A method for synthesizing a dialkyl hypophosphite flame retardant

Abstract

The application discloses a synthesis method of a dialkyl hypophosphite flame retardant, relates to the technical field of organic phosphorus compound preparation, and has the following scheme: in a pressure-resistant reaction kettle replaced by inert gas, phosphorus-containing gas and olefin are subjected to addition reaction under initiation conditions to obtain an addition product; the addition product is then oxidized and the system pH is adjusted; subsequently, the addition product is reacted with a 2-4 valence metal salt solution to form a salt, and the dialkyl hypophosphite flame retardant is obtained through separation, washing and drying. The dialkyl hypophosphite flame retardant has the following beneficial effects: the phosphorus-containing gas component is used as a starting phosphorus-containing source, the phosphorus-containing component is introduced into a target flame retardant structure formation path through addition-oxidation-salt formation cascade conversion, the path can be adapted to different initiation modes, olefin forms and solvent systems, and the process has good controllability; under the same phosphorus-containing raw material consumption conditions, the yield of the target product remains high and relatively concentrated, indicating that the reaction is smoothly connected; and the obtained product has good thermal stability and can meet the application requirements of the flame retardant.

Description

Technical Field

[0001] This invention relates to the field of organophosphorus compound preparation technology, and in particular to a method for synthesizing a dialkyl hypophosphite flame retardant. Background Technology

[0002] Dialkylphosphinate flame retardants, as an important class of organophosphorus halogen-free flame retardant materials, have established a relatively mature application foundation due to their good thermal stability and processing compatibility in engineering plastics and other systems. Correspondingly, their preparation technology has gradually evolved from early multi-step organophosphorus chemical routes to process routes optimized around the purity of the target product, reaction efficiency, and the stability of the salt formation process. Existing technologies can be broadly categorized into two types: one focuses on pre-constructing phosphorus-containing organic intermediates and further converting them into dialkylphosphinates and their metal salts; the other focuses on optimizing the reaction conditions, initiation methods, reaction media, and subsequent salt formation steps of phosphorus-containing raw materials with olefins to improve the efficiency and quality of target product preparation. This technological development trajectory indicates that current research mainly focuses on the preparation-end problem of "how to stably obtain the target flame retardant product," while systematic solutions are still lacking for how upstream phosphorus-containing by-products enter the target flame retardant preparation chain and how to shorten the phosphorus resource utilization path and improve the overall resource utilization level at the technical path level.

[0003] While existing patents cover various preparation routes for dialkylphosphinates and their metal salts, their main optimization focuses on intermediate route selection, reaction step sequence, equipment organization, or condition improvements for traditional phosphorus-containing raw material routes. They do not address the core issue of "the difficulty of integrating byproduct phosphorus-containing gases into the high-value-added synthesis pathway of the target flame retardant" at the technology chain level. For example, CN101830926B discloses a process for gradually constructing and ultimately obtaining dialkylphosphinate metal salt flame retardants from phosphorus-containing organic intermediates. Its technological focus is on multi-step organic phosphorus intermediate conversion and subsequent salt formation, but the route involves many steps, and the technical focus remains on the synthesis of the target product itself, without proposing a path-level solution for the resource utilization of upstream byproduct phosphorus-containing gases. For example, CN114685856B proposes a process optimization scheme for the preparation of aluminum diethylphosphinate, which involves traditional phosphorus-containing salt raw materials and controls temperature, pressure, and subsequent salt formation conditions. The improvements focus on reducing side reactions, increasing conversion efficiency, and facilitating industrial implementation. However, this type of scheme is still based on traditional phosphorus-containing raw material routes and does not directly connect to the high-value utilization of phosphorus-containing by-products. Similarly, CN119684356A discloses a continuous production process for dialkylphosphinates, focusing on solving problems such as continuous production, heat and mass transfer, and equipment organization efficiency. While this helps to intensify the production process, its optimization targets are still mainly the reaction organization and process equipment of existing preparation processes, without addressing the issue of reconstructing phosphorus-containing resource sources. In summary, the main shortcomings of existing technologies do not lie in their complete inability to produce the target product, but rather in the fact that most technological improvements remain at the level of "process optimization within existing raw material routes," failing to effectively address the following key technical deficiencies: Firstly, upstream phosphorus-containing byproduct gases are typically disposed of rather than used as raw materials for the preparation of the target flame retardant, resulting in a fragmented phosphorus resource utilization pathway. Secondly, the raw material chain of traditional routes is relatively long, and even if local process parameters are optimized, it is difficult to simultaneously improve the utilization level of phosphorus-containing resources and the burden on the preparation end at the technical path level. The fundamental reason why these problems have persisted for so long is that phosphorus-containing byproduct gases themselves have high technical barriers in terms of reactivity, process control, and safety management. Integrating them into the target flame retardant synthesis chain involves not only the feasibility of the front-end reaction but also coupling problems such as subsequent conversion connections, endpoint control, and compatibility of salt formation steps, which cannot be solved simply by replacing raw materials.

