EP0885326A1

EP0885326A1 - System of chemicals and method for deinking of waste paper

Info

Publication number: EP0885326A1
Application number: EP19970906401
Authority: EP
Inventors: Peter Wallberg; Mikael Perdin; Johan Jansson
Original assignee: Bim Kemi AB
Current assignee: Bim Kemi AB
Priority date: 1996-02-27
Filing date: 1997-02-27
Publication date: 1998-12-23
Also published as: SE9600730D0; WO1997032076A1; JP2000505510A; AU2110297A

Abstract

Chemical system that makes it possible in a cost effective and environmentally friendly way to deink waste paper at a lower pH than required in present methods, but with retained efficiency and quality. This has been obtained by a chemical system comprising the following components: a) a surface-active ester to release the printing-ink from the pulp fibers, b) a polyester based collector for aggregation and flotation of released printing-ink particles. The system may also contain an inhibitor for hydrogen peroxide decomposing enzymes, such as peroxidase and catalase.

Description

System of chemicals and method for deinking of waste paper

Background of the invention

In conventional waste paper production there are several steps that require high pH

(8,5-12,0). Not only is the pulp discolored, this results also in high chemical costs and has environmental disadvantages. The present invention describes a method to produce waste paper pulp, and other cellulose fiber pulp, at a lower pH with maintained yield and quality, at a higher cost-effectiveness.

Wastepaper has during the last years become an important raw material for the paper pulp industry. This adds high pressure on the papermaking pulp producers, who work hard to lower their costs, render the process more effective and fulfill the environmental laws without lowering the quality of the final product. When producing recycled fiber- and other cellulose fiber pulp the properties such as purity and lightness are very important. These are affected by several factors, such as the possibility to discharge and separate the printing-ink from the fiber surface at the production of recycled fiber pulp, and to optimize the increase in brightness at the bleaching process.

Deinking of recycled fibers can be divided into three steps. In the first step one dissolves the paper and releases the printing-ink from the fibers. The printing-ink is thereafter dispersed in the water phase and finally it is separated from the fibers. The separation is done industrially by the flotation- or wash process. The flotation process is most common in Europe, and is the process of most interest here.

The flotation process, which technically originates from the mining industry, refers to releasing as much of the printing-ink as possible from the pulp fiber suspension. Its disadvantages are rather high capital- and chemical costs, but these are compensated for by the high yield.

The flotation process is carried out in such a way that the recycled fiber raw material is heated through mechanical treatment in combination with chemical additions. There are different methods relating to chemical additions and how to beat the raw material, but common additives are sodium hydroxide and dispersion agents. The purpose of the mechanical treatment is that the fibers are rubbed against each other and this way. in the presence of the chemicals, efficient discharge of print-ink is obtained. A too strong mechanical influence, however, causes great damage to the fibers, which is not desirable in paper-making.

Thereafter follows a separation step wherein particle impurities are removed. This is followed by a purification step where small, heavy particles are removed and water is pressed away. In a dispersion step the discharge of printing-ink is continued by mechanical treatment under influence of chemicals, such as hydrogen peroxide, sodium hydroxide and water glass. Thereafter follows one more purification step where heavier rejects, such as gravel, are removed. The printing-ink and other small particles are thereafter removed in a flotation step. Different flotation techniques are used and in the more modern ones, rather small particles can be flotated by pressurizing the flotation cell. Small impurities are removed by washing, and to increase the brightness of the pulp it is bleached using hydrogen peroxide.

The following chemicals are used for conventional deinking.

Sodium hydroxide (NaOH)

Sodium hydroxide is used to obtain alkaline pH and to saponify and hydrolyze the resin in the printing-ink. The particles are separated from the fibers and can then be removed by flotation. pH 9,5-1 1, at which deinking is performed, makes the fibers swell making them more flexible. This results in mechanical tension between the fibers and the remaining printing-ink particles and causes them to discharge.

