United States Patent (19) (11) 4,154,806 Szabó Et Al
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United States Patent (19) (11) 4,154,806 Szabó et al. 45) May 15, 1979 54 PROCESS FOR THE PRODUCTION OF (56) References Cited NITROUS OXDE U.S. PATENT DOCUMENTS 75) Inventors: Zoltán Szabó; Jenö Trompler; 1,098,305 5/1914 Torley et al. ........................ 423/400 Erzsébet Hollós, née Rakosinyi, all of 2,111,277 3/1938 Castner et al. ....................... 423/400 Budapest, Hungary 2,425,582 8/1947 Vingee ................................. 423/400 3,411,883 11/1968 Smit ................................. 423/400X 73) Assignee: Eötvös Lóránd Tudományegyetem, FOREIGN PATENT DOCUMENTS Budapest, Hungary 276069 5/1913 Fed. Rep. of Germany ........... 423/400 (21) Appl. No.: 865,119 Primary Examiner-G. O. Peters 57 ABSTRACT (22 Filed: Dec. 28, 1977 Ammonium nitrate is mixed, in a weight ratio of higher than 1:5, with a melt containing ammonium hydrogen 30 Foreign Application Priority Data sulfate and ammonium sulfate respectively present in Dec. 30, 1976 HU) Hungary ............................. TO 1047 the melt in a ratio of at least 4:1. The resultant mixture is subjected to thermal decomposition at 200-240 de 51) Int. C.’.............................................. C01B 21/22 grees C to produce nitrous oxide. 52) U.S. C. .................................................... 423/400 58) Field of Search ......................................... 423/400 10 Claims, No Drawings 4,154,806 2 temperature, i.e. over 250 C., the nitrous oxide formed PROCESS FOR THE PRODUCTION OF NITROUS decomposes to higher nitrogen oxides and nitrogen. A OXDE further disadvantage of the increased temperature con sists in that ammonium nitrate sublimates and thus The invention concerns a process for the production causes material loss and operational problems. In spite of nitrous oxide (N2O) which takes place by thermal of these disadvantages of increased temperatures one decomposition of ammonium nitrate at lower tempera has not so far been able to reduce the operational tem tures with a good rate of conversion while avoiding the perature. formation of by-products. According to another known method the ammonium In medical science and in the food industry an ever 10 nitrate is mixed with smaller amounts, e.g. 0.5 weight increasing amount of nitrous oxide is used and the pre percent of calcium oxide, depending on its chloride scribed quality requirements therefor are very high. content, in order to be able to carry out the thermal The generally used starting material for the production decomposition more safely and to produce a purer of nitrous oxide is ammonium nitrate. The manufacture product. of this product nowadays takes place according to the 15 classical method of heating an ammonium nitrate melt, The decrease in the danger of explosion is achieved in wherein thermal decomposition ensues, and according the Lidow process by diluting the ammonium nitrate to the reaction with an inert material. According to this method a mix ture consistine of 60 weight percent of calcined sea sand and 40 weight percent of ammonium nitrate dried at 20 150° C. are heated in a reactor to 280 C. Because of the nitrous oxide and water (vapour) are formed. poor heat conductivity of the sand one cannot ensure The thermal decomposition of ammonium nitrate that the optimal temperature is maintained constant and takes place with appropriate efficiency over the melting consequently the nitrogen content of the end-product point of the product, i.e. over 169 C., but in general at increases. According to another known method a uni between 275-280 C. The handling of the process and 25 form heat treatment of the ammonium nitrate is the reduction of the risk of explosion are very difficult achieved by the utilization of a eutectic mixture consist tasks because of the high temperature and the exother ing of potassium nitrate and sodium nitrate, but the mic nature of the process; hence usually the process is increased temperature of about 280 C. could not be either a batch process or continuously operated reactors reduced and consequently the same difficulties were of small volumetric capacity are used in which only 30 relatively smaller quantities of ammonium nitrate are at present which are associated with the higher tempera higher temperatures in order to avoid local overheating ture. or to reduce the extent of any possible explosion. This The problems involved in the thermal decomposition safe mode of operation does not, however, allow the of ammonium nitrate have spurred researchers to the production capacity to be increased or provide the 35 development of other methods. According to DT-PS possibility of improving the yield; further, the require No. 1921 181 nitrous oxide is produced by decomposi ments for increasing the speed of reaction and the purity tion of ammonium nitrate in aqueous, chloride-contain of the end-product cannot be satisfied. On an industrial ing nitric acid solutions, in the presence of catalysts, scale larger batch quantities are used