A PROCESS FOR SEPARATION OF THE CELLULOSIC PART FROM A POLYESTER AND CELLULOSE COMPOSITION

Abstract

A process for separation of the cellulosic part from a raw material composition comprising polyester and cellulose is provided. A blend is prepared comprising a raw material composition comprising polyester and cellulose and a hydrolyzing liquor wherein the hydrolyzing liquor comprises a first mixture comprising an alkaline solution containing hydroxide ions. The hydrolyzing liquor is added to give the blend an effective alkali concentration in a range from 5 g/l to 150 g/l, wherein the effective alkali concentration is calculated as NaOH, and the hydrolyzing liquor:raw material composition ratio is from 1.5:1 up to 25:1 and keeping the blend at a temperature of 100° C. or above.

Claims

1. A process for separation of the cellulosic part from a raw material composition comprising polyester and cellulose containing composition, wherein the process comprises providing a blend, wherein the blend comprises a raw material composition and a hydrolyzing liquor, wherein the raw material composition comprises a polyester composition, wherein the polyester composition comprises 99%, or less, by weight of polyester and 1%, or more, by weight of cellulose containing component or components, wherein the hydrolyzing liquor comprises a first mixture comprising an alkaline solution containing hydroxide ions, the hydrolyzing liquor is added to give the blend an effective alkali concentration in a range from 5 g/l to 150 g/l, wherein the effective alkali concentration is calculated as NaOH, and the hydrolyzing liquor:raw material composition ratio is from 1.5:1 up to 25:1, i.e. from 1.5 dm3/kg up to 25 dm3/kg, and keeping the blend at a temperature of 100° C. or above.

2. A process for separation according to claim 1, wherein the hydrolyzing liquor is added to give the blend a charge of effective alkali, wherein the charge of effective alkali is calculated as weight of effective alkali (EA)/(dry weight of said “raw material composition” (i.e. dry weight of said “polyester composition”, and dry weight of any of said “further cellulose containing components”)), and wherein the charge of effective alkali is not more than 100%.

3. A process for separation according to claim 1, wherein the blend is kept at said temperature for at least 5 minutes.

4. A process for separation according to claim 1, wherein the first mixture is added in one step to the raw material composition to provide the blend; or an amount of the first mixture is added in a first step to raw material composition to provide a blend, then further amount, or amounts, of the first mixture is added in a second step, or in a second step and in any further step, to provide the blend.

5. A process for separation according to claim 1, wherein the blend further comprises a second mixture comprising an alkaline solution containing hydroxide ions, lignin residues and other dissolved wood components, wherein the second mixture is either added to the first mixture, or added to the blend; or a first amount of the second mixture is added in a third step to blend, then further amount, or amounts, of the second mixture is/are added in a fourth step, or in any further step or steps.

6. A process for separation according to claim 1, wherein the first mixture comprising an alkaline solution which comprises NaOH.

7. A process for separation according to claim 1, wherein the cellulose containing component or components, comprise cotton composition, and zero, one, two or more, of lignocellulosic composition, cellulose composition, regenerated cellulosic fibres composition.

8. A process for separation according to claim 1, wherein the process for separation further comprises a step, or steps, of physically separating.

9. A process for separation according to claim 1, wherein the process for separation is a continuous process, a batch process, or any combination of continuous processes and batch processes.

10. A process for separation according to claim 1, wherein the raw material composition comprises a polyester composition, wherein the polyester composition comprises 99%, or less, by weight of polyester and 1%, or more, by weight of cellulose containing component or components, wherein the polyester composition is, for example, a polycotton composition and wherein the raw material composition further comprises zero, one or two of further cellulose containing components, for example, zero, one, or two of lignocellulosic composition, cellulose composition, regenerated cellulosic fibres composition.

11. A process for separation according to claim 1, wherein the process for separation is integrated into an alkaline pulping process, such as the kraft process.

12. A cellulosic composition obtainable from a process according to claim 1; and/or a mixture comprising polyester hydrolysis products, which comprises ethylene glycol and terephthalic acid, wherein the mixture, comprising the polyester hydrolysis products, is obtainable from a process according to claim 1.

13. A pulp obtainable by a process for producing a pulp comprising the process for separation according to claim 1, and/or a pulp, wherein the pulp comprises, and/or is obtainable from, the cellulosic composition according to claim 1.

14. A dissolving pulp obtainable by a process for producing a dissolving pulp comprising the process for separation according to claim 1, and/or a dissolving pulp, wherein the dissolving pulp comprises, and/or is obtainable from, the cellulosic composition according to claim 1.

15. A paper pulp obtainable by a process for producing a paper pulp comprising the process for separation according to claim 1, and/or a paper pulp, wherein the paper pulp comprises, and/or is obtainable from, the cellulosic composition according to claim 1.

16. A regenerated cellulosic fibres product comprising regenerated cellulosic fibres composition, wherein the regenerated cellulosic fibres product comprises, or is producible from, a cellulosic composition according to claim 1.

17. Paper product comprising, or producible from, a cellulosic composition according to claim 12.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0185] Aspects of the invention will be described in greater detail in the following, with reference to the embodiments that are shown in the drawings, in which

[0186] FIG. 1 schematically shows “a process for separation of the cellulosic part from a raw material composition”, in accordance with the present invention and as described herein.

