MXPA99011383A - Method for producing highly pure aqueous hydroxylamine solutions - Google Patents

Abstract

The invention relates to a method for the production of highly pure aqueous solution from free hydroxylamine, wherein the diluted aqueous hydroxylamine solution is concentrated in a column, the vapor containing hydroxylamine is removed from the bottom of the column via a side-stream and highly pure hydroxylamine is obtained through condensation of the vapors. The inventive method is simple and mild, can be used in large-scale production and yields"electronic grade"hydroxylamine.

Description

PREPARATION OF AQUEOUS SOLUTIONS, VERY PURE, OF HYDROXYLAMINE The present invention relates to a process for the preparation of very pure aqueous solutions of free hydroxylamine. Aqueous, concentrated, very pure hydroxylamine solutions are used, among others, in the electronics industry, for example in combination with other substances for preliminary cleaning of circuit boards. For use in the electronics industry, concentrations of impurities, in particular metal ions, are usually required, well below 1 ppm, ie electronic grade products. However, commercially available aqueous hydroxylamine solutions currently contain impurities in the ppm range from the preparation, for example sodium sulfate or other metal compounds. Hydroxylamine is produced on a large industrial scale as a hydroxylammonium salt, usually as hydroxylammonium sulfate. However, it is often necessary to use an aqueous solution, highly concentrated, free of free hydroxylamine salts. In order to avoid the aforementioned problems and, in particular, the instability of hydroxylamine, those skilled in the art have to avoid the use of traditional large-scale chemistry methods to concentrate distillable substances, for example by distillation, in the recovery of solutions. of salt-free hydroxylamine. The distillation of hydroxylamine, on a laboratory scale, is still a particularly dangerous operation; see, Roth-Weller: Gefahrliche Chemische Reaktionen, Stoffinformationen Hydroxylamin, page 3, 1984, 2, Ecomed-Verlag. The distillation of hydroxylamine on an industrial scale has not yet been considered in technical publications. Instead, special methods have been used, although all of these have serious disadvantages. In this way, attempts have been made to isolate free hydroxylamine from aqueous salt solutions with the aid of ion exchangers; see, for example US-A-4, 147, 623, EP-A-1787, EP-A-237 052 and Z. Anorg. Ch. 288, 28-35 (1956). However, this process only gives rise to diluted solutions with low space-time yields. In addition, hydroxylamine reacts with multiple ion exchangers or decomposes with these. Another method consists of the electrodialysis of an aqueous solution of the hydroxylammonium salt in electrolysis cells with semipermeable membranes, as described for example in DE-A-33 47 259, JP-A-123 771 and JP-A-123 772 However, this process is technically complicated and expensive and to date has not been established in the industry.

