CN111334869A - A kind of preparation system and method of lyocell spinning solution - Google Patents

Abstract

The invention provides a preparation system and a preparation method of a lyocell spinning solution, wherein the system comprises a swelling device and a dissolving device, the swelling device is used for swelling dry pulp by an NMMO solution, the swelling device is a rotary drum, two ends of the rotary drum in the length direction are respectively provided with a feed inlet and a discharge outlet, the rotary drum enables materials in the rotary drum to freely fall back to the bottom from the bottom to a position close to the top in a rotating mode, and meanwhile, the swollen materials are conveyed towards the discharge outlet. Feeding cellulose dry pulp and an NMMO solution into a rotary drum, and repeatedly beating the mixed material in the rotary drum to obtain a swelled material; and discharging the swelled material from the rotary drum, and feeding the swelled material into a dissolving device for dissolving to obtain the lyocell spinning solution. The invention can process the mixing of the whole piece of pulp and the solvent, and the pulp and the solvent are more fully mixed in the beating process in the rotary drum. The present invention preferably employs segmented swelling to facilitate reducing the number of white cores. The invention is continuous production and has low energy consumption.

Description

A kind of preparation system and method of lyocell spinning solution

technical field

The invention relates to the technical field of lyocell fiber production, in particular to a preparation system and method of a lyocell spinning solution.

Background technique

Lyocell fiber (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 recovered, it is called 21. century green fiber.

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. Core and other problems are not conducive to subsequent spinning and other processes, and seriously affect the spinning quality. The preparation of spinning dope is mainly divided into two processes: wet method and dry method. The so-called wet method means that the cellulose pulp is mixed with water and pulped, and then the obtained pulp solution is squeezed to remove water, and then pulverized and mixed with NMMO, and swelled in the storage tank to fully combine NMMO with cellulose , the formation of cellulose porridge. After the swelling is completed, the obtained pulp is transported to a reactor (such as a thin film evaporator) for evaporation and dissolution to form a spinning dope.

The Chinese patent document with the application publication number CN 108004611 A discloses a method for preparing a solvent-based cellulose fiber spinning stock solution by using dry pulp, which first prepares an NMMO solution containing NaOH, and then gradually puts the pulp into the NMMO solution, Mixing evenly to obtain 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, the premix is Dehydration, dissolving and defoaming are carried out to obtain cellulose spinning stock solution.

The above-mentioned prior art belongs to the dry preparation of the lyocell spinning solution, and generally has the following characteristics: (1) the pulp does not need processing such as pulverization, and is directly mixed with the NMMO solution in the form of a pulp plate; Go to the hydropulping process. (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, which shortens the process flow. (3) Reducing the energy consumption of the thin film evaporator is conducive to the improvement of production capacity; the reason is that the moisture content of dry pulp is about 6%-7%. Compared with the wet process pulp (water content is 50%), the dry pulp belt The amount of water input is greatly reduced, which can reduce the energy consumption of film steam and is conducive to improving production capacity. (4) Reduce the evaporation steam consumption of NMMO solution; in the wet process, when wet pulp is mixed with NMMO solution, the NMMO concentration is about 80%-84%, while the concentration of NMMO solution required for dry pulp mixing is 75% %-80%. The NMMO solution is recycled in the production process, and the low-concentration NMMO solution is evaporated to obtain a high-concentration NMMO solution. In this process, by reducing the evaporation concentration of the final NMMO solution, the unit steam consumption can be reduced. (5) The dry pulp is mixed with the NMMO solution. Due to the low concentration of the NMMO solution, the degree of pre-dissolution can be reduced, which is conducive to the full contact and swelling of NMMO and cellulose.

However, in the above-mentioned dry preparation technology, the cellulose/NMMO/H ₂ O mixture is made by the mechanical external force provided by the hydraulic pulper. It is found in the production that in the spinning dope prepared by this method, it is still possible to observe obvious White core particles, which also shows that the direct mixing of dry pulp with NMMO solvent has certain disadvantages, 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 the mechanical agitation produces strong shearing, and the destruction of part of the fiber shape will also seriously affect the spinning quality.

