Method for preparing malononitrile through catalysis

Abstract

The invention relates to a method for preparing malononitrile through catalysis, and belongs to organic synthesis. The reaction formula is as follows; wherein R is H or alkyl of C1-C6; the specific preparation method comprises the following steps: (1) heating a compound shown as a formula I, and introducing the heated compound and ammonia gas into a fixed bed reactor filled with a catalyst for reaction; (2) condensing the reaction mixture obtained in the step (1), performing gas-liquid separation, and collecting liquid; and (3) carrying out negative pressure rectification on the liquid collected in the step (2) to obtain malononitrile. According to the method for preparing malononitrile through catalysis, cyanoacetic acid or ester thereof and ammonia gas are subjected to a catalytic dehydration reaction, and malononitrile can be synthesized in one step. According to the method, highly toxic raw materials are not used, the synthesis steps are short, the reaction conditions are mild, the raw materials can be recycled, the yield is high, and the method has good practicability and economical efficiency and is convenient for industrial production.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and more specifically to a method for catalytically preparing malononitrile. Background Technology

[0002] Malononitrile, also known as cyanoacetonitrile or dicyanomethane, is a colorless crystalline powder with a maximum temperature of 32-34℃, a minimum temperature of 220℃, and a maximum temperature of 112℃. It has a relative density of 1.049 and a refractive index of 1.4150. It is soluble in water, ethanol, and benzene, and slightly soluble in chloroform and acetic acid.

[0003] In pesticide applications, malononitrile is a raw material for the preparation of 2-amino-4,6-dimethoxypyrimidine and 2-chloro-4,6-dimethoxypyrimidine. It can be used to produce sulfonylurea herbicides such as bensulfuron-methyl, pyrimisulfuron-methyl, and nicosulfuron-methyl, and can also be used to manufacture other types of herbicides such as bispyribac-sodium. In pharmaceutical applications, malononitrile is commonly used to synthesize a series of important drugs such as vitamin B1, aminopterin, triamterene, and diuretics. In dye applications, malononitrile can be used to synthesize cyanide-containing dyes. At the same time, malononitrile also has important applications in metal corrosion prevention and crosslinking agents.

[0004] The synthesis methods for malononitrile include the propadiene oxidation ammonolysis method, the acetonitrile chlorocyanide gas-phase method, the acetonitrile high-temperature pyrolysis method, the acrylonitrile and aminoacetonitrile method, the cyanoacetate amination elimination method, and the diethyl malonate amination elimination method. These synthesis processes can be broadly classified into two categories: synthetic methods and dehydration methods. Synthetic methods require harsh conditions such as high temperature and high pressure, and use highly toxic substances such as hydrogen cyanide and chlorocyanide. Dehydration methods are complex, involve long steps, and generate a lot of waste. Therefore, both synthetic and dehydration methods face numerous challenges in industrial production. Summary of the Invention

[0005] To address the technical problems of harsh reaction conditions and the need to use highly toxic substances in existing malononitrile production processes, this invention provides a catalytic method for preparing malononitrile, thereby solving the aforementioned problems.

[0006] The technical solution of this invention is as follows: In a first aspect, the present invention provides a method for the catalytic preparation of malononitrile, wherein the reaction formula is as follows: ; Wherein R is H or a C1~C6 alkyl group; The specific preparation method is as follows: (1) The compound of formula I is heated and then introduced into a fixed-bed reactor containing a catalyst along with ammonia gas to carry out the reaction; (2) The reaction mixture obtained in step (1) is condensed and then subjected to gas-liquid separation to collect the liquid; (3) The liquid collected in step (2) is subjected to negative pressure distillation to obtain malononitrile.

[0007] The catalyst is at least one selected from PdCl2, Pd(OAc)2, Pd(OH)2, PdO, CuCl, CuCl2, Cu(OAc)2, CuO, Cu2O, V2O5, Al2O3, ZrO2, RuO2, RuCl3, Ru(OAc)3, Rh2O3, Rh(OAc)3, Rh2(OAc)4, RhCl3, MoO, Fe2O3, CoO, or NiO.

