RU2261222C1 - Method of production of monopotassium phosphate - Google Patents

Abstract

FIELD: medicine and microbiology; agriculture and food industry; methods of production of monopotassium phosphate.

SUBSTANCE: the invention is pertaining to production of monopotassium phosphate used as fertilizers, food additives, and also in medicine and microbiology. The method provides for neutralization of phosphoric acid by potassium carbonate up to pH not above 4.5 at the heightened temperature, separation of the produced admixture by filtration with the subsequent crystallization and separation of the finished product at cooling. Potassium carbonate take in the form of a water solution with the concentration necessary for production in the neutralized mixture of 23-30 % monopotassium phosphate. The neutralization process is conducted at the temperature of 70-78°C, and the mother liquor after separation of the finished product at the stage of a crystallization return into the process on the stage of dissolution of potassium carbonate. Reaction of the neutralization conduct up to pH = 3.8-4.5. The technical result is an increase of output of the finished product up to 95-97 % and creation of the wasteless production due to utilization of a mother liquor in the process.

EFFECT: the invention ensures increased output of the finished product up to 95-97 %, creation of the wasteless production due to utilization of a mother liquor in the process.

2 cl, 3 ex

Description

The invention relates to a method for producing monopotassium phosphate used as fertilizers, food additives, as well as in medicine and microbiology.

There is a method of producing monosubstituted phosphates of alkali metals or ammonium (in our case monopotassium phosphate is considered), which involves treating phosphoric acid with a potassium compound at an elevated temperature followed by crystallization of the product. According to this method, thermal phosphoric acid (judging by the content of impurities described in the description) is treated with a 45% potassium hydroxide solution. The temperature of the reaction mixture is 90-95 ° C, the pH of the mixture is 5.85-6.0. Then crystallization is carried out from a saturated solution at 80-85 ° C at a pH of 5.8-6.0. Then the product is dried for 24 hours. The product is obtained in the form of white crystals (ed. St. USSR No. 1782935, 01 B 25/30, BI No. 47, 1992).

The disadvantages of the method are large losses of the product due to the high crystallization temperature, since at this temperature potassium phosphate has a sufficiently high solubility. The use of expensive components - thermal phosphoric acid, potassium hydroxide.

The closest to the described by the technical nature and the achieved result is a known method for producing monopotassium phosphate, including the neutralization of phosphoric acid with potassium carbonate to a pH of not higher than 4.5 at an elevated temperature, separation of the mixture by filtration, followed by crystallization and separation of the finished product upon cooling (RF Patent No. 2164494, C 01 B 25/30, 2001).

This method uses dry potassium carbonate, which is metered into extraction phosphoric acid (EPA). The neutralization reaction is carried out at a temperature of 80-89 ° C to a pH of 3.5-4.5. Under these conditions, monopotassium phosphate in the amount of 45-48% is formed in the neutralized mixture, and the water-insoluble orthophosphates of iron, aluminum, calcium, magnesium fluorides and other compounds precipitate. Part of monopotassium phosphate also co-precipitates with impurities. The resulting mixture is separated on a filter at a temperature of 70-80 ° C. The filtered solution is cooled to a temperature of 15-20 ° C. The precipitated crystals of the pure product are separated and dried, and the mother liquor after the cooling step is removed from the process. The yield of pure product is 60-65%.

The disadvantage of this method is primarily the insufficiently high yield of pure product, large losses of monopotassium phosphate at the stage of separation of impurities and the presence of effluents in the form of mother liquors after the cooling stage.

We set the task of increasing the yield of the finished product and the creation of virtually waste-free production.

The problem is solved in the proposed method for the production of monopotassium phosphate, including the neutralization of phosphoric acid with potassium carbonate to a pH of not higher than 4.5 at an elevated temperature, separation of the resulting mixture by filtration, followed by crystallization and separation of the finished product upon cooling. According to this method, potassium carbonate is taken in the form of an aqueous solution with the concentration necessary to obtain 23-30% monopotassium phosphate in a neutralized mixture, the neutralization process is carried out at a temperature of 70-78 ° C at a pH of 3.8-4.5, and the mother liquor after separation the finished product at the stage of crystallization is returned to the process at the stage of dissolution of potassium carbonate.

