A continuously operated reactor and a method for preparing a crude ester

Abstract

The application discloses a continuously-operated reactor and a crude ester preparation method, and belongs to the field of chemical equipment, and solves the problems of poor mass transfer and heat transfer effect and large safety hazards of the crude ester preparation equipment in the prior art. In the application, the continuously-operated reactor is of a shell-and-tube structure, is internally provided with a material spraying pipe, a heat exchange pipe and a baffle, the heat exchange pipe is distributed around the material spraying pipe, the heat exchange area of unit volume of reaction mixture is up to 100 m2 / m3 or above, the refrigerant passes through the pipe, the reaction mixture passes through the shell, the second raw material is sprayed into the first raw material through multiple points, and the two raw materials rotate to flow and realize gradual mixing reaction; the reaction heat is rapidly removed by the refrigerant, the mass transfer and heat transfer effects are excellent, the safety hazards are eliminated, and the yield is improved.

Description

Technical Field

[0001] This invention relates to a continuously operating reactor and a method for preparing crude esters, belonging to the field of chemical equipment. Background Technology

[0002] Phosphite esters are a class of organic synthesis intermediates with wide applications, often used in the synthesis of highly efficient organophosphorus flame retardants, highly efficient, low-toxicity, broad-spectrum organophosphorus pesticides, and highly efficient phosphorus-containing antioxidants.

[0003] Phosphites include trialkyl phosphites and dialkyl phosphites, among which trimethyl phosphite, dimethyl phosphite, triethyl phosphite, and diethyl phosphite are the most widely used. These phosphites are obtained by reacting phosphorus trichloride with lower fatty alcohols (methanol or ethanol) as raw materials.

[0004] The reaction between phosphorus trichloride and lower fatty alcohols is very rapid, almost instantaneous upon contact, releasing a huge amount of heat. If the heat of reaction cannot be removed in time, it will inevitably cause the temperature of the reaction mixture itself to rise, leading to an increase in side reactions and even causing an explosion and safety accident.

[0005] Regarding reactors for synthesizing phosphites using phosphorus trichloride and methanol or ethanol as raw materials, utility model patent CN2281986Y, dated May 20, 1998, disclosed a continuous synthesis reactor for manufacturing trimethyl phosphite. This reactor is a traditional stirred reactor, with improvements to the stirring device and the addition of phosphorus trichloride nozzles, solving the mass transfer (mixing and dispersion) problem. However, it does not solve the heat transfer problem; heat transfer relies solely on the jacket. For example, in a 1 m³ reactor, the heat transfer area per unit volume of reaction mixture is only 4.6 m². The heat exchange area is far from sufficient ( / m3), inevitably leading to excessively high reaction temperatures, increased side reactions, and safety hazards. Furthermore, the yield of trimethyl phosphite is only 90%, not the claimed 95%. Invention patent CN102838632B, published on December 24, 2014, discloses a continuous production process of trimethyl phosphite using N,N-dimethylaniline, but the reactor described is still a traditional reaction vessel, suffering from the common problems of poor heat and mass transfer inherent in batch reactors. Utility model patent CN20686821 (20180112) 9U discloses a reaction vessel for the synthesis of dimethyl phosphite. The reaction vessel is still a traditional stirred reaction vessel, except that a coil is set in the reaction vessel to assist heat transfer. However, due to the limited space in the reaction vessel, the increased heat exchange area is limited, and there is a problem of poor mass transfer. On January 10, 2020, utility model patent CN209917847U disclosed a reaction device for the production of dimethyl phosphite. The reactor is a tubular reactor with two reactors connected in series. Feed is fed into the reactor, and the reactor is only used as a heat exchanger, which has a problem of poor mass transfer. In February 2018, Anhui Chemical Industry (44(1): 95-97) reported a continuous synthesis process of triethyl phosphite. The reactor is a microreactor. On June 23, 2023, invention patent application CN116272747A disclosed a device and process for the continuous preparation of trimethyl phosphite using a microchannel reactor. Microreactors have the advantages of excellent heat transfer, high yield, high production efficiency and high safety. However, microreactor technology is not mature and is currently in the laboratory research stage.

[0006] Currently, there is no satisfactory reactor available for the industrial production of phosphites, therefore it is necessary to research and design a new type of continuous operation reactor. Summary of the Invention

[0007] This invention provides a continuously operating reactor and a method for preparing crude ester, which has good mass and heat transfer effects, eliminates safety hazards, improves yield, and is suitable for industrial use.

