A method for industrial preparation of lyocell fiber spinning dope

Abstract

The present application relates to a kind of methods for preparing lyocell fiber spinning dope in industrialization, comprising the following steps: 1, preparing the first suspension with cellulose concentration less than or equal to 6wt%; 2, increasing the concentration of cellulose in the first suspension to 10-12wt% by pressure separation of part of the solvent, to obtain the second suspension; 3, grinding the second suspension to obtain the third suspension; 4, inputting the third suspension into a thin film evaporator, controlling the temperature in the thin film evaporator, and dissolving the third suspension under vacuum conditions to obtain the spinning dope with cellulose concentration of 11-13wt%. The present application is a new idea for preparing lyocell fiber spinning dope in industrialization, which can not only eliminate the hidden danger of dust generated in the grinding process of pulp, but also achieve more sufficient and uniform swelling and more uniform dissolution simultaneously, achieve better dissolution effect, and obtain high-quality fiber spinning dope.

Description

Technical Field

[0001] This invention relates to the field of novel cellulose fiber production technology, specifically to a method for the industrial preparation of lyocell fiber spinning dope. Background Technology

[0002] Lyocell fiber is a new type of green fiber produced through a physical dissolution-regeneration process using NMMO aqueous solution as a solvent. Compared with viscose fiber, the entire production process of lyocell fiber is environmentally friendly, and the fiber has higher strength and better dyeing properties. In recent years, more and more viscose fiber manufacturers have been transforming to lyocell fiber, and market competition has become increasingly fierce.

[0003] In industrial production, the preparation of lyocell fiber spinning dope requires first mixing pulp raw materials with a solvent to prepare a cellulose suspension. After the cellulose in the suspension has fully swollen, it is then dissolved in a dissolving device (e.g., a thin-film evaporator) to obtain the spinning dope. Currently, the industrial preparation of lyocell fiber spinning dope mainly uses a dry process. The conventional steps of the dry process are: first, the dry pulp raw material is pulverized; then, the pulverized pulp raw material is mixed with a high-concentration solvent (usually an NMMO aqueous solution), causing the cellulose in the pulp raw material to swell in the solvent, producing a cellulose suspension (or pulp porridge); then, the cellulose suspension is sent to a thin-film evaporator for vacuum dehydration and dissolution, finally obtaining the lyocell fiber spinning dope. In the traditional dry process, the swelling process is a crucial step, as the quality of the swelling directly affects the subsequent dissolution of cellulose in the thin-film evaporator, thus directly impacting the quality of the lyocell fiber spinning dope. In this field, those skilled in the art have been seeking effective methods to ensure that the cellulose in the pulp raw material swells more fully and uniformly in the solvent. Furthermore, the dry pulp grinding process easily generates dust, which can impact the workshop environment. This dust also poses flammable and explosive hazards, thus presenting certain safety risks. Moreover, during dry grinding, the grinding equipment is prone to overheating, causing the pulp to become keratinized during grinding. This results in a "white core" during the swelling process, affecting the dissolution effect and severely impacting the quality of the subsequent spinning solution. To address these issues, Chinese patent CN 114016141B offers a novel approach, providing a direct-dissolution method for preparing fiber spinning dope. This method specifically includes: S1) mixing pulp with a 72%–76% NMMO solution to induce swelling, obtaining a mixture at a temperature of 40°C–45°C; the pulp concentration in the mixture is 4%–5%; S2) pressing the mixture to obtain a pressed material at a temperature of 40°C–65°C; pressing the mixture until the pulp dryness is 35%–45%; S3) pulverizing the pressed material to obtain a pulverized material; and S4) dissolving the pulverized material with an 81%–85% NMMO solution under normal pressure to obtain the fiber spinning dope. The comparison shows that this method is completely different from the traditional dry process. This method first controls the solvent concentration and temperature at a low level, so that the pulp and solvent are mixed and swollen (equivalent to wetting) under these conditions, and then the pulp is pressed and crushed. Finally, the pulp raw material is directly dissolved under conditions of higher temperature and higher solvent concentration to obtain fiber spinning solution.In this method, because the temperature and solvent concentration are controlled very low in steps S1 and S2 (significantly lower than the temperature at which cellulose fully swells), the cellulose in the pulp only wets with the solvent and does not swell (because, according to the patent, under these temperature and solvent concentration conditions, the hydrogen bonding between solvent molecules and cellulose molecules is weak, so the cellulose raw material cannot swell sufficiently). Therefore, insufficient swelling is inevitable. This method does not actually consider how to achieve a more complete and uniform swelling effect, nor can it achieve one, which also has a significant impact on the subsequent dissolution effect. Secondly... In step S2 of this method, the mixture is only pressed to a dryness of 35%–45%. The pressed mixture still contains a large amount of low-concentration solvent, resulting in a significant water content. This mixture, after further pulverization, is directly added to a high-concentration solvent (81%–85%) for dissolution. The water from the mixture dilutes the high-concentration solvent, severely affecting the dissolution effect. Furthermore, in practice, the water content of the pressed mixture is difficult to control precisely, making it difficult to accurately control the actual solvent concentration during dissolution, which is detrimental to precise control of dissolution in industrial production. In addition, because the cellulose in the mixture does not swell sufficiently and uniformly, in step 4, when the mixture comes into contact with the high-concentration solvent for dissolution, the mixture that first comes into contact with the high-concentration solvent forms a gel-like substance that coats subsequent mixtures. This prevents some mixtures from fully contacting the solvent and dissolving completely, severely affecting the quality of the fiber spinning solution. Therefore, although this method can solve the problems of dry spinning to some extent, it also has many shortcomings. It cannot solve the problem of sufficient and uniform swelling of cellulose in the solvent, nor is it conducive to improving the dissolution effect and the quality of the fiber spinning solution. Therefore, how to achieve more sufficient and uniform swelling and better dissolution effect while solving the above-mentioned problems of traditional dry spinning processes, and thus obtain high-quality fiber spinning solutions, is an urgent problem to be solved. Summary of the Invention

[0004] The first aspect of this invention addresses the aforementioned technical problems by providing a novel method for the industrial-scale preparation of lyocell fiber spinning dope. This method not only eliminates the potential for dust generation during pulp pulverization and enhances the swelling effect of cellulose, achieving more thorough and uniform swelling, but also effectively prevents uneven dissolution caused by the "white core" phenomenon during the swelling process, thereby significantly improving the quality of the dope. The main concept is as follows:

[0005] An industrial method for preparing lyocell fiber spinning solution, employing a spinning solution preparation system comprising a swelling device, an extrusion device, a grinding and pulverizing device, and a thin-film evaporator connected in sequence; the method includes the following steps:

[0006] Step 1: Calculate the amount of pulp raw material to be fed, and put a certain amount of pulp raw material into a swelling device containing solvent for simultaneous wet crushing and swelling to obtain a first suspension with a cellulose concentration of less than or equal to 6 wt%. The temperature inside the swelling device is controlled at 75-80°C, and the solvent used is an NMMO aqueous solution with a concentration of 76-82 wt%.

[0007] Step 2: Input the first suspension into the extrusion device. The temperature inside the extrusion device is controlled at 80-85°C. Use extrusion to separate part of the solvent in the first suspension. By separating part of the solvent, the concentration of cellulose in the first suspension is increased to 10-12 wt% to obtain the second suspension.

[0008] Step 3: Input the second suspension into a pulverizing and grinding device for pulverizing and grinding. The temperature inside the pulverizing and grinding device is controlled at 80-85℃ to obtain the third suspension.