DE-A-35 28 463 describes the preparation of free hydroxylamine from hydroxylammonium sulfate by treatment with calcium oxide, strontium oxide or barium oxide and the separation of insoluble alkaline earth metal sulfates. In this method, the elimination of the sulphates obtained in finely divided form presents considerable difficulties. In addition, only diluted solutions are obtained and, when calcium oxide or calcium hydroxide is used, free hydroxylamine still contains large undesirable 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 disadvantageous with respect to the industrial production process. DE-A-12 47 282 discloses a process in which alcoholic solutions of free hydroxylamine are obtained by the reaction of hydroxylammonium sulfate with ammonia in alcohol as solvent and eliminating ammonium sulfate. A similar process is described in EP-A-108 294. However, alcohol solutions are inadequate and undesirable for various applications. For example, special precautions should be taken during the handling of these solutions, due to their reliability. further, the alcohol used should be, as a general rule, recovered by an expensive procedure, since the discharge of relatively large amounts of alcohol in wastewater treatment plants or in outlets is prohibited. Finally, DE-A-36 01 803 describes a process for obtaining aqueous solutions of free hydroxylamine, in which the hydroxylammonium sulfate is reacted with ammonia in lower alcohols, the precipitated ammonium sulphate is separated, water is added to the alcoholic solution of free hydroxylamine and the alcohol is distilled from the solution thus obtained. The aforementioned disadvantages of working with alcohol are applicable to this process as well. In addition, due to the instability of hydroxylamine together with the flammability of the alcohols, specific precautions are required in the final distillation step. For all processes of the prior art it is common that they are not suitable to be carried out on an industrial scale or give rise to additional highly non-economic security costs. For the decomposition of hydroxylamine, a temperature above 65 ° C is considered crucial. In a differential thermal analysis, the initial temperature of an aqueous solution at 50% concentration by weight of hydroxylamine (in a glass crucible) was determined as 70 ° C. The amount of heat released, viz. approximately 2.2 kJ / g of the solution at 50% concentration, confirms the high thermal potential of the material. A differential thermal analysis is a micro-thermoanalytical method that is used to explore in order to estimate thermal stability and thermal potential. The initial temperature is the lowest ambient temperature at which an appreciable exothermic reaction in the sample proceeds at a heating rate of 1 k / minute, starting at 30 °. For safety reasons, the processing temperature must be significantly lower than the start temperature. In the context of the preparation of hydroxylamine nitrate, US-A-4, 956, 168 describes the preparation of a slurry of hydroxylamine sulfate in alcohol at a temperature not exceeding 65 ° C. This slurry is then treated with ammonia to <; 65 ° C to produce an alcoholic solution of hydroxylamine. US-A-5, 472, 679 discloses a process for preparing an aqueous solution of hydroxylamine without alcohol by reacting a solution of hydroxylamine sulfate with a suitable base up to about 60 ° C. The mixture obtained is then subjected to distillation under reduced pressure at less than 65 ° C. This produces a solid residue (the salt formed in the release of hydroxylamine) and as distillate an aqueous solution of hydroxylamine containing 16-23% hydroxylamine. This process has the disadvantage that treatment under reduced pressure is required and the temperature has to be carefully controlled. In addition, the process requires working with solids. In a continuous process, the solid would have to be continuously separated. This can present large problems of process technology terms if the solid is one that tends to cake, for example, in the case of Na2S0xH20.

In addition, the "distillation" proceeds to dryness, more correctly described as evaporation, so that the low-boiling water evaporates first. High-boiling hydroxylamine accumulates. It is known that the tendency to decomposition of hydroxylamine increases with the concentration of hydroxylamine, and along with this the loss of hydroxylamine during the process. There is an increasing risk that explosive decomposition may occur due to the high concentration of hydroxylamine. It is known that pure hydroxylamine or hydroxylamine > 70% by weight decomposes explosively. Thus, adequate security requirements for the aforementioned process must be met. Finally, the remaining solid "still contains hydroxylamine residues (hydroxylamine adsorbed on the surface, hydroxylamine in the interstitial spaces in the solid.) Therefore, the solid has to be decontaminated in a separate process.

