CN106629645A - Method for double solution decomposition in the production process of monopotassium phosphate purification - Google Patents

Abstract

The invention relates to a method for purifying the metathesis solution in the production process of potassium dihydrogen phosphate. Feed grade calcium hydrogen phosphate is first subjected to pre-decomposition reaction with industrial-grade phosphoric acid, and then potassium hydrogen sulfate is added to carry out metathesis reaction. After the metathesis reaction, the first filtration is carried out. , to obtain the primary filter residue calcium sulfate and the primary filtrate; the primary filtrate is concentrated for the first time, cooled and precipitated, and then filtered for the second time to obtain the secondary filter residue and the secondary filtrate, and the secondary filter residue is returned to the metathesis reaction system The secondary filtrate is concentrated for the second time, then cooled and crystallized, and then filtered for the third time to obtain potassium dihydrogen phosphate product and crystallization mother liquor, and the crystallization mother liquor is returned to the pre-decomposition reaction system for recycling operation. Compared with the prior art, the present invention realizes the purification of the filtrate without adding impurity-removing reagents through the step-by-step concentration of the filtrate, and the impurities obtained by purifying the filtrate are returned to the metathesis reaction system to recover phosphorus and potassium, avoiding loss of phosphorus and potassium.

Description

A method for purifying double decomposition solution in the production process of potassium dihydrogen phosphate

technical field

The invention relates to a phosphate preparation process, in particular to a method for purifying a metathesis solution in the production process of potassium dihydrogen phosphate.

Background technique

Potassium dihydrogen phosphate is a chlorine-free compound fertilizer containing phosphorus and potassium. It has important applications in industry and agriculture: in industry, it is often used as a culture agent in the production of antibiotics such as penicillin, gibberellin and tetracycline. It is used as a culture agent for brewing yeast; in agriculture, because of its high nutritional content, it is a high-grade chlorine-free, phosphorus-potassium compound fertilizer, which has the effects of significantly increasing production, drought resistance, and cold resistance, and has special effects on preventing and controlling crop diseases and insect pests. At present, potassium dihydrogen phosphate in China is mainly prepared through the neutralization reaction of thermal phosphoric acid and potassium alkali. This method has mature technology and accounts for more than 90% of the total production capacity of potassium dihydrogen phosphate in the country, but its production cost is high.

Potassium dihydrogen phosphate is prepared from low-cost purified phosphate raw materials. In this process, feed-grade calcium hydrogen phosphate as a phosphorus source and industrial-grade potassium hydrogen sulfate as a potassium source are raw materials with a wide range of sources and low prices. Great market competitiveness.

Existing feed grade calcium hydrogen phosphate and potassium hydrogen sulfate prepare the technology of potassium dihydrogen phosphate often is to add potassium hydrogen sulfate solution and sulfuric acid to carry out metathesis reaction after feed grade calcium hydrogen phosphate beating, in order to guarantee phosphorus yield, the sulfuric acid that adds The amount of potassium hydrogen is far greater than the theoretical demand, and the yield of phosphorus is still low. After the metathesis reaction, because of adding excessive potassium hydrogen sulfate, the filtrate that filters still contains 3.8%～4.2% sulfate radicals and hydrogen ions. There are also other impurities brought by feed grade calcium hydrogen phosphate: including Mg, Al, Fe, etc. These impurities in the filtrate are very unfavorable to the subsequent crystallization of potassium dihydrogen phosphate. In order to remove impurities such as sulfate radicals, hydrogen ions and calcium ions in the metathesis filtrate, alkaline substances such as potassium hydroxide and barium hydroxide and barium salt reagents are often added to remove impurities. The main reaction is:

OH ^- +H ⁺ →H ₂ O

Ba ²⁺ +SO ₄ ^2- → BaSO ₄ ↓

Ca ²⁺ +H ₂ PO ₄ ^- +2H ₂ O→CaHPO ₄ 2H ₂ O↓

Ca ²⁺ +2SO ₄ ^2- +2K ⁺ +2H ₂ O→K ₂ Ca(SO ₄ ) ₂ 2H ₂ O↓

The impurity removal step will also form phosphorus and potassium-containing precipitates while removing sulfate, hydrogen ions, and calcium ions. This impurity precipitate is accompanied by a variety of substances, which is difficult to reuse and reduces the utilization of raw materials. rate; and the addition of alkaline reagents further increases production costs.

