A kind of synthetic method of malononitrile

Abstract

The present invention belongs to the technical field of organic synthesis, and specifically relates to a method for synthesizing malononitrile. Specifically disclosed is a method for synthesizing malononitrile, which uses acetonitrile and cyanogen chloride as raw materials, reacts in a fixed bed reactor containing a solid base catalyst, separates a crude product and unreacted raw materials by condensation, recycles the unreacted raw materials, and distills the crude product to obtain a synthetic method for malononitrile. The present invention has the advantages of mild reaction conditions, simple process, convenient operation, low cost, less three wastes, and easy industrial production.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and particularly relates to a method for synthesizing malononitrile. Background Art

[0002] Malononitrile, with the chemical formula NCCH2CN, is a colorless crystalline powder, soluble in water, ethanol, benzene, and slightly soluble in chloroform and acetic acid. Malononitrile is the raw material for preparing 2-amino-4,6-dimethoxypyrimidine and 2-chloro-4,6-dimethoxypyrimidine. It can be used in pesticides to produce herbicides such as benzylsulfuron-methyl, pyrazosulfuron-methyl, nicosulfuron-methyl and bispyribac-butyl, etc. It is used in medicine to synthesize a series of important drugs such as vitamin B1, aminopterin, and triamterene, and can also be used as a gold extractant.

[0003] According to literature reports, the synthesis process of malononitrile can be roughly divided into two categories, namely, dehydration method and synthesis method.

[0004] CN107827777A provides a method of mixing cyanoacetamide, phosphorus oxychloride and solid phosgene to obtain a suspension, heating it to 50-90°C, performing a heat preservation reaction, and then performing a distillation treatment to obtain malononitrile. This method has high production cost, low yield, many wastes, difficult treatment, and expensive and difficult to obtain raw materials.

[0005] The malononitrile production technology of Mitsubishi Gas Corporation of Japan and the malononitrile production technology of Roessler AG of Germany provide a process using acetonitrile and cyanogen chloride as raw materials, with a reaction temperature of 700-1000°C. The reaction temperature is high, the equipment investment is large, the process control requirements are strict, and it is not easy to industrialize production. Summary of the invention

[0006] The present invention mainly aims to avoid the above disadvantages and provide a method for synthesizing malononitrile which has the advantages of simple process, convenient operation, low cost, less three wastes and easy industrial production.

[0007]

[0008] The steps of the present invention include the following:

[0009] The raw materials acetonitrile and cyanogen chloride are heated and gasified, and then introduced into a fixed bed reactor filled with a solid base catalyst. The temperature of the reactor is controlled at 200-500°C, and the reaction pressure is controlled at 1-15Mpa.

[0010] The molar ratio of the raw materials acetonitrile and cyanogen chloride is 1-15:1.

[0011] The solid base catalyst is selected from Cd(OAc)2 / Al2O3, Cd(OAc)2 / NaY, Ca(OAc)2 / Al2O3, Ca(OAc)2 / NaY, CaO / NaY, Li2CO3 / NaY, Li2CO3 / Al2O3, Li2CO3 / NaY, Pb(OAc)2 / Al2O3, Pb(OAc)2 / NaY, Mg(OAc)2 / Al2O3, MgO / Al2O3, Mg(O Ac)2 / NaY, LiOH / NaY, NaOH / artificial zeolite, NaOH / Al2O3, KNO3 / TiO2, KF / TiO2, K2CO3 / TiO2, K2CO3 / Al2O3, KF / Al2O3, KF / ZnO, Mn(NO3)2 / artificial zeolite, Mn(OAc)2 / Al2O3, Mn(OAc)2 / NaY, Zn(OAc)2 / Al2O3, Zn(OAc)2 / NaY.

[0012] The catalyst is preferably Cd(OAc)2 / Al2O3, Ca(OAc)2 / Al2O3, Li2CO3 / Al2O3, Mg(OAc)2 / Al2O3, NaOH / Al2O3, Mn(OAc)2 / NaY, Cd(OAc)2 / NaY, K2CO3 / Al2O3, KF / Al2O3.

[0013] The reaction temperature is 200-500°C, preferably 280-400°C.

[0014] The reaction pressure is 1-15 MPa, preferably 5-10 MPa.

[0015] In the prior art, the conventional reaction temperature of this route is basically 700-1000°C, which is relatively high. However, after the present invention adopts the above catalyst and fixed bed reactor, the reaction temperature is greatly reduced and the reaction efficiency is improved.

