Method for preparing amorphous aluminum diethylphosphinate from potassium hypophosphite and use thereof

Abstract

This invention relates to the field of flame-retardant materials, specifically a method and application for preparing amorphous aluminum diethylphosphinate from potassium hypophosphite. The method includes: preparing potassium hypophosphite from yellow phosphorus and potassium hydroxide via a disproportionation reaction; dissolving the prepared potassium hypophosphite in water and reacting it with ethylene via a free radical addition reaction under the action of a free radical initiator to synthesize potassium diethylphosphinate; heating the prepared aqueous solution of potassium diethylphosphinate, adding an organic solvent, and mixing under ultrasonic vibration to obtain a mixed solution, adjusting the solution to be acidic; adding an aqueous solution of aluminum sulfate to the mixed solution and conducting a metathesis reaction under ultrasonic vibration; after the reaction is completed, filtering, washing, and drying to obtain the amorphous product of aluminum diethylphosphinate. This invention has low cost, achieves comprehensive resource utilization and clean production; the product has high purity; the particle size is suitable and uniform, and the product is continuously and uniformly distributed in the resin, achieving better flame-retardant effect.

Description

Technical Field

[0001] This invention relates to the field of flame retardant materials, specifically a method and application for preparing amorphous aluminum diethylphosphinate from potassium hypophosphate. Background Technology

[0002] In recent years, with the increasing awareness of environmental protection, safety, and health, countries around the world have begun to focus on the research, development, and application of environmentally friendly flame retardants. Halogenated flame retardants are prone to decomposition during combustion, producing toxic substances (such as hydrogen bromide and dioxins), posing a potentially huge hazard. Therefore, the development of halogen-free flame retardants has become a research hotspot in the field of flame retardants.

[0003] Aluminum diethylphosphinate (ADP) is a highly efficient halogen-free flame retardant with the chemical structure Al(PO2C4H) 10 3. It appears as a white powder with a density of approximately 1.35 g / cm³. 3 With a thermal decomposition temperature as high as 360℃, it has the advantages of pure white color, good hue, low smoke emission during flame retardancy, low dosage, and good mechanical properties. It is widely used in engineering plastics such as epoxy resin, polyurethane, polyamide, and polybutylene terephthalate (PBT).

[0004] The flame-retardant mechanism of aluminum diethylphosphonate involves the formation of a dense protective char layer at high temperatures. This char layer acts like a natural firewall, isolating oxygen and heat, thus significantly slowing the spread of flame. However, commonly synthesized diethylphosphonate flame retardants have high crystallinity, resulting in excessively large particles (exceeding millimeters). This leads to discontinuous distribution of the flame retardant during resin synthesis, causing intermittent distribution of the flame-retardant material and a decrease in flame-retardant performance. In applications such as the electronics industry, flame retardant performance must reach UL94 V-0 level when the material particle size is less than 0.4 mm. This requires the flame retardant to have good flowability to achieve a more uniform distribution. Excessively large crystalline particles lead to uneven distribution of the flame retardant; therefore, synthesizing a more uniform amorphous (i.e., non-crystalline) powder can significantly improve the flowability of the flame retardant.

[0005] Currently, there are many reports on the preparation methods of aluminum diethylphosphinate and dialkylphosphinate flame retardants, mainly including several technical routes: free radical addition-metathesis two-step method, crystal form control process, and ultrasonic-assisted synthesis process.

[0006] However, existing technologies have the following drawbacks: The raw material route is singular and the cost is high; the content of by-products is high, which affects the purity of the product and the performance of the polymer; the product crystallinity is too high, and the particles are large and uneven; the morphology control methods are limited and the industrial adaptability is limited; there is a lack of complete technical solutions from source to product. Summary of the Invention

[0007] The purpose of this invention is to provide a method and application for preparing amorphous diethylphosphinate aluminum from potassium hypophosphite. This method uses widely available yellow phosphorus and KOH as initial raw materials to prepare potassium hypophosphite, solving the problems of single raw material routes and high costs in existing technologies. Simultaneously, it recovers and utilizes the PH3 and H2 tail gases generated by the disproportionation reaction, achieving comprehensive resource utilization and clean production. It also addresses the problems of high by-product content (especially excessive addition by-products such as ethylbutylphosphinate aluminum), low product purity, and negative impacts on polymer mechanical properties in existing diethylphosphinate aluminum synthesis processes. Furthermore, it solves the problems of excessively high crystallinity, large and uneven particle size in existing diethylphosphinate aluminum products, ensuring continuous and uniform distribution of the product in the resin for better flame retardant effects. Finally, it simplifies the synthesis process, reduces the amount of organic solvents used, lowers production costs and environmental pollution, and achieves green production.

[0008] The specific technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing amorphous aluminum diethylphosphinate from potassium hypophosphate, comprising the following steps: Step (1) Potassium hypophosphite is prepared by disproportionation reaction using yellow phosphorus and potassium hydroxide as raw materials; Step (2) Dissolve the potassium hypophosphite prepared in step (1) in water and react it with ethylene under the action of a free radical initiator to synthesize potassium diethylphosphite; Step (3) Heat the potassium diethylphosphonate aqueous solution prepared in step (2), add an organic solvent, mix under ultrasonic vibration to obtain a mixture, and adjust the mixture to be acidic; Step (4) Add aluminum sulfate aqueous solution to the mixture described in step (3) and carry out metathesis reaction under ultrasonic vibration. After the reaction is completed, filter, wash and dry to obtain aluminum diethylphosphinate amorphous product.

[0009] As a preferred option, in step (1), the conditions for the disproportionation reaction are: the molar ratio of yellow phosphorus to potassium hydroxide is 1:3 to 5, the reaction temperature is 60 to 95°C, and the reaction time is 2 to 5 hours.

[0010] As a preferred option, in step (1), the phosphine and hydrogen mixture generated by the reaction is collected and transported to combustion treatment, and the combustion exhaust gas is absorbed by alkaline spray and then discharged in compliance with standards.

