Distillation: processes – separatory – Addition of material to distilland to inhibit or prevent...
Reexamination Certificate
1998-07-24
2001-10-09
Manoharan, Virginia (Department: 1764)
Distillation: processes, separatory
Addition of material to distilland to inhibit or prevent...
C203S014000, C203S028000, C203S075000, C203S076000, C203S077000, C203S078000, C203S079000, C203S080000, C423S387000
Reexamination Certificate
active
06299734
ABSTRACT:
The present invention relates to a process for the preparation of metal ion-free aqueous solutions of free hydroxylamine.
Hydroxylamine is an important intermediate for the chemical industry. However, particular caution is required in handling it because it irritates the eyes, the skin and the mucous membranes and can cause allergies. In particular, however, it is thermally unstable, ie. it decomposes slowly to explosively, especially in the presence of metal ions, in a strongly basic medium and in relatively high concentration.
Hydroxylamine is produced on a large industrial scale as hydroxylammonium salt, usually as hydroxylammonium sulfate, and is also used as such. Frequently, however, it is necessary to use a highly concentrated salt- and metal ion-free aqueous solution of free hydroxylamine. In order to avoid the abovementioned problems and in particular the instability of the hydroxylamine, those skilled in the art have avoided the use of traditional methods of large-scale chemistry for concentrating distillable substances, for example distillation, in the recovery of salt-free hydroxylamine solutions. The distillation of hydroxylamine, even on the laboratory scale, is even said to be a particularly dangerous operation; cf. Roth-Weller: Gefährliche Chemische Reaktionen, Stoffinformationen Hydroxylamin, page 3, 1984, 2, Ecomed-Verlag. The distillation of hydroxylamine on an industrial scale has therefore also never been considered in technical publications. Instead, special methods have been used, although all of them have serious disadvantages.
Attempts were thus made to isolate free hydroxylamine from aqueous salt solutions with the aid of ion exchangers; cf., for example, U.S. Pat. No. 4,147,623, EP-A-1787, EP-A-237052 and Z. Anorg. Ch. 288, 28-35 (1956). However, such a process leads only to dilute solutions with low space-time yields. Moreover, hydroxylamine reacts with many ion exchangers or is decomposed by them.
A further method comprises the electrodialysis of an aqueous hydroxylammonium salt solution in electrolysis cells with semipermeable membranes, as described, for example, in DE-A-33 47 259, JP-A-123771 and JP-A-123772. However, such a process is technically complicated and expensive and has to date not become established in industry.
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 removal of the insoluble alkaline earth metal sulfates. In this method, the removal of the sulfates 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 owing to the relatively good solubility of the calcium sulfate. When strontium compounds and barium compounds are used, the relatively high price and especially the toxicity are moreover disadvantages with regard to an industrial production process.
DE-A-12 47 282 describes a process in which alcoholic solutions of free hydroxylamine are obtained by reacting hydroxylammonium sulfate with ammonia in alcohol as a solvent and removing the ammonium sulfate. A similar process is described in EP-A-108 294. However, alcoholic solutions are unsuitable and undesirable for a number of applications. For example, particular precautions must be taken during the handling of such solutions, owing to their flammability. Furthermore, the alcohol used must as a rule be recovered by an expensive procedure, since the discharge of relatively large amounts of alcohol into wastewater treatment plants or into outfalls is prohibited.
Finally, DE-A-36 01 803 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 off, water is added to the alcoholic solution of free hydroxylamine and the alcohol is distilled off from the solution thus obtained. The abovementioned disadvantages of working with alcohol are applicable to this process too. Moreover, owing to the instability of the hydroxylamine in conjunction with the flammability of the alcohols, particular caution is required in the final distillation stage. Common to all prior art processes is that they are not suitable for being carried out on an industrial scale or give rise to uneconomically high additional safety costs.
A temperature above 65° C. is regarded as critical for the decomposition of hydroxylamine. In a differential thermal analysis, the onset temperature of a 50% strength by weight aqueous hydroxylamine solution (in a glass crucible) was determined as 70° C. The quantity of heat evolved, about 2.2 kJ/g of 50% strength by weight solution, confirms the high thermal potential of the substance. The differential thermal analysis is a microthermal analytical method which is used for estimating the thermal stability and the thermal potential. The onset temperature is the lowest ambient temperature at which a marked exothermic reaction takes place in the sample at the heating rate of 1 K/min, starting at 30° C. For safety reasons, processing temperatures should be substantially below the onset temperature.
Thus, in connection with the preparation of hydroxylamine nitrate, U.S. Pat. No. 4,956,168 states that a suspension of hydroxylamine sulfate in alcohol is prepared at a temperature which does not exceed 65° C. This suspension is then treated with ammonia at ≦65° C. in order to prepare an alcoholic hydroxylamine solution.
U.S. Pat. No. 5,472,679 in turn describes a process for the preparation of an alcohol-free, aqueous hydroxylamine solution by reacting a hydroxylamine sulfate solution with a suitable base at up to about 60° C. The mixture obtained is then subjected to a distillation under reduced pressure at less than 65° C. A solid residue (the salt formed on liberation of the hydroxylamine) and, as the distillate, an aqueous hydroxylamine solution which contains from 16 to 23% 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 very carefully controlled. It also has the following further disadvantages:
The precipitate makes it necessary to work with solids. In a continuous process, the solid would accordingly have to be continuously removed. This may present considerable process engineering problems if it is a solid which tends to cake, as, for example, in the case of sodium sulfate.
The distillation to dryness, correctly referred to as evaporating down, takes place in such a way that the low boiler water evaporates off first. The concentration of the high boiler hydroxylamine increases. It is known that the tendency of hydroxylamine to decompose increases with the concentration of hydroxylamine. Consequently, the losses of hydroxylamine increase during the process. There is a growing risk that, owing to the high concentration of hydroxylamine, an explosive decomposition may occur. It is known that pure hydroxylamine or hydroxylamine in a concentration of >70% by weight can decompose explosively. Thus, appropriate safety requirements must be met for the stated process.
The remaining solid will still contain residues of hydroxylamine (hydroxylamine adsorbed onto the surface, hydroxylamine in voids in the solid). The solid must therefore be decontaminated in a separate disposal procedure.
Hence, evaporating down is not a process which can be carried out advantageously on a large industrial scale.
WO 97/22551 describes a process for the preparation of aqueous solutions of free hydroxylamine. A hydroxylammonium salt is treated with a suitable base in water, any insoluble constituents are separated off from the resulting solution, the solution obtained is separated into an aqueous hydroxylamine fraction and salt fraction by distillation at above 80° C. and, if desired, the aqueous hydroxylamine solution obtained is concentrated in a distillation column by t
Mauer Peter
Schelling Heiner
Schneider Hans-Michael
Strofer Eckhard
Watzenberger Otto
BASF - Aktiengesellschaft
Keil & Weinkauf
Manoharan Virginia
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