US2242477A - Process of preparing hydroxylamine hydrochloride - Google Patents

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May 20, 1941. ossw p HAL 2,242,477

PROCESS OF PREPARING HYDROXYLAMINE HYDROCHLORIDE Q Filed July 28, 1938 11 ll 15 l mvemoas ATTORN EYS a0 A] [LL Y.

Patented May 20; 194i PROCESS OF PREPARING HYDROXYLAMINE HYDRQCHLORIDE Philipp Osswald, Hofheim-in-Taunus, and -Walter Geisler, Frankfort-on-thc-Main-Hochst, Germany, assignors, by mesne assignments, to Walther H. Duisberg, New York, N. Y.

Application July 28, 1938, Serial No. 221,678

' In Germany August 17, 1937 Claims.

The present invention relates to a process of preparing hydroxylamine hydrochloride.

"Itis known that the hydrochloride of hydroxylamine maybe obtained in the form of a' moreor less dilute aqueous solution by the electrolytic reduction of nitric acid containing hydrochloric acid. For the preparation of hydroxylamine hydrochloride in the solid state the aqueous solution was hitherto first electrolysed until it was free from nitric acid and then evaporated under reduced pressure at a temperature as low as possible. If the nitric acid is not completely removed before the evaporation, it would, during the concentration, decompose the hydroxylamine formed. I

This known process has the drawback that the elimination of the last residues of nitric acid is possible only with sacrifice of electrolytic efliciency and that theevaporation is combined with losses in yield and with the difiiculty that the vessels used have small resistance to hot solutions' containing hydrochloric acid.

Now we haveiound that the solubility of the hydroxylarnine hydrochloride depends to a very large extent on the concentration of the excess of hydrochloricacidpresent; and that this prop- 'erty'may be used for directly removing the hydroxylamine hydrochloride in the solid state by salting out the product. Thereby the special advantage is attained that the entire process constitutes a cycle for the circulation of the catholyte.' According to the measurements made, the

solubility of hydroirylamine hydrochlorid at C. in-the presence of hydrochloric acid is as follows:

Percent Grams oENHzOFLHF-l age of I in 10K} granis of the HCl solution.-

' 'This' strong action of salting'out fot thehy- 'drogen chloride makes itposlsible to avoid com- 'pl'e'tely the separation e; the nitric acid and the evaporation of the solutions obtained by direct "current electrolysis in"diaphragm cells. It is preferable'not to salt out thefproduct within the I cathodecompartment of the cell, for this would disturb theelectrolytic reduction, but to peri'orm the "salting out in a special vessel. By the *electrolysis the electrolyte in the'cell becomes poor in'hydrogenchloride, partly by the migraously turning over thevcrystals.

tion of chlorine ions to the anode and the simultaneous consumption of hydrogen ions at the cathode for the reduction of nitric acid, partly by the binding of hydrogen chloride to the hydroxylamine freshly formed in the cathode compartment of the cell. By the present process the electrolysis is carried out to such an extent that an electrolyte nearly saturated with hydroxylamine hydrochloride leaves the cathode compartment of the cell. This electrolyte poor in hydrogen chloride is now loaded in the vessel for salting out, while cooling, with such an amount of gaseous hydrogen chloride as has previously been consumed .in the electrolysis. A pure hydroxylamine hydrochloride settles atthe bottom of the liquid. Thecrystals formed arefiltered and, in order to liberate them from the adhering mother liquor, they may be washed with washing lye and water, whereby at oncea pure marketable product is obtained. The washing, however,

is not absolutely necessary, as the adhering impurities consist only of water,.hydrochloric acid and some nitric 'acid. When the productis carefully dried these impurities may be evaporated without decomposition of the. hydroxylamine hydrochloride. i It is possible, forinstance, to obtain the moist product still containing mother liquor in a completely. pure and dry statefby heating it for /2 to lhour to about 50 C. and simultane- The process has the advantage that the small quantities of nitric acid still contained inthe electrolyte do not have to befseparated by electrolysis before the salting out.