Contents of the invention

The present invention improves the existing technology and provides a method for purifying the metathesis solution in the production process of potassium dihydrogen phosphate. The method does not use expensive impurity removal reagents, and adopts steps to concentrate and return impurities to the system, avoiding the The loss of phosphorus and potassium during purification can produce potassium dihydrogen phosphate products that meet the industrial grade first-class products, which greatly reduces production costs.

The purpose of the present invention can be achieved through the following technical solutions:

A method for purifying the metathesis solution in the production process of potassium dihydrogen phosphate, comprising the following steps:

Feed-grade calcium hydrogen phosphate is pre-decomposed with industrial-grade phosphoric acid, and then potassium bisulfate is added for metathesis reaction. After the metathesis reaction, the first filtration is carried out to obtain the primary filter residue and primary filtrate, wherein the primary filter residue is calcium sulfate;

The primary filtrate is concentrated for the first time without adding additional reagents, cooled and precipitated, and then filtered for the second time to obtain the secondary filter residue and secondary filtrate, and the secondary filter residue is returned to the metathesis reaction system;

The secondary filtrate is concentrated for the second time, then cooled and crystallized, and then filtered for the third time to obtain potassium dihydrogen phosphate product and crystallization mother liquor. The crystallization mother liquor can replace industrial phosphoric acid and return to the pre-decomposition reaction system for recycling operation. It can also be used to prepare chlorine-free compound fertilizer. Potassium dihydrogen phosphate products meet the requirements of first-class industrial grade potassium dihydrogen phosphate.

Further, when feed-grade calcium hydrogen phosphate and industrial-grade phosphoric acid are pre-decomposed, the molar ratio of phosphoric acid to calcium hydrogen phosphate is 0.2-0.3:1. The reaction mechanism of the pre-decomposition reaction is to convert the part of calcium hydrogen phosphate that is insoluble in water into calcium dihydrogen phosphate that is slightly soluble in water. Rate.

Further, when feed-grade calcium hydrogen phosphate and industrial-grade phosphoric acid are subjected to pre-decomposition reaction, the reaction temperature is 50°C-70°C, and the reaction time is 1h-2h.

Further, the potassium-phosphorus molar ratio of potassium hydrogen sulfate and feed-grade calcium hydrogen phosphate is 0.9-1.1:1.

Further, when adding potassium bisulfate to carry out the metathesis reaction, the reaction temperature is 50° C. to 70° C., and the reaction time is 2 to 4 hours.

Among the present invention, feed grade calcium hydrogen phosphate and industrial grade phosphoric acid pre-decomposition reaction mix, preferably adopt following two kinds of ways:

Mode 1, after feed-grade calcium hydrogen phosphate is added with water and beaten, feed-grade calcium hydrogen phosphate slurry is obtained, and industrial-grade phosphoric acid and feed-grade calcium hydrogen phosphate slurry are added for pre-decomposition reaction;

When feed-grade calcium hydrogen phosphate is added with water and beaten to prepare feed-grade calcium hydrogen phosphate slurry, the volume of water added per kilogram of feed-grade calcium hydrogen phosphate is 2.5 to 5 liters.

Method 2: Mix the phosphoric acid solution obtained by mixing industrial-grade phosphoric acid and water with feed-grade calcium hydrogen phosphate, and perform pre-decomposition reaction while beating.

When mixing industrial-grade phosphoric acid and water, the mass percentage of the prepared phosphoric acid solution is preferably 20%-40%.

Further, when performing the first concentration, the concentration temperature is 80° C. to 90° C. After the first concentration, the mass fraction of potassium dihydrogen phosphate is 15% to 20%.

Further, the operating conditions of the cooling precipitation are as follows: the cooling precipitation temperature is 20° C. to 35° C., the cooling precipitation time is 3 hours to 6 hours, and the stirring speed is controlled to be 100 rpm/min to 150 rpm/min.

Further, when performing the second concentration, the concentration temperature is 80° C. to 90° C., and the mass fraction of potassium dihydrogen phosphate is 30% to 40% after the second concentration.

