CH620598A5 - Method for increasing the exchange turnover in ion exchange processes - Google Patents

Description

The invention relates to the method specified in the preamble of claim 1.

Ion exchange is most often used today for the treatment of raw water. With it it is possible to achieve a high separation effect between water and the dissolved ions. So you can z. B. in the desalination of raw water, the content of cations and anions to about three to six hundredths, so that the treated water meets the usual requirements. The usable volume capacity of the exchanger bed - generally referred to as NVK - is 70 to 80% of the total capacity of the exchanger bed, hereinafter only referred to as bed. These reactions are commonly referred to as loading, exhaustion, or usage. They are terminated when the bed is depleted of the ions it contains. These are brought to bed in the backlash commonly referred to as regeneration.

In order to be able to simply describe these processes, according to F. Helfferich, "Ion Exchange", McGraw-Hill, New York, 1962, the ions taking part in the ion exchange are counterions, the oppositely charged ions which are firmly anchored to the exchanger structure as polyions and the ions of the solution with the same name as the poly ions are referred to as co-ions (see Helfferich, pages 6 and 7). The affinity relationships between the counterions and the poly or co-ions are characterized by the separation factor (see Helfferich, page 153).

In order to distinguish the counterions from one another, those which are used in the reaction carried out according to the invention, e.g. B. the regeneration, used solution are referred to as exchanging and those of the bed as counterions to be exchanged. The exchanging counterions have a lower affinity than the ones to be exchanged when regenerating a strongly dissociated ion exchanger to the polyions. With the associated loading, the counterions to be exchanged reach the bed which is loaded with the exchanging counterions at the beginning of this reaction.

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When loading, the separation factor has a significantly higher value than 1, i.e. H. the counterions to be exchanged have a much higher affinity for the polyions than the counterions to be exchanged. During regeneration, the latter counterions have to be put on the bed again. The separation factor for strongly dissociated ion exchangers is less than 1. If the regeneration of weakly dissociated ion exchangers is concerned, the value of the separation factor is greater than 1 due to the hydrogen ion (cation exchanger) or hydroxyl ion (anion exchanger) content in the regeneration solution. The dissociation information refer to the cation exchangers to those loaded with hydrogen ions, to the anion exchangers to those loaded with hydroxyl ions.

Until a few years ago, industrial ion exchange was determined by the simple direct current process, in which the liquids in both exchange reactions of an exchange cycle are passed from top to bottom through the fixed bed. The term “simple” is intended to mean that all liquids flowing out of the bed are immediately carried away, i.e. H. be removed from the system. As a result of the aforementioned size ratios of the separation factors, it is necessary here to use a considerable excess of the exchanging counterions during the regeneration in order to remove the counterions to be exchanged from the bed to such an extent that the high separation effects mentioned at the outset can be achieved during loading .

In order to be able to compare this process with the other known processes, the regeneration of a cation exchanger loaded with sodium ions by hydrochloric acid, which can be carried out under defined conditions, is used below as an example. In the present case, approximately 180 to 200% of hydrochloric acid, based on the sodium ions removed from the bed - both measured in chemical equivalents (equ) - are required to load the bed with hydrogen ions to 90% of its total capacity. The concentration of the total waste water resulting from this ion exchange, hereinafter referred to as secondary waste water, is about 1 to 3% by weight.

In order to reduce the excess of regenerating agent, processes with stored fractions were used already at the beginning of the technical application of the ion exchange, in which one or more than one fraction, which was obtained in the previous exchange cycle, was added to the fixed bed during regeneration or were and only after this or these the fresh solution supplied to the system from outside and finally water. The following were obtained from the bed in turn: water and the used Régénérât that were carried away, and one or more than one fraction that was or were put back into storage. Subsequently used washing water was obtained, which was also carried away. The number of fractions was mostly 1, more rarely 2 to 4 and in a few cases using fractions with a very small volume 7 to 15. With this method, the hydrochloric acid requirement in the comparative example above could be reduced to 150 to 170% with otherwise the same result. The concentration of the secondary wastewater was also about 1 to 3% by weight. However, this so-called simple fraction process described in DE-PS 393 044 and DE-PS 397 848, for example, could not prevail despite various efforts because the effect achieved did not justify the technical effort. Today it is hardly used anymore.

An important development is the simple countercurrent process, which has been used for around 10 years, in which the liquids are passed through the fixed bed in one reaction of the exchange cycle from top to bottom and in the other from bottom to top. The escaping liquids are immediately carried away. In this process, it is not necessary to carry out the regeneration of the bed as far as in the aforementioned processes, since it is possible with the countercurrent principle to achieve high exchange conversions in both reactions at the same time. The chemicals used in the regeneration are therefore used with a good yield, and the separation effect during loading is even higher than in the simple direct current process. However, this can only be achieved with a relatively low NVK value. In the comparative example, the hydrochloric acid consumption according to this method is 120 to 130% with an NVK of 75% of the total capacity. The concentration of the secondary wastewater is also around 1 to 3% by weight.

Almost simultaneously with the countercurrent process, several processes have been developed in which the exchange reactions with standing exchanger fillings are carried out in a simple direct current process, the solutions and the water supplied from the outside being simultaneously introduced into the filling at distant locations. If a predetermined limit value of a characteristic property in the emerging solution has been reached, the supply of the liquids is switched off and the filling in its container is shifted by a certain section against the direction of flow of the liquids. The space thus freed up is filled with freshly regenerated or loaded exchange resin. Then the liquids are added again until the limit value is reached again. The number of sections flowed through during regeneration is greater than that during loading. This process uses the regeneration ions almost as well as the simple countercurrent process, and the value of the NVK is also roughly the same. You can also work with concentrated solutions in these processes than was possible in the previously listed processes. The regenerates obtained have a concentration of 40 to 60% of the solution supplied from the outside, and the concentration of the secondary wastewater is about 4 to 8% by weight. Despite these advantages, however, these known methods could not displace the simple countercurrent method because the systems required to carry them out are too complex.

