Patent Description:
Cellulosic fibers in post-consumer textile wastes are almost always accompanied by synthetic man-made fibers, such as polyester, nylon or elastane. The reclaiming of cellulosic fibers (i.e. cotton, Viscose, Modal or Lyocell) from such mixtures is a complex and difficult task. In particular, cellulosic fibers are prone to degradation in harsh chemical environments, rendering their use in processes for production of man-made cellulosic fibers unsuitable. Mechanical separation of these fibers on the other hand is very difficult due to the small density difference of the fiber species and other nearly identical physical properties. Thus, the required selectivity of the separation cannot be achieved in state of the art separation methods.

In the state of the art, processes are known for separating cellulosic fibers from polyester-blends by selectively dissolving the cellulosic fibers. in <CIT>, a solution of NMMO and water is used to dissolve the cellulosic fibers. Although in such processes cellulosic fibers can be selectively reclaimed from mixtures, the cellulosic fibers degrade during the dissolution and are not suitable as a starting material for the production of man-made cellulosic fibers.

In <CIT> a process for separating polyester and cotton fibers from textile waste is disclosed, in which said polyester and cotton fibers are intimately mixed. Therefore, the textile waste is grinded and dispersed in water to obtain a suspension containing said fibers. The suspension is stirred, whereby the cotton fibers soak up a quantity of the water and their weight is increased. In a subsequent process step, the polyester and cotton fibers are separated in a flotation process, whereby the lighter polyester fibers accumulate on top of the suspension. Although such mild process conditions are preferable to reclaim cellulosic fibers in good quality, such processes may hardly be suitable to reclaim the cellulosic fibers from the polyester fibers, since only a low selectivity can be obtained due to the very small density difference between the cotton fibers and polyester fibers. If such a process would be applied to reclaim cotton, this usually results in either a huge loss of cotton during the separation or a high contamination of the cotton with polyester. Furthermore, such processes have the disadvantage of long process times due to the slow soaking and flotation steps, which ultimately limit the process throughput.

In <CIT>, a process for recycling of textile waste is disclosed, wherein a face fiber is separated from other solid components with a different density than the face fibers, such as adhesives and solid particles. The waste mixture is dispersed in an aqueous solution and said solution is passed through a hydrocyclone to separate the mixture into a fraction of face fibers and a fraction of other solid components according to their density. Although such processes are suitable to separate fibrous components from solid particles, they may not be applied for the separation of different fiber species with similar density due to their low selectivity.

<CIT> discloses a method for the separation of a mixture of a polyester and a cellulose derivative from non-textile waste, which comprises polyethylene fibers and cellulosic fibers, particularly cellulose triacetate. The waste originates from photographic films. The method comprises introducing gas bubbles into an aqueous liquid medium containing the mixture, optionally in the presence of at least one wetting agent and at least on flotation agent, thereby separating the mixture by flotation into the polyester and the cellulose derivative.

Thus, it is an object of the present invention to provide a reliable, fast process for the separation of water-swellable fibers from other textile fibers, which are nearly similar in density.

The stated object is inventively achieved in that the aqueous solution is an alkaline aqueous solution and the target component fibers are swelled in the alkaline aqueous solution prior to step b), thereby increasing the density and weight of said target component, more particularly of the target component fibers, relative to the density and weight of the ancillary component wherein the density difference between target and ancillary component fibers is increased.

If the aqueous solution is an alkaline aqueous solution and the target component, i.e. the target component fibers are swelled in said alkaline aqueous solution prior to step b), a simple and reliable process step for increasing the density and weight of the target component, i.e. the target component fibers, can be obtained. By selectively increasing the density of the target component fibers, the density difference between target and ancillary component fibers is increased, giving rise to a more reliable and robust separation process with a better selectivity for separation of the components according to their respective density. Common processes of swelling fibers in water or saline solutions may on the one hand increase the weight of these fibers, but on the other hand have the disadvantage, that the density of the fibers is lowered due to the lower density of the solution. Contrary, the alkaline environment in the aqueous solution helps to efficiently swell the cellulose molecules by incorporating heavier alkaline ions into the fibrous structure of the target component fibers, thereby leading to an increase in density of said fibers.

In general, high-density target fraction in the sense of the present invention refers to a fraction of fibers to be reclaimed from the textile waste, where the average density of said target fraction fibers is higher than a density threshold value. In the same manner, low-density residual fraction in the sense of this invention refers to a fraction of fibers to be rejected in the separation, where the average density of said residual fraction fibers is lower than the density threshold value. The density threshold value is thus lower than the average density of the target component fibers and higher than the average density of the ancillary component fibers.

