Process for preparing halogenated diphosphate flame retardant V6 through continuous flow photocatalysis tubular reaction

Abstract

The invention discloses a process for preparing a halogenated bisphosphate flame retardant V6 through a continuous flow photocatalytic tubular reaction, and the flame retardant V6 is prepared from a 3, 9-dichloro-2, 4, 8, 10-tetraoxo-3, 9-diphosphaspiro [5.5] undecane SPDC solution through a two-step continuous flow photocatalytic reaction. The SPDC solution is subjected to a chlorination reaction in a photocatalytic chlorination reactor, then the obtained intermediate solution and metered ethylene oxide are simultaneously introduced into a photocatalytic condensation reactor for a condensation reaction, and the target product flame retardant V6 is obtained through post-treatment. According to the invention, tubular reaction and illumination catalysis are combined, and the size of a photocatalytic reactor is controlled, so that on one hand, reaction liquid can be uniformly and fully irradiated by light in the radial direction, and on the other hand, the tubular structure provides a huge illumination specific surface area, so that more reaction molecules have opportunities to contact photons in unit time; and the utilization efficiency and the reaction rate of photons are obviously improved. The method is high in reaction controllability, short in reaction retention time and high in product purity.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, specifically to a process for preparing halophosphate flame retardant V6 via a continuous flow photocatalytic tubular reaction. Background Technology

[0002] Flame retardant V6, chemically named 2,2-dichloromethyl-trimethylene-bis[bis(2-chloroethyl)phosphate], is a halophosphate ester, a colorless to yellow oily substance with a melting point of 275℃, a boiling point of 620.3±55℃, and a density of 1.464 g / mL. Due to the simultaneous presence of halogen and phosphorus elements within its molecule, it exhibits a good synergistic effect, achieving highly efficient flame retardancy in both the gas and solid phases. Furthermore, this type of flame retardant also possesses excellent thermal stability, low volatility, is colorless and odorless, and is resistant to hydrolysis. As an additive flame retardant, it is widely used in flexible and rigid polyurethane foams, and its ease of use and simple processing further enhance its market competitiveness.

[0003] This flame retardant is produced by reacting pentaerythritol with an organic solvent and excess phosphorus trichloride to generate cyclic SPDC. The excess phosphorus trichloride and the generated hydrogen chloride gas are extracted under negative pressure, and then chlorine is introduced to carry out a ring-opening reaction to generate a chlorine-containing intermediate. Then, excess chlorine gas is removed by negative pressure and nitrogen blowing, and then it reacts with ethylene oxide under the catalysis of a catalyst to generate crude V6. After alkali washing and solvent removal, refined product V6 is obtained.

[0004] Currently, literature reports that flame retardant V6 is generally synthesized using a batch reactor method.

[0005] Chinese invention patent CN103044484 A discloses a method for preparing a halophosphate flame retardant. In this method, flame retardant V6 undergoes a three-step reaction: pentaerythritol and phosphorus trichloride react to obtain a spirocyclic intermediate, which is then ring-opened by chlorine gas, and finally esterified under a catalyst to generate the target product. This invention suffers from low reaction efficiency, long reaction time, low utilization of chlorine and ethylene oxide, a large amount of gas escaping without timely reaction participation, and ineffective control over the reaction process. Summary of the Invention

[0006] To address the aforementioned technical problems in the existing technology, the present invention aims to provide a continuous flow photocatalytic tubular reaction process for preparing halophosphate flame retardant V6. Utilizing photocatalysis, the reaction conditions are made milder, and the selectivity and reactivity are significantly improved. Simultaneously, the excellent mass and heat transfer performance of the tubular reactor reduces the reaction time, increases the utilization rate of chlorine and ethylene oxide, simplifies the operation steps, allows for precise control of reaction parameters, enables seamless and efficient scale-up production, and facilitates the controllability and automation of the reaction process.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A process for preparing halophosphate flame retardant V6 via a continuous flow photocatalytic tubular reaction includes the following steps: Step 1: 3,9-Dichloro-2,4,8,10-tetraoxo-3,9-diphosspiro[5.5]undecane (SPDC) solution is delivered to the precooling tube by metering pump one, and then mixed with dry chlorine gas in T-type mixer one. The mixture enters the photocatalytic chlorination reactor and carries out the chlorination reaction under light. After a certain residence time, intermediate solution B is obtained. Step 2: The intermediate B solution is fed into a preheating tube, then mixed with preheated ethylene oxide in a T-type mixer. The mixture enters a photocatalytic condensation reactor, where a photocatalytic condensation reaction is carried out under illumination. The reaction liquid is collected and post-processed to obtain the target product, flame retardant V6. The reaction formula is as follows: .

