EP0807698B1 - Process and apparatus for the preparation of fibrets from cellulose derivatives - Google Patents

Description

The invention relates to a method for producing fibrets according to the Preamble of claim 1 and a device according to the Preamble of claim 21.

Fibrets are understood in the following as very fine fibers, which are characterized by very fine fiber diameters and thus by a very high mass-specific surface. Fibrets are typically produced by means of a precipitation process or by extrusion, in which case precipitation is usually integrated as a sub-process. Fibrets are partly present in the fiber composite or fiber network as a result of the production: the diameters of the individual fibers are generally less than 5 μm, mostly less than 1 μm. The dimensions of the fiber networks, which are referred to as agglomerates and which can be varied over a wide range by the conditions during production and by further processing steps, are up to 1 mm. However, agglomerate sizes of less than 200 µm are aimed for. With the dimensions mentioned, mass-specific surfaces of over 20 m ² / g are achieved.

The fibrets are mainly used in depth filters Liquid filtration is provided, these filters also used to detect the achieved quality of the fibrets can be used. For the optimal operation of Depth filtering is critical, small pore sizes with high porosity to realize. In terms of filtration technology, this results in high separation achieved low differential pressures. Embedding the fibrets in Fiber networks have cut short of particulate material Staple fibers also have the advantage that the fibers in the filter are very firm are involved and thus detachments as far as possible during the filtration can be excluded. The fiber structure in the agglomerate composite gives the filters a high strength with flexibility, what pleating is an advantage.

The use of fibrets is not on depth filters for liquid filtration limited. In nonwovens for air filtration, fibrets can, for example Replace glass fibers, their harmful effects when entering the Lung is known. Because the very large surface area of most polymers due to an intense white coloring, fibrets can be used as optical brighteners used in the paper industry. Small amounts remaining Solvents can cause the fibers to fuse during the process Carry out drying so that e.g. the strength is essential in nonwovens can be increased. Due to the large specific surface, the Fibrets can be largely accessible to a medium flowing through advantageous for adsorption processes, including the Chromatography processes can be used. This effect can be achieved through the Introduction of surface-active substances or by a chemical Modification of the starting material before the fibret production or in subsequent production process are supported.

Fibrets can generally be made from a variety of materials. The only limits are set by the solvent and the viscosity of the solution. As a result of their advantages in the choice of the solvent, fibrets made of cellulose esters, in particular cellulose acetate, with mass-specific surfaces over 20 m ² / g have mainly been presented in the literature. For use in depth filters for liquid filtration, fibrets made of cellulose acetate also have the advantage that, together with the pulp pulp that is used anyway, extensive material homogeneity is achieved. This ensures problem-free disposal. Compared to the currently preferred diatomaceous earth, perlites and / or metal oxides, the advantages of the very low ion emission and the complete biodegradability must be emphasized.

The production of fibrets from cellulose esters with solvents is basically e.g. from US 3,342,921, US 3,441,473, US 3,785,918, US 3,842,007, US 3,961,007, US 4,040,856, US 4,047,862, US 4,192,838, US 5,071,599 and US 5,175,276 known. Usually a solution (Dope) from a cellulose ester and a suitable solvent manufactured. The non-solvent for the cellulose ester that comes with the Solvents that are completely miscible can be present in such proportions be that the dissolving behavior of the cellulose ester in the solvent is not significantly affect. This solution is mostly under the influence of Shear forces in a non-solvent or precipitant for the Cellulose ester precipitated, which is completely miscible with the solvent.

For the precipitation process, single-component nozzle systems, stirring systems, Two-component nozzle systems and T-pipe systems used.

In single-substance nozzle systems, such as those in US 3,441,473 and US 4,040,856 will be described, the dope above the precipitation bath sprayed, so that an at least partially spontaneous evaporation of the Solvent is used. The one required to create fibrets Shear is the spontaneous change in state, such as Volume expansion, evaporation of the solvent and drop in temperature, on Nozzle outlet achieved. However, it was found that this process variant did not the required fiber fineness and homogeneity could be achieved. The Fiber diameters are predominantly above 1 µm.

Gew.-%) nach der Fällung daher nicht überschritten werden können. Da die Turbulenzen in steigendem Maße vom Feststoffgehalt abhängig sind, besitzt die Rühranordnung ein schlechtes Teillastverhalten. Ferner wird die Austrittsgeschwindigkeit des Dope aufgrund der Zentrifugalkräfte beeinflußt, weil die Extrusionsdüsen in der rotierenden Scheibe angeordnet sind. Die Fällbedingungen werden dadurch ebenfalls beeinträchtigt.Stirring systems, as described in US Pat. No. 4,047,862, have a rotating disc with radial extrusion openings through which the dope is introduced into the precipitation bath against a spaced, stationary peripheral wall. The dope emerges from the nozzles at a certain speed and is only slowed down on its way. Such systems have the disadvantage that the setting of a defined shear field is difficult. On the one hand, the shear gap must be chosen to be small in order to ensure an intensive shear field. On the other hand, at shorter distances there is a risk of the extrusion nozzles becoming blocked, which can only be prevented by a higher flow rate of the precipitant perpendicular to the shear field. Larger distances in turn cause the shear gradient to be too low. Furthermore, the fibrets produced dampen the turbulence to a great extent, since the distance between the extrusion opening and the wall of 1.6 mm is only insignificantly larger than the maximum agglomerate size of 1 mm, so that solids contents exceeding 1% by mass (

% By weight) cannot therefore be exceeded after the precipitation. Since the turbulence is increasingly dependent on the solids content, the stirring arrangement has poor part-load behavior. Furthermore, the exit velocity of the dope is influenced by the centrifugal forces because the extrusion nozzles are arranged in the rotating disk. This also affects the precipitation conditions.

