Preparation method of dihydric phosphate

Abstract

The invention belongs to the technical field of phosphate preparation, and particularly relates to a preparation method of dihydric phosphate. Uniformly mixing the composite extracting agent with a phosphoric acid aqueous solution, and standing to obtain a phosphoric acid-loaded extracting agent; wherein the composite extracting agent is a mixture of a component A, a component B and a component C, the component A is one or more of 3-amino-1-propanol, 3-dimethylamino-1-propanol, 3-amino-1-butanol, 3-dimethylamino-1-butanol or 3-amino-4, 4-dimethyl-1-pentanol, the component B is one or two of isoamyl alcohol or nonyl alcohol, and the component C is one or more of isoamyl alcohol or nonyl alcohol. The component C is one or more of n- / iso-tridecane-n- / iso-octadecane; carrying out double decomposition reaction on the phosphoric acid-loaded extracting agent and a chlorate aqueous solution, and layering to obtain a water phase; and concentrating the water phase, and recrystallizing to obtain the dihydric phosphate. The conversion rate of double decomposition reaction is high, the total utilization rate of phosphoric acid is greatly increased, and the production cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of phosphate preparation, and particularly relates to a method for preparing dihydrogen phosphate. Background Art

[0002] Potassium dihydrogen phosphate and sodium dihydrogen phosphate are important products of the phosphate industry and are widely used in industry, agriculture, chemical industry, food, medicine and other industries. Among them, high-purity potassium dihydrogen phosphate and sodium dihydrogen phosphate are widely used as materials for new energy batteries and optical crystals.

[0003] There are three main methods for preparing potassium dihydrogen phosphate or sodium dihydrogen phosphate: 1. Neutralization method: Potassium hydroxide or sodium hydroxide is used to neutralize phosphoric acid to prepare potassium dihydrogen phosphate or sodium dihydrogen phosphate. This method is mature in technology, with a short process flow, less equipment, low energy consumption, low investment, low chloride ion content in the prepared product, and high product purity. It is currently the main production method for feed-grade and food-grade potassium dihydrogen phosphate or sodium dihydrogen phosphate products. However, since potassium hydroxide is prepared by electrolysis of potassium chloride, the raw material price is high and the atom economy is poor.

[0004] 2. Double decomposition method: react potassium chloride or sodium chloride with sodium phosphate or its acidic salts to produce potassium dihydrogen phosphate or sodium dihydrogen phosphate. The advantages of this method are simple reaction process, easy operation, no need to use too many chemical reagents and equipment, and efficient preparation of potassium dihydrogen phosphate or sodium dihydrogen phosphate; the disadvantage is that the product is mixed with potassium salt or sodium salt, ammonium salt, and needs to be separated and purified, which has high energy consumption and low value.

[0005] 3. Combination of extraction and double decomposition: Select a suitable extractant, load phosphoric acid in an organic solvent, and then use the organic solvent containing phosphoric acid to react with an aqueous potassium chloride solution or an aqueous sodium chloride solution, extract most of the hydrochloric acid obtained, and potassium dihydrogen phosphate or sodium dihydrogen phosphate enters the aqueous phase. Through phase separation and separation, potassium dihydrogen phosphate or sodium dihydrogen phosphate crystals are obtained from the aqueous phase. This method uses low-cost potassium chloride or sodium chloride as raw materials, is simple to operate, has good reaction selectivity, high recovery rate, and has the advantage of reusable extractants. However, the extraction separation coefficient of chloride ion and dihydrogen phosphate of the currently publicly reported extractants (such as the preparation of potassium dihydrogen phosphate by liquid-liquid heterogeneous double decomposition method, Chen Lijuan, East China University of Science and Technology, 2010 and the preparation of potassium dihydrogen phosphate by liquid-liquid ion exchange method, Zhang Li, East China University of Science and Technology, 2012) can only reach a maximum of 161 for the extraction separation coefficient of chloride ion and dihydrogen phosphate, which is still relatively low, resulting in a low total utilization rate of phosphoric acid (total utilization rate of phosphoric acid is 68%), high production cost and high chloride ion content in the final product potassium dihydrogen phosphate or sodium dihydrogen phosphate, which cannot meet the quality indicators of high-quality products.