[0008] Further, in step 1), the molar flow ratio of SPDC to chlorine in the chlorination reaction is 1:2.0~2.1; in step 2), the molar flow ratio of ethylene oxide to SPDC in step 1) is 3.5~5.0:1, preferably 3.8~4.0:1.

[0009] Furthermore, in step 1), the temperature of the chlorination reaction precooling tube and the photocatalytic chlorination reactor is -10 to 35°C, preferably -5 to 0°C, and the residence time of the reaction liquid in the photocatalytic chlorination reactor is 10 to 300 seconds, preferably 10 to 90 seconds.

[0010] Furthermore, in step 2), the temperature of the condensation reaction preheating tube and the water bath of the photocatalytic condensation reactor is 30~60℃, preferably 40~50℃, and the residence time of the reaction liquid in the photocatalytic condensation reactor is 10~60min, preferably 20~40min.

[0011] Further, in step 1), the solvent of the SPDC solution is one or a combination of chlorobenzene, o-dichlorobenzene, p-dichlorobenzene, 1,2,4-trichlorobenzene, carbon tetrachloride, chloroform, and 1,2-dichloroethane; the mass concentration of SPDC in the SPDC solution is 20~70%.

[0012] Further, in step 1), the wavelength of the light source for the chlorination reaction is 380-420nm, preferably 390-410nm; in step 2), the wavelength of the light source for the condensation reaction is 420-480nm, preferably 450-460nm; both the photocatalytic chlorination reactor and the photocatalytic condensation reactor are made of transparent material.

[0013] Further, in step 2), a packing layer is provided inside the photocatalytic condensation reactor. This packing layer consists of a uniformly mixed mixture of nitrogen carbide g-C3N4 microspheres and transparent glass microspheres at a volume ratio of 0.5 to 2:1 to ensure the reactor's light transmittance. The particle size of both the nitrogen carbide g-C3N4 microspheres and the transparent glass microspheres is 1 to 2 mm, and the volume hourly space velocity (VHSV) of the reaction mixture through the packing layer is 1.0 to 6.0 h⁻¹. -1 Preferably, it is 1.5 to 3.0 h. -1 .

[0014] Furthermore, the volume ratio of nitrogen carbide g-C3N4 microspheres to transparent glass microspheres is 0.8 ~ 1.2 : 1.

[0015] Furthermore, the inner diameter of the photocatalytic chlorination reactor is 5 to 10 mm, and the inner diameter of the photocatalytic condensation reactor is 10 to 20 mm.

[0016] Further, in step 2), the post-processing steps are as follows: add NaOH solution to the reaction solution for washing, separate the liquid and remove solvent to obtain the purified target product, wherein the mass fraction of NaOH solution is 5~10%, and the mass of NaOH solution is 1.5~3 times the mass of the reaction solution.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) In this invention, SPDC solution is transported to a pre-cooling pipe, and chlorine gas is metered and transported. After mixing and contact, the solution enters a photocatalytic chlorination reactor for chlorination. After reacting for a certain residence time and temperature, an intermediate solution is obtained. Then, the obtained intermediate solution and metered ethylene oxide are simultaneously passed into a photocatalytic condensation reactor for condensation. After reacting for a certain residence time and temperature, the reaction liquid flows out of the reactor. After post-treatment, alkaline washing, separation, and solvent removal, purified product V6 is obtained. The total yield can reach more than 95%, and the purity can reach more than 99%.