Two-component nozzle systems, such as those in US 4,192,838, US 5,071,599 and U.S. 5,175,276 and the T-pipe systems described e.g. in the US 3,961,007, implement a similar principle. The Precipitation occurs with regard to the flow directions of dope and precipitation medium with two-component nozzles in direct current, with T-pipe systems in contrast in Countercurrent realized. With the two-component nozzles, the Nozzle diameters - usually> 2.5 mm - are designed to be as large as one Avoid solution failure at the nozzle opening. The Nozzle diameter is 20,000 times larger than the required Fiber diameter. Even with a turbulent flow of the precipitation medium in The narrowing of the valve nozzle creates turbulence and Concentration gradients, in addition to fine fibers, the formation of larger ones Condition fibers. This is all the more observable the higher the Solids content after precipitation. Solids contents over 1% by mass can Guarantee of the required fiber fineness must not be exceeded.

The countercurrent process in the T-pipe systems is regarding Vortex formation and thus the shear field formation is the more effective variant. However, the precipitation bath flow is braked very strongly, so that the Precipitation conditions vary widely. In addition to very fine fibers, the meet the aforementioned requirements is the formation of coarser fibers, especially with solids contents after the precipitation of approx. 1 Ma%, not too avoid. These dimensions can be worked up by following the steps In contrast to the agglomerate size, precipitation is only slightly influenced become. The partial load and clogging behavior of the counterflow variant is also to be rated negatively.

A disadvantage of the known manufacturing process is that large quantities Solvents must be circulated. For example in US 5,071,599 and US 5,175,276 for the production of 1 kg Fibrets called 8 kg of solvent, e.g. acetone. In the US 3,842,007 and US 3,961,007 are for example for 1 kg of fibrets between 20 and 80 kg or 33 kg of solvent, such as acetone, 1,4-dioxane or methyl acetate is required.

Since the fibrets have to be provided solvent-free or low in solvents for most applications, a process for separating the solvent from the fibrets is required. First of all, there is a filtration, in which a solution of solvent and non-solvent for the cellulose ester is separated from the fibrets. Because of the very large surface of the fibrets, a very porous filter cake with a low solids content is created. A maximum solids content of approximately 12% by mass is usually achieved for fibrets with a specific surface area> 20 m ² / g at a filtration differential pressure of up to 1 bar. At pressures above 1 bar or in a centrifugal force field, the solids content is up to 20% by mass. The amount of solvent remaining in the fibrets is too high for further processing in most applications. In addition, the fibret surface is not fully hardened due to the solvent contained in the solution. The network structure is partially lost when pressure is applied, which leads to clumping at high pressures. For this reason, it is usually filtered under the action of shear forces, with solids contents of at most 4% by mass being achieved with specific surfaces of over 20 m ² / g. In the most favorable case of 8 kg of solvent for 1 kg of fibrets, after filtration, fibrets to solvent are in a ratio of about 1: 1, otherwise the solvent predominates.

For the reasons mentioned, a washing process that partly also can be multi-stage, the filtration, such as in the US 3,961,007. In the course of these processes, the However, the concentration of the solvent in the filtrate is very low. A minor one Concentration of the solvent and the large amounts to be processed Solution, however, the cost of working up the solution is exponential increase. The workup is necessary because the solvent for economic design of the overall process and for the sake of Environmental protection returned to the process of fibrin production should be. Otherwise, the cost would have to be at least eight times The amount of solvent is fully allocated to the fibret costs and disposal costs would also be incurred. High volumes solution to be worked up with low concentration of the to be obtained Solvent processing costs can also rise sharply. The The process of fibrin production is therefore in most cases for both Applications economically uninteresting.

In addition, filtration to remove the solvent from the fibrets are not sufficient in most cases. After the precipitation is in Material of the fibrets still contain solvents, which by diffusion into the Liquid arrives and can be separated from there. Therefore, often Distillation used to remove acetone. The cost of this distillation are strong on the concentration of solvents and the volume of Fibret suspension dependent. Both sizes are also reflected in the Distillation volume and in the concentration of the solvent in the distillate down, which affects the cost of working up the distillate become. Again, these costs decide economic ones Possible uses of fibrets in subsequent products.

A device for producing fibrils is known from US Pat. No. 4,237,081 Known olefins, which works on the rotor-stator principle. The polymer solution is heated to temperatures above 100 ° C and central to the dispersion device fed. The fiber is produced by cooling the polymer solution in a shear field, for which a coolant is off-center at several points between is fed to the sprockets.

The object of the invention is a method and an apparatus to provide an economical production of the fibrets Cellulose derivatives with better quality allowed.

This task is accomplished with a method according to the characteristics of the Claim 1 solved. The device is the subject of claim 21.

The invention is based on the knowledge that a workup of the Fibrets separated components of the precipitation bath only make sense and is economical if the precipitating agent used for the precipitation bath is one may have the highest possible proportion of solvent and if one at the same time, the separated solvent fraction allows for the batch of the dope is reused, still have a non-solvent content can. The more "impure" the individual components are after processing allowed, the less effort. Contamination of the Solvent through the non-solvent and vice versa, has its place there Limit where the dope prepared with the treated solvent no longer applies is processable. On the one hand, too high a proportion of non-solvent can a premature precipitation and on the other hand too high a viscosity of the Lead dope.

It has been found that the precipitation in a conventional Dispersing device can be carried out according to the rotor / stator principle, if dope and precipitant are fed centrally into the dispersing device become. Such dispersing devices are e.g. from the company Ystral under the name "dispersing machine" and from the company IKA Mechanical engineering sold under the name "Dispax-Reaktor". This Devices usually contain two to six shaving rims, which are preferred alternately designed as stators and rotors. Reach the rotors Speeds up to 12000 revolutions per minute, so that in the precipitation bath Base flow speeds of up to preferably 100 m / sec can be achieved can. These known dispersing devices with their high Peripheral speeds are usually used for emulsification, Suspension, homogenization and dissolution of dispersion used. Even though also the use of discontinuous dispersion systems in the context of the invention is possible, the advantages of the continuous dispersion systems lie in the secure guarantee of uniform product quality.

Since the suspension formed from dope and precipitant at least in the shear field accelerated once, preferably at least twice alternately and is delayed, there is a high medium degree of turbulence over a long distance maintained so that a high viscosity dope can be processed. The suspension is alternately preferably a radial and Subject to cross flow.

The dope is preferably introduced into the precipitant through stationary nozzles initiated, in front of their outlet openings means for generating a flow be moved past.