[0009] Step 4: Input the third suspension into the thin-film evaporator, control the temperature inside the thin-film evaporator, and dissolve the third suspension under vacuum conditions to obtain a spinning solution with a cellulose concentration of 11-13 wt%. In this scheme, by controlling the amount of pulp raw material fed in, a low-concentration cellulose suspension (first suspension) is prepared, and the wet grinding and swelling of pulp are integrated in the swelling device. This simplifies the process and improves efficiency. It not only avoids the hidden danger of dust generation during pulp grinding, but also solves the problem of poor pulp swelling effect at higher solvent concentrations and higher pulp concentrations. It achieves more uniform and complete swelling of pulp raw materials in a simple way. In the traditional dry process, when pulp is mixed with a high-concentration NMMO solution after grinding, the concentration is usually controlled at 11-12 wt%. At this time, due to cellulose swelling, the fluidity of the entire system becomes poor, which is not conducive to solvent wetting of pulp and easily leads to uneven swelling. This method controls the concentration of the first suspension to below 6 wt%. Due to its lower concentration, the cellulose has better fluidity after swelling, which facilitates solvent penetration and wetting of the pulp. Under conditions of 75–80℃, and with the swelling device described in this method, more uniform and complete swelling can be achieved. Increasing the cellulose concentration in the first suspension through extrusion not only allows for more convenient and precise control of the cellulose concentration but also promotes more complete and uniform wetting and swelling of the cellulose. Controlling the cellulose concentration in the second suspension to 10–12 wt% further facilitates subsequent complete dissolution, achieving a better dissolution effect. By further pulverizing and grinding the second suspension while controlling the temperature at 80–85°C, the resulting third suspension is more conducive to achieving better dissolution. The pulverizing and grinding process not only makes the swelling more complete and uniform, resulting in a fully swollen third suspension, but more importantly, it also makes the swollen third suspension more uniform, significantly improving the dissolution effect and uniformity of the spinning solution, thereby enhancing spinnability and benefiting downstream spinning. The combination of the extrusion process and pulverizing and grinding effectively prevents uneven dissolution caused by the appearance of "white cores" during the swelling process. Finally, controlling the cellulose concentration in the spinning solution to 11–13 wt% effectively ensures the performance of the final fiber.This method is an improvement and optimization based on the traditional dry process. It does not adopt the technical route in Chinese patent CN 114016141 B, and therefore does not have the corresponding technical problems. Compared with the traditional dry process, this method can not only solve the technical problems existing in the traditional dry process, but also achieve more complete and uniform swelling and more uniform dissolution at the same time, resulting in better dissolution effect and obtaining high-quality fiber spinning solution. Compared with the technical route in Chinese patent CN 114016141 B, this method not only does not have the many shortcomings of that patent, but also effectively solves the problem of complete and uniform swelling of cellulose in solvent, and can effectively improve the dissolution effect and the quality of fiber spinning solution.

[0010] To address the issue of balancing economy and swelling effect, furthermore, in step 1, the concentration of cellulose in the first suspension is controlled to be 3-6 wt%. If the cellulose concentration in the first suspension is too low, the subsequent concentration step requires squeezing out more solvent. The squeezed-out solvent needs to be recovered, and generally, the recovered solvent contains some fiber residue, requiring purification and impurity removal before reuse. Excessive solvent squeezing not only leads to low efficiency but also places a heavy burden on solvent purification, significantly reducing the economic efficiency of this method. Conversely, if the cellulose concentration in the first suspension is too high, the viscosity of the entire suspension system will increase, resulting in poor flowability and making it difficult to achieve the desired pulp pulverization and swelling effect. Previous experiments have shown that when the cellulose concentration in the first suspension is between 3-6 wt%, the resulting suspension exhibits significant flowability, achieving better pulp pulverization and swelling effects. Simultaneously, production efficiency is improved, and production costs are significantly reduced.

[0011] Preferably, in step 1, the concentration of cellulose in the first suspension is controlled to be 5-6 wt%. This is beneficial for further cellulose swelling, not only achieving more complete and uniform swelling, but also ensuring that the resulting first cellulose suspension has good fluidity.

[0012] Preferably, in step 1, the concentration of cellulose in the first suspension is 5.5 wt% or 6 wt%.

[0013] Preferably, in step 1, the solvent concentration in the swelling device is 76 wt%; the temperature in the swelling device is 80°C. This ensures that the cellulose in the first suspension achieves more complete swelling.

[0014] Preferably, in step 2, the temperature inside the extrusion device is 80°C.

[0015] Preferably, in step 2, the concentration of cellulose in the second suspension is 11 wt%.

[0016] Preferably, in step 3, the temperature inside the crushing and grinding device is 80°C.

[0017] To achieve better evaporation and dissolution effects and improve the quality of the spinning solution, the thin-film evaporator is further designed as a vertical thin-film evaporator. This vertical thin-film evaporator includes an evaporation chamber enclosed by a shell, and an inlet and an outlet connected to the evaporation chamber. The lower end of the evaporation chamber has a conical structure. The inlet and outlet are located at the top and bottom of the evaporation chamber, respectively. The temperature within the thin-film evaporator is controlled to exhibit a gradient distribution along the direction from the inlet to the outlet. In step 4, the third suspension dissolves under gradient temperature and vacuum conditions to obtain the spinning solution. The gradient temperature distribution includes controlling the inlet temperature of the thin-film evaporator at 80–85°C, the upper section temperature at 75–80°C, the middle section temperature at 80–85°C, the lower section temperature at 85–95°C, the cone bottom temperature at 95–105°C, and the outlet temperature at 100–110°C. Sampling at this temperature setting not only achieves better evaporation and dissolution effects, but also allows for more precise control of the cellulose concentration in the spinning solution, ensuring that the cellulose concentration in the spinning solution meets the design requirements and improving the quality of the spinning solution.

[0018] Preferably, in step 4, the feed temperature of the thin-film evaporator is 80°C, the upper section temperature is 80°C, the middle section temperature is 85°C, the lower section temperature is 95°C, the cone bottom temperature is 100°C, and the outlet temperature is 100°C. This facilitates better evaporation and dissolution effects.

[0019] Preferably, in step 4, the concentration of cellulose in the spinning solution is 12.5 wt%. This ensures that the final fiber has good properties.

[0020] The second aspect of this invention addresses the problem of eliminating the potential dust generation during pulp crushing while simultaneously improving swelling efficiency and uniformity. Further, the swelling device includes a reaction vessel, a motor, and a stirring mechanism. The reaction vessel includes an internal cavity, a feed port, a solvent inlet, an assembly port, and a discharge port connected to the internal cavity, with a valve at the discharge port. The stirring mechanism includes a stirring shaft, a moving blade assembly, a stationary blade assembly, an inner barrel, and an impeller. The stirring shaft is vertically arranged, with its upper end connected to the output shaft of the motor, and its lower end extending into the internal cavity via the assembly port. The inner barrel is fixedly mounted in the internal cavity of the reaction vessel by a bracket, with the lower end of the stirring shaft at least inserted into the inner barrel. The inner barrel has a cylindrical structure. The stationary blade assembly is located inside the inner barrel and includes a central seat and multiple fixed blades. The central seat is fitted around the outside of the stirring shaft. Coaxial with the stirring shaft, one end of the fixed blade is connected to the central seat, and the other end is connected to the inner barrel. Each fixed blade is evenly distributed along the circumference of the stirring shaft, and at least the upper end of the fixed blade has a serrated structure, which is arranged along the length of the fixed blade. The moving blade assembly is constructed to adapt to the stationary blade assembly. The moving blade assembly includes a connecting part for connecting to the stirring shaft and multiple movable blades connected to the connecting part. Each movable blade is evenly distributed along the circumference of the stirring shaft and has a serrated structure along the length of the movable blade. The moving blade assembly is located inside the inner barrel and is positioned to adapt to the stationary blade assembly. The moving blade assembly is used to rotate relative to the stationary blade assembly under the drive of the stirring shaft, so that the moving blade assembly and the adjacent stationary blade assembly form a shearing engagement within the inner barrel, thereby crushing the pulp through the shearing engagement. The impeller is located on the stirring shaft and below the inner barrel, and the impeller rotates synchronously with the stirring shaft.In this scheme, because the concentration of cellulose in the first suspension is controlled at a low level, the system has good fluidity, and the wet pulverization of pulp raw materials can be achieved directly by stirring without the need for pre-pulverization of the dry raw materials. Based on this, to further improve the swelling efficiency and swelling uniformity, this scheme uses an impeller at the bottom of the inner tank to force the liquid flowing from top to bottom in the inner tank to flow from the outer tank upwards. This allows the impeller to assist the liquid in the inner tank to flow from top to bottom, which is more conducive to forming liquid circulation between the inner and outer tanks, thus facilitating more thorough pulverization and uniform swelling of the pulp. Furthermore, by arranging a stationary blade assembly and a moving blade assembly inside the inner tank, and installing saws on the stationary blade assembly and the moving blade assembly respectively... The toothed structure creates a shearing zone between the moving blade assembly and the adjacent stationary blade assembly within the inner tank. The circulating liquid within the reaction vessel continuously passes through this shearing zone, simultaneously achieving wet pulverization and swelling of the pulp. This also promotes thorough pulp pulverization and more uniform dispersion of cellulose in the solvent, resulting in a more complete and uniform swelling effect. In actual operation, this swelling device, combined with the above method, effectively eliminates the potential for dust generation during pulp pulverization and solves the problem of poor pulp swelling performance at higher solvent and pulp concentrations. Thus, it achieves a simple way to simultaneously improve swelling efficiency and swelling uniformity.