[0004] Based on the aforementioned state of the existing technology, there is an objective need for a new technological pathway for the preparation of dialkylphosphinate flame retardants. This pathway would specifically address the technical problems in existing technologies, such as the difficulty in integrating phosphorus-containing byproducts into the high-value-added synthesis chain of the target flame retardant, and the long raw material chain of traditional preparation routes, which makes it difficult to simultaneously improve the overall utilization level of phosphorus resources. More specifically, the challenge is not simply the feasibility of product preparation, but rather how to effectively connect the phosphorus resource utilization chain at the technological pathway level while ensuring the stable production of the target flame retardant. This would reduce the technical burden caused by the separation of upstream byproduct disposal and downstream product preparation in existing technologies, and ensure that the resulting product maintains the basic thermal stability required for flame retardant applications. These technological needs directly address the shortcomings of existing technologies and do not aim to expand application scenarios or add functional descriptions, but rather focus on the technical consistency between optimizing the phosphorus resource utilization pathway and preparing the target flame retardant. Summary of the Invention

[0005] Given the shortcomings of existing dialkylphosphinate flame retardant preparation technologies in terms of the resource utilization of phosphorus-containing by-product gases, and the difficulty of balancing the preparation of target products with the improvement of overall phosphorus utilization efficiency in traditional raw material routes, this invention provides a method for synthesizing dialkylphosphinate flame retardants to solve the technical problems in existing technologies, such as the difficulty of incorporating phosphorus-containing by-product gases into the high-value-added flame retardant preparation chain, the long raw material chain of traditional preparation routes, and the resulting heavy overall preparation burden.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for synthesizing a dialkylphosphinate flame retardant includes the following steps: S1: In a pressure-resistant reactor purged with an inert gas, phosphine and olefins are introduced into the reaction system, wherein phosphine is used as the starting phosphorus-containing raw material, and under the action of an initiator, phosphine and olefins undergo a free radical addition reaction to obtain an addition product, wherein the olefin is a gaseous olefin or a liquid olefin, and the initiator is a photoinitiator or a free radical initiator. S2: The addition product obtained in S1 is added to an aqueous solution containing an oxidant for oxidation reaction, followed by the addition of ammonia or alkali metal hydroxide to adjust the pH of the system to 6-8. S3: Add a 2-4 valent metal salt solution to the system obtained in S2 to carry out a salt formation reaction. After separation, washing and drying, the dialkylphosphinate flame retardant is obtained.

[0007] Preferably, S1 includes: Phosphine is introduced into a pressure-resistant reactor that has been purged with an inert gas, and the partial pressure of phosphine inside the reactor is controlled to be 0.05–10 MPa. A photoinitiator is added to the reactor, and gaseous olefins are continuously introduced and heated while being irradiated with ultraviolet light to cause phosphine to undergo a free radical addition reaction with the gaseous olefins. The reaction was terminated when the phosphine content in the reactor was less than 100 ppm.

