Method for producing regenerated cellulose material
By directly utilizing sodium sesquisulfate produced by the chlorine dioxide unit in the pulp mill as waste stream during the cellulose regeneration process, the problems of high energy consumption and high cost of traditional conversion processes have been solved, and efficient and environmentally friendly production of regenerated cellulose materials has been achieved.
Patent Information
- Application Number
- CN202480041655.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-06-22
- Filing Date
- 2024-06-05
- Publication Date
- 2026-01-23
AI Technical Summary
In existing technologies, the conversion process of sodium sesquisulfate byproducts generated during the production of chlorine dioxide in pulp mills is energy-intensive and costly, and also produces equivalent CO2 emissions, making it difficult to utilize effectively.
In the cellulose regeneration process, sodium sesquisulfate produced by the chlorine dioxide unit of the pulp mill is directly used as waste stream in the regeneration solution, bypassing the traditional conversion process. Cellulose is dissolved in an alkaline solution to form a suspension and then extruded into regenerated cellulose material.
It reduces the energy demand and chemical consumption of pulp mills, lowers production costs, and reduces CO2 equivalent emissions, achieving efficient utilization of pulp mill waste streams.
Smart Images
Figure CN121399326A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present specification relates to a method of producing regenerated cellulosic material. BACKGROUND
[0002] The global textile industry uses 100 million tons of virgin fibers each year, most of which are petroleum-based fibers. There is a need for renewable feedstock in the textile industry. Cotton production alone cannot meet this demand due to limitations in arable land usage and irrigation water. Increasing the use of cellulose from other sources, particularly wood, has become a highly focused issue today.
[0003] Regenerated cellulosic material refers to a cellulosic material that is manufactured by dissolving natural cellulose or converting it into a soluble cellulose derivative and then regenerating any cellulosic material, including, for example, fibers, filaments, textile fibers, cellulose beads, 3D objects, or films. Regeneration of cellulosic material has traditionally been performed under dilute acid conditions using about 8-10% sulfuric acid (H2SO4).
[0004] Chemical pulp mills produce a variety of waste streams, one of which is sodium hemi-sulfate (hemi-salt) produced in the chlorine dioxide generator / plant. Production of chlorine dioxide involves reduction of sodium chlorate with methanol under strongly acidic conditions. The solid by-product sodium hemi-sulfate is produced as a salt cake and separated by a filter. Production of one ton of chlorine dioxide produces 1.35 tons of sodium hemi-sulfate. Conventionally, the sodium hemi-sulfate is neutralized with NaOH to give sodium sulfate (Na2SO4). The Na2SO4is then sent to the pulp mill’s evaporation plant. Neutralization of 1.35 tons of sodium hemi-sulfate gives 1.46 tons of Na2SO4. Conversion of sodium hemi-sulfate to Na2SO4consumes NaOH and energy, resulting in cost. In addition, the conversion process generates a corresponding CO2equivalent emission. SUMMARY
[0005] It is an object of the present disclosure to provide a method of producing regenerated cellulosic material that is capable of utilizing waste streams from a pulp mill. The present disclosure focuses on utilizing the pulp mill by-product sodium hemi-sulfate to produce regenerated cellulosic material.
[0006] Typically, sodium disulfate, which is a by-product of the production of chlorine dioxide in a pulp mill, is converted to sodium sulfate and then fed to the evaporation plant of the pulp mill. The conventional conversion process of sodium disulfate to sodium sulfate includes a filtration process of the regeneration liquor from the chlorine dioxide production, and a double decomposition reaction in the presence of water at 70-85 degrees Celsius, followed by a second filtration process. The final stage of utilization of sodium sulfate requires pH adjustment by sodium hydroxide (NaOH). Therefore, the conventional conversion process of sodium disulfate is an energy and cost intensive process. In addition, the conversion process also generates corresponding CO2 equivalent emissions. As described herein, the conventional conversion process can be bypassed by using sodium disulfate in the regeneration solution in the process of cellulose regeneration, after which the sodium sulfate formed as a residue of sodium disulfate in the process of cellulose regeneration can be directly fed to the evaporation plant as is currently done in the conventional conversion process of sodium disulfate. This results in energy and cost savings, and reduction of CO2 equivalent emissions.
