MXPA00000993A - Method for producing an aqueous solution of free hydroxylamine - Google Patents

Abstract

The invention relates to a method for producing an aqueous solution of free hydroxylamine by treating a hydroxylammonium salt with ammonia in the counter-current in a stripping column. As a result, hydroxylamine is released and at the same time, the solution obtained is separated into an aqueous hydroxylamine solution and a salt fraction by distillation. The inventive method is simple and mild, and can be carried out on a large scale. The risk of decomposition is minimal due to the low thermal burden, the low concentration of hydroxylamine and the short residence time involved in the process.

Description

"PREPARATION OF AN AQUEOUS SOLUTION OF HIDROXIL7" FREE MINE " The present invention relates to a process for the preparation of aqueous solutions free of free hydroxylamine metal ion. Hydroxylamine is an important intermediate for the chemical industry. However, specific care is required in handling it because it irritates the eyes, skin and mucous membranes and can cause allergies. In particular, however, it is thermally unstable, that is, it decomposes slowly until explosively, especially in presence of metal ions, in an intensely 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. Frequently, however, it is necessary to use an aqueous solution free of metal ion and highly concentrated salt of free hydroxylamine. In order to avoid the aforementioned problems and in particular the instability of hydroxylamine, those skilled in the art have avoided the use of traditional large-scale chemistry methods to concentrate the release substances, for example distillation, in the recovery of salt-free hydroxylamine solutions. The distillation of hydroxylamine, even on a laboratory scale, is still said to be a particularly dangerous operation; see Rothler: Gefahrliche Chemische Reaktionen, Stoffinformationen Hydroxylamine, page 3, 1984, 2, Eco ed-Verlag. The distillation of hydroxylamine on an industrial scale has never been taken into account in technical publications until now. Instead, special methods have been used even when all of them have serious disadvantages. Therefore attempts were made to isolate the free hydroxylamine from the aqueous salt solutions with the help of ion exchangers; see, for example, U.S. Patent Number A-4,147,623, Patent Number EP-A-1787, Patent Number EP-A-237052 and Z. Anorg. Ch. 288, 28-35 (1956). However, this process leads only to diluted solutions with low space-time yields. In addition, hydroxylamine reacts with or decomposes with many ion exchangers. A further method comprises electrodialysis of an aqueous hydroxylammonium salt solution in electrolysis cells with semipermeable membranes, as described, for example, in Patent Numbers DE-A-33 41 259, JP-A-123771 and JP-A -123772. Nevertheless, - - This process is technically complicated and expensive and to date has not been established in the industry. Patent Number DE-A-35 28 463 discloses the preparation of free hydroxylamine from hydroxylammonium sulfate by treatment with calcium oxide, strontium oxide or barium oxide and the removal of the insoluble alkaline earth metal sulfates. In this method, the removal of the sulphates obtained in finely divided form presents considerable difficulties. In addition, only diluted solutions are obtained 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 more disadvantageous with respect to an industrial production process. Patent Number DE-A 12 47 282 describes a process in which alcoholic solutions of free hydroxylamine are obtained by reacting the hydroxylammonium sulfate with ammonia in alcohol or a solvent and removing the ammonium sulfate. It is described in similar process in the Patent Number EP-A-108 294. However, alcoholic solutions are inappropriate and undesirable - - for a number of applications. For example, specific precautions should be taken during the handling of these solutions, due to its flammability. In addition, the alcohol used must be recovered as a general rule by means of a costly procedure, since the discharge of relatively large quantities of alcohol to the wastewater treatment plants or to the discharges is prohibited. Finally, Patent Number DE-A-36 01 803 describes a process for obtaining aqueous solutions of free hydroxylamine, wherein the hydroxylammonium sulfate is reacted with ammonia in lower alcohols, the precipitated ammonium sulphate is separated, the water add to the free hydroxylamine alcohol solution and the alcohol is distilled from the solution obtained in this way. The aforementioned disadvantages of working non-alcohol are applicable to this process as well. In addition, due to the instability of hydroxylamine together with the flammability of the alcohols, specific care is required in the final distillation stage. It is common for all processes of the prior art that they are not suitable to be carried out on an industrial scale or to give rise to additional economically high safety costs.