It is further generally mentioned, that after the separation process, the target component content in the target fraction is higher than the target component content in the textile waste as provided and the ancillary component content in the target fraction is lower than the ancillary component content in the textile waste as provided, whereby the component contents are measured in reference to the total solid component weight of the fractions (without solution).

If, after dispersion of the comminuted textile waste in the aqueous solution, the suspension contains the textile waste in an amount of <NUM> % to <NUM> % by weight, the suspension may easily be handled and processed throughout the whole recycling process. If the suspension contains the textile waste in an amount of <NUM> % to <NUM> % by weight, reliability and efficiency of the process may be further improved.

The above mentioned advantages apply in particular to target component fibers that belong to the group of cellulosic fibers. Cellulosic fibers typically have a density in the order of <NUM>/mL to <NUM>/mL and a high swelling capacity compared to non-cellulosic fibers. In particular regenerated cellulosic fibers have the highest swelling capacity among them, enabling a significant increase of density due to the swelling. Such regenerated cellulosic fibers may be for example Rayon-, Lyocell- or Modal-fibers. Also the present invention can be successfully applied for reclaiming cotton fibers from textile waste. Besides their high water retention capacity, cellulosic fibers can be attacked by the alkaline solution in that the hydrogen bonds between the cellulose molecules of the cellulosic fibers can be opened up and hence ions of the alkaline solution can be incorporated into the cellulose chains. Thereby, the density of the cellulosic fibers is increased, improving the suitability for separation. Thus, the selectivity and reliability of the inventive process can be further improved.

The above mentioned advantages apply in particular, if the density of the water-swellable target component fibers is at least <NUM>/mL. Fibers with a density higher than <NUM>/mL exhibit a sufficiently high density in order to be reliably separated from relevant ancillary components after swelling.

In general it is mentioned, that in the context of this invention, density refers to the volumetric mass density of the respective substance.

The inventive process may be further improved if the ancillary component consists of textile fibers which are substantially non-swellable in water, more particularly synthetic non-cellulosic fibers with a density lower than the density of the target component fibers. In particular, if the fibers are not swellable in water, there will be substantially no increase in density of the ancillary component fibers due to the swelling. Furthermore, if the density of said ancillary component fibers is lower than the density of the target component fibers, the selectivity of the process can be further improved. In a preferable embodiment of this invention, the ancillary component fibers may be synthetic non-cellulosic fibers, such as e.g. polyester-, polyamide-, polypropylene-, or polyurethane-fibers. Such fibers usually need to be removed in cellulosic fiber recovery, because they increase the organic load of the effluent streams. Thus, if the inventive process is applied to textile wastes with such ancillary components, the overall chemical consumption of the recycling process may be drastically improved, resulting in a more economically and environmentally friendly process.

The inventive process may also be advantageously insensitive regarding contaminations, in particular if the textile waste comprises non-fibrous scrap, more particularly from rubber, leather, plastics or metal. Such scrap can be easily separated in said process without diminishing the quality of separation. Thus, a process with a high insusceptibility to pollution of the textile waste may be supplied.

The aforementioned advantages can be further improved, if the target component fibers are swelled in an alkaline aqueous solution with a pH between <NUM> and <NUM>. Such alkaline aqueous solution may easily be produced prior to dispersing the textile waste by adding an alkali hydroxide in such an amount to the aqueous solution, that a pH between <NUM> and <NUM> is obtained. Suitable alkali hydroxides may be for example caustic soda. If an alkaline solution with a pH between <NUM> and <NUM> is used, the chemical consumption of a subsequent alkaline cooking step, and thus of the whole recycling process, may be reduced, since the treatment of the textile waste in the alkaline solution serves as a first alkaline pre-treatment process prior to further alkaline treatment (e.g. said subsequent alkaline cooking process).

If further the target component fibers are swelled in the alkaline aqueous solution until the difference in density between the target component and the ancillary component is higher than <NUM>/mL, a high selectivity allowing a reliable separation of the fibers is obtained. The selectivity may be even further improved, if the density difference is more particularly higher than <NUM>/mL, even more preferably higher than <NUM>/mL. Process cycle times may thus be reduced due to the higher selectivity, enabling a higher process throughput.