[0021] Furthermore, the stationary blade assembly is positioned in the middle and / or lower part of the inner drum; the moving blade assembly is also positioned in the middle and / or lower part of the inner drum. Because at these locations, the pulp has already come into full contact with the solvent and swelled, significantly reducing its toughness. This not only makes it easier to pulverize the pulp, but also reduces the likelihood of jamming during the shearing action between the moving and stationary blade assemblies.

[0022] To further improve the uniformity of swelling, the movable paddle is further inclined horizontally to provide downward thrust. The serrated structure on the movable paddle is designed to match the serrated structure on the fixed paddle. This not only allows the serrated structure on the movable paddle to form a better shear fit with the serrated structure on the fixed paddle below, but also, because the movable paddle is rotating, it provides downward thrust to the liquid in the inner tank during rotation, pushing the liquid in the inner tank from top to bottom. This avoids blockage in the inner tank and drives the liquid to circulate along the height of the inner tank, which is more conducive to uniform swelling.

[0023] Furthermore, the stirring mechanism is equipped with multiple moving blade assemblies and multiple stationary blade assemblies, which are staggered along the height of the inner tank. This allows each stationary blade assembly to form a shearing interaction with its adjacent moving blade assembly, resulting in better shearing effect, higher efficiency, and improved uniformity of swelling.

[0024] The third aspect of this invention addresses the problem that during actual operation, the motor load increases significantly, and the moving and stationary blade assemblies are prone to jamming, leading to unstable system operation. Further, the stirring mechanism includes a first crushing component, installed on the stirring shaft, located inside the inner barrel and above the moving blade assembly, positioned at the middle or upper part of the inner barrel. This allows the first crushing component to individually crush the pulp entering the inner barrel. On one hand, it breaks the pulp into smaller pieces, facilitating faster and more thorough contact and swelling with the solvent. On the other hand, it slows down the pulp falling into the inner barrel, increasing the time it spends falling into the lower shearing zone, further promoting contact and swelling between the pulp and solvent. This significantly reduces the toughness of the pulp falling into the shearing zone, making it easier to crush and effectively preventing jamming.

[0025] Preferably, the first crushing assembly includes a connecting component for connecting the stirring shaft and a plurality of first crushing blades connected to the connecting component, each of the first crushing blades being evenly distributed along the circumference of the stirring shaft; the first crushing blades are arranged at an inclination in the horizontal direction to provide downward thrust, and the first crushing blades are also constructed with a serrated structure distributed along their length.

[0026] The fourth aspect of this invention addresses the problem that, during actual operation, pulp fed into the reaction tank tends to get stuck on the support of the inner tank, making it difficult to enter the inner tank and severely affecting the crushing and swelling process. Furthermore, the stirring mechanism includes a second crushing component, which is installed on the stirring shaft and located above the inner tank. The second crushing component rotates synchronously with the stirring shaft, and its rotation range covers the feeding port. This design, on the one hand, allows the second crushing component to crush the pulp that has not yet come into contact with the solvent during feeding, facilitating faster and more thorough contact and wetting swelling of the pulp with the solvent. On the other hand, it allows the pulp to enter the inner tank as much as possible during feeding, greatly reducing the possibility of pulp falling between the inner tank and the main tank, making the crushing and swelling process smoother and more efficient.

[0027] Preferably, the second crushing component includes a connecting part for connecting the stirring shaft and a plurality of second crushing blades connected to the connecting part, each of the second crushing blades being evenly distributed along the circumferential direction of the stirring shaft.

[0028] Compared with existing technologies, the method for preparing lyocell fiber spinning dope provided by this invention is a novel approach for the industrial preparation of lyocell fiber spinning dope. It not only eliminates the hidden danger of dust generated during pulp crushing, but also achieves more complete and uniform swelling and dissolution, resulting in better dissolution effect and obtaining high-quality fiber spinning dope. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of a spinning solution preparation system provided in Embodiment 1 of the present invention.

[0031] Figure 2 This is a schematic diagram of a swelling device in a spinning solution preparation system provided in Embodiment 1 of the present invention.

[0032] Figure 3 for Figure 2 Sectional view at point AA.

[0033] Figure 4 for Figure 2 A magnified view of a portion of point I in the middle.

[0034] Figure 5 This is a schematic diagram of a thin-film evaporator in a spinning solution preparation system provided in Embodiment 1 of the present invention.

[0035] Figure 6 This is a flowchart of a method for preparing spinning solution provided in Embodiment 2 of the present invention.

[0036] Figure 7 This is a comparison diagram of the high-concentration cellulose suspensions prepared in Example 2 and the comparative examples.

[0037] Figure 8 This is a comparison diagram of the spinning solutions prepared in Example 2 and the comparative examples.

[0038] Explanation of markings in the diagram: 11. Swelling device; 12. Feeding hopper; 13. Extrusion device; 14. Crushing and grinding device; 15. Screw conveyor; 16. Thin film evaporator; 17. Pipeline; 21. Reaction tank; 22. Insulation structure; 23. Motor; 24. Reducer; 25. Coupling; 26. Mounting frame; 27. Support; 31. Tank body; 32. Tank cover; 33. Frame; 34. Feed port; 35. Solvent inlet; 36. Discharge port; 37. Valve; 41. Stirring shaft; 42. Connecting component; 43. Movable paddle; 44. Middle... Core seat 44, fixed paddle 45, serrated structure 46, inner barrel 47, bracket 48, impeller 49; first crushing assembly 5, first crushing paddle 51; second crushing assembly 6, second crushing paddle 61; drive motor 71, extrusion cylinder 72, inlet 73, outlet 74, discharge port 75, rotating shaft 76, spiral blade 77; shell 81, toothed crushing roller 82; outer shell 91, evaporation chamber 92, film scraping mechanism 93, conical structure 94, feed inlet 95, glue outlet 96. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] like Figure 1 As shown, this embodiment provides a spinning solution preparation system, including a swelling device 11, an extrusion device 13, a grinding and pulverizing device 14, and a thin-film evaporator 16. The extrusion device 13 is located downstream of the swelling device 11, and the swelling device 11 is connected to the extrusion device 13. The grinding and pulverizing device 14 is located downstream of the extrusion device 13, and the extrusion device 13 is connected to the grinding and pulverizing device 14. The thin-film evaporator 16 is located downstream of the grinding and pulverizing device 14, and the grinding and pulverizing device 14 is connected to the thin-film evaporator 16.

[0042] In this embodiment, the main function of the swelling device 11 is to wet-crush and swell the pulp raw material, allowing the wet crushing and swelling to be completed simultaneously in the same device. Specifically, in actual use, the pulp raw material is directly added into the swelling device 11. The swelling device 11 can simultaneously realize the wet crushing and swelling of the pulp, making it an integrated device that can simultaneously achieve the wet crushing of the pulp raw material and the swelling of cellulose in the pulp raw material, ensuring the production of a low-concentration cellulose suspension. By configuring the swelling device 11 at the very front of this system, compared to existing designs, it not only avoids the potential for dust generation during pulp crushing but also solves the problem of poor pulp swelling performance at higher solvent and pulp concentrations, achieving more uniform and thorough swelling of the pulp raw material in a simple way.

