A preparation system and method of lyocell spinning solution

Abstract

The present invention provides a system and method for preparing a lyocell spinning solution. The system comprises a swelling device and a dissolving device. The swelling device is used for swelling dry pulp with NMMO solution. The swelling device is a rotary drum. A feed port and a discharge port are respectively provided at both ends of the length direction of the rotary drum. The rotary drum is rotated to bring the material inside from the bottom to a position close to the top and then freely falls back to the bottom, while conveying the swollen material toward the discharge port. The present invention feeds cellulose dry pulp and NMMO solution into the rotary drum, and the mixed material is repeatedly beaten in the rotary drum to obtain the swollen material; the swollen material is discharged from the rotary drum and sent to the dissolving device for dissolution to obtain the lyocell spinning solution. The present invention can process the mixing of a whole piece of pulp and a solvent. In the beating process in the rotary drum, the pulp and the solvent are more fully mixed. The present invention preferably adopts segmented swelling, which is conducive to reducing the number of white cores. The present invention is a continuous production with low energy consumption.

Description

Technical Field

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

[0002] Lyocell fiber is a regenerated cellulose fiber produced by a tertiary amine oxide (N-methylmorpholine-N-oxide) solvent spinning technology. Because the solvent can be recycled, it is called the green fiber of the 21st century.

[0003] In the process of preparing Lyocell fiber, the mixing and swelling effect of cellulose pulp in a certain concentration of NMMO aqueous solution is the key to the complete dissolution of cellulose. Uneven mixing and swelling can easily lead to uneven cellulose solid content in the solution, the formation of white cores and other problems, which is not conducive to subsequent spinning processes and seriously affects the spinning quality. The preparation of spinning solution is mainly divided into two processes: wet method and dry method. The so-called wet method is: cellulose pulp is mixed with water to make pulp, and then the obtained pulp solution is squeezed to remove water, and then mixed with NMMO after crushing, and swelled in a storage tank to make NMMO and cellulose fully combined to form cellulose porridge. After the swelling is completed, the obtained porridge is transported to a reactor (such as a thin film evaporator) for evaporation and dissolution to form a spinning solution.

[0004] A Chinese patent document with application publication number CN 108004611 A discloses a method for preparing a solvent-process cellulose fiber spinning stock solution using dry pulp, which comprises first preparing an NMMO solution containing NaOH, then gradually adding pulp into the NMMO solution, mixing uniformly, and obtaining a porridge-like mixture; evaporating and dehydrating the porridge-like mixture to swell the cellulose, then adding a stabilizer and an antioxidant to the swollen cellulose mixture, and mixing uniformly to obtain a premix; finally, dehydrating, dissolving, and defoaming the premix to obtain a cellulose spinning stock solution.

[0005] The above-mentioned prior art belongs to the dry process for preparing lyocell spinning solution, and generally has the following characteristics: (1) The pulp does not need to be processed by pulverization or other processing, and is directly mixed with the NMMO solution in the form of a pulp sheet; compared with the wet process, this saves the process of hydraulic pulping. (2) The process flow is simple; compared with the wet process, the dry pulp is mixed with the NMMO solution and then enters the thin film evaporator, shortening the process flow. (3) The energy consumption of the thin film evaporator is reduced, which is conducive to the improvement of production capacity; the reason is that the moisture content of the dry pulp is about 6%-7%, compared with the pulp in the wet process (water content is 50%), the amount of water brought into the dry pulp is greatly reduced, which can reduce the energy consumption of the film steam and is conducive to improving production capacity. (4) The unit steam consumption of the NMMO solution evaporation is reduced; when the wet pulp is mixed with the NMMO solution in the wet process, the NMMO concentration is about 80%-84%, while the concentration of the NMMO solution required for the dry pulp mixing is between 75%-80%. The NMMO solution is recycled during the production process, and the low-concentration NMMO solution is evaporated to obtain the high-concentration NMMO solution. In this process, the steam consumption can be reduced by reducing the final NMMO solution evaporation concentration. (5) Dry pulp is mixed with the NMMO solution. Since the concentration of the NMMO solution is low, the degree of pre-dissolution can be reduced, which is conducive to the full contact and swelling of NMMO and cellulose.

[0006] However, in the above-mentioned dry preparation technology, the mechanical external force provided by the hydraulic pulper is used to make the cellulose / NMMO / H2O mixture. It is found in production that obvious white core particles can still be observed in the spinning solution prepared by this method, which also shows that there are certain disadvantages in directly mixing dry pulp with NMMO solvent, and the swelling and dissolution effects need to be improved compared with the wet method. In addition, the mixed material has a certain viscosity, and mechanical stirring produces strong shear, which destroys the morphology of some fibers and seriously affects the spinning quality. Summary of the invention

[0007] In view of this, the present application provides a system and method for preparing a lyocell spinning solution. The preparation system provided by the present invention can continuously produce a lyocell spinning solution with sufficient swelling and good quality, thereby increasing output and reducing the production cost per unit bundle, which is conducive to promotion and application.

