A method for purifying sodium tetrachloroaluminate

Abstract

The application provides a purification method of sodium tetrachloroaluminate. The method comprises the following steps: S1, adding byproducts of sodium tetrachloroaluminate in the production process of methyl dichlorophosphine into water in batches for dissolution; S2, configuring an aqueous solution of zirconium oxychloride octahydrate, adding the aqueous solution into the aqueous solution of sodium tetrachloroaluminate at a certain speed, continuously heating and stirring for a certain time after the addition is completed, cooling to room temperature after adding anionic polyacrylamide into the system when fine white gel-like alum flowers appear in the system, and gradually cooling to room temperature until white solid precipitates with larger particles appear in the system; S3, filtering the reaction liquid to obtain a first filtrate, and the filter cake is a zirconium complex of total phosphorus impurities; and S4, adding a composite composed of zeolite, hematite and activated carbon into the first filtrate, stirring at room temperature for a certain time, standing, filtering to obtain a second filtrate, and the total phosphorus content and zirconium ion content in the second filtrate can meet the requirements of subsequent preparation of polyaluminum chloride.

Description

Technical Field

[0001] This invention belongs to the field of chemical production by-product treatment technology, specifically relating to a purification method for sodium tetrachloroaluminate. Background Technology

[0002] Methyl dichlorophosphine and diethyl methylphosphonate are both important organic chemical intermediates, crucial not only for the production of the herbicide glufosinate but also for various high-end flame retardants and pharmaceuticals. Currently, methyl dichlorophosphine is mainly prepared using the ternary complex method and the alkyl aluminum method. Both methods generate a large amount of sodium tetrachloroaluminate as a byproduct during preparation. Sodium tetrachloroaluminate contains small amounts of organic phosphine and inorganic phosphorus impurities (hereinafter referred to as total phosphorus), which is costly to dispose of as solid waste, and the aluminum resources contained within it cannot be effectively utilized, resulting in waste. How to achieve low-cost and green treatment of the aforementioned byproduct, sodium tetrachloroaluminate, is a critical issue that the industry urgently needs to address.

[0003] Patent CN105217667A discloses a process for recovering sodium tetrachloroaluminate in glufosinate production. The specific process involves adding sodium tetrachloroaluminate to a mixed solvent of alcohol and ether, using the ether as a complexing agent to re-complex with aluminum trichloride in the sodium tetrachloroaluminate, thereby precipitating sodium chloride and organophosphorus impurities. After filtering out the sodium chloride, the filtrate is cooled to precipitate aluminum trichloride. The aluminum trichloride is further purified and reused in the synthesis of methyldichlorophosphine. After several reuses, the complexing ability decreases, and sodium hydroxide is added to produce polyaluminum chloride. This recovery process suffers from drawbacks such as difficulty in crystallizing aluminum trichloride in the mother liquor, incomplete precipitation, poor crystal form, and inability to effectively filter it. Furthermore, the process uses a large amount of ether solvent, and the peroxides generated during the recovery process pose significant safety hazards in industrial implementation. The reprocessing of aluminum trichloride with decreased complexing ability is costly and energy-intensive, and total phosphorus impurities cannot be completely removed.

[0004] Patent CN109052444A discloses a method for preparing polyaluminum chloride using a byproduct generated during the production of diethyl methyl phosphite. Specifically, the method involves dispersing the byproduct sodium tetrachloroaluminate in a solvent, followed by analysis, collecting the filtrate, adding water to the filtrate and cooling it to allow hydrated aluminum chloride to crystallize, and then hydrolyzing and polymerizing the hydrated aluminum chloride to obtain polyaluminum chloride. This method uses a large amount of organic solvent, which is prone to volatile emissions and environmental pollution during recycling, making it neither economical nor environmentally friendly. Furthermore, it suffers from drawbacks such as long crystallization time after adding water to the filtrate, incomplete precipitation, irregular crystallization that is difficult to precipitate, and difficult filtration. Additionally, total phosphorus impurities cannot be completely removed.

