MXPA98004788A - Preparation of aqueous solutions of hydroxylamine li - Google Patents

Abstract

The present invention relates to an aqueous solution of hydroxylamine which is prepared by a process in which the solution obtained by the treatment of a hydroxylammonium salt with a base is separated by distillation in an aqueous solution of hydroxylamine and a fraction of salts. The novel process can be carried out in a simple and moderate way and at a large industrial scale. Due to the low thermal load, the low concentration of hydroxylamine and the short stay time in the process, the risk of decomposition is minimized

Description

PREPARATION OF AQUEOUS SOLUTIONS OF FREE HYDROXYLAMINE The present invention relates to a process for the preparation of aqueous solutions of free hydroxylamine. Hydroxylamine is an important intermediary for the chemical industry. It requires special precautions in its handling because it irritates the eyes, skin and mucous membranes and can cause allergies. In particular, however, it is thermally unstable, ie decomposes from slow to explosive, especially in the presence of metal ions, in a basic medium and in a relatively high concentration. Hydroxylamine is produced on a large industrial scale as a hydroxylammonium salt, usually as hydroxylammonium sulfate and is also used as such. However, it is often necessary to use a highly concentrated aqueous solution free of free hydroxylamine salt. To avoid the aforementioned problems and in particular the instability of hydroxylamine, those skilled in the art have avoided the use of traditional methods of large-scale chemistry to concentrate distillable substances, for example, distillation, in the recovery of aqueous solutions. salt-free hydroxylamine. The distillation of hydroxylamine, even on a laboratory scale, is said to be a particularly dangerous operation, see, Rothler: Gefahrliche Chemische Reationen, Stoffinformationen Hydroxylamin, page 3, 1984, 2, Eco ed-Verlag. The distillation of hydroxylamine on an industrial scale, therefore, has never been considered in technical publications. Instead, special methods have been used, although all of them have serious disadvantages. Attempts have been made to isolate free hydroxylamine from aqueous solutions of the salt with the aid of ion exchangers; see, for example, US-A-4,147,623, EP-A-1787, EP-A-237052, and Z. Anorg. Ch. 288, 28-35 (1956). However, this process gives rise only to diluted solutions with low space-time yields. In addition, hydroxylamine reacts with many ion exchangers or decomposes with these. Another method comprises the electrodialysis of an aqueous solution of the hydroxylammonium salt in electrolysis cells with semi-permeable membranes, as described, for example, in DE-A-3347259, JP-A-123771, and JP-A-123772. However, this process is technically complicated and expensive and to date has not been established in the industry. DE-A-3528463 discloses the preparation of free hydroxylamine from hydroxylammonium sulfate by treatment with calcic oxide, strontium oxide or barium oxide and the elimination of insoluble alkaline earth metal sulfates. In this method the elimination of the sulfates which are obtained in finely divided form presents considerable difficulties. In addition, only dilute solutions are obtained and, when calcium oxide or calcium hydroxide is used, free hydroxylamine still contains undesirably large amounts of ions due to the relatively good solubility of calcium sulfate. When strontium compounds and barium compounds are used, the relatively high price and especially the toxicity are further disadvantages with respect to an industrial production process. DE-A-1247282 discloses a process in which alcoholic solutions of free hydroxylamine are obtained by reacting hydroxylammonium sulfate with ammonia in alcohol as solvent and eliminating ammonium sulfate. A similar process is described in EP-A-108294. However, alcoholic solutions are undesirable and undesirable for multiple applications. For example, special precautions must be taken during the handling of these solutions due to their flammability. In addition, the alcohol that is used must, as a rule, be recovered by an expensive process, since the discharge of relatively large quantities of alcohol to wastewater treatment plants or drains is prohibited. By last, DE-A-3601803 describes a process for obtaining aqueous solutions of free hydroxylamine, in which hydroxylammonium sulfate is reacted with ammonia in lower alcohols, the precipitated ammonium sulfate is separated, water is added to the free hydroxylamine alcohol solution and the alcohol is distilled from the solution thus obtained. The aforementioned disadvantages for dealing with alcohol are applicable to this process as well. In addition, due to the instability of hydroxylamine together with the flammability of the alcohols, special precaution is required in the final distillation step. Common to all the processes of the prior art is that they are not suitable to be carried out on an industrial scale or they give rise to additional safety costs which are very high from the economic point of view. An object of the present invention is to provide a process for the preparation of aqueous solutions of free hydroxylamine which can be carried out in a simple manner and on an industrial scale. Surprisingly, we have found that this objective is achieved if the hydroxylamine is completely or at least to a relatively large degree released from a hydroxylammonium salt by means of a suitable base in the aqueous phase, and the solution obtained is it is separated by distillation in an aqueous solution of hydroxylamine and a fraction of the salt. The present invention, therefore, relates to a process for the preparation of an aqueous solution of free hydroxylamine, wherein: a) a hydroxylammonium salt is treated with a suitable base in water, b) any of the insoluble components is separated from the obtained solution, c) the solution obtained in step (a) or step (b) is separated by distillation in an aqueous fraction of hydroxylamine and a fraction of the salt, and d) if desired, the aqueous solution The hydroxylamine obtained is concentrated in a distillation column by separating the water, which may still contain some hydroxylamine, through the top of this column. Step (a) of the novel process is carried out in a conventional manner. Hydroxylammonium salts which are commonly used are hydroxylammonium salts of mineral acids, for example, of sulfuric acid, phosphoric acid or hydrochloric acid, usually in aqueous solution. The hydroxylammonium salt is reacted with a suitable inorganic base, for example, ammonia, sodium hydroxide, potassium hydroxide, or calcium hydroxide, in aqueous solution, the amount of the base is chosen so that the hydroxylammonium salt is completely or at least partially converted to free hydroxylamine. This can be carried out continuously or in batches and from about 0 to 100 ° C. The resulting aqueous solution contains free hydroxylamine and the salt originating from the base cation and the anion present in the hydroxylammonium salt. Depending on the type and concentration of the hydroalkylammonium salt, the base used to release the hydroxylamine and the temperature at which the reaction is carried out, some of the salt formed may be precipitated. If necessary, the solution can also be cooled to precipitate a relatively large amount of the salt. If such insoluble components, that is, salt precipitates, are present, they are advantageously separated in a conventional manner before step (c). Depending on the process conditions, for example, with the use of ammonia as the base or the use of sodium hydroxide as the base and relatively low concentration of the reactants, no precipitate is formed and step (b) can therefore , omit. The separation by distillation (step c)) of the solution obtained from step (a) or step (b) in an aqueous hydroxylamine solution and a fraction of the salt preferably is carried out with the aid of a distillation column. This is provided with a conventional package, for example, Raschig rings, Pall rings, chair elements, etc., and preferably has from 10 to 50 theoretical plates. The stabilized solution, to which additionally, if desired, stabilizer can be added if required, is fed directly to the top of the column (the upper part of the packing). In the distillation column the solution is separated in such a way that the fraction of the salt is removed in the lower part of the column and an aqueous solution of hydroxylamine in the upper part. To achieve this, it is preferred to treat the solution by passing water and / or steam countercurrent in the lower part of the column. At a concentration of hydroxylamine from 5 to 45% by weight in the feed solution, the flow rate of water or steam in general is from 1 to 8, in particular from 1 to 5 times the feed rate. The temperature of the introduced steam is, in general, from 80 to 180 ° C. The pressure in the distillation column is, in general, from 5 to 200 kPa (from 0.05 to 2 bar), preferably from 10 to 110 kPa (from 0.1 to 1.1 bar). It is particularly preferred to operate the distillation column at a relatively high pressure, i.e. from 50 to 110 kPa (0.5 to 1.1 bar), in particular at atmospheric pressure.

