A process for the preparation of aluminum diethylphosphinate with low by-product content

Abstract

The application discloses a method for preparing aluminum diethylphosphinate with low byproduct content, comprising the following steps: dispersing aluminum hypophosphite solid in an aqueous solution containing alkali metal hydroxide at a low concentration, the mass ratio of aluminum hypophosphite solid to water being 1:20-1000; making ethylene and aluminum hypophosphite solid undergo addition reaction under the initiation of a free radical initiator, the reaction temperature being 100-150 DEG C, the reaction pressure being 0.1-0.3 MPa, and the ethylene consumption in the reaction system being controlled to be sufficient for the reaction of aluminum hypophosphite solid, so as to obtain an aluminum monoethylphosphinate solution; collecting the filtrate through solid-liquid separation; introducing ethylene into the collected filtrate, so that the aluminum monoethylphosphinate in the filtrate and ethylene undergo addition reaction under the initiation of a free radical initiator, the reaction temperature being 100-150 DEG C, the reaction pressure being 0.1-0.3 MPa, and aluminum diethylphosphinate precipitate being obtained. The application successfully prepares an aluminum diethylphosphinate product with a byproduct content lower than 0.5 wt% or even lower than 0.1 wt%.

Description

Technical Field

[0001] This invention relates to the field of aluminum diethylphosphonate preparation technology, and specifically to a method for preparing aluminum diethylphosphonate with low byproduct content. Background Technology

[0002] As described in patents CN1284787C and CN1660858B, the synthesis of aluminum diethylphosphite typically involves two steps: (1) an addition reaction between water-soluble inorganic hypophosphite and ethylene in an aqueous medium, resulting in the ethylation of the inorganic hypophosphite to obtain water-soluble aluminum diethylphosphite; and (2) a metathesis reaction between the water-soluble aluminum diethylphosphite and a water-soluble aluminum salt to obtain aluminum diethylphosphite precipitate, which exhibits high hydrophobicity and good flame retardant properties. In these two steps, the first step, the addition reaction between ethylene and inorganic hypophosphite, is crucial. It is the controlling step of the entire preparation process, determining the reaction efficiency and product quality.

[0003] Inorganic hypophosphite is ethylated by addition reaction with ethylene, transforming into diethyl hypophosphite. The reaction mechanism is as follows: a water-soluble free radical initiator decomposes upon heating in the aqueous phase, generating free radicals. These free radicals first attack the more reactive phosphorus-hydrogen bond, causing it to break and producing hypophosphite free radicals. These hypophosphite free radicals then attack the double bond of ethylene, opening and combining with it to form new ethyl-containing phosphate free radicals. These free radicals continue to interact with the phosphorus-hydrogen bond of the hypophosphite, completing the addition reaction. The reaction formula is shown below:

[0004]

[0005] In the above addition reaction, since ethylene is in the gas phase and hypophosphite is dissolved in the aqueous phase, it is a gas-liquid reaction. In actual production, ethylene is present in large quantities in the reactor. In the presence of an initiator, the ethyl group in the diethylphosphite structure is initiated by the initiator to form a free radical, which then adds to ethylene, forming a byproduct of excessive ethylene addition, with the following side reactions:

[0006]

