FI20225409A1

FI20225409A1 - A process for preparing an alkaline cellulose dope

Info

Publication number: FI20225409A1
Application number: FI20225409A
Authority: FI
Inventors: Janak Sapkota; Teemu Pohjalainen; Matti Ristolainen; Pasi Virtanen; Harri Kosonen; Sakari Modig
Original assignee: Upm Kymmene Corp
Priority date: 2022-05-10
Filing date: 2022-05-10
Publication date: 2023-11-11
Also published as: WO2023218125A1

Abstract

A process for preparing a alkaline cellulose dope is disclosed. The process 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.

Description

A PROCESS FOR PREPARING AN ALKALINE CELLULOSE DOPE

TECHNICAL FIELD

The present disclosure relates to processes for preparing a alkaline cellulose dope, the alkaline cel- lulose dope, and a product obtainable from an alkaline cellulose dope.

BACKGROUND

Dissolution of cellulose is a challenging pro- cess; due to the cellulose molecular structure charac- terized 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 available. For example, it is pos- sible to dissolve cellulose in 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.

However, alkaline cellulose dopes, in partic- ular those with a relatively high cellulose concentra- tion, may not be stable for extended periods of time.

Further, obtaining an alkaline cellulose dope with higher cellulose concentrations may be challenging.

It may be desirable to have an alkaline cellulose dope

N with such a viscosity that forming shapes, such as spin-

N ning or extruding e.g. fibers from the solution is pos- 3 sible. However, if the concentration of the cellulose 2 30 is increased to increase viscosity, the more readily the

I alkaline cellulose dope may form gel-like structures. * Such gel-like structures may not be sufficiently fluid 8 for spinning or extruding. They may also render it more a challenging to filter the alkaline cellulose dope and/or

S 35 to transfer it forward in the process.

SUMMARY

A process for preparing a alkaline cellulose dope is disclosed. The process 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 CO; in the cold alkaline solution is reduced or prevented, and/or the concentration of carbonate ions in the cold alkaline solution is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the embodiments and constitute a part of this specification, illustrate various embodiments. In the drawings:

Figure 1 shows an embodiment of a process for preparing an alkaline cellulose dope;

Figure 2 describes an embodiment of a process for preparing an alkaline cellulose dope and a system for operating the process;

Figure 3 shows an embodiment of a process for preparing an alkaline cellulose dope;

Figure 4 shows another embodiment of an

N electrodialysis apparatus;

S Figure 5 shows another embodiment of an ro electrodialysis apparatus; o 30 Figure 6 illustrates Brookfield viscosities of > alkaline cellulose dope samples with different

E concentrations of carbonate ions; 2 Figure 7 shows tenacities of staple fibers are

D presented in as a function of stretching between the

S 35 first and second godet;

Figure 8 shows tenacities of staple fibers as a function of the elongation at break; and

Figure 9 illustrates the Brookfield viscosities of an alkaline cellulose dope sample stored for 0, 1, and 5 days in contact with air.

DETAILED DESCRIPTION

In a first aspect, a process for preparing a alkaline cellulose dope 1s disclosed. The process 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 CO; 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.

With the electrodialysis, it may be possible to produce a cold alkaline solution in an essentially carbonate free manner. Additionally or alternatively,

N the absorption and/or dissolution of CO; in the cold

N alkaline solution and subsequently to the alkaline

N cellulose dope may be reduced or prevented. = 30 Additionally, the electrodialysis technology

T may provide the recycling of sodium sulphate salt formed

E during coagulation. Na»»S04 salt may be split into o sulfuric acid and pure sodium hydroxide, which both are 3 major spinning chemicals.

N 35 CO, that is dissolved in water may mainly form

N carbonic acid. The carbonic acid may further react with alkaline agents present in the cold alkaline solution and/or in the alkaline cellulose dope.

Not to be bound by theory, it may be that CO; that is absorbed and dissolved in the alkaline cellulose dope may form carbonates in the alkaline cellulose dope.

The dissolved CO, and carbonates may have an effect on the pH of the alkaline 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. CO, 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.

At acidic conditions, carbonates may cause the formation of CO;, which then may increase the porosity of the products when they are coagulated from the alkaline cellulose dope. The increased porosity may reduce the strength of the products, for example of staple fibers.

Thus, if the absorption and/or dissolution of

CO, in the alkaline cellulose dope is reduced, and/or

CO; dissolved in the cellulose material and the cold alkaline solution and/or in the alkaline cellulose dope is reduced or removed at least partially, the amount of carbonates in the cold alkaline solution and/or in the alkaline cellulose dope may be reduced. a In the context of this specification, the term

N “carbonates” may refer to carbonates, such as Na, 0O;, 3 30 and/or bicarbonates, such as NaHC03, and/or to carbonate 2 and/or bicarbonate ions. The carbonates may further form

Ek bicarbonates, such that the carbonate and bicarbonate > ions are at equilibrium, the molar ratio of carbonates 8 to bicarbonates depending e.g. on the pH. For example, a 35 in alkaline cellulose dope, the pH tends to be so high

S that the carbonates are present mainly as carbonate ions (C03?") . In other solutions, such as water, 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 5 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 CO, 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 process, 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 CO; 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 CO; in the (cold) alkaline solution and/or in the alkaline «cellulose dope or to reduce the concentration of carbonate ions described in this

N specification.

N In some embodiments, the absorption and/or 3 30 dissolution of CO, in the cold alkaline solution may be 2 considered reduced, if the concentration of carbonate =E 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, 8 or 0.2 % (w/w) or lower, or 0.1 % (w/w) or lower . The a 35 concentration may be understood as the concentration

S 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 (HCl) 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 CO; generated from carbonates.

