Process for the preparation of aluminum diethylphosphinate

Abstract

The application belongs to the technical field of flame retardant preparation, and particularly relates to a preparation method of aluminum diethylphosphinate. The application is prepared by taking sodium hypophosphite and ethylene as reaction raw materials, water as a solvent, adding an initiator and a Lewis acid catalyst, and synergistically catalyzing the addition reaction of sodium hypophosphite and ethylene to synthesize sodium diethylphosphinate, and then reacting the sodium diethylphosphinate with an aluminum salt to generate aluminum diethylphosphinate. The method has the advantages of simple operation, short reaction time, high yield of aluminum diethylphosphinate, high product purity, and small corrosion to equipment, and is a very promising preparation method for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant preparation technology, specifically relating to a method for preparing aluminum diethylphosphinate. Background Technology

[0002] Halogenated flame retardants are among the most produced organic flame retardants globally. The advantages of halogenated flame retardants are low dosage, high flame retardant efficiency, and wide applicability. However, their disadvantages include the production of large amounts of dense smoke and corrosive hydrogen halide gases during combustion, as well as the release of highly toxic dioxins, which hinder firefighting and personnel evacuation, and corrode equipment. Charcoal-forming organophosphorus flame retardants are considered one of the most promising alternatives to halogenated flame retardants. Alkyl phosphinate flame retardants offer high flame retardant efficiency, minimal impact on mechanical properties, good color, and high hydrolytic stability. Furthermore, the presence of metal cations in alkyl phosphinates prevents the volatilization loss and environmental pollution of the flame retardant. Simultaneously, salts of these metal cations (such as zinc, magnesium, and aluminum) have good smoke-suppressing effects, with aluminum diethylphosphinate (ADP) being the most representative. In recent years, ADP, as a new type of halogen-free and environmentally friendly flame retardant, has been successfully applied to the flame retardant treatment of materials such as glass fiber reinforced nylon (PA) and polybutylene terephthalate (PBT) to produce high-value-added flame retardant products. It is favored by customers for its good color, low smoke density and high tracking index (up to 600V). It has been used in the electronics and electrical industry to manufacture flame retardant thin-walled electronic components, transparent sheets and films.

[0003] Currently, the main international producer of mature aluminum diethylphosphite is Clariant AG of Germany. Clariant has developed Exolit OP1311 and Exolit OP1312, with aluminum diethylphosphite as the main component. The former is primarily used for flame retardant GRPA6, and the latter for flame retardant GRPA66. These flame-retardant products have low density, require less flame retardant, have good mechanical properties, good color, low smoke density, and a relatively high tracking index, making them promising for applications in the electronics and electrical industries. Based on this, researchers both domestically and internationally have successively undertaken research and development work on aluminum diethylphosphite. To date, the prepared dialkylphosphite products always contain approximately 2.5 wt.% monoethylphosphite groups. In addition, the introduction of large amounts of sodium acetate into the wastewater generated during the post-processing purification of these processes increases industrial production costs by approximately 40%. Therefore, developing a more environmentally friendly, lower-cost process technology with low or even no monoethylphosphite group content is urgently needed. US6011172 and CN1280581 report methods for preparing dialkyl phosphonates from yellow phosphorus and alkyl halides. This method uses yellow phosphorus as the phosphorus source, yielding a mixture of dialkyl phosphonic acid, monoalkyl phosphonic acid, and hypophosphite. The yield of dialkyl phosphonic acid is low, only 16%. US6300516 and US6329544 report methods for preparing dialkyl phosphonates by reacting olefins with hypophosphite under the action of a peroxide radical initiator. In this method, the reaction temperature is determined by the decomposition temperature of the thermal initiator (organic or inorganic peroxide), and most peroxide initiators have decomposition temperatures greater than 100°C. Therefore, the required reaction temperature is generally high, resulting in significant energy consumption. Although this method improves the yield of dialkylphosphine or its salts (reaching approximately 90% molar percentage) compared to those reported in US6011172 and CN1280581, it still contains a large number of other byproducts that affect product purity. For example, polymerization reactions can occur due to excessive pressure, and butylphosphine or its salts are easily generated when using ethylene as a raw material. To address issues such as high energy consumption and reaction system safety, patent CN101891762A proposes a method for synthesizing diethylphosphinate with low temperature, low pressure, and high operational safety. However, its target product, aluminum diethylphosphinate, has a low effective content, only about 90%, and contains aluminum monoethylphosphinate and other unidentified compounds. These impurities will severely affect product quality and performance indicators such as initial decomposition temperature. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a method for preparing aluminum diethylphosphinate, which uses sodium hypophosphite as a raw material and employs a catalyst + initiator mode in a neutral solvent to efficiently synthesize aluminum diethylphosphinate. This invention has advantages such as simple operation, short reaction time, high yield of aluminum diethylphosphinate, high product purity, and low corrosivity to equipment, making it a preparation scheme with great potential for industrial application.