A fifth method was also developed at about the same time, in which fractions stored as in the simple fraction method are used, but which is fundamentally different from this. In this process, stored fractions are used not only in the exchange reaction, but also after their termination in the displacement of the reaction solution by water and preferably also before the start of the exchange reaction in the displacement of the water contained in the bed by the reaction solution. The mixing of the fractions obtained from the bed until their reuse in the next cycle is intentionally prevented or at least controlled. Special measures serve to ensure an even flow of liquids through the fixed bed. This method, for example described in DE-PS 1 442 500 and US-PS 3 448 043, which is also referred to as an intensive fraction process - hereinafter abbreviated IFP - has been developed for use in preparative purposes in which in at least one ion exchange reaction of the cycle, solutions are obtained whose salt content is of such a value that the higher expenditure for the plant and its operation is justified. With the IFP, the exchanging counterions can always be used to a high degree and work with concentrated solutions, so that the concentration of the solutions produced can reach 80 to 90% of that of the solutions used. In the comparative example, the hydrochloric acid expenditure drops to 103 in the IFP

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up to 104Cf. the NVK is 85 to 90% of the total capacity. The concentration of the secondary wastewater is about 10 to 15% by weight. Corresponding results are achieved in the regeneration of the ion exchangers used in the aforementioned cases for the treatment of raw water.

Despite these good results, the IFP has not found general application in the treatment of raw water. The advantage of this method over the simple countercurrent method that is mostly used today is present in terms of the amount of regenerating agent, but this alone is not sufficient to compensate for the greater effort for the system and the operation. The significantly higher concentration of secondary wastewater has so far not been so important that it would have played a role in the compensation.

Environmental protection has become increasingly important in recent years. There are already considerable demands on the purity of the discharged wastewater. In many industries there is wastewater that can no longer be discharged into the rivers or into the sea. As a result of the high separation effect mentioned at the outset, the ion exchange for removing the harmful or poisonous ions or the salts present in excessive amounts is more suitable per se than all other known processes, such as, for. B. electrodialysis or reverse osmosis. The first disadvantage of ion exchange is, however, that at least one equivalent of salt per equivalent of removed ion is obtained in the secondary waste water during cation exchange and at least two equivalents of salt per equivalent of removed salt during desalination. These minimum amounts would only be obtained if the equivalent amount of the regenerating agent were sufficient. The second disadvantage is that the concentration of the secondary wastewater is too low, so that its disposal poses at least the same problems as the original wastewater.

In order to be able to use ion exchange in the disposal of wastewater in industry and possibly also in municipalities, it must meet the following requirements:

1. The consumption of the exchanging counterions required for regeneration should be very close to the value equivalent to the counterions to be exchanged.

2. The secondary wastewater from the ion exchange should have a concentration as high as possible so that its abolition does not pose any insoluble problems. These problems are completely eliminated if the secondary waste water or salts can be used. The utilization, in which mostly the water has to be separated from the dissolved salt, is influenced by the concentration of the solution obtained. It carries part or u. U. also the total abolition costs. But even if the secondary wastewater is to be chemically treated, landfilled or transported to the sea, the costs for this depend on the concentration of the secondary wastewater.

3. The overall economy should be as cheap as possible, d. H. the total of all costs incurred in the ion exchange due to the construction and operation of the plant and the elimination of the secondary wastewater should be as low as possible, in particular to promote environmental protection.

None of the known ion exchange processes can meet all of these requirements. The IFP comes closest to this goal, which corresponds to the first two requirements, but can only partially meet the third requirement due to the effort for the investment. The judgment on the use of ion exchange to remove waste water is therefore generally negative. In Winnacker-Küchler, “Chemische Technologie”, C. Hanser Verlag, Munich, 1975, Volume 7, page 700, it states that the desalination of waste water by means of ion exchange is not a generally applicable practical solution.

The object of the invention is to carry out ion exchange processes in such a way that the disadvantages mentioned above are avoided. With the least possible effort for setting up and operating the system, the highest possible exchange turnover should be achieved, the exchange products to be discharged from the system should be able to be eliminated with as little effort as possible, in particular to be able to meet the requirements imposed by environmental protection. The exchange sales should be increased with constant or even lower chemical consumption z. B. for regeneration.

To achieve this object, a simple fraction process with one or more reaction fractions is used as the starting point in the preamble of claim 1 and the invention provides for this to be carried out according to the principles specified in the characterizing part of claim 1.

In order to largely prevent the relative displacement of the liquid particles which are simultaneously fed onto the bed from the feed line, the liquid to be fed onto the bed is evenly distributed over the bed cross section after leaving the feed line in the air space above the bed. Known devices, such as. B. a spiral nozzle used. For the same purpose, the height of the liquid layer located above the exchange layer of the bed is kept as low as possible, preferably between about 1 and 5 cm. The regulation of the layer height is carried out by means of known devices, such as. B. a pair of floats, in which one responds to the level of the exchange layer of the bed and the other to that of the liquid layer and the height difference of the two floats serves as an impulse for regulating the speed of the supply and / or discharge of the liquids. The damaging effect of the dead volume of this liquid layer is canceled out by the liquid jets arriving at high speed from the supply line, which keeps the layer in constant vigorous movement.

Adverse displacements of the liquid particles relative to one another can also occur within the bed itself, i. H. within the exchange layer. The shifts that occur in the direction of flow through the bed, that is to say in the longitudinal direction thereof, are of importance. In order to prevent or at least largely reduce this, the floor on which the bed rests within the exchanger tank is provided in a known manner with evenly distributed narrow flow gaps (filter nozzles) which do not let the resin particles through and cause a jam in the flow, as a result of which this is evenly distributed across the flow gaps. Together with the uniform application of the liquid to the bed surface, it is ensured in this way that the flow within the bed is practically always uniformly distributed over its cross-section and at least largely prevents individual liquid particles from leading or remaining behind.

Relative shifts can also occur in the space between the floor supporting the bed, the so-called nozzle floor, and the actual tank floor. This space is filled with liquid during the exchange reaction. In it, whole liquid quantities that have emerged from the bed at the same time can shift relative to each other. A liquid subset is to be understood as the totality of all liquid particles that leave the bed one after the other within a certain finite period of time, for example several seconds. These liquid subsets can shift relative to each other in the space below the nozzle bottom.

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especially when the density of the successive subsets increases. The relative shift between the subsets causes a large shift between liquid particles placed on the bed one after the other. In order to eliminate or at least reduce this effect of the floor space, its volume is reduced according to the invention as much as is technically possible. The remaining space can then z. B. filled in a known manner with packing.

In the method according to the invention, it is further provided, according to the characterizing part of claim 1, to keep the co-ion content of the one or more reaction fractions constant, for which purpose the volume of the reaction fraction (s), the volume and the co-ion content of the solution supplied from the outside and the volume of the liquids discharged from the system are kept constant.

