WO2023218125A1 - Procédé de préparation d'une solution de filage alcaline de cellulose - Google Patents

Procédé de préparation d'une solution de filage alcaline de cellulose Download PDF

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Publication number
WO2023218125A1
WO2023218125A1 PCT/FI2023/050251 FI2023050251W WO2023218125A1 WO 2023218125 A1 WO2023218125 A1 WO 2023218125A1 FI 2023050251 W FI2023050251 W FI 2023050251W WO 2023218125 A1 WO2023218125 A1 WO 2023218125A1
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WIPO (PCT)
Prior art keywords
alkaline
solution
cellulose dope
cellulose
dope
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PCT/FI2023/050251
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English (en)
Inventor
Matti Ristolainen
Sakari MODIG
Harri Kosonen
Pasi Virtanen
Janak SAPKOTA
Teemu POHJALAINEN
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Upm-Kymmene Corporation
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Publication of WO2023218125A1 publication Critical patent/WO2023218125A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/42—Electrodialysis; Electro-osmosis ; Electro-ultrafiltration; Membrane capacitive deionization
    • B01D61/422—Electrodialysis
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B1/00—Preparatory treatment of cellulose for making derivatives thereof, e.g. pre-treatment, pre-soaking, activation
    • C08B1/003—Preparation of cellulose solutions, i.e. dopes, with different possible solvents, e.g. ionic liquids
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D1/00—Oxides or hydroxides of sodium, potassium or alkali metals in general
    • C01D1/04—Hydroxides
    • C01D1/28—Purification; Separation
    • C01D1/38—Purification; Separation by dialysis
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
    • C01D5/00—Sulfates or sulfites of sodium, potassium or alkali metals in general
    • C01D5/006—Recovery of sodium sulfate from coagulation baths for the spinning of viscose
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G9/00—Compounds of zinc
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08B—POLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B1/00—Preparatory treatment of cellulose for making derivatives thereof, e.g. pre-treatment, pre-soaking, activation
    • C08B1/08—Alkali cellulose
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L1/00—Compositions of cellulose, modified cellulose or cellulose derivatives
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
    • D01D5/00—Formation of filaments, threads, or the like
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F1/00—General methods for the manufacture of artificial filaments or the like
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F13/00—Recovery of starting material, waste material or solvents during the manufacture of artificial filaments or the like
    • D01F13/02—Recovery of starting material, waste material or solvents during the manufacture of artificial filaments or the like of cellulose, cellulose derivatives or proteins
    • D—TEXTILES; PAPER
    • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
    • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F2/00—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof
    • D01F2/02—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof from solutions of cellulose in acids, bases or salts

Definitions

  • the present disclosure relates to processes for preparing a alkaline cellulose dope , the alkaline cellulose dope , and a product obtainable from an al kal ine cellulose dope .
  • cellulose Dissolution of cellulose is a challenging process ; due to the cellulose molecular structure characteri zed by multiple inter- and intramolecular hydrogen bonds , cellulose is a very stable molecule with low reactivity .
  • Processes for dissolving cellulose in aqueous solvent systems are avai lable .
  • a cold alkaline solution such as a 7 - 10 wt-% NaOH solution at a temperature of - 5 to 1 ° C .
  • Such cellulose solutions may be used for spinning and coagulating e . g . cellulose fibers .
  • alkaline cellulose dopes in particular those with a relatively high cellulose concentration, may not be stable for extended periods of time .
  • an alkaline cellulose dope with higher cellulose concentrations may be challenging . It may be desirable to have an alkal ine cellulose dope with such a viscosity that forming shapes , such as spinning or extruding e . g . fibers from the solution is possible . However, if the concentration of the cellulose is increased to increase viscosity, the more readily the alkaline cellulose dope may form gel-like structures . Such gel-like structures may not be sufficiently fluid for spinning or extruding . They may also render it more challenging to filter the alkaline cellulose dope and/or to transfer it forward in the process .
  • a process for preparing a alkaline cellulose dope may comprise providing a cellulose material and a cold alkaline solution, and dispersing and dissolving the cellulose material in the cold alkaline solution, thereby obtaining the alkaline cellulose dope .
  • Providing the cold alkaline solution may comprise generating an alkaline solution by electrodialysis , such that the absorption and/or dissolution of CO2 in the cold alkaline solution is reduced or prevented, and/or the concentration of carbonate ions in the cold alkaline solution is reduced .
  • Figure 1 shows an embodiment of a proces s for preparing an alkaline cellulose dope
  • Figure 2 describes an embodiment of a process for preparing an alkal ine cel lulose dope and a system for operating the process ;
  • Figure 3 shows an embodiment of a proces s for preparing an alkaline cellulose dope
  • Figure 4 shows another embodiment of an electrodialysis apparatus
  • Figure 5 shows another embodiment of an electrodialysis apparatus
  • Figure 6 illustrates Brookfield viscosities of alkaline cellulose dope samples with different concentrations of carbonate ions ;
  • Figure 7 shows tenacities of staple fibers are presented in as a function of stretching between the first and second godet ;
  • Figure 8 shows tenacities of staple fibers as a function of the elongation at break;
  • Figure 9 illustrates the Brookf ield viscosities of an alkaline cellulose dope sample stored for 0 , 1 , and 5 days in contact with air .
  • a process for preparing a alkaline cellulose dope may comprise providing a cellulose material and a cold alkaline solution, and dispersing and dissolving the cellulose material in the cold alkaline solution, thereby obtaining the alkaline cellulose dope , wherein providing the cold alkaline solution comprises generating an alkaline solution by electrodialysis .
  • the alkaline solution may be generated such that the absorption and/or dissolution of CO2 in the cold alkaline solution is reduced or prevented, and/or the concentration of carbonate ions in the cold alkaline solution and/or in the alkaline cellulose dope is reduced .
  • the electrodialysis it may be possible to produce a cold alkaline solution in an essentially carbonate free manner . Additionally or alternatively, the absorption and/or dissolution of CO2 in the cold alkaline solution and subsequently to the alkaline cellulose dope may be reduced or prevented .
  • electrodialysis technology may provide the recycling of sodium sulphate salt formed during coagulation .
  • Na2SO4 salt may be split into sulfuric acid and pure sodium hydroxide , which both are maj or spinning chemicals .
  • CO2 that is dissolved in water may mainly form carbonic acid .
  • the carbonic acid may further react with alkaline agents present in the cold alkaline solution and/or in the alkaline cellulose dope .
  • CO2 that is absorbed and dissolved in the alkaline cellulose dope may form carbonates in the alkaline cellulose dope .
  • the dissolved CO2 and carbonates may have an effect on the pH of the alkal ine cellulose dope and may thereby create local points in which gelation occurs . Such points of gelation may reduce the stability of the alkaline cellulose dope .
  • CO2 that is absorbed and dissolved in the alkaline cellulose dope may also reduce the solubility of the cellulose .
  • Carbonates thereby formed, or otherwise contained in the alkaline cellulose dope may also end up in products obtainable from alkaline cellulose dope .
  • carbonates may cause the formation of CO2 , which then may increase the porosity of the products when they are coagulated from the alkal ine cellulose dope .
  • the increased porosity may reduce the strength of the products , for example of staple fibers .
  • the amount of carbonates in the cold alkaline solution and/or in the alkaline cellulose dope may be reduced if the absorption and/or dissolution of CO2 in the alkaline cellulose dope is reduced, and/or CO2 dissolved in the cellulose material and the cold alkaline solution and/or in the alkaline cellulose dope is reduced or removed at least partially.
  • carbonates may refer to carbonates , such as Na2COs , and/or bicarbonates , such as NaHCCg , and/or to carbonate and/or bicarbonate ions .
  • the carbonates may further form bicarbonates , such that the carbonate and bicarbonate ions are at equil ibrium, the molar ratio of carbonates to bicarbonates depending e . g . on the pH .
  • the pH tends to be so high that the carbonates are present mainly as carbonate ions (COs 2- ) .
  • significant amounts of bicarbonates may be present .