[0016] More preferably, the reaction of the present invention is carried out using a continuous production process system, and the continuous production process system is specifically as follows: the continuous production process device includes a first raw material feed pump and a second raw material feed pump connected in parallel to a mixer according to the direction of the reaction materials, the mixer is subsequently connected to a first heat exchanger, and then to a first heating furnace, and then to a first fixed bed reactor, the outlet of the first fixed bed reactor is connected to the first heat exchanger through a pipeline and then to a gas-liquid separator, the liquid phase outlet of the gas-liquid separator is connected to a distillation tower via a product output pump; the gas phase outlet of the gas-liquid separator is connected to a low-temperature gas-liquid separator via a condenser, the liquid phase outlet of the low-temperature gas-liquid separator is connected to a second heat exchanger via a two-stage feed pump, and then to a second fixed bed reactor via a second heating furnace, and the outlet of the second fixed bed reactor is connected to the outlet pipeline of the first fixed bed reactor.

[0017] The outlet of the first fixed bed reactor is connected to the gas-liquid separator by a pipeline, and a regulating valve is provided, through which the heat exchange efficiency or the post-reaction material processing efficiency can be controlled by adjusting whether (or how much) the post-reaction material passes through the heat exchanger.

[0018] The distillation tower is provided with a reflux tank.

[0019] The process steps of the above continuous production process system specifically include:

[0020] (1) The raw materials acetonitrile and cyanogen chloride are heated and gasified, and then introduced into a first fixed bed reactor filled with a solid base catalyst. The reactor temperature is controlled at 200-500° C., and the reaction pressure is controlled at 1-15 MPa.

[0021] (2) After passing through the first fixed bed reactor, the reaction mixture is passed through a heat exchanger to be cooled to 100-200°C, and then enters a gas-liquid separator to separate the liquid product malononitrile and send it to a distillation tower for refined product. The uncondensed gas phase is passed through a condenser to continue cooling to 0-10°C, and then enters a low-temperature gas-liquid separator to discharge the by-product hydrogen chloride gas. The liquid raw material is pumped into a heat exchanger and a heating furnace for gasification and then enters a second fixed bed reactor. The reaction mixture is mixed with the reaction material of the first fixed bed reactor for a cyclic reaction.

[0022] The reaction temperature of the first fixed bed reactor and the second fixed bed reactor is set to 200-500°C, preferably 280-400°C.

[0023] The reaction temperature of the first fixed bed reactor and the second fixed bed reactor are set to a reaction pressure of 1 to 15 MPa, preferably 5 to 10 MPa.

[0024] The fixed bed reactor continuously feeds and discharges materials, and the conversion rate is difficult to reach 100%. In order to improve the utilization rate of raw materials, the residual raw materials are separated and recycled into the second fixed bed reactor for reaction. If the raw materials enter the first fixed bed reactor, part of the raw materials have been reacted, and the raw material ratio cannot be controlled. A separate fixed bed reaction is used to react the residual raw materials.

[0025] This route uses a fixed bed catalyst to lower the reaction temperature and make the reaction milder. The device described in this article reuses the raw materials that have not reacted completely, improves the utilization rate of the product and reduces the cost. At the same time, the heat exchanger and other devices set therein make full use of the waste heat resources in the reaction process, provide part of the heat energy for the overall reaction cycle, and maximize the recycling of heat energy resources.

[0026] The acetonitrile and cyanogen chloride feeds are controlled at low temperature as liquid feeds, pumped into the mixer for mixing, and enter the first heating furnace after heat exchange in the first heat exchanger. They are heated to a specified temperature in the first heating furnace, enter the reactor from the top of the first reactor, leave the first reactor from the bottom after the reaction, and mix with the mixture output from the second reactor.

[0027] The output mixture cooled by the first heat exchanger enters the gas-liquid separator, and the product is output from the lower layer. It enters the distillation tower through the product pump for further separation and refinement. The gas phase passes through the condenser and enters the low-temperature gas-liquid separator.