[0008] The technical solution adopted by the present invention is a continuously operating reactor, including a cylindrical body, with openings at both ends and respectively provided with a lower end cap and an upper end cap, and a plurality of spray pipes inside the cylindrical body; the cylindrical body also includes a plurality of heat exchange pipes.

[0009] The heat exchange tubes are arranged along the length of the spray tube; the spray tubes are evenly arranged inside the cylinder, and the heat exchange tubes are arranged around the spray tubes.

[0010] The optimized reactor described above for continuous operation has a cylindrical body with openings at both ends, which are sealed by a lower head and an upper head.

[0011] The cylinder is provided with a lower flange tube sheet and an upper flange tube sheet at its two end openings, respectively.

[0012] The heat exchange tubes and the injection tubes pass through the lower flange tube sheet and the upper flange tube sheet and are fixed to the lower flange tube sheet and the upper flange tube sheet.

[0013] The optimized, continuously operating reactor described above has a second feed main pipe and a second feed loop pipe inside the upper head; the second feed loop pipe is connected to the second feed main pipe.

[0014] Of all the spray pipes, the upper end of a portion of the spray pipes is connected to the second raw material main pipe, and the upper end of another portion of the spray pipes is connected to the second raw material ring pipe; the lower end of all the spray pipes is closed.

[0015] The side of the cylinder is provided with a first raw material inlet and a crude ester outlet that communicate with the interior of the cylinder.

[0016] The optimized, continuously operating reactor described above has several baffles installed inside the cylinder, and the baffles are segmental in shape.

[0017] All baffles are spaced apart along the axis of the cylinder; the radial azimuth angles of the segmental notches of two adjacent baffles differ by 90°;

[0018] The curved edge of the baffle plate is welded and fixed to the inner wall of the cylinder.

[0019] In the optimized continuously operating reactor described above, several groups of spray holes are spaced apart on the spray pipe. Each group of spray holes includes several spray holes, and all the spray holes in the same group are evenly distributed in a ring around the outer surface of the spray pipe.

[0020] The nozzle groups near the upper end of the spray tube are spaced apart from the upper end face of the spray tube; the nozzle groups near the lower end of the spray tube are spaced apart from the lower end face of the spray tube.

[0021] In the optimized, continuously operating reactor described above, all the spray pipes are divided into several groups of spray pipes, and each group of spray pipes has at least one spray pipe.

[0022] The spray tubes of the spray tube assembly are arranged in a ring; the spray tubes of the entire spray tube assembly are arranged in concentric circles around the axis of the cylinder and from the axis of the cylinder towards the inner wall of the cylinder.

[0023] There is at least one layer of heat exchange tubes arranged in a ring between two adjacent sets of spray tubes;

[0024] In the same group of spray tubes, there is at least one heat exchange tube between two adjacent spray tubes.

[0025] In the optimized, continuously operating reactor described above, one group of spray pipes has a single spray pipe, which is a central spray pipe located in the middle of the cylinder and arranged along the axis of the cylinder.

[0026] A method for preparing crude ester based on the above-described reactor includes the following steps:

[0027] 1) Preparation: Check and confirm the condition of the reactor, and prepare the first and second raw materials;

[0028] Refrigerant is introduced into the heat exchange tubes, and the first raw material is introduced through the first raw material inlet;

[0029] 2) Reaction: When the first raw material appears at the crude ester outlet, the second raw material is introduced through the second raw material main pipe to start continuous production;

[0030] 3) Shutdown: When production is finished and shutdown is required, stop the flow of the second raw material through the second raw material main pipe and stop the flow of the first raw material through the first raw material inlet. Open the vent valve at the crude ester outlet and the drain valve at the first raw material inlet, and put the remaining material in the reactor into the crude ester receiving tank.

[0031] Stop the refrigerant supply and put the refrigerant into the circulating refrigerant storage tank.

[0032] In step 2), the reaction temperature at the crude ester outlet is observed during the production process, and the flow rates of the first and second raw materials are adjusted proportionally to control the reaction temperature.

[0033] The first raw material is a low fatty alcohol, or a homogeneous solution formed by mixing a low fatty alcohol with a solvent and an acid-binding agent;

[0034] The second raw material is phosphorus trichloride, or a homogeneous solution formed by mixing phosphorus trichloride with a solvent;

[0035] The crude ester is a crude phosphite produced by the reaction of phosphorus trichloride with lower fatty alcohols;

[0036] The phosphite is one or more of the trialkyl phosphite or dialkyl phosphite.

