Method and system for producing microfibrillated cellulose

Abstract

This document discloses a method for producing microfibrillated cellulose (MFC), comprising the following steps: a) Providing the pulp suspension, mixed with the enzyme and purified, to the reactor tank; b) Forming a pre-treated pulp suspension by treating the purified pulp suspension in a reactor tank at a temperature between 40 and 80°C under controlled mixing by a stirring device; c) At the same time as mixing, add at least one oxidizing agent to the pre-treated pulp suspension; d) In order to inactivate the enzyme, the pre-treated pulp suspension is oxidized in the reactor tank at a high temperature of >80°C; and e) Discharge the pre-treated and pre-purified pulp suspension and subject it to further mechanical treatment to obtain MFC.

Description

Technical Field

[0001] The present invention relates to a method for producing microfibrillated cellulose.

Background Art

[0002] Microfibrillated cellulose ("MFC") is a material composed of cellulose microfibrils separable from the cellulose fiber wall. The liberated fibers have a diameter of less than 1000 nm, while the actual fibril diameter or particle size distribution, and / or aspect ratio (length / width) depend on the source and manufacturing method. The smallest fibrils are called elementary fibrils and can have a diameter of approximately 2 - 4 nm. On the other hand, when making MFC by using, for example, an extended refining process or a high pressure-drop disintegration process (e.g., high-pressure homogenization or fluidization), the main product obtained is generally in an aggregated form of elementary fibrils.

[0003] There are various methods for making MFC, which are, for example, single-pass or multi-pass refining, followed by pre-hydrolysis or enzymatic treatment and then refining or high-shear disintegration, or liberation of fibers. MFC can be produced from wood cellulose fibers, both from hardwood fibers and softwood fibers. It can also be produced from microbial sources, agricultural fibers (e.g., wheat straw pulp, bamboo, bagasse, etc.), or other wood fiber sources. Pulp-based ones are preferred, which include pulp from virgin fibers, such as mechanical, chemical, and / or thermomechanical pulp. MFC can also be made from waste paper or recycled paper. The term MFC also includes parenchymal MFC. MFC can also be obtained from plant fibers, such as sugar beet or potato-based plant fibers.

[0004] Further synonyms for MFC include, for example, cellulose microfibrils, fibrillated cellulose, nanofibrillated cellulose (NFCs), fibril aggregates, nanoscale cellulose fibrils, cellulose nanofibers, cellulose nanofibrils, cellulose microfibers, cellulose fibrils, cellulose nanofilaments, microfibril cellulose, microfibril aggregates, and cellulose microfibril aggregates.

[0005] Current research and development have shown that MFCs, due to their strength and barrier properties, can be suitable materials for packaging and coating packaging substrates. Therefore, MFCs have the potential to replace or complement currently used barrier films (including polymer and metal films), as well as internal strength chemicals, surface coatings, impregnation chemicals, and barrier coating chemicals.

[0006] However, current methods for efficiently manufacturing MFCs in terms of energy and materials have proven to have limited capacity and are difficult to upscale and industrially apply. Furthermore, manufacturing MFCs on an industrial scale involves high investment costs, which lead to high manufacturing costs.

[0007] the purpose The object of the present invention is to provide a method and system for manufacturing MFCs in which the drawbacks and problems of the prior art are minimized.

[0008] Another object of the present invention is to provide improved methods and systems that offer novel alternative methods for manufacturing MFCs, particularly in terms of production capacity and efficiency in terms of energy and materials.

[0009] overview The present invention is defined by the attached independent claims, each aspect of which is shown in the dependent claims, the following specification and the attached drawings.