The temperatures prevailing in the distillation column will depend on the pressure at which the column is operated. These are, in general, from 30 to 130 ° C. The aqueous fraction of hydroxylamine (vapor or liquid) separated by the top of the distillation column usually contains 10-150 g of hydroxylamine / 1 and, if desired, can be concentrated in a distillation column (step d) ). For convenience a conventional packed column containing the aforementioned packages is used. A column having from 4 to 20 theoretical plates is preferred. In general, the distillation column is operated from 1 to 200 kPa (from 0.01 to 2 bar), preferably from 5 to 120 kPa from 0.05 to 1.2 bar, particularly preferably from 30 to 110 kPa (from 0.1 to 1.1 bar ). The higher the final concentration proposed for the more moderate hydroxylamine will be the distillation (low pressure and low temperature). The distillation can be carried out continuously or in batches. The water that is separated by the upper part of the distillation column can be recycled as steam to the distillation column or can be passed as wastewater for wastewater treatment. In a particularly preferred embodiment, the distillation of the hydroxylamine from the saline solution and the partial concentration of the hydroxylamine solution are carried out in a single column, ie, a separation / distillation column. The water is distilled from the top and the concentrated hydroxylamine solution is removed about 1 to 3 plates on to feed the solution of hydroxylamine-containing salts from step (a) or step (b). The salt solution is fed in approximately half of the column (approximately 10-30 theoretical plates on the bottom). The fraction of hydroxylamine free salts is separated in the lower part of the column. The number of theoretical plates in the separation / distillation column is, in general, from 20 to 50 and the reflux ratio is adjusted to be from 0.5 to 3. Otherwise, the separation / distillation column is operated as It is described before. In another preferred embodiment, the separation of the hydroxylamine from the salt solution and the partial concentration of the hydroxylamine solution is carried out in the above separation / distillation column with an inserted divider wall. As already described, the water is distilled from the top and the fraction of hydroxylamine-free salts separates at the bottom. The hydroxylamine-containing salt solution is fed, as described, approximately half of the column (approximately 10-30 theoretical plates on the bottom). At the height of this feed stream a dividing wall is installed in the column on a height from 1 to 10, preferably from 1 to 5 theoretical plates, so that the column is divided vertically into two separate sections, the feeding being carried out approximately in the middle part of the dividing wall. The solution enriched in hydroxylamine can thus be separated in salt-free form in the area of the dividing wall, on the opposite side of the feed point. The divider wall separates the point of separation from the feed point. However, identical concentrations of hydroxylamine are present in both laao = of the dividing wall, but salt is present in the solution only on the side of the feed point. The salt-free solution enriched with hydroxylamine can be separated within the height of the dividing wall, at the height of the maximum concentration of hydroxylamine, preferably at the height of the feed stream or, if required, slightly below. Otherwise, the separation / distillation column having a dividing wall is operated as described above. - In an alternative mode to the modality with a dividing wall, it is also possible to join a side column to the separation / distillation column described above, in such a way that this side column is connected on the gas and liquid side, on and below one or more plates from the feed point, to the separation / distillation column, and the solution richer in hydroxylamine is separated by this side column and the latter is designed so as to prevent the passage of the salt-containing solution at the separation point of the lateral column. In another embodiment, the distillative separation of the hydroxylamine solution containing salts in an aqueous solution of salt-free hydroxylamine and a fraction of salts according to step (c) is carried out with the aid of an evaporator operating under moderate conditions, for example, a thin film evaporator, effecting evaporation as much as possible to dry salt. The hydroxylamine fraction is separated at the top and a fraction of salts substantially free of hydroxylamine at the bottom. The fraction of salts, if required, is discharged by means of a suitable mechanical device, for example, 2 counter-rotating helices, the evaporator mentioned, in general, operates from 0 to 100 ° C and from 1 to 200 kPa (from 0.01 at 2 bar), preferably from 2 to 110 kPa (from 0.02 to 1.1 bar). The hydroxylamine fraction obtained can, if desired, be concentrated in another distillation column (step d)) as already described. This can be done continuously or in batches. To keep the risk of decomposition of hydroxylamine very low, all solutions containing free hydroxylamine are stabilized by the addition of a stabilizer against decomposition. Suitable stabilizers are known, for example, hydroxyquinidines, such as 8-hydroxyquinoline, flavones, such as morin, hydroxyquinolines, such as 8-hydroxyquinoline, hydroxyanthraquinones, such as quinalisarin, which are used, if desired, in combination with