[0037] In the optimized method for preparing the crude ester described above, the refrigerant is a 50% ethylene glycol aqueous solution or a 25% calcium chloride aqueous solution that can be circulated at -30 to -20°C.

[0038] The advantages of this application are:

[0039] The second raw material is injected into the first raw material through multiple points. The reactants are gradually mixed during the flow process, and the heat of reaction is gradually released. The heat transfer area per unit volume of the reaction mixture is as high as 104 m2 / m3, which is 22.6 times that of the traditional reactor. The heat of reaction is quickly removed by the refrigerant, resulting in excellent heat transfer effect. This avoids the problem of local overheating caused by the instantaneous concentrated release of heat of reaction, thus eliminating safety hazards.

[0040] The baffles guide the flow, causing the reactants to rotate axially in either clockwise or counterclockwise. Combined with the dense heat exchange tubes and spray pipes guiding the radial flow, the reactants are mixed and reacted while flowing, resulting in a mild reaction, excellent mass transfer, and a yield of up to 98%.

[0041] The reactor has no rotating parts, saving energy, is not easily damaged, and has a long service life.

[0042] The reactor operates continuously, is simple to operate, and has high production efficiency, meeting the needs of large-scale industrial production. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the structure of this application;

[0044] Figure 2 for Figure 1 View from direction A;

[0045] Figure 3 for Figure 1 View from direction B;

[0046] In the diagram, the correspondence between component names and drawing numbers is as follows:

[0047] 1. Lower head; 2. Refrigerant inlet; 3. Lower head flange; 4. Lower flange gasket; 5. Lower flange tube sheet; 6. Shell; 7. Baffle plate; 8. Injector pipe; 9. Nozzle layer; 10. Expansion joint; 11. Heat exchanger tube; 12. Support; 13. Crude ester outlet; 14. Near main nozzle a; 15. Near main nozzle b; 16. Second raw material inlet; 17. Second raw material main pipe; 18. Central nozzle; 19. Spare inlet; 20. B raw material ring pipe; 21. Upper head; 22. Refrigerant outlet; 23. Upper head flange; 24. Upper flange gasket; 25. Upper flange tube sheet; 26. First raw material inlet. Detailed Implementation

[0048] The technical features of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0049] As shown in the figure, this embodiment is a continuously operating reactor. The reactor is a vertical shell-and-tube reactor, and the main body of the reactor consists of three parts: the lower head 1, the cylinder 6, and the upper head 21.

[0050] In this embodiment, both the lower end cap 1 and the upper end cap 21 are elliptical end caps, and the cylinder 6 is a cylindrical body with openings at both ends, which are closed by the lower end cap 1 and the upper end cap 21. A lower flange tube sheet 5 and an upper flange tube sheet 25 are respectively provided at the openings at both ends of the cylinder 6. Both the lower flange tube sheet 5 and the upper flange tube sheet 25 are integral flanges and tube sheets, made from a single steel plate, and serve as both flanges and tube sheets.

[0051] The upper end cap 21 has a second raw material main pipe 17 and a second raw material ring pipe 20 inside, and the second raw material ring pipe 20 is connected to the second raw material main pipe 17.

[0052] The cylinder 6 contains several spray pipes 8 and several heat exchange pipes 11. The heat exchange pipes 11 are arranged along the length of the spray pipes 8. Of all the spray pipes 8, the upper end of a portion of the spray pipes 8 is connected to the second raw material main pipe 17, the upper end of another portion of the spray pipes 8 is connected to the second raw material ring pipe 20, and the lower end of all the spray pipes 8 is closed.

[0053] In this embodiment, the spray pipe 8 is made of seamless steel pipe. Several through holes are constructed on the lower flange plate 5 and the upper flange plate 25. The lower and upper ends of the spray pipe 8 pass through these through holes on the lower flange plate 5 and the upper flange plate 25, respectively. The spray pipe 8 is fixed to the through holes on the lower flange plate 5 and the upper flange plate 25 by welding, and a seal is achieved between the outer surface of the spray pipe 8 and the through holes on the lower flange plate 5 and the upper flange plate 25 through welding or other methods. The bottom end of the spray pipe 8 is sealed, and the top end of the spray pipe 8 passes through the upper flange plate 25 and connects to the second raw material main pipe 17 or the second raw material ring pipe 20.