[0008] The invention provides a system for preparing a lyocell spinning solution, comprising a swelling device and a dissolving device, wherein the swelling device is used for swelling dry pulp with an NMMO solution, wherein the swelling device is a drum, and a feed inlet and a discharge outlet are respectively provided at both ends of the drum in the length direction, and the drum is rotated so that the material inside the drum is brought from the bottom to a position close to the top and then freely falls back to the bottom, and the swollen material is transported toward the discharge outlet at the same time.

[0009] In some preferred embodiments, the drum rotates in the following manner: the outer shell of the drum is fixed, a rotatable material-dispensing component is provided in the outer shell of the drum, and the material-dispensing component drives the material from the bottom of the drum to a position close to the top and then freely falls back to the bottom.

[0010] In some other preferred embodiments, the drum rotates in the form of: the outer shell of the drum rotates, and a material-shifting component that rotates with the outer shell of the drum is arranged inside the outer shell of the drum, and the material-shifting component drives the material from the bottom of the drum to a position close to the top and then freely falls back to the bottom.

[0011] Preferably, a spray belt is provided at the top of the outer shell of the drum or near the top between the feed port and the discharge port, the spray belt extends along the axial direction of the outer shell of the drum, and the NMMO solution is sprayed into the drum from the spray belt.

[0012] Preferably, two ends of the spray belt extend to two ends of the outer shell of the drum respectively.

[0013] Preferably, the drum has an adjustable inclination angle of 0 to 10°.

[0014] An embodiment of the present invention provides a method for preparing a lyocell spinning solution using the preparation system described above, comprising the following steps:

[0015] The dry pulp and the NMMO solution are added into a drum; the drum rotates, so that the material formed by the mixture of the dry pulp and the NMMO solution is repeatedly beaten in the drum to obtain a swollen material;

[0016] The swollen material is discharged from the drum and sent to a dissolving device for dissolution, such as evaporation dissolution, to obtain a lyocell spinning solution.

[0017] Preferably, the NMMO solution is added to the drum through a spray assembly, and the spray assembly forms a spray belt extending axially along the drum, and the spray belt includes at least two spray sections for spraying NMMO solutions of different concentrations, and in adjacent spray sections, the NMMO concentration sprayed by the front spray section is lower than the spray concentration of the rear spray section.

[0018] Preferably, the spray zone includes two spray sections, namely a first spray section in front and a second spray section in the back; further, the mass concentration of NMMO in the first spray section is preferably 72-78%, and the spray temperature is preferably 75-82°C.

[0019] Furthermore, the mass concentration of NMMO in the second spraying section is preferably 78-84%; and the spraying temperature is preferably 72-77°C.

[0020] Preferably, the time for the materials to be sprayed and mixed in the first spraying section is longer than the time for the materials to be sprayed and mixed in the second spraying section.

[0021] The embodiment of the present invention can also provide the use of the lyocell spinning solution prepared by the method described above in the production of lyocell fibers.

[0022] Compared with the prior art, the present invention adopts a rotary drum as the main equipment for mixing and swelling dry pulp and NMMO. The rotary drum drives the material inside from the bottom of the drum to a position close to the top by rotating, and then falls freely under the action of gravity and hits the bottom of the drum; because the drum itself has a certain inclination angle, the rotation process can transport the swollen material to the discharge port. Practice has proved that this natural beating process is beneficial to the swelling effect of dry pulp compared with the mechanical stirring process of the hydraulic pulper. Because the mixed material is beaten at the bottom of the drum by weightlessness, the solvent molecules can be prompted to enter between the cellulose molecular chains. The reason is that under the weightless state, the molecular chains of cellulose are in a stretched state, and the gaps between the molecular chains are relatively uniform, which is conducive to the solvent molecules entering between the molecular chains. At the moment when the material hits the bottom, it provides an opportunity for the NMMO molecules to penetrate into the gaps between the cellulose molecular chains, so that the NMMO solvent molecules can smoothly enter between the cellulose molecular chains, and promote the full swelling of the NMMO solvent molecules and cellulose. This significantly improves the swelling rate of dry pulp, especially after long-term repeated beating, which is sufficient to make the solvent and cellulose swell fully and evenly. In the embodiment of the present invention, the swollen material is directly sent to the dissolution device for dissolution to obtain a lyocell spinning solution. The present invention can process the whole piece of pulp and mix it with the solvent. During the beating process, the pulp and the solvent are mixed more fully, which is beneficial to improving the product quality. In addition, the present invention subversively adopts a segmented spray swelling technology to further reduce the number of white cores.

