Method for treating cellulosic waste material and resulting decolorized material

Abstract

A method for treating cellulosic waste material, bleached cellulosic pulp, and uses thereof includes providing a cellulosic waste material containing coloring substances, such as color pigments, dyes, colorants, and combinations thereof, pulping the waste material to produce a cellulosic pulp, and bleaching the pulp with ozone under alkaline conditions. After pulping, the recycled textile waste material is subjected to an ozone treatment carried out in the alkaline range, which allows the pulp to achieve excellent brightness without significantly impairing the viscosity of the pulp.

Description

[Technical Field]

[0001] The present invention relates to the treatment of recycled waste. In particular, the present invention relates to a method for treating recycled colored cellulosic waste. The present invention also relates to such bleached cellulosic pulp and its use in processes for the production of molded articles such as regenerated cellulosic products or cellulosic derivatives such as cellulose carbamate. [Background technology]

[0002] Cellulose is the most abundant renewable organic material on Earth and offers outstanding properties for textile applications. The viscose process remains the most widely used technology for producing regenerated cellulose fibers and films, despite its environmental challenges. Typically, the viscose process uses dissolving cellulose pulp, produced from virgin materials, as the starting material.

[0003] There is a need to develop simpler and more sustainable manufacturing processes, particularly to provide manufacturing processes that allow for expanded uses of regenerated cellulosic materials.

[0004] EP 3529282 and WO 2018104330 disclose a recycling process for cellulosic textile products, which involves treating cellulose in an alkaline step with oxygen under alkaline conditions at a pH in the range of 9 to 13.5, and bleaching the material with ozone under acidic conditions at a pH below 6.

[0005] Swedish Published Patent Application No. 2051513 discloses a method for ozone bleaching of pulp formed from regenerated cellulosic textile material, which method comprises adding at least one acid to lower the pH of the pulp and carrying out ozone bleaching at a low pH.

[0006] EP 3221511 provides a process for producing treated pulp to increase the overall process yield in a dissolution process, which comprises contacting the pulp with ozone under alkaline conditions with the aim of improving the dissolution yield of conventional pulping or cellulose production.

[0007] Finnish Published Patent Application No. 20175376 and Maattanen et al., Cellulose (2021) 28:3869-3886, disclose processes for treating textile-based materials, typically textile-based waste materials. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] European Patent No. 3529282 [Patent Document 2] International Publication No. 2018104330 [Patent Document 3] Swedish published patent application No. 2051513 [Patent Document 4] European Patent No. 3221511 [Patent Document 5] Finnish published patent application No. 20175376 [Non-patent literature]

[0009] [Non-Patent Document 1] Maattanen et al., Cellulose (2021) 28:3869-3886 Summary of the Invention

[0010] The invention is defined by the features of the independent claims. Some particular embodiments are defined in the dependent claims. [Means for solving the problem]

[0011] According to a first aspect of the present invention, there is provided a method of treating regenerated cellulosic waste material, the method comprising the steps of providing a cellulosic waste material containing a color pigment, dye, colorant, or combination thereof, pulping the waste material to produce a cellulosic pulp, and decolorizing the pulp with ozone under alkaline conditions.

[0012] According to a second aspect of the present invention, there is provided a bleached cellulosic pulp.

[0013] According to a third aspect of the present invention there is provided the use of decolorized textile pulp in a process for the manufacture of cellulose carbamate.

[0014] The present invention provides significant advantages. Surprisingly, subjecting regenerated cellulosic waste material containing coloring substances to ozone treatment conducted under alkaline conditions results in efficient decolorization of the material without impairing the mechanical properties of the cellulosic material. Tests have shown that materials treated as discussed herein will have significantly improved whiteness without significant degradation of molecular chains compared to materials treated with ozone under acidic conditions.

[0015] The present invention provides a process that is simple, easy to apply, inexpensive, and industrially applicable under mild conditions. In embodiments of the present invention, cellulose is efficiently removed from non-cellulosic components of blended textile products. The process can be carried out using existing infrastructure, including ozone treatment equipment such as ozone generators, reactors, and mixers; for example, the process can be carried out in a pulp mill. The resulting cellulose is highly amenable to further chemical processing, such as carbamation, and is generally suitable for dissolution in industrial processes such as the viscose and lyocell processes.

[0016] Other features and advantages will become apparent from the following description. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a graphical representation of CED viscosity and brightness as a function of pH for two series of samples subjected to ozone treatment with different ozone loads. DETAILED DESCRIPTION OF THE INVENTION

[0018] Unless otherwise stated herein or apparent from the context, any percentages referred to herein are expressed as weight percent based on the total weight of the respective composition.

[0019] Unless otherwise specified, experimentally measured or determined properties herein are measured or determined at room temperature, which is 25° C. unless otherwise indicated.

[0020] Unless otherwise specified, experimentally measured or determined properties herein are measured or determined at atmospheric pressure.

[0021] Also, please note that as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0022] As used herein, the term "about" refers to a value that is ±5% of the stated value.

[0023] As used herein, the term "CED viscosity" refers to the kinematic viscosity measured according to standard ISO 5351:2010, modified (also referred to as "ISO 5351 (modified)") by filtering the resulting cellulose solution and measuring and calculating the viscosity of the cellulose fraction of the material. This viscosity is measured in milliliters per gram.

[0024] "Whiteness" here refers to "CIE whiteness" and refers to values determined by ISO 11475:2017. ISO 11475:2017 specifies a whiteness index and measurement methodology, utilizing diffuse illumination with a CIE standard illuminant D65. CIE D65 is an outdoor daylight illuminant, and its defined spectral power distribution approximates average midday sunlight. Whiteness measures the reflectance of all wavelengths of light across the visible spectrum. The higher the measured whiteness (on a 0-100 scale, excluding brighteners), the whiter the regenerated cellulose appears. Therefore, while whiteness is an essential parameter for cellulosic textile pulp, standards typically used in the pulp industry, such as ISO brightness, do not clearly reflect the quality requirements for textile pulp.