Sodium hydroxide has, however, several disadvantages. When wood containing pulps, i.e. mechanically produced cellulose fiber pulp, are present in the process, the fibers become darker and yellowish at alkaline pH. This is due to remaining lignin, which reacts with the alkali forming chromophoric groups. This yellowness induced by alkali is particularly pronounced at pH above 10.2. Before the pulp is used for paper production it is given an acid-chock to counter act this effect. Laser printing-ink does not react with sodium hydroxide making office waste difficult to deink this wa> . Further, NaOH increases the COD- content (Chemical Oxygen Demand) and BOD- content (Biological Oxygen Demand) in the process water by releasing more organic oxygen consuming substances.

Hydrogen peroxide (H ₂O₂)

Hydrogen peroxide is used to decolor the chromophores that were produced at the alkaline pH in the pulp. It is added at different steps in the process, depending on whether it shall degrade the chro ophoric groups or if it shall bleach the pulp. For degradation of the chromophoric groups hydrogen peroxide is added to the pulper, otherwise it is added to the bleaching tower. The hydrogen peroxide reacts with the sodium hydroxide according to:

H₂0₂ + NaOH - HOO- + Na+ + H ₂0

The perhydroxy anion (HOO-) is the active bleaching chemical. Its concentration depends on pH, temperature and dosage of H ₂0₂ and the concentration of heavy metals such as Fe, Mn, Cu etc. Degradation of hydrogen peroxide results in lower brightness, which may be prevented by addition of sodium silicate and complexing agents. Microorganisms have also a negative effect on the bleaching process since they produce enzymes such as catalase and peroxidase that degrade hydrogen peroxide.

Sodium silicate (water glass, Na iOJ

Water glass prevents the degradation of hydrogen peroxide by forming colloids with the heavy metal ions thereby deactivating them. It has also a buffering effect at the pH at which hydrogen peroxide is active. Sodium silicate also prevents the particles from falling back on the fibers and has also some disperging effect on the printing-ink. It can also decrease the loss of fibers in the flotation step by reacting with calcium ions. A too high concentration of sodium silicate may, however, cause problems with depositions in the paper production machine.

Complexing agent (EDTA, DTP A)

DTPA (diethylentriaminpentaacetic acid) and EDTA (ethylendiamintetraacidic acid) are the complexing agents used, of which the DTPA is the more common one. They form soluble complexes with heavy metal ions that are easily removed. Through the complexation of heavy metal ions less hydrogen peroxide is degraded. The use of complex binders is, however, restricted by law in many countries, including Sweden.

Surfactants

Surfactants have many functions in the process of deinking. They can be dispersion agents, collectors, agents that prevent re-deposition etc. The molecules shall have a hydrophobic and a hydrophilic part, and the structure may consist of a straight, or branched chain, charged groups, one long and one short chain and it may contain double and single bonds. The HLB- (Hydrophilic- Lipophilic- balance)- value depends on. for example, the lengths of its parts and an optimal HLB-value for flotation is about 15. The nonionic surfactants are well dispersed in water under the soiling temperature.

Maximum effect is obtained just below the soiling point. The biodegradation of the surfactant is important since it follows the backwater out from the mill. The properties of the surfactants depend on temperature, pH, the composition of the process water, substances released from the pulp, and other factors that are specific for every individual mill.

Soap

Soap is a surfactant that is used in flotation because its calcium salt produces a foam that is easy to control. Fatty acid based soaps have been developed that give maximal deinking. For the soap to work satisfactorily calcium ions must be present at a concentration corresponding to at least 10 °dH. Calcium soaps act by two mechanisms. They agglomerate small particles making them more easy to remove and they prevent the printing-ink falling back onto the fibers.

Sulfuric acid

Sulfuric acid reduces the pH in the deinked pulp. A value around pH 7 is preferred to avoid that material is released ending up in the backwater, which may happen at higher pH.

Printing-ink

There are many problems with deinking. The raw material are papers of different qualities and particularly with different printing-inks, depending on the printing technique that was used. The colors vary considerably in their properties such as adsorption to the fibers. The main problem with deinking is the heterogeneous paper quality. The difference between journal paper and newspaper paper is their content of filler substances. Journal paper has a high degree of fillers, which gives a smooth surface with good printing properties. Typical raw material for deinking is a mixture of 60-70% newspaper paper and 30-40% journal paper.

