A process for the production of highly concentrated nitric acid

摘要

Concentrated nitric acid is obtained continuously by catalytically oxidising ammonia with oxygen or oxygen-containing gases, separating excess of water from the combustion gases, converting the gases into liquids which contain water-containing nitric acid and nitrogen oxides in proportions suitable for the production of concentrated nitric acid, and continuously pumping the liquids into a reaction space which is at a higher pressure, say at least 20 atmospheres up to 200 atmospheres, in which the conversion of the mixture of liquids into concentrated nitric acid takes place by reaction with oxygen or oxygen containing gases. The oxygen should be introduced into the reaction space in a fine state of distribution, e.g. through sieve plates or plates of ceramic material and may flow in counter current or co-current, or partially in both, to the mixture of liquids. A temperature of at least 70 DEG C. should prevail at at least one part of the space. The reaction space may consist of several sections forming a plurality of temperature and pressure stages and may contain fillers or baffles. Sieve bottoms with progressively increasing cross-sectional surfaces may be provided in the reaction space. A mixture of liquid nitric acid and liquid nitrogen tetroxide may be initially saturated with oxygen &c. without increase in pressure, pumped into the reaction space and treated therein with further oxygen. Ammonia is oxidised with air with or without the addition of steam. The nitric oxide mixture passes through a steam boiler 1, a condenser 2 which removes excess water and is oxidised to nitrogen peroxide in a water-cooled condenser 4. Simultaneously, nitric acid containing water condenses in the condenser 4. The oxidised and cooled gas flows through a tube 5 to a brine-cooled liquefier 6 where liquid nitrogen tetroxide condenses and is finally freed from the remainder of its nitrogen oxide content by contact with flowing concentrated nitric acid in a brine-cooled p tube 8. The condensates from the condenser 4, the liquefier 6 and if desired the tube 8 pass via conduits 10, 11 and 12 into a mixer 13 and leave it in the form of an emulsion at a temperature below 0 DEG C. The emulsion is fed to a pump 14 which pumps it at a pressure of 40--60 atmospheres through a conduit 15, which may contain a preheater, into an autoclave 16. A compressor 17 feeds oxygen, which may be preheated, through a conduit 18 and a distributing device into the autoclave 16. Non-absorbed gaseous constituents may leave the autoclave through a tube 19 and join the gases entering the tube 8. Concentrated nitric acid leaves the autoclave through a conduit 20, is relieved of its pressure and is freed from its nitrogen tetroxide content in a bleaching vat 21, which is heated at the bottom and cooled at the top. The nitric acid leaves at the bottom and the evaporated nitrogen oxides are returned to the liquefier 6 through a conduit 24. The nitric acid flowing from the tube 8 may if desired be conveyed to the bleaching vat 21, instead of to the mixer 13. According to a modification, ammonia is oxidised with preheated air, steam and nitric acid are condensed as before, the remaining gases are compressed to 5--10 atmospheres and then passed through an oxidiser and a heat exchanger before entering the liquifier for production of liquid nitrogen tetroxide, the condensed nitric acid is fed to an absorption vessel provided with sieve bottoms which replaces the tube 8, the combined condensates from the liquefier and the absorption vessel are supplied to the mixer, and the liquid on leaving the mixer is pumped to a pressure of 20 or 50 atmospheres and converted with oxygen as before. The energy of the waste gases is utilised in the compression of the nitrogen oxide containing gases. In the above processes the cold crude materials and the hot intermediate or final products may be used for producing heat exchange and the heat of the hot combustion products may be used for producing steam. Parts of the apparatus which are influenced by oxygen under pressure and the reaction liquids may be constructed of aluminium, aluminium alloys, acid-resisting steel, ferro-silicon, ceramic material, enamel, platinum metals, tantalum, niobium or the like. Specifications 273,718, [Class 1 (i), Chemical processes &c.], and 337,847, [Class 1 (ii), Inorganic compounds, other than &c.], are referred to. Lubricants.--The pressure pumps or compressors or some thereof are lubricated by means of inorganic colloids such as silicic acid or aluminium hydroxide, e.g. in the form of a brine or gel which may contain water, nitric acid or nitrogen tetroxide.