[0008] Preferably, S1 includes: Phosphine is introduced into a pressure-resistant reactor that has been purged with an inert gas and contains a solvent; A photoinitiator is added to the reactor, and gaseous olefins are continuously introduced and heated while being irradiated with ultraviolet light to cause phosphine to undergo a free radical addition reaction with the gaseous olefins. The criterion for terminating the reaction was that the number of moles of gaseous olefins consumed was twice the number of moles of phosphine introduced.

[0009] Preferably, S1 includes: Phosphine is introduced into a pressure-resistant reactor that has been purged with an inert gas and contains a solvent; A free radical initiator is added to the reactor, and gaseous olefins are continuously introduced while the temperature is increased, so that phosphine reacts with the gaseous olefins in a free radical addition reaction. The criterion for terminating the reaction was that the number of moles of gaseous olefins consumed was twice the number of moles of phosphine introduced.

[0010] Preferably, S1 includes: Liquid olefins are added to a pressure-resistant reactor that has been purged with inert gas, and phosphine is introduced. When the number of moles of phosphine introduced reaches 1 / 2 of the number of moles of the liquid olefins, the introduction of phosphine is stopped. A free radical initiator is added to the reactor and the temperature is raised to allow phosphine to undergo a free radical addition reaction with the liquid olefin for a reaction time of 0.1–48 h.

[0011] Preferably, the reaction temperature in step S1 is 10–200°C; More preferably, the reaction temperature in step S1 is 50–150°C.

[0012] Preferably, the salt formation reaction temperature in step S3 is 10–100°C; More preferably, the salt formation reaction temperature in step S3 is 30–80°C.

[0013] Preferably, the gaseous olefin is at least one selected from ethylene, propylene, butene, and isobutene; More preferably, the gaseous olefin is at least one of ethylene and butene.

[0014] Preferably, the liquid olefin is at least one of C5-C18 aliphatic olefins, C8-C18 aromatic olefins, or C4-C18 cyclic olefins.

[0015] More preferably, the liquid olefin is at least one of styrene, octene, and pentene.

[0016] Preferably, the photoinitiator is a free radical photoinitiator; More preferably, the photoinitiator is at least one of acetone, acetophenone, photoinitiator 1173, and photoinitiator 183.

[0017] Preferably, the free radical initiator is at least one of a peroxide or an azo compound; More preferably, the free radical initiator is at least one of ammonium persulfate, sodium persulfate, peracetic acid, perphenylacetic acid, and azobisisobutyronitrile.

[0018] Preferably, the amount of the initiator added is 0.1‰ to 10% of the molar amount of phosphine; More preferably, the amount of the initiator added is 1‰ to 10% of the molar amount of phosphine.

[0019] Preferably, the solvent is at least one selected from water, methanol, ethanol, ethyl acetate, toluene, and benzene; More preferably, the solvent is at least one selected from water, methanol, ethanol, and toluene.

[0020] Preferably, the oxidant is selected from at least one of hydrogen peroxide, hypochlorous acid, sodium hypochlorite, perchloric acid, sodium perchlorate, potassium permanganate, potassium dichromate, chromic acid, peracetic acid, perpropionic acid, perbutyric acid, sodium percarbonate, perbenzoic acid, osmium tetroxide, and ozone. More preferably, the oxidant is at least one of hydrogen peroxide, peroxybenzoic acid, and sodium percarbonate.

[0021] Preferably, the metal ions in the divalent to tetravalent metal salt solution are selected from at least one of aluminum ions, zinc ions, magnesium ions, calcium ions, iron ions, or zirconium ions.

[0022] This application also provides an application of a dialkyl hypophosphite flame retardant, wherein the dialkyl hypophosphite can synergistically retard flames alone or in combination with a halogen-free flame retardant.