[0023] In addition, the obvious disadvantage of the existing dry swelling method of hydraulic pulpers is that it is difficult to discharge the material. The material can only be discharged through a pipe. However, after the swelling is completed, the material is in a viscous state with poor fluidity, and due to stirring, the material will not gather together, resulting in high difficulty in discharging the material in the existing swelling implementation method. In contrast, due to the viscosity of the material itself in the drum of the present application, the material will gradually gather together during the beating process, and when it finally reaches the discharge port, the material will be in a "dough"-like state, making it easy to discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the structure of the swelling device in some embodiments of the present invention;

[0025] Figure 2 for Figure 1 AA schematic diagram;

[0026] Figure 3 for Figure 1 BB schematic diagram;

[0027] Figure 4 It is a schematic diagram of the structure of the swelling device in other embodiments of the present invention;

[0028] Figure 5 for Figure 4 AA schematic diagram;

[0029] Figure 6 This is a diagram showing the effect of obtaining a spinning solution by the swelling process of Example 1 of the present invention;

[0030] Figure 7 This is a diagram showing the effect of obtaining the spinning solution by the swelling process of Example 2 of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The invention provides a system for preparing a lyocell spinning solution, comprising a swelling device and a dissolving device, wherein the swelling device is used for swelling dry pulp with an NMMO solution, wherein the swelling device is a drum, and a feed inlet and a discharge outlet are respectively provided at both ends of the drum in the length direction, and the drum is rotated so that the material inside the drum is brought from the bottom to a position close to the top and then freely falls back to the bottom, and the swollen material is transported toward the discharge outlet at the same time.

[0033] The preparation system provided by the invention can continuously produce lyocell spinning solution with good quality and low energy consumption, thus being conducive to popularization and application.

[0034] See also Figure 1-3 , Figure 1 It is a schematic diagram of the structure of the swelling device in some embodiments of the present invention. Figure 2 , Figure 3 They are schematic diagrams of AA and BB respectively. Among them, 10 is the drum shell, 101 is the material-shifting beam, 102 is the beater, 103 is the support leg, 20 is the solvent spray belt, 30 is the transmission shaft, 301 is the spoke, 302 is the inlet impeller, 303 is the outlet impeller, 40 is the oil cylinder, 50 is the feed port, 60 is the discharge port, and 70 is the pulse high-pressure gas inlet.

[0035] The system for preparing the lyocell spinning solution according to some embodiments of the present invention comprises: Figure 1The swelling device shown is a drum with a stationary outer shell and a rotating internal structure, and the specific structure includes: a stationary drum outer shell 10 and a rotatable material-diverting crossbeam 101 arranged inside, preferably with a plurality of beaters 102. The outer shell 10 is the outer part of the drum, and the bottom can be supported by legs 103 fixed to the ground; the inner space of the drum outer shell is used for material mixing and swelling, and the material-diverting crossbeam 101 is used as a material-diverting component, and in combination with the beaters 102, the material is driven from the bottom of the drum to a position close to the top, and then freely falls back to the bottom.

[0036] In an embodiment of the present invention, the volume and structure suitable for spraying NMMO solution into the drum can be formed inside the shell 10. The inside of the shell 10 forms a long cylindrical mixing chamber; its length and diameter should be customized according to actual process requirements, for example, the length can be selected as 10 meters, and the actual length of the shell may reach tens of meters or even longer, and the diameter can be selected as 1m, 2m, etc. One end of the drum in the length direction is the feed end (the feed port end), and the other end is the discharge end (the discharge port end).

[0037] In addition, a plurality of solvent spray ports are disposed laterally (i.e., in the length direction) at the top or near the top of the drum shell 10, and are arranged along the axial direction of the drum shell to form a solvent spray belt 20 for spraying the solvent between the feed end and the discharge end, i.e., the NMMO solvent is sprayed from the spray belt into the drum. Preferably, both ends of the spray belt extend to both ends of the drum shell, respectively. When spraying the solvent, the spray belt can be divided into a plurality of spray sections according to the different concentrations of the sprayed solvent, i.e., the spray area for spraying solvents of the same concentration is regarded as one spray section. The spray belt of the present invention can form at least two spray sections for spraying solvents of different concentrations.

[0038] The swelling device is used for swelling dry pulp with NMMO solution. The present invention has no special limitation on the feeding form of materials such as NMMO solution and dry pulp, and the materials can enter the swelling device from the feeding port. Among them, the NMMO solution can be added to the drum through a spray assembly. In an embodiment of the present invention, the spray assembly has various forms, and there are no special restrictions on the specifications, segmented distances, etc. of each solvent spray port. For example, a row of multiple narrow and long spray holes can be set along the top of the drum shell along the head and tail of the drum, and the first spray section and the second spray section are divided according to the segmented spraying of solvents of different concentrations; or, a row of nozzles are installed on the top of the drum corresponding to the spray port, and the nozzle at the feed end sprays a solvent of one concentration, and the nozzle at the discharge end sprays another solvent of another concentration.

[0039] In addition, the drum may be provided with a temperature regulating jacket or an electric heating device (not shown). Figure 1It is shown in the figure) for independent segmented temperature control. A lifting device can be arranged under one end of the drum feed port to control the lifting of one end of the drum feed port relative to the discharge port. This is necessary. By adjusting the inclination angle, the conveying speed of the material in the drum is adjusted to control the mixing and swelling time.