[0006] Chinese patent CN110395707A discloses a method for preparing potassium dihydrogen phosphate, comprising the following steps: adding phosphate rock powder to wet-process phosphoric acid for reaction, and then performing solid-liquid separation to obtain primary purified phosphoric acid; adding potassium salt to the primary purified phosphoric acid, and then performing aging and filtering after the reaction to obtain secondary purified phosphoric acid; adding a complexing agent to the secondary purified phosphoric acid, and then performing stirring, standing and settling, and filtering to obtain tertiary purified phosphoric acid; extracting the tertiary purified phosphoric acid with tri-n-butylamine, and then adding potassium chloride for reaction to obtain a potassium dihydrogen phosphate solution; adjusting the pH value of the potassium dihydrogen phosphate solution to 4-5, and then vacuum concentrating, and then performing cooling crystallization, solid-liquid separation, and drying to obtain potassium dihydrogen phosphate. This patent uses an organic solvent to extract and purify phosphoric acid three times. Although it can help the purity of potassium dihydrogen phosphate to a certain extent, each extraction will cause the organic solvent and phosphoric acid to form a common interface, which will inevitably lead to a large loss rate of phosphoric acid. Because the separation coefficient of tri-n-butylamine for phosphate and hydrochloric acid is relatively low, the conversion rate of the reaction between phosphoric acid extracted by tri-n-butylamine and potassium chloride will be low, making it difficult to obtain high-purity potassium dihydrogen phosphate with a purity of more than 99.5%. Summary of the invention

[0007] The purpose of the present invention is to provide a method for preparing dihydrogen phosphate, which has a high double decomposition reaction conversion rate, greatly improves the total utilization rate of phosphoric acid and reduces the production cost, and can obtain a high-quality dihydrogen phosphate product with low chloride ions.

[0008] The method for preparing dihydrogen phosphate of the present invention comprises the following steps: (1) The composite extractant and the phosphoric acid aqueous solution are mixed uniformly and allowed to stand to obtain an extractant loaded with phosphoric acid; wherein the composite extractant is a mixture of component A, component B and component C, component A is one or more of 3-amino-1-propanol, 3-dimethylamino-1-propanol, 3-amino-1-butanol, 3-dimethylamino-1-butanol or 3-amino-4,4-dimethyl-1-pentanol, component B is one or both of isopentanol and nonanol, and component C is one or more of n- / isotridecane and n- / isooctadecane; (2) the phosphoric acid-loaded extractant undergoes a double decomposition reaction with a chloride salt solution, and layers are separated to obtain an aqueous phase; (3) The aqueous phase is concentrated and recrystallized to obtain dihydrogen phosphate.

[0009] In step (1), the volume ratio of component A, component B and component C is 1-2.5:0.5-3:5-9.

[0010] The preparation method of the composite extractant in step (1) is to mix component A, component B and component C evenly and then let stand for 30-90 minutes to obtain the composite extractant.

[0011] The mass concentration of the phosphoric acid aqueous solution in step (1) is 25-60%.

[0012] In step (1), the volume ratio of the composite extractant to the phosphoric acid aqueous solution is 4-10:1.

[0013] In step (1), the mixing temperature is 25-35° C. and the standing time is 1-3 h.

[0014] The chloride salt solution in step (2) is a potassium chloride solution or a sodium chloride solution, and the concentration of the chloride salt solution is 0.4-4 mol / L.

[0015] In step (2), the volume ratio of the phosphoric acid-loaded extractant to the chloride salt solution is 1-7.2:1.

[0016] The temperature of the metathesis reaction in step (2) is 60-80° C., and the time of the metathesis reaction is 2-3 hours.

[0017] In step (3), the recrystallization temperature is 5-30°C and the recrystallization time is 0.5-2h.

[0018] The composite extractant used in the present invention is a "network winding" liquid extractant with ion screening effect. The separation coefficient of the composite extractant for chloride ions and dihydrogen phosphate ions is not less than 400.