[0005] Patent CN111689508A discloses a method for treating sodium tetrachloroaluminate solid slag. Specifically, the method involves the following steps: mixing sodium tetrachloroaluminate solid slag with water for dissociation, then adding a separating agent to precipitate aluminum chloride hexahydrate, or directly mixing sodium tetrachloroaluminate solid slag with a separating agent for dissociation to precipitate aluminum chloride hexahydrate. After a first solid-liquid separation, solid aluminum chloride hexahydrate and a first filtrate are obtained. The first filtrate is then concentrated and crystallized, followed by a second solid-liquid separation to obtain solid sodium chloride and a second filtrate. This treatment method utilizes the classic industrial production method of aluminum chloride hexahydrate to crystallize aluminum chloride hexahydrate in concentrated hydrochloric acid. Although it does not require the use of large amounts of organic solvents, it does require the purchase of large quantities of hydrogen chloride gas or concentrated hydrochloric acid. The operation involves multiple filtration, washing, and large-scale water distillation processes. Considering the costs of labor, energy consumption, equipment corrosion, and downstream environmental disposal, and based on the current market price of aluminum chloride hexahydrate, this treatment method cannot achieve a balance between income and expenditure. It is costly, and the total phosphorus impurities in the obtained aluminum chloride hexahydrate and sodium chloride are not completely removed.

[0006] Patent CN111804704A discloses a method for treating sodium tetrachloroaluminate solid slag. The specific steps of this method are: mixing the sodium tetrachloroaluminate solid slag with water for dissociation, adding alkali for polymerization, followed by concentration and crystallization, solid-liquid separation to obtain sodium chloride solid and concentrated mother liquor, and then aging the concentrated mother liquor to obtain a liquid polyaluminum chloride product. This method uses relatively expensive sodium hydroxide to prepare low-value-added polyaluminum chloride. During the reaction, an oxidant is needed to oxidize organophosphorus compounds into inorganic phosphorus compounds. However, sodium tetrachloroaluminate dissolves in water, resulting in a strongly acidic system. Adding an oxidant will preferentially oxidize chloride ions in this strongly acidic system, producing highly toxic chlorine gas. This poses a significant safety hazard for large-scale applications. Completely oxidizing organophosphorus compounds into inorganic phosphorus requires a large amount of oxidant, which is costly and environmentally unfriendly. In addition, the treatment method washes the obtained sodium chloride solid with water, resulting in some sodium chloride remaining in the mother liquor as high-salt wastewater. Furthermore, incompletely oxidized organic phosphorus and oxidized inorganic phosphorus will coexist in the high-salt wastewater. After entering the biological system, they will cause the bacteria to die. Without other treatment, organic phosphorus wastewater will be generated, which cannot be directly discharged.

[0007] In summary, all existing treatment methods suffer from high safety risks, complex processes, high costs, and low efficiency in removing total phosphorus impurities. The root cause is that when sodium tetrachloroaluminate and total phosphorus impurities are dissolved in water simultaneously, the impurities cannot be effectively separated by conventional purification methods. Instead, a complex and costly process is required to initially purify sodium tetrachloroaluminate before further processing it into polyaluminum chloride. This approach cannot achieve truly large-scale industrial processing in an economical and effective manner. Summary of the Invention

[0008] The purpose of this invention is to address the above-mentioned shortcomings of the prior art by providing a purification method for sodium tetrachloroaluminate. This method achieves complete separation from total phosphorus impurities using a very simple processing method without changing the form of sodium tetrachloroaluminate in aqueous solution. Furthermore, the treated sodium tetrachloroaluminate aqueous solution can be directly used in the preparation of polyaluminum chloride.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] This invention provides a method for purifying sodium tetrachloroaluminate, comprising the following steps:

[0011] S1. Add sodium tetrachloroaluminate solid, a byproduct of the methyldichlorophosphine production process, to water in batches and stir thoroughly until completely dissolved.