[0023] Preferably, the halogen-free flame retardant includes: melamine cyanurate (MCA), melamine polyphosphate (MPP), zinc borate, spirophosphate (pentaerythritol dimethylphosphonate, CU), dimethyl methylphosphonate (DMMP), diethyl ethyl phosphate (DEEP), resorcinol bis(diphenyl phosphate) (RDP), bisphenol A bis(diphenyl phosphate) (BDP), phosphazene flame retardants, zinc diethylphosphinate (ZDP), aluminum diisobutylphosphinate, aluminum hydroxide, magnesium hydroxide, aluminum phosphite, and zinc borate.

[0024] This application also provides the application of a dialkyl hypophosphite flame retardant in a polymer, wherein the flame retardant can improve the flame retardant properties of the polymer.

[0025] Preferably, the polymer includes: polyethylene (PE), polypropylene (PP), polyisobutylene (PIB), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate (PC), acrylonitrile-butadiene-styrene terpolymer (ABS), nylon (PA), polyurethane (PU), and thermoplastic elastomer (TPE).

[0026] The beneficial effects of the technical solution provided by this invention are as follows: 1. This invention enables the preparation of dialkylphosphine salt flame retardants using phosphine as the starting phosphorus-containing raw material, and has clear technical feasibility.

[0027] Under different reaction organization methods, the corresponding dialkylphosphine salt flame retardants can be obtained, and the product yields are generally maintained in a high and relatively concentrated range, indicating that the reaction pathway of "phosphine participating in free radical addition-oxidation-salt formation" established in this invention can stably achieve the synthesis of the target product. Under initiation conditions, phosphine can undergo a free radical addition reaction with olefins to form a phosphorus-containing intermediate. This intermediate can be converted into the target dialkylphosphine salt structure after subsequent oxidation and metal ion salt formation, thereby allowing the phosphorus-containing component in phosphine to enter the target product chain.

[0028] 2. This invention has good adaptability to different initiation methods, olefin morphologies and reaction system conditions, and can stably achieve the target technical route.

[0029] Under photo-initiated and free radical-initiated conditions, in gaseous and liquid olefin systems, and under solvent-containing and different oxidation / salt-forming treatment conditions, the target flame retardant product can be obtained. This indicates that the technical solution of this invention does not depend on a single reaction condition, but rather has good route adaptability and process compatibility. This is because the key reaction steps of this invention employ an upstream construction mechanism centered on free radical addition, and achieve structurally oriented transformation through subsequent oxidation and salt-forming steps. This allows phosphorus-containing addition systems formed under different front-end reaction conditions to converge into the same target product formation pathway, thereby improving the overall stability of the process implementation.

[0030] 3. The dialkylphosphinate flame retardant obtained by this invention has a good thermal stability base and can meet the material performance requirements for use as a flame retardant.

[0031] Thermogravimetric analysis results showed that the mass of each sample remained relatively stable in the low to medium temperature range, with the main weight loss process concentrated in the higher temperature range. Furthermore, the overall thermogravimetric curves exhibited similar morphologies, indicating that the products prepared in this invention possess relatively consistent thermal decomposition behavior and good thermal stability. This is theoretically related to the synergistic effect between the intramolecular organic groups and inorganic metal components after the formation of the dialkylphosphinate metal salt structure. This structure allows the samples to exhibit a relatively clear decomposition stage and certain residual mass characteristics during heating.

[0032] 4. This invention realizes the transformation of phosphorus-containing by-products into target flame retardant product chains from a technical perspective, providing a technical solution to the problem of fragmented phosphorus resource utilization paths in existing technologies.