A temperature higher than 65 ° C is considered critical for the decomposition of hydroxylamine. In a differential thermal analysis, the initial temperature of a 50 weight percent concentration of the aqueous hydroxylamine solution (in a glass crucible) was determined to be 70 ° C. The amount of heat released, approximately 2.2 kJ / g of a 50 weight percent concentration solution, confirms the high thermal potential of the substance. Differential thermal analysis is a microthermal analytical method that is used to calculate thermal stability and thermal potential. The initial temperature is the lowest ambient temperature at which a marked exothermic reaction is carried out in the sample at the heating rate of 1 K / minute, starting at 30 ° C. For safety reasons, the processing temperatures should be. considerably lower than the initial temperature. Therefore, in connection with the preparation of hydroxylamine nitrate, U.S. Patent Number A-4 956 168 teaches that a suspension of hydroxylamine sulfate in alcohol is prepared at a temperature not exceeding 65 ° C. This suspension is then treated with ammonia to < 65 ° C in order to prepare a solution of alcoholic hydroxylamine.

US Patent Number A-5 472 679 in turn describes a process for the preparation of an aqueous hydroxylamine solution free of alcohol, by reacting a solution of hydroxylamine sulfate with an appropriate base at a temperature of up to about 60 ° C. The obtained mixture is then subjected to a distillation under reduced pressure at less than 65 ° C. A solid residue (the salt formed in liberation of the hydroxylamine) and, as the distillate, a solution of aqueous draydylamine containing from 16 percent to 23 percent by weight of hydroxylamine are obtained. This process has the disadvantage that it is carried out under reduced pressure and that the temperature must be controlled very carefully. It also has the following additional disadvantages: - The precipitated material makes it necessary to work with solids. In a continuous process, the solid would therefore have to be continuously removed. This can present considerable process engineering problems if it is a solid that tends to agglomerate, such as, for example, in the case of sodium sulfate. - The distillation to dryness, which is referred to correctly as reduction by evaporation, is carried out in such a way that the water in the low boiler evaporates first. The - The concentration of hydroxylamine in the boiler increases. It is known that the tendency of the hydroxylamine to decompose increases with the concentration of hydroxylamine. Consequently, losses of hydroxylamine increase during the process. There is an increasing risk that, due to the high concentration of hydroxylamine, explosive decomposition may occur. It is known that pure hydroxylamine or hydroxylamine at a concentration of > 70 percent by weight can decompose explosively. Therefore, appropriate security requirements for the manifested process must be filled. The remaining solid still contains hydroxylamine residues (hydroxylamine adsorbed to the surface, hydroxylamine in the voids in the solid, the solid must therefore be decontaminated in a separate discharge process.) Therefore, reduction by evaporation is not a process which can advantageously be carried out on a large industrial scale Patent Number WO 97/22551 describes a process for the preparation of aqueous solutions of free hydroxylamine A hydroxylammonium salt is treated with an appropriate base in water, any of the insoluble constituents are separated of the resulting solution, the obtained solution is separated into an aqueous hydroxylamine fraction and a salt fraction by distillation at a temperature greater than 80 ° C and, if desired, the obtained aqueous hydroxylamine solution is concentrated in a distillation column by extracting the water through the top of this column. This process provides a complete yield of free hydroxylamine only when using strong bases to release hydroxylamine. Due to economic reasons, the sodium hydroxide solution is preferably used as a strong economic base on a large industrial scale. Sodium sulfate is then formed as a by-product of the release of hydroxylamine. This salt is obtained as an aqueous solution. In the mentioned process, the released hydroxylamine is separated from the salt solution by steam purification. The feed to the scrubbing column must not contain a solid (precipitated salt), in order to avoid blockage of the column. In this process with the use of the sodium hydroxide solution, the solubility limit of the sodium sulfate in the aqueous hydroxylamine solution therefore imposes a limitation. The solubility of sodium sulfate at about 10 percent concentration by weight of the aqueous hydroxylamine solution is about 24 weight percent at 100 ° C. Because of this low solubility, the concentration of the free hydroxylamine in the release solution is also limited to about 10 weight percent at most, unless a solid separation step is included upstream. However, due to the easy decomposability of hydroxylamine, its sensitizing effect and the tendency of sodium sulfate to bind, this process is avoided in the industry when possible. The concentration of the limited hydroxylamine by the solubility of sodium sulfate limits the maximum capacity that can be achieved from the industrial plant. In addition, the use of the sodium hydroxide solution inevitably leads to the solution of the product that always contains metal ions (sodium ions), even if only in a small amount. It would be of considerable technical and economic advantage if it were possible to alternatively use economic ammonia. The water solubility of ammonium sulfate, 50.9 weight percent at 100 ° C is more than twice as high as that of sodium sulfate. The concentration of the hydroxylamine and therefore the capacity of the plant could therefore be much more than that bent. He - Ammonium sulfate obtained in neutralization can also be used as a valuable fertilizer while sodium sulphate must be discharged as a useless impurity. Using ammonia as the basis for the release of hydroxylamine, the introduction of metal ions into the product is automatically prevented. - However, ammonia is a "much weaker base than sodium hydroxide solution." Even though hydroxylamine can be completely displaced from hydroxylammonium sulfate by means of a sodium hydroxide solution, this can not be achieved with ammonia. Due