SU1074818A1 - Process for producing sodium cyanate - Google Patents

Abstract

1. A method of producing sodium cyanate, including reacting at 125-170 ° C of urea and sodium carbonate with stirring and batch adding urea to sodium carbonate, characterized in that, in order to increase the yield of the product and increase the content of the main vesh in the product Before adding each subsequent portion of urea, the reaction mixture is cooled to a temperature not higher than 120 ° C and the resulting sodium cyanate is maintained at 180-300 ° C until the impurities are gasified. 2. A method according to claim 1, characterized in that the urea is added to sodium carbonate in three equal portions.

Description

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00 The invention relates to the field of production of sodium cyanate, which can be used in mechanical engineering as a part of carbonitration for the nitriding of metals. A known method for producing sodium cyanate by continuously adding urea to preheated sodium carbonate at 150-300 ° C at a ratio of 1.6-2.0; 1. The time of the chemical stage is 180 minutes. 1. The disadvantages of this method are the low yield and purity of the target product, amounting to 90%. The closest to the invention by the technical essence to the achieved result is a method of obtaining sodium cyanate, including interaction at 120-200 ° C of urea and sodium carbonate with stirring and portioning of urea to the ratio (NH) - CO: 2.0-2, 2: 1. When the urea to sodium carbonate ratio of 1.5-1.99: 1 is reached, water is added to the reaction mass, it is evaporated and additional urea is mixed in to achieve the specified ratio 2. The disadvantages of this method are also low yield and purity of the target product, not exceeding 93-95%. The aim of the invention is to increase the product yield and increase the content of the main substance in the product. This goal is achieved by the fact that according to the method of producing sodium cyanate, including the interaction at 125-170 ° C of urea and sodium carbonate, when moving and batch adding urea to sodium carbonate in three equal portions. Moreover, the reaction mixture is cooled to a temperature of no higher than 120 ° C before adding each subsequent portion of urea and the resulting sodium cyanate is maintained at 180-300 ° C until the impurities are gasified. The requirement to lower the temperature to 120 ° C before loading each portion of urea is determined by the need to avoid its pyrolysis during feed and the condition of uneven distribution in volume, which at higher temperatures causes the formation of by-products. Lowering the temperature below 120 ° C is economically inefficient, as the energy consumption increases with subsequent heating, and the quality of the product does not improve. The recommended holding mode of the obtained sodium dianate at 180-300 ° C allows its purity to be increased due to the gasification of impurities, which starts at 180 ° C. At a temperature of 300 ° C, the decomposition of impurities ends and a further increase in temperature does not lead to an improvement in the quality of sodium cyanate. The total ratio of soda and urea in the synthesis should be stoichiometric. Urea is added to the reaction mixture in three equal portions. When urea is added in two operations, after melting, the reaction mass begins to harden to form strong conglomerators, for which high-quality mixing, special grinding devices are necessary. In the case of the addition of urea in three equal portions, the mechanical properties of the reaction mass during the synthesis process remain almost unchanged and it is an easily agitated powder, which allows the use of simpler types of agitators. A further increase in the number of servings of urea does not lead to an increase in the quality of the sweat product, but only increases the synthesis time. An example. 26.5 g (0.25 g mol of anhydrous sodium carbonate and 10 g (0.17 g mol) urea are placed in a heated oil-immersed reactor, after which the reaction mass is heated to 150 ° C for 30 minutes with vigorous stirring and maintained at this temperature is 40 minutes before the emission of NH stops. The temperature in the reactor is reduced to 120 ° C. After this, a new portion of urea is added 10 g (0.17 g mol), the reaction mass is heated to 150 ° C for 15 minutes and the holding time is repeated after adding the third portion of urea to the reactor, 10 g (0.17 g. - mol) the reaction temperature After reaching this temperature, the release of ammonia is stopped. The sodium cyanate obtained is heated to 300 ° C for 20 minutes and maintained at this temperature for 5 minutes. After cooling, 32.8 g of sodium cyanate is discharged from the reactor. The yield and content of the basic substance in the product is 97.8%. The table shows the yield and content of the basic substance in the product, depending on the synthesis conditions. The advantage of the proposed method before the known is that the yield and content of the basic substance in the product increased from 93-95% to 97.5-98.8%.

3 3 3 3

97,8

300 200 98.8 200 V7.5 180 98.2

Claims (2)

1. METHOD FOR PRODUCING SODIUM CYANATE, comprising reacting urea and sodium carbonate at 125-170 ° C with stirring and portionwise adding urea to sodium carbonate, characterized in that, in order to increase the yield of the product and increase the content of the main substance in the product, before each a subsequent portion of urea, the reaction mixture is cooled to a temperature not higher than 120 ° C and the resulting sodium cyanate is maintained at 180-300 ° C until gasification of impurities ceases. 2. The method according to π. 1, characterized in that the urea is added to sodium carbonate in three equal portions.