PROCESS FOR SOLVENT AND CELLULOSE RECOVERY IN THE MANUFACTURING OF CELLULOSIC SPINNED FIBERS

The present invention relates to an installation for the production of spunbond, comprising a spinning system, a device for dispensing coagulation liquid, at least one conveying device for depositing the spunbond and a collecting device for the spunbond. The invention also relates to a method for the recovery of solvent or cellulose in a plant for the production of spunbonded web, wherein spunbond filaments are extruded from a spinning system, laid down in a stretched manner to form a spunbonded web and later collected.

Background of the invention

Spunbonded nonwovens have been manufactured using the spunbond or meltblown process for many years. In the spunbond process, as described, for example, in GB 2 114 052 and EP 3 088 585, filaments are extruded through a nozzle and drawn off and drawn by an underlying drawing unit. In contrast, the extruded filaments in the meltblown process, as described for example in US Pat.

With both technologies, the filaments are placed on a storage surface, for example a perforated conveyor belt, in a random position to form a nonwoven, transported to post-processing steps and finally wound up as nonwoven rolls.

The known methods and devices have been developed mainly for the production of plastic filaments such as polypropylene and the publications to date deal mainly with the nozzles, the raw material used and the depositing systems necessary for depositing the fleece. In fact, the economically sensible and safety-compliant operation of production plants requires a closer look at the operating conditions of spunbond plants. When starting up thermoplastic spunbond systems, for example, the extruded filaments are either caught and disposed of by a device under the spinning system, or they are deposited on a so-called carrier fleece. Since the backing fleece was unrolled in front of the fleece deposit, On the one hand, the conveyor belt is protected from damage by hot filaments and, on the other hand, the freshly extruded filaments are already transported and wound up via the downstream consolidation and, if necessary, drying devices. On the one hand, the delivery conveyor belt is prevented from being damaged by the hot filaments during piecing, and on the other hand, the threading of the spunbonded nonwoven occurs automatically. As soon as the desired spunbond quality is achieved, the carrier fleece is cut off or torn off before the spunbond is deposited. The spunbond is then placed directly and immediately on the storage surface. Before the system is shut down, the carrier fleece is unrolled again in order to be able to repeat the start-up process already described for the next start-up.

In contrast to the already well-known spunbond and meltblown processes for thermoplastics, the transport of nonwovens for the production of cellulosic spunbonded nonwovens, for example from Lyocell spinning mass, has to solve additional tasks. The production of cellulosic spunbonded nonwovens using spunbond technology is described, for example, in US Pat. No. 8,366,988 and according to meltblown technology in US Pat. No. 6,358,461 and US Pat. No. 6,306,334. In this process, the lyocell spinning mass is drawn as in the already known spunbond and meltblown processes, but the filaments are additionally brought into contact with a coagulant before the fleece is deposited in order to regenerate the cellulose and produce dimensionally stable filaments. Due to the turbulence of the air, the wet filaments are laid down in a random layer as a non-woven fabric.

For the production of cellulosic spunbonded nonwovens, solvents are used which have to be recovered. In addition, the spinning masses produced, for example Lyocell spinning masses, are flammable and can cause damage to downstream system components, so that the start-up and shutdown procedure cannot be carried out as with thermoplastic spunbond systems. The initially still coarse, hot spinning mass filaments cannot simply be placed on a carrier fleece and transported via the dryer to the winder. It has been shown that when the system is started up, especially with small amounts of drawing air, the extruded filaments are still so coarse that they have such high solvent residues even after the washing process described in WO 2018/071928 A1, that solvent is lost in the further processing of the spunbonded nonwoven. Downstream system parts such as the hydroentanglement described in AT 503 625, dryer and winder are also soiled and corroded by the solvent. In extreme cases, the solvent-laden spunbonded web can for the most part still consist of spinning mass and start to burn in the dryer.

The loss of the solvent and system components damaged by corrosion and fire represent a considerable economic risk. Especially in the production of cellulosic spunbonded nonwovens, the loss of the solvent and the contact of the

Solvents with downstream equipment can be avoided for safety, economic and environmental reasons.

As already mentioned, the focus of the previous publications for processes for the production of thermoplastic spunbonded nonwovens (as described in US Pat. No. 3,849,241) is mainly on the spinning systems used for meltblown and spunbond. US Pat. No. 6,358,461 and US Pat. No. 8,282,877 describe the production of cellulosic spunbonded fabrics and US Pat Recovery of solvent and cellulose during the operation of a cellulosic spunbond plant.