In the context of this specification, the term “alkaline cellulose dope” may be understood as a solution comprising cellulose solubilized in an alkaline solution. For example, 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. In other words, 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

N dope may be coagulated in suitable conditions into solid

N cellulose, for example into type II cellulose. 3 30 In a second aspect, or in an embodiment of the © first aspect, a process for preparing an alkaline =E cellulose dope is disclosed. The process may comprise * providing a cellulose material and a cold al- 8 kaline solution, a 35 dispersing and dissolving the cellulose mate-

S rial in the cold alkaline solution, thereby obtaining the alkaline cellulose dope,

placing the alkaline cellulose dope in a stor- age 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 suffi- cient to contain a volume of the alkaline 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 utilized.

With such a storage tank, the air space within the storage tank, i.e. the space within the storage tank that is not filled with the alkaline cellulose dope, may be minimized. Thus it may be easier to reduce or minimize the amount of CO, within the air space and thereby reduce or minimize the amount of CO, that may dissolve in the alkaline cellulose dope. For example, a smaller volume of a protective gas within the air space may be reguired.

Maintaining a desired temperature within the storage tank may be easier. If 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 is easier. The risk of water conden- sation on the surface of the alkaline cellulose dope may

N also be reduced or minimized.

N Further, the cleaning of storage tanks for the 3 30 alkaline cellulose dope may be challenging, as upon 2 washing with water, the remaining alkaline cellulose

Ek dope may generate a sticky residue that may be * challenging to remove. Thus it may be beneficial to 8 utilize two storage tanks, one of which may be utilized a 35 for storing the alkaline cellulose dope, while one is

S being cleaned or otherwise maintained.

The process may be operated in a system com- prising 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.

In such a process, the alkaline cellulose dope may sub- sequently be placed in the second storage tank while the first storage tank is being maintained.

The storage tank and/or the first and the sec- ond storage tank may have a volume of e.g. equivalent to 2 to 24-hour production volume (the 24-hour produc- tion volume being the daily production volume).

The storage tank and/or the first and the sec- ond storage tank may have a volume sufficient to store a volume of the alkaline cellulose dope that is equiv- alent 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 produc- tion. The daily production volume may naturally depend on the process. The daily production volume could be, for example, about 140 m? of alkaline cellulose dope. In

N such a process, the storage tank and/or the first and

N the second storage tank could have e.g. a volume in the 3 30 range of about 11.7 to 140 m3, or in the range of about 2 11.7 to 70 m3. =E The process may be a continuous process. In- + stead of being stored, the alkaline cellulose dope may 8 be fed directly to production, for example to an extru- a 35 sion or printing apparatus, or other apparatus suitable

S 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 coagu- lating 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. In such solutions, CO, and/or carbonates may form ZnCOs;, which is poorly soluble. Thus the CO; that is absorbed and dissolved in the alkaline cellulose dope and/or carbonates in the alkaline cellulose dope may effectively reduce the amount of zinc ions derived from the ZnO in the solution. For environmental reasons, it may not be desirable to compensate for this simply by adding more of the zinc compound. The absorbed CO; may also form Na,C0O;, 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

N alkaline cellulose dope is spinned. Such holes may

N typically have e.g. a diameter of about 40 - 100 um. 3 30 With the process, it may be possible to improve 2 the stability of the alkaline cellulose dope. In =E particular, the stability may be improved e.g. such that * the viscosity of the alkaline cellulose dope does not 8 increase for a given period of time, at least not to a a 35 significant extent. The period of time may be e.g. at

S least 4 hours, or at least 12 hours, or at least 24 hours.

Additionally or alternatively, 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.

There may be various possibilities to reduce or remove CO, dissolved and/or the concentration of carbonate ions in the cellulose material and in the cold alkaline solution and/or in the alkaline cellulose dope at least partially, and/or to disperse and dissolve the cellulose material in the cold alkaline solution in conditions in which the absorption and/or dissolution of CO; and/or the concentration of carbonate ions in the alkaline cellulose dope is/are reduced. For example, 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 CO, 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.

Further, the absorption and amount of O, dissolved in the alkaline cellulose dope may also be reduced or prevented. The presence of 0, may cause undesirable degradation of cellulose and/or hemicelluloses and produce monosaccharides and other

N degradation products.

N Providing the cold alkaline solution may typ- 3 30 ically comprise mixing and/or dissolving an alkaline 2 agent, such as Na0H, and optionally a dissolution or

Ek stabilizing agent, for example a zinc compound, such as * ZnO, with water. They may be mixed at conditions suit- 8 able for dissolving the components in water, for example a 35 at an elevated temperature and such that the alkaline

S 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. However, as set out in the present disclosure, the (cold) alkaline solution may be generated by electrodialysis.

In the context of this specification, the term “ (cold) alkaline solution” may be understood as refer- ring to alkaline solution and/or to cold alkaline solu- tion. 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 so- lution 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) alka- line solution may be an aqueous alkaline solution.

As a skilled person will understand, the zinc compound, such as 4n0O, may be present in the (cold) alkaline solution and in the alkaline cellulose dope e.g. in the form of zincates. Solid zinc oxide may dis- solve in alkaline solutions to give soluble zincates as shown in the exemplary equation below:

ZnO + 2 NaOH + HO —> Na» [Zn (OH) 4]

N The (cold) alkaline solution may comprise the

N alkaline agent, such as NaOH, at a concentration in the 3 30 range of about 5 - 9 % (w/w), or about 6.5 - 8 % (w/w). © The (cold) alkaline solution may further com- = prise 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. 8 The (cold) alkaline solution may comprise ZnO a 35 and NaOH e.g. at a mass ratio in the range of 0.025 -

S 0.3.