Further, the operating conditions for cooling crystallization are as follows: the cooling crystallization temperature is 30°C-40°C, the cooling crystallization time is 5h-8h, and the stirring speed is controlled to be 60rpm/min-100rpm/min.

In the present invention, when the filtrate is concentrated and crystallized, it is carried out in two steps. For the first time, the concentrated and cooled precipitate is returned to the metathesis reaction kettle, and participates in the metathesis reaction together with feed grade calcium hydrogen phosphate; the second time is concentrated, cooled and crystallized, and the obtained crystal is filtered The mother liquor returns to the pre-decomposition reaction stage to replace the phosphoric acid for the pre-decomposition reaction.

In the present invention, potassium hydrogen sulfate is preferably added in the form of potassium hydrogen sulfate solution, and the mass percentage of potassium hydrogen sulfate solution is preferably 30% to 50%.

In the present invention, the feed-grade calcium hydrogen phosphate is prepared from wet-process phosphoric acid through a three-stage neutralization method.

In the present invention, said industrial-grade phosphoric acid can be hot-process phosphoric acid or wet-process phosphoric acid.

In the present invention, after the metathesis reaction is completed, the yield of phosphorus is more than 95%, and the yield of K is more than 99.5%. That is, the P loss rate in the filtered calcium sulfate is ≤5%, and the K loss rate is ≤0.5%.

The present invention utilizes the physical and chemical properties and solubility differences between the target product and impurity substances, and proposes a method of segmental concentration to reduce the content of impurities; at the same time, by circulating the precipitate to the previous metathesis step, the loss of phosphorus and potassium is reduced, and the diphosphate diphosphate is increased. Potassium hydrogen production yield.

In the process of the present invention, the potassium-phosphorus molar ratio of potassium hydrogen sulfate and feed-grade calcium hydrogen phosphate is 0.9 to 1.1:1, and no excessive potassium hydrogen sulfate is added. After the metathesis, the impurities in the solution are mainly sulfate radicals and feed-grade The raw material of calcium hydrogen phosphate carries calcium ions, iron ions and aluminum ions, etc., and the main impurities in the filtrate are sulfate and calcium ions. Based on the process of adding phosphoric acid for pre-decomposition, using the difference in solubility of substances, by controlling the degree of concentration of the filtrate, concentration is carried out step by step to further remove residual sulfate and calcium ions. After the first concentration, the main reaction is:

Ca ²⁺ +2SO ₄ ^2- +2K ⁺ +2H ₂ O→K ₂ Ca(SO ₄ ) ₂ 2H ₂ O↓

After concentration, cool down and precipitate, filter to obtain potassium gypsum (K ₂ Ca(SO ₄ ) ₂ 2H ₂ O) and the filtrate after purification; inevitably, a small amount of phosphate will be carried in the precipitation of potassium gypsum, and the precipitated product Returning to the metathesis reaction system, it can be decomposed into potassium sulfate and calcium sulfate:

K ₂ Ca(SO ₄ ) ₂ ·2H ₂ O→CaSO ₄ ·2H ₂ O+2K ⁺ +SO ₄ ^2-

Potassium sulfate is dissolved in water, so that potassium can be used again. At the same time, the phosphorus retained in the filter residue also enters the metathesis system and is also used again.

The present invention does not need to add alkaline substances such as potassium hydroxide or barium hydroxide to the metathesis filtrate to adjust the pH, nor does it need to purify the filtrate by adding other barium salts. The present invention only uses the method of distribution and concentration to remove impurities. The impurity removal effect of step-by-step concentration is compared with the use of reagents in the prior art for the impurity removal effect and cost, and the results are shown in Table 1:

Table 1 Purification effect and cost comparison of different purification methods for filtrate

It can be seen from Table 1:

1) The purification effect of step-by-step concentration on calcium ions is very significant, which is far superior to the purification effect on calcium ions by adding potassium hydroxide to adjust the pH;

2) The purifying effect of step-by-step concentration on sulfate is slightly lower than that of barium hydroxide;

3) The cost of step-by-step concentration is far lower than the cost of adding reagents to remove impurities.

By comparison, it can be found that the purification of the filtrate by stepwise concentration is superior to the purification by adding additional reagents such as potassium hydroxide and barium hydroxide.