The state described here is not reached immediately at the beginning of a new series of exchange cycles, but can only be achieved after several cycles have been carried out while keeping the aforementioned variables constant. In this steady state, the composition of all liquids participating in the exchange remains constant except for the statistical scatter. This reproducibility of the composition is necessary to achieve the advantageous industrial results of the method according to the invention.

With the aforementioned measures, a significant improvement in the exchange turnover that can be achieved with the simple fraction process is achieved by a comparatively low expenditure for the construction and operation of the plant. A further improvement in the process result is achieved if, according to claim 2, each reaction fraction is mixed in its container. This avoids the uncontrolled relative displacement of the liquid particles or liquid subsets. The fractions are mixed as much as possible during or shortly after their storage. This can be done in a known manner, e.g. B. with the help of stirrers or by a correspondingly strong vortex when introducing into the container.

The fraction (s) and, if applicable, the solution supplied from the outside, if this is fed in via the same pump, are generally not fed directly to the pump, but rather via a common reservoir, which leads them to the bed. In order to keep the mixing of solutions to be added in succession as low as possible in accordance with claim 3, it is provided that the volume of the storage container is kept as small as possible and that it may also be filled with packing elements.

In principle, the reaction fractions themselves can be examined to determine whether the co-ion content of the at least one reaction fraction is constant or not. However, it is more advantageous to control the composition of a solution obtained from the bed after the reaction fraction or, in the case of several, after the last reaction fraction. As long as the co-ion content of the control solution changes, the steady state has not yet been reached or is no longer present.

In order to properly perform this indicator function, the co-ion content of the control solution should change easily, even with small changes in the system. It has therefore proven to be advantageous to collect the control solution immediately after the (last) reaction fraction. In this case, the co-ion content of the solution is high enough to be able to determine it precisely, and it reacts quickly to changes in the system.

Reaching the steady state in the manner described does not mean that the system is in the optimal state. This is only achieved when the co-ion content of the reaction fractions is at a maximum with a fixed volume. This ensures that the ion exchange taking place in each fraction leads to a maximum conversion under the given conditions. The size of the maximum value also depends on the method used to displace the reaction solution from the bed. The displacement process determines the loss of Co ions and the associated counter ions in the used wash water, which is led away from the system. The greater the loss, the smaller the co-ion content of the reaction fraction (s).

On the other hand, the displacement process results in the dilution of the reaction fraction (s) by penetrating displacement water. The lower the dilution, the higher the ion content of the reaction fraction (s) at the same volume.

By observing the procedural conditions discussed, a considerable improvement in the results of the simple fractional process is already achieved, although they do not yet achieve the results achieved with a larger plant outlay, but under otherwise identical conditions in the IFP. It has now been found that the results of the process according to the invention, which works with a considerably smaller number of fractions, can be improved even further if the fraction size is determined in a suitable manner.

After this knowledge, the aim was to create a generally applicable rule that can be used regardless of the exchange reaction and its implementation conditions. This rule is specified in claim 5. It can also be advantageously used outside the scope of the invention, since in any case, i.e. H. independent of the aforementioned process engineering measures, leads to a reduction in the number of reaction fractions.

According to the invention, the exchange conversion achieved in contact with the bed is used as a characteristic parameter of the reaction fraction. In order to be able to indicate the conversion with a dimensionless number, the conversion achieved in each reaction fraction was based on the maximum possible exchange conversion under the given conditions - hereinafter referred to as MA. The MA is influenced by the composition of the individual reaction fraction and the bed in their task, the separation factor of the reaction under these conditions, the temperature, the throughput rate of the fraction, etc. H. through the entirety of the working conditions that determine the course of the ion exchange reaction. The value of the MA therefore varies from case to case; However, the percentage of the turnover achieved when the reaction fraction used was passed through creates a value which is equally valid for each exchange reaction.

When determining the MA, it is advantageously assumed that the bed is in a loaded state, which does not occur when the method is actually carried out. For this purpose, a solution, the composition of which corresponds to that of the solution introduced before the reaction fraction (which may also be a fraction), is added to the bed until an equilibrium is established between the two, the conditions of the actual implementation of the process being observed . The bed is then washed out. This condition is fully defined and reproducible. A further solution, the composition of which is equal to that of the reaction fraction to be investigated, is now applied to the bed prepared in this way. This is carried out under the conditions

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of the process, pass through the bed until equilibrium is reached, d. H. the outlet has the same composition as the inlet. Then the collected runout is analyzed and the amount of counterions exchanged is determined. This set represents the MA.

The co-ion content of the reaction fraction (s) is now advantageously chosen to be so large that the exchange conversion occurring when the reaction fraction (s) is passed through has the size specified in claim 5.

The displacement of one or more of the last reaction fraction from the bed can be carried out according to claim 6 by a single incorporated displacement fraction, which is preferably also homogenized in accordance with claim 2 in its container. This displacement has the advantage that the concentration of the Co ions in the reaction fraction (s) has the maximum achievable value, since the displacement of the ions in the used washing water of the bed is the lowest with this displacement method. The concentration of the Co ions in the (last) reaction fraction reaches a value which is practically the same as that in the solution supplied from the outside, except for the amount of water which the bed releases or absorbs as a result of the change in its hydration during the ion exchange. This amount of water varies from case to case and must therefore always be determined experimentally.

The co-ion concentration of the displacement fraction is expediently set such that it is kept at 30 to 70%, preferably 40 to 60%, of the co-ion concentration of the solution supplied from the outside. The co-ion concentration of the (last) reaction fraction is preferably kept practically the same as that of the solution supplied from the outside. The swelling pressure must be taken into account, which occurs when the concentration of the applied solution decreases, especially in the case of strongly dissociated ion exchangers in the exchange grain, the grain withdrawing water from the increasingly dilute solution. If the difference between the concentration of the (last) reaction fraction and the liquid used for displacement is too large, the swelling pressure can cause the exchange grain to burst. The concentration of the displacement fraction set in this way avoids such damage to the exchange grain. The concentration must be determined within the specified limits so that the difference between the Co ion concentration of the solution supplied from the outside and the displacement fraction does not exceed 2.0 to 2.5 eq / 1. This value can only be determined experimentally by trying out differently concentrated displacement fractions in a long-term test or when operating the system.

