Device and method for the recovery of alkaline solution, as well as

Apparatus and ancestors for the production of regenerated collulosic chorus

Molded bodies have one such ancestor

Technical area

The invention relates to a method for the recovery of alkaline

Solution from aqueous alkaline solution contaminated with hemicelluloses, in which the aqueous alkaline solution as a feed stream and process water as a countercurrent over an ion exchange diffusion dialysis with at least one dialysis membrane between feedstream and counterflow and thereby into an alkaline enriched diffusate as a recovered alkaline solution and a with Hemicellulose-enriched dialysate can be implemented.

In addition, the invention relates to a device for the recovery of alkaline solution from aqueous alkaline solution contaminated with hemicelluloses, having an ion exchange diffusion dialysis with at least one dialysis membrane and with at least one feed stream surface channel, for supplying aqueous alkaline solution contaminated with hemicelluloses as Feed flow to the dialysis membrane and for removing dialysate from the dialysis membrane, and a countercurrent surface channel, for supplying process water as countercurrent to the dialysis membrane and for removing diffusate from the dialysis membrane, with the feedstream in the feedstream surface channel and countercurrent in the countercurrent surface channel the dialysis membrane are separated and have an opposite flow direction and wherein the dialysis membrane is permeable to cations,so that alkaline cations from the feed stream are enriched in the diffusate, characterized in that the height of the feed stream surface channel and the countercurrent surface channel are each between 250 pm and 1000 pm, in particular between 400 pm and 600 pm, and that the device is a Degassing device, for removing gas components from the process water, upstream of the ion exchanger diffusion dialysis, through which the process water is passed.has before the ion exchanger diffusion dialysis, through which the process water is passed.has before the ion exchanger diffusion dialysis, through which the process water is passed.

The invention further relates to a method for producing regenerated cellulosic molded bodies comprising the aforementioned method and a device for producing cellulosic molded bodies.

State of the art

It is known that both in the production of pulp and in the alkalization of pulp in a viscose process, aqueous alkaline solutions arise as material flows which are enriched with hemicelluloses.

Hemicelluloses are generally understood to mean polyoses composed of pentoses and / or hexoses, such as xylose, arabinose, glucose, mannose or galactose. Hemicelluloses refer in particular to all polysaccharides except cellulose, which occur as a component of plant cell walls, the matrix of which consists of fibrillary, partially crystalline cellulose, as well as low molecular weight degradation products of cellulose, e.g. hydroxycarboxylic acids, which can be formed in the course of digestion processes. In contrast to cellulose, which is a non-branched homopolymer made from glucose, hemicelluloses are generally branched heteropolymers made from the above-mentioned pentoses and hexoses. Most of these have a homopolymer as the main chain to which branches from other sugars are bound and thus form an irregular macromolecule. Hemicelluloses also have significantly lower degrees of polymerization or chain lengths than cellulose. Such hemicelluloses can be, for example, xylans, mannans, galactans, or other pentosans or hexosans.

A distinction between celluloses (α-fraction) and hemicelluloses (β- and g-fraction) is defined in the prior art by the solubility in 17.5% sodium hydroxide solution (WÜSTENBERG, Tanja. Cellulose and cellulose derivatives: Basics, Effects and applications. Hamburg: Behr's Verlag, 2013.). While ß- and g-hemicelluloses can be dissolved in 17.5% sodium hydroxide solution, α-cellulose is insoluble. During the subsequent neutralization, the ß-hemicelluloses then precipitate, while the g-hemicelluloses remain in solution.

From the prior art (CN 103349908 A) a process for the recovery of sodium hydroxide solution from the press liquor obtained in a viscose process is known. The press liquor, which in the viscose process when pressing

of alkali cellulose and is usually an aqueous alkaline solution contaminated with hemicelluloses and containing sodium hydroxide solution, is conducted as a feed stream over a diffusion dialysis in order to obtain a recovered solution enriched with sodium hydroxide solution. However, such methods have the disadvantage that in order to achieve high recovery rates, very large membrane areas must be used compared to the flow rates. In the case of a compact design, however, the membranes suffer greatly from a drop in performance and throughput and, in particular, from short downtimes, which negatively affects the profitability of the process.

Disclosure of the invention

It is therefore an object of the invention to provide a method of the type mentioned at the outset, which enables a longer service life and is therefore more economical.

The invention solves the problem posed by the features of independent claim 1.

If gas components are removed from the process water of the countercurrent before being fed to the diffusion dialysis, it can be ensured that no gas bubbles form in the countercurrent of the ion exchanger diffusion dialysis, which negatively affect the exchange of substances over the dialysis membrane or permanently disrupt and ultimately come to a standstill can bring. By removing gas components, process water can namely be provided which is, in particular, essentially free of gas components, so that the service life of the dialysis membrane can be significantly increased. If process water containing gas components is passed over the dialysis membrane, it has been found that the flow of the process water on the dialysis membrane causes gas components to dissolve and thus gas bubbles to form. Such gas bubbles can grow steadily due to the continuous inflow of process water and finally block the transport of substances across the dialysis membrane completely. In order to remove the accumulated gas bubbles and to restore the functionality of the dialysis membrane, it is then necessary to regenerate them at regular short intervals by means of flushing. However, if process water is essentially free of gas components as a countercurrent in the

Ion exchange diffusion dialysis is used, the need for rinsing is considerably reduced and the service life is extended accordingly. In this way, a method according to the invention for recycling aqueous alkaline solutions can be created with a particularly low maintenance outlay.

In general, it is stated that the idle time of the ion exchanger diffusion dialysis or the dialysis membrane denotes the maximum operating time or operating time until a renewed rinsing, cleaning or replacement of the dialysis membrane is necessary due to a drop in yield.

