WO2021006798A1

WO2021006798A1 - Method for dissolving pulp from recycled textile material

Info

Publication number: WO2021006798A1
Application number: PCT/SE2020/050699
Authority: WO
Inventors: Lars Stigsson
Original assignee: Kiram Ab
Priority date: 2019-07-05
Filing date: 2020-07-02
Publication date: 2021-01-14

Abstract

A method for the manufacturing of cellulose dissolving pulp from virgin wood cellulose and crude recycled textile cellulosic material by charging recycled textile material to a brownstock washing step, an oxidative alkaline pulp bleaching step, and/or an acidic pulp treatment step of a kraft or sulfite pulp mill fiberline. Spent chemicals, effluents and/or organic residues from co-processing cellulosic pulps, textile pulp pre-treatment steps, pulp washing steps, pulp bleaching or pulp acidic treatment steps are recycled to the pulp mill chemicals recovery cycle and /or to the secondary effluent treatment plant.

Description

METHOD FOR DISSOLVING PULP FROM RECYCLED TEXTILE MATERIAL

FIELD OF THE DISCLOSURE:

The present disclosure relates to processes for producing dissolving cellulose pulp from recycled cotton and/or viscose textile material in a kraft or sulfite pulp process fiberline.

DESCRIPTION OF RELATED ART:

Research on recycling of textiles and production of new textiles from recycled textile material for example by the viscose or lyocell process have intensified over the last few years. The mechanical properties of the fibers reclaimed from cotton-based waste garments have been found to be good and even superior to traditional lyocell fibers. Haule, Carr, & Rigout, J Text Inst 107:23-33 (2016). It has also been

demonstrated that wood dissolving pulp can be blended with purified dissolving pulp prepared from cotton waste garments and that the resulting mixture can be regenerated into new textile fibers.

Methods for recycling textile material and spinning new fibers in standalone plants are disclosed in for example US 2016/0369456 and WO 2018/197756 and WO 2018/197756.

The known methods for manufacturing of new textile fibers from recycled cotton or viscose textile material by converting it to a dissolving pulp are associated with high investment and operating cost particularly related to new bleaching equipment and recycling of spent chemicals. Accordingly, there is a need for improved and less expensive methods for manufacturing of dissolving cellulose pulp from recycled cotton and viscose textile materials having reduced requirements for installing new process equipment and that recover, recycle, or incapacitate the chemicals involved.

BRIEF SUMMARY OF THE DISCLOSURE: The present disclosure provides advantages over existing methods in the preparation of dissolving pulp from recycled textile material that involves the integration of the textile dissolving pulp manufacturing process with existing kraft or sulfite virgin wood pulping and bleaching. The disclosure provides high quality cellulose dissolving pulp from recycled cotton and/or viscose textiles and virgin wood while reducing capital expenditures and lowering operational costs in comparison to existing manufacturing processes.

A process according to the disclosure may comprise a series of pre-treatment steps performed on recycled cellulosic feedstock to purify and/or depolymerize the material prior to co-processing with virgin cellulose in a bleaching plant. Spent pre- treatment and bleaching chemicals are at least partially recycled to an evaporation plant and concentrate is incinerated in a chemicals recovery boiler or used as feed for a biogas plant. It has surprisingly been discovered that oxidized white liquor originating from the recovery boiler smelt may be used at least partially for any alkaline pre- treatment and/or textile pulp bleaching stages.

BRIEF DESCRIPTION OF THE DRAWINGS:

The elements of the drawings are not necessarily to scale relative to each other, with emphasis placed instead upon clearly illustrating the principles of the disclosure. Like reference numerals designate corresponding parts throughout the several views of the drawings in which:

Fig. 1 is a schematic flowsheet of a kraft dissolving pulp elemental chlorine free (EOF) bleaching plant showing examples of where crude textile pulp may be introduced into the kraft pulp mill fiberline and

Fig. 2 is a schematic of a deinking process for the production of deinked paper pulp, showing the unit operations involved.