[0010] According to a first aspect of the present invention, a method for producing microfibrillated cellulose (MFC) is provided, the method comprising the following steps: a) A step of providing a mixture of purified pulp suspension and enzymes to a reactor tank; b) A step of forming a pre-treated pulp suspension by treating the purified pulp suspension with the enzyme in a reactor tank at a temperature between 40 and 80°C, under controlled mixing by a stirring device; c) Adding at least one oxidizing agent to the pre-treated pulp suspension while simultaneously mixing; d) A step of oxidizing the pretreated pulp suspension at a high temperature of >80°C in the reactor tank in order to inactivate the enzyme; and e) Discharge the pre-treated and pre-purified pulp suspension and subject it to further mechanical treatment to obtain MFC. It includes.

[0011] The present invention provides an improved method for pre-treating pulp, enabling controlled and improved enzymatic pulp pre-treatment applicable to pre-treated pulp. Thus, the present invention enables efficient adjustment / control of enzymatic treatment by rapid temperature increases to promote enzymatic hydrolysis, and rapid, uniform, and efficient inactivation by oxidation at high temperatures to denaturate the enzyme. This allows for predictable, high-quality, and high-yield industrially applicable MFC production while reducing variability in fiber properties (e.g., fiber length) between different batches. It should be noted that the method and system according to the present invention eliminate unpredictable variability in fiber length between batches, and the selected fiber length is reproducible. That is, this method leads to predictable fiber quality, which is advantageous.

[0012] Other advantages achieved by the method and system according to the present invention include improved flow behavior of the pulp suspension, efficient mixing, precise control of the temperature gradient during hydrolysis, and enzyme inactivation by oxidation, while maintaining energy efficiency throughout the process (i.e., not consuming excess energy solely for enzyme inactivation by heat). As a result, manufacturing costs are minimized, and the final product can be sold at a competitive market price.

[0013] The MFC material obtained by the method according to the present invention can be used for increased strength, for example, in wet end applications, and in other applications such as barrier fabrication, paper coating, surface sizing, adhesives, molded pulp, paper and / or cardboard production, and pulp manufacturing.

[0014] According to another aspect of the present invention, the concentration of the pulp suspension in step a) is between 2 and 15% by weight, more preferably between 3.5 and 8% by weight.

[0015] According to another aspect of the present invention, the pulp suspension used in step a) may include a mixture of different types of fibers, e.g., kraft pulp, sulfite, fines, reinforcing fibers, dissolved pulp, TMP, CTMP, or PGW. MFC can be produced from wood cellulose fibers, either from coniferous or hardwood fibers. It can also be produced from microbial sources, agricultural fibers (e.g., wheat straw pulp, bamboo, bagasse), or other non-wood fiber raw materials. It is preferable to produce it from pulp (including pulp from virgin fibers), e.g., mechanical, chemical, and / or thermochemical pulp). The pulp can be produced from waste paper or recycled paper. The pulp may be bleached or unbleached. Microfibrilized cellulose may contain some hemicellulose, the amount of which depends on the plant source. Microfibrilized cellulose can be produced from never-dried pulp. Never-dried MFCs have been found to have much higher enzyme accessibility compared to MFCs produced from dried pulp. The very low lignin content of the microfibrillated cellulose is also desirable, as lignin can negatively affect enzyme activity.

[0016] According to another aspect of the present invention, the pulp suspension purified in step a) is bleached kraft pulp having a kappa content of <50, more preferably <35, and even more preferably <25, and a hemicellulose content of >5%, for example >10%. The purified pulp may also be partially recycled material (including post-consumer waste or pre-consumer waste).

[0017] According to yet another aspect of the present invention, the pulp suspension purified in step a) has a Schöpper-Leighler (SR) value between 15 and 40, preferably between 15 and 35.

[0018] According to yet another aspect of the present invention, the enzyme is a hydrolyzing agent, preferably cellulase, hemicellulase, lignase, swollenin, or a mixture thereof. The cellulase may be exoglucanase or endoglucanase. The enzyme mixture may also include β-glucosidase. It is understood that “enzyme treatment” may also be called “enzyme treatment” or “enzyme cellulose hydrolysis.” The amount of enzyme may be, but is not limited to, 20 to 500 ECU per gram of dry pulp.