DE 1954775.8 describes a process for the preparation of aqueous solutions of free hydroxylamine, the solution obtained by treating a hydroxylammonium salt with a base being separated into an aqueous hydroxylamine fraction and a salt fraction by treatment with water or steam at > 80 ° C. Any desired concentration of the aqueous hydroxylamine solution obtained is carried out by distillation by evaporating the water in a column. In addition to hydroxylamine, poorly volatile impurities can also accumulate in the lower part. This problem, which is general in the case of residual products, is solved in industry, for example, by another distillation. In the case of hydroxylamine, however, this is problematic since the concentration of hydroxylamine over 50% by weight is unavoidable in another distillation of the solution, for example, 50% in concentration. However, the tendency of hydroxylamine to undergo decomposition also increases greatly. The distillation must, therefore, be carried out at low temperatures and pressures at a corresponding cost and with the corresponding time requirement, and can normally also be carried out only at a small scale. Accordingly, aqueous salt-free hydroxylamine solutions of electronic grade purity are complicated to prepare and therefore relatively expensive and, for economic reasons, their use is limited to some areas. An object of the present invention is to provide a simple process for the preparation of very pure hydroxylamine containing < 1 ppm of metal ions. We have found that this objective is achieved if, starting from the dilute hydroxylamine solution having a low salt content, the concentrated solution of very pure hydroxylamine with a < 1 ppm of metal ions is obtained by separating vapors containing hydroxylamine through a lateral outlet in the lower part of the column. Therefore, the present invention relates to a process for the preparation of an aqueous solution of free, very pure hydroxylamine by concentrating and purifying an aqueous solution of hydroxylamine, where the concentration is carried out in a column, the vapors containing hydroxylamine are eliminated. through a lateral intake in the lower part of the column, and very pure hydroxylamine is obtained by condensing the vapors. The very pure hydroxylamine solution thus obtained contains more than 20, preferably more than 40, in particular more than 50% by weight of hydroxylamine and < 1 ppm, in particular < 0.1 ppm of metal ions (in particular from the preparation or from the materials used for preparation and isolation). The aqueous hydroxylamine solution used as starting material for the novel process can be obtained in any manner known per se, for example by one of the processes established at the beginning. Particularly preferably, the dilute hydroxylamine solution is obtained by the process described in the application of German Patent No. 1954775.8, a hydroxylammonium salt being treated with a suitable base in water in a first step a) and, in a step b), the solution obtained, if necessary, after removal of the insoluble components, being separated into a fraction Hydroxylamine water and a salt fraction by treatment with water or steam a >; 80 ° C. Step (a) of the process is carried out in a conventional manner. In general, the hydroxylammonium salts used are the hydroxylammonium salts of mineral acids, for example, 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, potassium hydroxide or calcium hydroxide, in aqueous solution. The amount of the base is chosen so that the hydroxylammonium salt is converted completely or at least partially into the free hydroxylamine. This can be carried out continuously or in batches and from about 0 ° C to 100 ° C. The aqueous solution obtained contains free hydroxylamine and the salt originating from the base cation and the acid anion present in the hydroxylammonium salt. Depending on the type and concentration of the hydroxylammonium salt, the base used to release the hydroxylamine and the temperature at which the reaction is carried out, some of the salts formed may be precipitated. If necessary, the solution can also be cooled to precipitate a larger amount of the salt. If these insoluble components, ie the saline precipitates, are present, they advantageously separate in a conventional manner before step (b). Depending on the process conditions, for example with the use of ammonia as the base or the use of sodium as the base and relatively low concentration of the reactants, no precipitate is formed. The separation in step (b) of the solution obtained from step (a) in an aqueous fraction of hydroxylamine and a salt fraction preferably is carried out by treatment with water or steam in a tow column. The drag column generally used in a conventional plate column, for example, bubble tray column or sieve plate column, or a column having a conventional packing, for example Raschig rings, Pall rings, curved elements, etc. This preferably has from 5 to 70 theoretical plates. The stabilized solution, to which another stabilizer can, if required, be added, is fed directly to the top of the column (upper part of the package or the uppermost plate). In the drag column the solution is separated in such a way that the salt fraction is separated at the bottom of the column and an aqueous hydroxylamine fraction is separated at or above the feed plate, in particular at through the top. To achieve this it is preferable to treat the solution by passing water and / or steam countercurrently 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 the water or steam is, in general, from 1 to 8, in particular from 1 to 5 times the feed rate. The temperature of the water or steam introduced is, in general, from 80 to 180 ° C. If required, the lower part of the column is also heated. The temperatures prevailing in the upper part of the drag column depend on the pressure at which the column is operated. This pressure is, in general, from 5 to 300 kPa (from 0.05 to 3 bar), preferably from 50 to 300 kPa (0.5 to 3 bar), particularly preferably from 50 to 150 kPa (from 0.5 to 1.5 bar). The temperatures at the top of the tow column are, therefore, generally from 80 to 130 ° C, preferably from 90 to 120 ° C. The temperature of the introduced steam can be substantially higher, for example also 150 ° C. For convenience, however, it should not be so high that too much water evaporates from the saline solution and the salt starts to precipitate at the bottom of the column. If desired, a precipitator