Method for industrially preparing lyocell fiber spinning solution

Abstract

The invention relates to a method for industrially preparing a lyocell fiber spinning solution. The method comprises the following steps: step 1, preparing a first suspension with the cellulose concentration of less than or equal to 6wt%; step 2, increasing the concentration of cellulose in the first suspension to 10-12wt% in a manner of separating part of the solvent under pressure to obtain a second suspension; step 3, crushing and grinding the second suspension to obtain a third suspension; 4, inputting the third suspension into a film evaporator, controlling the temperature in the film evaporator, and dissolving the third suspension under a vacuum condition to obtain a spinning solution with the cellulose concentration of 11-13wt%; the method is a brand new thought for industrially preparing the lyocell fiber spinning solution, the hidden danger that dust is generated in the pulverization process of pulp can be eliminated, more sufficient and uniform swelling and more uniform dissolution can be synchronously achieved, the better dissolution effect is achieved, and the high-quality fiber spinning solution is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of novel cellulose fiber production, and in particular to a method for industrially preparing lyocell fiber spinning solution. Background Art

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

[0003] In the industrial production process, lyocell fiber spinning solution is prepared by mixing pulp raw material with solvent to prepare cellulose suspension, and then entering a dissolving device (e.g., thin film evaporator) to dissolve cellulose in the suspension after the cellulose is fully swollen to obtain spinning solution. At present, the industrial preparation of lyocell fiber spinning solution is mainly based on dry process, and the conventional steps of dry process are: firstly, the pulp raw material in dry state is crushed, and then the pulp raw material after crushing is mixed with a high concentration of solvent (usually NMMO aqueous solution) so that the cellulose in the pulp raw material swells in the solvent to obtain cellulose suspension (or porridge), and then the cellulose suspension is sent to the thin film evaporator for vacuum dehydration and dissolution, and finally the lyocell fiber spinning solution is obtained. In the traditional dry process, the swelling process is a very important link, and the quality of swelling is directly related to the dissolution effect of subsequent cellulose in the thin film evaporator, thereby directly affecting the quality of lyocell fiber spinning solution. In the art, the technical personnel of the industry have always sought effective means to ensure that the cellulose in the pulp raw material is more fully and more evenly swollen in the solvent. In addition, dry pulp is prone to generate dust during the pulverization process, which affects the workshop environment, and dust can also cause flammability and explosion hazards, so this process has certain safety hazards. Moreover, during the dry pulverization process, the pulverization device is prone to overheating, causing the pulp to keratinize during the pulverization process, resulting in the appearance of "white core" during the swelling process, affecting the dissolution effect, and thus seriously affecting the quality of the subsequent spinning solution. To solve these problems, Chinese patent CN 114016141B takes a different approach and provides a method for preparing fiber spinning solution by direct dissolution. The method specifically includes S1) mixing pulp with a NMMO solution with a mass concentration of 72% to 76% to obtain a mixed material; the temperature of the mixed swelling is 40°C to 45°C; the mass concentration of the pulp in the mixed material is 4% to 5%; S2) pressing the mixed material to obtain a pressed material; the pressing temperature is 40°C to 65°C; the mixed material is pressed to a pulp dryness of 35% to 45%; S3) crushing the pressed material to obtain a crushed material; S4) mixing the crushed material with a NMMO solution with a mass concentration of 81% to 85% under normal pressure to dissolve it to obtain a fiber spinning solution. By comparison, 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 swelled (equivalent to infiltration) under this condition, and then squeezed and crushed. Finally, the pulp raw material is directly dissolved under higher temperature and higher solvent concentration conditions to obtain fiber spinning solution.Among them, since the temperature and solvent concentration are controlled very low (much lower than the temperature at which cellulose is fully swollen) in steps S1 and S2, the cellulose in the pulp is only infiltrated with the solvent and basically does not swell (because according to the records in the patent, under the conditions of temperature and solvent concentration, the hydrogen bonding between the solvent molecules and the cellulose molecules is weak, so the cellulose raw material cannot be fully swollen), there must be a problem of insufficient swelling. Therefore, this method does not actually consider how to achieve a more sufficient and uniform swelling effect, and cannot achieve a more sufficient and uniform swelling effect, which also has a relatively obvious impact on the subsequent dissolution effect; secondly In step S2 of the method, the mixture is only squeezed to a dryness of 35% to 45%. The squeezed mixture still contains most of the low-concentration solvent, resulting in a large amount of water in the squeezed mixture. After being crushed, the mixture is directly thrown into a high-concentration solvent (concentration of 81% to 85%) for dissolution. The water brought by the mixture will dilute the concentration of the high-concentration solvent, seriously affecting the dissolution effect. In practice, it is difficult to accurately control the water content in the squeezed mixture, resulting in the actual solubility of the solvent in the dissolution process being difficult to accurately control, which is not conducive to accurately controlling the dissolution effect in industrial production. In addition, since the cellulose in the mixture is not fully and evenly swollen, in step 4, when the mixture contacts and dissolves with the high-concentration solvent, the mixture that first contacts the high-concentration solvent will form a gel and will wrap the subsequent mixture, resulting in part of the mixture being difficult to fully contact the solvent and unable to fully dissolve, seriously affecting the quality of the fiber spinning solution. Therefore, although this method can solve the problems existing in the dry process to a certain extent, the method itself also has the above-mentioned shortcomings. It can neither solve the problem of sufficient and uniform swelling of cellulose in the solvent, nor is it conducive to improving the dissolution effect and improving 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 existing in the traditional dry process, and obtain high-quality fiber spinning solution, needs to be solved urgently. Summary of the invention

[0004] The first aspect of the present invention is to solve the above technical problems and provide a new method for industrially preparing lyocell fiber spinning solution, which can not only eliminate the hidden danger of dust generated during pulp pulverization, improve the swelling effect of cellulose, and achieve more sufficient and uniform swelling, but also effectively prevent the uneven dissolution caused by the "white core" phenomenon during the swelling process, and effectively improve the quality of the glue solution. The main concept is:

[0005] A method for industrially preparing a lyocell fiber spinning solution, using a spinning solution preparation system, the spinning solution preparation system comprising a swelling device, an extrusion device, a crushing and grinding device and a thin film evaporator connected in sequence; the method comprises the following steps:

[0006] Step 1, calculating the feeding amount of pulp raw material, and feeding a fixed amount of pulp raw material into a swelling device filled with a solvent for simultaneous wet crushing and swelling to obtain a first suspension with a cellulose concentration of less than or equal to 6wt%, wherein the temperature in the swelling device is controlled at 75-80°C, the solvent is an NMMO aqueous solution, and the solvent concentration is 76-82wt%;

[0007] Step 2, inputting the first suspension into an extrusion device, controlling the temperature in the extrusion device to be 80-85° C., separating part of the solvent in the first suspension by extrusion, and increasing the concentration of cellulose in the first suspension to 10-12 wt % by separating part of the solvent, to obtain a second suspension;

[0008] Step 3, inputting the second suspension into a crushing and grinding device for crushing and grinding, wherein the temperature in the crushing and grinding device is controlled at 80-85° C., to obtain a third suspension;

