EP0407501A1 - Method and composition for deinking recycled paper pulp - Google Patents

Abstract

Amphoteric surfactants are useful in the flotation deinking of recycled waste paper, particularly paper that has been subjected to laser printing.

Description

"METHOD AND COMPOSITION FOR DEINKING RECYCLED PAPER PULP"

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention relates to reclamation of paper. In particular, it relates to a means for deinking paper, and is of especial use in deinking laser-printed paper.

2. DESCRIPTION OF THE PRIOR ART

There are currently two major types of process for deinking paper: washing and flotation. The former is the type predominantly used in the United States. Various reasons have been given for this. Horacek and Dewan in Tappi Vol. 65 July 1982 attribute this to the fact that washing is good for dealing with furnishes containing dispersible inks or if substantial ash removal is required. Whereas flotation is better at removing large non-dispersible ink particles such as those "encountered with food board or Xerox^® paper".

Most furnishes used in the United States are of the former category. Neither process is satisfactory for deinking laser-printed paper. Both deinking processes involve a repulping of printed paper waste during which the ink is removed from the fibers.

In both processes, the paper is converted to pulp in an aqueous caustic bath with strong agitation and, frequently, at elevated temperatures (120-140°F. being commonly employed).

In the washing process, various additives typically including a surfactant and a builder such as sodium silicate are also generally present to aid in removing the ink from the fiber and either dissolve or disperse it in the aqueous medium. In addition, bleach may also be added at this stage. The time for this treatment depends on the nature of the furnish (i.e. printed paper stock), caustic concentration, temperature and additives used, but generally does not exceed about 30 minutes. After the pulping step, the pulp is taken through various presses where inky liquor is removed and the pulp concentration increased. It then goes to screens where the liquor is drained away and the pulp is washed before being reslurried and fed to the paper machine.

In flotation processes, a foaming agent is added to the pulp which is then passed through various "cleansing" devices and fed to flotation cells. Ink particles are recovered in the foam.

A variety of surface active agents have been suggested previously for use as flotation agents when carrying out flotation deinking. For example, Suiwala and Feigenbaum in TAPPI Proceedings reports of the 1983 Pulping Conference (page 533) describe the use of alkyl phenol ethoxylates especially the nonyl phenol

ethoxylates and mixtures of such compounds with dodecyl phenol ethoxylates, noting that the ethylene oxide chain length and hydrophobe length correlate to deinking efficiency. It is indicated that certain such mixtures can achieve "good deinking (brightness) and low foam without detracting from other overall properties".

Woodward in Pulp & Paper November 1986, p. 59 lists a wide variety of deinking chemicals noting that ethoxylated linear alcohols and ethoxylated alkyl phenols are widely used as deinking aids and that fatty acid soaps act as collection chemicals in flotation deinking systems. It is also noted that solvents may be used to dissolve most inks and varnishes but that their cost prohibits their use in most deinking programs.

Solvents that have been used include aliphatic

hydrocarbons and it is pointed out that when a solvent in used a surfactant having good oil in water

emulsifying properties should also be used. It is, however, unclear whether these comments are made in the context of a washing or a flotation system.

Evans in Pulp & Paper, March 1984 describes use of a Krofta clarifier apparently to act as a flotation unit as a second stage deinker after an initial washing operation in a newsprint mill in

Thorold, Ontario. It is stated that polyelectrolytes are used to aid floe formation in the flotation.

Another description of the same plant is given in Tappi Journal, October 1983 where it is pointed out that the plant initially had problems with excessive foaming leading to the presence of foam in the effluent from the plant apparently a low foaming surfactant composition based on an alcohol ethoxylate/alkyl phenol ethoxylate was devised to cope with this. It is, however, unclear whether this was used in the washing or the flotation stage.

Cody in Pulp & Paper, November 1978 p. 123 refers to the use of a wide variety of surfactants including soaps, ethoxylated alkyl phenols, alkyl aryl sulfonates, poly phosphates, poly ethoxy ethanols and ethoxylated alcohols. It is unclear whether these are advocated for washing or flotation operation or both. Cody does, however, comment that "in flotation deinking an additional surfactant such as a detergent may be added to promote foaming".