[0025] As used herein, the term "cellulosic material" refers to a material containing cellulose. Typically, the content is at least 10% by weight of the material, and in particular cellulosic waste materials contain at least 20% by weight, for example at least 30%, or at least 40%, or at least 50%, or at least 60%, or at least 70% by weight of cellulose. Typically, the cellulose is present in the form of fibers. The term "cellulosic material" also encompasses lignocellulosic materials, i.e., materials containing both cellulose and lignin.

[0026] As used herein, the term "waste" generally refers to discarded or abandoned material, i.e., unused material (e.g., unsold textiles, cloth or other material left over after cutting), or material that is no longer used or usable for one of its original purposes, and also includes cellulosic powders produced during the processing of textile waste. As used herein, the term "recycled," when used in connection with cellulosic material, refers to material that has been discarded or abandoned and then recovered and returned for further processing.

[0027] As used herein, the term "pre-consumer waste" refers to waste that is collected after production, for example in a factory, but before it reaches the end consumer.

[0028] As used herein, the term "post-consumer waste" refers to waste that is generated at various levels after use of the final product by the ultimate consumer.

[0029] The "paper" referred to here is typically about 10 to about 120 g / m 2 , typically about 20-115 g / m 2 , or 60-110g / m 2 such as 30~110g / m 2 "Paperboard" (also called "corrugated board") refers to a fibrous material in web or sheet form having a basis weight of, for example, about 120 to 750 g / m, although these are not absolute limitations. 2 , typically about 130-700 g / m 2 , or 150 to approximately 500 g / m 2 This refers to a fibrous material in web or sheet form that has been formed into a mass or package having a basis weight of 1000 sq. ft.

[0030] The fibrous material of the paper or paperboard may comprise or consist of mechanical, semi-mechanical, or chemical pulp, or a combination thereof.

[0031] As used herein, the abbreviation "BDT" stands for bone dry (metric) ton and "adt" stands for air dry (metric) ton.

[0032] Generally, the present methods for treating cellulosic waste materials include, in a first step, providing a cellulosic waste material or a combination of cellulosic waste materials. The material, after optional mechanical treatment, is then subjected to pulping, particularly chemical pulping, in a second step. Such pulping is typically carried out at temperatures below 140°C, e.g., temperatures below 130°C, such as below 120°C, particularly below 110°C, below 105°C, or below 100°C. For example, acid pulping can be carried out at temperatures between about 60 and 95°C, while alkaline pulping is typically carried out at temperatures of at least 95°C.

[0033] In one embodiment, the chemical pulping process involves contacting the cellulosic waste material with an acid and an alkali. In particular, the material is subjected to a series of process steps in which it is separately contacted with an acid and an alkali. Typically, the material is first contacted with an acid and then with an alkali.

[0034] In one embodiment, when only cellulosic textile waste material is used, the pulping process specifically refers to an acid-alkali pretreatment process in which the textile waste material is contacted separately with acid and alkali, and does not refer to the Kraft process used in the context of wood pulp.

[0035] In a third step (after the acidic and / or alkaline treatment), the resulting pulp is subjected to ozonation under alkaline conditions to decolorize the pulp. The ozonation is carried out with ozone gas at high or medium consistency, at atmospheric pressure or, correspondingly, at a pressure of 2 to 15, typically 7 to 11 bar (g).

[0036] In one embodiment, after ozone treatment, the pulp is neutralized or at least some or all of the excess alkali is removed, optionally by washing with water, and the washed material is dewatered to reduce its moisture content.

[0037] In one embodiment, after ozone treatment, the pulp is washed on a filter and then subjected to carbamation.

[0038] In one embodiment, after or before the ozone treatment, the pulp is subjected to one or more bleaching stages, in particular using oxygen in at least one stage under alkaline conditions.

[0039] In one embodiment, after or before the ozone treatment, the pulp is subjected to one or more bleaching stages, in particular using, in at least one stage, hydrogen peroxide under alkaline conditions, optionally in combination with oxygen.

[0040] The resulting material can be used as conventional dissolving pulp for the production of moldings, for example by the viscose, lyocell or carbamate process.

[0041] The starting materials, processing steps, and products according to various embodiments will now be described in more detail.

[0042] The starting material for the process includes a cellulosic material containing a coloring substance. Such a material can impart color to the material or portions thereof. The colored material can be partially or completely colored. The color can be applied to the surface of the material or throughout the material.

[0043] In a first embodiment, the starting material comprises or consists of recycled paper, which comprises cellulose or lignocellulose. In one embodiment, the material comprises or consists of recycled paperboard comprising cellulose or lignocellulose. In one embodiment, the cellulosic waste material preferably comprises, consists of, or consists essentially of recycled pre-consumer waste, post-consumer waste, or industrial waste, or a combination thereof.

[0044] Examples of such recycled materials include mixed paper and board grades, old or used corrugated containers, old or used newspapers and magazines, and high quality deinked and pulp replacements. Paper and pulp industry waste products further include paper and board rolls, paper and board bobbins, and paper and board rejects, and zero fibres.

[0045] Cellulosic or lignocellulosic materials typically contain fibrous material formed by cellulose, lignin, and potentially hemicellulose. By nature, lignocellulosic materials also contain extractives (organic molecules) as well as metals and silica and other inorganic substances. Industrially processed materials such as paper or paperboard materials often contain inorganic or organic residues such as pigments, fillers, sizing agents, and other additives, in addition to coloring substances including color pigments, inks, and dyes. The fibrous material of recycled paper or paperboard can be bleached or unbleached.

