EP4731830A1

EP4731830A1 - A method of treating a regeneration solution of a process of producing regenerated cellulosic material

Info

Publication number: EP4731830A1
Application number: EP24740946.9A
Authority: EP
Inventors: Daniel RICO DEL CERRO; Matti Ristolainen
Original assignee: UPM Kymmene Oy
Current assignee: UPM Kymmene Oy
Priority date: 2023-06-22
Filing date: 2024-06-05
Publication date: 2026-04-29
Also published as: CN121532551A; FI20235730A1; UY40799A; WO2024261385A1

Abstract

This specification relates to method of treating a regeneration solution (102, 202a, 202b, 302, 402, 402c) of a process of producing regenerated cellulosic material (103, 203, 303, 403) in such a way that the recirculation of the regeneration solution (102, 202a, 202b, 302, 402, 402c) and its components and/or other chemicals is enabled. The process of producing regenerated cellulosic material comprises extruding a suspension (101, 201, 301, 401) comprising cellulose material and an alkaline solution into the regeneration solution (102, 202a, 202b, 302, 402). The method comprises providing alcohol (104, 204, 304, 404) into the regeneration solution (102, 202a, 202b, 302, 402c) so as to precipitate salt(s) (105, 205, 305, 405).

Description

A method of treating a regeneration solution of a process of producing regenerated cellulosic material

Technical field

This specification relates to a method of treating a regeneration solution of a process of producing regenerated cellulosic material.

Background

Annually, the textile industry worldwide uses 100 million tons of virgin fibers, majority of which are petroleum based. There is a demand for renewable feedstocks for textile industry. Cotton production alone cannot meet this demand because of restrictions on farmland use and availability of irrigation water. Increase in the use of cellulose from other sources, in particular wood, is of major interest nowadays.

Regenerated cellulosic material refers to cellulosic material manufactured by dissolution or suspension of cellulosic material or its conversion to a soluble cellulosic derivative and subsequent regeneration of cellulosic material for example as fibers, e.g., for textile industry purposes, or films. Regeneration of cellulosic material is typically performed in dilute acidic conditions, utilizing about 8-10 % sulfuric acid (H2SO4). Regeneration of the cellulosic material causes salts to be released into the regeneration solution, thereby posing challenges for recirculation of the regeneration solution.

Summary

It is an aim of this disclosure to provide a method for treating a regeneration solution of a process of producing regenerated cellulosic material, thereby enabling recirculation of the regeneration solution and its components and/or other chemicals. The method disclosed herein is an industrial scale process, the magnitude of the volume of the regeneration solution being in thousands of cubic meters. According to an embodiment, a method of treating a regeneration solution of a process of producing regenerated cellulosic material is provided. The process of producing regenerated cellulosic material comprises extruding a suspension comprising cellulose material and an alkaline solution into the regeneration solution. The method further comprises providing alcohol into the regeneration solution so as to precipitate salt(s).

According to another embodiment, a method of producing regenerated cellulosic material is provided. The method comprises providing cellulose material, dissolving the cellulose material in an alkaline solution so as to form a suspension, extruding the suspension into a regeneration solution so as to form regenerated cellulosic material, and treating the regeneration solution by the method disclosed above.

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:

Fig. 1 illustrates, by way of an example, an overview of the method of treating a regeneration solution of a process of producing regenerated cellulosic material,

Fig. 2 illustrates, by way of an example, an overview of the method comprising a two-stage regeneration system comprising a first regeneration and a second regeneration solution,

Fig. 3 illustrates, by way of an example, the recovery and recirculation of alkaline component, alcohol, water and/or salt(s) from the regeneration solution, and

Fig. 4 illustrates, by way of an example, an overview of the method of treating a regeneration solution of a process of producing regenerated cellulosic material, wherein the used regeneration solution is drawn away from the regeneration vessel for the treatment.

The figures are schematic. The figures are not in any particular scale.

Detailed

The solution is described in the following in more detail with reference to some embodiments, which shall not be regarded as limiting.

