METHOD AND SYSTEM FOR RECYCLING TEXTILE MATERIAL

Description

TECHNICAL FIELD

The invention relates to the field of recycling textile material. More specifically, the invention relates to a method and system for recycling textile material comprising cellulose, the method and system comprising bleaching/de-colorizing the textile material.

BACKGROUND

Over the recent years, recycling of textile material has gained interest. Processes for recycling cellulose from textile material comprising cellulose are known in the art, see for instance WO2018/073177A1. Recycled cellulose can be used for different purposes, for example for producing viscose. In the above-mentioned publication, the need for de-colorization/bleaching of the recycled textile material is identified, and it is suggested to use a combination of oxygen and ozone bleaching.

For the decolorized/bleached recycled textile material to be used in a following process such as the Lyocell or Viscose process, it has to reach a certain viscosity target at a target brightness to be able to be processed. Such pulp may be referred to as dissolving pulp and typically has an alpha cellulose content of over 90%.

Processes for bleaching of cellulose pulp from wood material using for instance ozone, hydrogen peroxide or chlorine dioxide are well known in the art, where ozone, hydrogen peroxide or chlorine dioxide reacts with and de-composes lignin originating from the wood material. When it comes to bleaching of pulp from textile material, the purpose of the bleaching is somewhat different—mainly to bleach or decompose color pigments contained in the pulp, which pulp mainly consists of cellulose and liquid (water). Despite the use of ozone, hydrogen peroxide or chlorine dioxide, it has however proven challenging to achieve sufficient brightness of the resulting pulp (from recycled textile material). Further, the oxidative properties of ozone and hydrogen peroxide will also attack the cellulose fibers and may reduce the viscosity of the resulting pulp to an unsatisfactorily low level. Thus, there is a need for a method for recycling textile material comprising improved bleaching/de-colorizing.

SUMMARY

An object of the invention is to solve or improve on at least some of the problems mentioned above in the background section.

These and other objects are achieved by the present invention by means of a method and a system according to the independent claims.

According to a first aspect of the invention, there is provided a method for recycling textile material comprising cellulose, the method comprising treating the textile material using Hot Caustic Extraction, HCE, and, after said treating, bleaching material obtained from the treating. The HCE is carried out at a temperature of at least 100° C. The bleaching comprises at least one (or two, or each) of:

• • ozone bleaching at a total ozone charge of more than 5 kg/odt;
  • chlorine dioxide bleaching, and
  • hydrogen peroxide bleaching at a total hydrogen peroxide charge of more than 13 kg/odt.

In other words, the method comprises treating the material using a HCE process at a temperature of at least 100° C. followed by bleaching. Put differently, the pulp/slurry obtained from the HCE process is subjected to bleaching. The bleaching may be described as comprising ozone bleaching at a total ozone charge of more than 5 kg/odt and/or chlorine dioxide bleaching and/or hydrogen peroxide bleaching at a total hydrogen peroxide charge of more than 13 kg/odt. The bleaching may alternatively be described as comprising at least one (or two, or each) of ozone bleaching, chlorine dioxide bleaching, and hydrogen peroxide bleaching, wherein the total ozone charge may be more than 5 kg/odt and/or the total hydrogen peroxide charge may be more than 13 kg/odt. The bleaching may also be described as comprising one or more bleaching stages, each comprising ozone bleaching (Z) and/or chlorine dioxide bleaching (D) and/or hydrogen peroxide (P) bleaching in the sense that there can be one bleaching stage being a Z, D or P stage, or any combination thereof (such as ZD), or there can be two or more bleaching stages, each being a Z, D, or P stage or any combination thereof. The total/overall ozone charge (of all stages comprising ozone bleaching) is more than 5 kg/odt, and/or the total/overall hydrogen peroxide charge (of all stages comprising hydrogen peroxide bleaching) is more than 13 kg/odt. It is understood that odt is an abbreviation for oven dry ton, where 1 ton=1000 kg, i.e. odt=oven dry metric ton (odmt).

It is understood that the textile material is provided to the treating step in mechanically disintegrated form, i.e. the textile material is not provided as whole garments or the like. Such mechanical disintegration may comprise cutting and/or shredding and/or refining and/or wet milling and/or re-slushing. The mechanical disintegration may be part of the method (as a method step preceding the treating), or the textile material may be provided in the mechanically disintegrated form, for example by mechanically disintegrating a batch of textile material prior to carrying out the method.