[0028] After passing through the low-temperature gas-liquid separator, the by-product hydrogen chloride gas is released from the upper layer, and the incompletely reacted raw materials are separated from the lower layer. Under the action of the pump, it re-enters the second heat exchanger for heat exchange and then enters the second heating furnace. It is heated to the specified temperature in the second heating furnace and enters the reactor from the upper part of the second reactor. After the reaction, it leaves the second reactor from the bottom and mixes with the mixture produced by the first reactor. After separation in the distillation tower, the pure product of malononitrile is output from the upper layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the continuous production process system in this application;

[0030] Figure 2 GC spectrum of malononitrile in Example 1;

[0031] Figure 3 The MS spectrum of malononitrile in Example 1;

[0032] Figure 4 The HNMR spectrum of malononitrile in Example 1;

[0033] Figure 5 Schematic diagram of the reaction system used in Comparative Example 1;

[0034] in, Figure 1 In: 1. first heating furnace, 2. first fixed bed reactor, 3. second fixed bed reactor, 4. second heating furnace, 5. gas-liquid separator, 6. low-temperature gas-liquid separator, 7. first heat exchanger, 8. condenser, 9. second heat exchanger, 10. first raw material feed pump, 11. second raw material feed pump, 12. product output pump, 13. second-stage feed pump, 14. distillation tower, 15. reflux tank, 16. mixer, 17. regulating valve;

[0035] Figure 5 In: 1. Feed pump ①, 2. Product pump, 3. Separator bottom pump, 4. Second-stage raw material tank, 5. Reflux tank ①, 6. Gas-liquid separator, 7. Tubular reactor, 8. Tubular reactor cooling section, 9. Distillation tower ①, 10. Distillation tower ②, 11. Feed pump ②, 12. Feed pump ③, 13. Mixer, 14. Reflux tank ②. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0037] Example 1

[0038] Acetonitrile (1.10 L / min, 21.19 mol / min) is pumped into the mixer (16) by the first raw material feed pump (10), and cyanogen chloride (0.50 L / min, 9.92 mol / min) is pumped into the mixer by the second raw material feed pump (11). The two materials are fully mixed in the mixer, and then enter the first heating furnace (1) after heat exchange in the first heat exchanger (7). The materials are heated to 280° C. in the first heating furnace (1) and enter the first fixed bed reactor (2) filled with Cd(OAc)2 / NaY from the top. The temperature of the fixed bed reactor is controlled at 280° C., and the reaction pressure is controlled at 5 MPa. After the reaction, the product leaves the first fixed bed reactor (2) from the bottom, mixes with the mixture produced by the second fixed bed reactor (3), and then enters the first heat exchanger (7) to be cooled to 100°C, and then enters the gas-liquid separator (5). The liquid product malononitrile is separated and pumped into the distillation tower (14) for distillation. The gas phase enters the condenser (8) to be cooled to 0°C, and enters the low-temperature gas-liquid separator (6). The by-product hydrogen chloride gas is separated and enters the acid gas treatment device. The liquid raw material that has not reacted completely is pumped into the second heat exchanger (9) through the second-stage feed pump (13), and then enters the second heating furnace (4) to be heated to 280°C, and then enters the second fixed bed reactor (3) for cyclic reaction.

[0039] The purity of the purified malononitrile obtained in this example is 98.6%, and the single conversion rate is 36.2% (calculated as cyanogen chloride). Figure 2-4 Shown: MS M + =66; 1 H NMR (500MHz, DMSO-d6) δ4.43 (s, 1H).

[0040] Example 2

[0041] Acetonitrile (2.10 L / min, 40.46 mol / min) is pumped into the mixer (16) by the first raw material feed pump (10), and cyanogen chloride (0.50 L / min, 9.92 mol / min) is pumped into the mixer by the second raw material feed pump (11). The two materials are fully mixed in the mixer, and then enter the first heating furnace (1) after heat exchange in the first heat exchanger (7). The materials are heated to 310°C in the first heating furnace (1) and enter the first fixed bed reactor (2) filled with Mn(NO3)2 / artificial zeolite from the top. The temperature of the fixed bed reactor is controlled at 310°C, and the reaction pressure is controlled at 6Mpa. After the reaction, the product leaves the first fixed bed reactor (2) from the bottom, mixes with the mixture produced by the second fixed bed reactor (3), and then enters the first heat exchanger (7) to be cooled to 120° C., and then enters the gas-liquid separator (5). The liquid product malononitrile is separated and pumped into the distillation tower (14) for distillation. The gas phase enters the condenser (8) to be cooled to 2° C., enters the low-temperature gas-liquid separator (6), separates the byproduct hydrogen chloride gas, and enters the acid gas treatment device. The liquid raw material that has not reacted completely is pumped into the second heat exchanger (9) through the second-stage feed pump (13), and then enters the second heating furnace (4) to be heated to 310° C., and then enters the second fixed bed reactor (3) for cyclic reaction.

[0042] The purity of the purified malononitrile obtained in this example is 97.9%, and the single conversion rate is 41.8% (calculated as cyanogen chloride).

