WO2012004196A1 - Metal ions - Google Patents

Abstract

The invention relates to a method and associated devices for supporting the cementing and/or for fixing impurities and/or for increasing the retention in a fiber suspension (1) by means of metal ions. In order to enable same independently of the pH value of the fiber suspension (1), the metal ions are at least predominantly electrolytically produced.

Description

 Metal ion

The invention relates to a method for supporting the sizing and / or fixing of contaminants and / or to increase the retention in a

Pulp suspension by means of metal ions.

The invention also relates to devices for aiding the sizing and / or fixing of contaminants and / or increasing the retention in one

Pulp suspension by means of metal ions, in particular for carrying out the method.

The increasing use of rejects and waste paper in papermaking and the increased reduction in the use of fresh water have led to an increase in harmful or disturbing substances in the water cycles. Also, chemical additives (e.g., oils, solvents, rosin size, sizing agents, adhesives, wet strength agents, retention aids, starch, biocide formulations,

Dispersants, bleaching chemicals, cleaning agents, dyes, complexing agents and solubilizers) which are specifically supplied to the process, contribute by enrichment in the circuits to an increase in the concentration of colloidally dissolved impurities directly or from the interaction with each other. Other sources include extracts from the pulps, lignin and lignin derivatives,

Hemicelluloses and carbohydrates.

The growing concentration of contaminants leads to a reduced efficiency of mostly cationic functional chemicals (eg retention polymers). The saturation of the process water at high process temperatures with colloidally dissolved, usually anionic impurities leads to precipitations and deposits in the cooler zones. Even low temperature gradients are sufficient to cause sticky deposits on hydrophobic or particularly adhesive surfaces (screen material, felt material, roll surfaces, low-flow zones). These can affect the process sensitively by the formation of holes in the paper, breaks, cleaning stops.

The high loads can also lead to increased microbiological activity, for example in laid paper, as there are easily metabolizable substances among them.

 Paper properties such as whiteness, opacity, color and strength are also affected by the presence of colloidal impurities.

In addition, an increased tendency to odor in the paper may occur. The dewatering and drying process in papermaking can also lead to a significant deterioration in runability due to the fate of these contaminants in the finest capillaries and have a speed-reducing effect.

 The contaminants may also result in lowering the surface tension and thereby increased foam, which in turn leads to paper defects and breaks.

The accumulation of contaminants in the entire water cycle system depends on the amount of raw materials supplied, the process temperature, the

Extractability, the water circulation rate, the amount discharged with the wastewater, the discharge of impurities with the paper produced and the supply of fresh water.

In particular, when water circulations are restricted, i. a reduced supply of fresh water and a correspondingly reduced removal of wastewater, an increased concentration of colloidally dissolved impurities in the circulation waters sets in.

To counteract this, it is known to supply aluminum ions to the pulp suspension by adding aluminum salts. The aluminum sulfate used in this case can be used in combination with inexpensive resin glue for sizing. It also contributes

Aluminum sulfate to improve the retention and fixation of impurities at.

The disadvantage here is that the sulfate ions are reduced in a biological clarification to sulfide, resulting in an odor and the corresponding

Bacterial growth is associated. Reuse of the waste water is so difficult. However, since predominantly calcium carbonate is used as a filler in papermaking, production of the fibrous web should be at neutral pH. Only then can a reaction and thus reduction of the calcium carbonate to form, the sheet formation disturbing CO2 bubbles are avoided. However, the neutral driving style has the disadvantage that the effectiveness of the

 Aluminum sulfate is lost, the sizing effect in combination with the resin glue is almost absent, the impurity fixation does not work and the positive effect on the retention disappears.

 Therefore, cationic polymers are increasingly used, but they are expensive and less effective than the aluminum sulfate.

The object of the invention is therefore to develop a method and a device for aiding the sizing and / or fixing of contaminants and / or increasing the retention in a pulp suspension by means of metal ions, which at least at neutral pH of the pulp suspension works.