[0009] Step 4, input the third suspension into the thin film evaporator, control the temperature in the thin film evaporator, and dissolve the third suspension under vacuum to obtain a spinning solution with a cellulose concentration of 11-13wt%. In this scheme, by controlling the feeding amount of pulp raw material, a low-concentration cellulose suspension (first suspension) is prepared, and the combination of pulp wet crushing and swelling is achieved in the swelling device, which can simplify the process and improve efficiency. It not only avoids the hidden danger of dust generation during pulp crushing, but also solves the problem of poor pulp swelling effect under high solvent concentration and high pulp concentration, and realizes more uniform and sufficient swelling of pulp raw material in a simple way. In the traditional dry method, when pulp is mixed with a high concentration NMMO solution after crushing, the concentration is usually controlled at 11-12wt%. At this time, due to the swelling of cellulose, the fluidity of the whole system becomes poor, which is not conducive to the infiltration of the solvent into the pulp, and easily leads to uneven swelling. In this solution, the concentration of the first suspension is controlled to be lower than 6wt%. After swelling, the cellulose has better fluidity due to its lower concentration, which is conducive to the penetration and infiltration of the solvent into the pulp. Under the temperature condition of 75-80°C, and in combination with the swelling device in this solution, more uniform and sufficient swelling can be achieved. Increasing the concentration of cellulose in the first suspension by extrusion can not only more conveniently and accurately control the concentration of cellulose, but also facilitate more sufficient and uniform infiltration and swelling of cellulose. Controlling the concentration of cellulose in the second suspension to 10-12wt% is more conducive to subsequent sufficient dissolution and achieves better dissolution effect. By continuing to crush and grind the second suspension and controlling the temperature to 80-85°C, the obtained third suspension is more conducive to achieving a better dissolution effect; the crushing and grinding process can not only make the swelling more sufficient and uniform to obtain a fully swollen third suspension, but more importantly: the crushing and grinding can also make the swollen third suspension more uniform, and can also greatly improve the dissolution effect and uniformity of the spinning solution, thereby improving the spinnability and facilitating the back-end spinning; and through the coordination of the extrusion process and the crushing and grinding, the problem of uneven dissolution caused by the appearance of the "white core" during the swelling process can be effectively prevented; finally, the concentration of cellulose in the spinning solution is controlled to 11-13wt%, which can effectively guarantee the performance of the final fiber.The present method is an improvement and optimization based on the traditional dry process, and does not adopt the technical route in Chinese patent CN 114016141 B. Therefore, there are no corresponding technical problems. Compared with the traditional dry process, the present method can not only solve the technical problems existing in the traditional dry process, but also achieve more sufficient and uniform swelling and more uniform dissolution at the same time, achieve better dissolution effect, and obtain high-quality fiber spinning solution; compared with the technical route in Chinese patent CN 114016141 B, the present method not only does not have many shortcomings existing in the patent, but also can effectively solve the problem of sufficient and uniform swelling of cellulose in the solvent, and can effectively improve the dissolution effect and the quality of the fiber spinning solution.

[0010] In order to solve the problem of balancing the economic efficiency and the swelling effect, further, in the step 1, the concentration of cellulose in the first suspension is controlled to be 3-6wt%. If the concentration of cellulose in the first suspension is too low, the subsequent concentration step needs to squeeze out more solvent, and the squeezed solvent needs to be recovered. Generally, the recovered solvent will contain some fiber residues, and the solvent needs to be purified and impurities removed before it can be reused. If too much solvent is squeezed out, not only the efficiency is low, but also a large load is imposed on the purification and impurity removal of the solvent, which greatly reduces the economic efficiency of the method; if the concentration of cellulose in the first suspension is too high, the system viscosity of the entire suspension will also increase, the fluidity will deteriorate, and it is difficult to achieve the ideal pulp crushing and swelling effect. The previous experiments show that when the concentration of cellulose in the first suspension is between 3-6wt%, the suspension formed shows obvious fluidity, which can achieve better pulp crushing and swelling effects, and at the same time, the production efficiency will be improved and the production cost will be greatly reduced.

[0011] Preferably, in step 1, the concentration of cellulose in the first suspension is controlled to be 5-6 wt %. This is beneficial to further cellulose swelling, not only achieving more complete and uniform swelling, but also ensuring that the obtained first 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 concentration of the solvent in the swelling device is 76 wt % and the temperature in the swelling device is 80° C. This ensures that the cellulose in the first suspension is more fully swollen.

[0014] Preferably, in step 2, the temperature in 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 in the crushing and grinding device is 80°C.

[0017] In order to achieve better evaporation and dissolution effect and improve the quality of spinning solution, further, the thin film evaporator adopts a vertical thin film evaporator, which includes an evaporation chamber surrounded by an outer shell and a feed port and a glue outlet connected to the evaporation chamber. The lower end of the evaporation chamber is constructed as a cone structure, and the feed port and the glue outlet are respectively arranged at the top and bottom of the evaporation chamber. The temperature in the thin film evaporator is controlled to be distributed in a gradient from the feed port to the glue outlet. In step 4, the third suspension is dissolved under the gradient distribution temperature and vacuum conditions to obtain the spinning solution; the gradient distribution temperature includes controlling the feed temperature of the thin film evaporator to 80-85°C, controlling the upper section temperature of the thin film evaporator to 75-80°C; controlling the middle section temperature of the thin film evaporator to 80-85°C; controlling the lower section temperature of the thin film evaporator to 85-95°C, and controlling the cone bottom temperature of the thin film evaporator to 95-105°C; and controlling the glue outlet temperature of the thin film evaporator to 100-110°C. Sampling such a temperature configuration can not only achieve better evaporation and dissolution effects, but also more accurately control the concentration of cellulose in the spinning solution, so that the concentration of cellulose in the spinning solution meets the design requirements and improves 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 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. This is conducive to achieving better evaporation and dissolution effects.

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

[0020] The second aspect of the present invention is to solve the problem of eliminating the hidden danger of dust generated during the pulp pulverization process and simultaneously improving the swelling efficiency and swelling uniformity. Furthermore, the swelling device includes a reaction tank, a motor and a stirring mechanism. The reaction tank includes an internal cavity, a feeding port connected to the internal cavity, a solvent inlet, an assembly port and a discharge port, and a valve is arranged at the discharge port; the stirring mechanism includes a stirring shaft, a moving knife assembly, a stationary knife assembly, an inner barrel and an impeller, wherein the stirring shaft is arranged vertically, the upper end of the stirring shaft is transmission-connected to the output shaft of the motor, and the lower end of the stirring shaft extends into the internal cavity through the assembly port; the inner barrel is fixedly arranged in the internal cavity of the reaction tank by a bracket, and the lower end of the stirring shaft is at least inserted into the inner barrel, and the inner barrel is constructed as a cylindrical structure; the stationary knife assembly is arranged in the inner barrel, and includes a center seat and a plurality of fixed paddles, and the center seat is sleeved on the outer side of the stirring shaft, and Coaxial with the stirring shaft, one end of the fixed paddle is connected to the center seat, and the other end is connected to the inner barrel, each fixed paddle is evenly distributed along the circumferential direction of the stirring shaft, at least the upper end of the fixed paddle is constructed with a sawtooth structure, and the sawtooth structure is arranged along the length direction of the fixed paddle; the moving knife assembly is constructed to adapt to the static knife assembly, the moving knife assembly includes a connecting component for connecting the stirring shaft and a plurality of movable paddles connected to the connecting component, each movable paddle is evenly distributed along the circumferential direction of the stirring shaft, and is constructed with a sawtooth structure along the length direction of the movable paddle; the moving knife assembly is located in the inner barrel and is arranged at a position adapted to the static knife assembly, the moving knife assembly is used to rotate relative to the static knife assembly under the drive of the stirring shaft, so that the moving knife assembly and the adjacent static knife assembly form a shear fit in the inner barrel, and the pulp is crushed by the shear fit; the impeller is arranged on the stirring shaft and is located below the inner barrel, and the impeller rotates synchronously with the stirring shaft.In this scheme, since the concentration of cellulose in the first suspension is controlled to be relatively low and the fluidity of the system is good, wet crushing of the pulp raw material can be achieved directly by stirring, and there is no need to pre-crush the raw material in a dry state. Based on this, in order to further improve the swelling efficiency and swelling uniformity, in this scheme, an impeller is arranged under the inner barrel to force the liquid in the inner barrel flowing from top to bottom to flow upward from the outer barrel, so that the impeller can play a role in assisting the inner barrel liquid to flow from top to bottom, which is more conducive to forming a circulation of the inner and outer barrel liquids, thereby being more conducive to sufficient crushing and sufficient and uniform swelling of the pulp; by arranging a stationary knife assembly and a moving knife assembly in the inner barrel, and arranging saw blades on the stationary knife assembly and the moving knife assembly respectively The tooth structure enables the moving knife assembly and the adjacent stationary knife assembly to form a shear matching area in the inner barrel, and the circulating liquid in the reaction tank can continuously pass through the shear matching area, which can not only realize the wet crushing and swelling of the pulp simultaneously, but also promote the full crushing of the pulp and promote the more uniform dispersion of cellulose in the solvent, thereby achieving a more sufficient and uniform swelling effect; in the actual operation process, the swelling device combined with the above method can not only effectively eliminate the hidden danger of dust generation during the crushing process of the pulp, but also solve the problem of poor pulp swelling performance under higher solvent concentrations and higher pulp concentrations, thereby achieving the effect of simultaneously improving the swelling efficiency and swelling uniformity in a simple way.

