United States Patent (19) 11 Patent Number: 4,645,579 Weiss et al. 45) Date of Patent: Feb. 24, 1987 (54 PREPARATION OF AOUEOUS 4,521,285 6/1985 De Witt et al............... 204/182.4 X HYDROXYLAMINE SOLUTIONS OTHER PUBLICATIONS 75 Inventors: Franz-Josef Weiss, Neuhofen; Chemical Abstracts, vol. 102, 1985, abstract No. 134403s, Wolfgang Habermann, Mainz; Peter Stamicarbon, B. V., "Circulating Process for Preparing Hammes, Ruppertsberg; Elmar and Working Up a Hydroxylammonium Salt Solution'. Frommer, Ludwigshafen; Erwin Chemical Abstracts, vol. 94, 1981, abstract No. 141,98ly, Thomas, Freinsheim; Peter Thoma, Chang, Y. et al., "Conversion of Hydroxylamine Hydro Frankenthal, all of Fed. Rep. of chloride to Hydroxylamine Nitrate by Electrodialysis Germany and Water Splitting". 73) Assignee: BASF Aktiengsellschaft, Fed. Rep. of Chemical Abstracts, vol. 83, 1975, abstract No. 181595e, Germany Maurel, A., "Continuous Transformation of a Hydroxy lamine Salt into Another Hydroxylamine Salt'. 21 Appl. No.: 685,254 Y. Chang et al., "Chemical Abstracts', Band 94, (1981), 22 Filed: Dec. 24, 1984 p. 134. 30 Foreign Application Priority Data Primary Examiner-John F. Niebling Dec. 28, 1983 DE Fed. Rep. of Germany ....... 3347259 Attorney, Agent, or Firm-Keil & Weinkauf 51) Int. Cl. .............................................. B01D 13/02 57 ABSTRACT 52 U.S.C. ................................. 204/1824; 204/101; Aqueous solutions of hydroxylamine are prepared from 204/102; 204/182.5 aqueous hydroxylammonium salt solutions by electrodi 58) Field of Search .................... 204/101, 102, 180 P, alysis by a method in which the aqueous hydroxylam 204/1824, 182.5, 72 monium salt solution is fed into the middle zone of an electrolysis cell, which is divided into a cathode zone, 56) References Cited an anode zone and a middle zone by means of semiper U.S. PATENT DOCUMENTS meable membranes, and is electrolyzed, and the catho 2,363,387 li/1944 Bock ..................................... 204/72 lyte used is an alkali metal hydroxide solution contain 2,737,486 3/1956 Bodaner ............................... 204/72 ing ammonia and/or amines. 3,402,115 9/1968 Campbell et al ... 204/72 X 3,766,038 10/1973 Beck et al. ....................... 204/180 P 8 Claims, No Drawings 4,645,579 1. 2 The electrolysis is carried out in a cell which is di PREPARATION OF AOUEOUS vided into a cathode zone, an anode zone and a middle HYDROXYAMINE SOLUTIONS Zone by means of two semipermeable membranes. The aqueous hydroxylammonium salt solution being electro Hydroxylamine is produced industrially in the form 5 lyzed is introduced into the middle zone. The anolyte of its salts, for example by catalytic reduction of nitric used in the anode Zone is, as a rule, an aqueous solution oxide or nitric acid. In the further conversion of the of an oxyacid, in particular one which corresponds to hydroxylammonium salts, for example to oximes, the the anion of the hydroxylammonium salt solution used. corresponding anions are liberated in the form of acids, Advantageously, the aqueous solutions employed con but it is often difficult to remove such foreign anions O tain from 0.1 to 50% by weight of the oxyacid. A partic from the reaction mixture again. If, on the other hand, ularly good current efficiency is achieved if, instead of free hydroxylamine is prepared by reacting a hydroxyl an aqueous acid solution, an aqueous solution of an ammonium salt with an alkali, the foreign anions cannot alkali metal hydroxide, e.g. sodium hydroxide, an alkali be removed completely in this case either. A process metal carbonate, e.g. sodium carbonate or an alkaline has also been disclosed in which the anions are removed 15 earth metal hydroxide, e.g. calcium hydroxide, is used. by electrodialysis. According to the processes described According to the invention, the catholyte used in the in German Laid-Open Application DOS No. 2,062,436, cathode Zone is an aqueous alkali metal hydroxide solu an aqueous solution of hydroxylammonium sulfate is tion which contains ammonia and/or amines. Examples subjected to electrolysis in the presence of cyclohexa of suitable solutions are aqueous solutions of lithium none, cyclohexanone oxime being formed. Because of 20 hydroxide, sodium hydroxide and potassium hydroxide, the instability of the hydroxylamine and the short life of the two last-mentioned compounds preferably being the semipermeable membranes, this procedure is not used. Advantageously, the catholyte contains from 0.1 very suitable for the preparation of aqueous solutions of to 25, in particular from 1 to 10, 9% by weight of alkali hydroxylamine. metal hydroxides. Aqueous solutions of tetraalkylam It is an object of the present invention to provide a 25 monium hydroxides, e.g. tetraethylammonium hydrox process for the preparation of aqueous solutions of hy ide, are also suitable. The alkali metal hydroxide soiu droxylamine which gives high yields and produces tions contain, for examole, from 0.001 to 50, preferably aqueous hydroxylamine solutions having a very