Phosphorus oxychloride preparation method based on hollow fiber membrane reactor

Abstract

The invention discloses a preparation method of phosphorus oxychloride based on a hollow fiber membrane reactor, and belongs to the technical field of preparation of inorganic chemical products. The hollow fiber membrane reactor comprises a plurality of groups of hollow fiber membrane reaction units and heat exchange units connected in series with liquid outlets of the hollow fiber membrane reaction units, and each hollow fiber membrane reaction unit is composed of a shell and a plurality of hollow fiber membrane filaments arranged in the shell; oxygen escapes in a molecular level through membrane filaments with the pore diameter of 0.1-1.0 nm, and is in efficient contact with phosphorus trichloride flowing in a shell pass on a gas-membrane-liquid three-phase interface to generate oxidation reaction; the reactor adopts a multi-stage series structure and is matched with a heat exchange unit to realize continuous temperature control and step-by-step reaction. Through the high specific surface area and the uniform mass transfer characteristic of the membrane reactor, the oxygen utilization rate and the phosphorus trichloride conversion rate are remarkably improved, the problems of non-uniform gas-liquid contact and low conversion rate in a traditional reactor are solved, and the membrane reactor is suitable for continuous and efficient industrial production of phosphorus oxychloride.

Description

Technical Field

[0001] This invention relates to the field of inorganic chemical product preparation technology, specifically to a method for preparing phosphorus oxychloride based on a hollow fiber membrane reactor, which is suitable for the industrial production of phosphorus oxychloride. Background Technology

[0002] Phosphorus oxychloride (POCl3) is an important inorganic chemical raw material widely used in the semiconductor industry, pharmaceuticals, pesticides, and materials science. In the semiconductor industry, it is used as a dopant and photoresist raw material; in the pharmaceutical industry, it is used to synthesize antibiotics and antitumor drug intermediates; in the pesticide industry, it can be used to prepare organophosphorus pesticides; and in materials science, it can be used to produce flame retardants and surface treatment agents. Currently, the mainstream methods for industrially preparing phosphorus oxychloride mainly fall into two categories: (1) Phosphorus pentachloride hydrolysis method This method uses phosphorus pentachloride (PCl5) and water as raw materials to generate phosphorus oxychloride and hydrogen chloride through a liquid-phase hydrolysis reaction. The reaction formula is PCl5 + H2O → POCl3 + 2HCl↑.

[0003] Its core drawbacks are: on the one hand, the raw material phosphorus pentachloride is a solid strong Lewis acid with extremely high reactivity and is hygroscopic. In the liquid phase system, it needs to be dissolved in the reaction medium first, but its solid dissolution rate is slow, resulting in a low initial reaction rate; on the other hand, the hydrogen chloride gas generated by the reaction requires a tail gas absorption device, which increases the equipment investment and operating costs.

[0004] (2) Phosphorus trichloride oxidation method This method uses phosphorus trichloride (PCl3) as raw material and oxygen, chlorine, or chlorine dioxide as oxidants to produce phosphorus oxychloride through an oxidation reaction. A typical reaction formula is 2PCl3 + O2 → 2POCl3. This method is currently the most widely used industrial method. However, in existing technologies, this method mainly relies on traditional reactors, such as stirred tank reactors.

[0005] The phosphorus trichloride oxidation process has significant shortcomings when using traditional reactors. This reaction is a gas-liquid two-phase reaction, and in traditional stirred tanks, the gas is dispersed in the form of bubbles, with the gas-liquid contact area typically not exceeding 500 m². 2 / m 3 Furthermore, the short contact time leads to low oxidant utilization and consistently low phosphorus trichloride conversion rate, resulting in inefficient conversion and ultimately waste of raw materials.