[0018] 2) Compared with the traditional batch process, the continuous flow photocatalytic tubular reaction adopted in this invention can precisely control and reduce the amount of chlorine and ethylene oxide used, avoid gas escape, eliminate cumbersome operations such as chlorine removal and catalyst addition, and reduce production and waste gas treatment costs.

[0019] 3) Compared with traditional batch reactor processes, the continuous flow photocatalytic tubular reaction of this invention uses LED light strips placed in a thin polytetrafluoroethylene tube and wrapped around the photocatalytic reactor, eliminating the chlorine removal operation, simplifying the process steps, and improving production time and space efficiency. In traditional batch reactor processes, a large excess of chlorine gas needs to be introduced during chlorination to ensure sufficient contact and complete reaction between the reactants and chlorine gas, thus requiring subsequent chlorine removal. However, this invention uses a continuous flow photocatalytic tubular reaction, with high mass and heat transfer efficiency and precise stoichiometric delivery, ensuring that chlorine gas reacts completely and promptly without excess or escape, thereby optimizing and eliminating the need for chlorine removal. 4) Compared with the traditional batch process, the continuous flow photocatalytic tubular reaction adopted in this invention has advantages such as low backmixing, fast mass and heat transfer, mild reaction conditions, narrow reactant residence time, good repeatability, high catalytic efficiency, almost no scale-up effect, easy real-time monitoring of reaction process, and low online equivalent, thereby achieving high safety performance. 5) Compared with traditional batch reactor processes, this invention combines "tubular reaction" with "photocatalysis." By controlling the size of the photocatalytic reactor, it ensures that the reaction liquid is uniformly and fully irradiated by light in the radial direction. Furthermore, the "tubular structure" provides a large specific surface area for light irradiation, allowing more reaction molecules to come into contact with photons per unit time, significantly improving photon utilization efficiency and reaction rate. This avoids the problem of low reaction efficiency caused by the rapid attenuation of light intensity with liquid depth in batch reactor processes.

[0020] 6) This invention uses a photocatalyst g-C3N4 uniformly mixed with glass microspheres to form a filling layer, which effectively prevents g-C3N4 aggregation, enhances light scattering and transmission, and improves photocatalytic efficiency. It can also improve fluid distribution and enhance mass transfer.

[0021] 7) This invention uses a photocatalytic chlorination reactor instead of a traditional batch reactor, avoiding the following disadvantages of traditional batch processes: small-scale production, long production cycle, low output, poor quality, and serious resource waste. The continuous operation mode makes it easier to automate the process, improves production safety, is convenient to operate, and has a high degree of continuity, making it suitable for industrial production. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the process and apparatus for preparing halophosphate flame retardant V6 by a continuous flow photocatalytic tubular reaction according to the present invention.

[0023] In the diagram: A. Nitrogen cylinder 1; B. Chlorine cylinder; C. Nitrogen cylinder 2; D. Ethylene oxide cylinder; 1. Drying tube; 2. Chlorine gas flow meter; 3. Check valve 1; 4. Precooling tube; 5. T-type mixer 1; 6. Thermometer 1; 7. Photocatalytic chlorination reactor; 8. LED light strip 1; 9. Thermometer 2; 10. Ethylene oxide gas flow meter; 11. Check valve 2; 12. Preheating tube 1; 13. T-type mixer 2; 14. Preheating tube 2; 15. Thermometer 3; 16. Photocatalytic condensation reactor; 17. LED light strip 2. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the scope described.

[0025] A schematic diagram of the apparatus for the continuous flow photocatalytic tubular reaction of the present invention to prepare halophosphate flame retardant V6 is shown below. Figure 1 The inlet of the T-type mixer-5 is divided into two paths. One path is connected to the check valve-3, the chlorine gas flow meter-2 and the drying tube-1 in sequence by a pipeline. The inlet of the drying tube-1 is connected to the nitrogen cylinder-A and the chlorine cylinder-B respectively. The other path is connected to the precooling tube-4 and the metering pump-P1 in sequence by a pipeline. The metering pump-P1 is used to transport the spiral ring intermediate A solution.