[0011] As a preferred option, in step (2), the conditions for the free radical addition reaction are as follows: the amount of free radical initiator is 0.5% to 3% of the mass of potassium hypophosphite, the ethylene pressure is 0.5 to 1.5 MPa, the reaction temperature is 80 to 150°C, the reaction time is 4 to 10 hours, and the reaction pressure is maintained at 0.8 to 1.2 MPa during the reaction.

[0012] As a preferred embodiment, in step (3), the prepared potassium diethylphosphonate aqueous solution is heated to 40-60°C and maintained thereon. The organic solvent is one or more of methanol, ethanol, acetonitrile, diethyl ether, toluene and N',N-dimethylformamide. The volume of the organic solvent is 5%-15% of the volume of the aqueous solution. The ultrasonic oscillation conditions are: frequency 20-40 kHz, time 20-30 minutes.

[0013] As a preferred option, in step (3), the concentration of dilute sulfuric acid used to adjust the mixture to be acidic is 1 to 3 mol / L, and the pH value of the mixture after adjustment is 1.0 to 4.0.

[0014] As a preferred embodiment, in step (4), the aluminum sulfate aqueous solution is a saturated aluminum sulfate aqueous solution at 30-60℃; the aluminum sulfate aqueous solution is added by dripping at a rate of 1.0-3.0 mL / min, and the dripping is completed in 5-8 minutes, with ultrasonic oscillation maintained during the dripping process at a frequency of 20-40 kHz; the molar ratio of potassium diethylphosphonate to aluminum sulfate is 6:1-5.

[0015] As a preferred option, in step (4), the conditions for the metathesis reaction are: controlling the reaction temperature at 40-60°C, continuing ultrasonic vibration for 2-4 hours after the addition is completed, and allowing the solution to stand for 4-6 hours after the reaction is completed.

[0016] Secondly, the present invention provides a flame retardant material comprising the following raw materials in parts by weight: 5-10 parts of amorphous aluminum diethylphosphinate, 70-80 parts of epoxy resin, and 10-25 parts of curing agent, wherein the amorphous aluminum diethylphosphinate is obtained by the method described above.

[0017] Thirdly, the present invention provides a method for preparing a flame-retardant material, comprising the following steps: Step (1) Heat 70-80 parts of epoxy resin until it melts; Step (2) 5-10 parts of amorphous aluminum diethylphosphonate obtained by the method of any one of claims 1 to 8 are ultrasonically dispersed in an organic solvent and then mixed with the epoxy resin of step (1) until homogeneous. The mixture is heated at a certain temperature to remove the organic solvent. Step (3) Weigh 10-25 parts of curing agent, melt it, and pour the liquid curing agent into the epoxy resin mixture in step (2) while it is hot. Stir it thoroughly and then pour it into the glue strip mold. Step (4) Place the mold into the curing equipment, cure it, then heat it to cure it again, cool it to room temperature, and demold it to obtain the epoxy resin flame retardant material containing amorphous aluminum diethylphosphinic acid. Attached Figure Description

[0018] Figure 1This is the XRD pattern of the amorphous aluminum diethylphosphonate product of Example 1 of the invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. 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 the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased.

[0020] Unless otherwise stated, all percentages in this invention represent mass fractions. Ratios are mass percentages, and concentrations are mass concentrations.

[0021] Unless otherwise specified, all materials, instruments, and equipment used below are conventional materials, instruments, and equipment or obtained through commercial channels; all testing methods used are existing methods unless otherwise specified.

[0022] Currently, there are many reports on the preparation methods of aluminum diethylphosphinate and dialkylphosphinate flame retardants, which can be mainly summarized into the following technical routes: (1) Two-step method of free radical addition-metathesis (mainstream industrial route) The synthesis of aluminum diethylphosphonate typically involves two steps: First, a water-soluble inorganic hypophosphite (such as sodium hypophosphite) undergoes an addition reaction with ethylene in the aqueous phase in the presence of a free radical initiator, ethylating the inorganic hypophosphite to obtain water-soluble aluminum diethylphosphite. Second, the water-soluble aluminum diethylphosphite undergoes a metathesis reaction with a water-soluble aluminum salt (such as aluminum sulfate) to obtain aluminum diethylphosphite precipitate. The key step in these two reactions is the first step, the addition reaction between ethylene and the inorganic hypophosphite, which determines the reaction efficiency and product quality.

[0023] The reaction mechanism of this technical route is as follows: the water-soluble free radical initiator decomposes upon heating in the aqueous phase to generate free radicals. These free radicals first attack the more reactive phosphorus-hydrogen bonds, causing them to break and generating hypophosphite free radicals. The hypophosphite free radicals then attack the double bonds of ethylene, opening and combining with them to form new ethyl-containing phosphonate free radicals. These free radicals continue to interact with the phosphorus-hydrogen bonds of hypophosphite, completing the addition reaction.

[0024] However, this route suffers from significant side reaction problems: the ethyl group in the diethylphosphinate structure may be initiated by the initiator to form a free radical, which then undergoes excessive addition with ethylene, generating byproducts such as ethylbutylaluminum phosphinate and butylbutylaluminum phosphinate. Ethylbutylaluminum phosphinate is the predominant byproduct, typically accounting for about 2 wt%, and these byproducts cannot be separated from diethylphosphinate. These excessively added dialkylaluminum phosphinate byproducts can cause polymer degradation, reducing the mechanical properties of the polymer material. Even when the reaction medium is changed from the organic solvent acetic acid to water, the byproduct content in the prepared diethylphosphinate remains high; the lowest reported byproduct (ethylbutylaluminum phosphinate) content is 0.9 mol%, and the negative effects persist.