The same adverse effect occurs even when the co-ion concentration of the displacement fraction is over 2.0 to 2.5 eq / l. In such cases, this displacement fraction is displaced from the bed instead of by means of water by at least one further displacement fraction, which was also stored and is stored again after its use, the co-ion concentration preferably decreasing from displacement fraction to displacement fraction by about 60 to 80% in each case . After this at least one further displacement fraction, the water is placed on the bed for displacement. In the above cases, the (first) displacement fraction can be used as a control solution.

In order to reduce the effort even further, however, in the method according to the invention it is preferably provided instead that the solution parts flowing out immediately after the one or last reaction fraction to be stored are not stored as displacement fractions or fractions for the next exchange reaction, but instead are removed from the system.

If the concentration of the solution supplied from the outside does not exceed 2.0 to 2.5 eq / 1, then the (last) reaction fraction can be displaced from the bed by water. This makes the system easier than in the previous case. In this case, some water mixes with the (last) reaction fraction and part of the solution supplied from the outside to the wash water removed. It has proven to be advantageous to stop the decrease in the (last) reaction fraction when its average co-ion concentration has reached the value specified in claim 7.

If water is used to displace the (last) reaction fraction, the solution flowing out of the bed after the (last) reaction fraction has been recovered is used as a control solution. The volume of the control solution is preferably less than 50% of the bed volume in order to adjust its concentration to an easily determinable work. The control solution is omitted after its composition has been determined.

In cases where the co-ion concentration of the solution supplied from the outside is above 2.0 to 2.4 eq / 1, the use of water for displacement would be harmful. Here, according to claim 8, one or more than one solution is used to displace the (last) reaction fraction instead of embedded displacement fractions, which solution is (are) made from the solution and water supplied from the outside in each exchange cycle. Most of the ion content of this solution (s) ends up in the (last) reaction fraction and a much smaller part as loss in the used wash water of the bed.

The concentration of the new solution (s) to be prepared is specified in claim 8. Here, too, the difference between the concentration of the solution supplied from outside and the newly prepared solution or between the newly prepared solution and water should not exceed 2.0 to 2.4 eq / 1. If this were the case, a second and possibly further solutions with a correspondingly reduced concentration would be newly prepared.

The volume of the newly prepared solution (s) results from the limitation of the amount of water used for dilution to the same or almost the same amount of water that the bed of the newly prepared solution (s) deprives when it is passed through. The result is that the co-ion concentration of the (last) reaction fraction is only slightly reduced and the emerging ion loss is kept low. This co-ion concentration is adjusted to about 75 to 85% of the concentration of the solution supplied from the outside.

In this case, the control solution to be used is collected after the (last) reaction fraction by displacing the newly prepared solution from the bed with water.

In each case discussed, it is sufficient if, according to the foregoing, only the co-ion concentration of the last reaction fraction is observed in several reaction fractions. The penultimate fraction arises in the next exchange cycle from the last and the one given before from the penultimate, etc. All the concentration values compared must always be corrected according to the change in bed hydration mentioned.

The control solution can be examined by analyzing the mixed solution, which is advantageously carried out with an automatic analysis device. At the same time, the co-ion content of this solution is obtained, which, when displaced with water or newly prepared solutions, is practically the same as the loss of ions. It is more expedient, however, to use a predetermined solution part of the control oil

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solution. Known physical methods are advantageously used for this purpose, e.g. B. pH, conductivity, density or color measurement, with which the value to be determined is obtained immediately.

After the steady state has set in, the ion content is used to determine the further measures to be taken. The required change in the state of the system is carried out according to claim 9. The maximum value of the Co ion content of the reaction fraction (s) is reached when the Co ion loss lies within the limits specified in claim 10. The amount of the loss is also important because the corresponding amount of ions is carried away with the secondary wastewater.

The method according to the invention enables working with concentrated solutions. It has been shown that the value of the MA is greater in concentrated solutions than under the same conditions in more dilute solutions. So was z. B. the value of the MA in the reaction between hydrochloric acid and the sodium ions of a strongly acidic cation exchanger when using a 4N chloride solution 556 meq and with a 1.8N chloride solution only 475 meq. In both cases the concentration of the solution was 55% of hydrogen ions and 45% of sodium ions of the total concentration. The total capacity of the bed, a strongly acidic cation exchanger made of polystyrene sulfonic acid, was 1200 meq. It is therefore advantageous if the co-ion concentration of the solution supplied from the outside is selected such that the co-ion concentration of the reaction fraction (s) is set to be higher than 2n, preferably higher than 3n. The ratio of the co-ion concentrations of the solution supplied from the outside and the reaction fraction results from the displacement process used.

At even higher concentrations in the range of about 5n, the inner capillaries of the exchange grain narrow, which reduces the rate of diffusion. As a result, it takes longer than at a lower concentration to reach a certain state. This again shows the advantage of the invention, in which the fractions are dimensioned according to the exchange turnover actually achieved. At these high concentrations it is necessary to increase the ionic content of the fraction in order to get the same conversion, expressed as a certain percentage of the MA, as at a lower concentration.

With the method according to the invention, it is advantageously possible to largely achieve the results of the IFP with one or a little more than one reaction fraction, but the effort for setting up and operating the associated system is much less, so that the ion exchange contrary to the general view is also applicable to the disposal of waste water with advantage.

In many cases, it is required that the solution to be removed as a product from the system has the highest possible concentration. The term product is also to be understood as the used regiment to be carried away, i.e. H. the product can be usable or worthless. In order to achieve the highest possible concentration, the water flowing out of the bed at the beginning of the exchange reaction and the product solution subsequently obtained must be separated from one another. For this purpose, it is advantageously provided that the volume of the first part of the liquid obtained from the bed at the start of the exchange reaction is measured such that the concentration of the remaining product solution is approximately 70 to 80% of the concentration of the solution supplied from the outside. The value of the latter is corrected by taking into account the amount of water mentioned which the bed releases or takes up during the exchange reaction. The ion loss which occurs under the given circumstances due to the omission of the first part makes up about 2 to 10% of the ion content of the product.

In order to reduce the mixing of the first part of the outflowing liquid and the product solution, displacement fractions are advantageously used, which are first placed on the bed filled with water and obtained from the bed after the first liquid part to be removed, stored and in the next exchange reaction to the same Way to be used again.

