EP3722501A1 - Method for the recovery of alkaline solution and method for producing regenerated cellulose moulded parts comprising such a method - Google Patents

Abstract

A method (100, 101, 102) for recovering an alkaline solution (1) from a waste liquor (2) contaminated with hemicelluloses (5) and a method (200, 300) for treating (210, 310) a starting material containing cellulose are used (203, 303) having such a method (100, 101, 102) shown, in which the waste liquor (2) as a feed stream (6) via a separation process (7, 50) into at least one alkaline-enriched target fraction (8), and at least a residual fraction (9) containing hemicelluloses (5) is separated. In order to obtain a recovered alkaline solution with high purity, it is proposed that the separation process (7, 50) is a chromatographic separation process (7, 50) and the feed stream (6) therein as part of a mobile phase (10) through an alkali-resistant stationary one Phase (11) is performed in order to separate this into the target fraction (8) and the remaining fraction (9).

Description

Technical area

Process for the recovery of alkaline solution from a waste liquor contaminated with hemicelluloses, in which the waste liquor is separated as a feed stream into at least one alkaline-enriched target fraction and at least one residual fraction containing hemicelluloses.

In addition, the invention relates to a method for producing regenerated cellulosic molded bodies comprising the aforementioned method, as well as a method for producing cellulose comprising the aforementioned method.

State of the art

It is known that both in processes for the production of cellulose and in processes for the production of regenerated cellulosic moldings (for example according to a viscose or modal process), waste liquors accumulate as material streams which are enriched and contaminated 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 apart from cellulose, which occur as a component of plant cell walls, the matrix of which consists of fibrillar, partially crystalline cellulose, as well as low molecular weight breakdown products of these polyoses and cellulose, e.g. hydroxycarboxylic acids, which can be formed during digestion processes. In contrast to cellulose, which is a non-branched homopolymer of glucose, hemicelluloses are heteropolymers of the above-mentioned pentoses and hexoses. Often these have a homopolymer or heteropolymer as the main chain, to which branches from other sugars are bound and thus an irregular one Form macromolecule. Hemicelluloses also have significantly lower degrees of polymerisation 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 γ-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 β- and γ-hemicelluloses can be dissolved in 17.5% sodium hydroxide solution, α-cellulose is insoluble. During the subsequent neutralization with sulfuric acid, the β-hemicelluloses then precipitate, while the γ-hemicelluloses remain in solution.

From the state of the 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 is obtained in the viscose process when alkali cellulose is pressed and is usually an aqueous alkaline solution (containing sodium hydroxide solution) contaminated with hemicelluloses, is fed as a feed stream through diffusion dialysis in order to obtain a recovered alkaline solution enriched with sodium hydroxide solution.

Processes for the recovery of alkaline solution from feed streams contaminated with hemicelluloses are generally faced with the challenge of achieving high purity in the recovered solution while at the same time keeping the dilutions in the recovered solution as low as possible. In particular, this requires a high degree of separation between hemicelluloses and alkaline solutions. Recovery processes known from the state of the art, such as nanofiltration or dialysis processes, can, however, in some cases only insufficiently meet these requirements, since such processes often have poor selectivity and lead to high dilution in the recovered solution, which in turn leads to an additional concentration of the recovered solution Solution is needed.

Disclosure of the invention

It is therefore an object of the invention to provide a method of the type mentioned at the beginning which ensures a high degree of purity of the recovered alkaline solution.

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

If the separation process is a chromatographic separation process and the feed stream is passed through a stationary phase as part of a mobile phase in order to separate it into the target fraction and the remaining fraction, a particularly high degree of separation between hemicelluloses and alkaline solutions can be achieved, and thus an alkaline solution enriched target fraction with low impurities can be obtained. If the stationary phase is also alkali-resistant, a reliable process with a long service life can be made possible at the same time.

In other words: the feed stream, which is fed from a waste liquor contaminated with hemicelluloses, is separated into the target fraction and the residual fraction using a chromatographic separation process. The waste liquor is usually an aqueous alkaline solution with a content of dissolved substances between 50 g / kg and 400 g / kg (including base and hemicelluloses) and is used as a waste product or as a material flow from various processes for processing, digestion and / or the processing of cellulose, such as processes for the production of cellulose or regenerated cellulosic molded bodies. The waste liquor, and thus the feed stream, has a number of dissolved substances: for example, these are the base of the alkaline solution, the hemicelluloses or impurities from a pulp. The base can be, for example, NaOH, KOH, or other alkaline solvents customarily used in such digestion and processing methods. In the chromatographic separation process, the feed stream is then passed through the stationary phase as part of the mobile phase in order to achieve the separation into target and residual fractions. The dissolved substances are taken up by the mobile phase and transported through the stationary phase as a transport medium. The solvent helps to transport the dissolved substances through the stationary phase, whereby these interact with the stationary phase. The strength of these interactions depends on both the nature of the substance and the mobile and stationary phase dependent. Stronger interaction with the stationary phase leads to higher mean residence times (retention times) in the separation column, as a result of which the substances are retained more strongly and thus migrate more slowly through the stationary phase. Due to the different strengths of the interactions between the different dissolved substances and the stationary phase, there is finally a spatial separation of the dissolved substances in the mobile phase, creating a separation profile along the stationary phase in the direction of flow. The separation profile reflects the local course of the concentrations of the dissolved substances in the mobile phase along the stationary phase. In the separation profile, areas can arise in which only individual dissolved substances, such as base or the hemicelluloses, are present in high concentration in the mobile phase. This spatial separation enables a targeted discharge of individual substances from the stationary phase according to their concentration distribution in the separation profile, which, in contrast to known methods such as dialysis or nanofiltration, enables the alkaline solution to be recovered with a high degree of separation.

The mobile phase is understood to mean in particular all liquid or dissolved substances that are transported through the chromatographic system. The mobile phase usually comprises both the substances that are dissolved in the feed stream and are introduced into the mobile phase as eluent via this, as well as those substances that are introduced into the mobile phase as mobile phase or eluent and thereby as transport medium for the dissolved substances are used.

