Method for preparing sodium dihydrogen phosphate by purifying crude sodium pyrophosphate

Abstract

The invention relates to the technical field of yellow phosphorus chemical industry, in particular to a method for preparing sodium dihydrogen phosphate by purifying crude sodium pyrophosphate. Comprising the following steps: mixing a byproduct crude sodium pyrophosphate with water, filtering and separating filter residues containing sodium chloride to obtain a sodium pyrophosphate crude filtrate; adding phosphoric acid into the sodium pyrophosphate coarse filtrate, and obtaining sodium dihydrogen phosphate coarse liquid without side reaction after sodium pyrophosphate is completely hydrolyzed into sodium dihydrogen phosphate; adding a decolorizing agent into the sodium dihydrogen phosphate crude solution, removing organic pigments in the sodium dihydrogen phosphate crude solution and reducing the impurity content of iron ions to obtain a decolorized sodium dihydrogen phosphate solution; carrying out filter pressing treatment on the decolored sodium dihydrogen phosphate solution, and removing suspended solids, decoloring agent residues and trace insoluble impurities to prepare a clear and transparent sodium dihydrogen phosphate refined solution; through the mode, the effects of efficiently purifying the byproduct crude sodium pyrophosphate and converting the byproduct crude sodium pyrophosphate into high-quality sodium dihydrogen phosphate, realizing resource cyclic utilization of the byproduct and reducing the purchase cost of raw materials are achieved.

Description

Technical Field

[0001] This invention relates to the field of yellow phosphorus chemical technology, and in particular to a method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate. Background Technology

[0002] Sodium pyrophosphate is a widely used and important chemical raw material. In chemical production, electroplating, metal surface treatment, and phosphate production processes, a large amount of crude sodium pyrophosphate is generated as a byproduct. This crude sodium pyrophosphate has a complex composition, containing various impurities such as sodium chloride, insoluble inorganic salts, organic pigments, iron ions, and heavy metals. Its purity is low, making it unsuitable for direct use as a high-quality raw material.

[0003] Currently, the industry's disposal methods for by-product crude sodium pyrophosphate are relatively simple, mostly involving exporting it as a low-grade product or discarding it directly. This not only fails to fully tap its potential resource value but also leads to problems such as warehousing accumulation and increased environmental treatment costs, resulting in serious resource idleness and waste. At the same time, the production process of sodium hexametaphosphate requires a large amount of high-quality sodium dihydrogen phosphate as raw material. At present, enterprises mainly rely on purchasing this raw material from external sources, resulting in high raw material procurement costs and severely restricting the market competitiveness of sodium hexametaphosphate products.

[0004] In conclusion, it is essential to propose a method for purifying crude sodium pyrophosphate and converting it into high-quality sodium dihydrogen phosphate, thereby achieving resource recycling of the byproduct and reducing raw material procurement costs. Summary of the Invention

[0005] The purpose of this invention is to provide a method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate, which achieves the goal of efficiently purifying and converting the by-product crude sodium pyrophosphate into high-quality sodium dihydrogen phosphate, realizing the resource recycling of by-products, and reducing raw material procurement costs.

[0006] To achieve the above objectives, the present invention provides a method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate, comprising the following steps:

[0007] The by-product crude sodium pyrophosphate is mixed with water, and the filter residue containing sodium chloride is separated by filtration to obtain sodium pyrophosphate crude filtrate.

[0008] Phosphoric acid was added to the crude filtrate of sodium pyrophosphate, and the sodium pyrophosphate was completely hydrolyzed to sodium dihydrogen phosphate to obtain a crude sodium dihydrogen phosphate solution without side reactions.

[0009] Add a decolorizing agent to the crude sodium dihydrogen phosphate solution to remove organic pigments and reduce the iron ion impurity content, thereby obtaining a decolorized sodium dihydrogen phosphate solution.

[0010] The decolorized sodium dihydrogen phosphate solution was subjected to pressure filtration to remove suspended solids, decolorizing agent residues, and trace amounts of insoluble impurities, resulting in a clear and transparent refined sodium dihydrogen phosphate solution.

