WO2025074037A1

WO2025074037A1 - Flotation method for separating fibres, and use of surfactant composition in processing recycled textile fibres

Info

Publication number: WO2025074037A1
Application number: PCT/FI2024/050522
Authority: WO
Inventors: Jean-Francois D'allest; Tea HANNUKSELA
Original assignee: Kemira Oyj
Current assignee: Kemira Oyj
Priority date: 2023-10-05
Filing date: 2024-10-04
Publication date: 2025-04-10
Anticipated expiration: 2026-04-05

Abstract

Method for separating synthetic, non-cellulose fibres from cellulose fibres in processing recycled textile fibres, the method comprises adding at least one surfactant to the aqueous textile fibres suspension and subjecting the aqueous textile fibres suspension to flotation to remove the synthetic, non-cellulose fibres. The surfactant comprises at least a main surfactant comprising a synthetic non-ionic surfactant selected from a group consisting of ethoxylated or ethoxylated and propoxylated fatty alcohols or fatty acids having chain length of C14 – C24, and any mixtures thereof.

Description

FLOTATION METHOD FOR SEPARATING FIBRES, AND USE OF SURFACTANT

COMPOSITION IN PROCESSING RECYCLED TEXTILE FIBRES

Field of the invention

5

The present invention relates to a method for separating synthetic, noncellulose fibres from cellulose fibres in processing recycled textile fibres. The invention also relates to a surfactant composition for use in flotation in a process of recycling textile fibres.

10

Background of the invention

Recycled textile waste comprises both synthetic, non-cellulose fibres and cellulose fibres. A fibre material obtained from recycled textile, which

15 contains the synthetic, non-cellulose fibres is not as valuable in a view of the reuse as a fibre material having low content of the synthetic, non-cellulose fibres. Therefore, in the processing of recycled textile waste the synthetic, non-cellulose fibres are removed from a textile fibres suspension. Typically, flotation is used to process diluted aqueous suspensions of fibres issued

20 from recycled textile waste to separate the synthetic, non-cellulosic fibres from the cellulosic fibres. Methods for separating synthetic, non-cellulose fibres from cellulose fibres are presented e.g. in the patent publications WO 2020/127453, WO 2013/182801 and WO 2019/138101. During the flotation stage, the more hydrophobic and lighter synthetic fibres are captured and

25 entrained by the air bubbles to the top of a flotation cell, from where they are removed from the liquid pulp with the foam rejects.

Fibres suspension in water issued from recycled textile is a low foaming material and therefore, one technical problem is to raise enough foam in the

30 flotation stage to remove the synthetic, non-cellulose fibres efficiently. Another challenge is to achieve the removal of synthetic, non-cellulose fibres with a selectivity as high as possible, i.e. a maximum removal of synthetic, non-cellulose fibres with a minimum loss of cellulosic fibres. Thus, there exists a need for efficient chemicals to use in separation by flotation of

35 synthetic, non-cellulose fibres from cellulose fibres in processing recycled textile fibres. Summary of the invention

It is an object of the present invention to reduce or even eliminate the above- mentioned problems appearing in prior art.

It is an object of the present invention to provide an improved method for separating by flotation cellulose fibres from non-cellulose fibres in processing recycled textile fibres with a high selectivity. Further, an object of the present invention is to provide a surfactant or a combination of the surfactants to help raising enough foam in the flotation stage and to provide an improved flotation selectivity in a separation of synthetic, non-cellulose fibres from cellulose fibres by flotation, with minimum loss of cellulose fibres.

In order to achieve among others the objects presented above, the invention is characterized by what is presented in the characterizing parts of the enclosed independent claims.

Some preferred embodiments of the invention will be described in the other claims.

The embodiments and advantages mentioned in this text relate, where applicable, both to the product, the method as well as to the uses according to the invention, even though it is not always specifically mentioned.