In the process according to the invention, saline wastewater is produced at two points: at the beginning of the exchange reaction, the loss of ions accounts for approximately 2 to 10% of the ion content of the solution supplied from outside, and approximately 0.2 to 4% in the end. These ions are found in the secondary wastewater leaving the system. In order to remove these ions, the invention provides for the diluted solutions obtained in addition to the product to be mixed with the water to be treated, as a result of which its salt content increases by approximately 3 to 15%. Although this results in a correspondingly higher consumption of regenerant, it is achieved in that only the concentrated Régénérât, the concentration of which is only slightly lower than that of the solution supplied from the outside, and the treated water, which are discharged or reused without difficulty, are achieved from the system can exit.

The method according to the invention can advantageously be used not only in the treatment of waste water, but also in the desalination of brackish water and in the softening or desalination of raw water. In many cases it is also possible to use the process for manufacturing chemical products from their raw materials, i.e. H. for preparative purposes.

The invention has the greatest advantage when used in exchange reactions whose separation factor is less than 1 and which are carried out using concentrated solutions. This includes the regeneration of strongly dissociated ion exchangers. But it can also be used to advantage in other cases. If one works with concentrated solutions, the exchange isoplane or breakthrough curve (see Helfferich, page 424) has a considerable expansion even if the separation factor is greater than 1; H. the amount of solution flowing out of the bed between the breakthrough of the exchanging ions until their entry concentration is reached is considerable. This is especially true if you are striving to work with a high NVK. The amount of water entering the product as a result of mixing is proportional to the bed volume and independent of the value of the NVK. So if you work with a higher NVK when using the same bed, i. H. exchanging a larger amount of counterions makes up less percentage of the amount of water mixed into the solution. Accordingly, the concentration of the product becomes higher the higher the NVK under otherwise unchanged conditions.

example 1

In the following, the results of the process according to the invention are compared on the one hand with those of the simple fraction process, and on the other hand with those of the IFP.

a) Simple functional procedure

The replication of the simple fractional process carried out on a technical scale in the laboratory is difficult because the dimensions of the bed and, accordingly, that of its container are very different. In the laboratory, the diameter of the bed is usually 50 to 100 mm, its height is 400 to 1000 mm, while on a technical scale diameters from 1000 to 4000 mm and

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Heights of 1000 to 2000 mm occur. Not only is the uniform distribution of the liquids flowing through the bed cross-section easier in the laboratory, but also the mixing ratios that cause the relative displacement of the liquid parts to one another,

are therefore much cheaper in the laboratory than on a technical scale. In order to approach the latter, changes had to be made to the commonly used laboratory equipment.

The space above the bed was filled with water and the liquids were introduced at a height of about 20 mm above the bed, the latter being based on the regenerated and backwashed state. Furthermore, a room was provided under the bed, the relative volume of which was smaller than the floor space is usually on a technical scale. Instead of 30% of the bed volume, the space here was only 20%. The liquid-filled space above the bed at its lowest level in the cycle accounted for a little less than 20% of the bed volume.

The volume of the bed used was 540 ml, its total capacity was 1080 meq. It contained a strongly acidic cation exchanger made of polystyrene sulfonic acid (Lewatit® S 100 from Bayer A.G., Leverkusen). As a reaction, the exchange of the calcium ions of the bed by hydrogen ions of a 4N hydrochloric acid was chosen for each of the variants below. This reaction forms the core of the desalination of raw water. The concentration was chosen from the outset to be higher than is usually the case with the simple fraction method in order to enable a comparison with the methods listed below. The flow rate of the liquids was 50 ml / min.

60% of the bed volume or 120% of the volume of the solution supplied from outside was selected as the fraction volume. When this solution was displaced from the bed, the amount of water was adjusted so that the loss in the control solution and in the separately used washing water ranged between 2.0 and 2.5%. This resulted in a co-ion concentration of the fractions of on average 1.9n. 3 reaction fractions were used.

In order to achieve the steady state for the comparison even in the simple fraction process, use has already been made of the measure specified in claim 1 under b) in this known process.

The exchange turnover was determined by determining the calcium ion content in the solution removed as a product. The bed was loaded with calcium ions from an in calcium chloride solution until the outlet became the same as the inlet. The entire outlet was collected and its hydrogen ion content was determined, which was used to control the exchange conversion. In the steady state, the calcium ion content of the product was equal to the hydrogen ion content in the outflow of the loading solution.

The known method was carried out according to the following scheme:

enema

Vol. In ml

Spout

Fraction 1 Fraction 2 Fraction 3 fed solution 4n HCl water

300 300 300

250

to

requirement

Preliminary run + product 920 fraction 1 300

Fraction 2,300

Fraction 3,300

Control solution 300

just the last solution given, here the control solution.

The fractions are all reaction fractions. The volume of the discharged solution, flow + product, was adjusted so that the loss approx. 2% of the co-ion content of the supplied solution was.

After 8 exchange cycles, the steady state appeared, in which the following results were obtained:

ic Calcium ion content in the preliminary run + product Chloride ion content in the preliminary run + product Hydrogen ion content in the loading solution Hydrochloric acid consumption in% of the removed Ca ion loss in control solution and used washing water, based on the co-ion content of the solution supplied from the outside, concentration of the co-ions in the fractions , on average

732 m val 990 mval 730 mval 137%

2.0% 1.9n

25th

b) Method according to the invention, displacement with water

The method according to the invention was carried out as a second variant. For this purpose, the volume at the points of the apparatus where there was a relative displacement of the solution parts was reduced to such an extent that operation could still be maintained. For this purpose, the amount of liquid above the bed was reduced to 5 to 25 ml, corresponding to 0.4 to 2 cm liquid height, and the space below the bed to 2.5% of the bed volume.

The working scheme was:

35

40

enema

Vol. In ml

Spout

Vol. In ml

Fraction 1

300

Preliminary run + product

593

Fraction 2

300

Fraction 1

300

Fraction 3

300

Fraction 2

300

supplied

Fraction 3

300

Solution 4n HCl

250

Water after

Control solution

300

requirement

The loss was reduced to 1.5% by appropriate measurement of the volume of the preliminary run + product.