[0007] Among these side reactions, the probability of further initiation decreases with increasing carbon chain length. In existing preparation processes, after the first addition reaction, an insoluble aluminum diethylphosphinate precipitate is formed by reacting with aluminum-containing compounds. Simultaneously, these byproduct dialkylphosphinate groups also combine with aluminum ions to form insoluble aluminum dialkylphosphite, which precipitates out along with the aluminum diethylphosphinate and cannot be separated. Therefore, due to the presence of side reactions in existing aluminum diethylphosphinate preparation processes, the prepared aluminum diethylphosphinate typically contains ethylbutyl aluminum diethylphosphinate, butylbutyl aluminum diethylphosphinate, ethylhexyl aluminum diethylphosphinate, butylhexyl aluminum diethylphosphinate, and hexylhexyl aluminum diethylphosphinate. The main byproduct is ethylbutyl aluminum diethylphosphinate, typically accounting for about 2% by weight. Furthermore, these byproducts cannot be separated from the aluminum diethylphosphinate; therefore, industrial products marketed as aluminum diethylphosphinate flame retardants actually contain a certain amount of byproducts. As described in patent CN1660857B, these excessively added aluminum dialkylphosphinate byproducts can cause polymer degradation and reduce the mechanical properties of the polymer material. The method proposed in patent CN1660857B reduces the proportion of byproducts by replacing the organic solvent acetic acid with water as the reaction medium. However, even in an aqueous phase, the byproduct content in the prepared aluminum diethylphosphinate is still not low. The lowest reported byproduct, as in Example 3, is 0.9% mol of aluminum ethylbutylphosphinate, which is still relatively high, indicating that the negative effects persist. Therefore, to address these negative impacts, it is necessary to prepare aluminum diethylphosphinate with a lower byproduct content in an aqueous phase to obtain a high-purity aluminum diethylphosphinate product.

[0008] Based on the principle of the addition reaction between ethylene and inorganic hypophosphite and the characteristics of industrial production, this invention develops a novel synthesis process to prepare aluminum diethylphosphinate with low by-product content, thereby solving the negative impact of high by-product content in existing aluminum diethylphosphinate. Summary of the Invention

[0009] This invention provides a method for preparing aluminum diethylphosphonate with low byproduct content, which solves the problem of high byproduct content in existing aluminum diethylphosphonate synthesis processes. This invention utilizes the stepwise addition reaction initiated by ethylene and low-concentration aluminum hypophosphite solid in an alkaline aqueous phase and the water solubility of monoethylphosphonates to successfully prepare aluminum diethylphosphonate products with byproduct content below 0.5 wt% or even below 0.1 wt%.

[0010] A method for preparing aluminum diethylphosphinate with low byproduct content, comprising:

[0011] Step 1: Disperse aluminum hypophosphite solid at a low concentration in an aqueous solution containing alkali metal hydroxide, with a mass ratio of aluminum hypophosphite solid to water of 1:20 to 1000. Allow ethylene to undergo an addition reaction with aluminum hypophosphite solid under the initiation of a free radical initiator. The reaction temperature is 100 to 150°C, and the reaction pressure is 0.1 to 0.3 MPa. Control the amount of ethylene consumed in the reaction system until the aluminum hypophosphite solid has fully reacted to obtain a monoethylphosphite aluminum solution. Separate the solid and liquid and collect the filtrate.

[0012] Step 2: Ethylene is introduced into the collected filtrate, causing the aluminum monoethylphosphonate in the filtrate to undergo an addition reaction with ethylene under the initiation of a free radical initiator. The reaction temperature is 100-150℃ and the reaction pressure is 0.1-0.3MPa, to obtain aluminum diethylphosphonate precipitate.

[0013] This invention utilizes the heterogeneous stepwise addition of ethylene with low-concentration insoluble aluminum hypophosphite solid under alkaline conditions and the water solubility of monoethyl aluminum hypophosphite. The provided method can significantly inhibit the excessive addition of ethylene and reduce the formation of by-products, resulting in a high-purity diethyl aluminum hypophosphite flame retardant product with low by-product content. The product has superior performance and can be widely used in halogen-free and environmentally friendly flame retardant applications in nylon, polyester, thermoplastic elastomers (TPE), and other fields.

[0014] This invention aims to overcome the high byproduct content in existing aluminum diethylphosphinate preparation processes. The inventors conducted in-depth research on the mechanism of the addition reaction between ethylene and inorganic hypophosphite, and discovered that:

[0015] First, the reaction between ethylene and the two pH bonds on the hypophosphite ion occurs stepwise. After the first pH bond reacts with ethylene, the reactivity of the other pH bond decreases. In other words, the reaction between ethylene and hypophosphite actually proceeds in two steps, which can be divided into the following two steps:

[0016]

[0017] Studies have found that the initial reaction step is more reactive, typically generating monoethylphosphine ions first. Diethylphosphine ions only begin to form after all inorganic hypophosphite has been converted to monoethylphosphite. Of course, there is a probability factor involved in initiation. Before the inorganic hypophosphite is completely converted to monoethylphosphine, a small amount of monoethylphosphine may be initiated to undergo addition with ethylene to form diethylphosphine. This is especially true under homogeneous gas-liquid reaction conditions, where ethylene and the initiator can have sufficient contact with the monoethylphosphite, increasing the probability of diethylphosphine formation.