When going through several acceleration and deceleration fields the dope emerging from the nozzles is detected and drawn off very quickly, so that No nozzle clogging can occur even at higher viscosities. Further become the fibrets by alternating acceleration and deceleration already largely homogenized, so that possibly on a downstream Homogenization treatment can be dispensed with. This is obvious to be attributed to the fact that over a long distance a high medium Turbulence can be maintained throughout Residence time in the dispersing device, which is usually between 0.03 and 0.5 sec. The turbulence itself is caused by the fibrets that form only slightly damped because of the turbulence caused by rotating machine parts generated and not by a turbulent flowing medium. this has the further advantage that the partial load behavior of the entire arrangement is very great good is. This means that in large areas the fibret quality from Total throughput of the precipitation bath and dope and their ratio is independent of each other.

The dope is preferably prepared with cellulose esters or cellulose ethers. Preferred are cellulose diacetate, cellulose triacetate, cellulose acetate butyrate, Cellulose acetate propionate, benzyl cellulose or ethyl cellulose and others suitable cellulose derivatives or mixtures of these materials. Prefers a cellulose diacetate with an acetyl value between 54 and 56% used. The proportion of cellulose derivatives in the dope is preferably 3 - 20% by mass. Lower concentrations are usually not economically attractive, larger proportions result in too high a viscosity. Depending on the proportion of Cellulose derivatives in the dope also have to be adjusted to the solvent content. Acetone can be used as the solvent. Acetic acid, methyl acetate, methyl ethyl ketone, 1,4-dioxane, acetaldehyde. Ethyl acetate, tetrahydrofuran or methyl isopropyl ketone or mixtures of the solvents mentioned become. The solvent acetone is particularly preferred.

Since it is only possible with great effort, completely from the precipitation bath remove pure solvent, which in turn is used to attach the dope to be used, it is from an economic point of view desirable if the solvent still contains non-solvents may be the main component of the precipitation bath.

Water, ethanol or are non-solvents for the cellulose ester Methanol preferred, the proportion of which in the dope can be up to 40% by mass.

The maximum non-solvent content based on the ratio Solvent for cellulose derivative depends on the precipitation point. The The higher the non-solvent content, the faster the precipitation point is reached is in the dope. The maximum salary is determined by the Precipitation point, which among other things is temperature-dependent. A is preferred Non-solvent content of 2 - 20% by mass below the concentration of the non-solvent at the respective precipitation point. In contrast to are in US 5,071,599 and US 5,175,276, the two-fluid nozzle systems describe, only up to 20% by weight of non-solvent permitted in the dope, see above that this proportion in the system cellulose acetate, acetone and water between 8.5% and 21% below the precipitation point.

Regardless of the setting of the dope near the precipitation point should also the ratio of solvent to cellulose derivative can be minimized. After this State of the art, as is known from US 4,192,838, US 5,071,599 and US 5,175,276 is known, the ratio can be a minimum of 4.4. lower Conditions usually cause the viscosity of the dope to be too high in the known methods have a negative effect on the fibret fineness. triggers for example, cellulose diacetate in acetone in a mass ratio of 1: 3, you get a gel-like consistency. The viscosity can, however can be reduced by adding water as a non-solvent. In In this regard, it is desirable to add water to just below to realize the precipitation point. However, this behavior is only at high Maintained cellulose derivative in dope and / or in low ratios Solvent: cellulose derivative observed. At low levels Cellulose esters in dope, as is the case, for example, in US Pat. No. 4,192,838, US 5,071,599 and US 5,175 276 the case, water acts because of the low viscosity of acetone mostly increases viscosity.

The prior art methods are for the production of fibrets with an acetone: water mass ratio of, for example, 2.8 and one Non-solvent content up to 2% by mass below the precipitation point in Dope unable. The viscosity is still despite the addition of water too high. As a result of the very high turbulence according to the invention The main advantage of the process is that higher viscosities of the Dopes can be processed with satisfactory results.

Since higher-viscosity dopes can be processed, conditions can Solvent: cellulose derivative between 4.4: 1 and 2.8: 1 realized without the quality of the fibrets deteriorating. Particularly good ones Results were achieved when the solvent was acetone, as Cellulose ester cellulose diacetate and water used as non-solvent were. A decrease in the acetone: cellulose diacetate ratio of 4.4: 1 to 2.8: 1 means that for the production of a given Amount of fibrets 36 Ma% less solvent must be used, which significantly reduces the manufacturing costs of fibrets.

The temperature of the dope is largely uncritical for the process. It good results have been obtained at room temperature. To reduce the Viscosity of the solution can be chosen up to a higher temperature for precipitation at overpressure and temperatures above 100 ° C. is preferred however, the ambient temperature as the most economical option.

The two or three components of the dope will be used appropriately mixed until a homogeneous solution is obtained. This solution is then fed to the dispersing device via a filter.

The volume flow of the precipitant in the precipitation bath is preferably so set that the fibret content in the precipitation bath is between 0.1 and 2.5% by mass. Differences in fibret quality could not be found even with a high proportion of fibret be determined. At concentrations between 2.5 and 3.5% by mass Another precipitation without clogging of the extrusion nozzles is realized however, accept compromises in fibret fineness and fibrethomogeneity. A range of 1-2.5% by mass is preferred for economic reasons. The method according to the invention is thus significantly better than the methods according to the state of the art, according to which the precipitation occurs only at concentrations between 0.1 and 1% by mass are possible. The meaning of this change is therefore essential, because with a precipitation of 2.5 Ma% compared to a precipitation of 1% by mass only 40% of the suspension amount is obtained. Among other things, this means that the plant can be designed 60% smaller, which is corresponding Investment cost savings. In the further course are then separate 60% less water / acetone solution from the fibrets and work up, which in turn saves on energy costs brings. Furthermore, a process of filtration following the precipitation before the complete solvent removal is preferably omitted. This has the Advantage that the filtration before complete Solvent separation damage to the morphology of the fibrets is avoided because the structure of the fibrets due to the still existing Solvent is not completely fixed.