[0006] To address the aforementioned shortcomings of traditional reactors, membrane reactors have gradually gained attention in the field of gas-liquid two-phase reactions. Among them, hollow fiber membrane reactors, with their large specific surface area (typically reaching 1000-5000 m²), have become particularly popular. 2 / m 3The advantages of a short mass transfer path and high gas-liquid contact efficiency can improve the mass transfer problem in the phosphorus oxychloride oxidation reaction. Therefore, developing a new type of reactor with high mass transfer efficiency is key to solving the industrial production of phosphorus oxychloride. Summary of the Invention

[0007] The present invention aims to provide a method for preparing phosphorus oxychloride based on a hollow fiber membrane reactor. By optimizing the membrane reactor design and material flow, the method solves the problems of low oxidant utilization rate and low phosphorus trichloride conversion rate in the prior art.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A hollow fiber membrane reactor includes several sets of hollow fiber membrane reaction units and a heat exchange unit connected in series with its liquid outlet, wherein the hollow fiber membrane reaction unit is composed of a shell and several hollow fiber membrane filaments disposed therein. Several hollow fiber membrane filaments are fixed inside the outer shell by two membrane filament fixing frames. The two membrane filament fixing frames are located at both ends of the outer shell and are sealed to the hollow fiber membrane filaments to stabilize the membrane filaments and isolate the gas-liquid flow path. The heat exchange unit is a hollow annular tube with a circulating medium inlet and a circulating medium outlet on the side wall. The circulating medium flows inside the annular tube, and the heat exchange unit has a material inlet and a material outlet at both ends.

[0009] In this invention, the membrane fiber fixing frame not only provides stable support for the hollow fiber membrane fibers, preventing them from shaking or shifting during the reaction, but also seals the gap between the hollow fiber membrane fibers and the outer shell, ensuring strict isolation of the gas-liquid flow path.

[0010] As a further embodiment of the present invention: the membrane reactor is composed of 3-5 stages of "hollow fiber membrane reaction units and heat exchange units" connected in series.

[0011] As a further embodiment of the present invention: when used in series, the liquid inlet of the first-stage hollow fiber membrane reactor unit is connected to the phosphorus trichloride conveying pipeline, the liquid outlet of the first-stage hollow fiber membrane reactor unit is connected to the material inlet of the heat exchange unit, the material outlet of the heat exchange unit is connected to the liquid inlet of the next-stage hollow fiber membrane reactor unit, and so on, with the outlet of the final-stage heat exchange unit connected to the finished product collection device; the gas inlets of each stage of the hollow fiber membrane reactor unit are respectively connected to the oxygen conveying pipeline, and the gas outlets of each stage of the hollow fiber membrane reactor unit are connected to the tail gas output pipeline.

[0012] As a further aspect of the present invention, the membrane reactor shell and the membrane fiber fixing frame are preferably made of polytetrafluoroethylene, steel-lined PTFE, titanium alloy or duplex stainless steel.

[0013] As a further aspect of the present invention: due to its resistance to phosphorus trichloride corrosion and its adaptability to different purity and cost requirements, the membrane reactor shell is an overall cylindrical sealed structure, with its inner diameter matching the size of the membrane fiber fixing frame.

[0014] As a further aspect of the present invention: the membrane reactor shell is provided with end caps at both ends, and a gas inlet and a gas outlet are respectively configured on the end caps at both ends; on the side wall of the membrane reactor shell, a liquid inlet is configured at the end near the gas inlet, and a liquid outlet is configured on the side wall at the opposite end; wherein, the liquid inlet is connected to a phosphorus trichloride delivery pipe, and the liquid outlet is connected to a product outlet pipe; the gas inlet is connected to an oxygen delivery pipe, and the gas outlet is connected to a gas output pipe, forming an independent flow path of "gas flowing inside the membrane and liquid flowing outside the membrane".

[0015] As a further aspect of the present invention, the membrane reactor shell sidewall is also provided with a temperature monitoring port and a pressure monitoring port, which are respectively connected to a temperature sensor and a pressure sensor to monitor the reaction parameters in real time.

[0016] As a further aspect of the present invention: the membrane fiber material is selected from one or a copolymer of polytetramethylpentene, polytetrafluoroethylene, polyvinylidene fluoride, perfluoroethylene propylene, polysulfone, polyethersulfone, silicone resin, and polydimethylsiloxane.

[0017] As a further aspect of the present invention, the diameter of the membrane filament is 0.5-1.0 mm.

[0018] As a further aspect of the present invention, the pore size of the membrane fiber is 0.1-1.0 nm. A membrane pore size of 0.1-1.0 nm allows oxygen molecules to escape into the liquid.

[0019] In the membrane reactor of the present invention, the membrane fibers can receive oxygen and, through their porous structure, allow the oxygen to diffuse uniformly to the outer surface of the membrane fibers at the molecular level, where it comes into full contact with the phosphorus trichloride flowing on the outside and undergoes an oxidation reaction.