[0019] According to yet another aspect of the present invention, the method comprises adding starch to the hydrolyzed pulp suspension before further oxidation, i.e., adding the amount of starch between steps b) and c). In this aspect, both the starch and the enzymatically treated pulp are subjected to a subsequent oxidation treatment at a high temperature. This is advantageous because the resulting oxidized starch improves runnability during the subsequent homogenization step. The starch also improves the fluidity and stability of the MFC.

[0020] According to yet another aspect of the present invention, the oxidizing agent is selected from the group comprising hydrogen peroxide (H2O2), peracetic acid (PAA), oxygen (O2), ozone (O3), sodium hydroxide (NaOH), sodium hypochlorite, potassium permanganate, and combinations thereof. The charge of hydrogen peroxide can vary between 2 and 40 kg / ADt, preferably between 2 and 16 kg / ADt. Higher charges require an acidic or chelate step in the pulp used to reduce the metal concentrations, mainly copper, manganese, and iron (which cause the decomposition of hydrogen peroxide). The charge of ozone can vary between 3 and 20 kg / ADt, preferably between 3 and 12 kg / ADt. Using ozone requires a pressurized reactor and an acidic or chelate step in the pulp used to reduce the metal concentrations in the pulp (mainly copper, manganese, and iron, which cause ozone to degrade the degree of polymerization of the pulp). The charge of NaOH depends on the required pH for the main oxidizing chemical.

[0021] According to yet another aspect of the present invention, the temperature of the contents in the reactor tank in step c) is between 45 and 100°C, for example, between 70 and 90°C. This means that when the oxidizing agent is added, the temperature of the pulp in the reactor tank is at least 45°C. This temperature may be between 45 and 70°C when the oxidizing agent is added, and thereafter the reactor tank is heated by a heat exchanger to a peak temperature between 90 and 100°C. The high temperature promotes oxidation and accelerates the denaturation of the enzymes.

[0022] According to yet another aspect of the present invention, the further mechanical treatment in step e) is homogenization and / or refining. The further mechanical treatment may include apparatus suitable for processing the pulp into an MFC suspension. For example, the further mechanical treatment arrangement may include at least one mechanical fiber processing apparatus. Each mechanical fiber processing apparatus may be selected from a group of other known mechanical fiber processing apparatuses suitable for use in processing pulp to MFC, or a combination thereof, including refiners, homogenizers / fluidizers, dust removers, deflakers, beaters, friction grinders, high-shear fibrillators (e.g., cavitron rotor / stator systems, steam explosion systems, or high-viscosity refining or milling systems), dispersers, ball mills, and other mechanical fiber processing apparatuses suitable for use in processing pulp to MFC. The pulp may pass through each of the mechanical fiber processing apparatuses used one or more times. Optionally, the fibrillation treatment arrangement may further include one or more preprocessing apparatuses, each configured for pretreatment of pulp by mechanical, enzymatic, or chemical modification. For example, a fibrillation treatment arrangement may include at least one mechanical fiber pretreatment device. Each mechanical fiber pretreatment device may be selected from a group of known mechanical fiber pretreatment devices suitable for mechanically pretreatment of cellulose fibers, including refiners, dust removers, deflakers, beaters, shredders, ball mills, rotor-stator mixers, ultrasonic devices, steam explosion devices, and other mechanical fiber pretreatment devices.

[0023] According to yet another aspect of the present invention, the stirring member is a spiral mixer or the like. In one example of the present invention, the stirring member is arranged and configured to generate an axial flow circulation pattern in the reactor tank, and the flow direction at the center of the tank is opposite to the flow direction adjacent to the tank wall. For example, the flow velocity determined at 1 cm from the reactor tank wall is at least 0.03 m / s, preferably at least 0.04 m / s, most preferably at least 0.05 m / s, for example 0.05 to 0.3 m / s. The flow rate is preferably determined from at least the midpoint (height / 2) of the container, but it is also possible to arrange and configure it at additional positions to determine the flow rate stability and changes in the flow rate.