SUMMARY OF THE INVENTION

In view of this, the present application provides a preparation system and method for 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, increasing yield and reducing The production cost per unit tow is beneficial to popularization and application.

The present invention provides a preparation system for lyocell spinning solution, comprising a swelling device and a dissolving device, the swelling device is used for swelling dry pulp with NMMO solution, wherein the swelling device is a rotating drum, and the length of the rotating drum is The two ends of the direction are respectively provided with a feeding port and a discharging port. The drum rotates to bring the material inside from the bottom to the position close to the top and then freely fall back to the bottom, while conveying the swollen material towards the discharging port. .

In some preferred embodiments, the rotation of the drum is specifically as follows: the outer shell of the drum is fixed, and a rotatable material removal component is arranged in the outer shell of the drum, and the material removal component drives the material from the bottom of the drum to near the top of the drum position and then free fall back to the bottom.

In some other preferred embodiments, the rotating drum is in the form of rotation: the outer shell of the drum rotates, and the outer shell of the drum is provided with a feeding part that rotates with it, and the feeding part drives the material from the bottom of the drum to the close The top position then free-falls back to the bottom.

Preferably, between the feeding port and the discharging port, a spray belt is provided on the top of the shell of the drum or at a position close to the top, and the spray belt extends along the axial direction of the shell of the drum, and the NMMO solution flows from The spray belt is sprayed into the drum.

Preferably, both ends of the spray belt extend to both ends of the outer shell of the drum, respectively.

Preferably, the rotating drum has an adjustable inclination angle of 0-10°.

An embodiment of the present invention provides a method for preparing a lyocell spinning solution using the aforementioned preparation system, comprising the following steps:

The dry pulp and NMMO solution are added into the drum; the drum rotates, and the material formed by mixing the dry pulp and the NMMO solution is repeatedly beaten in the drum to obtain the swollen material;

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

Preferably, the NMMO solution is added into the drum through a spray assembly, the spray assembly forms a spray belt extending along the axial direction of the drum, and the spray belt includes at least two sprays for spraying NMMO solutions of different concentrations In the adjacent spraying section, the NMMO concentration sprayed by the preceding spraying section is lower than the spraying concentration of the following spraying section.

Preferably, the spray belt includes two spray sections, namely the first spray section in front and the second spray section at the back; further, the mass concentration of NMMO in the first spray section is preferably It is 72 to 78%, and the shower temperature is preferably 75 to 82°C.

Further, the mass concentration of NMMO in the second spray section is preferably 78-84%; the spray temperature is preferably 72-77°C.

Preferably, the time for the materials to be sprayed and mixed in the first spray section is longer than the time for the materials to be sprayed and mixed in the second spray section.

The embodiments of the present invention can also provide the application of the lyocell spinning solution prepared by the method described above in the production of lyocell fibers.

Compared with the prior art, the present invention adopts a rotating drum as the main equipment for mixing and swelling dry pulp and NMMO. The rotating drum drives the internal material from the bottom of the rotating drum to a position close to the top in the form of rotation. Under the action of gravity, it falls freely and falls on the bottom of the drum; because the drum itself has a certain inclination angle, the swollen material can be transported to the discharge port during the rotation process. 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, it can promote the solvent molecules to enter between the cellulose molecular chains. The reason is that in the weightless state, the molecular chains of cellulose are in a stretched state, and the gap between the molecular chains is relatively uniform, which is conducive to the entry of solvent molecules between the molecular chains. The moment the material hits the bottom, it provides an opportunity for the NMMO molecules to penetrate into the gaps of the cellulose molecular chains, so that the NMMO solvent molecules smoothly enter between the cellulose molecular chains, and promote the full swelling of the NMMO solvent molecules and the cellulose. This significantly increases the swelling rate of dry pulp, especially after repeated beating for a long time, which is enough to fully and uniformly swell the solvent and cellulose. In the embodiment of the present invention, the swollen material is directly sent to a dissolving device for dissolution to obtain a lyocell spinning solution. The invention can handle the mixing of the whole pulp and the solvent, and during the beating process, the pulp and the solvent are more fully mixed, which is beneficial to improve the quality of the product. In addition, the present invention subverts the use of segmented spray swelling technology to further reduce the number of white cores.