Ortner in his chapter entitled "Flotation Deinking" in the TAPPI Monograph "Recycling of

Papermaking Fibers" refers to the use of soaps as frothers and collectors indicating that small amounts of synthetic surfactants such as ethoxylated fatty acids, alkyl benzol sulfonates (sic) and alkyl phenol polyglycol ethers are typically added to improve the flotation process.

SUMMARY OF THE PRESENT INVENTION

We have found that use of a particular

combination of chemicals in a flotation deinking process offers substantial advantages over prior art deinking systems. In particular, our new system for the first time opens a viable means for deinking laser printed paper.

The increasing use of laser printing for computer printouts has presented a problem for deinking operations. There is at present no system that can deink this type of furnish. With computer printout representing a large and growing source of furnish, it is impractical to segregate laser-printed from impact- printed or dot-matrix computer stock.

The present invention uses as its flotation system a combination of a high foaming surfactant that is a poor emulsifier, a terpene hydrocarbon and a solvent for the terpene.

Without wishing to be bound by any theory, we believe the terpene acts as a "capture agent" for the ink. The terpene itself dissolves in the solvent.

Since the surfactant used is not an emulsifier, this allows the ink particles to be held in suspension by the terpene/solvent combination until the ink is floated off with the terpene/solvent solution.

Accordingly, from the first aspect, the present invention provides a deinking system for

recycled paper furnish which comprises a mixture of high foaming low emulsifying surfactant, a terpene and a solvent for said terpene in a weight ratio of 0.125-8 : 0.125-16 : 1. More preferably, the ratio of surfactant: terpene: solvent is 1-6:0.125-8:1.

From a second aspect, the invention provides a flotation process for deinking paper wherein the

flotation agent employed comprises a high foaming low emulsifying surfactant, a terpene and a solvent for said terpene in a weight ratio of 0.125-4 : 0.0625-4 : 1 preferably 1-6 : 0.125-1 : 1.

Typically, the flotation agent used will provide for 0.5-4, more preferably 2-3 lbs of

surfactant, 0.25-4 lbs, more preferably 0.25-2 lbs of terpene and 0.5-4, preferably 0.5-2 lbs of terpene solvent per ton of furnish. (For the avoidance of doubt when used herein the term "ton" means 2,000 lbs).

DETAILED DESCRIPTION OF THE INVENTION

Surfactants of use in the present invention are those that are good foamers but have low emulsifying properties. Suitable surfactants include amphoteric carboxylates and sulfonates, betaines, sultaines and amino propionates having 10-16 carbon atoms. Useful amphoteric surfactants include both mono and

dicarboxylates such as those of the formula:

2

wherein R is an alkyl group of 10-16 carbon atoms, x is 1 or 2 and M is hydrogen or sodium.

Such compounds include:

cocoamphoacetate (sold under the trademarks MIRANOL CM CONC. and MIRAPON FA),

cocoamphopropionate (sold under the trademarks MIRANOL CM-SF CONC. and MIRAPON FAS),

cocoamphodiacetate (sold under the trademarks MIRANOL C2M CONC. and MIRAPON FB) ,

cocoamphodipropionate (sold under the trademarks MIRANOL C2M-SF CONC. and MIRAPON FBS),

lauroamphoacetate (sold under the trademarks

MIRANOL HM CONC. and MIRAPON LA), lauroamphodiacetate (sold under the trademarks MIRANOL H2M CONC. and MIRAPON LB),

lauroamphodipropionate (sold under the

trademarks MIRANOL H2M-SF CONC. AND MIRAPON LBS),

lauroamphodiacetate obtained from a mixture of lauric and myristic acids (sold under the trademark MIRANOL BM CONC.).

Somewhat less preferred are:

caproamphodiacetate (sold under the trademark MIRANOL S2M CONC),

caproamphoacetate (sold under the trademark MIRANOL SM CONC),

caproamphodipropionate (sold under the

trademark MIRANOL S2M-SF CONC),

stearoamphoacetate (sold under the trademark

MIRANOL DM).