[0033] This invention introduces phosphine into the synthesis process of the target dialkylphosphinate flame retardant, enabling phosphorus-containing components, which are normally difficult to directly enter the target product synthesis chain, to undergo addition, oxidation, and salt formation in the reaction system, thus forming the target flame retardant product. This effect represents a clear technical path reconstruction, connecting the upstream phosphorus-containing component treatment with the downstream target product preparation at the chemical reaction level. Therefore, it provides an implementable technical solution to address the problem of the separation between "phosphorus-containing by-product disposal" and "target flame retardant synthesis" in existing technologies. Attached Figure Description

[0034] Figure 1 The TGA graph shows the flame retardant synthesized in Example 1; Figure 2 The TGA graph shows the flame retardant synthesized in Example 2; Figure 3 The TGA graph shows the flame retardant synthesized in Example 3; Figure 4 The TGA graph shows the flame retardant synthesized in Example 4; Figure 5 The TGA graph shows the flame retardant synthesized in Example 5; Figure 6 The TGA graph shows the flame retardant synthesized in Example 6; Figure 7 The TGA graph shows the flame retardant synthesized in Example 7; Figure 8 The image shows the TGA graph of the flame retardant synthesized in Example 8. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Of course, the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0036] Example 1 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen. After controlling the partial pressure of phosphine in the reactor to be 0.05–0.4 MPa, 0.001 mol of acetone was added. Ethylene and phosphine were then continuously introduced, and a high-pressure mercury lamp was turned on to catalyze the reaction. When the amount of phosphine gas used reached 1 mol, the phosphine gas was turned off, and ethylene was continued to be introduced until the phosphine content in the reactor was less than 100 ppm, at which point the reaction was terminated. Subsequently, an aqueous solution containing 2 mol of hydrogen peroxide was added to the reaction product to carry out the oxidation reaction. After the reaction was completed, sodium hydroxide was added dropwise to dissolve the product and bring the pH of the system to 6-8.

[0037] The system temperature was then controlled at 30℃, and an aqueous solution of aluminum sulfate with a total aluminum ion content of 1 / 3 mol was added dropwise over 48 hours. After the addition was completed, the reaction continued for another 48 hours. After separation, washing, crushing, and drying, aluminum diethylphosphonate flame retardant was obtained.

[0038] Example 2 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen to control the partial pressure of phosphine at 10 MPa. Then, 0.01 mol of acetone was added, and ethylene / propylene (molar ratio of 1:1) and phosphine gas were introduced simultaneously. The high-pressure mercury lamp was then turned on to catalyze the reaction. When 1 mol of phosphine gas was used, the phosphine gas was turned off, and the ethylene / propylene gas mixture was continued to be introduced until the total amount of ethylene / propylene consumed was 2 mol, at which point the reaction ended.

[0039] Subsequently, an aqueous solution containing 2 mol of hydrogen peroxide was added to the reaction product to carry out an oxidation reaction. After the reaction was completed, sodium hydroxide was added dropwise to dissolve the product and adjust the pH of the system to 6-8. The system temperature was controlled at 30℃, and an aqueous solution of aluminum sulfate with a total aluminum ion content of 1 / 3 mol was added dropwise over 0.1 h. After the addition was completed, the reaction continued for another 0.1 h. The ethylpropylphosphonate aluminum flame retardant was obtained by separation, washing, crushing and drying.

[0040] Example 3 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen, which contained 0.01 mol of acetone and 100 ml of toluene. Simultaneously, a mixture of ethylene / propylene (molar ratio of 1:1) and phosphine gas were introduced. Then, a high-pressure mercury lamp was turned on to catalyze the reaction. When the amount of phosphine gas used reached 1 mol, the phosphine gas was turned off, and the mixture of ethylene / propylene gas was continued to be introduced until the total consumption of ethylene / propylene reached 2 mol, at which point the reaction ended.

