RU2170210C1 - Method of preparing sodium pyrophosphate - Google Patents

Abstract

FIELD: chemical industry. SUBSTANCE: disodium phosphate is thermally decomposed at 330-470 C in the presence of catalytic nitroammophos additive in amount of 0.3-3.0 wt % calculated for anhydrous disodium phosphate. Method makes it possible to increase yield of the desired product by about 2-4%, power consumption remaining unchanged. EFFECT: more efficient preparation method. 3 cl, 1 tbl

Description

 The invention relates to the production of alkali metal phosphates, in particular sodium pyrophosphate used in the chemical industry.

A known method of producing sodium pyrophosphate, including the neutralization of thermal phosphoric acid (70 - 80%) with soda ash to a pH of 8.8 - 9.0, followed by boiling the solution to remove CO ₂ and evaporating to a concentration of 48 - 50% Na ₂ HPO ₄ . A solution of Na ₂ HPO _{4 is} further mixed with 3-4 parts by weight a circulating product and heated to 360-400 ^o C. Sintered particles are cooled and crushed (I.L. Hoffman, N.V. Trutneva, Communication on scientific and technical works of NIUIF, N 2, 1957, p. 30).

 The disadvantages of this method include its complexity and multi-stage.

The closest analogue (prototype) to the claimed invention is a method for producing sodium pyrophosphate, including dehydration (decomposition) of disodium phosphate at 350-400 ^o C in the presence of ~ 1% of a catalytic additive - ammonium nitrate (M.E. Pozin, Technology of mineral salts, 1970, Part 2, pp. 1083-1084).

 The disadvantage of this method is the relatively low yield of the target product.

 The task of the invention is to develop an effective method for producing sodium pyrophosphate with an increased yield of the target product, which is the technical result of the invention.

 The technical result is achieved thanks to the method of producing sodium pyrophosphate, including the decomposition of disodium phosphate at elevated temperature in the presence of a catalytic additive based on ammonium nitrate - nitroammophos, used, preferably in an amount of 0.1 - 3.0%, based on anhydrous disodium phosphate.

The process of decomposition of disodium phosphate is carried out at 330-470 ^o C.

The process is described by the equation:
2Na ₂ HPO ₄ ---> Na ₂ PO ₃ - OO ₃ PNa ₂ + H ₂ O
One of the disodium phosphate crystalline hydrates is taken as the starting product, with the destruction of crystalline hydrate and the removal of crystallization water first.

 Disodium phosphate of high purity, of various shapes (anhydrous, two-, seven- and twelve-water) is produced by domestic industry.

 Introduction to the initial mixture as a catalyst of an industrial product - nitroammophos, which is a mixture of ammonium nitrate, mono- and diammonium phosphates, allows the process to be carried out at moderately high temperatures and at the same time not to introduce foreign impurities into the product, since disodium phosphate is removed from the product during decomposition ammonia and nitrogen oxides.

 The proposed method is illustrated by the following examples.

 A calculated amount of high purity disodium phosphate crystalline and catalyst are charged into a rotary drum furnace. The loading hatch is closed, the water vapor removal system is connected and heating is started. Depending on the composition of the crystalline hydrate, when heated to a certain temperature, the salt melts and, then, the process of dehydration of disodium phosphate begins.

After distillation of all crystallization water, the temperature in the drum is slowly increased to 330-470 ^o C. Upon reaching the desired temperature, the reaction mixture is maintained. At the end of the process, the product is cooled, the resulting anhydrous sodium pyrophosphate is discharged.

 In a heavy mixer, the anhydrous salt is mixed with the calculated amount of water (steam condensate or condensate obtained by dehydration of the initial salt) and, after averaging for 2-3 hours, is sent to grinding and packaging.

 As a result of the above techniques, easily soluble ten-sodium sodium pyrophosphate is obtained.

 The table shows the conditions of examples of synthesis from various crystalline hydrates of disodium phosphate.

 Examples 11 and 12 are carried out under conditions close to the prototype.

The time for distillation of water is determined by the final form of crystalline hydrate and the efficiency of the heater. A decrease in the synthesis temperature (decomposition of anhydrous disodium phosphate) below 330 ^o C leads to an increase in the duration of the decomposition process, which in turn increases the energy consumption.

An increase in temperature above 470 ^o C leads to a certain amount of sintered, fused pyrophosphate, which subsequently does not give ten-salt, which does not meet the requirements of consumers.

Claims (3)

 1. A method of producing sodium pyrophosphate by decomposition of disodium phosphate at elevated temperature in the presence of a catalytic additive based on ammonium nitrate, characterized in that nitroammophos is used as a catalytic additive.  2. The method according to claim 1, characterized in that nitroammophos is used in an amount of 0.1 to 3.0 wt.% Based on anhydrous disodium phosphate.  3. The method according to claim 1, characterized in that the decomposition process is carried out at 330 - 470 ° C.

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