[0008] Furthermore, the molar ratio of compound I to ammonia is 1:3 to 50.

[0009] Furthermore, the catalyst is at least one selected from PdO, CuO, Cu2O, V2O5, Al2O3, ZrO2, RuO2, Rh2O3, MoO, Fe2O3, CoO, or NiO.

[0010] Furthermore, the catalyst is a spherical catalyst with a diameter of 2-5 mm.

[0011] Furthermore, the catalyst is at least one of PdCl2, Pd(OAc)2, Pd(OH)2, CuCl, CuCl2, Cu(OAc)2, RuCl3, Ru(OAc)3, Rh(OAc)3, Rh2(OAc)4, or RhCl3.

[0012] Furthermore, the catalyst is a supported spherical catalyst with a diameter of 2-5 mm, and the support is alumina, zeolite, or molecular sieve.

[0013] Furthermore, in step (1), the reaction temperature is 150℃~450℃.

[0014] Furthermore, in step (1), the reaction pressure is 2 MPa to 25 MPa.

[0015] Furthermore, the production apparatus for the catalytic preparation of malononitrile includes a fixed-bed reactor I, a fixed-bed reactor II, a gas-liquid separator, and a negative-pressure distillation column; the inlet of the fixed-bed reactor I is connected to a heater and a heating furnace I, respectively; the inlet of the heater is connected to a vaporizer, which is used to heat liquid ammonia to vaporize it; the inlet of the heating furnace I is connected to a feed pump via a pipeline, which passes through heat exchanger I; the bottom outlet of the fixed-bed reactor I is connected to the gas-liquid separator via a pipeline, which passes through heat exchanger I and heat exchanger II in sequence; the gas-liquid... The top outlet of the separator is connected to the inlet of fixed-bed reactor one, and an ammonia compression circulation pump is provided between the gas-liquid separator and fixed-bed reactor one; the bottom outlet of the gas-liquid separator is connected to heater two, and a product pump is provided between the gas-liquid separator and heater two; the gas-liquid separator is connected to a negative pressure distillation column; the outlet of the negative pressure distillation column is connected to a buffer tank; the top outlet of the negative pressure distillation column is connected to a reflux tank; the bottom outlet of the negative pressure distillation column is connected to the inlet of fixed-bed reactor two, and a distillation column bottom pump is provided between the negative pressure distillation column and fixed-bed reactor two.

[0016] Furthermore, the fixed-bed reactor is configured as a multi-layer reactor, with each layer connected to a heater for introducing ammonia gas to react with the compound of formula I. This facilitates control of the reaction pressure, reaction temperature, and amount of ammonia gas used.

[0017] Furthermore, the fixed-bed reactor II is connected to a heater for introducing ammonia gas to continue the reaction with the unreacted intermediate.

[0018] The beneficial effects of this invention are as follows: The present invention provides a method for the catalytic preparation of malononitrile, which utilizes a catalytic dehydration reaction of cyanoacetic acid or its ester with ammonia to synthesize malononitrile in one step. This invention avoids the use of highly toxic raw materials, has a short synthesis process, mild reaction conditions, allows for the recycling of raw materials, and achieves high yield. It possesses excellent practicality and economic efficiency, facilitating industrial production. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the production apparatus for preparing malononitrile in Embodiment 1 of the present invention.

[0021] In the diagram, 1-vaporizer, 2-heater, 3-heater furnace one, 4-fixed bed reactor one, 5-fixed bed reactor two, 6-gas-liquid separator, 7-heater furnace two, 8-negative pressure distillation column, 9-reflux tank, 10-buffer tank, 11-raw material pump, 12-heat exchanger one, 13-heat exchanger two, 14-product pump, 15-bottom pump of distillation column, 16-ammonia compression circulation pump. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0023] In the following examples, the diameter of the spherical catalyst is 2-5 mm, and the loading of the supported spherical catalyst is 1%~6%.

