WO2011020982A1

WO2011020982A1 - Recycling of fibre products

Info

Publication number: WO2011020982A1
Application number: PCT/GB2009/050968
Authority: WO
Inventors: Peter Finan
Original assignee: Stephenson Group Limited
Priority date: 2009-08-03
Filing date: 2009-08-03
Publication date: 2011-02-24

Abstract

In a method of recycling printed paper, the collector chemical used to aid ink removal after pulping of the paper, comprises a saponaceous product formed by reaction of a fatty acid and a dialkanolamine, for example diethanolamine. Such a product is suitably liquid at ambient temperatures, and so is convenient for transportation and use. It is highly active.

Description

RECYCLING OF FIBRE PRODUCTS

This invention relates to a method of recycling fibre products, namely printed paper products. The invention relates in particular to a method of recycling fibre products involving subjecting them to a mechanical treatment to separate fibres, removing the ink therefrom (commonly known as "deinking"), and recovering the fibres.

The recycling of paper products is now an important industry. Initially, paper products, particularly for the box and board industry, were recycled without deinking.

A later development was the use of waste paper as a source of fibres for the production of newsprint, but now certain waste paper products can be deinked and used for higher quality papers, for example tissue, and writing papers. A common method of paper recycling is to subject waste paper to a mechanical pulping treatment to break the paper down into fibres in an aqueous medium, and then to use a flotation technique to remove ink. To remove the ink, a chemical, commonly referred to as a collector chemical, is present, and air is introduced at the beginning of the flotation unit. The air, in the presence of the collector chemical, transports ink to the surface of the aqueous medium. At the surface, the ink-rich foam is removed.

The collector chemical is an essential component, in assisting the transport of ink to the surface and trapping the ink in a stable foam at the surface. Thus, the collector chemical must, of course, cause the ink particles to be taken up efficiently and form a sufficiently stable foam, but there are other requirements to be borne in mind. For example, if solid, it should dissolve readily; if liquid, it should be easy to handle; it must be safe; it should be inexpensive to use; it should be easy to transport; and so forth.

The fatty acid soaps of alkali metals, for example sodium or potassium, are widely used as collector chemicals.

To saponify to form a fatty acid soap of an alkali metal just before introduction into the deinking unit requires extra equipment, in the form of a saponification plant at the paper mill, and an extra step. The fatty acids are available in a liquid form, either as hot molten fatty acids or in aqueous emulsion. A disadvantage of the former is in their transportation and disadvantages of the latter are that aqueous emulsions at most contain only 30% active material, and there can be problems of emulsifier build up. So, in both cases there is a penalty in terms of transportation costs.

A very small part of the market for collector chemicals is taken by synthetic detergents, for example ethoxylates, which are not derived from fatty acids. However, such detergents have not been found to be very efficient for the flotation process.

A third approach, which is more common than the approach of using synthetic detergents, but less common than the approach of using fatty acids saponified in situ or just before introduction into the deinking chamber, is to use alkali metal soaps of long-chain fatty acids, transported as soaps to the paper recycling plant. However, such soaps are naturally solid materials and have to be dissolved in situ or before introduction into the deinking chamber. Even though the soaps are available in pelletized form, there can be a problem since dissolution can still be slow. To avoid this problem, the soaps can be supplied in aqueous solution, but only to a maximum 30 wt% of the soap in the solution. So, again there is a penalty in terms of transportation cost.

In accordance with a first aspect of the present invention there is provided a method of removing ink from paper products, comprising providing an aqueous medium which contains paper fibres derived from the paper products, in substantially broken-down form, and which also contains a collector chemical, characterised in that the collector chemical comprises a salt formed by reaction of a fatty acid, and a dialkanolamine.

A dialkanolamine has the general formula:

R¹N(R²OH)₂ where R¹ is a hydrogen atom, or a hydrocarbyl group (preferably a Ci_-6 alkyl group); and each R² is, independently, an interlinking hydrocarbyl group (preferably d-β alkylene). Alkyl and alkylene groups may be branched, but are preferably unbranched. The hydroxyl moiety of the alkanol group is preferably a primary hydroxyl.

Preferably the collector chemical is formed from more than one fatty acid.