The invention is based on the insight that in order to achieve high brightness, in particular a brightness meeting the requirements of dissolving pulp, the homogeneity of the material prior to bleaching/de-colorization is important. The invention is further based on the insight that mechanical disintegration (as described above) alone of the textile material results in a homogeneity which is not high enough for known technologies such as ozone bleaching to achieve high brightness (without using excessive charges of ozone, which then results in unsatisfactory viscosity). The invention is further based on the insight that hot caustic extraction not only decolorizes the textile material, but also coverts the textile threads (of the mechanically disintegrated textile material) to a more homogenous pulp-like slurry. The inventors have realized that by combining hot caustic extraction with a following bleaching step, a synergetic effect is achieved which makes it possible to reach a high target brightness and at the same time preserve the viscosity compared with carrying bleaching stage(s) alone to reach the target brightness. The invention is further based on the insight that the above-described advantageous effect of the hot caustic extraction is particularly effective at temperatures of at least 100° C. The invention is further based on the insight that the preceding hot caustic extraction makes it possible to use relatively high charges of ozone or hydrogen peroxide (>5 kg/odt and >13 kg/odt, respectively) and still achieve the target viscosity.

In embodiments, the total/overall ozone charge (of all stages comprising ozone bleaching) is less than 12 kg/odt, preferably less than 10 kg/odt, or less than 8 kg/odt. Consequently, the total ozone charge may be within an interval of 5-12 kg/odt, or 5-10 kg/odt or 5-8 kg/odt.

In embodiments, the total/overall hydrogen peroxide charge (of all stages comprising hydrogen peroxide bleaching) is less than 40 kg/odt. Consequently, the total hydrogen peroxide charge may be within an interval of 13-40 kg/odt.

In embodiments, the hot caustic extraction is carried out (with the slurry comprising recycled textile material) at a consistency of at least 5 weight %, or at least 8 weight %, or more than 10 weight %, such as within an interval 10-12 weight %. Consistency is defined as the mass of dry pulp (textile fibers/material) divided by the mass of the pulp slurry.

In embodiments, the treating (hot caustic extraction) is carried out with an alkali charge of, or being equivalent to, at least 540 kg NaOH/odt, or at least 700 kg NaOH/odt.

In embodiments, the bleaching comprises one or more bleaching stages comprising ozone bleaching followed by chlorine dioxide bleaching. The chlorine dioxide bleaching may follow directly after the ozone bleaching, i.e. without intermediate washing, and may thus be referred to as a (ZD)-stage. This may be advantageous since a combination of chlorine dioxide and ozone results in a synergistic effect regarding brightness level. Therefore, an addition of chlorine dioxide directly after the ozone stage without intermediate washing may reinforce the bleaching effect in the sense that the brightness after the (ZD)-stage is comparable to the brightness achieved using ozone bleaching and chlorine dioxide bleaching with intermediate washing. Thus, the washing stage can be omitted to save cost and space. Furthermore, advantageous effects in terms of viscosity control may be achieved since ozone impacts viscosity while chlorine dioxide does not.

In embodiments, the bleaching comprises one or more bleaching stages comprising ozone bleaching followed by hydrogen peroxide bleaching. The hydrogen peroxide bleaching may follow directly after the ozone bleaching, i.e. without intermediate washing, and may thus be referred to as a (ZP)-stage. Hydrogen peroxide is a secondary reactions product in ozone bleaching, therefore an addition of hydrogen peroxide directly after the ozone stage without intermediate washing will reinforce the ozone bleaching stage. Alternatively, the hydrogen peroxide bleaching may follow after the ozone bleaching with an intermediate washing stage. In such embodiments, the hydrogen peroxide charge is advantageously more than 13 kg/odt.

In embodiments comprising chlorine dioxide bleaching, the chlorine dioxide charge may, if only one bleaching stage comprises chlorine dioxide bleaching, correspond to 30 kg active chlorine/odt or less. If two or more bleaching stages comprise chlorine dioxide bleaching, the total chlorine dioxide charge may correspond to 40 kg active chlorine/odt or less.

In embodiments, the method does not comprise treating with dithionite. Although dithionite may be effective for de-colorizing, it needs to be carried out without presence of air, which is a disadvantage compared to HCE.

In embodiments, the method comprises, after at least one, or each, bleaching stage, washing the pulp to remove dissolved material.

According to a second aspect of the invention, a system for recycling textile material comprising cellulose is provided. The system comprises a hot caustic extraction, HCE, arrangement arranged to receive said textile material (preferably in mechanically disintegrated form) and at least one bleaching arrangement arranged to bleach material received from the HCE arrangement. The HCE arrangement comprises means for adding a caustic solution to the textile material for caustic extraction thereof, and the HCE arrangement is configured to operate at 100° C. or more. One or more of the at least one bleaching arrangement comprises a chlorine dioxide bleaching apparatus.

In embodiments, one or more of the at least one bleaching arrangement comprises an ozone bleaching apparatus. The ozone bleaching apparatus may be arranged preceding/upstream and directly connected to the chlorine dioxide bleaching apparatus, i.e. the system may comprises a bleaching arrangement being a (ZD)-stage.