DETAILED DESCRIPTION OF THE DISCLOSURE:

Dissolving pulp, also called dissolving cellulose, is a bleached wood pulp or cotton linters that has an alfa cellulose content of greater than 90% and is further defined by quality parameters including hemicellulose content, brightness, and degree of depolymerisation (or Dp Value). Properties of dissolving pulp include a high level of brightness and uniform molecular weight distribution. Dissolving pulp is so named because it is not made into paper but is dissolved in a solvent into a homogeneous solution to make the cellulose polymers accessible. Once dissolved, it can be spun into textile fibers (for example by the viscose or lyocell or cold alkali process), or chemically reacted to produce derivatized celluloses, such as cellulose triacetate, a plastic-like material formed into fibers or films, or cellulose ethers such as methyl cellulose.

In order to obtain a cellulose dissolvable in certain weaker solvents such as sodium hydroxide, the molecular weight (or Dp value, degree of polymerization) of cellulose must be reduced to the Dp range corresponding to 150 - 500 repeating anhydroglucose units in the cellulose polymer chain. Both chemical and mechanical procedures can be used for achieving desired Dp values in a standalone dissolving pulp manufacturing process. According to the present disclosure, these procedures are preferably performed in a kraft or sulfite pulping and bleaching fiber line or alternatively can be performed in a standalone process and then the treated cellulose is added to the kraft or sulfite pulp mill fiberline.

Methods for controlling the Dp include oxidation with oxygen and strong oxidants such as ozone or hydrogen peroxide under alkaline or acidic conditions, enzymatic treatment, hydrolysis (acid or alkaline catalyzed), physical/mechanical degradation (e.g. via the thermomechanical energy input of the processing equipment) such as for example hydrothermal and steam explosion treatments, or combinations thereof. For example, an oxidant alone or together with a metal such as iron or manganese may be introduced into an alkaline oxygen delignification stage to achieve the desired level of depolymerization of cellulose polymers. A chlorine dioxide stage may be operated at harsher acidic conditions. The cellulose feed material may be purified and hydrolyzed to the desired Dp level by treatment with acids such as sulfuric acid. The exact chemical nature of the cellulose and molecular weight reduction method is not critical as long as the average molecular weight in the product dissolving pulp is in an acceptable range (Dp from about 200-550). The chemical and/or mechanical procedures for depolymerisation of the cellulose simultaneously purifies the pulp by removing hemicelluloses and lignin.

The present disclosure is based, at least in part, on the inventor’s discovery that recycled cotton, cotton linters, recycled viscose fibers, and/or waste and leftovers from cotton or viscose textile plants can be co-processed with virgin cellulose pulp in brownstock washers, oxygen delignification units and/or in kraft or sulfite mill

conventional bleaching plants to produce a dissolving pulp, or dissolving cellulose. The final dissolving cellulose pulp product shall have a brightness of at least 85 ISO and may be used for preparation of new textiles by any suitable regenerated cellulose process including cold alkali, viscose, and lyocell processes. Moreover, the effluents containing spent chemicals and organic COD/BOD material from treatment of waste textile can advantageously be recycled to the kraft or sulfite mill chemicals recovery cycle.

Examples of the disclosure may involve integration of recycled cellulosic textile feedstock into a kraft process fiberline. The kraft process, also known as kraft pulping or sulfate process, is a process for conversion of wood into wood pulp, which consists of almost pure cellulose fibers, the main component of many products such a paper and viscose textile garments. The kraft process involves the treatment of wood chips with a hot mixture of water, sodium hydroxide (NaOH), and sodium sulfide (Na₂S), known as white liquor, that breaks the bonds that link lignin, hemicellulose, and cellulose. Brown stock cellulose and spent cooking liquor, the latter called black liquor, are discharged from kraft pulping digesters. The technology entails several steps, both mechanical and chemical steps, starting with various pretreatments of wood, such as chipping and optionally pre-hydrolysis, followed by pulping and bleaching.