[0011] In the step of mixing the by-product crude sodium pyrophosphate with water, filtering to separate the filter residue containing sodium chloride, and obtaining the crude sodium pyrophosphate filtrate:

[0012] The by-product crude sodium pyrophosphate was mixed with water at a solid-liquid ratio of 1:2 to 8.

[0013] By controlling the mixing system to a low-temperature environment and adjusting the stirring intensity and stirring time, sodium pyrophosphate is dissolved and the dissolution of impurities is inhibited.

[0014] The mixed system was filtered to separate the filter residue containing sodium chloride, and the crude filtrate of sodium pyrophosphate was collected.

[0015] In the step of controlling the mixing system to a low-temperature environment, adjusting the stirring intensity and stirring time, dissolving sodium pyrophosphate and inhibiting the dissolution of impurities:

[0016] The low temperature environment is 15~25℃, the stirring speed is 100~500 rpm, and the stirring time is 0.5~3 hours.

[0017] In the step of adding phosphoric acid to the crude filtrate of sodium pyrophosphate and waiting for the sodium pyrophosphate to be completely hydrolyzed to sodium dihydrogen phosphate to obtain a crude sodium dihydrogen phosphate solution without side reactions:

[0018] Add phosphoric acid to the crude filtrate of sodium pyrophosphate, controlling the molar ratio of phosphoric acid to sodium pyrophosphate to be 1.8~2.5:1;

[0019] Heat the reaction system to 60-95℃, maintain the temperature and stir continuously;

[0020] The hydrolysis reaction time was controlled to be 2-6 hours, and the pH value of the system was adjusted between 1.5 and 3.5 throughout the process;

[0021] After the sodium pyrophosphate is completely hydrolyzed, the reaction is stopped, and a crude sodium dihydrogen phosphate solution without side reactions is obtained.

[0022] In the step of adding a decolorizing agent to the crude sodium dihydrogen phosphate solution to remove organic pigments and reduce the iron ion impurity content, thereby obtaining a decolorized sodium dihydrogen phosphate solution:

[0023] Add a decolorizing agent to the crude sodium dihydrogen phosphate solution, with the amount of decolorizing agent added being 0.1% to 2% of the mass of the crude sodium dihydrogen phosphate solution;

[0024] The temperature of the system after adding the decolorizing agent should be controlled at 40~80℃;

[0025] Maintain the system temperature and continue stirring to ensure that the decolorizing agent and crude liquid are in full contact for 0.5 to 4 hours;

[0026] After decolorization and impurity removal are completed, organic pigments are removed and the iron ion impurity content is reduced to obtain sodium dihydrogen phosphate solution.

[0027] In the step of performing pressure filtration on the decolorized sodium dihydrogen phosphate solution to remove suspended solids, decolorizing agent residue, and trace insoluble impurities, and obtaining a clear and transparent refined sodium dihydrogen phosphate solution:

[0028] The decolorized sodium dihydrogen phosphate solution is fed into a filter press, using a 200-500 mesh filter cloth.

[0029] Adjust the working pressure of the filter press to ~0.2~1.0 MPa;

[0030] Maintain the pressure of the filter press and control the filter press cycle to be 0.5 to 3 hours for filter press purification;

[0031] After the pressure filtration is completed, the filtrate is collected, and suspended solids, decolorizing agent residues and trace amounts of insoluble impurities are removed to obtain a clear and transparent sodium dihydrogen phosphate purified solution.

[0032] In the step of feeding the decolorized sodium dihydrogen phosphate solution into a filter press, using a filter cloth of 200-500 mesh:

[0033] 200-500 mesh filter cloth is made of either polyester or polypropylene.

[0034] This invention discloses a method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate, comprising the following steps: mixing by-product crude sodium pyrophosphate with water, filtering to separate the filter residue containing sodium chloride, obtaining a crude sodium pyrophosphate filtrate; adding phosphoric acid to the crude sodium pyrophosphate filtrate, and waiting for the sodium pyrophosphate to be completely hydrolyzed into sodium dihydrogen phosphate, obtaining a crude sodium dihydrogen phosphate solution without side reactions; adding a decolorizing agent to the crude sodium dihydrogen phosphate solution to remove organic pigments and reduce the iron ion impurity content, obtaining a decolorized sodium dihydrogen phosphate solution; subjecting the decolorized sodium dihydrogen phosphate solution to pressure filtration to remove suspended solids, decolorizing agent residue, and trace insoluble impurities, obtaining a clear and transparent refined sodium dihydrogen phosphate solution; through the above method, the by-product crude sodium pyrophosphate can be efficiently purified and converted into high-quality sodium dihydrogen phosphate, realizing the resource recycling of by-products and reducing raw material procurement costs. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a flowchart of the steps in the method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate according to the present invention.