In the method according to the invention, the aqueous alkaline solution contaminated with hemicelluloses is passed as a feed stream and the process water, which is essentially free of gas components, as a countercurrent over the dialysis membrane, the countercurrent flowing over the dialysis membrane in the opposite flow direction to the feed stream. The feed flow and counter flow are separated by the dialysis membrane, which is at least partially permeable. An ion concentration gradient is established between the alkaline solution in the feed stream and the process water in the countercurrent, which is compensated for by diffusion of ions through the dialysis membrane. Thus, alkali ions can diffuse from the aqueous alkaline solution through the dialysis membrane into the process water. As a result, the process water is alkaline enriched in countercurrent and leaves the ion exchange diffusion dialysis as a diffusate, which forms the recovered alkaline solution. At the same time, the feed stream is depleted alkaline, which increases the concentration of hemicelluloses, as these cannot pass through the dialysis membrane due to their particle size. The feed stream enriched in hemicelluloses then leaves the ion exchanger diffusion dialysis as dialysate and can possibly be fed to a further use. For example, the hemicelluloses can be separated from the dialysate using a suitable method. whereby the concentration of hemicelluloses increases, as these cannot pass through the dialysis membrane due to their particle size. The feed stream enriched in hemicelluloses then leaves the ion exchanger diffusion dialysis as dialysate and can possibly be fed to a further use. For example, the hemicelluloses can be separated from the dialysate using a suitable method. whereby the concentration of hemicelluloses increases, as these cannot pass through the dialysis membrane due to their particle size. The feed stream enriched in hemicelluloses then leaves the ion exchanger diffusion dialysis as dialysate and can possibly be fed to a further use. For example, the hemicelluloses can be separated from the dialysate using a suitable method.

It can be particularly advantageous in the process described above if the dialysis membrane is a cation exchange membrane, which is in particular semipermeable and is permeable to positively charged ions, that is, lets through positively charged ions and retains negatively charged ions. By using such a cation exchange membrane, the alkali cations in particular can be transported through the membrane into the countercurrent and the negatively charged Co ions can be retained. If the aqueous alkaline solution is an aqueous solution of sodium hydroxide solution, then Na t ions can pass the dialysis membrane from the feed stream to the countercurrent unimpeded, while OH ions are retained. At the same time, H 3 0+ ions are transported from the countercurrent into the feed stream, whereby the dialysate is essentially diluted by process water.

In the process according to the invention, aqueous alkaline solutions contaminated by hemicelluloses can thus be reprocessed, the recovered alkaline solution being essentially free of hemicelluloses. The recovered alkaline solution is also of high purity and can be fed back directly into various processes. In this way, a closed material cycle can be created, which can increase the environmental friendliness and cost efficiency of the process. In particular, the method according to the invention can be suitable for the recovery of sodium hydroxide solution, for example in the context of a pulp or viscose process.

The method according to the invention is particularly suitable when the aqueous alkaline solutions contaminated by hemicelluloses are, in particular, waste liquors from a pulp or viscose production. In particular, the aqueous alkaline solution can be a press liquor which is obtained in viscose production when cellulose is alkalized with caustic soda to form alkali cellulose and the alkalized cellulose is subsequently pressed out. Such a press liquor typically contains 10-20% by weight of sodium hydroxide solution and has a hemicelluloses content of between 0.5-5% by weight, based in each case on the total weight of the press liquor.

In addition, it is generally stated that process water is understood to mean water for use in industrial plants which must meet special, increased requirements for water quality, in particular with regard to water hardness, solids content and gas content. In particular, the process water in the present invention is softened and / or at least partially demineralized water.

In general, it is also stated that gas components are understood to mean substances which have a gaseous state of aggregation at the operating temperature of the process water, but have a solubility in water at a given partial pressure and are thus at least partially present in the process water as dissolved components.

If the process water is passed through a degassing device before being fed to diffusion dialysis, the gas components can be removed from the process water in a simple manner in terms of process technology. If at least 90% of the gas components contained therein are removed from the process water, then process water that is essentially free of gas components can be provided, which can further increase the reliability of the method according to the invention. Particularly preferably 90% of the O2 dissolved in the process water and 95% of the CO2 dissolved in the process water are removed in the degassing device.

The gas components can be removed particularly reliably from the process water when the process water is exposed to a vacuum in the degassing device. In this way, a cost-effective and technically simple method for degassing the process water can be provided, which can ensure reliable removal of the gas components. The process water can be passed over a gas-permeable membrane under vacuum to enable a high throughput. Alternatively, the process water in the degassing device can also be treated, for example, with ultrasound (for example via a sonotrode) or thermally in order to remove the gas components.

The inventive method for recycling aqueous alkaline solutions can be particularly advantageous if the process water has a maximum content of 1.0 mg / l of dissolved gas components before being fed to the diffusion dialysis and after the gas components have been removed. The content of dissolved gas components is advantageously less than or equal to 0.7 mg / l. If the content of dissolved gas components is below 1.0 mg / l or below 0.7 mg / l, the formation of gas bubbles on the dialysis membrane of the ion exchange diffusion dialysis can be reliably prevented, thereby ensuring a long service life of the dialysis membrane can. The cost efficiency of the process can thus be further improved.

Is the flow rate of the feed stream between 0.1 and 1, 0 mm / s, and the flow rate of the countercurrent between 0.5 and 2.5 mm / s, so the yield of the recovered alkaline solution and the efficiency of the process can be further increased. In a particularly advantageous embodiment of the method, the flow rate of the feed stream is between 0.2 and 0.5 mm / s, and the flow rate of the countercurrent is between 1.0 and 1.5 mm / s.

A particularly high yield in the recovery of alkali can be achieved if the ratio of the flow rate of the countercurrent to the flow rate of the feed stream is between 2: 1 and 5: 1. Due to the countercurrent flow of the process water in the feed stream at a higher flow rate than the aqueous alkaline solution, the difference in ion concentration between the streams can be kept constantly high, which in turn enables a constantly high ion exchange across the dialysis membrane in the process. Due to the increased flow rate of the process water, however, there is also a greater dilution of the alkaline solution in the diffusate by process water, which has a disadvantageous effect on the direct reusability of the recovered alkaline solution and makes additional concentration steps necessary. If the flow velocities are in the range of the ratios given above, a process with high yield and efficiency can be achieved with nevertheless moderate dilution of the diffusate.

