KR20180135742A - Method of preparing potassium sulfate - Google Patents

Abstract

The present invention relates to a method for preparing potassium sulfate, and specifically, provides a method for preparing potassium sulfate, which comprises the following steps: preparing potassium chloride and sulfuric acid; adding the potassium chloride and sulfuric acid to an alcoholic solvent and reacting the mixture; and precipitating the potassium sulfate prepared by the reaction in a solid phase.

Description

METHOD OF PREPARING POTASSIUM SULFATE < RTI ID = 0.0 >

To a process for producing potassium sulfate.

Potassium sulfate may have a colorless odorless monoclinic structure, or it may have an othorhombic structure that is a β-state. Phase transition from 583 DEG C or higher to the? Phase.

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

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

[Chemical Formula 1]

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

Potassium sulfate also dissolves in the generated hydrochloric acid because of its high solubility, and the distillation method is used to separate it. The distillation method has a corrosion problem due to the concentration of hydrochloric acid.

The second method involves reacting SO ₂ with oxygen in a Hargreaves process, producing potassium sulfate as a starting material with water and KCl, and evaporating hydrochloric acid. These methods have stability and economical problems.

Economically, it is intended to provide a method for producing potassium sulfate.

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

The main source of this potassium chloride is saline, and various substances besides potassium can be extracted in such brine.

A representative material is lithium, an energy element. The salty water from which lithium is extracted from the brine is high in potassium after sodium. The representative precipitation salt of potassium is potassium chloride, and the company that produces potassium chloride in brine is currently Chile SQM.

Potassium chloride is not produced domestically and all of it is imported. In 2008, the import volume was about 650,000 tons. In 2009, about 340,000 tons and 2010 about 540,000 tons, about 730,000 tons, an annual average of 3.5%.

Table 1 below shows the Pozuelos salt component of Argentina, which contains 10 grams of potassium per liter and 29 grams per liter of potassium chloride.

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 treated salt yield is 2.5 million tons, and the salted water in the section where the potassium chloride is precipitated requires about 500,000 m ³ , wherein 50 g / L (concentrated concentration) of potassium is precipitated as potassium chloride Therefore, about 70,000 tons can be produced.

If it is 20,000 tons of lithium carbonate, it is 140,000 tons, which is 19% of the annual imports of potassium chloride (730,000 tons, 430 billion won) and 81.7 billion won in import substitution effect.

In salt water, potassium chloride and sodium chloride are generally precipitated at the same time. To separate them, the barge method can be used. The flotation method is a method of selectively suspending a potassium compound using a surfactant such as SDS.

As described above, conventionally, potassium sulfate and sulfuric acid were reacted with an aqueous system to prepare potassium sulfate. However, this has a great problem in the treatment of hydrochloric acid, which is a by-product.

In one embodiment of the present invention, a method of changing the solvent is applied. To call potassium sulfate from potassium chloride, an acid called sulfuric acid should be used. However, when potassium chloride is dissolved in water and sulfuric acid is added in the molar ratio, potassium sulfate is dissolved as in the case of reacting with hydrochloric acid, and potassium sulfate powder can be obtained only by distillation of hydrochloric acid.

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

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

In conclusion, since potassium chloride is converted into potassium sulfate as shown in the following chemical formula 2, since no other cation is added, there is no secondary contamination and potassium sulfate and hydrochloric acid of high purity can be obtained.

(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, there is provided a method comprising: preparing potassium chloride and sulfuric acid; Adding the potassium chloride and sulfuric acid to an alcoholic solvent and then reacting; And a step of precipitating potassium sulfate produced by the reaction in a solid phase.

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

When the concentration of sulfuric acid is lower than the appropriate range, the potassium sulfate produced by the water contained in the sulfuric acid solution is dissolved again, so that potassium sulfate can not be obtained in a solid phase.

In the step of adding the potassium chloride and sulfuric acid to the alcohol-based solvent and then reacting, the alcohol-based solvent may be at least 30% by volume based on 100% by volume of the total reaction solution. More specifically, it may be at least 60 vol.%, And may be at most 90 vol.%.

As the content of alcoholic solvent increases, the extraction efficiency of potassium sulfate can be increased. However, the economic cost is reduced due to the increase in the cost of the alcoholic solvent.

Precipitating potassium sulfate produced by the reaction in a solid phase, and then separating the alcohol-based solvent in the residual filtrate. This can be carried out by a fractional distillation method, and the alcoholic solvent can be separated by distillation.