[0024] Example 1 A production apparatus for the catalytic preparation of malononitrile includes a fixed-bed reactor 4, a second fixed-bed reactor 5, a gas-liquid separator 6, and a negative-pressure distillation column 8. The inlet of the first fixed-bed reactor 4 is connected to a heater 2 and a furnace 3. The inlet of the heater 2 is connected to a vaporizer 1, which is used to heat liquid ammonia and vaporize it. The inlet of the furnace 3 is connected to a feed pump 11 via a pipe, which passes through a heat exchanger 12. The bottom outlet of the first fixed-bed reactor 4 is connected to the gas-liquid separator 6 via a pipe, which passes sequentially through heat exchanger 12 and heat exchanger 23. The gas-liquid separator 6... The top outlet of the gas-liquid separator 6 is connected to the inlet of the fixed-bed reactor 4. An ammonia compression circulation pump 16 is provided between the gas-liquid separator 6 and the fixed-bed reactor 4. The bottom outlet of the gas-liquid separator 6 is connected to the heating furnace 7. A product pump 14 is provided between the gas-liquid separator 6 and the heating furnace 7. The gas-liquid separator 6 is connected to the negative pressure distillation column 8. The outlet of the negative pressure distillation column 8 is connected to the buffer tank 10. The top outlet of the negative pressure distillation column 8 is connected to the reflux tank 9. The bottom outlet of the negative pressure distillation column 8 is connected to the inlet of the fixed-bed reactor 5. A distillation column bottom pump 15 is provided between the negative pressure distillation column 8 and the fixed-bed reactor 5.

[0025] In fixed-bed reactor 1 (4), the catalyst loading rate is 60–120 cm³. In fixed-bed reactor 2 (5), the catalyst loading rate is 30–60 cm³.

[0026] The method for catalytically preparing malononitrile according to the present invention is as follows: liquid ammonia is vaporized into ammonia gas after passing through vaporizer 1, and then heated by heater 2 before entering fixed-bed reactor 4. Compound of formula I is transported to heating furnace 3 by raw material pump 11 for heating, and after being heated, it enters fixed-bed reactor 4. After reacting with ammonia gas, the reaction liquid is discharged from the bottom outlet of fixed-bed reactor 4, passes through heat exchanger 12, exchanges heat with compound of formula I to reduce the temperature of the reaction liquid, and at the same time preheats compound of formula I; the cooled reaction liquid passes through heat exchanger 2 13 again for further heating. After cooling, the mixture enters the gas-liquid separator. The ammonia in the reaction liquid is separated and re-enters the fixed-bed reactor 4 to continue reacting with the subsequent compound of formula I. The liquid is transferred to the heating furnace 7 by the product pump 14, and after heating, it enters the negative pressure distillation column 8 for purification. The upper light component is the by-product, the middle component is the product malononitrile, and the lower heavy component is separated into the remaining product and intermediates. The heavy component is sent to the fixed-bed reactor 5 by the bottom pump 15 of the distillation column for re-reaction, and then enters the gas-liquid separator 6 together with the reaction liquid produced by the fixed-bed reactor 4.

[0027] Example 2 In the production apparatus of Example 1, malononitrile was prepared. The specific method is as follows:

[0028] Fixed-bed reactor 4 and fixed-bed reactor 5 are filled with supported spherical catalysts of palladium chloride supported on alumina, with a palladium chloride loading of 3%. The catalyst filling height in fixed-bed reactor 4 is 70 cm, and the catalyst filling height in fixed-bed reactor 5 is 30 cm.