[0040] In the above-mentioned embodiment of the present invention, the drum shell 10 is stationary, the transmission shaft 30 (external motor drive) drives the spoke 301 to rotate, the spoke 301 drives the outlet runner 303 to rotate, the runner 303 drives the material-digging beam 101 to rotate, the left end of the material-digging beam 101 is fixed on the inlet runner 302, and the material-digging beam 101 is ensured to reliably rotate close to the inner wall of the drum shell, the material-digging beam 101 drives the material to rise along the inner wall of the shell, and the material falls under the action of gravity, so that the material is repeatedly beaten to achieve material mixing, swelling, and slowly transported backward. Because the suspended material has a certain viscosity, the material will gather together during the rotation process, like "dough", and it will be beaten continuously and gathered after being crushed. In this beating process, pulp and solvent are mixed more fully. If the mixing is only carried out by components such as stirring blades, the material mixing uniformity is poor, and because there are many stirring dead angles, the swelling effect is poor. The present invention utilizes a beating method to fully mix and swell the pulp and the solvent, and the effect is better than that of blade stirring; there is no dead corner in the rotary drum, thereby achieving uniform swelling.

[0041] The embodiment of the present invention has no special restrictions on the structural design of the drum shell, material-digging components, etc., as long as the above-mentioned material-digging and material-beating functions can be achieved. Specifically, a plurality of short stick-shaped protruding components (i.e., beaters 102) are arranged inside the drum; the beaters 102 are directly fixed on the drum material-digging beam 101, and the material-digging beam 101 drives the beaters 102, so that the materials can be smoothly moved to a higher height, thereby improving the beating effect. In addition, the oil cylinder 40 drives the shell 10 to rise and fall. A feed port 50 and a discharge port 60 are respectively provided at both ends of the drum in the length direction. Pulp is fed into the drum from the feed port 50 and discharged from the discharge port 60. One end of the discharge port is also provided with a pulse high-pressure gas inlet 70. When the discharge port is blocked by material, the gas inlet 70 sprays high-pressure gas to break up the blocked material mass, so that the material can be smoothly discharged.

[0042] The tilt angle of the drum in the embodiment of the present invention is adjustable, and is used to adjust the material conveying rate, for example, between greater than 0 and less than 10°. In the present invention, the beaters arranged inside the drum are not only conducive to mixing and swelling, but also can transport the material backwards when it is tilted. The beaters described in the present invention are a plurality of short rod-shaped protrusions spaced apart from each other, and the overall shape is preferably consistent; the end away from the drum can be any shape such as a square head, a round head, a pointed head, and there is no special restriction on the number. Among them, it is best to use a wedge-shaped pointed beater to reduce the risk of the material being squeezed between the protrusion and the inner wall of the drum shell. In a preferred embodiment of the present invention, the plurality of raised components (beaters 102) are fixed to the corresponding material-discharging beam 101. In addition, the present invention has no special restrictions on the transmission structures such as spokes and wheels, and can use the following: Figure 3 The specific structure shown can also be designed in other ways.

[0043] In the preparation system described in the embodiment of the present invention, the drum of the swelling device is rotated at a certain inclination angle so that the material inside is brought from the bottom to a position close to the top and then freely falls back to the bottom, while the solvent is sprayed in sections. After the swelling is completed, the swollen material is transported to the dissolving device. The dissolving device is a reactor connected to the discharge port of the swelling device; the present invention has no special restrictions on the dissolving device, such as a thin film evaporator well known to those skilled in the art. The swollen material is dissolved in the reactor, and the resulting spinning solution is then sent to the spinning machine for spinning, thereby producing Lyocell fibers.

[0044] The preparation system provided by the invention can continuously produce lyocell spinning solution with sufficient swelling and good quality, thereby increasing the output and reducing the production cost of a unit tow.

[0045] In some other embodiments of the present invention, the structure of the swelling device is shown in Figure 4-5 . Among them, 11 is the drum shell, 111 is the material-shifting beam, 112 is the beater, 31 is the driving assembly, 51 is the feed port, and 61 is the discharge port.

[0046] The system for preparing the lyocell spinning solution according to other embodiments of the present invention comprises: Figure 4 The swelling device shown is a drum with a rotating shell structure, and the specific structure includes: a rotatable drum shell 11 and a material-shifting beam 111 arranged inside and rotating therewith, and preferably also provided with a plurality of beaters 112. The drum shell 11 rotates, and the material-shifting beam 111 fixed on the inner wall of the shell drives the material to beat in the cavity, that is, drives the material from the bottom of the drum to a position near the top and then freely falls back to the bottom, and is slowly transported backwards.

