KR102378525B1 - Method of preparing potassium sulfate - Google Patents

Abstract

A method for producing potassium sulfate, comprising the steps of: preparing potassium chloride and sulfuric acid; reacting after adding the potassium chloride and sulfuric acid to an alcoholic solvent; and precipitating the potassium sulfate produced by the reaction into a solid phase; may provide a method for producing potassium sulfate comprising.

Description

Method for producing potassium sulfate {METHOD OF PREPARING POTASSIUM SULFATE}

It relates to a method for producing potassium sulfate.

Potassium sulfate may have a colorless, odorless monoclinic structure or an othorhombic structure of β phase. In addition, it may undergo a phase transition to the α phase at 583° C. or higher.

Unlike sodium sulfate, it does not form a hydrate form unlike sodium sulfate, and its solubility is high at about 25° C. at 120 g/L. Other physical properties The density of the state is 2.66g/cm ³ , and the melting point is 1,069℃.

As a method for producing potassium sulfate, hydrochloric acid and potassium sulfate are generally obtained by reacting with sulfuric acid in a method similar to the LeBlanc method.

[Formula 1]

2 KCl + H ₂ SO ₄ -> 2 HCl + K ₂ SO ₄ (1)

Potassium sulfate also has high solubility, so it is all dissolved in the generated hydrochloric acid, and distillation is used to separate it. Since the distillation method concentrates hydrochloric acid, there is a problem of equipment corrosion.

The second method is the Hargreaves process, where SO ₂ and oxygen are reacted, potassium sulfate is produced using water and KCl as starting materials, and hydrochloric acid is evaporated. This method has problems of stability and economic feasibility.

An object of the present invention is to provide a method capable of economically producing potassium sulfate.

As mentioned above, a representative starting material for preparing potassium sulfate is potassium chloride.

The main source of such potassium chloride is brine, and various substances other than potassium can be extracted from this brine.

A typical material is lithium, which is an energy element. Lithium is extracted from brine, and the brine from which lithium is extracted has the highest content of potassium after sodium. The representative precipitated salt of potassium is potassium chloride, and the company that produces potassium chloride from brine is Chile SQM.

Potassium chloride is not produced in Korea and is imported in full. The import volume in 2008 was about 650,000 tons, about 340,000 tons in 2009, about 540,000 tons in 2010, and about 730,000 tons in 2011, increasing by an average of 3.5% annually.

Table 1 below is a component of the Argentine Pozuelos brine, with a potassium content of 10 g per liter, when converted to potassium chloride, about 29 g/L is dissolved.

element Na K Li Ca Mg S B Cl Concentration (g/L) 118 9.54 0.799 2.15 3.21 0.988 0.464 205.7

Based on the production of 10,000 tons of lithium carbonate, the amount of brine to be treated is 2.5 million tons, and about 500,000 m ³ of brine is required in the section where potassium chloride is precipitated, where 50 g/L (concentrated concentration) of potassium per liter is precipitated as potassium chloride Therefore, about 70,000 tons can be produced.

If the scale of lithium carbonate is 20,000 tons, it is 140,000 tons, which is 19% of the annual domestic potassium chloride import (73 thousand tons, 430 billion won), and has an import substitution effect of 81.7 billion won.

In brine, potassium chloride and sodium chloride are generally precipitated simultaneously. In order to separate them, a flotation method can be used. The flotation method is a method of selectively suspending potassium compounds using a surfactant such as SDS.

As described above, in the related art, potassium sulfate was prepared by reacting potassium chloride and sulfuric acid in an aqueous system. However, this has a major problem in the treatment of hydrochloric acid as a by-product.

Accordingly, in one embodiment of the present invention, a method of changing the solvent was applied. To convert potassium chloride to potassium sulfate, an acid called sulfuric acid must be used. However, when potassium chloride is dissolved in water and sulfuric acid is added according to the molar ratio, potassium sulfate is dissolved as in the case of reacting with hydrochloric acid, and potassium sulfate powder can be obtained only through distillation of hydrochloric acid.

Potassium sulfate is insoluble in alcoholic solvents, and sulfuric acid and hydrochloric acid are soluble in alcohol. Therefore, when the solvent is changed to alcohol, the potassium sulfate produced by the added sulfuric acid will be extracted as a salt, and the chlorine ion of potassium chloride decomposed by the sulfuric acid will become hydrochloric acid and dissolved in the alcohol.