  • Methods for determining the amount or concentration of carbonates may determine both carbonates and bicarbonates simultaneously, such that any references to the amount of carbonates , to carbonate content and/or to concentration of carbonate ions may refer to the amount of carbonates and bicarbonates and/or to concentration of carbonate and/or bicarbonate ions .
  • the absorption and/or dissolution of CO2 in the cold alkaline solution may be considered reduced, if it is reduced e . g . by at least 10 % , or at least 20 % , or at least 50 % as compared to a comparable proces s , for example to a comparable process which does not include one or more measures , such as generating an alkaline solution by electrodialysis , to reduce the absorption and/or dissolution of CO2 in the cold alkaline solution described in this specification .
  • the concentration of carbonate ions in the ( cold) alkaline solution and/or in the alkaline cellulose dope may be considered reduced, if it is reduced e . g . by at least 10 % , or at least 20 % , or at least 50 % as compared to a comparable process , for example to a comparable process which does not include one or more measures to reduce the absorption and/or dissolution of CO2 in the ( cold) alkal ine solution and/or in the alkaline cellulose dope or to reduce the concentration of carbonate ions described in this specification .
  • the absorption and/or dissolution of CO2 in the cold alkaline solution may be considered reduced, if the concentration of carbonate ions in the cold alkaline solution is 1 . 5 % (w/w) or lower, or 1 . 2 % (w/w) or lower, or 1 . 0 % (w/w) or lower, or 0 . 2 % (w/w) or lower , or 0 . 1 % (w/w) or lower .
  • the concentration may be understood as the concentration based on the total weight of the ( cold) alkaline solution .
  • the concentration of carbonate ions may be measured using the standard SCAN-N 32:98.
  • the standard is for white, green and black liquors and burnt lime sludge, but it may be used for other samples as well.
  • the accuracy of the method and detection limit may be improved by increasing the weight of the sample or by decreasing the volume of absorption cell solution. If the amount of alkaline solutions is increased, the volume of the reaction solution (HC1) may also be increased. It may be desirable to take care that the pH of the reaction solution is always below 2 and that the time of measurement is long enough to collect all CO2 generated from carbonates.
  • alkaline cellulose dope may be understood as a solution comprising cellulose solubilized in an alkaline solution.
  • the alkaline cellulose dope may be a cellulose spinning solution (i.e. an alkaline cellulose spinning solution) or a cellulose solution (i.e. alkaline cellulose solution) for extrusion, spinning, electrospinning, molding, casting, film forming, film extrusion, cellulose pearl production, coating, spraying and/or 3D printing.
  • it may refer to cellulosic material in alkaline solution suitable for use e.g. in spinning filaments, staple fibers, film making, cellulose pearl production, and various other purposes.
  • the cellulose alkaline cellulose dope may be coagulated in suitable conditions into solid cellulose, for example into type II cellulose.
  • a process for preparing an alkaline cellulose dope may comprise providing a cellulose material and a cold alkaline solution, dispersing and dissolving the cellulose material in the cold alkaline solution, thereby obtaining the alkaline cellulose dope, placing the alkaline cellulose dope in a storage tank, and processing the alkaline cellulose dope placed in the storage tank by forming it into a desired shape , such that a daily production volume of the alkaline cellulose dope is processed in a day, wherein the storage tank has a volume sufficient to contain a volume of the alkal ine cellulose dope that is equivalent to the daily production volume or smaller .
  • the stability of the alkaline cellulose dope , and thereby the process may be improved, when a relatively small storage tank is utili zed .
  • the air space within the storage tank i . e . the space within the storage tank that is not filled with the alkal ine cellulose dope
  • the air space within the storage tank may be minimi zed .
  • a smaller volume of a protective gas within the air space may be required .
  • Maintaining a desired temperature within the storage tank may be easier . I f the stability of the alkaline cellulose dope in the storage tank is compromised, then less alkaline cellulose dope is also lost , and the waste treatment thereof i s easier .
  • the ri sk of water condensation on the surface of the alkal ine cellulose dope may also be reduced or minimi zed .
  • the cleaning of storage tanks for the alkaline cellulose dope may be challenging, as upon washing with water, the remaining alkaline cellulose dope may generate a sticky residue that may be challenging to remove .
  • the process may be operated in a system comprising a first storage tank and a second storage tank, which are operated such that the alkaline cellulose dope is placed in the first storage tank while the second storage tank is being maintained.
  • the first and the second storage tank may both have a volume sufficient to contain a volume of the alkaline cellulose dope that is equivalent to the daily production volume or smaller.
  • the alkaline cellulose dope may subsequently be placed in the second storage tank while the first storage tank is being maintained.
  • the storage tank and/or the first and the second storage tank may have a volume of e.g. equivalent to 2 to 24-hour production volume (the 24-hour production volume being the daily production volume) .
  • the storage tank and/or the first and the second storage tank may have a volume sufficient to store a volume of the alkaline cellulose dope that is equivalent to a volume in the range of 1/12 to 1 x (i.e. 1/12 to 1 times) the daily production volume.
  • the daily production volume may be understood as referring to a volume of the alkaline cellulose dope that is processed, for example by forming it into a desired shape, within a day (i.e. 24 hours) of production.
  • the daily production volume may naturally depend on the process.
  • the daily production volume could be, for example, about 140 m 3 of alkaline cellulose dope.
  • the storage tank and/or the first and the second storage tank could have e.g. a volume in the range of about 11.7 to 140 m 3 , or in the range of about 11.7 to 70 m 3 .
  • the process may be a continuous process.
  • the alkaline cellulose dope may be fed directly to production, for example to an extrusion or printing apparatus, or other apparatus suitable for forming a desired shape from the alkaline cellulose dope .
  • the processing the alkaline cellulose dope placed in the storage tank by forming it into a desired shape may comprise or be e.g. extruding, spinning, film making, film extrusion, coating, casting, cellulose pearl production, spraying, electrospinning or printing and coagulating the alkaline cellulose dope and coagulating the alkaline cellulose dope into the desired shape .
  • the cold alkaline solution may include a zinc compound, such as ZnO, e.g. to stabilize the alkaline cellulose dope.
  • a zinc compound such as ZnO
  • CO2 and/or carbonates may form ZnCCg, which is poorly soluble.
  • ZnCCg which is poorly soluble.
  • the absorbed CO2 may also form Na2CO3, which is also not a desirable salt in the system.
  • Zinc carbonate crystals may form in the products coagulated from the alkaline cellulose dope. Such crystals may become loose from the surface of the products and end up in regeneration baths or washing baths. This may generate pores at the surfaces of the products. Further, large zinc carbonate crystals may obstruct e.g. the holes of a spinneret with which the alkaline cellulose dope is spinned. Such holes may typically have e.g. a diameter of about 40 - 100 pm.
  • the stability of the alkaline cellulose dope may be improved e.g. such that the viscosity of the alkaline cellulose dope does not increase for a given period of time, at least not to a significant extent.
  • the period of time may be e.g. at least 4 hours, or at least 12 hours, or at least 24 hours .
  • the concentration of the cellulose dissolved in the alkaline cellulose dope may be increased . It may also be possible to reduce the consumption of the zinc compound, such as ZnO, in cold alkaline solutions in which it is included, and thereby render the process more cost-effective and environmentally friendly .
  • any one of the process steps described below may be applied, alone or in combination with one or more other process steps described below, to reduce or remove CO2 dissolved and/or the concentration of carbonate ions in the cellulose material and the cold alkaline solution and/or in the alkaline cellulose dope at least partially .
  • the absorption and amount of O2 dissolved in the alkaline cellulose dope may also be reduced or prevented .
  • the presence of O2 may cause undesirable degradation of cellulose and/or hemicelluloses and produce monosaccharides and other degradation products .
  • Providing the cold alkaline solution may typically comprise mixing and/or dissolving an alkaline agent , such as NaOH, and optionally a dissolution or stabili zing agent , for example a zinc compound, such as ZnO, with water . They may be mixed at conditions suitable for dissolving the components in water, for example at an elevated temperature and such that the alkaline agent , such as NaOH, is added at a concentration of at least 40 % (w/w) .
  • the elevated temperature may be e . g . a temperature of at least 60 °C.
  • the resulting alkaline solution may then be diluted.