[0047] In an embodiment of the present invention, the interior of the outer shell 11 is a mixing chamber; its length and caliber should be customized according to actual process requirements. For example, the length can be selected to be 10 meters. In fact, the length of the shell may reach tens of meters, or even longer, and the diameter can be selected to be 1m, 2m, etc. One end of the drum in the length direction is the feed end (the feed port end), and the other end is the discharge end (the discharge port end). Between the feed port and the discharge port, a spray pipe can be extended into the mixing chamber of the drum. The spray pipe is provided with a row of spray nozzles. These spray nozzles form a spray belt, which extends along the axial direction of the outer shell of the drum and can extend to both ends; the NMMO solution is sprayed from the spray belt into the drum. Alternatively, the solvent and pulp both enter the swelling device (such as the discharge port) from the feed port. Figure 4 shown).

[0048] In these embodiments of the present invention, the drum housing 11 is driven to rotate by a driving assembly 31 (the driving assembly 31 is a conventional transmission mechanism composed of a motor and a gear), and a material-digging beam 111 fixed on the housing drives the material to beat in the cavity, and the material is mixed and swollen by repeated beating, and then slowly transported backward. Preferably, a plurality of short rod-shaped protruding parts (i.e., beaters 112) are arranged inside the drum; the beaters 112 are directly fixed on the drum-digging beam 111, and the material-digging beam 111 and the beaters 112 rotate with the housing to enhance the stirring effect. A feed port 51 and a discharge port 61 are respectively provided at both ends of the drum in the length direction, and pulp and NMMO solution are fed into the drum from the feed port 51, and the swollen material is discharged from the discharge port 61.

[0049] The inclination angle of the drum described in the above embodiment of the present invention can also be controlled, for example, it can be adjusted between greater than 0 and less than 10°. In the present invention, the beaters arranged inside the drum are not only conducive to mixing and swelling, but also can transport the material backward under the inclined condition. The beaters described in the present invention are a plurality of short rod-shaped protrusions spaced apart from each other, and the overall shape is preferably consistent; the end away from the drum can be any shape such as a square head, a round head, a pointed head, etc., and there is no special restriction on the number. In a preferred embodiment of the present invention, the plurality of raised components (beaters 112) are fixed on the corresponding material-selecting beams 111 and are evenly distributed along the circumference of the drum, such as Figure 5 The six groups of beaters are arranged in rows and spaced evenly in the longitudinal direction. In addition, the present invention has no special restrictions on the driving assembly.

[0050] After the dry pulp is swollen by the swelling device, it enters the dissolving device; the dissolving device is a reactor connected to the discharge port of the swelling device. The present invention has no special restrictions on the dissolving device, such as a thin film evaporator well known to those skilled in the art. The swollen material is dissolved in the reactor, and the obtained spinning solution is then sent to the spinning machine for spinning, thereby producing Lyocell fibers.

[0051] The present invention uses a rotary drum as the main equipment for mixing and swelling dry pulp with NMMO. The rotary drum drives the internal material to rotate through the rotating working process, and can be brought from the bottom to a position close to the top, and fall freely under the action of gravity and hit the bottom. The present invention can process the whole piece of pulp and the solvent. In the beating process, the pulp and the solvent are mixed more fully, and then a spinning solution and fiber with better quality can be obtained.

[0052] An embodiment of the present invention provides a method for preparing a lyocell spinning solution using the preparation system described above, comprising the following steps:

[0053] The dry pulp and the NMMO solution are added into a drum; the drum rotates, so that the material formed by the mixture of the dry pulp and the NMMO solution is repeatedly beaten in the drum to obtain a swollen material;

[0054] The swollen material is discharged from the drum and sent to a dissolving device for dissolution to obtain a lyocell spinning solution.

[0055] The invention can continuously produce lyocell spinning solution, improve quality, reduce energy consumption, and is suitable for large-scale production.

[0056] The embodiment of the present invention adopts a dry preparation process, using cellulose dry pulp as raw material, and the moisture content of the dry pulp is about 6%-7%. The amount of water brought into the dry pulp is relatively low, which can reduce the energy consumption of film steam and is beneficial to improving production capacity. Some specific embodiments of the present invention feed dry pulp from the feed port, and the feed rate can be 1.0-1.5t / min. Moreover, the embodiment of the present invention preferably adds the NMMO solution into the drum through the spray assembly, and the spray assembly forms a spray belt extending along the axial direction of the drum, that is, the pulp and the NMMO solution are added to the swelling device for mixing and swelling to obtain the swollen material.

[0057] Among them, the structure and other contents of the swelling device are as described above. For example, the inclination angle of the swelling device is adjustable between greater than 0 and less than 10°, and the rotation frequency of the drum is determined according to the actual process requirements, such as 3-5rpm. The feed amount of pulp and the sprayed NMMO solvent should be maintained in a certain ratio, and this ratio can be determined according to the actual process requirements. For example, the mass ratio of NMMO / cellulose in the formed swollen material can be determined to be 6.4 (the ratio relationship can also be changed according to the process requirements); then the pulp feed rate and the solvent spray rate can be determined according to this ratio.