If the target component fibers are swelled in the alkaline aqueous solution at a temperature between <NUM> and <NUM>, the efficiency of the swelling step can be improved. Even higher efficiency of the swelling may be obtained at temperatures between <NUM> and <NUM>, more preferably between <NUM> and <NUM>. Hence, the swelling step of the process may be accelerated, thereby further reducing the process cycle times.

The selectivity of the separation according to the inventive process can be further improved if the dispersed textile waste is separated according to the respective density of the components. Due to the swelling in the alkaline aqueous solution the density of the target component fibers is increased, thus, allowing for a reliable separation of said components. Thereby, the removal efficiency of the ancillary component in the target fraction can be at least <NUM> %, more particularly even at least <NUM> %. Hence in a suspension initially containing <NUM> % of target component fibers by weight of solids, the resulting target fraction may contain at least <NUM> - <NUM> % target component fibers by weight of solids. The removal efficiency is thereby considered as the percentage of the absolute mass of the ancillary component in the textile waste that has been removed from the target fraction and rejected to the residual fraction.

Such separation of the components in the dispersed textile waste according to their respective density in step b) of the inventive process can be performed via at least one mechanical separation device. Mechanical separation devices in the sense of this invention are preferably based on centrifugal or gravitational force, which are sensitive to differences in density and/or weight. Such devices may be for instance a hydrocyclone or a centrifuge. A hydrocyclone is a separation device that sorts particles in a liquid suspension based on the ratio of their centripetal force to fluid resistance. This ratio is high for dense particles, and low for light particles. It has one inlet, one underflow outlet at the bottom and one overflow outlet at the top. The underflow generally receives the high-density fraction, while the overflow receives the low-density fraction. Internally, inertia is countered by the resistance of the liquid, with the effect that larger or denser particles are transported to the wall for eventual exit at the underflow side with a limited amount of liquid, while the finer, or less dense particles, remain in the liquid and exit at the overflow side through a tube extending slightly into the body of the cyclone at the center. Additionally or alternatively, a separation according to the density of the components may also be performed by a flotation separation device. The flotation may be further supported by a suitable surfactant and/or flotation agent (e.g. a non-ionic tenside). A suitable flotation method would be for example dissolved air flotation (DAF).

A separation process with a particular high selectivity may be provided if the target fraction is subsequently passed to a second separation device. The second separation step may thereby use the same kind of separation device or a complementary separation device than in the first separation step. In one embodiment for example, the first separation step may employ a hydrocyclone and the second separation step a flotation device, or vice versa. In another embodiment, the separation may be performed by a cascade of <NUM>-<NUM> hydrocyclones. Likewise any other combination of separation devices according to this invention may be used.

If the textile waste is comminuted, more particularly to a size between <NUM> and <NUM>, prior to step a), a more reliable process may be provided. In particular, through the comminution, it can be ensured that the target component fibers are individually present in the suspension after step a). The individual accessibility of the fibers in the suspension is very important to allow for a component-selective separation. Additionally, an average size between <NUM> and <NUM> in terms of length is preferable to reduce the formation of aggregates or clogs and to improve the homogeneity of the suspension. Thus, a process with high reliability may be provided.

The homogeneity of the suspension may be further improved, if the textile waste is comminuted such that the target component fibers and the ancillary component fibers are substantially in the same size range. Furthermore, adverse effects that depend on the size of the comminuted fibers (such as friction and buoyancy) can be reduced if all components exhibit fiber sizes in a similar range, thus improving the quality of separation.

The dispersion of the components in the alkaline aqueous solution can be improved, if a surfactant agent, more particularly from the group of non-ionic tensides, is added to the alkaline aqueous solution. A more homogeneous solution may therewith be provided. If the surfactant agent is added in a concentration ≤ <NUM>% by weight a reliable, yet cost-effective process can be provided.

The process according to the present invention may also be particularly advantageous when it is used in the pulping of cellulose-based raw material from textile waste for the production of dissolving pulp. Dissolving pulp must meet high demands in terms of purity and degree of polymerization (DP-value) to be suitable for the production of molded cellulosic bodies. Textile waste usually contains a large number of contaminants that need to be removed thoroughly before a suitable dissolving pulp can be obtained therefrom. If a process according to any of claims <NUM> to <NUM> is used for reclaiming cellulosic raw material from textile waste, a dissolving pulp can be produced in very high purity without degrading the DP-value of the cellulosic raw material. Such a dissolving pulp may even meet the very high standards to be suitable for the production of cellulosic molded bodies of the Lyocell-type.