The yield of the recovered alkaline solution can be increased further if the aqueous alkaline solution is passed through a nanofiltration before it is fed to the ion exchange diffusion dialysis in the feed stream. In nanofiltration, the aqueous alkaline solution is separated into an alkaline permeate and a retentate enriched with hemicelluloses. The permeate then essentially has recovered alkaline solution and can be separated from the ion-exchange diffusion dialysis together with the recovered alkaline solution in order to recycle it. The retentate of nanofiltration, which has residues of aqueous alkaline solution and the majority of the hemicelluloses contained,

In addition to the nanofiltration, the aqueous alkaline solution can also be passed through a microfiltration before the nanofiltration. In this way, coarse impurities can be removed from the aqueous alkaline solution, which can form deposits in the nanofiltration and / or in the ion exchange diffusion dialysis. The permeate from the microfiltration is then preferably passed through the nanofiltration. The reliability of the method according to the invention can thus be further improved.

If, in order to clean the dialysis membrane, diffusate is passed in parallel flow over the dialysis membrane at regular intervals, the service life of the dialysis membrane can be extended and a particularly cost-efficient method can thus be created. The dialysis membrane is preferably rinsed by the diffusate consisting essentially of recovered alkaline solution in such a way that the dialysate is circulated both in the feed stream and in countercurrent in the same direction of flow. Deposits, such as hemicelluloses, can be efficiently removed from the dialysis membrane and the original throughput can be restored.

The method can be further distinguished in particular when the feed stream and the countercurrent are each passed through surface channels separated by the dialysis membrane. In a further embodiment, the dialysate can also be flow-connected to the feed stream via a surface channel and at the same time the diffusate can be flow-connected to the countercurrent via a further surface channel. The method according to the invention can therefore enable the use of surface ducts with preferably low overall heights, which further improve the efficiency of the method. In addition, the method can be implemented in a technically simple manner through the use of surface ducts. The surface channels can be formed, for example, by spaced-apart, parallel plates between which the dialysis membrane extends.

In addition, in the method according to the invention, the ion exchange diffusion dialysis can have a plurality of dialysis membranes, as a result of which the throughput of the method can be further improved. Such a previously mentioned method with a plurality of dialysis membranes can be further improved if the dialysis membranes are arranged in a membrane stack parallel to one another and in each case alternating between feed flow and counter flow

two dialysis membranes are fed. A cost-efficient process can be created in this way.

If, in a further step, acid is added to the hemicelluloses-enriched dialysate and a xylan-containing precipitate is precipitated from the resulting precipitation suspension, in addition to recovering alkaline solution, other usable substances can also be obtained from the aqueous alkaline solution contaminated with hemicelluloses will. This applies in particular to high-quality xylans, which can be precipitated from the dialysate by adding acid. Since the dialysate is already heavily enriched with hemicelluloses as a result of the ion exchange diffusion dialysis, a particularly efficient extraction of xylans from the dialysate can take place.

If the xylan-containing precipitate is subsequently separated from the residue of the precipitation suspension, for example by centrifugation, a xylan-containing composition can be obtained in a technically simple manner which is suitable for a large number of areas of application. The xylan-containing composition can then be washed and dried in order to remove residual impurities.

If, in addition, acid is continuously added to the precipitation suspension until the pH value falls below 4 in the precipitation suspension, the yield and quality of the precipitate produced can be significantly improved. At pH values ​​below 4, very advantageous conditions can be created for complete precipitation of the hemicelluloses. In addition, if the temperature of the precipitation suspension during the precipitation does not fall below a precipitation temperature of at least 40 ° C., an optimal particle size distribution can also be ensured during the precipitation. In particular, by keeping the precipitation suspension at an elevated precipitation temperature, the average particle size can be increased, which enables the precipitate to be filtered better.

The invention has also set itself the task of providing an initially mentioned device for carrying out the method, which prevents clogging of the dialysis membrane with gas bubbles in a technically simple manner.

The invention solves the problem posed by the features of claim 9.

If the device has a degassing device for removing gas components from the process water before the ion exchanger diffusion dialysis through which the process water is passed, gas components can be reliably removed from the process water. In ion exchange diffusion dialysis, the dialysis membrane is guided between low surface channels in order to maximize the surface area between the material flows and the dialysis membrane. In the low surface ducts, however, there are flow conditions which promote the formation of gas bubbles through outgassing of the gas components. In addition, the surface channels prevent the gas bubbles from being transported away, which leads to an accumulation of the gas bubbles in the surface channels and ultimately to a blockage of the exchange of substances via the dialysis membrane. Accordingly, removal of the gas components from the process water of the countercurrent can reliably prevent the formation of gas bubbles in the surface channels. This is particularly the case when the height of the surface channels is between 250 μm and 1000 μm, or in a preferred embodiment of the invention between 400 μm and 600 μm, since such surface channels with a low overall height suffer increasingly from the problem set out above. This is because the degassing device in the device can prevent process water with an excessively high gas component content from being fed to the dialysis membrane and thus essentially no gas bubbles being formed. A reliable device can thus be created, which enables a long service life, can thus be created.

If the dialysate is flow-connected with the aqueous alkaline solution via the feed stream surface channel and the diffusate with the process water via the countercurrent surface channel, a structurally simple device for the recovery of alkaline solution can be created. If the aqueous alkaline solution and dialysate are flow-connected in the feed stream, the aqueous alkaline solution intended for recovery can namely flow along the dialysis membrane and release alkaline ions to the counterflow during the entire contact time. In this way, the alkali ions are removed from the feed stream, while hemicelluloses remain in the feed stream. In addition, the process water and the diffusate are in countercurrent

Connected to the flow, the continuous flow of process water over the dialysis membrane can generate a constantly high ion concentration gradient between the feed flow and the counter flow, which is decisive for good ion transport over the dialysis membrane.

The degassing device in the device can be implemented in a structurally simple manner if it has a gas-permeable membrane under vacuum, over which the process water is passed in the degassing device in order to remove the gas components from the process water. By degassing the process water via a membrane under vacuum, the degassing device can remove gas components from the process water very reliably at a high throughput. In particular, at least 90% of the gas components can be removed from the process water in the degassing device.