Brief description of the invention

The object of the present invention is therefore to avoid the disadvantages described above. In particular, the loss of solvent is to be minimized in the system mentioned at the beginning and in the process mentioned at the beginning and the operational safety of downstream system parts is to be ensured.

The object is achieved by a system for the production of spunbonded nonwoven, comprising

• a spinning solution production,

• a spinning system,

• a device for dispensing coagulation liquid,

• At least one conveyor device for depositing the spunbond and

• a collecting device for the spunbond,

characterized in that at least one discharge device is provided between the device for dispensing coagulation liquid and the collecting device for the spunbonded nonwoven.

Furthermore, the object is achieved by a method for the recovery of solvent or cellulose in a plant for the production of spunbonded web, wherein spunbond filaments are extruded from a spinning system, laid down to form a spunbonded web and later collected, whereby when the plant is started up, when the plant is shut down or In the event of operational problems in the system, deposited spunbond is discharged prior to collection, with (a) the solvent being removed from the discharged spunbond and / or with (b) the discharged spunbond being fed to the spinning solution production.

To avoid the solvent-laden spunbonded web when starting up, switching off, or in the event of operational problems during production (spinning faults, accumulation of coarse fibers,

Spunbond still consists of spinning mass, ...) and to be able to recover the solvent, as well as to avoid contamination and, for example, the risk of fire in the hydroentanglement, a drying device or the collecting device, the system according to the invention fulfills the additional task of this solvent-laden spunbond, which does not have the desired properties, discharged and fed back into the production process.

Using the example of spunbonded web production from Lyocell spinning mass, it has been shown that the discharged spunbonded web pieces are fed to further cleaning steps in the NMMO recovery and then, for example, filtered, decanted, pressed or centrifuged, so that an NMMO solution is created again, which is cleaned, evaporated and the spinning mass production can be added. According to the invention, NMMO, which would have been lost when starting up and shutting down the system or in the event of production problems, could be purposefully discharged from the production system and subsequently recovered. It has been shown that the remaining cellulose after the solid / liquid separation, instead of being disposed of, can also be used again for the production of spinning pulp.

A further advantage of the method according to the invention, in addition to the economically and environmentally improved operation of the spunbonded nonwoven plant due to the solvent and cellulose recovery, is the protection of the downstream plant components. Since the solvent-laden spunbond is discharged after the transport device or after the washing device or after the solidification device, the flammable solvent or the spinning mass can be prevented from coming into contact with the hot dryer surface of a drying device.

If the spunbonded nonwoven is discharged with a water jet before the consolidation, it can also be prevented that solvents get into the water cycle of the hydroentanglement, which can cause corrosion of the system parts and the nozzle strips at this point.

Another advantage is the possibility of being able to discharge the spunbonded web at several points when starting up and when shutting down the system, but also in the event of production disruptions, especially at high speeds. If, for example, the spunbond is wrapped around a vacuum drum or a deflection roller during hydroentanglement, the spunbond can be torn off and discharged beforehand, the speed of the hydroentanglement reduced, the entanglement eliminated and the system restarted without the entire spinning process or even the spinning mass production having to stop. Particularly in the production of cellulosic spunbonded nonwovens, it has been found that the production of spinning material should be carried out constantly in order to achieve uniform product quality. The method according to the invention made it possible to minimize downtimes, since adjustments can be made to downstream parts of the plant without the spinning mass system and the spinning system having to be switched off or throttled. Only the speeds of the transport device are adjusted, the spunbond is discharged in front of the system part on which work is being carried out and the NMMO is recovered from the discharged spunbond - as already described - or the discharged spunbond is suspended and returned directly to the spinning mass production.

In the context of the invention, to simplify the description, spunbonded nonwoven in normal operation is understood to mean, on the one hand, a non-woven structure of regenerated cellulose filaments in the range of 0.1 μm to 250 μm filament diameter and with <500 mg / kg solvent, possibly bonded at intersections. On the other hand, spunbonded web is understood to mean a sheet of partially or not regenerated spunbond filaments with a diameter of 0.1 to 50,000 μm and a solvent concentration of> 500 mg / kg up to several million mg / kg when starting up, shutting down or in the event of production disruptions. The actual status can also be between the two examples mentioned, depending on the driving style.

With regard to the system, there are numerous advantageous design variants.

The extruded spinning mass filaments or also already regenerated filaments can be discharged against the transport direction after being deposited. If the spinning mass is not yet of the desired quality or if problems with downstream transport devices have to be eliminated, the discharge can take place immediately after the extrusion from the spinning system or in front of the transport device by moving the transport device backwards.