[0021] Furthermore, the stationary knife assembly is arranged at the position corresponding to the middle and / or lower part of the inner barrel; the moving knife assembly is also arranged at the position corresponding to the middle and / or lower part of the inner barrel. Because at these positions, the pulp has been fully contacted with the solvent and swelled, and the toughness is greatly reduced, which not only makes it easier to crush the pulp, but also makes the shearing cooperation between the moving knife assembly and the stationary knife assembly less likely to get stuck.

[0022] In order to further improve the uniformity of swelling, the movable paddle is arranged obliquely to the horizontal direction to provide downward thrust, and the sawtooth structure on the movable paddle is configured to match the sawtooth structure on the fixed paddle. Not only can the sawtooth structure on the movable paddle form a better shear fit with the sawtooth structure on the fixed paddle below, but also because the movable paddle is in a rotating state, the movable paddle can provide downward thrust for the liquid in the inner barrel during the rotation process, pushing the liquid in the inner barrel to flow from top to bottom, which can avoid blockage in the inner barrel and drive the liquid to circulate along the height direction of the inner barrel, which is more conducive to uniform swelling.

[0023] Furthermore, the stirring mechanism is equipped with a plurality of moving blade assemblies and a plurality of stationary blade assemblies, and the plurality of moving blade assemblies and the plurality of stationary blade assemblies are arranged alternately along the height direction of the inner barrel, so that the stationary blade assembly and the two adjacent moving blade assemblies can form a shearing coordination, which can not only achieve a better shearing effect and higher efficiency, but also help to further improve the uniformity of swelling.

[0024] The third aspect of the present invention is to solve the problem that the load of the motor increases significantly during the actual operation, and the moving knife assembly and the static knife assembly are very easy to get stuck, resulting in the system being unable to operate stably. Furthermore, the stirring mechanism also includes a first crushing assembly, which is installed on the stirring shaft, is located in the inner barrel, and is located above the moving knife assembly. The first crushing assembly is arranged at a position corresponding to the middle or upper part of the inner barrel. In order to use the first crushing assembly to crush the pulp entering the inner barrel alone, on the one hand, the first crushing assembly can be used to crush the pulp into smaller pieces, which is more convenient for the pulp to contact with the solvent more quickly and be soaked and swollen. On the other hand, it can slow down the pulp falling in the inner barrel, increase the time for the pulp to fall into the matching shearing zone below, and is more conducive to the pulp to fully contact with the solvent and swell, so that the toughness of the pulp falling into the matching shearing zone is greatly reduced, and it is easier to be crushed, effectively avoiding the problem of getting stuck.

[0025] Preferably, the first crushing assembly includes a connecting component for connecting the stirring shaft and a plurality of first crushing paddles connected to the connecting component, and the first crushing paddles are evenly distributed along the circumferential direction of the stirring shaft; the first crushing paddles are arranged obliquely to the horizontal direction to provide downward thrust, and the first crushing paddles are also constructed with a serrated structure distributed along their length direction.

[0026] The fourth aspect of the present invention aims to solve the problem that during actual operation, the pulp put into the reaction tank is easily hung on the bracket of the inner barrel and is not easy to enter the inner barrel, which seriously affects the crushing and swelling process. Furthermore, the stirring mechanism also includes a second crushing component, which is installed on the stirring shaft, and the second crushing component is located above the inner barrel. The second crushing component rotates synchronously with the stirring shaft, and the rotation range of the second crushing component covers the feeding port. Such a design, on the one hand, can use the second crushing component to crush the pulp that has not been exposed to the solvent when feeding, which is more convenient for the pulp to contact with the solvent more quickly and thoroughly and be infiltrated and swelled. On the other hand, when feeding, the pulp can enter the inner barrel as much as possible, which greatly reduces the possibility of the pulp falling between the inner barrel and the tank body, making the crushing and swelling process smoother and more efficient.

[0027] Preferably, the second crushing assembly comprises a connecting component for connecting to the stirring shaft and a plurality of second crushing paddles connected to the connecting component, and the second crushing paddles are evenly distributed along the circumferential direction of the stirring shaft.

[0028] Compared with the prior art, the method for preparing lyocell fiber spinning solution provided by the present invention is a new idea for industrially preparing lyocell fiber spinning solution, which can not only eliminate the hidden danger of dust generated during the pulp crushing process, but also achieve more sufficient and uniform swelling and more uniform dissolution, achieve better dissolution effect, and obtain high-quality fiber spinning solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

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

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

[0032] Figure 3 for Figure 2 Cross-sectional view at AA in the middle.

[0033] Figure 4 for Figure 2 A local enlarged schematic diagram of point I in the middle.

[0034] Figure 5 A schematic structural diagram of a thin film evaporator in a spinning solution preparation system provided in Example 1 of the present invention.

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

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

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

[0038] Explanation of the symbols in the figure: swelling device 11, receiving hopper 12, extrusion device 13, crushing and grinding device 14, screw conveyor 15, thin film evaporator 16, pipeline 17; reaction tank 21, insulation structure 22, motor 23, reducer 24, coupling 25, mounting frame 26, support 27; tank body 31, tank cover 32, frame 33, feeding port 34, solvent inlet 35, discharge port 36, valve 37; stirring shaft 41, connecting part 42, movable paddle 43, center The core seat 44, the fixed paddle 45, the serrated structure 46, the inner barrel 47, the bracket 48, the impeller 49; the first crushing assembly 5, the first crushing paddle 51; the second crushing assembly 6, the second crushing paddle 61; the driving motor 71, the extrusion cylinder 72, the inlet 73, the outlet 74, the discharge port 75, the rotating shaft 76, the spiral blade 77; the shell 81, the toothed crushing roller 82; the outer shell 91, the evaporation chamber 92, the scraping mechanism 93, the conical structure 94, the feed port 95, the glue outlet 96. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents the selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present invention.