to the resulting balance (NH2OH2) 2S04 + 2 NH OH > (NH4) 2S04 + 2 NH2O? T + 2 H20 only about 60 percent to 70 percent of the hydroxylamine present is released. The rest continues to be present in bound form as sulfate. Accordingly, only a hydroxylamine yield of 60 percent to 70 percent can be achieved by the aforementioned purification method. More than 30 percent of the hydroxylamine could leave the scrubbing column as hydroxylammonium sulfate through the bottom for wastewater treatment and would therefore be lost for industrial use. This - high hydroxylammonium load, plus an expensive wastewater treatment facility. The use of ammonia is therefore not an economical alternative to the simple-purification method. - An object of the present invention is to provide a process for the preparation of aqueous solutions free of free hydroxylamine metal ion which can be carried out simply and on an industrial scale and which allows the use of economical ammonia for the complete release and isolation of hydroxylamine free of metal ion. We have surprisingly found that this object is achieved if the hydroxylammonium salt in the aqueous phase is treated with ammonia by the countercurrent method and at the same time the solution obtained is separated into a solution of aqueous hydroxylamine and a fraction of salt being steam cleaned . The present invention therefore relates to a process for the preparation of an aqueous solution of free hydroxylamine by treating a solution of hydroxylammonium salt with a base and separating the resulting solution by distillation in an aqueous hydroxylamine solution and a salt fraction, wherein the solution is treated with ammonia or ammonia water as the base by the countercurrent method and at the same time the separation is effected by treatment with water and / or steam. The hydroxylammonium salts used are generally the hydroxylammonium salts of the mineral acids, for example sulfuric acid, phosphoric acid or hydrochloric acid, usually in an aqueous solution. The hydroxylammonium salt is treated in a countercurrent flow with ammonia or ammonia water in an aqueous solution. Instead of ammonia, other volatile bases are also suitable. Volatile bases useful, for example, are mono-, di- or trialkylamines, such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine or triethylamine, mono- and di- or trialkanolamines, such as diethanolamine, and cyclic amines such as pyrrolidine. or piperidine. The amount of the base is selected so that the hydroxylammonium salt converts completely or at least to a predominant degree into a free hydroxylamine. This can be done continuously or in batches and at a temperature of about 10 ° to 120 ° C. An aqueous solution containing the free hydroxylamine and a solution free of hydroxylamine containing the salt originating from the cation of the base and the acid anion present in the hydroxylammonium salt are also obtained. - ~ - The release of the hydroxylamine and the separation of the resulting solution in an aqueous hydroxylamine solution and a salt fraction are preferably carried out by treatment with ammonia and steam by the countercurrent method with the aid of a scrubbing column (column purification / reaction). This is provided with conventional trays, for example sieve trays or bubble trays, or with a conventional package, for example, Raschig rings, Pall rings, saddle elements, etc., and preferably has from 10 to 60 theoretical plates. The hydroxylammonium salt solution to which it can be added, and if additional stabilizer is required, is fed directly to the top of the column (upper part of the package or upper part or one of the upper trays). In the purification column, the neutralization and the separation of the solution are carried out, in such a way that the salt fraction is extracted in the lower part of the column and an aqueous hydroxylamine solution at the level of the feeding tray. , or above it. In order to achieve this, it is necessary to treat the hydroxylammonium salt solution by passing ammonia or ammonia water and water and / or steam in countercurrent to the bottom-of the column. When the water and / or the water of the ammonia are passed, the - The bottom must be properly heated by heat exchangers in order to evaporate the aqueous solutions. When ammonia water is used, the amount of water or steam that is going to be passed can be reduced or the introduction of it can be avoided. However, it may then be necessary to heat the bottom. At a concentration of hydroxylammonium sulfate of 5 percent to 80 percent by weight in the feed solution, the flow rate of water or steam is usually 1 to 8, in particular 1 to 5 times the rate of water. feeding. The temperature of the steam introduced is generally 80 ° C to 180 ° C. The pressure in the scrubbing / reaction column is generally from 5 to 300 kPa (from 0.05 to 3 bar), preferably from 10 to 110 kPa (from 0.1 to 1.1 bar). It is particularly preferred to operate the scrub / reaction column at 50 to 110 kPa (0.5 to 1.1 bar), in particular at atmospheric pressure. - The temperatures that prevail in the purification / reaction column depend on the pressure at which the column is operated. They are usually from 30 ° C to 130 ° C, preferably from 80 ° C to 130 ° C. The fraction of aqueous hydroxylamine (vaporous or liquid) extracted through the top of the scrub / reaction column usually contains 20 to - 300_ grams of hydroxylamine / 1 and, if desired, can be concentrated in a conventional industrial design distillation column. A column having 4 to 30 theoretical plates is preferred. The addition of a stabilizer can be advantageous. The obtained hydroxylamine solution, if desired, can be concentrated in a distillation column. It may be advantageous to add a stabilizer in addition before distillation. The hydroxylamine solution is preferably fed at a height of about one third of the theoretical plates of the distillation column. In the distillation column, water is obtained essentially free of hydroxylamine in the upper part and a hydroxylamine solution is obtained in the lower part whose concentration depends on the distillation conditions. 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 10 to 110 kPa (from 0.1 to 1.1 bar). The higher the proposed final concentration of hydroxylamine, the milder (low pressure and low temperature) will be the distillation. The distillation can be carried out continuously or in batches.