polyhydroxyphenols, such as pyrogallol. Other suitable stabilizers are benzonitrile, benzamidoxime, N-phenylthiourea, N-hydroxythiourea, reductones and / or reductonates, for example 2, 3-didehydrohexane-1-lactone, and alkali metal salts of ethylenediamine tetra acetic acid. The concentration of the stabilizers, for convenience, is from 5 x 10 -1 to 1, in particular from 5 x 10"3 to 5 x 10" ^, weight percent, based on the free hydroxylamine. The stabilizers that have proved to be particularly useful are 8-hydroxyquinoline and 8-hydroxyquinoline. The novel process has the advantage that it can be carried out in a simple and moderate way. The use of flammable substances is avoided. The concentration of hydroxylamine is low throughout the process. For example, the concentration is less than 45% by weight in the solution obtained from step (a) or (b) and less than 30%, in general, from 2 to 15% by weight in the distillation column or the column separation / distillation. Due to the mode of operation of the separation column or the separation / distillation column, the liquid retained is minimal and the time spent in the process is relatively short. In addition, the mode of operation of the separation column or the separation / distillation column makes it possible to employ higher pressures, in particular atmospheric pressure. Higher hydroxylamine concentrations occur only during concentration in the distillation column (step d)). The hydroxylamine concentration of the solution in step d) can be adjusted as desired, for example, in the range of 30 to 70% by weight. To reduce the risk of decomposition it is possible to introduce another stabilizer in the solution to be distilled. The necessary devices for the novel process can be produced from non-metallic materials, such as glass, ceramics and plastics. In this way decomposition initiated by metal ions is prevented. Nevertheless, it has surprisingly been found that apparatuses, for example, the thin film sizer, can also be produced from metallic materials without significantly high decomposition of the hydroxylamine. This is due to the short stay times of the hydroxylamine in the appliances. Due to the simple yet safe design of the process, only a small cost of capital is necessary to carry out the novel process on an industrial scale. In addition, the novel process can be scaled almost as desired. The novel process is further illustrated in relation to the flow diagrams shown in Figures 1 to 3: in step a), a suitable vessel 12 is charged with the hydroxylammonium salt or a hydroxyammonium salt solution 3, the base 2 being used and a stabilizer 1 (see figures 1 to 3). An aqueous solution 4 containing free hydroxylamine and the salt originating from the base cation and the anion present in the hydroxylammonium salt are obtained. If insoluble components are present in solution 4, these are separated in step (b) with the aid of a filtration apparatus 13, salt 11 and a 4 'solution are obtained (see figures 1 and 2). If required, then another stabilizer 1 'is added to solution 4 or 4'. The separation by distillation in an aqueous fraction of hydroxylamine and a fraction of salts is then carried out according to step (c). According to FIG. 1, the separation by distillation is carried out in a separation column 14, introducing solution 4 or 4 'in the upper part of the column. For this purpose, steam 10 is passed in the lower part of the column. The separation is carried out in such a way that in the lower part of the column the solution of salts 5 substantially free of hydroxylamine is separated, and an aqueous fraction of free hydroxylamine of salts 6 (in the form of vapor or liquid) is separated by the higher. (Heat exchangers 15 not described in more detail are provided in each of steps (c) and (d)). According to Figure 2, the solution 4 'is fed to the separation / distillation column 16. The lower part of the column consists of a section for the separation 16' and the upper part of a section for distillation 16". Solution 4 'is fed between these two sections, that is, at the top of the separation section The separation in the separation / distillation column 16 is effected in such a way that the salt solution substantially free of hydroxylamine 5 is separated in the lower part of the column and the water substantially free of hydroxylamine 9 through the upper part The salt free hydroxylamine solution 6 is removed by a lateral deviation According to figure 3, the distillative separation (step c) )) of the solution 4 is effected by means of a thin film evaporator 17. The fraction of salts substantially free of the resulting hydroxylamine 11 is removed at the bottom and a solution of hydroxylamine without salts 6 is obtained from the top. The hydroxylamine solution 6 obtained from step (c) can, if desired, be concentrated in a distillation column 18 (step d)). Advantageously, another stabilizer 1 '(figures 1 and 2) or 1' (figure 3) is added before distillation. The hydroxylamine solution 6 is fed at a height of about one third of the number of theoretical plates of the distillation column 18. In the distillation, the water substantially free of hydroxylamine 7 is obtained from the top, and a solution of hydroxylamine 8 whose concentration depends on the conditions of the distillation is obtained in the lower part. In the following examples, all hydroxylamine-containing solutions contain 0.01% by weight, based on the free hydroxylamine, of the stabilizer, eg, 8-hydroxyquin.Line, unless stated otherwise.