[0029] Methyl cyanoacetate was heated and vaporized in a heater at a rate of 1 mol / min. Liquid ammonia, after vaporization, entered the reaction system at a rate of 20 mol / min. The mixed gas entered fixed-bed reactor one at 5 MPa and 230 °C. The mixture was then cooled to 80 °C by heat exchanger one and entered a gas-liquid separator. Unreacted ammonia was separated from the gas-liquid separator and recycled back into fixed-bed reactor two. The liquid component was separated in a negative-pressure distillation column to obtain malononitrile as the product and methanol and dimethyl ether as byproducts. The intermediate cyanoacetamide and some incompletely separated malononitrile were recycled back into fixed-bed reactor two for further reaction. The resulting malononitrile was a colorless liquid that turned into a colorless transparent solid upon cooling, with a purity of 99.2%. The conversion rate for a single cycle, calculated based on methyl cyanoacetate, was 32.7%, and the overall yield was 72.9%.

[0030] Example 3 In the production apparatus of Example 1, malononitrile was prepared. The specific method is as follows:

[0031] Fixed-bed reactor 4 and fixed-bed reactor 5 are filled with nickel oxide spherical catalysts. The catalyst filling height in fixed-bed reactor 4 is 120 cm, and the catalyst filling height in fixed-bed reactor 5 is 60 cm.

[0032] Methyl cyanoacetate was heated and vaporized in a heater at a rate of 1 mol / min. Liquid ammonia, after vaporization, entered the reaction system at a rate of 20 mol / min. The mixed gas entered fixed-bed reactor one at 5 MPa and 230 °C. The mixture was then cooled to 80 °C by heat exchanger one and entered a gas-liquid separator. Unreacted ammonia was separated from the gas-liquid separator and recycled back into fixed-bed reactor one. The liquid component was separated in a negative-pressure distillation column to obtain malononitrile as the product and methanol and dimethyl ether as byproducts. The intermediate cyanoacetamide and some incompletely separated malononitrile were recycled back into fixed-bed reactor two for further reaction. The resulting malononitrile was a colorless liquid that turned into a colorless transparent solid upon cooling, with a purity of 98.3%. The conversion rate for a single cycle, calculated based on methyl cyanoacetate, was 24.5%, and the overall yield was 68.4%.

[0033] Example 4 In the production apparatus of Example 1, malononitrile was prepared. The specific method is as follows:

[0034] Fixed-bed reactor 4 and fixed-bed reactor 5 are filled with supported spherical catalysts of palladium hydroxide supported on molecular sieves, with a palladium hydroxide loading of 2%. The catalyst filling height in fixed-bed reactor 4 is 80 cm, and the catalyst filling height in fixed-bed reactor 5 is 35 cm.

[0035] Ethyl cyanoacetate was heated and vaporized in a heater at 2 mol / min. Liquid ammonia, after vaporization, entered the reaction system at 30 mol / min. The mixed gas entered a fixed-bed reactor at 8 MPa and 260 °C. The mixture was then cooled to 100 °C via heat exchanger one before entering a gas-liquid separator. Unreacted ammonia was separated from the gas-liquid separator and recycled back into the fixed-bed reactor. The liquid component was separated in a negative-pressure distillation column to obtain malononitrile as the product and byproducts ethanol, diethyl ether, and ethylene. The intermediate cyanoacetamide and some incompletely separated malononitrile were recycled back into a second fixed-bed reactor for further reaction. The resulting malononitrile was a colorless liquid that turned into a colorless, transparent solid upon cooling, with a purity of 99.4%. The conversion rate for a single cycle, calculated using methyl cyanoacetate, was 48.3%, and the overall yield was 84.6%.

[0036] Example 5 In the production apparatus of Example 1, malononitrile was prepared. The specific method is as follows:

[0037] Fixed-bed reactor 4 and fixed-bed reactor 5 are filled with cuprous oxide spherical catalysts. The catalyst filling height in fixed-bed reactor 4 is 110 cm, and the catalyst filling height in fixed-bed reactor 5 is 50 cm.