[0020] As a further aspect of the present invention: the specific surface area of ​​the membrane fiber is 1500-3000 m². 2 / m 3 Preferably 2000-2500 m 2 / m 3 1500-3000 m 2 / m 3 The specific surface area can effectively increase the gas-liquid contact area, providing support for the utilization rate of oxidant and the conversion rate of phosphorus trichloride.

[0021] As a further aspect of the present invention: the oxygen permeability of the membrane fibers, as a key performance indicator of the membrane, is affected by factors such as material permeability, pore size, thickness, and transmembrane pressure. Preferably, the oxygen permeability of the membrane fibers is 0.1-10 L / min / cm. 2 .

[0022] As a further aspect of the present invention, the heat exchange unit is made of graphite, duplex stainless steel or polytetrafluoroethylene.

[0023] As a further aspect of the present invention: the circulating medium in the heat exchange unit is flexibly selected according to the in-situ temperature control requirements, preferably heat transfer oil (preferably mineral-based heat transfer oil or alkylbenzene-based heat transfer oil) or circulating cooling water.

[0024] This invention also discloses a method for preparing phosphorus oxychloride based on a hollow fiber membrane reactor, comprising the following steps: Liquid phosphorus trichloride is continuously fed into the hollow fiber membrane reactor unit from the liquid inlet on the outside of the shell of the first-stage hollow fiber membrane reactor unit, while gaseous oxygen is fed in from the gas inlet at the top of the shell. During the process, oxygen in the hollow fiber membrane reactor unit escapes to the outer surface of the membrane fibers at the molecular level through the membrane fibers. The oxygen and phosphorus trichloride flowing along the membrane fibers form a "gas-membrane-liquid" three-phase interface and undergo an oxidation reaction. The reaction mixture is cooled to 40-75°C by the first-stage heat exchange unit and then enters the next-stage hollow fiber membrane reaction unit, where 30-80% of the initial flow rate of oxygen is added to continue the reaction. The final-stage reaction mixture is cooled to ≤45°C by the final-stage heat exchange unit and then continuously discharged. The material outlet of the final-stage heat exchange unit is connected to the finished product collection device to achieve 24-hour continuous operation.

[0025] As a further aspect of the present invention, the reaction temperature inside the membrane reactor is 70-95℃, preferably 85-95℃.

[0026] As a further aspect of the present invention, the oxygen pressure inside the membrane reactor is 0.01-0.15 MPa, preferably 0.01-0.05 MPa.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Highly efficient and uniform gas-liquid contact. This invention relies on the molecular-level pore size design of hollow fiber membrane fibers (0.1-1.0 nm), allowing oxygen to diffuse uniformly to the outer surface of the membrane fibers. Combined with the membrane fiber fixing frame, liquid phosphorus trichloride is guided to flow uniformly along the membrane fibers, forming a stable "gas-membrane-liquid" three-phase reaction interface, completely solving the problems of gas bubble aggregation and uneven contact in traditional batch reactors.

[0028] 2. High reaction efficiency and continuous process. The high specific surface area of ​​the membrane fibers in this invention improves mass transfer efficiency, and the independent flow path design supports continuous feeding of phosphorus trichloride and continuous product discharge; combined with multi-stage series connection, it is suitable for continuous production. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of a hollow fiber membrane reactor.

[0030] In the diagram: 1. Liquid inlet; 2. Gas inlet; 3. Hollow fiber membrane filament; 4. Outer shell; 5. Liquid outlet; 6. Gas outlet. Detailed Implementation

[0031] The technical solution and effects of the present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto. Example 1