[0043] Example 3

[0044] Acetonitrile (3.20 L / min, 61.66 mol / min) is pumped into the mixer (16) by the first raw material feed pump (10), and cyanogen chloride (0.50 L / min, 9.92 mol / min) is pumped into the mixer by the second raw material feed pump (11). The two materials are fully mixed in the mixer, and then enter the first heating furnace (1) after heat exchange in the first heat exchanger (7). The materials are heated to 340° C. in the first heating furnace (1) and enter the first fixed bed reactor (2) filled with KNO3 / TiO2 from the top. The temperature of the fixed bed reactor is controlled at 340° C., and the reaction pressure is controlled at 7 MPa. After the reaction, the product leaves the first fixed bed reactor (2) from the bottom, mixes with the mixture produced by the second fixed bed reactor (3), and then enters the first heat exchanger (7) to be cooled to 140° C., and then enters the gas-liquid separator (5). The liquid product malononitrile is separated and pumped into the distillation tower (14) for distillation. The gas phase enters the condenser (8) to be cooled to 4° C., enters the low-temperature gas-liquid separator (6), separates the byproduct hydrogen chloride gas, and enters the acid gas treatment device. The liquid raw material that has not reacted completely is pumped into the second heat exchanger (9) through the second-stage feed pump (13), and then enters the second heating furnace (4) to be heated to 340° C., and then enters the second fixed bed reactor (3) for cyclic reaction.

[0045] The purity of the purified malononitrile obtained in this example is 98.8%, and the single conversion rate is 48.7% (calculated as cyanogen chloride).

[0046] Example 4

[0047] Acetonitrile (4.20 L / min, 80.92 mol / min) is pumped into the mixer (16) by the first raw material feed pump (10), and cyanogen chloride (0.50 L / min, 9.92 mol / min) is pumped into the mixer by the second raw material feed pump (11). The two materials are fully mixed in the mixer, and then enter the first heating furnace (1) after heat exchange in the first heat exchanger (7). The materials are heated to 370° C. in the first heating furnace (1) and enter the first fixed bed reactor (2) filled with NaOH / Al2O3 from the top. The temperature of the fixed bed reactor is controlled at 370° C., and the reaction pressure is controlled at 9 MPa. After the reaction, the product leaves the first fixed bed reactor (2) from the bottom, mixes with the mixture produced by the second fixed bed reactor (3), enters the first heat exchanger (7), is cooled to 150°C, is sent to the gas-liquid separator (5), and the liquid phase product malononitrile is pumped into the distillation tower (14) for distillation; the gas phase is passed into the condenser (8) to be cooled to 5°C, enters the low-temperature gas-liquid separator (6), and the by-product hydrogen chloride gas is separated and enters the acid gas treatment device; the liquid phase raw material that has not reacted completely is pumped into the second heat exchanger (9) through the second-stage feed pump (13), and then enters the second heating furnace (4) to be heated to 370°C, and is passed into the second fixed bed reactor (3) for cyclic reaction.

[0048] The purity of the purified malononitrile obtained in this example is 99.1%, and the single conversion rate is 64.3% (calculated as cyanogen chloride).

[0049] Example 5

[0050] Acetonitrile (5.50 L / min, 105.98 mol / min) is pumped into the mixer (16) by the first raw material feed pump (10), and cyanogen chloride (0.50 L / min, 9.92 mol / min) is pumped into the mixer by the second raw material feed pump (11). The two materials are fully mixed in the mixer, and then enter the first heating furnace (1) after heat exchange in the first heat exchanger (7). The materials are heated to 400° C. in the first heating furnace (1) and enter the first fixed bed reactor (2) filled with K2CO3 / Al2O3 from the top. The temperature of the fixed bed reactor is controlled at 400° C., and the reaction pressure is controlled at 10 MPa. After the reaction, the product leaves the first fixed bed reactor (2) from the bottom, mixes with the mixture produced by the second fixed bed reactor (3), and then enters the first heat exchanger (7) to be cooled to 110° C., and then enters the gas-liquid separator (5). The liquid product malononitrile is separated and pumped into the distillation tower (14) for distillation. The gas phase enters the condenser (8) to be cooled to 3° C., enters the low-temperature gas-liquid separator (6), separates the byproduct hydrogen chloride gas, and enters the acid gas treatment device. The liquid raw material that has not reacted completely is pumped into the second heat exchanger (9) through the second-stage feed pump (13), and then enters the second heating furnace (4) to be heated to 400° C., and then enters the second fixed bed reactor (3) for cyclic reaction.

