A process for the synthesis of methacrylonitrile

Abstract

The application belongs to the technical field of fine chemical industry, and particularly relates to a method for preparing methacrylonitrile by gas-solid phase catalytic reaction under the action of a boron-based catalyst. By using boron as a mild Lewis acid center, not only can the nitrilation reaction of methacrylic acid (and / or alkyl methacrylate) and ammonia be effectively catalyzed, but also the carbonium ion polymerization process caused by the protonation of the C=C double bond under strong acid can be relieved, so that the generation of carbon deposition is inhibited. Since the catalyst itself does not have hydrogenation activity, the generation of by-products such as methyl isobutyrate and isobutyronitrile can be effectively inhibited. In addition, by introducing a hydrogen atmosphere into the reaction system, the generation of catalyst carbon deposition can be effectively relieved, and the running stability of the catalyst can be significantly prolonged.

Description

Technical Field

[0001] This invention belongs to the field of fine chemicals, specifically relating to a continuous heterogeneous catalytic synthesis method for methacrylonitrile. Background Technology

[0002] Methacrylonitrile (MAN) is an important fine chemical intermediate, and its core downstream product, polymethacrylimide (PMI), is a high-performance foam material. With its comprehensive properties including lightweight, high specific strength, excellent heat resistance, good wave transmission, and high closed-cell ratio, MAN has become an indispensable structural and functional material in aerospace, rail transportation, new energy vehicles, and high-end medical equipment, while also showing potential applications in pharmaceutical synthesis. In recent years, the global market demand for MAN has continued to grow, driving the continuous upgrading of related synthesis technologies. Therefore, developing green and efficient MAN synthesis processes has significant strategic and economic value.

[0003] Currently, the synthesis processes of methacrylonitrile are mainly divided into four categories. Each process has significant differences and challenges in terms of raw material sources, reaction safety, and target product selectivity: (1) Acetone cyanohydrin method: using highly toxic cyanide as raw material, there are serious safety hazards and environmental risks, and it is being gradually replaced by green processes. (2) Isobutylene ammoxidation method (such as the Asahi Kasei process): the raw materials are abundant, but it is a high-temperature, strongly exothermic gas-phase reaction. Ammonia and oxygen need to be introduced into the system at the same time, which poses a risk of runaway temperature and explosion. The side reactions are complex and easily generate a variety of byproducts such as hydrogen cyanide, acetonitrile, and acrylonitrile, resulting in low target product selectivity and high separation and purification costs. (3) Methacrylaldehyde liquid-phase catalytic oxidation ammoxidation method: developed by the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, it generates methacrylaldehyde through the catalytic oxidation of isobutylene, and then further oxidizes and ammoxidizes it to methacrylonitrile, which simplifies the separation process of intermediate products, but it still belongs to the category of ammoxidation and fails to fundamentally solve the safety hazards caused by runaway temperature. (4) Nitrile reaction of methacrylic acid (or ester) with ammonia: Methacrylonitrile is synthesized from methacrylic acid (or ester) and NH3 as raw materials under the action of a Lewis acidic oxide catalyst containing metal. Due to the presence of metal acidic centers in the catalyst, coking and deactivation are prone to occur; at the same time, during the coking process, the hydrogen gas generated by the dehydrogenation of organic matter will undergo a hydrogenation side reaction with methyl methacrylate and methacrylonitrile on the surface of the metal catalyst, generating a small amount of methyl isobutyrate and isobutyronitrile, which increases the difficulty of subsequent distillation and separation. Summary of the Invention

[0004] To address the shortcomings of the aforementioned processes, this invention provides an improved method for the nitrification of methacrylic acid (and / or alkyl methacrylates). This method employs a boron-based catalyst without metal components for the nitrification reaction of methacrylic acid (and / or alkyl methacrylates) with ammonia to synthesize methacrylonitrile. While suppressing coking, it effectively inhibits the formation of byproducts methyl isobutyrate and isobutyronitrile, avoiding the adverse effects of byproduct azeotropy on subsequent methacrylonitrile separation and purification. Furthermore, this invention creatively introduces a hydrogen-rich reaction atmosphere, thermodynamically suppressing the dehydrogenation reaction process, reducing coking accumulation, and significantly improving catalyst stability.

[0005] The first aspect of this application protects a method for synthesizing methacrylonitrile, which uses methacrylic acid and / or alkyl methacrylate as raw materials, which are vaporized and then reacted with ammonia in the presence of a catalyst to produce methacrylonitrile;

[0006] The catalyst is a boron-based catalyst.

[0007] Preferably, the boron-based catalyst is one or more of B2O3, BPO4, B2O3 / SiO2, B2O3 / BN, BPO4 / SiO2, BPO4 / BN, and BPO4 / B2O3.

[0008] Preferably, the catalyst needs to undergo N2 purging pretreatment at a temperature of 300-500°C.

[0009] Preferably, the vaporization is carried out in a vaporization chamber, and the raw material is pumped into the vaporization chamber by a high-pressure liquid pump at a flow rate of 0.001-0.1 mL / min, and the vaporization temperature is 120-250 ºC.

[0010] Preferably, the alkyl group of the alkyl methacrylate is C10. n H 2n+1 , n=1-4.

[0011] Preferably, the reaction temperature is 300-500 ºC and the reaction pressure is 10-500 kPa.