[0012] S2. Prepare an aqueous solution of zirconium oxychloride octahydrate and add it to the aforementioned aqueous solution of sodium tetrachloroaluminate at a certain rate. After the addition is complete, continue heating and stirring for a certain period of time. Cool down until fine white gel-like flocs begin to appear in the system. Then add anionic polyacrylamide to the system and gradually cool it to room temperature. Larger white solid precipitates will appear in the system.

[0013] S3. Filter the above reaction solution to obtain the first filtrate. The filter cake is a zirconium complex with total phosphorus impurities. The first filtrate is the sodium tetrachloroaluminate aqueous solution after removing impurities. At this time, a small amount of incompletely precipitated complex and a small amount of free zirconium ions still remain in the first filtrate.

[0014] S4. Add a complex composed of zeolite, hematite and activated carbon to the first filtrate, stir at room temperature for a certain time, let stand and then filter to obtain the second filtrate. At this time, the total phosphorus content and zirconium ion content in the second filtrate can meet the requirements for subsequent preparation of polyaluminum chloride.

[0015] Furthermore, in step S1, the total phosphorus impurities in the sodium tetrachloroaluminate are methylphosphonic acid, methylphosphonic acid, hypophosphoric acid, phosphoric acid, etc.

[0016] Furthermore, in step S1, the total phosphorus impurity content in sodium tetrachloroaluminate is between 500 ppm and 10,000 ppm.

[0017] Furthermore, in step S1, when sodium tetrachloroaluminate is dissolved in water, its mass ratio with water is 1:3.

[0018] Furthermore, in step S1, the rate at which sodium tetrachloroaluminate is added to water maintains the dissolution temperature between 30°C and 80°C.

[0019] Furthermore, in step S2, when preparing the aqueous solution of zirconium oxychloride octahydrate, the mass ratio of zirconium oxychloride octahydrate to water is 1:1.

[0020] Furthermore, in step S2, the mass ratio of zirconium oxychloride octahydrate to total phosphorus impurities in the sodium tetrachloroaluminate to be treated is 1:1 to 2:1.

[0021] Furthermore, in step S2, after adding the aqueous solution of zirconium oxychloride octahydrate to the aqueous solution of sodium tetrachloroaluminate, the temperature is raised to 80℃~100℃, and the stirring time is maintained at 1h~3h.

[0022] Furthermore, in step S2, the amount of anionic polyacrylamide added is 0.5‰ to 2‰ of the total mass of the system after the initial sodium tetrachloroaluminate is dissolved in water.

[0023] Furthermore, in step S3, the first filtrate still contains incompletely precipitated complexes, and the corresponding total phosphorus content in the system is 30 ppm to 100 ppm, and the zirconium ion content is 50 ppm to 250 ppm.

[0024] Furthermore, in step S4, the mass of zeolite added to the first filtrate is 0.5‰ to 1‰ of the total mass of the initial sodium tetrachloroaluminate dissolved in water, the mass of hematite added is 0.2‰ to 0.5‰ of the total mass of the initial sodium tetrachloroaluminate dissolved in water, and the mass of activated carbon added is 1‰ to 2‰ of the total mass of the initial sodium tetrachloroaluminate dissolved in water. The zeolite, hematite, and activated carbon are all in powder form.

[0025] Furthermore, in step S4, after adding zeolite, hematite, and activated carbon, the stirring temperature is room temperature, the stirring time is 30 min to 2 h, and the standing time is 10 min to 2 h.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] (1) This invention utilizes the flexible, multifunctional ligand properties of organophosphonic acid and inorganic phosphoric acid. The oxygen atoms in the organophosphonic acid and inorganic phosphoric acid form complexes with zirconium metal. These complexes are poorly soluble in water and are separated from the system as precipitates after the reaction. Since the precipitated substances readily form gels, the addition of anionic polyacrylamide significantly improves the properties of the precipitates, allowing them to form larger solid particles that facilitate filtration. For residual trace amounts of unprecipitated complexes and zirconium ions in the system, a synergistic adsorption effect can be effectively achieved by adding a combination of zeolite, hematite, and activated carbon.