In addition, the obvious disadvantage of the dry swelling of the existing hydraulic pulper is the difficulty of discharging, and the discharging of the hydraulic pulper can only be discharged through the pipeline. However, after the swelling is completed, the state of the material is viscous, with poor fluidity, and due to stirring, the materials will not aggregate together, resulting in high difficulty in discharging materials in the existing swelling implementation method. In contrast, due to the stickiness of the materials in the drum of the present application, the materials will gradually gather together during the beating process, and when they finally reach the discharge port, the materials will be in a state similar to "dough", which is easy to discharge.

Description of drawings

1 is a schematic structural diagram of a swelling device in some embodiments of the present invention;

Fig. 2 is the A-A schematic diagram of Fig. 1;

Fig. 3 is the B-B schematic diagram of Fig. 1;

4 is a schematic structural diagram of a swelling device in other embodiments of the present invention;

Fig. 5 is the A-A schematic diagram of Fig. 4;

Fig. 6 is the effect diagram that the swelling process of the embodiment of the present invention 1 obtains spinning dope;

Fig. 7 is the effect diagram of the spinning dope obtained by the swelling process of Example 2 of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

The present invention provides a preparation system for lyocell spinning solution, comprising a swelling device and a dissolving device, the swelling device is used for swelling dry pulp with NMMO solution, wherein the swelling device is a rotating drum, and the rotating drum The two ends in the length direction are respectively provided with a feeding port and a discharging port. The rotating drum makes the material inside the drum move from the bottom to the position close to the top and then freely fall back to the bottom. materials.

The preparation system provided by the invention can continuously produce the lyocell spinning solution, has good quality and low energy consumption, and is favorable for popularization and application.

Referring to Figures 1-3, Figure 1 is a schematic structural diagram of a swelling device in some embodiments of the present invention, and Figures 2 and 3 are schematic diagrams A-A and B-B, respectively. Among them, 10 is the drum shell, 101 is the material removal beam, 102 is the beater, 103 is the outrigger, 20 is the solvent spray belt, 30 is the transmission shaft, 301 is the spoke, 302 is the inlet runner, and 303 is the outlet runner , 40 is the oil cylinder, 50 is the feed port, 60 is the discharge port, and 70 is the pulse high pressure gas inlet.

The preparation system of the lyocell spinning solution according to some embodiments of the present invention includes the swelling device shown in FIG. 1 . The swelling device is a drum with a stationary outer shell and a rotating inner structure. The specific structure includes: a fixed and immobile drum The rotating drum shell 10 and the rotatable material-removing beam 101 provided inside, preferably a number of beaters 102 are also provided. The shell 10 is the outside of the drum, and the bottom can be supported by the outriggers 103 fixed on the ground; the inner space of the drum shell is used for material mixing and swelling. Near the top, then free fall back to the bottom.

In the embodiment of the present invention, a volume and structure suitable for spraying the NMMO solution to the inside of the rotating drum can be formed inside the casing 10 . The inside of the shell 10 forms a long cylindrical mixing cavity; its length and diameter should be customized according to the actual process requirements. For example, the length can be selected as 10 meters. In fact, the length of the shell may reach tens of meters or even longer, and the diameter can be selected 1m, 2m, etc. One end of the drum in the length direction is the feeding end (one end of the feeding port), and the other end is the discharging end (one end of the discharging port).

In addition, a plurality of solvent spray ports are arranged at the top of or near the top of the drum shell 10 laterally (ie, in the longitudinal direction), and are arranged along the axial direction of the drum shell to form a solvent spray belt 20 for feeding The solvent is sprayed between the material end and the discharge end, that is, 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 multiple spray sections according to the concentration of the spray solvent, that is, the spray area that sprays the same concentration of solvent 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.