The cellulose material may comprise cellulose and optionally hemicelluloses. Many sources of cellulose may additionally contain an amount of hemicelluloses.

For example, 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 solubil- ized 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 recy- cled 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

N referring to viscosity number in cupri-ethylenediamine

N (CED) solution. Cellulose material with a relatively low 3 30 CED viscosity may have better solubility and may © therefore allow for obtaining an alkaline cellulose dope =E with a higher concentration of the dissolved cellulose * in the alkaline cellulose dope and/or a more stable 8 alkaline cellulose dope. The CED viscosity may be a 35 measured e.g. according to the standard ISO 5351:2010.

O

N

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 stabilizing agent, for example the zinc compound, may e.g. be added in the alkaline solution after the electrodialysis.

The 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.

Flectrodialysis of a salt-containing solution, such as a salt-containing solution containing cations, for example Nat, K', or Lit ions, may generate a solution containing a hydroxide of the cations.

N The salt-containing solution may be an aqueous

N salt-containing solution. 3 30 The electrodialysis may be performed using an © apparatus comprising an anode, a cathode and a semi-

Ek permeable membrane. The anode and the cathode may be * placed on opposite sides of the semi-permeable membrane. 8 Ions are transported through the semi-permeable membrane a 35 under the influence of an electric potential created by

S the anode and the cathode.

The semi-permeable membrane may be e.g. a cation exchange membrane. However, in some embodiments, e.g. the electrodialysis may be performed using an apparatus comprising two semi-permeable membranes, such as a cation exchange membrane and an anion exchange membrane.

At the anode, the following reaction may take place:

HO — 2H* + 30, + 2e-

At the cathode, the following reaction may take place: 2H,O + 2e > 20H + H,

For example, when the salt-containing solution comprises Nao504,1, the following reactions may take place at the anode:

HO — 2H* + 30, + 2e 2H' + S0,? > H2S0,

At the cathode, the following reactions may take place: 2H:0 + 2e > 20H + H, 2Na* + 20H > 2NaOH

As a skilled person will understand, in the above equations, Nat ions could be replaced by other

N suitable cations, such as Kt, or Lit ions, and S044 ions

N could be replaced by other suitable anions, such as Cl” 3 30 ions, contained by the salt-containing solution. The 2 nature of the cations and the anions will depend on the

Ek salt(s) contained by the salt-containing solution. * An example of a suitable apparatus may comprise 8 a generation chamber for generating the alkaline a 35 solution and a reservoir for the salt-containing

S 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 salt- containing solution comprising cations, such as K', Nat and/or Lit 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. For example, the reservoir may be a low-pressure reservoir and the generation chamber a high-pressure generation chamber.

In such an embodiment, the cation exchange connector may function as a pressure barrier between the low-pressure reservolr 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 cation- selective membranes may be e.g. polyelectrolytes with negatively charged matter, which rejects negatively charged ions and allows positively charged ions to flow through.

To generate an alkaline solution comprising

KOH, NaOH and/or LiOH, water, such as deionized water, may be pumped through the generation chamber. A DC current may be applied between the anode and cathode.

N Under the applied field, the electrolysis of water

N occurs at both the anode and cathode of the apparatus. 3 30 As shown below, water may be oxidized to form H' ions 2 and oxygen gas at the anode in the reservoir. = HO + 26 > 2Ht + 202? 1 (at anode) * Water may be reduced to form OH ions and 8 hydrogen gas at the cathode in the generation chamber. a 35 2H,0 + 26 — 20H + H, j (at cathode)

S As H' ions, generated at the anode, displace cations, such as Kf, Nat and/or Lit ions, in the reservoir, the displaced ions may migrate across the cation exchange connector into the generation chamber.

These ions may combine with OH 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.

Further exemplary embodiments of suitable electrodialysis systems and apparatuses are described in the Examples.

The electrodialysis may be membrane electrodi- alysis.

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. In other words, the electrodi- alysis system used for the electrodialysis may comprise or be an on-line electrodialysis system or an on-line membrane electrodialysis system.

In an on-line electrodialysis system, the al- kaline solution that is generated may be directly used in the following steps of the process, e.g. without

N storing it prior to the following steps of the process.

N Thus the absorption of CO, in the alkaline solution may 3 30 be reduced. 2 The alkaline solution may be generated into a

Ek closed environment, such as a closed container for * mixing the cellulose into the alkaline solution. The 8 environment and/or the container may be closed in the a 35 sense that the alkaline solution is not in contact with

S an atmosphere or air surrounding the closed environment and/or container or another source of CO,. The closed environment may thus reduce the absorption of CO, 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 CO, into the alkaline solution and/or the alkaline cellulose dope. The protective gas may refer to atmosphere with a reduced CO, content, e.g. an atmosphere that does not comprise CO, or an atmosphere that comprises 100 ppm or less CO,; an atmosphere wherein the proportion of CO, is reduced as compared to the proportion of other gases contained in the atmosphere; and/or to an inert gas. As 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 con- tains 0.5 g/kg or less, or 0.25 g/kg or less, or 0.05 g/kg or less of CO, 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

N comprising NaOH, LiOH, KOH, and/or any mixture or com-

N bination thereof. 3 30 The (cold) alkaline solution may be a NaOH so- 2 lution. =E The (cold) alkaline solution may be a NaOH * solution generated by electrodialysis of a salt- 8 containing solution. a 35 The salt-containing solution may be considered

S 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.

If the salt-containing solution solution is a

NaCl solution, then the alkaline solution will be a Na0H solution; a HCl solution will additionally be generated.