[0037] Figure 2 This is a flowchart of steps S100 of the present invention.

[0038] Figure 3 This is a flowchart of steps S200 of the present invention.

[0039] Figure 4 This is a flowchart of steps S300 of the present invention.

[0040] Figure 5 This is a flowchart of steps S400 of the present invention. Detailed Implementation

[0041] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0042] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0043] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0044] Please see Figures 1-5 , Figure 1This is a flowchart of the method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate according to the present invention; Figure 2 This is a flowchart of steps S100 of the present invention; Figure 3 This is a flowchart of steps S200 of the present invention; Figure 4 This is a flowchart of steps S300 of the present invention; Figure 5 This is a flowchart of steps S400 of the present invention.

[0045] This invention provides a method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate, comprising the following steps:

[0046] S100: The by-product crude sodium pyrophosphate is mixed with water, and the filter residue containing sodium chloride is separated by filtration to obtain the crude sodium pyrophosphate filtrate.

[0047] In this embodiment, the by-product crude sodium pyrophosphate is mixed with water, and the filter residue containing sodium chloride is separated by filtration to obtain a crude sodium pyrophosphate filtrate. The specific process is as follows:

[0048] S101: Mix the by-product crude sodium pyrophosphate with water at a solid-liquid ratio of 1:2~8;

[0049] S102: Control the mixing system to a low temperature environment, adjust the stirring intensity and stirring time, dissolve sodium pyrophosphate and inhibit the dissolution of impurities. The low temperature environment is 15~25℃, the stirring speed is 100~500 rpm, and the stirring time is 0.5~3 hours.

[0050] S103: The mixed system is filtered to separate the filter residue containing sodium chloride, and the crude filtrate of sodium pyrophosphate is collected.

[0051] In the above process, the by-product crude sodium pyrophosphate is thoroughly mixed with water at a solid-liquid ratio of 1:2 to 8. The temperature of the mixed system is controlled at a low temperature of 15 to 25°C. The stirring equipment is adjusted to a speed of 100 to 500 rpm and stirred continuously for 0.5 to 3 hours to achieve efficient dissolution of sodium pyrophosphate while suppressing the dissolution of impurities such as sodium chloride to the greatest extent. Subsequently, the mixed system is filtered to separate the filter residue containing sodium chloride and collect the crude pyrophosphate filtrate.

[0052] S200: Add phosphoric acid to the crude filtrate of sodium pyrophosphate, and wait for the sodium pyrophosphate to be completely hydrolyzed into sodium dihydrogen phosphate to obtain a crude sodium dihydrogen phosphate solution without side reactions.

[0053] In this embodiment, phosphoric acid is added to the crude filtrate of sodium pyrophosphate, and the sodium pyrophosphate is completely hydrolyzed to sodium dihydrogen phosphate to obtain a crude sodium dihydrogen phosphate solution without side reactions. The specific process is as follows:

[0054] S201: Add phosphoric acid to the crude filtrate of sodium pyrophosphate, controlling the molar ratio of phosphoric acid to sodium pyrophosphate to be 1.8~2.5:1;

[0055] S202: Heat the reaction system to 60~95℃, maintain the temperature and stir continuously;

[0056] S203: Control the hydrolysis reaction time to 2-6 hours, and maintain the pH value of the system between 1.5 and 3.5 throughout the process;

[0057] S204: After the sodium pyrophosphate is completely hydrolyzed, the reaction is stopped, and crude sodium dihydrogen phosphate solution without side reactions is obtained.

[0058] In the above process, phosphoric acid is added to the crude sodium pyrophosphate filtrate, and the molar ratio of phosphoric acid to sodium pyrophosphate is strictly controlled at 1.8~2.5:1. The reaction system is heated to 60~95℃ and stirred continuously at this temperature. The hydrolysis reaction time is controlled at 2~6 hours, and the pH value of the system is stably controlled between 1.5 and 3.5 throughout the entire hydrolysis reaction. The reaction is stopped after the sodium pyrophosphate is completely hydrolyzed, and crude sodium dihydrogen phosphate solution without side reactions is obtained.