[0051] The purity of the purified malononitrile obtained in this example is 99.4%, and the single conversion rate is 70.9% (calculated as cyanogen chloride).

[0052] Comparative Example 1

[0053] Use Figure 5 The reaction system shown is used for the synthesis of malononitrile:

[0054] Acetonitrile (4.20 L / min, 80.92 mol / min) is pumped into the mixer by raw material feed pump ②, and cyanogen chloride (0.50 L / min, 9.92 mol / min) is pumped into the mixer by raw material feed pump ③. After the two materials are fully mixed in the mixer, they are introduced into the tubular reactor. The reaction temperature is 800°C. After coming out of the reactor, they are cooled to 0°C through the tubular reactor and enter the gas-liquid separator to separate the by-product hydrochloric acid gas. The by-product hydrochloric acid gas enters the acid gas treatment device. The liquid is pumped into the distillation tower ① through the bottom pump of the separator. The unreacted raw material at the top of the distillation tower is pumped into the reactor by the feed pump ① after passing through the raw material tank. The product malononitrile enters the distillation tower ② from the bottom of the tower for refining.

[0055] The purity of the purified malononitrile product obtained in this comparative example is 98.6%, and the single conversion rate is 26.2% (calculated as cyanogen chloride).

[0056] The process reaction temperature of Comparative Example 1 is relatively high, which is not conducive to industrial production, and the single conversion rate of the product is relatively low.

[0057] Comparative Example 2

[0058] Using the system of the present invention, Figure 1 The synthesis of malononitrile is carried out without a catalyst:

[0059] Acetonitrile (3.20 L / min, 61.66 mol / min) is pumped into the mixer (16) by the first raw material feed pump (10), and cyanogen chloride (0.50 L / min, 9.92 mol / min) is pumped into the mixer by the second raw material feed pump (11). The two materials are fully mixed in the mixer, and then enter the first heating furnace (1) after heat exchange in the first heat exchanger (7). The materials are heated to 900° C. in the first heating furnace (1) and enter the first fixed bed reactor (2) from the top. The temperature of the fixed bed reactor is controlled at 900° C., and the reaction pressure is controlled at 8 MPa. After the reaction, the product leaves the first fixed bed reactor (2) from the bottom, mixes with the mixture produced by the second fixed bed reactor (3), and then enters the first heat exchanger (7) to be cooled to 140°C, and then enters the gas-liquid separator (5). The liquid product malononitrile is separated and pumped into the distillation tower (14) for distillation. The gas phase enters the condenser (8) to be cooled to 4°C, and enters the low-temperature gas-liquid separator (6). The by-product hydrogen chloride gas is separated and enters the acid gas treatment device. The liquid raw material that has not reacted completely is pumped into the second heat exchanger (9) through the second-stage feed pump (13), and then enters the second heating furnace (4) to be heated to 900°C, and then enters the second fixed bed reactor (3) for cyclic reaction.

[0060] The purity of the purified malononitrile obtained in this comparative example is 98.2%, and the single conversion rate is 19.1% (calculated as cyanogen chloride).

[0061] Comparative Example 3

[0062] In an autoclave, add acetonitrile (100.00g, 2.44mol), hydrogen cyanide (18.45g, 0.3mol), add catalyst K2CO3 / Al2O3 (1.18g), slowly raise the temperature to 340°C, control the pressure to 7Mpa, react for 0.5-1h, and the raw material conversion rate is 49.3% (monitor the reaction by gas chromatography). After the reaction is completed, filter to remove the catalyst, recover the solvent at normal pressure, and obtain the product by vacuum distillation.

[0063] The purity of the purified malononitrile obtained in this comparative example is 98.1%, and the product yield is 41.6% (calculated as cyanogen chloride).

[0064] Comparative Example 4

[0065] Cyanoacetamide (84.00 g, 1.00 mol), salt (67.00 g, 1.15 mol) and dichloroethane (330 mL) were stirred and mixed for 15 min, and then phosphorus oxychloride (90.30 g, 0.59 mol) was added, heated to reflux, and after the reaction was completed, cooled to room temperature and filtered. The filter cake was washed with dichloroethane (50 mL), and the filtrate was combined. The solvent was recovered under normal pressure and the product was obtained by vacuum distillation.

[0066] The purity of the purified malononitrile obtained in this comparative example is 98.2%, and the yield is 53.3%.

[0067] Comparative Example 4 is a traditional synthesis process of malononitrile, which has many wastes, low yield and high cost.