Example 1 Release of hydroxylamine from hydroxylamine sulfate with ammonia. 538.3 g of hydroxylammonium sulfate, 330 g of water and 0.1 g of 8-hydroxyquinoline as stabilizer were initially taken in a double-jacketed, water-cooled glass vessel 31 which had a stirrer. 446 g of ammonia solution at 25% concentration were slowly added dropwise at room temperature with stirring. A clear solution containing 16.4% by weight of hydroxylamine was obtained Example 2 Release of hydroxylamine from hydroxylammonium sulfate with sodium hydroxide solution. 538.3 g of hydroxylammonium sulfate, 920 g of water and 0.1 g of 8-hydroxyquinoline as a stabilizer were initially taken in a double-jacketed, water-cooled glass container 31 which had a stirrer. 1008 g of 25% sodium hydroxide solution were slowly added dropwise at room temperature with stirring. A clear solution containing 8.4 wt% of hydroxylamine was obtained.

Example 3 Release of hydroxylamine from hydroxylammonium sulfate with sodium hydroxide solution and subsequent removal of the solids. 2204 g of hydroxylammonium sulfate, 1660 g of water and 0.5 g of 8-hydroxyquinoline as a stabilizer were initially taken in a double-jacket, water-cooled, 51-glass vessel that had an agitator. 2149 g of a 50% strength sodium hydroxide solution were slowly added dropwise at room temperature with stirring. The precipitated solid was then filtered. 2229 g of the wet filter cake consisting mainly of sodium sulfate hydrated with hydroxylamine residues were obtained. The filtrate (3780 g) contained approximately 220 g of hydroxylamine / 1. To increase the yield, the filter cake was washed with hydroxylammonium sulfate solution and water and the wash solution containing hydroxylamine was used for another synthesis. The filter cake was then dissolved in water, treated with solutions of iron (III) salts and oxidizing agents to destroy the adhering hydroxylamine residues and fed to the wastewater treatment.