The black liquor contains about 15% solids, primarily lignin and spent cooking chemicals, and is concentrated in multiple effect evaporators. After the first step, the black liquor contains about 20-30% solids. The weak black liquor is further

concentrated by evaporation to 65% to 80% solids, which is called heavy black liquor. The heavy black liquor is burned in a recovery boiler to recover the inorganic chemicals for reuse in the pulping process. The recovery boiler also generates high pressure steam which is fed to turbo generators, producing steam at high pressure for use by the mill and for generating electricity.

The molten salts ("smelt") produced in the recovery boiler are discharged and dissolved in a process water known as "weak wash". This process water, also known as "weak white liquor" is composed of all liquors used to wash lime mud and green liquor precipitates. The resulting solution of sodium carbonate and sodium sulfide is known as "green liquor". Green liquor is mixed with calcium oxide, which becomes calcium hydroxide in solution, to regenerate the highly alkaline white liquor used in the pulping process. Formed calcium carbonate is separated and burned in lime kilns to restore fresh calcium oxide.

Examples of the disclosure may involve integration of recycled cellulosic textile material feedstock into a sulfite pulping process. The sulfite process is often used for production of dissolving pulp for use in manufacturing of viscose fiber or cellulose derivatives. The sulfite process produces wood pulp comprising almost pure cellulose fibers by using various salts of sulfurous acid to extract lignin from wood chips in large pressure vessels called digesters. The salts used in the pulping process are either sulfites (SO₃ ^2-), or bisulfites (HSO₃-), depending on the pH. The counter ion may be sodium (Na⁺), calcium (Ca²⁺), potassium (K⁺), magnesium (Mg²⁺) or ammonium (NH₄ ⁺).

The spent cooking liquor from sulfite pulping is usually called brown liquor, but the terms red liquor (when the base is ammonium or magnesium), thick liquor and sulfite liquor are also used (compared to black liquor in the kraft process). Pulp washers, using countercurrent flow, remove spent cooking chemicals and degraded lignin and hemicellulose. The extracted brown liquor is concentrated in multiple effect evaporators.

If magnesium is used as cooking base, it may be recovered by combustion of the brown liquor in a boiler. Formed magnesium oxide fly ash is separated from the boiler flue gas and is dissolved in an aqueous solution forming a scrubbing liquid for capture of sulfurous oxide gases from the boiler. In this way, new sulfite cooking liquor is restored.

All pulping processes produce a brownish pulp still comprising some lignin.

Therefore, the pulps are bleached both for removal of lignin and also to achieve a high brightness. In a modern mill, brownstock (cellulose fibers containing approximately 1-3 % residual lignin) produced by the pulping process is first washed to remove some of the dissolved organic material and then further delignified by a variety of bleaching stages.

Brownstock pulp discharged from the digesters proceeds to washing stages where the used cooking liquors are separated from the cellulose fibers. Examples of the present method may comprise the addition of pre-processed recycled cotton, cotton linters, or recycled viscose fibers or residues from textile processing plants containing these fibers to one or more of the brownstock washing stages. Normally a pulp mill has three to five washing stages in series. Washing stages are also installed after oxygen delignification stages and between bleaching stages. Examples of the present method may comprise the addition of recycled cotton, cotton linters or recycled viscose fiber material to one or more oxygen delignification stages. Pulp washers use counter current flow between the stages such that the pulp moves in the opposite direction to the flow of washing solutions. Washing may include thickening / dilution, displacement, and diffusion processes involving pressure diffusers, atmospheric diffusers, vacuum drum washers, drum displacers, and/or wash presses.

Pulping processes include bleaching steps to remove essentially all of the residual lignin from the cellulose and to increase brightness of the cellulose pulp and may involve bleaching agents such as oxygen, chlorine dioxide and hydrogen peroxide. Modern pulp mills often have an alkaline oxygen delignification stage as a first delignification or bleaching step downstream of the digesters. In a kraft mill, the alkali used in the oxygen delignification step may be oxidized white liquor wherein the sodium sulfide in white liquor is oxidized to thiosulfate or sulfate. Spent alkali from this step may be used for washing the brownstock and may be added to the kraft chemicals recovery cycle for recovery and recycling of sodium and sulfur compounds.

