BACKGROUND

1.0 Field Of The Invention: The present invention is generally directed to a process and apparatus for deinking printed wastepaper in which a molten fatty acid in the form of a mist of fine droplets and having a relatively low Iodine Value is added to an aqueous slurry of the wastepaper prior to or after the addition of an alkali metal hydroxide.

2.0 Discussion Of Related Art:

Wastepaper is used in large quantities for the production of, for example, newsprint. Lightness and color are important quality features for papers of this type. To achieve these desirable features, the printing inks have to removed from the printed wastepaper. This is normally done by deinking processes which are generally conducted in two steps:

1. refining the printed wastepaper, i.e. fiberizing in water in the presence of the chemicals required for detachment of the printing ink particles; and

2. removing the detached printing ink particles f om the fiber suspension.

The second step can be carried out by washing or flotation [Ullmanns Encyclopadie der technischen Chemie, 4th Edition, Vol. 17, pp. 570-571 (1979)]. In flotation, which utilizes the difference in wetability between printing inks and paper fibers, air is forced or drawn through the fiber suspension. Small air bubbles attach themselves to the printing ink particles and form a froth at the surface of the water which is removed by savers.

The deinking of printed wastepaper is normally carried out at alkaline pH values in the presence of alkali metal hydroxides, alkali metal silicates, oxidative bleaches and surfactants at temperatures in the range from 30 to 50°C. Soap solutions are often used to detach and separate the printing inks [Ullmanns Encyclopadie der technischen Chemie, 4th Edition, Vol. 17, pp. 571-572 (1979)].

The soap solution is conventionally formed via a soap make-down system (i.e. by pre ixing a fatty acid composition, heated to a temperature of at least 60°C so that it is in liquid or molten form, with an alkali metal hydroxide in an amount sufficient to convert the fatty acid to soap) . The soap is present in an aqueous solution in a concentration of from about 5% to about 10% by weight. If the concentration of soap significantly exceeds 10% by weight, the solution tends to form a gel which hinders the deinking process. Use of a soap

solution is essential to conventional deinking processes. The soap solution is water soluble and effectively removes the ink from the paper fibers, disperses the ink into the aqueous medium and floats the ink to the top of the aqueous medium where the ink can readily be removed from the deinking vessel (i.e. flotation cell) .

While soap solutions effectively deink printed wastepaper, their preparation from a substantially pure molten fatty acid composition before entry into the pulper is time consuming and adds significantly to the overall cost of the deinking process.

It would be a significant advantage in processes for deinking printed wastepaper if the molten fatty acid composition could be added directly to the pulper and then combined with the alkali metal hydroxide in the pulper. This would eliminate the step of converting the molten fatty acid to an aqueous soap solution in a separate vessel.

However, the addition of the molten fatty acid composition directly to the pulper presents significant problems. The fatty acid composition generally has a melting point higher than the temperature of the aqueous slurry of the printed wastepaper. As a consequence, when a molten fatty acid composition enters the pulper it coagulates into a solid mass having a much lower surface area than the molten starting material. The solid mass does not readily combine with an alkali metal hydroxide (e.g. sodium hydroxide) present within the pulper and therefore does not readily form a soap solution. Thus, the deinking of printed wastepaper using substantially pure molten

fatty acid without a soap make-down system has not been commercially successful.

It would, therefore, be desirable to provide a process for deinking printed wastepaper in which molten fatty acid could be added directly to the pulper so as to eliminate the step of converting the fatty acid composition into a soap solution prior to entry into the pulper and/or flotation cell.

3.0 Summary Of The Invention:

The present invention is generally directed to a process and apparatus for deinking printed wastepaper in which a molten fatty acid is added directly to the pulper. The present invention eliminates the step of converting the fatty acid composition into a soap solution prior to its entry into the pulper. In particular, the present invention is directed to a process for deinking printed wastepaper comprising treating a slurry of printed wastepaper with a deinking effective amount of fine droplets of a molten fatty acid having a Iodine Value of from about 0 to 140.

BRIEF DESCRIPTION OF THE DRAWING

The following drawing is illustrative of an embodiment of the invention and is not intended to limit the invention as encompassed by the claims forming part of the application.

