Method for treating cellulosic waste material and decolorizing material obtained thereby

Abstract

A method of treating cellulosic waste material, decolorized cellulosic pulp and uses thereof. The method includes providing a cellulosic waste material containing colouring substances such as color pigments, dyes, colorants, and combinations thereof, pulping the 5 waste material to produce a cellulosic pulp, and decolorizing the pulp with ozone under alkaline conditions. By subjecting recycled textile waste material to ozone treatment in the alkaline range after pulping, excellent whiteness of the pulp is achieved without significantly compromising 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, mixed-color cellulosic waste. The present invention also relates to decolorized cellulose pulp itself and its use in a process for producing molded articles such as regenerated cellulose products or cellulose derivatives such as cellulose carbamates. Background Art

[0002] Cellulose is the most abundant renewable organic material on earth and excels in fiber applications. Despite the environmental challenges of the viscose process, it remains the most widely used technology for manufacturing regenerated cellulose fibers and films. Typically, in the viscose process, dissolving cellulose pulp produced from virgin materials is used as the starting material.

[0003] There is a need to develop simpler and more sustainable production processes, in particular to provide processes that allow for expanded applications of recycled cellulosic materials.

[0004] EP3529282B1 and WO2018104330A1 disclose a process for recycling cellulosic textiles. It discloses treating cellulose with oxygen in an alkaline step in the pH range of 9-13.5 under alkaline conditions and bleaching the material with ozone under acidic conditions of pH below 6.

[0005] SE2051513A1 discloses a method for ozone bleaching of pulp formed from recycled cellulosic textile material. The method comprises adding at least one acid to reduce the pH of the pulp and performing ozone bleaching at low pH.

[0006] EP3221511B1 provides a process for producing treated pulp to increase the overall process yield in a dissolving process. The method comprises the step of contacting the pulp with ozone under alkaline conditions in order to modify the yield of conventional pulping or dissolving cellulose production.

[0007] FI 20175376A1 and Määttänen et al. Cellulose (2021) 28:3869–3886 disclose a process for treating textile-based materials, typically textile-based waste materials. Summary of the invention

[0008] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0009] According to a first aspect of the present invention, there is provided a method for treating recycled cellulosic waste material, comprising the steps of providing a cellulosic waste material containing a color pigment, a dye, a colorant or a combination thereof, pulping the waste material to produce a cellulose pulp, and decolorizing the pulp with ozone under alkaline conditions.

[0010] According to a second aspect of the present invention, there is provided a decolorized cellulose pulp.

[0011] According to a third aspect of the present invention there is provided the use of a bleached textile pulp in a process for producing cellulose carbamate.

[0012] By means of the present invention, considerable benefits are obtained. Surprisingly, by subjecting recycled cellulosic waste material containing coloring matter to an ozone treatment carried out under alkaline conditions, effective decolorization of the material can be achieved without compromising the mechanical properties of the cellulosic material. As shown in tests, the whiteness of the material treated as described herein is significantly improved compared to material subjected to ozone treatment under acidic conditions, without substantial degradation of the molecular chains.

[0013] The present invention provides a simple, easy to use, inexpensive treatment method that can be industrially applied under moderate conditions. In embodiments of the present invention, cellulose is effectively removed from non-cellulose elements of mixed fiber textiles. The treatment can be carried out using existing infrastructure (including ozonation equipment such as ozone generators, reactors and stirrers), for example, it can be carried out in pulp mills. The cellulose obtained is easy to further chemically treat, such as carbamate, and is generally suitable for dissolution in industrial processes such as viscose and lyocell processes.

[0014] Other features and advantages will be apparent from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a graph of CED viscosity and whiteness versus pH for two groups of samples treated with ozone using different ozone loadings. DETAILED DESCRIPTION

[0016] Unless otherwise stated herein or clear from the context, any percentages mentioned herein are expressed as weight percentages based on the total weight of the corresponding composition.

[0017] Unless otherwise stated, the properties experimentally measured or determined herein are measured or determined at room temperature. Room temperature is 25°C unless otherwise stated.

[0018] Unless otherwise stated, properties that have been experimentally measured or determined herein were measured or determined at atmospheric pressure.

[0019] It must also be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless otherwise indicated.

[0020] As used herein, the term "about" refers to a value within ± 5% of the stated value.

[0021] In this context, the term "CED viscosity" stands for the dynamic viscosity measured according to standard ISO 5351:2010, which measures and calculates the viscosity of the cellulose part of a material by filtering a cellulose solution (also known as "ISO 5351, modified"). This viscosity is measured in ml / g.

[0022] In this context, "whiteness" stands for "CIE whiteness", which can be determined by ISO 11475:2017. ISO11475:2017 specifies a whiteness index and a measurement method that utilizes diffuse lighting, where the light source is configured as CIE standard illuminant D65. CIE D65 is an outdoor daylight illuminant with a defined spectral power distribution that approximates average midday sunlight. Whiteness measures the reflection of all wavelengths of light in the visible spectrum. The higher the measured whiteness level (0-100 scale, excluding whitening agents), the whiter the recycled cellulose appears. Therefore, whiteness is an essential parameter for cellulose textile pulp, while the ISO brightness, which is commonly used in the pulp industry, does not clearly reflect the quality requirements of textile pulp.