Bleaching of chemical pulps to reach the desired degree of lignin content and pulp brightness is frequently composed of four or more discrete steps, with each step designated by a letter in accordance with Tablel . Textile crude pulp can in practice be introduced upstream any of these bleaching stages in accordance with the present disclosure. Pulp brightness is defined as the amount of incident light reflected from paper under specified conditions, usually reported as the percentage of light reflected, so a higher number means a brighter or whiter paper. The international community uses ISO standards. The pulps produced in accordance with this disclosure should have a brightness level above about 85 ISO and preferably above about 88 ISO.

Downstream the bleach plant, the high brightness dissolving pulp originating from both virgin wood and from textile material may be further processed by drying, baling etc. These latter processing steps are advantageously performed in a co-processing mode wherein virgin cellulose dissolving pulp is co-processed with pulp originating from recycled textiles. The final dissolving pulp product shall have a brightness exceeding 85 ISO, preferably a brightness exceeding 88 ISO and most preferred a brightness exceeding 90 ISO. Spent chemicals and organic residues from textile material treatments are combined and processed in a kraft chemicals recovery system and/or kraft bleaching spent chemicals secondary treatment plant. Heat provided to any pulp co-processing step will come from the same source i.e. steam generators, bark boilers etc. In preferred examples, the textile material is pretreated by mechanical or thermomechanical procedures prior bleaching the textile fibers/material in a kraft or sulfite pulp mill. Such pretreatment preferably comprises a hydrothermal treatment in an aqueous solution at elevated temperature optionally in the presence of additives and an acidic catalyst. Any fibrous polyester material can be separated from cellulosic material for reuse prior to charging hydrothermally treated cellulose to the kraft or sulfite mill bleaching plant. Alternatively, or combined with hydrothermal treatment, the textile may be treated by a steam explosion procedure wherein the textile raw material is treated with hot steam (180°C to 240°C) and optional acidic catalysts under a pressure of from 1 to 3.5 MPa, followed by an explosive decompression to atmospheric pressure. This results in a rupture of the cellulosic textile material rigid structure, changing the starting material into a fibrous dispersed solid. Another pre-treatment procedure may consist of treatment with supercritical C02, wherein the liquid C02 is used as solvent for decomposed colorants.

Effluents from such treatments can, after optional neutralization, advantageously be charged to a kraft mill chemicals recovery cycle or to a pulp mill secondary effluent treatment plant.

Other methods of pre-treating the textile material such as shredding, de colorization and separation of buttons/zippers, non-cellulosic material including polyester polymers etc. may also be performed in the pulp mill area or at entirely other sites.

There are well known procedures for separation of polyester from cellulosic fibers including alkaline hydrolysis ( Negulescu, I. I., Kwon, H., Collier, B. J., Collier, J. R. and Pendse, A. (1998), Recycling cotton from cotton/polyester fabrics, Textile Chemist and Colorist, 30 (6): 31-5.) and in US Pat 3801273 and US Pat 3 317519). While alkaline hydrolysis of polyester and other fossil based fibers may be incorporated in the alkaline treatment steps of the pulp mill in the present disclosure using alkaline liquors present in a pulp mill ( sodium hydroxide, white liquor, green liquor, black liquor) the polyester fraction ( if any) is preferably separated upstream the kraft mill. Any

solubilized polyester in the processing of textile waste in accordance with the present disclosure will be incinerated in the chemicals recovery boiler or end up in secondary sewer treatment plants.

If deemed necessary, de-colorization or deinking of textile material may be performed by standard procedures well known in the art of deinking wastepaper. A variety of different deinking processes are used based on the combination of recovered paper being used and the desired final pulp requirements. Flotation deinking tends to be more selective than wash deinking and thus results in higher yields. The selectivity in both flotation and wash deinking can be dramatically enhanced by using one or more specially designed chemicals. It is well understood that flotation and wash deinking are dominated by different physico-chemical properties and as such the two processes usually require different types of chemical. Fig. 2 illustrates a typical deinking process in a recycled paper mill. The latter bleaching steps can be performed together with final bleaching of cellulose virgin pulp.