is also installed by droplets (separator of solid or liquid particles of the gases) on the feed plate or in the steam outlet in such a way that the salt is not dragged by the droplets. In the novel process, the aqueous hydroxylamine fraction that is taken from the top of the tow column and usually contains from 10 to 200 g of hydroxylamine / liter is brought to the desired final concentration of about 50% by weight. A conventional packed column containing the aforementioned packages or a suitable plate column is advantageously used for this purpose. A column having from 4 to 30 theoretical plates is preferred. Advantageously a descending film evaporator is used to heat the lower part of the column, but of course it is also possible to use other conventional heaters in the lower part, such as natural or forced circulation evaporators, plate heat exchangers, and so on. In general, the column for the concentration 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), and particularly preferably from 30 to 100 kPa (from 0.1 at 1.1 bar). The diluted hydroxylamine solution is fed at a suitable point, for example at the height of plates "1 to 10, to the concentration column.At the same time, it is possible to feed another stabilizer to the top of the column to improve the stabilization of the hydroxylamine solution The distilled water from the hydroxylamine solution is taken at the top of the column and usually contains less than 0.06% hydroxylamine.The lateral intake through which the vapors containing hydroxylamine are They take to obtain the very pure, highly concentrated hydroxylamine solution, preferably located below the first plate, but in such a way that the droplets are not dragged in. This is done, for example, by installing a separator of solid or liquid particles of them. A more highly concentrated solution of hydroxylamine with salt is obtained in the lower part of the column, its purity depends on the respective quantities that they are separated by the lateral taking and the taking of the inferior part. The amount taken through the lateral intake to produce aqueous, very pure hydroxylamine solution is further limited by the minimum vapor flow in the column that is required for the hydrodynamically stable operation. In an advantageous embodiment of the novel process, the vapors in the lower part of the column are separated from the discharge of the falling film evaporator to heat the lower part. According to the invention, the hydroxylamine solution taken from the lower part of the column through the lateral intake is separated in a condenser in the aqueous, very pure, concentrated hydroxylamine solution with a content of <; 1 ppm of impurities and steam containing hydroxylamine. The vapors exiting through the upper part of the condenser can be recycled to the column at a suitable point, for example at the height of plates 1 to 10, to recover the hydroxylamine still present. In a particularly advantageous embodiment of the novel process, an evaporator is installed below the supply of the vapors taken through the side inlet in the condenser, in such a way that, upon evaporation of some of the water in the hydroxylamine solution, very pure, the The concentration of the latter can be carried to the desired final concentration. The vapors rich in water vapor produced can in turn be recycled to the column at a suitable point to recover the hydroxylamine still present. In another very particularly preferred embodiment of the novel process, the vapors taken from the lower part of the concentration column are passed to a side column having an internal evaporator. This also makes it possible to reduce the hydroxylamine content of the stream of recycled vapors to the concentration column and substantially reduce the amount of vapor circulated between the concentration column and the electronic grade side unit. The use of the lateral column also makes it possible to separate up to 99% of the hydroxylamine solution as an electronic grade product from the bottom through the lateral intake, while the rest, approximately 1%, in this case highly contaminated hydroxylamine solution has to be separated by the bottom of the concentration column. However, this small amount can be recycled to recover the hydroxylamine in step (b) of the process to separate the salt according to DE 1954775.8. In order to obtain a particularly low concentration of the metal ion in the hydroxylamine, the parts of the side-take plant can be produced from metal-free materials and resistant to hydroxylamine, for example, from plastics such as polypropylene or polytetrafluoroethylene ( PTFE). When the condenser / evaporator unit is used to obtain the very pure hydroxylamine solution, up to 60% of the hydroxylamine solution can be taken as an electronic grade product at 50% concentration by weight in a ratio of the flow rate of the intake. steam from the bottom to the flow rate of the intake. of the condensate of the lower part of the lateral intake of 10: 1, without influencing the behavior of the distillation of the concentration column. The remaining 40% is obtained as 50% strength hydroxylamine solution with a standard salt content. When a lateral column is used it is possible to obtain up to 99% of the concentrated hydroxylamine solution as an electronic grade product through the lateral intake of the lower part in a ratio of the flow rate of the steam intake in the lateral column to the speed of the electronic grade product produced less than 6: 1. The novel process can, therefore, supply at the same time varying quantities of standard product and electronic grade, so that rapid adaptation to market requirements is possible. In addition, it is possible for the first time to economically and reliably prepare highly pure, aqueous grade hydroxylamine solution under continuous conditions on a large industrial scale. The continuous manual treatment of highly sensitizing hydroxylamine solutions is avoided, which "is unavoidable in small-scale production, and handling of the most highly concentrated hydroxylamine solutions, ie, over 50% concentration, is also dispensed. It gives rise to a high degree of operational safety inherent in the process.The solutions containing free hydroxylamine can be stabilized by adding a conventional stabilizer against decomposition.Figure 1 to 3 illustrates, by way of example, some modalities of the novel process. Figure 1 shows a schematic diagram of a concentration plant to obtain very pure hydroxylamine.