In the context of the method according to the invention, the fraction which is alkaline-enriched compared to the residual fraction is designated as the target fraction. This can advantageously consist essentially of recovered alkaline solution, subject to unavoidable impurities. The hemicelluloses and other unspecific impurities mainly remain in the residual fraction. The target fraction accordingly has a higher alkali concentration than the remaining fraction. At the same time, the target fraction is depleted in relation to the residual fraction of hemicelluloses, that is to say has a lower concentration of hemicelluloses than the residual fraction. The alkali concentration can in each case as Mole concentration (g / kg) of the mixture component, based on the total volume of the mixed phase, can be determined.

If the target fraction is essentially free from hemicelluloses, a target fraction containing an alkaline solution can be recovered from the waste liquor with particularly high purity.

If the concentration of alkaline solution in the target fraction is also higher than the concentration of alkaline solution in the feed stream, a target fraction can be obtained which is also alkaline-enriched compared to the feed stream. Additional subsequent process steps for concentrating the recovered alkaline solution can thus be dispensed with, whereby a process which is simpler and more efficient in terms of process technology can be created.

The reliability of the method for recovering alkaline solution can be further increased if the waste liquor in the feed stream has an alkali concentration of at least 50 g / kg, preferably of at least 70 g / kg. In addition, the recovered alkaline solution in the target fraction has an alkali concentration of at least 50 g / kg.

The reliability of the method can be further increased if the stationary phase has an ion exchange resin and the chromatographic separation method is thus ion exchange chromatography. Because of the ion exchange resin, the stationary phase can enable the dissolved substances to be separated on the basis of their charges. Such resins can be, for example, gel resins or macroporous resins that allow liquids to pass through. The ion exchange resin in particular forms a matrix of charged functional groups which can reversibly bind counterions.

The selectivity and selectivity of the process can be further improved if the ion exchange resin is a cation exchange resin. The stationary phase can thus reversibly bind cations from the mobile phase in the matrix and release them back to it. This is particularly advantageous if the dissolved substances have alkaline solutions, as in the case of the present invention. The cations of the alkaline solution (for example Na + ions in the case of a sodium hydroxide solution as the alkaline solution) have a high affinity to bind to the charged functional groups in the matrix of the cation exchanger, while others Substances such as hemicelluloses have a significantly lower affinity for binding to the functional groups. The alkaline solution therefore has a longer retention time in the stationary phase than the hemicelluloses, which enables the formation of a separation profile with a sharp demarcation between hemicelluloses and alkaline solution in the mobile phase.

The service life of the chromatographic separation process can be improved if the ion exchange resin is alkali-resistant. Such an alkali-resistant ion exchange resin can in particular be such that it is essentially not dissolved or degraded by the mobile phase, or that in permanent contact with an alkaline solution, which can have a pH of up to 14, no changes in structure or function of the resin occur. A particularly reliable method can thus be created.

The reliability of the process can be further improved if the cation exchange resin is selected from the group of the styrene-divinylbenzene copolymers. In particular, sulfonated styrene-divinylbenzene copolymers can preferably be suitable as cation exchange resins according to the invention. If such cation exchange resins have a degree of crosslinking greater than 2%, in particular greater than 4%, then the alkali resistance of the cation exchange resin can be further improved.

The reliability of the method can be further improved if a liquid solvent is supplied to the mobile phase as the mobile phase, in which the waste liquor contaminated with hemicelluloses is at least partially soluble. In this way it can be ensured that the individual dissolved substances from the waste liquor, which are introduced into the mobile phase via the feed stream, have a high solubility in the latter and do not precipitate out of it while it is passed through the stationary phase. Particularly preferred mobile solvents can be, for example, solvents which, on the one hand, reliably take up and transport the dissolved substances from the feed stream, and, on the other hand, allow the dissolved substances to be reliably and controlled dissolution from the stationary phase. A suitable choice of solvent can also influence the retention time of the dissolved substances in the mobile phase.

In one embodiment of the invention, an aqueous NaOH solution can be used as the mobile phase. This is particularly advantageous when the waste liquor for example an aqueous NaOH solution contaminated with hemicelluloses. The target fraction can then be a recovered NaOH solution with low impurities, which has a higher NaOH concentration than the waste liquor in the feed stream. In addition, contamination of the target fraction with foreign substances can be completely avoided.

In a further embodiment of the invention, water can be used as the mobile phase.

In the present invention, liquid chromatography is generally used as the chromatographic separation method, a liquid serving as the mobile phase, or the mobile phase being fed by a liquid mobile phase. The mobile phase therefore also leaves the stationary phase as a liquid eluate in which the separating profile is formed.

If, in the chromatographic separation process, the mobile phase is passed through a separation system with several separating columns connected in series with one another, a separation of the dissolved substances in the mobile phase and thus a sharp delimitation with small overlapping areas of the individual substances in the separation profile formed therein can be achieved in a particularly reliable manner. The separation system preferably forms a closed circuit in which the mobile phase circulates. In particular, through repeated circulation of the mobile phase in the separation system, an even more reliable delimitation of the substances in the separation profile can be achieved, which enables the alkaline solution to be recovered with high purity. The separation profile formed in the separation system corresponds to a local concentration distribution of dissolved substances in the separation system or in the separation columns of the separation system.

The advantages mentioned above can be expanded further if the chromatographic separation process is an SMB chromatography process. In an SMB chromatography process, the mobile phase circulates at least partially several times in the separation system, part of the mobile phase being discharged from the separation system in each case. The mobile phase can advantageously be discharged at those points in the separation system at which the concentration for a specific dissolved substance in the separation profile reaches its maximum, or at which the concentrations for all other dissolved substances Reach minimum. In this way it can be ensured that when part of the mobile phase is discharged as the eluate, it essentially contains only one desired dissolved substance (such as the alkaline solution to be recovered). Recovery of the alkaline solution with high purity can thus be achieved.