The swelling device is used to swell dry pulp with NMMO solution. The present invention does not specifically limit the feeding forms of materials such as NMMO solution and dry pulp, which can enter the swelling device from the feeding port. Wherein, the NMMO solution can be added into the drum through a spray assembly. In the embodiments of the present invention, the spray assemblies are in various forms, and there are no special restrictions on the specifications and segment distances of each solvent spray port. Exemplarily, a row of narrow and long multiple spray holes may be arranged on the top of the drum shell along the head and tail of the drum, and the first spray section and the second spray section may be divided according to different concentrations of solvent segmented spray; A row of nozzles is installed on the top of the drum corresponding to the spray port. The nozzle at the feed end sprays one concentration of solvent, and the nozzle at the discharge end sprays another concentration of solvent.

In addition, a temperature regulating jacket or electric heat tracing equipment (not shown in FIG. 1 ) may be provided outside the drum for independent section control of temperature. A lifting device can be set under one end of the feeding port of the drum to control the lifting and lowering of one end of the feeding port of the drum relative to the end of the discharge port. This is necessary. Mixed swelling time.

In the above-mentioned embodiment of the present invention, the drum shell 10 does not move, the transmission shaft 30 (driven by an external motor) drives the spokes 301 to rotate, the spokes 301 drive the outlet runner 303 to rotate, and the runner 303 drives the material removal beam 101 to rotate, and the material removal The left end of the beam 101 is fixed on the inlet runner 302 to ensure that the material removal beam 101 is close to the inner wall of the drum shell and rotates reliably. The material removal beam 101 drives the material to rise along the inner wall of the outer shell, and the material falls under the action of gravity, and it is repeatedly beaten like this. Realize material mixing, swelling, and slow backward conveyance. Due to the viscosity of the suspended material, during the rotation process, the material will gather together, like "dough", keep beating, and then aggregate after being crushed. During this beating process, the pulp and solvent are more thoroughly mixed. However, if only the stirring blades and other components are used for stirring and mixing, the mixing uniformity of the materials is poor, and the swelling effect is poor due to the existence of many stirring dead corners. In the present invention, the pulp and the solvent are fully mixed and swollen by beating, and the effect is better than that of blade stirring; there is no dead angle in the drum, so as to achieve uniform swelling.

In the embodiment of the present invention, there are no special restrictions on the structural design of the drum shell, the material-removing components, etc., as long as the above-mentioned functions of material-removing and material-beating can be realized. Specifically, a plurality of short-rod-shaped protruding parts (ie beaters 102) are arranged inside the drum; the beaters 102 are directly fixed on the drum material-removing beam 101, and the material-removing beam 101 drives the beaters 102 to smoothly move the material to the Higher height, improved beating effect. In addition, the oil cylinder 40 drives the casing 10 to ascend and descend. A feed port 50 and a discharge port 60 are respectively provided at both ends of the drum in the length direction. The pulp is fed from the feed port 50 to the inside of the drum, and discharged from the discharge port 60. One end of the discharge port also has a pulsed high-pressure gas inlet. 70. When the material outlet is blocked by the material, the gas inlet 70 sprays high-pressure gas to disperse the blocked material mass, so that the material can be output smoothly.

In the embodiment of the present invention, the inclination angle of the drum is adjustable, which 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 make the material convey backwards under inclined conditions. The beaters of the present invention are a plurality of short rod-shaped protrusions spaced apart from each other, and the overall shape is preferably the same; the end away from the drum can be any shape such as square, round, pointed, and the number is not limited. Among them, the wedge-shaped pointed beater is the best 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 protruding parts (the beaters 102 ) are fixed on the corresponding material-removing beams 101 . In addition, the present invention has no special limitations on the transmission structures such as the spokes, the runner, etc., the specific structure shown in FIG. 3 may be adopted, or other designs may be adopted.

In the preparation system according to the embodiment of the present invention, the rotating drum of the swelling device rotates 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, and is sprayed in sections at the same time. Solvent, the swelling is completed, and the swollen material is transported to the dissolving device. The dissolving device is a reaction kettle that communicates with the discharge port of the swelling device; the present invention does not have a special limitation 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 reaction kettle, and the obtained spinning dope is then sent to the spinning machine for spinning, thereby producing Lyocell fibers.