[0046] Different coloring substances have different properties. Ink, especially printing ink, is generally intended to permanently change the pigmentation of an item, usually paper, and may also change the item's texture. Ink may bleed, but is usually intended to stay roughly in place, which is essential for being able to write clearly. Dyes are also intended to permanently change the pigmentation of an item, usually fabric, but do not change the item's texture. Dyes typically soak into and spread through the material.

[0047] Typically, colored paper or paperboard materials comprise sheets or fibers or slivers of cellulosic or lignocellulosic material that have been applied with color pigments or dyes to impart colored areas to the original material, for example, in the form of figures, letters, or symbols. Such colored areas may be applied to the material by printing or other graphic techniques. Colored areas of paper or paperboard generally exist on the surface of the material or on the sheet of material.

[0048] In one embodiment, the recycled paper or paperboard material is subjected to mechanical treatments including removal of ash and impurities, deinking, washing and / or refining, in addition there is typically an acidic treatment to clean the material, remove inorganic materials such as metals, and adjust the viscosity and polydispersity of the polymer.

[0049] Delignification pulping or cooking is performed before ozone decolorization. The treatment may include an alkaline treatment using hydroxide or carbonate compounds to remove lignin and especially hemicellulose. The degree of polymerization of recycled paper from paperboard materials tends to decrease during delignification and pulping treatments and other pretreatments required to refine the material suitable for textile applications. If the treatment results in an unnecessarily low degree of polymerization, the recycled material cannot be used as a raw material. Therefore, it is particularly preferred to perform ozone decolorization under alkaline conditions, where the degree of polymerization remains relatively intact.

[0050] In a second particularly preferred embodiment, the material comprises, consists of or consists essentially of cellulose-containing textile waste material.

[0051] In one embodiment, the recycled textile waste comprises a majority of the material, for example, greater than 50% to 100% by weight of the regenerated cellulosic material comprises recycled textile waste.

[0052] In one embodiment, the cellulosic waste material comprises more than 50%, 60%, 70%, 80%, 90% or more than 95% by weight of cellulose-containing textile waste material, calculated on the total weight of the cellulosic waste material. In a preferred embodiment, 100% by weight of the cellulosic waste material comprises textile waste material.

[0053] In one embodiment, the material comprises or consists of a combination or mixture of the above materials. Thus, the material can include both textile waste and recycled paper and / or paperboard.

[0054] The regenerated cellulosic waste material can include pre- or post-consumer waste or industrial textile waste, such as work clothes, wipes or towels. It can include residual (pulp) fibers or fines or rejects from the pulping process or socket and can include waste collected from a variety of sources.

[0055] As used herein, the terms "pre-consumer waste" and "post-consumer waste" are equally applicable to both cellulosic waste that includes or consists of paper and paperboard materials and cellulosic waste that includes or consists of textile products.

[0056] Examples of post-consumer textile waste include clothing and household items that have been discarded or are not being used for some reason, for example, such waste includes clothing or household items that have been worn out, damaged, or outgrown.

[0057] In one embodiment, the regenerated cellulosic waste comprises or consists of textiles in municipal solid waste (also abbreviated as "MSW"), such as, but not limited to, discarded or used clothing, footwear, hats, carpets, and other household textiles, including towels, sheets, blankets, and pillowcases.

[0058] In one embodiment, the regenerated cellulosic textile waste material comprises or consists of mixed colored textile waste, which includes cotton or other natural fibers, regenerated cellulose fibers, or cellulosic derivative fibers.

[0059] In one embodiment, the mixed colored textile waste comprises, inter alia, fabric colorants, such as color pigments, dyes, colorants and combinations thereof, especially dyes.

[0060] In particular, mixed colored textile waste typically comprises a combination of textile materials obtained from several sources, including: recycled textiles, including natural fibers; and natural plant fibers, including seed fibers such as cotton and kapok; bast fibers, such as hemp, jute, kenaf, ramie, abaca, and linen (flax); leaf fibers, such as manila, sisal, bromeliad, and banana; and fruit fibers, such as coconut.

[0061] In addition to the cellulosic component, the waste material also contains non-cellulosic material. Typically, the non-cellulosic material comprises about 1-50% by weight of the cellulosic waste material, such as 2-40% by weight, for example 2.5-20% by weight.

[0062] Non-cellulosic fibers consist primarily of polyesters such as poly(ethylene) terephthalate, but fibers of other thermoplastic materials such as polyamides, polyurethanes, polyether-polyurea copolymers (e.g., elastane), polyisoprene, and polyethylene / polypropylene are also frequently found in textile waste.

[0063] In one embodiment, the cellulosic waste material comprises polycotton. "Polycotton" refers to a material made from a blend of cotton and man-made fibers, particularly polyester fibers, typically polyethylene terephthalate (PET).

[0064] In one embodiment, the blended textile material is a mixed color blended textile material.

[0065] Typically, cellulosic textile waste material also contains non-textile, non-fibrous or non-cellulosic elements such as labels and special prints, metal elements (ferrous or non-ferrous), rubber elements, leather elements, and plastic elements such as buttons and zippers, which are preferably removed prior to further processing of the material.

[0066] According to one embodiment, cellulosic (textile) waste material is optionally first subjected to one or more mechanical treatment steps, where the material is mechanically broken down to open up the structure within the material. The material is broken down in various mechanical devices (e.g., pulpers) to break down the material into particles of 0.01 to 1.00 cm. 2 The degraded cellulosic material may be provided in pieces having a size of 100 mm or smaller pieces corresponding to a single fiber unit.

[0067] In one embodiment, the material is mechanically refined and broken down by means of chopping, grinding, grinding or milling the textile material to open up the fiber structure in the material, hi a further embodiment, the textile material is broken down by means of chopping, grinding, grinding or milling the material to open up the thread structure in the material.

[0068] Generally, fibers having a size of up to 40 mm are provided.