If a target fraction containing a fibrous textile target component is separated from textile waste in a process according to any of claims <NUM> to <NUM>, and the target fraction after separation, preferably containing the alkaline aqueous solution, is subjected to an alkaline cooking process to remove residual contaminants in order to obtain the dissolving pulp, a preferred synergetic effect can be obtained: since the textile waste is already dispersed in an alkaline solution, the consumption of chemicals in the subsequent cooking process can be greatly reduced, resulting in an overall more cost-efficient and more economically friendly process.

Finally, the pulp may be washed and bleached prior to obtaining the dissolving pulp, to remove any residual alkaline solution.

The inventive process according to any of claims <NUM> to <NUM> may also advantageously be used in the production of regenerated cellulosic molded bodies from, cellulosic fibers are recovered from textile waste and the regenerated cellulosic molded bodies may subsequently be produced from said recovered fibers.

Thereby a dissolving pulp from textile waste may be obtained according to any of claims <NUM> to <NUM> and subsequently dissolved in a suitable solvent to form a spinning solution and said spinning solution is extruded through a spinneret and precipitated in a spin bath to obtain the cellulosic molded bodies. For instance, in the case of a Lyocell-process, such suitable solvent may more particularly contain water and a tertiary amine oxide.

In the following, the invention is exemplified based on embodiments with reference to the drawings. In particular.

In <FIG>, a process <NUM> according to a first embodiment of the invention is schematically depicted. Thereby, a textile waste <NUM> containing a target component <NUM> and an ancillary component <NUM> is comminuted in a first comminution device <NUM> and optionally a second comminution device <NUM>, to obtain a comminuted textile waste <NUM>. The first and second comminution devices <NUM>, <NUM> may be for instance a guillotine <NUM> and a cutting mill <NUM>, respectively, although other similar comminution devices <NUM>, <NUM> may also be used. The target component <NUM>, which shall be reclaimed from the textile waste <NUM>, <NUM>, contains at least one cellulosic fiber <NUM>, preferably cotton, and the ancillary component <NUM>, which shall be rejected from the textile waste <NUM>, <NUM>, contains at least one synthetic fiber <NUM>, such as polyester or elastane. However, the target component <NUM> may also contain one or multiple types of regenerated cellulosic fibers <NUM>, such as viscose-, Lyocell- or Modal-fibers, whereas the ancillary component <NUM> may also contain multiple types of non-cellulosic man-made fibers <NUM> such as (non-exclusive) polyester-, polyamide-, acrylic-, or elastane-fibers, which was not further shown in <FIG>. The different fibers <NUM>, <NUM> of the components <NUM>, <NUM> are usually intimately intertwined in the textile waste <NUM>, e.g. in the form of a fabric <NUM>. The comminuted textile waste <NUM> has a size between <NUM> and <NUM>, such that the fibers <NUM> of the target component <NUM> and the fibers <NUM> of the ancillary component <NUM> are individually present and the intimate intertwining of the fabric <NUM> is broken up, i.e. the fibers <NUM>, <NUM> can be separated from each other without further mechanical comminution treatment. However the comminuted textile waste <NUM> may also be provided in pre-ground form, where additional comminution steps in comminution devices <NUM>, <NUM> as described above are optional.

It can be further seen from <FIG>, that the comminuted textile waste <NUM> is supplied to a mixing device <NUM>, where it is mixed with an alkaline aqueous solution <NUM> and dispersed in it to form a suspension <NUM>. The alkaline aqueous solution <NUM> is similarly fed to the mixing device <NUM> through a suitable dispenser <NUM>. The aqueous solution <NUM> contains water <NUM> and an alkali hydroxide <NUM> (for example caustic soda) and preferably has a pH between <NUM> and <NUM>. The suspension <NUM> is preferably stirred in the mixing device <NUM> with a stirrer <NUM> for approximately <NUM> to <NUM>, to loosen up the comminuted textile waste <NUM> and to increase the homogeneity of the suspension <NUM>. The cellulosic fibers <NUM> of the target component <NUM> are water swellable and have a density higher than that of water and of the ancillary component <NUM>. Thus, the cellulosic fibers <NUM> are swelled in the alkaline aqueous solution <NUM> of the suspension <NUM>, whereby the cellulosic fibers <NUM> soak up the alkaline aqueous solution <NUM> and their density is increased. The non-cellulosic man-made fibers <NUM> of the ancillary component <NUM> on the other hand are substantially non-swellable in the aqueous solution <NUM>. Thus, the swelling leads to an increasing density difference between the cellulosic fibers <NUM> and non-cellulosic fibers <NUM>, ensuring a reliable separation of the components <NUM>, <NUM>. During the swelling, the alkaline aqueous solution <NUM> is kept at a temperature between <NUM> and <NUM> for the swelling to be most efficient. The swelling may be further improved and accelerated if the temperature is kept between <NUM> and <NUM>. In one embodiment, the mixing device <NUM> may be designed such that comminuted textile waste <NUM> and alkaline aqueous solution <NUM> are fed continuously into the mixing device <NUM>. In another embodiment, the mixing device <NUM> may be designed such that comminuted textile waste <NUM> and alkaline aqueous solution <NUM> are added and mixed discontinuously (i.e. in a batch process).