The preparation system provided by the invention can continuously produce the lyocell spinning solution, has sufficient swelling and good quality, increases the output and reduces the production cost per unit tow.

In other embodiments of the present invention, the structure of the swelling device is shown in Figures 4-5. Among them, 11 is the drum shell, 111 is the material pulling beam, 112 is the beater, 31 is the driving component, 51 is the feeding port, and 61 is the discharging port.

The preparation system of the lyocell spinning solution according to other embodiments of the present invention includes the swelling device shown in FIG. 4 . The swelling device is a drum with a rotating shell structure, and the specific structure includes: a rotatable drum shell 11 and the material-removing beam 111 arranged inside it, and preferably a number of beaters 112 are also arranged. The drum shell 11 rotates, and the material removal beam 111 fixed on the inner wall of the shell drives the material to be beaten in the cavity, that is, drives the material from the bottom of the drum to the position near the top and then freely falls back to the bottom, and slowly conveys backwards.

In the embodiment of the present invention, the inside of the shell 11 is a mixing cavity; its length and diameter should be customized according to the 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, Diameter can choose 1m, 2m and so on. One end of the drum in the length direction is the feeding end (one end of the feeding port), and the other end is the discharging end (one end of the discharging port). Between the feeding port and the discharging port, a spray pipe can be extended into the mixing cavity of the rotating drum, and a row of spray nozzles is arranged in the spray pipe. The belt extends in the axial direction of the outer shell of the drum, and can extend to both ends; the NMMO solution is sprayed into the drum from the spray belt. Alternatively, both solvent and pulp enter the swelling device from the feed port (as shown in Figure 4).

In these embodiments of the present invention, the drum shell 11 is driven to rotate by the drive assembly 31 (the drive assembly 31 is a conventional transmission mechanism composed of a motor and a gear), and the material-shifting beam 111 fixed on the shell drives the material in the cavity Beat, so repeatedly beat to achieve material mixing, swelling, and slowly conveyed backwards. Preferably, a plurality of short rod-shaped protruding parts (namely beaters 112) are arranged inside the drum; the beaters 112 are directly fixed on the drum pulling material beam 111, and the material pulling beam 111 and the beater 112 rotate with the casing to enhance the stirring effect. The two ends of the drum in the length direction are respectively provided with a feeding port 51 and a discharging port 61. The pulp and NMMO solution are fed into the drum from the feeding port 51, and the swollen material is discharged from the discharging port 61.

The inclination angle of the rotating drum in the above embodiments of the present invention can also be adjusted, 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 make the material convey backwards under inclined conditions. The beaters of the present invention are a plurality of short rod-shaped protrusions spaced apart from each other, and the overall shape is preferably the same; the end away from the drum can be any shape such as square, round, pointed, and the number is not limited. In a preferred embodiment of the present invention, the plurality of protruding parts (beaters 112) are fixed on the corresponding material-removing beams 111, and are evenly distributed along the circumference of the drum, as shown in FIG. Set in rows evenly spaced. In addition, the present invention has no particular limitation on the drive assembly.

After the dry pulp is swollen by the swelling device, it enters the dissolving device; the dissolving device is a reaction kettle connected with the discharge port of the swelling device. The present invention has no particular limitation 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 reaction kettle, and the obtained spinning dope is then sent to the spinning machine for spinning, thereby producing Lyocell fibers.

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

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:

The dry pulp and NMMO solution are added into the drum; the drum rotates, and the material formed by mixing the dry pulp and the NMMO solution is repeatedly beaten in the drum to obtain the swollen material;

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

The invention can continuously produce the lyocell spinning solution, improves quality, reduces energy consumption, and is suitable for large-scale production.

In the embodiment of the present invention, a dry preparation process is adopted, and dry cellulose pulp is used as a raw material, and the moisture content of the dry pulp is about 6%-7%. The lower amount of water brought in by dry pulp can reduce the energy consumption of film steam, which is beneficial to increase production capacity. In some specific embodiments of the present invention, the dry pulp is fed from the feeding port, and the feeding rate may be 1.0-1.5 t/min. Moreover, in the embodiment of the present invention, preferably, the NMMO solution is added into the drum through a 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 into the swelling device to mix and swell to obtain material after swelling.