[0019] The method for preparing dihydrogen phosphate of the present invention comprises the following specific steps: (1) Cl - and H 2 PO 4 - Preparation of ion sieving "network entanglement" composite extractant: Mix components A, B and C evenly and let stand for 30-90 minutes to prepare Cl - and H 2 PO 4 - Ion sieving action "network entanglement" composite extractant; (2) Preparation of an extractant loaded with phosphoric acid: the composite extractant and the phosphoric acid aqueous solution are mixed evenly and allowed to stand to obtain an extractant loaded with phosphoric acid; (3) Double decomposition reaction: The phosphoric acid-loaded extractant undergoes double decomposition reaction with the chloride salt solution, and separates the layers to obtain an aqueous phase and an oil phase; (4) Concentration and crystallization of dihydrogen phosphate: The aqueous phase after stratification in step (3) is evaporated, concentrated and recrystallized to obtain the dihydrogen phosphate product. The remaining aqueous phase solution during the crystallization process can be used to dissolve chloride salt in the next batch production; (5) Recovery of the extractant: The oil phase after stratification in step (3) is mixed thoroughly with an alkaline solution (e.g., aqueous ammonia solution) for stripping. The contents of chloride ions and dihydrogen phosphate in the raffinate exceed 99%. The organic phase after stripping is used as the extractant for the next reaction.

[0020] In the present invention, one or more alcohol solvents containing amino functional groups selected from 3-amino-1-propanol, 3-dimethylamino-1-propanol, 3-amino-1-butanol, 3-dimethylamino-1-butanol or 3-amino-4,4-dimethyl-1-pentanol are used as component A of the "acid group adsorption group"; one or two selected from isopentanol or nonanol are used as component B to wrap the acid group "adsorption site" of the "acid group adsorption group" component A, i.e., the amino functional group. Since the main chain length of the solvent in component B is similar to the main chain length of the main solvent in component A, the molecules of component A and component B are hydrogen bonded between the alcohol hydroxyl groups on the main chain, and the amino functional group of the acid group "adsorption center" of component A can be realized by controlling the thickness of the molecular layer of component B. The distance between the adsorbent group and the adsorbate molecule is adjusted to adjust the adsorption / desorption capacity, so that the acid radical ion adsorption capacity is better and easy to desorb; one or more of normal / isomeric tridecane-normal / isomeric octadecane is used as component C; when components A, component B and component C are evenly mixed, the hydrogen atoms of the long carbon chain alkanes in component C hydrogen bond with the hydroxyl groups in components A and component B, and component A is fully wrapped by the grid-entangled hydrogen bonds formed by components B and component C. Component A is similar to the acid radical "adsorption center" of the "porous liquid", and components B and component C are similar to the sieve pores of the "porous liquid", and component C can induce the diffusion of dihydrogen phosphate and chloride ions due to the long carbon chain of component C after wrapping components A and component B. When dihydrogen phosphate is mixed with three types of solvents and interacts with each other through the "network winding" structure formed by hydrogen bonds, the kinetic diameter of dihydrogen phosphate is too large and is blocked outside the sieve pores of the "porous liquid", and has a weak adsorption effect on the acid "adsorption center" of the "porous liquid". When the "network winding" composite extractant loaded with phosphoric acid interacts with potassium chloride or sodium aqueous solution, the chloride ion and dihydrogen phosphate ion are replaced at the contact interface between the extractant and the aqueous solution. Because the chloride ion kinetic diameter is small, it can enter the sieve pores of the "porous liquid". Because the charge density of Cl⁻ is high (small ion radius, concentrated charge), it has a good match with the positive charge area of ​​the protonated amino group, and the adsorption efficiency is significantly higher than that of the large-sized anion dihydrogen phosphate. Cl⁻ has a strong adsorption effect on the acid "adsorption center" of the "porous liquid", so the separation coefficient of dihydrogen phosphate and chloride ion can reach more than 400, and the conversion rate of the double decomposition reaction is high. The extractant can be recycled after recovery without secondary pollution, and the technical and economic efficiency is significantly improved.

