Process for preparing hydroxylammonium salts

#This application claims the priority of Swiss Application No. 6406/74 filed May 10, 1974.

#Catalysts containing platinum metal which catalyze the hydrogenation of nitric oxide in an acid medium to give hydroxylammonium salts are known. In addition to the desired hydroxylammonium salts, however, a substantial part of the nitric oxide is reduced to ammonium salts, nitrogen and nitrous oxide. These undesired by-products reduce the yield of the desired product and interfere with the economy of the commercial process. It has been suggested that a more selective reduction of nitric oxide to give hydroxylamine in an acid medium can be carried out. The use of catalysts containing platinum metal in which the catalysts are "poisoned" by the presence of elements As, Se, Sb, Te, S or Bi, has been disclosed by German Pat. No. 956,038, and the use of the elements Hg, As, Sb, Bi, has been taught by Japanese Patent Publication No. 54 750/1966.

#It has now been found the hydrogenation of nitric oxide in acid medium leads almost exclusively to the desired hydroxylammonium salts if selenium-modified platinum metal catalysts are employed as catalysts and if the hydrogenation of the nitric oxide is carried out at acid concentrations of at least 2N. Accordingly, the present invention relates to a process for the preparation of such salts by catalytic hydrogenation of nitric oxide in an acid medium wherein platinum containing catalysts having 15 to 50 atom percent of selenium, based on the amount of platinum, are employed and the hydrogenation of the nitric oxide is carried out at an acid concentration of at least 2N. Preferably, 20 to 30 atom percent of selenium, based on the platinum present, is used.

#The following Examples illustrate the invention.

#2 liters of 4.6N sulfuric acid is placed in a 2-liter reaction vessel equipped with a stirrer. 14 g of 1.0% platinum on activated carbon is added as the catalyst. About 10 liters of N.sub.2 is passed into the stirred suspension in 1/2 hour (the suspension being at a temperature of 30.degree. C), followed by about 20 liters of H.sub.2 over a period of about 15 minutes. 16 mg of SeO.sub.2 (corresponding to 20 atom percent of selenium based on the platinum) is dissolved in 100 ml of 4.6N sulfuric acid and added to the suspension, which is supplied with H.sub.2 and stirred. H.sub.2 then continues to be passed into the suspension for 1/2 hour at 30.degree. C.

#For nitric oxide hydrogenation, a mixture of 25 standard liters of nitric oxide and 75 standard liters of H.sub.2 per hour are then passed in at 40.degree. C. The acid concentration in the reaction vessel is kept constant at about 2N by hourly removal of product and addition of sulfuric acid (about 4.8N).