[0040] Example 1

[0041] like Figure 1 As shown, this embodiment provides a system for preparing a spinning solution, including a swelling device 11, an extrusion device 13, a crushing and grinding device 14 and a thin film evaporator 16. The extrusion device 13 is arranged downstream of the swelling device 11, and the swelling device 11 is communicated with the extrusion device 13; the crushing and grinding device 14 is arranged downstream of the extrusion device 13, and the extrusion device 13 is communicated with the crushing and grinding device 14; the thin film evaporator 16 is arranged downstream of the crushing and grinding device 14, and the crushing and grinding device 14 is communicated with 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, so that the wet-crushing and swelling are completed simultaneously in the same device. Specifically, in actual use, the pulp raw material is directly added to the swelling device 11, and the swelling device 11 can realize the wet-crushing and swelling of the pulp simultaneously. It is an integrated device that can simultaneously realize the wet-crushing of the pulp raw material and the swelling of the cellulose in the pulp raw material, ensuring that a low-concentration cellulose suspension is obtained. The swelling device 11 is configured at the front end of the system. Compared with the existing design, it not only avoids the hidden danger of dust generation during the pulp crushing process, but also solves the problem of poor pulp swelling performance at higher solvent concentrations and higher pulp concentrations, and realizes more uniform and full swelling of the pulp raw material in a simple way.

[0043] like Figure 1-Figure 4 As shown, in this embodiment, the swelling device 11 includes a reaction tank 21, a motor 23, a stirring mechanism, and a heat preservation structure 22, wherein the reaction tank 21 includes a tank body 31 having an internal cavity, a tank cover 32 sealing the top of the tank body 31, and a frame 33 supporting the tank body 31, and the tank cover 32 is installed on the top of the tank body 31. During implementation, the tank cover 32 can be detachably installed on the tank body 31 by fasteners such as bolts, so as to facilitate assembly and subsequent maintenance. Figure 2 As shown, the tank cover 32 is constructed with a feed port 34, a solvent inlet 7335 and an assembly port adapted to the stirring mechanism. When in use, pulp raw material can be added to the internal cavity of the reaction tank 21 through the feed port 34. The pulp raw material is preferably flake pulp. At the same time, 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 usually an NMMO aqueous solution. Correspondingly, the bottom of the tank body 31 is configured with a discharge port 36, such as Figure 2 As shown, a valve 37 is provided at the discharge port 36 , and the valve 37 can preferably be a gate valve, so that the valve 37 can be used to control the on-off of the discharge port 36 , thereby controlling whether the material in the reaction tank 21 is discharged through the valve 37 .

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

[0045] like Figure 1-Figure 4As shown, in this embodiment, the stirring mechanism includes a stirring shaft 41, a moving blade assembly, a stationary blade assembly, an inner barrel 47 and an impeller 49, wherein the motor 23 can be installed on a mounting frame, and the mounting frame can be installed on the tank cover 32 in the reaction tank 21, or can be installed on the frame 33. The stirring shaft 41 is arranged vertically, and the upper end of the stirring shaft 41 is connected to the output shaft of the motor 23 so that the stirring shaft 41 can be driven by the motor 23 to rotate; during implementation, the motor 23 can be connected to the stirring shaft 41 through a transmission mechanism, and the transmission mechanism can be a coupling 25, a reducer 24, a belt transmission mechanism or a chain transmission mechanism, etc. Figure 2 As shown, in this embodiment, the output shaft of the motor 23 is transmission-connected with the reducer 24, the reducer 24 is fixed to the tank cover 32 through a mounting bracket, and the output shaft of the reducer 24 is connected to the upper end of the stirring shaft 41 through a coupling 25, so that the motor 23 can be used to drive the stirring shaft 41 to rotate, and the reducer 24 can be used to reduce the rotation 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 body 31 through the assembly port. During implementation, a sealing structure is also provided at the assembly port. The sealing structure can be implemented using existing technology and will not be described in detail here. As shown in the figure, the inner barrel 47 is fixedly arranged in the internal cavity of the reaction tank 21, and the lower end of the stirring shaft 41 is at least inserted into the inner barrel 47. During 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; during implementation, the inner barrel 47 has a variety of installation methods. For example, the inner barrel 47 can be directly fixed to the bottom of the tank body 31 in the reaction tank 21, and the inner barrel 47 can also be fixed to the bottom of the tank body 31 through a bracket 48. At this time, there is a certain gap between the lower end of the inner barrel 47 and the bottom of the tank body 31, which is conducive to the circulation of materials in the reaction tank 21 along the height direction; in addition, the inner barrel 47 can also be fixed to the side wall of the tank body 31 through a bracket 48, such as Figure 2 As shown, multiple groups of brackets 48 can be arranged along the height direction of the inner barrel 47, so that it can not only be more firmly fixed to the inner barrel 47, avoiding shaking or deformation of the upper end of the inner barrel 47, but also improving reliability. Moreover, the brackets 48 are arranged between the inner barrel 47 and the side wall of the tank body 31, and will not occupy the space between the inner barrel 47 and the bottom of the tank body 31. It will neither interfere with the installation and operation of the impeller 49 nor form turbulence between the inner barrel 47 and the bottom of the tank body 31, thereby being more conducive to driving the material to circulate in the vertical direction.

[0047] In this embodiment, the stationary blade assembly includes a center seat 44 and a plurality of fixed paddles 45. The center seat 44 is configured with a center hole for passing the stirring shaft 41. The inner diameter of the center hole is larger than the outer diameter of the stirring shaft 41. Figure 2As shown, the center seat 44 is sleeved on 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, so as to achieve the purpose of restraining the fixed paddle 45. During implementation, each fixed paddle 45 can be evenly distributed along the circumferential direction of the center seat 44, so that each fixed paddle 45 can be evenly distributed along the circumferential direction of the stirring shaft 41. According to the needs of the process requirements, during implementation, each fixed paddle 45 can be arranged horizontally or tilted. The upper end of the fixed paddle 45 is constructed with a sawtooth structure 46, such as Figure 1-Figure 4 As shown, the sawtooth structure 46 is arranged along the length direction of the fixed paddle 45, which is more conducive to crushing the pulp. On this basis, the lower end of the fixed paddle 45 is further constructed as a sawtooth structure 46, or the side of the fixed paddle 45 is further constructed as a sawtooth structure 46, which is also conducive to crushing the pulp.

[0048] In this embodiment, the movable blade assembly is configured to be adapted to the stationary blade assembly, and the movable blade assembly includes a connecting component 42 for connecting the stirring shaft 41 and a movable paddle 43 connected to the connecting component 42. Figure 1-Figure 4 As shown; during implementation, the connecting component 42 can be constructed as a cylindrical structure, and the connecting component 42 is sleeved on the stirring shaft 41. The connecting component 42 can be fixed to the stirring shaft 41 by welding, or 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 knife assembly is provided with at least three movable paddles 43, and each movable paddle 43 is evenly distributed along the circumferential direction of the connecting component 42, so that each movable paddle 43 can be evenly distributed along the circumferential direction of the stirring shaft 41, which is conducive to achieving a better stirring and crushing effect. During implementation, the movable paddles 43 can be arranged horizontally or tilted. A serrated structure 46 is also constructed along the length direction of the movable paddle 43, such as Figure 2 As shown, it is more conducive to breaking the pulp.

[0049] During implementation, the moving knife assembly is located in the inner barrel 47 and is arranged at a position adapted to the stationary knife assembly, and the moving knife assembly can rotate relative to the stationary knife assembly under the drive of the stirring shaft 41, so that the moving knife assembly and the adjacent stationary knife assembly can form a shear fit in the inner barrel 47 (specifically, the movable paddle 43 in the moving knife assembly and the fixed paddle 45 in the stationary knife assembly form a shear fit), and form a shear fit area, so as to further crush the pulp by shear fit to achieve the purpose of crushing the pulp.