[0023] In this context, the term "cellulosic material" represents a material having a cellulose content. Typically, the content is at least 10 wt% of the material, in particular, the cellulosic waste material contains at least 20 wt%, such as at least 30 wt%, or at least 40 wt%, or at least 50 wt%, or at least 60 wt%, or at least 70 wt% 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.

[0024] In this context, the term "waste" generally refers to discarded or abandoned material, i.e. material that has not been utilized (e.g. unsold textiles, pieces of cloth or other material left after cutting), or material that is no longer used or available for its original purpose, and also includes cellulose powder generated during the processing of textile waste. In this context, the term "recycled", when used in conjunction with cellulosic material, refers to material that has been recovered and returned for further processing after being discarded or abandoned.

[0025] In this context, the term "pre-consumer waste" represents waste that is collected after production (e.g. at a factory) but before it reaches the final consumer.

[0026] In this context, the term “post-consumer waste” represents waste generated at all levels after the final consumer has used the finished product.

[0027] In this context, "paper" generally refers to a fibrous material in the form of a web or sheet with a grammage of about 10 to about 120 g / m 2 , usually about 20 to 115 g / m 2 or 30 to 110 g / m 2 , such as 60 to 110 g / m 2 "Paperboard" (also called "cardboard") means a fibrous material in web or sheet form, for example formed into blanks or packaging, having a grammage ranging from about 120 to about 750 g / m 2 , usually about 130 to 700 g / m 2 , or 150 to about 500 g / m 2 , but these are not absolute limitations.

[0028] The fibrous material of paper or paperboard may comprise or consist of mechanical, semi-mechanical or chemical pulp or a combination thereof.

[0029] In this context, the abbreviation "BDT" stands for bone dry (metric) tons, and "adt" stands for air dry (metric) tons.

[0030] Typically, the method for treating a cellulosic waste material comprises, in a first step, providing a cellulosic waste material or a combination of cellulosic waste materials. After an optional mechanical treatment, the material is subjected to pulping, in particular chemical pulping, in a second step. Such pulping is typically carried out at a temperature below 140°C, for example at a temperature of 130°C or lower, such as 120°C or lower, in particular 110°C or lower, 105°C or lower or 100°C or lower. For example, acidic pulping may be carried out at a temperature of about 60 to 95°C, while alkaline pulping is typically carried out at a temperature of at least 95°C.

[0031] In one embodiment, the chemical pulping step comprises contacting the cellulosic waste material with an acid and a base. Specifically, the material is subjected to a series of process steps in which the material is contacted with an acid and a base, respectively. Typically, the material is first contacted with an acid and then with a base.

[0032] In one embodiment, if only cellulosic textile waste material is used, the pulping step specifically refers to an acid-base pretreatment process of contacting the textile waste material with acid and base, respectively, instead of the kraft process used in wood pulping.

[0033] In the third step (after the acidic and / or alkaline treatment), the pulp obtained is ozonated under alkaline conditions to decolorize the pulp. The ozone treatment is carried out at high or medium consistency of the pulp, using ozone gas at atmospheric pressure, or correspondingly at a pressure of 2 to 15, typically 7 to 11 bar (g).

[0034] In one embodiment, after ozone treatment, the pulp is neutralized, or optionally at least part or all of the excess alkali is removed by washing with water, and the washed material is dewatered to reduce its moisture content.

[0035] In one embodiment, after ozone treatment, the pulp is washed on a filter and then subjected to carbamation.

[0036] In one embodiment, after or before the ozone treatment, the pulp is subjected to one or more bleaching stages, in particular under alkaline conditions using oxygen in at least one stage.

[0037] In one embodiment, after or before the ozone treatment, the pulp is subjected to one or more bleaching stages, in particular under alkaline conditions using hydrogen peroxide (optionally in combination with oxygen) in at least one stage.

[0038] The material obtained can be used as conventional dissolving pulp for making mouldings, for example by the viscose, lyocell or urethane processes.

[0039] Next, starting materials and processing steps and products according to various embodiments will be discussed in more detail.

[0040] The starting material for the process includes a cellulosic material containing a coloring substance. Such a material is capable of imparting color to the material or to a portion thereof. The coloring material may be partially or fully colored. The color may be imparted to the surface of the material or to the entire material.

[0041] In a first embodiment, the starting material comprises or consists of recycled paper comprising 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 or post-consumer waste or industrial waste or a combination thereof.

[0042] Examples of such recycled materials include mixed paper and paperboard grades, old or used corrugated containers, old or used newspapers and magazines and advanced deinking and pulp substitutes. Industrial waste from the paper and pulp industry also includes paper and paperboard rolls, paper and paperboard bobbins and paper and paperboard waste and zero fibers.

[0043] Cellulosic or lignocellulosic materials generally contain fibrous materials formed from cellulose, lignin and potentially hemicellulose. Naturally, lignocellulosic materials also contain extractives (organic molecules) and metals and silica and other inorganic substances. In addition to coloring substances (including coloring pigments, inks and dyes), industrially processed materials such as paper or paperboard materials often contain residues of inorganic or organic substances, such as pigments, fillers, sizes and other additives. The fibrous material of recycled paper or paperboard can be bleached or unbleached.