[0054] The heat exchange tube 11 is made of seamless steel pipe. The lower end of the heat exchange tube 11 is connected to the through hole of the lower flange tube plate 5, and the upper end of the heat exchange tube 11 is connected to the through hole of the upper flange tube plate 25 by expansion welding.

[0055] The spray pipe 8 has several sets of spray holes spaced apart. Each set of spray holes includes several spray holes, and all the spray holes in the same set are evenly distributed in a ring around the outer surface of the spray pipe 8. The spray hole sets near the upper end of the spray pipe 8 are spaced apart from the upper end face of the spray pipe 8, and the spray hole sets near the lower end of the spray pipe 8 are spaced apart from the lower end face of the spray pipe 8. In this embodiment, each spray pipe 8 has a layer of spray hole sets every 100 mm starting from 150 mm from the bottom. Each set of spray hole sets has four spray holes, which are evenly distributed. The diameter of the spray holes is Φ1, and the uppermost layer of spray holes is about 500 mm from the top of the upper flange plate 25.

[0056] All the spray pipes 8 are divided into several groups of spray pipes, each group having at least one spray pipe 8; the spray pipes 8 of the spray pipe groups are arranged in a ring; the spray pipes 8 of all the spray pipe groups are arranged in concentric circles around the axis of the cylinder 6, from the axis of the cylinder 6 towards the inner wall of the cylinder 6; there is at least one layer of heat exchange tubes 11 arranged in a ring between two adjacent groups of spray pipes; in the same group of spray pipes, there is at least one heat exchange tube 11 between two adjacent spray pipes 8. Furthermore, one group of spray pipes has one spray pipe 8, and this spray pipe 8 is the central spray pipe, which is located in the middle of the cylinder 6 and is arranged along the axis of the cylinder 6.

[0057] In this embodiment, such as Figure 2 As shown, except for the central nozzle 18 which is installed at the center of the cylinder 6 and is defined as the central layer, all the other spray pipes 8 and heat exchange pipes 11 inside the cylinder 6 are arranged in seven concentric circular layers. These seven layers are the first to the seventh layer from the center of the cylinder 6 to the outside of the cylinder 6.

[0058] All the spray pipes 8 are located in the central layer, the third layer, and the sixth layer from the inside out. The central layer has only one spray pipe, which is the central spray pipe 18. The spray pipes 8 in the third layer are evenly distributed on the ring together with the heat exchange pipes 11. The spray pipes 8 in the sixth layer are evenly distributed on the ring together with the heat exchange pipes 11.

[0059] The heat exchange tubes 11 are located on concentric circles from the first to the seventh layer, from the inside out. Except for the third and sixth layers where the heat exchange tubes 11 are combined with the spray tubes 8, the remaining layers consist of a single heat exchange tube 11 evenly distributed. Figure 2 As shown, Figure 2 In the middle, except for the round tubes marked as spray pipe 8 and center spray pipe 18, all other round tubes are heat exchange tubes 11.

[0060] Several baffles 7 are installed inside the cylinder 6. The baffles 7 are segmental in shape and are all spaced apart along the axis of the cylinder 6. The radial azimuth angles of the segmental notches of two adjacent baffles 7 differ by 90°. In this embodiment, from bottom to top, the radial azimuth angles of the notches of the baffles 7 differ by 90°. The baffles 7 are spot-welded to the outer heat exchange tube 11.

[0061] In this embodiment, as shown in the figure, the second raw material main pipe 17 is inserted into the upper end cap 21 from the second raw material pipe opening 16 located at the top of the upper end cap 21, connects to the second raw material ring pipe 20, and connects to the nearby near main nozzle a14, near main nozzle b15 and center nozzle 18. The second raw material ring pipe 20 is connected to other spray pipes 8.

[0062] The refrigerant inlet 2 is located on the lower head 1 and also serves as the refrigerant vent; a vent valve is added thereto. The refrigerant outlet 22 is located on the upper head 21 and also serves as the vent; a vent valve is added thereto.

[0063] In this application, the lower flange tube sheet 5 and the injection pipe 8 are sealed by welding, so that the interior of the lower end cap 1 forms a cavity that is only connected to the heat exchange tube 11. The refrigerant inlet 2 injects refrigerant into the lower end cap 1 and then flows into the heat exchange tube 11.