[0007] The present disclosure provides a method of producing a regenerated cellulose material. The method includes providing a cellulose material and dissolving the cellulose material in an alkaline solution having a temperature of 5 degrees Celsius or less, thereby forming a suspension. The method further includes providing sodium disulfate produced as a waste stream in a chlorine dioxide production plant of a pulp mill, for use in a regeneration solution, and extruding the suspension into the regeneration solution containing the sodium disulfate, thereby forming the regenerated cellulose material.
[0008] The approach disclosed herein provides a method of producing value added products by utilizing a pulp mill waste stream (sodium disulfate) for use in, for example, the field of textile industry. The method enables reduction in energy demand, required make-up chemicals, and generated CO2 equivalent emissions of the pulp mill. In addition, the method helps to reduce or avoid sulfuric acid consumption in the conventional process of cellulose regeneration. The disclosed method enables optimization of energy and chemicals from the perspective of pulp mill and value added product production. The method disclosed herein is an industrial scale process with a volume of the regeneration solution in the order of thousands of cubic meters. The method enables utilization of the residue or waste stream of the pulp mill, thereby complying with the European goal of zero residue. BRIEF DESCRIPTION OF DRAWINGS
[0009] The accompanying drawings are included to provide a further understanding of embodiments and are incorporated in and constitute a part of this specification, illustrate various embodiments. In the drawings: Figure 1 A schematic representation of an embodiment of a method for producing a regenerated cellulose material is shown. The figure is schematic. The figure is not in any particular scale.
[0010] Figure 2Scanning electron microscope (SEM) images of regenerated cellulose filaments produced by a) reference method, b) method disclosed herein are shown. These filaments are presented in cross-section.
[0011] Figure 3 Scanning electron microscope (SEM) images of regenerated cellulose filaments produced by a) reference method, b) method disclosed herein are shown. These filaments are presented in cross-section. DETAILED DESCRIPTION
[0012] The solution will be described in more detail below with reference to some embodiments, which are not to be seen as limiting.
[0013] In the present description and claims, unless otherwise stated, the percentage values relating to the amount of a material are all percentages by weight (wt%). The unit of thickness expressed in micrometers corresponds to pm. The unit of temperature expressed in degrees Celsius corresponds to °C. In the present application the following notations are used: 1 Cellulose material 2 Dissolution (dissolving the cellulose material in an alkaline solution, forming a suspension) 3 Extrusion (of the suspension) 4 Pulp mill 5 Chlorine dioxide installation 6 Sodium metabisulfate 7 Regeneration solution 8 Regenerated cellulose material 9 Purification (of the regeneration solution) 10 Evaporation installation 11 Purified regeneration solution 12 Extracted / recovered sodium sulfate Cellulose is a polysaccharide consisting of linear chains of several hundred to several thousand beta (1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall of green plants, various algae and oomycete organisms. Native cellulose is cellulose I, having structure I α and I β . Regenerated cellulose, i.e. artificial cellulose, is cellulose II. The conversion of cellulose I to cellulose II is irreversible.
[0014] Cellulose can be obtained from pulp. Pulp refers to lignocellulosic material that is separated from wood, fiber crops, waste paper or rags by chemical and / or mechanical means. The wood and other plant material used for pulping contains cellulose fibers, lignin and hemicellulose. The raw material for wood pulp can come from, for example, birch, bamboo, beech, eucalyptus, softwood (i.e. spruce or pine), maple or poplar. The pulp can be pretreated.
[0015] The regenerated cellulose material can be made from cellulose material extracted from pulp. Alternatively or additionally, the cellulose material can also be derived from, for example, hemp, flax, sisal, jute, kenaf, bamboo, agricultural fibers, or recycled fibers (e.g., recycled cotton and cotton linter). The cellulose material can or can not contain hemicellulose. The cellulose material is chemically solubilized to form a colloidal suspension, which is then extruded into, for example, continuous filaments or films.
[0016] In the context of the present specification, the term "regenerated cellulose material" includes fibers / filaments, films, cellulose beads, and three-dimensional objects. The regenerated cellulose fibers / filaments described herein can be used in the textile industry, among other uses, as cellulose textile fibers.
[0017] In the context of the present specification, the term "extrusion" refers to a process of forming an object having a fixed cross-sectional profile by pushing a material through a die or nozzle having the desired cross-section. Extrusion also encompasses spinning, which is a special form of extrusion.