[0187] FIG. 2 schematically shows “a process for separation of the cellulosic part from a raw material composition”, in accordance with the present invention and as described herein.

DETAILED DESCRIPTION

[0188] The embodiments of the present invention as described in the following are to be regarded only as examples and are in no way intended to limit the scope of the present invention.

[0189] FIG. 1 schematically shows “a process for separation of the cellulosic part from a raw material composition”, in accordance with the present invention and as described herein. Here FIG. 1 may schematically represent a “process for separation of the cellulosic part from a raw material composition” that is integrated into an alkaline pulping process, such as the kraft process. In an alkaline pulping process, such as the kraft process, dissolving pulp, or paper pulp, is produced from lignocellulosic material.

[0190] Here the “raw material composition”, RMC, which comprises “polycotton composition”, PCC, i.e. “polyester and cellulose containing component”, and a “lignocellulosic composition”, LC, i.e. one “further cellulose containing component”, and a “hydrolyzing liquor”, HL, are provided into a vessel, here a digester, DIG. Thereby, is a “blend” formed and hydrolysis of polyester will be performed in the digester, DIG. By said hydrolysis of polyester, is the cellulosic part, CP, recovered in the “raw material composition”, RMC.

[0191] The “hydrolyzing liquor”, HL, comprises here a “first mixture”, FM, (here industrial white liquor), and a “second mixture”, SM, (here industrial black liquor) and after hydrolysis of polyester also polyester hydrolysis products, PHP. After hydrolysis of polyester a part of a mix of “the polyester hydrolysis products”, PHP, and the “second mixture”, SM, goes to a “chemical recovery”, CR, and the other part of the mix of “the polyester hydrolysis products”, PHP, and the “second mixture”, SM, goes (is recycled back) to the digester, DIG.

[0192] The “first mixture”, FM, is added to the digester, DIG, in a “first step” (1st step). Said “first step” (1st step) may comprise batchwise, and/or continuous, addition/s of said “first mixture”, FM, to the digester, DIG. When the “process for separation of the cellulosic part from a raw material composition” is integrated into an alkaline pulping process, such as the kraft process, said “first step” (1st step) comprises batchwise, and/or continuous, addition/s of said “first mixture”, FM, to the digester, DIG, wherein said “first mixture”, FM, is chemically recovered in the “chemical recovery”, CR, from a part of a mix of the “polyester hydrolysis products”, PHP, and the “second mixture”, SM.

[0193] In the chemical recovery, CR, there may also be included several process steps to isolate ethylene glycol, EG, and terephthalic acid, TPA.

[0194] The second mixture, SM, is added to the digester, DIG, in a “third step” (3rd step). Said “third step” (3rd step) may comprise batchwise, and/or continuous, addition/s of said second mixture, SM, to the digester, DIG.

[0195] When the “process for separation of the cellulosic part from a raw material composition” is integrated into an alkaline pulping process, such as the kraft process, said “third step” (3rd step) comprises batchwise, and/or continuous, addition/s of a part of the second mixture, SM, together with a part of the polyester hydrolysis products, PHP, to the digester, DIG.

[0196] The second mixture, SM, and the polyester hydrolysis products, PHP, are comprised in “products in solution” from the digester, DIG, and thus, another part of the mix of “the second mixture, SM, and the polyester hydrolysis products, PHP” is added, and recycled back, to the digester, DIG, in said “third step” (3rd step).

[0197] The “hydrolyzing liquor”, HL, will then comprise a “first mixture”, FM, (here industrial white liquor), a “second mixture”, SM, (here industrial black liquor) and polyester hydrolysis products, PHP.

[0198] In a “physically separating” step, PSEP, here comprising e.g. filtering, and optionally screening and washing, the solid cellulosic part, CP, as a cellulosic composition, CC, comprising the cellulosic part, CP, is recovered.

[0199] The cellulosic part, CP as a cellulosic composition, CC, comprising the cellulosic part, CP may then be subjected to “further treatment”, FT, which may comprise additional cleaning, and/or purification, process steps, e.g. comprising bleaching of recovered cellulosic part, and/or, for example, washing, screening and/or viscosity adjustments of recovered cellulosic part, and/or drying.

[0200] FIG. 2 schematically shows “a process for separation of the cellulosic part from a raw material composition”, in accordance with the present invention and as described herein. Here FIG. 2 may schematically also represent a “process for separation of the cellulosic part from a raw material composition” that is integrated into an alkaline pulping process, such as the kraft process. In an alkaline pulping process, such as the kraft process, dissolving pulp, or paper pulp, is produced from lignocellulosic material.

[0201] Here a “polycotton composition”, PCC, i.e. “polyester and cellulose containing component”, is provided to a “separate digester for polycotton composition”, DIGCP.

[0202] The “polycotton composition”, PCC, i.e. “polyester and cellulose containing component”, and “hydrolyzing liquor”, HL are provided to the “separate digester for polycotton composition”, DIGCP. A “blend” is formed and hydrolysis of polyester will be performed in the “separate digester for polycotton composition”, DIGCP. By said hydrolysis of polyester, is the cellulosic part, CP, recovered in the “polycotton composition”, PCC.

[0203] A “first mixture”, FM, (here industrial white liquor) is added in a “first step” (1st step) to the “separate digester for polycotton composition”, DIGCP, wherein the “first step” (1 st step) may comprise batchwise, and/or continuous, addition/s of said “first mixture”, FM, to the “separate digester for polycotton composition”, DIGCP.