[0028] (2) The impurity removal agents used in the method of the present invention do not react with sodium tetrachloroaluminate, and can achieve the technical purpose of completely separating the impurities while keeping the sodium tetrachloroaluminate in the aqueous solution unchanged. Compared with the previous technical solutions that require changing the form of sodium tetrachloroaluminate in the aqueous solution, the technical solution of the present invention has short steps, simple operation, no need to add acid or alkali, and high efficiency in precise removal of impurities. The treated sodium tetrachloroaluminate aqueous solution can be directly used in the next step of polyaluminum chloride production. It is a highly creative, novel and practical industrial treatment method. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the specific embodiments of this invention are described in further detail below. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0030] The zeolite, hematite, and activated carbon used in this invention are all commercially available.

[0031] The process for generating sodium tetrachloroaluminate, a byproduct in the production of methyldichlorophosphine in this invention, is as follows:

[0032] Aluminum powder and chloromethane are reacted to obtain a sesqui-part reaction solution. Phosphorus trichloride is then added to the sesqui-part reaction solution and mixed to react. After removing excess phosphorus trichloride by evaporation, sodium chloride is added to the system to carry out a dissociation reaction. Methyl phosphorus dichloride is then distilled off, and the residue is sodium tetrachloroaluminate.

[0033] Example 1

[0034] This embodiment provides a method for purifying sodium tetrachloroaluminate, including the following steps:

[0035] Step S1: Add 500g of sodium tetrachloroaluminate to 1500g of water in batches. The total phosphorus content of the sodium tetrachloroaluminate is 3253ppm (ppm is mg / L, which is equivalent to a mass of about 4.88g). The addition rate is maintained at an internal temperature of 60°C, and the mixture is stirred thoroughly to ensure complete dissolution.

[0036] Step S2: Dissolve 5g of zirconium oxychloride octahydrate in 5g of water to prepare an aqueous solution. Add the aqueous solution dropwise to the aqueous solution in step S1. After the addition is complete, heat the mixture to 90℃ and stir continuously for 1.5h. Cool the mixture until fine white gel-like flocs begin to appear in the system. Then add 2g of anionic polyacrylamide to the system. After gradually cooling to room temperature, larger white solid precipitates appear in the system.

[0037] Step S3: Filter the above reaction solution. The filter cake is a total phosphorus impurity-zirconium complex. The total phosphorus content in the first filtrate is measured to be 55 ppm and the zirconium ion content is 78 ppm.

[0038] In step S4, 1.6g of zeolite, 0.4g of hematite, and 2.2g of activated carbon were added to the first filtrate. The mixture was stirred at room temperature for 1 hour, allowed to stand for 20 minutes, and then filtered to obtain the second filtrate. The total phosphorus content in the filtrate was measured to be 1.37ppm and the zirconium ion content was 0.25ppm. The second filtrate can be directly used for the subsequent preparation of polyaluminum chloride.

[0039] Example 2

[0040] This embodiment provides a method for purifying sodium tetrachloroaluminate, including the following steps:

[0041] Step S1: Add 1000g of sodium tetrachloroaluminate to 3000g of water in batches. The total phosphorus content of the sodium tetrachloroaluminate is 5282ppm (ppm is mg / L, which is equivalent to about 15.85g). The addition rate is maintained at an internal temperature of 65℃, and the mixture is stirred thoroughly to ensure complete dissolution.

[0042] In step S2, 22.2g of zirconium oxychloride octahydrate was dissolved in 22.2g of water to prepare an aqueous solution. This aqueous solution was then added dropwise to the aqueous solution in step S1. After the addition was complete, the temperature was raised to 85℃ and the reaction was stirred continuously for 2 hours. The temperature was then lowered until fine white gel-like flocs began to appear in the system. Then, 4.8g of anionic polyacrylamide was added to the system. After gradually cooling to room temperature, larger white solid precipitates appeared in the system.

[0043] Step S3: Filter the above reaction solution. The filter cake is a total phosphorus impurity-zirconium complex. The total phosphorus content in the first filtrate is measured to be 81 ppm and the zirconium ion content is 94 ppm.