[0025] (2) Crystal form control process (morphology control route) To improve the dispersibility and flowability of aluminum diethylphosphonate in resins, existing technologies have focused on controlling crystal morphology. For example, by adding a crystallizing agent to an aqueous solution of dialkylphosphonic acid and / or its alkali metal salt, a dialkylphosphonate is formed by reacting with a metal compound, achieving an angle of repose of 20°–40°, thus solving the problem of poor flowability and uneven distribution of flame retardants in resins. However, this method essentially still prepares crystalline products and does not fundamentally solve the problem of uneven morphology caused by excessively large crystal nuclei. Another existing technology uses sodium diethylphosphonate and water-soluble aluminum salts as raw materials, water as a solvent, and a water-soluble surfactant as a crystal aggregator to prepare a high-density product. However, this existing technology focuses on increasing bulk density and does not address the control of amorphous morphology.

[0026] (3) Ultrasonic-assisted synthesis process Regarding the preparation of amorphous dialkylphosphinate aluminum, sodium dipropylphosphinate and aluminum sulfate were used as raw materials, with an appropriate amount of organic solvent as a mixed co-solvent. The product, exhibiting an amorphous morphology, was prepared via a metathesis reaction under ultrasonic oscillation conditions. Using sodium dipropylphosphinate as the starting material, i.e., the product has a propyl alkyl chain, the relevant preparation method uses commercially available sodium salt as the direct raw material. For the diethylphosphinate aluminum system, there are currently no systematic reports on the preparation of amorphous products using potassium hypophosphite as the initial raw material via an ultrasonic-assisted metathesis reaction.

[0027] Other existing technologies offer three synthetic methods for dialkyl phosphonates: the AlCl3 catalytic method has low yield and significant pollution problems; the Grignard reagent method involves numerous steps and is complex, making it unsuitable for large-scale production; and the free radical addition method is relatively simple, has high yield, and is suitable for large-scale production. While this literature compares the synthetic methods, it does not cover a systematic study of amorphous morphology control or potassium hypophosphite feedstock routes.

[0028] It is evident that existing technologies have the following drawbacks: (1) The raw material route is simple and the cost is high: At present, the synthesis of aluminum diethylphosphite mainly uses sodium hypophosphite as the starting material. Sodium hypophosphite needs to go through an additional sodium salt replacement process, which results in high raw material costs. In addition, the introduction of sodium salt increases the burden of subsequent washing and desalination.

[0029] (2) High content of by-products affects product purity and polymer performance: During the addition reaction of ethylene, due to the non-selectivity of the free radical initiation process, by-products such as aluminum ethyl butyl phosphinate are easily generated. These by-products cannot be removed by simple washing and will precipitate out together with aluminum diethyl phosphinate, causing polymer degradation and reducing the mechanical properties of the material.

[0030] (3) The product has high crystallinity, large and uneven particles: The aluminum diethylphosphinate prepared by traditional methods has high crystallinity, resulting in excessively large particle size (some exceeding the millimeter level). During resin processing, it has poor flowability and discontinuous distribution, which directly affects the flame retardant effect and makes it difficult to meet the requirements of UL94 V-0 level for particle fineness and uniform distribution.

[0031] (4) Limited methods for morphology control and limited industrial applicability: Existing morphology control techniques mainly rely on adding crystallizing agents or surfactants to regulate crystal growth, but these methods often increase the complexity of the system and have limited effect on controlling amorphous morphology. Some patents use ultrasound-assisted synthesis, but this is only applicable to systems with specific alkyl chain lengths, and there is a lack of systematic research on the preparation of amorphous morphology in diethyl systems.

[0032] (5) Lack of complete technical solutions from source to product: Currently, there are no reports of patented technologies covering the entire chain from the preparation of potassium hypophosphite from yellow phosphorus and KOH to the amorphous synthesis and application of aluminum diethylphosphinate. Furthermore, there is a lack of systematic recovery and utilization solutions for the large amount of phosphine and hydrogen tail gas generated during the disproportionation reaction of raw material yellow phosphorus and KOH, resulting in resource waste and environmental pollution.

[0033] Furthermore, in a first aspect, embodiments of the present invention provide a method for preparing amorphous aluminum diethylphosphinate from potassium hypophosphite, comprising the following steps: Step (1) Potassium hypophosphite is prepared by disproportionation reaction using yellow phosphorus and potassium hydroxide as raw materials; Step (2) Dissolve the potassium hypophosphite prepared in step (1) in water and react it with ethylene under the action of a free radical initiator to synthesize potassium diethylphosphite; Step (3) Heat the potassium diethylphosphonate aqueous solution prepared in step (2), add an organic solvent, mix under ultrasonic vibration to obtain a mixture, and adjust the mixture to be acidic; Step (4) Add an aqueous solution of aluminum sulfate to the mixture described in step (3) and carry out a metathesis reaction under ultrasonic vibration. After the reaction is completed, filter, wash and dry to obtain an amorphous product of aluminum diethylphosphonate. The washing can be done with deionized water at least three times, and then with ether or anhydrous ethanol once; the drying is done at 105-120°C for 2-4 hours.

[0034] The technical solution of this invention is divided into three stages: Phase 1: Preparation of potassium hypophosphite The reaction of yellow phosphorus (white phosphorus, P4) with potassium hydroxide (KOH) aqueous solution is a typical alkaline disproportionation reaction. This reaction needs to be carried out under heating and air-free conditions. The main products are phosphine and potassium hypophosphite, while various side reactions produce byproducts such as biphosphine, phosphite, and phosphate.

[0035] (1) Main reaction: disproportionation reaction (to produce potassium hypophosphite) Reaction equation: P4 + 3KOH + 3H2O ═ 3KH2PO2 + PH3↑ This potassium phosphate formation reaction is a first-order reaction with respect to P4 and with respect to OH. - This is a first-order reaction with an overall second-order reaction, and the activation energy Ea ≈ 40 kJ / mol. This reaction is exothermic.

[0036] Reaction mechanism: disproportionation reaction (phosphorus is simultaneously oxidized and reduced). Reduction: 1 mol of P in 1 mol of P4 decreases from 0 to -3, producing phosphine (PH3). Oxidation: 3 mol of P increases from 0 to +1 oxidation state, producing potassium hypophosphite (KH2PO2). Redox ratio: The molar ratio of oxidized phosphorus (KH2PO2) to reduced phosphorus (PH3) is 3:1.