The methods according to the prior art have to be used in particular for higher ones Viscosity of the dope with a large excess of the precipitation medium work against the dope to create sufficient turbulence. With the two-component nozzle systems according to US 4,192,838 and US 5,071,599 and US 5,175,276 is a minimum ratio of precipitation bath: dope of 11: 1 been realized. The method according to the invention allows production of fibrets at precipitation bath conditions: dope from 10: 1 to 2.5: 1. this has The following advantages: The concentration of the cellulose derivative in the dope can be chosen small. This can lead to lower viscosities preferably be useful if fibrets are not out of the system Cellulose diacetate - acetone - water are to be produced. Are in the dope Containing 5% by mass of the cellulose ester, there is one after the precipitation Mass ratio of precipitation bath: dope of 2.5: 1, the suspension of 1.43% by mass Fibrets. The advantages of high fibret concentrations are also with potentially high dope viscosities can be used. Furthermore, fluctuations affect in the volume flows of precipitation bath and / or dope in wide areas not the fibret quality and the partial load behavior are excellent. The cause of these advantages lie in the fact that the sizes are largely decoupled Volume flow and turbulence.

Finally, another advantage of the process is that in the precipitation bath higher solvent concentrations than according to the prior art can be present. According to US 5,071,599, the acetone content for the System acetone-cellulose diacetate-water in the precipitation bath maximum 15% be. Above this value, that in the suspension leads Acetone causes the fiber to solidify over a long period of time extends. The surfaces of the fibrets that have not yet completely solidified can glue and form lumps without a porous fibret structure. When using the inventive method, however, the shear is high enough to to separate such lumps until the fibers have completely solidified. The longer solidification times of the fibrets also contribute to finer fibrillation and associated with a higher surface area because during the entire solidification time attack shear forces affecting the fibrillation intensify. For example with the system cellulose diacetate - water - acetone Acetone levels of up to 25% by mass are possible in the precipitation bath.

Higher concentrations of solvent in the dope are with respect to the others Refurbishment cheap. The higher the solvent content in the suspension, what is meant by the precipitation bath after the precipitation, the higher it is in the distillate (separated solvent plus residual non-solvent), see above that correspondingly fewer work-up stages of the distillate are necessary. This procedure has disadvantages with regard to explosion protection not, because in practically all variants the lower explosion limit of 2.5 vol .-% Acetone is exceeded for an economical design of the process.

The device for producing the fibrets provides that the feed line for the precipitant opens centrally into the dispersing device, and that the Feed line for the dope at least one nozzle within the Has dispersing device.

Precipitation bath and dope are used to achieve the precipitation in the Dispersing device combined. The precipitation bath flows, as from Homogenisierund Dispersing tasks is known through the dispersing machine. The The feed line for the precipitant preferably encloses the feed line for the dope.

The nozzle is preferably radially outward on the innermost ring gear aligned. In a preferred embodiment, this is in the direction of flow of the precipitation bath first Spider part of the rotor, followed by a spider of a stator, etc. The distance between the ring gear and the nozzle is small to choose the actual one Precipitation in the zone of the shear field to be carried out by the before Nozzle opening as teeth are generated. The distance can be between 0.01 and 5 mm, preferably 0.01-0.1 mm. It is also possible with the first ring gear in the direction of flow of the precipitation bath Equip nozzles for adding the dope.

The nozzle diameter can be selected in large ranges because of these parameters has little influence on the quality of the fibrets in the intended area. A nozzle diameter between 5 and 10 mm is preferred. lower However, nozzle diameters are possible. Because during the use of the Disperser no clogging of the nozzles occur, is also the Use of larger nozzles, although possible from the point of view of fibret quality, is not required. With low volume flow ratios of Precipitant to dope or with a high total volume flow is Distribution of the dope flow over several nozzles makes sense. Are preferred these nozzles are arranged symmetrically within the innermost ring gear. If, for example, three nozzles are provided, they are star-shaped arranged. The supply line to the nozzles is in this case preferably in the center of the dispersing device. To at all nozzles to find the same conditions with regard to the flow of the precipitation bath the precipitant is also introduced centrally into the dispersing device. This is ensured by the fact that the feed line of the precipitant preferably encloses the supply line of the dope.

It is generally believed that the formation of fibrets after initiation of the dope into the precipitation bath takes place very quickly. The time of origin is in the Order of magnitude of 0.001 - 0.5 sec. Then the fibret morphology be fixed. However, it is believed that when the Fibrets first forms an outer shell, because on the concentration bales in the Scherfeld in the outside areas first of all the necessary for the precipitation Concentration of non-solvent is reached. Through this bowl must the solvent to the outside and / or the non-solvent to the inside diffuse. One more time passes until the core hardens Time that is greater than the specified precipitation time. Because the outer Morphology has already developed in this period, the fibers act despite the soft inner core in the process according to the prior art in to such an extent that it prevents turbulence from breaking up is more possible. By using a disperser it is possible by means of the high shear effect applied by the rotors To split fibers with a soft inner core and therefore the fineness of the fibrets to increase.

The dispersing device according to the invention also has a positive effect regarding the agglomerate size of the fibrets. Depending on the choice of rotor-stator geometries and the rotor speed can also Agglomerate sizes up to 1 mm can be achieved. However, are preferred such arrangements and speeds, the agglomerate sizes below 200 microns result. These dimensions are achieved in that End area of the shear field in contrast to the arrangements according to the state the technology still have sufficient shear forces available, the size of the Can minimize fibra agglomerates.

• Es werden stärkere Scherkräfte erzeugt, weil höhere Differenzen der Grundströmungsgeschwindigkeiten auf engem Raum abgebaut werden. Dadurch wird eine feinere Fibrillierung der Fibrets erreicht, wobei größere Viskositäten des Dopes verarbeitbar sind.
• Es steht ein größerer Scherraum als beim Stand der Technik zur Verfügung, in dem der Auf- und Abbau der Grundströmungsgeschwindigkeiten mehrmals erfolgt. Dadurch wird ebenfalls eine feinere Fibrillierung der Fibrets erzielt, das Teillastverhalten ist besser und die Feinheiten in der Wahl der Prozeßparameter werden größer.
• Im Scherraum gilt das Prinzip der Zwangsförderung, so daß ein Ausweichen von Teilströmungen in Zonen geringer Turbulenz nicht möglich ist.