[0059] S300: Add a decolorizing agent to the crude sodium dihydrogen phosphate solution to remove organic pigments and reduce the impurity content of iron ions, thereby obtaining a decolorized sodium dihydrogen phosphate solution.

[0060] In this embodiment, a decolorizing agent is added to the crude sodium dihydrogen phosphate solution to remove organic pigments and reduce the iron ion impurity content, thereby obtaining a decolorized sodium dihydrogen phosphate solution. The specific process is as follows:

[0061] S301: Add a decolorizing agent to the crude sodium dihydrogen phosphate solution, the amount of decolorizing agent added being 0.1%~2% of the mass of the crude sodium dihydrogen phosphate solution;

[0062] S302: Control the temperature of the system after adding the decolorizing agent at 40~80℃;

[0063] S303: Maintain the system temperature and stir continuously to ensure that the decolorizing agent and crude liquid are in full contact for 0.5 to 4 hours;

[0064] S304: After decolorization and impurity removal are completed, organic pigments are removed and the iron ion impurity content is reduced to obtain sodium dihydrogen phosphate solution.

[0065] In the above process, a decolorizing agent is added to the crude sodium dihydrogen phosphate solution. The amount of decolorizing agent added is 0.1% to 2% of the mass of the crude sodium dihydrogen phosphate solution. The temperature of the system after adding the decolorizing agent is controlled at 40 to 80°C. This temperature is maintained and the mixture is continuously stirred to ensure that the decolorizing agent and the crude sodium dihydrogen phosphate solution are in full contact for 0.5 to 4 hours, thereby completing the decolorization and impurity removal operation. This effectively removes organic pigments from the crude solution and reduces the content of impurities such as iron ions, resulting in a decolorized sodium dihydrogen phosphate solution.

[0066] S400: The decolorized sodium dihydrogen phosphate solution is subjected to pressure filtration to remove suspended solids, decolorizing agent residues and trace amounts of insoluble impurities, resulting in a clear and transparent refined sodium dihydrogen phosphate solution.

[0067] In this embodiment, the decolorized sodium dihydrogen phosphate solution is subjected to pressure filtration to remove suspended solids, decolorizing agent residue, and trace amounts of insoluble impurities, thereby obtaining a clear and transparent purified sodium dihydrogen phosphate solution. The specific process is as follows:

[0068] S401: Feed the decolorized sodium dihydrogen phosphate solution into a filter press, using a 200-500 mesh filter cloth;

[0069] S402: Adjust the working pressure of the filter press to ~0.2~1.0 MPa;

[0070] S403: Maintain the pressure of the filter press and control the filter press cycle to be 0.5~3 hours for filter press purification;

[0071] S403: After the pressure filtration is completed, collect the filtrate, remove suspended solids, decolorizing agent residue and trace insoluble impurities to obtain a clear and transparent sodium dihydrogen phosphate purified solution.

[0072] In the above process, the decolorized sodium dihydrogen phosphate solution is fed into a filter press. A 200-500 mesh filter cloth is selected, and the material of the 200-500 mesh filter cloth is either polyester or polypropylene. The working pressure of the filter press is adjusted to 0.2-1.0 MPa, and this filtration pressure is maintained. The filtration cycle is controlled to 0.5-3 hours to perform deep filtration purification of the solution. After the filtration is completed, the filtrate is collected, which effectively removes suspended solids, decolorizing agent residues and trace insoluble impurities from the solution, and finally obtains a clear and transparent refined sodium dihydrogen phosphate solution.