The system can furthermore have at least one washing system, a discharge device being provided between the transport device and the washing system.

The system can furthermore have at least one solidification system, a discharge device being provided between the transport device and the solidification system.

The system can furthermore have a drying device, a discharge device being provided between the transport device or the solidification system connected in front of it and the drying device.

The system can also have a discharge device after the drying device.

It is preferably provided that the transport device is in several parts and a discharge device is provided between two parts of the transport device. For example, the transport device can be a conveyor belt. In the simplest case, it is a multi-part conveyor belt, the discharge device being arranged between two conveyor belt parts.

In the simplest case, the discharge device can have an opening for the spunbonded nonwoven to fall through. In one embodiment, the discharge device is designed as a shaft under the gap between parts of the transport device. The gap between the conveyor devices can be between 2 and 200 cm, preferably 5 and 100 cm, even more preferably 10 and 50 cm. The shaft can either cover the entire width of the transport device or only part of it. The spunbonded nonwoven can passively fall into the shaft and to the comminution device, or it can be actively brought to the comminution device by air nozzles, water nozzles or other conveying devices known to the person skilled in the art.

The discharged solvent-laden spunbond can be recycled. For this purpose, a comminution device can be provided, the inlet of the comminution device being connected to the discharge device. The solvent-laden spunbond can then be comminuted.

In one embodiment it is provided that the output of the comminution device is connected to the production of the spinning solution. In this case, the shredded material can be fed back into the spunbond process.

If necessary, a further discharge device can be provided between the comminution device and the production of the spinning solution. In this case, too large an amount of shredded material can be retained or contaminated material can be eliminated entirely.

It is preferably provided that a suspension container is provided between the comminution device and the production of the spinning solution. In this way, the shredded material can be ideally prepared for the next spinning process.

The positions for discharging spunbonded nonwoven can be after the spinning system, after the delivery conveyor belt, after washing, after solidification and after the dryer

are located, for example, to reuse edge cut material for the production of spinning pulp.

Each discharge device can be followed by at least one comminution device and one suspension container. Further variants are possible depending on the system design.

The ejected spunbonded nonwoven can also be transported from several ejecting devices via conveying devices to a comminuting device.

The comminution device can have a suspension container or several suspension containers which are filled alternately. The suspension containers can thus be operated either continuously or discontinuously, depending on the technical design. A suspension pump can continue the suspension.

For low cellulose contents, the suspension pump can be designed, for example, as a gear pump or a worm gear pump. In the case of high cellulose contents, for example, a screw conveyor, a metering screw, a conveyor belt or a metering belt weigher can also be used for metering the recovered cellulose for the renewed production of spinning pulp

The discharge process can take place at web transport speeds between 5 and 1000 m / min, preferably 10 and 500 m / min, even more preferably between 15 and 250 m / min.

The conveying devices can also be rotating rollers or drums. The discharge devices are adapted, depending on the layout of the transport device, so that the spunbonded nonwoven can be discharged at these points and the method according to the invention can be implemented.

With regard to the method, provision can also be made for the discharged spunbonded nonwoven to be suspended again and mixed with fresh cellulose and fresh solvent before it is fed to the spinning solution production.

It is preferably provided that the comminuted spunbonded web before it

Spinning solution production is supplied, is mixed with solvent.

Surprisingly, the suspension produced could even directly derive the

Spinning pulp production are supplied and thus the NMMO and the already used

Cellulose that has already been processed into spunbonded nonwovens can be dissolved again into spinning mass and spun without any visible restrictions in terms of spinnability or product properties.

The process according to the invention can be used in the production of cellulosic spunbonded webs in order to recover the solvents used to dissolve the cellulose, for example tertiary amine oxides or ionic liquids.

Detailed description of the invention

In the present invention, a method and a system are provided which allow the distances or gaps between two system parts or transport devices to be used for discharging solvent-laden spunbonded nonwovens, the discharged spunbonded nonwovens to be comminuted, suspended and the suspension produced either subsequently to be fed to the solvent work-up or to be added directly to the production of spinning pulp.

The method according to the invention enables an economically, environmentally, technically safe and operationally improved operation of a spunbonded line for the production of cellulosic spunbonded webs, since the spunbonded web can be discharged and adjustments to downstream equipment can be made without shutting down the spinning mass production or the spinning system. As a result, the solvent can be recovered and contamination of downstream equipment can be prevented, thus minimizing the risk of corrosion and fire.

In order to better illustrate the invention, the essential features are illustrated using preferred embodiments of the method according to the invention using the following figures.

Fig. 1 shows schematically a system according to the invention.