- Water or steam drawn through the top of the distillation column can be recycled, either directly or after compression or superheating, as scrubbing steam to the bottom of the scrub / reaction column or passed off as wastewater for wastewater treatment. If required, a means for separating retained droplets (e.g., a windshield wiper) can be installed above the feed tray. In a particularly preferred embodiment, the neutralization with ammonia is carried out by the countercurrent method and the hydroxylamine clearance of the salt solution is carried out in combination with the partial concentration of the hydroxylamine solution in only one column, i.e. , a purification / reaction / distillation column. The water is distilled through the top and the concentrated hydroxylamine solution is removed to approximately 1 to 3 trays above the feed of the salt solution containing the hydroxylammonium sulfate. The salt solution is fed in more or less half of the column (from approximately 10 to 40 theoretical plates above the bottom). The required ammonia or ammonia water is fed either directly at the bottom or, preferably, from 1 to 5 trays per - above the bottom. The latter method has the advantage that the trays below the ammonia feed point serve to completely purify the ammonia from the lower discharge solution below the feed point. The salt fraction free of hydroxylamine is extracted as an inferior product of the column. The number of theoretical plates in the purification / reaction / distillation column, it is usually from 20 to 50 and the reflux ratio in the rectification section is adjusted so that it is from 0.5 to 3. Otherwise, the purification / reaction / distillation column is made to work as described above. foregoing. The step of the novel process has the advantage that it can be carried out in a simple and smooth manner. The introduction of metal ions is reliably avoided. The use of flammable substances and solids is avoided. The concentration of hydroxylamine is low throughout the entire process. For example, it is less than 30 weight percent in the purification / reaction column and in the purification / reaction / distillation column. Due to the operation mode of the purification / reaction column and the purification / reaction / distillation column, the retention of the liquid is minimal and the residence time in the process is relatively short. In addition, the mode of - - operation of the purification / reaction column and the purification / reaction / distillation column makes it possible to employ higher pressures, in particular atmospheric pressure. Due to the relatively short residence times, the release of the hydroxylamine in the scrub / reaction column and the scrubbing / scrubbing / distillation column can, if desired, also be carried out without the addition of the stabilizer. The decomposition that takes place is only slightly higher than that of the stabilized solutions. The addition of suitable stabilizers, as described, for example, in Patent Number WO 97/22551, can reduce the decomposition of hydroxylamine to a minimum. The highest concentrations of hydroxylamine occur only during the concentration in-? A-distillation column. The concentration of the hydroxylamine can be adjusted as desired for example within the range of 30 percent to 70 percent by weight. _In order to reduce the risk of decomposition, the stabilizer can be introduced into the solution to be distilled. The apparatus required for the novel process can be produced from non-metallic materials, such as glass, ceramics and plastics. The decomposition initiated by the metal ions is therefore prevented.