[0069] In one embodiment, the pieces of material are broken down into single particles with fiber lengths of ≦25 mm, preferably ≦10 mm, and suitably 1-6 mm in length. The fiber diameter can be less than 0.1 mm, e.g., less than 0.05 mm, e.g., about 15 μm, such as 10-50 μm. Breaking the material down to these sizes provides fibers with an optimally sized surface area for contact with liquids in subsequent chemical processes.

[0070] In one embodiment, the regenerated cellulosic material is screened to provide a blended material comprising cellulose, in one embodiment the blended textile material contains cellulose in at least 50% by weight of the material, suitably at least 60% by weight of the material, in particular at least 70% by weight of the material, preferably 80% by weight of the material, most preferably the blended textile material comprises 80% by weight of cellulosic material.

[0071] In one embodiment, the non-cellulosic fibers, preferably less than 20% by weight (on a dry weight basis) of the non-cellulosic fiber component, are polyester.

[0072] In one embodiment, the regenerated cellulosic material is subjected to one or more chemical treatment steps, optionally after a mechanical pretreatment to open up the structure.

[0073] In a preferred embodiment, the cellulosic material is contacted with an acid in a first chemical step to obtain acid-treated fibers. Thus, the material is contacted with an acid to provide a slurry or fiber bed.

[0074] In one embodiment, the acid acts on the cellulosic fiber to adjust the degree of polymerization of the cellulose, in particular to reduce the degree of polymerization, in one embodiment, the degree of polymerization in terms of viscosity is reduced from a maximum CED viscosity in the range of 500 to 2500 ml / g, preferably 600 to 1000 ml / g, more preferably 700 to 900 ml / g, especially 800 ml / g, to a minimum CED viscosity in the range of 200 to 550 ml / g, preferably 250 to 500 ml / g, suitably 250 to 450 ml / g, especially 300 to 350 ml / g.

[0075] In one embodiment, the acid further attacks the monomeric non-cellulosic components and inorganic and organic components, dissolving said components for washing away in subsequent steps.

[0076] When measuring the viscosity of a cellulosic material, only the cellulosic portion is taken into account; the non-cellulosic portion does not contribute to the viscosity.

[0077] In one embodiment, the acid used in the acid treatment step is selected from the group consisting of mineral acids such as H2SO4 and persulfuric acid, organic acids such as formic acid, acetic acid, performic acid, peracetic acid, peracetic acid, and acidic side streams of other industrial processes, including pulp mill effluents, and mixtures thereof. The mixture may include a combination of mineral acids, a combination of organic acids, a combination of peracids, or any combination of mineral acids, organic acids, or peracids, whether organic or inorganic.

[0078] In a preferred embodiment, the regenerated cellulosic material is contacted with H2SO4.

[0079] In one embodiment, the initial acid charge is in the range of 1 to 50 g / L, such as 1 to 40 g / L or 2 to 30 g / L. In one embodiment, the acid concentration at the end of acid digestion is in the range of 1 to 25 g / L. Different acids offer different benefits, for example, oxidative acids such as peracids improve dye removal, and strong mineral acids improve acid hydrolysis. Organic acids, on the other hand, are biodegradable and more environmentally friendly, as long as sulfate emissions are kept to zero.

[0080] In a further embodiment, the cellulosic material is contacted with the acid at a temperature in the range below 140°C, such as 50-135°C, preferably 60-120°C, especially 65-100°C, such as 60-95°C, suitably >70°C.

[0081] In a further embodiment, the degraded cellulosic material is contacted with the acid for a period of from 10 to 600 minutes, such as from 30 to 240 minutes, preferably from 30 to 120 minutes, typically from 40 to 90 minutes.

[0082] In addition to reducing the degree of polymerization of the cellulose fraction, the first chemical step provides the benefit of dissolving metals, which can then be washed out of the slurry in a subsequent washing step. In one embodiment, the first chemical step further comprises dissolving additional acid-soluble impurities present in the degraded textile material for washing out of the slurry.

[0083] The acid-treated fibers are then contacted with alkali in a second chemical step, which washes the non-cellulosic components from the slurry, resulting in a slurry that essentially contains purified cellulosic fibers, although small amounts of non-cellulosic components may remain.

[0084] In one embodiment, the acid-treated fiber is washed with water before contacting it with alkali in the second chemical step. In one embodiment, the acid-treated fiber is pressed before contacting it with alkali in the second chemical step.

[0085] In a further embodiment, the acidic cooking liquor from the first chemical step is replaced by alkaline cooking liquor for the second chemical step.

[0086] In another embodiment, the fibrous pulp obtained from the process is pressed and washed before the next processing step.

[0087] In one embodiment, the second chemical step involves contacting the acid-treated fiber with an alkali selected from the group consisting of NaOH, KOH, organic (non-ionic) superbases, and mixtures thereof. In a further embodiment, the alkali selected from the group consisting of NaOH, KOH, organic (non-ionic) superbases, and mixtures thereof is included in sulfur-containing cooking liquor from a conventional pulping process. In certain embodiments, superbases are efficient catalysts for the hydrolysis of non-cellulosic materials, such as polyesters. In one embodiment, NaOH is used, optionally included in sulfur-containing cooking liquor from a conventional pulping process. One advantage of using NaOH is that it is readily available at pulp mills. In one embodiment, the initial alkali loading is in the range of 25 to 100 g / L, measured after neutralization of any acid residues remaining in the acid-treated material.

[0088] Contacting the fibers with alkali provides a number of benefits: first, it cleanses non-cellulosic components, such as polymeric non-cellulosic components and keratin, including wool, hair, and skin residues, from the cellulose, and second, it swells the cellulose, making it more accessible to reagents for subsequent processing.

[0089] In one embodiment, the acid-treated fiber is contacted with alkali at a temperature in the range of 95 to 140°C or less, typically 100 to 130°C, and preferably 105 to 120°C or about 110°C.