  • the (cold) alkaline solution may be generated by electrodialysis.
  • (cold) alkaline solution may be understood as referring to alkaline solution and/or to cold alkaline solution.
  • the alkaline solution may be cooled to a desired temperature to obtain the cold alkaline solution, or the alkaline solution may be generated at a temperature at which the alkaline solution generated may be considered to be a cold alkaline solution.
  • the alkaline agent in the (cold) alkaline solution may comprise or be e.g. NaOH, LiOH, KOH, and/or any mixture or combination thereof.
  • the alkaline agent may comprise or be e.g. NaOH, LiOH, and/or any mixture or combination thereof.
  • Additional organic hydroxide may also be included in the (cold) alkaline solution, such as tetrabutylammonium hydroxide, etc.
  • the (cold) alkaline solution may be an aqueous alkaline solution.
  • the zinc compound such as ZnO
  • the alkaline cellulose dope e.g. in the form of zincates.
  • Solid zinc oxide may dissolve in alkaline solutions to give soluble zincates as shown in the exemplary equation below:
  • the (cold) alkaline solution may comprise the alkaline agent, such as NaOH, at a concentration in the range of about 5 - 9 % (w/w) , or about 6.5 - 8 % (w/w) .
  • the alkaline agent such as NaOH
  • the (cold) alkaline solution may further comprise about 0 - 3 % (w/w) , or 0.1 - 2.5 % (w/w) , or 0.5 - 1.3 % (w/w) of the zinc compound, such as ZnO.
  • the (cold) alkaline solution may comprise ZnO and NaOH e.g. at a mass ratio in the range of 0.025 - 0.3.
  • the cellulose material may comprise cellulose and optionally hemicelluloses. Many sources of cellulose may additionally contain an amount of hemicelluloses.
  • pulp may comprise a mixture of cellulose and hemicelluloses. The mixture may comprise e.g. at least 9 wt-%, or at least 13 wt-%, or at least 15 wt-%, or 10 - 23 wt-%, or 13 - 18 wt-% of hemicelluloses on the basis of the total dry weight of the cellulose and hemicelluloses.
  • the hemicelluloses may also be solubilized in the alkaline cellulose dope.
  • the cellulose material may comprise or be e.g. pulp.
  • the pulp may be hydrolyzed pulp.
  • the pulp may be alkaline soluble pulp.
  • the pulp may comprise or be e.g. wood pulp (such as hardwood and/or softwood pulp) , non-wood pulp, and/or agropulp.
  • the pulp may be chemical pulp, such as kraft pulp.
  • the pulp may, additionally or alternatively, be never dried pulp, such as never dried kraft pulp.
  • the cellulose material or the pulp may comprise or be recycled fiber.
  • the pulp may be pre-treated, for example by a mechanical pre-treatment (up to 5 h) followed by a 2-3- h enzymatic hydrolysis utilizing cellulolytic enzymes.
  • the cellulose material such as pulp, may have a CED viscosity in the range of 100 - 300 ml/g, or in the range of 140 - 200 ml/g, or in the range of 150 - 180 ml/g.
  • the term "CED viscosity" may be understood as referring to viscosity number in cupri-ethylenediamine (CED) solution.
  • Cellulose material with a relatively low CED viscosity may have better solubility and may therefore allow for obtaining an alkaline cellulose dope with a higher concentration of the dissolved cellulose in the alkaline cellulose dope and/or a more stable alkaline cellulose dope.
  • the CED viscosity may be measured e.g. according to the standard ISO 5351:2010.
  • the cellulose material may be in solid form, e . g . as dry pulp . Alternatively, it may be e . g . in the form of a slurry .
  • Providing the cold alkaline solution may comprise generating the alkaline solution by electrodialysis and by cooling the alkaline solution, thereby obtaining the cold alkaline solution .
  • Any additional components of the cold alkaline solution such as the dissolution or stabili zing agent , for example the zinc compound, may e . g . be added in the alkaline solution after the electrodialysis .
  • electrodialysis may, additionally or alternatively, be referred to as electrolysis . These terms are sometimes used interchangeably, although electrodialysis may be understood as referring to a form of electrolysis . Electrodialysis may be understood as referring to a process in which a membrane , such as a semi-permeable and/or charged membrane , and an electrical potential difference are used to separate ionic species from an aqueous solution . With the electrodialysis , it may be possible to electrochemically split a salt-containing solution into at least two solutions with different compositions .
  • Electrodialysis of a salt-containing solution such as a salt-containing solution containing cations , for example Na + , K+, or Li+ ions , may generate a solution containing a hydroxide of the cations .
  • the salt-containing solution may be an aqueous salt-containing solution .
  • the electrodialysis may be performed using an apparatus comprising an anode , a cathode and a semi- permeable membrane .
  • the anode and the cathode may be placed on opposite sides of the semi-permeable membrane . Ions are transported through the semi-permeable membrane under the influence of an electric potential created by the anode and the cathode .
  • the semi-permeable membrane may be e.g. a cation exchange membrane.
  • the electrodialysis may be performed using an apparatus comprising two semi-permeable membranes, such as a cation exchange membrane and an anion exchange membrane .
  • the salt-containing solution comprises Na 2 SO4
  • the following reactions may take place at the anode :
  • Na + ions could be replaced by other suitable cations, such as K+, or Li+ ions
  • SO 4 2- ions could be replaced by other suitable anions, such as Cl“ ions, contained by the salt-containing solution.
  • suitable cations such as K+, or Li+ ions
  • SO 4 2- ions could be replaced by other suitable anions, such as Cl“ ions, contained by the salt-containing solution.
  • the nature of the cations and the anions will depend on the salt(s) contained by the salt-containing solution.
  • An example of a suitable apparatus may comprise a generation chamber for generating the alkaline solution and a reservoir for the salt-containing solution.
  • the generation chamber may comprise a cathode, such as a perforated platinum (Pt) cathode, at which hydroxide ions are formed.
  • the electrolyte reservoir may comprise an anode, such as a Pt anode, and a saltcontaining solution comprising cations, such as K+, Na + and/or Li+ ions.
  • the generation chamber may be connected to the reservoir by means of a cation exchange connector, which permits the passage of ions from the reservoir into the generation chamber while preventing the passage of anions from the reservoir into the generation chamber.
  • the cation exchange connector may also function as a physical barrier between the reservoir and the generation chamber.
  • the reservoir may be a low-pressure reservoir and the generation chamber a high-pressure generation chamber.
  • the cation exchange connector may function as a pressure barrier between the low-pressure reservoir and the generation chamber.
  • the cation exchange connector may comprise or be e.g. a membrane.
  • the membrane may be e.g. semi-permeable membrane, such as a cation-selective membrane.
  • Examples of cationselective membranes may be e.g. polyelectrolytes with negatively charged matter, which rejects negatively charged ions and allows positively charged ions to flow through .
  • water such as deionized water
  • a DC current may be applied between the anode and cathode. Under the applied field, the electrolysis of water occurs at both the anode and cathode of the apparatus. As shown below, water may be oxidized to form H+ ions and oxygen gas at the anode in the reservoir.
  • Water may be reduced to form 0H ⁇ ions and hydrogen gas at the cathode in the generation chamber.
  • the displaced ions may migrate across the cation exchange connector into the generation chamber .
  • These ions may combine with 0H ⁇ ions generated at the cathode to produce the KOH, NaOH and/or LiOH solution , which may then be used as the cold alkaline solution for dispersing and dissolving the cellulose material .
  • the concentration of generated KOH, NaOH and/or LiOH may be determined by the current applied to the apparatus and the water flow rate through the generation chamber .
  • Similar electrodialysis systems may be used e . g . in chromatography systems to generate eluents online .
  • the electrodialysis may be membrane electrodialysis .
  • the alkaline solution may be generated on-line .
  • the alkaline solution may be generated by an on-line electrodialysis system or an on-line membrane electrodialysis system .
  • the electrodialysis system used for the electrodialysis may comprise or be an on-line electrodialysis system or an on-line membrane electrodialysis system .
  • the alkal ine solution that is generated may be directly used in the following steps of the process , e . g . without storing it prior to the following steps of the process .