[0021] The beneficial effects of the present invention are as follows: In view of the shortcomings of low extraction separation coefficient of chloride ion and dihydrogen phosphate in the existing extraction and double decomposition combined method, low total utilization rate of phosphoric acid, and high chloride ion content in the final product potassium dihydrogen phosphate or sodium dihydrogen phosphate, the present invention provides a "network winding" composite extractant with ion screening effect. The composite extractant is composed of 3 types of long-chain structure solvents. After the 3 types of solvents are mixed, they form an intertwined "network winding" structure through hydrogen bonds, which has an ion screening effect on chloride ions and dihydrogen phosphate, and the separation coefficient of dihydrogen phosphate and chloride ions can reach more than 400. The double decomposition reaction conversion rate of the present invention is high, the total utilization rate of phosphoric acid is greatly improved, and the production cost is reduced, and a high-quality dihydrogen phosphate product with low chloride ions can be obtained. DETAILED DESCRIPTION

[0022] The present invention is further described below with reference to the embodiments.

[0023] Example 1 (1) The composite extractant and 35wt.% phosphoric acid aqueous solution are mixed uniformly at 30°C in a volume ratio of 6:1, and allowed to stand for 2 hours to obtain an extractant loaded with phosphoric acid; wherein the composite extractant is a mixture of component A, component B and component C, component A is 3-amino-1-propanol, 3-dimethylamino-1-propanol and 3-amino-1-butanol, and the volume ratio of 3-amino-1-propanol, 3-dimethylamino-1-propanol and 3-amino-1-butanol is 0.5:0.5:0.3; component B is isopentanol and nonanol, and the volume ratio of isopentanol to nonanol is 0.6:0.4; component C is n-tridecane, 2-methyldodecane and n-hexadecane, and the volume ratio of n-tridecane, 2-methyldodecane and n-hexadecane is 0.3:0.3:0.4; component A, component B and component C are fully mixed uniformly in a volume ratio of 1:1:6, and allowed to stand for 50 minutes to obtain a composite extractant; (2) Take 136 mL of the phosphoric acid-loaded extractant and 20 mL of potassium chloride solution (concentration 3.8 mol / L) to carry out double decomposition reaction at a reaction temperature of 80 °C, a stirring speed of 500 r / min, a reaction time of 2 hours, separate the layers, and obtain an aqueous phase; (3) The aqueous phase was concentrated and recrystallized at 10°C for 1 h to obtain potassium dihydrogen phosphate.

[0024] The content of potassium dihydrogen phosphate is 99.85%, the content of chloride ion is 0.15%, and the separation coefficient β is 401.

[0025] Example 2 (1) The composite extractant and 25 wt.% phosphoric acid aqueous solution are mixed uniformly at 30° C. in a volume ratio of 4:1, and allowed to stand for 2 hours to obtain an extractant loaded with phosphoric acid; wherein the composite extractant is a mixture of component A, component B and component C, component A is 3-amino-1-propanol and 3-dimethylamino-1-propanol, and the volume ratio of 3-amino-1-propanol to 3-dimethylamino-1-propanol is 0.5:0.5; component B is isopentanol; and component C is n-tridecane; component A, component B and component C are fully mixed uniformly in a volume ratio of 2:1:5, and allowed to stand for 30 minutes to obtain a composite extractant; (2) Take 80 mL of the phosphoric acid-loaded extractant and 80 mL of sodium chloride solution (concentration 0.4 mol / L) to carry out double decomposition reaction at a reaction temperature of 80 °C, a stirring speed of 500 r / min, a reaction time of 2 hours, separate the layers, and obtain an aqueous phase; (3) The aqueous phase was concentrated and recrystallized at 5°C for 2 h to obtain sodium dihydrogen phosphate.

[0026] The content of sodium dihydrogen phosphate is 99.75%, the chloride ion content is 0.16%, and the separation coefficient β is 414.