The sole figure is a schematic view of one embodiment of the invention for deinking printed wastepaper in which a

substantially pure molten fatty acid composition is fed through at least one nozzle which atomizes the molten composition into a mist of fine droplets and injects the same directly into the pulper.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides for the direct addition of a molten fatty acid composition into a pulper to deink printed wastepaper. In accordance with the invention, the molten fatty acid composition is added to the pulper as a mist of fine droplets collectively having a large surface area. The fine droplets of the fatty acid composition therefore readily react with an alkali metal hydroxide to form a soap solution. The resulting solution is particularly adapted for removing ink from the printed wastepaper. Referring to the sole drawing, the principal components employed to carry out the present invention include a storage tank 2 for storing the molten fatty acid composition, a feed pump 4 for transferring the molten fatty acid composition to a pulper, a filter 6 for removing contaminants from the molten fatty acid composition to produce a substantially pure feed, a flowmeter 8 for metering the molten fatty acid feed to the pulper, at least one nozzle 10 for converting the molten fatty acid feed into a mist of fine droplets and a pulper 12 for combining the mist of molten fatty acid with an aqueous slurry containing the printed wastepaper.

A fatty acid composition is fed from a source not shown via a conduit 14 to the storage tank 2. The fatty acid

composition which may be employed in the present invention include those having a relatively high degree of saturation as measured by the Iodine Value. The fatty acid composition has an Iodine Value generally in the range of from 0 to about 140, preferably from 0 to about 80. The preferred fatty acid composition includes straight chain fatty acids having from 8 to 22 carbon atoms and mixtures thereof. The fatty acid composition should have a melting point of at least about 50°C.

The fatty acid composition is maintained in the molten state by applying heat such as with a heating coil 18 which receives steam via a conduit 16 and removes condensate via a line 20. The molten fatty acid composition, heated to a temperature above its titre (melting point) , preferably to a temperature of at least 60°C, most preferably about 70°C, moves from the tank 2 via a conduit 22 to the feed pump 4 where pressure is applied to generate a feed stream having a constant flowrate of about 5 liters/minute to 25 liters/minute.

The pressurized feed is then sent via a conduit 24 to the filter 6 which improves the purity of the fatty acid composition by removing contaminants such as carbon particles and the like. The resulting purified feed stream is divided into a recycled stream which flows back to the tank 2 via a conduit 26 and a valve 28 and a process stream which flows via a conduit 30 and a valve 32 to the flowmeter 8. The conduit 30 is preferably purged with steam after the passage of each charge of the molten fatty acid composition. The steam which is provided from a source (not shown) through a conduit 34 and a valve 36, removes residual amounts of the fatty acid composition. In addition, the

steam preheats the conduit 30 to operation temperatures (i.e. above the titre of the fatty acid composition) to insure passage of the fatty acid composition in molten form.

The process stream then passes through a flowmeter which controls the rate at which the purified molten fatty acid composition is sent via a conduit 38 to the nozzle 10. The flowmeter 8, which is conventional in the art, regulates the flow of the process stream on a volume or mass basis. The flowmeter 8 registers the amount of the fatty acid composition which passes into the pulper until a predetermined amount is reached and then the flowmeter shuts off thereby terminating the flow of the fatty acid composition into the pulper.

The metered process stream containing the purified molten fatty acid composition is then sent to at least one injection nozzle which atomizes the molten composition into a mist of fine droplets. The nozzle generates a molten fatty acid composition having a very large surface area. The large surface area enables the molten fatty acid composition to more readily react with the alkali metal hydroxide in the pulper 12 to form a soap solution.

The size of the droplets of the fatty acid composition obtained from the nozzle should be sufficient to promote a reaction with the alkali metal hydroxide. It is desirable for the fine droplets to have a typical particle size of from about 200 to 900 microns, preferably about 300 to 500 microns. Particles of this size can readily be.produced from conventional nozzles.