Other useful compounds include the sulfonate analogs of these carboxylates such as those of the formula:

for example, cocoamphohydroxy propyl sulfonate (MIRANOD^® CS CONC.) and oleoamphohydroxy propyl sulfonate.

Suitable betaines include those of the

formulae:

where R is an alkyl group of 10-16 carbon atoms, each R¹ is methyl or 2-hydroxy ethyl.

Such compounds include cocamidopropyl betaine, lauroamido propyl betaine, oleamide propyl betaine and mixtures such as coco/oleamido propyl betaine.

Suitable sultaines include those of the formula:

where R is an alkyl group of 10-16 carbon atoms and each R¹ is methyl or 2-hydroxy ethyl.

Suitable aminopropionates include those of the formula: (zwitterionic form)

where R is alkyl of 10-16 carbon atoms. A suitable compound in this class is disodium

lauriminodipropionate.

Particularly, useful compounds in all of these classes are compounds wherein the R group is derived from coconut fatty acids or coconut oil.

Terpenes used in the present invention are normally monoterpenes. Suitable terpene hydrocarbons include d-limonene, dipentene, alpha- and beta-pinene, and various grades of turpentine oil or distilled turpentine. We have found that mixtures of terpenes such as that sold under the trademark DIPENTENE NO. 122 (Hercules Incorporated, Wilmington, Delaware), steam distilled wood turpentine such as that sold under the trademark SDW Turpentine (also Hercules Incorporated) and commercial grade d-limonene (as obtained for Pine Derivatives Marketing Inc.) are particularly useful.

As solvent for the terpene, petroleum distillates or mineral spirits or, especially, mineral oil may be used. The hydrocarbon solvent and terpene hydrocarbon should be essentially water-insoluble.

useful mineral oil solvents include both light mineral oils having a specific gravity of 0.83 to 0.86 at 25ºC. and heavy mineral oils having a specific gravity of 0.875-0.905, for example, Drakeol 7 or

Drakeol 35 supplied by Penreco.

The compositions of the present invention may be found as a preformed mixture. Alternatively, they may be added separately to a recycled paper furnish.

The use of the compositions is a paper

deinking operation.

The chemicals used in the flotation deinking are mixed with the recycled paper pulp to be deinked and also normally with additional steam and/or water in a mixing tank.

The chemicals added at this stage are the flotation chemicals described above, typically in amounts of 2-3 lbs/ton of surfactant, 0.25-2 lbs per ton of terpene and 0.5-2 lbs per ton of solvent such as mineral oil. Additional chemicals used in deinking processes such as caustic soda, sodium peroxide or a mixture of caustic soda and hydrogen peroxide may also be used. It is not normally necessary to use builder chemicals such as sodium silicates sodium citrate or polyphosphates when using the surfactants of the present invention. In appropriate cases, however, they may also be added.

After the chemicals have been added to the recycled paper pulp, the mixture is passed to a dump chest where it is typically held for a few (say 1-2) hours.

From the dump chest the mixture is passed to one or more pre-cleaning operations; for example, vibrating screens, deflakers and sand traps.

The mixture is then passed to one or more primary flotation cells or a flotation machine in which compressed air and the pulp stock are typically

introduced into the bottom of a cell and froth recovered from the top, for example, by passage over a weir.

Typically, flotation is carried out for periods of less than 1 hour depending upon the type of apparatus employed. In some cases, satisfactory results may be obtained with a duration of less than 10 minutes (say 7-10 minutes) in other cases duration of more than 30 minutes may be required.

The bulk of the pulp is typically recovered from a side outlet in the flotation cell. Suitable flotation cells for this purpose are commercially available. For example, such cells and machines are produced by Voith, Sankey, Escher-Wyss, Swemac, Lamort (France), Outokumpo oy (Finland) and Aukawa (Japan).