low from 0.02 to 10, in particular from 0.05 to 0.8, 9% by content of anions. weight of ammonia and/or amines. Suitable amines are We have found that this object is achieved by a pro 30 primary, secondary or tertiary amines, for example cess for the preparation of aqueous solutions of hydrox those which possess alkyl radicals of 1 to 4 carbon ylamine from an aqueous hydroxylammonium salt solu atoms at the nitrogen atom, which can furthermore tion by electrodialysis, the aqueous hydroxylammonium have a hydroxyl or alkoxy group as a substituent, e.g. salt solution being fed into the middle zone of an elec tripropylamine, tributylamine, dipropylamine, n trolysis cell which is divided into a cathode zone, an 35 propylamine, dibutylamine, isobutylamine, 2-methoxye anode Zone and a middle zone by means of semiperme thylamine, 3-methoxypropylamine, ethanolamine, di able membranes, and being electrolyzed, wherein the ethanolamine or methoxymethylamine. Cyclic amines, catholyte used is an aqueous alkali metal hydroxide such as aminoethyl-morpholine, aminoethylpyrrolidine solution containing ammonia and/or amines. or cyclohexylamine, and polyamines obtainable by re The novel process has the advantages that it takes 40 acting amines with ethyleneimine are also suitable. place with high yields, the decomposition of the hy The electrolysis is advantageously carried out using a droxylamine is suppressed, the semipermeable mem current density of from 0.1 to 10, in particular from 1 to branes, in particular for the cathode space, have a fairly 3.5, kA/m2. Advantageously, the temperature is kept at long life, and aqueous hydroxylamine solutions having a from 10° to 40° C., preferably from 15° to 28° C. during very low content of anions, e.g. < 10 ppm, can be pre 45 this procedure. pared. Advantageously used cathodes are corrosion-resist According to the invention, aqueous solutions of ant materials having a low hydrogen overvoltage, e.g. hydroxylammonium salts are used as starting materials, stainless steels, chromium nickel steels, nickel, nickel particularly suitable hydroxylammonium salts being iron alloys containing from 65 to 95% by weight of those of oxyacids, such as sulfuric acid, nitric acid, 50 iron, or iron coated with nickel-iron alloys, but prefera phosphoric acid and carboxylic acids, e.g. acetic acid or bly graphite or alkali-resistant titanium or zirconium propionic acid. Hydroxylammonium sulfate and phos alloys, such as titanium-iron, titanium-nickel, zirconi phate solutions have become particularly important um-iron or zirconium-nickel. Examples of suitable industrially. As a rule, 5-30% strength by weight aque anode materials are titanium, tantalum, niobium or ni ous hydroxylammonium salt solutions are used. In the 55 obium-tantalum alloys which are doped at the surface preparation of highly concentrated, i.e. >25% strength with platinum metals, platinum metal oxides or, prefera by weight, hydroxylamine solutions, the hydroxylam bly, platinates and have a low oxygen overvoltage. The monium sulfate consumed is supplemented until the latter should be less than 300 mV at 1 kA/m2. desired hydroxylamine concentration is reached. To Advantageously, the electrolysis is carried out in the avoid dilution effects as a result of osmosis, comoounds 60 absence of molecular oxygen in the middle zone. The which increase the osmotic pressure are added to the content of molecular oxygen should not exceed 20 ppm. catholyte in this procedure. Suitable compounds are It has also proven advantageous if the aqueous hy low molecular weight water-soluble compounds which droxylammonium salt solution being electrolyzed con are inert under the reaction conditions, e.g. sugar or tains a stabilizer. Examples of suitable stabilizers are urea or its derivatives. Advantageously, the hydrox 65 8-hydroxyquinaldine, flavones, such as morin, hydrox ylammonium salt solutions used contain less than 1 ppm yguinolines, such as 8-hydroxyquinoline, anthocyani of metal ions of sub-groups 1, 2, 5, 6, 7 and 8 of the dines, such as cyanidinium chloride and hydroxyan Periodic Table. thraquinones, such as quinalizarine, which, if required, 4,645,579 3 4. are used in combination with polyhydroxyphenols such applied on the membrane surfaces which separate the as pyrogallol. Other suitable stabilizers are quercetin, middle compartment from the anode and cathode benzonitrile, benzamidoxime, isocyanates, N-phenyl-N- spaces. The anode space contains a titanium grid elec hydroxythiourea, reductones and/or reductonates, e.g. trode which has an area of dm2 and is doped at the 2,3-didehydrohexono-1,4-lactone, and alkali metal salts surface with platinates of the type Lio.3Pt3O4. The cath of ethylenedianinetetraacetic acid. The concentration ode has an area of 1 dim2 and consists of nickel. The of stabilizers is advantageously from 5.10 to 1, in catholyte used is a 5% strength aqueous sodium hydrox particular from 5.10-3 to 5.10-2, 7% by weight, based ide solution containing 0.1% of dibutylamine, while the on the hydroxylammonium salt.