The mist of the molten fatty acid composition is sprayed from the nozzle 10 into the pulper 12 which contains an aqueous solution of deinking chemicals as described hereinafter. The process water for the aqueous solution is provided through a conduit 40 while the deinking chemicals are provided through a conduit 42. The printed wastepaper to be deinked enters the pulper 12 via a conveyor 44.and is present in a concentration typically in the range of from about 4 to 20% by weight, more typically 10 to 14% by weight. The printed wastepaper is refined at a temperature of from 20 to 60°C in the aqueous slurry typically containing as deinking chemicals from about 0.5 to 3% by weight of each of hydrogen peroxide, sodium silicate (35% by weight 37-40°βe) and an alkali metal hydroxide, preferably sodium hydroxide, based on the weight of the printed wastepaper. The residence time of the printed wastepaper in the pulper during the deinking process is from about 10 to 30 minutes. The conditioned pulp is removed from the pulper via the conduit 46.

The type of ink which may be removed from the printed wastepaper in accordance with the present invention may be oil based or water based. For water-based inks, the aqueous slurry of the wastepaper may also contain water-soluble polymers and/or copolymers containing amino and/or ammonium groups such as disclosed in United States Patent Application Serial No. 07/689,262 filed May 23, 1991, incorporated herein by reference.

The following example is illustrative of an embodiment of the invention and is not intended to limit the invention as encompassed by the claims forming part of the application.

EXAMPLE 1 20 tons of molten fatty acid having an Iodine Value of 12 and a titre (melting point) of 55°C (Olinor 4010 produced by Henkel Canada Limited) was kept at 65-70°C in a 30 ton bulk storage tank equipped with a heating coil. The material was continuously circulated through a 1 inch insulated and steam- traced recycle line equipped with a feed pump and an in-line bag filter. A 1 inch spray line which was branched off from the recycle line and positioned as closely as possible to the pulper. A batch pulper capable of handling 8.6 ADMT (Air Dried

Metric Tons) of printed wastepaper at 12% consistency was equipped with a set of 4 spraying nozzles having the following specifications: Fulljet nozzle spray, female, 3/8 inch, Cat. No. 3/8 GS9.5 (John Brooks Company Ltd., Mississauga, Ontario L4W 1Y1) .

The pulper was first charged with 55 tonnes of recirculated White Water at 45°C and followed by:

(1) 90 liters of sodium hydroxide (50%) ;

(2) 86 Kg of sodium silicate (40 Be) ; (3) 7 liters of DTPA (diethylenetriamine penta acetic acid, 40%) ; and

(4) 130 liters of hydrogen peroxide (50%) .

The fatty acid spray line was first steam purged through a micromotion mass flowmeter all the way to the nozzle heads for one (1) minute or until the line was hot and clear.

While the pulper agitator was on, the fatty acid valve at the tee-off position of the spray line was opened while the valve at

the recycle line was gradually closed to build up a line pressure of 60 psi. Molten fatty acid was metered through the flowmeter and sprayed directly into the contents of the pulper in fine droplets having a typical particle size of from about 212μ to 850μ. After a total of 66 kg of molten fatty acid was registered by the mass flowmeter in 5-minute spraying time, the fatty acid valve on the recycle line was opened and the valve on the spray line was closed. Without delay, the spray line was purged for one minute with 120 pound steam to clean the line and nozzles. This completed the batch cycle of the fatty acid spraying application.

As soon as the fatty acid droplets hit the alkaline White Water, they were saponified instantaneously into a water soluble sodium soap solution without forming lumps of unreactive fatty acid. This sodium soap solution, having a concentration of about 0.12%, acted as a surfactant for the detaching/dispersing of the ink particles from the fiber and eventually, in the presence of hard water, agglomerated and floated the ink particles to the surface in its final active chemical form - precipitated calcium soap.

In an alternate embodiment of the invention, the alkali metal hydroxide is added to the pulper after the fine mist of molten fatty acid is injected into the pulper. When the molten fatty acid enters the pulper, it cools and forms small microbeads of solid fatty acid. The surface area of the microbeads is sufficiently large so that substantially all of the fatty acid reacts with the subsequently added alkali metal hydroxide to form the soap solution necessary to deink the printed wastepaper.