[0026] The outlet of T-type mixer 5 is connected to one inlet of T-type mixer 13 via a pipeline, which is connected to photocatalytic chlorination reactor 7, metering pump 2P2, preheating pipe 214, and T-type mixer 213. The other inlet of T-type mixer 213 is connected to preheating pipe 12, check valve 21, and ethylene oxide gas flow meter 10 via a pipeline. The inlet of ethylene oxide gas flow meter 10 is connected to nitrogen cylinder 2C and ethylene oxide cylinder D via pipelines.

[0027] The outlet of T-type mixer 13 is connected by a pipeline to photocatalytic condensation reactor 16.

[0028] LED light strip 1 8 is installed on the outside of the photocatalytic chlorination reactor 7, and LED light strip 2 17 is installed on the outside of the photocatalytic condensation reactor 16.

[0029] Thermometer 6 and thermometer 9 are installed on the inlet and outlet pipes of the photocatalytic chlorination reactor 7, respectively, and thermometer 15 is installed on the outlet pipe of the T-type mixer 13.

[0030] In addition, in the experiments of the embodiments and comparative examples of the present invention, the LED light strip 8 was placed inside a transparent and flexible polytetrafluoroethylene (PTFE) thin tube, and then tightly wrapped around the outside of the photocatalytic chlorination reactor. This eliminated the risk of short circuits caused by bath liquid penetration and improved the electrical safety and long-term operational stability of the entire system. Subsequently, the photocatalytic chlorination reactor and the LED light strip 8 wrapped in the PTFE thin tube were placed together in an ice-ethanol bath. The temperature of the photocatalytic chlorination reaction was controlled by setting the temperature of the ice-ethanol bath.

[0031] LED strip 217 is placed inside a transparent, flexible polytetrafluoroethylene (PTFE) tube and then tightly wound around the outside of the photocatalytic condensation reactor. The photocatalytic condensation reactor and the PTFE-covered LED strip 217 are then placed together in a water bath. The temperature of the photocatalytic condensation reaction is controlled by adjusting the temperature of the water bath.

[0032] In this embodiment, both LED strip 8 and LED strip 17 are commercially available LED strips of specific wavelengths. To ensure photocatalytic efficiency, LED strips with a rated power of approximately 15-20 W / m are tightly wound to achieve the aforementioned light intensity.

[0033] The preparation method of g-C3N4 microspheres in the photocatalytic condensation reactor in this embodiment is as follows: Industrial-grade g-C3N4 powder (95%-98%) purchased from Shandong Jingbo Environmental Protection Materials Co., Ltd. is mixed with a 5% sodium alginate aqueous solution at a mass ratio of 5:1 and ground into a uniform slurry. The slurry is then dripped into a 0.3 mol / L calcium chloride solution using a syringe pump through a 1.2 mm inner diameter needle and cured for 2 hours. The mass of the calcium chloride solution is more than 10 times the mass of the slurry. The cured microspheres are then removed, washed with deionized water, dried at 80℃ for 12 hours, and finally sieved to obtain microspheres with a particle size of 1-2 mm, thus obtaining the g-C3N4 microspheres.

[0034] Example 1: 338.51 g of SPDC chlorobenzene solution (chlorobenzene mass 7 / 10) was transported to a -5 to 0°C pre-cooling tube. 2.0 equivalents of chlorine gas (i.e., the molar amount of chlorine gas is twice the molar amount of SPDC) were metered and supplied. After contact in a mixer, the solution entered a photocatalytic chlorination reactor. The photocatalytic chlorination reactor and the LED light strip wrapped with a thin polytetrafluoroethylene tube were placed together in a -5 to 0°C ice-ethanol bath for chlorination reaction to obtain an intermediate solution. The photocatalytic chlorination reactor had an inner diameter of 5 mm, the light source wavelength for the chlorination reaction was 405 nm, and the residence time of the chlorination reaction solution was 30 s.