Typical method according to the present invention for separating synthetic, non-cellulose fibres from cellulose fibres in processing recycled textile fibres, comprising

- preparing an aqueous textile fibres suspension comprising cellulose fibres and synthetic, non-cellulose fibres,

- adding at least one surfactant to the aqueous textile fibres suspension, and

- subjecting the aqueous textile fibres suspension to flotation to remove the synthetic, non-cellulose fibres, and in which method the surfactant comprises at least a main surfactant comprising a synthetic non-ionic surfactant selected from a group consisting of ethoxylated or ethoxylated and propoxylated fatty alcohols or fatty acids having chain length of C14 - C24, and any mixtures thereof. The invention also relates use of a surfactant composition comprising at least a main surfactant comprising a synthetic non-ionic surfactant selected from a group consisting of ethoxylated or ethoxylated and propoxylated fatty alcohols or fatty acids having a chain length of C14 - C24, and any mixtures thereof, in flotation in processing recycled textile fibres, in which synthetic, non-cellulose fibres are separated from cellulose fibres.

Now, it has been found that the specific main surfactant or a combination of the specific main surfactant with certain co-surfactants is efficient for improving flotation selectivity in a separation of the synthetic, non-cellulose fibres from cellulose fibres in flotation when processing recycled textile fibres. It has been observed that a main surfactant comprising non-ionic ethoxylated or ethoxylated and propoxylated fatty alcohols or fatty acids and having high molecular weight is especially efficient for improving flotation selectivity with a minimum loss of cellulosic fibres.

Further, it has been observed that the specified main surfactant in combination with a non-ionic or anionic co-surfactant(s) further increases or controls the amount of the foam to be formed in the flotation stage. Fibres suspension in water issued from recycled textile is a low foaming material and by a method according to the present invention the foaming of the aqueous textile fibres suspension can be increased for providing efficient separation of the synthetic, non-cellulose fibres from cellulose fibres. During the flotation stage, the more hydrophobic and lighter synthetic, non-cellulose fibres are captured and entrained by the air bubbles, and then they can be removed on the top of a flotation cell.

Detailed description of the invention

In the present invention, a surfactant comprising a hydrophilic part and hydrophobic part is used when separating by flotation synthetic, non- cellulose fibres from cellulose fibres. A surfactant according to the present invention comprises at least a main surfactant comprising a synthetic non- ionic surfactant selected from a group consisting of ethoxylated fatty alcohols or fatty acids having a chain length of C14 - C24, or ethoxylated and propoxylated fatty alcohols or fatty acids having a chain length of C14 - C24, or any mixtures thereof. According to an embodiment of the present invention, a main surfactant may comprise ethoxylated fatty alcohol(s) or fatty acid(s) having a chain length of C14 - C24. In another embodiment of the present invention, a main surfactant may comprise ethoxylated and propoxylated fatty alcohol(s) or fatty acid(s) having a chain length of C14 - C24. According to an embodiment of the present invention the ethoxylated or the ethoxylated and propoxylated fatty alcohols or fatty acids has preferably a chain length of C16 - C20. The long chain length of the hydrocarbon chain improves the collection of the hydrophobic synthetic, non-cellulose fibres onto the air bubbles in flotation. Further, the combination of ethoxylation and propoxylation of the fatty alcohol or fatty acid is effective to balance foam control and collection efficiency.

Hydrocarbon chain of the ethoxylated or the ethoxylated and propoxylated fatty alcohols or fatty acids can be linear or branched. Further, the hydrocarbon chain of the fatty alcohols or fatty acids may be saturated or unsaturated. In one preferred embodiment a main surfactant comprises ethoxylated or ethoxylated and propoxylated fatty alcohol(s) or fatty acid(s) having a linear and saturated hydrocarbon chain with a chain length of C14 - C24, preferably a chain length of C16 - C20, more preferably a main surfactant comprises ethoxylated and propoxylated fatty alcohol(s) or fatty acid(s) having a linear and saturated hydrocarbon chain with a chain length of C14 - C24 or C16 - C20.