Effluents from decolorization or de-inking whether such operations are performed in standalone units or in units processing virgin cellulose pulp are concentrated in evaporators and combusted in a furnace generating molten sodium carbonate or processed in a secondary pulp mill effluent treatment plant. Removal of colorants from recycled cotton material under alkaline conditions is preferred in the practice of the present disclosure.

It has been shown that oxidized sulfur compounds are inert to bleaching of cellulose originating from cotton and viscose so a preferred alkali source for use in an oxygen bleaching or extraction stage of the present disclosure can be oxidized white liquor, which is available in most kraft pulp mills and is commonly used as internal alkali source. In order to liberate cellulosic fibers from the textile material prior to or after any decolorization, the textile material should be disintegrated, for example by shredding or steam explosion treatment.

After the recycled textile cellulose material has been pretreated into a sufficiently pure cellulosic pulp, it may be combined with virgin cellulose pulp and be co-processed together with virgin pulp starting for example at a brownstock pulp washing plant.

Pretreatment of the recycled textile cellulose material may be performed at the mill site or externally or some steps of the pretreatment may be performed externally with others performed at the mill site. The combined pulps can then be bleached by any of the common bleaching sequences practiced such as, for example, by ECF bleaching sequences such as OODEDED or by TCF bleaching sequences such as OPaaP or OZEP (See Table 1 ). In sulfite mills, the O stage may be operated with Mg(OH)₂ as alkali in order to enable effluent integration into a MgO recovery boiler. The dissolving pulps so produced from virgin wood pulp and recycled cellulosic textiles can be produced by joint bleaching treatments in any volume proportions and be dried and baled together.

Viscosity of the final dissolving pulp can be adjusted by selecting the conditions in bleaching or A stages by varying operating parameters such as time, temperature, additives including Mn or Fe addition to OP stages, harsher conditions in an ozone stage etc. Normally the viscosity of the final dissolving pulp is adjusted to a range from about 170 - 1800 ml/g (intrinsic viscosity) or about 200-2000 DP (degree of polymerization) depending on application of the dissolving pulp. The degree of polymerization (DP) for raw materials ranges from 1000 for standard wood pulp to 3500 for cotton fibre, which correspond to a molecular weight range of from 160,000 to 560,000 of the cellulose polymers.

In one example, recycled cotton, cotton linters, recycled viscose fibers, or waste or leftovers from cotton or viscose textile plants is directly or indirectly charged to a sulfite pulp mill bleach plant pulp washing step, ozone bleaching step (Z) and a peroxide bleaching step (P) wherein an effluent from a bleaching step is concentrated by evaporation or membrane filtration.

Fig. 1 is a schematic diagram of a kraft dissolving pulp elemental chlorine free (ECF) bleaching plant showing examples of where crude textile pulp (1 ) suitably may be introduced into the kraft pulp mill fiberline. A crude textile pulp (1 ) comprising

substantially recycled cotton and/or viscose textile fibers is charged to a pulp storage vessel (2) (medium consistency or low consistency pulp storage) upstream the fiberline screenroom. The crude textile pulp (1 ) consistency may vary dependent on upstream treatments (disintegration, swelling/treatment in alkali, hydrothermal treatment etc.). The crude cellulose pulp (1 ) preferably comprises at least 3 % by weight recycled textile material. Brown virgin pulp discharged from the kraft digester(s) (4) is blended with crude textile pulp in any proportion and the combined pulps are transferred to the fiberline brownstock washing area (5). The combined pulp discharged from brownstock washers is transferred to the oxygen bleaching steps, often also referred to as oxygen delignification steps, as virgin pulps are both bleached and delignified simultaneously. Oxidized white liquor provides alkalinity in the O steps. After oxygen bleaching and EOF bleaching with chlorine dioxide in one or more stages (denoted D stages) and optional treatment with peroxide (P) or ozone (Z) and sulfuric acid (A) stages for adjustment of brightness and/or pulp viscosity (Dp value), the product dissolving pulp (9) is discharged for further combined treatments such as drying, baling and export, for example to viscose plants.