[0038] Ethyl cyanoacetate was heated and vaporized in a heater at 2 mol / min. Liquid ammonia, after vaporization, entered the reaction system at 30 mol / min. The mixed gas entered a fixed-bed reactor at 8 MPa and 260 °C. The mixture was then cooled to 100 °C via heat exchanger one before entering a gas-liquid separator. Unreacted ammonia was separated from the gas-liquid separator and recycled back into the fixed-bed reactor. The liquid component was separated in a negative-pressure distillation column to obtain malononitrile as the product and byproducts ethanol, diethyl ether, and ethylene. The intermediate cyanoacetamide and some incompletely separated malononitrile were recycled back into a second fixed-bed reactor for further reaction. The resulting malononitrile was a colorless liquid that turned into a colorless, transparent solid upon cooling, with a purity of 97.9%. The conversion rate for a single cycle, calculated using methyl cyanoacetate, was 18.7%, and the overall yield was 57.3%.

[0039] Example 6 In the production apparatus of Example 1, malononitrile was prepared. The specific method is as follows:

[0040] Fixed-bed reactor 4 and fixed-bed reactor 5 are filled with ruthenium oxide spherical catalysts. The catalyst filling height in fixed-bed reactor 4 is 60 cm, and the catalyst filling height in fixed-bed reactor 5 is 30 cm.

[0041] Isopropyl cyanoacetate was heated and vaporized in a heater at a rate of 1 mol / min. Liquid ammonia, after vaporization, entered the reaction system at a rate of 30 mol / min. The mixed gas entered a fixed-bed reactor at 10 MPa and 300 °C. The mixture was then cooled to 100 °C via a heat exchanger and entered a gas-liquid separator. Unreacted ammonia was separated from the gas-liquid separator and recycled back into the fixed-bed reactor. The liquid component was separated in a negative-pressure distillation column to obtain malononitrile as the product and isopropanol, isopropyl ether, and propylene as byproducts. The intermediate cyanoacetamide and some incompletely separated malononitrile were recycled back into a second fixed-bed reactor for further reaction. The resulting malononitrile was a colorless liquid that turned into a colorless, transparent solid upon cooling, with a purity of 99.6%. The conversion rate for a single cycle, calculated using methyl cyanoacetate, was 67.5%, and the overall yield was 84.1%.

[0042] Example 7 In the production apparatus of Example 1, malononitrile was prepared. The specific method is as follows:

[0043] Fixed-bed reactor 4 and fixed-bed reactor 5 are filled with cobalt oxide spherical catalysts. The catalyst filling height in fixed-bed reactor 4 is 100 cm, and the catalyst filling height in fixed-bed reactor 5 is 45 cm.

[0044] Isopropyl cyanoacetate was heated and vaporized in a heater at a rate of 1 mol / min. Liquid ammonia, after vaporization, entered the reaction system at a rate of 30 mol / min. The mixed gas entered a fixed-bed reactor at 10 MPa and 300 °C. The mixture was then cooled to 100 °C via a heat exchanger and entered a gas-liquid separator. Unreacted ammonia was separated from the gas-liquid separator and recycled back into the fixed-bed reactor. The liquid component was separated in a negative-pressure distillation column to obtain malononitrile as the product and isopropanol, isopropyl ether, and propylene as byproducts. The intermediate cyanoacetamide and some incompletely separated malononitrile were recycled back into a second fixed-bed reactor for further reaction. The resulting malononitrile was a colorless liquid that turned into a colorless, transparent solid upon cooling, with a purity of 97.4%. The conversion rate for a single cycle, calculated using methyl cyanoacetate, was 21.8%, and the overall yield was 63.4%.