If the salt-containing solution is a Na,S0O; solution (e.g. salt generated from a regeneration bath), then the products will be a NaOH solution; a NaHSO., and option- ally HS0, containing solution will be additionally gen- erated.

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 H, gas. The H, gas may be collected. The H, gas may be utilized for other purposes, for example combined with CO, 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 O, (oxygen) gas. 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

N or more salts, and optionally one or more other compo-

N nents. 3 30 The salt-containing solution may e.g. comprise 2 NaOH or other alkaline agent, in addition to a salt

Ek (i.e. one or more salts), such as e.g. Na2S0O.,, * The alkaline solution may be a NaOH solution 8 generated by electrodialysis of a salt-containing solu- a 35 tion. The salt-containing solution may comprise NaCl,

S NaHSO, and/or Na,SO, as the salt. The Na,S0O, (and/or Na-

HSO.) 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 ob- tained from recovery boiler ash obtained by electro- static precipitation. Such a solution may comprise Na, S04 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 acidifi- cation, or by the ash leaching process (suitable for e.g. NaCl). Thus it may be possible to utilize side streams from a pulp mill in providing the cold alkaline solution. The NaCl, i.e. a salt -containing solution com- prising 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 osmo- sis 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

Na,50, or NaCl, i.e. a salt-containing solution compris- ing Na2S0, or NaCl, may also be obtainable or obtained e.g. from chlorine dioxide manufacturing as a byproduct.

Various processes for manufacturing chlorine dioxide are available, and the byproduct(s) may depend on the pro- cess. For example, a methanol-based chlorine dioxine manufacturing process including a metathesis unit may

N produce a solution comprising NaoSO,.

N The electrodialysis may generate a NaOH solu- 3 30 tion from a Na;S0, solution (i.e. a salt-containing so- © lution comprising Na,S0s). The electrodialysis may sim-

Ek ultaneously generate a solution comprising NaHSO, and/or * HoSO4. The method may further comprise processing the 8 alkaline cellulose dope by forming it into a desired a 35 shape, and the processing may comprise coagulating the

S cellulose from the alkaline cellulose dope in a regen- eration bath containing NaHS0, and/or H2S04. The Na2S0.

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 NaHSO, and/or H2S0; solution from the NaS0, solution, and the

NaHSO, and/or H,S04 solution may be used in the regener- ation bath.

In this manner, it may be possible to recycle solutions from the regeneration bath to the electrodi- alysis. The resulting (cold) alkaline solution may also be of high quality and may comprise a low concentration of carbonate ions. As the alkaline solution may be gen- erated on-site and may thus be protected from CO, 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 trans- ported. Such commercially obtained alkaline solutions may be challenging to protect from exposure to CO, and may not be guaranteed to contain significant amounts of

CO; dissolved therein and/or carbonate ions.

A salt solution comprising a sulphate salt, such as NaHSO,; and/or NaS0,, may be purified prior to the electrodialysis. This may be done e.g. by precipi- tation and subsequent filtration.

For example, a Na;S50, solution obtainable from a regeneration bath may contain organic substances, such as carbohydrates. Such organic substances may be removed

N e.g. by filtration.

N The concentration of carbonate ions in the 3 30 (cold) alkaline solution may be 1.5 % (w/w) or lower, 2 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 concen- * tration may be understood as the concentration based on 8 the total weight of the (cold) alkaline solution. a 35 The electrodialysis may also be used such that

S it may remove a component of the salt-containing solu- tion at least partially, thereby producing an alkaline solution that is better suited for solubilizing cellu- lose.

The salt-containing solution may comprise car- bonates, such as Na,CO3 and/or NaHCOs,

Salt-containing solutions comprising car- bonates, such as Na;C0O; and/or NaHC0O3, may not be well suited for electrodialysis. The carbonates as poorly soluble salts may also be detrimental to alkaline cel- lulose 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. How- ever, in some embodiments, it may be possible to remove carbonate ions at least partially by electrodialysis.

In an embodiment, the alkaline solution is gen- erated by electrodialysis of a salt-containing solution comprising a carbonate salt, such as Na.CO3, thereby generating the alkaline solution and a solution com- prising HCO3, and removing CO, formed from the H,CO; at least partially from the solution.

In other words, 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. Na,S04), dissolved therein. When the salt-contain- ing solution is subjected to the electrodialysis, the salt-containing solution may be used as the electrolyte solution. The electrodialysis of the salt-containing

N solution may generate the solution comprising HCO3 de-

N rived from the carbonate salt. The H,CO; may form CO; in 3 30 the solution, and the resulting CO, may then be removed © from the solution at least partially. At the same time, =E the electrodialysis generates the alkaline solution. In * this manner, a salt-containing solution that contains 8 carbonates may be treated by electrodialysis such that a 35 it is more suitable for use as an alkaline solution in

S 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. For example, the salt-containing solution may be a mildly alkaline salt- containing 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,CO3 and/or

NaHCO;, Electrodialysis of such a salt-containing solu- tion may remove the carbonates (carbonate ions) at least partially, such that an alkaline solution is obtained.

For example, when the salt-containing solution comprises Na.CO3, the following reactions may take place at the anode:

HO —> 2H' + 150, + 2e 2H" + C0:3? > HC03

The HO; may then form gaseous CO, which may be removed at least partially:

HCO3 > HO + CO2 1

In embodiments in which water is fed into the electrodialysis, the water may be purified and/or degassed prior to feeding the water into the electrodialysis so as to remove CO, dissolved therein at least partially. The water may be degassed and/or purified e.g. by boiling, heating, ion exchange, reverse

N osmosis, nanofiltration, precipitation, ion exclusion

N chromatography, acidification and/or any combination 3 30 thereof, to remove carbonate ions and optionally other © ions at least partially. =E A suitable ion exchange resin may be used for * removing carbonate ions and optionally other ions at 8 least partially. Such ion exchange resins and methods a 35 for using them are known. The ion exchange may be

S performed, for example, by adding Ca(OH), or CaO to the water to precipitate carbonate ions as CaC03 and subsequently to remove remaining Ca?" ions at least partially by ion exchange.

