JPH05186216A - Production of potassium sulfate and hydrochloric acid - Google Patents

Abstract

PURPOSE:To produce high-purity potassium sulfate and hydrochloric acid at a low energy cost according to a wet process in a method for producing the potassium sulfate and hydrochloric acid from sulfuric acid and potassium chloride. CONSTITUTION:(1) Sulfuric acid is made to react with a solution of potassium chloride and a potassium salt in hydrochloric acid at 60-150 deg.C to produce a solution or a slurry of potassium hydrogensulfate and hydrogen chloride. (2) Potassium chloride is added to the resultant solution or slurry of the potassium hydrogensulfate and the obtained mixture is then dissolved in water at 60-150 deg.C to carry out reaction. (3) Methanol is added to the aqueous solution of the potassium salt to deposit crystals of potassium sulfate at 60-130 deg.C and the deposited potassium sulfate is separated. (4) The separated solution is distilled to respectively circulate the methanol, water and the solution of the potassium salt in hydrochloric acid to the steps (3), (2) and (1) for use.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing potassium sulfate and hydrochloric acid by reacting potassium chloride with sulfuric acid. Most of potassium sulfate is used as a fertilizer. Potassium chloride is generally used as a potassium fertilizer, but potassium sulfate is preferably used for crops such as tobacco, spinach, and cucumber that dislike chlorine ions. Therefore,
The chlorine content standard of potassium sulfate for fertilizer is strict
It is 1.0% or less (all concentrations are% by weight). Hydrochloric acid is a major basic chemical product with a wide range of uses such as metal refining, metal acid washing, metal chloride and organic chloride production, neutralizing agent in chemical product production, and hydrolysis of proteins and carbohydrates.

[0001]

2. Description of the Related Art A method for producing potassium sulfate from potassium chloride and sulfuric acid is represented by the following formula and formula or a combination of formulas, wherein 1 mol of sulfuric acid is reacted with 2 mol of potassium chloride. Potassium sulfate and 2 mol of hydrogen chloride are obtained. K Cl + H ₂ SO ₄ → KHSO ₄ + H Cl KHSO ₄ + K Cl → K ₂ SO ₄ + H Cl 2 K Cl + H ₂ SO ₄ → K ₂ SO ₄ + 2H Cl

[0002] As an industrial manufacturing method, a dry method has been known for a long time in which stoichiometric amounts of potassium chloride and sulfuric acid are mixed, and an acid-resistant muffle furnace is used as a reactor to ignite at a high temperature of 400 to 600 ° C for a long time. Has been. In this dry method, the one-step method in which the reactions of and are carried out at once in one reactor, and the reaction of the formula is carried out near room temperature, and only the reaction of the formula is ignited at a high temperature of 400 to 500 ° C. There is a two-step method.

However, in these dry methods, the corrosion of the equipment due to the high-temperature hydrogen chloride gas generated is great, and the life of the muffle furnace is as short as 1-2 years. Further, the heat conduction from the muffle furnace to the kneaded product of potassium chloride and concentrated sulfuric acid is poor and the energy loss is large, so that a large amount of equipment cost and energy cost are required. In addition, the reaction rate is slow near the end point of the reaction due to the solid phase reaction, and it is extremely difficult to reduce the residual chlorine concentration in the product potassium sulfate to 1% or less. Furthermore, there are many problems as an industrial production method, such as decomposition gas such as SO ₂ mixed in hydrogen chloride gas due to high temperature reaction.

In contrast, US Pat. No. 4,045,543 proposes a wet method carried out in an aqueous solution in order to proceed the reaction with mild temperature conditions. However, in this method, about 10 times as much water as the product potassium sulfate has to be distilled off, the energy cost is high, and it cannot be used at all as an industrial production method. In addition, Japanese Patent Publication No.
No. 454 and JP-B No. 47-20456 describe a method of using alcohol as a crystallization agent. However, even with these methods, about 6 times as much alcohol and water as the product potassium sulfate must be distilled off.

On the other hand, Japanese Patent Publication No. 42-27246 discloses that
It is disclosed that the reaction of (1) is carried out dry and only the reaction of (2) is carried out wet. However, even with this method, 6.5 times as much water as the product potassium sulfate must be distilled off. Japanese Examined Patent Publication No. 61-4772 proposes a method in which up to 50% of the reaction of (2) is carried out by a dry method and the remaining 50% is completed by a wet method. 2.5
It has been reduced to double the amount. However, in this method, the dry reaction temperature is as high as 300 to 350 ° C., and twice the amount of the inorganic salts as the product potassium sulfate must be circulated, so that there are problems in the material and production efficiency of the apparatus.