According to the invention, the object with regard to the method has been achieved in that the fibrous suspension directly or indirectly supplied metal ions are at least predominantly produced electrolytically. By electrolysis, the metal ions are freshly dissolved and can so quickly for the purpose of sizing, Störstofffixierung and / or

Retention improvement before they are possibly bound by side reactions. This ensures the effectiveness of the metal ions over a wide pH range, especially in neutral driving, which also allows the use of calcium carbonate as a filler.

Furthermore, such a salinization of water cycles, a

Odor nuisance and bacterial growth, as described above avoided.

 In addition, the metal anodes are much cheaper than polymers

Process chemicals are.

In the interest of a rapid and comprehensive action of the metal ions, it is advantageous if the electrolytic production of the metal ions takes place at least partially, preferably entirely, in the pulp suspension.

With regard to construction, application and improved distribution of the Al ³⁺ ions, it may, however, be advantageous if the electrolytic production of the metal ions takes place at least partially in a solvent, preferably water, which is subsequently added to the pulp suspension.

 In order to support the electrolysis, conductive salts should be present in the solvent.

Regardless of whether the electrolysis takes place in the pulp suspension or a solvent, the metal ions should be formed of iron, magnesium, cobalt, nickel, copper, zinc or titanium ions, but preferably aluminum ions ,

The preferred Al ³⁺ ion is particularly effective. Control of the electrolysis is relatively easy and is preferably done such that the electrolysis at constant voltage difference between the

Electrodes or at constant current. The connection or disconnection of individual electrolysis reactors can be helpful here. With regard to a device according to the invention is essential that the

 Pulp suspension is passed into an electrolysis space in which are connected to a DC voltage source and coming into contact with the pulp suspension electrodes, wherein the anode has a metal surface. For this purpose, the electrolysis space can be formed to simplify a Bütte, in particular a machine chest or a Mischbütte.

If the metal ions are not in the pulp suspension but in a

Solvent, especially water to be produced, it should

Solvents are passed into an electrolysis room, in which connected to a DC voltage source and in contact with the solvent

Coming electrodes are located, wherein the anode has a metal surface and the solvent is passed to the electrolysis space in a mixing chamber to which the pulp suspension is guided. Again, the electrolysis room in a simple version of a

 White water container of a machine for producing a paper, cardboard, tissue or another fibrous web are formed.

For the realization of the mixing chamber, it may be advantageous if it is formed by a chest or the headbox of a machine for producing a paper, cardboard, tissue or another fibrous web.

Regardless of the medium in which the metal ions are produced, it may be advantageous if the electrolysis space from the headbox of a machine for

Production of a paper, cardboard, tissue or another fibrous web is formed. Usually the cathode should be used to avoid disturbing reactions

Have surface of inert material such as diamond or stainless steel. In contrast, the anode should have a surface of iron, magnesium, cobalt, nickel, copper, zinc or titanium, but preferably of aluminum.

However, it may also be advantageous that the cathode consists of the same material as the anode. This allows a reversal of the current direction in the interest of uniform wear of the electrodes and to avoid the

Passivation of the anode surface.

The invention will be explained in more detail below with reference to several exemplary embodiments. In the attached drawing shows:

 FIG. 1 shows a schematic cross section through part of a paper machine with preceding stock preparation 4;

FIG. 2 shows a schematic cross section through an electrolysis chamber 3 and FIG. 3 shows an electrolysis at the headbox 8.

The electrolysis takes place in an electrolysis space 3 according to Figure 2, in which the pulp suspension 1 or fresh or white water 2 is passed. In the electrolysis space 3 there are two electrodes 12,13, each with a pole of a

DC voltage source are connected.

 In this case, the cathode 12 is formed for example by an inert diamond electrode, while the connected to the positive pole of the DC voltage source anode 13 is made of aluminum.