Flotation

When the collector is added, the printing-ink is dispersed in the water phase. The particles must now be modified so they can readily be flotated. If one makes small hydrophilic particles more hydrophobic. it results in some agglomeration to heavier particles with a hydrophobic surface structure. To adhere onto the rising air bubbles it is necessary that they have the right size.

If the particle is too light, it will follow the flow around the bubble and there is no effect. If the particle is too heavy it collides with the air-bubble , but the adhesion is too weak. The particle falls off and no flotation takes place. Previous studies have shown that optimal particle size for flotation is 10-100 μm. These particles stick onto the air bubbles that are rising up to the surface and form a foam that can be removed.

The hydrophobic surface structure favors adsorption to the air bubbles. This can be understood from the principles of surface chemistry, which predicts hydrophobic substances to orient towards the air phase in the interface between air and water. This is a thermodynamically favored process. The particles are made hydrophobic by addition of surface-active chemicals.

Collector chemicals

Conventional flotation chemicals require rather hard water to obtain the desired effect. This causes problem with deposition of CaCO , in the equipment. Since some time back there are alternatives to the original flotation chemicals, such as the so called synthetic collectors that do not require hard water.

WO 91/03599 describes a collector, which consists of a polyester based on a polyalkylene glycol and a di- or tricarboxylic acid. Tall oil is used in the polymerization reaction to control the chain length of the final polymeric product.

WO 95/00699 describes an improved collector, which is composed of a polyester based on a polyalkylene glycol and a di- or tricarboxylic acid. A saturated fatty acid with 12- 18 carbon atoms is used in the polymerization reaction to have a better control of the reaction and to obtain a more defined product.

Enzyme inhibitor

In the production of recycled- and cellulose fiber pulp hydrogen peroxide is used, as mentioned above. However, it is degraded by the enzymes peroxidase and catalase that are produced by bacteria that often are present in cellulose based pulp, particularly waste paper pulp. To compensate for the loss, overdosages of up to 6-8 times are common, which gives high chemical costs.

By using an inhibitor to these enzymes one can decrease the degree of overdosage. WO 95/17546 describes an inhibitor of peroxide decomposing enzymes, such as peroxidase and catalase, that has at least one inhibiting substance such as hydroxyl amine and its alkyl derivatives, which have 1 -10 carbon atoms in a straight or a branched chain.

Lower pH in the deinking process of waste paper pulp

It would be very advantageous if one could deink waste paper pulp at a lower pH than today. Besides avoiding the undesired coloring of the paper pulp, the pollution of backwater would be decreased, i.e. the water that is reused in the process and at some stage is returned to nature. The process water is cleaner since less organic substance is released from the fibers, i.e. the COD- values decreases. From an environmental point of view this is of most importance and it may in the future be possible to have a mill with a closed water system.

By deinking at lower pH it should be possibly to decrease and even exclude the use of sodium hydroxide, and also of those chemicals, such as hydrogen peroxide, that counteracts the negative effects caused by the basic milieu. If sodium hydroxide is not added, it must be replaced by other chemicals that have the same function, i.e. that discharge the printing-ink from the fibers. In addition a chemical is needed to aggregate and flotate the printing-ink, since sodium hydroxide also has a saponificating effect.

The object of the invention and its most important characteristics

The object of the present invention is to obtain a chemical system to deink waste paper at lower pH than that used today, that is cost effective and environmentally friendly. This has been obtained by a chemical system comprising the following components: a) a surface active ester for discharging the printing-ink from the pulp fibers, b) a polyester based collector for aggregation and flotation of the discharged printing- ink particles.

The surface-active ester comprises preferentially a product produced by esterfication of ethoxylated alcohol and a mixture of fatty- and resin acids.

The polysester based collector comprises preferentially a polyester obtained by a reaction between: a) polyalkylene glycol b) di- and/or tricarboxylic acid and/or anhydrides thereof, and c) a saturated fatty acid with 12-18 carbon atoms and/or tall oil, and which polyester has a molecular weight between 3.000-10.000.