  • the absorption of CO2 in the alkaline solution may be reduced .
  • the alkaline solution may be generated into a closed environment , such as a closed container for mixing the cellulose into the alkal ine solution .
  • the environment and/or the container may be closed in the sense that the alkaline solution is not in contact with an atmosphere or air surrounding the closed environment and/or container or another source of CO2 .
  • the closed environment may thus reduce the absorption of CO2 into the alkaline solution and/or the alkaline cellulose dope.
  • the environment and/or the container for mixing the cellulose into the alkaline solution may further comprise a protective gas.
  • the protective gas may reduce the absorption of CO2 into the alkaline solution and/or the alkaline cellulose dope.
  • the protective gas may refer to atmosphere with a reduced CO2 content, e.g.
  • the alkaline cellulose dope may have a low temperature, humidity may condense and even freeze on the surface of the alkaline cellulose dope. This may have adverse effects on the alkaline cellulose dope. The humidity of the atmosphere in contact with the alkaline cellulose dope may also be reduced, when using a protective gas.
  • the (cold) alkaline solution may comprise contains 0.5 g/kg or less, or 0.25 g/kg or less, or 0.05 g/kg or less of CO2 dissolved therein based on the total weight of the (cold) alkaline solution.
  • the (cold) alkaline solution may comprise e.g. NaOH, LiOH, KOH, and/or any mixture or combination thereof .
  • the (cold) alkaline solution may be a solution comprising NaOH, LiOH, KOH, and/or any mixture or combination thereof.
  • the (cold) alkaline solution may be a NaOH solution .
  • the (cold) alkaline solution may be a NaOH solution generated by electrodialysis of a saltcontaining solution.
  • the salt-containing solution may be considered to be an electrolyte solution in the electrodialysis.
  • the contents of the alkaline solution will thus depend on the contents of the salt-containing solution.
  • the alkaline solution will be a NaOH solution; a HC1 solution will additionally be generated.
  • the salt-containing solution is a Na2SO4 solution (e.g. salt generated from a regeneration bath) , then the products will be a NaOH solution; a NaHSO4, and optionally H2SO4 containing solution will be additionally generated .
  • the salt of the salt-containing solution may be any suitable salt comprising sodium, potassium, lithium, sulfur, chloride and/or phosphorous.
  • the electrodialysis may produce H2 gas.
  • the H2 gas may be collected.
  • the H2 gas may be utilized for other purposes, for example combined with CO2 formed in a pulp mill lime kiln; in a reduction process, such as a catalytical reduction process for producing a biofuel; and/or as a fuel.
  • the electrodialysis may produce O2 (oxygen) gas.
  • O2 oxygen
  • the oxygen gas generated may be used e.g. in the fiberline of a pulping process, for example in an oxygen delignification stage.
  • the salt-containing solution may be obtainable or obtained from various sources and in various ways. Therefore the contents of the salt-containing solution may vary.
  • the salt-containing solution may comprise one or more salts, and optionally one or more other components .
  • the salt-containing solution may e.g. comprise NaOH or other alkaline agent, in addition to a salt (i.e. one or more salts) , such as e.g. Na2SO 4 .
  • the alkaline solution may be a NaOH solution generated by electrodialysis of a salt-containing solution.
  • the salt-containing solution may comprise NaCl, NaHSO4 and/or Na2SO4 as the salt.
  • the Na2SO4 (and/or Na- HSO4) may be obtainable or obtained from a pulp mill recovery process. It may be obtainable or obtained e.g. from the fly ash of a recovery boiler of the pulp mill.
  • the salt-containing solution may be obtainable or obtained from recovery boiler ash obtained by electrostatic precipitation.
  • Such a solution may comprise Na2SO4 and/or NaCl .
  • Such a solution may further comprise other salts, such as potassium (K+) and chloride salts (Cl“) and carbonate ions.
  • Such other salts may be removed, if desired; for example, by precipitation and/or acidification, or by the ash leaching process (suitable for e.g. NaCl) .
  • the NaCl i.e. a salt-containing solution comprising NaCl
  • the NaCl may be obtainable or obtained e.g. from reverse osmosis of sea water. Reverse osmosis may be used to produce pure (potable) water from sea water. In addition to the pure (potable) water, the reverse osmosis may produce a salt-containing solution comprising NaCl, the NaCl being present at a higher concentration than in the sea water from which it is produced.
  • the Na2SO4 or NaCl i.e. a salt-containing solution comprising Na2SO4 or NaCl
  • Various processes for manufacturing chlorine dioxide are available, and the byproduct (s) may depend on the process.
  • a methanol-based chlorine dioxine manufacturing process including a metathesis unit may produce a solution comprising Na2SO4.
  • the electrodialysis may generate a NaOH solution from a Na2SO4 solution (i.e. a salt-containing solution comprising Na2SO4) .
  • the electrodialysis may simultaneously generate a solution comprising NaHSO4 and/or H2SO4.
  • the method may further comprise processing the alkaline cellulose dope by forming it into a desired shape, and the processing may comprise coagulating the cellulose from the alkaline cellulose dope in a regeneration bath containing NaHSCg and/or H2SO4.
  • the Na2SO4 solution (which may thus be used as the salt-containing solution in the electrodialysis ) may be obtainable or at least partially obtained from the regeneration bath .
  • the electrodialysis may generate a NaHSCg and/or H2SO4 solution from the Na2SO4 solution, and the NaHSCg and/or H2SO4 solution may be used in the regeneration bath .
  • the resulting ( cold) alkaline solution may also be of high quality and may comprise a low concentration of carbonate ions .
  • the alkaline solution may be generated on-site and may thus be protected from CO2 from the air, its concentration of carbonate ions may be lower than that of an alkaline solution, such as a NaOH solution, commercially obtained, stored and transported .
  • Such commercially obtained alkaline solutions may be challenging to protect from exposure to CO2 and may not be guaranteed to contain significant amounts of CO2 dissolved therein and/or carbonate ions .
  • a salt solution comprising a sulphate salt such as NaHSCg and/or Na2SO4 , may be purified prior to the electrodialysis . This may be done e . g . by precipitation and subsequent filtration .
  • a Na2SO4 solution obtainable from a regeneration bath may contain organic substances , such as carbohydrates . Such organic substances may be removed e . g . by filtration .
  • the concentration of carbonate ions in the ( cold) alkaline solution may be 1 . 5 % (w/w) or lower, or 1 . 2 % (w/w) or lower, or 1 . 0 % (w/w) or lower, or 0 .2 % (w/w) or lower, or 0 . 1 % (w/w) or lower .
  • the concentration may be understood as the concentration based on the total weight of the ( cold) alkaline solution .
  • the electrodialysis may also be used such that it may remove a component of the salt-containing solution at least partially, thereby producing an alkaline solution that is better suited for solubilizing cellulose.
  • the salt-containing solution may comprise carbonates, such as Na2COs and/or NaHCCg.
  • Salt-containing solutions comprising carbonates, such as Na2COs and/or NaHCCg, may not be well suited for electrodialysis.
  • the carbonates as poorly soluble salts may also be detrimental to alkaline cellulose dopes obtainable from a cold alkaline process, i.e. a process according to one or more embodiments described in this specification.
  • the carbonates may be removed by acidifying the salt-containing solution. However, in some embodiments, it may be possible to remove carbonate ions at least partially by electrodialysis.
  • the alkaline solution is generated by electrodialysis of a salt-containing solution comprising a carbonate salt, such as Na2COs, thereby generating the alkaline solution and a solution comprising H2CO3, and removing CO2 formed from the H2CO3 at least partially from the solution.
  • a carbonate salt such as Na2COs
  • the salt-containing solution may comprise at least the carbonate salt, but optionally also one or more other salts, such as a sulphate salt (e.g. Na2SO4) , dissolved therein.
  • a sulphate salt e.g. Na2SO4
  • the salt-containing solution may be used as the electrolyte solution.
  • the electrodialysis of the salt-containing solution may generate the solution comprising H2CO3 derived from the carbonate salt.
  • the H2CO3 may form CO2 in the solution, and the resulting CO2 may then be removed from the solution at least partially.
