Preparation method of dihydrogen phosphate

Abstract

The present invention belongs to the technical field of phosphate preparation, and particularly relates to a method for preparing dihydrogen phosphate. A composite extractant is mixed uniformly with an aqueous phosphoric acid solution and left standing 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 two of isoamyl alcohol or nonanol, and component C is one or more of normal / isomeric tridecane - normal / isomeric octadecane; the extractant loaded with phosphoric acid is subjected to a metathesis reaction with an aqueous chloride solution, and after layering, an aqueous phase is obtained; the aqueous phase is concentrated and recrystallized to obtain dihydrogen phosphate. The metathesis reaction of the present invention has a high conversion rate, greatly improves the total utilization rate of phosphoric acid and reduces the production cost at the same time.

Description

Technical Field

[0001] The present 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 in the phosphate industry, and are widely used in industries such as industry, agriculture, chemical industry, food and medicine. 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 mainly the following three existing methods for preparing potassium dihydrogen phosphate or sodium dihydrogen phosphate:

[0004] 1. Neutralization method: Potassium hydroxide or sodium hydroxide is used to carry out acid-base neutralization with phosphoric acid to prepare potassium dihydrogen phosphate or sodium dihydrogen phosphate. This method has mature technology, short process flow, few equipment, low energy consumption, less investment, low chloride ion content in the prepared product, and high product purity; currently, it is 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 used has a high price and poor atom economy.

[0005] 2. Double decomposition method: Potassium chloride or sodium chloride reacts 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 can efficiently prepare potassium dihydrogen phosphate or sodium dihydrogen phosphate; the disadvantages are that the product is mixed with potassium salts, sodium salts, and ammonium salts, and the product needs to be separated and purified, with high energy consumption and low value.

[0006] 3. Extraction and double decomposition combination method: Select a suitable extractant, load phosphoric acid in an organic solvent, and then react the organic solvent containing phosphoric acid with an aqueous solution of potassium chloride or an aqueous solution of sodium chloride to extract most of the hydrochloric acid obtained. Potassium dihydrogen phosphate or sodium dihydrogen phosphate enters the aqueous phase, and 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, has simple operation, good reaction selectivity, high recovery rate, and more advantages for the reusable extractant. However, the currently reported extractants (for example, the extractant prepared by compounding trioctylamine, n-octanol and sulfonated kerosene in 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 research on the process of preparing potassium dihydrogen phosphate by liquid-liquid ion exchange method, Zhang Li, East China University of Science and Technology, 2012) have a maximum extraction separation coefficient of chloride ions and dihydrogen phosphate radicals of only 161, and the separation coefficient is still low, resulting in a low total utilization rate of phosphoric acid (the total utilization rate of phosphoric acid is 68%), high production cost and high chloride ion content in the final product of potassium dihydrogen phosphate or sodium dihydrogen phosphate, and it cannot meet the quality indicators of high-quality products.

[0007] Chinese Patent CN110395707A discloses a preparation method of potassium dihydrogen phosphate, which includes the following steps: adding phosphate rock powder into wet-process phosphoric acid for reaction, and then performing solid-liquid separation to obtain primary purified phosphoric acid; adding potassium salt into the primary purified phosphoric acid, aging and filtering after reaction to obtain secondary purified phosphoric acid; adding a complexing agent into the secondary purified phosphoric acid, stirring, standing and settling, and then filtering to obtain tertiary purified phosphoric acid; extracting the tertiary purified phosphoric acid with tri-n-butylamine, 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, then performing vacuum concentration, and obtaining potassium dihydrogen phosphate through cooling crystallization, solid-liquid separation and drying. Although this patent uses organic solvents to extract and purify phosphoric acid three times, which can help to a certain extent with the purity of potassium dihydrogen phosphate, each extraction will cause the formation of a common interface between the organic solvent and phosphoric acid, inevitably resulting in a relatively large loss rate of phosphoric acid; due to the low separation coefficient of tri-n-butylamine for separating phosphate radicals and hydrochloric acid, the conversion rate of the phosphoric acid extracted with tri-n-butylamine and potassium chloride in the reaction will be low, making it difficult to obtain high-purity potassium dihydrogen phosphate with a purity above 99.5%. Summary of the Invention

[0008] The purpose of the present invention is to provide a preparation method of dihydrogen phosphate salts, with a high conversion rate of double decomposition reaction, greatly improving the total utilization rate of phosphoric acid while reducing production costs, and obtaining high-quality dihydrogen phosphate salt products with low chloride ions.