[0018] Secondly, when the insoluble inorganic aluminum hypophosphite is dispersed in water, an addition reaction still occurs in the presence of an initiator and ethylene. The results appear similar to the conventional preparation process, i.e., using insoluble aluminum hypophosphite and water-soluble hypophosphite, and the addition reaction is similar. However, the reaction process differs from the conventional addition process. With water-soluble hypophosphite, the hypophosphite dissolves in water, forming a homogeneous system and undergoing a gas-liquid reaction. With insoluble aluminum hypophosphite, the aluminum hypophosphite is dispersed in the aqueous phase, in a suspended state, and a gas-liquid-solid reaction occurs. Furthermore, the experiment revealed that the generated monoethylphosphite aluminum is water-soluble with high solubility. That is, during the addition process, the insoluble inorganic aluminum hypophosphite suspension gradually decreases or even disappears completely as the addition proceeds, resulting in a homogeneous aqueous solution. If the addition reaction continues, insoluble diethylphosphite aluminum will be generated, and new precipitates will appear.

[0019] Based on the previous research results, the inventors discovered through further experiments that when aluminum hypophosphite is dispersed at a low concentration in an alkaline aqueous solution, an addition reaction occurs under low ethylene pressure. Combined with a specific process, this can significantly reduce the content of byproducts. This is significantly different from existing processes, which use soluble hypophosphite to add to ethylene, resulting in high byproduct formation.

[0020] In step one, the method for preparing the aluminum hypophosphite solid may include: reacting hypophosphite and / or soluble hypophosphite with an aluminum-containing compound in water to generate aluminum hypophosphite precipitate, and filtering and washing the precipitate to obtain the aluminum hypophosphite solid.

[0021] In the method for preparing solid aluminum hypophosphite, the soluble hypophosphite can be an alkali metal salt, such as sodium hypophosphite or potassium hypophosphite.

[0022] In the method for preparing the aluminum hypophosphite solid, the aluminum-containing compound is at least one of aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum hydroxide, and aluminum acetate.

[0023] In the method for preparing the aluminum hypophosphite solid, if a soluble hypophosphite is used, the aluminum-containing compound can be selected as an aluminum salt compound; if hypophosphite is used, the aluminum-containing compound can be selected as aluminum hydroxide.

[0024] In the method for preparing solid aluminum hypophosphite, after the reaction is completed, filtration is required to separate the aluminum hypophosphite precipitate, and it is preferable to wash it with water multiple times to reduce the residue of hypophosphite or hypophosphite and reduce its impact on subsequent reactions.

[0025] In the method for preparing the aluminum hypophosphite solid, the reaction temperature can be 20–120°C.

[0026] In the method for preparing the aluminum hypophosphite solid, the reaction pressure can be 0.01 to 10 MPa.

[0027] In step one, the mass ratio of solid aluminum hypophosphite to water is 1:20–1000. Studies have found that excessively high concentrations of aluminum hypophosphite in the reaction system can lead to an increase in byproducts.

[0028] In step two, the content of aluminum monoethylphosphonate in the filtrate is below 5 wt%. Studies have found that excessively high concentrations of aluminum monoethylphosphonate in the filtrate will lead to an increase in byproducts.

[0029] In steps one and two, the free radical initiator can be independently selected from peroxides and / or azo compounds, preferably water-soluble peroxides, and more preferably includes at least one of hydrogen peroxide, potassium persulfate, sodium persulfate, and ammonium persulfate.

[0030] In steps one and two, the addition reaction conditions are independently set as follows: reaction temperature 100–150 °C and reaction pressure 0.1–0.3 MPa. The reaction hardly proceeds below 100 °C, and excessively high reaction pressure will lead to an increase in byproducts.