The device according to the invention also has the following advantages:

• Stronger shear forces are generated because higher differences in the basic flow velocities are reduced in a small space. This results in a finer fibrillation of the fibrets, whereby larger viscosities of the dope can be processed.
• A larger shear space is available than in the prior art, in which the basic flow velocities are built up and down several times. This also results in a finer fibrillation of the fibrets, the part-load behavior is better and the finer points in the choice of process parameters become larger.
• The principle of forced delivery applies in the shear chamber, so that it is not possible to avoid partial flows in zones of low turbulence.

Exemplary embodiments are described below with reference to the drawings explained.

Figur 1

eine schematische Darstellung der gesamten Anlage zur Herstellung von Fibrets,

Figur 2

einen vertikalen Schnitt durch eine Dispergiereinrichtung und

Figur 3

einen Schnitt längs der Linie III-III durch die in Figur 2 gezeigte Dispergiereinrichtung,

Figur 4

eine graphische Darstellung des Turbulenzgrades in Abhängigkeit vom Düsenabstand und

Figur 5

eine graphische Darstellung der Wasserkonzentration von der CA-Konzentration.

Show it:

Figure 1

a schematic representation of the entire plant for the production of fibrets,

Figure 2

a vertical section through a dispersing device and

Figure 3

3 shows a section along the line III-III through the dispersing device shown in FIG. 2,

Figure 4

a graphic representation of the degree of turbulence depending on the nozzle distance and

Figure 5

a graphical representation of the water concentration from the CA concentration.

FIG. 1 shows the plant for the production of fibrets. The Raw material, for example cellulose diacetate, is fed via the feed line 1 a dope preparation tank 2 supplied to the solvent via line 31 is fed from the processing plant 26. Via a double line 3 the dope fed to a disperser 40 where the precipitation is carried out. The precipitant is in a precipitation bath 8 set in the non-solvent 26 via line 27 from the processing plant, preferably water is supplied. Over a Precipitation bath feed line 9, the precipitant used in the Disperser 40 initiated where the precipitant with the dope is merged. This is explained in connection with FIG. 2 become.

The precipitation bath suspension with the fibrets produced is transferred via the Precipitation bath drain 13 fed to the distillation plant 12. Over a Steam feed line 15 is fed to the distillation plant 12, and via the solvent return line 17 becomes the separated solvent first fed to the treatment plant 26 via a heat exchanger 16, where the treatment of the solvent takes place in such a way that it afterwards can be used again in the dope preparation tank 2 or the precipitation bath preparation tank 8 can.

After the solvent has been removed, the fibrets are over the The discharge line 19 is fed to a high-pressure homogenizer 20. From there the fibrets pass into a stacking tank 22 and further into a drum filter 24, where the fibrets are concentrated to the desired final concentration, the precipitation bath also via the return line 25 Processing plant 26 is supplied. The fibrets prepared in this way are fed to further processing via the fibreta lead 23. Of the Processing plant 26 becomes the treated solvent, the one can contain a certain proportion of non-solvent and the non-solvent, which in turn can contain a portion of solvent the lines 27 and 31 introduced into the tanks 2 and 8.

In Figure 2, the dispersing device 40 is shown in vertical section. About the curved feed line 9, the precipitant is in the interior of the Dispersing device 40 supplied. The double line 3 is located within the feed line 9 and is enclosed by this, so that both the Dope and the precipitant centrally into the dispersing device 40 can be initiated. The branches out within the housing 41 Double line 3 and passes into the nozzles 46 and 47, which together with the Nozzles 48 and 49, which is shown in Figure 3, arranged in a star shape are. The nozzles extend radially outwards and end in a short distance in front of the innermost ring gear 50, which is part of the rotor 44 is. This rotor 44 is driven by a drive shaft 65, which is extends down from the housing 41 and by a motor (not shown) is driven. The seal to the housing 41 takes place via a mechanical seal 64. The rotor 44, which has a base plate 10, comprises, in addition to the first ring gear 50, at a distance from it another one Sprocket (third sprocket) 52. Between the two sprockets 50 and 52 is the second ring gear 51, which belongs to the stator 43. The Stator 43, which has an annular base plate 11, is above the Nozzles 46-49 arranged so that the second ring gear 51 is down extends, and is attached to the housing 41. Below the rotor is a Another stator 45 is arranged, the outer or fourth ring gear 53rd having.

Since the precipitation bath feed line 9 is sealed against the stator 43, this becomes Precipitant fed centrally and flows around the nozzles 46 to 49. The dope, which is fed through the double line 3, exits in the radial direction Nozzles 46 to 49 out and into the shear field. that is through the sprockets 50 - 53 extends into the outer region 14. Dope and precipitant will be first gripped by the ring gear 50 and accelerated. Due to the radial flow direction of dope and precipitant, which the Cross flow is superimposed. leaves the dope or the nascent Fibrets located through the gaps 54 between the teeth 55 of the first Sprocket 50 in the radial direction, the zone 60, where dope and Precipitating agents are delayed. Then the liquid gets into a another zone 61 between the ring gear 50 and the ring gear 51, where the Fluid is accelerated again. This ring gear 51 is because it is for Stator heard, fixed. The fibrets arrive on the way successively into the further zones 62 and 63 between the gear rings 51 and 52 or 52 and 53, where again accelerations and decelerations alternate. After leaving the fourth ring gear 53, the fibrets together with the precipitation bath in the form of a suspension the discharge pipe 13 discharged. With this device, fibrets prepared, which are described in the following examples.

The course of the average degree of turbulence of the Dope / precipitant mixture depending on the distance from the nozzle according to the prior art (US 4,047,862 - curve I) and according to Invention (curve II) shown. A must for the production of fibrets minimum degree of turbulence exceeded by the straight line III is marked. Below curve III is the turbulence for the precipitation too low, so that the desired fineness of the fibrets is not achieved.