[0006]

As described above, although a number of methods for producing potassium sulfate by a wet method have been proposed, a highly economical process superior to the dry method does not yet exist, and the method is industrially used. The current situation is that it has not been implemented.
The object of the present invention is to improve the drawbacks of the conventional dry and wet processes for producing potassium sulfate from potassium chloride and concentrated sulfuric acid as described above, to provide a highly economical potassium sulfate having a high chlorine content and a low chlorine content. To provide a manufacturing method.

[0007]

[Means for Solving the Problems] As a result of intensive studies on the method for producing potassium sulfate and hydrochloric acid from potassium chloride and sulfuric acid, the inventors of the present invention found that sulfuric acid and potassium chloride and potassium salts obtained by distillation of the reaction solution If a hydrochloric acid solution is reacted to produce potassium hydrogen sulfate and hydrogen chloride, then the obtained potassium hydrogen sulfate and potassium chloride are dissolved in water, and methanol is added to precipitate crystals of potassium sulfate. The present invention has been accomplished by finding that pure potassium sulfate and hydrochloric acid can be economically produced under mild temperature conditions.

That is, according to the present invention, in producing potassium sulfate and hydrochloric acid from potassium chloride and sulfuric acid, a) sulfuric acid and a hydrochloric acid solution of potassium chloride and potassium salt are added.
Step of producing potassium chloride solution or slurry liquid and hydrogen chloride by reacting at 60 to 150 ° C. b) Potassium hydrogen sulfate solution or slurry solution obtained in step a) is further supplemented with potassium chloride. After the addition, a step of dissolving in water at 60 to 150 ° C, c) methanol is added to the aqueous potassium salt solution obtained in step b) to precipitate crystals of potassium sulfate at 60 to 130 ° C, and then the precipitated potassium sulfate. The method for producing potassium sulfate and hydrochloric acid is characterized by comprising the step of separating

In the present invention, the separated liquid in step c) is further distilled to separate into methanol, water, an azeotropic hydrochloric acid and a hydrochloric acid solution of potassium, and the hydrochloric acid solution of methanol, water and potassium is added in steps a) to a). It can be recycled to c) and concentrated hydrochloric acid can be produced from the hydrogen chloride obtained from step a) and azeotropic hydrochloric acid. As a result, the amounts of methanol and water used are extremely small, and the operating temperatures in steps a) to c) are almost the same temperature, which is a mild temperature condition. Therefore, potassium sulfate and hydrochloric acid are extremely advantageously produced. It Embodiments of the present invention will be described below.

The raw materials sulfuric acid and potassium chloride usually have a purity of 95
% Or more industrial concentrated sulfuric acid and industrial potassium chloride are used. In the method for producing potassium sulfate and hydrochloric acid from potassium chloride and sulfuric acid, the two-step reaction of the formulas is carried out as described above. At a temperature of 150 ° C or lower, the reaction does not proceed even if potassium chloride is present in excess, and the excess potassium chloride reduces the fluidity of the reaction solution. Therefore, potassium chloride is used twice in step a) and step b). It is preferable to supply it separately.

The amount of potassium chloride with respect to sulfuric acid in step a) is 1.0 to 2.0 mole times, preferably 1.0 to 1.4 mole times. When the amount of potassium chloride is lower than 1.0 times, the reaction of the formula is not completed, so that the amount of hydrogen chloride produced in step a) is decreased and the amount of azeotropic hydrochloric acid is increased. As a result, the amount of concentrated hydrochloric acid produced is decreased. The amount of potassium chloride in step b) can be eliminated by increasing the amount of potassium chloride to 2.0 times the amount of sulfuric acid, but the slurry flow of the reaction solution (mixture of potassium hydrogen sulfate and hydrochloric acid solution of potassium salt) as described above. Since the ratio of the potassium salt solution to hydrochloric acid must be increased due to the decrease in the acidity, the amount of potassium chloride to sulfuric acid is 1.0 to 1.
It is preferably 4 molar times.

As the hydrochloric acid solution of potassium salt, a hydrochloric acid distillation column effluent in the distillation of the separated liquid from step c), or a solution of hydrochloric acid and potassium salt having a composition close to this is used. This solution is an azeotropic solution or a hydrochloric acid solution having a concentration close to that, and is an aqueous solution containing 20 to 70% of potassium sulfate and hydrochloride.
The hydrochloric acid solution of potassium salt is used in a weight ratio of 0.1 to 2.0 times, preferably 0.2 to 1.0 times that of sulfuric acid. By adding this solution, the slurry property of sulfuric acid and potassium chloride in the reactor is improved and mixing becomes extremely easy, and since the produced hydrogen chloride exceeds the azeotropic composition,
It can be quickly gasified and efficiently taken out of the reaction system. The hydrogen chloride contains water due to equilibrium vapor pressure.