If the dialysis membrane has a thermoplastic, in particular a polyetheretherketone (PEEK), an inexpensive and reliable device can be created. PEEK membranes can be characterized by a very high mechanical and chemical stability, which means that a long service life can be achieved. In addition, very thin membranes, in particular with a thickness of less than or equal to 100 μm, can be used without any loss of mechanical and chemical stability, whereby the throughput can be increased further.

If the ion exchanger diffusion dialysis has several dialysis membranes and several feedflow and countercurrent surface channels, with at least one feedflow surface channel or one countercurrent surface channel being arranged between two dialysis membranes, the available dialysis membrane surface can be effectively increased. If several dialysis membranes are used, the feed flow and counter flow can each be conducted in parallel over all dialysis membranes and thus the throughput of the device can be significantly increased.

If, in addition, the dialysis membranes are arranged parallel to one another in a membrane stack, with a feed-flow surface channel and a counter-flow surface channel alternating between two dialysis membranes, a particularly compact device can be used despite the high dialysis membrane surface

be created, which enables a high throughput with a small footprint.

The process according to the invention can also be advantageously used in a process for producing regenerated cellulosic molded bodies according to claim 15.

In such a process for producing regenerated cellulosic molded bodies, such as, for example, a viscose or modal process, a cellulose is made alkaline in an alkalization stage with sodium hydroxide solution in order to obtain an alkali cellulose. The alkali cellulose, i.e. the alkalized cellulose, is then separated by pressing from the excess sodium hydroxide solution, which is referred to as press lye and contains hemicelluloses in an aqueous alkaline solution. The press liquor is thus an aqueous alkaline solution contaminated by hemicelluloses, which is then separated in a process according to one of claims 1 to 8 into a fraction containing essentially hemicelluloses and a fraction containing essentially sodium hydroxide solution. The fraction containing essentially hemicelluloses is formed from the dialysate of the ion exchange diffusion dialysis and the fraction containing essentially sodium hydroxide solution is formed from the diffusate of the ion exchange diffusion dialysis. Such a process can be distinguished by a high recovery yield of sodium hydroxide solution, which can significantly improve the economic efficiency of the process.

Such a process for producing regenerated cellulosic molded bodies can also be particularly notable if the fraction containing essentially sodium hydroxide solution is returned to the alkalization stage for reuse in the process - preferably in the viscose or modal process -, in particular for further alkalinization of cellulose . This enables a process with a closed material cycle to be created, which can be operated in a resource-saving and cost-efficient manner.

The invention further relates to a device for producing regenerated cellulosic molded bodies from cellulose.

Such a device can be distinguished according to the invention if the device for the production of regenerated cellulosic moldings from pulp, in particular by the viscose or modal process, has an alkalization stage in which pulp is alkalized with caustic soda to form alkali cellulose and freed from the excess press liquor by pressing and a recovery stage with an ion exchanger diffusion dialysis for separating the press liquor into a fraction containing essentially hemicelluloses and a fraction containing essentially sodium hydroxide, the press liquor being fed from the alkalization stage to the recovery stage and the fraction containing essentially sodium hydroxide being returned to the alkalization stage will.

If the press liquor from the alkalization stage is fed to the recovery stage, which has an ion exchanger diffusion dialysis, a device can be created which is structurally simple in the recovery stage, the press liquor in a fraction containing essentially hemicelluloses and in a fraction containing essentially Separates caustic soda. The fraction essentially containing sodium hydroxide solution can then be returned to the alkalization stage, it being possible to create a device for producing regenerated cellulosic molded bodies with a closed sodium hydroxide solution circuit. Such a device can be distinguished by particularly high efficiency.

Such a device mentioned above can be particularly characterized if the recovery stage for separating the press liquor into a fraction containing essentially hemicelluloses and a fraction containing essentially sodium hydroxide solution, a device containing the ion exchange diffusion dialysis, according to one of claims 9 to 14 has.

Brief description of the drawings

The embodiments of the invention are described below with reference to the drawings. Show it:

1 shows a schematic representation of a device and a method for recovering alkaline solution according to a first embodiment,

2 shows a schematic representation of a device and a method for recovering alkaline solution according to a second embodiment,

3 shows a schematic representation of a method for recovering alkaline solution according to a third embodiment,

4 shows a flow diagram for the schematic representation of a method for producing regenerated cellulosic molded bodies, and FIG

5 shows a diagram with experimental measured values ​​for the method according to the invention for recovering alkaline solution.

Ways of Carrying Out the Invention

1 shows a device 100 according to a first embodiment for recovering alkaline solution 1 from aqueous alkaline solution 2 contaminated with hemicelluloses 22. The device 100 comprises an ion exchange diffusion dialysis 3 with a dialysis membrane 4. The dialysis membrane 4 is arranged between two surface channels 5, 6. The feed stream surface channel 5 has a feed 7 for the aqueous alkaline solution 2 contaminated with hemicelluloses 22 to the dialysis membrane 4 and an outlet 8 for the dialysate 9 from the dialysis membrane 4. The countercurrent surface channel 6, on the other hand, has a feed 11 for the process water 10 to the dialysis membrane 4 and a discharge 12 for the diffusate 13 from the dialysis membrane 4. The aqueous alkaline solution 2 is flow-connected to the dialysate 9 via the feed stream surface channel 5 and forms with it the feed stream 14 of the ion exchanger diffusion dialysis 3 the countercurrent 15 of the ion exchanger diffusion dialysis 3. The dialysis membrane 4 is semipermeable for positively charged ions (cations) 18, 19, so that, for example, alkaline cations 18 can diffuse from the feed stream 14 through the dialysis membrane 4 into the countercurrent 15. In the embodiment, the dialysis membrane 4 contains a thermoplastic material, namely, polyetheretherketone. In the case of sodium hydroxide solution as an aqueous alkaline solution 2, for example as a waste product from cellulose, viscose or modal production 500 (see FIG. 4), the alkaline cations 18 are Nat ion. The diffused alkaline cations 18 then accumulate in the countercurrent 15 and there form the diffusate 13 which contains the recovered alkaline solution 1. At the same time, to balance the charge, cations 19 can diffuse from the countercurrent 15 through the dialysis membrane 4 into the feed stream 14. Since the countercurrent 15 contains process water 10, the cations 19 from the countercurrent 15 are essentially H 3 0 +ions from the process water 10. Negatively charged ions (anions) 20, 21, in particular OH ions, are retained in the respective streams 14, 15 due to the ion selectivity of the dialysis membrane 4 and can there in turn with the respectively diffused cations 18, 19 Make ties. The feed stream 15 is thus depleted of alkaline cations 18 and enriched with cations 19 from the process water 10, while the hemicelluloses 22 are retained by the dialysis membrane 4 and are finally excreted via the dialysate 9. The dialysate 9 thus has the residue 29 diluted with process water 10 and containing hemicelluloses 22, which can optionally be processed in further process steps.