Compared with the prior art, the present invention realizes the purification of the filtrate without adding impurity removal reagents such as potassium hydroxide and barium hydroxide through the step-by-step concentration of the filtrate, which reduces the cost of the filtrate purification. The impurities obtained from the filtrate mainly contain sulfur, calcium and potassium, as well as a small amount of phosphorus and magnesium, etc. These impurities can be returned to the metathesis reaction system to recover phosphorus and potassium, avoiding the loss of phosphorus and potassium, and improving the utilization of raw materials The efficiency further reduces the production cost and has a great competitive advantage.

Description of drawings

Fig. 1 is the process flow chart of the method of the present invention.

detailed description

The method for purifying the metathesis solution in the production process of potassium dihydrogen phosphate according to the present invention is that the feed grade calcium hydrogen phosphate is first subjected to a pre-decomposition reaction with industrial-grade phosphoric acid, and then potassium hydrogen sulfate is added to carry out the metathesis reaction, and after the metathesis reaction, the first filtration is carried out to obtain a The first-grade filter residue and the first-grade filtrate, wherein the first-grade filter residue is calcium sulfate; the first-grade filtrate is concentrated for the first time without adding additional reagents, and cooled and precipitated, and then filtered for the second time to obtain the second-grade filter residue and the second-grade filtrate. The first-grade filter residue is returned to the metathesis reaction system; the second-grade filtrate is concentrated for the second time, then cooled and crystallized, and then filtered for the third time to obtain potassium dihydrogen phosphate product and crystallization mother liquor. The crystallization mother liquor can replace industrial phosphoric acid and return to the preliminary In the decomposition reaction system, cyclic operation is carried out, and it can also be used to prepare chlorine-free compound fertilizer.

During specific implementation, the process is as shown in Figure 1, including the following steps:

1. Beat feed grade calcium hydrogen phosphate and water to prepare slurry, and the mass ratio of the volume of added water to feed grade calcium hydrogen phosphate is 2.5-5L/kg.

2. Prepare industrial-grade phosphoric acid into a phosphoric acid solution with a mass percentage of 20% to 40%. Add phosphoric acid solution to the slurry for pre-decomposition reaction. The reaction temperature is 50°C to 70°C. The phosphorus-to-phosphorus molar ratio of calcium hydrogen phosphate is 0.2-0.3. The reaction mechanism of the pre-decomposition reaction is to convert the poorly water-soluble calcium hydrogen phosphate into slightly water-soluble calcium dihydrogen phosphate.

3. After the pre-decomposition reaction is carried out for 1h to 2h, the potassium hydrogensulfate solution is prepared into a potassium hydrogensulfate solution with a mass percentage of 30% to 50%, and then slowly added to carry out the double decomposition reaction. The reaction temperature is 50°C to 70°C. The molar ratio of potassium hydrogen sulfate to potassium hydrogen phosphate in the slurry is 0.9-1.1.

4. After the metathesis reaction is carried out for 2h to 4h, the calcium sulfate and the filtrate are filtered out.

5. Purify the filtrate, control the amount of concentration, evaporate the filtrate so that the mass fraction of potassium dihydrogen phosphate in the filtrate reaches 15% to 20%, the concentration temperature is 80°C to 90°C, cool and precipitate for 3h to 6h, and control the stirring speed to 100rpm/min～150rpm/min, cooling precipitation temperature is 20℃～35℃, after filtration, the filter residue is returned to the system, mixed with feed grade calcium hydrogen phosphate slurry, and participates in metathesis reaction, and the filtrate obtained after filtration is concentrated for the second time.

6. Continue to concentrate the purified filtrate, evaporate the filtrate so that the mass fraction of potassium dihydrogen phosphate in the filtrate reaches 30% to 40%, the concentration temperature is 80°C to 90°C, cool and crystallize for 5h to 8h, and control the stirring speed to 60rpm/ min～100rpm/min, cooling and crystallization temperature is 30℃～40℃, and the product and crystallization mother liquor are obtained by filtration.

7. The crystallization mother liquor can replace industrial phosphoric acid, return to the feed grade calcium hydrogen phosphate slurry for pre-decomposition reaction, and carry out cyclic operation, and can also be used for the production of chlorine-free compound fertilizer.