  • the electrodialysis generates the alkaline solution.
  • a salt-containing solution that contains carbonates may be treated by electrodialysis such that it is more suitable for use as an alkaline solution in preparing the alkaline cellulose dope.
  • the salt-containing solution may, at least in some embodiments , comprise an alkaline agent , such as NaOH, prior to the electrodialysis .
  • the salt-containing solution may be a mildly alkaline saltcontaining solution comprising the carbonate salt .
  • the salt-containing solution may be a solution comprising NaOH, or NaOH, LiOH, KOH, and/or any mixture or combi nation thereof , and carbonates , such as Na 3 CO 3 and/or NaHCOs . Electrodialysis of such a salt-containing solution may remove the carbonates ( carbonate ions ) at least partially, such that an alkaline solution is obtained .
  • the salt-containing solution comprises Na2CO3
  • the following reactions may take place at the anode :
  • the H2CO 3 may then form gaseous CO2 , which may be removed at least partially :
  • the water may be purified and/or degassed prior to feeding the water into the electrodialysis so as to remove CO2 dissolved therein at least partially .
  • the water may be degassed and/or purified e . g . by boiling, heating, ion exchange , reverse osmosis , nanofiltration, precipitation, ion exclusion chromatography, acidification and/or any combination thereof , to remove carbonate ions and optionally other ions at least partially .
  • a suitable ion exchange res in may be used for removing carbonate ions and optionally other ions at least partially .
  • Such ion exchange resins and methods for using them are known .
  • the ion exchange may be performed, for example , by adding Ca (OH) 3 or CaO to the water to precipitate carbonate ions as CaCO 3 and subsequently to remove remaining Ca 2+ ions at least partially by ion exchange.
  • the water may be purified by acidification, so as to remove carbonate ions, and subsequently by anion exchange to remove anions derived from the acid added in the acidification.
  • chloride (Cl-) and/or sulphate (SO4 2- ) ions may be exchanged to hydroxyl ions (0H ⁇ ) by anion exchange .
  • the water may be purified by boiling or heating.
  • the boiling or heating may remove air (including O2 and CO2) .
  • the boiling or heating may be done under reduced pressure (e.g. under a partial vacuum) .
  • the boiled or heated water may then be kept under an atmosphere with a reduced CO2 content, such as by feeding an inert gas, e.g. helium (He) or nitrogen (N2) gas, to the atmosphere under which the boiled water is kept.
  • an inert gas e.g. helium (He) or nitrogen (N2) gas
  • the term "reduced pressure” may be understood as referring to a pressure that is lower than atmospheric pressure.
  • the reduced pressure may be e.g. a partial vacuum.
  • the reduced pressure used or required may depend e.g. on the temperature.
  • the reduced pressure may be such that it is capable of degassing at least partially but does not cause a significant amount of water to evaporate.
  • the reduced pressure may be e.g. a pressure in the range of 80 - 800 mbar, , or in the range of 100 - 200 mbar.
  • partial vacuum may refer to a pressure in the range of 80 - 800 mbar, or in the range of 100 - 200 mbar.
  • the absolute concentration of CO2 in the atmosphere may be reduced, while the concentration or proportion of CO2 relative to other gases in the atmosphere may remain the same.
  • the water is typically not pure water or contain only H2O, but may contain amounts of other components e.g. dissolved therein, for example CO2 and/or carbonate ions.
  • the water may comprise 0.5 g/kg or less, or 0.25 g/kg or less, or 0.05 g/kg or less of CO2 dissolved therein based on the total weight of the water.
  • the concentration of carbonate ions in the water may be 1.5 % (w/w) or lower, or 1.2 % (w/w) or lower, or 1.0 % (w/w) or lower, or 0.2 % (w/w) or lower, or 0.1 % (w/w) or lower.
  • the concentration may be understood as the concentration based on the total weight of the water.
  • the term "atmosphere with a reduced CO2 content” may be understood as referring to an atmosphere that does not comprise CO2 or an atmosphere that comprises 100 ppm or less CO2 •
  • the atmosphere with a reduced CO2 content may comprise 50000 ppm or less O2.
  • the atmosphere with a reduced CO2 content may be formed by an inert gas, such as helium, argon and/or nitrogen gas, or other suitable inert gas.
  • the term “atmosphere with a reduced CO2 content” may refer to an atmosphere wherein the proportion of CO2 is reduced as compared to the proportion of other gases contained in the atmosphere.
  • the atmosphere with a reduced CO2 content may contain 1.5 g/m 3 of CO2 or less.
  • the cellulose material may be a slurried pulp suspension prepared by mixing pulp, such as hydrolyzed pulp, or other suitable pulp, with water.
  • the water may be e.g. water purified according to one or more embodiments described in this specification.
  • the mixing may be done using a mixing device with sufficient mixing power so as to separate fibers from each other and to avoid fiber bundles in the alkaline cellulose dope.
  • the mixing with such a mixing device may also assist in bringing energy into the system under mixing, such that solid-gas interfaces in the system may be replaced with solid-liquid interfaces .
  • the temperature of the slurried pulp suspension may be adj usted to a desired temperature , such as a temperature in the range of 0 °C to 5 ° C .
  • the mixing may be continued .
  • the cellulose material may then be dispersed and dissolved in the cold alkal ine solution .
  • the temperature of the cold alkaline solution and/or of the cellulose material may be adj usted to a temperature in the range of -5 ° C to 5 ° C before and/or during this step .
  • the cellulose material may be dispersed and dissolved in the cold alkaline solution e . g . by feeding the cellulose material and the cold alkaline solution into a continuous reactor or a high consistency dissolving unit in which partial or full dissolution of the cellulose may be achieved .
  • a higher concentration of the dissolved cellulose in the alkaline cellulose dope may be obtained .
  • the concentration of the dissolved cellulose in the alkaline cellulose dope may be at least 5 % (w/w) , or at least 7 % (w/w) , or at least 8 % (w/w) , or at least 9 % (w/w) , or at least 10 % (w/w) , or at least 11 % (w/w) , or at least 12 % (w/w) .
  • the concentration of the dissolved cellulose in the alkaline cellulose dope may be in the range of about 5 - 12 % (w/w) .
  • the temperature of the cold alkaline solution may be e . g . in the range of -20 to 5 ° C, or in the range of -4 to 5 ° C when dissolving the cellulose material and/or of the alkaline cellulose dope .
  • the cold alkaline solution may contain 0 . 5 g/kg or less , or 0 . 25 g/kg or less , or at 0 . 05 g/kg or less of CO2 dissolved therein based on the total weight of the cold alkaline solution .
  • the concentration of carbonate ions in the cold alkaline solution may be 1.5 % (w/w) or lower, or 1.2 % (w/w) or lower, or 1.0 % (w/w) or lower, or 0.2 % (w/w) or lower, or 0.1 % (w/w) or lower (based on the total weight of the cold alkaline solution) .
  • the process may further comprise forming the alkaline cellulose dope into a desired shape.
  • the alkaline cellulose dope may be formed into a desired shape by extruding, spinning, film making, film extrusion, cellulose pearl production, coating, casting, spraying, electrospinning or printing and coagulating the alkaline cellulose dope.
  • the alkaline cellulose dope may be extruded e.g. through a die or a nozzle.
  • the viscosity of the alkaline cellulose dope may be adjusted so as to be desirable e.g. for extrusion, film making, film casting, spinning, and/or spraying.
  • the consistency of the alkaline cellulose dope may be e.g. in the range of 5 - 12 wt-%.
  • the cellulose of the alkaline cellulose dope may be considered to be coagulated and/or regenerated when a desired shape is obtained therefrom.
  • the cellulose is not necessarily actually regenerated cellulose in the sense that it would have undergone the viscose process and subsequent regeneration.
  • the terms "coagulated” and "regenerated” may refer to cellulose that is precipitated and/or crystallized from the solubilized state. It may be crystallized at least partially into cellulose II; or partially into cellulose I and partially into cellulose II.
  • the coagulated cellulose is in the form of cellulose II.