[0032] like Figure 1 As shown, this embodiment provides a hollow fiber membrane reactor, including several sets of hollow fiber membrane reaction units and a heat exchange unit connected in series with its liquid outlet. The hollow fiber membrane reaction unit consists of a shell 4 and several hollow fiber membrane filaments 3 disposed therein. Several hollow fiber membrane filaments 3 are fixed inside the outer shell 4 by two membrane filament fixing frames. The two membrane filament fixing frames are located at both ends of the outer shell 4 and are sealed to the hollow fiber membrane filaments 3 to stabilize the membrane filaments and isolate the gas-liquid flow path. The outer shell 4 is provided with end caps at both ends, and gas inlet 2 and gas outlet 6 are respectively provided on the end caps at both ends; on the side wall of the outer shell, a liquid inlet 1 is provided at the end near the gas inlet 2, and a liquid outlet 5 is provided at the other side wall diagonally opposite to it; wherein, the liquid inlet 1 is connected to the phosphorus trichloride delivery pipe, and the liquid outlet 5 is connected to the product outlet pipe; the gas inlet 2 is connected to the oxygen delivery pipe, and the gas outlet 6 is connected to the gas output pipe, forming an independent flow path of "gas flowing inside the membrane and liquid flowing outside the membrane"; The heat exchange unit is a hollow annular tube with a circulating medium inlet and a circulating medium outlet on the side wall. The circulating medium flows inside the annular tube, and the heat exchange unit has a material inlet and a material outlet at both ends.

[0033] In this embodiment, the outer shell has a diameter of 100 mm, and the membrane filaments 3 in the hollow fiber membrane reaction unit have a diameter of 1 mm, filling the outer shell 4.

[0034] In this invention, the membrane reactor is composed of 3-5 stages of hollow fiber membrane reaction units and heat exchange units connected in series. When used in series, the liquid inlet of the first-stage hollow fiber membrane reaction unit is connected to a phosphorus trichloride delivery pipeline, the liquid outlet of the first-stage hollow fiber membrane reaction unit is connected to the material inlet of the heat exchange unit, the material outlet of the heat exchange unit is connected to the liquid inlet of the next-stage hollow fiber membrane reaction unit, and so on, with the outlet of the last-stage heat exchange unit connected to a finished product collection device; the gas inlets of each stage of the hollow fiber membrane reaction unit are connected to oxygen delivery pipelines, and the gas outlets of each stage of the hollow fiber membrane reaction unit are connected to tail gas output pipelines. The gas pressures of each stage of the hollow fiber membrane reaction unit can be the same or different.

[0035] In this invention, the membrane reactor shell and membrane fiber holder are preferably made of polytetrafluoroethylene (PTFE), PTFE-lined steel, titanium alloy, or duplex stainless steel. In this embodiment, the shell 4 is made of industrial pure titanium, and the membrane fiber holder is made of PTFE. The hollow fiber membrane fibers are fixed between two membrane fiber holders using a fiber arranger and then fixed inside the shell. The inner diameter of the shell matches the size of the membrane fiber holder.

[0036] In this invention, a temperature monitoring port and a pressure monitoring port are also provided on the side wall of the outer shell, which are respectively connected to a temperature sensor and a pressure sensor to monitor the reaction parameters in real time.

[0037] In this invention, the membrane fiber material is selected from one or a copolymer of polytetramethylpentene, polytetrafluoroethylene, polyvinylidene fluoride, perfluoroethylene propylene, polysulfone, polyethersulfone, silicone resin, and polydimethylsiloxane.

[0038] In this embodiment, the membrane fiber material is polytetrafluoroethylene, and the pore size of the membrane fiber is 0.1-1.0 nm, with a specific surface area of ​​1500-3000 m². 2 / m 3 Preferably 2000-2500 m 2 / m 3 The oxygen permeability of the membrane fibers is 0.1-10 L / min / cm. 2 .

[0039] In this invention, the heat exchange unit is made of graphite, duplex stainless steel, or polytetrafluoroethylene (PTFE). This embodiment uses PTFE, and the internal circulating medium is flexibly selected according to the in-situ temperature control requirements, preferably heat transfer oil (preferably mineral-based or alkylbenzene-based heat transfer oil) or circulating cooling water.

[0040] This embodiment also provides a method for preparing phosphorus oxychloride based on a hollow fiber membrane reactor, comprising the following steps: Liquid phosphorus trichloride is continuously fed into the hollow fiber membrane reactor unit from the liquid inlet on the outside of the shell of the first-stage hollow fiber membrane reactor unit, while gaseous oxygen is fed in from the gas inlet at the top of the shell. During the process, oxygen in the hollow fiber membrane reactor unit escapes to the outer surface of the membrane fibers at the molecular level through the membrane fibers. The oxygen and phosphorus trichloride flowing along the membrane fibers form a "gas-membrane-liquid" three-phase interface and undergo an oxidation reaction. The reaction mixture is cooled to 40-75°C by the first-stage heat exchange unit and then enters the next-stage hollow fiber membrane reaction unit, where 30-80% of the initial flow rate of oxygen is added to continue the reaction. The final-stage reaction mixture is cooled to ≤45°C by the final-stage heat exchange unit and then continuously discharged. The material outlet of the final-stage heat exchange unit is connected to the finished product collection device to achieve 24-hour continuous operation.