A particularly reliable method for the recovery of alkaline solution can be created if the mobile phase or the feed stream are fed into the separation system (and into the mobile phase) at different positions between two flow-connected separation columns and the target fraction or the remaining fraction respectively be discharged from the separation system at different positions between two flow-connected separation columns. For example, according to the separation profile in the mobile phase, the target fraction can always be discharged at that position in the separation system at which the highest concentration of those dissolved substances is present that are to be recovered via the target fraction, i.e. in particular the alkaline solution in the case of the target fraction. The target fraction can preferably be discharged at that position at which the relative concentration of the alkaline solution is highest, that is to say the concentrations of all other dissolved substances are lowest. A target fraction with a very high purity can be obtained in this way. Equivalent to this, the remaining fraction can be discharged at that position in the separation system at which, according to the separation profile, the concentrations of the other dissolved substances are maximum or the concentration of the alkaline solution is minimal. In addition, mobile phase and feed stream can be introduced at appropriate positions in the separation system in order to ensure a continuous flow of mobile phase in the separation system.

The yield of the recovered alkaline solution can be increased further if the feed stream is passed through a nanofiltration before it is fed to the chromatographic separation process, and the mobile phase is charged with the permeate or the retentate from the nanofiltration instead of the feed stream. Nanofiltration separates the feed stream into an alkaline permeate and a retentate enriched with hemicelluloses. Due to the high degree of separation of the nanofiltration, the majority of the alkaline solution contained in the feed stream can pass through the nanofiltration as permeate, while the solution in the feed stream Substances that consist of large molecules, such as hemicelluloses, are retained by the nanofiltration as retentate and excreted. The permeate can then comprise essentially recovered alkaline solution and optionally residues of hemicelluloses. The retentate, on the other hand, can contain the majority of the hemicelluloses from the feed stream and residues of alkaline solution. If the mobile phase of the separation process is charged with the permeate from nanofiltration instead of the feed stream, the hemicellulose load in the chromatographic separation process can be significantly reduced, whereby a process for recovering the alkaline solution with high purity can be achieved. On the other hand, the mobile phase of the separation process can also be charged with the retentate from the nanofiltration, whereby the residues of alkaline solution can be reliably recovered from the retentate and a method for recovering alkaline solution with a very high recovery rate can be created. In addition, a residual fraction containing hemicelluloses essentially free of alkaline solution can be created, which is particularly suitable for further processing, for example the separation and isolation of polysaccharides such as xylans, mannans, galactans, etc.

If the feed stream is also passed through a pre-filtration before it is fed to the chromatographic separation process, unwanted particles and / or coarse impurities can be reliably removed from the feed stream, which can have a detrimental effect on the stationary phase in the chromatographic separation process, for example through the formation of deposits . The particles can be removed particularly reliably if the prefiltration is a microfiltration. The permeate of the prefiltration then contains the feed stream from which particles have been removed, which can then be fed to the chromatographic separation process directly or via an optionally upstream nanofiltration. The reliability of the method according to the invention can thus be further improved.

If the eluent is passed through a degassing device before it is fed to the chromatographic separation process, the gas components can be removed from the eluent in a process-technically simple manner. If the gas components contained therein are removed from the solvent, a solvent that is essentially free of gas components can be provided, which can further increase the reliability of the method according to the invention. By removing the gas components from the eluent, it can be ensured that no gas bubbles form in the stationary phase of the chromatographic separation process, which negatively impair or permanently disrupt the exchange of substances via the stationary phase and ultimately bring it to a standstill. In addition, too high an O ₂ content in the mobile phase can damage the resin of the stationary phase and thus significantly shorten the service life. By removing the gas components from the solvent, a reliable process with a long service life can be created.

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

The gas components can be removed from the solvent particularly reliably if the solvent is exposed to a vacuum in the degassing device. In this way, a cost-effective and technically simple method for degassing the solvent can be provided, which can ensure reliable removal of the gas components. The solvent can be passed over a gas-permeable membrane under vacuum in order to enable a high throughput. Alternatively, the solvent 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 method according to the invention can also be advantageously used in a method according to claim 10.

In such a process, in which a starting material containing cellulose is treated with an aqueous alkaline treatment solution and in a further step a waste liquor contaminated with hemicelluloses is obtained from the starting material treated with the treatment solution, this waste liquor can be used as a feed stream to a process for the recovery of alkaline Solution according to any one of claims 1 to 9 are fed, wherein a recovered alkaline solution is obtained from the target fraction. The waste liquor can be obtained, for example, by separating the starting material treated with the treatment solution, for example by filtering, pressing, washing out, dissolving out, etc. of the treatment solution, at least part of the used treatment solution being obtained as waste liquor together with any dissolving, washing or filtering liquid. Treatment of the starting material with an alkaline solution in the context of the present invention can be, for example, alkalizing or dissolving the cellulose contained in the starting material. Such a starting material can be, for example, a pulp or a pulp precursor. In the course of the process according to one of claims 1 to 9, the feed stream containing the waste liquor can be separated into a target fraction and a residual fraction, the target fraction having the recovered alkaline solution and the remaining fraction largely containing the hemicelluloses from the waste liquor. The recovered alkaline solution obtained in this way can be recovered with high purity and low levels of impurities.

Such a process mentioned above can be particularly suitable in a process for the production of regenerated cellulosic shaped bodies, the starting material being a cellulose, preferably a chemical pulp (dissolving pulp), which is suitable for the production of regenerated cellulosic shaped bodies.

The advantages mentioned can be further improved if the recovered alkaline solution is used for further treatment of the starting material in the method described above. The recovered alkaline solution can be returned to the treatment stage in which the starting material is treated with the alkaline solution in order to treat further starting material. A particularly cost-efficient process with little use of resources can thus be created.

If the treatment includes an alkalization of the starting material in order to obtain alkali cellulose, the aforementioned effects and advantages can be used particularly advantageously in a viscose or modal process. Viscose and modal processes are processes for the production of regenerated cellulosic moldings in which an aqueous NaOH solution is used as the treatment solution. In an alkalization stage (treatment stage), the cellulose (starting material) is treated with the NaOH solution for alkalization or conversion of cellulose into alkali cellulose, and then the NaOH solution is separated again from the alkali cellulose by pressing. From the Waste liquor or press liquor can then be obtained according to a method according to one of claims 1 to 9, a recovered, NaOH-containing, alkaline solution by being fed as a feed stream to the separation process, whereby a more cost-efficient viscose or modal process with lower resource consumption can be created.