In a further process step according to the embodiment in <FIG>, the swelled target component fibers <NUM> and the ancillary component fibers <NUM> in the suspension <NUM> are separated according to their respective density through a suitable separation device <NUM>. In the present embodiment, the separation device <NUM> is a hydrocyclone <NUM>. Therefore, the suspension <NUM> is fed via a pump <NUM> into an inlet <NUM> of the hydrocyclone <NUM>. In the hydrocyclone <NUM>, the suspension <NUM> is separated into a high-density target fraction <NUM> and a low-density residual fraction <NUM>. The density difference between the cellulosic fibers <NUM> and non-cellulosic fibers <NUM> is at least <NUM>/mL, which can be increased significantly due to swelling, e.g. up to <NUM>/mL or greater. In particular, the cellulosic fibers <NUM> of the target component <NUM> have a density usually greater than <NUM>/mL and are thus predominantly separated into the high-density target fraction <NUM> of the suspension <NUM>. Whereas the non-cellulosic fibers <NUM> of the ancillary component <NUM> have a density usually lower than <NUM>/mL (for polyethylene fibers) and are thus predominantly separated into the low-density residual fraction <NUM> of the suspension <NUM>. The high-density target fraction <NUM> leaves the hydrocyclone <NUM> through the bottom outlet <NUM> (underflow outlet) and is fed into a first tank <NUM>. The low-density residual fraction <NUM> leaves the hydrocyclone <NUM> through the top outlet <NUM> (overflow outlet) and is fed into a second tank <NUM>. Thus, the target fraction <NUM> in the first tank <NUM> is enriched with cellulosic fibers <NUM> of the target component <NUM> and the residual fraction <NUM> in the second tank <NUM> is enriched with non-cellulosic fibers <NUM> of the ancillary component <NUM>. To retain the cellulosic fibers <NUM>, the target fraction <NUM> may be filtered to remove the residual aqueous solution <NUM>. With such a process <NUM>, the removal efficiency of the ancillary component <NUM> in the target fraction <NUM> may easily be at least <NUM> %, more particularly greater than <NUM> %.

<FIG> schematically depicts a process <NUM> according to a second embodiment of the invention. The comminuted textile waste <NUM>, containing the target component <NUM> and the ancillary component <NUM> may be similarly prepared as depicted in <FIG>. Equally, the comminuted textile waste <NUM> may be directly supplied to the process <NUM>. As shown in <FIG>, the target component <NUM>, which shall be reclaimed from the textile waste <NUM>, contains at least one cellulosic fiber <NUM>, preferably cotton, and the ancillary component <NUM>, which shall be rejected from the textile waste <NUM>, contains at least one synthetic fiber <NUM>, such as polyester or elastane.

In <FIG>, the comminuted textile waste <NUM> is again supplied to a mixing device <NUM> and mixed with an alkaline aqueous solution <NUM> whereby the suspension <NUM> if formed. The further treatment of the components <NUM>, <NUM> is identical as described above for <FIG>.