Additionally or alternatively, 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.

For example, chloride (C17) and/or sulphate (S042) ions may be exchanged to hydroxyl ions (OH) by anion exchange.

Additionally or alternatively, the water may be purified by boiling or heating. The boiling or heating may remove air (including O; and CO). 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

CO, content, such as by feeding an inert gas, e.g. helium (He) or nitrogen (N,) gas, to the atmosphere under which the boiled water is kept.

In the context of this specification, 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. For example, 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

N in the range of 80 — 800 mbar, , or in the range of 100

N — 200 mbar. In the context of this specification, the 3 30 term “partial vacuum” may refer to a pressure in the 2 range of 80 - 800 mbar, or in the range of 100 - 200 =E mbar. As a skilled person will understand, under reduced * pressure the absolute concentration of CO, in the 8 atmosphere may be reduced, while the concentration or a 35 proportion of CO, relative to other gases in the

S atmosphere may remain the same.

As a skilled person will understand, the water is typically not pure water or contain only HO, but may contain amounts of other components e.g. dissolved therein, for example CO, 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 CO, 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.

In the context of this specification, the term "atmosphere with a reduced CO, content” may be understood as referring to an atmosphere that does not comprise CO, or an atmosphere that comprises 100 ppm or less CO,. The atmosphere with a reduced CO, content may comprise 50000 ppm or less Op. The atmosphere with a reduced CO, content may be formed by an inert gas, such as helium, argon and/or nitrogen gas, or other suitable inert gas. In an embodiment, the term "atmosphere with a reduced CO, content” may refer to an atmosphere wherein the proportion of CO, is reduced as compared to the proportion of other gases contained in the atmosphere.

For example, the atmosphere with a reduced CO; content may contain 1.5 g/m? of CO, or less.

N The cellulose material may be a slurried pulp

N suspension prepared by mixing pulp, such as hydrolyzed 3 30 pulp, or other suitable pulp, with water. The water may 2 be e.g. water purified according to one or more

Ek embodiments described in this specification. The mixing * may be done using a mixing device with sufficient mixing 8 power so as to separate fibers from each other and to a 35 avoid fiber bundles in the alkaline cellulose dope. The

S 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-liguid interfaces.

The temperature of the slurried pulp suspension may be adjusted 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 alkaline solution. The temperature of the cold alkaline solution and/or of the cellulose materia] may be adjusted 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.

With one or more embodiments of the process described in this specification, 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 3 (w/w), or at least 10 % (w/w), or at least 11 % (w/w), or at least 12 % (w/w). The concentration of

N the dissolved cellulose in the alkaline cellulose dope

N may be in the range of about 5 -— 12 % (w/w). 3 30 The temperature of the cold alkaline solution 2 may be e.g. in the range of -20 to 5 °C, or in the range =E of -4 to 5 °C when dissolving the cellulose material * and/or of the alkaline cellulose dope. 8 The cold alkaline solution may contain 0.5 g/kg a 35 or less, or 0.25 g/kg or less, or at 0.05 g/kg or less

S of CO, 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 alka- line 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 cellu- lose 1s not necessarily actually regenerated cellulose in the sense that it would have undergone the viscose process and subsequent regeneration. In this case, the terms “coagulated” and “regenerated” may refer to cel- lulose that is precipitated and/or crystallized from the

N solubilized state. It may be crystallized at least par-

N tially into cellulose II; or partially into cellulose I 3 30 and partially into cellulose II. Typically, the coagu- 2 lated cellulose is in the form of cellulose II.

Ek The shape may be e.g. a pellet, a powder, a > film, a filament, a staple fiber, a bead, a melt, a 3D 8 shape, a coating, a hotmelt adhesive, a container, a a 35 casing, a packaging article, a filmic label, a paper, a

S medical device, a plastic or composite profile, an abrasive particle, an abrasive film or paper, and/or a

3D printing filament. The shape 1s 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 extru- sion. For example, 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 coag- ulating the cellulose contained in the shape. The re- generation solution may be an acidic regeneration solu- tion, such as a sulphuric acid solution. However, in some embodiments, 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 im- mersed in a second washing bath. Such a second washing bath could comprise e.g. water or another neutral solu- tion.

An alkaline cellulose dope is disclosed. 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 CO, dis- solved therein.

The concentration of carbonate ions in the al- kaline cellulose dope may be 1.5 % (w/w) or lower, or a 1.2 & (w/w) or lower, or 1.0 % (w/w) or lower, or 0.2

N % (w/w) or lower, or 0.1 % (w/w) or lower. The concen- 3 30 tration may be understood as the concentration based on © the total weight of the alkaline cellulose dope.

Ek The alkaline cellulose dope may have a viscos- * ity in the range of 2000 — 100000 mPas, or in the range 8 of 2000 - 20000 mPas, or in the range of 2000 - 10000 a 35 mPas, or in the range of 3000 - 8000 mPas, or in the

S 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. If 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 1s 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

N dope from a cold alkaline process may be such that it

N does not comprise residues of N-methylmorpholine 4-oxide 3 30 (NMMO) and/or ionic liquids (ionic solvents). In other © words, the product obtainable by coagulating alkaline

Ek cellulose dope from a cold alkaline process may not * encompass products obtainable from the viscose, lyocell 8 or Ioncell® processes. a 35 The product may have a CED viscosity in the

S 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 abra- sive particle, an abrasive film or paper, and/or a 3D printing filament.