In this description and claims, the percentage values relating to an amount of a material are percentages by weight (wt.%) unless otherwise indicated. Unit of thickness expressed as microns corresponds to pm. Unit of temperature expressed as degrees C corresponds to °C. The following reference numbers are used in this application:

101 , 201 , 301 , 401 suspension

102, 202a, 202b, 302, 402 regeneration solution

402c used regeneration solution

103, 203, 303, 403 regenerated cellulosic material

104, 204, 304, 404 alcohol

105, 205, 305, 405 salt(s)

The present disclosure provides a method of treating a regeneration solution of a process of producing regenerated cellulosic material, wherein the process of producing regenerated cellulosic material comprises extruding a suspension comprising cellulose material and an alkaline solution into the regeneration solution and the method comprises providing alcohol into the regeneration solution so as to precipitate salt(s).

Cellulose is a polysaccharide consisting of a linear chain of several hundred to many thousands of 0(1 — >4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall of green plants, many forms of algae and the oomycetes. Natural cellulose is cellulose I, with structures l_a and Ip. Regenerated, i.e. man-made, cellulose is cellulose II. Conversion of cellulose I to cellulose II is irreversible. Cellulose may be obtained from pulp. Pulp refers to lignocellulosic material separated chemically and/or mechanically from wood, fiber crops, waste paper or rags. Wood and other plant materials for pulp-making contain cellulose fibers, lignin and hemicelluloses. Feedstock for wood pulp may originate for example from birch, bamboo, beech, eucalyptus, softwood (i.e., spruce or pine), maple or aspen. Pulp may be pre-treated.

Regenerated cellulosic material may be made from cellulose material that is extracted from pulp. Alternatively or additionally, cellulose material may originate for example from hemp, flax, sisal, jute, kenaf, bamboo, agricultural fibers, or recycled fibers (e.g., recycled cotton and cotton linter). Cellulose material may be with or without hemicellulose. Cellulose material is chemically dissolved to form a colloidal suspension and subsequently extruded for example as a continuous filament or film.

The cellulose material may comprise or consist of at least one of the following: cellulosic pulp, pre-treated cellulosic pulp, hemp fibers, flax fibers, sisal fibers, jute fibers, kenaf fibers, bamboo fibers, agricultural fibers, and recycled fibers.

Within context of this specification, term “regenerated cellulosic material” comprises fibers, films, cellulosic beads, and 3D objects. Regenerated cellulosic fibers/filaments disclosed herein may particularly find use as cellulosic textile fibers in textile industry.

Within context of this specification, term “extrusion” refers to a process for forming objects of a fixed cross-sectional profile by pushing material through a die or nozzle of the desired cross-section. Extrusion also covers spinning, which is a specialized form of extrusion.

Within context of this specification, terms “fiber”, “filament”, “staple fiber” and “filament fiber” are used interchangeably to refer to natural or man-made substances that are significantly longer than they are wide. Cellulose fibers or cellulosic fibers refer to fibers predominantly consisting of cellulose. Within context of this specification, term “regeneration solution” refers to a solution by which the cellulosic material is coagulated or formed in the aimed shape or physical form. The regeneration solution can also be called a regeneration bath, a coagulation bath or a spinning bath.

According to an embodiment, the method of producing regenerated cellulosic material comprises providing cellulose material and dissolving the cellulose material in an alkaline solution, preferably at a temperature of 5 degrees C or lower, so as to form a suspension. The process of forming the suspension may also be called a cold alkali process.

The alkaline solution used for dissolving the cellulose material may comprise at least one of the following: sodium hydroxide (NaOH), potassium hydroxide (KOH), and lithium hydroxide (LiOH) as the alkaline component. NaOH may be preferred over the more expensive KOH and LiOH. The alkaline solution is an aqueous solution.

The alkaline solution preferably further comprises additive(s), such as zinc oxide (ZnO) and/or urea. The purpose of the additive(s) is to enhance the cellulose dissolution/dispersion in the alkaline solution. Urea may also be used for forming cellulose carbamate.