[0035] Next, the obtained intermediate solution was preheated to 40°C and mixed with 4.0 equivalents of ethylene oxide (i.e., the molar amount of ethylene oxide was 4 times the molar amount of SPDC), and then introduced into a photocatalytic condensation reactor. The photocatalytic condensation reactor and the LED light strip wrapped with polytetrafluoroethylene thin tubes on its outside were placed together in a 40°C water bath environment to carry out the condensation reaction. The photocatalytic condensation reactor had an inner diameter of 5 mm and contained a packed layer consisting of a uniformly mixed mixture of 1-2 mm diameter g-C3N4 microspheres and 1-2 mm transparent glass microspheres in a 1:1 volume ratio. The volume hourly space velocity (VHSV) of the reaction mixture through the packed layer was 2.0 h⁻¹. -1 The residence time of the condensation reaction solution was 30 min. The reaction solution flowed out of the reactor and was post-treated by washing with 7% NaOH solution of twice the mass of the reaction solution, separating the liquid, and removing the chlorobenzene solvent by rotary evaporation to obtain the target product flame retardant V6 215.64 g, with a yield of 96.51% and a purity of 99.62%.

[0036] Example 2: 304.66 g of 1,2-dichloroethane solution of SPDC (1 / 3 by mass) was transported to a pre-cooling tube at -5 to 0°C. 2.0 equivalents of chlorine gas (i.e., the molar amount of chlorine gas is twice the molar amount of SPDC) were metered in. After contact in a mixer, the solution entered a photocatalytic chlorination reactor. The photocatalytic chlorination reactor and the LED light strip wrapped with a thin polytetrafluoroethylene tube were placed together in an ice-ethanol bath at -5 to 0°C for the chlorination reaction to obtain an intermediate solution. The photocatalytic chlorination reactor had an inner diameter of 10 mm, the light source wavelength for the chlorination reaction was 405 nm, and the residence time of the chlorination reaction solution was 30 s.

[0037] Next, the obtained intermediate solution was preheated to 40°C and mixed with 4.0 equivalents of ethylene oxide (i.e., the molar amount of ethylene oxide was 4 times the molar amount of SPDC), and then introduced into a photocatalytic condensation reactor. The photocatalytic condensation reactor and the LED light strip wrapped with PTFE thin tubes on its outside were placed in a 40°C water bath environment to carry out the condensation reaction. The photocatalytic condensation reactor had an inner diameter of 5 mm and was filled with a uniformly mixed mixture of 1-2 mm diameter g-C3N4 microspheres and 1-2 mm transparent glass microspheres in a 1:1 volume ratio to ensure the reactor's light transmittance; the volume hourly space velocity (VHSV) of the reaction mixture through the packing layer was 2.0 h⁻¹. -1 The residence time of the condensation reaction solution was 30 min. The reaction solution flowed out of the reactor and underwent post-treatment by washing with 7% NaOH solution of twice the mass of the reaction solution, separating the liquid, and removing the solvent by rotary evaporation to obtain the target product flame retardant V6, with a yield of 96.26% and a purity of 99.48%.

[0038] Example 3: The experimental steps of Example 3 are the same as those of Example 1, with the only difference being: ①In Example 3, the raw material solution for the chlorination reaction was replaced with 375.03g of o-dichlorobenzene solution of SPDC, with o-dichlorobenzene accounting for 4 / 5 of the mass.

[0039] ②In Example 3, the inner diameter of the photocatalytic condensation reactor was replaced with 10 mm, and the volume hourly space velocity of the reaction mixture through the packing layer was 3.0 h⁻¹. -1 The residence time of the condensation reaction solution was 20 min, and the other reaction conditions remained unchanged. The final experimental result was that the target product flame retardant V6 was obtained with a yield of 95.80% and a purity of 99.60%.

[0040] Example 4: The experimental steps of Example 4 are the same as those of Example 1, with the only difference being: ①In Example 4, the residence time of the chlorination reaction solution was changed to 10 s.

[0041] ②In Example 4, the volume hourly space velocity (VHSV) of the reaction mixture in the condensation reaction through the packed layer was 3.0 h⁻¹. -1 The residence time of the condensation reaction solution was 20 min, and the other reaction conditions remained unchanged. The final experimental result was that the target product flame retardant V6 was obtained with a yield of 95.63% and a purity of 99.12%.