For example, 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

N alkaline cellulose dope.

N The product may be a filament and/or a staple 3 30 fiber. Such a product may have a tenacity of 15 cN/tex © or greater. i

EXAMPLES

8 Reference will now be made in detail to various a 35 embodiments, an example of which is illustrated in the

S accompanying drawing.

The description below discloses some embodiments in such a detail that a person skilled in the art is able to utilize the embodiments based on the disclosure. Not all steps or features of the embodiments are discussed in detail, as many of the steps or features will be obvious for the person skilled in the art based on this specification.

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. However, the apparatus 1 is not necessarily in the form of a cartridge. The apparatus may comprise a generation chamber 2 for generating the alkaline solution and a reservoir 3 for the salt- containing 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 comprise 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 Nat ions. The generation chamber 2 may be connected to the reservoir 3 by means of a cation exchange connector 7, which permits the passage

N of ions from the reservoir 3 into the generation chamber

N 2 while preventing the passage of anions from the 3 30 reservoir 3 into the generation chamber 2. The cation © exchange connector 7 may also function as a physical =E barrier between the reservoir and the generation * chamber. For example, the reservoir 3 may be a low- 8 pressure reservoir and the generation chamber 2 a high- a 35 pressure generation chamber. In such an embodiment, the

S 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.

To generate an alkaline solution comprising

KOH, NaOH and/or LiOH, water, such as deionized water, indicated as HO, may be pumped through the generation chamber 2 with a pump 8. The alkaline solution is depicted in this schematic illustration as NaOH. 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 1. As shown below, water may be oxidized to form H' ions and oxygen gas at the anode 5 in the reservoir 3.

HO + 26 > 2Ht + 202? 1 (at anode)

To remove 0? generated at the anode 5 in the reservoir 3, the reservoir may be provided with a vent 9.

Water may be reduced to form OH ions and hydrogen gas at the cathode 4 in the generation chamber 2. 2H,0 + 2e > 20H + H, 1 (at cathode)

Ho generated at the cathode 4 may be removed and collected e.g. at a degas module 10.

As H' ions, generated at the anode 5, displace cations, such as Kf, Nat and/or Lit ions, in the reservoir, the displaced ions may migrate across the

N cation exchange connector 7 into the generation chamber

N 2. These ions may combine with OH ions generated at the 3 30 cathode 4 to produce the alkaline solution, which may 2 then be used as the cold alkaline solution for =E dispersing and dissolving the cellulose material. The * concentration of generated KOH, NaOH and/or LiOH may be 8 determined by the current applied to the apparatus and a 35 the water flow rate through the generation chamber 2.

O

N

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. However, as a skilled person will understand, 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 electrodialysis at 1 on-line. It 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 alkaline solution is not in contact with an atmosphere or another source of CO, after it is generated and directed into the container 11. The closed environment may thus reduce the absorption of CO; 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 CO, into the alkaline solution and/or the alkaline cellulose dope.

A cellulose material 12, such as pulp, is

N provided. The cellulose material 12 may be e.g. a

N cellulose material according to one or more embodiments 3 30 described in this specification. 2 Additives 13, such as a dissolution or

Ek stabilizing agent, for example a zinc compound, such as * Zn0, may be added in the container 11. 8 The cellulose material 12 may then be dispersed a 35 and dissolved in the alkaline solution in the container

S 11, such that an alkaline cellulose dope is obtained.

Prior to this, 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 eguivalent to the daily production volume or smaller.

However, it will be understood that the system may, in some embodiments, comprise only a single storage tank 14.

From the storage tank(s) 14 and 14’ or from previous process stages, the alkaline cellulose dope may

N be fed to the production system 15, which may be e.g.

N an extrusion or printing apparatus. In this exemplary 3 30 embodiment, the system 15 comprises an extrusion 2 apparatus capable of extruding and coagulating the =E alkaline cellulose dope into a shape, such as a filament * or a film. However, other types of apparatuses may be 8 contemplated. In the production system 15, the alkaline a 35 cellulose dope is driven by a screw 16 run by a motor

S 17 through a die 18. At the 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 (H2S04) solution. In the regeneration bath 10, the solubilized cellulose (and hemicelluloses, if present) from the cellulose material are coagulated. The coagulated filament or other shape may then be processed further.

As depicted schematically by the arrow at 21, the electrodialysis at 1 may generate a Hy;SO, solution from a Na,S0; solution, and the H2S0; solution may be directed to and used in the regeneration bath 20.

Alternatively or additionally, the electrodialysis at 1 may generate a NaOH solution from a NapS0, solution. The Nay;30, solution may be obtainable or at least partially obtained from the regeneration bath 20 containing the HSO. solution. In such an embodiment, an apparatus 22 for removing zinc compounds from the regeneration bath may be used to remove zinc compounds from the Na,S0s; solution. For example, in the apparatus 22, the zinc present in the regeneration bath and subsequently in the Na»S0, 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. After the precipitated zinc is removed,

N remaining carbonate ions may be removed from the Na,S0.

