CN1067657C

CN1067657C - Method for prodn. of potassium sulfate by circulating potassium hydrogen sulfate and decomposing potassium chloride

Info

Publication number: CN1067657C
Application number: CN98112150A
Authority: CN
Inventors: 王励生; 明勇; 金作美
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-07-17
Filing date: 1998-07-17
Publication date: 2001-06-27
Anticipated expiration: 2018-07-17
Also published as: CN1242341A

Abstract

The present invention relates to a method for preparing potassium sulfate by the circulation of potassium bisulfate and the decomposition of potassium chloride. The present invention is characterized in that the method takes sulphuric acid and potassium chloride as raw materials under a comparatively moderate condition (at a low temperature) and adopts the technical line of the circulation of potassium bisulfate to prepare potassium sulfate to obtain potassium sulfate products in which more than 50% of K2O, not more than 1.5% of Cl and not more than 0.5% of free acid are contained. The potassium sulfate products can reach the standard of national high-quality products. The method for preparing potassium sulfate by the circulation of potassium bisulfate and the decomposition of potassium chloride has the advantages of the thermal decomposition and the double decomposition method as well as overcomes the defects that the thermal decomposition method has strong corrosiveness to equipment, and has high power consumption and large one-time investment, and potassium sulfate obtained by the double decomposition method has low product purity, high chlorine content and a low potassium utilization rate.

Description

Method for producing potassium sulfate by decomposing potassium chloride with circulating potassium bisulfate

The present invention relates to a method for preparing potassium sulfate, which belongs to the field of inorganic fertilizers.

Potassium sulfate is a chlorine-free potassium fertilizer, and is required by a plurality of chlorine-resistant crops such as tobacco, tea, orange, grape, watermelon, potato, beans and the like, which increases year by year. The price of potassium sulfate in the current market is as high as 2200 yuan/ton, and the supply is still short. China needs to spend a large amount of money on importing potassium sulfate by foreign exchange every year.

The method for preparing potassium sulfate by using potassium chloride as a raw material mainly comprises two methods:

1. thermal decomposition method

The representative technical route is a Mannheim (Mannbeim) furnace method and an improved Japanese Chisso process, the process method has the advantages of high reaction conversion rate and high product purity, the technology introduced from Japan in China is provided with a ten-thousand-ton-grade factory, and the thermal decomposition process is carried out in two steps:

the first step is that at a lower temperature, sulfuric acid reacts with potassium chloride to generate potassium bisulfate; the second step is that potassium chloride reacts with potassium bisulfate at the high temperature of 400-700 ℃ to generate potassium sulfate, and hydrogen chloride gas generated in the reaction process needs to be recovered. Potassium hydrogen sulfate and hydrogen chloride gas have strong corrosivity on equipment at high temperature, and only a special silicon carbide reaction furnace and a high-grade alloy steel device which are expensive are adopted to recover hydrogen chloride, so that the equipment investment is large, the energy consumption is high, the potassium sulfate cost is high, and the method is unfavorable for supporting agricultural development.

2. Double decomposition method

The other method is that firstly sulfuric acid reacts with potassium chloride to generate potassium bisulfate, and after the generated hydrogen chloride gas is volatilized out of the system, alkaline substances such as ammonia water are added into the system to neutralize acid in the reaction liquid, so as to generate potassium sulfate and byproducts such as ammonium chloride. The double decomposition method overcomes the defects of large one-time investment and serious equipment corrosion of the thermal decomposition method, but the obtained potassium sulfate product has low purity, high ammonia content and low potassium utilization rate, and the treatment and recycling process of the mother liquor is complex and long.

The invention aims to provide a method for preparing potassium sulfate by decomposing potassium chloride with circulating potassium bisulfate, which is characterized in that sulfuric acid and potassium chloride are used as raw materials under mild (low temperature) conditions, a technical route of circulating potassium bisulfate is adopted to prepare the potassium sulfate, and a potassium sulfate product containing K is obtained₂O is more than 50 percent,reaches the national high-grade product standard, has the advantages of a thermal decomposition method and a double decomposition method and overcomes the defects of the thermal decomposition method and the double decomposition method.

