GB2086955A - Process for Recovering Waste Paper - Google Patents

Abstract

The invention relates to the recovery of waste paper based on cellulose by a chemical pulping process especially by means of a washing or flotation method, wherein the pulping operation is carried out by using a urea-formaldehyde condensate as additive.

Description

SPECIFICATION Process for Recovering Waste Paper The present invention relates to a process for recovering waste paper by means of a chemical pulping operation, especially by means of a washing or flotation method. The process comprises carrying out the pulping operation by using a urea-formaldehyde condensate as additive.

The urea-formaldehyde condensates (hereinafter referred to as UF condensates) employed in the process of the invention advantageously have a BET surface area of 3 to 75 m2/g, preferably 3 to 30 m2/g, and, most preferably, 5 to 25 m2/g. The specific BET surface area is determined by the nitrogen absorption according to the method of Brunauer, Emmett and Teller [cf. Chem. Ing. Techn. 32, pp.

349-354(1960) and pp.568-589 (1963).] The UF condensates suitable for the treatment process of the invention are known per se. These UF condensates and the production thereof are described e.g. in an article by A. Renner in "Die Makromolekulare Chemie" 149, pp. 1-27 (1971) or in German Offenlegungsschrift specifications 2 556 017 and 2 641 218. The UF condensates are obtained by reaction of 1 mole of urea and 1.3 to 1.8, preferably 1.4 to 1.5, moles of formaldehyde, in aqueous solution and under suitable conditions.

The reaction to obtain the UF condensate is conducted preferably in two steps. In the first step, the urea and the formaldehyde are reacted in accordance with the conventional condensation methanism to form a low molecular water-soluble precondensate, and then, in a second step, an acid catalyst is added in order to hasten the formation of the UF condensate. An insoluble, finely particulate solid is obtained.

The amount of water in the reaction solution should advantageously not be substantially smaller than the total weight of the reactants and, during the actual formation and precipitation of the insoluble condensate particles, should always be present in substantial excess of the total weight of all other components of the reaction mixture.

The reaction temperature during the formation of the precondensate in the first step is usually in the range from 200 to 1000C, preferably from 600 to 800 C. It is advantageous to adjust the pH value to 6 to 9, preferably to 6.5 to 7.5, by adding an aqueous inorganic strong base, e.g. a solution of sodium hydroxide. The formation of the precondensate is usually complete after half an hour to 3 hours.

The formation of the precondensate is conveniently carried out in the presence of an ionic or nonionic surfactant, e.g. a cationic quaternary ammonium compound, an anionic fatty alcohol sulfonate, a non-ionic polyethylene glycol ether, preferably a salt of a sulfosuccinate, especially sodium dodecylbenzenesulfonate. The amount of surfactant employed is usually 1 to 3% by weight, based on the sum of the weight of urea and formaldehyde used in the reaction. Ionic surfactants as a rule effect an increase in the surface area of the condensate, whereas non-ionic surfactants induce an opposite effect.

It can be expedient to use a macromolecular water-soluble protective colloid with polyelectrolyte character during the formation of the precondensate, i.e. during the first reaction step. Examples of suitable protective colloids are gelatin, tragacanth, agar-agar or polyvinyl pyrrolidones, especially polymers of acrylic and methacrylic acid, in particular polymethacrylic acid. The amount of protective colloid employed is 1 to 3% by weight, based on the sum of the weight of urea and formaldehyde.

Polyvinyl pyrrolidones and polymethacrylic acid are especially suitable, as they do not effect any increase in the specific surface area.

One of the most important conditions for the successful manufacture of suitable infusible and insoluble finely particulate UF condensates is the use of a gelling catalyst in the second reaction step, e.g. of an inorganic and/or organic acid or an anhydride thereof, e.g. sulfurous acid, sulfuric acid, sulfamic acid, phosphoric acid, hydrochloric acid, chloroacetic acid, maleic acid or the anhydride thereof. In general, suitable gelling catalysts are those which have an ionisation constant greater than about 10-4. A particularly preferred gelling catalyst is sulfuric acid. The most preferred gelling catalysts are the acid ammonium and amine salts of sulfuric acid, e.g. ammonium, methylamine or ethanolamine hydrogen sulfate. These acids and salts are preferably employed in the form of 1 to 1 5% by weight aqueous solutions.