[0050] like Figure 2As shown, during implementation, the stationary knife assembly is preferentially arranged at a position corresponding to the middle and / or lower part of the inner barrel 47, and correspondingly, the moving knife assembly is also preferentially arranged at a position corresponding to the middle and / or lower part of the inner barrel 47, because, at these positions, the pulp has been fully in contact with the solvent and swelled, and the toughness is greatly reduced, which not only makes it easier to crush the pulp, but also makes the shear cooperation between the moving knife assembly and the stationary knife assembly less likely to get stuck, so that the cooperation between the moving knife assembly and the stationary knife assembly can play a stronger shearing effect and crush the pulp better and more stably.

[0051] During implementation, the sawtooth structure 46 on the movable paddle 43 can be configured to match the sawtooth structure 46 on the fixed paddle 45 to achieve more efficient shearing cooperation. During implementation, the width direction of the movable paddle 43 can be inclined to the horizontal direction, as shown in the figure, so that the sawtooth structure 46 constructed on the movable paddle 43 is also inclined to the horizontal direction, not only so that the sawtooth structure 46 on the movable paddle 43 can form a better shearing cooperation with the sawtooth structure 46 on the fixed paddle 45 below, but also because the movable paddle 43 is in a rotating state, with the inclined sawtooth structure 46, the movable paddle 43 can provide a downward thrust (playing the role of a propeller) for the liquid in the inner barrel 47 during the rotation process, pushing the liquid in the inner barrel 47 to flow from top to bottom, which can avoid blockage in the inner barrel 47, and drive the liquid to circulate along the height direction of the inner barrel 47, which is more conducive to uniform swelling. During implementation, the specific inclination angle can be determined according to actual needs, and no examples are given here.

[0052] In a more preferred embodiment, the movable paddle 43 is arranged obliquely to the horizontal direction, the fixed paddle 45 is also arranged obliquely to the horizontal direction, and the inclination direction of the movable paddle 43 is opposite to the inclination direction of the movable paddle 43, such as Figure 2 or Figure 4 As shown, it is beneficial to achieve better shear coordination and can more effectively disperse the cellulose in the liquid, which is beneficial to achieve more uniform swelling.

[0053] In implementation, the number of moving knife assemblies and the number of stationary knife assemblies can be determined according to actual needs. In implementation, at least one moving knife assembly and one stationary knife assembly are required. In order to further improve the wet crushing effect and swelling uniformity, in a more preferred embodiment, the stirring mechanism is configured with multiple moving knife assemblies and multiple stationary knife assemblies, and the multiple moving knife assemblies and the multiple stationary knife assemblies are respectively arranged in a staggered manner along the height direction of the inner barrel 47. For example, Figure 2 As shown, the stirring mechanism is equipped with three moving knife assemblies and two stationary knife assemblies. The three moving knife assemblies and the two stationary knife assemblies are arranged alternately, so that the moving knife assemblies are located above and below the stationary knife assemblies, so that the stationary knife assembly and the two adjacent moving knife assemblies can form a shear coordination, which can not only achieve better shear effect and higher efficiency, but also help to further improve the uniformity of swelling.

[0054] During implementation, dry pulp as pulp raw material is added into the reaction tank 21 from the feed port 34 above the reaction tank 21, and can enter the inner barrel 47 from the upper end of the inner barrel 47 driven by the liquid (solvent) in 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 soaked with the solvent. At this time, the pulp toughness is relatively high. If this pulp directly enters the coordinated shearing area of ​​the moving knife assembly and the stationary knife assembly for shearing, it will not only cause a significant increase in the load of the motor 23, but also it is very easy to get stuck, which is not conducive to the stable operation of the system. For this reason, in a further embodiment, the stirring mechanism also includes a first crushing assembly 5, and the first crushing assembly 5 is installed on the stirring shaft 41. The first crushing assembly 5 is located in the inner barrel 47 and above the moving knife assembly. Figure 2 As shown, during implementation, the first crushing component 5 is preferably arranged at a position corresponding to the middle or upper part of the inner barrel 47, so as to individually crush the pulp entering the inner barrel 47. On the one hand, the first crushing component 5 is used to break the pulp into smaller pieces, which is more convenient for the pulp to contact with the solvent more quickly and be soaked and swelled. On the other hand, it can slow down the falling pulp and increase the time for the pulp to fall into the matching shear zone below, which is more conducive to the full contact and swelling of the pulp with the solvent, so that the toughness of the pulp falling into the matching shear zone is greatly reduced, which is easier to be crushed and effectively avoids the problem of jamming.

[0055] In implementation, the structure of the first crushing assembly 5 can be the same as that of the moving knife assembly. For example, in implementation, the first crushing assembly 5 can include a connecting component 42 for connecting the stirring shaft 41 and a first crushing paddle 51 connected to the connecting component 42. The number of the first crushing paddles 51 can be multiple, and each first crushing paddle 51 is evenly distributed along the circumferential direction of the connecting component 42. In implementation, the first crushing paddle 51 is also configured with a sawtooth structure 46 distributed along its length direction, such as Figure 2 Similarly, the width direction of the first crushing paddle 51 can be inclined to the horizontal direction, so that the sawtooth 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 effect of crushing the pulp, and is also conducive to pushing the liquid in the inner barrel 47 to flow from top to bottom, so that the crushed pulp can flow to the matching shearing area below.

[0056] During implementation, since the stirring shaft 41 is usually arranged at the center of the reaction tank 21, the feeding port 34 can only be arranged at a position deviated from the center of the reaction tank 21, and the pulp raw material used in this embodiment is flaky dry pulp, which makes it difficult for the pulp raw material fed from the feeding port 34 to enter the inner barrel 47; if the pulp does not enter the inner barrel 47 or most of it is between the inner barrel 47 and the tank body 31 during feeding, the pulp is easy to hang on the bracket 48 of the inner barrel 47, making it more difficult for the pulp to enter the inner barrel 47, seriously affecting the crushing and swelling. For this reason, in a further embodiment, the stirring mechanism also includes a second crushing assembly 6, which is installed on the stirring shaft 41, and the second crushing assembly 6 is located above the inner barrel 47, such as Figure 2 As shown, the second crushing assembly 6 rotates synchronously with the stirring shaft 41. On the one hand, the second crushing assembly 6 can be used to crush the pulp that has not been in contact with the solvent when feeding, which makes it easier for the pulp to contact with the solvent more quickly and be soaked and swelled. On the other hand, when feeding, the pulp can be allowed to enter the inner barrel 47 as much as possible, greatly reducing the possibility of the pulp falling between the inner barrel 47 and the tank body 31.

[0057] In implementation, the second crushing assembly 6 may include a connecting component 42 for connecting to the stirring shaft 41 and a second crushing paddle 61 connected to the connecting component 42. The number of the second crushing paddles 61 may be multiple, and the second crushing paddles 61 are evenly distributed along the circumferential direction of the stirring shaft 41, such as 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 movable 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 sawtooth structure 46 arranged along its length direction, which is conducive to achieving a better crushing effect on the falling pulp.

[0058] In practice, the second crushing blade 61 should have a sufficient length to cover the feed port 34. Figure 2 As shown, the pulp fed from the feed port 34 can directly fall onto the rotating second crushing assembly 6, so that the second crushing assembly 6 can be used to perform the first crushing on the fed pulp. After the pulp enters the inner barrel 47, the first crushing assembly 5 can be used to perform the second crushing on the pulp, so that the pulp that falls into the matching shearing zone is fully in contact with the solvent and swells, and the toughness is greatly reduced, so that it can be crushed by the shearing cooperation of the moving knife assembly and the stationary knife assembly in the matching shearing zone, thereby being more conducive to more sufficient and uniform swelling of the pulp in 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 body 31 to obtain a uniformly swollen cellulose suspension.