[0031] In step one, the molar ratio of ethylene to solid aluminum hypophosphite is 0.1 to 3:1. The degree of reaction is controlled according to the amount of ethylene consumed. According to the reaction formula, a complete reaction occurs when the molar ratio of ethylene to aluminum hypophosphite is 3:1. If the ratio is lower than this, the aluminum hypophosphite cannot react completely, and there will be precipitate in the reaction system. The conversion rate of aluminum hypophosphite will decrease, but it is beneficial to reduce the content of by-products.

[0032] In step two, the molar ratio of ethylene to aluminum monoethylphosphonate is 0.1 to 3:1. According to the reaction formula, a complete reaction occurs. The molar ratio of ethylene to aluminum monoethylphosphonate is 3:1. If the ratio is lower than this, aluminum monoethylphosphonate cannot react completely, and the conversion rate of aluminum monoalkylphosphonate decreases, but it is beneficial to reduce the content of by-products.

[0033] The addition reactions in steps one and two need to be carried out under alkaline conditions. Although they can also be carried out under acidic or neutral conditions, the amount of byproducts will increase under acidic or neutral conditions. The required alkaline conditions can be provided by the alkali metal hydroxide. In step one, the alkali metal hydroxide can be sodium hydroxide and / or potassium hydroxide. In step one, the mass ratio of the alkali metal hydroxide to water can be 1:50 to 10000.

[0034] After the reaction in step one is complete, solid-liquid separation is required to remove unreacted aluminum hypophosphite, byproducts, and a small amount of diethylphosphinate. The filtrate is then collected for use in step two. Failure to perform solid-liquid separation will result in an increase in byproducts.

[0035] Step two may also include filtering and washing (specifically, washing with water) to obtain aluminum diethylphosphonate precipitate, thereby reducing the residual aluminum monoethylphosphonate in the product.

[0036] This invention provides a specific method for preparing aluminum diethylphosphinate with low byproduct content, comprising:

[0037] Step I: React hypophosphite and / or soluble hypophosphite with an aluminum-containing compound in water to generate aluminum hypophosphite precipitate. Filter and wash the precipitate to obtain the aluminum hypophosphite solid. The reaction formula is as follows:

[0038]

[0039] Step II: The aluminum hypophosphite solid obtained in Step I is dispersed at a low concentration in an aqueous solution containing an alkali metal hydroxide. The mass ratio of aluminum hypophosphite solid to water is 1:20–1000. An addition reaction is initiated by a free radical initiator between ethylene and the aluminum hypophosphite solid. The reaction temperature is 100–150 °C, and the reaction pressure is 0.1–0.3 MPa. The amount of ethylene consumed in the reaction system is controlled until the aluminum hypophosphite solid has fully reacted, yielding a monoethylphosphite aluminum solution. The filtrate is collected after solid-liquid separation. The reaction formula is as follows:

[0040]

[0041] Step III: Ethylene is introduced into the filtrate obtained in Step II, causing an addition reaction between the aluminum monoethylphosphonate in the filtrate and ethylene under the initiation of a free radical initiator. The reaction temperature is 100–150°C, and the reaction pressure is 0.1–0.3 MPa, resulting in a precipitate of aluminum diethylphosphonate. This precipitate is then filtered and washed to obtain aluminum diethylphosphonate with a low byproduct content. The reaction formula is as follows:

[0042]

[0043] The possible composition of byproducts contained in the aluminum diethylphosphinate prepared by the method of the present invention includes one or more of the following: aluminum ethylbutylphosphinate, aluminum dibutylphosphinate, aluminum ethylhexylphosphinate, aluminum butylhexylphosphinate, aluminum hexylhexylphosphinate, etc.

[0044] The total weight percentage of byproducts in the aluminum diethylphosphonate prepared by the method of the present invention is less than 0.5%, preferably less than 0.1%.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0046] 1. The aluminum diethylphosphinate prepared by the method of the present invention has a low by-product content and can be better used as a flame retardant in materials such as polyester, nylon, thermoplastic elastomer (TPE), polyurethane, epoxy resin, and POK.