[0064] The upper flange tube sheet 25 and the spray pipe 8 are sealed by welding, the second raw material main pipe 17 and the second raw material port 16 are sealed by connection, and the upper end cap 21 is also sealed by connection with other pipe bodies, so that the upper end cap 21 forms a cavity that is only connected to the heat exchange tube 11. The refrigerant in the heat exchange tube 11 flows into the upper end cap 21 and then flows back through the refrigerant outlet 22 for recycling.

[0065] Other equipment in this application includes a first raw material inlet 26 located at the lower part of the cylinder 6, which also serves as a vent, and is equipped with a vent valve. The crude ester outlet 13 is located at the upper part of the cylinder 6, serving as a discharge outlet, observation point, temperature measurement point, and venting point, and is equipped with a sight glass, a resistance thermometer, and a vent valve.

[0066] Both the lower head flange 3 and the upper head flange 23 are type B flat-welded flanges. Both the lower flange gasket 4 and the upper flange gasket 24 are non-metallic gaskets. The expansion joint 10 is located in the middle of the cylinder 6 and is a corrugated expansion joint. The support 12 is located approximately one-third of the way up the cylinder 6 and is a symmetrical suspended type B support.

[0067] The operation method of the above reactor is as follows:

[0068] 1) Preparation: Check and confirm that the reactor is ready to start up. Prepare the first raw material and the second raw material. Introduce refrigerant into the tube side of the reactor through refrigerant inlet 2 and refrigerant outlet 22. Introduce the first raw material into the shell side through the first raw material inlet 26 at the specified flow rate.

[0069] 2) Reaction: When the sight glass of crude ester outlet 13 shows the appearance of the first raw material, the second raw material is introduced through the second raw material main pipe 17 at a specified flow rate to start continuous production. During the production process, pay attention to the reaction temperature displayed by the thermal resistance thermometer of crude ester outlet 13. The reaction temperature is indirectly controlled within the specified range by adjusting the flow rates of the first and second raw materials according to the ratio.

[0070] 3) Shutdown: When production is completed and shutdown is required, stop the flow of the second raw material through the second raw material main pipe 17, stop the flow of the first raw material through the first raw material inlet 26, open the vent valve of the crude ester outlet 13 and the drain valve of the first raw material inlet 26, put the shell side material into the crude ester receiving tank, stop the flow of refrigerant into the tube side of the reactor through the refrigerant inlet 2 and the refrigerant outlet 22, open the drain valve of the refrigerant inlet 2 and the vent valve of the refrigerant outlet 22, and put the tube side refrigerant into the circulating refrigerant storage tank.

[0071] The first raw material is a lower fatty alcohol, or a homogeneous solution formed by mixing a lower fatty alcohol with a solvent and an acid-binding agent. The second raw material is phosphorus trichloride, or a homogeneous solution formed by mixing phosphorus trichloride with a solvent. The crude ester is a crude phosphite produced by reacting phosphorus trichloride with a lower fatty alcohol. The phosphite is one or more of trialkyl phosphite or dialkyl phosphite.

[0072] In this embodiment, the refrigerant is a 50% ethylene glycol aqueous solution or a 25% calcium chloride aqueous solution that can be circulated at -30 to -20°C.

[0073] In this application, the lower head 1 of the reactor is used to distribute refrigerant to the heat exchange tubes. The upper head 21 of the reactor is used to collect refrigerant from the heat exchange tubes, and simultaneously to distribute the second raw material to each injection pipe through the second raw material main pipe 17 and the second raw material ring pipe 20.

[0074] The reactor of this invention is divided into a tube side and a shell side. The refrigerant flows through the tube side, and the reaction mixture flows through the shell side. In the shell side, the second raw material is injected into the first raw material through multiple points. Radial and axial mixing and mass transfer are achieved by the guidance of heat exchange tubes and baffles, and heat transfer is achieved by the refrigerant in the heat exchange tubes.

[0075] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should be protected by the present invention.

