EP4731829A1

EP4731829A1 - A method of producing regenerated cellulosic material

Info

Publication number: EP4731829A1
Application number: EP24733656.3A
Authority: EP
Inventors: Daniel RICO DEL CERRO
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: UY40798A; FI131613B1; WO2024261386A1; FI20235731A1; CN121399326A

Abstract

This specification relates to a method of producing regenerated cellulosic material for example for use in textile industry. The method enables utilization of a residue or side stream of a pulp mill. The method comprises providing cellulose material (1), dissolving (2) the cellulose material (1) in an alkaline solution at a temperature of 5 degrees C or lower so as to form a suspension, providing sodium sesquisulfate (6) produced as a waste stream in a chlorine dioxide plant of a pulp mill (4) for use in a regeneration solution (7) and extruding (3) the suspension into a regeneration solution (7) comprising sodium sesquisulfate (6) so as to form regenerated cellulosic material (8).

Description

A method of producing regenerated cellulosic material

Technical field

This specification relates to a method 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 of natural cellulose or its conversion to a soluble cellulosic derivative and subsequent regeneration of any cellulosic material including for example fibers, filaments, textile fibers, cellulose beads, 3D objects or films. Regeneration of cellulosic material is traditionally performed in dilute acidic conditions, utilizing about 8-10 % sulfuric acid (H2SO4).

Chemical pulp mills produce a number of waste streams, sodium sesquisulfate (sesqui salt) produced in the chlorine dioxide generator/plant being one of them. Chlorine dioxide production includes reduction of sodium chlorate by methanol in strongly acidic conditions. The solid byproduct, sodium sesquisulfate, is produced as a salt cake and separated with a filter. Production of one ton of chlorine dioxide generates 1.35 tons of sodium sesquisulfate. Conventionally the sodium sesquisulfate is neutralized with NaOH to produce sodium sulfate (Na2SO4). Na2SO4 is then fed into the evaporation plant of the pulp mill. Neutralization of 1.35 tons of sodium sesquisulfate produces 1.46 tons of Na2SO4. Conversion of sodium sesquisulfate to Na2SO4 consumes NaOH and energy and causes costs. Furthermore, the transformation process has associated CO2 equivalent emissions.

It is an aim of this disclosure to provide a method for producing regenerated cellulosic material, the method enabling utilization of a waste stream of a pulp mill. The present disclosure focuses on the utilization of pulp mill byproduct sodium sesquisulfate in regenerated cellulosic material production.

Conventionally the sodium sesquisulfate, that is produced as a side product of chlorine dioxide production in a chlorine dioxide plant of a pulp mill, is transformed to sodium sulfate, which is then fed into evaporation plant of the pulp mill. The conventional transformation process of sodium sesquisulfate to sodium sulfate includes a filtration process of the regeneration liquors from chlorine dioxide production and a metathesis reaction at 70-85 degrees C in presence of water followed by a second filtration process. The final stage for the utilization of the sodium sulfate requires a pH adjustment by sodium hydroxide (NaOH). Thus, the conventional transformation process of sodium sesquisulfate is both energy consuming and costly process. Furthermore, the transformation process has associated CO2 equivalent emissions. The conventional transformation process can be bypassed as disclosed herein by utilizing sodium sesquisulfate in the regeneration solution in the cellulose regeneration, after which sodium sulfate, that is formed as the residue of sodium sesquisulfate in the cellulose regeneration, can be fed into the evaporation plant as it is currently done in the conventional sodium sesquisulfate transformation process. This leads to energy and cost savings and reduced CO2 equivalent emission.

The present disclosure provides a method of producing regenerated cellulosic material. The method comprises providing cellulose material and dissolving the cellulose material in an alkaline solution at a temperature of 5 degrees C or lower so as to form a suspension. The method further comprises providing sodium sesquisulfate produced as a waste stream in a chlorine dioxide plant of a pulp mill for use in a regeneration solution, and extruding the suspension into the regeneration solution comprising sodium sesquisulfate so as to form regenerated cellulosic material. The solution disclosed herein provides a method for creating added value products for use e.g., in textile industry by utilizing pulp mill waste stream (sodium sesquisulfate). The method enables reducing the pulp mill’s energy needs, make-up chemicals needed, as well as CO2 equivalent emissions produced. Further, the method helps at decreasing or avoiding consumption of sulfuric acid in traditional regeneration of cellulosic material. The disclosed method enables optimization of energy and chemicals from both pulp mill and production of added value products’ perspective. The method disclosed herein is an industrial scale process, the magnitude of the volume of the regeneration solution being in thousands of cubic meters. The method enables utilization of a residue or waste stream of a pulp mill, thereby aligning with the European targets toward zero residues.

Brief of the

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 shows a representation of an embodiment of a process for producing regenerated cellulosic material. The figure is schematic. The figure is not in any particular scale.

Fig. 2 shows scanning electron microscope (SEM) images of regenerated cellulosic filaments produced by a) a reference method, b) the method disclosed here. The filaments are presented as cross sections.