[0090] In a further embodiment, the acid-treated fiber is contacted with the alkali for a period of from 30 minutes to 240 minutes, typically from 60 minutes to 180 minutes, preferably from 60 minutes to 120 minutes.

[0091] In one embodiment, after an alkaline pulping step of the type described above, the CED viscosity of the textile material is in the range of 500-2500 ml / g, preferably 600-1000 ml / g, more preferably 700-900 ml / g, especially 800 ml / g, and the final viscosity after both the acid and alkaline steps is 200-550 ml / g, preferably 250-500 ml / g, suitably 250-450 ml / g, especially 300-350 ml / g.

[0092] The acid and alkaline treatment steps are carried out in suitable equipment. One type of reactor for carrying out the acid and alkaline treatment includes a mixing reactor, in which the fiber is mixed with the cooking liquor. Another type of reactor is a digester, either a single digester or a set of digesters, in which a slurry formed by the fiber and cooking liquor (i.e., acid or alkaline solution) is circulated by a pump.

[0093] As used herein, a "digester" is understood to be a pressurized or non-pressurized vessel in which a fiber suspension is maintained for an extended period of time to allow the intended chemical reactions to occur. Feeding can occur both at the top or bottom of the vessel, and fiber discharge can be facilitated by a discharge device. Such digesters can be equipped with internal screens to displace liquor while retaining the fiber within the digester. The vessel can be of both vertical and horizontal configuration and can be operated as a batch or continuous process.

[0094] Another example of a set of reactors through which the slurry can be circulated is a medium consistency loop. Screw-type continuous reactors are also suitable for use in embodiments. In one embodiment, the slurry is circulated through the reactor(s) by a pump.

[0095] In this context, "medium consistency" should be understood to refer to a concentrated suspension of fibers, water, and chemicals that can still be transported by means of a pump designed for that purpose. Typically, such a suspension may contain 3-15% fiber, more often 6-12% fiber, in the form of pulp or pulp derived from recycled cotton. Medium consistency can also be understood to refer to a concentrated suspension of fibers, water, and chemicals that can still be transported by means of a pump designed for that purpose. Typically, such a suspension may contain 3-15% fiber, more often 6-12% fiber, from regenerated cellulose.

[0096] As used herein, "high consistency" should be understood to refer to a higher consistency than "medium consistency."

[0097] In one embodiment, a non-pressurized vessel is used when operating at temperatures below 100° C., for example during acidic treatment. In one embodiment, a pressurized vessel is used when operating at temperatures above 100° C., for example during alkaline treatment (see below).

[0098] After the pulping step, the pulp is subjected to an ozone step in which it is contacted with ozone under alkaline conditions to decolorize the pulp using ozone, for example, by decomposing or removing dyes, colorants and / or pigments in the pulp from the pulp.

[0099] If desired, the pulp can be washed after the pulping step(s) with water or preferably alkaline filtrate.

[0100] In a preferred embodiment, the process step is carried out under alkaline conditions immediately prior to ozone decolorization (i.e., without any intervening or intermediate chemical treatment step). In one embodiment, the ozone treatment is carried out on the pulp obtained from the alkaline treatment without an intermediate washing step.

[0101] Ozone treatment is carried out by treating pulp in an aqueous medium. Typically, the pulp is dispersed in an aqueous medium, which preferably contains at least some alkaline agent to maintain the pH in the alkaline range. The pulp slurry preferably has a consistency of 1 to 50% by weight, particularly 1 to 25% by weight or 1 to 15% by weight. Thus, the pulp can be subjected to ozonation at its high or medium consistency, and suitably, the ozonation is carried out at medium consistency. A consistency in the range of 5 to 15% by weight is particularly preferred. In high consistency bleaching, the pulp has a consistency of at least 30% by weight, preferably 35 to 45% by weight.

[0102] The ozonation of the pulp slurry is preferably carried out under mixing of the slurry to facilitate contact of the ozone with the cellulosic material.

[0103] The ozone dosage for decolorization is in the range of 0.5 to 30.0 kg / BDT, e.g., 0.5 to 15 kg / BDT, 1 to 12 kg / BDT, or 1.5 to 10 kg / BDT, preferably about 2.0 to about 6.0 kg / BDT. The temperature for ozonation of pulp can vary within a wide range. It is preferred to operate at a temperature of the aqueous ozonation medium in the range of 45 to 95°C, preferably 60 to 85°C.

[0104] During ozonation, the initial pH of the aqueous medium is typically greater than 8, preferably between 10 and 13. As the treatment progresses, the pH of the pulp typically decreases. It is preferable to maintain the pH in the alkaline range during ozonation, particularly throughout the entire ozonation. If necessary, the pH can be adjusted by adding an alkaline agent. Preferably, the ozonation of the pulp is carried out under conditions such that the final pH of the aqueous medium at the end of ozonation is greater than 7. The initial pH is preferably adjusted with a sodium hydroxide dosage of 0.1 to 5 kg / BDT, e.g., 0.2 to 4 kg / BDT.

[0105] In one embodiment, sodium hydroxide is used to achieve alkaline conditions with an aqueous medium dosage of NaOH in the range of about 0.01 to 0.5 wt. %, for example about 0.05 to 0.25 wt. % (calculated from the pulp (BDT)).

[0106] The alkaline agent used may be the same as in the alkaline treatment step described above.

[0107] Typically, the ozone acts on the substrate immediately, hi some embodiments, the ozone gas is provided in contact with the pulp for up to 2.5 hours.

[0108] In one embodiment, the final CED viscosity after the ozone bleaching step and optional peroxide and / or oxygen bleaching is 200-550 ml / g, preferably 220-390 ml / g, suitably 250-350 ml / g, and particularly 300-350 ml / g. These intrinsic viscosities correspond to an average degree of polymerization (DP) of the cellulose carbamate of 254-776, preferably 325-669, suitably 325-622, and particularly 397-471. DP is determined by the following formula: DP 0.905 =0,75[η] (commonly known from the literature).