As a rule, 20 to 100 mmols of gelling catalyst are used per mole of urea, whereupon the pH value of the reaction mixture in the second step, i.e. in the reaction to form the condensate, is lowered to 3 to 1.5.

The second step of the formation of the UF condensate is advantageausly carried out in the temperature range from 200 to 1000C, preferably from 400 to 650 C. Strong fluctuations in the temperature of the reaction mixture must be avoided when adding the gelling catalyst. It is therefore advantageous to preheat the aqueous catalyst solution to the temperature of the reaction mixture before adding this. A white gel is normally obtained within 1 5 to 30 seconds, whereupon the reaction is brought to completion, preferably over the course of a further 1/2 hour to 3 hours.

The insoluble condensate, which is obtained in the form of a white gel, is conveniently mechanically comminuted and mixed with approximately equal parts of water. The pH is adjusted with alkali or ammonia, preferably with sodium hydroxide, to 6 to 9, preferably to 7.5, and the condensate is then separated by conventional methods from the aqueous liquid, e.g. by filtration, centrifuging, or evaporation to dryness. The product can be dried by different methods, e.g. by spray drying or convection drying. Although the UF condensate consists basically of fine particles, it is advantageous to subject the solid product to comminution or deagglomeration in order to diminish the average agglomerate size and to improve the adsorption values for oil or other fluids And thus to bring it to full strength for use as auxiliary pigment within the scope of the invention.To this end the UF condensate can be comminuted in different grinding machines or impact mills, e.g. in ball mills, attrition mills, jet mills, or mills with rapidly rotating disce, to give UF condensate particles having an average particle size of 2 to 10, preferably 4 to 6, microns (,us). The primary particles have a diameter of 0.1 to 0.5 cm, preferably 0.11 to 0.35 ,um.

The UF condensates are employed in the practice of this invention primarily as additives for recovering and after-bleaching fibrous matter from waste paper, said fibrous matter having a higher degree of whiteness than that obtained by means of the conventional treatment process. The amounts in which the UF condensates are added to the fibrous matter vary from 0.1 to 10% by weight, preferably from 0.5 to 4% by weight, based on the weight of the dry waste paper.

Waste paper is usually understood as comprising printed, coloured, water-resistant, bituminous and/or coated waste paper based on cellulose and originating from printing works, paper processing plants, public authorities, industry and commerce, and private households.

The printed products can be prepared by any kind of process, e.g. intaglio, offset or gravure printing. Sorted or unsorted, groundwood-free or groundwood-containing waste paper can be employed in the practice of this invention. If desired, the printed paper to be regenerated can be shredded or crushed. It is preferred to use mixtures of press publications, e.g. illustrated magazines and newsprint. The waste paper can be present in a density of 1 to 8, preferably 2 to 6% by weight.

The recovery of waste paper according to the practice of this invention is advantageously effected in alkaline medium by the deinking process by washing, flotation, or a combination of these methods.

In this process, the waste paper, generally a pulp suspension, is treated with an alkaline aqueous solution which can contain a number of deinking chemicals such as alkalies, water glass or peroxides, and further ingredients such as detergents, foaming agents, flotation agents, emulsifiers and dispersants, as well as polyols or fatty acids. These latter form alkali metal soaps in the alkaline liquor.

The deinking process of the invention can be carried out in the temperature range from 100 to 600C, preferably at room temperature.

Preferably, waste paper which is saturated with water is treated in a closed contained (pulper) with an alkaline preparation which contains 0.5 to 4% by weight of UF condensate and 0.1 to 1% by weight of a non-ionic or anionic surfactant, based on the weight of the dry waste paper. This treatment effects release and dispersion of the printing ink and fibre mucilages (waste products). These are then removed from the pulp suspension by washing out or by separation of the flotation foam. If desired, the treatment can be combined with a bleaching, e.g. with hydrogen peroxide or sodium peroxide.