[0204] When the “process for separation of the cellulosic part from a raw material composition” is integrated into an alkaline pulping process, such as the kraft process, said “first step” (1st step) comprises batchwise, and/or continuous, addition/s of said “first mixture”, FM, to the “separate digester for polycotton composition”, DIGCP, wherein said “first mixture”, FM, is chemically recovered in a “chemical recovery”, CR, from a part of a mix of “polyester hydrolysis products”, PHP, and a “second mixture”, SM from a further digester, DIG and from the “separate digester for polycotton composition”, DIGCP. Note that “polycotton composition”, PCC would be present in the mix from the further digester, DIG, and from the “separate digester for polycotton composition”, DIGCP, only if not all polyester is hydrolyzed.

[0205] The second mixture, SM, is added to the “separate digester for polycotton composition”, DIGCP, in a “fourth step” (reference “4th step” is not shown in FIG. 2). Said “fourth step” may comprise batchwise, and/or continuous, addition/s of said second mixture, SM, to the “separate digester for polycotton composition”, DIGCP.

[0206] When the “process for separation of the cellulosic part from a raw material composition” is integrated into an alkaline pulping process, such as the kraft process, said “fourth step” comprises batchwise, and/or continuous, addition/s of said second mixture, SM, to the “separate digester for polycotton composition”, DIGCP, wherein the second mixture, SM, is added as a part of a mix of “polyester hydrolysis products”, PHP, and a “second mixture”, SM from a digester, DIG.

[0207] Into the further digester, DIG, a “lignocellulosic composition”, LC, i.e. one of “further cellulose containing component” is provided.

[0208] Part of the “first mixture”, FM, is added to the digester, DIG, in a “second step” (2nd step). Said “second step” (2nd step) may comprise batchwise, and/or continuous, addition/s of said “first mixture”, FM, to the digester, DIG. When the “process for separation of the cellulosic part from a raw material composition” is integrated into an alkaline pulping process, such as the kraft process, said “second step” (2nd step) comprises batchwise, and/or continuous, addition/s of said “first mixture”, FM, to the digester, DIG, wherein said “first mixture”, FM, is chemically recovered in the “chemical recovery”, CR, from a part of a mix of the “polyester hydrolysis products”, PHP, and the “second mixture”, SM.

[0209] Part of a second mixture, SM, is added to the digester, DIG, in a “third step” (3rd step). Said “third step” (3rd step) may comprise batchwise, and/or continuous, addition/s of said second mixture, SM, to the digester, DIG.

[0210] When the “process for separation of the cellulosic part from a raw material composition” is integrated into an alkaline pulping process, such as the kraft process, said “third step” (3rd step) comprises batchwise, and/or continuous, addition/s of a part of mix of second mixture, SM, together with polyester hydrolysis products, PHP, to the digester, DIG.

[0211] The part of mix of second mixture, SM, together with polyester hydrolysis products, PHP are comprised in “products in solution” from DIG (recycled back) and in “products in solution” from DIGCP.

[0212] Further a part of the “first mixture”, FM, is added to the digester, DIG, in a “second step” (2nd step). Said “second step” (2nd step) may comprise batchwise, and/or continuous, addition/s of said “first mixture”, FM, to the digester, DIG. When the “process for separation of the cellulosic part from a raw material composition” is integrated into an alkaline pulping process, such as the kraft process, said “second step” (2nd step) comprises batchwise, and/or continuous, addition/s of said “first mixture”, FM, to the digester, DIG.

[0213] The part of the “first mixture”, FM, is chemically recovered in the “chemical recovery”, CR, from a part of a mix of the “polyester hydrolysis products”, PHP, and the “second mixture”, SM, from DIG and DIGCP.

[0214] By the additions here above in said “second step” (2nd step) and said “third step” (3rd step) a blend comprising a “hydrolyzing liquor”, HL, is formed. The blend comprises here in DIG a “hydrolyzing liquor”, HL, comprising here a “first mixture”, FM, (here industrial white liquor), and a “second mixture”, SM, (here industrial black liquor), polyester hydrolysis products, PHP, and “polycotton composition” if not all polyester is hydrolyzed. After hydrolysis of polyester parts of mix of “the polyester hydrolysis products”, PHP, and the “second mixture”, SM from DIG go to the “third step” (recycled back to DIG), to the “fourth step” (DIGCP) and to a “chemical recovery”, CR.

[0215] In the chemical recovery, CR, there may also be included several process steps to isolate ethylene glycol, EG, and terephthalic acid, TPA.

[0216] In a “physically separating” step, PSEP, here comprising e.g. filtering, and optionally screening and washing, the cellulosic part, CP, as a cellulosic composition, CC, comprising the cellulosic part, CP, is recovered.

[0217] The solid cellulosic part, CP as a cellulosic composition, CC, comprising the cellulosic part, CP, from the digester, DIG and the “separate digester for polycotton composition”, DIGCP, may then be subjected to “further treatment”, FT, which may comprise additional cleaning, and/or purification, process steps, e.g. comprising bleaching of recovered cellulosic part, and/or, for example, washing, screening and/or viscosity adjustments of recovered cellulosic part, and/or drying.