Surprisingly, however, it has been found that apparatuses can also be produced from special metallic materials such as platinum or gold, without a significant higher decomposition of hydroxyamine being observed. Due to the design of the simple process, but at the same time safe, only a small capital cost is necessary to carry out the novel process on an industrial scale. In addition, the process can be increased virtually as desired. The novel process is further illustrated with reference to the flow charts shown in Figures 1 and 2: In accordance with Figure 1, the release of the hydroxylamine and the isolation of the hydroxylamine are carried out in a purification column A / reaction, the hydroxylammonium salt solution 1 which is fed to the top of the column. Ammonia 2 and steam 3 are passed to the bottom of the column. The separation is effected by extracting the solution 4 of salt essentially free of hydroxylamine in the lower part of the column and a fraction 5 of aqueous hydroxylamine free of salt (in vaporous or liquid form) through the upper part. If desired, stabilizer 6 can be added at the top of the scrubbing column. According to Figure 2, solution 1 of the hydroxylamine salt is fed to a scrubbing / reaction / distillation column A + B. The lower part of the column consists of a section A of purification and the upper part of section B of distillation. The hydroxylammonium salt solution 1 is fed between these two sections, that is, towards the top-of the purification section. The release of hydroxylamine and the separation of hydroxylamine in the purification / reaction / distillation column are carried out in such a way that the salt solution 4 essentially free of hydroxylamine is extracted in the lower part of the column and the water 8 essentially free. of hydroxylamine through the top, the salt-free hydroxylamine solution 5 which is from about 5 percent to 60 percent by weight concentration is removed through a side outlet. If desired, a stabilizer may be added to the top of the scrubbing column A 6 and / or to the top of the distillation column B 7. The examples that will be given below illustrate the invention without restricting it. ~ - - The experiments were carried out in an experimental laboratory apparatus consisting essentially of a stirred kettle, a glass purification column and a glass distillation column and below with corresponding storage containers., regulated supply pumps, product containers in scales, steam connection with the lower part of the column and condensers in downstream. The scrubbing column had an internal diameter of 50 millimeters, a height of 3000 millimeters and was filled with gaskets with a diameter of 5 millimeters. The distillation column was a double jacket column having an internal diameter of 45 millimeters and a height of 2.5 meters and filled with 5 millimeter diameter gaskets. The starting material was a 25 weight percent concentration of a hydroxylammonium sulfate solution. If required, a stabilizer is added to the hydroxylammonium sulfate solution. In the comparison examples, the solution was continuously passed by means of a pump to a stirred glass kettle of 100 milliliter capacity through which the flow was continuous. At the same time, the base was continuously added to the agitated boiler by means of a pump in an amount sufficient to establish the desired, detectable pH neutralization point.