[0042] Example 5: The experimental steps of Example 5 are the same as those of Example 1, with the only difference being: ①In Example 5, the inner diameter of the photocatalytic chlorination reactor was changed to 10 mm; ②In Example 5, the inner diameter of the photocatalytic condensation reactor was replaced with 10 mm. The photocatalytic condensation reactor and the LED light strip wrapped with polytetrafluoroethylene thin tubes on its outer side were placed together in a 50°C water bath environment. The volume hourly space velocity of the reaction mixture through the packing layer was 3.0 h⁻¹. -1 The residence time of the condensation reaction solution was 20 min, and the other reaction conditions remained unchanged. The final experimental result was that the target product flame retardant V6 was obtained with a yield of 95.01% and a purity of 99.59%.

[0043] Comparison with Example 1: Original autoclave process Take 350.21 g of SPDC in a chlorobenzene solution (chlorobenzene accounts for 7 / 10 of the total mass). In a flask, pass a large amount of chlorine gas under normal pressure for approximately 2 hours. After chlorination, heat the flask to 35°C in a water bath, and purge residual chlorine gas with nitrogen while evacuating for 40 minutes. Then add titanium tetrachloride (1% of the mass of SPDC) as a catalyst. Replace the air with nitrogen 2-3 times, and then pass 4.5 equivalents of ethylene oxide (4.5 times the molar amount of SPDC). React at 80°C for 1.5 hours. Afterward, wash the reaction solution with twice its mass of 7% NaOH solution, separate the layers, and remove the chlorobenzene solvent by rotary evaporation to obtain the target product, flame retardant V6, with a yield of 86.78% and a purity of 98.42%.

[0044] Comparison with Example 2: Using only g-C3N4 microspheres to fill the fixed bed The experimental procedure of Example 2 was repeated in Example 1, with the only difference being that the photocatalytic condensation reactor in Example 2 was filled only with g-C3N4 microspheres with a diameter of 1-2 mm, and the volume hourly space velocity of the reaction mixture through the g-C3N4 microsphere packing layer was 1.0 h⁻¹. -1 With the other reaction conditions unchanged, the final experimental result was: the target product flame retardant V6 was obtained with a yield of 78.21% and a purity of 97.89%.

[0045] Comparison Example 3: Tubular reaction without photocatalysis The experimental procedure of Example 3 was repeated in Example 1, with the only difference being: ①The chlorination reaction in Comparative Example 3 does not use photocatalysis.

[0046] ② In the condensation reaction of Comparative Example 3, photocatalysis was not used, and the other reaction conditions remained unchanged. The final experimental result was: the target product flame retardant V6 was obtained with a yield of 68.86% and a purity of 97.75%.

[0047] Comparison with Example 4: The photocatalytic chlorination reactor is too large. The experimental procedure of Example 4 was repeated in Example 1, with the only difference being: ① The inner diameter of the photocatalytic chlorination reactor in Comparative Example 4 was replaced with 20 mm.

[0048] ②Compared with Example 4, the condensation reaction was carried out under the same conditions. The final experimental result was: the target product flame retardant V6 was obtained with a yield of 88.21% and a purity of 98.12%.

[0049] Comparison Example 5: The size of the photocatalytic condensation reactor is too large. The experimental procedure of Comparative Example 5 was repeated in Example 1, except that the inner diameter of the photocatalytic condensation reactor in the condensation reaction of Comparative Example 5 was replaced with 20 mm, while the other reaction conditions remained unchanged. The final experimental result was that the target product flame retardant V6 was obtained with a yield of 82.68% and a purity of 97.86%.

[0050] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A process for preparing halophosphate flame retardant V6 via a continuous flow photocatalytic tubular reaction, characterized in that... Includes the following steps: Step 1: 3,9-Dichloro-2,4,8,10-tetraoxo-3,9-diphosspiro[5.5]undecane (SPDC) solution is delivered to the precooling tube by metering pump one, and then mixed with dry chlorine gas in T-type mixer one. The mixture enters the photocatalytic chlorination reactor and carries out the chlorination reaction under light. After a certain residence time, intermediate solution B is obtained. Step 2: The intermediate B solution is transported to the preheating tube, and then mixed with the preheated ethylene oxide in the T-type mixer. The mixture enters the photocatalytic condensation reactor and undergoes a photocatalytic condensation reaction under light. The reaction liquid is collected and post-processed to obtain the target product flame retardant V6.