[0044] Different coloring substances have different properties. Generally speaking, inks, especially printing inks, are intended to permanently change the coloring of an item (usually paper), and they may also change the texture of the item. Inks may bleed, but are generally expected to stay roughly where they are applied, which is important for being able to write clearly. Dyes are also expected to permanently change the coloring of an item (usually fabric), but not the texture of the item. Dyes generally wet out the material and spread.

[0045] Typically, colored paper or paperboard materials include sheets or threads or fragments of cellulosic or lignocellulosic material containing coloring pigments or dyes provided to impart to the original material colored areas, for example in the form of graphic logos, text or symbols. Such colored areas may be imparted to the material by printing or other graphic techniques. The colored areas of paper or paperboard are typically present on the surface of the material or on a sheet of the material.

[0046] In one embodiment, the recycled paper or recycled paperboard material is subjected to mechanical treatment involving removal of ash and impurities, deinking, washing and / or refining. In addition, there is usually an acid treatment, by which the material is washed and inorganic substances such as metals are removed, and the viscosity and polydispersity of the polymer are adjusted.

[0047] Delignification pulping or cooking is performed before ozone decolorization. Processing may include alkaline treatment using hydroxide or carbonate compounds to remove lignin, especially hemicellulose. During the delignification and pulping process and other pretreatments required to purify the material suitable for textile use, the degree of polymerization of recycled paper or paperboard materials tends to decrease. If the degree of polymerization is reduced to an unnecessarily low level due to the treatment, the recycled material cannot be used as a raw material. Therefore, it is particularly preferred to carry out ozone decolorization under alkaline conditions where the degree of polymerization remains relatively intact.

[0048] In a second particularly preferred embodiment, the material comprises, consists of, or consists essentially of a cellulose-containing textile waste material.

[0049] In one embodiment, recycled textile waste comprises a majority of the material, for example, greater than 50 wt % and up to 100 wt % of the recycled cellulosic material comprises recycled textile waste.

[0050] In one embodiment, the cellulosic waste material comprises more than 50wt%, 60wt%, 70wt%, 80wt%, 90wt% or 95wt% of the textile waste material comprising cellulose, calculated from the total weight of the cellulosic waste material. In a preferred embodiment, 100wt% of the cellulosic waste material comprises textile waste material.

[0051] In one embodiment, the material comprises, consists of, or consists essentially of a combination or mixture of the above materials.Thus, the material may include both textile waste and recycled paper and / or cardboard.

[0052] Recycled cellulosic waste can include pre- or post-consumer waste or industrial textile waste, such as work clothes, rags or towels. Residual (pulp) fibers or fines or rejects from pulping processes or outlets, and can include waste collected from a variety of sources.

[0053] In the present context, the terms "pre-consumer waste" and "post-consumer waste" apply equally to cellulosic waste comprising or consisting of paper and paperboard materials and to cellulosic waste comprising or consisting of textiles.

[0054] Examples of post-consumer textile waste include clothing and household items that have been discarded or not used for any reason. For example, such waste includes clothing or household items that have been worn, damaged or no longer used.

[0055] In one embodiment, the recycled cellulosic waste includes or consists of textiles in municipal solid waste (also abbreviated as "MSW"). Such waste is formed, for example, of discarded or used clothing, footwear, headwear, carpets, and other household textiles (including towels, sheets, blankets, and pillowcases), but is not limited thereto.

[0056] In one embodiment, the recycled cellulosic textile waste material comprises or consists of melange textile waste comprising cotton or other natural fibers, regenerated cellulose fibers or cellulose derivative fibers.

[0057] In one embodiment, the mixed color textile waste specifically includes textile colorants, such as color pigments, dyes, colorants and combinations thereof, especially dyes.

[0058] Specifically, mixed-color textile waste typically includes a combination of textile materials obtained from multiple sources: recycled textiles containing natural fibers; and natural plant fibers, which include seed fibers, such as cotton and kapok; bast fibers, such as hemp, jute, kenaf, ramie, abaca and linen (flax); leaf fibers, such as abaca, sisal, bromelain and banana; and fruit fibers, such as coconut husk.

[0059] The waste material comprises, in addition to the cellulosic fraction, non-cellulosic material. Typically, the non-cellulosic material comprises about 1 to 50 wt%, such as 2 to 40 wt%, such as 2.5 to 20 wt% of the cellulosic waste material.

[0060] Non-cellulosic fibers consist mainly of polyesters such as poly(ethylene terephthalate), but textile waste also frequently includes fibers of other thermoplastic materials such as polyamides, polyurethanes, polyether-polyurea copolymers (e.g., elastane), polyisoprene, and polyethylene / polypropylene.

[0061] 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).

[0062] In one embodiment, the mixed fiber textile material is a heathered, mixed fiber textile material.

[0063] Typically, cellulosic textile waste materials also contain non-textile or non-fiber or non-cellulose elements, such as labels and certain printed matter, metal elements (ferrous or non-ferrous), rubber elements, leather elements and plastic elements (such as buttons and zippers). It is best to remove these elements before further processing the material.

[0064] According to one embodiment, when desired, the cellulosic (textile) waste material is first subjected to one or more mechanical treatment steps, wherein the material is mechanically broken down to open up structures in the material. The material can be broken down using various mechanical devices (such as in a pulper) to provide particles with a size of 0.01 to 1.00 cm 2 Fragments of decomposed cellulosic material within the region or even smaller fragments corresponding to individual fiber units.