45 The exchange turnover in the 3 reaction fractions was between 85 and 95% of the MA.

After 10 cycles the steady state appeared, in which the following results were obtained:

55

Vol. In ml

Calcium ion content in the lead + product Chloride ion content in the lead + product Hydrogen ion content in the loading solution Hydrochloric acid consumption in% of the removed calcium ions

Loss in control solution and used washing water, based on the co-ion content of the supplied solution Concentration of the co-ions in the fractions

771 mval. 993 mval

772 meq

1.5% 3.4 to 3.5n

60

The indication “as required” means that the volume of the water is measured so that one is in the outlet of the bed

The reduction in the relative displacement of the liquid parts led to the following results:

Hydrochloric acid consumption was reduced from 137 to 130%; the regenerated capacity rose from 732 to 771 meq;

The volume of the forerun and product was reduced from 920 to 593 ml. The simplest variant of the method according to the invention has already brought about a considerable improvement in the results.

9

620 598

c) Method according to the invention, displacement with stored fractions

The third variant was to carry out the method in which the solution supplied was displaced from the exchanger bed by stored fractions. As is known, this achieves that the reaction fractions have the highest possible concentration, namely practically the same as the solution supplied, and the loss is the lowest. The volume of the reaction fractions was reduced from 300 to 200 ml, considering that the ion content of a fraction in the previous case was between 1020 and 1050 meq, whereas if the volume of 300 ml had been maintained, it would have been between 1260 and 1275 meq. With a volume of the fractions of 200 ml, their ion content had dropped to 840 to 850 meq. Exchange sales had decreased only slightly compared to the fractions containing 1020 to 1050 meq. Here it was between 80 and 90% of the MA.

The working scheme was:

enema

Fraction 1 Fraction 2 Fraction 3 fed solution 4n HCl fraction 4) Fraction 5 water

Vol. In ml

Spout

Vol. In ml

400 400 400

250

100

100

to

requirement

Preliminary run + product 547

Fraction 1 Fraction 2

Fraction 3 Fraction 4 Fraction 5

400 400

400 100 100

15 Fractions 1 to 3 are reaction and 4 and 5 displacement fractions.

The following results were obtained in the steady state reached after 20 cycles:

enema

Vol. In ml

Spout

Vol. In ml

Fraction 1

200

Preliminary run + product

547

Fraction 2

200

Fraction 1

200

Fraction 3

200

Fraction 2

200

supplied

Solution 4n HCl

250

Fraction 3

200

Fraction 4

100

Fraction 4

100

Fraction 5

100

Fraction 5

100

Water after

requirement

25th

Fractions 1 to 3 are reaction and 4 and 5 displacement fractions.

After 12 cycles, the steady state appeared, in which the following results were obtained:

Calcium ion content in the lead + product 769 mval 40

Chloride ion content in the lead + product 1016 meq

Hydrogen ion content in the loading solution 773 meq hydrochloric acid consumption in% of the removed calcium ions 130%

Loss in used washing water, on the 45th

Co-ion content of the supplied solution based on 0.3%

Co-ion concentration of the fractions 4.2 to 4.25n

The differences to the results of the variant under so b) are so slight that it can be determined that the displacement of the solution supplied from the outside by water is practically equivalent to the displacement by stored fractions if, in the former case, according to the teaching of the invention Procedure. In practice, it will be sufficient in many cases to only use water.

d) Method according to the invention, double fraction size In this variant, the effect of enlarging the reaction fractions is to be determined. It must be taken into account here that fractions in which the exchange turnover was in or near the optimal area were already used in the last two variants.

The volume of the reaction fractions was doubled. This resulted in their total volume of 1200 ml and their 65 total ion content of around 5,000 meq. The exchange turnover in the fractions was between 96 and 99% of the MA. The working scheme was:

Calcium ion content in the lead + product 798 meq

Chloride ion content in the lead + product 1003 meq

Hydrogen ion content in the loading solution 792 meq hydrochloric acid consumption in% of the removed

Calcium ions 126% loss in used wash water on the

Co-ion content of the supplied solution based on 0.25%

Co-ion concentration of the fractions 4.2 to 4.5n

30th

In comparison to variant c) it follows that the increase in the fraction size has led to a decrease in acid consumption by 4%.

e) Application of the IFP

As a last variant, a series of tests which had been carried out earlier and in which the IFP was used was used for comparison. In this series of experiments, the reaction fractions at the same concentration had only half the volume as in variant d). However, their number was twice as large, so that the volume of the reaction fractions stored was the same. The total co-ion content was also identical. In this series of experiments, an exchange turnover of 790 meq was achieved, which is practically identical to the value obtained in d).

This comparison shows that the reduction in the number of reaction fractions does not change the exchange conversion of the reaction in the sense of the process according to the invention.

In summary, it can be said that the method according to the invention brings considerable advantages even in its simplest form compared to the known simple fraction method. It has also been shown that the reduction in the number of fractions compared to the IFP does not cause a deterioration in the results.

Example 2

The method according to the invention has now been checked in the exchange reaction between monovalent ions in comparison to the IFP.

Tartaric acid should be produced from its sodium salt using a strongly acidic cation exchanger loaded with hydrogen ions. When regenerating, 4N hydrochloric acid should be used in the IFP.

The bed contained 500 ml Lewatit S 100, its total capacity was 1000 mequ. The throughput rate of the liquids was 4000 ml / h for loading and 3000 ml / h for regeneration.

The first step was to set the working conditions

620 598

10th

Regeneration a loading with a sodium chloride solution was carried out. For the subsequent regeneration, the IFP was applied with the following working scheme:

enema

Vol. In ml

Spout

Vol.

fraction

1

150

Preliminary run + product

540

fraction

2nd

150

fraction

1

150

fraction

3rd

150

fraction

2nd

150

fraction

4th

150

fraction

3rd

150

fraction

5

150

fraction

4th

150

fraction

6

150

fraction

5

150

fraction

7

150

fraction

6

150

fraction

8th

150

fraction

7

150

supplied

Solution 4n HCl

245

fraction

8th

150

fraction

9

100

fraction

9

100

fraction

10th

100

Fraction 10

100

fraction

11

100

Fraction 11

100

water

upon need

Fractions 1 to 8 are reaction fractions and 9 to 11 displacement fractions.

After reaching the steady state, the solution removed at the beginning of the regeneration, first run + product, contained 970 meq chloride ions, 903 meq sodium ions and 67 meq hydrogen ions.

The co-ion concentration of the last reaction fraction, fraction 8, was 4.04n, that of the first displacement fraction used as a control solution, fraction 9, 2.5n. The acid consumption was 108.5% and the NVK 90.8% of the total capacity.