[0045] Example 8 In the production apparatus of Example 1, malononitrile was prepared. The specific method is as follows:

[0046] Fixed-bed reactor 4 and fixed-bed reactor 5 are filled with supported spherical catalysts of rhodium acetate supported on zeolite, with a rhodium acetate loading of 5%. The catalyst filling height in fixed-bed reactor 4 is 90 cm, and the catalyst filling height in fixed-bed reactor 5 is 30 cm.

[0047] tert-butyl cyanoacetate was heated and vaporized in a heater at a rate of 3 mol / min. Liquid ammonia, after vaporization, was introduced into the reaction system at a rate of 30 mol / min. The mixed gas entered a fixed-bed reactor at 15 MPa and 350 °C. The mixture was then cooled to 100 °C via a heat exchanger and entered a gas-liquid separator. Unreacted ammonia was separated from the gas-liquid separator and recycled back into the fixed-bed reactor. The liquid component was separated in a negative-pressure distillation column to obtain malononitrile as the product and isopropanol, isopropyl ether, and propylene as byproducts. The intermediate cyanoacetamide and some incompletely separated malononitrile were recycled back into a second fixed-bed reactor for further reaction. The resulting malononitrile was a colorless liquid that turned into a colorless, transparent solid upon cooling, with a purity of 98.2%. The conversion rate for a single cycle, calculated using methyl cyanoacetate, was 28.4%, and the overall yield was 53.1%.

[0048] Example 9 In the production apparatus of Example 1, malononitrile was prepared. The specific method is as follows:

[0049] Fixed-bed reactor 4 and fixed-bed reactor 5 are filled with alumina spherical catalysts. The catalyst filling height in fixed-bed reactor 4 is 120 cm, and the catalyst filling height in fixed-bed reactor 5 is 50 cm.

[0050] Cyanoacetic acid was heated and vaporized in a heater at a rate of 3 mol / min. Liquid ammonia, after vaporization, entered the reaction system at a rate of 120 mol / min. The mixed gas entered a fixed-bed reactor at 20 MPa and 420 °C. The mixture was then cooled to 90 °C by a heat exchanger and entered a gas-liquid separator. Unreacted ammonia was separated from the gas-liquid separator and recycled back into the fixed-bed reactor. The liquid component was separated in a negative-pressure distillation column to obtain malononitrile as the product and isopropanol, isopropyl ether, and propylene as byproducts. The intermediate cyanoacetamide and some incompletely separated malononitrile were recycled back into a second fixed-bed reactor for further reaction. The resulting malononitrile was a colorless liquid that turned into a colorless, transparent solid upon cooling, with a purity of 97.1%. The conversion rate for a single cycle, calculated using methyl cyanoacetate, was 23.9%, and the overall yield was 45.2%.

[0051] Comparative Example 1 The traditional malononitrile synthesis process is employed, and the specific method is as follows:

[0052] 2262 g (20 mol) of ethyl cyanoacetate and 7000 g (60 mol) of 30% concentrated ammonia solution were added to a reaction flask and heated under reflux for 2 h. After the reaction was completed, the reaction solution was cooled to 0-10 °C. After filtration and drying, a crude product was obtained. Then, the crude cyanoacetamide was added to ethanol and heated to reflux to dissolve. Activated carbon was then added for decolorization and purification. After filtration, the filtrate was cooled to precipitate, and the precipitate was filtered and dried to obtain 1295 g (15.4 mol) of purified cyanoacetamide with a purity of 98.3% and a yield of 77.0%.

[0053] 1261 g (15 mol) of cyanoacetamide, 1052 g (18 mol) of sodium chloride, and dichloroethane were stirred and mixed for 1 h. Then, 1380 g (9 mol) of phosphorus oxychloride was added, and the mixture was heated under reflux for 8 h. After the reaction was complete, the reaction mixture was cooled to room temperature, filtered, and the filter cake was washed with dichloroethane. The filtrates were combined, and the solvent was evaporated to obtain crude malononitrile. The crude product was distilled under reduced pressure, and the fraction collected at 113 °C to 118 °C (3.3 kPa) yielded 607.7 g (9.2 mol) of colorless liquid or solid malononitrile with a purity of 97.1% and a yield of 61.3%. The overall yield of the two steps, calculated using ethyl cyanoacetate, was 47.2%.