[0065] In one embodiment, the material is mechanically refined and broken down to open the textile structure in the material by chopping, grinding, pulverizing or milling the textile material. In another embodiment, the textile material is broken down to open the yarn structure in the material by chopping, grinding, pulverizing or milling the material.

[0066] Typically, fibers are provided in sizes up to 40 mm.

[0067] In one embodiment, the material fragments are broken down into individual particles with a fiber length of ≤25 mm, preferably ≤10 mm, suitably 1 to 6 mm in length. The diameter of the fibers may be less than 0.1 mm, for example less than 0.05 mm, such as 10 to 50 μm, for example about 15 μm. Breaking down the material into these sizes provides the fibers with a surface area of ​​optimal size for contact with the liquid in the subsequent chemical step.

[0068] In one embodiment, the recycled cellulosic material is sorted to provide a mixed fiber material comprising cellulose. In one embodiment, the cellulose content of the mixed fiber textile material is 50 wt% or more of the material, suitably 60 wt% or more of the material, in particular 70 wt% or more of the material, preferably 80 wt% of the material, most preferably, the mixed fiber textile material comprises 80 wt% cellulose.

[0069] In one embodiment less than 20% by weight (on a dry weight basis) of the non-cellulosic fibres (suitably the non-cellulosic fibre component) are polyester.

[0070] In one embodiment, the recycled cellulosic material is subjected to one or more chemical treatment steps, optionally after mechanical pretreatment to open the structure.

[0071] 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 a fiber bed.

[0072] In one embodiment, the acid acts on the cellulose fibers to adjust the degree of polymerization of the cellulose, in particular to reduce the degree of polymerization. In one embodiment, the degree of polymerization 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, in particular 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, in particular 300 to 350 ml / g) in terms of viscosity.

[0073] In one embodiment, the acid further acts on the monomeric non-cellulosic and inorganic and organic components, thereby dissolving said components for washing out in a subsequent step.

[0074] When measuring the viscosity of a cellulosic material, only the cellulosic portion is considered; the non-cellulosic portion has no effect on the viscosity.

[0075] 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, and acidic side streams from other industrial processes including pulp mill wastewater, and mixtures thereof. The mixture may include a combination of mineral acids, a combination of organic acids, a combination of peracids, or a combination of any mineral acid, organic acid, and peracid (whether organic or inorganic).

[0076] In a preferred embodiment, the recycled cellulosic material is contacted with H2SO4.

[0077] 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 the acid cook is in the range of 1 to 25 g / l. Various acids provide various benefits, for example oxidizing acids, such as peracids improve dye removal, and strong mineral acids improve acid hydrolysis. On the other hand, organic acids are biodegradable and are more environmentally friendly as long as sulfate emissions are kept at zero.

[0078] In another embodiment the cellulosic material is contacted with the acid at a temperature below 140°C, such as 50 to 135°C, preferably 60 to 120°C, especially 65 to 100°C, such as 60 to 95°C, suitably >70°C.

[0079] In another embodiment, the decomposed cellulosic material is contacted with the acid for 10 to 600 minutes, such as 30 to 240 minutes, preferably 30 to 120 minutes, typically 40-90 minutes.

[0080] In addition to reducing the degree of polymerization of the cellulose fraction, the first chemical step also has the benefit of dissolving metals. Once the metals are dissolved, they can be washed out of the pulp in a subsequent washing step. In one embodiment, the first chemical step also includes dissolving other acid-soluble impurities present in the decomposed textile material so that they can be washed out of the pulp.

[0081] The acid treated fibers are then contacted with an alkali in a second chemical step. Contact with the alkali washes the non-cellulose components from the pulp to provide a pulp comprising substantially purified cellulose fibers, although small amounts of non-cellulose may remain.

[0082] In one embodiment, the acid treated fibers are washed with water prior to contacting with the base in the second chemical step. In one embodiment, the acid treated fibers are pressed prior to contacting with the base in the second chemical step.

[0083] In another embodiment, the acidic cooking liquor in the first chemical step is replaced by an alkaline cooking liquor in the second chemical step.

[0084] In another embodiment, the fiber pulp obtained by the treatment is pressed and washed before the next processing step.

[0085] In one embodiment, the second chemical step comprises contacting the acid treated fibers with a base selected from NaOH, KOH, organic (nonionic) superbases and mixtures thereof. In another embodiment, the base selected from NaOH, KOH, organic (nonionic) superbases and mixtures thereof is contained in a sulfur-containing cooking liquor from a conventional pulping process. In a particular embodiment, superbases are effective catalysts for hydrolyzing non-cellulose such as polyesters. In one embodiment, NaOH is used, optionally contained in a sulfur-containing cooking liquor from a conventional pulping process. One benefit of using NaOH is that it is readily available in a pulp mill. In one embodiment, the initial charge of base is in the range of 25 to 100 g / l, measured after neutralizing any acid residues remaining in the acid treated material.

[0086] Contact of fibres with alkali produces several effects. Firstly, non-cellulosic components (e.g. polymeric non-cellulosic components and keratin, including wool, hair and skin residues) are washed out of the cellulose and secondly, the cellulose swells, thereby increasing the accessibility of reagents in subsequent processes.

