Process for the preparation of aluminium dialkylphosphinates with different alkyl groups

Abstract

The application discloses a preparation method of aluminum dialkyl hypophosphite with different alkyl groups, and comprises the following steps: (1) dispersing aluminum hypophosphite solid in a low concentration in a solvent system containing alkali metal hydroxide and water, the mass ratio of the aluminum hypophosphite solid to water being 1:20-1000; under the initiation of a free radical initiator, making olefin 1 and the aluminum hypophosphite solid to have an addition reaction at 100-150 DEG C and 0.1-0.3 MPa, and controlling the consumption of the olefin 1 to be sufficient for the reaction of the aluminum hypophosphite solid, so as to prepare an aluminum monoalkyl hypophosphite solution, filtering the precipitate, and collecting the filtrate; (2) continuously feeding olefin 2 different from the olefin 1 into the filtrate, and making the aluminum monoalkyl hypophosphite and the olefin 2 to have an addition reaction under the initiation of the free radical initiator at 100-150 DEG C and 0.1-0.3 MPa, so as to obtain aluminum dialkyl hypophosphite with different alkyl groups. The purity of the aluminum dialkyl hypophosphite with different alkyl groups prepared by the application is above 99.5%.

Description

Technical Field

[0001] This invention relates to the field of aluminum dialkylphosphinate preparation technology, specifically to a method for preparing aluminum dialkylphosphinate with different alkyl groups. This method can obtain high-purity aluminum dialkylphosphinate with different alkyl groups and has lower corrosivity, making it suitable for use as a flame retardant for polymer materials. Background Technology

[0002] Organic aluminum hypophosphite flame retardants, due to their high phosphorus content, exhibit excellent flame retardancy. Furthermore, the introduction of alkyl groups into their molecular structure significantly enhances their hydrophobicity and thermal decomposition temperature compared to inorganic hypophosphites. When applied to polymer materials, they do not migrate or absorb moisture, can withstand high processing temperatures, and do not cause a decrease in the material's insulation properties. They also demonstrate good compatibility with the matrix resin, maintaining the mechanical properties of the matrix material. Because of these characteristics as excellent flame retardants, they are widely used in flame retardant applications for engineering plastics requiring high processing temperatures, high shear strength, and high CTI values, particularly in glass fiber reinforced nylon and polyester.

[0003] In the commercialization of organic phosphonates, Clariant's OP series of flame retardants, aluminum diethylphosphonate, is the most successful, with its molecular structure and preparation method disclosed in its series of patents.

[0004] According to patent documents published by Clariant, the synthesis of organic aluminum hypophosphite flame retardants is usually completed in two steps: (1) water-soluble inorganic hypophosphite undergoes an addition reaction with an olefin in an aqueous medium, alkylating the inorganic hypophosphite to obtain a water-soluble alkylated hypophosphite; (2) the water-soluble alkylated hypophosphite undergoes a metathesis reaction with a water-soluble aluminum salt to obtain an organic aluminum hypophosphite precipitate, which has high hydrophobicity and good flame retardant properties. Based on its synthesis mechanism, organic aluminum hypophosphite flame retardants are obtained by introducing alkyl groups into the molecular structure through the addition of inorganic hypophosphite with an olefin. Therefore, usually only dialkyl phosphites with the same alkyl group can be obtained, such as the commercially successful diethyl aluminum hypophosphite, which has the following molecular structure.

[0005]

[0006] However, for aluminum dialkylphosphinates with different alkyl groups, the molecular structures are as follows:

[0007]

[0008] R1 and R2 are different, both being alkyl groups with at least 2 carbon atoms. The synthesis of aluminum ethylpropyl phosphite, aluminum ethylbutyl phosphite, etc., requires the addition of two olefins to hypophosphite. If the aforementioned preparation method is followed, a mixture containing multiple dialkyl aluminum phosphites is usually obtained, making it difficult to obtain high-purity dialkyl aluminum phosphites with different alkyl groups. Furthermore, because acidic aluminum sulfate is used in the second step of aluminum salt synthesis, it remains in the product, making the product acidic and corrosive.

[0009] No reports have been found regarding the preparation of aluminum dialkylphosphinates with different alkyl groups, especially high-purity products. Therefore, new synthetic processes need to be developed to obtain high-purity aluminum dialkylphosphinates with different alkyl groups.