Thus, in one embodiment of the residue 29 containing hemicelluloses 22, acid can be added and a xylan-containing precipitate can be precipitated from the resulting precipitation suspension, although this was not shown in detail in the figures.

The surface channels 5, 6 each have a height 23, 24 which is between 250 pm and 1000 pm. In a further preferred embodiment of the invention, the height 23, 24 of the surface channels 5, 6 is in each case between 400 μm and 600 μm. Due to the low height 23, 24 of the surface channels 5, 6, a large ratio between the area of ​​the dialysis membrane 4 and the height 23, 24 of the surface channels 5, 6 is achieved, which is the cause of a high throughput of ions 18, 19 through the dialysis membrane 4. At the same time, gas bubbles can form in the surface channels 5, 6 due to the outgassing of gas components. Due to the low heights 23, 24, the gas bubbles formed can only be inadequately transported away from the respective surface channel 5, 6, whereby the gas bubbles ultimately the surface channel 5,

To avoid the formation of gas bubbles, the device 100 has a degassing device 25 connected upstream of the ion exchanger diffusion dialysis 3, through which the process water 10 is passed before it enters the countercurrent surface channel 6 via the feed 11 as degassed process water 10 ' is directed. According to the first embodiment of the device 100 shown in FIG. 1, the process water 10 in the degassing device 25 is passed over a gas-permeable membrane 26 which is under vacuum 27. The gas components 28 dissolved in the process water 10, in particular O2 and CO2, are removed therefrom. The degassed process water 10 ′, which is thus essentially free of gas components 28, is then fed to the countercurrent 15 of the ion exchanger diffusion dialysis 3. For this purpose, the degassing device 25 can, for example, as shown in FIG. 1, have a pump 30 for generating the vacuum 27. Alternatively, as shown in the exemplary embodiment of the device 101 in FIG. 2, the degassing device 25 can also be any other device which achieves a reliable removal of gas components 28 in the process water 10, such as a sonotrode, for example.

In Fig. 2, a further device 101 is shown according to a second embodiment of the invention. The device 101 also has an ion exchange diffusion dialysis 31 which comprises a plurality of dialysis membranes 41, 42, 43, 44 and 45. The ion exchanger diffusion dialysis 31 also has several feed flow surface channels 51, 52, 53 and several countercurrent surface channels 61, 62, 63, with a feed flow surface channel 51, 52, 53 or a countercurrent surface channel between the dialysis membranes 41 to 45 61, 62, 63 is arranged. The dialysis membranes 41 to 45 thereby form a membrane stack 46 in which they are arranged parallel to one another. In the membrane stack 46, a feed flow surface channel 52, 53 and a counterflow surface channel 61, 62 then alternate between the dialysis membranes 41 to 45.

Via feed lines 7, the aqueous alkaline solution 2 contaminated with hemicelluloses 22 is introduced simultaneously into all feed stream surface channels 51, 52, 53 so that the aqueous alkaline solution 2 is fed in parallel to all dialysis membranes 41 to 45. This results in an effective enlargement of the dialysis membrane area and increases the throughput of the device

101. The feed stream surface channels 51, 52, 53 of the ion exchanger diffusion dialysis 31 also have outlets 8, via which the dialysate 9, which forms the residue 29 containing hemicelluloses 22, can be removed from the dialysis membranes 41 to 45. The countercurrent surface channels 61, 62, 63 in turn have inlets 11 for the process water 10, or for the process water 10 'degassed in the degassing device 25, to the dialysis membranes 41 to 45, as well as outlets 12 for the diffusate 13 from the dialysis membranes 41 to 45 on.

The aqueous alkaline solution 2 is thus flow-connected to the dialysate 9 via all feed stream surface channels 51, 52, 53 and forms the feed stream 14 therein. The countercurrent 15, on the other hand, is formed in the countercurrent surface channels 61, 62, 63, via which the degassed process water 10 ′ is flow-connected to the diffusate 13. Compared to the first exemplary embodiment in FIG. 1, feed stream 14 and countercurrent 15 are separated by a plurality of dialysis membranes 41 to 45 and each have flow directions 16, 17 that are opposite to one another.

The surface channels 51, 52, 53, 61, 62, 63 each have a height 23, 24 in the device 101, as already shown in FIG. 1 for the device 100, which is between 250 μm and 1000 μm . The feed flow surface channels 51, 52, 53 each have a height 23 and the counterflow surface channels 61, 62, 63 each have a height 24 (only shown for the surface channels 51, 62 in FIG. 2).

As already explained for the first embodiment, the cations 18, 19 in the membrane stack 46 of the second embodiment can also diffuse from the feed stream 14 into the countercurrent 15 through the semipermeable dialysis membranes 41 to 45. Cations 18 are again enriched in the countercurrent 15, the diffusate 13 being formed in parallel in the countercurrent surface channels 61, 62, 63 and excreted as a common recovered alkaline solution 1 via the discharges 12 from the ion exchange diffusion dialysis 31. To compensate for the charge, cations 19 again diffuse from the countercurrent 15 through the dialysis membrane 4 into the feed stream 14. 53 diffuse into the two adjacent countercurrent surface channels 61, 62 and 62, 63, and the cations 19 diffuse from the countercurrent surface channel 61 and 62 into the two adjacent feedstream surface channels 51, 52 and 52, 53, which the The efficiency and throughput of the diffusion increases significantly. The number of surface channels 51, 52, 53, 61, 62, 63 is not limited and can be adapted as desired to the given conditions.