Additionally or alternatively, if the crude textile pulp has been pre-treated with alkali, with or without oxidant such as oxygen, hydrogen peroxide or ozone present, or has been hydrothermally or thermomechanically treated, the crude textile pulp may be charged to the fiber line further downstream the ECF bleaching sequence (3). Herein the crude textile pulp is charged to a filtrate tank (6) upstream a chlorine dioxide stage D. The ECF bleach plant comprises several wash presses (7) washing and

concentrating the combined virgin and crude textile pulp from different treatment stages. Normally, the washing of pulp is performed in a counter current fashion saving washing liquid. The filtrates are collected in filtrate tanks (8). Alkaline filtrates from oxygen chemicals treatment (O, P or EOP) or alkaline extraction stages E is combined and recycled to the brownstock washers. Alkaline filtrates and washing liquids are finally discharged through line (10) and are further concentrated by evaporation prior to incineration in a recovery boiler for recovery of sodium compounds. Any organic compounds expelled from the crude textile material (colorant rests, textile finishing agents rests etc.) are therefore incinerated in the recovery boiler. Acidic filtrates (11) from the bleach plant D or A stages (and Z stages, if any) can also be combined and be further treated by, for example, neutralization followed by secondary treatments such as COD/BOD removal, de-salting and discharge to effluent recipient or concentration and incineration in the recovery boiler.

In a preferred example, the cellulose dissolving pulp produced in accordance with the present disclosure comprises at least 5 % by weight cellulose originating from waste textile material. The co-processed and intermixed combined dissolving pulp is preferably dried in a pulp drying plant prior to baling.

Further examples of the disclosure include:

Example 1 : A method for the manufacturing of cellulose dissolving pulp, said method comprising:

providing a source of cellulosic pulp comprising at least 3 % by weight recycled textile material to at least one of a brownstock washing step, an oxidative alkaline pulp bleaching step, and an acidic pulp treatment step of a kraft or sulfite pulp mill fiberline, and

recovering said cellulose dissolving pulp from the kraft or sulfite pulp mill fiberline.

Example 2: The method of example 1 , further comprising recycling spent chemicals, effluents and/or organic residues from cellulosic pulp pre-treatment steps, pulp washing steps, pulp bleaching or pulp acidic treatment steps to a kraft or sulfite mill recovery boiler.

Example 3: The method of example 1 , further comprising recycling spent chemicals, effluents and/or organic residues from cellulosic pulp pre-treatment steps, pulp washing steps, pulp bleaching or pulp acidic treatment steps, after optional neutralization, to the kraft or sulfite pulp mill secondary effluent treatment plant.

Example 4: The method of any preceding examples, wherein:

said pulp mill is a kraft dissolving pulp mill having brownstock washers, an alkaline oxygen bleaching step, and a bleaching sequence;

said bleaching sequence comprises one or both of a chlorine dioxide (D) stage and an ozone (Z) bleaching stage; and recycled textile pulp is charged to the pulp mill fiber line upstream the pulp mill screen room after digesters or recycled textile pulp is charged to any bleaching or pulp treatment step upstream of pulp drying.

Example 5: The method of example 1 , wherein said pulp mill is a sulfite pulp mill and said providing a source of cellulosic pulp comprises the introduction of said cellulosic pulp into a brownstock washing step or upstream a peroxide (P) bleaching, an ozone (Z) bleaching or a peracetic acid (Paa) bleaching step.

Example 6: The method of any of the preceding examples, wherein alkalinity provided in an alkaline bleaching step is provided by charging oxidized white liquor.