The chemical system may contain an inhibitor to hydrogen peroxide degrading enzymes, such as peroxidase and catalase. The inhibitor is composed of at least one inhibiting substance, such as hydroxylamine and its alkyl derivatives having 1-10 carbon atoms in a straight or branched chain such as, for example, methyl hydroxylamine, and its salts and addition salts, such as hydroxylammonium sulfate or hydroxylammonium chloride; thiocyanate salts, such as ammonium thiocyanate; formic acid; ascorbic acid, and nitrites, such as sodium nitrite, potassium nitrite, magnesium nitrite and calcium nitrite.

Advantages of the invention

Paper pulp does not become yellowish by chromophoric groups that are formed from the lignin at high pH.

Paper pulp does not have to be bleached to the same extent, since it is not discolored.

The chemical release of the printing-ink does not give rise to extensive foaming in the pulper step, which minimizes cavitation in pumps, dewatering of the filter, running problems and production loss. Backwater is cleaner because less organic substance is discharged from the fibers at a lower pH. In addition, components soluble in alkali, for example printing-inks, melting glue, adhesives for print sealing, dispersion adhesive, binder for coating, and additives for paper production, such as wet strength agents, are avoided in the backwater.

Lower chemical- and biological oxygen demand, i.e. lower COD and BOD- values.

Lower burden on the purification plants, since the wastewater is cleaner, which makes it possible to the pulp- and papers mills to close their systems.

Lower burden on the environment since the wastewater is cleaner and the containing chemicals are biologically degradable, or biologically readily degradable (according to OECD's norms 301 and 302).

Lower chemical cost since consumption of sodium hydroxide, hydrogen peroxide, water glass and sulfur acid is reduced.

Lower loss of fiber compared to when conventional chemicals are used at neutral pH.

Biocides are avoided

Description of the drawings

Fig.1 is a block diagram showing the bleaching process with waste paper pulp as raw material.

Fig.2. is a block diagram showing variations in brightness before and after flotation. Fig.3. is a block diagram showing COD-values (Chemical Oxygen Demand) before and after flotation. Fig.4. is a block diagram showing the backwater purity before and after flotation. Fig.5. is a block diagram showing variations in brightness before and after flotation.

Description of the examples In a pulper 1 recycled paper, water and a surface-active ester of the kind Bimex 400® from Bim Kemi AB were added. The fiber suspension was purified and dewatered through a coarse screener 2, in a turbo separator 3 and in reject screening cyclones 4. After the belt press 5 the pulp was passed through a chemical mixer (not shown). The pulp was then sent to a bleaching tower 6, cleaned in a sand vortex cleaner, where after a polyester based collector of the kind BIMCO from Bim Kemi AB was added and flotated in the primary- and second flotation cells 8 and 9. The pulp is then passed through a vortex cleaner 10, a fine screening 1 1 and a light reject separator 12, a disc filter 13, screw presses 14, dispersion step (Flota pulpers) 15 and finally the pulp was transferred to a storage tower 16 before it was transferred to the mill.

Some of the separated water from the belt press 5 went to the microflotation unit 17 and formed backwater I that was returned to the pulper 1 by backwater tank 18, where an inhibitor to hydrogen peroxide decomposing enzyme of the kind Bimozym from Bim kemi AB was added. Separated material from the micro flotation unit 17 went to the centrifuge 19, which was placed after the secondary flotation step 9, and the liquid from the centrifuge 19 was returned to the micro flotation step 17.

Liquid from disc filters 13 went to the backwater tank 20, where also drainage water from the press section 21 in the paper machine, and an inhibitor to peroxide decomposing enzymes such as Bimozym from Bim Kemi AB was added. From backwater tank II 20 the backwater II was going to the backwater tank 18 and then to the pulper 1.

Brightness sheets were made of the pulp before and after flotation and the brightness was measured in lSO%. The numbers indicates the chemical dosage (Table 1).

The backwater from the production of brightness sheets was filtered through a Millipore filter and the brightness was measured in ISO%. The number indicates the chemical dosage (Table 1 ). The deinking process described in Fig. 1 is an example of a process where the additives mentioned above may be included. The additions of the surface-active ester, which is a nonionic tenside, may be made to the pulper 1 or a similar, instead of. or in combination with sodium hydroxide. It is desirable to avoid in as large extent as possible that the pulp is colored yellowish by the chromophoric groups formed when the lignin is reacting with the alkali, i.e. it is desirable that the pH is kept bellow about 10.2. The surface-active esters are obtained through esterfication of etoxylated alcohols and a mixture of fatty- and resin acids.