[0087] In one embodiment, the acid treated fiber is contacted with the base at a temperature of 95 to 140°C or less, typically 100 to 130°C, suitably 105 to 120°C or about 110°C.

[0088] In another embodiment, the acid-treated fiber is contacted with the base for a period of time ranging from 30 minutes to 240 minutes, typically from 60 minutes to 180 minutes, and preferably from 60 minutes to 120 minutes.

[0089] In one embodiment, after the above-mentioned alkaline pulping stage, the CED viscosity of the textile raw material is in the range of 500 to 2500 ml / g, preferably 600 to 1000 ml / g, more preferably 700 to 900 ml / g, in particular 800 ml / g, and the final viscosity after both the acidic step and the alkaline step is 200 to 550 ml / g, preferably 250 to 500 ml / g, suitably 250 to 450 ml / g, in particular 300 to 350 ml / g.

[0090] The acid and alkaline treatment steps are carried out in suitable equipment. One type of reactor for carrying out the acid and alkaline treatments includes a mixing reactor in which the fibers are mixed with a cooking liquor. Another type of reactor is a digester, either a single digester or a group of digesters, in which a slurry formed of fibers and a cooking liquor (i.e., an acidic or alkaline solution) is circulated by pumping.

[0091] In this context, a "digester" is understood to be a container, pressurized or not, in which a fiber suspension is held for a long time in order for the desired chemical reaction to occur. The feed may be to the top or bottom of the container, and the discharge of the fibers may be enhanced by a discharge device. Such a digester may be equipped with an internal screen to displace the liquid while retaining the fibers within the digester. The vessel may have both vertical and horizontal configurations and may be operated in a batch or continuous process.

[0092] Another example of a reactor train in which the slurry can be circulated is a medium consistency loop. A screw-type continuous reactor is also suitable for use in embodiments. In one embodiment, the slurry is circulated in the reactor by pumping.

[0093] In this context, "medium consistency" is understood to describe a thick suspension of fibers, water and chemicals, which can still be transported by pumps designed for this purpose. Typically, such a suspension may contain 3-15% fibers, more often 6-12% fibers, in the form of pulp or pulp from recycled cotton. Medium consistency can also be understood to describe a thick suspension of fibers, water and chemicals, which can still be transported by pumps designed for this purpose. Typically, such a suspension may contain 3-15% fibers from recycled cellulose, more often 6-12% fibers.

[0094] In the present context, "high consistency" is understood to mean a consistency that is greater than "medium consistency".

[0095] In one embodiment, when operating at temperatures below or up to 100°C, such as during acidic treatment, a non-pressurized vessel is used. In one embodiment, when operating at temperatures above 100°C, such as during alkaline treatment (see below), a pressurized vessel is used.

[0096] After the pulping step, the pulp is subjected to an ozone step in which the pulp is contacted with ozone under alkaline conditions in order to decolorize the pulp using ozone, for example by decomposing or removing dyes, colorants and / or pigments in the pulp.

[0097] If desired, the pulp can be washed after the pulping step with water or, preferably, with an alkaline filtrate.

[0098] In a preferred embodiment, the process steps immediately preceding the ozone decolorization are carried out directly (ie without any intervening or intermediate chemical treatment steps) under alkaline conditions. In one embodiment, the pulp obtained from the alkaline treatment is subjected to the ozone treatment without an intermediate washing step.

[0099] The ozone treatment is carried out by ozonating the pulp in an aqueous medium. Typically, the pulp is dispersed in an aqueous medium, which preferably contains at least some alkaline agent to keep the pH in the alkaline range. The consistency of the pulp slurry is preferably 1 to 50 wt%, in particular 1 to 25 wt% or 1 to 15 wt%. Therefore, the pulp can be subjected to ozonation at a high or medium consistency of the pulp, suitably, ozonation is carried out at a medium consistency. A consistency in the range of 5 to 15 wt% is particularly preferred. In high consistency decolorization, the consistency of the pulp is at least 30 wt%, suitably in the range of 35-45 wt%.

[0100] Ozonation of the pulp slurry is preferably carried out with mixing of the slurry to facilitate contact of the cellulosic material with the ozone.

[0101] The ozone dosage in the bleaching is in the range of 0.5 to 30.0 kg / BDT, for example 0.5 to 15 kg / BDT or 1 to 12 kg / BDT or 1.5 to 10 kg / BDT, preferably about 2.0 to about 6.0 kg / BDT. The ozone treatment temperature of the pulp can vary within a wide range. It is preferred to operate at a temperature of the aqueous ozonating medium in the range of 45-95° C., preferably 60-85° C.

[0102] During the ozonation process, the initial pH of the aqueous medium is generally above 8, preferably between 10 and 13. As the treatment proceeds, the pH of the pulp generally decreases. It is preferred to keep the pH in the alkaline range during the ozonation, in particular during the entire ozonation period. If necessary, an alkaline agent can be added to adjust the pH. Preferably, the ozonation of the pulp is carried out under conditions where the final pH of the aqueous medium at the end of the ozonation is above 7. The initial pH is preferably adjusted with a sodium hydroxide dosage of 0.1 to 5 kg / BDT, for example 0.2-4 kg / BDT.

[0103] In one embodiment, sodium hydroxide is used to achieve alkaline conditions with an aqueous medium dosage of NaOH ranging from about 0.01 to 0.5 wt%, such as about 0.05 to 0.25 wt%, calculated from pulp (BDT).