N solution at least partially by acidifying the Na,S0, 3 30 solution prior to subjecting it to the electrodialysis 2 at 1. As another option, ZnSO; is more soluble in water

Ek than Na»S0, e.g. at a temperature of 20 °C. These * differences in solubility could be utilized for removing 8 ZNSO, at least partially. a 35 Figure 3 shows an embodiment of a process for

S preparing an alkaline cellulose dope. In this exemplary embodiment, 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 subjected to filtration and deaeration at 28. The resulting alkaline cellulose 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. However, as a skilled person will understand, 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 sulfate solution, may be removed e.g. by precipitation and filtration at 32. Optionally, sulphuric acid may be added to the filtered sodium

N sulfate solution at 33 to remove carbonates. The

N purified sodium sulfate solution may then be fed into 3 30 the electrodialysis 1 as the salt-containing 2 (electrolyte) solution. =E In addition to the sodium hydroxide 25, he * electrodialysis 1 may generate other products, which may 8 be utilized for various purposes. Sulfuric acid 34 a 35 obtainable from the electrodialysis 1 may be reused e.g.

S 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.

Figure 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 NaS0, solution) may flow through the first compartment 37, and water may flow through the second compartment 38. The electrochemical reactions occurring at the anode and the cathode are depicted. From the first compartment 37, a solution comprising H2S0, and

Na,504, or in some embodiments, only H2S0,4, may be

N obtained. From the second compartment 38, an alkaline

N solution comprising NaOH as the alkaline agent may be 3 30 obtained. © Figure 5 depicts another electrodialysis =E apparatus 1. It is similar to the one depicted in Fig. * 4, except that instead of two compartments, it has three 8 compartments. The apparatus 1 comprises, again, an anode a 35 and a cathode. The anode is in contact with a first

S 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 39 and a second semi-permeable membrane 39’. 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 Na,S0; solution) may flow through the third compartment 40, and water or an alkaline solution, such as a NaOH solution, may flow through the second compartment 38. Water and optionally a salt solution (in this example, a Nay30; solution) may flow through the first compartment 37. The electrochemical reactions occurring at the anode and the cathode are depicted.

From the third compartment 40, sulphate ions may pass through the anion exchange membrane 39’ to the first compartment 37, where they form HSO, with protons generated at the anode. From the first compartment 37, a solution comprising HS50, may thus be obtained. From the third compartment 40, Nat 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. From the second compartment 38, an alkaline solution comprising NaOH as the alkaline agent may be obtained. The solution from the third compartment may be e.g. purged.

N The electrodialysis apparatuses 1 shown in

N Figs. 4 and 5 may both produce a 10-15 wt-% NaOH 3 30 solution. However, the apparatus shown in Fig. 5 differs 2 from the one shown in Fig. 4 at least in that the =E sulphuric acid solution produced may contain less Na.S0,. * The conversion into H50, may be as high as 50-60 % with 8 the apparatus depicted in Fig. 4 and as high as nearly a 35 100 % with the apparatus depicted in Fig. 5. However,

S the three-compartment apparatus of Fig. 5 is more complex and likely to be more costly.

EXAMPLE 1

An alkaline cellulose dope was prepared from pretreated kraft pulp having CED viscosity 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 alkaline solution such that an alkaline solution containing 3 wt- % ZnO was obtained. Production of the alkaline solution was done under inert N, atmosphere to prevent absorption of CO; to the alkaline solution.

Dissolving of the cellulose was done by combining extremely low CO; content water and washed cellulose under inert N, 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 N, 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 N, atmosphere, to obtain the alkaline cellulose dope.

EXAMPLE 2

N The effect of the concentration of carbonate

N ions to the stability of alkaline cellulose dope was 3 30 investigated by producing an alkaline cellulose dope © with a low concentration of carbonate ions. Dope samples =E containing different amounts of carbonate ions (% (w/w) * based on the total weight of the alkaline cellulose 8 dope, ranging from 0.01 to 1.8 %)were produced by a 35 leading CO; gas into the newly-made dope. The newly-made

S 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. When the concentration of carbonate ions exceeded 1.2 % (W/W), the viscosity increased, indicating that the stability was reduced. when the concentration of carbonate ions exceeded 1.5 % (w/w), the stability was reduced to a significant extent.

EXAMPLE 3

Pretreated kraft pulp having CED viscosity of 170 ml/g was used in a spinning trial.

Extremely low CO, content water was produced by heating RO water to 60 °C and evaporating more than 5 % of water and CO, with reduced pressure. Pressure was so low that the water was boiling. This extremely low CO: 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 just before using. Production of alkali solution was done under inert N, atmosphere.

Dissolving of cellulose was done by combining the extremely low CO, content water and the washed

N cellulose under inert N, atmosphere and reducing

N temperature close 1 °C (without freezing the water). 3 30 When temperature was reached the alkali solution with 2 temperature close -15 °C was added under inert N, =E atmosphere. Mixing was continued for 30 minutes and * temperature at the end of dissolving step was 2 °C. 8 Temperature was slowly increased to 15 *C, while a 35 maintaining inert N, atmosphere.

S At this stage the cellulose solution was divided to two parts, where the other part was treated under inert N, atmosphere (Spinning solution (i.e. alkaline cellulose dope) A) whereas the absorption of

CO; 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 just 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 % H2S0. and 15 % NayS04). 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

N fibers made out of spinning solution B. It may be

N concluded that spinning solution A has much better 3 30 stretchability and regeneration proceeds more evenly. 2 The mechanical properties of staple fibres made out of

Ek spinning solution A are much better. For the textile * fibers both tenacity and elongation at break are 8 important properties and with spinning solution A a 35 tenacity can be above 20 cN/tex and elongation at break

S 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 3 (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.

EXAMPLE 4

An alkaline cellulose dope sample containing 7.4 % (w/w) of cellulose was stored for 5 days in a container at 4 °C, such that it was in contact with air in the container. Samples of the alkaline cellulose dope were taken on days 0, 1, and 5, and the Brookfield viscosities of the samples were measured.

Figure 9 illustrates the Brookfield 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.