[0043] like Figures 1-4 As shown, in this embodiment, the swelling device 11 includes a reaction vessel 21, a motor 23, a stirring mechanism, and a heat insulation structure 22. The reaction vessel 21 includes a vessel body 31 with an internal cavity, a lid 32 sealing the top of the vessel body 31, and a frame 33 supporting the vessel body 31. The lid 32 is installed on the top of the vessel body 31. In practice, the lid 32 can be detachably installed on the vessel body 31 using bolts or other fasteners for assembly and subsequent maintenance. Figure 2 As shown, the tank cover 32 has a feed port 34, a solvent inlet 7335, and an assembly port adapted to the stirring mechanism. During use, pulp raw material, preferably flake pulp, can be added to the internal cavity of the reaction tank 21 through the feed port 34. Simultaneously, the required solvent can be added to the internal cavity of the reaction tank 21 through the solvent inlet 7335. In this embodiment, the solvent is typically an NMMO aqueous solution. Correspondingly, a discharge port 36 is provided at the bottom of the tank body 31, such as... Figure 2 As shown, a valve 37 is provided at the discharge port 36. The valve 37 can preferably be a gate valve so as to control the opening and closing of the discharge port 36, thereby controlling whether to discharge the material in the reaction tank 21.

[0044] like Figure 2 As shown, the insulation structure 22 is disposed on the outside of the tank 31, mainly used to provide stable temperature conditions for the swelling device 11. In implementation, the insulation structure 22 can be implemented using existing technology. For example, the insulation structure 22 can adopt an existing jacket structure, so as to use the jacket structure to precisely control the temperature inside the reaction tank 21 and ensure that the swelling device 11 achieves a better swelling effect. Of course, in some other embodiments, the insulation structure 22 may also include an insulation layer, and the material of the insulation layer may include insulation cotton, etc.

[0045] like Figures 1-4As shown, in this embodiment, the stirring mechanism includes a stirring shaft 41, a moving blade assembly, a stationary blade assembly, an inner tank 47, and an impeller 49. The motor 23 can be mounted on a mounting bracket, which can be mounted on the tank cover 32 in the reaction vessel 21 or on a frame 33. The stirring shaft 41 is vertically arranged, and its upper end is connected to the output shaft of the motor 23 for driving the stirring shaft 41 to rotate. In implementation, the motor 23 can be connected to the stirring shaft 41 via a transmission mechanism, such as a coupling 25, a reducer 24, a belt drive mechanism, or a chain drive mechanism. Figure 2 As shown, in this embodiment, the output shaft of the motor 23 is connected to the reducer 24 for transmission. The reducer 24 is fixed to the tank cover 32 by a mounting bracket. The output shaft of the reducer 24 is connected to the upper end of the stirring shaft 41 by a coupling 25. Thus, the motor 23 can drive the stirring shaft 41 to rotate, and the reducer 24 can reduce the speed and increase the torque.

[0046] like Figure 2 As shown, the lower end of the stirring shaft 41 extends into the internal cavity of the tank 31 via the assembly port. In implementation, a sealing structure is also provided at the assembly port. This sealing structure can be implemented using existing technology and will not be elaborated here. As shown in the figure, the inner barrel 47 is fixedly installed in the internal cavity of the reaction vessel 21, and the lower end of the stirring shaft 41 is at least inserted into the inner barrel 47. In implementation, the inner barrel 47 can be constructed as a cylindrical structure, and the central axis of the inner barrel 47 can coincide with the central axis of the stirring shaft 41. In implementation, the inner barrel 47 has multiple installation methods. For example, the inner barrel 47 can be directly fixed to the bottom of the tank 31 in the reaction vessel 21, or the inner barrel 47 can be fixed to the bottom of the tank 31 via a bracket 48. In this case, there is a certain gap between the lower end of the inner barrel 47 and the bottom of the tank 31, which facilitates the circulation of materials along the height direction within the reaction vessel 21. Furthermore, the inner barrel 47 can also be fixed to the side wall of the tank 31 via a bracket 48, such as... Figure 2 As shown, multiple sets of brackets 48 can be arranged along the height direction of the inner barrel 47. This not only allows for a more secure fixation to the inner barrel 47, preventing the upper end of the inner barrel 47 from shaking or deforming and improving reliability, but also ensures that the brackets 48 are arranged between the inner barrel 47 and the side wall of the tank body 31, without occupying the space between the bottom of the inner barrel 47 and the tank body 31. This avoids interfering with the installation and operation of the impeller 49 and prevents turbulence between the bottom of the inner barrel 47 and the tank body 31, thus making it more conducive to driving the material to circulate vertically.

[0047] In this embodiment, the stationary blade assembly includes a central seat 44 and a plurality of fixed blades 45. The central seat 44 is configured with a central hole for the stirring shaft 41 to pass through, and the inner diameter of the central hole is larger than the outer diameter of the stirring shaft 41. Figure 2As shown, the center seat 44 is fitted onto the outside of the stirring shaft 41 and is coaxial with the stirring shaft 41. One end of the fixed paddle 45 is connected to the center seat 44, and the other end is connected to the inner barrel 47, thereby achieving the purpose of constraining the fixed paddle 45. In implementation, each fixed paddle 45 can be evenly distributed along the circumference of the center seat 44, so that each fixed paddle 45 can be evenly distributed along the circumference of the stirring shaft 41. According to the process requirements, each fixed paddle 45 can be arranged horizontally or inclined in implementation. The upper end of the fixed paddle 45 is constructed with a serrated structure 46, such as... Figures 1-4 As shown, the serrated structure 46 is arranged along the length of the fixed paddle 45, which is more conducive to breaking up the pulp. On this basis, further constructing the lower end of the fixed paddle 45 as a serrated structure 46, or further constructing the side of the fixed paddle 45 as a serrated structure 46, is also conducive to breaking up the pulp.

[0048] In this embodiment, the moving blade assembly is configured to be adapted to the stationary blade assembly. The moving blade assembly includes a connecting part 42 for connecting the stirring shaft 41 and a movable paddle 43 connected to the connecting part 42, such as... Figures 1-4 As shown; in implementation, the connecting component 42 can be constructed as a cylindrical structure, sleeved on the stirring shaft 41. The connecting component 42 can be fixed to the stirring shaft 41 by welding, or it can be detachably installed on the stirring shaft 41 by fasteners such as bolts or screws. The number of movable paddles 43 connected to the connecting component 42 can be one, two, three, four, etc. In a preferred embodiment, the connecting component 42 of the moving blade assembly is provided with at least three movable paddles 43, each movable paddle 43 being evenly distributed along the circumference of the connecting component 42, thereby enabling the movable paddles 43 to be evenly distributed along the circumference of the stirring shaft 41, which is beneficial for achieving better stirring and crushing effects. In implementation, the movable paddles 43 can be arranged horizontally or inclined. A serrated structure 46 is also constructed along the length direction of the movable paddles 43, such as... Figure 2 As shown, this is more conducive to crushing pulp.

[0049] During implementation, the moving blade assembly is located inside the inner barrel 47 and positioned to match the stationary blade assembly. The moving blade assembly can rotate relative to the stationary blade assembly under the drive of the stirring shaft 41, thereby enabling the moving blade assembly and the adjacent stationary blade assembly to form a shearing engagement within the inner barrel 47 (specifically, the movable blade 43 in the moving blade assembly forms a shearing engagement with the fixed blade 45 in the stationary blade assembly), forming a shearing engagement zone. This allows for further crushing of the pulp through shearing engagement, achieving the purpose of pulverizing the pulp.

[0050] like Figure 2As shown, during implementation, the stationary blade assembly is preferably positioned in the middle and / or lower part of the corresponding inner barrel 47. Correspondingly, the moving blade assembly is also preferably positioned in the middle and / or lower part of the corresponding inner barrel 47. This is because at these positions, the pulp has fully contacted the solvent and swelled, significantly reducing its toughness. This not only makes it easier to crush the pulp, but also makes it less likely for the shearing cooperation between the moving blade assembly and the stationary blade assembly to jam. This allows the cooperation between the moving blade assembly and the stationary blade assembly to achieve a stronger shearing effect and better and more stable pulp crushing.