FIG. 2 shows the viscosity of spinning mass made from fresh cellulose in comparison with reused cellulose made from spunbonded nonwoven.

1 shows a system 1 according to the invention, the method steps also being explained with reference to system 1. Through the spinning system 2, extruded and drawn spinning mass filaments 5 are deposited to form a spunbonded nonwoven 8 and are discharged at several discharge devices 14 by interrupting the main process flow. In normal operation, the filaments 5 can be sprayed with a coagulation liquid from a device 6 for dispensing coagulation liquid in order to regenerate the cellulose and stabilize the shape of the filaments 5, before the process air 4 and the filaments 5 on the transport device 7 in the form of a conveyor belt impinge and the spunbond 8 is formed. The spunbond 4 is then washed in the main process flow in a washing device 10, if necessary solidified in a solidification plant 11,

It has been shown that when starting up, shutting down or in the event of production problems, for example the failure of the device 6 for dispensing coagulation liquid or the washing device 10, during the production of spunbonded fabrics from Lyocell spinning mass, over 500 ppm NMMO, sometimes over 5000 ppm NMMO, in extreme cases more than 50,000 ppm NMMO remain in the spunbond. Without the method according to the invention, the solvent-laden spunbonded nonwoven would be transported via the consolidation system 11, the drying device 12, to the collecting device 13. Over a longer period of time, the NMMO collects in the water circuit of the solidification system 11 and can cause corrosion of the system parts and the solidification nozzles. During prolonged operation, the NMMO can accumulate in the drying device 12 and cause fires in the drying device 12.

It has been shown that the solvent losses at productivities of the spinning system 2 between 10 kg / h / m and 1000 kg / h / m cellulose throughput are so high that a new method has to be developed in order to solve the problems already described.

According to the invention, the gaps between conveyor belts 7, 9 are used to the extent that discharge devices 14 (not shown in detail) can be installed which enable the solvent-laden spunbonded web to be discharged. According to the invention, the discharge from the main process flow already results in greater flexibility for the system operator, since they can carry out activities on downstream system parts without the spinning solution production 3 and the spinning system 2 having to be switched off or throttled beforehand.

The discharged spunbonded web is comminuted to pieces of spunbonded web in a comminution device 15 and suspended in the suspension container 16 by adding liquid 17 that it can be recovered by, for example, a feed pump 18 either via line 19 for NMMO recovery (not shown in detail) or via a line 20 for Spinning solution production 3 can be promoted (not shown in detail). It has been shown that the discharged spunbonded nonwoven can be blended into a transportable suspension through the comminution step and mixing with liquid. This step makes the recovery of NMMO or the addition to the spinning solution production possible in the first place.

The discharge devices 14 can be located after the spinning material line, after the spinning system 2, before or after the transport device 7 and before or after the transport device 9 assigned to the washing device 10. In addition, discharge devices 14 can be located between the solidification system 11 and the

Drying device 12 are located. It is also possible for discharge devices 14 to be arranged after the drying device 12 and in front of the collecting device 13 in order to discharge products of poor quality, feed them to recovery and process them again into spinning mass. Depending on the process control and system layout, other positions for the discharge device 14 are also possible. A system 1 can therefore have one or more reject devices 14. The moisture content of the discharged spunbonded webs per kg of cellulose can be 0.1 kg / kg to 10 kg / kg in the laundry area and 0 to 4 kg / kg in the area after drying.

The ejected spunbonded nonwoven is used via the ejection device 14

Crushing device 15 out. The comminution device 15 can, for example, be a mill, preferably a cutting mill, which can comminute 10 to 5000 kg / h, preferably 100 to 2000 kg / h, even more preferably 200 to 1000 kg / h of spunbonded nonwoven. The comminuted spunbonded nonwoven pieces are in the range from 10 μm to 100 mm in length, preferably 0.1 mm to 50 mm, even more preferably 1 mm to 10 mm in length. Depending on the strength and the desired degree of comminution of the spunbonded nonwoven, other comminution devices known to the person skilled in the art can also be used.

The comminuted spunbond pieces are mixed with liquid 17 in the suspension container 16 and blended to form a transportable suspension. The suspension container 16 can have a stirrer in order to increase the homogeneity of the suspension. In a

The suspension container can also be heated in order to achieve the

To improve the water absorption of the cellulose and to increase the swelling.