[0047] 2. The method for preparing aluminum diethylphosphonate with low by-product content provided by the present invention overcomes the defect of high by-product content in existing synthesis processes, and can obtain aluminum diethylphosphonate with higher purity and superior performance. Detailed Implementation

[0048] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0049] Example 1

[0050] Step 1: Dissolve 264g of sodium hypophosphite in 1600g of water and transfer the solution to a 3L reactor. Heat the solution to 80℃ and add 371.7g of 46wt% aluminum sulfate solution to the reactor over 60 minutes. A white precipitate will gradually form, indicating the reaction is complete. Filter the solution and wash the precipitate with hot water to obtain aluminum hypophosphite precipitate.

[0051] Step 2: In a 3L pressure vessel, add 2000g of water, then disperse 74g of the previously prepared aluminum hypophosphite precipitate into the water, add 1g of sodium hydroxide, stir well, heat to 110℃, and introduce ethylene. Maintain a constant pressure of 0.3MPa inside the reactor. Then, continuously pump in a 2wt% sodium persulfate solution using a peristaltic pump, measuring the ethylene consumption. The reaction time is approximately 1.5 hours, consuming 28.3g of ethylene. Reduce the pressure and temperature of the reactor to approximately 90℃, filter, and collect the filtrate.

[0052] Step 3: Add the filtrate to the aforementioned pressure vessel, heat to 110℃, introduce ethylene, and maintain the pressure inside the reactor at a constant 0.3MPa. Then, continuously pump in a 2wt% sodium persulfate solution using a peristaltic pump, measuring the ethylene consumption. The reaction ends when no more ethylene is consumed, with a reaction time of approximately 2.5 hours and an ethylene consumption of 28.7g. Reduce the pressure and temperature of the reactor to approximately 90℃, filter, wash the precipitate with hot water, and vacuum dry at 130℃. Perform phosphorus NMR analysis on the precipitate; its composition is shown in Table 1.

[0053] Table 1: Results of precipitate composition analysis

[0054]

[0055] Example 2

[0056] The procedure was the same as in Example 1, except that the amount of aluminum hypophosphite in step two was 55.5 g. Phosphorus NMR analysis was performed on the precipitate from step three, and the results are shown in Table 1.

[0057] Example 3

[0058] The procedure was the same as in Example 1, except that the reaction pressure was 0.2 MPa in steps two and three. Phosphorus NMR analysis was performed on the precipitate from step three, and the results are shown in Table 1.

[0059] Comparative Example 1

[0060] Using existing processes, a soluble hypophosphite is first added to ethylene to obtain a soluble dialkylphosphinate, which is then reacted with aluminum sulfate to obtain aluminum dialkylphosphinate. The reaction steps are as follows:

[0061] Step 1: Dissolve 264g of sodium hypophosphite in 1600g of water and transfer the solution to a 3L reactor. Add 2g of sodium hydroxide, stir well, heat to 110℃, introduce ethylene, and control the pressure inside the reactor to be constant at 0.3MPa. Then, continuously pump in a 2wt% sodium persulfate solution using a peristaltic pump. The reaction will end in about 4 hours.

[0062] Step 2: The reaction solution obtained in Step 1 was heated to 90℃, and 371.7g of 46wt% aluminum sulfate solution was added to the reaction vessel over 60 minutes. A white precipitate gradually formed, indicating the reaction was complete. The mixture was filtered, the precipitate was washed with hot water, and then dried under vacuum at 130℃. The precipitate product was analyzed by phosphorus NMR spectroscopy, and the results are shown in Table 1.

[0063] Comparative Example 2

[0064] The procedure was the same as in Example 1, except that the amount of aluminum hypophosphite in step two was 259 g. Phosphorus NMR analysis was performed on the precipitate product from step three, and the results are shown in Table 1.

[0065] Comparative Example 3

[0066] The procedure was the same as in Example 1, except that the reaction pressure was 1.0 MPa in steps two and three. Phosphorus NMR analysis was performed on the precipitate from step three, and the results are shown in Table 1.