The swelled target component fibers <NUM> and the ancillary component fibers <NUM> in the suspension <NUM> are then separated according to their respective density through a number of suitable separation devices <NUM>. According to the embodiment in <FIG>, a cascade <NUM> of three consecutive hydrocyclones <NUM>, <NUM>, <NUM> is employed. The suspension <NUM> is fed via a pump <NUM> into the inlet <NUM> of the first hydrocyclone <NUM>. The first hydrocyclone <NUM> then separates the suspension <NUM> into a first high-density fraction <NUM> and a first low-density fraction <NUM>. The first high-density fraction <NUM> leaves the first hydrocyclone <NUM> through the bottom (underflow) outlet <NUM> and is fed via a first three-way valve <NUM> into the inlet <NUM> of the second hydrocyclone <NUM>. In the second hydrocyclone <NUM>, the first high-density fraction <NUM> is again separated into a second high-density fraction <NUM> and a second low-density fraction <NUM>, whereby the second high-density fraction <NUM> leaves the second hydrocyclone <NUM> through its bottom outlet <NUM> and is further fed into the inlet <NUM> of the third hydrocyclone <NUM>. The third hydrocyclone <NUM> concludes the three-stage hydrocyclone cascade <NUM> by separating the second high-density fraction <NUM> into a third high-density fraction <NUM> and a third low-density fraction <NUM>. The third high-density fraction <NUM>, which leaves the third hydrocyclone <NUM> through its bottom outlet <NUM>, forms the target fraction <NUM> of the separation process <NUM>. The target fraction <NUM>, leaving the hydrocyclone cascade <NUM>, is enriched with cellulosic fibers <NUM> of the target component <NUM>. The low-density fractions <NUM>, <NUM> that leave the second and third hydrocyclones <NUM>, <NUM> through their top outlets <NUM>, <NUM> are fed back to the respective three-way valve <NUM>, <NUM> before the input of the previous hydrocyclones <NUM>, <NUM>. The low-density fraction <NUM> from the top outlet <NUM> of the first hydrocyclone <NUM> forms the residual fraction <NUM>, which is enriched with the non-cellulosic fibers <NUM> of the ancillary component <NUM>. Such a hydrocyclone cascade <NUM> is able to obtain a higher removal efficiency of the ancillary component <NUM>, leading to a more reliable process <NUM>. Finally, after separation, the target fraction <NUM> and the residual fraction <NUM> may be filtered to remove the aqueous solution <NUM>. Additionally, between the connected bottom outlets <NUM>, <NUM> and inlets <NUM>, <NUM> of the hydrocyclones <NUM>, <NUM>, <NUM>, pumps or means for conditioning the suspensions <NUM>, <NUM> may be employed to adjust the content of solids in the respective suspension <NUM>, <NUM>, which is not further depicted in the figures.

<FIG> depicts a process <NUM> according to a third embodiment of the invention. Again, as described for <FIG> and <FIG>, the comminuted textile waste <NUM>, containing the target component <NUM>, with at least one cellulosic fiber <NUM>, and the ancillary component <NUM>, with at least one synthetic fiber <NUM>, may be prepared and fed into the mixing device <NUM> accordingly, where it is mixed with an alkaline aqueous solution <NUM>, forming the suspension <NUM>. The swelled target component fibers <NUM> and the ancillary component fibers <NUM> in the suspension <NUM> are then separated in two consecutive separation devices <NUM>, namely a hydrocyclone <NUM> and a flotation cell <NUM>. In the combined hydrocyclone-flotation separator <NUM>, the suspension <NUM> is first pumped via a pump <NUM> into the inlet <NUM> of the hydrocyclone <NUM>. Therein the suspension <NUM> is separated into a first high-density fraction <NUM> and a first low-density fraction <NUM>. The first high-density fraction <NUM> leaves the first hydrocyclone <NUM> through its bottom outlet <NUM> and is fed into a conditioner <NUM> prior to feeding into the flotation cell <NUM>. The first low-density fraction <NUM> leaves the hydrocyclone <NUM> through its top outlet <NUM> and is passed through a filter <NUM> to partially reclaim a suspension <NUM>, which is also supplied to the conditioner <NUM>. In the conditioner <NUM>, a part of the reclaimed suspension <NUM> is mixed with the first high-density fraction <NUM> and an additional flotation agent <NUM>, to improve the separation of the components <NUM>, <NUM> in the flotation cell <NUM>. The conditioner <NUM> also helps to adjust the solid particle content of the high-density fraction <NUM> to achieve an ideal input consistency for the separation in the flotation cell <NUM>. The flotation agent <NUM> may be a coagulant (such as ferric chloride or aluminum sulfate) to coagulate the particles and/or a flocculant to conglomerate the particles into bigger clusters, which improves the flotation efficiency. The conditioned suspension <NUM> is then fed into the flotation cell <NUM>, wherein air <NUM> is introduced into the flotation cell <NUM> through an aerating device <NUM> and forms bubbles <NUM> at nucleation sites on the surface of the fibers <NUM>, <NUM> of the suspended components <NUM>, <NUM>. The air <NUM> is introduced into the suspension <NUM> in the form of air-pressurized water <NUM>, which is stored in a pressurizer <NUM> and fed into the flotation cell <NUM> through the aerating device <NUM>. A pressure reduction valve <NUM> may limit the amount of pressurized water <NUM> flowing from the pressurizer <NUM> into the flotation cell <NUM>. Upon entering the suspension <NUM>, the pressurized water <NUM> releases the air <NUM> in form of air bubbles <NUM> to the suspension <NUM>. The air bubbles <NUM> adhere to the fibers <NUM>, <NUM>, resulting in a separation of the suspension <NUM>, where the low-density fibers <NUM> float to the surface and form a froth layer <NUM> on top of the suspension <NUM>. The high-density fibers <NUM> on the other hand are too heavy to be lifted by the air bubbles <NUM> and sink to the bottom, where they form a sediment <NUM>. Due to the swelling of the target component fibers <NUM> in the alkaline aqueous solution <NUM> and their resulting increase in density, a reliable separation may be achieved. The selectivity and effectiveness of the separation however depends on several parameters, such as amount of air <NUM> introduced into the flotation cell <NUM>, as well as the flotation agents <NUM> added to the suspension <NUM>, so the flotation may be specifically adjusted depending on the components <NUM>, <NUM> that need to be separated. The froth <NUM> formed on top of the suspension <NUM> is removed via a skimmer <NUM> and is joined with the first low-density fraction <NUM> to form the low-density residual fraction <NUM>, enriched with the ancillary component <NUM> (i.e. the polyester fibers <NUM>). The sediment <NUM> is ejected at the bottom of the flotation cell <NUM> and forms the high-density target fraction <NUM>, which is enriched with the target component <NUM> (i.e. the cotton fibers <NUM>). After the separation, the target fraction <NUM> and the residual fraction <NUM> may be filtered to remove the aqueous solution <NUM>.