[0027] Example 3 (1) The composite extractant and 60 wt.% phosphoric acid aqueous solution are mixed uniformly at 25° C. in a volume ratio of 10:1, and allowed to stand for 3 hours to obtain an extractant loaded with phosphoric acid; wherein the composite extractant is a mixture of component A, component B and component C, component A is 3-amino-1-propanol; component B is isopentanol and nonanol, and the volume ratio of isopentanol to nonanol is 0.6:0.4; component C is n-tridecane and 2-methyldodecane, and the volume ratio of n-tridecane to 2-methyldodecane is 0.5:0.5; component A, component B and component C are fully mixed uniformly in a volume ratio of 2:1:6, and allowed to stand for 90 minutes to obtain a composite extractant; (2) Take 107 mL of the phosphoric acid-loaded extractant and 20 mL of potassium chloride solution (concentration 3 mol / L) to carry out double decomposition reaction at a reaction temperature of 60 °C, a stirring speed of 500 r / min, a reaction time of 3 hours, separate the layers, and obtain an aqueous phase; (3) The aqueous phase was concentrated and recrystallized at 30°C for 0.5 h to obtain potassium dihydrogen phosphate.

[0028] The content of potassium dihydrogen phosphate is 99.83%, the content of chloride ion is 0.11%, and the separation coefficient β is 426.

[0029] Example 4 (1) The composite extractant and 50 wt.% phosphoric acid aqueous solution are mixed uniformly at 35° C. in a volume ratio of 8.5:1, and allowed to stand for 1 hour to obtain an extractant loaded with phosphoric acid; wherein the composite extractant is a mixture of component A, component B and component C, component A is 3-amino-1-propanol and 3-amino-1-butanol, and the volume ratio of 3-amino-1-propanol to 3-amino-1-butanol is 0.5:0.5; component B is isopentanol and nonanol, and the volume ratio of isopentanol to nonanol is 0.3:0.7; component C is n-tridecane and n-octadecane, and the volume ratio of n-tridecane to n-octadecane is 0.6:0.4; component A, component B and component C are fully mixed uniformly in a volume ratio of 2:3:7, and allowed to stand for 60 minutes to obtain a composite extractant; (2) Take 110 mL of the phosphoric acid-loaded extractant and 30 mL of potassium chloride solution (concentration 2 mol / L) to carry out double decomposition reaction at a reaction temperature of 70 °C, a stirring speed of 500 r / min, a reaction time of 3 hours, separate the layers, and obtain an aqueous phase; (3) The aqueous phase was concentrated and recrystallized at 15°C for 1.2 h to obtain potassium dihydrogen phosphate.

[0030] The content of potassium dihydrogen phosphate is 99.89%, the content of chloride ion is 0.11%, and the separation coefficient β is 450.

[0031] Example 5 (1) The composite extractant and 40 wt.% phosphoric acid aqueous solution are mixed uniformly at 30° C. in a volume ratio of 6.8:1, and allowed to stand for 2 hours to obtain an extractant loaded with phosphoric acid; wherein the composite extractant is a mixture of component A, component B and component C, component A is 3-dimethylamino-1-propanol and 3-amino-4,4-dimethyl-1-pentanol, and the volume ratio of 3-dimethylamino-1-propanol to 3-amino-4,4-dimethyl-1-pentanol is 0.7:0.3; component B is isopentanol and nonanol, and the volume ratio of isopentanol to nonanol is 0.6:0.4; component C is 2-methyldodecane and n-hexadecane, and the volume ratio of 2-methyldodecane to n-hexadecane is 0.7:0.3; component A, component B and component C are fully mixed uniformly in a volume ratio of 2.5:0.5:9, and allowed to stand for 50 minutes to obtain a composite extractant; (2) 143 mL of the phosphoric acid-loaded extractant and 20 mL of sodium chloride solution (concentration 4 mol / L) were taken for double decomposition reaction at a reaction temperature of 65 °C, a stirring speed of 500 r / min, a reaction time of 2.5 hours, and layers were separated to obtain an aqueous phase; (3) The aqueous phase was concentrated and recrystallized at 20°C for 0.8 h to obtain sodium dihydrogen phosphate.

[0032] The content of sodium dihydrogen phosphate is 99.90%, the content of chloride ion is 0.10%, and the separation coefficient β is 432.

[0033] Comparative Example 1 The composite extractant is a mixture of trioctylamine, n-octanol and sulfonated kerosene, the volume ratio of trioctylamine, n-octanol and sulfonated kerosene is 1:1:6, and the other steps are the same as in Example 1.