[0037] (2) Major side reaction: further disproportionation of hypophosphite (to form phosphite, major side reaction) Reaction equation: KH₂PO₂ + KOH ═ K₂HPO₃ + H₂↑ The main product, potassium hypophosphite, is unstable in hot alkali and will continue to disproportionate, producing potassium phosphite and hydrogen gas.

[0038] The formation of potassium phosphite is a first-order reaction with respect to P4 and with respect to OH. -This is a second-order reaction, with an overall reaction order of three. The rate is proportional to the square of the base concentration, which is the core difference between the side reaction and the main reaction. This indicates that at high base concentrations, the rate constant of the side reaction will exceed that of the main reaction, becoming the dominant reaction. The activation energy of this reaction is Ea≈50-60 kJ / mol, making it an exothermic reaction, and the degree of exothermicity is much higher than that of the main reaction.

[0039] Therefore, since the activation energies of the main reaction (Ea≈40kJ / mol) and the main side reaction (Ea≈50-60kJ / mol) are relatively close, and the exothermic degree of the main side reaction is much higher than that of the main reaction, the chemical reaction rate of the main side reaction is proportional to the square of the base (KOH) concentration.

[0040] Secondly, the mixed gas generated by the reaction is collected in a gas tank and then treated harmlessly by combustion: PH3 is burned to produce P2O5 and water, H2 is burned to produce H2O, and the tail gas is then treated by alkaline spray absorption to achieve compliant emissions.

[0041] Second stage: Synthesis of potassium diethylphosphonate (free radical addition reaction) The potassium hypophosphite (KH2PO2) prepared above was dissolved in water and reacted with ethylene gas (C2H4) under pressure with a free radical initiator.

[0042] The reaction mechanism is as follows: the free radical initiator decomposes upon heating to generate a primary free radical, which attacks the PH bond in the hypophosphite group to generate a hypophosphite free radical; this free radical undergoes addition with the ethylene double bond to form an ethyl-containing phosphonate free radical; this free radical further reacts with the PH bond of another molecule of potassium hypophosphite to complete chain transfer, ultimately generating diethyl potassium hypophosphite.

[0043] The reaction pathway is: KH2PO2 + 2C2H4 ═ K[(C2H5)2PO2] (potassium diethylphosphonate) During the addition reaction, the reaction temperature and ethylene pressure must be strictly controlled to avoid excessive addition and the formation of byproducts such as ethyl butyl phosphinate.

[0044] Third stage: Preparation of amorphous form of aluminum diethylphosphinic acid (metathesis reaction) The synthesized potassium diethylphosphonate aqueous solution was heated, and an appropriate amount of organic solvent was added. The mixture was thoroughly mixed under ultrasonic vibration, and the pH of the mixture was adjusted to 1.0–4.0. Then, an aluminum sulfate aqueous solution was added dropwise to the mixture, and a metathesis reaction was carried out under continuous ultrasonic vibration. 6K[(C2H5)2PO2] + Al2(SO4)3 ═ 2Al[(C2H5)2PO2]3↓ + 3K2SO4 The resulting white precipitate of aluminum diethylphosphonate is filtered, washed, and dried to obtain an amorphous product.

[0045] Ultrasonic oscillation plays a crucial role in this process: high-frequency ultrasonic oscillation can effectively control the formation of larger aluminum diethylphosphonate crystal nuclei, preventing the nuclei from growing along a certain crystal axis to form a dominant crystal face. This allows the small crystal nuclei to have the same properties in all directions, ultimately forming a relatively regular amorphous morphology. The addition of organic solvents helps the diethylphosphonate ions to dissolve better and participate in the reaction, while also better promoting the dispersion of the generated aluminum diethylphosphonate into an amorphous form.

[0046] This invention innovatively uses the disproportionation reaction of yellow phosphorus with KOH to prepare potassium hypophosphite as the starting material, avoiding the cumbersome steps of introducing sodium salt and subsequent washing and desalination in the traditional sodium hypophosphite route.

[0047] In this embodiment of the invention, potassium hypophosphite is prepared using yellow phosphorus and KOH as initial raw materials. The raw materials are widely available and inexpensive, and the yield of the reaction product potassium hypophosphite (KH2PO2) is high, which effectively reduces the overall production cost of aluminum diethylphosphite.

[0048] In the amorphous product of aluminum diethylphosphinate in this embodiment of the invention, the content of byproducts such as aluminum ethylbutylphosphinate can be controlled at <0.5wt%, which is significantly lower than that of the prior art. The high-purity product will not cause polymer degradation, which is beneficial to maintaining the mechanical properties of the substrate.

[0049] The aluminum diethylphosphonate product prepared in the embodiments of the present invention exhibits an amorphous morphology, with uniform particles, pure white color, narrow particle size distribution, and excellent flowability.

[0050] The embodiments of this invention involve fewer process steps, milder operating conditions, and simpler equipment, making them suitable for industrial production. The ultrasonic equipment is existing and has been successfully applied in the chemical industry, offering good technical and economic advantages.

[0051] In one implementation method, the conditions for the disproportionation reaction in step (1) are: a molar ratio of yellow phosphorus to potassium hydroxide of 1:3 to 5, a reaction temperature of 60 to 95°C, and a reaction time of 2 to 5 hours. These parameters ensure that the reaction proceeds continuously towards the main reaction direction to generate potassium hypophosphite.

[0052] This invention appropriately lowers the reaction temperature (slightly lower than the main reaction temperature), but should not drastically reduce the temperature to the point of creating a low-temperature environment (<50°C), which would affect the overall chemical reaction rate. Furthermore, it reduces the concentration of the base (KOH) to weaken the rate constant of the main side reaction (potassium hypophosphite formation). Under these conditions, the reaction continuously proceeds towards the main reaction direction of potassium hypophosphite formation. Additionally, air must be isolated to prevent spontaneous combustion of P4, explosion of PH3, and the formation of phosphates through deep oxidation.

