RU2178386C1 - Method of potassium dihydrogen phosphate producing - Google Patents

Abstract

FIELD: inorganic chemistry, chemical technology. SUBSTANCE: invention relates to production of alkaline metal phosphates, in part, potassium dihydrogen phosphate used in food, medicinal and microbiological industries. Method of production of potassium dihydrogen phosphate involves neutralization of phosphoric acid with potassium hydroxide or potassium carbonate in the parent molar ratio K₂O/P₂O₅ = (1.18-1.5): 1, filtration of saturated solution to remove impurities and keeping in crystallizer for 20-30 min. Then the saturated solution is cooled to 20-30 C, phosphoric acid is added to the ratio K₂O/P₂O₅ = (1.05-1.1): 1 followed by cooling to 15-25 C and separation of commercial product by centrifugation. EFFECT: increased yield of ready product, large crystals of potassium dihydrogen phosphate. 1 tbl

Description

 The invention relates to the production of alkali metal phosphates, in particular potassium phosphoric acid monosubstituted, used in the food, medical and microbiological industries.

 A known method of producing potassium phosphoric acid monosubstituted, including the processing of technical potash or filtered sludge obtained by carbonization of technical potassium alkali with phosphoric acid without heating at room temperature, followed by separation of the mixture with separation of potassium phosphoric acid monosubstituted by centrifugation and processing of the filtrate into potassium tripolyphosphate RF patent N 2105713, IPC C 01 B 25/30, publ. 02.27.98, Bull. N 6).

 The disadvantages of this method include the low quality of marketable potassium phosphoric acid monosubstituted due to the presence of a large number of impurities (sulfates, chlorides) in it, as well as a low product yield (40% of stoichiometry), which generally makes the process ineffective.

 The closest analogue to the claimed invention is a method for producing potassium phosphoric acid monosubstituted, including the neutralization of phosphoric acid with a potassium-containing reagent to form a saturated solution, crystallization upon cooling, and separation of the commercial product from the mother liquor (Ed. St. USSR N 1782935, IPC C 01 B 25 / 30, 25/28, publ. 11.06.90, Bull. N 47).

The known method provides for the neutralization of phosphoric acid with potassium hydroxide to a pH of 5.8-6.0. Monosubstituted potassium phosphoric acid is crystallized from a saturated solution at 90 - 85 ^o C. The product is separated from the mother liquor and dried.

 The disadvantage of this method is its low profitability, due to the low productivity of the process and the presence of energy-intensive drying operations, in addition, the cost-effectiveness of the process is adversely affected by the fact that it provides chemically pure raw materials.

 As shown by experiments conducted under the conditions of the known method, a low yield of a commercial product (52%) is caused by the formation under these conditions of potassium phosphoric acid monosubstituted in the form of small crystals that are poorly separated from the mother liquor.

 The claimed invention is directed to the development of a highly economical method for the production of marketable potassium phosphoric acid monosubstituted, which allows to ensure high productivity of the process and high quality of the commercial product.

 The technical result of the developed method is to increase the yield of the finished product by obtaining large crystals of potassium phosphoric acid monosubstituted.

The specified technical result is achieved by the method of producing potassium phosphoric acid monosubstituted (monopotassium phosphate), including the neutralization of phosphoric acid with a potassium-containing reagent to form a saturated solution, crystallization upon cooling and separation of the commercial product from the mother liquor, in which neutralization is carried out with potassium hydroxide or potassium carbonate in the initial molar K ₂ O / P ₂ O ₅ equal to (1.18-1.5): 1, the saturated solution is filtered to separate impurities, kept before crystallization for After 20-30 minutes, then cooled to 20-30 ^o C, add phosphoric acid to a ratio of K ₂ O / P ₂ O ₅ equal to (1.05-1.1): 1, followed by cooling to 15-25 ^o C and separation of the commercial product by centrifugation.

 The essence of the proposed method is as follows.

 The conducted studies allowed us to establish that the neutralization of phosphoric acid with potassium hydroxide or potassium carbonate in the claimed ratio of components, filtration to separate impurities and exposure to crystallization of a saturated solution of potassium phosphoric acid monosubstituted for an experimentally established time with subsequent crystallization upon cooling under the stated conditions provide significant reducing the content of impurities in the finished product and obtaining large crystals of potassium phosphate formic acid monosubstituted.

 The study of the chemistry of the process was not part of the task. However, we can assume that the claimed conditions contribute to the formation of complex compounds (coagulants), the withdrawal of which from the process ensures the formation and growth of large crystals of potassium phosphoric acid monosubstituted instead of small crystals obtained by the implementation of known technical solutions.