Subsequently, the recovered alkaline solution obtained can then be returned to the alkalization stage for further alkalization of cellulose. Alternatively, the recovered alkaline solution can also be used for the solution of a cellulose derivative (for example cellulose xanthogenate) to produce a spinning mass. In this way, viscose or modal processes can be created with a closed material cycle, which can be characterized by high economic efficiency.

Alternatively, if the treatment includes chemical removal of hemicelluloses from the starting material, the treatment solution having an extraction liquor, the advantageous effects of the method can be particularly noticeable in a method for producing a pulp, in particular the production of chemical pulp. In such a method for producing a pulp, or pulp process, a starting material, which is preferably a pulp obtained from a cooking stage, is treated in an extraction stage as a treatment stage with an alkaline solution as extraction liquor. The extraction liquor can preferably be an aqueous NaOH solution. The treatment with the extraction liquor detaches the hemicelluloses from the starting material and in a subsequent step the extraction liquor is separated from the starting material by washing and / or pressing and a waste liquor contaminated with hemicelluloses is obtained. The extraction stage thus includes the chemical removal of hemicelluloses from the starting material. The waste liquor obtained can then be fed to a process for the recovery of alkaline solution according to one of Claims 1 to 9, a target fraction with recovered alkaline solution being obtained.

The recovered alkaline solution obtained in this way can then be returned to the extraction stage in the pulp process for further removal of hemicelluloses from the starting material. That way, a Pulp processes with a closed cycle and lower resource consumption are created.

Brief description of the drawings

Fig. 1

eine schematische Darstellung eines Verfahrens zur Rückgewinnung von alkalischer Lösung gemäß einer ersten Ausführungsform,

Fig. 2

eine schematische Darstellung eines Verfahrens zur Rückgewinnung von alkalischer Lösung gemäß einer zweiten Ausführungsform in einem ersten Verfahrensschritt,

Fig. 3

eine schematische Darstellung des Verfahrens gemäß Fig. 2 in einem zweiten Verfahrensschritt,

Fig. 4

eine schematische Darstellung eines Verfahrens zur Rückgewinnung von alkalischer Lösung gemäß einer dritten Ausführungsform,

Fig. 5

eine schematische Darstellung eines Verfahrens zur Herstellung von regenerierten cellulosischen Formkörpern,

Fig. 6

eine schematische Darstellung eines Verfahrens zur Herstellung eines Zellstoffs, und

Fig. 7

die Analyseergebnisse eines Trennprofils in einer mobilen Phase gemäß einem ersten Beispiel.

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

Fig. 1

a schematic representation of a method for recovering alkaline solution according to a first embodiment,

Fig. 2

a schematic representation of a process for the recovery of alkaline solution according to a second embodiment in a first process step,

Fig. 3

a schematic representation of the method according to Fig. 2 in a second process step,

Fig. 4

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

Fig. 5

a schematic representation of a process for the production of regenerated cellulosic moldings,

Fig. 6

a schematic representation of a method for producing a pulp, and

Fig. 7

the analysis results of a separation profile in a mobile phase according to a first example.

Ways of Carrying Out the Invention

In the Figures 1 to 4 processes 100, 101, 102 for recovering alkaline solution 1 from a waste liquor 2 are shown. The waste liquor 2 is an aqueous alkaline solution 2 which has at least one base 4 and hemicelluloses 5 as dissolved substances 3. The waste liquor 2 is then passed as a feed stream 6 through a chromatographic separation process 7, 50, the feed stream 6 being separated into at least one target fraction 8 and a residual fraction 9.

In Fig. 1 shows a chromatographic separation process 7 with a separation column 12 according to a first embodiment of the invention, in which a mobile phase 10 is passed over a stationary phase 11 in the separation column 12, the mobile phase 10 being fed with the feed stream 6 and the feed stream 6 as part the mobile phase 10, the stationary phase 11 passes. The substances 3 dissolved in the waste liquor 2 thus reach the mobile phase 10 via the feed stream 6 and are transported in the mobile phase 10 through the stationary phase 11. The mobile phase 10 itself is also supplied by a solvent 13 as the mobile phase 14, which ensures the transport of the dissolved substances 3. In the exemplary embodiment, the solvent 13 can preferably be water or an aqueous alkaline solution, such as sodium hydroxide solution. The dissolved substances 3 interact in the manner specific for the type of dissolved substances 3 during transport through the stationary phase 11 with this, whereby they are eluted from the stationary phase 11 with different retention times and pass into the mobile phase 10 and thus finally are present in target fraction 8 and residual fraction 9 in different concentrations and concentration ratios to one another. The stationary phase 11 preferably consists of a sulfonated polystyrene-divinylbenzene resin as the cation exchange resin 15, which forms a matrix 16 of negatively charged functional groups 17 distributed in the separation column 12. The cations 18 of the base 4 can accordingly interact more strongly with the functional groups 17 in the cation exchange resin 15 and thus have a longer retention time in the stationary phase 11 than the hemicelluloses 5.

Due to the delay of the base 4 with respect to the hemicelluloses 5 when passing through the stationary phase 11, a spatial separation or retardation of the dissolved substances 3 takes place along the stationary phase 11 in the separation column 12 in the flow direction 19. As a result of this spatial separation, a separation profile 20 is formed in the mobile phase 10 which reflects the local distribution of the concentrations of the dissolved substances 3 in the mobile phase 10 after the separation column 12. When the mobile phase 10 emerges from the separation column 12 of the chromatographic separation process 7, the local distribution of the separation profile 20 in the mobile phase 10 is then reflected as a time-dependent concentration distribution 21, 22 of the dissolved substances 3 and can be used as a concentration 27, or one of the Concentration 27 linearly dependent size of the respective dissolved substance 3 as a function of time 28 can be represented.

The concentration distribution 21 of the hemicelluloses 5 and the concentration distribution 22 of the base 4 each have different positions of the concentration maxima 23, 24, whereby the separation profile 20 can be divided into two regions 25, 26. The first area 25 represents that Part of the separation profile 20 in which the mobile phase 10 predominantly contains hemicelluloses 5 as dissolved substances 3, while the second area 26 represents the part of the separation profile 20 in which the mobile phase 10 almost exclusively contains the base 4 as dissolved substances 3.