The purpose of the invention is realized by adopting the following technical measures:

1. dissolving a raw material potassium chloride by using a potassium bisulfate circulating solution at 70-105 ℃, wherein the decomposition process can be represented by the following formula:

the evolution of hydrogen chloride is low at this stage.

2. Cooling the reaction liquid of decomposing potassium chloride by potassium bisulfate to 5-30 ℃, separating out potassium sulfate crystals, filtering and separating, and washing the crystals by potassium sulfate saturated solution to obtain the potassium-containing potassium₂High-quality potassium sulfate product with O more than 52%, Cl less than 1.5% and free acid less than or equal to 0.5%.

3. The mother liquid after separating potassium sulfate contains a large amount of potassium chloride and hydrogen chloride, and the mother liquid and the potassium sulfate washing liquid are respectively sent to a reaction concentration device, and sulfuric acid is added to carry out the reaction of decomposing potassium chloride by sulfuric acid to generate potassium hydrogen sulfate and hydrogen chloride. The reaction temperature is 70-130 ℃, most of the generated hydrogen chloride volatilizes and escapes in the reaction concentration process, and hydrochloric acid by-products are prepared by absorbing with water in an absorption device.

4. The potassium bisulfate solution volatilized from the hydrogen chloride gas contains a large amount of potassium bisulfate and a small amount of potassium sulfate and potassium chloride, so that potassium bisulfate circulating liquid is formed, and the circulating liquid is sent to a reaction device for heating and dissolving potassium chloride to decompose potassium chloride and enters a next circulating system.

The invention has the following advantages:

1. compared with the traditional thermal decomposition method, the reaction temperature of the potassium chloride and the potassium bisulfate is reduced from 400-700 ℃ to about 100 ℃, and the requirement of expensive high-temperature-resistant and corrosion-resistant equipment materials is eliminated, so that the energy consumption can be reduced by 60 percent, and the equipment investment can be reduced by 50 percent.

2. The invention does not need to add dechlorinating agent (such as NH)₄OH) and a complicated process for recovering ammonium chloride as a byproduct can be omitted, and the present invention is more advantageously used particularly in areas lacking ammonia or having a difficult supply of ammonia.

3. The potassium bisulfate mother liquor is recycled, so that no waste liquor is discharged, and the environmental protection is facilitated.

4. High purity of product, containing K₂O is more than 50 percent, Cl is less than or equal to 1.5 percent, free acid is less than or equal to 0.5 percent, the utilization rate of potassium is as high as 98.5 percent, the energy consumption is low, and the production cost is low.

5. In the process of preparing the potassium bisulfate circulating liquid, hydrogen chloride is discharged out of the system by nearly 100 percent under the condition of nearly boiling, and 32 percent hydrochloric acid by-product can be prepared after absorption.

The process flow of the invention is given by the following figures and examples:

FIG. 1 is a process flow diagram for producing potassium sulfate by decomposing potassium chloride with circulating potassium bisulfate.

(1) Potassium chloride, (2) a heating dissolving tank, (3) cooling crystallization, (4) filtering separation, (5) a potassium sulfate saturated solution, (6) a washing tank, (7) a concentration device, (8) sulfuric acid, (9) a potassium bisulfate circulating tank, (10) a potassium sulfate product, (11) a hydrogen chloride recovery tank, and (12) a hydrochloric acid byproduct.

Examples

The present invention is described in detail below by way of examples, it should be noted that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention, and those skilled in the art can make many insubstantial modifications and adaptations of the present invention based on the above description.