[0018] In the context of the present specification, the terms "fiber," "filament," "staple fiber," and "filament fiber" are used interchangeably to refer to a natural or man-made substance having a length substantially greater than a width. Cellulose fiber or cellulosic fiber refers to a fiber that is primarily composed of cellulose.
[0019] In the context of the present specification, the term "regeneration solution" refers to a solution used to coagulate or form a cellulose material into a target shape or physical form. The regeneration solution can also be referred to as a regeneration bath, a coagulation bath, or a spinning bath. The regeneration solution can also include a two-stage regeneration system that includes a first regeneration solution and a second regeneration solution.
[0020] A method of producing a regenerated cellulose material is provided. The method includes providing a cellulose material and dissolving the cellulose material in an alkaline solution at 5 degrees Celsius or less, thereby forming a suspension. The method includes providing sodium metabisulfite produced as a waste stream in a pulp mill chlorine dioxide plant for use in a regeneration solution. The method also includes extruding the suspension into the regeneration solution comprising sodium metabisulfite, thereby forming the regenerated cellulose material.
[0021] The cellulosic material can comprise, or consist of, at least one of: cellulosic pulp, pretreated cellulosic pulp, hemp fibers, flax fibers, sisal fibers, jute fibers, kenaf fibers, agricultural fibers, and recycled fibers. In one example, the cellulosic material comprises, or consists of, cellulosic pulp and / or pretreated cellulosic pulp.
[0022] The alkaline solution for dissolving the cellulosic material can comprise, as an alkaline component, at least one of: sodium hydroxide (NaOH), potassium hydroxide (KOH), and lithium hydroxide (LiOH). NaOH can be more preferred than the more expensive KOH and LiOH. The alkaline solution is an aqueous solution. Further, according to one embodiment, the alkaline solution comprises an additive, such as zinc oxide (ZnO) and / or urea. The purpose of the additive is to enhance the dissolution / dispersion of cellulose in the alkaline solution. Urea can also be used to form cellulose carbamates.
[0023] Preferably, the duration of the dissolving step (comprising dissolving the cellulosic material in the alkaline solution at a temperature of 5 degrees Celsius or less) is about 1 to 5 minutes. For example, the lower temperature can be -30 degrees Celsius to 5 degrees Celsius. Thereafter, the formed suspension can be brought to room temperature.
[0024] As previously mentioned, the dissolving step results in the formation of a suspension of dissolved cellulose. In particular, the suspension can be a colloidal suspension. A colloidal suspension refers to a heterogeneous mixture in which one substance (consisting of microscopically dispersed insoluble particles) is suspended in another substance. In other words, a colloidal suspension comprises solid particles uniformly dispersed in a liquid. Thus, as a result of the dissolving step, the cellulose is uniformly dispersed in the alkaline solution.
[0025] In one example, the formed suspension comprises 5 to 10 weight percent of NaOH, KOH, or LiOH, 0.1 to 3 weight percent of an additive, and / or 5 to 15 weight percent of the cellulosic material. In a specific example, the suspension comprises 5 to 10 weight percent of NaOH, 0.1 to 3 weight percent of ZnO as an additive, and 5 to 15 weight percent of the cellulosic material.
[0026] The viscosity of the alkaline cellulose suspension can be adjusted to be suitable for processing. Cellulose material is regenerated or formed from the alkaline cellulose suspension by extruding the resulting suspension into a regeneration solution comprising sodium metabisulfite produced as a waste stream in a pulp mill chlorine dioxide plant.
[0027] The sodium metabisulfite is transferred from the chlorine dioxide plant for use in a regeneration solution. By regeneration solution is meant for acidifying the regeneration solution. The sodium metabisulfite can be transferred after filtration, before dilution or after dilution, preferably before dilution. If the sodium metabisulfite is used before dilution, the sodium metabisulfite can be transferred in its filtered (solid) form, which is more economical because of the smaller volume compared to transferring the filtered sodium metabisulfite which is diluted. However, the sodium metabisulfite can also be diluted or re-concentrated as required by the technology. Thus, the sodium metabisulfite can be used for acidifying the regeneration solution as a solid waste stream or as a diluted waste stream, preferably as a solid waste stream. In an example, the 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 a sodium metabisulfite solution.
[0028] As mentioned before, the sodium metabisulfite used in the regeneration solution is produced as a waste stream or side stream from the production of chlorine dioxide in a pulp mill. Preferably, the regenerated cellulose is produced in the vicinity of the pulp mill, or as an integral part of the pulp mill. Thus, the sodium metabisulfite used can be produced in-house and used as described herein without the need for long distance transportation.