In the procedure according to Fig. 1 is, in order to separate the feed stream 6, which is led as part of the mobile phase 10 through the separation column 12, into the target fraction 8 and the secondary fraction 9, the mobile phase 10 at the exit from the separation column 12 according to the areas 25, 26 of the separation profile separated. The first area 25, which is characterized by a high concentration 27 of hemicelluloses 5, is excreted as residual fraction 9, while the second area 26, which is characterized by a high concentration 27 of the base 4, is obtained as target fraction 8. The target fraction 8 then contains the recovered alkaline solution 1, while the remaining fraction 9 contains a solution 29 enriched with hemicelluloses. The target fraction 8 then has a higher concentration of the base 4 in relation to the hemicelluloses 5 than the residual fraction 9 and the waste liquor 2, while the residual fraction 9 has a higher concentration of the hemicelluloses 5 in relation to the base 4 than the target fraction 8 and the waste liquor 2 has.

In the Fig. 2 and 3 a method 101 according to a second embodiment of the invention is shown, in which a mobile phase 10 by an SMB chromatography method 50 with a separation system 51 of several (in the exemplary embodiment shown by way of example with eight separation columns) separation columns 52.1, 52.2, 52.3, 52.4, 52.5, 52.6, 52.7, 52.8 (52.1-52.8), the separation columns 52.1-52.8 being flow-connected to the separation system 51 in series via nodes 53.1, 53.2, 53.3, 53.4, 53.5, 53.6, 53.7, 53.8 (53.1-53.8) and form a closed circuit. The stationary phase 11 is distributed over all separating columns 52.1-52.8 and also has a polystyrene-divinylbenzene resin as the cation exchange resin 15. The mobile phase 10 circulates at least partially several times in the stationary phase 11 in the separation system 51. As a result of the circulation of the mobile phase 10, there is a spatial separation of the dissolved substances 3 due to the different retention times of the dissolved substances 3, equivalent to that described above for the first embodiment along the stationary phase 11 in the separation system 51 in the flow direction 54. This spatial separation of the dissolved substances 3 in turn forms a separation profile 60 in which the different concentration distributions are found 61, 62 for the hemicelluloses 5 and the base 4 reflect. The separating profile 60 can be divided into areas I, II, III, IV, V, VI, VII, VIII, which respectively correspond to the respective part of the mobile phase 10 in the separating columns 52.1-52.8. The concentration distributions 61, 62 therefore indicate the respective concentration 63 of the dissolved substance 3 as a function of the position 64 in the separation system 51.

To feed the mobile phase 10, the feed stream 6 and the eluent 14 are fed into the separation system 51 at different positions in each process step. This takes place in each case at different nodes 53.1-53.8 between two flow-connected separating columns 52.1-52.8. In an equivalent manner, target fraction 8 and residual fraction 9 are discharged from the separation system 51 at different positions in each process step. This also always takes place at different nodes 53.1-53.8 between two flow-connected separating columns 52.1-52.8 corresponding to the local concentration 63 of the dissolved substances 3 in the separating profile 60.

It is noted that the configuration of the method 101 described below is purely exemplary and only serves to illustrate the method principle, this configuration being selected on the basis of a fictitious separation profile 60 or fictitious concentration distributions 61, 62. The actual configuration, in particular the positions of the feed stream 6 and mobile phase 14 and the discharge of target fraction 8 and remaining fraction 9, depend on the type of base 4 and the actual concentrations of base 4 and hemicelluloses 5 in the waste liquor 2.

Fig. 2 represents a first step of the method 101, wherein the feed stream 6 is supplied at the node 53.8 between the separation columns 52.8 and 52.1 and the mobile phase 14 is supplied to the mobile phase 10 in the separation system 51 at the node 53.4 between the separation columns 52.4 and 52.5. While eluent 14 is fed to the mobile phase at node 53.4, target fraction 8, which contains recovered alkaline solution 1, is simultaneously discharged from mobile phase 10 at node 53.6 between separation columns 52.6 and 52.7. Equivalently, the remaining fraction 9 is discharged from the mobile phase at the node 53.2 between the separating columns 52.2 and 52.3, while the feed stream 6 is fed in at the node 53.8. The solvent 14 is thus over the Separating columns 52.5 and 52.6 are flow-connected to the target fraction 8, and the feed stream is flow-connected to the remaining fraction 9 via the separating columns 52.1 and 52.2.

The removal of the target fraction 8 at the node 53.6 takes place at a position in the separation system 51 at which, according to the concentration distributions 61, 62 in the separation profile 60, only the base 4 is present as dissolved substance 3 in the mobile phase 10. This can be identified in the separation profile 60 as area VI of the mobile phase 10, which is located in the separation column 52.6. The target fraction 8 thus consists essentially only of recovered alkaline solution 1 with a very high purity. On the other hand, the residual fraction 9 is removed at the node 53.2, i.e. at a position in the separation system 51 at which only hemicelluloses 5 are present as dissolved substances 3 in the mobile phase 10, as can be seen from the separation profile 60 in area II, which is located in the separation column 52.2.

At the end of the process step, the supply of mobile phase 14 and feed stream 6 and the removal of target fraction 8 and remaining fraction 9 are ended. The supply and removal then advances in the flow direction 54 in the separation system 51 by a node 53.1-53.8.

In Fig. 3 method 101 is off Fig. 2 shown in a further process step, with the supply of solvent 14 now takes place at node 53.5 between the separation columns 52.5 and 52.6, the supply of feed stream 6 takes place at node 53.1 between the separation columns 52.1 and 52.2, the removal of target fraction 8 at node 53.7 between the Separating columns 52.7 and 52.8 takes place and the removal of residual fraction 9 takes place at node 53.3 between the separation columns 52.3 and 52.4. In comparison to the first process step in Fig. 2 moved forward by one node 53.1-53.8.