According to the present invention, the main surfactant has a high degree of ethoxylation, or a high degree of ethoxylation and propoxylation. The high degree of the ethoxylation and propoxylation improves main surfactant selectivity to collect synthetic, non-cellulose fibres. According to the present invention, ethoxylated or ethoxylated and propoxylated fatty alcohols or fatty acids contain ethylene oxide (EO) moieties. In an embodiment of the present invention a degree of ethoxylation of the ethoxylated or the ethoxylated and propoxylated fatty alcohols or fatty acids may be in the range of 5 to 100 ethylene oxide (EO) moieties, preferably 10 to 40 EO moieties. According to the present invention, ethoxylated and propoxylated fatty alcohols or fatty acids contain propylene oxide (PO) moieties. In an embodiment of the present invention a degree of propoxylation of the ethoxylated and propoxylated fatty alcohols or fatty acids may be in the range of 1 to 40 propylene oxide (PO) moieties, preferably 5 to 20 PO moieties. The distribution of the EO and PO moieties in the ethoxylated and propoxylated fatty alcohols or fatty acids can be statistical (random) or in blocks. In an embodiment of the present invention, the blocks structure of the hydrophilic moiety is preferred, since it has been observed to better balance foam control and collection selectivity in the foaming. The ethoxylated and propoxylated part of the non-ionic surfactant can be terminated or not with a PO moiety. In an embodiment of the present invention, the termination with a PO group is preferred, which also has been observed to better balance foam control and collection selectivity in the foaming. In one preferred embodiment of the present invention, the ethoxylated and propoxylated hydrophilic moiety of the fatty alcohols or fatty acids has a blocks structure, and is terminated with a PO group.

According to the present invention, the main surfactant has a cloud point temperature which can be any temperature in between 20°C and 100°C. In a preferred embodiment of the present invention, the main surfactant has a cloud point temperature, which differs from the flotation temperature of the textile fibres suspension in maximum of 0°C to -10°C, preferably in maximum of 0°C to -5°C. In an embodiment of the present invention, the cloud point temperature of the main surfactant is substantially equal to the flotation temperature of the fibre suspension. According to one embodiment of the present invention, the cloud point temperature of the main surfactant in slightly below the flotation temperature of the textile fibres suspension improves the efficacy and flotation selectivity of the main surfactant. In an embodiment of the present invention, the cloud point temperature of the main surfactant may be maximum of 10°C, preferably maximum of 5°C lower than the flotation temperature of the textile fibres suspension in a flotation stage. In an exemplary embodiment, flotation temperature in processing recycled textile fibres may be in the range of 50 - 70°C, preferably 55 - 65°C, and hence the cloud point temperature of the main surfactant may be in the range of 40 - 70°C or 45 - 70°C, and preferably 45 - 65°C or 50 - 65°C. The cloud point temperature of the non-ionic surfactant is the temperature above which the surfactant is not water soluble anymore and precipitates as microparticles dispersed in the water phase. According to an embodiment of the present invention, a main surfactant is added to a textile fibres suspension in an amount of 0.05 to 10 kg/t (ton) of textile fibres. In a preferred embodiment of the present invention, a main surfactant is added to the textile fibres suspension in an amount of 0.1 to 3 kg/t (ton) of textile fibres.

Textile fibres suspension, which are naturally a very poorly foaming material, may require the addition of the co-surfactant in combination with the main surfactant into the textile fibres suspension for increasing the amount of the foam. According to an embodiment of the present invention, a main surfactant is used in combination with at least one co-surfactant to control the amount of the foam and increase the removal of the synthetic, non-cellulose fibres at the same time. In an embodiment of the present invention the co- surfactant comprises non-ionic and/or anionic surfactant. Hence, a method according to the present invention further comprises adding at least one co- surfactant comprising non-ionic and/or anionic surfactant. In an embodiment of the present invention, a co-surfactant may comprise non-ionic biobased surfactant. The co-surfactant is added first to increase and control the amount of the foam in the flotation stage. In an embodiment of the present invention, a co-surfactant has a hydrophilic-lipophilic balance (HLB) > 7.