Figure 2 shows a schematic diagram of a plant for the lateral intake. Figure 3 shows a schematic diagram of another modality of a plant for lateral intake. Figure 1 shows a concentration column 1. The diluted aqueous hydroxylamine solution 2 is fed to about half of column 1. The water is distilled at the top of column 1 and condensed in a condenser 4 and the water is separated by the pipe 8 _a at the speed corresponding to the rate > of established reflux and recycled to the column through the pipe 7. The hydroxylamine solution containing salt 6 is taken from the bottom of the column and some of it is recycled through an evaporator 3 to the bottom of the column. the spine.

To obtain the very pure hydroxylamine solution, the vapors containing hydroxylamine 9 are separated by the lateral outlet located at the bottom of the column and are then condensed in a condenser 13. The very pure hydroxylamine solution 11 is separated below the condenser 13 and steam containing hydroxylamine 10 is recycled to column 1 through a flow regulator 12. Figure 2 shows a plant from the side-take of the novel process. The vapors 9 separated by the lateral outlet in the lower part of the simply indicated concentration column 1 are introduced to the side plant below a condenser 13 and on an evaporator 14. The hydroxylamine concentration of the very pure hydroxylamine solution 11 can to vary by practical evaporation, in the evaporator 14, of the condensed hydroxylamine solution in the condenser 13. The vapors 10 enriched in hydroxylamine can in turn be recycled to the concentration column 1 by a flow regulator 12. The particularly preferred embodiment shown in Figure 3 consists of an additional column in the plant of the lateral intake. The vapors containing hydroxylamine 9 taken from the bottom of the concentration column 1 (simply indicated) is passed to a side column 15 in the vicinity of the bottom. At the top of this column, the water containing hydroxylamine 10 is condensed by means of a condenser 13 and recycled to the concentration column 1. The very pure hydroxylamine solution 11 is obtained from the bottom of the side column 15. In this particularly preferred embodiment of the invention, up to 99% of the hydroxylamine 2 fed to the concentration column 1 can be obtained as the electronic grade product 11. The following examples illustrate the invention with reference to Figure 1, without limitation of the invention.