The structure and the like of the swelling device are as described above. For example, the inclination angle of the swelling device can be adjusted between more than 0° and less than 10°, and the rotation frequency of the drum is determined according to actual process requirements, such as 3-5 rpm. The feeding amount of pulp and the NMMO solvent sprayed should be maintained at a certain ratio, which 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 proportioning relationship can also be changed according to the process requirements); then the feeding speed of the pulp and the spraying of the solvent can be determined according to this ratio. shower speed.

According to the embodiment of the present invention, the moving beam in the drum can push the material to rise. 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, maintaining this state and continuing to move repeatedly. Preferably, when spraying NMMO solvent, at least two spray sections for spraying different concentrations are formed on the spray belt, and in adjacent spray sections, the concentration of NMMO sprayed by the previous spray section lower than the spray concentration of the subsequent spray section. That is to say, the present invention preferably adopts segmented spraying of solvent, for example, it is divided into two segments, or three or more spraying methods can be used; Time is proportional to length.

In some specific embodiments of the present invention, the spray belt includes two spray sections, which are a first spray section at the front and a second spray section at the back. Wherein, 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.

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

For the stepwise spraying of the NMMO solution in the present invention, solvents of different concentrations can be added in sequence, that is, the front nozzle sprays one concentration solvent, and the rear nozzle sprays another concentration solvent; in the present invention, preferably, the first spray concentration is lower than The subsequent spray concentration 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. This buffering condition, combined with the addition of a high NMMO concentration solution, weakens the extent to which the NMMO solvent locally dissolves the pulp to form a gel, which would prevent the cellulose from fully swollen, which is undesirable.

Preferably, the time for the materials to be sprayed and mixed in the first spray section is longer than the time for the materials to be sprayed and mixed in the second spray section. In the embodiment of the present invention, controlling the time of pulp conveying in the drum is also a key parameter. Too fast conveying speed means that the swelling time of pulp is too short, the swelling is difficult to reach a sufficient degree, and too long conveying time increases cost and reduce production efficiency.

For example, some embodiments of the present invention control the swelling time to 150 min (ie the time from entering the drum to exiting the drum). This time is related to the length, inner diameter, rotation speed and inclination angle of the drum, because the length and inner diameter are fixed parameters (of course, the drum can be replaced and adjusted), the present invention can control the swelling time by adjusting the inclination angle and rotation speed.

After the swelling is completed, in the embodiment of the present invention, the swollen material is directly sent to a dissolving device such as a reaction kettle for dissolving to prepare a Lyocell spinning solution.

Wherein, in the present invention, there are no special restrictions on the device for dissolving, such as a thin film evaporator, process conditions, etc., and a common evaporation and dissolving process in the art can be used. In the embodiment of the present invention, in the obtained cellulose suspension, the mass ratio of NMMO/cellulose is 6-7, for example, 6.4.

The present invention also provides the application of the lyocell spinning solution obtained by the aforementioned preparation method in the production of lyocell fibers; the obtained lyocell spinning solution is transported to a spinning machine for conventional spinning, producing Lyocell fibers are obtained.

The above method of the present invention has good swelling effect and low number of white cores. In addition, the present invention has simple technological process, low energy consumption, and is suitable for large-scale production.

In order to further understand the present application, the preparation system and method of the lyocell spinning solution provided by the present application will be specifically described below with reference to the examples. However, it should be understood that these embodiments are implemented on the premise of the technical solution of the present invention, and the detailed implementation manner and specific operation process are given, only to further illustrate the features and advantages of the present invention, rather than to claim the present invention The protection scope of the present invention is not limited to the following examples.

Example 1

1. Main raw materials

1. The NMMO aqueous solution as a solvent has a concentration of 75% and 83%, respectively;

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

Second, the main equipment:

1. The rotating drum with the structure shown in Figure 1-3 is adopted, that is, the outer casing is fixed, and the material pulling parts such as the material pulling beam move around the inner wall of the outer casing to achieve the purpose of scraping the material on the inner wall of the outer casing. The drum is 20 meters long and 2 meters in diameter.