[0058] The moving crossbeam in the drum described in the embodiment of the present invention can move the material upward, and when the material is close to the top of the drum, it falls back to the bottom of the drum due to its own gravity, maintains this state, and continues to move repeatedly. Preferably, when spraying the NMMO solvent, at least two spray sections for spraying different concentrations are formed on the spray belt, and in adjacent spray sections, the NMMO concentration sprayed by the front spray section is lower than the spray concentration of the rear spray section. That is, the present invention preferably adopts segmented spraying of the solvent, for example, in two sections, and can also adopt a spraying method of three sections or more; the control of the mixing time ratio of each section can be determined by the length ratio of each section, that is, the spraying time of each section is proportional to the length.

[0059] In some specific embodiments of the present invention, the spray belt includes two spray sections, namely a first spray section in front and a second spray section in the back. The mass concentration of NMMO in the first spray section is preferably 72-78%, and the spray temperature is preferably 75-82°C. The mass concentration of NMMO in the second spray section is preferably 78-84%; the spray temperature is preferably 72-77°C. In other specific embodiments of the present invention, the spray concentration of the spray belt is consistent.

[0060] NMMO is highly soluble in water, and easily soluble in polar organic solvents such as ethanol and methanol. It also has high solubility in hot acetone and benzene, and is insoluble in general organic solvents; it can combine with 1-4 water molecules, and its chemical properties are relatively stable at room temperature. NMMO aqueous solution is a high-quality solvent for cellulose, but cellulose is difficult to dissolve smoothly in concentrated NMMO aqueous solution due to its high crystallinity and many hydrogen bonds. In the dry process, the mass concentration of NMMO solution required for dry pulp mixing is generally between 75% and 80%. NMMO solution is recycled in the production process, and low-concentration NMMO solution is evaporated to obtain high-concentration NMMO solution. In this process, the steam consumption can be reduced by reducing the final evaporation concentration of the NMMO solution.

[0061] For the segmented spraying of NMMO solution of the present invention, different concentrations of solvents can be added in segments in sequence, that is, the front nozzle sprays a solvent of one concentration, and the rear nozzle sprays another solvent of another concentration; the present invention preferably has a lower spray concentration in the front than in the rear, which also has a positive effect on swelling. In the embodiment of the present invention, the NMMO concentration added first is relatively low, and then the NMMO solution with a relatively high concentration is added. The advantage is that after the low NMMO concentration solution is added first, the pulp is already in the NMMO solution environment, and the pulp is partially swollen. Under this buffering condition, the high NMMO concentration solution is added, which weakens the degree of gel formation by the NMMO solvent to partially dissolve the pulp. This gel will prevent the full swelling of cellulose, which is not expected to occur.

[0062] Preferably, the material is sprayed and mixed for a longer time in the first spraying section than in the second spraying section. In the embodiment of the present invention, controlling the time of conveying the pulp in the drum is also a key parameter. Too fast a conveying speed means that the pulp swelling time is too short, and it is difficult to achieve a sufficient degree of swelling. Too long a conveying time increases costs and reduces production efficiency.

[0063] For example, some embodiments of the present invention control the swelling time to 150 minutes (i.e., the time from the pulp entering the drum to the pulp being discharged from the drum). This time is related to the length, inner diameter, rotation speed and tilt angle of the drum. Since the length and inner diameter are fixed parameters (of course, they can be adjusted by replacing the drum), the present invention can control the swelling time by adjusting the tilt angle and rotation speed.

[0064] After the swelling is completed, the embodiment of the present invention directly sends the swollen material into a dissolving device such as a reaction kettle for dissolution to prepare a Lyocell spinning solution.

[0065] The present invention has no special restrictions on the dissolution device such as thin film evaporator, process conditions, etc., and the evaporation dissolution process commonly used in the art can be used. In an embodiment of the present invention, the mass ratio of NMMO / cellulose in the obtained cellulose suspension is 6 to 7, for example 6.4.

[0066] The present invention also provides the use of the Lyocell spinning solution obtained by the preparation method as described above in the production of Lyocell fibers; that is, the obtained Lyocell spinning solution is transported to a spinning machine for conventional spinning to produce Lyocell fibers.

[0067] The method of the present invention has good swelling effect and low white core quantity. In addition, the process flow of the present invention is simple, the energy consumption is low, and it is suitable for large-scale production.

[0068] In order to further understand the present application, the system and method for preparing the lyocell spinning solution provided by the present application are specifically described below in combination with the examples. However, it should be understood that these examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following examples.

[0069] Example 1

[0070] 1. Main raw materials

[0071] 1. NMMO aqueous solution as solvent, with concentrations of 75% and 83% respectively;

[0072] 2. Pulp raw material: wood pulp (South African Sappi pulp, water content 6%, degree of polymerization 520).

[0073] 2. Main equipment:

[0074] 1. Use Figure 1-3 The drum of the structure shown in the figure has a fixed outer shell, and the material-moving beam and other material-moving parts rotate along the inner wall of the outer shell to scrape the material on the inner wall of the outer shell. The drum is 20 meters long and 2 meters in diameter.