[0104] The alkaline agent used may be the same as that discussed above in the alkaline treatment step.

[0105] Typically, the ozone acts immediately on the substrate. In some embodiments, ozone gas is fed into contact with the pulp for up to 2.5 hours.

[0106] In one embodiment, after the ozone decolorization step and optional peroxide and / or oxygen bleaching, the final CED viscosity is 200 to 550 ml / g, preferably 220 to 390 ml / g, suitably 250 to 350 ml / g, especially 300 to 350 ml / g. These intrinsic viscosities correspond to an average degree of polymerization (DP) of cellulose carbamate of 254 to 776, preferably 325 to 669, suitably 325 to 622, especially 397 to 471. DP is calculated using the following formula: DP 0.905 = 0.75 [η] (usually known from the literature).

[0107] After ozonation and an optional dewatering stage, a decolorized pulp is obtained, the CIE brightness of which exceeds 77, for example in the range of 78-95, preferably in the range of 80-90, as determined by ISO 11475:2017. As demonstrated by the experimental data given to illustrate some particularly advantageous embodiments, the decolorized cellulose 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, in particular at least 82, for example at least 84. In one embodiment, the CIE brightness is in the range of 78-95, typically 80-90.

[0108] Surprisingly, ozone treatment in the alkaline range does not significantly reduce the viscosity of the material; in particular, the viscosity loss is smaller than that obtained with ozone under acidic conditions.

[0109] It appears that, compared to the use of ozone in bleaching, ozone in the decolorization process of colored cellulosic waste will act on the colorants and coloring pigments and other coloring components by oxidation and achieve a major decomposition of the colorants and coloring pigments rather than the cellulosic material itself. Therefore, working under alkaline conditions can achieve excellent decolorization results while maintaining high viscosity.

[0110] In addition, there are several other benefits to using ozone to decolorize waste materials. Ozonation reacts quickly. Ozone appears to break the conjugated chains or double bonds of the dye molecules that provide the color. Organic dyes are degraded without generating large amounts of sludge or residues that require further treatment. The dye's bond to the cellulose may be broken, so no residue remains on the fiber. In fact, ozone appears to have good selectivity for the coloring components, while being less reactive with carbohydrate structures.

[0111] In one embodiment of the present technology, the degree of polymerization of a cellulosic fiber material that may be recycled colored cellulosic fiber raw material for textiles is adjusted in an acidic stage, while ozone is used to bleach the fibers in an alkaline stage.

[0112] The above discussion regarding the effects of ozone on colorants and coloring pigments and other coloring components of cellulosic materials represents only possible explanations and theories, and the present technology is not limited to the explanations and theories proposed.

[0113] After the ozone treatment, in one embodiment, the pulp is subjected to washing. By washing, alkali and (usually) colorants and coloring pigments and other coloring components can be removed.

[0114] In one embodiment, the ozone treated pulp is subjected to oxygen treatment, chlorine dioxide treatment, or peroxide treatment, or a combination thereof.

[0115] In one embodiment, oxygen bleaching is performed on the pulp that has not been subjected to neutralization after the ozone treatment. Any oxygen treatment can be combined with an oxidative alkaline treatment in an alkaline step. In one embodiment, the oxygen bleaching step (as an alternative or in addition to post-treatment) is performed before ozone decolorization.

[0116] The ozone treatment may also be optionally followed by peroxide oxidation under alkaline conditions, optionally in combination with oxygen bleaching before or after the peroxide oxidation. Thus, in one embodiment, the peroxide oxidation is performed on a pulp that has not been subjected to neutralization and / or washing after the ozone treatment. In one embodiment, the ozone treated fibers are pressed prior to contact with hydrogen peroxide.

[0117] In one embodiment, the ozone treated material is optionally washed and hydrogen peroxide bleached under the following conditions: the pulp medium is made alkaline with sodium hydroxide to a sodium hydroxide content in the range of about 0.1 to 1 wt % of dry cellulose. The consistency of the pulp slurry is adjusted to a medium consistency level, such as 8 to 10 wt %, and a dosage of hydrogen peroxide of about 0.4 to 0.75 wt % of dry cellulose is used. Hydrogen peroxide bleaching is carried out at a temperature of about 50 to 90 or 60 to 80 degrees Celsius for 30 to 150 minutes, such as 60 to 120 minutes.

[0118] After the ozonation and latent oxygen and / or peroxide steps, the treated material is dehydrated. In one embodiment, the material is dehydrated to a water content of less than 50%, preferably less than 20%, such as 15 to 5 wt%.

[0119] In one embodiment, a cellulosic textile material is provided having an average intrinsic viscosity of 220 to 390 ml / g and a CIE whiteness in the range of 78-95, such as 80-90.

[0120] The pulp thus obtained can be used for the same purposes as conventional dissolving. Thus, it can be used to make molded products selected from staple fibers, filament yarns, filament bundles, shortcuts, flocks and films. The pulp can also be used for the same purposes as conventional long fiber pulps, for example in nonwoven applications.

[0121] In one embodiment, the treated material, particularly a textile material, is mixed with urea to provide a mixture, and the mixture is heated to a temperature of 130 to 150° C. to react the cellulose with the urea to form cellulose carbamate.