Duration of the dissolving step comprising dissolving the cellulose material in alkaline solution, preferably at a temperature of 5 degrees C or lower may be about 1 to 5 minutes. After that, the formed suspension may be allowed to reach room temperature. For example, the lowered temperature may be from -30 to 5 degrees C.

As mentioned, as a result of dissolving a suspension is formed. Particularly, the suspension may be a colloidal suspension. Colloidal suspension refers to a heterogeneous mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. In other words, the colloidal suspension is composed of solid particles uniformly dispersed in a liquid. Thus, as a result of the dissolving step, cellulose is uniformly dispersed in the alkaline solution. For example, the suspension may comprise from 5 to 10 wt.% of alkaline component, from 0.1 to 3 wt.% of additive(s), and/or from 5 to 15 wt.% of cellulose material. In a specific example the suspension comprises from 5 to 10 wt.% of NaOH, from 0.1 to 3 wt.% of ZnO as an additive and from 5 to 15 wt.% of cellulose material.

In the process of producing regenerated cellulosic material the suspension is extruded into a regeneration solution so as to form regenerated cellulosic material. The regenerated cellulosic material forms by coagulation (i.e., regeneration) of the extruded suspension in the regeneration solution. During the coagulation, cellulose of the suspension is solidified into the desired forms of the regenerated cellulosic material (i.e., fibers, films, cellulosic beads or 3D objects). Terms “coagulation” and “regeneration” may refer to precipitation and/or crystallization of cellulose from the solubilized state. Cellulose may be crystallized at least partially into cellulose II. Typically, the coagulated cellulose is in the form of cellulose II.

The regeneration/coagulation process releases salt(s) into the regeneration solution. For example, when acidic aqueous solution containing sulfuric acid is utilized as the regeneration solution, sulfate salt is released into the regeneration solution. When the alkaline solution of the suspension contains ZnO, zincate salt is released into the regeneration solution.

The salt(s) released to the regeneration solution are the reason why the regeneration solution cannot be recirculated and reused as such. Majority or all of the salt(s) are soluble to the aqueous regeneration solution. Thus, prior to recirculating the regeneration solution for reuse, the salt(s) have to be removed.

The method of treating the regeneration solution comprises providing alcohol into the regeneration solution so as to precipitate salt(s). The salt(s) refers to the salt(s) released to the regeneration solution by the regeneration/coagulation process for forming the regenerated cellulosic material. The regeneration solution may be an acidic, alkaline or neutral aqueous solution.

The acidic aqueous solution as the regeneration solution may comprise at least one of the following: sulfuric acid, hydrochloric acid, sodium sesquisulfate, an organic acid, and a mixture of organic acids. An example of organic acids is citric acid. The acidic aqueous solution as the regeneration solution may have acid concentration (v/v) of from 2 to 15 %, more preferably from 5 to 12 %, and even more preferably from 8 to 10 %. Sodium sesquisulfate may originate from chlorine dioxide plant of a pulp mill. The sole source of sulfate ions (if present) in the regeneration solution is sulfuric acid and/or sodium sesquisulfate. This means that no additional sulfate is added to the regeneration solution. Thus, the regeneration solution according to this disclosure deviates, e.g., from the one of a viscose (rayon) process, which includes addition of additional sulfate (such as zinc sulfate or sodium sulfate) to the acidic regeneration solution.

Alcohol may be provided to the regeneration solution prior to extruding the suspension. In that case, the extrusion takes place into a regeneration solution comprising alcohol. Alternatively, the extrusion may take place into a regeneration solution devoid of alcohol. In that case, alcohol is provided only after the extrusion and formation of the regenerated cellulosic material, i.e., to the used regeneration solution. It is also possible to draw the used regeneration solution away from regeneration vessel to be treated by adding alcohol.

The alcohol provided into the regeneration solution may be a short chain alcohol. The alcohol may be at least one of the following: methanol, ethanol, isopropanol or propanol, or any other alcohol having a boiling point lower than that of water. Preferably the alcohol is ethanol. Methanol may not be a preferred option.