[0041] An aqueous solution containing 2 mol of hydrogen peroxide was added to the reaction product to carry out an oxidation reaction. After the reaction was completed, sodium hydroxide was added dropwise to dissolve the product, bringing the pH of the system to 6-8. Toluene was then distilled off. The system temperature was controlled at 80℃, and an aqueous solution of aluminum sulfate with a total aluminum ion content of 1 / 3 mol was added dropwise over 12 hours. After the addition was completed, the reaction continued for 4 hours. After separation, washing, crushing and drying, aluminum ethylpropylphosphonate flame retardant was obtained.

[0042] Example 4 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen and contained 0.1 mol of azobisisobutyronitrile, 500 ml of ethanol, and 2 mol of 1-octene. When the amount of phosphine gas added reached 1 mol, the phosphine gas was turned off, and the temperature was raised to 60°C. The reaction was stopped when the phosphine content in the reactor was ≤100 ppm.

[0043] An aqueous solution containing 2 mol of hydrogen peroxide was added to the reaction product for oxidation. After the reaction was completed, sodium hydroxide was added dropwise to dissolve the product and bring the pH of the system to 6-8. The ethanol was then distilled off. The system temperature was then controlled at 80°C. An aqueous solution containing 1 / 3 mol of aluminum ions was added dropwise over 12 hours. After the addition was completed, the reaction was continued for 4 hours. After separation, washing, pulverizing, and drying, aluminum dioctylphosphinate flame retardant was obtained.

[0044] Example 5 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen and contained 0.1 mol of azobisisobutyronitrile and 2 mol of styrene. When the amount of phosphine gas added reached 1 mol, the phosphine gas was turned off, the temperature was raised to 60℃ and kept at that temperature for 24 hours to stop the reaction.

[0045] Subsequently, an aqueous solution containing 2 mol of hydrogen peroxide was added to the reaction product for oxidation. After the reaction was completed, sodium hydroxide was added dropwise to dissolve the product and bring the pH of the system to 6-8. At the same time, the system temperature was controlled at 80℃. Aqueous aluminum sulfate solution with a total aluminum ion content of 1 / 3 mol was added dropwise over 12 hours. After the addition was completed, the reaction was continued for 4 hours. After separation, washing, crushing and drying, aluminum bis(2-phenylethyl)phosphonate flame retardant was obtained.

[0046] Example 6 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen and contained 0.05 mol of peracetic acid and 2 mol of 1-hexene. When the amount of phosphine gas added reached 1 mol, the phosphine gas was turned off, the temperature was raised to 60℃ and held for 8 hours.

[0047] Subsequently, excess osmium tetroxide was added to the reaction product for oxidation. After the reaction was complete, the mixture was filtered, and the resulting solution was returned to the reaction vessel. Sodium hydroxide was then added dropwise to dissolve the solution, bringing the pH of the system to 6-8. Meanwhile, the system temperature was controlled at 80℃, and an aqueous solution of aluminum sulfate with a total aluminum ion content of 1 / 3 mol was added dropwise over 12 hours. After the addition was completed, the reaction continued for 36 hours. After separation, washing, crushing and drying, aluminum dioctylphosphinate flame retardant was obtained.

[0048] Example 7 Phosphine gas was continuously introduced into a reactor containing 0.05 mol of sodium persulfate and 200 ml of ethanol, which had been pre-purified with high-purity nitrogen. Isobutylene was also continuously introduced. The temperature was raised to 60°C and the reaction continued until about 1 mol of phosphine was consumed. Then, the introduction of phosphine gas was stopped, and the reaction was terminated after about 2 mol of isobutylene was consumed.

[0049] Subsequently, an aqueous solution containing excess sodium percarbonate was added to the reaction product to carry out an oxidation reaction. After the reaction was completed, the pH of the system was adjusted to 6-8, and the ethanol was distilled off. Meanwhile, the system temperature was controlled at 100℃, and an aqueous solution of aluminum sulfate with a total aluminum ion content of 1 / 3 mol was added dropwise over 3 hours. After the addition was completed, the reaction continued for 30 hours. After separation, washing, crushing and drying, aluminum diisobutylphosphinate flame retardant was obtained.