Addition of polyester-based collector is made before or at the flotation 8. The collector is composed of etoxylated alcohols, saturated- and unsaturated dicarboxylic acids, and fatty- and resin acids according to WO 91/03599 and WO 95/00699.

Addition of inhibitor is made in a step that involves hydrogen peroxide, for example, into the water from the micro flotation 17, or in the draining water from the press section in the paper machines 21. The inhibitors are described in WO 95/17546.

Example

The invention is described with two ester-based chemicals. A surface-active ester, which is a nonionic tenside, called Bimex 400®, which is chosen because it has good dispersion properties for printing-ink, and a nonionic polyester, called BIMCO. which is a collector with good aggregation properties at neutral pH. These chemicals are also from an environmental point of view very advantageous since they are classified as biologically degradable, or biologically readily degradable.

Bimex 400® is a surface-active ester supplied by Bim Kemi AB and is obtained through esterfication of etoxylated alcohols and a mixture of fatty and resin acids.

BIMCO is a polyester of dicarboxylic acid and polyol, supplied by Bim Kemi AB. The syntheses are described in WO 91/03599 and WO95/00699. Several chemical combinations have been used in the pulper and in the flotation to compare the properties of the ester-based chemicals Bimex 400® and BIMCO with conventional chemical (table 1). pH is measured at different steps in the process, which makes it possible to compare the brightness of the pulp. Optimal dosage of the ester- based chemicals was also established. The experiments are performed in laboratory scale, but with equipment that well correspond to the industrial process shown in figure 1 , which exemplifies where in the process Bimex 400®, BIMCO and the inhibitor Bimozym may be added.

Table 1

Dosage Bimex BIMCO Fatty acid Soap Caustic Hydrogen Water nr. g 400^R solution peroxide glass

1. # # # # # # #

2. # 1.2 # # # # #

3. 0.35 # # # # # #

4. 0.175 0.6 # # # # #

5. # # # # 0.5 0.15 0.65

6. # 1.2 # # 0.5 0.15 0.65

7. 0.35 # # # 0.5 0.15 0.65

8. 0.175 0.60 # # 0.5 0.15 0.65

9. 0.15 # # r # # #

10. 0.25 # # # # # a

1 1. 0.30 # # # # # #

12. 0.25 0.25 # # # #

13. 0.25 0.35 # # # # #

14. 0.25 0.50 # # # # #

15. 0.25 0.10 # # # # #

16. 0.10 0.10 # # # # #

17. 0.10 0.25 # # # # # 18. 0.25 0.10 # # # # #

19. 0.25 0.10 rr # # # #

20. # # 0.60 0.25 0.5 0.15 0.65

21. 0.25 # # # # # #

22. # 0.1 # # # # #

23. 0.25 0.1 # # # # #

24. # # # # #

* ^#

The doses are expressed in weight-% of chemicals added with respect to the dry mass of paper.

Dissolving waste paper:

Newspapers and journal papers were torn into approximately 4*4 cm pieces and their dryness was determined in a microwave oven. The paper (59.9 g newspaper and 30.3 g journal paper) was loaded into the pulper (Noram, Lorentzen & Wetter). Thereafter 2 liter of 50 °C water and chemicals (only Bimex 400® in experiments at neutral pH, and the combination of Bimex 400® and sodium hydroxide in the alkaline experiments) (Table 1) were added under stirring. The suspension was left for 10 minutes. The pulper was activated for 10 minutes (after

2 minutes it was checked that the suspension was homogeneously dissolved). pH was measured (Table 2; pH after pulper). The fiber pulp suspension was then pressed four times using a wire gauze, each time using 0.5 liter, to a dryness of 14-15%, i.e. the fiber suspension had a mass of 650 g. Any bleaching chemicals (hydrogen peroxide and water glass) were added, whereafter the suspension was incubated in an incubator at 45