The remaining filtrate is an aqueous solution containing hydrochloric acid, and potassium.

And separating the alcohol-based solvent in the residual filtrate, the filtrate from which the alcohol-based solvent has been separated can be reused as the potassium chloride and sulfuric acid raw material 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 species, and any alcohol-based solvent having a low solubility for potassium sulfate and a relatively high solubility for potassium chloride can be applied to the present invention.

It is possible to provide a process capable of directly converting potassium chloride to potassium sulfate. The process can be shortened and high purity can be achieved, thereby ensuring economical efficiency.

The used solvent can be recovered in a reusable state.

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

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

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled 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, firstly, 18.82 g of KCl is added using 30 ml of alcohol as a solvent and stirred. Ethyl alcohol was used in 94.5% of DAEJUNG alcohol, KCl was used in DAEJUNG Potassium Chloride and 99% of Extra Pure grade was used for alcohol.

Next, diluted sulfuric acid is prepared for each concentration to understand the reactivity depending on the sulfuric acid concentration. The concentration of sulfuric acid is 10%, 15%, 20%, 30%, 40%, 50% and 70%.

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

Sulfuric acid 70% solution of SAMCHUN chemical was used for sulfuric acid.

For the production of sulfuric acid by concentration, the desired concentration is prepared by mixing Deionized water with 70% sulfuric acid. Concentrated 10% sulfuric acid was diluted with 73.56 ml of 70% sulfuric acid in 7.45 ml of deionized water, diluted with 44.95 ml of 15% sulfuric acid and 7.43 ml of 70% sulfuric acid to a concentration of 20% sulfuric acid. dilute 70% sulfuric acid (7.43 ml) with 40% sulfuric acid in 16.34 ml of deionized water. Dilute 7.43 ml of 70% sulfuric acid in 9.20 ml of 40% sulfuric acid and add 4. 504 ml of concentrated sulfuric acid to 4.904 ml of deionized water. It is prepared by diluting 7.43 ml of 70% sulfuric acid.

Prepare seven slurries containing a mixture of KCl and an alcohol solvent prepared to measure the reactivity of each sulfuric acid concentration.

order of experiment

KCl 18.82g + Ethyl alcohol 30ml The mixture is stirred for 30 minutes. Then, the sulfuric acid prepared for each concentration is added to each slurry of the solution one by one.

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

By analyzing the K and S concentrations in the filtrate, the conversion of K ₂ SO _{4 to} KCl in the alcohol solvent can be grasped, and furthermore the mineral phase analysis can be performed to find out what type of solid precipitate remains unconverted KCl.

Sulfuric acid Depending on concentration K2SO4  Conversion rate change result

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

The low concentration of S means that the amount of dissolved KCl in the solution is large, which means that the lower the dilution ratio of sulfuric acid in the alcohol solvent, the more the KCl is dissolved, and the conversion to K ₂ SO ₄ is easy.

However, the high dilution factor suggests that the conversion of K ₂ SO ₄ into K ₂ SO ₄ is easy due to the high input of DI water, but the resulting potassium sulfate is dissolved again in water and the conversion is somewhat detrimental. As a result, the concentration of K in the filtrate is high at a low sulfuric acid concentration.

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

 [Table 2]

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

XRD mineral analysis showed that K ₂ Cl ₂ and K ₃ H (SO ₄ ) ₂ K (HSO ₄ ) were produced in solution with high hydrogen ion concentration and K ₂ SO ₄ was not produced in solution with high concentration of sulfuric acid. However, in the 20% that the sulfuric acid concentration decreases was confirmed that K ₂ SO ₄ in a single-phase 10% sulfuric acid, as shown in Figure 2 could be confirmed that the K ₂ SO ₄ is started to generate.

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

The higher the sulfuric acid concentration, the higher the S concentration in the solution, and it is considered that potassium sulfate was not obtained, and it is judged that KCl and sulfuric acid are in a slurry state together in the solution. This is consistent with the XRD results.

As the sulfuric acid concentration was lower than 50%, the concentration of S was lowered to produce potassium sulfate, but due to the small amount of K ₃ H (SO ₄ ) ₂ and K (HSO ₄ ) produced in the acid solution, the XRD phase analysis .