In a flotation deinking method, it is convenient, but not essential, that the gas passed through the aqueous medium is air. Hydrophobic particles, formed from the combination of fatty acid(s) with calcium ions present (whether in the water or foam fillers in paper), then float to the surface, collecting hydrophobic ink particles along the way. This process is preferably carried out at 45⁰C, but preferably at least at 4O⁰C.

The use of a salt formed by reaction of the dialkanolamine and a fatty acid may ameliorate many of the problems encountered with prior art methods. Although salts formed by reaction of the dialkanolamine and certain fatty acids may be solid materials at room temperature (and it should be noted that the use of such materials is within the scope of the present invention in its broadest aspect), certain such reaction products are liquids, or else have a melting point sufficiently close to normal ambient temperatures (~ 2O⁰C) that they may be made liquid by addition of appropriate fluidiser components. Shorter-chain or unsaturated fatty acids can be derived as liquids at relatively high concentrations, but saturated Ci₆ and Ci₈ fatty acid soaps are very difficult to make as liquids, except at low concentration (< 5 wt%).

Preferred salts formed by reaction of the dialkanolamine and fatty acid(s) used in the present invention are liquid at normal temperatures of use and transportation, for example in the range 5-25⁰C, or are components of collector chemical concentrates which are liquid within that temperature range (for example being liquefiable by addition of fluidiser component(s)). Such salt reaction products of the dialkanolamine and fatty acid(s) are preferred for use in the method of the present invention because they are readily transportable in high concentration, up to 100% for certain examples which are liquid without the requirement of a fluidiser component, or at least 50%, preferably at least 75%, and most preferably at least 90% by weight of total collector chemical concentrate for other examples. Thus, such collector materials have the advantage of being pre-manufactured saponaceous materials, which do not have to be dissolved to form a liquid composition on site. Preliminary experimental tests have shown that the efficiency of such saponaceous products in the removal of ink from fibre products is high. The collector chemical may be added to the aqueous medium as a concentrate (i.e. the pure salt or mobilised with a fluidiser component), or may be pre-diluted to a ready-to-use solution for better dispersion in the aqueous medium. Pre-dilution is preferably into water, suitably in a ratio of 1 part collector chemical to 3 - 100 parts water, wt/wt, preferably 1 part collector chemical to 5 - 20 parts water.

A fluidiser component, when present, is preferably a compound having one or more hydroxyl groups. Preferably it is a small molecule of MW less than 400, preferably less than 300, preferably less than 200, and most preferably less than 150. Water may be a suitable fluidiser compound. Alternatively a suitable fluidiser compound may be an organic compound, preferably selected from a polyhydric alcohol, a polyoxyalkylene glycol and a glycol ether. Examples of suitable polyhydric alcohols are alkylene glycols, for example C-i-s alkylene glycols, for example ethylene glycol, monopropylene glycol and hexylene glycol, glycerol, polyalkylene glycols, for example polyethylene glycol, and the series of polyhydric alcohols available from Shell under the Trade Mark DOBANOL. An especially preferred polyhydric alcohol fluidiser component is a Ci_-8 alkylene glycol, most preferably monopropylene glycol. Examples of suitable polyoxyalkylene glycols are polyethylene oxide glycol, polypropylene oxide glycol and the copolymers thereof. Examples of suitable glycol ethers are ethylene glycol ethers, propylene glycol ethers, diethylene glycol ethers and dipropylene glycol ethers. Suitable glycol ethers also include dialkyl glycol ethers and esterified glycol ethers. A suitably glycol ether may be defined by the formula