[0059] like Figure 2As shown, the impeller 49 is arranged on the stirring shaft 41 and is located below the inner barrel 47, so that the impeller 49 can rotate synchronously with the stirring shaft 41. The centrifugal force generated by the rotation of the impeller 49 forces the liquid in the inner barrel 47 flowing from top to bottom to flow upward from the outer barrel, 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 in the inner and outer barrels, thereby being more conducive to the full crushing and fully uniform swelling of the pulp.

[0060] To improve the stability of the stirring shaft 41, in a more perfect solution, the stirring shaft 41 can be connected to the tank body 31 through a bearing, for example, the upper end of the stirring shaft 41 can be connected to the tank cover 32 through a bearing. To prevent the lower end of the stirring shaft 41 from swinging, during implementation, a support 27 adapted to the stirring shaft 41 is further provided at the bottom of the tank body 31, and the lower end of the stirring shaft 41 can be rotatably constrained to the support 27, such as Figure 2 As shown, the support 27 can be used to effectively constrain the lower end of the stirring shaft 41 to prevent 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, and to separate part of the solvent in the cellulose suspension by extrusion, so as to increase the cellulose concentration in the suspension. In implementation, the extrusion device 13 can use existing extrusion equipment. In this embodiment, the extrusion device 13 can preferably use a variable pitch spiral extrusion separator, such as Figure 1 As shown, the screw extrusion separator includes an extrusion barrel 72 and a driving motor 7123. The extrusion barrel 72 is constructed as a cylindrical structure. The outer sides of the two ends of the extrusion barrel 72 are respectively constructed with an inlet 73 and an outlet 74. At the same time, the extrusion barrel 72 is also constructed with a discharge port 75. A rotating shaft 76 is arranged in the extrusion barrel 72. One end of the rotating shaft 76 is drivingly connected to the driving motor 7123. A spiral blade 77 adapted to the extrusion barrel 72 is arranged on the rotating shaft 76 in the extrusion barrel 72 so as to transport the cellulose suspension from the inlet 73 to the outlet 74, and the pitch of the spiral blade 77 is variable, for example, Figure 1As shown, the pitch of the spiral blade 77 gradually decreases from the inlet 73 to the center of the extrusion cylinder 72; the pitch of the spiral blade 77 gradually increases from the center of the extrusion cylinder 72 to the outlet 74, and the discharge port 75 can be preferably constructed 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 transported toward the outlet 74 under the drive of the spiral blade 77. During the transportation process, the cellulose suspension is simultaneously squeezed, and part of the solvent in the cellulose suspension is separated by squeezing, so as to increase 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 crushing and grinding device 14 is to crush and grind the high-concentration cellulose suspension coming out of the screw extruder separator. The crushing and grinding can not only make the swollen high-concentration cellulose suspension more uniform, but also greatly improve the dissolution effect and uniformity of the spinning solution, thereby improving the spinnability and facilitating the back-end spinning. In implementation, the crushing and grinding device 14 can use existing crushing and grinding equipment. In this embodiment, Figure 1 As shown, the crushing and grinding device 14 includes a shell 81, a driving motor 7123 and a toothed crushing roller 82 or a comb-pin crushing roller arranged in the shell 81, and the shell 81 is constructed with an inlet 73 and an outlet 74. The inlet 73 of the crushing and grinding device 14 is connected to the outlet 74 of the extrusion device 13, and the outlet 74 of the crushing and grinding device 14 is connected to the downstream thin film evaporator 16, so that the high-concentration cellulose suspension after crushing and grinding can enter the thin film evaporator 16.

[0063] In a more perfect embodiment, the system further comprises a screw conveyor 15, the outlet 74 of the crushing and grinding device 14 is connected to the screw conveyor 15, and the screw conveyor 15 can be connected to the thin film evaporator 16 through a pipeline 17, such as Figure 1 As shown, a screw conveyor 15 is used to convey the crushed and ground high-concentration cellulose suspension to a thin film evaporator 16 .

[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 conditions and realize cellulose dissolution. During implementation, the thin film evaporator 16 can adopt an existing thin film evaporator 16, and the thin film evaporator 16 includes an evaporation chamber 92 surrounded by a shell 91 and a feed port 95 and a glue outlet 96 connected to the evaporation chamber 92. For example, in this embodiment, the thin film evaporator 16 adopts a vertical thin film evaporator 16, such as Figure 1As shown, a film scraping mechanism 93 for scraping film is arranged in the evaporation chamber 92 , the lower end of the evaporation chamber 92 is also constructed as a conical structure 94 , a feed inlet 95 is arranged at the top of the evaporation chamber 92 , and a glue outlet 96 is arranged at the bottom of the evaporation chamber 92 .

[0065] In a more perfect embodiment, the system further comprises a receiving hopper 12, such as Figure 1 As shown, the receiving hopper 12 is disposed 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 so as to receive the cellulose suspension discharged from the swelling device 11 , thereby achieving 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 solution using the system, such as Figure 6 As shown, the following steps are included:

[0068] Step 1, preparing a first suspension, including calculating the feeding amount of pulp raw material so as to accurately control the feeding concentration of the pulp raw material; directly feeding a fixed amount of pulp raw material into a swelling device 11 filled with a solvent, and simultaneously wet-crushing and swelling the pulp through the swelling device 11 to obtain a first suspension with a cellulose concentration of less than or equal to 6wt%. Since the cellulose concentration in the first suspension is relatively low, the first suspension is actually a low-concentration cellulose suspension. In this step, the solvent used is an NMMO aqueous solution.

[0069] In the specific implementation, in order to make the cellulose concentration in the first suspension meet the requirements, the required amount of pulp raw material can be calculated according to the amount of solvent in the swelling device 11, the parameters of the pulp raw material, etc.; the solvent of the set concentration is input into the reaction tank 21 of the swelling device 11, and at the same time, the sheet-shaped dry pulp raw material can be quantitatively added into the reaction tank 21 of the swelling device 11 through the feeding port 34. After the pulp raw material enters the reaction tank 21, it is crushed by the rotating second crushing component 6 and smoothly falls into the inner barrel 47, so that the pulp contacts with the solvent; the pulp flows downward along the inner barrel 47, and when passing through the first crushing component 5, it is crushed again by the first crushing component 5, and is decelerated by the turbulence of the first crushing component 5, so that the pulp contacts with the solvent fully. , and swelling occurs, which greatly reduces the toughness of the pulp; then, the pulp falls into the matching shearing zone below, and is crushed by the shearing cooperation of the passive knife assembly and the static knife assembly in the matching shearing zone, and the distribution of cellulose in the liquid is more dispersed and more even, achieving more sufficient and uniform swelling; then, the pulp flows out through the lower end of the inner barrel 47, and can rise along the channel between the inner barrel 47 and the reaction tank 21 under the action of the impeller 49, and re-enter the inner barrel 47 from the top of the inner barrel 47, and so on. The cycle allows the pulp to be fully crushed and more fully and evenly swollen in the swelling device 11, thereby obtaining a first suspension, which is finally discharged through the discharge port 36 at the bottom of the tank body 31 and enters the downstream extrusion device 13.