EXPERIMENTALS

Comparative Examples

[0218] In Palme et al. “Textiles and Clothing Sustainability” (2017) 3:4 is, as already mentioned herein, a process for separation of cotton and polyester (in their case polyethylene terephthalate, PET) from mixed textiles is described. In the process for separation in Palme et al., 5 to 15% by weight NaOH in water and a temperature in the range of between 70 and 90° C. were used for the hydrolysis of polyester. Addition of a phase transfer catalyst, in their case benzyltributylammonium chloride (BTBAC), was shown to shorten the time for the hydrolysis of polyester. However, Palme et al. also showed that the separation can be performed without the phase transfer catalyst, but this required longer treatment times resulting in more cotton degradation.

[0219] It is beneficial if the hydrolysis is carried out without any catalyst: One reason is the cost of the catalyst and another is that the types of phase transfer catalysts suggested for hydrolysis of polyester will make the handling of the spent liquor after hydrolysis more complicated, since one more component is added. For example, the type of phase transfer catalyst used in Palme et al., BTCAC, contains organically bound nitrogen, which will contribute to the emissions of NO.sub.x if incinerated in a recovery boiler, cf. e.g. Adams, editor (1997) “Kraft recovery boilers” pp. 226-229.

[0220] In Palme et al., the time dependence of hydrolysis at 70, 80, and 90° C. and 10% NaOH (reagent grade) with BTBAC present is compared to hydrolysis at 90° C. and 10% NaOH without any addition of BTBAC. In the trials, 5 g textile was added to 500 g of the treatment solution. Hydrolysis without BTBAC was much slower than with this additive. Nevertheless, after approximately 150 min, the PET had been completely degraded. A look at the charge of alkali, however, reveals that the amount of costly sodium hydroxide used in the treatment is 1000% NaOH on dry textile. Consequently, there is a need for new disclosures to create an industrially sound process for the separation of cellulose from a polyester composition.

Example 1, Trials No. 1-3

[0221] Discarded polycotton sheets (i.e. “a raw material composition” in accordance with the present invention and “a polyester composition” in accordance with the present invention) from a supplier of service textiles where cut in pieces, with the size of approximately 1 cm×1 cm, using a pair of scissors. Small portions of the pieces (ca. 5 g each) were subjected to milling in a Wiley mill and then analyzed for polyester content according to SS-EN ISO 1833-11:2017. The sheets were composed of a mixture of polyethylene terephthalate (PET) and cotton, and the part that not was hydrolyzed is denoted polyester. The analyzed content of polyester in the samples varied from 55.0 to 56.4% by weight, see Table 1.

TABLE-US-00001 TABLE 1 Analysis of the polyester content in the sheets Sample Polyester content (% by weight) 1 56.2 2 55.0 3 56.4 4 56.3

[0222] Pieces of the cut sheets were treated in autoclaves with alkaline solutions (i.e. “a hydrolyzing liquor” in accordance with the present invention and “a first mixture” in accordance with the present invention) in order to investigate the extent of polyester removal during different treatments. 50 g, oven-dry weight, of polycotton sheet pieces (i.e. “a raw material composition” in accordance with the present invention and “a polyester composition” in accordance with the present invention) was put in the autoclaves together with the alkaline solution (i.e. “a hydrolyzing liquor” in accordance with the present invention) and the liquor to sheet ratio was adjusted to 6 dm.sup.3/kg. The autoclaves were closed and put in a hot air oven in which they were rotated. During the treatment in the hot air oven, the temperature in the autoclaves was measured. The temperature, which at the start was 25° C., was increased in a controlled way to a selected maximum temperature for the treatment. The temperature was raised from 25° C. to 70° C. over a period of 30 minutes at a constant rate. The temperature was stabilized at 70° C. for 15 minutes before further temperature increase. After stabilization, the treatment temperature was again increased using a temperature increase of 0.75° C./min up to desired cooking temperature. The cooking was then maintained until the desired time at cooking temperature had been reached. After the cooking, the autoclaves were rapidly cooled down to 20° C. using cool water. After the cook, the solid residue was carefully washed with deionized water and then the percentage of polyester in the solid residue was determined.

[0223] The alkaline solutions (i.e. “a hydrolyzing liquor” in accordance with the present invention) used were prepared from NaOH of analytical grade (i.e. “a first mixture” in accordance with the present invention) or with industrial white liquor with a concentration of effective alkali (EA) of 127 g/l (calculated as NaOH) and a sulfidity (S) of 36% (i.e. “a first mixture” in accordance with the present invention), which corresponds to [OH.sup.−]=3.175 mol/l and [SH.sup.−]=0.7 mol/l. Furthermore, trials were conducted where the treatment solution contained a mixture of the industrial white liquor (i.e. “a first mixture” in accordance with the present invention) and industrial black liquor (i.e. “a second mixture” in accordance with the present invention). Black liquor is spent cooking liquor obtained from the kraft process and the main dissolved components in this liquor are dissolved wood components and residual cooking chemicals. The residual effective alkali concentration in the black liquor used was 6 g/l. When black liquor was added, the sum of EA in white liquor and in the black liquor was considered as the alkali charge (% EA on dry sheets).