Ci_-6 alkyl-(O-X¹)_n-O-R¹ where X¹ is an ethylene or propylene residue, R¹ is a hydrogen atom or a d-6 alkyl group or a (Ci_-6 alkyl)carbonyl group, and n is the integer 1 or 2. A preferred alkyl group, including the alkyl group of an (alkyl) carbonyl group, is a Ci_-4 alkyl group, for example butyl, (e.g. n-butyl), propyl (e.g. n-propyl, i-propyl), ethyl and methyl. R¹ is preferably a hydrogen atom. Examples of especially preferred examples of glycol ethers are dipropylene glycol monobutyl ether and ethylene glycol monobutyl ether (also called butyl glycol, butyl ethoxol, and 2-butoxyethanol, the latter being especially preferred. When the collector chemical is formulated as a concentrate with such a fluidiser compound, such as a glycol ether, optionally in water, it may be particularly suitable for addition directly to the deinking chamber, preferably into the water process therein, at a high concentration of the collector chemical, for example 20% wt/wt of the concentrate. The dialkanolamine is preferably a diethanolamine, where each R² is ethylene, having the general formula R¹N(CH₂CH₂OH)₂. R¹ is preferably a hydrogen atom or a C-ι-₆ alkyl group. Preferably, the diethanolamine is a secondary amine where R=H. Preferably therefore, the dialkanolamine comprises diethanolamine, preferably substantially solely or in major proportion. For example a commercially available composition comprising 85 wt% of diethanolamine and 15 wt% of a mixture of other amines, may suitably be employed. Preferably, however, the diethanolamine employed is of at least 95 wt% purity, preferably 99 wt%.

The strength of the ionic bond between the cation and anion of the collector chemical is believed to be important. If the bond is too strong, calcium exchange (to furnish the calcium/fatty acid salt) is slow. A weaker bond makes the exchange both kinetically and thermodynamically more favourable. Amine salts give weaker bonds than sodium or potassium salts, and are thus more suitable. The selection of a dialkanolamine, preferably diethanolamine, followed research overturning the teachings of a previous application PCT/GB91 /00434, in which triethanolamine was considered the most favourable collector chemical. Considering the most suitable commercially available amines: morpholine is flammable, has an offensive odour, and as a strong base gives a strong ionic bond with fatty acids; monoethanolamine is undesirable for the same reasons; and triethanolamine forms a three-dimensional complex with calcium ions, with the nitrogen and three oxygen atoms of each triethanolamine moiety now believed to form ligands which prevent carboxylate moieties of fatty acids complexing, thus resulting in poor deinking performance. Therefore, dialkanolamines which do not substantially complex with calcium ions, are selected for their excellent deinking performance. Fatty acid based soaps in accordance with the present invention are therefore particularly suitable where higher calcium levels prevail in the aqueous medium.

Suitable fatty acids may readily be selected, forming soaps with the dialkanolamine which are useful in the method. Typically, such fatty acids may be Ci₂-₂₂ fatty acids, or fatty acids having equivalent properties, for example C₂₄-₄₄ dicarboxy fatty acids, effectively dimers of C₁₂-₂₂ monocarboxy fatty acids.

Those skilled in the art will be aware of the very wide range of fatty acids which would lend themselves to use in the method of the present invention. Preferably, though not essentially, a fatty acid is selected, which provides a salt reaction product with the dialkanolamine selected which is liquid at normal temperatures of use, or which can be made liquid by addition of an appropriate fluidiser component, as referred to more fully above. Preferably, a collector chemical formed from more than one fatty acid is also a liquid at normal temperatures. Examples of suitable fatty acids may include saturated fatty acids, mono-unsaturated fatty acids, di-unsaturated fatty acids and tri-unsaturated fatty acids, fatty acids with hydroxy groups in the molecule, and cyclic fatty acids. It will be appreciated by those skilled in the art that the commercially available fatty acids of this type will typically comprise a mixture of different fatty acids most of which are within the definition C₁₂-₂₂ fatty acid. Examples of individual fatty acids of this type include lauric acid, myristic acid, palmitic acid, stearic acid, palmitoleic acid, oleic acid, linoleic acid, ricinoleic acid, linolenic acid, arachidic acid and erucic acid. Preferably, the fatty acid is a blend of fatty acids from C₁₂ to C₂₂ which when used in the method causes a dense foam capable of holding hydrophobic ink particles.

Generally, a blend of i) Ci₂-i₄-saturated, ii) Ci_6-i₈-saturated, and/or iii) C₁₈-₂₂- unsaturated fatty acids gives better performance than a single fatty acid. Preferably, therefore, there is present a compound of i) or ii), and iii). Most preferably, there is present a blend of all of i), ii) and iii).