[0122] The obtained material may also be processed into conventional market dissolving pulp, ie dried to a predetermined moisture content of less than 20 wt%, such as about 10 wt%, and preferably cut into sheets and baled, making it suitable for transport to another location.

[0123] Example 1 Recycled mixed color sorted cotton textile waste containing 4.0±2.8% non-cellulose fibers with a CED viscosity of 800±200 ml / g (based on CED viscosity measurement according to a modified version of ISO 5351. The obtained cellulose solution was filtered to measure and calculate the viscosity of the cellulose fraction of the material) was mechanically shredded to break down the fabric structure to form fragments with a fiber size of ≤25 mm. The non-cellulose fibers were mainly polyester, but traces of nylon, isoprene-containing materials (elastics) and polyethylene / polypropylene were also detected.

[0124] 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 a final washing liquid pH of 8.3. The viscosity of the chemically pretreated material was 357 ml / g (ISO 5351, modified) and the brightness was 71.1.

[0125] In the next stage, ozone bleaching is carried out to remove the remaining color traces in the textile fibers while maintaining the textile material viscosity ≥ 300 ml / g after the final bleaching stage. The goal is to keep the intrinsic viscosity drop of cellulose below 15%. The reaction vessel is filled with warm water and the pretreated textile material is dispersed in the reactor to achieve a consistency of 10wt%. The pH is adjusted by adding NaOH. The reaction temperature is 60°C.

[0126] In the first test, the ozone dose was 2.1 kg / adt and the initial pH of the six test points was adjusted with sodium hydroxide solution or with sulfuric acid. The initial pH was 3.5, 5.5, 6.4, 10.7 (NaOH 0.05wt%), 11.5 (NaOH 0.15wt%) and 11.7 (NaOH 0.23wt%). After ozone treatment, the final pH of the test points was 3.1, 4.0, 4.9, 7.2, 9.0 and 10.0, respectively.

[0127] The textile-water slurry samples were washed and the whiteness and viscosity of the samples were measured. Figure 1 Whiteness (ISO 11475) and viscosity (ISO 5351, modified) values ​​are shown as a function of final pH.

[0128] In the second test, the ozone dose was 3.8 kg / adt and the initial pH of the seven test points was adjusted with sodium hydroxide solution or with sulfuric acid. The initial pH values ​​were 3.3, 5.6, 6.9, 10.9 (NaOH 0.05wt%), 11.6 (NaOH 0.16wt%), 11.8 (NaOH 0.22wt%) and 11.9 (NaOH 0.30wt%). After ozone treatment, the final pH of the test points was 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. Figure 1 Whiteness (ISO 11475) and viscosity (ISO 5351, modified) values ​​are shown as a function of final pH.

[0129] As can be seen from the attached figure, at an ozone dose of 2.1 kg / adt, the whiteness of the samples increased from about 76 (CIE WI) to more than 80 (CIE WI) by increasing the pH from the acidic to the alkaline range. For a higher dose (3.8 kg / adt), the increase was greater: the whiteness rose from about 76 (CIE WI) to values ​​in the range of 82% to 84%. Regarding viscosity, under alkaline conditions, a slight decrease in viscosity was observed for both doses. However, the decrease under alkaline conditions was less than that under acidic conditions.

[0130] Example 2 Recycled mixed color sorted cotton textile waste was treated as described in Example 1 and had a CED viscosity of 800 ± 200 ml / g (based on CED viscosity measurement according to ISO 5351, revised edition). The viscosity of the chemically pretreated material was 330 ml / g (ISO 5351, revised edition) and the whiteness was 73.1 (CIE WI). The treated textile raw material was used for decolorization tests.

[0131] Ozone decolorization was performed using a MC loop and a pressure reactor. The loop was first filled with warm demineralized water, and then the shredded textile (290 kg, BD) was poured into the system. Next, the raw materials and water slurry were fed to the pressure reactor. 20 kg / BDT of NaOH was fed to the reactor, the consistency was measured to be 6.6% and the pH was 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 time was 155 minutes. The total ozone charge was 4.6 kg / BDT. After the ozone stage, the ozone was removed by adding 3.9 m 3 Water was used to cool the slurry. The cooled and 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, revised version) and the brightness was 81.5 (CIE WI).

[0132] Next, the ozone bleached textile material was subjected to a peroxide stage. The ozone treated material was pumped to the reactor and the pulp consistency in the pressure reactor was 6.2%. The reaction mixture was heated to a reaction temperature of 80°C and the pH was adjusted to 11.6 with NaOH. The reaction time of the peroxide stage was 60 minutes and the hydrogen peroxide charge was 5 kg / BDT. The viscosity of the resulting bleached pulp was 308 ml / g (ISO 5351, modified) and the brightness was 85.1 (CIE WIE).

[0133] Example 3 Using the decolorized pulp obtained according to Example 2, the carbamation process was carried out as described in Finnish Patents Nos. 112869 and 112795 and International Patent Application Publication No. WO 2021 / 038136 A. Urea was dissolved in water and then added to the pulp to 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 the cellulose carbamate to DP 306, corresponding to a viscosity of 236 ml / g (ISO 5351). After the addition of chemicals, the target dry matter content was adjusted to 70 % to facilitate flexible compaction using a Kahl apparatus. The granulated (compacted) pulp was returned to the mixing reactor and steam was started. The temperature was raised to 135-140 °C. The total reaction time was 3 hours. After carbamation, the pulp was ground twice using a grinder to increase solubility.