[0053] In one embodiment, in step (1), the phosphine and hydrogen mixture generated by the reaction is collected and transported to combustion treatment, and the combustion exhaust gas is absorbed by alkaline spray and then discharged in compliance with standards.

[0054] Potassium hypophosphite (KH2PO2) is an important intermediate raw material for the synthesis of organophosphite flame retardants. Traditionally, potassium hypophosphite is prepared by the disproportionation reaction of yellow phosphorus (P4) and potassium hydroxide (KOH) in aqueous solution, producing byproducts such as phosphine (PH3) and hydrogen (H2). Direct emission of these exhaust gases without treatment would cause serious environmental pollution and safety hazards; therefore, a reasonable exhaust gas recovery and treatment scheme is a key aspect of this process.

[0055] This invention provides a solution for treating the PH3 and H2 tail gases generated during the disproportionation reaction by combustion absorption, thereby achieving clean production. The PH3 and H2 tail gases generated during the preparation of potassium hypophosphite are collected in gas tanks, treated by combustion, and absorbed by alkaline solution, thus achieving the harmlessness and resource utilization of the tail gases.

[0056] In one embodiment, the conditions for the free radical addition reaction in step (2) are as follows: the amount of free radical initiator is 0.5% to 3% of the mass of potassium hypophosphite, the ethylene pressure is 0.5 to 1.5 MPa, the reaction temperature is 80 to 150°C, the reaction time is 4 to 10 hours, and the reaction pressure is maintained at 0.8 to 1.2 MPa during the reaction. The above parameters limit the yield of the intermediate product diethyl potassium hypophosphite.

[0057] In one embodiment, in step (3), the prepared potassium diethylphosphonate aqueous solution is heated to 40-60°C and maintained. The organic solvent is one or more of methanol, ethanol, acetonitrile, diethyl ether, toluene and N',N-dimethylformamide. The volume of the organic solvent is 5%-15% of the volume of the aqueous solution. The ultrasonic oscillation conditions are: frequency 20-40kHz, time 20-30min.

[0058] In this embodiment of the invention, an appropriate amount of organic solvent (methanol, ethanol, acetonitrile, diethyl ether, toluene, and N',N-dimethylformamide, etc.) is introduced into the metathesis reaction system. This not only improves the solubility and mass transfer efficiency of diethylphosphonate in the reaction system, but also promotes the uniform dispersion and amorphous formation of the product. Ultrasonic oscillation promotes the uniform dispersion and amorphous formation of the product.

[0059] The embodiments of the present invention use a small amount of organic solvent, only 5% to 15% of the volume of the aqueous solution, and achieve effective recovery and utilization of tail gas, resulting in low wastewater generation, which meets the requirements of green chemistry and clean production.

[0060] In one embodiment, in step (3), the concentration of dilute sulfuric acid used to adjust the mixture to be acidic is 1 to 3 mol / L, and the pH value of the mixture after adjustment is 1.0 to 4.0.

[0061] The present invention provides a suitable medium environment for the formation of aluminum diethylphosphonate by precisely controlling the acidic medium conditions and adjusting the pH of the mixture to an acidic range of 1.0 to 4.0 with dilute sulfuric acid, which is beneficial to improving the reaction yield and product purity.

[0062] In one embodiment, in step (4), the aluminum sulfate aqueous solution is a saturated aluminum sulfate aqueous solution at 30-60°C; the aluminum sulfate aqueous solution is added by dripping at a rate of 1.0-3.0 mL / min, and the dripping is completed in 5-8 minutes. During the dripping process, ultrasonic oscillation is maintained at a frequency of 20-40 kHz; the molar ratio of potassium diethylphosphonate to aluminum sulfate is 6:1-5.

[0063] Here, the aluminum salt is added dropwise in conjunction with ultrasonic oscillation. The aluminum sulfate aqueous solution is added to the reaction system slowly (1-3 mL / min) under ultrasonic oscillation conditions, which achieves rapid and uniform mixing of the reactants at the molecular level and avoids rapid growth of crystal nuclei caused by local supersaturation.

[0064] In one embodiment, the conditions for the metathesis reaction in step (4) are: controlling the reaction temperature at 40-60°C, continuing ultrasonic oscillation for 2-4 hours after the addition is completed, and allowing the solution to stand for 4-6 hours after the reaction is completed.

[0065] Here, ultrasonic oscillation assists the metathesis reaction to form an amorphous form. By utilizing the cavitation effect and mechanical oscillation effect of ultrasound, the preferential growth of aluminum diethylphosphinate crystal nuclei along specific crystal planes is effectively suppressed, making the crystal orientation isotropic, thereby obtaining an amorphous product.

[0066] In this embodiment of the invention, ultrasonic oscillation is applied to the entire process of the metathesis reaction of aluminum diethylphosphonate (including the dropping process and the reaction process), which is one of the core steps. After the above ultrasonic treatment, the final crystal form is better.

[0067] Secondly, embodiments of the present invention also provide a flame retardant material comprising the following raw materials in parts by weight: 5-10 parts of amorphous aluminum diethylphosphinate, 70-80 parts of epoxy resin, and 10-25 parts of curing agent, wherein the amorphous aluminum diethylphosphinate is obtained by the method described above.

[0068] In this embodiment of the invention, adding 5-10 parts by weight of the amorphous product of the present invention to epoxy resin achieves UL94 V-0 or V-1 flame retardant performance, which is significantly better than that of conventional crystalline products. This is because the amorphous fine particles are more continuously and uniformly distributed in the resin, forming a denser char layer, which provides better heat insulation and oxygen barrier properties, thus significantly improving flame retardant performance.