The liquid 17 used for the suspension can be fully demineralized water or a solution of the solvent and water used for the production of the spinning mass. In the case of the production of spunbonded nonwovens from Lyocell spinning mass, the liquid 17 for the suspension can have between 0 and 85% NMMO, preferably 10 to 80% NMMO, even more preferably between 20 and 78% NMMO. The suspension produced has between 1 to 95%, preferably 2 to 50%, even more preferably 3 to 30% cellulose content. Since the suspensions produced are either pumped for solvent recovery, or as an additive to the production of spinning pulp, and the viscosity of the suspension is greatly reduced

Cellulose content and the type of solvent depends on the cellulose content and the concentration of the solvent depending on the position of the discharge device (moisture content of the spunbonded nonwoven at this point) and the use of the suspension. It has been shown that the cellulose content of the suspension should preferably be below 20% if the suspension is transported to NMMO recovery, since later purification steps, the solid / liquid separation and subsequently the NMMO evaporation in the NMMO that is already present -Preparation cycles of the Fyocell process can be carried out better. If the suspension is to be used again for the production of spinning mass, higher cellulose contents> 20% are advantageous, since the cellulose content can be better adjusted in the later spinning mass.

2 shows that the viscosity of the spinning mass deviates only slightly from the viscosity of a spinning mass made of fresh cellulose, despite the renewed comminution and loosening of the spunbonded nonwoven (measurement using a Kinexus rheometer, from Malvem measuring system CP4 / 40, oscillation measurement at 100 ° C. with 0.004 and 30Hz, evaluation with rSpace for Kinexus, both samples measured with the same pulp and moisture content). With the method according to the invention, spunbonded nonwovens that have already been produced and sluiced out can be reused. Thus, for example, Fyocell spinning masses with 4 to 17% pulp content can be produced from 100%, preferably 1 to 50%, even more preferably 2 to 30% reused cellulose from recovered spunbonded nonwoven.

EXPECTATIONS

1. Plant (1) for the production of spunbond (8), comprising

• a spinning solution production (3),

• a spinning system (2),

• a device (6) for dispensing coagulation liquid,

• At least one conveyor device (7, 9) for depositing the spunbonded nonwoven (8) and

• a collecting device (13) for the spunbonded nonwoven (8),

characterized in that at least one discharge device (14) is provided between the device (6) for dispensing coagulation liquid and the collecting device (13) for the spunbonded nonwoven (8).

2. Plant according to claim 1, characterized in that the at least one

The discharge device (14) is conductively connected to the spinning solution production (3).

3. Plant according to claim 1 or claim 2, characterized in that the at least one discharge device (14) is provided on the conveying device (7, 9) in the region of the deposit of the spunbonded nonwoven (8).

4. Plant according to one of claims 1 to 3, characterized by a

Drying device (12), the at least one discharge device (14) being provided between the conveying device (7, 9) and the drying device (12).

5. Plant according to one of claims 1 to 4, characterized by a

Drying device (12) and a collecting device (13), the at least one discharge device (14) being provided between drying device (12) and collecting device (13).

6. Plant according to one of claims 1 to 5, characterized in that the

The conveyor device (7, 9) is in several parts and the at least one discharge device (14) is provided between two parts of the conveyor device (7, 9).

7. Plant according to claim 6, characterized in that part of the conveying device (7, 9) has a washing device (10), the at least one discharge device (14) being provided in front of the washing device (10).

8. Plant according to claim 6 or claim 7, characterized in that part of the

Conveying device (7, 9) has a washing device (10), wherein after the

Washing device (10) which has at least one discharge device (14).

9. Plant according to one of claims 1 to 8, characterized by a shredding device (15), wherein the input of the shredding device (15) is connected to the at least one discharge device (14).

10. Plant according to claim 9, characterized in that the output of the comminuting device (15) is connected to the spinning solution production (3).

11. Plant according to one of claims 8 to 10, characterized in that a suspension container (16) is provided between the comminuting device (15) and the spinning solution production (3).

12. A method for recovering solvent or cellulose in a plant (1) for the production of spunbonded nonwoven (8), wherein spunbond filaments (5) are extruded from a spinning system (2), laid down in a stretched manner to form a spunbonded nonwoven (8) and later collected, characterized in that when the system (1) is started up, when the system (1) is switched off or in the event of operational problems with the system (1), the spunbonded nonwoven (8) is discharged prior to collection, with (a) the solvent from the discharged spunbonded nonwoven (8) is withdrawn and / or wherein (b) the discharged spunbonded nonwoven (8) is fed to the spinning solution production (3).

13. The method according to claim 12, characterized in that the discharged spunbond (8) is comminuted before it is fed to the spinning solution production (3).

14. The method according to claim 12 or claim 13, characterized in that the discharged spunbond (8) is mixed with solvent before it is fed to the spinning solution production (3).