EXAMPLE 1 1600 g / h of a solution of hydroxylamine stabilized, practically without salt, aqueous 2 at 3.2% by weight concentration were fed to a glass bubble tray column 1 with a diameter of 50 mm and 30 bubble trays, on the eighth tray. The column was operated at 30 mbar. The small amount of the stabilizer that was dissolved in the hydroxylamine solution was further dosed in column 1 on the highest tray, No. 30. The water 8 was distilled down the bottom of column 1, with the reflux rate 0.5. . The distillate still contained a residual amount of 0.06% by weight of hydroxylamine. Approximately 75 ml / h of a 50% strength by weight hydroxylamine solution were discharged from the bottom of the column by means of a pump. The discharge from the bottom contained up to 45 ppm of sodium sulfate. A transfer section to a condenser arranged in lateral position 13 was also mounted in the lower part of the column, below the first tray. As a result of the back pressure of the column, caused by the loss of pressure through the sieve plates, the vapor was forced from the bottom of the concentration column 1 to the condenser mounted in lateral position 13. steam flow rate was limited by a manual valve 12 in the discharge of the lower part of the condenser 13. The vapor 10 leaving through the upper part of the condenser passed to the eighth tray of the concentration column 1. Approximately 18 ml / h of a hydroxylamine solution of about 20-35% by weight of concentration 11 were condensed in condenser 13 and transported to a separate receiver by means of a laboratory pump. The stabilizer was added continuously to this solution. The concentration of the metal ions was less than 0.1 ppm.

Example 2 A solution of hydroxylamine of approximately 10% by weight concentration was concentrated to 50% by weight in a column of glass bubble trays 5 mm in height and 0.3 m in diameter at approximately 77 ° C and 0.3 bar . The vapor was separated from the bottom of the column through the PTFE tubes and passed to a storage vessel mounted in the side position 51 with a double jacket cooling medium. A part of the vapors condensed in it. The non-condensed vapors were recycled to the fifth tray of the column through the PTFE steam tube. The amount of steam was manually limited by an intake valve. The condensed vapor in the cooled receiver was then concentrated to 50% by weight (very pure product). The hydroxylamine solutions produced (50% by weight in each case) had the following composition (metal content in mg / kg, analytical precision: 0.1 mg / kg): Standard product (without very pure product (with lateral separation) lateral separation) Boro 3.0 < 0.1 Sodium 9.0 < 0.1 Potassium 0.3 < 0.1 Calcium 0.2 < 0.1 Aluminum 1.0 < 0.1 Silicon 24.0 < 0.1 Iron 0.1 < 0.1 Metals 38 < 0.1 total All concentrations of metal ions in the very pure product were below the detection limit of 0.1 mg / kg. The purity required of < 0.1 -mg of metal / kg of solution was obtained with certainty. In another experiment, a hydroxylamine solution was prepared by concentrating on the column of bubble trays without lateral separation (standard product).

Claims (1)

1. CLAIMS A process for the preparation of very pure aqueous hydroxylamine solution by the concentration and purification of an aqueous hydroxylamine solution, where the concentration is carried out in a column, the vapors containing hydroxylamine are separated through a lateral capture in the part lower column and very pure hydroxylamine is obtained by condensing the vapors. The process as recited in claim 1, wherein the hydroxylamine solution proposed for concentration and purification is obtained by: a) treating a solution of hydroxylamine with a suitable base in water, and b) separating the solution obtained, if necessary after separation of insoluble components, in an aqueous hydroxylamine fraction and a salt fraction by treatment with water or steam at < 80 ° C. The process as recited in claim 1 or 2, wherein the condensation of the very pure hydroxylamine solution is carried out by introducing the hydroxylamine-containing vapors, separated by the lateral intake, below a condenser and above an evaporator and partially evaporating. again in the evaporator, the condensed hydroxylamine solution in the condenser, so that a very pure, more highly concentrated hydroxylamine solution is obtained. The process as recited in claim 1 or 2, wherein the vapors containing hydroxylamine taken by a lateral intake in the lower part of the column are passed to a side column and very pure hydroxylamine solution is obtained in the lower part from ~~ the side column. The process as mentioned in any of the preceding claims, wherein the lateral intake is connected on the gas side to the concentration column. The process as mentioned in any of the preceding claims, wherein the metal-free and hydroxylamine-resistant materials are used for the parts of the side-take plant.