Due to the continuous flow of mobile phase 10 in the flow direction 54, the separating profile 60 has also moved further in the separating system 51 during the first method step, which is shown in FIG Fig. 3 can be seen on the changed separation profile 60 'with the changed concentration distributions 61', 62 'of the hemicelluloses 5 and base 4. The area VI provided for the removal of target fraction 8 from the mobile phase 10 has now been moved further by an area to area VII, which is located in the separation column 52.7 in accordance with the separating profile 60 '. By the Moving the removal of target fraction 8 to node 53.7, a mobile phase 10 can again be removed as target fraction 8 in the second process step, which essentially only has base 4 as dissolved substance 3 and is a recovered alkaline solution 1 with high purity. Likewise, the removal of residual fraction 9 has been moved further by a node 53.1-53.9, which in turn removes a mobile phase 10 as residual fraction 9, which essentially only has hemicelluloses 5 as dissolved substance 3.

After completion of the second method step, the supply and removal are then again advanced in the flow direction 54 in the separating system 51 by a node 53.1-53.8. This can be repeated with further process steps until the configuration of the first process step in Fig. 2 is reached again, thus completing a complete cycle of the process. The further process steps were not shown in detail in the figures. A new cycle can then be started with the first method step as described above. Any number of cycles can follow one another.

In Fig. 4 a method 102 according to a further embodiment of the invention is shown, which includes the Fig. 2 and 3 described method 101 expanded. The method 102 has an SMB chromatography method 50 identical to the method 101. The above description for the method 101 therefore applies equivalently to the method 102. In addition, in the method 102, the feed stream 6 is passed through a nanofiltration 70 and a prefiltration 80 upstream of the nanofiltration 70 before being fed to the separation system 51. The waste liquor 2 in the feed stream 6 is fed to the prefiltration 80 as feed 81, with coarse impurities 84 being removed from the feed stream 6 as retentate 83. The permeate 82 from the prefiltration 80 is then fed as feed 71 to the nanofiltration 70, with a retentate 73 with a hemicellulose residue 74 having a high hemicellulose concentration being excreted. The permeate 72 of the nanofiltration 70 thus already has a significantly reduced hemicellulose concentration than the waste liquor 2 and the load of hemicelluloses 5 in the SMB chromatography process 50 can thus be significantly reduced. The permeate 72 can then be used as purified waste liquor 2 'in the feed stream 6 in a first process step - as for Fig. 2 - are fed into the separation system 51 at the node 53.8.

In a further embodiment of the method 102, the use of a prefiltration 80 can be dispensed with and the waste liquor 2 in the feed stream 6 can be fed directly as feed 71 to the nanofiltration 70.

In addition, the solvent 13 in the solvent 14 is passed through a degassing device 90 before it is supplied to the separation system 51 in the separation process 50. As in Fig. 4 shown, the solvent 13 is guided in the degassing device 90 over a gas-permeable membrane 91 which is under vacuum 92. The gas components 93 dissolved in the solvent 13, in particular O ₂ and CO ₂ , are removed therefrom. The degassed solvent 13 ′, which is thus essentially free of gas components 13 ′, is then fed to the separation system 51 as a solvent 14. This is in Fig. 4 - analogous to the in Fig. 2 first method step shown - shown as a feed at node 53.4 in the separation system 51. Alternatively, the degassing device 90 can also be any other device which enables the gas components 93 to be removed from the solvent 13.

In a further embodiment of the process 102, which is not shown in detail in the figures, the feed stream 6 is instead of the SMB chromatography process 50 to a chromatographic separation process 7, according to the first in Fig. 1 illustrated embodiment of the method 100, supplied and separated into target fraction 8 and residual fraction 9 via this.

In Fig. 5 a method 200 according to the invention for producing regenerated cellulosic molded bodies 201 is shown. Process 200 is, in particular, a viscose or modal process for the production of viscose or modal fibers 202. In process 200, a starting material 203 comprising cellulose is treated in a treatment stage 210 with an aqueous alkaline treatment solution 205. The treatment of the starting material 203 is an alkalization, with a cellulose 204 containing cellulose as the starting material 203 being alkalized in an alkalization stage 211 with sodium hydroxide 206 as the treatment solution 205 in order to obtain an alkalized cellulose (an alkali cellulose) 208 as the treated starting material 207. In a further step, the treatment solution 205 is removed or separated again from the treated starting material 207 by a separation 220, whereby a waste liquor 2 contaminated with hemicelluloses 5 is obtained. In the viscose or modal process 200 is the separation 220 a pressing 221, whereby the pressing 221 of the alkalized cellulose 208 results in the excess caustic soda 206 as press lye 209, which contains hemicelluloses 5 dissolved from the cellulose 204 and forms the waste caustic 2.

The pressed alkali cellulose 214 is then processed further in a maturing and dissolving stage 240 to form a viscose 215. In the maturing and dissolving stage 240, the pressed alkali cellulose 214 is converted into a cellulose derivative, for example cellulose xanthate, and then dissolved in a solvent, for example sodium hydroxide solution, in order to obtain the spinnable viscose 215. The viscose 215 is then spun in an extrusion stage 250 to form the regenerated cellulosic molded bodies 201, in particular the viscose fibers 202.

The press liquor 209 obtained as waste liquor 2 when the alkalized pulp 208 is pressed 221 is fed to a recovery stage 230 in order to recover the alkaline solution 1 from the waste liquor 2. The recovery stage 230 has a method 100 according to the invention, to which the waste liquor 2 is fed as feed stream 6 and is separated into a target fraction 8 and a secondary fraction 9. A recovered alkaline solution 1, that is to say recovered sodium hydroxide solution, is obtained from the target fraction 8, which in turn is fed to the alkalization stage 211 in the method 200 for reuse for alkalizing pulp 204. Alternatively or additionally, in a further embodiment of the invention, the recovered alkaline solution 1 can also be fed to the dissolving stage 240 to dissolve a cellulose derivative and to produce the viscose 215.

In a further embodiment of the method 200 for producing regenerated cellulosic molded bodies 201, which was not shown in more detail in the figures, the recovery stage 230 has a method 101 to separate the press liquor 209 into target fraction 8 and secondary fraction 9. In yet another embodiment, the recovery stage 230 has a method 102. The sodium hydroxide solution 206 used can thus be conducted in a circuit 260 and always obtained again as recovered alkaline solution 1 and used again.