[0010] Based on the principle of the addition reaction between olefins and inorganic hypophosphite and the characteristics of industrial production, this invention develops a novel synthesis process to prepare high-purity aluminum dialkylphosphinates with different alkyl groups, thus solving the problem that existing synthesis processes are unable to obtain high-purity aluminum dialkylphosphinates with different alkyl groups. Summary of the Invention

[0011] The main objective of this invention is to prepare high-purity dialkyl phosphonates with different alkyl groups, overcoming the shortcomings of existing synthesis processes with low purity. The newly developed process utilizes the stepwise addition reaction between olefins and low-concentration aluminum hypophosphite solids in alkaline aqueous solution and the water solubility of monoalkyl phosphonates, resulting in dialkyl phosphonates with different alkyl groups having a purity of over 99.5%.

[0012] The aluminum dialkylphosphinates with different alkyl groups described in this invention have the following molecular structures:

[0013]

[0014] R1 and R2 are different; both are alkyl groups with at least 2 carbon atoms.

[0015] The specific technical solution is as follows:

[0016] A method for preparing dialkylphosphinate aluminum with different alkyl groups, comprising the following steps:

[0017] (1) Aluminum hypophosphite solid is dispersed at a low concentration in a solvent system containing alkali metal hydroxide and water. The mass ratio of aluminum hypophosphite solid to water is 1:20 to 1000. Under the initiation of a free radical initiator, olefin 1 and aluminum hypophosphite solid undergo an addition reaction at 100 to 150 °C and 0.1 to 0.3 MPa. The consumption of olefin 1 is controlled until the aluminum hypophosphite solid reacts completely to prepare a monoalkyl aluminum hypophosphite solution. The precipitate is filtered and the filtrate is collected.

[0018] (2) An olefin 2, which is different from olefin 1, is continuously introduced into the filtrate, so that the monoalkyl aluminum phosphinate and olefin 2 undergo an addition reaction at 100-150°C and 0.1-0.3 MPa under the initiation of a free radical initiator to obtain dialkyl aluminum phosphinate precipitates with different alkyl groups.

[0019] The present invention will now be described in detail.

[0020] This invention aims to solve the problem of preparing high-purity dialkyl aluminum hypophosphite with different alkyl groups using existing processes. The inventors conducted extensive and in-depth research. Addressing the shortcomings of existing synthetic processes, the mechanism of the addition reaction between olefins and inorganic hypophosphite was studied in depth, and the results showed that:

[0021] 1) The reaction between the alkene and the two pH bonds on the hypophosphite ion proceeds in steps. Furthermore, after the first pH bond reacts with the alkene, the reactivity of the other pH bond decreases. Therefore, the reaction between the alkene and hypophosphite ion actually occurs in two steps, which can be broken down into the following two steps:

[0022]

[0023] Where R is H or an alkyl group.

[0024] Studies have found that the initial reaction step is more reactive, typically generating monoalkyl phosphine ions first. Only after all inorganic hypophosphite ions have been converted to monoalkyl hypophosphite ions does the formation of dialkyl phosphine ions begin. Of course, the initiation reaction also involves probability. Before the inorganic hypophosphite ions are completely converted to monoalkyl phosphine ions, a small amount of monoalkyl phosphine ions may be initiated to undergo addition with olefins to generate dialkyl phosphine ions. This is especially true under homogeneous gas-liquid reaction conditions, where the olefin and the initiator can have sufficient contact with the monoalkyl hypophosphite ions, increasing the probability of dialkyl phosphine ion formation. Here, using only one olefin, we obtain aluminum dialkyl phosphine with two identical alkyl groups.

[0025] 2) Preparation of dialkylphosphinate aluminum with two different alkyl groups: To prepare dialkylphosphinates with two different alkyl groups, two olefins are required. There are two methods for using two olefins (olefin 1 and olefin 2):

[0026] (I) When olefin 1 (denoted as R'1) and olefin 2 (denoted as R'2) are added to the reaction system at the same time, three reactions will occur simultaneously, as shown in the following reaction equations:

[0027]

[0028] The resulting products include dialkylphosphinates with two identical R1 alkyl groups, dialkylphosphinates with two identical R2 alkyl groups, and dialkylphosphinates with two different alkyl groups R1 and R2. Furthermore, due to the difference in reaction rates between the two olefins, the dialkylphosphinate of the olefin with the faster reaction rate is usually obtained, resulting in a low proportion of dialkylphosphinates with two different alkyl groups. These soluble dialkylphosphinates are all water-soluble, and the aluminum dialkylphosphinates obtained after reacting with aluminum-containing compounds are insoluble in water. Therefore, it is difficult to separate the different types of aluminum dialkylphosphinates, making it difficult to obtain high-purity dialkylphosphinates with two different alkyl groups using this method.