[0054] As can be seen, Comparative Example 1 represents the traditional synthesis process of malononitrile, which requires two steps to prepare malononitrile. This process is lengthy and complex. Furthermore, it generates a significant amount of waste, resulting in a much lower yield compared to Example 4, leading to higher production costs.

[0055] Comparative Example 2 The specific method for preparing malononitrile using a tubular reactor is as follows:

[0056] Acetonitrile (4.20 L / min, 80.92 mol / min) and cyanogen chloride (0.50 L / min, 9.92 mol / min) were pumped into the mixer using feed pump one, respectively. After thorough mixing, the mixture was introduced into a tubular reactor at a reaction temperature of 800°C. After the reaction, the reaction liquid flowed out of the tubular reactor and cooled to 0°C, then pumped into a gas-liquid separator. The separated byproduct, hydrogen chloride, entered an acid gas treatment unit. The liquid was pumped into distillation column one via a product pump at the bottom of the gas-liquid separator. Unreacted feed from the top of distillation column one was pumped back into the reactor via a feed tank. The product, malononitrile, was purified in a negative pressure distillation column from the bottom. The resulting malononitrile was a colorless liquid that turned into a colorless, transparent solid upon cooling. The product purity was 98.6%, the single-pass conversion rate was 26.2% (based on cyanogen chloride), and the overall yield was 68.3%.

[0057] It can be seen that the raw material cyanogen chloride used in Comparative Example 2 is a highly toxic substance, posing a significant safety hazard. Furthermore, the reaction temperature is high, and the process control requirements are stringent, making it difficult to scale up for industrial production.

[0058] Comparative Example 3 In the production apparatus of Example 1, malononitrile was prepared. The apparatus differed from that of Example 1 in that both fixed-bed reactor 1 and fixed-bed reactor 2 in Example 1 were replaced with tubular reactors, and the tubular reactors did not contain a catalyst. The specific method is as follows:

[0059] Isopropyl cyanoacetate was heated and vaporized in a heater at a rate of 1 mol / min. Liquid ammonia, after vaporization, entered the reaction system at a rate of 30 mol / min. The mixed gas entered tubular reactor one at 10 MPa and 300 °C. The mixture was then cooled to 100 °C by heat exchanger one and entered a gas-liquid separator. The remaining unreacted ammonia was separated from the gas-liquid separator and recycled back into tubular reactor two. The liquid component entered a negative pressure distillation column to separate the product malononitrile and the byproducts isopropanol, isopropyl ether, and propylene. The intermediate cyanoacetamide and some incompletely separated product malononitrile were recycled back into tubular reactor two to continue the reaction. The resulting product malononitrile was a colorless liquid that turned into a light brown solid upon cooling, with a purity of 86%. The conversion rate for a single cycle, calculated based on methyl cyanoacetate, was 6.1%, and the overall yield was 38.7%.

[0060] In summary, existing malononitrile synthesis processes can be broadly categorized into two types: the dehydration method, represented by Comparative Example 1, and the synthesis method, represented by Comparative Example 2. Both methods have significant drawbacks. This invention employs a catalytic dehydration method, combining the advantages of the dehydration method (low toxicity of raw materials and low reaction temperature) with the synthesis method (ease of automation and low waste generation). This method offers excellent practicality and economy, facilitating industrial production. Comparative Example 3, which did not include a catalyst, demonstrates that without one, the reaction rate is slow and incomplete, resulting in a significant decrease in product purity and overall yield. The product's color also darkens considerably, indicating the formation of tar and byproducts, making product purification difficult.