Fig. 3 shows scanning electron microscope (SEM) images of regenerated cellulosic filaments produced by a) a reference method, b) the method disclosed here. The filaments are presented lengthwise.

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:

1 Cellulose material

2 Dissolving (the cellulose material in alkaline solution as to form a suspension)

3 Extruding (the suspension)

4 Pulp mill

5 Chlorine dioxide plant

6 Sodium sesquisulfate

7 Regeneration solution

8 Regenerated cellulosic material

9 Purifying (the regeneration solution)

10 Evaporation plant

11 Purified regeneration solution

12 Extracted/recovered sodium sulfate

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 cellulosic material that is extracted from pulp. Alternatively or additionally, cellulosic 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.

Within context of this specification, term “regenerated cellulosic material” comprises fibers/filaments, 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. The regeneration solution may comprise also a two-stage regeneration system which includes a first regeneration solution and a second regeneration solution.

A method of producing regenerated cellulosic material is provided. The method comprises providing cellulose material, and dissolving the cellulose material in an alkaline solution at a 5 degrees C or lower so as to form a suspension. The method comprises providing sodium sesquisulfate produced as a waste stream in a chlorine dioxide plant of a pulp mill for use in a regeneration solution. The method further comprises extruding the suspension into the regeneration solution comprising sodium sesquisulfate so as to form regenerated cellulosic material. 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. In an example, the cellulose material comprises or consists of cellulosic pulp and/or pre-treated cellulosic pulp.

The alkaline solution that is used in 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. In addition, according to an embodiment, the alkaline solution 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.

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

As mentioned, the dissolving step results in formation of a suspension of dissolved cellulose material. Particularly, the suspension may be a colloidal suspension. Colloidal suspension refers to a heterogenous 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.

In an example, the formed suspension comprises from 5 to 10 wt.% of NaOH, KOH or LiOH, 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.

The viscosity of the alkaline cellulose suspension may be adjusted so as to be desirable for processing. Cellulosic material is regenerated or formed from the alkaline cellulose suspension by extruding the produced suspension into the regeneration solution comprising sodium sesquisulfate produced as a waste stream in a chlorine dioxide plant of a pulp mill.

From the chlorine dioxide plant the sodium sesquisulfate is transferred for use in the regeneration solution. Use in the regeneration solution refers to use in acidification of the regeneration solution. The sodium sesquisulfate can be transferred either prior to or after its dilution once it has been filtered, preferably prior to dilution. If the sodium sesquisulfate is taken for use prior to dilution, the sodium sesquisulfate can be transferred in its filtered (solid) form, which is more economical as the transferred volume is smaller compared to transferring the diluted filtered sodium sesquisulfate. However, the sodium sesquisulfate can be diluted or re-concentrated according to technical needs. Thus, the sodium sesquisulfate as a solid waste stream or a diluted waste stream, preferably as a solid waste stream, is used for acidification of the regeneration solution. In an example, desired pH of the regeneration solution is from 0.5 to 1.5, for example about 0.9. In an exemplary embodiment, the regeneration solution consists of sodium sesquisulfate solution.

As mentioned, the sodium sesquisulfate, that is used in the regeneration solution, is produced as a waste stream or side stream of chlorine dioxide production in a chlorine dioxide plant of a pulp mill. Preferably the production of the regenerated cellulose takes place close to or as an integral part of the pulp mill. Thus, the sodium sesquisulfate used can be produced internally and long transportation is not needed for providing it for use as disclosed herein.

In an embodiment, the sodium sesquisulfate has iron content below 500 ppm, phosphorus content below 800 ppm, and/or chloride content below 0.5 ppm. Preferably total chlorine content (elemental chlorine) is up to 800 ppm. The regeneration solution may have sodium sesquisulfate concentration of from 5 to 18 wt.%. The alkaline cellulose suspension is formed into desired shape by extruding the suspension through e.g. a die or a nozzle into the regeneration solution. The regenerated cellulosic material may be formed e.g. into fibers, films, cellulosic beads or 3D objects. Particularly, the fibers may find use as textile fibers. The regenerated cellulosic material forms by coagulation (i.e., regeneration) of the extruded suspension in the regeneration solution comprising sodium sesquisulfate, waste stream of a pulp mill as a feedstock. During the coagulation, cellulose of the suspension solidifies into the desired form. 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, sulfate salt is released into the regeneration solution containing sodium sesquisulfate. When the alkaline solution of the suspension contains ZnO, zincate salt is released into the regeneration solution. Prior to recirculating the regeneration solution for reuse, the salt(s) have to be removed. The sole source of sulfate ions in the regeneration solution is 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.

The regeneration solution may be purified. The regeneration solution can be purified by providing alcohol so as to precipitate salt(s). Alcohol is preferably provided to the regeneration solution after extruding the suspension. In that case, the extrusion takes place into a regeneration solution containing no alcohol. Alcohol may be added after taking the regeneration solution for purification. For example, the purification may take place in a vessel that is different from the vessel wherein the extrusion takes place. Alternatively, alcohol may be provided into the regeneration solution prior to extruding the suspension. In that case, the extrusion takes place into a regeneration solution comprising alcohol. The precipitated salt(s) can be separated from the regeneration solution. The separated salt(s) can be treated to form chemicals for reuse in the method. Alcohol may also be recovered from the regeneration solution, for example by distillation, and reused for regeneration solution purification. Purified regeneration solution may be recirculated back for reuse in regeneration solution.