The necessary quantity of nitric" acid is added to the mother liquor remaining 'afterthe salting out andthis liquor is then reconducted into the cathode compartment of thefcell where'it issaturated"again with freshly forrned hydrokylai nine v hydrochloride. T ereby thfjc ci isc'lo'sedfior the mainduantitjl of the catholyte;

- A man ortion of thegcatholyte; namely the increase of volume formediby fjl'il're washing lyjie, the addition ofni'tric acid 'a'nd sometimes by electric osmosis; however; has-to be-worked separately from time meme; 301i course, theincrease of volume will be confined as mii has p ssibi ity avoiding or atleast sparingly'using washing lye and by applying suitable diaphragm's which do not'lend themselves to electric osmosis'i ln this respect it is important 'thatthfe quantity of nitric "acid necessary need not be added,*as hitherto usual in the former asolution of 50="per cent strength, but itmay beadded in form-eta solution of per centstrength if it is" distributed in the large volume of electrolyte in the cycle..

A decomposition of the hydroxylamine hydrochloride hereby does not occur, notwithstanding that only a small quantity of water is added to the electrolyte.

The still remaining increase of electrolyte is worked up by treating it with a large excess of further gaseous hydrogen chloride. According to the table given above a product of an initial content of hydroxylamine hydrochloride of 22.2 per cent may be salted out until it contains 3.6 per cent of hydroxylamine hydrochloride at 10 C. or 3.0 per cent at C. The small residue of non-precipitated hydroxylamine hydrochloride is lost for the catholyte; but this is not of great importance as it is only a small portion of the entire volume of the solution. This mother liquor which remains after the solid hydroxylamine hydrochloride has been separated and is not reconducted to the catholyte is preferably used for saturating the anolyte for the sake of saving its hydrogen chloride.

Generally the hydroxylamine hydrocloride is periodically salted out and filtered with suction in a separate vessel. If a storage vessel for the catholyte is intercalated in the cycle before the cell, the catholyte may continuously flow through the cathode compartment of the cell. In this manner a solution poor in hydroxylamine hydrochloride and rich in hydrogen chloride and nitric acid continuously enters this compartment of the cell and simultaneously a solution rich in hydroxylamine hydrochloride and poor in hydro-' gen chloride and nitric acid flows out. Thus the rates of concentration, temperature, conductivity and the like within the cathode compartment do not change during the electrolysis, this being advantageous for the working and for the control oi the electrolysis.

The following example illustrates the invention, but it is not intended to-limit it thereto:

The process 01' the invention is diagrammatically illustrated by the accompanying diagram.

The numbers indicated in the example relate to the preparation of 1 kilo of hydroxylamine hydrochloride in any desired unit of time.

The catholyte I used for the electrolysis originally contains 20 per cent of hydrogen chloride,

1 per cent of nitric acid and 79 per cent of water. 102 kilos of this catholyte are necessary for obtaining 1 kilo of hydroxylamine hydrochloride, the inevitable losses being taken into consideration. The catholyte I is reduced in the cathode compartment of a diaphragm cell 3 in a manner itself known, for instance with 2900 amperehours 2|, -i. e. with an electrolytic efliciency 01' about 80 per cent. During this process the catholyte is circulated between the said compartment of the cell for the electrolysis and the vessel for, salting out. By the electrolysis the catholyte I first assumes a concentration of about 22 per cent of hydroxylamine hydrochlo-- ride besides 10.6 per cent of hydrogen chloride. When this concentration has been attained 20 to 30 liters of the catholyte flow oil. at 4 during the predetermined unit of time into a well cooled vessel 5 for salting out. At 23 such a quantity of dry gaseous hydrogen chloride is introduced into this vessel as corresponds with the acidity lost by the catholyte during its previous passage through the cell 3, i. e. so large a quantity that the catholyte again contains 20 per cent of hydrogen chloride. By this procedure solid hydroxylamine hydrochloride is precipitated. By a simple filtering with suction a crude salt 6 with a content of 85 per cent of the pure producl (the rest consists of water and hydrochlorii acid) is obtained, which, when washed with 0.] kilo of fresh water I yield a pure salt 8 of 95 to 98 per cent strength. Under the condition: indicated above the yield amounts to about 1 kilc of pure hydroxylamine hydrochloride. The washing lye 9 is combined with the main quantity of the catholyte l0 remaining by the precipitation of the hydroxylamine hydrochloride and the mixture is conducted tostorage II. The washing lye, however, may also repeatedly be used for washing the crude salt (this process is not illustrated in the diagram) beforethe crude salt is washed with fresh water. From the storage vessel ll about 101 kilos of the catholyte I! are reconducted into the cathode compartment of the diaphragm cell 3. In an uninterrupted current 1.20 kilos of nitric acid I: of 90 per cent strength run into the catholyte 12. The entire volume of the catholyte l2 and the nitric acid l3 added is about the same as that of the originally applied catholyte I. As owing to the addition of washing lye and fresh nitric acid and probably owing to electric osmosis within the cell the volume of the catholyte permanently increases, it is not possible to reconduct into thel cathode compartment of the cell the entire quantity of the catholyte loaded with fresh nitric acid. Therefore about 0.43 kilo of the catholyte contained inthe vessel 5 for salting out are separated l4 and conducted to a further vessel II for a further still more intensive salting outwith hydrogen chloride l6 while cooling. The catholyte l4 contains about 0.1 kilo of hydroxylamine hydrochloride; about 85 per cent thereof II are obtained and worked up together with the main quantity of the crude salt 6. The residual solution I! of this salting out which contains about 30 to 33 per cent of hydrogen chloride is at I 0 conducted to the anode compartment of the cell in order to saturate the anolyte 2 with hydrogen chloride. An amount of the anolyte consumed 20 which corresponds with the aforesaid addition and still contains about 7 per cent of hydrogen chloride flows of! at 22 and cannot further be utilized. In the anode chamber the small quantity of 0.015 kilo of hydroxylamine hydrochloride still present is, of course. de-