[0061] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for catalytically preparing malononitrile, characterized in that, The reaction formula is as follows: ； Wherein R is H or a C1~C6 alkyl group; The specific preparation method is as follows: (1) The compound of formula I is heated and then introduced into a fixed-bed reactor containing a catalyst along with ammonia gas to carry out the reaction; (2) The reaction mixture obtained in step (1) is condensed and then subjected to gas-liquid separation to collect the liquid; (3) The liquid collected in step (2) is subjected to negative pressure distillation to obtain malononitrile; The catalyst is at least one selected from PdCl2, Pd(OAc)2, Pd(OH)2, PdO, CuCl, CuCl2, Cu(OAc)2, CuO, Cu2O, V2O5, Al2O3, ZrO2, RuO2, RuCl3, Ru(OAc)3, Rh2O3, Rh(OAc)3, Rh2(OAc)4, RhCl3, MoO, Fe2O3, CoO, or NiO.

2. The method for catalytic preparation of malononitrile according to claim 1, characterized in that, The molar ratio of compound I to ammonia is 1:3 to 50.

3. The method for catalytic preparation of malononitrile as described in claim 1, characterized in that, The catalyst is at least one of PdO, CuO, Cu2O, V2O5, Al2O3, ZrO2, RuO2, Rh2O3, MoO, Fe2O3, CoO, or NiO.

4. The method for catalytic preparation of malononitrile as described in claim 3, characterized in that, The catalyst is a spherical catalyst with a diameter of 2-5 mm.

5. The method for catalytic preparation of malononitrile according to claim 1, characterized in that, The catalyst is at least one of PdCl2, Pd(OAc)2, Pd(OH)2, CuCl, CuCl2, Cu(OAc)2, RuCl3, Ru(OAc)3, Rh(OAc)3, Rh2(OAc)4, or RhCl3.

6. The method for catalytic preparation of malononitrile as described in claim 5, characterized in that, The catalyst is a supported spherical catalyst with a diameter of 2-5 mm, and the support is alumina, zeolite, or molecular sieve.

7. The method for catalytic preparation of malononitrile according to claim 1, characterized in that, In step (1), the reaction temperature is 150℃~450℃.

8. The method for catalytic preparation of malononitrile according to claim 1, characterized in that, In step (1), the reaction pressure is 2 MPa to 25 MPa.

9. The method for catalytic preparation of malononitrile according to claim 1, characterized in that, The production equipment used for the catalytic preparation of malononitrile includes a fixed-bed reactor I, a fixed-bed reactor II, a gas-liquid separator, and a negative pressure distillation column; The inlet of the fixed-bed reactor 1 is connected to a heater and a heating furnace 1, respectively. The inlet of the heater is connected to a vaporizer, which is used to heat liquid ammonia and vaporize it. The inlet of the heating furnace 1 is connected to a feed pump via a pipe, which passes through a heat exchanger 1. The bottom outlet of the fixed-bed reactor 1 is connected to a gas-liquid separator via a pipe, which passes through heat exchanger 1 and heat exchanger 2 in sequence. The top outlet of the gas-liquid separator is connected to the inlet of the fixed-bed reactor 1, and an ammonia compression circulation pump is provided between the gas-liquid separator and the fixed-bed reactor 1. The bottom outlet of the gas-liquid separator is connected to a heating furnace 2, and a product pump is provided between the gas-liquid separator and the heating furnace 2. The gas-liquid separator is connected to a negative pressure distillation column. The outlet of the negative pressure distillation column is connected to a buffer tank. The top outlet of the negative pressure distillation column is connected to a reflux tank. The bottom outlet of the negative pressure distillation column is connected to the inlet of the fixed-bed reactor 2, and a distillation column bottom pump is provided between the negative pressure distillation column and the fixed-bed reactor 2.

10. The method for catalytic preparation of malononitrile according to claim 9, characterized in that, The fixed-bed reactor is configured as a multi-layer reactor, with each layer connected to a heater.

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