The reaction temperature in step a) is 60 to 150 ° C., preferably 70 to 130 ° C., and the solid-liquid or solution reaction is carried out for 0.2 to 5 hours. The hydrogen chloride gas produced is separated and recovered, and potassium hydrogen sulfate in the form of slurry or solution is obtained.

In step b), potassium chloride is added in step a).
Add so that the total amount with potassium chloride added in step 2 is about 2.0 times the molar amount of sulfuric acid. Further, water is added to dissolve the entire solution so that the water content becomes 30 to 60%. The melting temperature is 60 to 150 ° C, preferably 70 to 130 ° C.

In step c), methanol is added to the aqueous potassium salt solution obtained in step b) to crystallize potassium sulfate. The ratio of methanol to water is 0.5 to 3.
0, preferably 0.6 to 2.5. The temperature at which methanol is added is 60 to 130 ° C, and the reflux of methanol can be used to control this temperature. The crystals of potassium sulfate crystallized by the addition of methanol are separated from the liquid by filtration or centrifugal sedimentation while maintaining the crystallization temperature.
Since the potassium sulfate crystal obtained in the present invention has a good sedimentation property, any type of solid-liquid separator which is usually used can be used.

The liquid separated in step c) is subjected to fractional distillation to recover a hydrochloric acid solution of methanol, water, azeotropic hydrochloric acid and potassium salt, respectively. The components can be separated by distillation either by batch distillation using one distillation column or continuous distillation using three distillation columns. In the case of continuous distillation,
The distillate component and the hydrochloric acid solution of potassium salt may be first separated, or may be finally separated, and the method with the smallest energy cost can be selected depending on the ratio of each component and the scale of the apparatus.

The hydrochloric acid solutions of methanol, water and potassium salts separated by fractional distillation are recycled in steps c), b) and a) respectively as described above. Concentrated hydrochloric acid is prepared from the separated azeotropic hydrochloric acid by absorbing the hydrogen chloride obtained in step a). The absorption tower may be of any type used in normal gas absorption, but the wet wall type or packed column type is particularly preferable. Each of the above steps can be performed in a batch system, a continuous system, or a combination of a batch system and a continuous system. Further, it is preferable to carry out each step under atmospheric pressure or under a pressure of 10 atm or less.

The potassium sulfate obtained by the method of the present invention has a very low chloride ion concentration, and can be used sufficiently as a fertilizer as it is or after being neutralized with calcium hydroxide, ammonia or the like and then dried. Furthermore, by adding a simple washing operation with methanol or water, a higher purity potassium sulfate can be easily produced.

[0018]

EXAMPLE The process according to the invention was carried out according to FIG.
2.03 kg of potassium chloride having a purity of 98.5% and 2.15 kg of 98% sulfuric acid were supplied to the reactor 1 through the lines 11 and 12, respectively, and the discharge liquid of the hydrochloric acid distillation column 9 having a potassium salt concentration of 35% and a hydrochloric acid concentration of 18% was supplied.
1.22 kg was added from the line 13 and stirred at 110 ° C. for 50 minutes for reaction, and 0.87 kg of hydrogen chloride and 0.32 kg of water were distilled out from the line 16.

Next, while maintaining 110 ° C., potassium chloride
1.35 kg of water was added from line 11 and 4.25 kg of water from line 14, and after dissolution, it was transferred to tank 2 using line 15.
Supply potassium chloride and sulfuric acid to reactor 1 and then tank
The time required to complete the transfer of the aqueous potassium salt solution to 2 is just
It was 60 minutes.

The crystallizer 3 was maintained at 75 ° C., and an aqueous potassium salt solution was supplied from line 17 at 9.84 kg / h and methanol from line 18 at 7.01 kg / h. The potassium sulfate slurry liquid was continuously withdrawn using line 19 so that the average residence time in crystallizer 3 was 30 minutes, and potassium sulfate was filtered off in separator 4 while maintaining 75 ° C.

The potassium sulphate cake 4.15 kg / h is line 20
Was transferred to the dryer 5 by means of, and was pre-dried at 120 ° C, neutralized with calcium hydroxide 0.02kg / h, and further dried at 120 ° C to obtain product potassium sulfate from line 24 at 3.95kg / h. .. The chlorine concentration in the product potassium sulfate was 0.3%, and the free acid was less than 0.1% as sulfuric acid.

The filtrate was supplied to the methanol distillation column 6 through the line 21, and the water-methanol-hydrochloric acid vapor from the dryer 5 was supplied through the line 23. The methanol distillation column 6 was distilled at a top temperature of 64-65 ° C and a bottom temperature of 105-108 ° C to distill methanol at 7.01 kg / h. The distilled methanol was returned to the crystallizer 3 using the line 18. Methanol distillation column
The eluate of 6 was supplied to the water distillation column 7 using the line 25.