It is believed that iii), the C₁₈-₂₂ -unsaturated fatty acids (eg. C18:1 - oleic, C18:2 - linoleic, C18:3 - α-linolenic acid) combine first with calcium ions, and have an anti- foaming effect in the aqueous medium. The Ci_2-i₄-saturated (i)) fatty acids (e.g. C12:0

- lauric, C14:0 - myristic) are thought to produce foam, thus producing an overall dynamic system where foam is created on one hand, as is necessary for deinking, and dampened on the other, to prevent the foam from being too loose and incapable of holding hydrophobic ink particles. Therefore, the present invention provides foams of an appropriate density and texture for optimal deinking. The Ci_6-i₈-saturated (ii)) fatty acids (e.g. C16:0 - palmitic, C18:0 - stearic) are thought to be involved in the bulk of the ink collection work, by calcium complexation, followed by ink particle capture (micelles), and flotation to the surface to reside in the dense foam. The dense foam can then be simply skimmed off mechanically to give a highly effective deinking process leaving bright pulp.

Preferably C₁₂-₁₄ saturated fatty acids comprise at least 15 wt% of the total fatty acid content, more preferably at least 20 wt%, and most preferably at least 24 wt%. Preferably the C₁₂-₁₄ saturated fatty acids comprise at most 35 wt% of the total fatty acid content, more preferably at most 30 wt%, and most preferably at most 26 wt%.

Preferably Ci_6-i8 saturated fatty acids comprise at least 12 wt% of the total fatty acid content, more preferably at least 17 wt%, and most preferably at least 21 wt%. Preferably the Ci_6-i8 saturated fatty acids comprise at most 32 wt% of the total fatty acid content, more preferably at most 27 wt%, and most preferably at most 23 wt%. Despite the difficulty in obtaining salts of these fatty acids in liquid form, and the consequential difficulty in obtaining salts of a blend of fatty acids comprising such C₁6- ₁8 saturated fatty acids in liquid form, the present invention provides a liquid collector chemical comprising such C₁6-₁8 saturated fatty acids.

Preferably C₁8-₂₂ unsaturated fatty acids comprise at least 40 wt% of the total fatty acid content, more preferably at least 45 wt%, and most preferably at least 51 wt%. Preferably the C₁8-₂₂ unsaturated fatty acids comprise at most 63 wt% of the total fatty acid content, more preferably at most 57 wt%, and most preferably at most 53 Wt%.

There may be traces of C_8-io fatty acids, possibly greater than 0.2 wt% of the total fatty acid content, but preferably less than 5 wt% of the total fatty acid content, more preferably less than 2 wt%, and most preferably less than 1 wt%.

Preferably the relative proportions of the C12-14 saturated and C18-22 unsaturated fatty acids are adjusted to ensure the predominant collector chemical, comprising C₁6- ₁8 saturated fatty acid salts, is a liquid at normal temperatures, preferably at 5 to 25⁰C. The preferred commercially available fatty acids are characterised by a high degree of unsaturation. Preferably fatty acids which are unsaturated - having at least one multiple unsaturated bond - provide at least 20 wt% of the total fatty acid content, preferably at least 35 wt%, and most preferably at least 45 wt%. Preferably such unsaturated fatty acids comprise at most 70 wt% of the total fatty acid content, more preferably at most 60 wt%, and most preferably at most 55 wt%. Preferably at least 70 wt% of the total unsaturated fatty acid content is mono-unsaturated fatty acids, more preferably at least 80 wt%, most preferably at least 85 wt%. To this end, it is preferably to obtain the C₁8-₂₂ unsaturated fatty acids from Palm Fatty Acid Distillate.

Preferably the collector chemical comprises, as a proportion of the total fatty acid content, the following fatty acids:

C₁₂ (saturated) - 10-25 wt%

C_M (saturated) - 2-13 wt%

C₁6 (saturated) - 10-35 wt%

C18 (saturated) - 0.1-10 wt%

C₁8 (mono-unsaturated) - 20-65 wt%

C₁8 (multiply-unsaturated) - 1-15 wt% where the amounts preferably total 95 wt%, more preferably 97 wt%, and most preferably 99 wt%. The remainder may be traces of other fatty acids such as C₈, C₁0, and possibly also Ci₇.

