to 56 given in Table 6, when using waste paper in the form of newspapers (experiments 41 to 48), the water hardness, the NaOH concentration and the amount of ion exchanger used were varied. As an ion exchanger (SAB) was used, with 25% Na₂O₃ or 25% NaHCO₃ was modified. At 100 ° dH, 2% of ion exchangers according to the invention with 1% NaOH gave the same result as 3% ion exchanger and 2% NaOH. Both experiments (42 and 43) were better than the comparison experiment (41) with water glass.
    As expected, the degrees of whiteness were improved by reducing the water hardness (tests 44 to 48). The best result of this series was achieved with the ion exchanger according to the invention, modified with 25% NaHCO₃ and adjusting the pH to 7.5 (experiment 48).
    Experiments 49 to 56 used waste paper in the form of a 50/50 mixture of newspapers and magazines. The water hardness was 20 ° dH. Was varied the use of water glass, ion exchanger (here on a zeolite basis, modified with NaHCO₃), DTPA and NaOH.
    Remarkably, the result of the standard test 50 (3% water glass, 0.3% DTPA, 2% NaOH) could be achieved in test 52 (3% ion exchanger, no DTPA, no NaOH).
  • 2.3 pulp bleaching (Table 7)
    The results of the investigation show that replacing the water glass with the modified inorganic ion exchanger produces whiteness gains.

Claims (9)

1. An additive for an alkaline, peroxide-containing bleaching agent for pulp, wood pulp, waste paper and/or mixtures thereof, which also contains, optionally, water glass and/or a complexing agent, characterised in that it represents a water-insoluble inorganic silicate ion exchanger modified with an alkali carbonate or an alkali hydrogen carbonate.
2. A bleaching agent additive according to claim 1, characterised in that the silicate ion exchanger is modified by being coated with 1 to 70, preferably with 5 to 50% by weight (in relation to the total bleaching agent additive) of an alkali carbonate or alkali hydrogen carbonate.
3. A bleaching agent additive according to claim 1 or 2, characterised in that the silicate ion exchanger has a BET surface area of at least 30 m²/g and a cation exchange capacity of at least 30 meq/100g.
4. A bleaching agent additive according to any one of claims 1 to 3, characterised in that the silicate ion exchanger is a smectitic clay mineral, an attapulgite and/or a natural zeolite or a synthetic zeolite.
5. A bleaching agant additive according to claim 4, characterised in that the smectitic clay mineral is a mineral from the montmorillonite/beidellite series, in particular bentonite, hectorite, saponite or nontronite, or an acid-activated mineral from the montmorillonite/beidellite series.
6. A bleaching agent additive according to claim 5, characterised in that the smectitic mineral clay mineral is acid-activated bentonite.
7. Use of the bleaching agent additive according to any one of claim 1 to 6 in a bleaching agent for pulp, wood pulp, waste paper and/or mixtures thereof which contains hydrogen peroxide and also, optionally, water glass, alkali hydroxide and/or a complexing agent.
8. Use according to claim 7, characterised in that the bleaching agent contains 20 to about 300, preferably 30 to 200g, of additive per mol of hydrogen peroxide.
9. A method of bleaching pulp, wood pulp, waste paper and/or mixtures thereof, wherein the materials to be bleached are treated with a bleaching agent containing hydrogen peroxide and, optionally, alkali hydroxide, water glass and/or a complexing agent, characterised in that the treatment is carried out with a bleaching agent according to claim 7 or 8 at a pH value of from 7.0 to 12.0, in particular from 7.5 to 9.0.