Alternatively, the alcohol is one having a boiling point higher than that of water.

Once the alcohol has been provided into the regeneration solution, ratio of the alcohol : water in the regeneration solution may be at least 40 : 60, preferably at least 45 : 55, more preferably at least 80 : 20, and even more preferably at least 90 : 10.

The precipitated salt(s) preferably are separated from the regeneration solution. Separation of the precipitated salt(s) enables recirculation of the regeneration solution and/or its components as well as the salt(s) themselves. The salt(s) may be separated for example by filtering, centrifugal force or settling.

The method may further comprise treating (e.g., by carbonizing and/or calcining) the separated precipitated salt(s) to form chemicals for reuse in the method or elsewhere. For example, sodium sulfate may be recirculated to be used for adjusting pulp mill balance. The sodium sulfate may be directed to an evaporation plant or any other suitable location in a pulp mill. ZnO obtained may be recirculated for reuse in suspension as an additive of the alkaline solution.

For example, when Na2SO4 and ZnSO4 are precipitated by the addition of alcohol and subsequently separated from the regeneration solution, the salts may be dissolved in water and treated with Na2COs. ZnSO4 reacts with Na2COs to form ZnCOs, which precipitates into water while Na2SO4 remains in solution. In other words, Na2COs may be added to transform ZnSO4 to ZnCOs, thereby separating the salts present in the solution. ZnCOs may be further calcined to form ZnO. The formed ZnO may be used in alkaline solution for forming suspension. As mentioned above, Na2SO4 may be used for adjusting pulp mill balance or elsewhere. For example, Na2SO4 may be treated by electrolysis to form NaOH and H2SO4. NaOH may be reused for forming a suspension and H2SO4 may be reused in regeneration solution.

Still further, the method may comprise recovering at least one of alkaline component, alcohol and water from the regeneration solution, preferably after separating the precipitated salt(s). Recovery of alkaline component is possible when the regeneration solution is neutral or alkaline aqueous solution. Herein, the alkaline component refers to the alkaline component comprised by the alkaline solution used for preparing the suspension. Thus, the alkaline component is NaOH, KOH, or LiOH. It has been demonstrated that about 50- 70 % of the NaOH used can be recovered by utilizing the process as disclosed herein. Recovered NaOH can be recirculated, i.e. directed for reuse in preparing a new suspension comprising cellulose material and NaOH. When regeneration solution is acidic, then recycling of the alkaline component is not possible in form of base, but in form of salt, due to a neutralization reaction.

Alcohol may be recovered by distillation, preferably continuous distillation, or by any other known method. For example, when the alcohol used is ethanol, ethanol can be recovered as mainly ethanol and ethanol-water azeotrope by distillation. The ethanol-water azeotrope has a boiling point lower than that of water, thereby requiring less energy for the recovery. The recovered alcohol may be recirculated for use in treating regeneration solution. Ethanol-water azeotrope can be recirculated as such for use on treating the regeneration solution. If pure water is recovered, the recovered water may be recirculated for use in regeneration solution and/or suspension.

The recovered alkaline component may be recirculated, i.e. directed for reuse in preparing a new suspension comprising cellulose material and alkaline component. Higher alcohol content, and thus lower water content, used in the regeneration solution for precipitating the salt(s) maximizes the recovery of the alkaline component. The lower the alcohol content, the more diluted the alkaline component will be. Recovery of diluted alkaline component may be challenging.

Only one regeneration solution may be utilized. Alternatively, a two-stage regeneration system comprising a first regeneration solution and a second regeneration solution may be utilized.

In an embodiment comprising a two-stage regeneration system, the first regeneration solution may be for example neutral aqueous solution or alkaline aqueous solution, the second regeneration solution in that case being an acidic aqueous solution. For example, in the two-stage regeneration system alcohol may be provided to the first regeneration solution and optionally also to the second regeneration solution. Effect obtained by the two-stage system having a neutral or alkaline aqueous solution as the first regeneration solution when compared to a single regeneration solution comprising an acidic aqueous solution is that the recovery of alkaline component is enabled. Alcohol and/or water may be separated by distillation, thus leaving the alkaline component behind. The alkaline component may be recirculated for use in suspension.