2. The process for preparing halophosphate flame retardant V6 by continuous flow photocatalytic tubular reaction as described in claim 1, characterized in that... In step 1), the molar flow ratio of SPDC to chlorine in the chlorination reaction is 1:2.0~2.1; in step 2), the molar flow ratio of ethylene oxide to SPDC in step 1) is 3.5~5.0:1, preferably 3.8~4.0:

1.

3. The process for preparing halophosphate flame retardant V6 by continuous flow photocatalytic tubular reaction as described in claim 1, characterized in that... In step 1), the temperature of the chlorination reaction precooling tube and the photocatalytic chlorination reactor is -10 ~ 35℃, preferably -5 ~ 0℃, and the residence time of the reaction liquid in the photocatalytic chlorination reactor is 10 ~ 300s, preferably 10 ~ 90s.

4. The process for preparing halophosphate flame retardant V6 by continuous flow photocatalytic tubular reaction as described in claim 1, characterized in that... In step 2), the temperature of the condensation reaction preheating tube and the water bath of the photocatalytic condensation reactor is 30-60℃, preferably 40-50℃, and the residence time of the reaction liquid in the photocatalytic condensation reactor is 10-60min, preferably 20-40min.

5. The process for preparing halophosphate flame retardant V6 by continuous flow photocatalytic tubular reaction as described in claim 1, characterized in that... In step 1), the solvent of the SPDC solution is one or a combination of chlorobenzene, o-dichlorobenzene, p-dichlorobenzene, 1,2,4-trichlorobenzene, carbon tetrachloride, chloroform, and 1,2-dichloroethane; the mass concentration of SPDC in the SPDC solution is 20-70%.

6. The process for preparing halophosphate flame retardant V6 by continuous flow photocatalytic tubular reaction as described in claim 1, characterized in that... In step 1), the light source wavelength for the chlorination reaction is 380-420nm, preferably 390-410nm; in step 2), the light source wavelength for the condensation reaction is 420-480nm, preferably 450-460nm; both the photocatalytic chlorination reactor and the photocatalytic condensation reactor are made of transparent material.

7. The process for preparing halophosphite flame retardant V6 by continuous flow photocatalytic tubular reaction as described in claim 1, characterized in that... Step 2) The photocatalytic condensation reactor is equipped with a packed layer, which consists of a uniformly mixed nitrogen carbide g-C3N4 microspheres and transparent glass microspheres in a volume ratio of 0.5 to 2:1 to ensure the reactor's light transmittance. The particle size of both the nitrogen carbide g-C3N4 microspheres and the transparent glass microspheres is 1 to 2 mm, and the volume hourly space velocity (VHSV) of the reaction mixture through the packed layer is 1.0 to 6.0 h⁻¹. -1 Preferably, it is 1.5 to 3.0 h. -1 .

8. The process for preparing halobisphosphate flame retardant V6 by continuous flow photocatalytic tubular reaction as described in claim 7, characterized in that... The volume ratio of nitrogen carbide g-C3N4 microspheres to transparent glass microspheres is 0.8 ~ 1.2 :

1.

9. The process for preparing halophosphate flame retardant V6 by continuous flow photocatalytic tubular reaction as described in claim 1, characterized in that... The inner diameter of the photocatalytic chlorination reactor is 5-10 mm, and the inner diameter of the photocatalytic condensation reactor is 5-10 mm.

10. The process for preparing halophosphite flame retardant V6 by continuous flow photocatalytic tubular reaction as described in claim 1, characterized in that... In step 2), the post-processing steps are as follows: add NaOH solution to the reaction solution for washing, separate the liquid and remove solvent to obtain the purified target product, wherein the mass fraction of NaOH solution is 5~10% and the mass of NaOH solution is 1.5~3 times the mass of the reaction solution.

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