  • the shape may be e.g. a pellet, a powder, a film, a filament, a staple fiber, a bead, a melt, a 3D shape, a coating, a hotmelt adhesive, a container, a casing, a packaging article, a filmic label, a paper, a medical device, a plastic or composite profile, an abrasive particle, an abrasive film or paper, and/or a 3D printing filament.
  • the shape is not particularly limited. Various shapes may be extruded, spun, formed into a film, cast, sprayed, printed, coated or molded from the alkaline cellulose dope.
  • the extruded shape such as a filament or any other shape, may be coagulated and washed after extrusion.
  • the method may comprise immersing the extruded shape in a regeneration bath (or one or more regeneration baths) .
  • the regeneration bath may contain a regeneration solution, which then may assist in coagulating the cellulose contained in the shape.
  • the regeneration solution may be an acidic regeneration solution, such as a sulphuric acid solution.
  • the regeneration solution may be e.g. water or a mildly alkaline solution.
  • the extruded and coagulated shape may be immersed in one or more washing baths. For example, after a washing bath containing an acidic washing solution, the extruded shape may be immersed in a second washing bath. Such a second washing bath could comprise e.g. water or another neutral solution.
  • the alkaline cellulose dope may contain 0.5 g/kg or less, or 0.25 g/kg or less, or 0.05 g/kg or less of CO2 dissolved therein.
  • the concentration of carbonate ions in the alkaline cellulose dope may be 1.5 % (w/w) or lower, or 1.2 % (w/w) or lower, or 1.0 % (w/w) or lower, or 0.2 % (w/w) or lower, or 0.1 % (w/w) or lower.
  • the concentration may be understood as the concentration based on the total weight of the alkaline cellulose dope.
  • the alkaline cellulose dope may have a viscosity in the range of 2000 - 100000 mPas, or in the range of 2000 - 20000 mPas, or in the range of 2000 - 10000 mPas, or in the range of 3000 - 8000 mPas, or in the range of 4000 - 6000 mPas, or in the range of 3000 - 6000 mPas .
  • the alkaline cellulose dope may have a viscosity of 10000 mPas or lower within a time period of at least 24 hours of the dissolution of the cellulose material into the alkaline cellulose dope . I f the stability of the alkaline cellulose dope is reduced, the viscosity may increase , in particular during storage .
  • the viscosity of the alkaline cellulose dope may not increase by more than 50 % , or by more than 20 % , or by more than 10 % , within a period of time of at least 24 hours of the dissolution of the cellulose material into the alkaline cellulose dope .
  • the period of time may be e . g . at least 4 hours , or at least 12 hours , or at least 24 hours .
  • a product obtainable by coagulating alkaline cellulose dope from a cold alkaline process is also disclosed .
  • the product may comprise 1 . 0 % (w/w) or less of carbonate ions .
  • the product may comprise 0 .2 % (w/w) or less , or 0 . 1 % (w/w) or less of carbonate ions .
  • the product may be obtainable by coagulating alkaline cellulose dope according to one or more embodiments described in this specification .
  • the product obtainable by coagulating alkaline cellulose dope from a cold alkaline process may be such that it does not comprise xanthates of the cellulose and/or sulphur covalently bound to the cellulose .
  • the product obtainable by coagulating alkaline cellulose dope from a cold alkaline process may be such that it does not comprise residues of N-methylmorpholine 4 -oxide (NMMO) and/or ionic liquids ( ionic solvents ) .
  • NMMO N-methylmorpholine 4 -oxide
  • ionic solvents ionic solvents
  • the product may have a CED viscosity in the range of 100 - 300 ml /g, or in the range of 140 - 200 ml /g, or in the range of 150 - 180 ml /g .
  • the product may be obtainable from the alkaline cellulose dope by extrusion, spinning, electrospinning, molding, casting, film forming, film extrusion, cellulose pearl production, coating, spraying and/or printing and coagulating the alkaline cellulose dope .
  • the product may be obtainable from the alkaline cellulose dope according to one or more embodiments described in this specification by extruding, spinning, molding, film forming, casting, spraying, electrospinning, coating or printing and coagulating the alkaline cellulose dope .
  • the product may be e . g . a pellet , a powder , a film, a filament , a staple fiber, a bead, a melt , a 3D shape , a coating, a hotmelt adhesive , a container, a casing, a packaging article , a filmic label , a paper, a medical device , a plastic or composite profile , an abrasive particle , an abrasive film or paper, and/or a 3D printing filament .
  • the product may be a sausage casing obtainable by extruding and coagulating the alkaline cellulose dope , or a sausage casing obtainable by coating and/or impregnating a fibrous reinforcement with the alkaline cellulose dope .
  • the outside or the outside and the inside of the fibrous reinforcement may be coated .
  • the product may be a paper or cardboard obtainable by coating the paper or cardboard with the alkaline cellulose dope .
  • the product may be a f ilament and/or a staple fiber .
  • Such a product may have a tenacity of 15 cN/tex or greater .
  • Figure 1 describes an embodiment of a process for preparing an alkaline cellulose dope , and in particular providing the cold alkaline solution comprises generating an alkaline solution by electrodialysis .
  • the alkaline solution is generated in an electrodialysis apparatus 1 .
  • An example of a suitable apparatus 1 may include a cartridge .
  • the apparatus may comprise a generation chamber 2 for generating the alkaline solution and a reservoir 3 for the saltcontaining solution, i . e . an electrolyte reservoir .
  • the generation chamber 2 may comprise a cathode 4 , such as a perforated platinum ( Pt) cathode , at which hydroxide ions are formed .
  • the reservoir 3 may compri se an anode 5 , such as a Pt anode , and a salt-containing solution 6 comprising cations .
  • the cations are depicted in this schematic embodiment as Na + ions .
  • the generation chamber 2 may be connected to the reservoir 3 by means of a cation exchange connector 7 , which permits the passage of ions from the reservoir 3 into the generation chamber 2 while preventing the passage of anions from the reservoir 3 into the generation chamber 2 .
  • the cation exchange connector 7 may also function as a physical barrier between the reservoir and the generation chamber .
  • the reservoir 3 may be a low- pressure reservoir and the generation chamber 2 a high- pressure generation chamber .
  • the cation exchange connector 7 may function as a pressure barrier between the low-pressure reservoir and the generation chamber.
  • the cation exchange connector may comprise or be e.g. a membrane.
  • the membrane may be e.g. semi-permeable membrane, such as a cation-selective membrane .
  • water such as deionized water, indicated as H2O
  • H2O deionized water
  • a DC current may be applied between the anode 5 and cathode 4. Under the applied field, the electrolysis of water occurs at both the anode 5 and cathode 4 of the apparatus
  • water may be oxidized to form H+ ions and oxygen gas at the anode 5 in the reservoir 3.
  • the reservoir may be provided with a vent 9.
  • Water may be reduced to form 0H ⁇ ions and hydrogen gas at the cathode 4 in the generation chamber 2.
  • H2 generated at the cathode 4 may be removed and collected e.g. at a degas module 10.
  • the displaced ions may migrate across the cation exchange connector 7 into the generation chamber
  • Figure 2 describes an embodiment of a process for preparing an alkaline cellulose dope and a system for operating the process .
  • Alkaline solution is provided by generating it in an electrodialysis apparatus 1 , for example an electrodialysis apparatus 1 described in Fig . 1 , Fig . 4 or Fig . 5 .
  • the alkaline solution may alternatively be produced by conventional means (for example , by dissolving NaOH or another suitable alkaline agent in water in suitable conditions ) .
  • the alkaline solution may be generated by the electrodialysi s at 1 on-line .
  • I t may be generated into a closed environment , such as a closed container 11 for mixing cellulose material 12 into the alkaline solution .
  • the environment and/or the container may be closed in the sense that the alkal ine solution is not in contact with an atmosphere or another source of CO2 after it is generated and directed into the container 11 .
  • the closed environment may thus reduce the absorption of CO2 into the alkaline solution and/or the alkaline cellulose dope .
  • the environment and/or the container for mixing the cellulose into the alkaline solution may further comprise a protective gas .
  • the protective gas may reduce the absorption of CO2 into the alkaline solution and/or the alkaline cellulose dope .
  • a cellulose material 12 such as pulp, is provided .