A non-ionic co-surfactant according to an embodiment the present invention comprises non-ionic synthetic surfactant selected from a group consisting of ethoxylated fatty alcohols or fatty acids having a chain length of C4 - C18, and any mixtures thereof, preferably ethoxylated fatty alcohols or fatty acids having a chain length of C8 - C14, and any mixtures thereof. Hydrocarbon chain of the ethoxylated fatty alcohols or fatty acids can be linear or branched. Further, the hydrocarbon chain may be saturated or unsaturated. In one preferred embodiment a non-ionic co-surfactant comprises the ethoxylated fatty alcohol(s) or fatty acid(s) having a linear and saturated hydrocarbon chain with a chain length of C4 - C18, preferably a chain length of C8 - C14. According to the present invention, the non-ionic co-surfactant comprising ethoxylated fatty alcohol(s) or fatty acid(s) has a degree of ethoxylation in the range of 3 to 100 ethylene oxide (EO) moieties, preferably 5 to 20 EO moieties. According to the present invention, the co-surfactant has a cloud point temperature which can be any temperature in between 20°C and 100°C. In a preferred embodiment of the present invention, the non-ionic co-surfactant comprising ethoxylated fatty alcohol(s) or fatty acid(s) has a cloud point temperature, which differs from a flotation temperature of the textile fibres suspension in maximum of 0°C to -15°C, preferably in maximum of 0°C to -10°C for improving the efficacy of the co-surfactant.

According to an embodiment of the present invention, an anionic cosurfactant can be any anionic surfactant known in the art. Anionic cosurfactant according to an embodiment of the present invention comprises anionic synthetic surfactant. Anionic co-surfactants contain anionic functional groups at their head, such as sulphate, sulphonate, phosphate and carboxylate. Anionic co-surfactants can be soaps. Anionic co-surfactants may also incorporate ethylene oxide groups. Anionic co-surfactant may comprise one anionic surfactant or it may be a combination of two or more anionic surfactants. In an exemplary embodiment according to the present invention, an anionic co-surfactant comprises sodium dodecyl sulphate (SDS). Anionic co-surfactants are commonly cheap chemicals and very foaming at low dosages, wherein they are preferably used in flotation.

According to an embodiment of the present invention, the method comprises adding a co-surfactant comprising non-ionic biobased surfactant. The hydrophilic part of the biobased surfactant can be different kind of sugar heads. In an exemplary embodiment of the present invention, non-ionic biobased co-surfactant is selected from a group consisting of alkyl poly glycosides (APG), alkyl poly pentosides (APP) and any mixtures thereof. The biobased co-surfactant can be used alone in combination with the main surfactant, or the surfactant used in the present invention may comprise main surfactant and non-ionic biobased co-surfactant and synthetic non-ionic and/or anionic co-surfactant. Biobased surfactants are from renewable resources, and they are more biodegradable and less toxic than synthetic ethoxylated fatty alcohol-based surfactants. Biobased surfactants are more sustainable than standard synthetic non-ionic surfactants.

According to an embodiment of the present invention, a co-surfactant is added to a textile fibres suspension in an amount of 0.01 to 5 kg/t (ton) of textile fibres. In a preferred embodiment of the present invention, a co- surfactant is added to the textile fibres suspension in an amount of 0.05 to 2 kg/t (ton) of textile fibres. In one preferred embodiment according to the present invention, a main surfactant is used in combination with non-ionic synthetic co-surfactant, wherein

- the main surfactant comprises ethoxylated or ethoxylated and propoxylated fatty alcohol(s) or fatty acid(s) having a linear and saturated hydrocarbon chain with a chain length of C14 - C24, preferably a chain length of C16 - C20, more preferably a main surfactant comprises ethoxylated and propoxylated fatty alcohol(s) or fatty acid(s) having a linear and saturated hydrocarbon chain with a chain length of C14 - C24 or C16 - C20, and

- non-ionic synthetic co-surfactant comprises the ethoxylated fatty alcohol(s) or fatty acid(s) having a linear and saturated hydrocarbon chain with a chain length of C4 - C18, preferably a chain length of C8 - C14.

A method for separating by flotation synthetic, non-cellulose fibres from cellulose fibres in processing recycled textile fibres, comprising

- adding at least one surfactant to the aqueous textile fibres suspension, and

- subjecting the aqueous textile fibres suspension to flotation to remove the synthetic, non-cellulose fibres.

