METHOD FOR PROCESSING HEXAFLUOROSILICIC ACID TO PRODUCE HYDROGEN FLUORIDE

Abstract

This patent relates to the byproduct recovery of mineral raw materials in the chemical industry, namely, processing aqueous solutions of hexafluorosilicic acid (HSA) formed specifically during the process of producing phosphoric acid with hydrogen fluoride (HF). This method consists of neutralizing an aqueous solution of HSA with an alkaline agent to produce ammonium fluoride and subsequently combusting it in a fire of an oxygen-containing oxidant and a hydrogen-containing fuel. It is characterized by the alkaline neutralization, which occurs in two stages. In the first stage, the aqueous hexafluorosilicic acid solution is neutralized with an alkaline agent to obtain a suspension of the correspondent hexafluorosilicate in water, after which the water is removed from the suspension. In the second stage, solid hexafluorosilicate is treated with an ammonia-containing agent to produce an aqueous solution of ammonium fluoride. Its solid products are filtered, then the aqueous ammonium fluoride solution is burned in an oxygen-containing oxidant. Hydrogen fluoride and water are condensed from the combustion products, and then the hydrogen fluoride is extracted. The technical result achieved by applying the proposed patent consists in the reduction of energy costs due to the removal of water, which is introduced into the process cycle with the hexafluorosilicic acid, by way of synthesizing a intermediate hexafluorosilicate poorly soluble in water, then crystallizing and separating it from water through filtration, centrifugation or any other method that leads to a significant reduction in energy consumption at the stage of separating water from ammonium bifluoride in the evaporator. 1 independent claim, 2 dependent claims, 1 FIGURE.

Claims

1. This method of processing hexafluorosilicic acid to produce hydrogen fluoride consists of neutralizing an aqueous solution of HSA with an alkaline agent to produce ammonium fluoride and subsequently combusting it in a fire of an oxygen-containing oxidant and a hydrogen-containing fuel. It is characterized by the alkaline neutralization, which occurs in two stages. In the first stage, the aqueous hexafluorosilicic acid solution is neutralized with an alkaline agent to obtain a suspension of the corresponding hexafluorosilicate in water, after which the water is removed from the suspension. In the second stage, solid hexafluorosilicate is treated with an ammonia-containing agent to produce an aqueous solution of ammonium fluoride. Its solid products are filtered, then the aqueous ammonium fluoride solution is burned in an oxygen-containing oxidant. Hydrogen fluoride and water are condensed from the combustion products, and then the hydrogen fluoride is extracted.

2. The method in claim 1 is characterized by the use of ammonia or ammonia water as the ammonia-containing agent.

3. The method in claim 1 is characterized by the ammonium fluoride solution being preliminarily subjected to evaporation and the resulting ammonium bifluoride being sent to combustion in an oxygen-containing oxidant.

Description

EXAMPLES OF METHOD APPLICATION

Example 1

[0036] A typical waste from the production of phosphoric acid using extraction method is a 20.5% aqueous solution of HSA, which is fed into reactor 1 in the amount of 3.51 kg. With vigorous mixing, 0.8 kg of an aqueous solution of 50% NaOH is channeled into the same apparatus. The temperature in reactor 1 is maintained at 25° C. Reactor 1 discharges 4.31 kg of a suspension of sodium hexafluorosilicate in water to phase separator 2, which is a filter that separates 1.1 kg of solid sodium hexafluorosilicate from 3.21 kg of filtrate.

[0037] The solid salt is dispensed into amination reactor 3, where it is continuously mixed with 0.37 kg of ammonia gas and 0.96 kg of water, which are also fed to the reactor, forming silicon dioxide, sodium fluoride and ammonium fluoride.

[0038] The obtained suspension of silicon dioxide, calcium fluoride and ammonium fluoride solution is channeled into filter 4, where 0.85 kg of the solid amination products are separated from 1.98 kg of ammonium fluoride solution. To remove the ammonium fluoride solution residue from the precipitate, it is washed once with 0.4 kg of hot water. Next, the ammonium fluoride solution is directed to tunnel burner type reactor 5 at a flowrate of 157 mg/s through a pneumatic nozzle. Oxygen at a flowrate of 71 mg/s and methane at a flowrate of 10 mg/s are also fed to the reactor, forming a mixture of hydrogen fluoride, nitrogen and water. Next, the hydrogen fluoride and water mixture is sent to liquid phase separation unit 6, where it is separated from the non-condensable combustion products. Next, the mixture of HF and water is sent to water separation unit 7 to remove the water. This unit is a reactor, into which 98% sulfuric acid is fed in addition to the water-containing product, which produces HF, with a residual 0.02% water content and 75% sulfuric acid in the amount 28 kg per 1 kg of HF.

[0039] Therefore, the water in the HSA solution was removed by filtration, rather than evaporation, which created no energy costs for evaporating the solutions. The overall energy consumption was lowered by more than twice.

Example 2

[0040] In neutralization reactor 1, 3.45 kg of 45% aqueous HSA solution, with continuous mixing, is neutralized with 0.561 kg of CaO. Next, 4.01 kg of calcium hexafluorosilicate suspension is discharged from reactor 1 and sent to filter 2, where 1.888 kg of calcium hexafluorosilicate is separated from 2.123 kg of filtrate.

[0041] Therefore, the water in the HSA solution was removed by filtration, rather than evaporation.

[0042] The solid salt is dispensed into amination reactor 3, where it is continuously mixed with 0.356 kg ammonia gas and 2.176 kg of 25% aqueous ammonia solution, forming silicon dioxide, calcium fluoride and ammonium fluoride.

[0043] The obtained suspension of silicon dioxide, calcium fluoride and ammonium fluoride solution is channeled into filter 4, where 1.362 kg of solid amination products are separated from 3.358 kg of ammonium fluoride solution. To remove the ammonium fluoride solution residue from the precipitate, it is washed once with 0.3 kg of hot water. Then the ammonium fluoride solution is sent to evaporator 8, where water and ammonia are stripped, and ammonium bifluoride forms.

[0044] Thus, two times less water is subjected to evaporation than in case of producing ammonium bifluoride from an aqueous solution of hexafluorosilicic acid via one stage of amination.

[0045] This pre-evaporated ammonium bifluoride is sent at a flowrate of 80 mg/s to tunnel burner type reactor 5, which also receives a 121 mg/s supply of oxygen and methane at 18 mg/s, forming a mixture of hydrogen fluoride, nitrogen and water. Next, the hydrogen fluoride and water mixture is sent to liquid phase separation unit 6 and separated from the non-condensable combustion products. Next, the mixture of HF and water is sent to water separation unit 7 to remove the water. This unit is a reactor, into which 93% sulfuric acid is fed in addition to the water-containing product, which produces HF, with a residual 0.02% water content and 75% sulfuric acid in the amount 7.34 kg per 1 kg of HF.

[0046] As evident from the data above, the issue facing the patent's authors has been resolved, namely that of creating a method of processing HSA to obtain hydrogen fluoride and making it possible to lower energy consumption of the process at the evaporation stage by at least twice.