In the water distillation column 7, the top temperature was 98 to 102 ° C. and the bottom temperature was 110 ° C., and water was distilled at a rate of 1.30 kg / h. The hydrogen chloride concentration in the distilled water was less than 0.1%. The distilled water was stored in water tank 8 via line 26. The eluate of the distillation column 7 was supplied to the hydrochloric acid distillation column 9 using a line 28.

In the hydrochloric acid distillation column 9, the column top temperature is 108 to 109 ° C.,
Distill at a bottom temperature of 115 to 120 ° C and add 20% azeotropic hydrochloric acid to 3.35 kg.
Distilled into line 29 at / h. A part of the azeotropic hydrochloric acid was extracted from the line 30 at 0.28 kg / h, and the rest was supplied to the hydrochloric acid absorption tower 10. The hydrochloric acid absorption tower 10 is supplied with hydrogen chloride through line 16.
Supply 0.32kg / h of water accompanied with 0.87kg / h at 25 ~ 35 ℃
Soluble in azeotropic hydrochloric acid at 4.36% 35% hydrochloric acid from line 31.
Obtained in kg / h.

[0025]

According to the present invention, in a method for producing potassium sulfate and hydrochloric acid from sulfuric acid and potassium chloride, a hydrochloric acid solution of a potassium salt separated by azeotropic distillation is added to the method to obtain a mild temperature of 60 to 150 ° C. Hydrogen chloride can be easily generated under the conditions, and the reaction of can be allowed to proceed more rapidly. Further, in the present invention, by reacting a certain amount of water and methanol skillfully, the reaction of can be rapidly completed to produce high-purity potassium sulfate and hydrochloric acid. Moreover, the present invention can significantly reduce the energy cost, which was a drawback of the conventional wet method, and improve the economical efficiency.
It has extremely high industrial value.

[0026]

[Brief description of drawings]

FIG. 1 is a flow sheet diagram showing an embodiment of the present invention. 1 ... Potassium chloride / sulfuric acid reactor 17 ... Potassium salt aqueous solution supply line 2 ... Potassium salt aqueous solution tank 18 ... Methanol circulation line 3 ... Potassium sulfate crystallizer 19 ... Potassium sulfate slurry liquid extraction line 4 ... Separator 20 ... Potassium sulfate cake Carry-out line 5 ... Neutralization / dryer 21 ... Filtrate supply line 6 ... Methanol distillation tower 22 ... Calcium hydroxide supply line 7 ... Water distillation tower 23 ... Water / methanol / hydrochloric acid vapor recovery line 8 ... Water tank 24 ... Product potassium sulfate Carry-out line 9… Hydrochloric acid distillation column 25… Methanol distillation column eluate line 10… Hydrochloric acid absorption column 26… Water circulation line 11… Potassium chloride supply line 27… Water supply line 12… Sulfuric acid supply line 28… Water distillation column eluate line 13… elution hydrochloric acid solution circulation line 29… azeotropic hydrochloric acid distillate line 14… water circulation line 30… azeotropic hydrochloric acid extraction line 15… potassium salt aqueous solution extraction line 3 1… 35% hydrochloric acid product extraction line 16… Hydrogen chloride discharge line 32… Waste gas purge line

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mariko Abe 182 Shinwari, Tayuhama, Niigata City, Niigata Prefecture Mitsubishi Gas Chemical Co., Ltd. Niigata Research Center

Claims (3)

[Claims] 1. When producing potassium sulfate and hydrochloric acid from potassium chloride and sulfuric acid, a) adding sulfuric acid and a hydrochloric acid solution of potassium chloride and potassium salt.
Step of producing potassium chloride solution or slurry liquid and hydrogen chloride by reacting at 60 to 150 ° C. b) Potassium hydrogen sulfate solution or slurry solution obtained in step a) is further supplemented with potassium chloride. After the addition, a step of dissolving in water at 60 to 150 ° C, c) methanol is added to the aqueous potassium salt solution obtained in step b) to precipitate crystals of potassium sulfate at 60 to 130 ° C, and then the precipitated potassium sulfate. Method for producing potassium sulfate and hydrochloric acid, characterized by having a step of separating 2. The separated liquid obtained in step c) is separated into methanol, water, azeotropic hydrochloric acid and a hydrochloric acid solution of potassium salt by distillation, methanol is added in step c), water is added in step b) and potassium salt. The method for producing potassium sulfate and hydrochloric acid according to claim 1, wherein the hydrochloric acid solution of 1 is used in step a). 3. Azeotropic hydrochloric acid separated by distillation and step a)
A method for producing potassium sulfate and hydrochloric acid according to claim 2, wherein concentrated hydrochloric acid is produced from hydrogen chloride obtained in