[0050] Example 8 Phosphine gas was continuously introduced into a reactor containing 0.05 mol of ammonium persulfate and 200 ml of water, which had been pre-purified with high-purity nitrogen. Simultaneously, 1-butene was continuously introduced. The temperature was raised to 60°C and the reaction continued until approximately 1 mol of phosphine was consumed. Then, the introduction of phosphine gas was stopped, and the reaction was terminated after approximately 2 mol of 1-butene was consumed.

[0051] Subsequently, an aqueous solution containing excess sodium percarbonate was added to the reaction product to carry out an oxidation reaction. After the reaction was completed, the pH of the system was adjusted to 6-8, and the ethanol was distilled off. Meanwhile, the system temperature was controlled at 100℃, and an aqueous solution of aluminum sulfate with a total aluminum ion content of 1 / 3 mol was added dropwise over 3 hours. After the addition was completed, the reaction continued for 25 hours. After separation, washing, crushing and drying, aluminum dibutylphosphinate flame retardant was obtained.

[0052] Experimental test: 1. TGA Testing The testing method is as follows: Take about 5-10 mg of the dried sample and place it in the sample crucible of the thermogravimetric analyzer. Perform the temperature test under a nitrogen atmosphere. The nitrogen flow rate is 40-60 mL / min, the heating rate is 10 ℃ / min, and the test temperature range is room temperature to 800 ℃. Record the thermogravimetric curve (TGA) of the sample.

[0053] Table 1. Example Data

[0054] As can be seen from Examples 1-8 and the results in Table 1, under the same phosphine consumption conditions, different implementation routes can all obtain the corresponding dialkylphosphine flame retardants. Furthermore, the product yields of each example generally remain in a high and relatively concentrated range, indicating that the technical route of this invention using phosphine as the starting phosphorus source is not only applicable to a single reaction condition, but also has good process feasibility and route adaptability under photoinitiation and free radical initiation, gaseous olefins and liquid olefins, solvent-containing conditions, and different subsequent oxidation / salting treatments. In principle, this shows that phosphine can effectively participate in the free radical addition with olefins under initiation conditions and is relatively stably converted into the target dialkylphosphine flame retardant during subsequent oxidation and metal ion salting processes, thereby realizing the conversion and utilization of by-product phosphorus-containing components into the target product chain. Combined with... Figures 1 to 8 Further analysis of the TGA curves showed that the products obtained in each embodiment maintained relatively stable mass in the low to medium temperature range. The main weight loss process was concentrated in the higher temperature range, and the overall morphology of the curves was similar. This indicates that the products obtained in different embodiments all have a good thermal stability and similar thermal decomposition characteristics. This reflects that the route of the present invention can still form a dialkylphosphinate metal salt structure with relatively consistent thermal behavior when changing the type of olefin, the initiation method, and some process parameters. At the same time, there are certain differences in the position of the main weight loss region and the residual mass at the tail end of the curves, indicating that different organic group structures and salt formation systems will affect the decomposition path and residual characteristics. However, this difference is a reasonable change caused by the difference in product structure and does not affect the stable realization of the target flame retardant preparation effect of the technical route of the present invention. The yield results in Table 1 are summarized as follows: Figures 1 to 8 Thermogravimetric analysis shows that the present invention can not only reliably convert phosphine into dialkylphosphinate flame retardants, but also the resulting product exhibits good thermal stability, providing a material basis for its subsequent application as a flame retardant. The experimental results also support the technical feasibility of the present invention in optimizing the utilization path of phosphorus-containing resources.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing a dialkylphosphinate flame retardant, characterized in that, The steps include the following: S1: In a pressure-resistant reactor purged with an inert gas, phosphine and olefins are introduced into the reaction system, wherein phosphine is used as the starting phosphorus-containing raw material, and under the action of an initiator, phosphine and olefins undergo a free radical addition reaction to obtain an addition product, wherein the olefin is a gaseous olefin or a liquid olefin, and the initiator is a photoinitiator or a free radical initiator. S2: The addition product obtained in S1 is added to an aqueous solution containing an oxidant for oxidation reaction, followed by the addition of ammonia or alkali metal hydroxide to adjust the pH of the system to 6-8. S3: Add a 2-4 valent metal salt solution to the system obtained in S2 to carry out a salt formation reaction. After separation, washing and drying, the dialkylphosphinate flame retardant is obtained.