[0029] In an embodiment, the sodium metabisulfite has an iron content of less than 500 ppm, a phosphorous content of less than 800 ppm, and / or a chloride content of less than 0.5 ppm. Preferably, the total chlorine content (elemental chlorine) is at most 800 ppm.
[0030] The concentration of the sodium metabisulfite in the regeneration solution can be from 5 to 18 wt.%. The alkaline cellulose suspension is shaped into a desired shape by extruding the suspension through, for example, a die or nozzle into the regeneration solution. The regenerated cellulose material can be shaped into, for example, fibers, films, cellulose beads or three-dimensional objects. In particular, the fibers can be used as textile fibers. The regenerated cellulose material is formed by coagulating (i.e. regenerating) the suspension by extruding the suspension in a regeneration solution comprising sodium metabisulfite, the waste stream of a pulp mill as a raw material. During coagulation, the cellulose in the suspension is set into the desired form. The terms "coagulation" and "regeneration" can refer to the precipitation and / or crystallization of the cellulose from a dissolved state. The cellulose can be at least partially crystallized into cellulose II. Typically, the coagulated cellulose is in the form of cellulose II.
[0031] The regeneration / coagulation process releases salts into the regeneration solution. For example, sulphate salts are released into the regeneration solution containing sodium metabisulphate. When the alkaline solution of the suspension contains ZnO, zincate salts are released into the regeneration solution. These salts must be removed before the regeneration solution can be recycled. The only source of sulphate ions in the regeneration solution is sodium metabisulphate. This means that the regeneration solution is not additionally charged with sulphate salts. Thus, the regeneration solution of the present disclosure is different from, for example, the regeneration solution in the viscose (rayon) process, which involves the addition of additional sulphate salts (e.g. zinc sulphate or sodium sulphate) to the acidic regeneration solution.
[0032] The regeneration solution can be purified. The regeneration solution can be purified by providing an alcohol so as to precipitate the salts. Preferably, the alcohol is provided to the regeneration solution after the suspension is extruded. In this case, the extrusion is performed in a regeneration solution that does not contain alcohol. The alcohol can also be added after the purification of the regeneration solution. For example, the purification can be performed in a different vessel than the vessel in which the extrusion is performed. Alternatively, the alcohol can also be provided to the regeneration solution before the suspension is extruded. In this case, the extrusion is performed in a regeneration solution that contains alcohol.
[0033] The precipitated salts can be separated from the regeneration solution. The separated salts can be processed to form chemicals that can be reused in the process. The alcohol can also be recovered from the regeneration solution, for example by distillation, and reused for the purification of the regeneration solution. The purified regeneration solution can be recycled for reuse in the regeneration solution.
[0034] When NaOH is used as the alkaline component of the alkaline solution with which the suspension is prepared, once the suspension is extruded into the regeneration solution, the sodium metabisulphate in the regeneration solution reacts with the NaOH in the suspended cellulose to form sodium sulphate. The sodium sulphate can be recovered from the purified regeneration solution and fed into the evaporation plant of the pulp mill.
[0035] Figure 1 A process overview of the regenerated cellulose material described herein is shown. A cellulose material (1) is provided and then dissolved (2) in an alkaline solution to form a suspension. The suspension is further extruded (3) into a regeneration solution (7) to form a regenerated cellulose material (8). The regeneration solution comprises sodium metabisulphate (6) that is produced as a waste stream at a chlorine dioxide plant (5) in a pulp mill (4). The regenerated cellulose material (8) can be extracted from the regeneration solution for its intended use (e.g. as a textile fibre). The regeneration solution can be further purified (9). The purified regeneration solution (11) can be recycled for use in the regeneration solution (7) and the recovered sodium sulphate (12) is fed into the evaporation plant (10) of the pulp mill (4).