In order to carry out the method according to the invention, the value of the MA was first determined for 3 different composite solutions in order to determine the influence of a separation factor which may change with the bed composition:

1. A solution was placed on the bed fully loaded with sodium ions, which contained 4 eq / 1 chloride ions and 2 eq / 1 sodium and hydrogen ions each. After the leaking solution had the same composition as the inlet, the entire outlet was analyzed. As a result, the bed took up 465 meq of hydrogen ions. That is the value for the MA.

2. A solution was placed on the bed, which was again completely loaded with sodium ions, the chloride ion concentration of which was 4 equiv / 1 here too, but which contained 3.1 equiv / 1 sodium and 0.9 equiv / 1 hydrogen ions. In this case the MA was 256 meq.

3. The bed was loaded with 745 meq sodium and 256 meq hydrogen ions. The solution applied to it again contained 4 eq / 1 chloride ions at 1.98 eq / 1 sodium and 2.02 eq / 1 hydrogen ions. The MA was 238 meq.

When determining the MA, the loading curve of the bed also resulted, which represents the amount of ions (H ions) absorbed by the bed as a function of the amount of Co ions (Cl ions) passed through.

From these measurements, it was found that for an intended exchange conversion of 91 to 93% of the MA, an amount of chloride ions of approximately 1200 meq must be contained in the individual reaction fractions. At a 4n concentration, the volume of the individual reaction fractions was 300 ml. 3 reaction fractions were prepared. The process according to the invention was then carried out according to the following scheme.

Inlet vol. In ml Outlet vol. In ml

Fraction 1

300

Preliminary run + product

520

Fraction 2

300

Fraction 1

300

Fraction 3

300

Fraction 2

300

supplied

Solution 4n HCl

245

Fraction 3

300

Fraction 4

100

Fraction 4

100

Fraction 5

100

Fraction 5

100

Fraction 6

100

Fraction 6

100

Water after

requirement

After reaching the steady state, the solution removed at the beginning of the regeneration contained 975 meq chloride ions, 910 meq sodium ions and 65 meq hydrogen ions.

The co-ion concentration of the last reaction fraction, fraction 3, was 4, In, that of the first displacement fraction, fraction 4, 2.5n used as the control solution and that of the last displacement fraction, fraction 6, 0.26n. The loss was 0.5 meq.

The acid consumption here was 107.7% and the NVK 91.0% of the total capacity.

The results in the two methods are practically the same. The reduction in the number of reaction fractions from 8 to 3 did not affect the results. The total volume of the reaction fractions in the process according to the invention was 25% lower than in the IFP, without this causing a reduction in the exchange turnover.

Now the task set at the outset to obtain tartaric acid from sodium tartrate was accomplished by using the sodium tartrate solution instead of the sodium chloride solution during loading. The solution produced contained 150 g / 1 tartaric acid. After reaching steady state, 900 meques of sodium ions were taken up from the tartrate solution through the bed. In the tartaric acid solution obtained, the sodium ion content was 80 ppm, based on 100% tartaric acid.

Example 3

A wastewater contains around 5 g / 1 sodium citrate calculated as citric acid. On the one hand, the solution is too dilute to be processed further in this state, but on the other hand, the citric acid that can be obtained from it has a value. The sodium citrate solution was passed over a strongly acidic cation exchanger made of Lewatit S 100 in order to replace the sodium ions with hydrogen ions. The solution of citric acid thus obtained was placed on a weakly basic anion exchanger made from a partially substituted amine on a polystyrene skeleton, Lewatit MP 62. According to the invention, the cation exchanger was regenerated with hydrochloric acid, while the anion exchanger was regenerated with a 2.5N sodium hydroxide solution in a simple direct current process. The sodium citrate obtained, the concentration of which exceeded 100 g / l, was returned to production.

The regeneration of the cation exchanger contained in a bed of 530 ml with a total capacity of 1060 meq was carried out according to the following procedure.

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

11

620 598

enema

Vol. In ml

Spout

Vol. In ml

Reaction fraction fed solution 4nHCl fed solution 2n HCl water

600

175

100

to

requirement

Preliminary run + product 598 reaction 600

fraction

Control solution 200

The throughput rate was 3000 ml / h.

After the steady state had been adjusted, the chloride content of the solution removed was 890 meq, thereof 870 meq sodium chloride and 20 meq hydrochloric acid. The control solution contained 8 meq of chloride ions. When the bed was loaded with sodium ions of sodium citrate, 865 meq of citric acid was produced.

With 900 meq hydrochloric acid, 870 meq sodium ions of the bed could be replaced by hydrogen ions, so that the acid consumption was 103.4%. 82% of the total capacity of the bed could be used.

The exchange conversion in the fraction whose Co ion concentration in the steady state was 3.05n was 96% of the MA after repeated determination. The co-ion concentration of the control solution was 0.04n, making the loss

Example 4

A wastewater is to be desalinated which arises in the production of ammonium nitrate and contains small amounts of this salt. The wastewater with 8 g / 1 ammonium nitrate is first passed through a strongly acidic cation exchanger, then through a weakly basic anion exchanger and thus completely desalinated. The loading takes place in the upstream, the regeneration in the downstream. The wastewater is passed through two pairs of the above-mentioned ion exchangers, of which the second pair is freshly regenerated, while the first has already been used in the loading. A third couple is now being regenerated. When the first pair is exhausted, the second takes its place and the freshly regenerated one takes its place. The exhausted couple is regenerated. A dilute solution of nitric acid emerged from the first cation exchanger, which was largely taken up by the first anion exchanger. The water emerging from the first bed pair contained around 20 ppm of aminium nitrate, after the second this content was only 2 ppm.

A bed with 500 ml Lewatit S 100 was used as the cation exchanger and a bed with 750 ml Lewatit MP 62 as the anion exchanger.

The working schemes for the regeneration of the cation exchanger using the process according to the invention were:

enema

Vol. In ml

Spout

Vol. In ml

Fraction 1

400

leader

354

Fraction 2

300

Fraction 1

400

Fraction 3

300

Fraction 2

300

Fraction 4

300

product

210

supplied

Solution4.7nHN03

168

Fraction 3

300

supplied

Solution 2.3n HN03 88

Fraction 4

300

Water after

Control solution

300

After the control solution had been obtained, the bed was washed out with 1.5 l of water in order to reduce the residual ammonium nitrate content in the demineralized water produced.