[0005] This invention is achieved through the following technical solution: The method for preparing diethylphosphite aluminum according to the present invention uses sodium hypophosphite and ethylene as reactants, water as solvent, and adds an initiator and Lewis acid catalyst to synergistically catalyze the addition reaction of sodium hypophosphite and ethylene to synthesize sodium diethylphosphite. Sodium diethylphosphite reacts with aluminum salt to generate diethylphosphite aluminum.

[0006] Specifically, the following steps are included: (1) Place an aqueous solution of sodium hypophosphite in a reactor, add Lewis acid catalyst, introduce ethylene, control the internal pressure and temperature of the reactor, slowly add initiator, and after the reaction is complete, prepare a sodium diethylphosphite solution system. (2) Add aluminum salt solution to sodium diethylphosphonate solution system and react to obtain white precipitate of aluminum diethylphosphonate; (3) Wash and dry the white precipitate of aluminum diethylphosphonate to obtain white powdered aluminum diethylphosphonate.

[0007] Preferably, in step (1), the Lewis acid catalyst is one of CuBr2, CuCl2, FeCl3, and AlCl3, and the amount added is 0.1-5 mol of sodium hypophosphite.

[0008] In step (1), the initiator is one of sodium persulfate, azobisisobutyramidine hydrochloride, ammonium persulfate, and cumene hydroperoxide, and the amount added is 0.1-5 mol% of sodium hypophosphite, and the initiator is added for 3-8 hours.

[0009] In step (1), the initiator is dissolved in water at a mass concentration of 5-25%.

[0010] In step (1), the reaction temperature is 30-100℃ and the pressure is 0.2-2MPa. After the initiator is added, the reaction is stirred for 1-2 hours.

[0011] In step (2), the aluminum salt is one of aluminum sulfate, aluminum chloride, and aluminum nitrate, and the amount added is 3-6 times the molar amount of sodium hypophosphite.

[0012] In step (2), the aluminum salt is dissolved in water with a mass concentration of 20-60%.

[0013] In step (2), the reaction temperature is 50-90℃ and the reaction time is 2-8h.

[0014] In step (3), the washing liquid used for washing is water at 45-50℃, and the washing is performed 3-5 times. The vacuum degree of the drying process is 0.085-0.09MPa, and the drying temperature is 125-130℃.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention uses water as a solvent, avoiding the problem of reaction corrosion. It employs a synergistic effect of a free radical initiator and a Lewis acid catalyst. The free radical initiator initiates the breaking of the phosphine hydrogen bonds in sodium hypophosphite, and then the Lewis acid catalyst stabilizes the phosphine free radicals, increasing the rate of the free radical addition reaction. This synergistic effect efficiently catalyzes the preparation of diethylaluminum hypophosphite, resulting in a white solid product with fine particles, high purity, and good thermal stability. Chinese invention patent CN114685856A discloses a method for preparing diethylaluminum hypophosphite using sodium hypophosphite and ethylene as raw materials, employing methyl ketone initiators, and using heating and pressure as initiation conditions. However, heating and pressure alone cannot initiate the reaction with methyl ketone initiators, so this method also uses microwaves as an initiation condition to prepare diethylaluminum hypophosphite. However, microwave treatment is difficult to operate industrially. In comparison, this invention is more suitable for industrial production, is simple to operate, and has low energy consumption. Detailed Implementation

[0016] To enable those skilled in the art to better understand the technical content of this invention, the preferred embodiments of this invention are further described below with reference to specific examples. Unless otherwise specified, the equipment and reagents used in each embodiment are all commercially available.