[0029] (II) Different olefins R'1 and R'2 are added in stages. As introduced above, the reaction between the olefin and the two PH bonds on the hypophosphite is a stepwise addition. However, since soluble hypophosphite is used, the generated monoalkyl hypophosphite is also soluble. At this time, some monoalkyl phosphite will still be initiated and react with the olefin to generate dialkyl phosphite with two identical alkyl groups. Although this scheme yields dialkyl phosphite with different alkyl groups with higher purity than the previous scheme of adding two olefins at the same time, these dialkyl phosphite with the same alkyl groups are difficult to separate from the mixture. Therefore, high-purity aluminum dialkyl phosphite cannot be obtained.

[0030] In summary, existing methods make it difficult to prepare high-purity aluminum dialkylphosphinates with different alkyl groups.

[0031] Based on previous research results, the inventors surprisingly discovered through experiments that dispersing insoluble inorganic aluminum hypophosphite in water, in the presence of an initiator and an olefin, still results in an addition reaction. The results appear similar to conventional preparation processes, i.e., using insoluble aluminum hypophosphite and water-soluble hypophosphite, with a similar addition reaction. However, the reaction process differs from conventional addition processes. 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, remaining in a suspension, resulting in a gas-liquid-solid reaction. Furthermore, the experiments revealed that the generated monoalkyl aluminum hypophosphite is water-soluble. During the addition process, the insoluble inorganic aluminum hypophosphite suspension gradually decreases or even disappears completely as the addition proceeds, yielding a homogeneous aqueous solution. If the addition reaction continues, insoluble dialkyl aluminum hypophosphite is generated, resulting in new precipitates. Therefore, an olefin R'1 can be added to aluminum hypophosphite to produce a soluble monoalkyl (R1) aluminum hypophosphite salt. In this process, there is still a chance to form some dialkyl aluminum hypophosphite of R1. However, the dialkyl aluminum hypophosphite of R1 is a precipitate. Therefore, the reaction system can be filtered before adding another olefin R'2. The filtrate obtained is a high-purity monoalkyl (R1) aluminum hypophosphite solution. At this time, the second olefin R'2 is added, and the monoalkyl aluminum hypophosphite of R1 and the olefin R'2 undergo an addition reaction to produce dialkyl aluminum hypophosphite precipitates with different alkyl groups R1 and R2, and the purity is very high. However, this process still generates two or more over-addition dialkylphosphinate byproducts, R'1 and R'2, in a certain proportion. To further improve the purity, the inventors further discovered that by dispersing aluminum hypophosphite at a low concentration in an alkaline aqueous solution and conducting an addition reaction under low olefin pressure, combined with a certain process, the content of byproducts can be greatly reduced, resulting in higher purity dialkylphosphinate with different alkyl groups.

[0032] In one embodiment, step (1) involves preparing the aluminum hypophosphite solid by dissolving hypophosphite and / or soluble hypophosphite in water, reacting it with an aluminum-containing compound to prepare an aluminum hypophosphite precipitate, and then filtering and washing it to obtain the aluminum hypophosphite solid.

[0033] In the method for preparing solid aluminum hypophosphite, the soluble hypophosphite can be an alkali metal salt, such as sodium hypophosphite or potassium hypophosphite.

[0034] In the method for preparing the aluminum hypophosphite solid, the aluminum-containing compound may be at least one of aluminum sulfate, aluminum chloride, aluminum nitrate, aluminum hydroxide, and aluminum acetate.

[0035] In the method for preparing the aluminum hypophosphite solid, if a soluble hypophosphite is used, it can be reacted with an aluminum salt compound; if hypophosphite is used, it can be reacted with aluminum hydroxide.

[0036] In the method for preparing the aluminum hypophosphite solid, the washing can be performed multiple times with clean water to reduce the residue of hypophosphite or hypophosphite and reduce its impact on subsequent reactions.

[0037] In the method for preparing the aluminum hypophosphite solid, the reaction temperature can be 20–120°C and the pressure can be 0.01–10 MPa.

[0038] In steps (1) and (2), the free radical initiator can be a peroxide and / or an azo compound, preferably a water-soluble peroxide, and more preferably includes at least one of hydrogen peroxide, potassium persulfate, sodium persulfate, and ammonium persulfate.