- The base hydroxylamine was released by reaction with a solution of sodium hydroxide or ammonia. The free base hydroxylamine was purified from the aqueous salt solution with steam (from about 1 to 6 kilograms of steam / kilogram of feed) in the scrubbing column. The steam was passed directly to the bottom of the column. The salt solution was continuously extracted at the bottom of the column. The steam from the scrubbing column, which contains from about 2 percent to 10 weight percent hydroxylamine, was passed to the bottom tray of the downstream distillation column. The distilled water (water essentially free of hydroxylamine) was extracted at the top of the distillation column. A part of the condensed material was recycled to the column as reflux. The aqueous hydroxylamine solution (3 percent to 40 weight percent hydroxylamine) was extracted from the bottom.

Comparison Example 1: Obtaining the free hydroxylamine hydroxylammonium sulfate using a sodium hydroxide solution and subsequently separating a hydroxylamine solution - of the sodium sulphate solution by steam cleaning in a column. 1012 grams per hour of the stabilized hydroxylammonium sulfate solution and 296 grams per hour of concentration were mixed to 50 weight percent of a sodium hydroxide solution in a stirred kettle reactor and the discharge solution was passed directly through. to the top of the debug column. The feed solution contained about 8.2 weight percent hydroxylamine. 3500 grams per hour of steam were passed to the bottom of the scrubbing column. The steam that leaves the top of the scrubbing column passed directly to the distillation column. This was operated at a reflux ratio of about 0.6 at atmospheric pressure. The lower part of the distillation column was not heated. The discharge of the lower liquid was cooled and collected. It contained about 7 weight percent hydroxylamine. The discharge of the solution from the bottom of the scrubbing column contained about 0.2 weight percent hydroxylamine. Losses of hydroxylamine through the total experimental apparatus as a result of decomposition were approximately 3.3 percent in - weight. The yield of hydroxylamine was 94 weight percent.

Comparison Example 2: Hydroxylammonium sulfate is obtained by free hydroxylamine using ammonia and subsequently separating an aqueous hydrosylamine solution from an ammonium sulfate solution by steam purification in a column. The experiment was carried out in a manner similar to Example 1. 710 grams per hour of the hydroxylammonium sulfate solution and 541 grams per hour of ammonia water (24.9 weight percent NH3) were used. The feed solution contained about 6.1 weight percent hydroxylamine. The experimental conditions - pH, temperature and pressure - were the same as in Example 1. The discharge from the bottom of the distillation column contained only 3.3 weight percent hydroxylamine. On the other hand, the discharge of the solution from the bottom of the distillation column contained about 2.5 weight percent hydroxylamine. The decomposition of hydroxylamine was about 6.6 weight percent. The hydroxylamine yield was only 59 - percent in weight. Due to the low concentration of ammonia base, only a certain amount of the hydroxylamine was released into the stirred kettle and about 32 weight percent of the hydroxylamine used left the scrubbing column not converted as hydroxylammonium sulfate through the discharge on the bottom.

Example 1: Obtaining free hydroxylamine hydroxylammonium sulfate using ammonia in the countercurrent process by direct passage to the bottom of the scrubbing column while simultaneously removing a solution of aqueous hydroxylamine from the ammonium sulfate solution by steam stripping. 710 grams per hour of the stabilized hydroxylammonium sulfate solution was passed directly to the top of the scrubbing column, and 3500 grams per steam hour of 1.5 bar (approximately 130 °) were fed to the bottom of the scrubber column. C) and at the same time 631 grams per hour of ammonia water The discharge of the solution from the bottom of the scrubbing column contained approximately 0.16 weight percent of hydroxylamine The product discharged from the bottom of the column of The distillation contained 5.35 percent by weight of hydroxylamine. droxylamine was approximately 3.5 weight percent. The yield of hydroxylamine was therefore 94 weight percent. As a result of the countercurrent treatment, the hydroxylamine was thus surprisingly released almost completely even by the weak base ammonia and at the same time it was isolated. No increased decomposition was observed. The result is even more surprising since ammonia is only very slightly soluble in water under the prevailing operating conditions.