[0017] Example 1 The method for preparing aluminum diethylphosphinate according to the present invention includes the following steps: (1) Dissolve 44g (0.4mol) sodium hypophosphite monohydrate in 200mL of deionized water and stir thoroughly to obtain an aqueous solution of sodium hypophosphite. Then transfer it to a 500mL jacketed pressure-resistant reactor, add 2.7g CuCl2 and stir thoroughly. Introduce ethylene at 30℃ to maintain the pressure inside the reactor at 0.2MPa and reach saturation. Then dissolve 0.1g sodium persulfate in 2mL of deionized water and add it slowly and evenly over 3h. Continue stirring for 1h to obtain a reaction mixture of sodium diethylphosphite.

[0018] (2) At 50℃, a 20% (1.2 mol aluminum sulfate) aqueous solution was added at a constant rate to the sodium diethylphosphonate solution obtained in (1) within 1 h, and the reaction was continued for 1 h to obtain a white precipitate of aluminum diethylphosphonate.

[0019] (3) The obtained white precipitate of aluminum diethylphosphonate was washed three times in hot water at 50°C, and then dried in a vacuum drying oven at 0.085 MPa and 130°C to obtain white powdered aluminum diethylphosphonate.

[0020] According to the P-NMR spectrum (D2O), the aluminum diethylphosphite content was 100%, with no other impurities. The weight of aluminum diethylphosphite was 48g, and the yield was 92%.

[0021] Example 2 The method for preparing aluminum diethylphosphinate according to the present invention includes the following steps: (1) Dissolve 44g (0.4mol) sodium hypophosphite monohydrate in 200mL of deionized water and stir thoroughly to obtain an aqueous solution of sodium hypophosphite. Then transfer it to a 500mL jacketed pressure-resistant reactor, add 0.055g AlCl3 and stir thoroughly. Introduce ethylene at 100℃ to maintain the pressure inside the reactor at 2MPa and reach saturation. Then dissolve 5.4g of azobisisobutyramidine hydrochloride in 22mL of deionized water and add it slowly and evenly over 8h. Continue stirring and react for 2h to obtain a reaction mixture of diethyl sodium hypophosphite.

[0022] (2) At 90℃, a 60% (2.4 mol aluminum sulfate) aqueous solution was added at a constant rate to the sodium diethylphosphonate solution obtained in (1) within 7 h, and the reaction was continued for 1 h to obtain a white precipitate of aluminum diethylphosphonate.

[0023] (3) The obtained white precipitate of aluminum diethylphosphonate was washed three times in hot water at 50°C, and then dried in a vacuum drying oven at 0.09 MPa and 130°C to obtain white powdered aluminum diethylphosphonate.

[0024] According to the P-NMR spectrum (D2O), the aluminum diethylphosphite content was 100%, with no other impurities. The weight of aluminum diethylphosphite was 49g, and the yield was 94%.

[0025] Example 3 The method for preparing aluminum diethylphosphinate according to the present invention includes the following steps: (1) Dissolve 44g (0.4mol) sodium hypophosphite monohydrate in 200mL of deionized water and stir thoroughly to obtain an aqueous solution of sodium hypophosphite. Then transfer it to a 500mL jacketed pressure-resistant reactor, add 1.3g FeCl3 and stir thoroughly. Introduce ethylene at 60℃ to maintain the pressure inside the reactor at 1MPa and reach saturation. Then dissolve 1.8g ammonium persulfate in 11mL of deionized water and add it slowly and evenly over 5h. Continue stirring and react for 1h to obtain a reaction mixture of sodium diethylphosphite.

[0026] (2) At 70°C, a 50% (1.6 mol aluminum chloride) aqueous solution was added at a constant rate to the sodium diethylphosphonate solution obtained in (1) over 6 hours. The reaction was continued for 1 hour to obtain a white precipitate of aluminum diethylphosphonate.