The preferred alkali is sodium hydroxide, which is employed as a rule in the form of a 2 to 1 5% aqueous solution for maintaining a pH value of 8 to 10. It is also possible to employ further alkali metal hydroxides such as potassium hydroxide, as well as alkali metal salts, e.g. sodium carbonate. The non ionic and/or anionic surfactants are employed as detergents, wetting agents, foaming agents, dispersants and/or emulsifiers.

Representative examples of non-ionic surfactants are: adducts of preferably 5 to 80 moles of alkylene oxides, especially ethylene oxide, individual ethylene oxide units of which can be replaced by substituted epoxides such as styrene oxide and/or propylene oxide, with higher unsaturated or saturated fatty alcohols, fatty acids, fatty amines or fatty amides containing 8 to 22 carbon atoms, or with phenylphenol or alkylphenols, the alkyl moieties of which contain at least 4 carbon atoms; alkylene oxide condensation products, especially ethylene oxide and/or propylene oxide condensation products;; reaction products of fatty acid containing 8 to 22 carbon atoms and a primary or secondary amine which contains at least one hydroxy-lower alkyl or lower alkoxy-lower alkyl group, or alkylene oxide adducts of these hydroxyalkylated reaction products, the reaction being so conducted that the molecular ratio of hydroxyalkylamine to fatty acid can be 1:1 and greater than 1, e.g. 1.1:1 to 2:1; and adducts of propylene oxide with a trihydric to hexahydric aliphatic alcohol containing 3 to 6 carbon atoms, e.g. glycerol or pentaerythritol, said polypropylene oxide adducts having an average molecular weight of 250 to 1800, preferably 400 to 900.

Very suitable non-ionic surfactants are alkylene oxide reaction products of the formula

wherein R is hydrogen, alkyl or alkenyl each containing a maximum of 18, preferably 8 to 16, carbon atoms, o-phenyl-phenyl or alkylphenyl containing 4 to 12 carbon atoms in the alkyl moiety, one of Z, and Z2 is hydrogen and the other is methyl, m is an integer from 1 to 1 5 and the sum of n1+n2 is 3 to 10.

Especially preferred surfactants are fatty alcohol polyglycol ethers, in particular adducts of 3 to 10 moles of ethylene oxide and 3 to 10 moles of propylene oxide with aliphatic monoalcohols containing 8 to 1 6 carbon atoms.

It is also possible to use mixtures of non-ionic surfactants.

Representative examples of anionic surfactants are: sulfated aliphatic alcohols which contain 8 to 1 8 carbon atoms in the alkyl chain, e.g. sulfated lauryl alcohol, oleyl alcohol or coconut fatty alcohol; sulfated unsaturated fatty acids or fatty acid lower alkyl esters which contain 8 to 20 carbon atoms in the fatty radical, e.g. oleic acid or ricinic acid and oils containing such fatty acids, e.g. castor oil; alkylsulfonates containing 8 to 20 carbon atoms in the alkyl chain, e.g. dodecylsulfonate; alkylarylsulfonates with linear or branched alkyl chain containing at least 6 carbon atoms, e.g.

nonyl- or dodecylbenzenesulfonates or 3,7-diisobutylnaphthalenesulfonates; sulfonates of polycarboxylic acid esters, e.g. dioctylsulfosuccinates; the alkali metal, ammonium or amine salts of fatty acids containing 10 to 20 carbon atoms, e.g.

rosin salts, classified as soaps; esters of polyalcohols, especially mono- or diglycerides of fatty acids containing 12 to 1 8 carbon atoms, e.g. monoglycerides of lauric, stearic or oleic acid; and the adducts of 1 to 60 moles of ethylene oxide and/or proplyene oxide with fatty acids, fatty acid amides or fatty alcohols, each containing 8 to 22 carbon atoms, which adducts are converted with an organic dicarboxylic acid, e.g. maleic acid, malonic acid or sulfosuccinic acid, but preferably with an inorganic polybasic acid such as o-phosphoric acid or, in particular, sulfuric acid, into an acid ester.

The anionic surfactants are normally in the form of their alkali metal salts, ammonium salts or amine salts. It is also possible to use mixtures of anionic surfactants alone or in combination with nonionic surfactants.