[0044] In step S4, 3.5g of zeolite, 1.4g of hematite, and 5.2g of activated carbon were added to the first filtrate. The mixture was stirred at room temperature for 1.5h, allowed to stand for 30min, and then filtered to obtain the second filtrate. The total phosphorus content in the filtrate was measured to be 2.14ppm and the zirconium ion content was 0.38ppm. The second filtrate can be directly used for the subsequent preparation of polyaluminum chloride.

[0045] Example 3

[0046] This embodiment provides a method for purifying sodium tetrachloroaluminate, including the following steps:

[0047] Step S1: Add 5 kg of sodium tetrachloroaluminate to 15 kg of water in batches. The total phosphorus content of the sodium tetrachloroaluminate is 7356 ppm (ppm is mg / L, which is equivalent to a mass of approximately 110.3 g). The addition rate is maintained at an internal temperature of 70°C, and the mixture is stirred thoroughly to ensure complete dissolution.

[0048] In step S2, 176.5g of zirconium oxychloride octahydrate was dissolved in 176.5g of water to prepare an aqueous solution. This aqueous solution was then added dropwise to the aqueous solution in step S1. After the addition was complete, the temperature was raised to 95℃ and the reaction was stirred continuously for 2.5h. The temperature was then lowered until fine white gel-like flocs began to appear in the system. Then, 12.5g of anionic polyacrylamide was added to the system. After gradually cooling to room temperature, a white solid precipitate with larger particles appeared in the system.

[0049] Step S3: Filter the above reaction solution. The filter cake is a total phosphorus impurity-zirconium complex. The total phosphorus content in the first filtrate is 95 ppm and the zirconium ion content is 108 ppm.

[0050] In step S4, 14g of zeolite, 8g of hematite, and 37g of activated carbon were added to the first filtrate. The mixture was stirred at room temperature for 2 hours, allowed to stand for 1 hour, and then filtered to obtain the second filtrate. The total phosphorus content in the filtrate was measured to be 2.58ppm and the zirconium ion content was 0.41ppm. The second filtrate can be directly used for the subsequent preparation of polyaluminum chloride.

[0051] The method for determining the total phosphorus content in the sodium tetrachloroaluminate solid samples to be processed in Examples 1-3 above is as follows: take 10g of the corresponding batch of sodium tetrachloroaluminate sample, dissolve it in 30g of water, and determine the total phosphorus content. The first filtrate and the second filtrate are directly taken for the determination of total phosphorus content.

[0052] Total phosphorus content determination: Beijing Lianhua Yongxing Technology 5B-1(V8) Intelligent Multi-parameter Digestion Water Quality Analyzer, Ammonium Molybdate Spectrophotometric Method.

[0053] Zirconium ion content determination: Beijing Jitian EXPEC7000 inductively coupled plasma mass spectrometer (ICP-MS).

[0054] Comparative Example 1

[0055] Step S1: Add 5 kg of sodium tetrachloroaluminate to 15 kg of water in batches. The total phosphorus content of the sodium tetrachloroaluminate is 7356 ppm (ppm is mg / L, which is equivalent to a mass of approximately 110.3 g). The addition rate is maintained at an internal temperature of 70°C, and the mixture is stirred thoroughly to ensure complete dissolution.

[0056] In step S2, 176.5g of zirconium oxychloride octahydrate was dissolved in 176.5g of water to prepare an aqueous solution. This aqueous solution was then added dropwise to the aqueous solution from step S1. After the addition was complete, the temperature was raised to 95°C and the reaction was stirred continuously for 2.5 hours. During the cooling process, small white gel-like flocs began to appear. After cooling to room temperature and waiting for a period of time, the system was directly filtered. During filtration, it was found that due to the extremely small size and soft, gel-like texture of the solids produced, only about one-quarter of the original volume of filtrate was collected, and it was difficult to filter out any more filtrate. Extending the filtration time did not improve the situation, and further processing could not be carried out.