[0075] A spray belt is arranged on the top of the drum shell. The first spray section (i.e. the front half) sprays a solvent with a concentration of 75%; the second spray section (i.e. the rear half) sprays a solvent with a concentration of 83%. The length ratio of the two spray sections is 1:1.

[0076] 2. The swelling rate test equipment model is DD5M low-speed centrifuge.

[0077] 3. Implementation Instructions

[0078] The pulp is continuously conveyed to the feeding port of the drum. The pulp entering the drum is conveyed backward along the drum under the stirring of the drum stirring component. The rotating speed of the material-dispensing beam is 3-5rpm.

[0079] The spray belt on the top of the drum sprays the solvent into the drum according to the preset concentration (i.e. the first half sprays 75% of the solvent, and the second half sprays 83% of the solvent); the spraying is carried out throughout the whole process without stopping.

[0080] In production, the pulp is continuously fed into the drum at a feeding rate of 1.06 t / min, and the drum maintains normal and stable operation. In this way, the speed of spraying pure NMMO corresponding to the pulp feeding rate of 1.06 t / min is 6.4 t / min (satisfying the relationship of NMMO / cellulose = 6.4). In this operation, it is set to spray 3.2 t / min uniformly in the first half of the spray belt, and 3.2 t / min uniformly in the second half of the spray belt. According to the spray concentration of each part, the spray speed of the solvent with a concentration of 75% in the first half of the spray belt is 4.27 t / min; the spray speed of the solvent with a concentration of 83% in the second half of the spray belt is 3.86 t / min. The spray temperature of the first half is 75-82 ° C; the spray temperature of the second half is 72-77 ° C. As mentioned earlier, the solvent is sprayed in the form of a spray belt, which is necessary to effectively avoid the problem of the solvent not having time to mix with the pulp locally due to concentrated spraying. When spraying, the solvent that has no time to mix will flow out quickly backwards, resulting in the inability to complete the swelling process of cellulose.

[0081] In this operation, the swelling time is controlled at 150 min (that is, the time from the pulp entering the drum to the pulp being discharged from the drum).

[0082] After this operation, the swollen material can directly enter the reactor for evaporation and dissolution.

[0083] Take 3 portions of the material swollen by this operation, 2 kg each, and conduct swelling rate test.

[0084] The weight of the first centrifuged material is 1.93 kg, the weight of the second centrifuged material is 1.92 kg, and the weight of the third centrifuged material is 1.94 kg. Thus, the corresponding swelling rates are 96.5%, 96.0% and 97.0%, respectively, and the average swelling rate is 96.65%.

[0085] The swelling rate of the existing process is generally 88-92%, such as the swelling material (suspension) prepared by the wet method. By comparison, it can be seen that the cellulose suspension prepared by the technology of the present application has an excellent swelling effect.

[0086] In addition, after the material with poor swelling effect is evaporated and dissolved to prepare the spinning solution, a large amount of white cores will still remain in the solution. Based on this, in order to further prove the above swelling effect, a small sample of the spinning solution obtained in this embodiment was taken out, placed in an environment with excellent sunlight, and observed with a magnifying glass with a magnification of 5 times. Except for a small amount of bubbles, basically no white core particles (such as Figure 6 ). This is almost impossible to achieve with traditional dissolution technology.

[0087] Example 2

[0088] 1. Main raw materials

[0089] 1. The concentration is 80% NMMO aqueous solution;

[0090] 2. Pulp raw material: wood pulp (South African Sappi pulp, water content 6%, degree of polymerization 520).

[0091] 2. Main Equipment

[0092] 1. Use Figure 4-5 The drum shown (the material-moving parts such as the moving beam are directly fixed on the inner wall of the drum shell, and the drum shell rotates under the drive of the external bearing and power assembly), NMMO solvent and pulp are transported to the drum from the pulp inlet. The drum is 20 meters long and 2 meters in diameter.

[0093] 2. The swelling rate test equipment model is DD5M low-speed centrifuge.

[0094] 3. Implementation Instructions

[0095] In production, the pulp is continuously fed into the drum at a feeding rate of 1.06 t / min, and the drum maintains normal and stable operation, with a drum rotation speed of 3-5 rpm. Thus, the pulp feeding rate of 1.06 t / min corresponds to a pure NMMO injection rate of 6.4 t / min (satisfying the relationship of NMMO / cellulose = 6.4). In this operation, the NMMO concentration used is 80%, and the injection rate of the NMMO aqueous solution is 8.0 t / min. The solvent NMMO is added from the feed port at a rate of 8 t / min, and the temperature is 78 degrees Celsius.

[0096] In this operation, the swelling time is controlled at 150 min (that is, the time from the pulp entering the drum to the pulp being discharged from the drum).

[0097] After this operation, the swollen material can directly enter the reactor for evaporation and dissolution.

[0098] Take 3 portions of 2 kg of the material swollen by this operation and perform swelling rate test.

[0099] The weight of the first centrifuged material is 1.89 kg, the weight of the second centrifuged material is 1.90 kg, and the weight of the third centrifuged material is 1.89 kg. Thus, the corresponding swelling rates are 94.7%, 95.0% and 94.7%, respectively, and the average swelling rate is 94.80%.