[0039] The higher the carbon number of an olefin, the lower its reactivity. Furthermore, the reactivity of the PH bond in hypophosphite decreases after the first addition reaction with an olefin. Therefore, preferably, this invention uses a less reactive olefin (an olefin with a larger carbon number) for the initial reaction, followed by a more reactive olefin (an olefin with a smaller carbon number) for the reaction with the second PH bond, resulting in a faster reaction rate and higher conversion. In a preferred embodiment, the method for preparing dialkyl phosphinates with different alkyl groups according to this invention involves olefin 1 having a larger carbon number than olefin 2. For example, olefin 1 is propylene or isobutylene, olefin 2 is ethylene, and the corresponding dialkyl phosphinates with different alkyl groups are ethylpropyl aluminum phosphinate or ethylbutyl aluminum phosphinate.

[0040] In step (1), the mass ratio of aluminum hypophosphite solid to water is 1:20 to 1000. Studies have found that excessively high aluminum hypophosphite concentrations will lead to an increase in excessive addition byproducts.

[0041] Preferably, in step (2), the mass percentage of aluminum monoalkylphosphinate in the filtrate does not exceed 5%. Excessively high concentrations of aluminum monoalkylphosphinate in the filtrate will lead to an increase in excessive addition byproducts.

[0042] In step (1), olefin 1 and solid aluminum hypophosphite undergo an addition reaction at 100–150 °C and 0.1–0.3 MPa; in step (2), monoalkyl aluminum hypophosphite and olefin 2 undergo an addition reaction at 100–150 °C and 0.1–0.3 MPa under the initiation of a free radical initiator. Below 100 °C, the reaction hardly proceeds; excessive pressure will lead to an increase in byproducts.

[0043] In one embodiment, the molar ratio of olefin 1 to solid aluminum hypophosphite in step (1) is 0.1 to 3:1. The degree of reaction is controlled according to the amount of olefin consumed. According to the reaction formula, for a complete reaction to occur, the molar ratio of olefin 1 to aluminum hypophosphite is 3:1. If the ratio is lower than this, the aluminum hypophosphite cannot react completely, and the conversion rate of aluminum hypophosphite decreases, but it is beneficial to reduce the content of by-products.

[0044] In one embodiment, the molar ratio of olefin 2 to aluminum monoalkylphosphinate in step (2) is 0.1 to 3:1. According to the reaction formula, for the reaction to proceed completely, the molar ratio of olefin 2 to aluminum monoalkylphosphinate is 3:1. Below this ratio, the aluminum monoalkylphosphinate cannot react completely, resulting in a lower conversion rate, but this is beneficial for reducing the content of byproducts.

[0045] Steps (1) and (2) need to be carried out under alkaline conditions. Although the reaction can also be carried out under acidic or neutral conditions, the amount of excessive addition byproducts will increase under acidic or neutral conditions. The required alkaline conditions are provided by an alkali metal hydroxide. In step (1), the alkali metal hydroxide can be sodium hydroxide and / or potassium hydroxide, etc. In step (1), the mass ratio of the alkali metal hydroxide to water can be 1:50 to 10000.

[0046] After the reaction in step (1) is completed, filtration is required to remove unreacted aluminum hypophosphite, excessive addition byproducts, and a small amount of R1 dialkylphosphinate aluminum. The filtrate is then used for the reaction in step (2). Failure to perform filtration will result in an increase in byproducts.

[0047] In one embodiment, after obtaining the dialkyl phosphonates aluminum precipitates with different alkyl groups in step (2), the precipitates are further filtered and washed to separate the dialkyl phosphonates aluminum precipitates containing R1 and R2. The precipitates can be washed with water to reduce the residual R1 monoalkyl phosphonates aluminum precipit ...

[0048] In one embodiment, the method for preparing dialkylphosphinate aluminum of the present invention with different alkyl groups includes the following steps:

[0049] S1, dissolve hypophosphite and / or soluble hypophosphite in water, react with an aluminum-containing compound to prepare aluminum hypophosphite precipitate, filter and wash the precipitate to obtain solid aluminum hypophosphite, the reaction formula is as follows:

[0050]