[0027] (3) The obtained white precipitate of aluminum diethylphosphonate was washed three times in hot water at 50°C, and then dried in a vacuum drying oven at 0.09 MPa and 130°C to obtain white powdered aluminum diethylphosphonate.

[0028] According to the P-NMR spectrum (D2O), the aluminum diethylphosphite content was 100%, with no other impurities. The weight of aluminum diethylphosphite was 49g, and the yield was 94%.

[0029] Example 4 The method for preparing aluminum diethylphosphinate according to the present invention includes the following steps: (1) Dissolve 44g (0.4mol) sodium hypophosphite monohydrate in 200mL of deionized water and stir thoroughly to obtain an aqueous solution of sodium hypophosphite. Then transfer it to a 500mL jacketed pressure-resistant reactor, add 1g CuBr2 and stir thoroughly. Introduce ethylene at 80℃ to maintain the pressure inside the reactor at 1.5MPa and reach saturation. Then dissolve 2.4g of cumene hydroperoxide in 10mL of deionized water and add it slowly and evenly over 5h to obtain a reaction mixture of sodium diethylphosphite.

[0030] (2) At 70°C, a 40% (1.2 mol aluminum nitrate) aqueous solution was added at a constant rate to the sodium diethylphosphonate solution obtained in (1) over 4 hours. The reaction was continued for 1 hour to obtain a white precipitate of aluminum diethylphosphonate.

[0031] (3) The obtained white precipitate of aluminum diethylphosphonate was washed three times in hot water at 50°C, and then dried in a vacuum drying oven at 0.09 MPa and 130°C to obtain white powdered aluminum diethylphosphonate.

[0032] According to the P-NMR spectrum (D2O), the aluminum diethylphosphite content was 100%, with no other impurities. The weight of aluminum diethylphosphite was 47g, and the yield was 90%.

[0033] Example 5 The method for preparing aluminum diethylphosphinate according to the present invention includes the following steps: (1) Dissolve 44g (0.4mol) sodium hypophosphite monohydrate in 200mL of deionized water and stir thoroughly to obtain an aqueous solution of sodium hypophosphite. Then transfer it to a 500mL jacketed pressure-resistant reactor, add 2g CuCl2 and stir thoroughly. Introduce ethylene at 90℃ to maintain the pressure inside the reactor at 1MPa and reach saturation. Then dissolve 4.7g sodium persulfate in 20mL of deionized water and add it slowly and evenly over 6h to obtain a reaction mixture of sodium diethylphosphite.

[0034] (2) At 70°C, a 50% (1.6 mol aluminum sulfate) aqueous solution was added at a constant rate to the sodium diethylphosphonate solution obtained in (1) within 1 h, and the reaction was continued for 1 h to obtain a white precipitate of aluminum diethylphosphonate.

[0035] (3) The obtained white precipitate of aluminum diethylphosphonate was washed three times in hot water at 50°C, and then dried in a vacuum drying oven at 0.09 MPa and 130°C to obtain white powdered aluminum diethylphosphonate.

[0036] According to the P-NMR spectrum (D2O), the aluminum diethylphosphite content was 100%, with no other impurities. The weight of aluminum diethylphosphite was 50g, and the yield was 96%.

[0037] Comparative Example 1 The preparation method of aluminum diethylphosphinate includes the following steps: (1) Dissolve 44g (0.4mol) sodium hypophosphite monohydrate in 200mL of deionized water and stir thoroughly to obtain an aqueous solution of sodium hypophosphite. Then transfer it to a 500mL jacketed pressure-resistant reactor and introduce ethylene at 30°C to maintain the pressure inside the reactor at 0.8MPa and reach saturation. Then dissolve 0.8g sodium persulfate in 10mL of deionized water and add it slowly and evenly over 6h to obtain a reaction mixture of sodium diethylphosphite.

[0038] (2) At 50℃, a 20% (1.2 mol aluminum sulfate) aqueous solution was added at a constant rate to the sodium diethylphosphonate solution obtained in (1) within 1 h, and the reaction was continued by stirring to obtain a white precipitate of aluminum diethylphosphonate.