[0041] The reaction temperature inside the membrane reactor is 70-95℃, preferably 85-95℃. The oxygen pressure inside the membrane reactor is 0.01-0.15 MPa, preferably 0.01-0.05 MPa. Example 2

[0042] In this embodiment, three sets of "hollow fiber membrane reaction units and heat exchange units" are connected in series to prepare phosphorus oxychloride. Oxygen is introduced into each stage of the hollow fiber membrane reaction unit at a pressure of 0.012 MPa through the internal channels of the membrane fibers (the membrane fibers are made of PTFE, with a pore size of 0.2 nm and a specific surface area of ​​2000 m²). 2 / m 3 Oxygen permeability is 4 L / min / cm 2 Adjust the pressure to maintain stability and control the molar ratio of phosphorus trichloride to oxygen to be 2:1.5; Phosphorus trichloride flows into the outer cavity of the membrane fiber through the liquid inlet and flows along the outer surface of the membrane fiber. It undergoes an oxidation reaction with molecular oxygen permeating the membrane fiber at the gas-membrane-liquid three-phase interface. The reaction temperature is 85±2℃. The heat of the reaction is exchanged by the circulating medium (320# heat transfer oil) of the heat exchange unit at 55℃. The resulting mixture flows through the secondary and tertiary reaction units to deepen the reaction. The oxygen replenishment of the secondary and tertiary reaction units is 45% and 34% of the initial flow rate, respectively. Finally, the phosphorus oxychloride product is cooled to 35℃ by the tertiary heat exchange unit and discharged from the liquid outlet.

[0043] In this embodiment, the final product has a phosphorus oxychloride content of 99.17%. Example 3

[0044] In this embodiment, four sets of "hollow fiber membrane reaction units and heat exchange units" are connected in series, with oxygen pressures at each stage being 0.014 MPa, 0.018 MPa, 0.020 MPa, and 0.025 MPa, respectively. The method for preparing phosphorus oxychloride is as follows: Oxygen is introduced into the hollow fiber membrane reactor unit (the membrane fiber is made of polysulfone, with a pore size of 0.7 nm and a specific surface area of ​​2500 m²) through the internal channels of the membrane fiber at a pressure of 0.014 MPa. 2 / m 3 Oxygen permeability is 8 L / min / cm 2 Adjust the pressure to maintain stability and control the molar ratio of phosphorus trichloride to oxygen to be 2:1.8; Phosphorus trichloride flows into the outer cavity of the membrane fiber through the liquid inlet. As it flows along the outer surface of the membrane fiber, it undergoes an oxidation reaction with molecular-level oxygen permeating the membrane fiber at the "gas-membrane-liquid" three-phase interface. The reactor temperature is controlled at 90±2℃. The reaction heat is continuously exchanged and removed by the circulating medium (320# heat transfer oil) in the heat exchange unit. The temperature of the heat exchange unit is 50℃. The generated mixture flows through the secondary to quaternary reaction units in sequence to deepen the reaction. The oxygen replenishment of the secondary to quaternary reaction units is 48%, 40%, and 35% of the initial flow rate, respectively. Finally, the phosphorus oxychloride product is cooled to 35℃ by the quaternary heat exchange unit and discharged from the liquid outlet.

[0045] In this embodiment, the final product has a phosphorus oxychloride content of 99.41%.