[0070] According to the previous experimental research, when implementing, the concentration of the solvent in the swelling device 11 can be preferentially controlled to be 76-82wt%, and the more preferred solution is to control the concentration of the solvent to be 78-80wt%, for example, the concentration of the solvent is 78wt% or 79wt% or 80wt%, and the temperature in the swelling device 11 can be controlled to be 75-80°C, which is more conducive to pulp wet crushing and swelling, especially to achieve more sufficient swelling. According to the previous experimental research, considering the fluidity of the suspension in the swelling device 11 and the economy of the entire production process, when implementing, the concentration of cellulose in the first suspension prepared by the swelling device 11 can be preferentially controlled to be 3-6wt%, and more preferably, the concentration of cellulose in the first suspension prepared by the swelling device 11 can be further controlled to be 5-6wt%, for example, 5wt%, 5.5wt%, 6wt%, etc., which can not only achieve better pulp crushing and swelling effects, but also effectively reduce the difficulty of the process and improve the economy of the process. For example, in this embodiment, the concentration of the solvent in the swelling device 11 is controlled to 76wt%, and the temperature in the swelling device 11 is controlled to 80°C, and a first suspension with a cellulose concentration of 6wt% is obtained by adding a suitable proportion of dry pulp raw materials.

[0071] More specifically, in this step, cellulose swells in the solvent to form a suspension, and as the cellulose concentration increases, the viscosity of the entire suspension increases. When the cellulose concentration is high, the fluidity of the system deteriorates, which makes it difficult to stir the swelling device 11. Therefore, in step 1, the method preferentially prepares a low-concentration first suspension, and then concentrates the first suspension. Figure 7 As shown, according to the previous experimental results, when the cellulose concentration in the first suspension is between 3 and 6wt%, the formed suspension shows obvious fluidity, and the swelling device 11 can achieve good pulp crushing and swelling effects. When the cellulose concentration in the first suspension is higher than 6wt%, for example, when it reaches 7wt%, the fluidity of the suspension is significantly deteriorated, showing a blocky feeling. At this time, the swelling device 11 will have an obvious sense of frustration during stirring, and the suspension is also easy to stick to the wall in the swelling device 11, making it difficult to achieve the ideal pulp crushing and swelling effect. Therefore, this step 1 requires that the cellulose concentration in the first suspension be strictly controlled below 6wt%.

[0072] In addition, in actual operation, if the cellulose concentration in the first suspension is too low, the subsequent concentration step needs to squeeze out more solvent, and the squeezed solvent needs to be recovered. Generally, the recovered solvent will contain some fiber residues, and the solvent needs to be purified and impurities removed before it can be reused. If too much solvent is squeezed out, it will not only be inefficient, but also cause a large load on the solvent purification and impurity removal, greatly reducing the economy of this system and this process. If the cellulose concentration in the first suspension is appropriately increased, not only will the production efficiency be improved, but the production cost will be greatly reduced. Therefore, under the premise of not affecting the operation of the entire process and system, it is necessary to control the lower limit of the cellulose concentration in the first suspension, and the higher the lower limit, the better. Therefore, the cellulose concentration in the first suspension can be preferentially controlled to 5-6wt%, which can not only effectively reduce the difficulty of implementing the process, significantly improve the economy of the process method, but also improve production efficiency.

[0073] Step 2, increasing the concentration of cellulose in the first suspension, including conveying the first suspension to an extrusion device 13, separating part of the solvent in the first suspension by extrusion, so as to increase the concentration of cellulose in the first suspension to a set threshold by separating part of the solvent, and obtaining a second suspension, such as Figure 6 shown.

[0074] In the specific implementation, after the first suspension discharged from the swelling device 11 enters the screw extrusion separator, it can move toward the outlet 74 under the drive of the spiral blade 77. In this process, the first suspension is gradually squeezed by the spiral blade 77, and part of the solvent in the first suspension is separated by extrusion. This part of the solvent is discharged from the screw extrusion separator through the discharge port 75 to achieve separation from the first suspension, thereby achieving the purpose of increasing the cellulose concentration in the first suspension. According to previous experimental studies, in this process, the temperature in the screw extrusion separator can be controlled to 80-85°C, and the separation amount of the solvent can be controlled by adjusting the pitch of the screw extrusion separator in advance, thereby achieving the purpose of accurately increasing the cellulose concentration in the first suspension. In the implementation, the screw extrusion separator can be used to preferentially increase the cellulose concentration in the first suspension to 10-12wt%, so the second suspension is actually a high-concentration cellulose suspension. For example, in this embodiment, the temperature in the screw extrusion separator is controlled to 80°C, and the cellulose concentration in the first suspension after the extrusion separation process is 11wt%.

[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 made more sufficient and uniform to obtain a fully swollen third suspension. More importantly, on the one hand, the crushing and grinding can also make the swollen third suspension more uniform. On the other hand, it can also greatly improve the dissolution effect and uniformity of the spinning solution, thereby improving the spinnability and facilitating the back-end spinning.

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

[0077] Step 4, preparing spinning solution, including conveying the crushed and ground third suspension to the thin film evaporator 16, controlling the temperature in 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] In order to achieve a better evaporation and dissolution effect, during implementation, the temperature in the thin film evaporator 16 is controlled to be distributed in a gradient along the direction from the feed port 95 to the glue outlet 96, and the third suspension is dissolved under the gradient temperature and vacuum conditions to obtain the spinning solution, such as Figure 5As shown, the temperature in gradient distribution includes controlling the feed temperature of the thin film evaporator 16 to 80-85°C, controlling the upper section temperature of the thin film evaporator 16 to 75-80°C; controlling the middle section temperature of the thin film evaporator 16 to 80-85°C; controlling the lower section temperature of the thin film evaporator 16 to 85-95°C, controlling the cone bottom temperature of the thin film evaporator 16 to 95-105°C; and controlling 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 of the thin film evaporator 16 is 80°C, the middle section temperature is 85°C, the lower section temperature is 95°C, the cone bottom temperature is 100°C, the glue outlet temperature is 100°C, and a spinning solution with a cellulose concentration of 12.5wt% is obtained, which is beneficial to subsequent spinning.

[0079] Comparative Example 1

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

[0081] Comparative Example 2

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

[0083] Comparative Example 3

[0084] The main difference between this comparative example 3 and example 2 is that the pulp raw material is dry-ground and then put into a stirring device filled with NMMO aqueous solution for stirring, that is, the pulp raw material is first ground and then added to the NMMO aqueous solution for stirring. The stirring device here adopts the existing stirring device, and the stirred liquid is input into the extrusion device 13 in example 2. The other process steps and the equipment used are the same as those in example 2. Finally, lyocell fiber spinning stock solution is obtained.

[0085] During the experiment, the lyocell fiber spinning solutions prepared in the above-mentioned Example 2, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were tested and analyzed, specifically including: (1) the high-concentration cellulose suspension prepared in Example 2 and each comparative example (the suspension extracted is the suspension before entering the thin film evaporator 16, which is equivalent to the third suspension in Example 2) was observed, such as Figure 7 (2) The spinning solutions prepared in Example 2 and the comparative examples were observed. Figure 8 As shown; (3) The refractive index of the spinning solutions prepared in Example 2 and each comparative example was tested, and 10 sets of data were tested for each sample. The test results are shown in Table 1; (4) The spinning solutions prepared in the above Example 2 and each comparative example were directly used for spinning, and the spinning results are shown in Table 2.