[0051] In implementation, the serrated structure 46 on the movable paddle 43 can be configured to fit the serrated structure 46 on the fixed paddle 45 for more efficient shearing engagement. In implementation, the width direction of the movable paddle 43 can be tilted horizontally, as shown in the figure, so that the serrated structure 46 constructed on the movable paddle 43 is also tilted horizontally. This not only allows the serrated structure 46 on the movable paddle 43 to form a better shearing engagement with the serrated structure 46 on the fixed paddle 45 below, but also, because the movable paddle 43 is rotating, the tilted serrated structure 46, in conjunction with the movable paddle 43, provides downward thrust (acting as a propeller) to the liquid in the inner tank 47 during rotation, pushing the liquid in the inner tank 47 from top to bottom. This avoids blockage in the inner tank 47 and drives the liquid to circulate along the height direction of the inner tank 47, which is more conducive to uniform swelling. The specific tilt angle can be determined according to actual needs, and will not be listed here.

[0052] In a more preferred embodiment, the movable propeller 43 is arranged inclined in a horizontal direction, and the fixed propeller 45 is also arranged inclined in a horizontal direction, and the tilting direction of the movable propeller 43 is opposite to that of the fixed propeller 45. Figure 2 or Figure 4 As shown, this facilitates better shear coordination and more effective dispersion of cellulose in the liquid, resulting in more uniform swelling.

[0053] In implementation, the number of moving blade components and the number of stationary blade components can be determined according to actual needs. At least one moving blade component and one stationary blade component are required. To further improve the wet pulverization effect and swelling uniformity, in a more preferred embodiment, the stirring mechanism is equipped with multiple moving blade components and multiple stationary blade components, which are staggered along the height direction of the inner barrel 47. For example, ... Figure 2 As shown, the stirring mechanism is equipped with three moving blade assemblies and two stationary blade assemblies. The three moving blade assemblies and the two stationary blade assemblies are arranged alternately, so that there are moving blade assemblies above and below the stationary blade assemblies. This allows the stationary blade assemblies to form shearing and matching with the two adjacent moving blade assemblies, which can not only achieve better shearing effect and higher efficiency, but also help to further improve the uniformity of swelling.

[0054] In implementation, dry pulp, as the raw material, is added to the reaction tank 21 through the feed port 34 above the reaction tank 21. It can also enter the inner tank 47 from the top under the influence of the liquid (solvent) inside the reaction tank 21. At this time, the contact time between the pulp and the solvent is relatively short, and the pulp is not completely in contact with and wetted by the solvent. Therefore, the pulp has high toughness. If this pulp directly enters the shearing zone between the moving blade assembly and the stationary blade assembly for shearing, it will not only significantly increase the load on the motor 23 but also easily cause jamming, which is detrimental to the stable operation of the system. Therefore, in a further embodiment, the stirring mechanism also includes a first crushing component 5. The first crushing component 5 is installed on the stirring shaft 41 and is located inside the inner tank 47, above the moving blade assembly. Figure 2 As shown, during implementation, the first crushing component 5 is preferably positioned in the middle or upper part of the corresponding inner barrel 47 to crush the pulp entering the inner barrel 47 individually. On the one hand, the first crushing component 5 crushes the pulp into smaller pieces, making it easier for the pulp to come into complete contact with the solvent and swell more quickly. On the other hand, it can slow down the falling pulp, increasing the time for the pulp to fall into the lower shearing zone, which is more conducive to the pulp coming into full contact with the solvent and swelling. This significantly reduces the toughness of the pulp falling into the shearing zone, making it easier to crush and effectively avoiding jamming.

[0055] In implementation, the structure of the first crushing component 5 can be the same as that of the moving blade component. For example, in implementation, the first crushing component 5 may include a connecting part 42 for connecting the stirring shaft 41 and a first crushing blade 51 connected to the connecting part 42. Multiple first crushing blades 51 can be used, and each first crushing blade 51 is evenly distributed along the circumference of the connecting part 42. In implementation, the first crushing blade 51 also has a serrated structure 46 distributed along its length direction, such as... Figure 2 As shown, this is more conducive to crushing pulp. Similarly, the width direction of the first crushing paddle 51 can be inclined to the horizontal direction, so that the serrated structure 46 constructed on the first crushing paddle 51 can also be inclined to the horizontal direction, as shown in the figure, and can achieve the function of crushing pulp. It is also conducive to pushing the liquid in the inner tank 47 from top to bottom, so that the crushed pulp can flow to the lower cooperating shearing zone.

[0056] In practice, since the stirring shaft 41 is usually located at the center of the reaction tank 21, the feeding port 34 can only be located at a position off-center from the center of the reaction tank 21. Furthermore, the pulp raw material used in this embodiment is sheet-like dry pulp, making it difficult for the pulp raw material fed into the inner tank 47 through the feeding port 34 to easily enter the inner tank 47. If, during feeding, the pulp does not enter the inner tank 47 or mostly remains between the inner tank 47 and the tank body 31, the pulp is easily caught on the support 48 of the inner tank 47, making it even more difficult for the pulp to enter the inner tank 47, severely affecting crushing and swelling. Therefore, in a further embodiment, the stirring mechanism also includes a second crushing component 6, which is installed on the stirring shaft 41 and located above the inner tank 47. Figure 2 As shown, the second crushing component 6 rotates synchronously with the stirring shaft 41. On the one hand, the second crushing component 6 can crush the pulp that has not come into contact with the solvent during feeding, making it easier for the pulp to come into complete contact with the solvent and swell more quickly. On the other hand, during feeding, the pulp can enter the inner tank 47 as much as possible, greatly reducing the possibility of the pulp falling between the inner tank 47 and the tank body 31.

[0057] In implementation, the second crushing assembly 6 may include a connecting component 42 for connecting the stirring shaft 41 and a second crushing impeller 61 connected to the connecting component 42. Multiple second crushing impellers 61 may be used, and each second crushing impeller 61 is evenly distributed along the circumferential direction of the stirring shaft 41. Figure 2 As shown; in implementation, the structure of the second crushing paddle 61 can be the same as or different from the structure of the movable paddle 43 in the moving blade assembly. In this embodiment, the second crushing paddle 61 can be arranged horizontally, and the side of the second crushing paddle 61 is provided with a serrated structure 46 arranged along its length direction, which is beneficial to achieve a better crushing effect on the falling pulp.

[0058] During implementation, the second crushing impeller 61 should be of sufficient length to cover the feed inlet 34, such as... Figure 2 As shown, the pulp fed from the feed port 34 can fall directly onto the rotating second crushing component 6, allowing the second crushing component 6 to perform the first crushing of the added pulp. After the pulp enters the inner tank 47, it can be crushed a second time by the first crushing component 5, ensuring that the pulp falling into the shearing zone comes into full contact with the solvent and swells, significantly reducing its toughness. This allows it to be crushed by the shearing action of the moving and stationary blade components in the shearing zone, thus facilitating a more thorough and uniform swelling of the pulp within the swelling device 11. Finally, the liquid in the reaction tank 21 is discharged from the discharge port 36 at the bottom of the tank 31, resulting in a uniformly swollen cellulose suspension.

[0059] like Figure 2As shown, the impeller 49 is set on the stirring shaft 41 and located below the inner barrel 47, so that the impeller 49 can rotate synchronously with the stirring shaft 41. Through the centrifugal force of the impeller 49 rotation, the liquid in the inner barrel 47 flowing from top to bottom is forced to flow from the outer barrel upward, so that the impeller 49 can play a role in assisting the liquid in the inner barrel 47 to flow from top to bottom, which is more conducive to the formation of liquid circulation between the inner and outer barrels, and thus more conducive to the full crushing and full and uniform swelling of the pulp.

[0060] To improve the stability of the stirring shaft 41, in a more refined design, the stirring shaft 41 can be connected to the tank body 31 via bearings. For example, the upper end of the stirring shaft 41 can be connected to the tank cover 32 via bearings. To prevent the lower end of the stirring shaft 41 from swaying, in practice, a support 27 adapted to the stirring shaft 41 is also provided at the bottom of the tank body 31, with the lower end of the stirring shaft 41 rotatably constrained by the support 27. Figure 2 As shown, the support 27 is used to effectively constrain the lower end of the stirring shaft 41, preventing the lower end of the stirring shaft 41 from swinging significantly during rotation, thereby improving the stability of the stirring shaft 41 during rotation.