A method of producing regenerated cellulosic material is also provided. The method comprises providing cellulose material and dissolving the cellulose material in an alkaline solution so as to form a suspension. The method also comprises extruding the suspension into a regeneration solution so as to form regenerated cellulosic material, and treating the regeneration solution by the method as disclosed herein.

An overview of the method of treating a regeneration solution of a process of producing regenerated cellulosic material is illustrated in Fig. 1. As shown by the horizontal arrows, the process of producing regenerated cellulosic material 103 comprises extruding a suspension 101 comprising cellulose material and an alkaline solution into the regeneration solution 102. The regenerated cellulosic material 103 forms in the regeneration solution 102. The method as disclosed herein comprises providing alcohol 104 into the regeneration solution 102 so as to precipitate salt(s) 105. The generic overview presented in Fig. 1 includes the possibility of having a two-stage regeneration system, even if not being explicitly illustrated. Fig. 1 also covers the options of providing alcohol to the regeneration solution prior to extruding the suspension, providing alcohol only after the extrusion, or drawing the used regeneration solution away from regeneration vessel to be treated by adding alcohol.

Fig. 2 illustrates the method comprising a two-stage regeneration system comprising a first regeneration solution 202a and a second regeneration solution 202b. Alcohol 204 is provided to the first regeneration solution 202a and optionally also to the second regeneration solution 202b so as to precipitate salt(s) 205.

Fig. 3 illustrates the recovery of alkaline component, alcohol 304, water and/or salt(s) 305 from the regeneration solution 302. Also, their recirculation for use in the method or elsewhere is shown by dashed lines. The recovery and recirculation presented in Fig. 3 also applies to Figures 1 , 2 and 4. Fig. 4 specifically illustrates the method of treating a regeneration solution of a process of producing regenerated cellulosic material, wherein the used regeneration solution 402c is drawn away from the regeneration vessel for the treatment.

Example

In an example, cellulosic pulp was dissolved in alkaline solution comprising NaOH at a temperature of 5 degrees C or lower so as to form a suspension. The suspension comprised from 5 to 10 wt.% of NaOH, from 0.1 to 3 wt.% of ZnO as an additive and from 5 to 15 wt.% of cellulosic pulp. The suspension was extruded into a regeneration solution so as to form regenerated cellulosic material. The regeneration solution was an acidic aqueous solution comprising H2SO4 and had a concentration of from 8 to 10 % (v/v) in terms of H2SO4.

Ethanol as an alcohol was provided to the regeneration solution after the extrusion. After addition of ethanol, ratio of the alcohol : water in the regeneration solution was at least 90 : 10. Caused by the addition of ethanol, Na2SO4 and ZnSO4 salts were precipitated from the regeneration solution. The salts were separated from the regeneration solution by filtration. After filtration, the formed salts (Na2SO4 and ZnSO4, both being water soluble) were dissolved in water and treated with Na2COs. ZnSO4 reacted with Na2COs to form ZnCOs, which precipitated into water while Na2SO4 remained in solution. In other words, Na2COswas added to transform ZnSO4 to ZnCOs, thereby separating the salts present in the solution. ZnCOs was further calcined to form ZnO. ZnO formed was used in alkaline solution for forming suspension. Na2SO4was used for adjusting pulp mill balance or elsewhere. Na2SO4 may also be treated by electrolysis to form NaOH and H2SO4.

Ethanol was recovered from the regeneration solution by continuous distillation as mainly ethanol and ethanol-water azeotrope. The recovered alcohol was recirculated for use in treating regeneration solution. Recovered water was recirculated for use in regeneration solution and/or suspension. Recirculation for use in suspension requires the water-azeotrope fraction being disposed prior to recirculation.