^CC for 1 hour. pH was measured (Table 2; pH before flotation). 250 ml of fiber suspension was diluted with 45 °C water to 3.5 liter, using the previously by press removed water, and the pulp was left for 1 minute. The sample was mixed in a kitchen mixer for one minute and a 0.5 liter sample was taken for production of brightness sheets. Flotation with esters and/or sodium hydroxide

The flotation cell was placed in a warm (45 °C) water-bath, and the remaining 3 liters of fiber pulp suspension were poured into the cell and stirred (1000 turns/min). Any flotation chemicals, such as BIMCO, fatty acid and soap, were added to the cell and the temperature was checked. The inkfoam sucker and the airflow (8 liter/ inute) were started. Flotation went on for 12 min. During the flotation all foam was sucked off and 45 °C water was added to keep the level in the flotation cell constant. After completed flotation the air supply was closed and pH and backwater were measured (table 2; pH after flotation). 0.5 liter of fiber pulp suspension was taken for brightness sheet production and the ink mud was stored. Double tests were performed on all flotation samples. They were analyzed as follows.

Production of brightness sheets

The fiber pulp suspension (0.5 liter) was diluted to 1 ,0 liter, pH was adjusted with diluted sulfuric acid to 5.0 and mixed in a mixer for 1 minute. The samples were divided into two batches of 0.5 liter each. These were filtered through a Bϋchner funnel, 1 1 cm in diameter, using Munktell filter nr 3. The filter paper was removed from the funnel and 3 sheets of blotting paper were placed under and over the filter paper and rolled over 10 times by a Cobb-roller. The sheets were dried and the brightness was measured in ISO% (Fig. 2 and Table 2).

Backwater purity

50-ml filtrate was taken from each sample sheet production and was filtered through 45 μm Millipore filter, where after it was dried and the brightness was measured in ISO% (Fig. 4 and Table 3). Ink mud

The volume was measured on the foam that was removed by suction. The microwave was tare with two glass fiber plates. 1 ml of sample was added between the plates and the microwave was started, and the dryness read out (Table 3).

Fiber loss

To determine the fiber loss sample sheets were made from pulp before and after the flotation. All sheets were produced using the same amount of sample, so the mass difference gave a good estimate of the fiber loss.

At conventional chemical dosage with soap, fatty acid emulsion, sodium hydroxide and water glass at alkaline pH (table 1 , dosage 20), fiber loss was about 15%. The soap is a natrone soap of fatty acids, and fatty acid emulsions containing fatty acids with about

18 carbon atoms that are dispersed in the water solution.

With the ester based chemicals at neutral pH the fiber loss was about 1 %, and with the conventional collectors, i.e. with soap and fatty acid emulsions (table I . dosage 21 ) at neutral pH the fiber loss was about 36%. This shows that the fiber loss at neutral pH is much lower when the ester based chemicals are used compared to when the conventional chemicals soap and fatty acid emulsion are used. Further, the fiber loss with the ester based chemicals at neutral pH is acceptable (about 19%). compared to the loss when using the conventional chemicals at a higher pH (about 15%).

COD values

COD values were measured with the instrument ARAS (Dr. Bruno Lange GmbH) relative to a standard from Labinett Instrument AB. Table 2

Dosage no. Brightness Brightness after pH after the pH before pH after before flotation flotation pulper flotation flotation (ISO%) (ISO%)