When current flows from the anode 13 of Al ³⁺ - ions in the pulp suspension 1 or the water 2 over. At the cathode 12 there is, inter alia, the formation of hydrogen.

The amount of Al ³⁺ ions generated thereby can be controlled by voltage and / or current. Advantageously, the current intensity or the voltage or the voltage difference is kept constant. Furthermore, as can be seen in FIG. 1, it is quite possible to have a plurality of electrolysis spaces 3, for example in the form of laid paper 5, 6 or a headbox 8

be provided, which can be activated or deactivated as needed.

If the Al ³⁺ ions are generated in a solvent such as water 2, the conductivity may be increased to intensify the electrolysis by the addition of conductive salts. To reduce the consumption of metal ions by side reactions

(For example, to minimize the formation of insoluble Al (OH) ₃ ), the water 2 should be mixed with the metal ions as quickly as possible to the pulp suspension 1.

This mixing takes place in a mixing chamber 9, which can be formed by a chest 5,6, a white water tank 14, a mixing device in front of the headbox 8 or a headbox 8. The Al ³⁺ ions are generated in this way close to the site of action, which significantly increases the efficiency. The Al ³⁺ ions react with the existing, primarily anionic components, such as glue, impurities, fibers, fines and fillers. Since this is possible even at neutral pH, calcium carbonate can continue to be used as a filler.

In addition, can be dispensed with the use of expensive, polymeric fixative for fixing the contaminants. The use of low-cost glues remains possible.

The plant shown in Figure 1 for the production of a paper web begins with the stock preparation 4, in which the fresh or recovered paper fibers are dissolved and treated. From there, the pulp suspension 1 passes to a mixing chest 5, in which the mixing with water 2, but also with fillers and additives 15, such as fixing or sizing agents takes place. The mixing bin 5 is followed by a machine chest 6, from which the pulp suspension 1 passes into the constant part 7. In the constant part 7 of paper machines, the highly consistent accepts formed by the treated fibers and fillers with the in the

Paper machine collected collected white water 2 diluted and then fed to the headbox 8 of the paper machine.

At the headbox 8 close then the former 10 for sheet formation and the

Press section 1 1 for dewatering, in which the resulting white water 2 is collected and fed into a white water tank 14.

Thereafter, the paper web is dried, possibly painted and smoothed, before it can be wound up.

Depending on the need for Al ³⁺ - ions electrolysis spaces 3 can in this case

Pulp suspension 1 in the stock preparation 4 or in the constant part 7 be present. It is also possible that the mixing 5, the machine chest 6 or the

Headbox 8 to form the electrolysis space 3. The same can be done independently

Electrolysis spaces 3 are arranged between these units.

If alternatively or additionally, the, the pulp suspension 1 for

Dilution supplied water 2 AI ³⁺ - should have ions, so the water 2 before feeding into the stock preparation 4 and / or in the mixing chest 5 and / or the machine chest 6 and / or the constant part 7 and / or the headbox 8 by a separate electrolysis space 3 are performed. The mixing of the mixed water with Al ³⁺ ions 2 with the

Pulp suspension 1 is then carried out in a mixing chamber 9, which is formed for the sake of simplicity of the Mischbütte 5, the machine chest 6 or the headbox 8. However, other containers or mixing devices are possible. The white water tank 14 may itself act as an electrolysis space 3. However, that is It is also possible to supply the additional water 2 to the white water tank 14 via an electrolysis space 3.

As a result, the duration of action of the AI ³⁺ ions from generation to the headbox 8 is between a few seconds and a few minutes. When generating the Al ³⁺ ions in the headbox 8, the duration of action is in the range of milliseconds.

In the headbox 8 shown in Figure 3 is a

Dilution water headbox, as described for example in EP985762, EP 1 645 684 or DE 10 2004 049 261.

 In the headbox 8, at least the high-consistency stream and usually also a low-consistency stream via a transverse distributor 16 over the width of the

Paper machine led. The sectionally controlled mixing of high and low consistency flow allows an efficient influencing of the

Basis weight cross profile of the paper web.