[0134] The cellulose carbamate obtained from the carbamate process is further dissolved to produce cellulose carbamate fibers by a wet spinning process. The ground air-dried cellulose carbamate powder is slurried and dissolved in an aqueous sodium hydroxide solution 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 is then filtered using a two-stage backwash filtration process using a 20 μm filter medium in the second filtration stage. The filtered and degassed cellulose carbamate dope is wet spun using an acidic spinning bath optimized for the cellulose carbamate process, which contains sodium sulfate, free sulfuric acid, and aluminum sulfate.

[0135] The linear density of the produced stable fibers was 1.25 dtex (ISO 1973). The breaking strength of the staple fibers was 2.58 cN / dtex and the elongation at break of the fibers was 10.6% (ISO 5079). The results show that decolorized cellulose pulp is a suitable material for the production of man-made cellulose staple fibers and filaments.

[0136] The test results show that subjecting recycled textile waste material to ozone treatment in the alkaline range after pulping has surprising advantages compared to ozone treatment in the acidic range: the brightness increases significantly, while the viscosity of the material (pulp) remains essentially at its initial level, i.e., no significant decrease in viscosity is observed.

Claims

1. A method for treating cellulosic waste material, comprising: - providing cellulosic waste materials containing coloring matter such as color pigments, dyes, colorants and combinations thereof, - pulping the waste material to produce cellulose pulp, and - decolorizing the pulp with ozone under alkaline conditions, Wherein, the cellulosic waste material comprises more than 50 wt % of textile waste material comprising cellulose.

2. The method of claim 1, wherein the cellulosic waste material further comprises a cellulosic waste material selected from the group consisting of: - recycled paper containing cellulose or lignocellulose, - recycled paperboard containing cellulose or lignocellulose, and - A combination of these.

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

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

5. A method according to any one of the preceding claims, wherein the cellulosic waste material comprises or consists of a melange polyester-cotton material.

6. A method according to any one of the preceding claims, wherein the cellulosic waste material is subjected to mechanical treatment prior to pulping.

7. The method according to any one of the preceding claims, wherein the cellulosic waste material is subjected to an acid treatment and to an alkali treatment, preferably in that order, prior to the ozone decolorization step.

8. The method according to any one of the preceding claims, wherein the process step immediately before the ozone decolorization is carried out under alkaline conditions and the process step immediately after the alkaline ozone decolorization is carried out under alkaline conditions.

9. A method according to any one of the preceding claims, comprising decolorizing the pulp using ozone by decomposing dyes, colorants and / or pigments in the pulp or removing them from the pulp.

10. A method according to any preceding claim comprising decolorizing the pulp without substantially degrading the cellulosic polymers.

11. The method according to any one 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 does not decrease by more than 15% during the bleaching, preferably by less than 10%.

12. The method according to any one of the preceding claims, wherein decolorization with ozone is carried out by ozonating the pulp in an aqueous medium, the initial pH of the medium during ozonation being generally above 8, preferably between pH 10-13, and preferably the final pH of the medium after ozonation being above 7.

13. The method according to any one of the preceding claims, wherein the decolorizing with ozone is performed by ozonating the pulp in an aqueous medium at a temperature in the range of 45-95°C, preferably 60-85°C.

14. The method according to any one of the preceding claims, wherein the ozone dosage in the decolorization ranges from 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. The method according to any of the preceding claims, wherein after or before the ozone decolorization step, the pulp is subjected to one or more bleaching stages, in particular using hydrogen peroxide under alkaline conditions in at least one stage.

16. The method according to any one of the preceding claims, wherein the decolorized pulp has a CIE brightness of at least 78, such as 80 or higher, such as at least 82, such as 84 to 98, as determined by ISO 11475:2017.

17. A method according to any one of the preceding claims, wherein the pulp is subjected to ozonation in an aqueous medium having a consistency of 1 to 50 wt%, in particular 1 to 25 wt%, such as 5 to 15 wt%.

18. The method according to any one of the preceding claims, wherein after the decolorization, the pulp is dewatered to a moisture content of less than 50 wt%, preferably less than 20 wt%.

19. The method according to any one of the preceding claims, wherein the pulp is dried to a moisture content below 20 wt%, in particular about 10 wt%, and is preferably provided in the form of bales of dry pulp sheets.

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

21. Decolorized cellulose pulp obtained by the process of any one of claims 1 to 20.

22. Decolorized cellulose pulp according to claim 21, having an average intrinsic viscosity of 220 to 390 ml / g and a CIE brightness of 78 or more, such as in the range of 78 to 95, such as 80 to 90.

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

24. The use according to claim 23, wherein the decolorized cellulose pulp after the decolorization is mixed with urea to provide a mixture, and the mixture is heated to a temperature of 130 to 150°C so that the cellulose undergoes a reaction with the urea to form cellulose carbamate, and optionally the cellulose carbamate is used to make staple fibers, filament yarns, filament tows, chopped fibers, fluff or films.

25. Use of decolorized cellulose pulp according to claim 21 or 22 in a process for producing viscose or lyocell fibers or for making nonwoven products.

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