1 also shows a method 200, according to a first embodiment of the invention, for recovering alkaline solution 1 from aqueous alkaline solution 2 contaminated with hemicelluloses 22. In method 200, aqueous alkaline solution 2 is used as feed stream 14 passed through an ion exchange diffusion dialysis 3. In addition, degassed process water 10 ′ is conducted as a countercurrent 15 over the ion exchanger diffusion dialysis 3, in which the feed stream 14 and countercurrent 15 are conducted with opposite flow directions 16, 17 over at least one dialysis membrane 4. The flow over the dialysis membrane 4, which is semipermeable, converts the feed stream 14 and the countercurrent 15 into an alkaline-enriched diffusate 13 and a dialysate 9 enriched with hemicelluloses. The diffusate 13,

Before the process water 10 is supplied as degassed process water 10 'to the ion exchanger diffusion dialysis 3 as a countercurrent 15, gas components 28 are removed from the process water 10. In one embodiment of the invention, the process water 10 is passed through a degassing device 25, in which the process water 10 is brought into contact with a gas-permeable membrane 26 which is under vacuum 27 and thus removes the gas components 28 from the process water 10. The degassed process water 10 ′ is then fed to the ion exchanger diffusion dialysis 3. The degassing device 25 removes at least 90% of the gas components 28 from the process water 10. In particular, at least 90% of the O2 and 95% of the CO2 are removed from the process water 10.

In order to enable an efficient alkali conversion in the ion exchanger diffusion dialysis 3 from the feed stream 14 into the diffusate 13, the feed stream 14 has a flow rate in the feed stream flow channel 5 between 0.1 mm / s and 1.0 mm / s. In a further advantageous embodiment variant, the flow rate in the feed stream flow channel 5 is between 0.2 and 0.5 mm / s. In contrast, the flow velocity of the countercurrent 15 in the countercurrent flow channel 6 is, according to the invention, between 0.5 mm / s and 2.5 mm / s. In a further embodiment variant, the flow velocity in the countercurrent flow channel 6 is between 1.0 and 1.5 mm / s.

To carry out the method 200, as shown in FIG. 1, a device 100 is used which has the ion exchange diffusion dialysis 3.

Alternatively, a method 201 according to a further embodiment of the invention can be carried out using a device 101, as shown in FIG. In such a method 201, the ion exchange diffusion dialysis 31 has a plurality of dialysis membranes 41 to 45. The dialysis membranes 41 to 45 are arranged parallel to one another in a membrane stack 46 and the feed stream 14 and countercurrent 16 are each supplied alternately between two dialysis membranes 41 to 45. The method 201 can thus be operated very cost-effectively with a high throughput.

3 shows a method 202 according to a third embodiment of the invention which, as for the method 200 shown in FIG. 1, has a device 100 with an ion exchange diffusion dialysis 3 with a single dialysis membrane 4. In the method 202, the aqueous alkaline solution 2 is passed through a nanofiltration 70 before it is fed to the ion exchange diffusion dialysis 3. As feed 71, the aqueous alkaline solution 2 is fed directly to the nanofiltration 70 or the permeate 82 is fed to an upstream microfiltration 80, in which this is separated into an alkaline-enriched permeate 72 and a retentate 73 enriched with hemicelluloses. The permeate 72 is separated out and the retentate 73 is fed as feed stream 14 to the ion exchanger diffusion dialysis 3. Since the permeate 72 from the nanofiltration 70 already has a high alkali concentration and is almost completely free of hemicelluloses 22, the permeate 72 can be excreted as recovered alkaline solution 1 together with the diffusate 13 from the ion exchange diffusion dialysis 3. The retentate 73 of the nanofiltration 70, on the other hand, has the residue of hemicelluloses and part of the original amount of alkali. The retentate 73 is then passed as a filtered aqueous alkaline solution 2 ′ over the ion exchange diffusion dialysis 3 in order to convert the remaining alkali concentration into the diffusate 13. the permeate 72 can be excreted as recovered alkaline solution 1 together with the diffusate 13 of the ion exchange diffusion dialysis 3. The retentate 73 of the nanofiltration 70, on the other hand, has the residue of hemicelluloses and part of the original amount of alkali. The retentate 73 is then passed as a filtered aqueous alkaline solution 2 ′ over the ion exchange diffusion dialysis 3 in order to convert the remaining alkali concentration into the diffusate 13. the permeate 72 can be excreted as recovered alkaline solution 1 together with the diffusate 13 of the ion exchange diffusion dialysis 3. The retentate 73 of the nanofiltration 70, on the other hand, has the residue of hemicelluloses and part of the original amount of alkali. The retentate 73 is then passed as a filtered aqueous alkaline solution 2 ′ over the ion exchange diffusion dialysis 3 in order to convert the remaining alkali concentration into the diffusate 13.

As shown in FIG. 3, in addition to the nanofiltration 70, the aqueous alkaline solution 2 is previously passed through a microfiltration 80 which removes the coarse impurities 84 from the aqueous solution 2. The aqueous alkaline solution 2 is fed as feed 81 to microfiltration 80, and permeate 82 is fed to microfiltration 80 as feed 71 to nanofiltration 70. The impurities 84 contained in the retentate 83 are eliminated accordingly.

In the method 200, 201 and 202 according to FIGS. 1, 2 and 3, the dialysis membranes 4 and 41 to 45 can be cleaned at regular intervals in order to remove deposits, for example due to hemicelluloses 22. Diffusate 13 is passed through feed stream surface channels 5, 51, 52, 53 and through countercurrent surface channels 6, 61, 62, 63, diffusate 13 having parallel flow directions 16, 17 in feed stream 14 and countercurrent 15. The diffusate 13 is circulated in parallel through feed stream 14 and countercurrent 15 for a predetermined cleaning time, although this was not shown in more detail in the figures.

4 shows a method 500 according to the invention for producing regenerated cellulosic molded bodies 501. Process 500 is in particular a viscose or modal process for the production of viscose or modal fibers 502. In process 500, a cellulose 503 is alkalized in an alkalization stage 510 with caustic soda 504 in order to obtain an alkalized cellulose (alkali cellulose) 505. In a further step, a press liquor 506 is separated from the alkalized cellulose 505 by pressing 520 from the alkali cellulose 505. The pressed-out alkali cellulose 505 is then further processed in a maturing and dissolving stage 540 to form a viscose, which is spun out in an extrusion stage 550 to form the regenerated cellulosic molded bodies 501, in particular the viscose fibers 502.

