CS227957B1 - Method of producing dinitrogen oxide - Google Patents

Description

The invention relates to a process for the continuous production of nitrous oxide by quantitative thermal decomposition of ammonium nitrate under a steady-state thermal regime in a decomposition retort.

The course of thermal decomposition of ammonium nitrate is influenced by the purity of the raw material, the design of the reactor and the way of decomposition. Thermal decomposition of ammonium nitrate produces nitrous oxide according to the following main reaction:

NH ₄ NO ₃ - »N ₂ 0 + 2H ₂ 0 '

The thermodynamic analysis showed that this reaction can proceed spontaneously up to 324 ° C. Looking at 220 ° C for the start of the decomposition of ammonium nitrate, the main chemical reaction can take place in a temperature range of 220 to 324 ° C. In addition to this major chemical reaction, undesired side reactions can also take place to produce elemental nitrogen, oxygen, higher nitrogen oxides and reaction water. These chemical side reactions occurring in the thermal decomposition of ammonium nitrate are characterized by a greater thermal color than the main chemical reaction and can occur at any temperature higher than 220 ° C. In addition to these reactions, dissolution occurs in the ammonium nitrate melt according to the chemical equation.

nh ₄ no ₃ -> NH 4 + hno ₃

Dissociation results in the occurrence of free nitric acid in the ammonium nitrate melt, which, through its catalytic effect, leads to thermal decomposition of the ammonium nitrate in an undesirable direction. It has been verified that if thermal decomposition of ammonium nitrate predominates side reactions with the development of higher nitrogen oxides, accompanied by a sudden increase in the reaction temperature, even by sufficiently reducing the temperature, thermal decomposition cannot be stabilized in favor of the 227957 major chemical reaction. The above-mentioned drawbacks have no method of nitrous oxide by quantitative thermal decomposition of continuously dosed ammonium nitrate at a temperature corresponding to concentration, which consists in injecting a melt with a concentration of at least 90% by weight and a pH of 7-9 into a zone heated to 220-324 °. C, preferably 250 to 290 ° C.

In order to suppress the formation of nitric acid in the melt of ammonium nitrate, it is necessary for the melt to be heated to the decomposition temperature as soon as possible after having previously adjusted the pH to 7-9 with ammonia. This can be ascertained by feeding the ammonium nitrate melt pH 7 to 9 directly to a site in the decomposition retort at 220 to 324 ° C, preferably 250 to 290 ° C, which is made possible by the construction of the decomposition retort B by using a metering pump. The adverse effect of impurities present in ammonium nitrate, in particular the effect of ferric ions, is limited by the addition of small amounts of phosphate ions.

As has been said, it is important how the ammonium nitrate melt reaches the decomposition temperature without creating unfavorable conditions leading to decomposition in an undesirable direction. Therefore, some processes, NSR patent 1921181 or US patent 3411883, lead to the decomposition of ammonium nitrate in an aqueous solution or in the melt of some salts. In another method, ammonium nitrate is decomposed in the presence of the catalytic effect of chloride ions.

A further process for the production of nitrous oxide (Chem. And Ind. 1964, 49, 2,019 to 2,020) by thermal decomposition of ammonium nitrate is carried out in the presence of catalysts such as barium pyrophosphate, trinotriminophosphate and the like. characterized in that nitrous oxide is produced by thermal decomposition of ammonium nitrate in multicomponent solutions, wherein one part of the ammonium nitrate is heated with at least five parts of the multicomponent mixture containing the mineral acids or salts thereof, boric oxide and the salt of the mineral acid used; must be stirred in the reactor.

The process for the continuous production of nitrous oxide by the quantitative thermal decomposition of the ammonium nitrate according to the invention under a steady-state temperature regime in the decomposition retort is characterized by the simplicity of controlling the decomposition and the safe operation.

Example

206.42 kg.l ^- 'aqueous solution of ammonium nitrate having a concentration of 76.21% by weight is fed to the evaporator where the concentration is increased to 96.76% by weight; the melt thus formed is adjusted to pH 8 with ammonia and introduced into the decomposition retort at a temperature of 170 ° C. In the retort, there is a quantitative thermal decomposition of ammonium nitrate to form a gas mixture and volume composition (based on dry gas): 97.40% N ₂ O, 0.27% NO, 0.17% NO ₂ , 1.07% N ₂ , 1.07% NH4 and 0.02% Og.

The 200 ° C retort gas mixture is cooled by passing through a condenser where most of the reaction water is separated, enters a system of series-connected absorption columns with potassium permanganate, caustic soda and water absorption to separate higher nitrogen oxides, and ammonia. The thus-washed mixture gas of volume composition (based on dry gas): 97.94% Ngo, 1.85% _N2, 0.20% _O2, 0.01% NH, enters the separator through a medium-pressure compressor, then the molecular sieve (where the last residue of impurities and water is separated) and a high-pressure compressor from which a practical finished product of 97.95% N ₂ O, 1.85% N ₂ and 0.20% O ₂ Collected in tanks at a temperature of 25 ° C and a pressure of 6.4 MPa. A liquid phase is taken from the containers for filling the cylinders.

Claims (1)

SUBJECT OF THE INVENTION Process for producing nitrous oxide by quantitative thermal decomposition of a continuously charged ammonium nitrate melt having a temperature corresponding to a concentration, characterized in that the melt with a concentration of at least 90% by weight and a pH of 7 to 9 is injected into a zone heated to 220 to 324 ° C, preferably 250 to 290 ° C.