[0061] In this embodiment, the main function of the extrusion device 13 is to extrude the uniformly swollen cellulose suspension, separating some of the solvent from the cellulose suspension through extrusion, thereby increasing the cellulose concentration in the suspension. In implementation, the extrusion device 13 can be an existing extrusion equipment. In this embodiment, a variable pitch screw extrusion separator is preferred as the extrusion device 13. Figure 1 As shown, the screw extrusion separator includes an extrusion cylinder 72 and a drive motor 7123. The extrusion cylinder 72 has a cylindrical structure, with an inlet 73 and an outlet 74 on the outer sides of both ends. The extrusion cylinder 72 also has a discharge port 75. A rotating shaft 76 is installed inside the extrusion cylinder 72, with one end connected to the drive motor 7123. The rotating shaft 76 inside the extrusion cylinder 72 is equipped with helical blades 77 adapted to the extrusion cylinder 72 to transport the cellulose suspension along the direction from the inlet 73 to the outlet 74. The pitch of the helical blades 77 is variable, for example, as shown... Figure 1As shown, the pitch of the spiral blades 77 gradually decreases from the inlet 73 to the center of the extrusion cylinder 72; and gradually increases from the center of the extrusion cylinder 72 to the outlet 74. The discharge port 75 can be preferentially located at the center of the extrusion cylinder 72. In actual use, the cellulose suspension enters the spiral extrusion separator from the inlet 73 and is conveyed towards the outlet 74 under the drive of the spiral blades 77. During the conveying process, the cellulose suspension is simultaneously extruded, separating some of the solvent from the cellulose suspension through extrusion, thereby increasing the concentration of cellulose in the suspension to a preset range. The separated solvent can be discharged from the spiral extrusion separator through the discharge port 75 for recycling and reuse.

[0062] In this embodiment, the main function of the pulverizing and grinding device 14 is to pulverize and grind the high-concentration cellulose suspension exiting the screw extrusion separator. Pulverizing and grinding not only makes the swollen high-concentration cellulose suspension more uniform, but also significantly improves the dissolution effect and uniformity of the spinning solution, thereby enhancing spinnability and benefiting downstream spinning. In implementation, the pulverizing and grinding device 14 can employ existing pulverizing and grinding equipment. In this embodiment, such as… Figure 1 As shown, the grinding and pulverizing device 14 includes a housing 81, a drive motor 7123, and a toothed grinding roller 82 or a comb-type grinding roller disposed in the housing 81. The housing 81 is configured with an inlet 73 and an outlet 74. The inlet 73 of the grinding and pulverizing device 14 is connected to the outlet 74 of the extrusion device 13, and the outlet 74 of the grinding and pulverizing device 14 is connected to the downstream thin film evaporator 16, so that the high-concentration cellulose suspension after grinding and pulverizing can enter the thin film evaporator 16.

[0063] In a more complete embodiment, the system further includes a screw conveyor 15, and the outlet 74 of the crushing and grinding device 14 is connected to the screw conveyor 15. The screw conveyor 15 can be connected to the thin-film evaporator 16 via a pipe 17. Figure 1 As shown, the high-concentration cellulose suspension after crushing and grinding is conveyed to the thin-film evaporator 16 by the screw conveyor 15.

[0064] like Figure 1 and Figure 5 As shown, in this embodiment, the main function of the thin-film evaporator 16 is to heat and evaporate the solvent in the high-concentration cellulose suspension under vacuum negative pressure and achieve cellulose dissolution. In implementation, the thin-film evaporator 16 can be an existing type. The thin-film evaporator 16 includes an evaporation chamber 92 enclosed by a shell 91, and an inlet 95 and an outlet 96 connected to the evaporation chamber 92. For example, in this embodiment, the thin-film evaporator 16 is a vertical type, such as... Figure 1As shown, the evaporation chamber 92 is provided with a film scraping mechanism 93 for scraping film. The lower end of the evaporation chamber 92 is also constructed as a conical structure 94. The feed inlet 95 is located at the top of the evaporation chamber 92, and the glue outlet 96 is located at the bottom of the evaporation chamber 92.

[0065] In a more refined implementation, the system also includes a receiving hopper 12, such as... Figure 1 As shown, the receiving hopper 12 is located at the inlet 73 of the extrusion device 13 and is connected to the extrusion device 13. The receiving hopper 12 corresponds to the valve 37 above it so as to receive the cellulose suspension discharged from the swelling device 11, thereby realizing the connection between the swelling device 11 and the extrusion device 13.

[0066] Example 2

[0067] Based on the system provided in Example 1, this embodiment also provides a method for industrially preparing lyocell fiber spinning solutions using this system, such as... Figure 6 As shown, it includes the following steps:

[0068] Step 1: Prepare the first suspension, including calculating the amount of pulp raw material to accurately control its concentration; directly adding a fixed amount of pulp raw material into a swelling device 11 containing solvent, simultaneously wet grinding and swelling of the pulp in the swelling device 11 to obtain a first suspension with a cellulose concentration less than or equal to 6 wt%. Since the cellulose concentration in the first suspension is low, it is actually a low-concentration cellulose suspension. In this step, the solvent used is an NMMO aqueous solution.

[0069] In practical implementation, to ensure that the cellulose concentration in the first suspension meets the requirements, the required amount of pulp raw material to be added can be calculated based on the amount of solvent in the swelling device 11 and the parameters of the pulp raw material. A solvent of a set concentration is introduced into the reaction tank 21 of the swelling device 11. Simultaneously, sheet-like dry pulp raw material can be quantitatively added into the reaction tank 21 of the swelling device 11 through the feed port 34. After entering the reaction tank 21, the pulp raw material is crushed by the rotating second crushing component 6 and falls smoothly into the inner tank 47, allowing the pulp to come into contact with the solvent. The pulp flows downwards along the inner tank 47, and when it passes the first crushing component 5, it is crushed again by the first crushing component 5 and its flow is slowed down by the first crushing component 5, ensuring sufficient contact between the pulp and the solvent. The pulp swells, significantly reducing its toughness. It then falls into the lower shearing zone, where it is pulverized by the shearing action of the passive and static blades, resulting in a more dispersed and uniform distribution of cellulose in the liquid, achieving more complete and uniform swelling. The pulp then flows out from the lower end of the inner tank 47 and rises along the channel between the inner tank 47 and the reaction tank 21 under the action of the impeller 49, re-entering the inner tank 47 from above. This cycle ensures the pulp is fully pulverized and swells more evenly within the swelling device 11, yielding a first suspension. This first suspension is finally discharged through the outlet 36 at the bottom of the tank 31 and enters the downstream extrusion device 13.

[0070] Based on preliminary experimental studies, during implementation, the solvent concentration in the swelling device 11 can be preferentially controlled at 76–82 wt%, with a more favorable option being 78–80 wt%, such as 78 wt%, 79 wt%, or 80 wt%. The temperature within the swelling device 11 can also be controlled at 75–80°C, which is more conducive to wet pulp grinding and swelling, especially to achieving more complete swelling. Considering the fluidity of the suspension within the swelling device 11 and the overall economic efficiency of the production process, the cellulose concentration in the first suspension prepared by the swelling device 11 can be preferentially controlled at 3–6 wt%. More preferably, the cellulose concentration in the first suspension prepared by the swelling device 11 can be further controlled at 5–6 wt%, such as 5 wt%, 5.5 wt%, or 6 wt%, which can achieve better pulp grinding and swelling effects, effectively reduce the difficulty of process implementation, and improve the economic efficiency of the process. For example, in this embodiment, the concentration of the solvent in the swelling device 11 is controlled to 76 wt%, and the temperature in the swelling device 11 is controlled to 80°C. By adding an appropriate proportion of dry pulp raw material, a first suspension with a cellulose concentration of 6 wt% is obtained.