[0024] According to yet another aspect of the present invention, the fiber length L c (l) of the pulp after step d) is measured using a Valmet Fiber Image Analyzer (Valmet FS5) UHD with Valmet analyzer client 2.25 software and is 0.2 to 2 mm, preferably 0.3 to 1.7 mm.

[0025] According to yet another aspect of the present invention, the amount of Fe in the processed pulp is measured according to the standard ISO 12830:2019 and is less than 30 mg / kg, more preferably less than 17 mg / kg, based on the dry pulp.

[0026] According to yet another aspect of the present invention, the amount of copper in the processed pulp is measured according to the standard ISO 12830:2019 and is less than 3.0 mg / kg, preferably less than 1.2 mg / kg, based on the dry pulp.

[0027] According to yet another aspect of the present invention, the amount of manganese in the processed pulp is measured according to the standard ISO 12830:2019 and is less than 1.5 mg / kg, preferably less than 1.0 mg, based on the dry pulp.

[0028] According to yet another aspect of the present invention, the method is arranged to operate as a semi - continuous process. With the settings according to the present invention, two or more reactor tanks can be used in parallel, with enzymatic treatment and inactivation being carried out in one of them, and one of them being designed to supply materials for further mechanical treatment to obtain an MFC.

[0029] According to yet another aspect of the present invention, the system comprises a control arrangement which includes a self - learning artificial intelligence unit based on a convolutional neural network arranged to assist in the temperature control of the pulp material. Also, it is within the scope of the present invention to include deep learning and / or machine vision, or other applicable systems usable for IR imaging of the reactor, and to provide an improved feedback loop for improved temperature regulation, whereby pulp processing (including hydrolysis and oxidation, for example) is optimized.

Brief Description of the Drawings

[0030] [Figure 1] The system according to an example of the present invention is schematically shown.

Modes for Carrying Out the Invention

[0031] The drawings schematically show a system capable of implementing the present invention.

[0032] Figure 1 schematically shows System 1 according to the present invention for pre-treating cellulose pulp before the production of MFC. As can be seen here, System 1 includes a reactor tank 2 configured to receive a purified pulp suspension P. A hydrolyzing agent is added to the pulp suspension in the form of an enzyme 3 before the pulp P is added to the reactor tank 2. This means that the enzyme and pulp enter the reactor tank 2 as a mixture. The enzyme may be added to the reactor tank 2 separately. The pulp suspension is treated in the reactor tank 2 at a temperature between 40 and 80°C under controlled mixing by a stirring member 7, thereby forming a pre-treated pulp suspension. The amount of enzyme may be, but is not limited to, 20 to 500 ECU per gram of dry pulp. When the hydrolysis of the pulp reaches the desired level, the treatment is interrupted by enzymatic denaturation. According to the present invention, this is achieved by adding at least one oxidizing agent 4 to the pre-treated pulp suspension simultaneously with mixing, and oxidizing the pre-treated pulp suspension in a second reactor tank 2 at a high temperature of >80°C. A temperature control unit (e.g., at least one heat exchanger 5) is connected to the reactor tank 2 in a closed loop and is configured to control and regulate the temperature of the contents of the reactor tank. Thus, the temperature and mixing in the reactor tank 2 are optimized to achieve efficient and uniform enzymatic hydrolysis of the pulp and to raise the temperature during denaturation by adding the oxidizing agent 4. A sufficient level of enzyme inactivation is achieved when no detectable residual enzyme remains. Enzyme inactivation in the pulp slurry can be measured by conventional methods known to those skilled in the art, for example, using the Megazyme Cellulase Assay Kit (product code: K-CellG5-4V). Once inactivation is complete, the pre-treated pulp inside the reactor tank 2 can be cooled by the heat exchanger 5.