TABLE-US-00002 TABLE 2 Results from the cooking in Trials No. 1-3 Polyester Time at content Alkali Cooking cooking in solid charge temper- temper- residue Trial Alkaline (% EA on dry ature ature (% by No. solution sheets) (° C.) (min.) weight) 1 NaOH 28 140 20 15.2 2 White liquor 28 140 20 8.1 3 White liquor + 28 140 20 0.79 black liquor

[0224] The results from Trials No. 1-3 in Table 2 illustrate the effect of alkali solution (i.e. “a hydrolyzing liquor” in accordance with the present invention) used on the polyester content in the solid residue (i.e. “the cellulosic part” in accordance with the present invention) after cooking. In Trial No. 1, in which NaOH was used, the percentage of polyester in the solid residue (i.e. “the cellulosic part” in accordance with the present invention) was 15.2% and in Trial No. 2 where industrial white liquor (i.e. “a first mixture” in accordance with the present invention) was used as the alkali source (i.e. “a hydrolyzing liquor” in accordance with the present invention), the percentage of polyester remaining in the solid residue (i.e. “the cellulosic part” in accordance with the present invention) was 8.1%. The results related to Trial No. 3 show that the combination (i.e. “a hydrolyzing liquor” in accordance with the present invention) of industrial white liquor (i.e. “a first mixture” in accordance with the present invention) and black liquor (i.e. “a second mixture” in accordance with the present invention) resulted in a cook where only 0.79% polyester remained in the solid residue (i.e. “the cellulosic part” in accordance with the present invention). These results show that it is not only the alkalinity of the treatment solution, in combination with treatment time and temperature, that governs the extent of polyester removal from polyester containing textiles, but surprisingly also the type of alkaline liquor is of decisive importance.

[0225] It is, however, important to note that the amount of alkali that is charged must exceed the alkali consumption due to the amount of alkali required for the neutralization of acids liberated during the hydrolysis of the ester bonds in the polyester. Otherwise, the alkali promoted hydrolysis of the ester bonds will stop when the alkali is consumed.

[0226] Furthermore, inspection of the solid residues (i.e. “the cellulosic part” in accordance with the present invention) from Trial No. 3 using a light microscope showed that the only fibers detected were cotton fibres.

[0227] In the present Example 1, a liquor to sheet ratio applied was 6 dm.sup.3/kg. However, a satisfactory result may be obtained at other ratios as well, but in an industrial application it is beneficial to minimize the water usage and the amount of added alkali. If the ratio is increased, more process solution will be needed and more alkali in the hydrolyzing liquor is needed to reach a sufficient alkali concentration in the hydrolyzing liquor. If the alkali concentration in the hydrolyzing mixture is decreased, reaction temperature and/or reaction time must be increased. The limits regarding the preferred hydrolyzing liquor:raw material composition ratio is also dependent on whether the hydrolysis if the polyester is carried out in a step also containing e.g. wood chips (i.e. “further cellulose containing component” in accordance with the present invention), see Examples 2 and 3 where the conditions during the polyester hydrolysis, to a large extent, are adjusted to meet the requirements for the removal of non-cellulosic constituents from the wood material. Regarding temperature and alkali concentration, there is a balance between cellulose degradation and hydrolysis of polyester. The cleavage of cellulose chains in alkaline solutions becomes significant at temperatures of about 170° C., since at this temperature alkaline hydrolysis of polysaccharides becomes important (Fengel and Wegener (1989) “Wood. Chemistry, ultrastructure, reactions” Walter de Gruyter, Berlin, pp 299-300). Of course, one could go somewhat higher in temperature, if the decrease in reaction time will justify the higher degree of cellulose degradation, but in practice, a maximum temperature should be limited to 180° C.

Example 2

[0228] In order to produce material for an investigation of how of the solid residue (cotton fibres) (i.e. “the cellulosic part” in accordance with the present invention and “the cellulosic composition obtained from the process of separation” in accordance with the present invention) performs in a bleach sequence after hydrolysis of the polyester part of the sheets, pieces of the sheets (i.e. “a raw material composition” in accordance with the present invention and “a polyester composition” in accordance with the present invention) were subjected to cooking with a combination (i.e. “a hydrolyzing liquor” in accordance with the present invention) of industrial white liquor (i.e. “a first mixture” in accordance with the present invention) and black liquor (i.e. “a second mixture” in accordance with the present invention). Four autoclaves were charged with 100 g (dry weight) of sheet pieces (i.e. “a raw material composition” in accordance with the present invention and “a polyester composition” in accordance with the present invention) each, and the cooking procedure was the same as in Example 1. Alkali charge, cooking temperature and time at cooking temperature are shown in Table 3 along with the cooking results. In this trial, also the limiting viscosity of the treated material was determined.

TABLE-US-00003 TABLE 3 Results from the cooking in Trial No. 4 Time at Alkali charge Cooking cooking Polyester content Trial Alkaline (% EA on dry temperature temperature Viscosity in solid residue No. solution sheets) (° C.) (min.) (dm.sup.3/kg)) (%) 4 White liquor + 30 140 60 743 0.29 black liquor