Example 7: The method of any of the preceding examples further comprising:

treating cellulosic pulp originating from both virgin wood and/or recycled textile material by oxidative bleaching and/or acidic treatments to produce a dissolving quality pulp with brightness exceeding 85 ISO, and

washing and drying said cellulosic pulp to form a dried cellulose dissolving pulp.

Example 8: The method of any preceding examples wherein:

the cellulosic pulp comprising recycled textile material is co-processed with virgin cellulose pulp in at least one of an oxygen bleaching step (O), a chlorine dioxide bleaching step ( D), a peroxide bleaching step (P) , an ozone step (Z) and an acid step (A) and wherein the proportion of virgin pulp is at least corresponding to 5 % of the total pulp flow and that co-processed and intermixed combined dissolving pulp is dried in a pulp drying plant prior to baling.

Example 9: The method according to example 8, further comprising pretreating the cellulosic pulp comprising recycled textile material by one or more of a hydrothermal, thermomechanical, alkaline swelling treatment, treatment with supercritical C02 and a mechanical fabric disintegration procedure prior to charging the pulp to the kraft or sulfite pulp mill fiber line. Example 10: The method according to example 9, wherein hydrothermal pre-treatment of the textile pulp material is performed in aqueous media at a temperature in the range of 100 C to 220 C in closed pressure vessel systems.

Example 11 : The method according to example 10 wherein the aqueous media further comprises one or more of ozone, hydrogen peroxide, perborates, alkali hydroxide and surfactants.

Example 12: The method according to any of examples 8 to 11 , wherein aqueous effluents from any hydrothermal treatment or thermomechanical treatment is

concentrated and finally incinerated in a recovery boiler or utilized for manufacturing of biogas.

Example 13: The method according to any of examples 8 to 12, wherein a

thermomechanical treatment comprises a steam explosion treatment wherein textile pulp material is treated by steam and optional additives at a temperature in the range of 100-250 C in a closed pressurized vessel for a time period of from 1 minute to 220 minutes where after pressure is abruptly released forming a cellulosic pulp with cellulose polymers in the Dp range of 150 -700 repeating anhydroglucose units and at least on residue stream that is further treated in the kraft or sulfite pulp mill chemicals recycling plants.

Example 14: The method according to any of examples 8 to 13, wherein a textile material pulp pre-treatment step is adjusted by charge of chemicals and/or selection of temperature and retention time conditions so that the Dp range of the resulting pulp is in the range from about 150 to 1000 prior to charging the pulp to the kraft or sulfite pulp mill fiberline.

Example 15: The method according to any of examples 8 to 14, further comprising processing at least a portion of spent bleaching chemicals by concentration in an evaporator and incineration in a recovery boiler furnace thereby generating molten sodium carbonate.

Example 16: The method according to example 15 wherein sodium carbonate is causticized to form white liquor and wherein at least a portion of the white liquor is oxidized prior to charging at least a portion of oxidized white liquor to an oxygen (O) or peroxide (P) step bleaching cellulosic pulp comprising recycled textile material.

Example 17: A sulfite pulp mill bleach plant processing cellulosic pulp comprising recycled textile material comprising at least one of an ozone bleaching step (Z) and a peroxide bleaching step (P) and wherein an effluent from a bleaching step is concentrated by membrane filtration.

Claims

CLAIMS:

1. A method for the manufacturing of cellulose dissolving pulp, said method comprising:

providing a source of mechanically or chemically pre-treated cellulosic pulp comprising at least 3 % by weight recycled textile material to at least one of a

brownstock washing step, an oxidative alkaline pulp bleaching step, and an acidic cellulose pulp treatment step of a kraft or sulfite pulp mill fiberline, and

recovering said cellulose dissolving pulp from the kraft or sulfite pulp mill fiberline,

the method further comprising one or both of; a) recycling spent chemicals, effluents and/or organic residues from cellulosic pulp pre-treatment steps, pulp washing steps, pulp bleaching or pulp acidic treatment steps to a kraft or sulfite mill recovery boiler, or b) recycling spent chemicals, effluents and/or organic residues from cellulosic pulp pre-treatment steps, pulp washing steps, pulp bleaching or pulp acidic treatment steps, after optional neutralization, to a kraft or sulfite pulp mill secondary effluent treatment plant.