Example 4 Obtaining an aqueous solution of hydroxylamine (HA) from hydroxylamine (HA) / ammonium sulfate (AS) solution using a separation column. An aqueous solution with a content of 218 g of HA / 1 and 680 g of AS / 1 was added at a rate of 300 ml / h to the highest plate in a separation column. The glass separation column with a height of 2 m and a diameter of 35 mm was filled with Raschig rings, 3 mm glass over a height of 1.8 m. 1000 ml / h of distilled water were fed to the bottom of the column, the column was at 40 kPa. The lower temperature was 84 ° C. 1000 ml / h of aqueous solution of salt-free HA with a content of 39.0 g of I-1A / h, corresponding to 59.6% of the total HA feed stream, were distilled from the top of the column. 300 ml / h of ammonium sulfate solution containing 86.0 g / 1 of HA were removed from the bottom of the column. This corresponds to 39.4% of the total HA in the feed stream. The concentration of HA in the column was not more than 100 g / 1. The amount of liquid in the column was 20-225 mi, depending on the load. The time of stay of the liquid in the column was thus only 1.5-10 min. At this low concentration and within the short time, the rate of decomposition is low. Other experiments are mentioned in the following table.

Table 1 Separation of an aqueous solution of HA from an aqueous solution of HA / AS.

* The residues of the column were heated by means of a thermostat. ? The water was fed as superheated steam during the simultaneous heating of the waste.

Example 5 Obtaining an aqueous solution of HA from an aqueous solution of HA / Na 2 SO using a separation column. An aqueous solution with a content of 273 g of HA / 1 and 288 g of Na 2 SO 4 / l was added at a rate of 202 ml / h to the highest plate of a separation column. The glass separation column with a height of 2 m and a diameter of 35 mm was filled with 5 mm glass Raschig rings over a height of 1.8 m. The column was at atmospheric pressure. 1760 ml / h of super heated steam were passed in the lower part of the column. 544 ml / h of sodium sulphate solution with a content of 6.8 g / 1 of HA were taken from the bottom of the column. This corresponds to 6.7% of the total HA in the feed stream. 1519 ml / h of aqueous solution without salts with a content of 34.2 g of HA / 1, corresponding to 94.2% of the total HA in the feed stream, were distilled at the top of the column. Other comparable experiments are mentioned in the following table.

Table 2 Separation of an aqueous solution of HA from an aqueous solution of HA / sodium sulfate.

Example 6 Obtaining an aqueous solution of HA from an aqueous solution of sodium HA / sulfat.o using a separation / distillation column. An aqueous solution with a content of 221 g of HA / 1 and 540 g of AS / 1 was added at a rate of 202 ml / h to the eleventh plate of a glass column with bubble tray with a diameter of 35 mm a total height of 1.6 m and 21 plates (the bottom plate = plate 1). 1300 ml / h of super heated steam are fed to the bottom of the column. The pressure in the column was 99 kPa. 180 ml / h of water substantially free of HA (0.6 g of HA / 1) were taken in the upper part of the column at a temperature in the upper part of 99.8 ° C and a reflux ratio of 1: 3 (reflux: feeding). The. aqueous solution of HA (product solution) was taken at a rate of 1180 ml / h and a concentration of 44 g / 1 by the side stream of plate 12. 400 ml / h of solution of salts were taken at the bottom of the spine. The profile of the experimentally determined column is shown in Table 3. The concentration of 389.5 g / 1 of HA in the residual product was still relatively high due to the fact that, due to the lack of space, the number of plates in the column in the separation section it was too small. In addition, the point of derivation of the lateral current and the relation of the reflux have not yet been optimized.