The alcohol in which the hydrochloric acid is dissolved is distilled and reused, and the remaining substance after the alcohol is distilled becomes an aqueous hydrochloric acid solution. The aqueous hydrochloric acid solution may also contain unreacted potassium ions.

In conclusion, there is an advantage in that potassium sulfate and hydrochloric acid of high purity can be obtained without secondary contamination because another cation is not input to convert potassium chloride to potassium sulfate as shown in Chemical Formula 2 below.

[Formula 2]

In solvent system: 2KCl _(s) + Alcohol _(aq) + H ₂ SO _{4 (aq)} -> K ₂ SO ₄ (s) + 2HCl _(aq)

That is, in one embodiment of the present invention, preparing potassium chloride and sulfuric acid; reacting after adding the potassium chloride and sulfuric acid to an alcoholic solvent; and precipitating the potassium sulfate produced by the reaction into a solid phase; may provide a method for producing potassium sulfate comprising.

In the step of preparing the potassium chloride and sulfuric acid, the concentration of the sulfuric acid may be 10 to 20 g / L. When the concentration of sulfuric acid exceeds the appropriate range, potassium chloride is not sufficiently dissolved in the solution, so that the reaction is difficult to proceed.

When the concentration of sulfuric acid is lower than the appropriate range, potassium sulfate produced due to water contained in the sulfuric acid solution is dissolved again, and potassium sulfate cannot be obtained as a solid phase.

In the step of reacting after adding the potassium chloride and sulfuric acid to the alcoholic solvent, with respect to 100% by volume of the total reaction solution, the alcohol-based solvent may be 30% by volume or more. More specifically, it may be 60% by volume or more, and may be 90% by volume or less.

When the content of the alcohol-based solvent is increased, it is possible to increase the extraction efficiency of potassium sulfate. However, the economical efficiency is reduced due to the increase in the cost of the alcohol-based solvent.

Precipitating the potassium sulfate produced by the reaction into a solid phase; Thereafter, the method may further include separating the alcohol-based solvent in the residual filtrate. This may be performed by a fractional distillation method, and may be separated by distilling an alcoholic solvent.

The filtrate remaining at this time is an aqueous solution containing hydrochloric acid and potassium.

Separating the alcohol-based solvent in the residual filtrate; by, the alcohol-based solvent is separated filtrate can be reused as raw materials for potassium chloride and sulfuric acid in the step of preparing the potassium chloride and sulfuric acid.

The alcohol-based solvent may be methanol, ethanol, propanol, butanol, or a combination thereof. The present invention is not limited to the above-mentioned alcohol types, and any alcoholic solvent having a low solubility in potassium sulfate and a relatively high solubility in potassium chloride may be applied to the present invention.

It is possible to provide a process for the direct conversion of potassium chloride to potassium sulfate. The process can be shortened and high purity can be achieved, thereby securing economic feasibility.

The used solvent can be recovered in a reusable state.

The purity of the reaction product, potassium sulfate, can be 95% or more, and the conversion rate from lithium chloride to lithium sulfate can be 80%.

1 and 2 are XRD component analysis results of the salt extracted after the reaction according to an embodiment of the present invention.
3 is a graph showing the results of component analysis in the filtrate after the reaction according to the dilution ratio of sulfuric acid.
4 is a schematic diagram of an alcohol solvent recovery experiment.

Hereinafter, with reference to the accompanying drawings, various embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. The present invention may be embodied in many different forms and is not limited to the embodiments/embodiments described herein.

experimental method

As a specific experimental method, first, using 30 ml of alcohol as a solvent, 18.82 g of KCl was added and stirred. At this time, DAEJUNG Hwageum Ethyl alcohol 94.5%, KCl was DAEJUNG Hwageum Potassium Chloride, and 99% of Extra Pure grade was used for the alcohol.

Next, dilute sulfuric acid is prepared by concentration to determine the reactivity according to the concentration of sulfuric acid. The concentration of sulfuric acid is 10%, 15%, 20%, 30%, 40%, 50%, and 70%.

The % concentration described in this example means g/L.

The sulfuric acid used at this time was a 70% solution of Sulfuric Acid manufactured by SAMCHUN Chemicals.