2. The synthesis method according to claim 1, characterized in that, S1 includes: Phosphine is introduced into a pressure-resistant reactor purged with inert gas, and the partial pressure of phosphine inside the reactor is controlled to be 0.05–10 MPa. A photoinitiator is added to the reactor, and gaseous olefins and phosphine are continuously introduced while the temperature is increased. At the same time, ultraviolet light is applied to induce a free radical addition reaction between the phosphine and the gaseous olefins. The reaction is terminated when the phosphine content in the reactor is less than 100 ppm.

3. The synthesis method according to claim 1, characterized in that, S1 includes: Phosphine is introduced into a pressure-resistant reactor that has been purged with an inert gas and contains a solvent; A photoinitiator is added to the reactor, and gaseous olefins are continuously introduced and heated while being irradiated with ultraviolet light to cause phosphine to undergo a free radical addition reaction with the gaseous olefins. The criterion for terminating the reaction was that the number of moles of gaseous olefins consumed was twice the number of moles of phosphine introduced.

4. The synthesis method according to claim 1, characterized in that, S1 includes: Phosphine is introduced into a pressure-resistant reactor containing solvent and free radical initiator, which has been replaced with an inert gas, and gaseous olefins are continuously introduced and heated to allow phosphine to undergo a free radical addition reaction with the gaseous olefins. The criterion for terminating the reaction was that the number of moles of gaseous olefins consumed was twice the number of moles of phosphine introduced.

5. The synthesis method according to claim 1, characterized in that, S1 includes: Liquid olefins and free radical initiators are added to a pressure-resistant reactor purged with inert gas, and phosphine is introduced. When the number of moles of phosphine introduced reaches 1 / 2 of the number of moles of liquid olefins, the introduction of phosphine is stopped. The temperature is then increased to allow phosphine to undergo a free radical addition reaction with the liquid olefin. The reaction ends when the phosphine content in the reactor is less than 100 ppm.

6. The synthesis method according to any one of claims 1 to 5, characterized in that, The reaction temperature in step S1 is 10–200°C; The salt formation reaction temperature in step S3 is 10–100°C.

7. The synthesis method according to any one of claims 1 to 5, characterized in that, The gaseous olefin is at least one of ethylene, propylene, butene, and isobutene; The liquid olefin is at least one of C5-C18 aliphatic olefins, C8-C18 aromatic olefins, or C4-C18 cyclic olefins.

8. The synthesis method according to any one of claims 1 to 5, characterized in that, The photoinitiator is a free radical type photoinitiator; The free radical initiator is at least one of peroxide or azo compound; The amount of the initiator added is 0.1‰ to 10% of the molar amount of phosphine.

9. The synthesis method according to claim 3 or 4, characterized in that, The solvent is at least one selected from water, methanol, ethanol, ethyl acetate, toluene, and benzene.

10. The synthesis method according to any one of claims 1 to 5, characterized in that, The oxidant is selected from at least one of hydrogen peroxide, hypochlorous acid, sodium hypochlorite, perchloric acid, sodium perchlorate, potassium permanganate, potassium dichromate, chromic acid, peracetic acid, perpropionic acid, perbutyric acid, sodium percarbonate, perbenzoic acid, osmium tetroxide, and ozone. The metal ions in the divalent to tetravalent metal salt solution are selected from at least one of aluminum ions, zinc ions, magnesium ions, calcium ions, iron ions, or zirconium ions.

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