Curve I describes the degree of turbulence between the rotating nozzles and the fixed wall, which is only 0.1875 inch (= 4.7625 mm), but ultimately for the production of fibres less than this route is available. The one for fibrin production required degree of turbulence is reached just behind the nozzles, and falls then exponentially, so that only a relatively short distance for the Fibrin production is available.

In contrast, the shear field according to the invention extends at one Dispersing device according to Figures 2 and 3 over about 14 mm (distance Sprocket 50 to sprocket 53), the after the exit from the nozzle the minimum degree of turbulence required for fibrin production is exceeded and remains constant. Curve II only falls when the outside area is reached (see Figure 2) 14 steeply. While according to US 4,047,863 Circumferential speeds of approx. 30 m / sec Rotation speed of the rotor of the dispersing device in this Example at 41 m / sec.

Example 1:

480 g of a cellulose diacetate (CA) from Eastman Chemical Company (type CA 398-3) are dissolved in 3840 g of acetone and 480 g of water. The resulting dope thus contains 10 Ma% CA, 10 Ma% water and 80 Ma% acetone. The ratio of acetone to water is 8. The dope is passed into the precipitation bath at ambient temperature with a mass flow of 3 kg / min through a four-jet nozzle, each with a diameter of 5 mm and the ends of which are 0.10 mm from the inner rotor directed. Water is also used as the precipitation medium at ambient temperature and enters the precipitation chamber with a mass flow of 34.5 kg / min. The mass flows of precipitation bath and dope are in a ratio of 11.5 to 1. The dispersing machine is equipped with four sprockets of the "fine" specification (see Table 1). The precipitation takes place at a speed of 12,000 min ^-1 . After the precipitation, CA fibrets are present with a concentration of 0.8% by mass. Acetone is 6.5% by weight. The values mentioned and the values for the following tests are compared in Table 2. The acetone is removed by open distillation at ambient pressure. After the acetone has been removed, the fibrets are homogenized in one stage using a high-pressure homogenizer from APV GAULIN, type LAB 60, at a pressure of 150 bar. The fibrets are concentrated with a suction filter for storage. A filter cake with a solids concentration of 8.6% by mass is formed.

In terms of concentrations, this variant is in the range of the Technology, only the precipitation was carried out with the dispersing machine according to the Invention was carried out and the filtration was carried out after the precipitation waived.

Example 2:

Daten für Ausführungsbeispiele Parameter Beispiel 1 2 3 4 5 6 7 8 9 10 Dopezusammensetzung in g CA 480 480 480 480 480 480 480 480 480 480 Aceton 3840 3840 3840 3840 2400 1680 2400 2400 2400 1680 Wasser 480 480 480 480 550 510 550 550 550 840 Dopezusammensetzung in % CA 10 10 10 10 14 18 14 14 14 16 Aceton 80 80 80 80 70 63 70 70 70 56 Wasser 10 10 10 10 16 19 16 16 16 28 Verhältnis Aceton : CA 8 8 8 8 5 3,5 5 5 5 3,5 Fällbadzusammensetzung in % Wasser 100 100 100 100 100 100 95 90 85 95 Aceton 0 0 0 0 0 0 5 10 15 5 Massenströme in kg/min Dope 3,0 3,0 3,00 3,0 3,0 3,0 3,0 3,0 3,0 3,0 Fällbad 34,5 22,0 15,75 12,0 21,7 29,7 21,9 21,6 21,7 29,1 Massenstromverhältnis Fällbad zu Dope 11,5 7,3 5,25 4,0 7,2 9,9 7,3 7,2 7,2 9,7 Suspensionzusammensetzung in % CA 0,8 1,2 1,6 2,0 1,7 1,65 1,7 1,7 1,7 1,5 Aceton 6,4 9,6 12,8 16,0 8,5 5,80 12,8 17,3 21,7 9,8 Wasser 92,8 89,2 85,6 82,0 89,8 92,55 85,5 81,0 76,6 88,7 The experiment was carried out analogously to experiment 1, except that the precipitation bath mass flow was reduced to 22 kg / min. There was a ratio of the mass flows of precipitation bath to dope of 7.3 and a concentration of the fibrets after precipitation of 1.2 mass% (at 9.6 mass% acetone). High-pressure homogenization was dispensed with.

Data for exemplary embodiments parameter example 1 2 3 4 5 6 7 8th 9 10 Dope composition in g CA 480 480 480 480 480 480 480 480 480 480 acetone 3840 3840 3840 3840 2400 1680 2400 2400 2400 1680 water 480 480 480 480 550 510 550 550 550 840 Dope composition in% CA 10 10 10 10 14 18 14 14 14 16 acetone 80 80 80 80 70 63 70 70 70 56 water 10 10 10 10 16 19 16 16 16 28 relationship Acetone: CA. 8th 8th 8th 8th 5 3.5 5 5 5 3.5 Precipitation bath composition in% water 100 100 100 100 100 100 95 90 85 95 acetone 0 0 0 0 0 0 5 10 15 5 Mass flows in kg / min Dope 3.0 3.0 3.00 3.0 3.0 3.0 3.0 3.0 3.0 3.0 precipitation bath 34.5 22.0 15.75 12.0 21.7 29.7 21.9 21.6 21.7 29.1 Mass flow ratio precipitation bath to dope 11.5 7.3 5.25 4.0 7.2 9.9 7.3 7.2 7.2 9.7 Suspension composition in% CA 0.8 1.2 1.6 2.0 1.7 1.65 1.7 1.7 1.7 1.5 acetone 6.4 9.6 12.8 16.0 8.5 5.80 12.8 17.3 21.7 9.8 water 92.8 89.2 85.6 82.0 89.8 92.55 85.5 81.0 76.6 88.7

Example 3:

The experiment was carried out analogously to experiment 1, except that the precipitation bath mass flow reduced to 15.75 kg / min. There was a ratio of the mass flows Precipitation bath to dope of 5.25 and a concentration of the fibrets after the precipitation of 1.6 Ma% (at 12.8 Ma% acetone). On high pressure homogenization was waived.

Example 4:

The experiment was carried out analogously to experiment 1, except that the precipitation bath mass flow reduced to 12 kg / min. There was a ratio of the mass flows Precipitation bath to dope of 4.0 and a concentration of the fibrets after the precipitation of 2.0 mass% (at 16.0 mass% acetone). On high pressure homogenization was waived.