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

Example 1:

Mix 280kg of feed grade calcium hydrogen phosphate and 700kg of water in the reactor evenly, add 155.05kg of phosphoric acid solution with a mass percentage of 20%, the reaction temperature is 50°C, and add 646.29kg of sulfuric acid with a mass percentage of 30% after 1 hour of reaction Potassium hydrogen phosphate solution, the reaction time is 2h; filter after the reaction to obtain calcium sulfate and filtrate, the filtrate is concentrated, so that the mass fraction of potassium dihydrogen phosphate in the filtrate reaches 15%, the concentration temperature is 80°C, cool and precipitate for 3h, and control the stirring speed It is 100rpm/min, and the cooling precipitation temperature is 20°C. After filtering, 40.81kg of filter residue is obtained, which is returned to the system, mixed with feed grade calcium hydrogen phosphate slurry, and participates in the metathesis reaction, and the obtained filtrate is filtered for the second concentration; Concentrate for the second time to make the mass fraction of potassium dihydrogen phosphate reach 30%, the concentration temperature is 80°C, cool and crystallize for 5h, control the stirring speed to 60rpm/min, cool and crystallize at 30°C, and filter to obtain 62.03kg of product and 556.41kg of crystals The content of potassium dihydrogen phosphate in the obtained potassium dihydrogen phosphate product in the mother liquor is 98.34%, which meets the requirements of industrial-grade first-class potassium dihydrogen phosphate.

Example 2:

Mix 390kg of feed grade calcium hydrogen phosphate and 1950kg of water in the reactor, add 161.98kg of phosphoric acid solution with a mass percentage of 40%, the reaction temperature is 70°C, and add 540.11kg of 50% by mass of sulfuric acid after 2 hours of reaction Potassium hydrogen solution, the reaction time is 4h; filter after the reaction to obtain calcium sulfate and filtrate, the filtrate is concentrated so that the mass fraction of potassium dihydrogen phosphate is 20%, the concentration temperature is 90 ° C, cooling and precipitation for 6h, control the stirring speed to 150rpm /min, the cooling precipitation temperature is 35°C, after filtering, 56.84kg of filter residue is obtained, which is returned to the system, mixed with feed grade calcium hydrogen phosphate slurry, and participates in the metathesis reaction, and the filtrate obtained by filtering is concentrated for the second time; When concentrating for the second time, make the mass fraction of potassium dihydrogen phosphate reach 40%, the concentration temperature is 90°C, cool and crystallize for 8h, control the stirring speed to 100rpm/min, cool and crystallize at 40°C, filter to obtain 123.97kg of product and 555.45kg of crystallization mother liquor . The quality of the obtained potassium dihydrogen phosphate product is that the potassium dihydrogen phosphate content is 98.33%, which meets the requirements of the first-class industrial grade potassium dihydrogen phosphate.

Example 3:

Mix 300kg of feed grade calcium hydrogen phosphate and 1132.46kg of water in the reactor, add 427.27kg of crystallization mother liquor, add 43.72kg of impurities after 2 hours of reaction, and then add 379.22kg of 50% potassium hydrogensulfate solution by mass , the reaction temperature is 80°C, and the reaction time is 4h; filter after the reaction to obtain calcium sulfate and filtrate, and concentrate the filtrate so that the mass fraction of potassium dihydrogen phosphate is 20%, the concentration temperature is 90°C, cool and precipitate for 3h, and control stirring The speed is 100rpm/min, and the cooling precipitation temperature is 35°C. After filtering, 45.87kg of filter residue is obtained, which is returned to the system, mixed with feed-grade calcium hydrogen phosphate slurry, and participates in the metathesis reaction. The obtained filtrate is filtered for the second concentration , the mass fraction of potassium dihydrogen phosphate is 40%, the concentration temperature is 80°C, cooling and crystallization is carried out for 5h, the stirring speed is controlled to be 60rpm/min, the cooling crystallization temperature is 30°C, and 166.97kg of product and 593.57kg of crystallization mother liquor are obtained by filtration. The potassium dihydrogen phosphate content in the potassium dihydrogen phosphate product is 98.37%, which meets the requirements of the first-class industrial grade potassium dihydrogen phosphate.