The top of the drum shell is provided with a spray belt, the first spray section (ie the first half) sprays 75% solvent; the second spray section (ie the second half) sprays 83% solvent, two sprays The ratio of the length of the shower section is 1:1.

2. The model of the test equipment for swelling rate is DD5M low-speed centrifuge.

3. Implementation Instructions

The pulp is continuously conveyed to the feeding port of the rotating drum, and the pulp entering the rotating drum is agitated by the rotating drum stirring part and conveyed backward along the rotating drum; the orbiting speed of the material-discharging beam is 3-5rpm;

The spray belt at the top of the drum sprays the solvent into the drum according to the preset concentration (that is, the first half is sprayed with a solvent with a concentration of 75%, and the second half is sprayed with a solvent with a concentration of 83%); stop.

During production, the above pulp was continuously put into the drum at a feeding speed of 1.06t/min, and the drum kept running normally and stably. In this way, the pulp feeding speed of 1.06t/min corresponds to the injection speed of pure NMMO is 6.4t/min (satisfying the relationship of NMMO/cellulose=6.4). In this operation, the first half of the spray belt is set to spray 3.2t/min evenly, and the second half of the spray belt is evenly sprayed for 3.2t/min. According to the spray concentration of each part, the spray rate of the solvent with a concentration of 75% in the first half of the spray belt is 4.27t/min; the spray rate of the solvent with a concentration of 83% in the second half of the spray belt is 3.86 t/min t/min. The spraying temperature of the first half is 75-82℃; the spraying temperature of the second half is 72-77℃. As mentioned earlier, the solvent is sprayed in the form of a spray belt, which is necessary to effectively avoid the problem that the solvent cannot be locally mixed with the pulp caused by a concentrated spray. The solvent that is too late to mix during a little spray will flow backwards quickly, resulting in the inability to complete the swelling process of the cellulose.

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

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

Take 3 parts of the material swollen by this operation, each part is 2kg, and carry out the swelling ratio test.

The weight of the first centrifuged material was 1.93 kg, the weight of the second centrifuged material was 1.92 kg, and the weight of the third centrifuged material was 1.94 kg. Thus, the corresponding swelling ratios are 96.5%, 96.0% and 97.0%, respectively, and the average swelling ratio is 96.65%.

At present, the swelling rate of the existing technology is generally 88-92%, such as the swelling material (suspension) prepared by the wet method. It can be seen from the comparison that the cellulose suspension prepared by the technology of the present application has an excellent swelling effect.

In addition, after the materials with poor swelling effect are prepared into spinning dope by evaporation and dissolution, more white cores will remain in the solution. Based on this, in order to further prove the above swelling effect, in the spinning dope obtained in this example, a small sample of the dope 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 air bubbles , basically no white core particles were found (as shown in Figure 6). This is almost impossible for traditional dissolution processes.

Example 2

1. Main raw materials

1. The concentration is 80% NMMO aqueous solution;

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

2. Main equipment

1. The drum as shown in Figure 4-5 is used (the shifting parts such as the toggle beam are directly fixed on the inner wall of the drum shell, and the drum shell rotates under the drive of external bearings and power components), NMMO solvent and slurry The pulp is transported into the drum from the pulp inlet. The drum is 20 meters long and 2 meters in diameter.

2. The model of the test equipment for swelling rate is DD5M low-speed centrifuge.

3. Implementation Instructions

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

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

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

Take 3 parts of 2kg of the swollen material by this operation, and carry out the swelling ratio test.

The weight of the first centrifuged material was 1.89 kg, the weight of the second centrifuged material was 1.90 kg, and the weight of the third centrifuged material was 1.89 kg. Thus, the corresponding swelling ratios are 94.7%, 95.0% and 94.7%, respectively, and the average swelling ratio is 94.80%.

At present, the swelling ratio of the existing technology is generally 88-92%, and it can be seen from the comparison that the swollen material obtained by this operation has an excellent swelling effect.