To prepare sulfuric acid by concentration, 70% sulfuric acid is mixed with deionized water to prepare a target concentration. For concentration 10% sulfuric acid, dilute 7.43ml of 70% sulfuric acid in 73.56ml of deionized water. For concentration of 15% sulfuric acid, dilute 7.43ml of 70%sulfuric acid in 44.95ml of deionized water. For concentration of 20% sulfuric acid, dilute 7.43ml of 70% sulfuric acid in 30.65ml of deionized water. ml, dilute 7.43 ml of 70% sulfuric acid in 16.34 ml of deionized water for 30% sulfuric acid, and 7.43 ml of 70% sulfuric acid in 9.20 ml of deionized water for 40% sulfuric acid. It is prepared by diluting 7.43 ml of 70% sulfuric acid.

To check the reactivity of each sulfuric acid concentration, prepare 7 slurries prepared by mixing alcohol solvent and KCl.

order of experiment

KCl 18.82g + Ethyl alcohol 30ml Stir for 30 minutes. After that, each concentration of sulfuric acid prepared by concentration is added to the solution slurry No. 1 for each concentration.

After stirring for 1 hour, filtration is carried out, and the concentration of each filtrate and the mineral phase of the solid precipitate are analyzed.

By determining the concentrations of K and S in the filtrate, the conversion rate of K ₂ SO ₄ in KCl in an alcohol solvent can be determined, and additional mineral phase analysis is performed to determine what type of solid precipitate unconverted KCl remains.

sulfuric acid according to concentration K2SO4 Conversion rate change result

Table 2 below shows the ICP analysis results for the concentrations of K and S in the filtrate. As can be seen from the results, it can be seen that the higher the dilution factor of sulfuric acid, the lower the concentration of S and the higher the concentration of K.

A low concentration of S means a large amount of dissolved amount in the solution, which means that KCl is dissolved in large numbers as the dilution ratio of sulfuric acid in the alcohol solvent is low, and it can be seen that conversion to K ₂ SO ₄ is easy.

However, a high dilution ratio means that the amount of DI water is large, so conversion to K ₂ SO ₄ is easy, but the resulting potassium sulfate is dissolved again in water, so the conversion rate may suffer somewhat. Accordingly, the K concentration in the filtrate under the condition of low sulfuric acid concentration is high.

In addition, in 5% sulfuric acid, the amount of water is relatively higher than that of insoluble alcohol, so K ₂ SO ₄ does not precipitate but appears to be dissolved in water as it is.

[Table 2]

1 and 2 are XRD component analysis results of the salt extracted after the reaction according to an embodiment of the present invention.

As a result of XRD mineral phase analysis, in a solution with a high concentration of sulfuric acid, a substance formed in a solution with a high concentration of hydrogen ions of unreacted KCl and K ₃ H(SO ₄ ) ₂ K(HSO ₄ ) was generated, but K ₂ SO ₄ was not generated. However, at 20% where the sulfuric acid concentration was lowered, it was confirmed that K ₂ SO ₄ was started to be formed, and a single phase of K ₂ SO ₄ was confirmed in 10% sulfuric acid as shown in FIG. 2 .

3 is a graph showing the results of component analysis in the filtrate after the reaction according to the dilution ratio of sulfuric acid.

The higher the sulfuric acid concentration, the higher the S concentration in the solution, which indicates that potassium sulfate was not obtained, and it was determined that KCl and sulfuric acid were in a slurry state together in the solution. This is also consistent with the XRD results.

As the sulfuric acid concentration was lower than 50%, potassium sulfate was produced as the concentration of S was lowered, but K ₃ H(SO ₄ ) ₂ and K(HSO ₄ ) were generated in small amounts in the acidic solution, as a result of XRD phase analysis. matches with

However, the XRD phase analysis result is shown in FIG. 2 that the generation of K ₂ SO ₄ started from 20% of the sulfuric acid concentration and a single phase was obtained in 10% diluted sulfuric acid.

That is, when the concentration of sulfuric acid is high (the dilution ratio of sulfuric acid is low), KCl remains insoluble in the acidic solution and it is judged that the _K concentration in the solution is low. ₄ was precipitated as solubility was lowered by ethanol.

After that, at low sulfuric acid concentration, it was re-dissolved in DI water and the reaction occurred as in general water, and all dissolved and the target product was not obtained.

If the amount of the organic solvent added to this solution is increased, it is expected that the desired product will be precipitated, but since it is not so desirable in consideration of economic feasibility, it was decided not to proceed with the additional test.

However, the conversion rate from potassium chloride to potassium sulfate was 65.7%, which was rather low at 37% by volume of the amount of the alcohol solvent input compared to the reaction solution.