In relation to the relative proportions of the dialkanolamine, the fatty acid and the fluidiser component, when present, the dialkanolamine and the fatty acids are desirably present in approximately stoichiometric proportion, but preferably at least a 0.95:1 molar ratio of dialkanolamine/carboxylate of fatty acids, most preferably at least 1 :1. The fluidiser component, when present as part of a collector chemical concentrate, is desirably present in small quantity relative to the other two components. For example the fluidiser component may be present as 0-30% by weight based on the total weight of the collector chemical concentrate.

The collector chemical is preferably substantially transparent as a concentrate, or when further diluted with a fluidiser component, which may include a glycol ether, and / or water, for instance, to make a ready-to-use solution. The collector chemical is therefore preferably a homogenous single-phase liquid. A concentrate may suitably contain at least 20% wt/wt of collector chemical, preferably at least 30% wt/wt, preferably at least 40% wt/wt, preferably at least 50% wt/wt, preferably at least 60% wt/wt. It may suitably contain up to 90% wt/wt of collector chemical.

The preparation of a saponaceous reaction product which is liquid at normal ambient temperatures (~ 2O⁰C), which is a preferred composition for use in the method of the present invention, may simply be prepared, in many cases, by mixing the dialkanolamine and the fatty acid, suitably at ambient temperature, and adding, at any convenient stage, a fluidiser component, if required. Alternatively the dialkanolamine may be added to a pre-formed mixture of the fatty acid(s) and the fluidiser component. The conditions may be selected by the skilled person, using trial and error and analysis of the reaction products if necessary, to provide that a salt is the primary product formed, rather than an ester (from a tertiary amine) or an amide or ester (from a primary or secondary amine). It should be noted that in accordance with the present invention, a salt should be the major product, if it is not the only product. Thus, minor quantities of covalent reaction products can be tolerated. An indication that the salt formation has proceeded to completion is that the resulting liquid is substantially transparent, and remains transparent when diluted with water to form a ready-to-use solution. Cloudiness in either is an indication of incomplete salt formation. The Applicants have found that the salt formation does not proceed to completion if performed in a diluted medium, such as would be hypothetically used to directly form a ready-to-use solution. Instead the salt formation must be carried out in a concentrated form to directly form the collector chemical, either using pure ingredients, or ingredients slightly diluted with the fluidiser component. Infra Red spectroscopy or titration for free alkanolamine may also be used to monitor for complete salt formation. Dilution to give a ready-to-use solution may then ensue.

The method in accordance with the invention may for example be a flotation deinking method, or a wash deinking method, or a dual method. The method may be of particular benefit in relation to flotation deinking.

The present invention provides a liquid source of pre-ionised fatty acids with a very high fatty acid content that is soluble in water to facilitate rapid calcium exchange for efficient deinking. Emulsions of fatty acids, non-saponified, and non-pre-ionised fatty acids are all inferior in the deinking method according to the present invention. Therefore the collector chemical is preferably a homogenous single-phase liquid and not an emulsion.

In accordance with a second aspect of the present invention there is provided any novel collector chemical or collector chemical concentrate which is herein described or defined.

In accordance with a third aspect of the present invention there is provided a method of recycling printed paper products, comprising: subjecting the paper products to a mechanical treatment (pulping) in an aqueous medium until substantially broken down into fibres; adding to the medium, before, during or after the mechanical treatment, a collector chemical; passing a gas through the aqueous medium containing the fibres and the collector chemical and removing the ink-rich foam on the surface and/or removing ink by successive cycles of draining and rinsing; and recovering the cleansed paper pulp; characterised in that the collector chemical is the reaction product of a dialkanolamine as defined above and a fatty acid as defined above.

Preferably, the collector chemical is present, in use in the process, in an amount from about 0.01 to about 2 wt%, for example from about 0.05 wt% to about 2 wt%, preferably from about 0.1 to about 1 wt%, most preferably from about 0.15 wt% to about 0.5 wt%, based on weight of dry waste paper. The collector chemical can be added to the aqueous medium before, during, or after the completion of the mechanical treatment. Preferably it is added after the completion of the mechanical treatment, at the deinking stage, most preferably shortly before or substantially at the commencement of ink removal. The collector chemical may be added as a diluted ready-to-use solution, preferably an aqueous solution.