However, the production of K ₂ SO ₄ from a sulfuric acid concentration of 20% was started and a single phase was obtained in 10% diluted sulfuric acid. The results of XRD analysis are shown in FIG.

That is, higher the sulfuric acid concentration (low dilution of the sulfuric acid), in an acidic solution, and it is determined that the low-K concentration of KCl is left not melted solution, the lower the sulfuric acid concentration of KCl Thereafter as the dissolution reaction and the sulfuric acid and the reaction K ₂ SO ₄ was precipitated as the solubility was lowered by ethanol.

Then, at low sulfuric acid concentration, the reaction took place as it was reused in DI water and reacted as in the case of general water, and all of them were dissolved and the desired product could not be obtained.

If the amount of organic solvent is increased in this solution, it is expected that the desired product will be precipitated. However, it is not preferable considering economical efficiency.

However, the conversion rate of potassium alcohol to potassium sulfate was somewhat low at 37% by volume in terms of the volume ratio of the charged alcohol solvent to the reaction solution.

Therefore, the experiment was carried out by increasing the alcohol solvent to 62 vol% (50 ml) relative to the volume of the reaction solvent.

As a result, the amount of K ₂ SO ₄ dissolved in the water was further increased by increasing the ratio of the total solvent to the insoluble state as the amount of the alcohol solvent increased.

Concentration of alcohol was 62.7% (50ml) and the conversion rate was 84.3% and the purity was 96.4%. In the experiment, alcohol content of 10% sulfuric acid 37 vol% there was.

Alcohol recovery experiment

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

[Table 3]

* Ingredients 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 were actually present in sulfuric acid dilution.

Therefore, water must remain as it is in fractional distillation, and only alcohol should be evaporated and recovered by distillation. Considering that the boiling point of water is 100 ° C and the boiling point of ethanol is 78 ° C, the decompression is carried out at a temperature of about 80 ° C to 350 mbar.

Since the amount of water contained in ethanol is 350 ml, the pressure was reduced until the concentration of the concentrate became 350 ml. In fact, the concentrate was maintained at 350 ml without further evaporation.

In other words, it was found that the ethanol evaporated under the reduced pressure of 80 mV and 350 mbar, but the water was not evaporated. The schematic diagram of the experiment 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. The results of the ICP chemical composition analysis are shown in Table 4.

[Table 4]

* Unit g / L

That is, the total amount of alcohol used as an organic solvent in the conversion of K ₂ SO ₄ can be recovered and the amounts of impurities in the ethanol are K (<0.0003 g / L), Cl (0.028 g / It can be judged that re-use is possible.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims and their equivalents. It will be understood that the invention may be embodied in other specific forms without departing from the spirit or scope of the invention. It is therefore to be understood that the embodiments and / or the examples described above are illustrative in all aspects and not restrictive.

Claims (10)

Preparing potassium chloride and sulfuric acid;
Adding the potassium chloride and sulfuric acid to an alcoholic solvent and then reacting; And
Precipitating potassium sulfate produced by the reaction in a solid phase;
&Lt; / RTI &gt;
The method according to claim 1,
Preparing said potassium chloride and sulfuric acid,
And the concentration of sulfuric acid is 10 to 20 g / L.
The method according to claim 1,
Adding the potassium chloride and sulfuric acid to the alcoholic solvent and then reacting,
Wherein the alcoholic solvent is at least 30% by volume based on 100% by volume of the total reaction solution.
The method according to claim 1,
Precipitating potassium sulfate produced by the reaction in a solid phase,
And separating the alcohol-based solvent in the residual filtrate.
5. The method of claim 4,
Separating the alcohol-based solvent in the residual filtrate,
Wherein the filtrate from which the alcoholic solvent has been separated is recycled as the potassium chloride and sulfuric acid raw materials in the step of preparing the potassium chloride and sulfuric acid.
5. The method of claim 4,
Separating the alcoholic solvent in the residual filtrate,
&Lt; / RTI &gt; is carried out for fractional distillation.
The method according to claim 1,
Wherein the alcohol-based solvent is methanol, ethanol, propanol, butanol, or a combination thereof.
The method according to claim 1,
Wherein the potassium chloride is extracted from a solution containing lithium.
9. The method of claim 8,
Wherein the solution containing lithium is brine.
10. The method of claim 9,
Wherein the potassium chloride is obtained by separating by distillation of sodium chloride and potassium chloride extracted from brine.

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