It is obvious to a person skilled in the art that with the advancement of technology, the basic idea

N may be implemented in various ways. The embodiments are

N thus not limited to the examples described above; 3 30 instead they may vary within the scope of the claims. © The embodiments described hereinbefore may be =E used in any combination with each other. Several of the * embodiments may be combined together to form a further 8 embodiment. A process, a product, or a use, disclosed a 35 herein, may comprise at least one of the embodiments

S described hereinbefore. It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments.

The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item refers to one or more of those items. The term “comprising” is used in this specification to mean including the feature (s) or act (s) followed thereafter, without excluding the presence of one or more additional features or acts.

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Claims

I. A process for preparing an alkaline cellulose dope, wherein the process comprises 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, such that the absorption and/or dissolution of CO; in the cold alkaline solution is reduced or prevented, and/or the concentration of carbonate ions in the cold alkaline solution is reduced.
2. The process according to claim 1, wherein the electrodialysis is membrane electrodialysis.
3. The process according to claim 1 or 2, wherein the alkaline solution is generated online, such as by an on-line electrodialysis system or an on-line membrane electrodialysis system.
4. The process according to any one of claims 1 — 3, wherein the alkaline solution contains 0.5 g/kg or less, or 0.25 g/kg or less, or 0.05 g/kg or less of CO; dissolved therein based on the total weight of the alkaline solution, and/or wherein the concentration of carbonate ions in the alkaline solution is 1.5 % (w/w) A or lower, or 1.2 % (w/w) or lower, or 1.0 % (w/w) Or S lower, or 0.2 % (w/w) or lower, or 0.1 % (w/w) or lower.
N 5. The process according to any one of claims = 30 1 — 4, wherein the alkaline solution is a solution — comprising NaOH, LiOH, KOH, and/or any mixture or E combination thereof.
x 6. The process according to any one of claims > 1 - 5, wherein the electrodialysis produces H; gas, and N 35 the H; gas is collected.
N 7. The process according to any one of claims 1 - 6, wherein the alkaline solution is a NaOH solution generated by electrodialysis of a salt-containing solution, wherein the salt-containing solution comprises NaCl, Na2S04, NaHCO; and/or Na,COs; as the salt; wherein the NaCl, Na504, NaHCO: and/or Na,COsz is optionally obtainable or obtained from a pulp mill recovery process.
8. The process according to any one of claims 1 - 7, wherein the electrodialysis generates a NaOH solution from a NayS0Os solution; wherein the method further comprises processing the alkaline cellulose dope into a desired shape, and the processing comprises coagulating the cellulose from the alkaline cellulose dope in a regeneration bath containing NaHSO, and/or H,S0.; and the Na,S0s solution is obtainable or at least partially obtained from the regeneration bath.
9. The process according to claim 8, wherein the electrodialysis generates a NaHS0O, and/or H2S0. solution from the Na,S0; solution, and the NaHS0. and/or H2S04 solution is used in the regeneration bath.
10. The process according to any one of claims 1 - 9, wherein the alkaline solution is generated by electrodialysis of a salt-containing solution comprising a carbonate salt, such as NaHCO; and/or Na»CO:3, thereby generating the alkaline solution and a solution comprising NaHCO; and/or H,CO3, and removing CO, formed from the HCO; at least partially from the solution. N
11. The process according to any one of claims N 1 - 10, wherein water fed into the electrodialysis is 3 30 purified and/or degassed prior to feeding the water into © the electrodialysis so as to remove CO, dissolved =E therein at least partially. *
12. The process according to any one of claims 8 1 - 11, wherein the process further comprises a 35 placing the alkaline cellulose dope in a S 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 alkaline cellulose dope that is equivalent to the daily production volume or smaller.
13. The process according to claim 12, wherein the process is 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; and wherein the first and the second 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.
14. The process according to claim 12 or 13, wherein the storage tank has, and/or the first and the second storage tank 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 the daily production volume.
15. The process according to any one of claims 1 - 14, wherein the process is a continuous process.
16. An alkaline cellulose dope, wherein the alkaline cellulose dope contains 0.5 g (C0,/kg or less N dissolved therein based on the total weight of the N alkaline cellulose dope; and/or wherein the 3 30 concentration of carbonate ions in the alkaline 2 cellulose dope is 1.5 % (w/w) or lower. Ek
17. The process according to any one of claims * 1 - 15 or the alkaline cellulose dope according to claim 8 16, wherein the alkaline cellulose dope has a viscosity a 35 in the range of 2000 - 100000 mPas, or in the range of S 2000 — 20000 mPas, or in the range of 2000 - 10000 mPas, or in the range of 3000 - 6000 mPas.
18. The process according to any one of claims 1 - 15 or 17 or the alkaline cellulose dope according to claim 16 or 17, wherein the alkaline cellulose dope has 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.
19. A product obtainable by coagulating alkaline cellulose dope from a cold alkaline process, wherein the product comprises 1.0 % (w/w) or less of carbonate ions.
20. The product according to claim 19, wherein the product is obtainable from the alkaline cellulose dope according to any one of claims 16 - 18 by extruding, spinning, electrospinning, molding, casting, film forming, coating, cellulose pearl production, spraying, or printing and coagulating the alkaline cellulose dope.
21. The product according to claim 19 or 20, wherein the product is 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 sausage 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.
22. The product according to any one of claims 19 — 21, wherein the product has a CED viscosity in the range of 100 - 300 ml/g, or in the range of 140 - 200 a ml/g, or in the range of 150 - 180 ml/g. N
23. The product according to any one of claims 3 30 19 — 22, wherein the product is a filament and/or a © staple fiber and has a tenacity of 15 cN/tex or greater. = a o 3 N 35 N