The press liquor 506 then contains hemicelluloses 22 in an aqueous alkaline solution 2, and is in a recovery stage 530 in a process 200 in a fraction 507 containing essentially hemicelluloses and

separated into a fraction 508 containing essentially sodium hydroxide solution. The fraction 508 is the recovered alkaline solution 1, which is produced in the process 200 as an alkaline-enriched diffusate 13. The fraction 507 is in turn the dialysate 9 enriched with hemicelluloses 22 from the process 200.

The press liquor 506 can, however, also be separated according to a method 201 or 202, or according to a method according to one of claims 1 to 13 into a fraction 507 containing essentially hemicelluloses and a fraction 508 containing essentially sodium hydroxide solution, which is the For the sake of simplicity, however, it was only shown for the method 200 in FIG. 5.

The fraction 508 containing essentially sodium hydroxide solution, which contains the recovered alkaline solution 1, is then returned to the alkalization stage 510 for reuse in the process 500, in particular for the further alkalization of cellulose 503.

The invention also relates to a device for producing regenerated cellulosic molded bodies 501 from cellulose 503, in particular for carrying out the method 500, which, however, was not shown in detail in the figures. The device has an alkalization stage 510 in which pulp 503 is alkalized with sodium hydroxide 504 to form alkali cellulose 505 and is freed from the excess press liquor 506 by pressing 520. The device also has a recovery stage 530 with an ion exchanger diffusion dialysis 3, 31 for separating the press liquor 506 into a fraction 507 containing essentially hemicelluloses and a fraction 508 containing essentially sodium hydroxide solution,

The recovery stage 530 for separating the press liquor 506 into a fraction 507 containing essentially hemicelluloses and a fraction 508 containing essentially sodium hydroxide has, according to the invention, a device 100, 101 according to one of claims 9 to 14, which has an ion exchange diffusion dialysis 3 , 31 contains.

Examples

To demonstrate the advantages according to the invention of the method for recovering alkaline solution from aqueous alkaline solution contaminated with hemicelluloses, two comparative experiments V1 and V2 were carried out.

The tests were carried out on a system with: FKD Fumatech cation exchange membrane (unreinforced, thickness 0.7-1 mm); Membrane stack with a total of 700 dialysis membranes; specific flow rate of the feed of 0.5 l / m 2 h, specific flow rate of the process water of 1.0 l / m 2 h.

In the first experiment V1, in accordance with the method according to the invention, the gas components were removed from the process water of the countercurrent before being fed to the ion exchanger diffusion dialysis.

In the second experiment V2 (comparative example), the removal of the gas components from the process water of the countercurrent was dispensed with, and the process water was fed directly to the ion exchanger diffusion dialysis.

In both experiments V1, V2, the change in the yield of the recovered alkaline solution was measured over the operating time since the last cleaning of the dialysis membrane.

5 shows a diagram 700 which shows the change in the yield 710 in percent, based on the maximum yield, over the operating time 720 in hours. Experiment V1 is represented by the measuring points 701, which were recorded at regular time intervals. From the measurement points 701 of experiment V1 it can be seen in particular that a very constant and stable yield 710 can be achieved in the method according to the invention after the gas components have been removed from the process water. Even after an operating time 720 of 24 hours, no decrease in the yield 710 could be found. Experiment V2, represented by the measuring points 702, on the other hand, shows a curve in the yield 710 that falls from the start of operation.

Table 1 shows yields after different operating times (corresponding to the values ​​of curves 701 and 702 in FIG. 5) for experiments V1 and V2.

Table 1: Change in the yield in effective alkali (EA [%]) with continuous operating time

Example EA [

V1 97.30 98.26 98.47 99.10 99.22

V2 97.70 94.54 90.94 72.94 71.50

According to experiments V1 and V2 it is thus shown that the method according to the invention for recycling aqueous alkaline solutions according to claims 1 to 8 has a particularly low maintenance outlay, and the need for rinsing is significantly reduced and the service life is extended accordingly.

Expectations

1. A method for recovering alkaline solution (1) from aqueous alkaline solution (2) contaminated with hemicelluloses (22), in which the aqueous alkaline solution (2) as a feed stream (14) and process water (10) as a countercurrent (15) an ion exchange diffusion dialysis (3, 31) with at least one dialysis membrane (4, 41, 42, 43, 44, 45) between feed stream (14) and countercurrent (15) can be performed and in an alkaline-enriched diffusate (13) as recovered alkaline solution (1) and a dialysate (9) enriched with hemicelluloses (22) are converted, characterized in that gas components (28) from the process water (10) of the countercurrent (15 ) must be removed.

2. The method according to claim 1, characterized in that the process water (10) before being fed to the ion exchanger diffusion dialysis (3, 31) is passed through a degassing device (25), in which at least 90% of the process water (10) contained therein Gas components (28), in particular 90% of the O2 dissolved therein and in particular 95% of the CO2 dissolved therein, are removed.

3. The method according to claim 1 or 2, characterized in that the process water (10) before being fed to the ion exchanger diffusion dialysis (3, 31) has a content of a maximum of 1.0 mg / l, in particular of a maximum of 0.7 mg / l , on dissolved gas components (28).

4. The method according to any one of claims 1 to 3, characterized in that the flow rate of the feed stream (14) between 0.1 and 1, 0 mm / s, in particular between 0.2 and 0.5 mm / s, and the flow rate of the countercurrent (15) is between 0.5 and 2.5 mm / s, in particular between 1.0 and 1.5 mm / s.

5. The method according to any one of claims 1 to 4, in which the aqueous alkaline solution (2) is passed through a nanofiltration (70), in which it is separated into an alkaline permeate (72) and a retentate (73) enriched with hemicelluloses , the permeate (72) being separated out and the retentate (73) being fed as a feed stream (14) to the ion exchange diffusion dialysis (3, 31).