1. 40.23 51.83 7.17 7.60 8.41

2. 39.65 55.28 6.80 7. 1 1 8.17

3. 44.42 53.97 6.87 7.08 8.15

4. 42.64 54.26 6.66 6.85 8.05

5. 37.87 46.54 9.32 8.79 8.47

6. 39.90 50.02 9.28 8.74 8.52

7. 42.87 52.15 9.35 9.01 8.75

8. 42.91 50.42 9.40 8.93 8.71

9. 43.48 48.58 7.08 7.23 8.28

10. 44.13 50.76 7.06 7.22 8.25

1 1. 44.23 49.46 6.99 7.10 8.16

12. 46.97 50.53 7.70 7.76 8.38

13. 46.72 50.71 8.05 8.04 8.31

14. 44.94 49.1 1 8.08 8.02 8.35

15. 43.29 55.57 7.26 7.44 8.30

16. 43.08 53.33 7.12 7.31 8.08

17. 43.44 55.30 7.12 7.37 8.20

18. 44.24 54.21 7.20 7.39 8.1 1

19. 44.32 55.01 7.19 7.35 8.07

20. 41.33 54.61 9.58 8.69 8.71

21. 44.0 50.51 7.0 7.18 8.30

22. 42.92 49.12 7.15 7.38 8.20

23. 43.85 56.65 7.13 7.33 8.18

24. 42.9 47.69 7.09 7.28 8.23 Table 3

Dosage Δ-brightness before Δ-brightness befor Backwater brightness Volume Solid no. and after flotation. and after flotation. after flotation. (ml) reject (g) Handsheet (ISO%) Backwater. Millipore Millipore filter filter (ISO%) (ISO%)

1. 1 1.60 -0.30 91.26 1 128 9.47

2. 15.64 1.38 92.49 943 7.98

9.55 1.94 91.55 583 4.57

4. 1 1.63 1.46 92.06 420 5.27

5. 8.67 1.10 88.63 550 2.89

6. 10.13 1.45 90.14 688 5.48

7. 9.28 1.43 90.24 365 3.50

8. 7.51 3.42 89.37 355 3.23

9. 5.1 1.25 86.98 515 3.01

10. 6.63 0.33 87.61 420 3.19

1 1. 5.53 1.08 87.88 300 2.70

12. 3.57 0.96 87.69 253 4.17

13. 3.99 0.95 90.25 190 1.47

14. 4.16 2.96 89.74 198 1.32

15. 12.28 1.13 91.54 423 5.76

16. 10.25 0.48 91.09 446 5.48

17. 1 1.86 -0.36 91.14 455 8.43

18. 9.97 -0.23 90.73 410 6.23

19. 10.69 0.25 92.17 335 6.05

20. 13.29 1.58 90.27 395 4.03

21. 6.51 # # # #

22. 6.20 # # # #

23. 12.80 # # # #

24. 4.79 # # # # Results

In total 24 combinations of chemicals were tested. The experiments show that pulp treated with 0.25% Bimex 400® and 0.10% BIMCO (dosage nr. 15 and 23) at neutral pH gave best result with respect to pulp brightness, cost, and backwater purity. Compared to pulp treated with the conventional chemicals sodium hydroxide, hydrogen peroxide and water glass (dosage nr. 5) at higher pH, the new method is superior.

Pulp treated with optimized dose of ester based chemicals has a higher brightness both before and after flotation, compared to pulp treated with sodium hydroxide (Fig. 2). This is due to that deinking took place at a lower pH (table 2). If the amount of the surface-active ester Bimex 400® is insufficient the effect is deteriorated, since the surface-active agent alone is insufficient to discharge the printing-ink particles. If the amount of Bimex 400® is too high the effect is also deteriorated, since the surface- active agent is above the critical micelle binding concentration. Optimal doses for the surface-active esters are 0.0005-2%, preferably 0.005-1% and more preferably 0.05- 0.5% based on the weight of dry fiber mass.

The optimal dose of the polyester based collector is 0,0005-5%, preferably 0,005-4% and more preferably 0,05-1 % based on the weight of dry fiber.

It is important that the surface-active esters do not cause foaming in the pulper and in the flotation step, since this may give drift problems and production loss. The ester based chemicals have a quite normal foaming, based on volume and on solid losses from the flotation (table 3).

The fiber loss at neutral pH is considerably lower (19%) when the ester based chemicals are used compared to when the conventional chemicals soap and fatty acid emulsion (36%) are used. With the ester based chemicals one avoids the continued release of organic substances in the flotation step, i.e. COD-values (chemical oxygen demand) are lower after flotation than with the conventional chemicals (Fig. 3). The backwater purity is higher with the ester based chemicals than with conventional chemicals such as sodium hydroxide (Fig. 4).