[0071] More specifically, in this step, cellulose swells in the solvent to form a suspension, and the viscosity of the entire suspension increases with increasing cellulose concentration. When the cellulose concentration is high, the system's fluidity decreases, making stirring in the swelling device 11 difficult. Therefore, this method prioritizes preparing a low-concentration first suspension in step 1, and then concentrates the first suspension subsequently. Figure 7 As shown in the previous experimental results, when the cellulose concentration in the first suspension is between 3 and 6 wt%, the resulting suspension exhibits significant fluidity, and the swelling device 11 can achieve good pulp pulverization and swelling effects at this time. When the cellulose concentration in the first suspension is higher than 6 wt%, for example, reaching 7 wt%, the fluidity of the suspension deteriorates significantly, exhibiting a lumpy texture. At this time, the swelling device 11 will experience noticeable jerking during stirring, and the suspension is also prone to sticking to the wall of the swelling device 11, making it difficult to achieve the ideal pulp pulverization and swelling effect. Therefore, in step 1, the cellulose concentration in the first suspension needs to be strictly controlled below 6 wt%.

[0072] Furthermore, in actual operation, if the cellulose concentration in the first suspension is too low, the subsequent concentration step requires squeezing out more solvent. This squeezed-out solvent needs to be recovered, and generally, the recovered solvent contains some fiber residue. The solvent needs to be purified and removed before reuse. If too much solvent is squeezed out, not only is the efficiency low, but the solvent purification process is also overloaded, significantly reducing the economic efficiency of the system and process. Appropriately increasing the cellulose concentration in the first suspension can improve production efficiency and significantly reduce production costs. Therefore, without affecting the overall process and system operation, it is necessary to control the lower limit of the cellulose concentration in the first suspension, and the higher the lower limit, the better. Thus, the cellulose concentration in the first suspension can be preferentially controlled at 5–6 wt%, which can effectively reduce the difficulty of process implementation, significantly improve the economic efficiency of the process, and increase production efficiency.

[0073] Step 2: Increase the concentration of cellulose in the first suspension, including feeding the first suspension to an extrusion device 13 and using extrusion to separate a portion of the solvent from the first suspension, so as to increase the concentration of cellulose in the first suspension to a set threshold by separating the solvent, thereby obtaining a second suspension. Figure 6 As shown.

[0074] In practical implementation, after the first suspension discharged from the swelling device 11 enters the screw extrusion separator, it moves towards the outlet 74 driven by the screw blades 77. During this process, the screw blades 77 gradually squeeze the first suspension, separating some of the solvent from the first suspension through squeezing. This solvent is discharged from the screw extrusion separator through the discharge port 75, achieving separation from the first suspension and thus increasing the cellulose concentration in the first suspension. According to previous experimental studies, the temperature inside the screw extrusion separator can be controlled at 80-85°C, and the amount of solvent separated can be controlled by pre-adjusting the screw pitch in the screw extrusion separator, thereby precisely increasing the cellulose concentration in the first suspension. In practice, the screw extrusion separator can be used to preferentially increase the cellulose concentration in the first suspension to 10-12 wt%. Therefore, the second suspension is actually a high-concentration cellulose suspension. For example, in this embodiment, the temperature inside the screw extrusion separator is controlled at 80°C, and the cellulose concentration in the first suspension after extrusion separation is 11 wt%.

[0075] Step 3, crushing and grinding, includes conveying the second suspension to the crushing and grinding device 14 for crushing and grinding. Through the crushing and grinding process, the swelling can be more complete and uniform, resulting in a fully swollen third suspension. More importantly, on the one hand, crushing and grinding can also make the swollen third suspension more uniform, and on the other hand, it can also greatly improve the dissolution effect and uniformity of the spinning solution, thereby improving the spinnability and benefiting the downstream spinning process.

[0076] During the pulverizing and grinding process, the temperature inside the pulverizing and grinding device 14 can be preferentially controlled at 80-85°C. For example, in this embodiment, the temperature inside the pulverizing and grinding device 14 is 80°C, which is more conducive to swelling and dissolution. The third suspension after pulverizing and grinding by the pulverizing and grinding device 14 is fed into the thin-film evaporator 16 via the screw conveyor 15.

[0077] Step 4: Prepare spinning solution, including conveying the pulverized and ground third suspension to the thin film evaporator 16, controlling the temperature inside the thin film evaporator 16, and dissolving the third suspension under vacuum conditions to obtain a spinning solution with a cellulose concentration of 11-13 wt%.

[0078] To achieve better evaporation and dissolution effects, during implementation, the temperature within the thin-film evaporator 16 is controlled to exhibit a gradient distribution along the direction from the feed inlet 95 to the glue outlet 96. The third suspension is then dissolved under gradient temperature and vacuum conditions to obtain the spinning solution. Figure 5As shown, the gradient temperature distribution includes controlling the feed temperature of the thin-film evaporator 16 to 80-85°C, the upper section temperature of the thin-film evaporator 16 to 75-80°C, the middle section temperature of the thin-film evaporator 16 to 80-85°C, the lower section temperature of the thin-film evaporator 16 to 85-95°C, the cone bottom temperature of the thin-film evaporator 16 to 95-105°C, and the glue outlet temperature of the thin-film evaporator 16 to 100-110°C. For example, in this embodiment, the feed temperature of the thin-film evaporator 16 is 80°C, the upper section temperature is 80°C, the middle section temperature is 85°C, the lower section temperature is 95°C, the cone bottom temperature is 100°C, and the glue outlet temperature is 100°C, resulting in a spinning solution with a cellulose concentration of 12.5 wt%, which is beneficial for subsequent spinning.

[0079] Comparative Example 1

[0080] Since Example 2 provides a method for preparing lyocell fiber spinning solution based on an industrialized system, for comparison with the technical solution in Example 2, Comparative Example 1 uses a traditional dry pulverization and swelling preparation process to prepare lyocell fiber spinning solution. The specific process includes: taking equal amounts of pulp raw materials, first dry pulverizing the pulp raw materials, then adding the pulverized pulp to an NMMO aqueous solution to obtain a high-concentration cellulose suspension with a concentration of 11 wt%, wherein the concentration of the NMMO aqueous solution is 76 wt%, and the preparation temperature is 80°C. Then, it is further pulverized and ground, and finally, the pulverized and ground suspension is fed into a thin-film evaporator 16 for dissolution to obtain the lyocell fiber spinning solution.

[0081] Comparative Example 2

[0082] The main difference between Comparative Example 2 and Example 2 is that Comparative Example 2 does not involve a crushing and grinding step, while the other process steps and equipment used are the same as in Example 2. Finally, lyocell fiber spinning solution is obtained.

[0083] Comparative Example 3

[0084] The main difference between Comparative Example 3 and Example 2 is that the pulp raw material is dry-crushed and then put into a stirring device containing NMMO aqueous solution for stirring. That is, the pulp raw material is crushed first, and then the crushed material is added to the NMMO aqueous solution for stirring. The stirring device used here is an existing stirring device. The stirred liquid is input into the extrusion device 13 in Example 2. Other process steps and equipment used are the same as in Example 2. Finally, lyocell fiber spinning dope is obtained.

[0085] During the experiment, the lyocell fiber spinning solutions prepared in Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were tested and analyzed, specifically including: (1) Observing the high-concentration cellulose suspensions prepared in Example 2 and each comparative example (the extracted suspension is the suspension before entering the thin-film evaporator 16, equivalent to the third suspension in Example 2), such as Figure 7 As shown; (2) The spinning solutions prepared in Example 2 and each comparative example were observed, as shown Figure 8 As shown; (3) The refractive index of the spinning solutions prepared in Example 2 and each comparative example was tested. Ten sets of data were tested for each sample. The test results are shown in Table 1; (4) The spinning solutions prepared in Example 2 and each comparative example were directly used for spinning. The spinning results are shown in Table 2.

[0086] Table 1. Refractive index test results of the spinning solutions prepared in Example 2 and each comparative example.

[0087]

[0088] (Note: The higher the refractive index of the solution, the better the dissolution effect. Generally, in production, the refractive index of the spinning solution for lyocell fibers is required to be above 1.5.)