Therefore, as an additional experiment, the alcohol solvent was increased to 62% by volume (50ml) relative to the volume of the reaction solvent, and the experiment was carried out.

As a result, as the amount of alcohol solvent increased, the ratio of the total solvent insoluble state increased, so that K ₂ SO ₄ dissolved in water was additionally precipitated.

The 10% sulfuric acid alcohol 37% by volume (30ml) experiment showed a conversion rate of 65.7% and the purity was 98.6% after washing, and the 62% alcohol (50ml) experiment showed a conversion rate of 84.3% and a purity of 96.4%. there was.

alcohol recovery experiment

The recovery method of alcohol used as a solvent was tested based on fractional distillation. The main impurities in the alcohol used for KCl conversion are K, Cl, and S. Table 3 shows the ICP analysis results of alcohol before recovery.

[Table 3]

* Components of alcohol before recovery (unit g/L)

In 500 ml of alcohol containing K, Cl, and S, 350 ml of water and 150 ml of ethanol, which were actually used for diluting sulfuric acid, are present.

Therefore, during fractional distillation, water must remain as it is, and only alcohol evaporates and must be recovered by distillation. Considering that the boiling point of water is 100°C and the boiling point of ethanol is 78°C, the pressure was reduced to 350 mbar at a temperature of about 80°C.

In addition, since the amount of water contained in ethanol was 350 ml, the pressure was carried out until the concentration of the concentrated solution became 350 ml, and in fact, it was observed that the concentrated solution was maintained without evaporating any more at 350 ml.

That is, it was found that ethanol was evaporated under reduced pressure evaporation conditions of 80° C. and 350 mbar, but water was not evaporated. A schematic diagram of the experiment performed by the above method is shown in FIG. 4 as follows.

After the final vacuum evaporation experiment, the amount of concentrated water was 350 ml, and the amount of distilled ethanol was 150 ml. At this time, the ICP chemical composition analysis results are shown in Table 4.

[Table 4]

* Unit g/L

That is, when converting K ₂ SO ₄ , the entire amount of alcohol used as an organic solvent can be recovered, and the amount of impurities in ethanol is K (<0.0003 g/L), Cl (0.028 g/L), S (<0.0003 g/L) As such, it can be judged that it can be reused.

The present invention is not limited to the above embodiments and/or embodiments, but may be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains may change the technical spirit or essential features of the present invention It will be understood that the present invention may be implemented in other specific forms without not doing so. Therefore, it should be understood that the embodiments and/or embodiments described above are illustrative in all respects and not restrictive.

Claims (10)

preparing potassium chloride and sulfuric acid;
reacting after adding the potassium chloride and sulfuric acid to an alcoholic solvent; and
precipitating the potassium sulfate produced by the reaction into a solid phase;
including,
In the step of preparing the potassium chloride and sulfuric acid;
A method for producing potassium sulfate, wherein the concentration of sulfuric acid is 10 to 15 g / L.
delete The method of claim 1,
In the step of reacting after adding the potassium chloride and sulfuric acid to the alcohol solvent;
With respect to 100% by volume of the total reaction solution, the alcohol-based solvent is a method for producing potassium sulfate that is 30% by volume or more.
The method of claim 1,
Precipitating potassium sulfate produced by the reaction into a solid phase;
Method for producing potassium sulfate further comprising the step of separating the alcoholic solvent in the residual filtrate.
5. The method of claim 4,
Separating the alcohol-based solvent in the residual filtrate; by,
A method for producing potassium sulfate wherein the filtrate from which the alcohol-based solvent is separated is reused as raw materials for potassium chloride and sulfuric acid in the step of preparing the potassium chloride and sulfuric acid.
5. The method of claim 4,
Separating the alcohol-based solvent in the residual filtrate;
A process for the production of potassium sulfate, which is carried out for fractional distillation.
The method of claim 1,
The alcohol-based solvent is methanol, ethanol, propanol, butanol, or a combination thereof.
The method of claim 1,
The method for producing potassium sulfate, wherein the potassium chloride is extracted from a solution containing lithium.
9. The method of claim 8,
The method for producing potassium sulfate that the solution containing lithium is brine.
10. The method of claim 9,
The potassium chloride is a method for producing potassium sulfate that is obtained by separation by flotation of sodium chloride and potassium chloride extracted from brine.

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