[0039] (3) The obtained white precipitate of aluminum diethylphosphonate was washed three times in hot water at 50°C, and then dried in a vacuum drying oven at 0.085 MPa and 130°C to obtain white powdered aluminum diethylphosphonate.

[0040] The content of aluminum diethylphosphite was characterized as 60% by P-NMR spectroscopy (D2O). The weight of aluminum diethylphosphite was 15g, and the yield was 29%.

[0041] Comparative Example 2 The preparation method of aluminum diethylphosphinate is the same as in Example 1, except that the amount of CuCl2 added is 0.01g, and the content of aluminum diethylphosphinate is 80% according to the p-NMR spectrum (D2O). The weight of aluminum diethylphosphite is 25g, and the yield is 48%.

[0042] Comparative Example 3 The preparation method of aluminum diethylphosphonate is the same as in Example 1, except that the amount of sodium persulfate added is 0.05 g, and the content of aluminum diethylphosphonate is 50% according to the p-NMR spectrum (D2O). The weight of aluminum diethylphosphonate is 10 g, and the yield is 19%.

[0043] Comparative Example 4 The preparation method of aluminum diethylphosphinate is the same as in Example 1, except that the ethylene pressure is 0.1 MPa, and the content of aluminum diethylphosphinate is 20% as characterized by π nuclear magnetic resonance (D2O) spectrum. The weight of aluminum diethylphosphinate is 5 g, and the yield is 10%.

Claims

1. A method for preparing aluminum diethylphosphinate, characterized in that: Sodium hypophosphite and ethylene are used as reactants, water is used as solvent, and an initiator and Lewis acid catalyst are added to synergistically catalyze the addition reaction of sodium hypophosphite and ethylene to synthesize sodium diethylphosphite. Sodium diethylphosphite reacts with aluminum salt to produce aluminum diethylphosphite.

2. The method for preparing aluminum diethylphosphinate according to claim 1, characterized in that: Specifically, the following steps are included: (1) Place an aqueous solution of sodium hypophosphite in a reactor, add Lewis acid catalyst, introduce ethylene, control the internal pressure and temperature of the reactor, add an initiator, and after the reaction is complete, prepare a sodium diethylphosphite solution system. (2) Add aluminum salt solution to sodium diethylphosphonate solution system and react to obtain aluminum diethylphosphonate precipitate; (3) Wash and dry the aluminum diethylphosphonate precipitate to obtain a white powdered aluminum diethylphosphonate.

3. The method for preparing aluminum diethylphosphinate according to claim 2, characterized in that: In step (1), the Lewis acid catalyst is one of CuBr2, CuCl2, FeCl3, and AlCl3, and the amount added is 0.1-5 mol of sodium hypophosphite.

4. The method for preparing aluminum diethylphosphinate according to claim 2, characterized in that: In step (1), the initiator is one of sodium persulfate, azobisisobutyramidine hydrochloride, ammonium persulfate, and cumene hydroperoxide, and the amount added is 0.1-5 mol% of sodium hypophosphite, and the initiator is added for 3-8 hours.

5. The method for preparing aluminum diethylphosphinate according to claim 2, characterized in that: In step (1), the initiator is dissolved in water at a mass concentration of 5-25%.

6. The method for preparing aluminum diethylphosphinate according to claim 2, characterized in that: In step (1), the reaction temperature is 30-100℃ and the pressure is 0.2-2MPa.

7. The method for preparing aluminum diethylphosphinate according to claim 2, characterized in that: In step (2), the aluminum salt is one of aluminum sulfate, aluminum chloride, and aluminum nitrate, and the amount added is 3-6 times the molar amount of sodium hypophosphite.

8. The method for preparing aluminum diethylphosphinate according to claim 2, characterized in that: In step (2), the aluminum salt is dissolved in water with a mass concentration of 20-60%.

9. The method for preparing aluminum diethylphosphinate according to claim 2, characterized in that: In step (2), the reaction temperature is 50-90℃ and the reaction time is 2-8h.