In accordance with a fourth aspect of the present invention there is provided a method of preparing a ready-to-use solution, comprising mixing the collector chemical or collector chemical concentrate of the second aspect with water (and / or another fluidiser component). Preferably the water comprises at least 30 wt% of the final mixture, preferably at least 50 wt%, more preferably at least 65 wt%. Preferably the water is at a temperature of at least 4O⁰C before mixing, preferably at least 5O⁰C, most preferably at least 65⁰C. According to a sixth aspect of the present invention there is provided a ready-to- use solution comprising the product of the method of the fifth aspect.

It may be desirable to employ products such as sodium hydroxide, sodium silicate and hydrogen peroxide in the pulping and/or deinking steps, as is standard.

Preferred features of any aspect are also preferred features of any other aspect.

The invention will now be further described, by way of example.

Example 1

A saponaceous material which is liquid at ambient temperature was prepared from a blend of the following fatty acids:

Ci₂ (saturated) - 15-22 wt%

C_M (saturated) - 5-10 wt%

Ci6 (saturated) - 16-24 wt%

da (saturated) - 1-5 wt%

Ci8 (mono-unsaturated) - 40-50 wt%

Ci8 (multiply-unsaturated) - 5-10 wt% where the amounts are given as a weight percentage of the total fatty acid content. Traces of C₈, Ci₀ and Ci₇ saturated fatty acids were also present, and comprised 1 wt% of the total fatty acid content.

The fatty acid blend was obtained by blending: a mixture of palm fatty acid distillate, other C₁₂-₁8 distillates,

and oleic acid - 55 wt %

diethanolamine - 22.5 wt%

monopropylene glycol - 22.5 wt%

The amount of diethanolamine was calculated to achieve approximately a 1 :1 molar ratio of diethanolamine/carboxylate of fatty acids. This was done by calculating the average moles of carboxylate based on an average molecular weight of the range of fatty acids. Where insufficient diethanolamine is used, the resulting collector chemical remains cloudy, especially when diluted with water.

The fatty acids were first mixed with monopropylene glycol to form a fatty acid mixture. Diethanolamine was then added to the fatty acid mixture to form a substantially transparent liquid, characterised as a collector chemical concentrate containing the collector chemical as a fatty acids-diethanolamine salt composition. The formation of the amine salt was confirmed by infra-red spectroscopy, and by titration of free alkanolamine.

A ready-to-use soap solution was formed by diluting the collector chemical concentrate as follows:

Collector chemical (concentrate) - 38 wt%

- Hot deionised water - 62 wt%

The collector chemical concentrate was added to deionised water heated at 7O⁰C, and the soap solution was left to cool to room temperature (~ 2O⁰C). This solution had excellent fluidity at lower temperatures and excellent stability.

Deinking tests took place in a standard laboratory flotation cell. The waste paper previously pulped to mechanically break down the paper substantially into fibres was added to the flotation cell in standard dilution in water. After briefly agitating the pulp mixture, a first pulp sample was taken. The liquid soap was added in one batch as the ready-to-use solution at the rate of 0.4 wt% (0.15 wt% of collector chemical concentrate) based on the weight of the dry paper.

The flotation cell was started and allowed to run for 2 minutes at 45⁰C with an air flow of 2 litres/minute, before skimming off the first surface foam. After a further 2 minutes a second pulp sample was taken. Both the first and second pulp samples were drained through a mesh to make a circular sheet of paper, which was then air dried.

The efficiency of the process was assessed by measuring the brightness of the first pulp sample, which was 55.0 UV+ and the brightness of the second pulp sample leaving the flotation cell after deinking which was 60.0 UV+. The brightness was measured as a UV measurement on a standard spectophotometer. The result was highly satisfactory given the short deinking times.

Example 2

A further blend may be obtained by using solvents for the purpose of fluidising and dispersing, such as water and butyl ethoxol, an example of which is: a mixture of palm fatty acid distillate, other C12-18 distillates,

and oleic acid - 37.31 wt %

diethanolamine - 15.19 wt %

monopropylene glycol - 13.50 wt %

butyl ethoxol - 19.00 wt %

water - 15.00 wt %

In tests corresponding to those described in Example 1 this concentrate, when used at a concentration of 0.15% wt in the flotation cell, delivered from a pre-diluted solution of 1 %wt of the concentrate, gave an brightness gain on 12.3; and a brightness gain of 10.8 when used at a concentration of 0.15% wt in the flotation cell, delivered into the cell as such, i.e. without pre-dilution.