Claims

Claims:

1. A method of treating a regeneration solution (102, 202a, 202b, 302, 402, 402c) of a process of producing regenerated cellulosic material (103, 203, 303, 403), wherein the process of producing regenerated cellulosic material comprises extruding a suspension (101 , 201 , 301 , 401 ) comprising cellulose material and an alkaline solution into the regeneration solution (102, 202a, 202b, 302, 402), and the method comprises providing alcohol (104, 204, 304, 404) into the regeneration solution (102, 202a, 202b, 302, 402, 402c) so as to precipitate salt(s) (105, 205, 305, 405).

2. The method according to claim 1 , wherein the suspension (101 , 201 , 301 , 401 ) has been produced by dissolving the cellulose material in the alkaline solution at a temperature of 5 degrees C or lower.

3. The method according to any of the preceding claims, wherein the regeneration solution (102, 202a, 202b, 302, 402) is acidic, alkaline or neutral aqueous solution.

4. The method according to claim 3, wherein the acidic aqueous solution comprises at least one of the following: sulfuric acid, hydrochloric acid, sodium sesquisulfate, an organic acid, and a mixture of organic acids.

5. The method according to claim 3 or 4, wherein the acidic aqueous solution has acid concentration of from 2 to 15 % (v/v).

6. The method according to any of the preceding claims, wherein the alcohol (104, 204, 304, 404) is a short chain alcohol.

7. The method according to any of the preceding claims, wherein the alcohol (104, 204, 304, 404) is at least one of the following: methanol, ethanol, isopropanol or propanol, or any other alcohol having a boiling point lower than water.

8. The method according to any of the preceding claims, wherein ratio of the alcohol : water in the regeneration solution (102, 202a, 202b, 302, 402c) is at least 40 : 60, preferably at least 45 : 55, more preferably at least 80 : 20, even more preferably at least 90 : 10.

9. The method according to any of the preceding claims, wherein the method further comprises

- separating the precipitated salt(s) (105, 205, 305, 405) from the regeneration solution (102, 202a, 202b, 302, 402c).

10. The method according to claim 9, wherein the salt(s) (105, 205, 305, 405) is/are separated by filtering, centrifugal force or settling.

11. The method according to claim 9 or 10, wherein the method further comprises

- treating the separated precipitated salt(s) (105, 205, 305, 405) to form chemicals for reuse in the method or elsewhere.

12. The method according to any of the preceding claims, wherein the method further comprises

- recovering at least one of alkaline component, alcohol (104, 204, 304, 404) and water from the regeneration solution (102, 202a, 202b, 302, 402c).

13. The method according to claim 12, wherein the alcohol (104, 204, 304, 404) is recovered by continuous distillation.

14. The method according to any of the claims 9-13, wherein the method further comprises recirculating

- the recovered alkaline component for use in suspension, and/or

- the recovered alcohol (104, 204, 304, 404) for use in treating regeneration solution, and/or

- the recovered water for use in regeneration solution (102, 202a, 202b, 302, 402) and/or suspension, and/or

- the recovered precipitated salt (105, 205, 305, 405) for adjusting pulp mill balance or to be used elsewhere, and/or

- obtained zinc oxide for use in suspension.

15. The method according to any of the preceding claims, wherein the regeneration solution (102, 202a, 202b, 302, 402) comprises one regeneration solution, or a two-stage regeneration system comprising a first regeneration solution (202a) and a second regeneration solution (202b).

16. A method of producing regenerated cellulosic material (103, 203, 303, 403), the method comprising

- providing cellulose material, - dissolving the cellulose material in an alkaline solution so as to form a suspension (101 , 201 , 301 , 401 ),

- extruding the suspension (101 , 201 , 301 , 401 ) into a regeneration solution (102, 202a, 202b, 302, 402) so as to form regenerated cellulosic material (103, 203, 303, 403), and - treating the regeneration solution (102, 202a, 202b, 302, 402c) by a method according to any of the preceding claims.