Claims

1. A continuously operating reactor, comprising a cylindrical body (6), with openings at both ends and respectively provided with a lower end cap (1) and an upper end cap (21), and having a plurality of spray pipes (8) inside the cylindrical body (6); characterized in that: The cylinder (6) also has several heat exchange tubes (11). The heat exchange tube (11) is arranged along the length of the spray tube (8); the spray tube (8) is evenly arranged inside the cylinder (6), and the heat exchange tube (11) is arranged around the spray tube (8). The cylinder (6) is equipped with several baffles (7), which are in the shape of a circular segment; All baffles (7) are spaced apart along the axis of the cylinder (6); the radial azimuth angles of the circular notches of two adjacent baffles (7) differ by 90°; The arc-shaped edge of the baffle (7) is welded and fixed to the inner wall of the cylinder (6); The spray pipe (8) is provided with several sets of spray holes at intervals. Each set of spray holes includes several spray holes. All the spray holes in the same set of spray holes are evenly distributed in a ring around the outer surface of the spray pipe (8). The nozzle group near the upper end of the nozzle (8) is spaced apart from the upper end face of the nozzle (8); the nozzle group near the lower end of the nozzle (8) is spaced apart from the lower end face of the nozzle (8). All the spray pipes (8) are divided into several spray pipe groups, and each spray pipe group has at least one spray pipe (8). The spray tubes (8) of the spray tube group are arranged in a ring; the spray tubes (8) of the entire spray tube group are arranged in a concentric circle around the axis of the cylinder (6) and from the axis of the cylinder (6) toward the inner wall of the cylinder (6); There is at least one layer of heat exchange tubes arranged in a ring between two adjacent sets of spray tubes (11). In the same group of spray tubes, there is at least one heat exchange tube (11) between two adjacent spray tubes (8).

2. The continuously operating reactor according to claim 1, characterized in that: The cylinder (6) is a cylindrical body with openings at both ends. The openings at both ends of the cylinder (6) are closed by the lower end cap (1) and the upper end cap (21). The cylinder (6) is provided with a lower flange tube plate (5) and an upper flange tube plate (25) at the two ends of the opening. The heat exchange tube (11) and the spray tube (8) pass through the lower flange tube sheet (5) and the upper flange tube sheet (25) and are fixed to the lower flange tube sheet (5) and the upper flange tube sheet (25).

3. The continuously operating reactor according to claim 1, characterized in that: The upper end cap (21) has a second raw material main pipe (17) and a second raw material ring pipe (20); the second raw material ring pipe (20) is connected to the second raw material main pipe (17); Of all the spray pipes (8), the upper end of a portion of the spray pipes (8) is connected to the second raw material main pipe (17), and the upper end of the other portion of the spray pipes (8) is connected to the second raw material ring pipe (20); the lower end of all the spray pipes (8) is closed. The side of the cylinder (6) is provided with a first raw material inlet (26) and a crude ester outlet (13) that communicate with the interior of the cylinder (6).

4. The continuously operating reactor according to claim 1, characterized in that: One of the spray pipe groups has a spray pipe (8) and this spray pipe (8) is the central spray pipe, which is located in the middle of the cylinder (6) and is set along the axis of the cylinder (6).

5. A method for preparing crude ester using a reactor according to any one of claims 1 to 4, characterized in that: Includes the following steps: 1) Preparation: Check and confirm the condition of the reactor, and prepare the first and second raw materials; Refrigerant is introduced into the heat exchange tube (11), and the first raw material is introduced through the first raw material inlet (26); 2) Reaction: When the first raw material appears at the crude ester outlet (13), the second raw material is introduced through the second raw material main pipe (17) to start continuous production; 3) Shutdown: When production is finished and shutdown is required, stop the supply of the second raw material through the second raw material main pipe (17), stop the supply of the first raw material through the first raw material inlet (26), open the vent valve of the crude ester outlet (13) and the drain valve of the first raw material inlet (26), and put the reactor's remaining material into the crude ester receiving tank. Stop the refrigerant supply and put the refrigerant into the circulating refrigerant storage tank; In step 2), the reaction temperature at the crude ester outlet (13) is observed during the production process, and the flow rates of the first and second raw materials are adjusted proportionally and the reaction temperature is controlled.

6. The method for preparing crude ester according to claim 5, characterized in that: The first raw material is a low fatty alcohol, or a homogeneous solution formed by mixing a low fatty alcohol with a solvent and an acid-binding agent; The second raw material is phosphorus trichloride, or a homogeneous solution formed by mixing phosphorus trichloride with a solvent; The crude ester is a crude phosphite produced by the reaction of phosphorus trichloride with lower fatty alcohols; The phosphite is one or more of the trialkyl phosphite or dialkyl phosphite.

7. The method for preparing crude ester according to claim 5, characterized in that: The refrigerant is a 50% ethylene glycol aqueous solution or a 25% calcium chloride aqueous solution that can be circulated at -30 to -20°C.

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