[0229] Prior the actual bleaching, the cotton material (i.e. “the cellulosic part” in accordance with the present invention and “the cellulosic composition obtained from the process of separation” in accordance with the present invention) obtained after the cooking was mechanically treated in order to liberate the cotton fibres from threads and the fabric-like structure of the treated sheets that partly remained. The mechanical treatment was carried out using two different devices: An apparatus designed for the laboratory-wet disintegration of chemical pulps, designed according to ISO 5263, and a PFI mill designed for the laboratory beating of pulp, the PFI mill and the procedure is described in ISO 5264. In the procedure for the liberation of cotton fibres applied, the cotton material was first treated in the apparatus for wet-disintegration where 15 g (dry weight) cotton material suspended in 2 litres of deionized water was treated each time. The extent of the treatment is given by the number of revolutions of the propeller in the apparatus, and in this case, the number of revolutions was 90 000. After this, the material, 30 g each time, was subjected to beating in the PFI-mill using 3000 revolutions. After the beating, the cotton material (i.e. “the cellulosic part” in accordance with the present invention and “the cellulosic composition obtainable from the process of separation” in accordance with the present invention) was subjected to wet-disintegration again (15 g, dry weight, in 2 litres deionized water each time), but this time using 30 000 revolutions. In total 120 g (dry-weight) defibrated cotton material was produced. In the following description of the bleaching, this material is denoted pulp (i.e. “pulp obtainable by a process for producing a pulp” in accordance with the present invention and “pulp obtainable from the cellulosic composition” in accordance with the present invention).

[0230] The pulp was bleached using a D/A-EP-D/Q-PO sequence. Between each bleaching step the pulp was washed with deionized water.

[0231] The D/A step (acidic step in combination with chlorine dioxide) was performed at 90° C. and a pulp consistency of 10% for 150 minutes in plastic bags. The ClO.sub.2 charge was 1.9 kg/ton dry pulp (5 kg/t as active chlorine) and 9 kg H.sub.2SO.sub.4/ton dry pulp was added.

[0232] The EP-step (alkaline extraction fortified with hydrogen peroxide) was performed in plastic bags at 80° C. and a pulp consistency of 10% for 70 minutes. The H.sub.2O.sub.2 and NaOH charges were 2 and 3 kg/ton dry pulp, respectively.

[0233] The D/Q-step (chlorine dioxide bleaching step with a subsequent EDTA treatment without washing in between) was performed in plastic bags at 80° C. and a pulp consistency of 10% for 120 minutes in the D-step. The ClO.sub.2 charge was 1.5 kg/ton dry pulp (4 kg/ton dry pulp as active chlorine). At the end of the D-step, EDTA (0.5 kg/ton dry pulp) and NaOH (0.5 kg/ton dry pulp) were charged to the pulp and allowed to react for 5 minutes before washing of the pulp.

[0234] The last bleaching step (the PO-step, pressurized peroxide bleaching) was performed at 85° C. and 10% pulp consistency for 120 minutes in autoclaves. NaOH and MgSO.sub.4 charges were 8 and 1 kg/ton dry pulp, respectively, while the H.sub.2O.sub.2 charge was 3 kg/ton dry pulp.

[0235] After the bleaching, the pulp (i.e. “pulp obtainable by a process for producing a pulp” in accordance with the present invention and “pulp obtainable from the cellulosic composition” in accordance with the present invention) was analyzed, and the results are summed up in Table 4 together with examples from literature showing experimental values for three commercial dissolving pulps analyzed at our lab. The results demonstrate that the pulp obtained from the discarded sheets has properties that indicate that it would perform very well as a dissolving pulp (i.e. “dissolving pulp obtainable by a process for producing a pulp” in accordance with the present invention and “dissolving pulp obtainable from the cellulosic composition” in accordance with the present invention) for viscose production. Especially the high alkali resistance (low solubility in 18 and 10 wt % NaOH solutions, R-18 and R-10, respectively) is highly valued by viscose producers, since a high alkali resistance indicates that there will be a high cellulose yield in the viscose production. It may also be noted that when the bleached pulp from Trial No. 4 was analyzed for Klason lignin content, no Klason lignin was detected. If polyester had been present in the bleached pulp, it would have been contributing to the analyzed value, since the procedure for Klason lignin includes acid hydrolysis of carbohydrates leading to a total solubilization of the carbohydrates, leaving possible traces of polyester in the solid phase (in the Klason lignin determination of different lignocellulosic materials, the solid residue is considered to reflect the lignin content in the sample).

TABLE-US-00004 TABLE 4 Results from analyses of the pulp obtained after bleaching of the pulp originating from Trial No. 4 and from three different commercial dissolving pulps Relative carbohydrate Alkali Brightness Viscosity Klason composition (%) resistance (%) Pulp (% ISO) (dm.sup.3/kg) lignin (%) Glucan Xylan Mannan R-18 R-10 Bleached 91.9 373 0.0 99.6 0.3 <0.1 98.5 95.1 pulp from Trial No. 4 Pulp A 90.9 402 0.0 95.4 4 0.2 96.2 91.8 Hardwood Kraft Pulp B 93.7 376 0.0 95.5 3.7 0.5 96.7 92.9 Hardwood Kraft Pulp C 93.7 490 0.3 96.8 2.3 0.2 93.6 89.7 Hardwood Sulfite

Example 3

[0236] Three different prehydrolysis kraft pulps (PHK pulps) were produced in the laboratory from Eucalyptus chips (Eucalyptus globulus) with varying amounts of discarded sheets added to the wood chips. For details about PHK pulp, P- and H-factors it is here referred to WO2018115290. In this example, the sheets (of the same origin as in Example 1) (i.e. “a polyester composition” in accordance with the present invention) were first cut in pieces and then subjected to milling in a Wiley mill. This type of milling induces a large degree of fiber cutting. Therefore, when the pieces of sheets were milled, a powder-like material consisting of shortened textile fibres were obtained.