[0067] Comparative Example 4

[0068] The procedure was the same as in Example 1, except that sodium hydroxide was not used in step two. Phosphorus NMR analysis was performed on the precipitate from step three, and the results are shown in Table 1.

[0069] Comparative Example 5

[0070] The procedure was the same as in Example 1, except that sodium hydroxide was not used in step two, and 3g of 98wt% concentrated sulfuric acid was added. The precipitate from step three was analyzed by phosphorus NMR spectroscopy, and the results are shown in Table 1.

[0071] Comparative Example 6

[0072] The implementation process was the same as in Example 1, except that filtration was not performed in step two. Phosphorus NMR analysis was performed on the precipitate from step three, and the results are shown in Table 1.

[0073] Comparative Example 7

[0074] The implementation process was the same as in Example 1, except that the reaction temperature in step two was 90°C. The reaction rate was almost negligible.

[0075] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for preparing aluminum diethylphosphinate with low byproduct content, characterized in that, include: Step 1: Disperse aluminum hypophosphite solid at a low concentration in an aqueous solution containing alkali metal hydroxide, with a mass ratio of aluminum hypophosphite solid to water of 1:20~1000. Allow ethylene to undergo an addition reaction with aluminum hypophosphite solid under the initiation of a free radical initiator. The reaction temperature is 100~150℃ and the reaction pressure is 0.1~0.3 MPa. Control the amount of ethylene consumed in the reaction system until the aluminum hypophosphite solid has fully reacted to obtain a monoethylphosphite aluminum solution. Separate the solid and liquid and collect the filtrate. Step 2: Ethylene is introduced into the collected filtrate, so that the aluminum monoethylphosphonate in the filtrate and ethylene undergo an addition reaction under the initiation of a free radical initiator. The reaction temperature is 100~150℃ and the reaction pressure is 0.1~0.3 MPa, to obtain aluminum diethylphosphonate precipitate. In step one, the molar ratio of ethylene to solid aluminum hypophosphite is 0.1~3:1; In step two, the molar ratio of ethylene to aluminum monoethylphosphinate is 0.1~3:1; The total weight percentage of byproducts in the aluminum diethylphosphonate prepared by the method is less than 0.5%.

2. The method according to claim 1, characterized in that, In step one, the method for preparing the aluminum hypophosphite solid includes: reacting hypophosphite and / or soluble hypophosphite with an aluminum-containing compound in water to generate aluminum hypophosphite precipitate, and filtering and washing the precipitate to obtain the aluminum hypophosphite solid.

3. The method according to claim 2, characterized in that, In the preparation method of the aluminum hypophosphite solid: The soluble hypophosphite is a salt of an alkali metal; The aluminum-containing compound is at least one of aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum hydroxide, and aluminum acetate; The reaction temperature is 20~120℃, and the reaction pressure is 0.01~10 MPa.

4. The method according to claim 1, characterized in that, In step two, the content of aluminum monoethylphosphonate in the filtrate is less than 5 wt%.

5. The method according to claim 1, characterized in that, In steps one and two, the free radical initiators are independently selected from peroxides and / or azo compounds.

6. The method according to claim 5, characterized in that, In steps one and two, the free radical initiators are independently selected from water-soluble peroxides.

7. The method according to claim 6, characterized in that, In steps one and two, the free radical initiator is independently selected from at least one of hydrogen peroxide, potassium persulfate, sodium persulfate, and ammonium persulfate.

8. The method according to claim 1, characterized in that, In step one: The alkali metal hydroxide is sodium hydroxide and / or potassium hydroxide; In the aqueous solution containing the alkali metal hydroxide, the mass ratio of the alkali metal hydroxide to water is 1:50~10000.

9. The method according to claim 1, characterized in that, Step two also includes filtering and washing the resulting aluminum diethylphosphinate precipitate.

10. The method according to claim 1, characterized in that, The total weight percentage of byproducts in the aluminum diethylphosphonate prepared by the method is less than 0.1%.

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