Example 5:

The experiment was carried out in the same way as experiment 1, except that it was a mass ratio Acetone adjusted to CA of 5. With a mass flow ratio precipitation bath too Dope of 7.2 after precipitation is 1.7 Ma% fibrets with 8.5 Ma% acetone in front.

Example 6:

The experiment was carried out in the same way as experiment 1, except that it was a mass ratio Acetone adjusted to CA from 3.5. With a mass flow ratio precipitation bath too Dope of 9.9 after precipitation 1.65 Ma% Fibrets at 5.80 Ma% Acetone before.

Example 7:

The experiment was carried out analogously to experiment 5, only in the precipitation bath in this case Contain 5 Ma% acetone. This resulted in a after precipitation Acetone content of 12.8% by mass. On a high pressure homogenization waived.

Example 8:

The experiment was carried out analogously to experiment 5, except that there was 10% by mass acetone in the precipitation bath contain. After the precipitation this resulted in an acetone content of 17.3%. High-pressure homogenization was not used.

Example 9:

The experiment was carried out analogously to experiment 5, except that 15% by mass of acetone was present in the precipitation bath contain. After the precipitation this resulted in an acetone content of 21.7% by mass. High-pressure homogenization was not used.

Example 10:

Experiment 10 was carried out analogously to experiment 6, except that the dope was additional Water was added up to a content of 28% by mass. Were in the precipitation bath 5% by weight acetone present. The fibrets showed one after the precipitation Concentration of 1.5 Ma% at an acetone concentration of 9.8 Ma%.

Example 11:

The preparation was carried out analogously to experiment 5, but instead of Gear rim geometries "fine", the gear rim geometries "coarse" were.

Example 12:

The preparation was carried out analogously to experiment 5, but instead of Gear rim geometries "fine" the rotor rings with the geometry "coarse" and the stator sprockets were equipped with the "fine" geometry.

Each of the samples had specific surfaces above 20 m ² / g and individual fiber dimensions, preferably below 1 µm. However, further parameters such as homogeneity, accessibility of the fiber networks for the flow etc. are decisive for the filtration.

The quality of the fibrets produced was therefore assessed using a filter layer. The following composition was selected for the filter layer: 25% CA fibrets 35% microcrystalline cellulose with a modal particle size distribution at 28 µm 30% Long fiber pulp, unground 10% Long fiber pulp, ground to 80 ° SR.

Based on the total solids, 0.4% by weight of an epichlorohydrin resin was added to adjust the wet strength. The layers had a basis weight of 1350 g / m ² .

The layers were tested with a test suspension of 0.5% by weight of raw raw cane sugar in water. The test area was 100 cm ² . The throughput was determined after 30 min at a differential pressure of 1 bar. After a filtration period of 15 minutes, the turbidity measurement was sampled to determine the separation effect. The initial turbidity for all layers in the test series carried out in parallel was approximately 2.40 TE / F. Each of the filter layers produced with the described fibrets was tested in three runs. Table 3 shows the mean values. Results of the filtration tests Layer with fibrets Throughput in 30 min Turbidity of the sample Example No .: liter TE / F 1 12.1 0.24 2 13.5 0.28 3 13.8 0.29 4 14.2 0.32 5 14.4 0.30 6 15.2 0.36 7 14.1 0.29 8th 13.7 0.26 9 13.3 0.24 10 15.7 0.39 11 14.1 0.33 12 14.3 0.29

Differences can be seen between the layers. These are but not so clearly that the fibrets according to one of the embodiments should be rejected regarding the use in filter layers. mostly is a slightly higher turbidity with a correspondingly higher throughput connected. As a relation for the assessment of the filtration behavior Throughput and separation efficiency is used, this behavior not to be rated negatively. There is also the possibility of using Changes in the formulation of the filter layer change the filtration behavior.

The fibrets of sample 9 are positive. The addition of acetone the precipitation medium has a better fibrillation effect here. On the other hand has the geometry of the sprockets used in the examined area no significant influence on the quality of the fibrets.

5 shows the dependence of the maximum possible water content on the Concentration of the cellulose acetate in the dope (both in%) at one Temperature of 20 ° C applied. The acetone content is determined by the respective CA and water concentrations are subtracted from 100% by mass.

In addition to the concentration at the precipitation point (curve I), there are also the maximum possible concentrations of water according to the invention (curve II) and according to the prior art (US 5,071,599 and US 5,175,376) - curve III - applied. According to the prior art, between 5 and 15% by mass Cellulose acetate must be dissolved in the dope. The cellulose acetate is in a solution which can contain a maximum of 20% by mass of water. The indication for that Water thus refers to the two-substance system acetone + water, while the information according to the invention always for the three-component system acetone + Water + Ca apply. At 5% by mass of cellulose acetate, according to the state of the art Technology thus only 20% of 95%, i.e. 19 Ma% water can be included.

The diagram shows that the greatest difference to the prior art is at 5% by mass of cellulose acetate and the smallest at 15% by mass of cellulose acetate. 5% by mass of cellulose acetate: Fällpunktskonzentration: 5.0 Ma% cellulose acetate 39.7 mass% water 55.3 mass% acetone Maximum water content according to the invention 5.0 Ma% cellulose acetate 37.7 mass% water 57.3 mass% acetone State-of-the-art maximum water content 5.0 Ma% cellulose acetate 19.0 mass% water 76.0 mass% acetone Difference in water content compared to the prior art 18.7 Ma% (based on dope) 15% by mass of cellulose acetate: Fällpunktskonzentration: 15.0% by mass of cellulose acetate 25.5 mass% water 59.5 mass% acetone Maximum water content according to the invention 15.0% by mass of cellulose acetate 23.5 mass% water 61.5 mass% acetone State-of-the-art maximum water content 15.0% by mass of cellulose acetate 17.0% water 68.0 mass% acetone Difference in water content compared to the prior art 6.5% by mass (based on dope)