[0089] Table 2 shows the results of directly applying the spinning solutions prepared in Example 2 and each comparative example to spinning.

[0090]

[0091]

[0092] According to Table 1, Table 2, Figure 7 , Figure 8 The results lead to the following conclusions:

[0093] (1) Comparing Example 2 and Comparative Example 1, it can be seen that the high-concentration cellulose suspension prepared by the traditional dry pulverization and swelling process exhibits unevenly swollen "white cores" (see reference). Figure 8 The high-concentration cellulose suspension prepared using the process method provided in Example 2 did not exhibit a significant "white core," indicating that the process method provided in Example 2 can achieve a better swelling effect for cellulose.

[0094] Furthermore, the refractive index of the spinning solution prepared using the method provided in Example 2 is higher than that of the spinning solution prepared using the traditional dry pulverization and swelling process, indicating that the spinning solution prepared using this method has a better dissolution effect (refer to Table 1). In addition, from the perspective of spinning performance, the spinnability of the spinning solution prepared using the process provided in Example 2 is also better than that of the traditional dry pulverization and swelling process (refer to Table 2). Therefore, the method provided by this invention can not only improve the swelling effect of cellulose and effectively prevent the formation of "white core" during the swelling process, but also greatly improve the quality of the spinning solution, which is more beneficial for downstream spinning.

[0095] (2) Comparing Example 2 and Comparative Example 2, it can be seen that in the method provided by the present invention, by configuring the crushing and grinding step, not only can the swollen high-concentration cellulose suspension (third suspension) be made more uniform (see reference). Figure 8 It can also significantly improve the solubility and uniformity of the spinning solution (see Table 1), thereby improving spinnability (see Table 2), which is beneficial for downstream spinning.

[0096] (3) Comparing Example 2 and Comparative Example 3, it can be seen that in the process method provided by the present invention, when preparing a low-concentration cellulose suspension (first suspension) by feeding pulp, whether or not the pulp is crushed beforehand does not affect the swelling effect of cellulose (see reference). Figure 8 The dissolution effect is shown in Table 1, and the spinnability of the final spinning solution is not significantly affected (see Table 2). Therefore, the present invention adopts the method of directly feeding pulp without crushing, which can eliminate the hidden danger of dust generated during the crushing process of pulp in the traditional dry crushing and swelling process.

[0097] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for industrially preparing lyocell fiber spinning solution, characterized in that, A spinning solution preparation system is provided, comprising a swelling device, an extrusion device, a grinding and pulverizing device, and a thin-film evaporator connected in sequence. The swelling device includes a reaction vessel, a motor, and a stirring mechanism. The reaction vessel includes an internal cavity, a feed port, a solvent inlet, an assembly port, and a discharge port connected to the internal cavity, with a valve at the discharge port. The stirring mechanism includes a stirring shaft, a moving blade assembly, a stationary blade assembly, a first crushing assembly, an inner barrel, and an impeller. The stirring shaft is vertically arranged, with its upper end connected to the output shaft of the motor, and its lower end extending into the internal cavity via the assembly port. The inner barrel is fixedly mounted in the internal cavity of the reaction vessel by a bracket, with the lower end of the stirring shaft inserted into the inner barrel at least. The inner barrel has a cylindrical structure. The stationary blade assembly is located inside the inner barrel and includes a central seat and multiple fixed blades. The central seat is sleeved on the outside of the stirring shaft and coaxial with it. One end of each fixed blade is connected to the central seat, and the other end is connected to the inner barrel. The fixed blades are evenly distributed along the circumference of the stirring shaft, and at least the upper end of each fixed blade has a serrated structure, which is arranged along the length of the fixed blade. The moving blade assembly is adapted to the stationary blade assembly. The moving blade assembly includes a connecting part for connecting the stirring shaft and multiple movable blades connected to the connecting part. Each movable blade is evenly distributed along the circumference of the stirring shaft and has a serrated structure along its length. The moving blade assembly is located inside the inner barrel and positioned to adapt to the stationary blade assembly. The moving blade assembly rotates relative to the stationary blade assembly under the drive of the stirring shaft, so that the moving blade assembly and the adjacent stationary blade assembly form a shearing engagement within the inner barrel, crushing the pulp by shearing. A first crushing component is installed on the stirring shaft, located inside the inner barrel, and above the moving blade assembly. The first crushing component is positioned at the middle or upper part of the corresponding inner barrel. An impeller is located on the stirring shaft and below the inner barrel. The impeller rotates synchronously with the stirring shaft. The method includes the following steps: Step 1: Calculate the amount of pulp raw material to be fed into a swelling device containing solvent for simultaneous wet grinding and swelling, to obtain a first suspension with a cellulose concentration of 5-6 wt%. Ensure the first suspension has good fluidity to achieve more uniform swelling. The temperature inside the swelling device is controlled at 75-80℃, and the solvent used is an NMMO aqueous solution with a concentration of 76-82 wt%. Step 2: Input the first suspension into the extrusion device. The temperature inside the extrusion device is controlled at 80~85℃. Use extrusion to separate part of the solvent in the first suspension. By separating part of the solvent, the concentration of cellulose in the first suspension is increased to 10~12 wt%, and a second suspension is obtained. Step 3: Input the second suspension into a pulverizing and grinding device for pulverizing and grinding. The temperature inside the pulverizing and grinding device is controlled at 80~85℃ to obtain a fully swollen third suspension. Step 4: Input the third suspension into the thin-film evaporator, control the temperature inside the thin-film evaporator, and dissolve the third suspension under vacuum conditions to obtain a spinning solution with a cellulose concentration of 11~13wt%.

2. The method for industrially preparing lyocell fiber spinning solution according to claim 1, characterized in that, The concentration of cellulose in the first suspension is 5.5 wt% or 6 wt%.

3. The method for industrially preparing lyocell fiber spinning solution according to claim 1, characterized in that, In step 1, the concentration of the solvent in the swelling device is 76 wt%; the temperature in the swelling device is 80°C. In step 2, the temperature inside the extrusion device is 80°C; the concentration of cellulose in the second suspension is 11 wt%. In step 3, the temperature inside the crushing and grinding device is 80°C.

4. The method for industrially preparing lyocell fiber spinning solution according to claim 1, characterized in that, The thin-film evaporator is a vertical thin-film evaporator, which includes an evaporation chamber enclosed by an outer shell and an inlet and an outlet connected to the evaporation chamber. The lower end of the evaporation chamber has a conical structure. The inlet and outlet are respectively located at the top and bottom of the evaporation chamber. The temperature inside the thin-film evaporator is controlled to have a gradient distribution along the direction from the inlet to the outlet. In step 4, the third suspension is dissolved under gradient temperature and vacuum conditions to obtain the spinning solution. The gradient temperature distribution includes controlling the inlet temperature of the thin-film evaporator to 80~85℃, the upper section temperature of the thin-film evaporator to 75~80℃, the middle section temperature of the thin-film evaporator to 80~85℃, the lower section temperature of the thin-film evaporator to 85~95℃, the cone bottom temperature of the thin-film evaporator to 95~105℃, and the outlet temperature of the thin-film evaporator to 100~110℃.

5. The method for industrially preparing lyocell fiber spinning solution according to claim 4, characterized in that, In step 4, the feed temperature of the thin film evaporator is 80°C, the upper section temperature of the thin film evaporator is 80°C, the middle section temperature of the thin film evaporator is 85°C, the lower section temperature of the thin film evaporator is 95°C, the cone bottom temperature of the thin film evaporator is 100°C, and the glue outlet temperature of the thin film evaporator is 100°C. In step 4, the concentration of cellulose in the spinning solution is 12.5 wt%.

6. The method for industrially preparing lyocell fiber spinning solution according to any one of claims 1-5, characterized in that, The stationary knife assembly is located at the middle and / or lower part of the corresponding inner tub; the moving knife assembly is also located at the middle and / or lower part of the corresponding inner tub.

7. The method for industrially preparing lyocell fiber spinning solution according to any one of claims 1-5, characterized in that, The stirring mechanism is equipped with multiple moving blade assemblies and multiple stationary blade assemblies, which are arranged alternately along the height direction of the inner barrel.

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