The froth is passed to a secondary flotation unit 5, the pulp effluent from which may be recycled to the feed into the primary flotation unit. The froth from the secondary flotation unit is centrifuged and the

chemicals and ink recovered.

The pulp from the flotation cells or machines is normally passed to a further cleansing operation 5, such as screens and filters and then passed for further processing 6 such as bleaching, thickening and

dewatering before passage to a storage tank 7 from which it may be passed to a paper making machine.

The present invention will now be illustrated by the following examples and experiments.

In all cases:

1. The deinking chemicals and 15 ml of 6% aqueous sodium hydroxide were added to about 2 1 of tap water in a 3 liter capacity stainless steel beaker.

2. While stirring, 50 g of dry furnish (cut into approximately 1 inch squares) was added. Stirring was continued for 30 minutes either at 60ºF. or 120°F.

3. The slurry was then subjected to high shear (Waring Blender at setting 3) for 1 minute to assure that the fibers were free.

4. The slurry was then placed in a 2 1 stainless steel beaker (which is placed in a plastic dishpan) and stirred while air was bubbled through by means of a sparge tube (PYREX brand, Fisher catalog No. 11-137E) positioned beneath the stirrer. The foam produced carried the ink particles and was allowed to overflow from the beaker and be captured in a plastic dishpan. This flotation step was continued for 30 or 45 minutes.

5. The slurry was then poured into a handsheet machine, diluted further with water, then drained. to form the handsheet.

6. The sheet was then dried for 20 mintues in an oven at 90°C

7. Between each flotation run the sparge tube was soaked in concentrated sulfuric acid then thoroughly rinsed with water before use.

The number of specks/cm² is an average of at least six readings taken at random locations on the topside of the handsheet. Brightness values are

obtained using a Photovolt Reflection Meter, Model 670 calibrated at 72.5% before each reading.

Conditions and results are shown in TABLE 1 using 50gm of a mixed furnish (one-third each of impact print, dot-matrix print and laser print). In

experiments 1-3, pulping was carried out a 120°F. and, in experiment 4, at 60°F. Flotation time was 30 minutes for experiments 1 and 2 and 45 minutes for 3 and 4. The d-limonene used in these and subsequent experiments was Brazilian CP. Orange Oil from PDM Inc. For all experiments, the mineral oil used was Drakeol 7 (Light Mineral Oil USP) from Penreco. Other grades of dlimonene and of mineral oil have been found to be equally effective.

*MIRAPON^® FBS (cocoamphodipropionate - Miranol)

These results demonstrate the value of having mineral oil present as well as the value of a long flotation time.

In TABLE II are shown results using 50 gm of laser printed furnish. In all cases, the flotation time was 45 minutes and the amphoteric used was MIRAPON^® FBS . For experiment 5, pulping temperature was 120ºF. and for all other experiments it was 60° F .

From this, it can be seen that there is a slight loss in effectiveness when mineral oil is not present, a greater loss when the terpene is left out and a significantly greater loss when both are absent.

TABLE III shows the effect on handsheet quality from use of various foaming agents. All

experiments were conducted using 50gm of laser printed furnish, 0.025gm of d-limonene, 0.05gm of mineral oil and 0.05gm of foaming agent shown. In all cases, pulping temperature was 60ºF. and flotation time was 45 minutes. g

a) Ethoxylated (9.5 moles E . O) nonylphenol (GAF) b) Cocamidopropyl Hydroxysultaine (Miranol)

c) Lauroamphodiacetate (Miranol)

d) Disodium Lauriminodipropionate (Miranol)

e) Cocamidopropyl Betaine (Miranol)

f) Capryloamphopropionate (Miranol)

g) Dissodium Lauryl Sulfosuccinate (Miranol)

h) Capryloamphodiacetate (Miranol)

As can be seen, best results were obtained with coconut-range amphoterics (experiments 9 , 13 and

16) , with lauryl-based materials being intermediate (experiments 14 , 15 and 18) . The capry lie-based

products (experiments 17 and 19 were rather poor as expected since these are poor foamers . With IGEPAL CO- 630 (experiment 10) , although it is an excellent foaming agent, it is also a good emulsifier and this is believed to be the reason for its poor performance in this system. The same is true for the foaming agents of experiments 20, 21 and 22.