In all above shown embodiments according to <FIG>, the target fraction <NUM> and the residual fraction <NUM> may be subsequently filtered to at least partially remove the aqueous solution <NUM>, which is not further depicted in the figures. Thereby, the filtered aqueous solution <NUM> may be recycled and reused to form a closed-loop recycling process with a minimal ecological footprint. Additionally, the filtered aqueous solution may be used in several process stages (e.g. between subsequent separation devices (<NUM>) to adjust the consistency of the input suspensions, which has not been shown in the figures.

In the following, the invention is demonstrated according to examples <NUM> to <NUM>. The results are summarized in Table <NUM>.

In each of examples <NUM> to <NUM>, <NUM> of post-consumer textile waste, comprising cotton fibers as target component and polyester (PET) fibers as ancillary component (cotton fiber content <NUM>%, PET fiber content <NUM>%), were cut on a Pierret N40 guillotine in 1x1 cm<NUM> pieces and afterwards grinded on a Herbold SF <NUM>/<NUM> cutting mill with a <NUM> round mesh. The comminuted textile waste was then dispersed in an aqueous solution, followed by subsequent addition of <NUM> % Lucramul® WT <NUM> (non-ionic wetting agent) by weight. In examples <NUM> to <NUM>, <NUM> of an alkaline aqueous solution with a pH of <NUM> was used (obtained by addition of aqueous NaOH). The mixture (in total <NUM>) was then stirred for <NUM> at a temperature of <NUM> to obtain a homogeneous suspension and to accelerate the swelling of the cellulosic fibers. Example <NUM> shows a comparative example with no pH adjustment (neutral aqueous solution).

In example <NUM>, according to the aforementioned procedure, <NUM> of textile waste (<NUM>% cotton and <NUM>% PET content) were dispersed in <NUM> of alkaline aqueous solution and the resulting suspension was pumped to a single hydrocyclone (e.g. Radiclone BM80-I), i.e. the suspension contained <NUM> % textile waste by weight and had a pH of <NUM>, and the suspension was subsequently separated into a target fraction and a residual fraction. The target fraction was reclaimed from the underflow (bottom) outlet of the hydrocyclone, whereas the residual fraction was separated from the input stream via the overflow (top) outlet.

The following results could be obtained with this setup: after separation, the target fraction contained <NUM> % of PET fibers by weight (of fibers) and <NUM> % cotton fibers by weight (of fibers). The resulting target fraction thereby contained <NUM> % fibers. <NUM> % of the textile waste was rejected to the residual fraction and <NUM> % of the initial cotton component was lost to the residual fraction. The resulting removal efficiency of the PET component was <NUM> %.