[0051] S2, the aluminum hypophosphite solid obtained in step S1 is dispersed at a low concentration in a solvent system containing alkali metal hydroxide and water, with a mass ratio of aluminum hypophosphite solid to water of 1:20-1000. Under the initiation of a free radical initiator, an addition reaction is carried out between olefin R'1 and aluminum hypophosphite solid at 100-150℃ and 0.1-0.3 MPa. The degree of reaction is controlled according to the consumption of olefin R'1 until the aluminum hypophosphite solid has fully reacted, to prepare a monoalkyl (R1) aluminum hypophosphite solution. The precipitate is filtered, and the filtrate is collected. The reaction formula is as follows:

[0052]

[0053] S3, a second alkene R'2, different from alkene R'1, is added to the filtrate collected in step S2. This causes the monoalkyl (R1) aluminum phosphite to undergo an addition reaction with alkene R'2 at 100–150 °C and 0.1–0.3 MPa under the initiation of a free radical initiator, yielding dialkyl aluminum phosphite precipitates with different alkyl groups (R1 and R2). The precipitates are then filtered and washed. The reaction formula is as follows:

[0054]

[0055] The method for preparing aluminum dialkylphosphinates with different alkyl groups described in this invention yields aluminum dialkylphosphinates with different alkyl groups with a purity of over 99.5%.

[0056] Compared with the prior art, the beneficial effects of this invention are as follows:

[0057] The aluminum dialkylphosphinates with different alkyl groups prepared by this invention have lower acidity and are less corrosive because the final step is an addition reaction and the reaction medium is under weakly alkaline conditions. There is no acidic aluminum sulfate in the final precipitation step of existing preparation methods.

[0058] The aluminum dialkylphosphinates with different alkyl groups prepared by this invention can be used as flame retardants in materials such as polyester, nylon, thermoplastic elastomers (TPE), polyurethane, epoxy resin, and POK.

[0059] The novel process for preparing aluminum dialkylphosphinates with different alkyl groups provided by this invention overcomes the defects of existing synthesis processes. The raw material aluminum hypophosphite and the intermediate by-products of this invention are both water-insoluble precipitates, which can be quickly and easily separated from the target intermediate product solution without affecting subsequent reactions or the purity of the final product. Only the target intermediate product solution needs to be taken for a second-step olefin addition reaction to obtain aluminum dialkylphosphinates with different alkyl groups with higher purity and superior performance. Detailed Implementation

[0060] 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.

[0061] Example 1: Preparation of aluminum ethylpropylphosphinic acid

[0062] 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.

[0063] 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 propylene. Maintain a constant pressure of 0.3MPa inside the reactor. Then, continuously pump in a 2wt% sodium persulfate solution using a peristaltic pump. Measure the propylene consumption; when 42.3g of propylene is consumed, the reaction is complete, taking approximately 2.5 hours. Reduce the pressure and temperature of the reactor to approximately 90℃, filter, and collect the filtrate.

[0064] Step 3: Add the filtrate to the aforementioned pressure vessel, heat to 105℃, 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 3.0 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. Disperse 10g of the precipitate in 100g of water, stir thoroughly, let stand for 1 hour, and test the pH value of the solution; the results are shown in Table 1.

[0065] Table 1: Results of precipitate composition analysis and pH test

[0066] Components Example 1 Comparative Example 1 Aluminum ethylpropylphosphonate (mol%) 99.88 77.98 Aluminum dipropylphosphonate (mol%) 0.05 20.20 Aluminum diethylphosphonate (mol%) 0.02 1.32 Other (mol%) 0.05 0.50 pH 5.1 4.0

[0067] Comparative Example 1

[0068] Using existing processes, a soluble hypophosphite is first added to an olefin to obtain a soluble dialkylphosphinate, which is then reacted with aluminum sulfate to obtain aluminum dialkylphosphinate. The reaction steps are as follows:

[0069] 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, and heat to 110℃. Introduce propylene 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. Measure the amount of propylene consumed. When approximately 126.7g of propylene is consumed, stop introducing propylene and introduce ethylene instead until no more ethylene is consumed. The reaction is then complete. The total reaction time is 5.5 hours.

[0070] Step 2: Heat the reaction solution obtained in Step 1 to 95℃, and add 420g of 46wt% aluminum sulfate solution to the reactor over 60 minutes. A white precipitate gradually forms, indicating the reaction is complete. Filter the solution, wash the precipitate with hot water, and vacuum dry it at 130℃. Perform phosphorus NMR analysis and pH testing on the precipitate; the results are shown in Table 1.

[0071] Example 2 Synthesis of aluminum ethylbutylphosphinate

[0072] The implementation process was the same as in Example 1, except that propylene was replaced with isobutylene in step two, and the amount of isobutylene consumed was 56.7g. Phosphorus NMR analysis and pH testing were performed on the precipitate, and the results are shown in Table 2.