[0073] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0074] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate, characterized in that, Includes the following steps: The by-product crude sodium pyrophosphate is mixed with water, and the filter residue containing sodium chloride is separated by filtration to obtain sodium pyrophosphate crude filtrate. Phosphoric acid was added to the crude filtrate of sodium pyrophosphate, and the sodium pyrophosphate was completely hydrolyzed to sodium dihydrogen phosphate to obtain a crude sodium dihydrogen phosphate solution without side reactions. Add a decolorizing agent to the crude sodium dihydrogen phosphate solution to remove organic pigments and reduce the iron ion impurity content, thereby obtaining a decolorized sodium dihydrogen phosphate solution. The decolorized sodium dihydrogen phosphate solution was subjected to pressure filtration to remove suspended solids, decolorizing agent residues, and trace amounts of insoluble impurities, resulting in a clear and transparent refined sodium dihydrogen phosphate solution.

2. The method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate as described in claim 1, characterized in that, In the step of mixing the by-product crude sodium pyrophosphate with water, filtering to separate the filter residue containing sodium chloride, and obtaining the crude sodium pyrophosphate filtrate: The by-product crude sodium pyrophosphate was mixed with water at a solid-liquid ratio of 1:2 to 8. By controlling the mixing system to a low-temperature environment and adjusting the stirring intensity and stirring time, sodium pyrophosphate is dissolved and the dissolution of impurities is inhibited. The mixed system was filtered to separate the filter residue containing sodium chloride, and the crude filtrate of sodium pyrophosphate was collected.

3. The method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate as described in claim 2, characterized in that, In the steps of controlling the mixing system to a low-temperature environment and adjusting the stirring intensity and time to dissolve sodium pyrophosphate and inhibit the dissolution of impurities: The low temperature environment is 15~25℃, the stirring speed is 100~500 rpm, and the stirring time is 0.5~3 hours.

4. The method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate as described in claim 1, characterized in that, In the step of adding phosphoric acid to the crude filtrate of sodium pyrophosphate and waiting for the sodium pyrophosphate to be completely hydrolyzed to sodium dihydrogen phosphate to obtain a crude sodium dihydrogen phosphate solution without side reactions: Add phosphoric acid to the crude filtrate of sodium pyrophosphate, controlling the molar ratio of phosphoric acid to sodium pyrophosphate to be 1.8~2.5:1; Heat the reaction system to 60-95℃, maintain the temperature and stir continuously; The hydrolysis reaction time was controlled to be 2-6 hours, and the pH value of the system was adjusted between 1.5 and 3.5 throughout the process; After the sodium pyrophosphate is completely hydrolyzed, the reaction is stopped, and a crude sodium dihydrogen phosphate solution without side reactions is obtained.

5. The method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate as described in claim 1, characterized in that, In the step of adding a decolorizing agent to crude sodium dihydrogen phosphate solution to remove organic pigments and reduce the iron ion impurity content, thereby obtaining a decolorized sodium dihydrogen phosphate solution: Add a decolorizing agent to the crude sodium dihydrogen phosphate solution, with the amount of decolorizing agent added being 0.1% to 2% of the mass of the crude sodium dihydrogen phosphate solution; The temperature of the system after adding the decolorizing agent should be controlled at 40~80℃; Maintain the system temperature and continue stirring to ensure that the decolorizing agent and crude liquid are in full contact for 0.5 to 4 hours; After decolorization and impurity removal are completed, organic pigments are removed and the iron ion impurity content is reduced to obtain sodium dihydrogen phosphate solution.

6. The method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate as described in claim 1, characterized in that, In the step of performing pressure filtration on the decolorized sodium dihydrogen phosphate solution to remove suspended solids, decolorizing agent residues, and trace insoluble impurities, and obtaining a clear and transparent refined sodium dihydrogen phosphate solution: The decolorized sodium dihydrogen phosphate solution is fed into a filter press, using a 200-500 mesh filter cloth. Adjust the working pressure of the filter press to ~0.2~1.0 MPa; Maintain the pressure of the filter press and control the filter press cycle to be 0.5 to 3 hours for filter press purification; After the pressure filtration is completed, the filtrate is collected, and suspended solids, decolorizing agent residues and trace amounts of insoluble impurities are removed to obtain a clear and transparent sodium dihydrogen phosphate purified solution.

7. The method for purifying crude sodium pyrophosphate to prepare sodium dihydrogen phosphate as described in claim 6, characterized in that, In the step of feeding the decolorized sodium dihydrogen phosphate solution into a filter press, using a filter cloth of 200-500 mesh: 200-500 mesh filter cloth is made of either polyester or polypropylene.

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