The flow rate of the liquid was 5 3600 ml / h. Fractions 1 and 2 are displacement fractions and 3 and 4 reaction fractions. The exchange turnover in the latter was 88 and 93% of the MA.

The control solution has an exceptionally high concentration of 0.18n to ensure that the io Co ion concentration of the reaction fractions is high, here 4.5n. This corresponds to more than 90% of the concentration of the supplied solution of 5.On corrected according to the water absorption of the bed.

The flow water, the control solution and the used washing water were added to the wastewater to be desalinated and desalted again in the next exchange cycle. The ammonium ion content of the mixture to be desalted again was 55 mequ. The ammonium nitrate content in the wastewater to be desalinated was 925 mequ. The concentration 20 of the ammonium nitrate solution obtained was 3.9 n, corresponding to 27.5% by weight, so that the solution to be desalted was concentrated almost 40 times.

The anion exchanger was regenerated as follows:

25th

enema

Vol. In ml

Spout

Vol. In ml

Control solution *

200

leader

813

Fraction 1

300

Fraction 1

300

Fraction 2

300

Fraction 2

300

Fraction 3

300

product

252

Fraction 4

300

Fraction 3

300

supplied solution

7.3n NH4OH

Fraction 4

300

Fraction 5

200

Fraction 5

200

Fraction 6

200

Fraction 6

200

Water as needed

Control solution

200

* from the previous cycle.

requirement

45 After receiving the control solution, the bed was washed out with 2.5 l of water. Fractions 1 and 2 or 5 and 6 are displacement fractions and fractions 3 and 4 are reaction fractions. The exchange turnover in the last was about 95% of the MA.

The Co ion concentration of the last reaction fraction was 5.15n, that of the control solution 0.046n. The use of the control solution as the first solution to be applied enables the hydroxyl ions contained therein to be used in a known manner.

55 In the various diluted solutions that were formed in the places mentioned above, 70 meq of ammonium ions were contained. In this case, these diluted solutions were again added to the wastewater to be desalinated and desalted again. The concentration of the ammonium nitrate solution obtained was 28% by weight.

The concentration of the combined product solutions of the cation and anion exchanger was 27.7% by weight. This solution can be returned directly to production.

65 The consumption of regenerating agents was 118%, based on the equivalent amount of the imported ammonium nitrate. Since the amount of ions returned with the diluted solutions together,

620 598

12

quantity supplied, was 13.5%, the effective replenisher consumption was around 104%.

With the method according to the invention it is thus possible to obtain a further processable concentrate and a very pure water which can also be used directly from a wastewater. The consumption of the regenerating agents is within economically acceptable limits. The process described can be used in the treatment of waste water containing ammonia or ammonium salt on the one hand and nitrate or nitric acid on the other hand. Was 0.8%. It has thus been shown that in this case 5, using a single reaction fraction, an effect equivalent to that of 3 reaction fractions in Example 2 can be achieved.

Claims (10)

620 598 1. A method for increasing the exchange conversion in ion exchange processes in which one or more reaction fractions incorporated in the previous implementation of the same exchange reaction, an externally supplied solution of the exchanging ions and water onto the bed loaded with the ions to be exchanged, washed out and filled with water is given and the same number of reaction fractions with the same volume are collected and stored from the bed after removal of the water and a solution obtained as product, as previously given, in order to carry out the same exchange reaction in the same manner and in the same order as the next time to be given up beforehand, characterized in that a) a displacement of those liquid particles, which take place on the bed simultaneously or immediately one after the other, takes place in the flow direction until the discharge from the container de s bed is largely prevented and b) the co-ion content of the reaction fraction (s) is kept constant by keeping the volume of the reaction fraction (s), the solution supplied from the outside and the liquids removed from the system and the co-ion content of the solution supplied from the outside constant is held. 2. The method according to claim 1, characterized in that each reaction fraction is mixed in its container. 2nd PATENT CLAIMS 3. The method according to claim 1 or 2, characterized in that the mixing of the reaction fraction (s) with one another and possibly with the solution supplied from the outside on the way from the fraction containers to the feed line of the bed is largely prevented. 4. The method according to any one of claims 1 to 3, characterized in that in order to keep the co-ion content of the reaction fraction (s) constant, the composition of a solution obtained after the (last) reaction fraction from the bed is checked and, if necessary, adapted. 5. The method according to any one of claims 1 to 4, characterized in that when the reaction fraction (s) are passed through during their contact with the bed, the exchange conversion occurring to over 50%, preferably over 70%, with particular preference over 85% of the maximum possible exchange turnover takes place. 6. The method according to any one of claims 1 to 5, characterized in that a previously incorporated displacement fraction of constant volume is used to displace the (last) reaction fraction from the bed, whose Co ion concentration is lower than that of the solution supplied from the outside and the after Recovery of the (last) reaction fraction from the bed is collected, stored and reused the next time the same exchange reaction is carried out in the same manner as it occurred, the displacement fraction being displaced from the bed by water, the co-ion concentration of the displacement fraction being 30 up to 70%, preferably 40 to 60%, of the co-ion concentration of the solution supplied from the outside is maintained. 7. The method according to any one of claims 1 to 5, in which water is used to displace the (last) reaction fraction, characterized in that the co-ion concentration of the (last) reaction fraction higher than 65%, preferably higher than 75%, of the Co -Ion concentration of the solution supplied from outside. 8. The method according to any one of claims 1 to 5, characterized in that one or more than one solution is used to displace the (last) reaction fraction, each of which is prepared anew from a part of the solution supplied from the outside and from water in each exchange cycle is (are), with the use of several newly prepared solutions their co-ion concentration decreases from solution to solution, and water is displaced onto the bed to displace the newly produced (last) solution, the co-ion concentration of the first newly produced solution to 30 to 70%, preferably to 40 to 60%, of the co-ion concentration of the solution supplied from the outside and the co-ion concentration of any further newly prepared solution (s) to 20 to 30% of the co-ion concentration of the previous newly prepared solution Solution is set. 9. The method according to any one of claims 1 to 8, characterized in that to adjust the composition of the solution obtained from the bed after the (last) reaction fraction, the total volume of the liquids removed at the beginning of the exchange reaction is used, the concentration of the solution being increased of the total volume can be reduced and increased by reducing the total volume. 10. The method according to any one of claims 1 to 9, characterized in that the diluted solutions obtained in addition to the product during the implementation of the process are mixed with the water to be treated and are prepared together with it.