stroyed. By the continuous removal of the excess of solution I from the cycle the impurities which may be formed in the catholyte I, for in- I precipitating the hydroxylamine hydrochloride.

2. In the process of preparing solid hydroxylamine hydrochloride by reduction of aqueous solutions of mixtures of hydrochloric acid and nitric acid in diaphragm cells by direct current electrolysis tosuch an extent that the catholyte in th e'cathode compartment of these cells is nearly saturated with hydroxylamine hydrochloride, the step which comprises removing the catholyte from the cell, introducing gaseous hydrogen chloride into the catholyte, while cooling, in a special vessel outside the cell, and thus precipitating the hydroxylamine hydrochloride; filtering the precipitated hydroxylamine hydrochloride from the mother liquor and drying the catholyte from the cell, introducing gaseous hydrogen chloride into the catholyte, while cooling, in a special vessel outside the cell, and-thus precipitating the hydroxylamine hydrochloride, filtering the precipitated hydroxylamine hydrochloride from the mother liquor and drying the filtered salt, adding a quantity of 90 per cent nitric acid to the mother liquor sufficient to bring its nitric acid content to that of the original catholyte and returning the treated motherliquor'as catholyte to the diaphragm cell.

4. In theprocess of preparing solid hydroxylamine hydrochloride by reduction of aqueous solutions of mixtures of hydrochloric acid and nitric acid in diaphragm cells by direct current electrolysis to such an extent that the catholyte in the cathode compartment of these cells is nearly saturated with hydroxylamine hydrochloride, the step which comprises removing the catholyte from the cell, introducing gaseous hydrogen chloride into the catholyte, while cooling, in a special vessel outside the cell, and thus precipitating the hydroxylamine hydrochloride, filtering the precipitated hydroxylamine hydrochloride from the mother liquor and drying the filtered salt, separating a part of the mother liquor equivalent in amount to the increase in volume of the catholyte occurring in the process cycle, adding gaseous hydrogen chloride to said part of the mother liquor under intense cooling until the solution is saturated with hydrogen chloride thereby precipitating all but a practi-' cally negligible portion of the hydroxylamine hydrochloride, adding" a quantity of 90 per cent nitric acid to the remainder of the mother liquor sufficient 'to bring its nitric acid content to that of the original catholyte and returning the treated mother liquor as catholyte to the diaphragm cell.

5. A process as defined in claim 4 in which the portion of the mother liquor saturated with hydrogen chloride is subjected to filtration to remove precipitated hydroxylamine hydrochloride and the filtrate is returned to the anode compartment of the diaphragm cell.

PHILIPP OSSWALD. WALTER GEISLER.

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