[0237] Prior to the prehydrolysis step, air-dried wood chips were impregnated with water over-night. Thereafter, the impregnated wood chips (i.e. “further cellulose containing component” in accordance with the present invention) together with the milled sheets (i.e. “a polyester composition” in accordance with the present invention) were put in in the autoclaves (the same cooking equipment as in Examples 1 and 2 was used) and the water to solid material ratio was adjusted to 1.5 dm.sup.3 water/kg solid material by addition of deionized water to the autoclaves. The total weight of wood chips and sheet material was 300 g dry weight (i.e. “raw material composition” in accordance with the present invention) in each autoclave.

[0238] In the prehydrolysis step, a lab procedure where a good control over the P-factor is achieved was used. The temperature was increased from 25° C. to 70° C. over a period of 30 minutes at a constant rate. The temperature was stabilized at 70° C. for 10 minutes before further temperature increase. After stabilization, the treatment temperature was again increased using a temperature increase of 1.8° C./min up to 170° C. Then, the temperature was kept constant until the desired P-factor was reached.

[0239] After the prehydrolysis step, the autoclaves were rapidly cooled down to 45° C. using cool water before white liquor (i.e. “a hydrolyzing liquor” in accordance with the present invention and “a first mixture” in accordance with the present invention) was charged to the autoclaves and the liquor to wood+sheet material ratio was adjusted to 4:1 using water. The charge of effective alkali was calculated as g EA/(g dry wood chips+dry sheet material). In the reference cooking, without any addition of sheet material, the charge of EA was 21%, and in the autoclaves containing 10% and 20% sheet material, the charge of effective alkali was 22% and 23%, respectively. The reason for the increased EA charge when sheet material was added was that pre-trials showed that the alkaline consumption during the treatment leading to hydrolysis of the polyester in the sheet material consumes more alkali than the reactions of the wood material during cooking do during pulping.

[0240] In the cooking-step the temperature was increased to a cooking temperature of 160° C., and the H-factor was recorded with high accuracy using a similar procedure as for the hydrothermal step. Initially temperature was set to 45° C. at 5 minutes. Thereafter, the temperature was raised to 70° C. in 15 minutes. After 15 minutes at 70° C., the temperature was increased with 0.75° C./min to cooking temperature, 160° C. The temperature was then maintained 160° C. until a H-factor of 400 was reached. The cook was terminated by rapid cooling of the autoclaves with cool water down to 20° C. After the cook, the kappa number, viscosity, carbohydrate composition and alkali resistance were determined, see Table 5.

TABLE-US-00005 TABLE 5 Results from PHK cooks using eucalyptus wood chips Relative carbohydrate Trial Sheet material Kappa Viscosity composition (%) No. in the cook (%) number (dm.sup.3/kg) Glucan Xylan Mannan 5 0 9.5 1072 97.50 2.34 0.16 6 10 7.2 1032 97.68 2.17 0.15 7 20 7.3 955 97.79 2.05 0.16

[0241] The results in Table 5 show that addition of the milled sheet material to the wood chips resulted in a pulp (i.e. “pulp obtainable by a process for producing a pulp” in accordance with the present invention and “pulp obtainable from the cellulosic composition” in accordance with the present invention) with a higher cellulose content than when eucalyptus wood chips only were used as the raw material. This is a natural consequence of the addition of sheet material to the pulping, since the sheets are virtually free from xylan. A high cellulose content of the pulp is a positive characteristic for dissolving pulp, since this type of pulp is used for the production of regenerated cellulose fibres, which principally should be made up by pure cellulose. Accordingly, these results imply that this new procedure for separating cellulose from discarded textiles containing cellulosic material can be implemented in existing production facilities for the production of dissolving pulp (i.e. “dissolving pulp obtainable by a process for producing a pulp” in accordance with the present invention and “dissolving pulp obtainable from the cellulosic composition” in accordance with the present invention).

Example 4

[0242] In a series of trials, the possibilities of implementing the new process in production of pulp intended for papermaking were investigated. To study one aspect of this embodiment of the invention, sheet material was added to cooks where Scandinavian softwood chips, a mixture of Norway spruce (Picea abies) and Scots pine (Pinus silvestris), were pulped. The properties of the resulting pulp (i.e. “pulp obtainable by a process for producing a pulp” in accordance with the present invention and “pulp obtainable from the cellulosic composition” in accordance with the present invention) were then analysed using standard methods for pulp characterization.

[0243] In the case of papermaking pulps, the morphological fiber characteristics are of vital importance for the performance of the pulp in papermaking and the properties of the produced paper. The trials in Examples 1-3 show that the separation of cellulose from sheets containing polyester and cellulose can be performed using milled sheets (Examples 2-3) or using sheets were the structure of the fabric to a large extent is intact (Example 1). This example, i.e. Example 4, compares the effects of two different pretreatments aiming for disintegration of the sheets prior to pulping: Milling in a Wiley mill leading to a large degree of fiber cutting and milling in a hammer mill, in which the fiber cutting is not that severe.