  • the cellulose material 12 may be e . g . a cellulose material according to one or more embodiments described in this specification .
  • Additives 13 such as a dissolution or stabili zing agent , for example a zinc compound, such as ZnO, may be added in the container 11 .
  • the cellulose material 12 may then be dispersed and dissolved in the alkaline solution in the container 11 , such that an alkaline cellulose dope is obtained .
  • the alkaline solution may be cooled, so as to form cold alkaline solution .
  • the alkaline cellulose dope may be temporarily stored in a storage tank 14 prior to being fed into a production system 15 .
  • the storage tank 14 may have a volume sufficient to contain a volume of the alkaline cellulose dope that is equivalent to the daily production volume or smaller .
  • the daily production volume may be understood as referring to a volume of the alkaline cellulose dope that is processed in the production system 15 within a day ( i . e . 24 hours ) of production .
  • the process may thus be a continuous or a semi-continuous process .
  • the system depicted in Fig . 2 may, in some embodiments , comprise a first storage tank 14 and a second storage tank 14 ' , which are operated such that the alkaline cellulose dope is placed in the first storage tank 14 while the second storage tank 14 ' is being maintained; and wherein the first 14 and the second 14 ' storage tank both have a volume sufficient to contain a volume of the alkaline cellulose dope that is equivalent to the daily production volume or smaller .
  • the system may, in some embodiments , comprise only a single storage tank 14 .
  • the alkaline cellulose dope may be fed to the production system 15 , which may be e . g . an extrusion or printing apparatus .
  • the system 15 comprises an extrusion apparatus capable of extruding and coagulating the alkaline cellulose dope into a shape , such as a filament or a film .
  • the alkaline cellulose dope is driven by a screw 16 run by a motor 17 through a die 18 .
  • the alkaline cellulose dope is extruded into a shape 19 , such as a filament; however, the alkaline cellulose dope could alternatively be extruded into various other shapes or profiles, such as into a film.
  • the wet filament 19 may then be immersed in a regeneration bath 20 containing e.g. a sulphuric acid (H2SO4) solution.
  • H2SO4 sulphuric acid
  • the solubilized cellulose (and hemicelluloses, if present) from the cellulose material are coagulated.
  • the coagulated filament or other shape may then be processed further.
  • the electrodialysis at 1 may generate a H2SO4 solution from a Na2SO4 solution, and the H2SO4 solution may be directed to and used in the regeneration bath 20.
  • the electrodialysis at 1 may generate a NaOH solution from a Na2SO4 solution.
  • the Na2SO4 solution may be obtainable or at least partially obtained from the regeneration bath 20 containing the H2SO4 solution.
  • an apparatus 22 for removing zinc compounds from the regeneration bath may be used to remove zinc compounds from the Na2SO4 solution.
  • the zinc present in the regeneration bath and subsequently in the Na2SO4 solution may be removed by precipitating them as zinc carbonates.
  • the apparatus 22 may comprise e.g a filter for removing the precipitated zinc, e.g. in the form of precipitated zinc carbonates.
  • ZnSCg is more soluble in water than Na2SO4 e.g. at a temperature of 20 °C. These differences in solubility could be utilized for removing ZnSCg at least partially.
  • FIG. 3 shows an embodiment of a process for preparing an alkaline cellulose dope.
  • hydrolyzed pulp 2 obtainable from the fiberline 23 of a pulping process is dissolved in direct cold alkali dissolution at 24 , i . e . the hydrolyzed pulp 2 is dissolved in cold alkaline solution at 24 .
  • the cold alkaline solution is obtained from a sodium hydroxide solution 25 , i . e an alkaline solution, obtained from electrodialysis 1 .
  • Additives such as ZnO, may be added to the sodium hydroxide solution at 26 .
  • the sodium hydroxide solution containing the additives may then be mixed with the hydrolyzed pulp at 24 ; water 27 may be added .
  • the hydrolyzed pulp 2 is then dissolved in the cold sodium hydroxide solution at 24 , such that an alkaline cellulose dope is obtained .
  • the obtained alkaline cellulose dope is subsequently subj ected to filtration and deaeration at 28 .
  • the resulting alkaline cel lulose dope is used as a spinning solution and extruded through spinnerets at 29 into a regeneration bath 20 to obtain textile fibers , which may then be washed at 30 .
  • the alkaline cellulose dope could alternatively be formed into various other shapes using various other processes for forming such shapes .
  • a sodium sulfate solution 31 obtainable from the regeneration bath 20 may then be processed and circulated further .
  • Impurities such as zinc compounds in the sodium sul fate solution, may be removed e . g . by precipitation and filtration at 32 .
  • sulphuric acid may be added to the filtered sodium sulfate solution at 33 to remove carbonates .
  • the purified sodium sulfate solution may then be fed into the electrodialysis 1 as the salt-containing (electrolyte ) solution .
  • he electrodialysis 1 may generate other products , which may be utili zed for various purposes .
  • Sulfuric acid 34 obtainable from the electrodialysis 1 may be reused e . g . at 33 for acidifying the sodium sulfate solution to remove carbonate ions , and/or at the regeneration bath 20.
  • Another options to utilize the sulfuric acid 34 obtainable from the electrodialysis 1 may include e.g. using it in a pulp mill process at the fiberline at 23, or in obtaining hydrolyzed pulp 2.
  • Hydrogen 35 and oxygen 36 generated by the electrodialysis 1 may be collected and optionally reused, for example the oxygen 36 may be used at the fiberline 23, and the hydrogen 35 may be used as a reducing agent, in a catalytical process such as biofuel production, and/or as a fuel for generating energy.
  • FIG. 4 shows another electrodialysis apparatus 1.
  • the apparatus comprises an anode, a cathode, a first compartment 37 and a second compartment 38, and a semi-permeable membrane 39 connecting the first compartment 37 and the second compartment 38.
  • the semi-permeable membrane 39 may be e.g. a cation exchange membrane.
  • the anode is in contact with the first compartment 37 and the cathode in contact with the second compartment 38.
  • the apparatus 1 may operate as a flow-through apparatus, i.e. the salt-containing solution (in this example, a Na2SO4 solution) may flow through the first compartment 37, and water may flow through the second compartment 38.
  • the salt-containing solution in this example, a Na2SO4 solution
  • water may flow through the second compartment 38.
  • the electrochemical reactions occurring at the anode and the cathode are depicted.
  • a solution comprising H2SO4 and Na2SO4, or in some embodiments, only H2SO4 may be obtained.
  • an alkaline solution comprising NaOH as the alkaline agent may be obtained .
  • Figure 5 depicts another electrodialysis apparatus 1. It is similar to the one depicted in Fig. 4, except that instead of two compartments, it has three compartments.
  • the apparatus 1 comprises, again, an anode and a cathode.
  • the anode is in contact with a first compartment 37 and the cathode in contact with a second compartment 38.
  • a third compartment 40 lies between the first compartment 37 and the second compartment 38, separated from them by a first semi-permeable membrane
  • the first semi-permeable membrane 39 may be a cation exchange membrane and the second semi-permeable membrane 39' may be an anion exchange membrane.
  • the apparatus 1 may again operate as a flow- through apparatus.
  • a salt-containing solution in this example, a Na2SO4 solution
  • water or an alkaline solution such as a NaOH solution
  • Water and optionally a salt solution in this example, a Na2SO4 solution
  • sulphate ions may pass through the anion exchange membrane 39' to the first compartment 37, where they form H2SO4 with protons generated at the anode. From the first compartment 37, a solution comprising H2SO4 may thus be obtained.
  • Na + ions may pass through the cation exchange membrane 39 to the second compartment 38, where they form NaOH with hydroxide ions generated at the cathode.
  • an alkaline solution comprising NaOH as the alkaline agent may be obtained. The solution from the third compartment
  • 40 may be e.g. purged.
  • the electrodialysis apparatuses 1 shown in Figs. 4 and 5 may both produce a 10-15 wt-% NaOH solution. However, the apparatus shown in Fig. 5 differs from the one shown in Fig. 4 at least in that the sulphuric acid solution produced may contain less Na2SO4.