[0068] Although the present invention has been described in detail by referring to the accompanying drawings and in combination with the preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and these modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art who is familiar with the present invention may easily think of changes or substitutions within the technical scope disclosed by the present invention, and all of these shall be within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection described in the claims.

Claims

1. A method for synthesizing malononitrile, characterized in that: The synthesis steps include: heating and gasifying raw materials acetonitrile and cyanogen chloride, and passing them into a fixed bed reactor equipped with a solid base catalyst, wherein the reactor temperature is controlled at 200-500° C., and the reaction pressure is controlled at 1-15 MPa, wherein the molar ratio of the raw materials acetonitrile and cyanogen chloride is 1-15:1; and the solid base catalyst is selected from Cd(OAc)2 / Al2O3, Cd(OAc)2 / NaY, Ca(OAc)2 / Al2O3, Ca(OAc)2 / NaY, CaO / NaY, Li2CO3 / NaY, Li2CO3 / Al2O3, Li2CO3 / NaY, Pb(OAc)2 / Al2O3, Pb(OAc)2 / NaY, Mg(OAc)2 / Al2O3, MgO / Al2O3, Mg(OAc)2 / NaY, LiOH / NaY, NaOH / artificial zeolite, NaOH / Al2O3, KNO3 / TiO2, KF / TiO2, K2CO3 / TiO2, K2CO3 / Al2O3, KF / Al2O3, KF / ZnO, Mn(NO3)2 / artificial zeolite, Mn(OAc)2 / Al2O3, Mn(OAc)2 / NaY, Zn(OAc)2 / Al2O3, Zn(OAc)2 / NaY.

2. The method for synthesizing malononitrile according to claim 1, characterized in that The catalyst is selected from Cd(OAc)2 / Al2O3, Ca(OAc)2 / Al2O3, Li2CO3 / Al2O3, Mg(OAc)2 / Al2O3, NaOH / Al2O3, Mn(OAc)2 / NaY, Cd(OAc)2 / NaY, K2CO3 / Al2O3, and KF / Al2O3.

3. The method for synthesizing malononitrile according to claim 1, characterized in that The reaction temperature is 280-400°C.

4. The method for synthesizing malononitrile according to claim 1, characterized in that The reaction pressure is 5-10 MPa.

5. The method for synthesizing malononitrile according to claim 1, characterized in that The reaction is carried out using a continuous production process system, and the continuous production process system is specifically as follows: the continuous production process device includes a first raw material feed pump and a second raw material feed pump connected in parallel to a mixer according to the direction of the reaction materials, the mixer is subsequently connected to a first heat exchanger, then connected to a first heating furnace, and then connected to a first fixed bed reactor, the outlet of the first fixed bed reactor is connected to the first heat exchanger through a pipeline and then connected to a gas-liquid separator, the liquid phase outlet of the gas-liquid separator is connected to a distillation tower via a product output pump; the gas phase outlet of the gas-liquid separator is connected to a low-temperature gas-liquid separator via a condenser, the liquid phase outlet of the low-temperature gas-liquid separator is connected to a second heat exchanger via a two-stage feed pump, and then connected to a second fixed bed reactor via a second heating furnace, and the outlet of the second fixed bed reactor is connected to the outlet pipeline of the first fixed bed reactor.

6. The method for synthesizing malononitrile according to claim 5, characterized in that The outlet of the first fixed bed reactor is connected to the gas-liquid separator through a pipeline and is provided with a regulating valve; the distillation tower is provided with a reflux tank.

7. The method for synthesizing malononitrile according to claim 5, characterized in that: The process steps of the continuous production process system include: (1) The raw materials acetonitrile and cyanogen chloride are heated and gasified, and then introduced into a first fixed bed reactor filled with a solid base catalyst, the reactor temperature is controlled at 200-500°C, and the reaction pressure is controlled at 1-15 MPa; (2) After passing through the first fixed bed reactor, the reaction mixture is passed through a heat exchanger to be cooled to 100-200°C, and then enters a gas-liquid separator to separate the liquid product malononitrile and send it to a distillation tower for refined product. The uncondensed gas phase is passed through a condenser to continue cooling to 0-10°C, and then enters a low-temperature gas-liquid separator to discharge the by-product hydrogen chloride gas. The liquid raw material is pumped into a heat exchanger and a heating furnace for gasification and then enters a second fixed bed reactor. The reaction mixture is mixed with the reaction material of the first fixed bed reactor for a cyclic reaction.

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