[0057] In summary, the method provided by this invention achieves precise removal of total phosphorus impurities from sodium tetrachloroaluminate in water through coordination complexation without altering its existing form. This process is simple to operate, low in cost, requires no additional processing equipment, and exhibits high efficiency in removing total phosphorus impurities. The treated solution can then be directly used for the preparation of polyaluminum chloride (PAC). This method overcomes the limitations of previous methods, which required extensive acid and alkali treatment or washing with large amounts of organic solvents to remove total phosphorus impurities from sodium tetrachloroaluminate. These methods resulted in secondary pollution, significant equipment investment, and extremely low processing efficiency. Furthermore, the total phosphorus impurities could not be completely removed, and repeated treatments still required the preparation of an aqueous solution before PAC preparation. Incomplete removal of total phosphorus impurities led to their introduction into the subsequently prepared PAC, resulting in substandard PAC quality and severely limiting its application in water treatment.

[0058] For any points not covered above, existing technologies shall apply.

[0059] Although specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, without departing from the direction of the invention or exceeding the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for purifying sodium tetrachloroaluminate, characterized in that, The specific steps include the following: S1. Add sodium tetrachloroaluminate solid, a byproduct of the methyldichlorophosphine production process, to water in batches and stir thoroughly until completely dissolved. S2. Prepare an aqueous solution of zirconium oxychloride octahydrate and add it to the aforementioned aqueous solution of sodium tetrachloroaluminate at a certain rate. After the addition is complete, continue heating and stirring for a certain period of time. Cool down until fine white gel-like flocs begin to appear in the system. Then add anionic polyacrylamide to the system and gradually cool it to room temperature. Larger white solid precipitates will appear in the system. S3. Filter the above reaction solution to obtain the first filtrate. The filter cake is a zirconium complex with total phosphorus impurities. S4. Add a complex composed of zeolite, hematite and activated carbon to the first filtrate, stir at room temperature for a certain time, let stand and then filter to obtain the second filtrate, which can be directly used to prepare polyaluminum chloride. In step S2, the mass ratio of zirconium oxychloride octahydrate to total phosphorus impurities in sodium tetrachloroaluminate to be treated is 1:1 to 2:

1. After adding the zirconium oxychloride octahydrate aqueous solution to the sodium tetrachloroaluminate aqueous solution, the temperature is raised to 80℃ to 100℃ and stirred for 1h to 3h.

2. The purification method according to claim 1, characterized in that, In step S1, the total phosphorus impurities in the sodium tetrachloroaluminate include methylphosphonic acid, methylphosphonic acid, hypophosphoric acid, and phosphoric acid.

3. The purification method as described in claim 1, characterized in that, In step S1, the total phosphorus impurity content in sodium tetrachloroaluminate is between 500 ppm and 10,000 ppm.

4. The purification method according to claim 1, characterized in that, In step S1, the mass ratio of sodium tetrachloroaluminate to water is 1:

3.

5. The purification method according to claim 1, characterized in that, In step S2, the mass ratio of zirconium oxychloride octahydrate to water is 1:

1.

6. The purification method according to claim 1, characterized in that, In step S2, the amount of anionic polyacrylamide added is 0.5‰ to 2‰ of the total mass of the system after the initial sodium tetrachloroaluminate is dissolved in water.

7. The purification method according to claim 1, characterized in that, In step S3, the total phosphorus content in the first filtrate is 30 ppm to 100 ppm, and the zirconium ion content is 50 ppm to 250 ppm.

8. The purification method according to claim 1, characterized in that, In step S4, the mass of zeolite added to the first filtrate is 0.5‰ to 1‰ of the total mass of the initial sodium tetrachloroaluminate dissolved in water, the mass of hematite added is 0.2‰ to 0.5‰ of the total mass of the initial sodium tetrachloroaluminate dissolved in water, and the mass of activated carbon added is 1‰ to 2‰ of the total mass of the initial sodium tetrachloroaluminate dissolved in water. The zeolite, hematite, and activated carbon are all in powder form.

9. The purification method as described in claim 8, characterized in that, In step S4, the stirring temperature is room temperature, the stirring time is 30 min to 2 h, and the standing time is 10 min to 2 h.