[0033] The pre-purified and pre-treated pulp is then discharged and subjected to further mechanical processing 6 to obtain MFCs. Further mechanical processing 6 can be achieved in a homogenizer or purification unit. For this, at least one homogenizer 6 is connected to the reactor tank 2 and is configured to mechanically process the pulp, circulating the material for the required time at the target fibrillation gap, pressure, and flow rate to obtain MFCs. Multiple homogenizers (e.g., 2 to 5) in series with an intermediate heat exchanger may also be installed to cool the material. The number of homogenizers in series depends on the average size and distribution (i.e., degree of fibrillation) required for the MFCs in the intended application.

[0034] In some cases, oxidizing agents can raise the pH level of the pulp. Therefore, it is advisable to add pH-adjusting additives before mechanically processing the pulp.

[0035] In one embodiment, System 1 includes at least two reactor tanks arranged in parallel. According to the present invention, such a plurality of reactor tanks are arranged to process pulp alternately, thereby enabling the semi-continuous production of MFCs.

[0036] The present invention also relates to a method for pre-treating pulp in MFC manufacturing. The method includes the following steps: a) A step of providing the purified pulp suspension P, mixed with the enzyme, to the reactor tank 2; b) A step of forming a pre-treated pulp suspension by treating the purified pulp suspension with the enzyme 3 in a reactor tank 2 at a temperature between 40 and 80°C, under controlled mixing by a stirring member 7; c) Adding at least one oxidizing agent 4 to the pre-treated pulp suspension at the same time as mixing; d) A step of oxidizing the pretreated pulp suspension in the reactor tank at a high temperature of >80°C in order to inactivate the enzyme; and e) Discharge the pre-treated and pre-purified pulp suspension and subject it to further mechanical treatment 6 to obtain MFC. [Examples]

[0037] Example 1 Coniferous kraft pulp was pre-purified to SR18 and enzymatically treated with Ecopulp R (AB enzyme) cellulase at a concentration of 80 ECU per gram of dry cellulose for 90 minutes. The pulp concentration was 5.0%. Experimental samples were taken from this process. Initial enzyme activity was determined from the supernatant after centrifugation using Cellulase Assay Kit CellG5 (Megazyme), but the incubation time was extended to 16 hours to improve sensitivity. After determining the enzyme activity, the enzymatically treated pulp was heated to 90°C for 120 minutes and allowed to cool to room temperature. Then, a 30% hydrogen peroxide solution was added to the enzymatically treated pulp, and the pulp was mixed with a mixing rod for 1 minute. The sample was allowed to stand at room temperature for 10-30 minutes. Then, the sample was centrifuged, the supernatant was collected, and stored in a refrigerator overnight. The following day, the enzyme activity of the supernatant was analyzed in the same manner as described above.

[0038] The enzyme activity was 0.012 in the heat-treated and hydrogen peroxide-treated samples (0.035 before treatment).

[0039] Example 2 The same enzyme-treated pulp as in Example 1 was used after determining the enzyme activity. A 30% hydrogen peroxide solution was added to the enzyme-treated pulp, and the pulp was mixed with a mixing rod for 1 minute. The enzyme-treated pulp was then heated to 90°C for 120 minutes and allowed to cool to room temperature. The pulp was then centrifuged, and the enzyme activity of the supernatant was determined in the same manner as in Example 1. The enzyme activity was 0.000. This indicates that hydrogen peroxide should be added before heat treatment to optimally inactivate the enzyme.

[0040] TIFF2026518891000002.tif54170

[0041] In summary, a simplified and improved process for manufacturing MFCs is proposed and implemented on an industrial scale. The resulting pre-treated pulp will have uniform quality due to efficient hydrolysis in the tank and careful control of process parameters (e.g., temperature changes, mixing operations, and uniform distribution within one or more reaction tanks). Scalability is deemed improved compared to current process solutions due to the simplification, as is the ability to maintain the process at high hygienic standards.