6. The method according to claim 5, wherein the aqueous alkaline solution (2) is passed through a microfiltration (80) before the nanofiltration (70), the permeate (82) of the microfiltration (80) being passed over the nanofiltration (70) .

7. The method according to any one of claims 1 to 6, wherein for cleaning the dialysis membrane (4, 41, 42, 43, 44, 45) at regular intervals diffusate (13) in parallel flow over the dialysis membrane (4, 41, 42, 43 , 44, 45).

8. The method according to any one of claims 1 to 7, in which, in a further step, acid is added to the hemicelluloses (22) enriched dialysate (9) and a xylan-containing precipitate is precipitated from the resulting precipitation suspension.

9. The method according to claim 8, in which acid is continuously added to the dialysate until the pH falls below 4 in the precipitation suspension and the temperature of the precipitation suspension does not fall below a precipitation temperature during precipitation, the precipitation temperature at least 40 ° C is.

10. The method according to any one of claims 1 to 9, characterized in that the method (200, 201, 202) is carried out using a device (100, 101) according to one of claims 1 1 to 16.

11. Device for recovering alkaline solution (1) from aqueous alkaline solution (2) contaminated with hemicelluloses (22), having an ion exchange diffusion dialysis (3, 31) with at least one dialysis membrane (4, 41, 42, 43, 44, 45) and each with at least one feed stream surface channel (5, 51, 52, 53) which has a feed (7) for aqueous alkaline solution (2) contaminated with hemicelluloses (22) as a feed stream (14) to the dialysis membrane (4, 41 , 42, 43, 44, 45), and a discharge (8) for dialysate (9) from the dialysis membrane (4, 41, 42, 43, 44, 45), and a counterflow surface channel (6, 61, 62 , 63), which has a feed (11) for process water (10) as countercurrent (15) to the dialysis membrane (4, 41, 42, 43, 44, 45) and a discharge (12) for diffusate (13) from the dialysis membrane (4, 41, 42, 43, 44, 45),wherein the feed stream (14) im

Feed flow surface channel (5, 51, 52, 53) and the counter flow (15) in the counter flow surface channel (6, 61, 62, 63) are separated by the dialysis membrane (4, 41, 42, 43, 44, 45) and have an opposite flow direction (16, 17) and wherein the dialysis membrane (4, 41, 42, 43, 44, 45) is semipermeable, so that alkaline ions (18) from the aqueous alkaline solution (2) via the dialysis membrane (4, 41, 42, 43, 44, 45) are transported into the diffusate (13) which contains the recovered alkaline solution (1), characterized in that the height (23, 24) of the feed stream surface channel (5, 51, 52, 53) and the countercurrent surface channel (6, 61, 62, 63) are each between 250 pm and 1000 pm, in particular between 400 pm and 600 pm, and that the device (100, 101) has a degassing device (25),for removing gas components (28) from the process water (10), upstream of the ion exchanger diffusion dialysis (3, 31) through which the process water (10) is passed.

12. The device according to claim 11, wherein the dialysate (9) with the aqueous alkaline solution (2) via the feed stream surface channel (5, 51, 52, 53) and the diffusate (13) with the process water (10) via the Countercurrent surface channel (6, 61, 62, 63) are flow-connected.

13. The device according to claim 1 1 or 12, characterized in that the degassing device (25) has a gas-permeable membrane (26) under vacuum (27), over which the process water (10) in the degassing device (25) is guided, to remove the gas components (28) from the process water (10).

14. Device according to one of claims 11 to 13, in which the dialysis membrane (4, 41, 42, 43, 44, 45) comprises a thermoplastic, in particular polyetheretherketone.

15. Device according to one of claims 11 to 14, in which the ion exchange diffusion dialysis (31) has several dialysis membranes (41, 42, 43, 44, 45) and several feed stream (51, 52, 53) and countercurrent surface channels (61 , 62, 63), with at least one feed stream surface channel (52, 53) or one countercurrent surface channel (61, 62) being arranged between two dialysis membranes (41, 42, 43, 44, 45).

16. The device according to claim 15, wherein the dialysis membranes (41, 42, 43, 44, 45) are arranged parallel to one another in a membrane stack (46), with a feed stream surface channel (52, 53) and a countercurrent surface channel alternating (61, 62) is arranged between two dialysis membranes (41, 42, 43, 44, 45).

17. A method for producing regenerated cellulosic moldings, in particular a viscose method, in which a cellulose (503) is alkalized in an alkalization stage (510) with sodium hydroxide solution (504) in order to obtain an alkali cellulose (505), by pressing (520) a press liquor (506) ) is separated from the alkalized pulp (505) which has hemicelluloses (22) in an aqueous alkaline solution (2), and the press liquor (506) in a method (200, 201, 202) according to one of claims 1 to 10 in a fraction (507) containing essentially hemicelluloses (22) and a fraction (508) containing essentially recovered sodium hydroxide solution is separated.

18. The method according to claim 17, in which the fraction (508) containing essentially recovered sodium hydroxide solution is returned to the alkalization stage (510) for reuse in the viscose process (500), in particular for further alkalization (510) of pulp (503).

19. Apparatus for producing regenerated cellulosic molded bodies from cellulose (503), in particular according to the viscose process (500), having an alkalization stage (510) in which cellulose (503) is alkalized with sodium hydroxide solution (504) to form alkali cellulose (505) and is made alkaline by pressing (520 ) is freed from the excess press liquor (506) and a recovery stage (530) with an ion exchange diffusion dialysis (3, 31) for separating the press liquor (506) into a fraction (507) containing essentially hemicelluloses (22) and into a fraction (508) containing essentially recovered sodium hydroxide solution, the press liquor (506) being fed from the alkalization stage (510) to the recovery stage (530) and the fraction (508) containing essentially recovered sodium hydroxide solution being returned to the alkalization stage (510).

20. The device according to claim 19, wherein the recovery stage (530) for separating the press liquor (506) into a fraction (507) containing substantially hemicelluloses (22) and a fraction (508) containing substantially

Recovered sodium hydroxide solution has a device (100, 101) containing the ion exchange diffusion dialysis (3, 31) according to one of Claims 1 1 to 16.