and the tempera between about 100-160° C. According to DT-PS No. 2 ture of thermal decomposition is also higher but this 037975 nitrous oxide is produced by oxidation of solu requires extraordinarily expensive apparatus and safety tions of hydroxylamine containing also nitric oxide technological and automation measures, yet account and/or oxygen in the presence of a platinum metal cata must still be taken of the danger of explosion associated lyst. with this process. According to GB-PS No. 1 150510 nitrous oxide is The development of an economic process which is 45 produced from a solution of nitric acid by electrolysis acceptable from a safety point of view is for this reason with the aid of acid-resistant steel cathodes. an unsolved problem. Numerous attempts have been The last-mentioned processes are in general not eco made to improve the production capacity, the effi nomical, difficult to carry out and produce relatively ciency of production and the quality of the end impure nitrous oxide; consequently a thorough purifica product. Some methods are known which improve 50 tion of the product is absolutely necessary. individual parameters of the nitrous oxide production An aim of the invention is the development of a pro but no single process has hitherto satisfied all the desid cess starting from ammonium nitrate which process is erata. easy to handle, can be carried out safely, involves a The thermal decomposition of ammonium nitrate is a reduced danger of explosion and which takes place by highly complicated process the details of which have 55 the thermal decomposition of ammonium nitrate to not yet been fully clarified and which takes place in produce nitrous oxide at a high rate of conversion and various directions under the influence of certain addi of high purity. tives. The amounts of nitrous oxide, nitric oxide, nitro The solution of the task was made possible by carry gen dioxide, nitrogen, water, oxygen, ammonia, and ing out the thermal decomposition under conditions nitric acid depend on the temperature, duration of the 60 fundamentally different from those known hitherto. It reaction, water content and pressure. If, for instance, was shown that the theory according to which in the transition metal oxides are added to the ammonium course of thermal decomposition of the ammonium nitrate in a molar ratio of 1:10-100 then according to nitrate acidification of the ammonium nitrate should be some tests the rate of thermal decomposition increases. avoided is not sound. According to prevailing opinion it However, it is a disadvantage of this method that the 65 was considered that the acidification of the ammonium thermal decomposition is displaced in the direction of nitrate causes the formation of nitrogen-containing nitrogen formation, particularly in the presence of chro gases, i.e. harmful by-products and the danger of explo mium oxides and manganese oxides, because at higher sions associated therewith. This opinion was widely 4,154,806 3 4. accepted for the reason that a stronger acid can set the ammonium nitrate present in the gas phase can be nitric acid free from the nitric salt and therefore the transformed into the desired end-product. acidification of the ammonium nitrate melt had to be The composition of the multi-component salt solution avoided during thermal decomposition. A 1:1 mixture or salt melt consists of a mineral acid, preferably sul of ammonium hydrogen sulphate and ammonium ni 5 phuric acid or an acid anhydride e.g. boron trioxide, or trate decomposes explosively and nitrous oxide results. in given cases from a mixture of the same, further de However, the thermal decomposition of ammonium composition may contain one or more salts, particularly nitrate begins already at 160 C. and takes place up to ammonium salts of mineral acids. In desired cases the 240 C. at high speed. The lowering of the temperature composition suited for the thermal decomposition may is in general favourable but the last-mentioned mixture 10 contain other salts or mineral acids, e.g. potassium and is nevertheless not in practice suitable for the manufac sodium salts. ture of nitrous oxide because the yield of the desired A mixture of the salt solution or salt melt consisting end-products only amounts to 80% and numerous side of sulphuric acid and ammonium sulphate provides products, such as nitrogen, as well as nitric oxide and particularly favourable results. This composition is a nitric dioxide form in a quantity higher than 5%. 15 mixture of ammonium hydrogen sulphate and ammo It has been found that the formation of nitrous oxide nium sulphate. It is advantageous but not decisive that in the thermal decomposition of ammonium nitrate can the mixture should form a homogeneous solution or be influenced in a favourable direction if a portion of the melt at the given reaction temperature. The weight acid salt component is displaced at the expense of the ratio of the ammonium hydrogen sulphate and the am ammonium nitrate portion and at the same time, by the 20 monium sulphate is preferably adjusted to at least 4:1.