In addition, after the materials with poor swelling effect are prepared into spinning dope by evaporation and dissolution, more white cores will remain in the solution. Based on this, in order to further prove the above swelling effect, a small sample of the original solution was taken from the solution dissolved in this operation, placed in an environment with excellent sunlight, and observed with a magnifying glass with a magnification of 5 times, basically no white core particles (such as Figure 7). This is almost impossible for traditional dissolution processes.

The test proves that: through the preparation system of the present invention, the pulp and the solvent form a mixture, and under its own gravity, repeated beating can promote the solvent and the pulp to fully swell, probably because such beating process can make the solvent repeatedly from Different angles try to enter the molecular gap of the pulp, and it is uniform and gentle, avoiding external force tearing and affecting the physical and chemical properties of cellulose.

In addition, the use of drum-type swelling equipment has a great advantage, that is, the single-line production capacity of cellulose fibers is greatly improved. In the existing process, whether it is the dry production mentioned in the background, or other wet processes, it is necessary to use a hydropulper or a pulping equipment similar to an underwater pulper, which is not only small in volume, but also can be driven by the rotation of the blades. The material is directly mixed, which determines the limited weight added to the pulp. 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 the annual production capacity of hundreds of thousands or even more can be achieved. This is unpredictable for the existing technology. The improvement of single-line production capacity will undoubtedly reduce product costs and create broad prospects for product promotion.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the technical principles of the present invention, various modifications to these embodiments can be realized, while These modifications should also be regarded as the scope of protection of the present invention.

Claims (10)

1. a preparation system of a lyocell spinning solution, comprising a swelling device and a dissolving device, after the dry pulp is swollen by the swelling device, enters the dissolving device and dissolves into a spinning stock solution, and the swelling device swells the dry pulp with an NMMO solution , characterized in that the swelling device is a rotating drum, and the two ends of the rotating drum in the length direction are respectively provided with a feeding port and a discharging port. The top position then freely falls back to the bottom, while conveying the swollen material towards the discharge port. 2. The preparation system according to claim 1, characterized in that, the rotating drum is specifically in the form of: the outer shell of the drum is fixed, and the outer shell of the drum is provided with a rotatable feeding part, and the feeding part is Drive the material from the bottom of the drum to the position near the top and then freely fall back to the bottom. 3. The preparation system according to claim 1, wherein the rotating drum is specifically in the form of: the outer shell of the rotating drum rotates, and the outer shell of the rotating drum is provided with a feeding part that rotates with it, and the feeding part is Drive the material from the bottom of the drum to the position near the top and then freely fall back to the bottom. 4. The preparation system according to claim 2 or 3, characterized in that, between the feeding port and the discharging port, a spray belt is provided on the top of the shell of the rotating drum or at a position close to the top, and spraying The belt extends in the axial direction of the outer shell of the drum, from which the NMMO solution is sprayed into the drum. 5 . The preparation system according to claim 4 , wherein the two ends of the spray belt respectively extend to the two ends of the outer shell of the rotating drum. 6 . 6. The preparation system according to claim 5, wherein the rotating drum has an adjustable inclination angle of 0-10°. 7. A method for preparing a lyocell spinning solution using the preparation system according to any one of claims 1 to 6, characterized in that, comprising the following steps: The dry pulp and NMMO solution are added into the drum; the drum rotates, and the material formed by mixing the dry pulp and the NMMO solution is repeatedly beaten in the drum to obtain the swollen material; The swollen material is discharged from the drum and sent to a dissolving device for dissolution to obtain a lyocell spinning solution. 8. The preparation method according to claim 7, wherein the NMMO solution is added into 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 There are two spray sections for spraying NMMO solutions of different concentrations. In adjacent spray sections, the NMMO concentration sprayed by the previous spray section is lower than that of the subsequent spray section. 9 . The preparation method according to claim 8 , wherein the spray belt comprises two spray sections, which are respectively a first spray section in front and a second spray section at the back; the The mass concentration of NMMO in the first spray section is 72-78%, and the spray temperature is 75-82°C. 10 . The preparation method according to claim 9 , wherein the time for the materials to be sprayed and mixed in the first spray section is longer than the time for the materials to be sprayed and mixed in the second spray section. 11 .

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