In the method according to the present invention, at least a main surfactant is added to the textile fibres suspension prior to a flotation stage. In an embodiment according to the present invention a method further comprises adding a co-surfactant, which may comprise non-ionic and/or anionic surfactant and/or non-ionic biobased surfactant as described above. The cosurfactants are commonly added to the textile fibres suspension prior to a flotation stage. The main surfactant and co-surfactant(s) can be added in a form of pre-mixture or they may be added separately to the textile fibres suspension. In a preferred embodiment of the present invention, the main surfactant and the co-surfactant(s) are added separately to control the dosage of each surfactant individually. Textile fibres suspension issued from recycled textile comprises cellulose fibres and synthetic, non-cellulose fibres. Cellulose fibres include all fibres originating from natural sources, such as e.g. cotton, linen, jute, wool, wood, etc. and all modified cellulose forms. In one embodiment, the non-cellulose fibres are synthetic fibres comprising man-made polymers. Examples of synthetic fibres comprising man-made polymers include but are not limited to fibres based on nylon, fibres based on polyester, fibres based on acrylic, fibres based on modacrylic, fibres based on polyurethane, and fibres based on polyolefin. In an embodiment, the non-cellulose fibres comprise polyester. In an embodiment, the non-cellulose fibres comprise elastane. In one embodiment, the non-cellulose fibres comprise polyacrylonitrile. Cellulose fibres are commonly mixed with smaller amounts of synthetic, non-cellulose fibres in commercially available textiles. Textile fibres suspension may also comprise other non-cellulose fibres that are desired to remove. In a typical embodiment according to the present invention, the textile fibres suspension comprises a high fraction of cellulose fibres with smaller quantities of non- cellulose fibres. In a typical embodiment of the present invention, the maximum length of the textile fibres in the textile fibres suspension is a few millimetres. In an exemplary embodiment of the present invention a maximum length of the fibres in the textile fibres suspension is in the range of 1 - 5 mm or 2 - 5 mm. In an embodiment according to the present invention, the textile fibres suspension has a concentration of synthetic, non-cellulose fibres in the range of 0.1 % to 20%, calculated by the weight of the total fibres fraction.

The concentration of the textile fibres in the aqueous textile fibres suspension in the feed of the flotation cell is typically in the range of 0.1 - 2 weight-%, preferably 0.2 - 1 weight-%, calculated by the weight of the total textile fibres suspension.

The preparing of the textile fibres suspension and the flotation can be performed with the known methods and equipment in the art. EXPERIMENTAL

Chemicals used in the Examples:

- Surfactant A: ethoxylated and propoxylated fatty alcohol. Linear saturated C16-20, 21 EO, 9PO, block structure of the hydrophilic moiety. PO terminated. Cloud point 58°C.

- Surfactant B: ethoxylated and propoxylated fatty alcohol. Linear saturated C18, 17EO 14PO, block structure of the hydrophilic moiety. PO terminated. Cloud point 39°C.

- Surfactant C: ethoxylated fatty alcohol, linear saturated C12-14, 7EO. Cloud point 55°C.

- Surfactant D: anionic surfactant (soap), tall oil fatty acid (mainly oleic and linoleic fatty acids) partially saponified (35%) with potassium hydroxide.

- Surfactant E: anionic surfactant, sodium dodecyl sulphate (SDS).

- Surfactant F: biobased surfactant, octyl and decyl glucoside.

- Surfactant G: biobased surfactant, octyl and hexadecyl glucoside.

- Surfactant H: biobased surfactant, C8-12 alkylglycosides D-pentose, D- glucose.

- Surfactant I: biobased surfactant, amyl-capryl and lauryl xylosides.

- Surfactant J: biobased surfactant, caprylyl-capryl polyglycosides.

- Surfactant K: ethoxylated fatty alcohol, linear saturated C10-12, 6EO. Cloud point 54°C.

- Surfactant L: ethoxylated fatty alcohol, branched saturated C12-14, 7EO. Cloud point 54°C.