[0086] Table 1 Refractive index test results of spinning solutions prepared in Example 2 and comparative examples

[0087]

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

[0089] Table 2 Results of directly using the spinning solutions prepared in Example 2 and Comparative Examples for spinning

[0090]

[0091]

[0092] According to Table 1, Table 2, Figure 7 , Figure 8 As a result, we can draw the following conclusions:

[0093] (1) By comparing Example 2 with Comparative Example 1, it can be seen that in the high-concentration cellulose suspension prepared by the conventional dry pulverization and swelling process, uneven swelling of the "white core" will occur (refer to Figure 8 ), while the high-concentration cellulose suspension prepared by the process method provided in Example 2 did not show obvious "white core", indicating that the process method provided in Example 2 can achieve better swelling effect of cellulose.

[0094] Moreover, the refractive index of the spinning solution prepared by the method provided in this embodiment 2 is also higher than that of the spinning solution prepared by the traditional dry pulverization swelling process, indicating that the spinning solution prepared by this method has a better dissolution effect (refer to Table 1). In addition, from the spinning situation, the spinnability of the spinning solution prepared by the process method provided in this embodiment 2 is also better than that of the traditional dry pulverization swelling process (refer to Table 2). Therefore, the method provided by the present invention can not only improve the swelling effect of cellulose and effectively prevent the appearance of "white core" during the swelling process, but also greatly improve the quality of the spinning solution, which is more conducive to the back-end spinning.

[0095] (2) By comparing Example 2 with 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 (the third suspension) be made more uniform (reference Figure 8 ), and can also greatly improve the dissolution effect and uniformity of the spinning solution (see Table 1), thereby improving the spinnability (see Table 2), which is beneficial to the back-end spinning.

[0096] (3) By comparing Example 2 and Comparative Example 3, it can be seen that in the process provided by the present invention, when pulp is fed to prepare a low-concentration cellulose suspension (first suspension), whether the pulp is crushed in advance does not affect the swelling effect of cellulose (reference Figure 8 ) and dissolution effect (see 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 pulverizing pulp, which can eliminate the hidden danger of dust generation during the pulverization process of pulp in the traditional dry pulverization and swelling process.

[0097] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for industrially preparing lyocell fiber spinning solution, characterized in that: A spinning solution preparation system is used, the spinning solution preparation system comprises a swelling device, an extrusion device, a crushing and grinding device and a thin film evaporator which are connected in sequence; the method comprises the following steps: Step 1, calculating the feeding amount of pulp raw material, and feeding a fixed amount of pulp raw material into a swelling device filled with a solvent for simultaneous wet crushing and swelling to obtain a first suspension with a cellulose concentration of less than or equal to 6wt%, wherein the temperature in the swelling device is controlled at 75-80°C, the solvent is an NMMO aqueous solution, and the solvent concentration is 76-82wt%; Step 2, inputting the first suspension into an extrusion device, controlling the temperature in the extrusion device to be 80-85° C., separating part of the solvent in the first suspension by extrusion, and increasing the concentration of cellulose in the first suspension to 10-12 wt % by separating part of the solvent, to obtain a second suspension; Step 3, inputting the second suspension into a crushing and grinding device for crushing and grinding, wherein the temperature in the crushing and grinding device is controlled at 80-85° C., to obtain a third suspension; Step 4: input the third suspension into a thin film evaporator, and control the temperature in the thin film evaporator to dissolve the third suspension under vacuum conditions to obtain a spinning solution with a cellulose concentration of 11 to 13 wt%.

2. The method for industrially preparing lyocell fiber spinning solution according to claim 1, characterized in that: In the step 1, the concentration of cellulose in the first suspension is 3-6 wt %.

3. The method for industrially preparing lyocell fiber spinning solution according to claim 2, characterized in that: In the step 1, the concentration of cellulose in the first suspension is 5-6 wt %.

4. The method for industrially preparing lyocell fiber spinning solution according to claim 3, characterized in that: The concentration of cellulose in the first suspension was 5.5 wt% or 6 wt%.

5. 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 in the extrusion device is 80° C.; the concentration of cellulose in the second suspension is 11 wt %; In step 3, the temperature in the crushing and grinding device is 80°C.

6. 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 surrounded by an outer shell, and a feed port and a glue outlet connected to the evaporation chamber. The lower end of the evaporation chamber is constructed as a cone structure, and the feed port and the glue outlet are respectively arranged at the top and bottom of the evaporation chamber. The temperature in the thin film evaporator is controlled to be distributed in a gradient from the feed port to the glue outlet. In step 4, the third suspension is dissolved under the gradient temperature and vacuum conditions to obtain a spinning solution; the gradient temperature includes controlling the feed temperature of the thin film evaporator to 80-85°C, controlling the upper section temperature of the thin film evaporator to 75-80°C; controlling the middle section temperature of the thin film evaporator to 80-85°C; controlling the lower section temperature of the thin film evaporator to 85-95°C, controlling the cone bottom temperature of the thin film evaporator to 95-105°C; and controlling the glue outlet temperature of the thin film evaporator to 100-110°C.

7. The method for industrially preparing lyocell fiber spinning solution according to claim 6, characterized in that: In the 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%.

8. The method for industrially preparing lyocell fiber spinning solution according to any one of claims 1 to 7, characterized in that: The swelling device comprises a reaction tank, a motor and a stirring mechanism, wherein the reaction tank comprises an internal cavity, a feeding port connected to the internal cavity, a solvent inlet, an assembly port and a discharge port, and a valve is arranged at the discharge port; the stirring mechanism comprises a stirring shaft, a moving knife assembly, a stationary knife assembly, an inner barrel and an impeller, wherein: The stirring shaft is arranged vertically, the upper end of the stirring shaft is drivingly connected to the output shaft of the motor, and the lower end of the stirring shaft extends into the internal cavity through the assembly opening; The inner barrel is fixedly arranged in the inner cavity of the reaction tank by a bracket, and the lower end of the stirring shaft is at least inserted into the inner barrel, and the inner barrel is constructed as a cylindrical structure; The static blade assembly is arranged in the inner barrel, and includes a center seat and a plurality of fixed paddles. The center seat is sleeved on the outer side of the stirring shaft and is coaxial with the stirring shaft. One end of the fixed paddle is connected to the center seat, and the other end is connected to the inner barrel. The fixed paddles are evenly distributed along the circumferential direction of the stirring shaft. At least the upper end of the fixed paddle is configured with a sawtooth structure, and the sawtooth structure is arranged along the length direction of the fixed paddle. The movable blade assembly is configured to match the stationary blade assembly. The movable blade assembly includes a connecting component for connecting the stirring shaft and a plurality of movable paddles connected to the connecting component. The movable paddles are evenly distributed along the circumferential direction of the stirring shaft, and a sawtooth structure is configured along the length direction of the movable paddles. The movable blade assembly is located in the inner barrel and is arranged at a position matching the stationary blade assembly. The movable blade assembly is configured to rotate relative to the stationary blade assembly under the drive of the stirring shaft, so that the movable blade assembly and the adjacent stationary blade assembly form a shearing fit in the inner barrel, and the pulp is crushed by shearing. The impeller is arranged on the stirring shaft and is located below the inner barrel, and the impeller rotates synchronously with the stirring shaft.

9. The method for industrially preparing lyocell fiber spinning solution according to claim 8, characterized in that: The stationary knife assembly is arranged at a position corresponding to the middle and / or lower part of the inner barrel; the movable knife assembly is also arranged at a position corresponding to the middle and / or lower part of the inner barrel.

10. The method for industrially preparing lyocell fiber spinning solution according to claim 8, characterized in that: The stirring mechanism is equipped with a plurality of moving knife assemblies and a plurality of stationary knife assemblies, and the plurality of moving knife assemblies and the plurality of stationary knife assemblies are arranged alternately along the height direction of the inner barrel.

Images