Example 2: Obtaining free hydroxylamine hydroxylammonium sulfate using ammonia in a manner similar to Example 1 but with a higher column charge and only a stoichiometric addition of ammonia. 1421 grams per hour of the stabilized hydroxylammonium sulfate solution were passed directly to the top of the scrubbing column. They were fed to the bottom of the purification column 3500 grams per hour of steam of 1.5 bar and at the same time 370 grams per hour of ammonia water. The discharge of the solution from the bottom of the scrubbing column contained about 1.7 weight percent hydroxylamine. The product discharge from the bottom of the distillation column contained 8.7 weight percent hydroxylamine. The decomposition of the hydroxylamine was about 4.4 weight percent. The yield of hydroxylamine was therefore 82 weight percent. Even with the stoichiometric addition of ammonia and a considerably increased column loading, it was possible to achieve a hydroxylamine yield well above the equilibrium value (see Comparison Example 2). With an optimal design of the scrubbing column and optimal column loading, a considerably higher hydroxylamine yield can be achieved here.

Example 3: Obtaining hydroxylammonium sulfate-free hydroxylamine using ammonia in the countercurrent process by passing directly to the bottom of the scrubbing column while simultaneously separating an aqueous hydroxylamine solution from the - Ammonium sulfate solution by steam purification in the absence of a stabilizer. The extract of Example 1 was repeated in the same manner (541 grams per hour instead of 631 grams per hour of ammonia water). However, no stabilizer was added to the hydroxylammonium sulfate solution, ie the release and isolation of the hydroxylamine were carried out in the complete absence of the stabilizer. The discharge of the solution from the bottom of the scrubbing column again contained only about 0.16 weight percent hydroxylamine. The discharge of the product from the bottom of the distillation column contained 5.2 weight percent hydroxylamine. The decomposition of the hydroxylamine was only about 4.4 weight percent. The yield of hydroxylamine was therefore 94 weight percent. This experiment showed that the usual high performance can be achieved by countercurrent treatment in a scrubbing column due to the short residence time, even without the addition of a stabilizer. The decomposition is only very slightly higher.

Claims (11)

- CLAIMS

1. A process for the preparation of an aqueous solution of free hydroxylamine by treating a solution of hydroxylammonium salt with a base and separating the resulting solution by distillation in an aqueous hydroxylamine solution and a salt fraction, wherein the hydroxylammonium salt solution is treats with ammonia or ammonia water as the base by the countercurrent method and at the same time the separation is effected by treatment with water or steam.

2. A process according to claim 1, wherein the countercurrent treatment and the separation by distillation are carried out with the aid of a scrubbing column.

3. A process according to claim 2, wherein the solution obtained is treated in the countercurrent process by passing water or steam and ammonia or ammonia water towards the lower part of the column.

4. A process according to claim 2 or 3, wherein the aqueous hydroxylamine solution is extracted through the top of the scrubbing column.

5. A process according to any of claims 2 to 4, wherein the scrubbing column is operated at from 5 to 300, preferably from 10 to 110 kPa.

6. A process according to any of the preceding claims, wherein the obtained aqueous hydroxylamine solution is concentrated in a distillation column

7. A process according to claim 6, wherein the distillation column is made operate from 1 to 200, preferably from 10 to 110, kPa

8. A process according to claim 6 or 7, wherein the water drawn through the top of the distillation column is recycled, if requires in gaseous form, to the bottom of the scrubbing column

9. A process according to claim 6, wherein the clearance of the free hydroxylamine from the salt solution and the concentration of the hydroxylamine solution are carried performed in a purification / distillation column

10. A process according to claim 9, wherein the removal of the concentrated hydroxylamine solution is carried out from 1 to 3 trays per Above the feed of the salt solution and water is extracted through the top and the salt fraction in the bottom of the column.

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