[0073] Example 3

[0074] The procedure was the same as in Example 2, except that the amount of aluminum hypophosphite precipitate in step two was 55.5 g. Phosphorus NMR analysis and pH testing were performed on the precipitate, and the results are shown in Table 2.

[0075] Example 4

[0076] The procedure was the same as in Example 2, except that the reaction pressure was 0.2 MPa in steps two and three. Phosphorus NMR analysis and pH testing were performed on the precipitate, and the results are shown in Table 2.

[0077] Comparative Example 2

[0078] The procedure was the same as in Comparative Example 1, except that propylene was replaced with isobutylene in step one, and the amount of isobutylene consumed was 168.8 g. Phosphorus NMR analysis and pH testing were performed on the precipitate, and the results are shown in Table 2.

[0079] Table 2: Precipitate composition analysis and pH test results

[0080] Components Example 2 Comparative Example 2 Example 3 Example 4 Aluminum ethyl butylphosphinate (mol%) 99.87 76.07 99.89 99.91 Aluminum dibutylphosphonate (mol%) 0.06 22.35 0.05 0.04 Aluminum diethylphosphonate (mol%) 0.02 1.08 0.02 0.02 Other (mol%) 0.05 0.5 0.04 0.03 pH 5.0 3.9 5.0 5.0

[0081] Comparative Example 3

[0082] The implementation process was the same as in Example 2, except that the amount of aluminum hypophosphite in step two was 259g. Phosphorus NMR analysis was performed on the precipitate product from step three, and the results are shown in Table 3.

[0083] Comparative Example 4

[0084] The implementation process was the same as in Example 2, 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 3.

[0085] Comparative Example 5

[0086] The procedure was the same as in Example 2, 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 3.

[0087] Comparative Example 6

[0088] The procedure was the same as in Example 2, 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 3.

[0089] Comparative Example 7

[0090] The implementation process was the same as in Example 2, 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 3.

[0091] Comparative Example 8

[0092] The implementation process was the same as in Example 2, except that the reaction temperature in step two was 90°C. The reaction rate was almost negligible.

[0093] Table 3: Results of Precipitate Component Analysis

[0094]

[0095] 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 dialkylphosphinate aluminum with different alkyl groups, characterized in that, Including the following steps: (1) Aluminum hypophosphite solid is dispersed at a low concentration in a solvent system containing alkali metal hydroxide and water. The mass ratio of aluminum hypophosphite solid to water is 1:20~1000. Under the initiation of a free radical initiator, olefin 1 and aluminum hypophosphite solid undergo an addition reaction at 100~150℃ and 0.1~0.3 MPa. The consumption of olefin 1 is controlled until the aluminum hypophosphite solid reacts completely to prepare a monoalkyl aluminum hypophosphite solution. The precipitate is filtered and the filtrate is collected. (2) An olefin 2, which is different from olefin 1, is introduced into the filtrate. The number of carbon atoms in olefin 1 is greater than that in olefin 2. The monoalkyl aluminum phosphinate reacts with olefin 2 under the initiation of a free radical initiator at 100~150℃ and 0.1~0.3 MPa to obtain dialkyl aluminum phosphinate precipitates with different alkyl groups. In step (1), the molar ratio of olefin 1 to solid aluminum hypophosphite is 0.1~3:1, and in step (2), the molar ratio of olefin 2 to monoalkyl aluminum hypophosphite is 0.1~3:

1. The purity of the dialkylphosphinate aluminum prepared by the method is above 99.5%.

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

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

4. The preparation method according to claim 1, characterized in that, In steps (1) and (2), the free radical initiators are, respectively, peroxides and / or azo compounds.

5. The preparation method according to claim 4, characterized in that, In steps (1) and (2), the free radical initiators are water-soluble peroxides.

6. The preparation method according to claim 5, characterized in that, In steps (1) and (2), the free radical initiator independently includes at least one of hydrogen peroxide, potassium persulfate, sodium persulfate, and ammonium persulfate.

7. The preparation method according to claim 1, characterized in that, In step (2), the mass percentage of the aluminum monoalkylphosphinate in the filtrate does not exceed 5%.

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

9. The preparation method according to claim 1, characterized in that, After obtaining aluminum dialkylphosphinate precipitates with different alkyl groups in step (2), the precipitates are further filtered and washed.

Images