2. The method of claim 1 , wherein the textile material comprises at least one of recycled cotton, cotton linters, recycled viscose fibers, and waste or leftovers from cotton or viscose textile plants.

3. The method of any preceding claims, wherein:

4. The method of claim 1 , wherein said pulp mill is a sulfite pulp mill and said providing a source of mechanically or chemically pre-treated cellulosic pulp comprises the introduction of said cellulosic pulp into a brownstock washing step or upstream a peroxide (P) bleaching, an ozone (Z) bleaching or a peracetic acid (Paa) bleaching step.

5. The method of any of the preceding claims, wherein alkalinity provided in an alkaline bleaching step is provided by charging oxidized white liquor.

6. The method of any of the preceding claims further comprising:

7. The method of any preceding claims wherein:

the cellulosic pulp comprising recycled textile material is co-processed with cellulosic textile fiber material in at least one of an oxygen bleaching step (O), a chlorine dioxide bleaching step ( D), a peroxide bleaching step (P) , an ozone step (Z) and an acid step (A) and wherein the proportion of cellulosic textile fiber material is at least corresponding to 5 % of the total pulp flow and that co-processed and intermixed combined dissolving pulp is dried in a pulp drying plant prior to baling.

8. The method according to claim 7, further comprising pretreating the cellulosic pulp comprising recycled textile material by one or more of a hydrothermal,

thermomechanical, alkaline swelling treatment, treatment with supercritical C02 and a mechanical fabric disintegration procedure prior to charging the pulp to the kraft or sulfite pulp mill fiber line.

9. The method according to claim 8, wherein hydrothermal pre-treatment of the textile pulp material is performed in aqueous media at a temperature in the range of 100 C to 220 C in closed pressure vessel systems.

10. The method according to claim 9 wherein the aqueous media further comprises one or more of ozone, hydrogen peroxide, perborates, alkali hydroxide and surfactants.

11. The method according to any of claims 7 to 10, wherein aqueous effluents from any hydrothermal treatment or thermomechanical treatment is concentrated and finally incinerated in a recovery boiler or utilized for manufacturing of biogas.

12. The method according to any of claims 7 to 11 , wherein a thermomechanical treatment comprises a steam explosion treatment wherein textile pulp material is treated by steam and optional additives at a temperature in the range of 100-250 C in a closed pressurized vessel for a time period of from 1 minute to 220 minutes where after pressure is abruptly released forming a cellulosic pulp with cellulose polymers in the Dp range of 150 -700 repeating anhydroglucose units and at least on residue stream that is further treated in the kraft or sulfite pulp mill chemicals recycling plants.

13. The method according to any of claims 7 to 12, wherein a textile material pulp pre-treatment step is adjusted by charge of chemicals and/or selection of temperature and retention time conditions so that the Dp range of the resulting pulp is in the range from about 200 to 1000 prior to charging the pulp to the kraft or sulfite pulp mill fiberline.

14. The method according to any of claims 7 to 13, further comprising processing at least a portion of spent bleaching chemicals by concentration in an evaporator and incineration in a recovery boiler furnace thereby generating molten sodium carbonate.

15. The method according to claim 14 wherein sodium carbonate is causticized to form white liquor and wherein at least a portion of the white liquor is oxidized prior to charging at least a portion of oxidized white liquor to an oxygen (O) or peroxide (P) step bleaching cellulosic pulp comprising recycled textile material.

16. The method according to any of the preceding claims wherein recycled cotton, cotton linters, recycled viscose fibers and waste or leftovers from cotton or viscose textile plants is directly or indirectly charged to a sulfite pulp mill bleach plant pulp washing step, ozone bleaching step (Z) and a peroxide bleaching step (P) and wherein an effluent from a bleaching step is concentrated by evaporation or membrane filtration.