The effect of using other terpenes is demonstrated in TABLE IV. In these experiments, 50gm of laser-printed furnish was used with a pulping

temperature of 60°F. and a flotation time of 45 mintues.

Here it can be seen that comparable results were

obtained using any of the three coconut-range

amphoterics. Also, leaving out the mineral oil gave poorer results.

Claims

C L A I M S

1. A method for deinking waste paper which comprises admixing therewith a deinking system comprising a mixture of high foaming low emulsifying surfactant, a terpene and a solvent for said terpene in a weight ratio of 0.125-8 :

0.125-16 : 1 and to produce a furnish thereafter subjecting said furnish to a flotation operation to recover ink

particles from froth produced by said flotation.

2. A method for deinking paper according to claim 1, wherein said deinking system is employed in amounts to produce a concentration of 1-4 lbs of said surfactant,

0.25-4 lbs of terpenes and 0.5-4.0 lbs of solvent per ton of furnish.

3. A method for deinking paper according to claim 2, wherein said deinking system is employed in amounts to produce a concentration of 2-3 lbs of surfactant, 0.25-2.0 lbs of terpene and 0.5-2.0 lbs of solvent per ton of

furnish.

4. A method according to claim 1, 2 or 3, wherein the paper to be deinked comprises laser-printed paper.

5. A method according to claim 1, 2, 3 or 4, wherein said high foaming low emulsifying surfactant is selected from the group consisting of amphoteric carboxylate,

betaine, sultaine, and amino propionate surfactants.

6. A method according to any one of claims 1-5, wherein said high foaming low emulsifying surfactant is an amphoteric surfactant of the formula:

or

wherein R is an alkyl group of 10-16 carbon atoms, x is 1 or 2 and M is hydrogen or sodium.

7. A method according to any one of claims 1-5, wherein said high foaming low emulsifying surfactant is a betaine of the formula:

where R is an alkyl group of 10-16 carbon atoms, each R¹ is methyl or 2-hydroxy ethyl.

8. A method according to any one of claims 1-5, wherein said high foaming low emulsifying surfactant is a sultaine of the formula:

where R is an alkyl group of 10-16 carbon atoms and each R¹ is methyl or 2-hydroxy ethyl.

9. A method according to any one of claims 1-5, wherein said high foaming low emulsifying surfactant is an amino propionate surfactant of the formula: (zwitterionic form)

where R is alkyl of 10-16 carbon atoms.

10. A method according to any one of the preceding claims, wherein said terpene is a mono terpene.

11. A method according to any one of the preceding claims, wherein said terpene is selected from the group consisting of d-limonene, dipentene, alpha-pinene, β-pinene, turpentine oil and distilled turpentine.

12. A method according to any one of the preceding claims, wherein said solvent for terpene is substantially insoluble in water.

13. A method according to any one of the preceding claims, wherein said solvent for terpene is a mineral oil.

14. A method according to any one of the preceding claims, wherein said mineral oil has a specific gravity in the range 0.83 to 0.9 at 25°C

15. A deinking system which comprises a mixture of high foaming low emulsifying surfactant, a terpene and a solvent for said terpene in a weight ratio of 0.125-8 :

0.125-16 : 1.

16. A deinking system according to claim 1, wherein the ratio of high foaming low emulsifying surfactant :

terpene : solvent for said terpene is 1-6 : 0.25-8 : 1.

17. A deinking system according to either of claims 15 or 16, wherein the emulsifying surfactant is as defined in any one of claims 5 to 9.

18. A deinking system according to any one of claims 15 to 17, wherein the terpene is as defined in any one of claims 10 to 12.

19. A deinking system according to any one of claims 15. to 18, wherein the solvent is as defined in either of claims 13 and 14.

20. A system according to any one of claims 16 to 19, wherein a caustic alkali is also present.

21. A system according to claim 20, wherein sodium hydroxide is present.