Description of the methods:

Pulping step

Composition of the sheets of textile fibres: cellulosic fibres and 1-10% of synthetic fibres, calculated by the weight of the total composition. The textile fibres are dispersed in water to make a fibres pulp with a concentration of 10%. This dispersion is made with a Hobart lab mixer model H600T, at a temperature of about 40°C, with a pulping time of 30 minutes at speed 3. The pH of the fibres dispersion is about 8.0. Flotation step

A sample of the fibres pulp from the pulping step (named later on: initial fibres pulp) is weighted and then diluted with hot water into a Voith Delta 25 lab flotation cell, which has a total capacity of 23 litres. The final fibres pulp concentration after complete dilution and before flotation is about 0.30%. The temperature of the water used for dilution is adjusted according to the desired flotation temperature. The surfactant(s) to be tested (1 or 2 surfactants) are then added to the flotation cell and mixed 2 minutes with the fibres pulp. Then air injection is started for 10 minutes (air flow rate = 10 litre/minute). Hot water is slowly and regularly added in the flotation cell to maintain a regular flow of foam reject during the batch flotation.

In a homologous series of trials (each example), all flotation trials are performed with samples of fibres pulp from the same initial fibres pulp at 10% concentration.

Trial analysis

All the foam rejected from the flotation cell during the flotation trial is entirely collected to determine the flotation yield and the removal efficiency of the synthetic fibres from the pulp.

The total mass of flotation rejects is measured. A sample of the rejects is weighted, filtered on a MonodurTM Woven Mesh (synthetic fabric), and dried in an oven at 70°C overnight to determine the textile fibres concentration in the rejects, and further the total mass of dry fibres rejects.

The dried sample of fibres is then mixed with concentrated sulfuric acid (75%) to dissolve the cellulosic fibres fraction. The non dissolved fibres fraction (i.e. the synthetic fibres) is then filtered on a glass frit (Por 2), rinsed with water, dried at 70°C overnight, and weight. This allows the calculation of the mass fraction of synthetic fibres in the dry fibres rejects, and further the total mass of dry synthetic fibres in the total mass of dry fibres rejects. The same method is applied to determine the fraction of the synthetic fibres in the initial fibres pulp. The flotation yield is calculated the following way:

Flotation yield (%) = 100 x (total mass of initial dry fibres pulp - total mass of dry fibres rejects) / (total mass of initial dry fibres pulp).

The removal efficiency of the synthetic fibres is calculated the following way: Removal efficiency of the synthetic fibres (%) = 100 x total mass of dry synthetic fibres in the rejects / total mass of dry synthetic fibres in the initial dry fibres pulp.

Example 1 :

Flotation trials are done with an initial pulp concentration of 0.33% and at a temperature of 62°C. The tested surfactants, the surfactants dosages, and the results are gathered in Table 1. In the trial with surfactant D (soap), a solution of sodium hydroxide (20%) is added (20 kg/t) to the flotation cell to increase the surfactant efficiency.

Compared to the blank, the surfactant A shows a much higher flotation selectivity, with a much higher synthetic fibres removal efficiency along with a small reduction of the flotation yield. Best flotation selectivity with surfactant A is achieved at dosages between 1 .1 and 4.5 kg/t.

Compared to the surfactant A, the surfactant D shows a much lower flotation selectivity, with a lower synthetic fibres removal efficiency and a slightly lower flotation yield.

Table 1 .

Example 2:

Flotation trials are done with an initial pulp concentration of 0.30% and at a temperature of 63°C or 45°C. The tested surfactants, the surfactants dosages, the flotation temperature, and the results are gathered in Table 2. In the trial with surfactant D (soap), no alkali is added to the flotation cell.

Compared to the surfactant D, the surfactants A and B, at flotation temperature just above their respective cloud points, show much higher flotation selectivity thanks to a much higher synthetic fibres removal efficiency.

Table 2.

Example 3:

Flotation trials are done with an initial pulp concentration of 0.30% and at a temperature of 61 °C. The tested surfactants, the surfactants dosages, and the results are gathered in Table 3.

Compared to the surfactant A, the surfactant C shows a lower flotation selectivity despite a higher synthetic fibres removal efficiency, due to a lower flotation yield. The surfactant C has a stronger foaming power than the surfactant A (more foam rejects involving a lower flotation yield).