1. 165 kg of potassium bisulfate circulating liquid is added at the temperatureDissolving 91.2 kg of potassium chloride containing 95% of potassium chloride at the temperature of 95-100 ℃, after the dissolution is finished, conveying the solution into a crystallization tank at the temperature of 25 ℃, crystallizing and separating out potassium sulfate in the crystallization tank, washing crystals by using a saturated potassium sulfate solution, and drying to obtain about 100 kg of potassium sulfate, wherein the product contains K₂53.8 percent of O, less than or equal to 0.29 percent of Cl, free acid (replaced by H)₂SO₄The amount) is less than or equal to 0.45 percent, and reachesthe standard of special-grade products. Mother liquor and washing liquid after potassium sulfate separation are respectively sent to a reaction concentration device, 58.6 kg of 98% concentrated sulfuric acid is added, 45.95 kg of hydrogen chloride gas is discharged in the reaction concentration process, 140 kg of 32% hydrochloric acid by-product can be obtained by absorbing with water, 165 kg of potassium bisulfate circulating liquid is obtained at the same time, and the circulating liquid is sent to a heating dissolving tank to dissolve potassium chloride.

2. 87 kg of 98 percent potassium chloride is dissolved in 144 kg of solution of potassium bisulfate under the near boiling condition, potassium sulfate crystals are separated out from the solution in a crystallization tank at the temperature of 20 ℃, and a potassium sulfate product with 76.6 kg is obtained after separation, washing and drying, wherein the potassium sulfate product contains K₂53.7 percent of O, less than or equal to 0.34 percent of Cl and less than or equal to 0.41 percent of free acid, respectively sending the mother liquor and the washing liquor after the potassium sulfate is separated to a reaction concentration device, adding 48.5 kilograms of 93 percent concentrated sulfuric acid, discharging 35.35 kilograms of hydrogen chloride gas in the reaction concentration process, absorbing by water to obtain 110 kilograms of 32 percent hydrochloric acid by-product, simultaneously obtaining 144 kilograms of potassium bisulfate circulating solution, and sending the solution to a heating dissolving tank to dissolve potassium chloride.

3. Purity is as containing K₂157 kg of O60% potassium chloride, 287.41 kg of potassium bisulfate dissolved at about 100 ℃, the solution is sent to a cooling crystallization tank with the temperature of 22 ℃ after the dissolution is finished, potassium sulfate is crystallized and separated out, and 174 kg of potassium sulfate is obtained after separation, washing and drying, wherein the product contains K₂53.2 percent of O, less than or equal to 0.3 percent of Cl and less than or equal to 0.38 percent of free acid, respectively sending the mother liquor and the washing liquor after the potassium sulfate is separated to a reaction concentration device, adding 102 kg of 98 percent concentrated sulfuric acid, discharging 80 kg of hydrogen chloride gas in the reaction concentration process, absorbing with water to obtain 250 kg of 32 percent hydrochloric acid by-product, simultaneously obtaining 288.0 kg of potassium bisulfate circulating solution, and sending the solution to a heating dissolving tank to dissolve potassium chloride.

Claims

1. A method for preparing potassium sulfate by decomposing potassium chloride with circulating potassium bisulfate is characterized in that:

a. dissolving potassium chloride in circulating potassium bisulfate solution at 70-105 deg.C, and its decomposition process is represented by the following formula The evolution of hydrogen chloride by volatilization is low at this stage,

b. cooling the reaction liquid of decomposing potassium chloride by potassium bisulfate to 5-30 ℃, separating out potassium sulfate crystals, filtering and separating, washing the crystals by a potassium sulfate saturated solution to obtain a potassium sulfate product,

c. separating potassium sulfate to obtain mother liquid containing great amount of potassium chloride and hydrogen chloride, feeding the mother liquid and potassium sulfate washing liquid to a reaction concentration device, adding sulfuric acid to decompose potassium chloride with sulfuric acid to produce potassium bisulfate and hydrogen chloride at 70-130 deg.c, volatilizing most of the hydrogen chloride during the reaction concentration process, absorbing with water in an absorption device to obtain hydrochloric acid as side product,

d. the potassium bisulfate solution volatilized from the hydrogen chloride gas contains a large amount of potassium bisulfate and a small amount of potassium sulfate and potassium chloride, so that potassium bisulfate circulating liquid is formed, and the circulating liquid is sent to a reaction device for heating and dissolving potassium chloride to decompose potassium chloride and enters a next circulating system.