In Fig. 6 A method 300 according to the invention for producing a pulp (pulp method) 301 is shown. The method 300 is in particular a method for producing a chemical pulp 302, which is suitable as a starting material for producing regenerated cellulosic molded bodies. Such chemical pulp 302 is often also referred to as dissolving pulp or dissolving wood pulp (DWP). In the context of method 300, a cellulose-containing starting material 303 is treated in a treatment stage 310 with an aqueous alkaline treatment solution 305. The treatment of the starting material 303 in the pulp process 300 is a chemical removal of hemicelluloses 5 in an extraction step 311 as treatment step 310, a cellulose precursor 304 being treated as starting material 303 containing cellulose in an extraction step 311 with an aqueous solution containing sodium hydroxide 306 as treatment solution 305 and the hemicelluloses 5 are removed from the pulp precursor 304 by the sodium hydroxide solution 306. The pulp precursor 304 is preferably a pulp obtained from a cooking stage of a pulp process which, in addition to cellulose, also contains non-cellulosic constituents, for example wood-specific impurities such as hemicelluloses 5. Because of the impurities, such a pulp precursor 304 is generally not suitable as a starting material 203 for the production of cellulosic molded bodies 201 according to a method 200 (as in Fig. 5 shown) suitable. In a further step, the treatment solution 305 is removed or separated again from the treated starting material 307 by separating 320, as a result of which a waste liquor 2 contaminated with hemicelluloses 5 is obtained. In the pulp process 300, the separation 320 is a washing 321 and / or pressing 321, the contaminated extraction liquor 309 being obtained through the washing or pressing 321 of the treated pulp precursor 308, which comprises hemicelluloses 5 removed from the pulp precursor 304 and the Waste liquor 2 forms.

In a subsequent process step, the cellulose residue 214, which is obtained as a cellulose-containing residue when separating 320 the treated starting material 307 from the extraction liquor 309, is washed in a downstream washing step 340 and finally the finished chemical pulp 302 is obtained. Further optional processing steps are also possible in other design variants, but were not shown in more detail in the figures.

The extraction liquor 309 is obtained as waste liquor 2 when separating 320 from the treated pulp precursor 308 and is fed to a recovery stage 330, which has a process 101 according to the invention, as feed stream 6 and is separated into a target fraction 8 and a secondary fraction 9. Equivalently, in further embodiments of the method 300 for separating the feed stream 6 into target fraction 8 and secondary fraction 9, the recovery stage 330 can also have a method 100 or a method 102. A recovered alkaline solution 1, that is to say recovered sodium hydroxide solution 312, is obtained from the target fraction 8, which in turn is fed to the extraction stage 311 in the process 300 for re-treatment of the pulp precursor 304. The sodium hydroxide solution 306 used is thus obtained again in a circuit 360 as recovered sodium hydroxide solution 312 and can be used again.

Examples

The invention is illustrated below using several examples.

In all the examples given, chromatographic separation processes with one or more separation columns of the type GE Healthcare XK 16/40 were used. A cation exchange resin based on styrene-divinylbenzene copolymer of the Finex CS11GC-320NA type was used as the stationary phase in the separation columns.

Example 1:

In Example 1, a chromatographic separation process with a single separation column was used to separate the waste liquor. A sodium hydroxide solution contaminated with hemicelluloses from a viscose process was used as waste liquor, with a NaOH content of 63.1 g / kg and an organic carbon (TOC) content of 22.8 g / kg. The temperature in the separation column during the separation process was kept at 40 ° C. An aqueous sodium hydroxide solution with an NaOH content of 24.4 g / kg was used as the mobile phase or solvent for the separations. The flow rate of the mobile phase through the separation column was 10 ml / min. 1 ml of the sample was added as a feed stream to the mobile phase and, after a defined time, the composition of the mobile phase (separation profile) was determined every 20 seconds. In Fig. 7 the separation profile 400 is shown in the mobile phase as a function of time 410. The curves 421, 422 show the refractive index or the UV-Vis absorption of the mobile phase in arbitrary units 420 as a function of time 410. The curve 421 shows the relative change in the refractive index, while the curve 422 shows the change in the absorption of the mobile phase at a wavelength of 250 nm. Both the refractive index 412 and the UV-Vis absorption 422 each show maxima 425, 426 at the times 411 and 412. The curve 431 also shows the organic carbon content (TOC) 430 as a function of time 410. From the TOC content in Curve 431 shows that the total organic load in the maximum 435 essentially coincides exclusively in time with the maximum 425 in refractive index and absorption of the curves 421, 422 at the point in time 411. The maximum 425 accordingly corresponds to a high concentration of hemicelluloses and other organic impurities in the mobile phase, while the maximum 426 corresponds to a high concentration of NaOH in the mobile phase. The separation profile 400 can therefore be separated into two fractions 451, 452 in terms of time, with the remaining fraction 451, which contains the hemicelluloses, being removed from the mobile phase up to the separation time 450, and the target fraction 452, which contains the recovered sodium hydroxide solution, from the separation time 450 will. The NaOH concentration in the removed target fraction was finally 27.5 g / kg, while the TOC content was less than or equal to 0.1 g / kg. The remaining fraction finally contained well over 90% of the organic components, including β- and γ-hemicelluloses. The alkaline solution (caustic soda) recovered in this way has a high degree of purity, but is in a dilute form. After a concentration step, the sodium hydroxide solution can be used again as an alkalizing or dissolving solution in the viscose process.

Example 2:

According to Example 2, an SMB chromatography process was used as the separation process with a separation system consisting of four separation columns in series to separate the waste liquor. The waste liquor was a sodium hydroxide solution contaminated with hemicelluloses, with a NaOH content of 173 g / kg and a TOC content of 12.9 g / kg, which was obtained as press liquor in a viscose process. An aqueous sodium hydroxide solution with an NaOH content of 15 g / kg was used as the mobile phase. Mobile phase and feed stream (waste liquor) were continuously fed to the separation system and separated into target fraction and residual fraction. The target fraction accounted for a total of 75% of the total volume flow, while the remaining fraction was taken with 25%. The won target fraction accordingly had an NaOH content of 98 g / kg and a TOC content of 0.3 g / kg. The recovered sodium hydroxide solution was thus present in a significantly higher concentration than in Example 1 and can be used again as an alkalizing or dissolving solution in the viscose process without further concentration steps.