[0109] As a result of the ozone treatment, and after any dewatering step, bleached pulp is obtained having a CIE brightness, as determined by ISO 11475:2017, greater than 77, for example in the range of 78 to 95, preferably 80 to 90. As evidenced by the experimental data provided to illustrate some particularly advantageous embodiments, the bleached cellulosic pulp has an average intrinsic viscosity of 220 to 390 ml / g and a CIE brightness of at least 78, such as at least 80, particularly at least 82, for example at least 84. In one embodiment, the CIE brightness is in the range of 78 to 95, typically 80 to 90.

[0110] Surprisingly, ozone treatment in the alkaline range does not significantly reduce the viscosity of the material, in particular the viscosity loss is less than that obtained with ozone under acidic conditions.

[0111] In contrast to the use of ozone in bleaching, the ozone used in decolorizing colored cellulosic wastes appears to have an oxidizing effect on the colorants and pigments as well as other coloring components, primarily decomposing the colorants and pigments rather than the cellulosic materials. For this reason, alkaline conditions provide excellent decolorization while maintaining high viscosity.

[0112] Furthermore, using ozone to decolorize waste materials has several other advantages: the ozonation reaction is fast; ozone is believed to cleave the conjugated chains or double bonds of the dye molecules that give off the color; organic dyes are decomposed and do not produce significant sludge or residue for further processing; the dye bonds to cellulose can be broken so that no residue remains on the fiber; indeed, ozone is believed to have good selectivity for coloring components, but little reactivity with carbohydrate structures.

[0113] In one embodiment of the present technology, the degree of polymerization of cellulosic fiber material of the feedstock of regenerated colored cellulosic fiber, potentially used in textile products, is adjusted in an acid stage, while decolorization of the fiber is carried out in an alkaline stage using ozone.

[0114] The above discussion of the effects of ozone on colorants and color pigments, as well as other colored components of cellulosic materials, represents only possible explanations and theories, and the present technology is not limited to the proposed explanations and theories.

[0115] After ozone treatment, the pulp is, in one embodiment, washed to remove the alkali and, typically, the colorants and color pigments and other coloring components.

[0116] In one embodiment, the ozonated pulp is subjected to an oxygen treatment, a chlorine dioxide treatment, or a peroxide treatment, or a combination thereof.

[0117] In one embodiment, oxygen bleaching is performed on unneutralized pulp after ozone treatment. The optional oxygen treatment can be combined with the oxidative alkaline treatment in an alkaline step. In one embodiment, the oxygen bleaching step is performed before ozone decolorization, instead of or in addition to the post-treatment.

[0118] The ozone treatment may be followed by peroxide oxidation under alkaline conditions, optionally in combination with oxygen bleaching before or after peroxide oxidation. Thus, in one embodiment, peroxide oxidation is performed on pulp, and the pulp has not been neutralized and / or washed after ozone treatment. In one embodiment, the ozone-treated fibers are pressed before being contacted with hydrogen peroxide.

[0119] In one embodiment, the ozonated material is optionally washed and subjected to hydrogen peroxide bleaching under the following conditions: the pulp medium is made alkaline with sodium hydroxide to reach a sodium hydroxide content in the range of about 0.1-1% by weight of dry cellulose. The consistency of the pulp slurry is adjusted to a medium consistency level, e.g., 8-10% by weight, and hydrogen peroxide is used at a dosage of about 0.4-0.75% by weight of dry cellulose. Hydrogen peroxide bleaching is carried out at a temperature of about 50-90°C, or 60-80°C, for 30-150 minutes, e.g., 60-120 minutes.

[0120] After ozone treatment and possible oxygen and / or peroxide steps, the treated material is dehydrated. In one embodiment, the material is dehydrated to a moisture content of less than 50% by weight, preferably less than 20% by weight, such as 15-5% by weight.

[0121] In one embodiment, there is provided a cellulosic textile material having an average intrinsic viscosity of 220-390 ml / g and a CIE whiteness index in the range of 78-95, such as 80-90.

[0122] The pulp obtained in this way can be used for the same purposes as conventional dissolution. Therefore, it can be used to produce molded products selected from staple fibers, filament yarns, filament bundles, short cuts, flocks, and films. The pulp can also be used for the same purposes as conventional long-fiber pulp, such as nonwoven fabric applications.

[0123] In one embodiment, the treated material, particularly a textile material, is mixed with urea to provide a mixture, and the mixture is heated to 130-150°C to react the cellulose with the urea to form cellulose carbamate.

[0124] The resulting material can also be processed as conventional market dissolving pulp, i.e., dried to a predetermined moisture content of less than 20% by weight, for example about 10% by weight, preferably cut into sheets, baled, and made suitable for transport to another location. Example 1

[0125] Sorted mixed-color recycled cotton textile waste, containing 4.0±2.8% non-cellulosic fibers and having a CED viscosity of 800±200 ml / g (based on CED viscosity measurement according to modified ISO 5351; the resulting cellulose solution is filtered to measure and calculate the viscosity of the cellulose fraction of the material), was mechanically shredded to disintegrate the fabric structure, forming fragments with fibers ≤25 mm in size. The non-cellulosic fibers were primarily polyester, although traces of nylon, isoprene-containing materials (elastic bands), and polyethylene / polypropylene were also detected.

[0126] The shredded material was chemically pretreated using a two-stage cooking procedure: in the first, acidic stage, the shredded material was treated with sulfuric acid at 90°C for 60 minutes. In the second, alkaline stage, the washed, acid-treated material was chemically pretreated with sodium hydroxide at 110°C for 120 minutes, with the pH value of the final wash liquor being 8.3. The viscosity of the chemically pretreated material was 357 ml / g (ISO 5351 (modified)) and the brightness was 71.1.