[0009] The preparation method of dihydrogen phosphate salts described in the present invention includes the following steps:

[0010] (1) Mixing a composite extractant evenly with an aqueous phosphoric acid solution, and standing 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 several 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 two of isoamyl alcohol or nonanol, and component C is one or several of normal / isomeric tridecane - normal / isomeric octadecane;

[0011] (2) Performing a double decomposition reaction on the extractant loaded with phosphoric acid and an aqueous chloride solution, and separating the layers to obtain an aqueous phase;

[0012] (3) Concentrating and recrystallizing the aqueous phase to obtain dihydrogen phosphate salts.

[0013] In step (1), the volume ratio of component A, component B and component C is 1-2.5:0.5-3:5-9.

[0014] The preparation method of the composite extractant in step (1) is to mix component A, component B and component C evenly and then stand for 30-90 minutes to obtain it.

[0015] In step (1), the mass concentration of the phosphoric acid aqueous solution is 25 - 60%.

[0016] In step (1), the volume ratio of the composite extractant to the phosphoric acid aqueous solution is 4 - 10:1.

[0017] In step (1), the mixing temperature is 25 - 35°C, and the standing time is 1 - 3 h.

[0018] In step (2), the chloride salt aqueous solution is a potassium chloride aqueous solution or a sodium chloride aqueous solution, and the concentration of the chloride salt aqueous solution is 0.4 - 4 mol / L.

[0019] In step (2), the volume ratio of the extractant loaded with phosphoric acid to the chloride salt aqueous solution is 1 - 7.2:1.

[0020] In step (2), the temperature of the metathesis reaction is 60 - 80°C, and the time of the metathesis reaction is 2 - 3 hours.

[0021] In step (3), the recrystallization temperature is 5 - 30°C, and the recrystallization time is 0.5 - 2 h.

[0022] The composite extractant used in the present invention is an ion sieving "network winding" liquid extractant, and the separation factor of the composite extractant for the two ions of chloride ion and dihydrogen phosphate ion is not less than 400.

[0023] The preparation method of the dihydrogen phosphate salt described in the present invention includes the following specific steps:

[0024] (1) Preparation of the Cl - and H2PO4 - ion sieving "network winding" composite extractant: Mix component A, component B, and component C evenly and then stand for 30 - 90 minutes to prepare the Cl - and H2PO4 - ion sieving "network winding" composite extractant;

[0025] (2) Preparation of the extractant loaded with phosphoric acid: Mix the composite extractant with the phosphoric acid aqueous solution evenly and stand to obtain the extractant loaded with phosphoric acid;

[0026] (3) Metathesis reaction: Carry out a metathesis reaction between the extractant loaded with phosphoric acid and the chloride salt aqueous solution, and layer to obtain an aqueous phase and an oil phase;

[0027] (4) Concentration and crystallization of the dihydrogen phosphate salt: Take the aqueous phase after layering in step (3), evaporate and concentrate it, and recrystallize to obtain the dihydrogen phosphate salt product. The remaining aqueous phase solution in the crystallization process can be used to dissolve the chloride salt during the next batch of production;

[0028] (5) Recovery of the extractant: The oil phase after layering in step (3) is fully mixed with an alkaline solution (such as an ammonia water solution) for back extraction. The contents of chloride ions and dihydrogen phosphate ions in the raffinate exceed 99%. The organic phase after back extraction is used as the extractant for the next reaction.

[0029] In the present invention, one or several alcohol solvents containing amino functional groups such as 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 radical adsorption group"; one or two of isopentanol or nonanol are used as component B to wrap the acid radical "adsorption site", i.e., the amino functional group, of component A of the "acid radical adsorption group". Since the main chain length of the solvent in component B is similar to that of the main solvent in component A, the molecules of component A and component B form hydrogen bonds between the alcohol hydroxyl groups on the main chain. By controlling the thickness of the molecular layer of component B, the distance between the amino functional group of the acid radical "adsorption center" of component A and the adsorbed substance molecules can be achieved, thereby regulating the adsorption / desorption ability, so that the acid radical ion adsorption ability is good and it is easy to desorb; one or several of normal / isomeric tridecane - normal / isomeric octadecane are used as component C; when component A, component B, and component C are mixed evenly, the hydrogen atoms of the long carbon chain alkanes in component C form hydrogen bonds with the hydroxyl groups in component A and component B. Component A is fully wrapped by the grid-wound hydrogen bonds formed by component B and component C. Component A is similar to the acid radical "adsorption center" of "porous liquid", and component B and component C are similar to the screening pores of "porous liquid". Moreover, due to the long carbon chain of component C, the extended chain after wrapping component A and component B can play an inducing role in the diffusion of dihydrogen phosphate and chloride ions. When dihydrogen phosphate interacts with the "network-wound" structure formed by hydrogen bonds after mixing with the three types of solvents, the kinetic diameter of dihydrogen phosphate is relatively large and it is blocked outside the screening pores of the "porous liquid", and has a weak adsorption effect on the acid radical "adsorption center" of the "porous liquid"; when the "network-wound" composite extractant loaded with phosphoric acid interacts with potassium chloride or sodium aqueous solution, a replacement of chloride ions and dihydrogen phosphate ions occurs at the interface between the extractant and the aqueous solution. Because the kinetic diameter of chloride ions is small, they can enter the screening pores of the "porous liquid". Also, due to the relatively high charge density of Cl⁻ (small ionic radius and concentrated charge), its matching degree with the positive charge region of the protonated amino group is good, and the adsorption efficiency is significantly higher than that of the large-size anion dihydrogen phosphate. Cl⁻ has a strong adsorption effect on the acid radical "adsorption center" of the "porous liquid". Therefore, the separation coefficient of dihydrogen phosphate and chloride ions can reach more than 400, and the conversion rate of the metathesis reaction is high. After the extractant is recovered, it can be recycled without secondary pollution, and the technical economy is significantly improved.