Compared to the surfactant A, the surfactants F and G (alkyl polyglucosides), and the surfactants H, I and J (alkyl polypentosides) show all a lower flotation selectivity, with a much lower synthetic fibres removal efficiency and/or a lower flotation yield. Among the group of surfactants F to J, the surfactant G shows the best results with a higher synthetic fibres removal efficiency but a lower flotation yield compared to surfactant A.

Table 3.

Example 4:

Flotation trials are done with an initial pulp concentration of 0.30% and at a temperature of 43°C. The tested surfactants, the surfactants dosages, and the results are gathered in Table 4.

Compared to the surfactant B, the surfactant C and to a lower extent the surfactant A show a lower flotation selectivity at this lower flotation temperature due to a much lower flotation yield, despite a higher synthetic fibres removal efficiency. At flotation temperature below their cloud points (around 55-60°C), the surfactants A and C are more foaming, i.e. more foam rejects, and less effective as collectors of the synthetic fibres. The surfactant A achieves a higher flotation selectivity than the surfactant C: higher synthetic fibres removal efficiency at about same total flotation yield.

Compared to the surfactant B, the surfactants F and G (alkyl polyglucosides), and the surfactants H, I and J (alkyl polypentosides) show all a much lower flotation selectivity, due to a much lower flotation yield while the synthetic fibres removal efficiency is in the same range. Table 4.

Example 5:

Flotation trials are done with an initial pulp concentration of 0.32% and at a temperature of 62°C or 42°C. The tested surfactants, the surfactants dosages, the flotation temperature, and the results are gathered in Table 5.

Surfactant E, combined with either surfactant B or surfactant A at flotation temperature just above their respective cloud points, achieves a much higher flotation selectivity than the surfactant E alone: higher synthetic fibres removal efficiency at about same total flotation yield.

At flotation temperature just above the cloud points of surfactant A and C, the association of surfactant A with surfactant C achieves a much higher flotation selectivity than the association of surfactant A with surfactant E: higher synthetic fibres removal efficiency and higher total flotation yield.

At flotation temperature just above the cloud point of surfactant C, the association of surfactant C with surfactant E achieves a higher flotation selectivity than the association of surfactant E with either surfactant K or L: higher synthetic fibres removal efficiency at about same total flotation yield. Table 5.

Example 6:

Flotation trials are done with an initial pulp concentration of 0.30% and at a temperature of 63°C or 45°C. The tested surfactants, the surfactants dosages, the flotation temperature, and the results are gathered in Table 6. In the trial with surfactant D (a soap), a solution of sodium hydroxide (20%) is added (20 kg/t) to the flotation cell to increase the surfactant efficiency.

In the flotation trials where 2 surfactants are combined, the amount of water added during the 10 minutes flotation is reduced to decrease the amount of rejected foams. This is done to increase the flotation yield, at the expense however of the synthetic fibres removal efficiency.

At flotation temperature just above the cloud point of surfactant B, the association of surfactant B with surfactant E achieves a lower flotation selectivity than the surfactant B used alone: lower flotation yield for a slightly higher synthetic fibres removal efficiency.

At flotation temperature just above the cloud point of surfactant A and C, the association of surfactant A with either surfactant C, or surfactant D, or surfactant E, achieves a lower flotation selectivity than the surfactant A used alone: much lower synthetic fibres removal efficiency with the same flotation yield.

Table 6.

Example 7:

Flotation trials are done with an initial pulp concentration of 0.33% and at a temperature of 62°C. The tested surfactants, the surfactants dosages, the flotation temperature, and the results are gathered in Table 7.

At flotation temperature just above the cloud point of the surfactant A and C, in the association of surfactant A with surfactant C, the increase of the dosage of surfactant A involves a reduction of flotation selectivity, via the reduction of the flotation yield (synthetic fibres removal efficiency unchanged).