In embodiments, one or more of the at least one bleaching arrangement further comprises a hydrogen peroxide bleaching apparatus. The hydrogen peroxide bleaching arrangement may be arranged after/downstream of, and optionally directly connected to, an ozone bleaching arrangement, i.e. the system may comprise a bleaching arrangement being a ZP or (ZP) stage.

The features of the embodiments described above are combinable in any practically realizable way to form embodiments having combinations of these features. Further, all features and advantages of embodiments described above with reference to the first aspect of the invention may be applied in corresponding embodiments of the system according to the second aspect of the invention and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

Above discussed and other aspects of the present invention will now be described in more detail using the appended drawings, which show presently preferred embodiments of the invention, wherein:

FIG. 1 shows a flowchart illustrating an embodiment of the method according to the first aspect of the invention, and

FIG. 2 shows a flowchart illustrating another embodiment of the method according to the first aspect of the invention. FIG. 2 also illustrates an embodiment of the system according to the second aspect of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a flowchart illustrating an embodiment of the method according to the first aspect of the invention.

The method comprises mechanically disintegrating 1 the recycled textile material. The mechanically disintegrating step comprises cutting and/or shredding and/or refining and/or wet milling and/or re-slushing.

The mechanically disintegrated textile material is thereafter treated 2 using Hot Caustic Extraction, HCE. The treating (HCE) is carried out with a NaOH charge of at least 540 kg NaOH/odt and at a temperature of at least 100° C. The HCE is carried out (with the slurry comprising recycled textile material) at a consistency of more than 10 weight %, such as within an interval 10-12 weight %. The pulp/slurry formed in the treating/HCE stage is thus provided to the following step at medium consistency (MC).

After the HCE treating step 2, the pulp is washed 3 and thereafter subjected to ozone bleaching 4 at a total ozone charge of more than 5 kg/odt. Finally, the pulp is washed 5 to remove dissolved material from the ozone bleaching stage.

Other embodiments correspond to the embodiment in FIG. 1 except that the ozone bleaching is replaced with chlorine dioxide bleaching. Yet other embodiments correspond to the embodiment in FIG. 1 except that the ozone bleaching is replaced with hydrogen peroxide bleaching at a total charge of more than 13 kg/odt.

FIG. 2 shows a flowchart illustrating another embodiment of the method according to the first aspect of the invention. Steps 11-12 correspond to steps 1-2 described above with reference to FIG. 1.

The pulp/slurry formed in the HCE treating step 12 is washed 13 and thereafter subjected to a bleaching stage 14 comprising ozone bleaching followed directly (without intermediate washing) by chlorine dioxide bleaching. Bleaching stage 14 is thus a (ZD)-stage.

After the bleaching stage 14, the pulp is washed 15 to remove dissolved material from the bleaching stage, whereafter it is subjected to a second bleaching stage 16 comprising hydrogen peroxide bleaching (a P-stage). Finally, the pulp is washed 17 to remove dissolved material from the hydrogen peroxide bleaching stage.

The ozone charge in step 14 is more than 5 kg/odt (for example within an interval 5-10 kg/odt), and/or the hydrogen peroxide charge in step 16 is more than 13 kg/odt (for example within an interval 13-40 kg/odt). Consequently, one or both of the ozone charge and the hydrogen peroxide charge is/are within said intervals.

Other embodiments correspond to the embodiment in FIG. 2 except that steps 16 and 17 are omitted. Yet other embodiments correspond to the embodiment in FIG. 2 except that step 13 is replaced with a (ZP)-stage and step 16 is replaced with a D-stage.

FIG. 2 could also be said to illustrate an embodiment of the system according to the second aspect of the invention, which embodiment comprise:

• • an apparatus for mechanically disintegrating 11 (such as a refiner);
  • a HCE arrangement 12 comprising means for adding a caustic solution to the textile material for caustic extraction thereof, wherein the HCE arrangement is configured to operate at 100° C. or more;
  • washing apparatuses 13, 15, 17
  • a bleaching arrangement 14 comprising an ozone bleaching apparatus directly followed by a chlorine dioxide bleaching apparatus, and
  • a bleaching arrangement 16 comprising a hydrogen peroxide bleaching apparatus.
    Such arrangements, apparatuses are all well-known in the art and will not be described in further detail here.

In the above-described embodiments, ozone is added as a gas mixture, for example with 8-16% ozone by weight in an ozone-air mixture, preferably 10-12% ozone by weight. The ozone bleaching of bleaching stages 4, 14 may be performed for a duration of 10-60 seconds at a temperature of 40-70° C.

The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. For example, depending on the required brightness of the resulting pulp, one or more bleaching stages may be added prior to or after the bleaching stage 4/bleaching stages 14, 16. Further, one or more dewatering/thickening stages may be added if needed, for example to adjust pulp consistency prior to bleaching.