[0030] The beneficial effects of the present invention are as follows:

[0031] In view of the disadvantages in the existing combined extraction and double decomposition method, such as the low extraction separation coefficients of chloride ions and dihydrogen phosphate ions, the low overall utilization rate of phosphoric acid, and the high chloride ion content in the final products of potassium dihydrogen phosphate or sodium dihydrogen phosphate, the present invention provides a "network winding" composite extractant with ion sieving function. This composite extractant is composed of three types of long-chain structure solvents. After the three types of solvents are mixed, they form an intertwined "network winding" structure through hydrogen bonds, which has an ion sieving effect on chloride ions and dihydrogen phosphate ions. The separation coefficient of dihydrogen phosphate ions and chloride ions can reach more than 400. The double decomposition reaction of the present invention has a high conversion rate, greatly improves the overall utilization rate of phosphoric acid and reduces the production cost, and can obtain high-quality dihydrogen phosphate products with low chloride ion content. Detailed implementation mode

[0032] The following further describes the present invention in conjunction with embodiments.

[0033] Example 1

[0034] (1) The composite extractant and 35 wt.% phosphoric acid aqueous solution are mixed evenly at a volume ratio of 6:1 at 30 °C and left standing for 2 h to obtain the extractant loaded with phosphoric acid. Among them, 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. 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 isoamyl alcohol and nonanol, and the volume ratio of isoamyl alcohol 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 evenly at a volume ratio of 1:1:6 and left standing for 50 minutes to obtain the composite extractant;

[0035] (2) Take 136 mL of the extractant loaded with phosphoric acid and 20 mL of potassium chloride solution (concentration 3.8 mol / L) for double decomposition reaction. The reaction temperature is 80 °C, the stirring speed is 500 r / min, the reaction time is 2 hours, and after stratification, the aqueous phase is obtained;

[0036] (3) The aqueous phase is concentrated and recrystallized at 10 °C for 1 h to obtain potassium dihydrogen phosphate.

[0037] The content of potassium dihydrogen phosphate is 99.85%, the chloride ion content is 0.15%, and the separation coefficient β is 401.

[0038] Example 2

[0039] (1) The composite extractant is mixed with 25 wt.% phosphoric acid aqueous solution at a volume ratio of 4:1 and stirred evenly at 30 °C, then left standing for 2 h to obtain the phosphoric acid-loaded extractant. Among them, 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 isoamyl alcohol; component C is n-tridecane. Component A, component B and component C are fully mixed evenly at a volume ratio of 2:1:5 and left standing for 30 minutes to obtain the composite extractant.

[0040] (2) Take 80 mL of the phosphoric acid-loaded extractant and 80 mL of sodium chloride solution (concentration 0.4 mol / L) for metathesis reaction. The reaction temperature is 80 °C, the stirring speed is 500 r / min, the reaction time is 2 hours, and after layering, the aqueous phase is obtained.

[0041] (3) The aqueous phase is concentrated and recrystallized at 5 °C for 2 h to obtain sodium dihydrogen phosphate.

[0042] The content of sodium dihydrogen phosphate is 99.75%, and the chloride ion content is 0.16%. Among them, the separation coefficient β is 414.

[0043] Example 3

[0044] (1) The composite extractant is mixed with 60 wt.% phosphoric acid aqueous solution at a volume ratio of 10:1 and stirred evenly at 25 °C, then left standing for 3 h to obtain the phosphoric acid-loaded extractant. Among them, the composite extractant is a mixture of component A, component B and component C. Component A is 3-amino-1-propanol; component B is isoamyl alcohol and nonanol, and the volume ratio of isoamyl alcohol 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 evenly at a volume ratio of 2:1:6 and left standing for 90 minutes to obtain the composite extractant.

[0045] (2) Take 107 mL of the phosphoric acid-loaded extractant and 20 mL of potassium chloride solution (concentration 3 mol / L) for metathesis reaction. The reaction temperature is 60 °C, the stirring speed is 500 r / min, the reaction time is 3 hours, and after layering, the aqueous phase is obtained.