[0042] In view of the above detailed description of the present invention, other modifications and variations will also become apparent to those skilled in the art. However, it should be clear that such other modifications and variations can be made without departing from the spirit and scope of the present invention.

Claims

1. A method for producing microfibrillated cellulose (MFC), comprising the following steps: a) A step of providing a mixture of the purified pulp suspension and the enzyme to a reactor tank; b) A step of forming a pre-treated pulp suspension by treating the purified pulp suspension with the enzyme in a reactor tank at a temperature between 40 and 80°C, under controlled mixing by a stirring device; c) Adding at least one oxidizing agent to the pre-treated pulp suspension at the time of mixing; d) A step of oxidizing the pretreated pulp suspension at a high temperature of >80°C in the reactor tank in order to inactivate the enzyme; and e) Discharge the pre-treated and pre-purified pulp suspension and subject it to further mechanical treatment to obtain MFC. Methods that include...

2. The method according to claim 1, wherein the concentration of the pulp suspension in step a) is between 3.5 and 8 wt%.

3. The method according to claim 1, wherein the purified pulp suspension in step a) is bleached kraft pulp having a kappa content of <25 and a hemicellulose content of >5%.

4. The method according to claim 1, wherein the refined pulp is a recycled material including post-consumer waste or pre-consumer waste.

5. The method according to claim 1, wherein the Schöpper-Leighler (SR) value of the purified pulp suspension in step a) is between 15 and 40, preferably between 15 and 35.

6. The method according to claim 1, wherein the enzyme is a hydrolyzing agent, preferably a cellulase.

7. The method according to claim 1, further comprising the step of adding starch between steps b) and c).

8. The oxidizing agent is H ２ O ２ , peracetic acid (PAA), oxygen (O ２ ), ozone (O ３ The method according to claim 1, selected from the group comprising ), NaOH, sodium hypochlorite, potassium permanganate, and combinations thereof.

9. The method according to claim 1, wherein the temperature of the contents in the reactor tank in step c) is between 45 and 100°C, for example between 70 and 90°C.

10. The method according to claim 1, wherein the further mechanical treatment in step e) is homogenization and / or purification.

11. The method according to claim 1, wherein the stirring member is a spiral mixer.

12. d) Fiber length L of the pulp after step ｃ The method according to claim 1, wherein (l) is measured with an FS5 fiber analyzer and is 0.2 to 2 mm, preferably 0.3 to 1.7 mm.

13. The method according to claim 1, wherein the amount of Fe in the pulp after processing is less than 20 mg / kg, more preferably less than 15 mg / kg, based on the dry pulp.

14. The method according to claim 1, wherein the amount of copper in the pulp after processing is less than 0.15 mg / kg based on the dry pulp.

15. A system for producing microfibrillated cellulose (MFC), A reactor tank (2) configured to receive a mixture of purified pulp suspension (P) and enzyme (3), wherein the reactor tank is configured to support the hydrolysis of the pulp at a temperature between 40 and 80°C under mixing controlled by a stirring member (7), thereby forming a pre-treated pulp suspension; - A configuration for adding at least one oxidizing agent (4) to the pre-treated pulp suspension while simultaneously mixing it in the tank (2); - At least one heat exchanger unit (5) connected in a closed loop to a reactor tank (2), the heat exchanger unit being arranged and configured to control the temperature of the contents of the reactor tank; Discharge means for discharging an inactivated and pre-treated pulp suspension, and for further purification to obtain MFC, A system that includes this.

16. The system according to claim 15, further comprising at least one fluidizer, high-speed mixer, extruder, grinder, refiner, or preferably one homogenizer (6), which is coupled to the reactor tank (2) and configured to be used to mechanically treat the hydrolyzed pulp to obtain MFC.

17. The system according to claim 15, further comprising a control arrangement configuration including a self-learning artificial intelligence unit based on a convolutional neural network, which is arranged to assist in temperature control of pulp material.

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