In example <NUM>, <NUM> of textile waste (<NUM>% cotton and <NUM>% PET content) were dispersed in <NUM> alkaline aqueous solution (pH <NUM>, <NUM> % of textile waste by weight of fibers). Other than in example <NUM>, the resulting suspension was pumped to a <NUM>-stage hydrocyclone cascade (Radiclone BM80-I), whereby the underflow outlet of the first hydrocyclone stage was used as input for the second hydrocyclone stage, and so forth. The target fraction was reclaimed from the underflow outlet of the fifth hydrocyclone stage and the residual fraction was collected from the overflow outlets of all subsequent hydrocyclone stages.

The following results could be obtained with this setup: after separation, the target fraction contained <NUM> % of PET fibers by weight and <NUM> % cotton fibers by weight. The resulting target fraction thereby contained <NUM> % fibers. <NUM> % of the textile waste was rejected to the residual fraction and <NUM> % of the initial cotton component was lost to the residual fraction. The resulting removal efficiency of the PET component was <NUM> %.

In example <NUM>, equally, <NUM> of textile waste (<NUM>% cotton and <NUM>% PET content) were dispersed in <NUM> alkaline aqueous solution (pH <NUM>, <NUM> % of textile waste by weight). Therein, the resulting suspension was pumped to a <NUM>-stage hydrocyclone cascade (Radiclone BM80-I), followed by a dissolved air flotation (DAF) treatment. Hence the suspension was supplied to the <NUM>-stage hydrocyclone and the underflow outlet stream was subjected to the flotation. The target fraction thus was reclaimed from the flotation output (bottom sediment) and the residual fraction was collected from the overflow outlet of the hydrocyclone stage as well as from the reject (froth layer) of the flotation.

The following results could be obtained regarding example <NUM>: after flotation, the target fraction contained <NUM> % of PET fibers by weight and <NUM> % cotton fibers by weight. The target fraction had a solid fiber content of <NUM> %. In total, <NUM> % of the textile waste was rejected to the residual fraction and <NUM> % of the initial cotton component was lost to the residual fraction. The resulting removal efficiency of the PET component was <NUM> %.

Example <NUM> shows a comparative example for example <NUM>, where the textile waste was not treated in an alkaline aqueous solution. Instead, the <NUM> of textile waste (<NUM>% cotton and <NUM>% PET content) were dispersed in <NUM> aqueous solution (water) without adjustment of the pH value. The resulting suspension was again pumped to a single hydrocyclone (e.g. Radiclone BM80-I), whereby the suspension contained <NUM> % textile waste by weight. The suspension was separated into a target fraction and a residual fraction. The target fraction was reclaimed from the underflow outlet of the hydrocyclone, whereas the residual fraction was separated from the input stream via the overflow outlet.

The following results could be obtained with this setup: after separation, the target fraction contained <NUM> % of PET fibers by weight and <NUM> % cotton fibers by weight. The resulting target fraction thereby contained <NUM> % fibers. <NUM> % of the textile waste was rejected to the residual fraction and <NUM> % of the initial cotton component was lost to the residual fraction. The resulting removal efficiency of the PET component was only <NUM> %, which is significantly less than in example <NUM>, where the cotton component was swollen in an alkaline solution prior to separation.

Claim 1:
A process for separating a fibrous target component (<NUM>) from textile waste (<NUM>, <NUM>), said textile waste (<NUM>, <NUM>) containing the target component (<NUM>) and at least one ancillary component (<NUM>), whereby the target component (<NUM>) consists of water-swellable textile fibers (<NUM>) with a density higher than the density of water, wherein the ancillary component comprises non-cellulosic man-made fibers that are substantially non-swellable in the aqueous solution, the process (<NUM>, <NUM>, <NUM>) comprising the steps:
a) dispersing the comminuted textile waste (<NUM>) in an aqueous solution (<NUM>) to obtain a suspension (<NUM>) containing the textile waste (<NUM>), and
b) mechanically separating the dispersed textile waste (<NUM>) into a high-density target fraction (<NUM>) comprising the target component (<NUM>), and a low-density residual fraction (<NUM>) comprising the at least one ancillary component (<NUM>), according to the respective density of said components (<NUM>, <NUM>),
characterized in that, the aqueous solution (<NUM>) is an alkaline aqueous solution (<NUM>) and the target component fibers (<NUM>) are swelled in the alkaline aqueous solution (<NUM>) prior to step b), thereby increasing the density and weight of said target component (<NUM>) relative to the density and weight of the ancillary component (<NUM>) wherein the density difference between target and ancillary component fibers is increased.