[0046] (3) The aqueous phase is concentrated and recrystallized at 30 °C for 0.5 h to obtain potassium dihydrogen phosphate.

[0047] The content of potassium dihydrogen phosphate is 99.83%, and the chloride ion content is 0.11%. Among them, the separation coefficient β is 426.

[0048] Example 4

[0049] (1) The composite extractant is mixed with 50 wt.% phosphoric acid aqueous solution at a volume ratio of 8.5:1 and stirred evenly at 35 °C, then left standing for 1 h to obtain the phosphoric acid-loaded extractant. The composite extractant is a mixture of component A, component B, and component C. Component A is a mixture of 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 a mixture of isoamyl alcohol and nonanol, and the volume ratio of isoamyl alcohol to nonanol is 0.3:0.7. Component C is a mixture of 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 evenly at a volume ratio of 2:3:7 and left standing for 60 minutes to obtain the composite extractant.

[0050] (2) Take 110 mL of the phosphoric acid-loaded extractant and 30 mL of potassium chloride solution (concentration 2 mol / L) for metathesis reaction. The reaction temperature is 70 °C, the stirring speed is 500 r / min, the reaction time is 3 h, and after layering, the aqueous phase is obtained.

[0051] (3) The aqueous phase is concentrated and recrystallized at 15 °C for 1.2 h to obtain potassium dihydrogen phosphate.

[0052] The content of potassium dihydrogen phosphate is 99.89%, the chloride ion content is 0.11%, and the separation coefficient β is 450.

[0053] Example 5

[0054] (1) The composite extractant is mixed with 40 wt.% phosphoric acid aqueous solution at a volume ratio of 6.8:1 and stirred evenly at 30 °C, then left standing for 2 h to obtain the phosphoric acid-loaded extractant. The composite extractant is a mixture of component A, component B, and component C. Component A is a mixture of 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 a mixture of isoamyl alcohol and nonanol, and the volume ratio of isoamyl alcohol to nonanol is 0.6:0.4. Component C is a mixture of 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 evenly at a volume ratio of 2.5:0.5:9 and left standing for 50 minutes to obtain the composite extractant.

[0055] (2) Take 143 mL of the phosphoric acid-loaded extractant and 20 mL of sodium chloride solution (concentration 4 mol / L) for metathesis reaction. The reaction temperature is 65 °C, the stirring speed is 500 r / min, the reaction time is 2.5 h, and after layering, the aqueous phase is obtained.

[0056] (3) The aqueous phase is concentrated and recrystallized at 20 °C for 0.8 h to obtain sodium dihydrogen phosphate.

[0057] The content of sodium dihydrogen phosphate is 99.90%, and the content of chloride ions is 0.10%. Among them, the separation coefficient β is 432.

[0058] Comparative Example 1

[0059] The composite extractant is a mixture of trioctylamine, n-octanol and sulfonated kerosene. The volume ratio of trioctylamine, n-octanol to sulfonated kerosene is 1:1:6. Other steps are the same as those in Example 1.

[0060] The content of potassium dihydrogen phosphate is 98.63%, and the content of chloride ions is 0.77%. Among them, the separation coefficient β is 165.

[0061] Comparative Example 2

[0062] The composite extractant is a mixture of component A and component B. Other steps are the same as those in Example 1.

[0063] The content of potassium dihydrogen phosphate is 97.52%, and the content of chloride ions is 0.78%. Among them, the separation coefficient β is 132.

[0064] Comparative Example 3

[0065] The composite extractant is a mixture of component A and component C. Other steps are the same as those in Example 1.

[0066] The content of potassium dihydrogen phosphate is 98.23%, and the content of chloride ions is 0.67%. Among them, the separation coefficient β is 146.

[0067] Comparative Example 4

[0068] The composite extractant is a mixture of component B and component C. Other steps are the same as those in Example 1.

[0069] The content of potassium dihydrogen phosphate is 98.7%, and the content of chloride ions is 0.42%. Among them, the separation coefficient β is 139.

[0070] Cl - and H2PO4 - The calculation formula for the separation coefficient β is:

[0071]

[0072] Among them, β is the separation coefficient of Cl - relative to H2PO4 - ; is the total concentration of Cl - in the organic phase at equilibrium, mol / L; is the total concentration of H2PO4 - in the organic phase at equilibrium, mol / L; is the total concentration of Cl - in the aqueous phase at equilibrium, mol / L; is the total concentration of H2PO4 in the aqueous phase at equilibrium, mol / L; the larger β is, the better the separation effect of the two elements. - The detection results of Examples 1-5 and Comparative Examples 1-4 are shown in Table 1.

[0073] The detection results of Examples 1-5 and Comparative Examples 1-4 are shown in Table 1.

[0074]

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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