[0036] Examples
[0037] Regenerated cellulose filaments were formed using a reference method (sulfuric acid (8.9%) in the regeneration solution) and the method disclosed herein (sodium metabisulfate from a pulp mill (8.9%) in the regeneration solution). Figure 2 and Figure 3 Scanning electron microscope (SEM) images of regenerated cellulose filaments are shown. Figure 2 Regenerated cellulose filaments are shown in cross-section in FIG. 1. Figure 3 In FIG. 2, the longitudinal morphology (500x magnification) of regenerated cellulose filaments is shown. Figure 2 a) and 3a) show regenerated cellulose filaments produced using a reference method, Figure 2 b) and 3b) show regenerated cellulose filaments produced using the method disclosed herein. The SEM images show that the appearance of the cellulose filaments obtained using the regeneration solution containing metabisulfate is very similar to that of the cellulose filaments obtained using the traditional method. Furthermore, the mechanical properties (toughness and elongation at break) of the filaments obtained by the reference method and the disclosed method are comparable.
Claims
1. A method of producing regenerated cellulosic material, the method comprising: - providing a cellulosic material (1), - dissolving (2) the cellulosic material (1) in an alkaline solution at a temperature of 5 degrees Celsius or less, thereby forming a suspension, - providing sodium metabisulfite (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) containing sodium metabisulfite (6), thereby forming a regenerated cellulosic material (8).
2. The method of claim 1, wherein, The cellulosic material (1) comprises or consists of cellulose pulp and / or pre-treated cellulose pulp.
3. The method of claim 1 or 2, wherein, The alkaline solution comprises at least one of: sodium hydroxide, potassium hydroxide, and lithium hydroxide.
4. The method of any one of the preceding claims, wherein, The alkaline solution comprises an additive, such as zinc oxide and / or urea.
5. The method of any one of the preceding claims, wherein, The lower temperature is -30 degrees Celsius to 5 degrees Celsius.
6. The method of any one of the preceding claims, wherein, The suspension comprises: - 5 to 10 weight percent of sodium hydroxide, - 0.1 to 3 weight percent of an additive, and / or - 5 to 15 weight percent of cellulosic material.
7. The method of any one of the preceding claims, wherein, The sodium metabisulfite (6) is used for acidification of the regeneration solution (7) as a solid waste stream or a diluted waste stream, preferably as a solid waste stream.
8. The method of any one of the preceding claims, wherein, The sodium metabisulfite (6) has an iron content of less than 500 ppm, a phosphorous content of less than 800 ppm, and / or a chloride content of less than 0.5 ppm.
9. The method of any one of the preceding claims, wherein, The concentration of sodium metabisulfite (6) in the regeneration solution (7) is 5 to 18 weight percent.
10. The method of any of the preceding claims, further comprising: The regeneration solution (7) is purified (9) by providing an alcohol to precipitate salts, forming a purified regeneration solution (11).
11. The method of claim 10, further comprising: Sodium sulfate (12) is recovered from the purification (9) of the regeneration solution (7) and fed into an evaporation plant (10) of the pulp mill (4).
12. The method of claim 10 or 11, further comprising: The purified regeneration solution (11) is fed into the regeneration solution (7) for reuse.
13. The method of any one of the preceding claims, wherein, The regenerated cellulosic material (8) comprises a fiber, a film, a cellulose bead, or a three-dimensional object. The cellulosic material (1) comprises or consists of cellulose pulp and / or pre-treated cellulose pulp. The alkaline solution comprises at least one of: sodium hydroxide, potassium hydroxide, and lithium hydroxide. The alkaline solution comprises an additive, such as zinc oxide and / or urea. The lower temperature is -30 degrees Celsius to 5 degrees Celsius. The suspension comprises: - 5 to 10 weight percent of sodium hydroxide, - 0.1 to 3 weight percent of an additive, and / or - 5 to 15 weight percent of cellulosic material. The sodium metabisulfite (6) is used for acidification of the regeneration solution (7) as a solid waste stream or a diluted waste stream, preferably as a solid waste stream. The sodium metabisulfite (6) has an iron content of less than 500 ppm, a phosphorous content of less than 800 ppm, and / or a chloride content of less than 0.5 ppm. The concentration of sodium metabisulfite (6) in the regeneration solution (7) is 5 to 18 weight percent. The regeneration solution (7) is purified (9) by providing an alcohol to precipitate salts, forming a purified regeneration solution (11). Sodium sulfate (12) is recovered from the purification (9) of the regeneration solution (7) and fed into an evaporation plant (10) of the pulp mill (4). The purified regeneration solution (11) is fed into the regeneration solution (7) for reuse. The regenerated cellulosic material (8) comprises a fiber, a film, a cellulose bead, or a three-dimensional object.