[0069] Thirdly, embodiments of the present invention also provide a method for preparing a flame-retardant material, comprising the following steps: Step (1) Heat 70-80 parts of epoxy resin until it melts; Step (2) 5-10 parts of amorphous aluminum diethylphosphonate obtained by the method of any one of claims 1 to 8 are ultrasonically dispersed in an organic solvent and then mixed with the epoxy resin of step (1) until homogeneous. The mixture is heated at a certain temperature to remove the organic solvent. Step (3) Weigh 10-25 parts of curing agent, melt it, and pour the liquid curing agent into the epoxy resin mixture in step (2) while it is hot. Stir it thoroughly and then pour it into the glue strip mold. Step (4) Place the mold into the curing equipment, cure it, then heat it to cure it again, cool it to room temperature, and demold it to obtain the epoxy resin flame retardant material containing amorphous aluminum diethylphosphinic acid.

[0070] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a method for preparing amorphous aluminum diethylphosphonate from potassium hypophosphate and its application.

[0071] The experimental materials involved in the examples are shown in Table 1 below: Table 1

[0072] The reactor used in this example is a 316L reactor.

[0073] The method for preparing amorphous aluminum diethylphosphinate from potassium hypophosphite according to an embodiment of the present invention includes the following steps: Step (1) Preparation of potassium hypophosphate (1.1) Add the measured amount of deionized water and potassium hydroxide to the reaction vessel, stir to dissolve, and prepare a concentrated KOH aqueous solution with a concentration of 30% to 50%.

[0074] (1.2) Under nitrogen protection, yellow phosphorus is slowly added to the reactor, the reaction temperature is controlled at 60-95℃, the molar ratio of yellow phosphorus to KOH is 1:3-5, the reaction time is 2-5 hours, and potassium hypophosphite, phosphine and hydrogen are produced.

[0075] (1.3) After the reaction is complete, the reaction solution is filtered to remove unreacted yellow phosphorus and insoluble matter. The filtrate is concentrated by vacuum evaporation, cooled and crystallized, and then centrifuged to obtain potassium hypophosphite crystals. The mother liquor for crystallization can be recycled.

[0076] (1.4) Tail gas treatment: The PH3 and H2 mixed gas generated by the reaction is collected in a gas tank and then transported to the combustion furnace for combustion treatment (PH3 is burned to generate P2O5 and H2O, and H2 is burned to generate H2O). The combustion tail gas is treated by an alkaline spray absorption tower and discharged after meeting the standards.

[0077] Step (2) Synthesis of potassium diethylphosphonate (2.1) Dissolve the potassium hypophosphite prepared in step (1) in deionized water to prepare a potassium hypophosphite aqueous solution of 0.5 to 1.5 mol / L, and add a free radical initiator. The amount of initiator is 0.5% to 3% of the mass of potassium hypophosphite.

[0078] (2.2) Transfer the solution to a high-pressure reactor, replace the air in the reactor with nitrogen, then introduce ethylene gas to a pressure of 0.5–1.5 MPa, raise the temperature to 80–150 °C, and stir the reaction for 4–10 hours. Maintain the reaction pressure at 0.8–1.2 MPa during the reaction.

[0079] (2.3) After the reaction is completed, the reactor is cooled to room temperature and the pressure is released. The reaction solution is then distilled under reduced pressure to remove unreacted ethylene and some water, and concentrated to obtain an aqueous solution of potassium diethylphosphonate.

[0080] Step (3) Preparation of amorphous aluminum diethylphosphinic acid (3.1) Heat the potassium diethylphosphonate aqueous solution prepared in step (2) to 40-60°C, add an organic solvent, the volume of the organic solvent being 5%-15% of the volume of the aqueous solution, and ultrasonically vibrate at a frequency of 20-60 Hz for 10-30 minutes to obtain a mixture.

[0081] (3.2) Adjust the pH of the mixture to 1.0 to 4.0 using 1 to 3 mol / L dilute sulfuric acid solution.

[0082] (3.3) Prepare a saturated aqueous solution of aluminum sulfate at 40-60℃. The molar ratio of potassium diethylphosphonate to aluminum sulfate is 6:1-5 (i.e., n(K[(C2H5)2PO2]): n(Al2(SO4)3) = 6:1-5. In actual operation, the aluminum salt is appropriately in excess, and it is generally controlled according to n(K[(C2H5)2PO2]): n(Al2(SO4)3) = 6:1.5-2.5).

[0083] (3.4) Under ultrasonic oscillation conditions of 20 to 40 kHz, add the saturated aqueous solution of aluminum sulfate to the above mixture at a dropping rate of 1.0 to 3.0 mL / min. The ultrasonic oscillation is maintained during the dropping process, and the dropping is completed in 3 to 10 minutes.

[0084] (3.5) After the addition is complete, control the reaction temperature at 40-60℃ and continue ultrasonic vibration for 2-4 hours. After the reaction is complete, let the mixed solution stand for 4-6 hours.

[0085] (3.6) The white precipitate was obtained by filtration with a sand core funnel. The precipitate was washed three times with deionized water and then washed once with ether or anhydrous ethanol.

[0086] (3.7) Place the washed precipitate into an oven and dry it at 105-120℃ for 2-4 hours to obtain a white solid powder, which is the amorphous product of aluminum diethylphosphonate.

[0087] The amorphous product of aluminum diethylphosphonate prepared above was applied to epoxy resin flame retardants according to the following mass ratio formulation, and the preparation method is as follows: Amorphous aluminum diethylphosphonate: 5-10 parts; Epoxy resin (such as bisphenol A type epoxy resin DGEBA): 70-80 parts; Curing agent (such as diaminodiphenylmethane DDM, diaminodiphenyl sulfone DDS, etc.): 10-25 parts.

[0088] Epoxy resin is heated to 90-110℃ to give it good fluidity. Amorphous diethylphosphonate aluminum product is ultrasonically dispersed in 5-10 mL of acetone and then mixed with epoxy resin. The mixture is heated for 30-60 minutes to remove the acetone. The curing agent is weighed, melted, and added to the mixture while hot. After thorough stirring, the mixture is poured into a mold and cured at 100℃ for 2 hours. Then, the temperature is raised to 150℃ and cured for 5 hours. After cooling and demolding, the flame-retardant epoxy resin material is obtained.