Example 3:

In Example 3, equivalent to Example 2, an SMB chromatography method was used as the separation method with a separation system with four separation columns. The same waste liquor with a content of 173 g / kg NaOH and a TOC content of 15.1 g / l was fed in as a feed stream. The target fraction accounted for 38% of the total volume flow, while the remaining fraction accounted for 62%. The target fraction obtained had an NaOH content of 180 g / kg and a TOC content of 0.1 g / kg.

Example 4:

In Example 4, an SMB chromatography process with a separation system consisting of four separation columns was again used as the chromatographic separation process. A sodium hydroxide solution contaminated with γ-hemicelluloses with an NaOH content of 165 g / kg and a TOC content of 5.1 g / kg was used as the waste liquor. Deionized water was used as the mobile phase. Mobile phase and waste liquor as a feed stream were continuously fed to the mobile phase in the separation system. A target fraction was obtained as a 36% share of the total volume flow (residual fraction 64%), the NaOH content of which was 181 g / kg and the TOC content of 0.08 g / kg. The recovered alkaline solution (sodium hydroxide solution) could be used as alkalization solution in an alkalization step in the viscose process without further processing steps.

Example 5:

In example 5, an SMB chromatography process with a separation system consisting of four separation columns was also used to separate the feed stream into target and residual fractions. The waste liquor used was an extraction liquor contaminated with hemicelluloses from a cold alkali extraction (extraction stage) of an oxygen-bleached hardwood sulfate pulp, which contained an NaOH content of 97 g / kg and a TOC content of 31.4 g / kg. A NaOH solution with 20 g / kg NaOH was again added continuously to the mobile phase as the mobile phase fed. The target fraction obtained, which made up 87% of the total volume flow (remaining fraction 13%), had an NaOH content of 57 g / kg and a TOC content of 0.7 g / kg. This recovered alkaline solution can, after an optional concentration step, be used again in a pulp process (e.g. as extraction liquor).

Claims (14)

Process for the recovery of alkaline solution (1) from a waste liquor (2) contaminated with hemicelluloses (5), in which the waste liquor (2) as a feed stream (6) via a separation process (7, 50) into at least one alkaline-enriched target fraction (8 ), and at least one residual fraction (9) containing hemicelluloses (5) is separated, characterized in that the separation process (7, 50) is a chromatographic separation process (7, 50) and the feed stream (6) therein as part of a mobile phase ( 10) is passed through an alkali-resistant stationary phase (11) in order to separate it into the target fraction (8) and the remaining fraction (9). Method according to Claim 1, characterized in that the alkali-resistant stationary phase (11) has an ion exchange resin (15), in particular a cation exchange resin (15). Method according to Claim 2, characterized in that the cation exchange resin (15) is selected from the group comprising sulfonated polystyrene-divinylbenzene resins. Method according to one of Claims 1 to 3, characterized in that a liquid solvent (13) is fed to the mobile phase (10) as a mobile phase (14) in which the waste liquor (2) contaminated with hemicelluloses (5) is at least partially soluble is. Process according to one of Claims 1 to 4, characterized in that in the chromatographic separation process (50), in particular in the SMB chromatography process (50), the mobile phase (10) is passed through a separation system (51) with several separation columns ( 52.1, 52.2, 52.3, 52.4, 52.5, 52.6, 52.7, 52.8), the separation system (51) in particular forming a closed circuit and in particular the mobile phase (10) circulating at least partially several times in the separation system (51). Method according to claim 5, characterized in that the eluent (14) or the feed stream (6) each at different positions, in particular at nodes (53.1, 53.2, 53.3, 53.4, 53.5, 53.6, 53.7, 53.8), between two flow-connected separation columns (52.1, 52.2, 52.3, 52.4, 52.5, 52.6, 52.7, 52.8) are fed into the separation system (50) and the target fraction (8) or the remaining fraction (9) each at different positions between two flow-connected separation columns ( 52.1, 52.2, 52.3, 52.4, 52.5, 52.6, 52.7, 52.8) are discharged from the separation system (50). Process according to one of Claims 1 to 6, characterized in that the feed stream (6), before being fed to the chromatographic separation process (50), is passed through a nanofiltration (70), in which it is converted into an alkaline permeate (72) and one with hemicelluloses (5) enriched retentate (73) is separated, the permeate (72) or the retentate (73) being fed as feed stream (6) to the mobile phase (10) of the chromatographic separation process (50). Process according to one of Claims 1 to 7, characterized in that the feed stream (6) is passed through a prefiltration (80) before being fed to the chromatographic separation process (50) in order to remove unwanted particles (84) and / or impurities (84) . Process according to one of Claims 1 to 8, characterized in that before it is fed to the chromatographic separation process (50), the solvent (13) is passed through a degassing device (90) in order to remove gas components (93) from the liquid solvent (13). Method in which a cellulose-containing starting material (203, 303) is treated in a first step (210) with an aqueous alkaline treatment solution (205, 305) and in a further step (220) a waste liquor (2) contaminated with hemicelluloses (5) is treated ) is obtained from the starting material (207, 307) treated with the treatment solution (205, 305), the waste liquor (2) being fed as a feed stream (6) to a method (100, 101, 102) according to one of claims 1 to 9 and thereby a recovered alkaline solution (1) is obtained from the target fraction (8). Method according to claim 10, characterized in that the method (200) is a method for producing regenerated cellulosic molded bodies (201), wherein the cellulose-containing starting material (203) is a cellulose (204), in particular a chemical cellulose (204). Process according to claim 11, characterized in that the process (200) is a viscose or modal process, and that the treatment (210) comprises an alkalization (211) of the starting material (203) to obtain alkali cellulose (208), the treatment solution (205) sodium hydroxide solution (206). The method according to claim 10, characterized in that the method (300) is a method for producing a cellulose (301), in particular a chemical cellulose (302), and that the treatment (310) is a chemical removal (311) of hemicelluloses (5 ), wherein the treatment solution (305) comprises an extraction liquor (306). Method according to one of Claims 10 to 14, characterized in that the recovered alkaline solution (1) is used for further treatment (210, 310) of the starting material (203, 303).

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