The above descriptions of the embodiments are for those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described here to other embodiments without creative efforts. Therefore, the present invention is not limited to the above-mentioned embodiments. Improvements and modifications made by those skilled in the art according to the disclosure of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims (10)

1. in a kind of purifying phosphoric acid potassium dihydrogen production process double decomposition solution method, it is characterised in that comprise the following steps：

Calcium hydrophosphate fodder is first and PHOSPHORIC ACID TECH.GRADE carries out predecomposition reaction, and adding potassium acid sulfate carries out metathesis reaction, First time filtration is carried out after metathesis reaction, one-level filter residue and one-level filtrate is obtained, wherein one-level filter residue is calcium sulfate；

One-level filtrate carries out first time concentration, and cools down precipitation, then carries out second filtration, obtains two grades of filter residues and two grades of filters Liquid, two grades of filter residues are returned in metathesis reaction system；

Two grades of filtrates carry out second concentration, then carry out crystallisation by cooling, then carry out third time filtration, obtain potassium dihydrogen phosphate product Product and crystalline mother solution, crystalline mother solution is returned in predecomposition reaction system, is circulated operation.

2. in a kind of purifying phosphoric acid potassium dihydrogen production process according to claim 1 double decomposition solution method, its feature It is that when calcium hydrophosphate fodder and PHOSPHORIC ACID TECH.GRADE carry out predecomposition and react, phosphoric acid and the mol ratio of calcium monohydrogen phosphate be 0.2～ 0.3：1.

3. in a kind of purifying phosphoric acid potassium dihydrogen production process according to claim 1 double decomposition solution method, its feature It is that when calcium hydrophosphate fodder and PHOSPHORIC ACID TECH.GRADE carry out predecomposition reaction, reaction temperature is 50 DEG C～70 DEG C, the reaction time For 1h～2h.

4. in a kind of purifying phosphoric acid potassium dihydrogen production process according to claim 1 double decomposition solution method, its feature It is that the potassium phosphorus mol ratio of potassium acid sulfate and calcium hydrophosphate fodder is 0.9～1.1：1.

5. in a kind of purifying phosphoric acid potassium dihydrogen production process according to claim 1 double decomposition solution method, its feature When being to add potassium acid sulfate to carry out metathesis reaction, reaction temperature is 50 DEG C～70 DEG C, and the reaction time is 2～4h.

6. in a kind of purifying phosphoric acid potassium dihydrogen production process according to claim 1 double decomposition solution method, its feature When being to carry out for the first time concentration, thickening temperature is 80 DEG C～90 DEG C, makes the potassium dihydrogen phosphate mass fraction be after concentrating for the first time 15%～20%.

7. in a kind of purifying phosphoric acid potassium dihydrogen production process according to claim 1 double decomposition solution method, its feature It is that the operating condition for cooling down precipitation is：Cooling precipitation temperature is 20 DEG C～35 DEG C, and the cooling sedimentation time is 3h～6h, is controlled Mixing speed is 100rpm/min～150rpm/min.

8. in a kind of purifying phosphoric acid potassium dihydrogen production process according to claim 1 double decomposition solution method, its feature Be that when carrying out second concentration, thickening temperature is 80 DEG C～90 DEG C, second concentrate after make the potassium dihydrogen phosphate mass fraction be 30%～40%.

9. in a kind of purifying phosphoric acid potassium dihydrogen production process according to claim 1 double decomposition solution method, its feature It is that the operating condition of crystallisation by cooling is：Crystallisation by cooling temperature is 30 DEG C～40 DEG C, and the crystallisation by cooling time is 5h～8h, is controlled Mixing speed is 60rpm/min～100rpm/min.

10. in a kind of purifying phosphoric acid potassium dihydrogen production process according to claim 1 double decomposition solution method, its feature It is that calcium hydrophosphate fodder adds water after beating, obtains calcium hydrophosphate fodder slip, adds PHOSPHORIC ACID TECH.GRADE and feed grade phosphorus Sour hydrogen calcium slip carries out predecomposition reaction；

Or, PHOSPHORIC ACID TECH.GRADE and the mixed phosphoric acid solution of water are mixed with calcium hydrophosphate fodder, carry out while beating pre- Decomposition reaction.