[0089] Example 1

[0090] In this embodiment: Step (1) Preparation of potassium hypophosphate: Add 300 mL of deionized water and 85 g (1.5 mol) KOH (concentration 22.08 wt%) to a reactor equipped with a stirrer, condenser and gas collection device. After stirring and dissolving, slowly add 31 g (0.25 mol) of yellow phosphorus under nitrogen protection, control the reaction temperature at 85℃ and react for 3 hours.

[0091] During the reaction, the generated mixed gases (PH3 and H2) were continuously collected into a gas storage tank. After the reaction was completed, the reaction solution was filtered to remove unreacted yellow phosphorus (about 3 g, which could be recycled). The filtrate was concentrated to 1 / 3 of its original volume by vacuum evaporation, cooled to room temperature for crystallization, and centrifuged to obtain 38.2 g of white potassium hypophosphite crystals, with a yield of 82.5% (based on yellow phosphorus).

[0092] Gas collection system: The mixed gas in the gas storage tank is transported to the combustion furnace for combustion treatment (ignition temperature 350℃). After combustion, the exhaust gas is treated by a 3% NaOH solution spray absorption tower before being discharged in compliance with standards.

[0093] Step (2) Synthesis of potassium diethylphosphonate 25.5 g (0.3 mol) of potassium hypophosphite prepared in step (1) was dissolved in 250 mL of deionized water, and 0.3 g of ammonium persulfate initiator was added. The mixture was then transferred to a 500 mL high-pressure reactor. After purging the reactor with nitrogen three times, ethylene was introduced to a pressure of 1.0 MPa, and the temperature was raised to 120 °C. The reactor was stirred for 6 hours. During the reaction, the reaction pressure was maintained at 0.8–1.2 MPa using a gas supply device. After the reaction was completed, the reactor was cooled to room temperature, the pressure was released, and the reaction solution was concentrated to approximately 100 mL by vacuum distillation to obtain an aqueous solution of potassium diethylphosphite (concentration 3.0 mol / L). The potassium diethylphosphite content was analyzed by sampling.

[0094] Step (3) Preparation of amorphous aluminum diethylphosphinic acid Dilute the potassium diethylphosphonate aqueous solution (containing 0.3 mol of potassium diethylphosphonate) prepared in step (2) to 100 mL, heat to 50 °C, add 5 mL of anhydrous ethanol, and sonicate at 40 Hz for 20 minutes. Adjust the pH of the mixture to 2.5 with 2 mol / L dilute sulfuric acid.

[0095] Prepare a saturated aqueous solution of aluminum sulfate at 50℃ (dissolve 49 g of Al2(SO4)3·18H2O in about 100 g of water). Take 12.7 g (about 0.11 mol, with an excess of about 10% aluminum salt) of the above saturated aqueous solution and add it to the above mixture at a dropping rate of 2 mL / min under ultrasonic vibration at 30 kHz. Maintain the solution temperature at 50℃ during the dropping process and complete the dropping in 6 minutes.

[0096] After the addition was complete, the mixture was ultrasonically vibrated at 50°C for 3 hours, then allowed to cool naturally to room temperature and stand for 5 hours. The precipitate was filtered using a sintered glass funnel, washed three times with deionized water, and then washed once with diethyl ether. The precipitate was placed in an oven and dried at 110°C for 3 hours to obtain 19.8 g of a white solid powder product, with a yield of 89.6% (based on potassium diethylphosphonate), in an amorphous form, with a purity of 98.87%.

[0097] Preparation of flame-retardant epoxy resin material in this embodiment: 10 g of bisphenol A type epoxy resin (DGEBA) was heated to 100°C. 0.53 g (5% by mass) of the amorphous product of aluminum diethylphosphonate prepared in (3) was ultrasonically dispersed in 5 mL of acetone and then mixed with epoxy resin. The mixture was heated at 100°C for 30 minutes to remove the acetone.

[0098] Weigh 2.54 g of diaminodiphenylmethane (DDM) and melt it at 100°C. While still hot, pour the liquid DDM into the epoxy resin mixture above, stir thoroughly for about 1 minute, and then pour it into a molding die. Place the die in an oven and cure at 100°C for 2 hours, then raise the temperature to 150°C and cure for 5 hours. Cool to room temperature and demold to obtain an epoxy resin flame retardant material containing 5% amorphous aluminum diethylphosphinate.

[0099] Example 2

[0100] In this embodiment: Unlike Example 1, in step (2) the synthesis of potassium diethylphosphite, the concentration of potassium hypophosphite solution was 0.85 mol / L; in step (3) the preparation of amorphous aluminum diethylphosphite, the reaction temperature was controlled at 45℃, the aluminum salt dropping rate was 1.5 mL / min, ultrasonic vibration was performed for 3.5 h, and the mixture was allowed to stand for 4.5 h. The final yield of aluminum diethylphosphite was 91.8% (based on potassium diethylphosphite), the purity was 98.23%, and it was in an amorphous form.

[0101] Example 3

[0102] In this embodiment: Unlike Example 1, in step (2) the synthesis of potassium diethylphosphonate, the concentration of potassium hypophosphite solution was 1 mol / L; in step (3) the preparation of amorphous aluminum diethylphosphite, the reaction temperature was controlled at 55℃, the aluminum salt dropping rate was 2.5 mL / min, ultrasonic vibration was performed for 3 h, and the mixture was allowed to stand for 5 h. The final yield of aluminum diethylphosphite was 90.6% (based on potassium diethylphosphite), the purity was 99.78%, and it was in an amorphous form.

[0103] The diethylaluminum hypophosphite products of Examples 1-3 were analyzed using an X-ray diffraction analyzer. None of the diethylaluminum hypophosphite products showed characteristic diffraction peaks, indicating that they have an amorphous structure. Taking Example 1 as an example, the XRD pattern of diethylaluminum hypophosphite is shown in the figure.