When NaOH is used as the alkaline component of the alkaline solution used for preparing the suspension, sodium sesquisulfate of the regeneration solution reacts with NaOH of the suspended cellulose once it is extruded into the regeneration solution, thereby forming sodium sulfate. The sodium sulfate may be recovered from the purified regeneration solution and fed into an evaporation plant of a pulp mill.

Figure 1 illustrates an overview of a process for producing regenerated cellulosic material as provided herein. Cellulose material (1 ) is provided, and the cellulose material (1 ) is dissolved (2) in an alkaline solution as to form a suspension. The suspension is further extruded (3) into a regeneration solution (7) so as to form regenerated cellulosic material (8). The regeneration solution comprises sodium sesquisulfate (6), that is formed in a pulp mill (4) at a chlorine dioxide plant (5) as a waste stream of chlorine dioxide production. The regenerated cellulosic material (8) can be extracted from the regeneration solution for its desired application (e.g., for use as textile fibers). The regeneration solution can be further purified (9). The purified regeneration solution (11 ) can be recirculated for use in the regeneration solution (7) and the recovered sodium sulfate (12) be fed to an evaporation plant (10) of a pulp mill (4).

Example

Regenerated cellulosic filaments were formed by using a reference method, where sulfuric acid (8.9 %) was used in the regeneration solution, as well as with the method disclosed herein, utilizing sodium sesquisulfate (8.9 %) from a pulp mill in the regeneration solution. Figures 2 and 3 show scanning electron microscope (SEM) images of regenerated cellulosic filaments. In Figure 2 the regenerated cellulosic filaments are presented as cross sections. In Figure 3 the regenerated cellulosic filaments are presented lengthwise (with 500x magnification). Figures 2a) and 3a) show the regenerated cellulosic filaments produced with the reference method and Figures 2b) and 3b) show the regenerated cellulosic filaments produced with the method disclosed herein.

The SEM images show that the appearance of the cellulosic filaments obtained by using a regeneration solution comprising sesquisulfate very well resembles that of those gained by using the conventional method. Further, comparable mechanical properties (tenacity and elongation at break) were observed for filaments obtained by the reference method and the method according to this disclosure.

Claims

Claims:

1. A method of producing regenerated cellulosic material, the method comprising

- providing cellulose material (1 ),

- dissolving (2) the cellulose material (1 ) in an alkaline solution at a temperature of 5 degrees C or lower so as to form a suspension,

- providing sodium sesquisulfate (6) produced as a waste stream in a chlorine dioxide plant of a pulp mill (4) for use in a regeneration solution (7), and

- extruding (3) the suspension into the regeneration solution (7) comprising sodium sesquisulfate (6) so as to form regenerated cellulosic material (8).

2. The method according to claim 1 , wherein the cellulose material (1 ) comprises or consists of cellulosic pulp and/or pre-treated cellulosic pulp.

3. The method according to claim 1 or 2, wherein the alkaline solution comprises at least one of the following: sodium hydroxide, potassium hydroxide, and lithium hydroxide.

4. The method according to any of the preceding claims, wherein the alkaline solution comprises additive(s), such as zinc oxide and/or urea.

5. The method according to any of the preceding claims, wherein the lowered temperature is from -30 to 5 degrees C.

6. The method according to any of the preceding claims, wherein the suspension comprises

- from 5 to 10 wt.% of sodium hydroxide,

- from 0.1 to 3 wt.% of additive(s), and/or

- from 5 to 15 wt.% of cellulose material.

7. The method according to any of the preceding claims, wherein the sodium sesquisulfate (6) as a solid waste stream or a diluted waste stream, preferably as a solid waste stream, is used for acidification of the regeneration solution (7).

8. The method according to any of the preceding claims, wherein the sodium sesquisulfate (6) has iron content below 500 ppm, phosphorus content below 800 ppm, and/or chloride content below 0.5 ppm.

9. The method according to any of the preceding claims, wherein the regeneration solution (7) has sodium sesquisulfate (6) concentration of from 5 to 18 wt.%.

10. The method according to any of the preceding claims, further comprising purifying (9) the regeneration solution (7) by providing alcohol so as to precipitate salt(s) and form purified regeneration solution (11 ).

11. The method according to claim 10, further comprising recovering sodium sulfate (12) from the purification (9) of the regeneration solution (7), and feeding the sodium sulfate (12) into an evaporation plant (10) of a pulp mill (4).

12. The method according to claim 10 or 11 , further comprising feeding the purified regeneration solution (11 ) for reuse in regeneration solution (7).

13. The method according to any of the preceding claims, wherein the regenerated cellulosic material (8) comprises fibers, films, cellulosic beads or 3D objects.