It will be appreciated that the terms "paper" and "paper products" have been widely used in this specification as shorthand terms for cellulose fibre mats wet laid by a non-woven process and is intended to include materials such as tissue, card and the like.

It is conventional in the art to state that the mechanical treatment of waste paper breaks the paper down in "fibres". That conventional terminology has been used In this specification it will be appreciated that such "fibres" of broken-down paper may themselves comprise smaller fibrils, and that the method of the invention does not require that the waste paper be broken down into discrete, individual cellulose strands. The terms "ink, "print" and "deinking" etc. are used herein in a broad sense to denote marking on paper, however produced, including by, for example, photocopying where it might otherwise strictly be said that the marking applied is not "ink" nor is applied by conventional "printing".

Claims

1. A method of removing ink from paper products, comprising providing an aqueous medium which contains paper fibres derived from the paper products, in substantially broken-down form, and which also contains a collector chemical, characterised in that the collector chemical comprises a salt formed by reaction of a fatty acid, and a dialkanolamine of the general formula:

R¹N(R²OH)₂ where R¹ is a hydrogen atom, or a hydrocarbyl group; and each R² is, independently, an interlinking hydrocarbyl group.

2. The method as claimed in claim 1 , wherein the dialkanolamine is a diethanolamine of a general formula R¹N(CH₂CH₂OH)₂ wherein R¹ represents a hydrogen atom or a

Ci-6 alkyl group.

3. The method as claimed in claim 2, wherein the diethanolamine is diethanolamine, where R¹ is a hydrogen atom.

4. The method as claimed in any preceding claim, wherein the collector chemical comprises more than one fatty acid.

5. The method as claimed in claim 4, wherein the fatty acids comprise Ci_2-22 fatty acids, or C_24-44 dicarboxy fatty acids.

6. The method as claimed in any preceding claim, wherein the collector chemical is supplied in liquid form, being itself a liquid or a component of a liquid collector chemical concentrate at temperatures in the range about 5-25°C, the concentration of the collector chemical in the liquid being in the range about 50-100 wt%.

7. The method as claimed in claim 6, wherein said chemical collector is a component of a liquid collector chemical concentrate which also comprises a fluidiser component which acts to help keep the collector chemical concentrate in liquid form at ambient temperatures.

8. The method as claimed in claim 7, wherein the fluidiser component selected is a polyhydric alcohol or a polyoxyalkylene glycol, a glycol ether or water.

9. The method as claimed in claim 8, wherein the fluidiser component is a glycol ether may be defined by the formula

Ci_-6 alkyl-(O-X¹)_n-O-R¹ where X¹ is an ethylene or propylene residue, R¹ is a Ci_-6 alkyl group or a (Ci_-6 alkyl)carbonyl group or preferably a hydrogen atom and n is the integer 1 or 2.

10. A method as claimed in any preceding claim wherein the collector chemical is provided as a concentrate containing at least 20% wt/wt of the collector chemical; which concentrate is added directly to the deinking unit or is diluted into water prior to addition to the deinking unit.

1 1. A collector chemical, or a collector chemical concentrate containing a collector chemical; the collector chemical being as defined in any preceding claim.

12. A method of recycling printed paper products, comprising: subjecting the paper products to a mechanical treatment (pulping) in an aqueous medium until substantially broken down into fibres; adding to the medium, before, during or after the mechanical treatment, a collector chemical; passing a gas through the aqueous medium containing the fibres and the collector chemical and removing the ink-rich foam on the surface in that the collector chemical is the reaction product of a dialkanolamine, according to any preceding claim, and a fatty acid, according to any preceding claim.

13. A method of preparing a ready-to-use solution, comprising mixing the collector chemical or collector chemical concentrate of any preceding claim with water.

14. A ready-to-use solution, comprising the product of the method of claim 13.

15. A method of removing ink from paper products, a collector chemical or collector chemical concentrate comprising a collector chemical, a method of recycling printed paper products, a method of preparing a ready-to-use solution, and a ready-to-use solution as substantially hereinbefore described with reference to the Examples.