Table 3 Profile of HA concentration in g of HA / 1 in the separation / distillation column with lateral derivation.

Example 7 Obtaining an aqueous solution of hydroxylamine from a solution of hydroxylamine / sodium sulphate by distillation in a thin film evaporator. 1193 g of filtrate obtained in Example 3 were slowly metered to the top of a thin film glass evaporator (length 1 m, diameter 10 cm) with rotating teflon cleaning blades. The thin film evaporator was operated at 50-60 ° C and 25-40 mbar. 7144 g of the distillate, with an approximate content of 25% by weight of hydroxylamine, was distilled. The distillate obtained was free of salts. The residual product of the thin film evaporator (448 g) consisted essentially of sodium sulfate with hydroxylamine residues and water. To increase the yield, the hydroxylamine residues that adhere to the waste product were washed by water and reused by adding them again to the thin film evaporator or recycled to the synthesis stage. The residual product was dissolved in water, treated with solutions of iron (III) salts and oxidizing agents to destroy any remaining traces of hydroxylamine and fed to wastewater treatment.

Example 8 Concentration of salt-free aqueous hydroxylamine solutions by distillation.

In a glass distillation column filled with Raschig rings (packing height 80 cm, internal diameter 4.5 cm) and with divider for reflux (reflux ratio: discharge 2.1), 30 mg of 8-hydroxyquinoline as stabilizer were added to 630 g of the distillate obtained from example 7, and the mixture was initially taken in the residues and concentrated by distillation at a temperature lower than 40 ° C and at a pressure of 25-40 mbar. The distillate (368 g) contained only 5 g of hydroxylamine / 1 and could be recycled to the synthesis or, for example, to thin film evaporation. The hydroxylamine solution (254 g) remaining in the residues contained 139.5 g of hydroxylamine and 114.5 g of water, corresponding to a hydroxylamine concentration of 55% by weight.

Claims (11)

1. A process for the preparation of an aqueous solution of free hydroxylamine, wherein: a) a hydroxylammonium salt is treated with a suitable base in water, b) any of the insoluble components are separated from the solution obtained, c) the solution obtained in step (a) or step (b) is separated into an aqueous fraction of hydroxylamine and a fraction of salts by passing water or steam countercurrent in the lower part of the column and with the help of a separation column at a temperature of> 80 ° C, and d) if desired, the aqueous hydroxylamine solution obtained is concentrated by distillation 2.

The process according to claim 1, wherein the aqueous hydroxylamine solution is derived in or on the feed plate of the separation column 3.

The process according to claim 1 or 2, wherein the separation column is operated from 5 to 300, preferably from 50 to 150 kPa 4.

The process according to any of the reiv above indications, wherein the distillation column is operated from 10 to 150, preferably from 20 to 60 kPa, in step (d).

The process according to claims 1 to 4, wherein the separation of the free hydroxylamine from the salt solution and the concentration of the hydroxylamine solution are carried out in a separation / distillation column, the solution of concentrated hydroxylamine is separated from 0 to 5 plates on the feed stream of the salt solution from step (a) or step (b) and water is derived from the top of the salt fraction in the bottom of the column.

6. The process according to claim 5, wherein a separation / distillation column is used in which a vertical divider wall is introduced at the height of the feed point so that the side of the feed stream carrying the salts is separated by the dividing wall from the opposite point of separation for the solution rich in hydroxylamine, free of salts.

The process according to claim 6, wherein the vertical divider wall extends over a height of about 1 to 5 theoretical plates and the feed stream is in the region of half the height of the divider wall.

The process according to claim 5, wherein the side column is attached to the separation / distillation column and the salt-free hydroxylamine-rich solution is removed through this side column.

The process according to claim 8, wherein the side column is connected on the gas and liquid side, on one or more plates and below one or more plates from the feed point, to the separation column / distillation and is designed so that the passage of the solution containing salts at the point of separation of the lateral column is omitted.

The process according to claim 1 to 9, wherein the water or steam derived from the top in the separation / distillation column in step (c) or in the distillation column in step (d) it is fed back completely or partly to the lower part of the separation column.

11. The process according to any of the preceding claims, wherein a stabilizer against decomposition is added to all solutions containing free hydroxylamine.