[0127] In the next step, ozone bleaching was performed to remove residual color traces from the textile fibers while maintaining the viscosity of the textile material at ≥ 300 ml / g after the final bleaching step. The goal was to keep the reduction in intrinsic viscosity of the cellulose below 15%. The reaction vessel was filled with warm water and the pretreated textile material was dispersed in the reactor to a concentration of 10 wt%. The pH was adjusted by adding NaOH. The reaction temperature was 60°C.

[0128] In the first test, the ozone dosage was 2.1 kg / adt, and the initial pH for the six test points was adjusted with sodium hydroxide solution or sulfuric acid. The initial pH values were 3.5, 5.5, 6.4, 10.7 (0.05 wt.% NaOH), 11.5 (0.15 wt.% NaOH), and 11.7 (0.23 wt.% NaOH). The final pH of the test points after ozone treatment were 3.1, 4.0, 4.9, 7.2, 9.0, and 10.0, respectively.

[0129] The textile-water slurry samples were washed and the whiteness and viscosity of the samples were measured. The whiteness (ISO 11475) and viscosity (ISO 5351 (modified)) values as a function of final pH are shown in Figure 1.

[0130] In the second test, the ozone dosage was 3.8 kg / adt, and the initial pH for seven test points was adjusted with sodium hydroxide solution or sulfuric acid. The initial pH values were 3.3, 5.6, 6.9, 10.9 (0.05 wt.% NaOH), 11.6 (0.16 wt.% NaOH), 11.8 (0.22 wt.% NaOH), and 11.9 (0.30 wt.% NaOH). After ozone treatment, the final pH values for the test points were 3.1, 4.1, 5.3, 7.8, 7.8, 8.3, and 9.7, respectively. The textile-water slurry samples were washed, and the whiteness and viscosity of the samples were measured. Whiteness (ISO 11475) and viscosity (ISO 5351 (modified)) values as a function of final pH are shown in Figure 1.

[0131] As can be seen from the accompanying figures, by increasing the pH from the acid to alkaline range, the brightness of the samples increased from about 76 (CIE WI) to over 80 (CIE WI) at an ozone dosage of 2.1 kg / adt. At higher dosages (3.8 kg / adt), the increase was even greater, with the brightness rising from about 76 (CIE WI) to values in the range of 82-84%. A slight decrease in viscosity was observed for both dosages under alkaline conditions. However, the decrease was smaller under alkaline conditions than under acidic conditions. Example 2

[0132] Sorted mixed-color recycled cotton textile waste with a CED viscosity of 800±200 ml / g (based on CED viscosity measurement according to ISO 5351 (modified)) was treated as described in Example 1. The viscosity of the chemically pretreated material was 330 ml / g (ISO 5351 (modified)) and the whiteness was 73.1 (CIE WI). The treated textile raw material was used for the decolorization test.

[0133] Ozone decolorization was carried out using an MC loop and a pressure reactor. The loop was first filled with warm soft water, and shredded textiles (290 kg, BD) were discharged into the system. The raw material and water slurry were then fed into the pressure reactor. 20 kg / BDT of NaOH was fed into the reactor, and the concentration was measured to be 6.6% at a pH of 11.9. The textile-water slurry was heated to 70°C. The estimated ozone concentration fed to the reaction was 16 wt%, and the feed duration was 155 minutes. The total ozone loading was 4.6 kg / BDT. After the ozone stage, the slurry was cooled by adding 3.9 m3 of water. The cooled, diluted slurry was dewatered in a screw press. The pH of the filtrate was 9.9. The viscosity of the ozone-decolorized material was 320 ml / g (ISO 5351 (modified)) and the brightness was 81.5 (CIE WI).

[0134] The peroxide stage was then carried out on the ozone-bleached textile material. The ozone-treated material was pumped into the reactor, and the concentration of the slurry in the pressure reactor was 6.2%. The reaction mixture was heated to 80°C and the pH was adjusted to 11.6 with NaOH. The reaction time in the peroxide stage was 60 minutes, and the hydrogen peroxide loading was 5 kg / BDT. The resulting bleached pulp had a viscosity of 308 ml / g (ISO 5351 (modified)) and a brightness of 85.1 (CIE WIE). Example 3

[0135] The bleached pulp obtained in Example 2 was subjected to a carbamation treatment as described in Finnish Patents Nos. 112869 and 112795 and WO 2021 / 038136. Urea was dissolved in water and added to the pulp to achieve a nitrogen content of 1.8 wt.% in the cellulose carbamate. Hydrogen peroxide (0.6 wt.%) was added to control the final degree of polymerization of cellulose carbamate with a DP of 306, corresponding to a viscosity of 236 ml / g (ISO 5351). After chemical addition, the target dry matter content was adjusted to 70% to facilitate flexible compression using a Kahl apparatus. The pelletized (compressed) pulp was returned to the mixing reactor, where steam was initiated. The temperature rose to 135-140°C. The total reaction time was 3 hours. After carbamation, the pulp was ground twice in a grinder to improve solubility.

[0136] The cellulose carbamate obtained from the carbamation process was further dissolved for the production of cellulose carbamate fibers by a wet spinning process. The milled, air-dried cellulose carbamate powder was slurried and dissolved in aqueous sodium hydroxide containing dissolved zinc oxide (1.0 wt%) to form a cellulose carbamate dope with a sodium hydroxide content of 6.5 wt% and a cellulose carbamate content of 7.2 wt%. The cellulose carbamate dope obtained from the dissolution process was subsequently filtered using a two-stage backflush filtration process, with a 20 μm filter medium in the second filtration stage. The filtered and degassed cellulose carbamate dope was wet spun using an acidic spin bath optimized for the cellulose carbamate process, containing sodium sulfate, free sulfuric acid, and aluminum sulfate.