To obtain pure monopotassium phosphate and reduce its losses at the stage of neutralization, it is necessary to avoid crystallization of impurities together with monopotassium phosphate, therefore, in the process of neutralization, the concentration of an aqueous solution of potassium carbonate and the reaction temperature are selected. The determining factor is the concentration of monopotassium phosphate in the neutralized solution. At the declared concentration, co-crystallization of impurities with monopotassium phosphate does not occur. Impurities are deposited on the filter at a temperature of 60-69 ° C. The solubility of impurities depends on the temperature of the neutralization process. They remain in solution and then crystallize with the finished product. In the proposed process, impurities are deposited to the maximum extent on the filter; therefore, the filtrate is pure, all monopotassium phosphate is in solution and, therefore, after crystallization, the yield of the finished product significantly increases. The pH at the stage of neutralization cannot be lower than 3.8, since the desired K ₂ O content in the finished product is not maintained.

Using the proposed method allows to increase the yield of the finished product from 60-65% (according to the prototype) to 95-97%. In addition, the entire mother liquor obtained after the crystallization step is returned to the process. The amount of sediment remaining on the filter depends on the amount of phosphoric acid and does not exceed 5% by weight of the finished product, therefore, there is no waste in production except this solid residue.

The method is illustrated by the following examples.

Example 1. In the reactor load 2.5 tons of a solution of K ₂ CO ₃ with a concentration of 20% K ₂ CO ₃ and 1290 kg of a solution of orthophosphate acid with a concentration of 55% H ₃ PO ₄ . The neutralization reaction is carried out with stirring to a pH of 3.8, at a temperature of 70 ° C. In this case, a solution of monopotassium phosphate with a mass fraction of 27% KH ₂ PO ₄ and a precipitate of insoluble impurities (FePO ₄ , AlPO ₄ , KF, K ₂ SiF ₆ ) in the amount of 3.1 kg are obtained, which is separated on a filter at a temperature of 60 ° C. Next, a clean solution of monopotassium phosphate is evaporated to a mass fraction of 40% KH ₂ PO ₄ , cooled to a temperature of 20 ° C. The precipitated crystals are separated and dried. It turns out 650 kg of monopotassium phosphate and 1800 kg of a mother liquor containing 18.5% KH ₂ PO ₄ , from which 300 kg of monopotassium phosphate are additionally isolated. The total yield of the product will be 96.4%.

Example 2. 1800 kg of mother liquor with a concentration of 18.5% KH ₂ PO ₄ , 338 kg of potash and 350 kg of water are loaded into the reactor. The resulting solution was neutralized with 960 kg of phosphoric acid with a concentration of 50% H ₃ PO ₄ . The reaction temperature is 75 ° C, pH 4.1. This results in a solution of monopotassium phosphate with a mass fraction of 30% KH ₂ PO ₄ and a precipitate of insoluble impurities in the amount of 2.8 kg, which is separated on the filter at a temperature of 65 ° C. Next, a clean solution of monopotassium phosphate is evaporated to a mass fraction of 40% KH ₂ PO ₄ , cooled to a temperature of 20 ° C. The precipitated crystals are separated and dried. The mother liquor is returned to the stage of preparation of the potash solution. Received 650 kg of monopotassium phosphate, 1830 kg of a mother liquor containing 18% KH ₂ PO ₄ . The total yield of the product was 97.0%.

Example 3. In the reactor load 2.5 tons of a solution of K ₂ CO ₃ with a concentration of 16% K ₂ CO ₃ and 1034.5 kg of a solution of phosphoric acid with a concentration of 55% H ₃ PO ₄ . The process is carried out with stirring, a temperature of 78 ° C and a pH of 4.5. In this case, a solution of monopotassium phosphate is formed with a mass fraction of 23% KH ₂ PO ₄ and a precipitate of 4.8 kg, which is separated on the filter at a temperature of 69 ° C. Next, a pure solution of monopotassium phosphate is evaporated to a mass fraction of 40% KH ₂ PO ₄ , cooled, the precipitated crystals are separated and dried. It turns out 550 kg of monopotassium phosphate and 1400 kg of a mother liquor containing 17% KH ₂ PO ₄ . The total yield of the product will be 95%.

Claims (2)

1. The method of producing monopotassium phosphate, including the neutralization of phosphoric acid with potassium carbonate to a pH of not higher than 4.5 at an elevated temperature, separation of the mixture by filtration, followed by crystallization and separation of the finished product upon cooling, characterized in that the potassium carbonate is taken in the form of an aqueous solution with a concentration required to obtain 23-30% monopotassium phosphate in a neutralized mixture, the neutralization process is carried out at a temperature of 70-78 ° C, and the mother liquor after separation of the finished product at the crystalline stage ization is recycled to the stage of dissolution of potassium carbonate. 2. The method according to claim 1, characterized in that the stage of neutralization is carried out to pH = 3.8-4.5.