[0244] Prior to the cooking step, air-dried wood chips were impregnated with water over-night. Thereafter, the impregnated wood chips together with the milled sheets were put in in the autoclaves (the same cooking equipment as in Examples 1-3 was used). Thereafter, white liquor (i.e. “a hydrolyzing liquor” in accordance with the present invention and “a first mixture” in accordance with the present invention) was charged to the autoclaves and the liquor to wood+sheet material ratio was adjusted to 4:1 using water. The charges of effective alkali and percentage of sheet material added are shown in Table 6. The temperature was raised from 25 to 70° C. in 15 minutes. After 15 minutes at 70° C., the temperature was increased to 167° C. in 120 minutes. The temperature was then maintained 167° C. until a H-factor of 1200 was reached. After the cook, residual alkali was determined, and after washing the resulting pulps were characterized, see Tables 6 and 7. Furthermore, handsheets prepared from the pulps were analyzed, see Table 8.

TABLE-US-00006 TABLE 6 Data from the cooks (Trials No. 8-10) Sheet material EA Residual Trial in the cook charge EA No. (%) Sheet milling (%) (g/l) 8 0 — 20 9 9 30 Wiley mill 23 9 10 30 Hammer mill 23 9

TABLE-US-00007 TABLE 7 Characteristics of the pulps produced in Trials No. 8-10 Relative carbohydrate Trial Kappa Viscosity Klason composition (%) No. number (dm.sup.3/kg) lignin (%) Arabinan Galactan Glucan Xylan Mannan 8 27.9 1094 3.30 0.7 0.3 84.4 8.2 6.5 9 21.7 915 2.54 0.5 0.3 88.1 6.2 4.9 10 20.8 904 2.36 0.5 0.3 88.7 5.8 4.7

[0245] The analyses in Table 7 show that the introduction of milled sheet material to the cook increased the cellulose content of the pulps (increased glucan contents show that). Furthermore, the kappa number decreased. It is also notable that the Klason lignin content decreased when sheet material was added to the cook, which indicates that the pulp was virtually free from any polyester residues, cf. the discussions concerning Klason lignin content in Experiment 2. The cooking results regarding Trials No. 9 and 10 were very much the same, which indicates that the type of milling did not affect the cooking reactions to any large extent. It was, however, expected that the Hammer mill in Trial No. 10 would result in longer fibres that would increase the tearing resistance of handsheets prepared from the pulp. Even though a tendency for higher rearing resistance can be seen for the pulp including sheet material produced in a Hammer mill (Trial No. 10), no astonishing effect was revealed, see Table 8. Nevertheless, the outcome of this trial is that sheet material treated according to one aspect of the present invention can be used in papermaking.

TABLE-US-00008 TABLE 8 Tearing resistance of handsheets prepared from pulps prepared in Trials No. 8-10. Three different levels of beating in a PFI-mill was applied for each pulp prior to the hand sheet preparation (0, 2000 and 9000 revs, in the PFI mill) Tearing resistance index (Nm.sup.2/kg) Trial PFI revolutions No. 0 2000 9000 8 15.8 12.2 10.5 9 14.9 11.9 9.8 10 16.1 15.1 11.1

Example 5

[0246] Discarded textiles are very seldom made up by a single type of textile fibers and even if e.g. a T-shirt has a tag on it that says that the T-shirt is 100% cotton, the tag itself may contain polyester. Furthermore, in e.g. cotton textiles, many hems and other details are sewn with polyester threads. This means that the use of discarded cellulose textiles for the production of e.g. dissolving pulp, which is a product containing cellulose of high purity, will require separation processes for the removal of also minor amounts of non-cellulosic constituents, such as, polyester threads.

[0247] In a separate experiment, a cotton towel cut in pieces (ca 2 cm×2 cm) with a pair of scissors (i.e. “a raw material composition” in accordance with the present invention and “a polyester composition” in accordance with the present invention) was subjected to kraft cooking according to the procedure described in Example 4 with a charge of effective alkali of 8%. Analysis of the spent cooking liquor showed that the concentration of effective alkali decreased from 20 g/l down to 8.5 g/l, which means that the towel consumed 4.6% EA. This alkali consumption was expected, since cellulose is known to undergo some reactions that consume alkali under cooking conditions, cf. e.g. E. Sjöström (1981) “Wood chemistry. Fundamentals and applications” Academic Press, New York. pp 43-46.

[0248] Moreover, a visual inspection revealed that the polyester threads in the hems had been completely hydrolyzed during the kraft cooking step. The outcome of this trial is that treatment according to the present invention is very beneficial for upgrading also relatively pure cellulosic fabrics/materials. This means that the present invention is applicable also when the material to be treated contains as little as fractions of one percent of polyester, since such contaminants, if present in e.g. a dissolving pulp, can be expected to cause major process disturbances for the producer of regenerated cellulose fibres.

[0249] Analytical Methods Used in the Examples

TABLE-US-00009 Polyester content (i.e. the SS-EN ISO 1833-11: 2017 percentage of the sample not hydrolysed in the analysis) EA (effective alkali) and SCAN N 30: 85 Sulfidity Residual EA SCAN N 33: 94 Kappa number ISO 302: 2012 Klason lignin content Determined as the solid residue after acid hydrolysis according to Theander, O. and Westerlund, E. A. (1986) J. Agric. Food Chem. 34(2), 55-71 Brightness SS-ISO 2470-2: 2008 Limiting viscosity ISO 5351: 2010 Carbohydrate composition SCAN CM 71: 09 R10 and R18 ISO 699: 2015 Beating in an PFI mill SS-EN ISO 5264-2: 2011 Handsheet preparation EN ISO 5269-1: 2005 Tearing resistance SS-EN ISO 1974: 2012