[0137] The linear density of the produced stable fiber was 1.25 dtex (ISO 1973). The fiber strength at break of the staple fiber was 2.58 cN / dtex, and the fiber elongation at break was 10.6% (ISO 5079). The results indicate that bleached cellulosic pulp is a suitable material for producing artificial cellulosic staple fibers and filaments.

[0138] The test results show the surprising advantages obtained by subjecting the recycled textile waste material to an ozone treatment carried out in the alkaline range after pulping, as opposed to an ozone treatment in the acid range: a clear increase in brightness is obtained, while the viscosity of the material (pulp) is essentially maintained at its initial level, i.e., no significant decrease in viscosity is observed.

Claims

1. A method for treating cellulosic waste material comprising: providing a cellulosic waste material containing a coloring substance, such as a color pigment, a dye, a colorant, and combinations thereof; pulping the waste material to produce a cellulosic pulp; and decolorizing the pulp with ozone under alkaline conditions; wherein the cellulosic waste material comprises greater than 50% by weight of a textile waste material comprising cellulose.

2. the cellulosic waste material recycled paper containing cellulose or lignocellulose, recycled paperboard containing cellulose or lignocellulose, and Combinations of these, 10. The method of claim 1, further comprising a cellulosic waste material selected from:

3. 3. The method of claim 1 or 2, wherein the cellulosic waste material comprises, consists of, or consists essentially of regenerated cellulosic waste material, such as recycled pre-consumer or post-consumer or industrial waste, or a combination thereof.

4. 4. The method of any one of claims 1 to 3, wherein the cellulosic waste material is mixed colored textile waste comprising cotton fibers or other natural fibers, regenerated cellulose fibers, cellulosic derivative fibers, or combinations thereof.

5. 10. The method of any preceding claim, wherein the cellulosic waste material comprises or consists of a mixed colored polycotton material.

6. 10. The method of any of the preceding claims, wherein the cellulosic waste material is subjected to a mechanical treatment prior to pulping.

7. 10. A method according to any preceding claim, wherein the cellulosic waste material is subjected to an acid treatment and an alkaline treatment, preferably in that order, prior to the ozone decolorization step.

8. 10. The method according to any of the preceding claims, wherein the treatment step immediately preceding the ozone decolorization is carried out under alkaline conditions and the treatment step immediately following the alkaline ozone decolorization is carried out under alkaline conditions.

9. 10. The method of any preceding claim, comprising decolorizing the pulp using ozone by decomposing dyes, colorants and / or pigments in the pulp or removing them from the pulp.

10. 10. The method of any preceding claim, comprising decolorizing the pulp without essentially degrading the cellulose polymer.

11. 10. The method of any of the preceding claims, comprising carrying out the ozone bleaching such that the intrinsic viscosity of the cellulose of the pulp, determined by ISO 5351, decreases by no more than 15%, preferably less than 10%, during the bleaching.

12. 10. A method according to any preceding claim, wherein the decolourisation with ozone is carried out by ozonating the pulp in an aqueous medium, the initial pH of said medium being typically above 8 during ozonation, preferably between pH 10 and 13, and preferably the final pH of said medium after ozonation being above 7.

13. 10. A method according to any of the preceding claims, wherein decolorization with ozone is carried out by ozonating the pulp in an aqueous medium at a temperature in the range of 45 to 95°C, preferably 60 to 85°C.

14. 10. The method according to any of the preceding claims, wherein the ozone dosage in the decolorization is in the range of 0.5 to 30.0 kg / BDT, such as 0.5 to 12 kg / BDT or 1 to 10 kg / BDT, preferably 2.0 to 6.0 kg / BDT.

15. 10. A method according to any of the preceding claims, wherein after or before the ozone decolourisation step, the pulp is subjected to one or more bleaching stages, in particular at least one stage using hydrogen peroxide under alkaline conditions.

16. 10. The method of any preceding claim, wherein the bleached pulp has a CIE whiteness, as determined by ISO 11475:2017, of 80 or more, such as at least 78, such as at least 82, for example from 84 to 98.

17. 10. The method according to any of the preceding claims, wherein the pulp is subjected to ozone treatment in an aqueous medium at a consistency of 1 to 25 wt.%, such as 1 to 50 wt.%, in particular 5 to 15 wt.%.

18. 10. A method according to any of the preceding claims, wherein the pulp, after bleaching, is dewatered to a moisture content of less than 50% by weight, preferably less than 20% by weight.

19. 10. A method according to any of the preceding claims, wherein the pulp is dried to a moisture content of less than 20% by weight, in particular about 10% by weight, and is preferably provided as a bale of dried pulp sheet.

20. 10. The method according to any of the preceding claims, wherein the dye is selected from organic dyes such as azo compounds, azomethines, anthraquinones, triarylmethanes, quinolines, dioxazines, stilbenes, amines, alum or compounds containing sulfonate groups.

21. Bleached cellulosic pulp obtainable by the method according to any one of claims 1 to 20.

22. 22. The bleached cellulosic pulp of claim 21, having an average intrinsic viscosity of 220 to 390 ml / g and a CIE whiteness of 78 or greater, for example in the range of 78 to 95, such as 80 to 90.

23. 23. Use of the bleached textile pulp according to claim 21 or 22 in a process for producing cellulose carbamate.

24. 24. The use according to claim 23, wherein the bleached cellulosic pulp after bleaching is mixed with urea to obtain a mixture, and the mixture is heated to 130-150°C to react the cellulose with the urea to form cellulose carbamate, and optionally the cellulose carbamate is used for the production of staple fibers, filament yarns, filament bundles, short cuts, flock or film.

25. 23. Use of the decolorized cellulosic pulp according to claim 21 or 22 in the production of viscose or lyocell or in the process of making nonwoven products.

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