  • the conversion into H2SO4 may be as high as 50-60 % with the apparatus depicted in Fig. 4 and as high as nearly 100 % with the apparatus depicted in Fig. 5.
  • the three-compartment apparatus of Fig. 5 is more complex and likely to be more costly.
  • An alkaline cellulose dope was prepared from pretreated kraft pulp having CED viscos ity of 170 ml /g was used in the spinning trial .
  • An alkaline solution containing 18 wt-% NaOH was prepared by electrodialysis using an electrodialysis apparatus similar to that described in Fig . 1 .
  • ZnO was added to the alkal ine solution such that an alkaline solution containing 3 wt- % ZnO was obtained .
  • Production of the alkaline solution was done under inert N2 atmosphere to prevent absorption of CO2 to the alkaline solution .
  • Dissolving of the cellulose was done by combining extremely low CO2 content water and washed cellulose under inert N2 atmosphere and reducing temperature close 1 °C (without freezing the water) . When temperature was reached the alkaline solution with temperature close - 15 °C was added under inert N2 atmosphere . Mixing was continued for 30 minutes and temperature at the end of dissolving step was 2 °C . Temperature was slowly increased to 15 °C, while maintaining inert N2 atmosphere , to obtain the alkaline cellulose dope .
  • the effect of the concentration of carbonate ions to the stability of alkaline cellulose dope was investigated by producing an alkaline cellulose dope with a low concentration of carbonate ions .
  • Dope samples containing different amounts of carbonate ions ( % (w/w) based on the total weight of the alkaline cellulose dope , ranging from 0 . 01 to 1 . 8 % ) were produced by leading CO2 gas into the newly-made dope .
  • the newly-made alkaline cellulose dope was prepared in a similar manner as in Example 3 .
  • the concentration of carbonate ions of the dope samples were determined by the standard SCAN-N 32 : 98 .
  • the Brookfield viscosities of the alkaline cellulose dope samples were measured and plotted as the function of the concentration of carbonate ions as shown in Fig . 6 .
  • concentration of carbonate ions exceeded 1 . 2 % (w/w)
  • the viscosity increased, indicating that the stabi lity was reduced
  • concentration of carbonate ions exceeded 1 . 5 % (w/w)
  • the stability was reduced to a significant extent .
  • Pretreated kraft pulp having CED viscosity of 170 ml /g was used in a spinning trial .
  • Extremely low CO2 content water was produced by heating RO water to 60 °C and evaporating more than 5 % of water and CO2 with reduced pressure . Pressure was so low that the water was boiling .
  • Thi s extremely low CO2 content water was used to wash the pulp ( 50 g water/g cellulose ) , but also for the production of alkali solution containing 18 wt-% NaOH and 3 wt-% ZnO . Both of the chemicals were analytical grade , and the bottles were opened j ust before using . Production of alkali solution was done under inert N2 atmosphere .
  • Dissolving of cellulose was done by combining the extremely low CO2 content water and the washed cellulose under inert N2 atmosphere and reducing temperature close 1 °C (without freezing the water) . When temperature was reached the alkali solution with temperature close - 15 °C was added under inert N2 atmosphere . Mixing was continued for 30 minutes and temperature at the end of dissolving step was 2 °C . Temperature was slowly increased to 15 °C, while maintaining inert N2 atmosphere .
  • the cellulose solution was divided to two parts , where the other part was treated under inert N2 atmosphere ( Spinning solution ( i . e . alkaline cellulose dope ) A) whereas the absorption of CO2 was not prevented to the other part ( Spinning solution B) .
  • the viscosity of solution at this point was 4560 mPas .
  • Both cellulose solutions were filtered using 3 filters ( 25 pm, 10 pm and 5 pm) and centrifuged ( 1000 g, g-forces ) and transferred to spinning vessel . Both samples were mixed all the time very slowly to keep the concentration of carbonate ions of the sample constant .
  • Spinning took place in the next morning . Viscosity and the concentration of carbonate ions of spinning solutions were measured j ust before spinning . Spinning solutions A and B had viscosities and concentrations of carbonate ions of 4320 mPas and 0 . 09 % (w/w) , and 12610 mPas and 1 . 05 % (w/w) , respectively . Temperature of both spinning solutions were 21 °C . Spinning of these two spinning solutions were done using spinneret having 250 holes and using exactly same spinning parameters ( regeneration bath had 10 % H2SO4 and 15 % Na2SO4 ) . Fibers were washed with RO water and dried using the air dryer ( 60 °C) .
  • Tenacities of staple fibers are presented in Figure 7 as a function of stretching between the first and second godet .
  • Figure 8 shows tenacities of staple fibers as a function of the elongation at break .
  • Figure 7 shows that the staple fibres made out of spinning solution A can be stretched much more than the staple fibers made out of spinning solution B . It may be concluded that spinning solution A has much better stretchability and regeneration proceeds more evenly .
  • the mechanical properties of staple fibres made out of spinning solution A are much better .
  • both tenacity and elongation at break are important properties and with spinning solution A tenacity can be above 20 cN/tex and elongation at break still close to 20 % , whereas the staple fibers made out of spinning solution B did not reach the combination of tenacity 15 cN/tex and elongation at break 15 % .
  • the concentration of carbonate ions of dry staple fibers produced from spinning solution A was measured, and it was only 0 . 08 % (w/w) .
  • Low concentration of carbonate ions of spinning solution thus enables production of high tenacity fibers with low porosity and low carbonate content . It is more difficult to wash fibers with high porosity .
  • Figure 9 illustrates the Brookf ield viscosities of the samples . It was found that the viscosity of the alkaline cellulose dope increased upon storage , indicating that its stability had decreased the more the longer the storage time .

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Abstract

L'invention concerne un procédé de préparation d'une solution alcaline pour le filage de cellulose. Le procédé peut comprendre la fourniture d'un matériau cellulosique et d'une solution alcaline froide, et la dispersion et la dissolution du matériau cellulosique dans la solution alcaline froide, ce qui permet d'obtenir la solution alcaline pour le filage de cellulose. La fourniture de la solution alcaline froide peut comprendre la génération d'une solution alcaline par électrodialyse, de sorte que l'absorption et/ou la dissolution de CO2 dans la solution alcaline froide est réduite ou empêchée, et/ou que la concentration d'ions carbonate dans la solution alcaline froide est réduite.
PCT/FI2023/050251 2022-05-10 2023-05-08 Procédé de préparation d'une solution de filage alcaline de cellulose WO2023218125A1 (fr)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0426649A1 (fr) * 1989-10-31 1991-05-08 Lenzing Aktiengesellschaft Procédé pour la purification étagée de solutions aqueuses contenant du sulfate alcalin et installation pour la mise en oeuvre de ce procédé
WO2017178532A1 (fr) * 2016-04-14 2017-10-19 Treetotextile Ab Procédé de filage de cellulose dissoute
WO2020251463A1 (fr) * 2019-06-13 2020-12-17 Treetotextile Ab Fibres produites à partir de déchets cellulosiques recyclés

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0426649A1 (fr) * 1989-10-31 1991-05-08 Lenzing Aktiengesellschaft Procédé pour la purification étagée de solutions aqueuses contenant du sulfate alcalin et installation pour la mise en oeuvre de ce procédé
WO2017178532A1 (fr) * 2016-04-14 2017-10-19 Treetotextile Ab Procédé de filage de cellulose dissoute
WO2020251463A1 (fr) * 2019-06-13 2020-12-17 Treetotextile Ab Fibres produites à partir de déchets cellulosiques recyclés

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
BUTKOVA N. T. ET AL: "Effect of conditions in preparing the caustic soda solution on the sodium carbonate content of viscose fibres", FIBRE CHEMISTRY, vol. 22, 1 September 1991 (1991-09-01), pages 312 - 314, XP093061494, DOI: https://doi.org/10.1007/BF00552518 *
GUNNARSSON MARIA ET AL: "The CO 2 capturing ability of cellulose dissolved in NaOH(aq) at low temperature", GREEN CHEMISTRY, vol. 20, no. 14, 14 June 2018 (2018-06-14), GB, pages 3279 - 3286, XP093061497, ISSN: 1463-9262, DOI: 10.1039/C8GC01092G *

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