[0100] At present, the swelling rate of the existing process is generally 88-92%. By comparison, it can be seen that the swollen material obtained by this operation has an excellent swelling effect.

[0101] In addition, after the material with poor swelling effect is evaporated and dissolved to prepare the spinning solution, a large number of white cores will still remain in the solution. Based on this, in order to further prove the above swelling effect, a small sample of the stock solution was taken from the solution dissolved by this operation, placed in an environment with excellent sunlight, and observed with a magnifying glass with a magnification of 5 times, and basically no white core particles (such as Figure 7 ). This is almost impossible to achieve with traditional dissolution technology.

[0102] The test strongly proves that: through the preparation system of the present invention, pulp and solvent form a mixed material, which is repeatedly beaten under its own gravity, which can cause the solvent and pulp to fully swell. This may be because such a beating process can make the solvent repeatedly try to enter the molecular gaps of the pulp from different angles, and in a uniform and gentle manner, avoiding external tearing and affecting the physical and chemical properties of cellulose.

[0103] In addition, the use of a rotary drum swelling device has another great benefit, which is to greatly increase the single-line production capacity of cellulose fibers. In existing processes, whether it is the dry production mentioned in the background or other wet processes, a hydraulic pulper or a pulping device similar to a water pulper is required. These not only have a small volume, but also directly stir the material through the rotation of the blades, which determines that the weight of the added pulp is limited. At present, the annual single-line production capacity is difficult to exceed 20,000 tons. With the technology of the present invention, the single-line production capacity will have a qualitative leap, and can reach an annual production capacity of more than 100,000 or even more. This is difficult to predict with existing technologies. The increase in single-line production capacity will undoubtedly reduce product costs and create broad prospects for product promotion.

[0104] The above descriptions are only preferred embodiments of the present invention. It should be pointed out that professionals in this technical field can implement various modifications to these embodiments without departing from the technical principles of the present invention, and these modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A system for preparing a lyocell spinning solution, comprising a swelling device and a dissolving device, wherein the dry pulp is swollen by the swelling device and then enters the dissolving device to be dissolved into a spinning solution, wherein the swelling device is used to swell the dry pulp with a NMMO solution, and wherein: The swelling device is a drum, and a feed port and a discharge port are respectively provided at both ends of the length direction of the drum. The drum itself has an inclination angle relative to the horizontal direction, and through the form of rotation, the material inside is brought from the bottom to a position close to the top and then freely falls back to the bottom, while the swollen material is transported toward the discharge port; A spray belt is provided at the top of the outer shell of the drum or near the top between the feed port and the discharge port, and the spray belt extends along the axial direction of the outer shell of the drum, and the NMMO solution is sprayed from the spray belt into the drum; the spray belt includes at least two spray sections for spraying NMMO solutions of different concentrations, and in adjacent spray sections, the NMMO concentration sprayed by the front spray section is lower than the spray concentration of the rear spray section; The drum is rotated in a specific manner: the outer shell of the drum is fixed, a rotatable material-digging component is arranged inside the outer shell of the drum, the material-digging component is a material-digging beam fixed with a plurality of beaters, the material-digging beam drives the beaters, and the material-digging component drives the material from the bottom of the drum to a position close to the top and then freely falls back to the bottom; Alternatively, the drum rotates in the form of: the outer shell of the drum rotates, and a material-shifting component that rotates with the outer shell of the drum is arranged inside the outer shell of the drum, the material-shifting component is a material-shifting beam fixed with a plurality of beaters, the material-shifting beam and the beaters rotate with the outer shell, and the material-shifting component drives the material from the bottom of the drum to a position close to the top and then freely falls back to the bottom.

2. The preparation system according to claim 1, characterized in that: The two ends of the spray belt extend to the two ends of the outer shell of the drum respectively.

3. The preparation system according to claim 2, characterized in that: The rotating drum has an adjustable inclination angle of 0-10°.

4. A method for preparing a lyocell spinning solution using the preparation system according to any one of claims 1 to 3, characterized in that: The following steps are involved: Adding dry pulp and NMMO solution into a drum; rotating the drum to repeatedly beat the material formed by the mixture of dry pulp and NMMO solution in the drum to obtain a swollen material; adding the NMMO solution into the drum through a spray assembly, and the spray assembly forms a spray belt extending along the axial direction of the drum; The swollen material is discharged from the drum and sent to a dissolving device for dissolution to obtain a lyocell spinning solution.

5. The preparation method according to claim 4, characterized in that: The spray zone includes two spray sections, namely a first spray section in front and a second spray section in the back; the mass concentration of NMMO in the first spray section is 72-78%, and the spray temperature is 75-82°C.

6. The preparation method according to claim 5, characterized in that: The time for the materials to be sprayed and mixed in the first spraying section is longer than the time for the materials to be sprayed and mixed in the second spraying section.

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