[0104] Flame retardant performance test The flame-retardant epoxy resin materials of Examples 1-3 were tested on a horizontal and vertical flammability tester according to the ANSI / UL-94-2010 standard, with a sample size of 130 mm × 120 mm × 5 mm and a flame height of 20 mm.

[0105] Test results show that the epoxy resin material containing 5% amorphous aluminum diethylphosphonate achieves the UL94V-0 level in flame retardancy (where V-0 level means that in the vertical burning test, the total afterflame time after the sample is ignited is automatically extinguished within 51-55 seconds).

[0106] The flame retardant performance of the pure epoxy resin material without flame retardant (i.e., only epoxy resin, without the addition of diethylaluminum hypophosphite flame retardant) only reached the UL94 HB level. The amorphous product of this invention exhibits excellent flame retardant effect even at low addition levels.

[0107] Comparative Example 1 Unlike Example 1, ultrasonic treatment was performed only during the dropping process. The final yield of diethylphosphite was approximately 71.8% (based on potassium diethylphosphite), with a purity of 86.23%.

[0108] Comparative Example 2 Unlike Example 1, sonication was performed only during the reaction process. The final yield of diethylaluminum hypophosphite was approximately 65.3% (based on potassium diethylphosphite), with a purity of 82.23%.

[0109] Therefore, it can be seen that the ultrasonic treatment in both the dropping and reaction processes of Example 1 resulted in a product yield and purity that were superior to the simple sum of the effects of Comparative Examples 1 and 2.

[0110] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing amorphous aluminum diethylphosphonate from potassium hypophosphite, characterized in that, Includes the following steps: Step (1) Potassium hypophosphite is prepared by disproportionation reaction using yellow phosphorus and potassium hydroxide as raw materials; Step (2) Dissolve the potassium hypophosphite prepared in step (1) in water and react it with ethylene under the action of a free radical initiator to synthesize potassium diethylphosphite; Step (3) Heat the potassium diethylphosphonate aqueous solution prepared in step (2), add an organic solvent, mix under ultrasonic vibration to obtain a mixture, and adjust the mixture to be acidic; Step (4) Add aluminum sulfate aqueous solution to the mixture described in step (3) and carry out metathesis reaction under ultrasonic vibration. After the reaction is completed, filter, wash and dry to obtain aluminum diethylphosphinate amorphous product.

2. The method according to claim 1, characterized in that, In step (1), the conditions for the disproportionation reaction are: the molar ratio of yellow phosphorus to potassium hydroxide is 1:3 to 5, the reaction temperature is 60 to 95°C, and the reaction time is 2 to 5 hours.

3. The method according to claim 1, characterized in that, In step (1), the phosphine and hydrogen mixture generated by the reaction is collected and transported to combustion treatment. The combustion exhaust gas is absorbed by alkaline spray and then discharged in compliance with standards.

4. The method according to claim 1, characterized in that, In step (2), the conditions for the free radical addition reaction are: the amount of free radical initiator is 0.5% to 3% of the mass of potassium hypophosphite, the ethylene pressure is 0.5 to 1.5 MPa, the reaction temperature is 80 to 150℃, the reaction time is 4 to 10 hours, and the reaction pressure is maintained at 0.8 to 1.2 MPa during the reaction.

5. The method according to claim 1, characterized in that, In step (3), the prepared potassium diethylphosphonate aqueous solution is heated to 40-60°C and maintained. The organic solvent is one or more of methanol, ethanol, acetonitrile, diethyl ether, toluene and N',N-dimethylformamide. The volume of the organic solvent is 5%-15% of the volume of the aqueous solution. The ultrasonic oscillation conditions are: frequency 20-40kHz, time 20-30 minutes.

6. The method according to claim 1, characterized in that, In step (3), the concentration of dilute sulfuric acid used to adjust the mixture to be acidic is 1 to 3 mol / L, and the pH value of the mixture after adjustment is 1.0 to 4.

0.

7. The method according to claim 1, characterized in that, In step (4), the aluminum sulfate aqueous solution is a saturated aluminum sulfate aqueous solution at 30-60℃; the aluminum sulfate aqueous solution is added by dripping at a rate of 1.0-3.0 mL / min, and the dripping is completed in 5-8 minutes. During the dripping process, ultrasonic oscillation is maintained at a frequency of 20-40 kHz; the molar ratio of potassium diethylphosphonate to aluminum sulfate is 6:1-5.

8. The method according to claim 1, characterized in that, In step (4), the conditions for the metathesis reaction are: controlling the reaction temperature at 40-60°C, continuing ultrasonic vibration for 2-4 hours after the addition is completed, and allowing the solution to stand for 4-6 hours after the reaction is completed.

9. A flame-retardant material, characterized in that: The raw materials comprise the following parts by weight: 5-10 parts of amorphous aluminum diethylphosphinate, 70-80 parts of epoxy resin, and 10-25 parts of curing agent, wherein the amorphous aluminum diethylphosphinate is obtained by the method described in any one of claims 1-8.

10. A method for preparing a flame-retardant material, characterized in that: Includes the following steps: Step (1) Heat 70-80 parts of epoxy resin until it melts; Step (2) 5-10 parts of amorphous aluminum diethylphosphonate obtained by the method of any one of claims 1 to 8 are ultrasonically dispersed in an organic solvent and then mixed with the epoxy resin of step (1) until homogeneous. The mixture is heated at a certain temperature to remove the organic solvent. Step (3) Weigh 10-25 parts of curing agent, melt it, and pour the liquid curing agent into the epoxy resin mixture in step (2) while it is hot. Stir it thoroughly and then pour it into the glue strip mold. Step (4) Place the mold into the curing equipment, cure it, then heat it to cure it again, cool it to room temperature, and demold it to obtain the epoxy resin flame retardant material containing amorphous aluminum diethylphosphinic acid.

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