At flotation temperature just above the cloud point of the surfactant A and C, at the same surfactant dosages (respectively 2.2 kg/t + 1.8 kg/t), the associations of surfactant A with either surfactant C, or surfactant F, or surfactant G show about the same flotation selectivity: about same flotation yield, and same synthetic fibres removal efficiency. Table ?.

Claims

1 . Method for separating synthetic, non-cellulose fibres from cellulose fibres in processing recycled textile fibres, the method comprising

- adding at least one surfactant to the aqueous textile fibres suspension, and

- subjecting the aqueous textile fibres suspension to flotation to remove the synthetic, non-cellulose fibres, characterized in that the surfactant comprises at least a main surfactant comprising a synthetic non-ionic surfactant selected from a group consisting of ethoxylated or ethoxylated and propoxylated fatty alcohols or fatty acids having chain length of C14 - C24, and any mixtures thereof.

2. Method according to claim 1 , characterised in that the ethoxylated or the ethoxylated and propoxylated fatty alcohols or fatty acids has preferably a chain length of C16 - C20.

3. Method according to claim 1 or 2, characterised in that a degree of ethoxylation of the ethoxylated or the ethoxylated and propoxylated fatty alcohols or fatty acids is in the range of 5 to 100 ethylene oxide (EO) moieties, preferably 10 to 40 EO moieties.

4. Method according to any of the preceding claims, characterised in that a degree of propoxylation of the ethoxylated and propoxylated fatty alcohols or fatty acids is in the range of 1 to 40 propylene oxide (PO) moieties, preferably 5 to 20 PO moieties.

5. Method according to any of the preceding claims, characterised in that the ethoxylated and propoxylated hydrophilic moiety of the fatty alcohols or fatty acids has a block structure, and is terminated with a PO group.

6. Method according to any of the preceding claims, characterised in that the hydrocarbon chain of the ethoxylated or ethoxylated and propoxylated fatty alcohols or fatty acids is linear and saturated.

7. Method according to any of the preceding claims, characterised in that the main surfactant has a cloud point temperature, which differs from a flotation temperature of the textile fibres suspension in maximum of 0°C to -10°C, preferably in maximum of 0°C to -5°C.

8. Method according to any of the preceding claims, characterised in that the method further comprises adding a co-surfactant comprising non-ionic and/or anionic surfactant(s) to the aqueous textile fibres suspension.

9. Method according to claim 8, characterised in that the co-surfactant comprises non-ionic surfactant selected from a group consisting of ethoxylated fatty alcohols or fatty acids having a chain length of C4 - C18, and any mixtures thereof, preferably ethoxylated fatty alcohols or fatty acids having a chain length of C8 - C14, and any mixtures thereof.

10. Method according to claim 9, characterised in that a degree of ethoxylation of the ethoxylated fatty alcohols or fatty acids is in the range of 3 to 100 ethylene oxide (EO) moieties, preferably 5 to 20 EO moieties.

11 . Method according to claim 9 or 10, characterised in that the ethoxylated fatty alcohols or fatty acids has a cloud point temperature, which differs from a flotation temperature of the textile fibres suspension in maximum of 0°C to -15°C, preferably in maximum of 0°C to -10°C.

12. Method according to any of the preceding claims, characterised in that the method further comprises adding a co-surfactant comprising non-ionic biobased surfactant selected from a group consisting of alkyl poly glycosides APG, alkyl poly pentosides APP and any mixtures thereof.

13. Method according to any of the preceding claims 8-12, characterised in that the main surfactant and co-surfactant(s) are added separately to the aqueous textile fibres suspension.

14. Use of a surfactant composition comprising at least a main surfactant comprising a synthetic non-ionic surfactant selected from a group consisting of ethoxylated or ethoxylated and propoxylated fatty alcohols or fatty acids having a chain length of C14 - C24, and any mixtures thereof, in flotation in processing recycled textile fibres, in which synthetic non-cellulose fibres are separated from cellulose fibres.

15. Use according to claim 14, characterised in that the surfactant composition further comprises a co-surfactant comprising non-ionic and/or anionic surfactant, and/or non-ionic biobased surfactant selected from a group consisting of alkyl poly glycosides APG, alkyl poly pentosides APP and any mixtures thereof.