In this case, the high-consistency stream formed by the pulp suspension 1 and / or the low-consistency stream formed essentially by water 2 can be passed over an electrolysis space 3. The mixing chamber 9 is in this case formed by the headbox 8 itself, in which both streams are mixed anyway.

Additionally or alternatively, the electrolysis space 3 for the formation of Al ³⁺ - ions in the pulp suspension 1 in the nozzles of the headbox 8, regardless of the type of headbox. 8

The mixing chamber 9 can also be formed by a turbulence generator and / or by the turbulent flow zone directly after the turbulence generator of the headbox 8.

Claims

claims 1 . Method for aiding the sizing and / or fixing of contaminants and / or increasing the retention in a pulp suspension (1) by means of metal ions,  characterized in that the metal ions are generated at least predominantly electrolytically. 2. The method according to claim 1,  characterized in that the electrolytic production of the metal ions takes place at least partially in the pulp suspension (1). 3. The method according to claim 2,  characterized in that the electrolytic production of the metal ions takes place exclusively in the pulp suspension (1). 4. The method according to claim 1 or 2,  characterized in that the electrolytic production of the metal ions takes place at least partially in a solvent, preferably water (2), which is subsequently added to the pulp suspension (1). 5. The method according to claim 4,  characterized in that conductive salts are dissolved in the solvent. 6. The method according to any one of the preceding claims,  characterized in that the metal ions of iron, magnesium, Cobalt, nickel, copper, zinc or titanium ions, but preferably of aluminum ions are formed. 7. The method according to any one of the preceding claims,  characterized in that the electrolysis at constant  Voltage difference between the electrodes (12,13) takes place. 8. The method according to any one of the preceding claims,  characterized in that the electrolysis is carried out at a constant current. 9. Device for supporting the sizing and / or fixing of  Interfering substances and / or for increasing the retention in a pulp suspension (1) by means of metal ions, in particular for carrying out the method according to one of the preceding claims,  characterized in that the pulp suspension (1) in a  Electrolysis space (3) is guided in which connected to a DC voltage source and with the pulp suspension (1) coming into contact  Electrodes (12,13) are located, wherein the anode (13) has a metal surface. 10. Apparatus according to claim 9,  characterized in that the electrolysis space (3) from a chest (5,6) is formed. 1 1. Apparatus for aiding the sizing and / or fixing of  Interfering substances and / or for increasing the retention in a pulp suspension (1) by means of metal ions, in particular for carrying out the method according to one of claims 1 to 8, characterized in that a solvent is led into an electrolysis space (3) in which electrodes (12, 13) connected to a DC voltage source and coming into contact with the solvent are located, wherein the anode (13) has a metal surface and the Solvent after the electrolysis space (3) is passed into a mixing chamber (9), to which the pulp suspension (1) is guided. 12. Device according to claim 1 1,  characterized in that the electrolysis space (3) of a  White water container (14) of a machine for producing a paper, cardboard, tissue or another fibrous web is formed. 13. Device according to claim 1 1 or 12,  characterized in that the mixing space (9) is formed by a chest (5, 6). 14. Device according to claim 1 1 or 12,  characterized in that the mixing chamber (9) from the headbox (8) of a machine for producing a paper, cardboard, tissue or another fibrous web is formed. 15. Device according to one of claims 1 1 to 14,  characterized in that the solvent is formed substantially by water (2). 16. Device according to one of claims 9 to 15,  characterized in that the electrolysis space (3) from the headbox (8) of a machine for producing a paper, cardboard, tissue or another fibrous web is formed. 17. Device according to one of claims 9 to 16,  characterized in that the cathode (12) has a surface of inert material. 18. Device according to one of claims 9 to 17,  characterized in that the anode (13) has a surface of iron, Magnesium, cobalt, nickel, copper, zinc or titanium, but preferably of aluminum has.