The claimed range of the initial molar ratio K ₂ O / P ₂ O _{5 of} (1.18 -1.5): 1 was established experimentally. It turned out that carrying out neutralization with an initial ratio of K ₂ O / P ₂ O ₅ exceeding 1.5: 1 leads to the fact that during subsequent refinement in the crystallizer it is necessary to add a larger amount of purified acid, which will inevitably increase the cost of the process and worsen its technique -economic indicators. When the lower limit of the claimed ratio is not achieved, precipitation of crystals of the finished product is already observed at the filtration stage, which ultimately reduces the yield of the commercial product.

 Subsequent filtration of the saturated solution ensures the separation of insoluble impurities, and exposure to crystallization for 20-30 minutes prevents the formation of an inlaid monopotassium phosphate layer on the heat transfer walls of the mold and thereby increase the removal of the finished product from the mold.

 It was found that exposure to a saturated solution of less than 20 minutes does not provide a high yield of the finished product, while exceeding the proposed time interval leads to an unreasonable increase in the time of the process and thereby reduce productivity.

 In the course of studies it was found that the two-stage refinement of the solution in the claimed conditions significantly affects both the increase in the output of potassium phosphoric acid monosubstituted, and the improvement of its quality.

Studies have shown that the initial cooling of the initial saturated solution leads to joint crystallization of both monosubstituted and disubstituted potassium phosphate, while adding phosphoric acid to the established ratio of K ₂ O / P ₂ O ₅ equal to (1.05-1.1): 1, allows you to go into the crystallization region of monopotassium phosphate, and subsequent cooling to 15 - 25 ^o C ensures its high yield.

 The following is an example confirming the possibility of implementing the claimed invention to obtain the above technical result.

 Example 1

A 450 g solution of potassium hydroxide with a density of 1.4 g / cm ³ is fed into the reactor with a working stirrer, then 85% phosphoric acid in the amount of 220 liters is poured (K ₂ O / P ₂ O ₅ ratio is 1.40: 1). After checking the end of the neutralization reaction, the saturated solution is filtered to separate impurities and kept in the mold for 20 minutes, then cold water is fed into the jacket to cool to a temperature of 25 ^o C, after which phosphoric acid is added to a molar ratio of K ₂ O / P ₂ O ₅ equal to 1.06: 1. The resulting suspension is cooled to a temperature of 17 ^o C. The resulting crystals are separated in a centrifuge.

 The yield of the finished product was 87% of stoichiometry, the content of the main substance was 99.6%, the content of impurities meets the requirements of TU 6-09-5324-87 for potassium dihydrogen orthophosphate, qualification of ChP.

 Example 2

A solution of technical potash (potassium carbonate) with a density of 1.28 g / cm ³ in the amount of 500 liters is fed into the reactor with a working stirrer, then 85% phosphoric acid in the amount of 137 liters is poured (K ₂ O / P ₂ O ₅ ratio is 1.3: 1). After checking the end of the neutralization reaction, the saturated solution is filtered to separate impurities and kept in the mold for 20 minutes, then cold water is fed into the jacket to cool to a temperature of 25 ^o C, after which phosphoric acid is added to a molar ratio of K ₂ O / P ₂ O ₅ equal to 1.07: 1. The resulting suspension is cooled to a temperature of 20 ^o C. The resulting crystals are separated in a centrifuge.

 The yield of the finished product was 85% of stoichiometry, the content of the main substance was 98.0%, the content of impurities corresponds to the requirements of TU 6-09-5324-87 for potassium dihydrogen phosphate, qualification Ch.

 The results of experimental studies are shown in the table.

 The table compares the indicators of the proposed method (experiments NN 2, 5, 8, 11 and 14) and experiments, the conditions for which go beyond the limits regulated by the claims (experiments NN 1, 3, 4, 6, 7, 9, 10, 12, 13 and 15).

 As can be seen from the materials presented, only the totality of the claimed features provides the opportunity to achieve optimal performance in the process of obtaining potassium phosphoric acid monosubstituted. If the claimed ratios of the components are violated, the process characteristics deteriorate (experiments NN 1, 3, 4, 9, 10, 12, 15) or unjustified energy costs (experiments NN 6, 7, 13).

 Thus, the claimed invention successfully solves the problem of creating an economical method for producing potassium phosphoric acid monosubstituted, which allows for optimal process performance and high quality commercial product.

Claims (1)

A method for producing potassium phosphoric acid monosubstituted, including neutralizing phosphoric acid with a potassium reagent to form a saturated solution, crystallizing upon cooling and separating the commercial product from the mother liquor, characterized in that the neutralization is carried out with potassium hydroxide or potassium carbonate at the initial molar ratio of K ₂ O / P ₂ o _5, equal to (1,18-1,50): 1, the saturated solution is filtered to remove impurities prior to crystallization is maintained for 20-30 minutes, then cooled to 20-30 ^o C, is added osfornuyu acid to a ratio K ₂ O / P ₂ O _5, equal to (1.05-1.1): 1, followed by cooling to 15-25 ^o C and a commercial product separation by centrifugation.

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