Fig. 5 shows the brightness before and after flotation at neutral pH after addition of only 0.25% Bimex 400® (dosage 21 ), only 0.10% BIMCO (dosage 22). a combination of 0.25% Bimex 400® and 0.10% BIMCO (dosage 23) and without addition of any of the components above (dosage 24). As seen, dosage 23 gave best results.

In summary, deinking of pulp, using a surface-active ester for releasing of printing-ink from the pulp fibers and a polyester based collector for aggregation and flotation of released printing-ink particles around neutral pH, gives a bright pulp, lower running cost and a production method that is more friendly to the environment, than pulp produced using conventional alkaline methods.

Claims

1. Chemical system designed for deinking of recycled fiber pulp or other cellulose fiber based pulp by the flotation process or a similar process, characterized in, that it comprises the following components: a) a surface active ester for releasing the printing-ink from the pulp fibers, b) a polyester based collector for aggregation and flotation of the released printing-ink particles.

2. Chemical system according to claim 1, characterized in, that the surface-active ester comprises a product produced by esterfication of an ethoxylated alcohol and a mixture of fatty and resin acids.

3. Chemical system according to claim 1 or 2, characterized in, that the polyester based collector contains a polyester obtained by the reaction of a) polyalkylene glycol b) di- and/or tricarboxylic acid, and/or anhydrides thereof, and c) a saturated fatty acid with 12-18 carbon atoms and/or tall oil, and which polyester has a molecular weight between 3.000-10.000.

4. Chemical system according to claim 3, characterized in, that all starting material in the collector are aliphatic carboxylic acids and alcohols.

5. Chemical system according to claim 4, characterized in, that the polyalkylene glycol is polyethylene glycol, polypropylene glycol or a mixture thereof.

6. Chemical system according to any of the claims 3-5, characterized in, that the di- and tricarboxylic acids are preferentially chosen from the group maleic acid, fumaric acid, adipic acid, citric acid, oxalic acid and sebacic acid, and/or their anhydrides.

7. Chemical system according to any of the claims 3-6, characterized in, that the collector is produced by a reaction between polyethylene glycol and maleic acid, stearic acid and /or tall oil.

8. Chemical system according to any of the preceding claims, characterized in, that it also contains an inhibitor to hydrogen peroxide decomposing enzymes, such as peroxidase and catalase.

9. Chemical system according to claim 8, characterized in, that the inhibitor is composed of at least one inhibiting substance, such as hydroxylamine and its alkyl derivatives having 1-10 carbon atoms in straight or branched chain, such as, for example, methyl hydroxylamine, and their salts and addition salts, such as hydroxylammonium sulfate and hydroxylammonium chloride; thiocyanate salts, such as ammonium thiocyanate; formic acid; ascorbic acid, and nitrites, such as sodium nitrite, potassium nitrite, magnesium nitrite and calcium nitrite.

10. Chemical system according to claim 8 or 9, characterized in, that the inhibitor also contains one or more complexing agents and/or one or more tensides.

11. Chemical system according to claim 9, characterzed in, that the inhibitor contains hydroxylamine, hydroxylammonium sulfate. and/or hydroxylammonium chloride.

12. Chemical system according to claim 1 or 2, characterized in, that the dosage of the surface-active ester is 0,0005-2%), preferentially 0,005-1% and more preferentially 0,05-0,5%. based on the weight of dry fiber.

13. Chemical system according to any of the claims 3-7, characterized in, that the dosage of the polyester based collector is 0,0005-5%, preferentially 0.005-4% and more preferentially 0,05-1%), based on the weight of dry fiber.

14. Chemical system according to any of the proceeding claims, characterized in, that it is intended to be used in a pH-range 4- 10, particularly pH 6,0-8,5.

15. Procedure for deinking recycled fiber pulp or other cellulose fiber based pulp by the flotation process or by a similar process, characterized in, that, either before or during the dispersion of the pulp, a surface-active ester is added to discharge the printing-ink from the pulp fibers, and, before or at the flotation, a polyester based collector for aggregation and flotation of the released printing-ink particles is added.

16. Procedure according to claim 15, characterized in, that an inhibitor to hydrogen peroxide decomposing enzymes, such as peroxidase and catalase, is added to a process step involving peroxide.