Figure 5 clearly shows the advantages of the invention, which consist in that the Cellulose acetate content can be chosen much larger (see expanded area according to the invention) and that the water content can be significantly higher, which, as described above, has decisive advantages in the Litigation (elimination of the filtration level) and the process costs (Preparation with less effort).

reference numeral

1

Supply line for cellulose derivative

2

Dope makeup tank

3

dope line

8th

Fällbadansatztank

9

coagulation bath

10

baseplate

11

ring-shaped base plate

12

distillation plant

13

Fällbadableitung

14

outdoors

15

steam supply

16

heat exchangers

17

Solvent recycling line

19

discharge

20

high-pressure homogenizer

22

Storage tank

23

Fibretableitung

24

drum filter

25

Return line

26

processing plant

27

management

31

management

40

disperser

41

casing

42

inner space

43

inner stator

44

rotor

45

outer stator

46

jet

47

jet

48

jet

49

jet

50

first ring gear

51

second ring gear

52

third ring gear

53

fourth ring gear

54

gap

55

tooth

60

first zone

61

second zone

62

third zone

63

fourth zone

64

Mechanical seal

65

drive shaft

Claims (29)

1. A process for the manufacture of fibrets, in which a dope is fed centrally to a dispersing device operating according to the rotor/stator principle and is introduced into a precipitant, and the suspension formed from dope and precipitant is alternately accelerated and decelerated in the shearing field of the dispersing device at least once, the dope being precipitated and the fibrets being formed, and in which the fibrets, the solvent and the precipitant are subsequently separated off, characterised in that a cellulose derivative, such as a cellulose ester or a cellulose ether, and a solvent suitable therefor is used for the dope, and
   that the precipitant also is introduced into the dispersing device centrally.
2. A process according to claim 1, characterised in that the suspension is alternately accelerated and decelerated at least twice.
3. A process according to claim 2, characterised in that the suspension is subjected alternately to a radial flow and a transverse flow.
4. A process according to any one of claims 1 to 3, characterised in that the dope is introduced into the precipitant through stationary nozzles (46-49) past whose outlet orifice means for generating a flow are moved.
5. A process according to any one of claims 1 to 4, characterised in that cellulose diacetate, cellulose triacetate, cellulose acetate butyrate, cellulose acetate propionate, benzylcellulose or ethylcellulose or mixtures of those materials are used for making up the dope.
6. A process according to claim 5, characterised in that a cellulose diacetate having an acetyl value between 54 and 56 % is used.
7. A process according to any one of claims 1 to 6, characterised in that the content of cellulose derivative in the dope is 3-20 %.
8. A process according to any one of claims 1 to 7, characterised in that the ratio of solvent to cellulose derivative in the dope is adjusted to 2.8-4.4.
9. A process according to any one of claims 1 to 8, characterised in that acetone, acetic acid, methyl acetate, methyl ethyl ketone, 1,4-dioxane, acetaldehyde, ethyl acetate, tetrahydrofuran or methyl isopropyl ketone or mixtures of those solvents are used as solvent.
10. A process according to any one of claims 1 to 9, characterised in that a non-solvent is additionally added to the dope.
11. A process according to claim 10, characterised in that the water, ethanol or methanol is added as the non-solvent.
12. A process according to either of claims 10 and 11, characterised in that the non-solvent content is at least 2 % below the non-solvent content (precipitation point content) at which precipitation commences for the cellulose derivative/solvent mixture used.
13. A process according to claim 12, characterised in that the non-solvent content is 220 % below the precipitation point content.
14. A process according to any one of claims 10 to 13, characterised in that the non-solvent content in the dope is up to 40 %.
15. A process according to any one of claims 1 to 14, characterised in that basic flow speeds of up to 100 m/sec are produced in the precipitation bath.
16. A process according to any one of claims 1 to 15, characterised in that the volume flow of the precipitant is so adjusted that the fibret content in the precipitation bath is between 1 and 2.5 % by mass.
17. A process according to any one of claims 1 to 16, characterised in that the volume flows of precipitation bath and dope are adjusted to a ratio of between 10:1 and 2.5:1.
18. A process according to any one of claims 1 to 17, characterised in that the precipitation bath contains, after precipitation, up to 25 % by mass solvent.
19. A process according to any one of claims 1 to 18, characterised in that the solvent content in the precipitation bath after precipitation is 15 - 25 % by mass.
20. A process according to any one of claims 1 to 19, characterised in that, after removal of the solvent, the fibrets are homogenised without prior filtration.
21. An apparatus for the manufacture of fibrets, comprising a device for making up a dope from cellulose derivatives and solvent using a dispersing device (40) operating according to the rotor and stator principle, which dispersing device (40) has at least two toothed rings (50) to (53) of which at least one toothed ring (50) is a component part of the rotor (44) of the dispersing device (40), and comprising a central feed line for dope and a feed line for precipitant and comprising a device for separating the fibrets from solvent and precipitant, characterised in that the feed line (9) for the precipitant opens into the dispersing device (40) centrally, and
    that the feed line (3) for the dope has at least one nozzle (46 to 49) inside the dispersing device (40).
22. An apparatus according to claim 21, characterised in that the nozzle (46-49) is oriented radially outward toward the first toothed ring (50).
23. An apparatus according to claim 21 or 22, characterised in that the first toothed ring (50) is a component part of the rotor (44) of the dispersing device (40).
24. An apparatus according to any one of claims 21 to 23, characterised in that the nozzle-to-toothed ring distance is 0.01-5 mm.
25. An apparatus according to claim 24, characterised in that the nozzle-to-toothed ring distance is 0.01-1 mm.
26. An apparatus according to any one of claims 21 to 25, characterised in that the nozzle diameter is 5 - 10 mm.
27. An apparatus according to any one of claims 21 to 26, characterised in that at least two nozzles (46, 47, 48, 49) are arranged symmetrically inside the first toothed ring (50).
28. An apparatus according to any one of claims 21 to 27, characterised in that the precipitant feed line (9) for the precipitant surrounds the dope line (3).
29. An apparatus according to any one of claims 21 to 28, characterised in that the at least one nozzle (46 - 49) is arranged outside the toothed rings (50 - 53) of the dispersing device (40) and is oriented radially inward toward the outermost toothed ring (53).

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