[0046] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A hollow fiber membrane reactor, characterized in that, It includes several hollow fiber membrane reaction units and a heat exchange unit connected in series with its liquid outlet, wherein the hollow fiber membrane reaction unit is composed of a shell and several hollow fiber membrane filaments disposed therein; Several hollow fiber membrane filaments are fixed inside the outer shell by two membrane filament fixing frames. The two membrane filament fixing frames are located at both ends of the outer shell and are sealed to the hollow fiber membrane filaments to stabilize the membrane filaments and isolate the gas-liquid flow path. The outer shell is provided with end caps at both ends, and gas inlet and gas outlet are respectively configured on the end caps at both ends; on the side wall of the outer shell, a liquid inlet is configured at the end near the gas inlet, and a liquid outlet is configured on the side wall at the opposite end; wherein, the liquid inlet is connected to the phosphorus trichloride delivery pipe, and the liquid outlet is connected to the product outlet pipe; the gas inlet is connected to the oxygen delivery pipe, and the gas outlet is connected to the gas output pipe, forming an independent flow path of "gas flowing inside the membrane and liquid flowing outside the membrane"; The heat exchange unit is a hollow annular tube with a circulating medium inlet and a circulating medium outlet on the side wall. The circulating medium flows inside the annular tube, and the heat exchange unit has a material inlet and a material outlet at both ends.

2. The hollow fiber membrane reactor according to claim 1, characterized in that, The membrane reactor consists of 3-5 stages of hollow fiber membrane reaction units and heat exchange units connected in series. When used in series, the liquid inlet of the first-stage hollow fiber membrane reaction unit is connected to the phosphorus trichloride delivery pipeline, the liquid outlet of the first-stage hollow fiber membrane reaction unit is connected to the material inlet of the heat exchange unit, the material outlet of the heat exchange unit is connected to the liquid inlet of the next-stage hollow fiber membrane reaction unit, and so on, with the outlet of the last-stage heat exchange unit connected to the finished product collection device; the gas inlets of each stage of the hollow fiber membrane reaction unit are connected to oxygen delivery pipelines, and the gas outlets of each stage of the hollow fiber membrane reaction unit are connected to the tail gas output pipeline.

3. The hollow fiber membrane reactor according to claim 2, characterized in that, The outer shell and the membrane fiber fixing frame are preferably made of polytetrafluoroethylene, steel-lined PTFE, titanium alloy or duplex stainless steel.

4. The hollow fiber membrane reactor according to claim 2, characterized in that, The outer shell is a cylindrical, sealed structure, and its inner diameter matches the size of the membrane fiber fixing frame.

5. The hollow fiber membrane reactor according to claim 2, characterized in that, The outer casing sidewall is also provided with a temperature monitoring port and a pressure monitoring port, which are respectively connected to a temperature sensor and a pressure sensor to monitor the reaction parameters in real time.

6. The hollow fiber membrane reactor according to claim 2, characterized in that, The membrane fiber material is selected from one or a copolymer of polytetramethylpentene, polytetrafluoroethylene, polyvinylidene fluoride, perfluoroethylene propylene, polysulfone, polyethersulfone, silicone resin, and polydimethylsiloxane.

7. The hollow fiber membrane reactor according to claim 2, characterized in that, The membrane filaments have a diameter of 0.1-1.0 mm, a pore size of 0.1-1.0 nm, and a specific surface area of ​​1500-3000 m². 2 / m 3 Oxygen permeability is 0.1-10 L / min / cm³. 2 .

8. The hollow fiber membrane reactor according to claim 2, characterized in that, The circulating medium in the heat exchange unit is heat transfer oil or circulating cooling water.

9. A method for preparing phosphorus oxychloride based on the hollow fiber membrane reactor according to any one of claims 2 to 8, characterized in that, The preparation method includes the following steps: Liquid phosphorus trichloride is continuously fed into the hollow fiber membrane reactor unit from the liquid inlet on the outside of the shell of the first-stage hollow fiber membrane reactor unit, while gaseous oxygen is fed in from the gas inlet at the top of the shell. During the process, oxygen in the hollow fiber membrane reactor unit escapes to the outer surface of the membrane fibers at the molecular level through the membrane fibers. The oxygen and phosphorus trichloride flowing along the membrane fibers form a "gas-membrane-liquid" three-phase interface and undergo an oxidation reaction. The reaction mixture is cooled to 40-75°C by the first-stage heat exchange unit and then enters the next-stage hollow fiber membrane reaction unit, where 30-80% of the initial flow rate of oxygen is added to continue the reaction. The final-stage reaction mixture is cooled to ≤45°C by the final-stage heat exchange unit and then continuously discharged. The material outlet of the final-stage heat exchange unit is connected to the finished product collection device to achieve 24-hour continuous operation.

10. The preparation method according to claim 9, characterized in that, The reaction temperature inside the membrane reactor is 70-95℃, and the oxygen pressure is 0.01-0.15 MPa.

Images