[0034] The content of potassium dihydrogen phosphate is 98.63%, the content of chloride ion is 0.77%, and the separation coefficient β is 165.

[0035] Comparative Example 2 The composite extractant is a mixture of component A and component B, and the other steps are the same as in Example 1.

[0036] The content of potassium dihydrogen phosphate is 97.52%, the content of chloride ion is 0.78%, and the separation coefficient β is 132.

[0037] Comparative Example 3 The composite extractant is a mixture of component A and component C, and the other steps are the same as in Example 1.

[0038] The content of potassium dihydrogen phosphate is 98.23%, the content of chloride ion is 0.67%, and the separation coefficient β is 146.

[0039] Comparative Example 4 The composite extractant is a mixture of component B and component C, and the other steps are the same as in Example 1.

[0040] The content of potassium dihydrogen phosphate is 98.7%, the content of chloride ion is 0.42%, and the separation coefficient β is 139.

[0041] Cl - and H 2 PO 4 - The calculation formula of separation coefficient β is:

[0042] Where β is Cl - Relative to H 2 PO 4 - The separation factor of is the Cl in the organic phase at equilibrium - Total concentration, mol / L; is the H in the organic phase at equilibrium 2 PO 4 - Total concentration, mol / L; is the Cl in the aqueous phase at equilibrium - Total concentration, mol / L; is the H in the water phase at equilibrium 2 PO 4- The total concentration, mol / L; the larger the β, the better the separation effect of the two elements.

[0043] The test results of Examples 1-5 and Comparative Examples 1-4 are shown in Table 1.

[0044]

Claims

1. A method for preparing dihydrogen phosphate, characterized in that The steps include: (1) The composite extractant and the phosphoric acid aqueous solution are mixed uniformly and allowed to stand to obtain an extractant loaded with phosphoric acid; wherein the composite extractant is a mixture of component A, component B and component C, component A is one or more of 3-amino-1-propanol, 3-dimethylamino-1-propanol, 3-amino-1-butanol, 3-dimethylamino-1-butanol or 3-amino-4,4-dimethyl-1-pentanol, component B is one or both of isopentanol and nonanol, and component C is one or more of n- / isotridecane and n- / isooctadecane; (2) the phosphoric acid-loaded extractant undergoes a double decomposition reaction with a chloride salt solution, and layers are separated to obtain an aqueous phase; (3) The aqueous phase is concentrated and recrystallized to obtain dihydrogen phosphate.

2. The method for preparing dihydrogen phosphate according to claim 1, characterized in that In step (1), the volume ratio of component A, component B and component C is 1-2.5:0.5-3:5-9.

3. The method for preparing dihydrogen phosphate according to claim 1, characterized in that The preparation method of the composite extractant in step (1) is to mix component A, component B and component C evenly and then let stand for 30-90 minutes to obtain the composite extractant.

4. The method for preparing dihydrogen phosphate according to claim 1, characterized in that The mass concentration of the phosphoric acid aqueous solution in step (1) is 25-60%.

5. The method for preparing dihydrogen phosphate according to claim 1, characterized in that In step (1), the volume ratio of the composite extractant to the phosphoric acid aqueous solution is 4-10:

1.

6. The method for preparing dihydrogen phosphate according to claim 1, characterized in that In step (1), the mixing temperature is 25-35° C. and the standing time is 1-3 h.

7. The method for preparing dihydrogen phosphate according to claim 1, characterized in that The chloride salt solution in step (2) is a potassium chloride solution or a sodium chloride solution, and the concentration of the chloride salt solution is 0.4-4 mol / L.

8. The method for preparing dihydrogen phosphate according to claim 1, characterized in that In step (2), the volume ratio of the phosphoric acid-loaded extractant to the chloride salt solution is 1-7.2:

1.

9. The method for preparing dihydrogen phosphate according to claim 1, characterized in that The temperature of the metathesis reaction in step (2) is 60-80° C., and the time of the metathesis reaction is 2-3 hours.

10. The method for preparing dihydrogen phosphate according to claim 1, characterized in that In step (3), the recrystallization temperature is 5-30°C and the recrystallization time is 0.5-2h.

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