The addition of the UF condensate employed in the practice of this invention to the pulp suspension of the deinking process results in a substantial increase in the white content or degree of whiteness of the regenerated paper pulp, so that it is not necessary to bleach the pulp. In addition, an improved resistance to yellowing is attained and the strength is not impaired.

The invention is illustrated in more detail by the following Example, in which parts and percentages are by weight unless otherwise stated.

Example 200 g of a mixture groundwood-containing illustrated magazine paper and newsprint, in the weight ratio of 30:70, are soaked at room temperataure in 4 litres of water in a pulper. Then 7.2 g of the adduct of 6 moles of ethylene oxide and 6 moles of propylene oxide with 1 mole of a C12C,4 fatty alcohol and 4 g of the UF condensate (BET surface area 20 m2/g) of German Offenlegungsschrift 2 641 218, product A), are added, whereupon the pulp is stirred for 1 hour at room temperature, while keeping the pH value of the suspension constantly at 9 with sodium hydroxide. The pulp is then transferred to a defibrator and the suspension is diluted with water to a solids content of 10 g/l. The dilute suspension is agitated for 30 minutes and allowed to settle.

The scum which forms on the surface and which contains detached printing ink particles, fillers and mucilages, is skimmed off. The residual fibre suspension is stirred and centrifuged, and then the fibres are collected and compressed to a sheet. The degree of whiteness of the regenerated fibrous matter is determined by means of a Zeiss RFC-3 spectrophotometer fitted with D65/10 illumination.

Degree of whiteness: 51 points according to the method of Tappi with a reflectance at 460 ,um. The degree of whiteness of the fibrous matter obtained without addition of the UF condensate is 49.5 points according to Tappi (reflectance at 460 ,um).

Regenerated paper pulp having a good degree of whiteness is also obtained by using as additive a UF condensate of BET surface area 6,5 m2/g according to German Offenlegungsschrift 2 556 017, product A, instead of the UF condensate (BET surface area 20 m2/g), employed in this Example.

Claims (14)

Claims

1. A process for recovering waste paper by a chemical pulping operation, which process comprises carrying out the pulping operation by using a urea-formaldehyde condensate as additive.

2. A process according to claim 1, wherein the urea-formaldehyde condensate has a specific surface area of 3 to 75 m2/g.

3. A process according to claim 2, wherein the urea-formaldehyde condensate has a specific area of 3 to 30 m2/g.

4. A process according to either of claims 1 or 2, wherein 0.1 to 10% by weight, of the ureaformaldehyde condensate is used, based on the weight of the dry waste paper.

5. A process according to claim 4 wherein 0.5 to 4% by weight of the urea-formaldehyde condensate is used, based on the weight of the dry waste paper.

6. A process according to any one of claims 1 to 5, wherein an anionic or non-ionic surfactant, or a mixture thereof, is used in addition to the urea-formaldehyde condensate.

7. A process according to claim 6, wherein the surfactant is a fatty alcohol polyglycol ether.

8. A process according to claim 7, wherein the surfactant is an adduct of 3 to 10 moles of ethylene oxide and 3 to 10 moles of propylene oxide with an aliphatic monoalcohol containing 8 to 1 6 carbon atoms.

9. A process according to any one of claims 6 to 8, wherein 0.1 to 1 % by weight of the surfactant is used, based on the weight of the dry waste paper.

10. A process according to any one of claims 1 to 9, wherein the pulping operation is carried out in the temperature range from 10 to 600 C.

11. A process according to claim 10, wherein the pulping operation is carried out at room temperature.

12. A process according to any one of claims 1 to 11, wherein the waste paper is soaked in water and treated with an alkaline preparation which contains 0.5 to 4% by weight of a urea-formaldehyde condensate and 0.1 to 1% by weight of a non-ionic or anionic surfactant, based on the weight of the waste paper.

1 3. A process according to any one of claims 1 to 12, wherein the waste products are removed from the fibre suspension by washing out.

14. A process according to any one of claims 1 to 12, wherein the waste products are removed from the fibre suspension by a flotation method.

1 5. A process for recovering waste paper according to claim 1 substantially as described with reference to the Example.

1 6. Waste paper when recovered by a process claimed in any of the preceding claims.