[0012] Preferably, the molar ratio of ammonia to methacrylic acid and / or alkyl methacrylate is (2-15):1.

[0013] Preferably, the reaction system atmosphere comprises a mixture of nitrogen and hydrogen.

[0014] Preferably, the volume ratio of nitrogen to hydrogen is (3-30):1.

[0015] Preferably, the volume ratio of nitrogen to hydrogen is 6:1.

[0016] Preferably, the liquid hourly space velocity (LHSV) of the feedstock is 0.06-27 mL·g. -1 ·h -1 The total gas hourly space velocity (GHSV) of the reaction is 126-90000 mL·g -1 ·h -1 .

[0017] Preferably, the reaction is carried out in a fluidized bed reactor or a fixed bed reactor; more preferably, the reaction is carried out in a fixed bed reactor.

[0018] Preferably, the gas after the reaction is filtered to retain the byproduct solid methacrylamide; the filtered gas is then condensed by a condenser to obtain a crude product liquid mixture containing methacrylonitrile, alkyl methacrylate, alcohol and water.

[0019] The second aspect of this application protects a methacrylonitrile prepared according to a method for synthesizing methacrylonitrile.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] (1) This invention utilizes a boron-based catalyst without metal components for the gas-solid multiphase nitrification reaction of methacrylic acid (and / or alkyl methacrylate) with ammonia. Boron, as a mild Lewis acidic center, not only effectively catalyzes the nitrification reaction of methacrylic acid (and / or alkyl methacrylate) with ammonia, but also mitigates the carbocation polymerization process caused by the protonation of the C=C double bond under strong acid conditions, thereby inhibiting the formation of coke deposits. Since the catalyst contains no metal components, the hydrogenation side reaction between alkyl methacrylate and methacrylonitrile is avoided, inhibiting the formation of methyl isobutyrate and isobutyronitrile from the source, thus solving the problem in traditional processes where byproducts form an azeotrope with methacrylonitrile, interfering with subsequent separation and purification.

[0022] (2) The present invention innovatively introduces a hydrogen-containing reaction atmosphere, and by adding a small amount of hydrogen, the carbon deposition process caused by dehydrogenation of organic matter is suppressed from the perspective of thermodynamic equilibrium; at the same time, hydrogen can react with the surface carbon layer to undergo methanation reaction, further reducing carbon accumulation and significantly improving the stability of the catalyst. Attached Figure Description

[0023] The following figures are for illustrative purposes only and are not intended to limit the scope of the invention, wherein:

[0024] Figure 1 This application describes the design structure and principle of the catalyst active center.

[0025] Figure 2 The image shows a gas chromatogram of the reaction product obtained in Example 1 of this application.

[0026] Figure 3 The gas chromatogram of the reaction product obtained for Comparative Example 1 of this application is shown.

[0027] Figure 4 The reaction performance results are for Example 1 in this application.

[0028] Figure 5 The reaction performance results are for Example 2 in this application.

[0029] Figure 6 The reaction performance results are for Example 3 in this application.

[0030] Figure 7 The reaction performance results are for Example 4 in this application.

[0031] Figure 8 The reaction performance results are for Example 5 in this application.

[0032] Figure 9 The reaction performance results are for Example 6 in this application.

[0033] Figure 10 The reaction performance results are for Example 7 in this application.

[0034] Figure 11 The results show the long-cycle reaction performance of Example 5 in this application.

[0035] Figure 12 The reaction performance results are for Comparative Example 1 in this application.

[0036] Figure 13 The reaction performance results are for Comparative Example 2 in this application.

[0037] Figure 14 The results are the analysis results of catalyst coke content after 5 h of reaction in Example 6 and Comparative Example 1 of this application.

[0038] Figure 15 This is a chromatogram of hydrogen produced by the dehydrogenation reaction of the catalyst in Comparative Example 1 in this application. Detailed Implementation

[0039] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, a detailed description of specific embodiments of this application is provided below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0040] To facilitate understanding of the present invention, a more complete description of this application will be given below with reference to relevant embodiments. Preferred embodiments of the present application are given below. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that a thorough and complete understanding of the disclosure of this application will be achieved.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0042] As used herein, the terms "and / or," "or / and," and "and / or" encompass any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or," "or / and," and "and / or," it should be understood that, in this application, the technical solution undoubtedly includes solutions connected by "logical AND," and also undoubtedly includes solutions connected by "logical OR."

[0043] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0044] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0045] This document only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0046] Unless otherwise specified, the temperature parameters in this application may be either constant temperature processing or processing within a certain temperature range. The constant temperature processing allows temperature fluctuations within the precision range controlled by the instrument, such as ±5°C, ±4°C, ±3°C, ±2°C, or ±1°C.

[0047] In this document, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0048] In this application, terms such as "further," "even further," and "particularly" are used to describe purposes and indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0049] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0050] In the description of the application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0051] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0052] The monomeric catalysts used in the following examples, such as B2O3, SiO2, BN, and BPO4, can be derived from commercially available sources or prepared using conventional processes in the art, unless otherwise specified. Binary boron-based composite catalysts are prepared by solid-phase grinding. Equal masses of boron-based catalysts (B2O3, BN, or BPO4) are mixed with SiO2 or boron-based catalysts (B2O3, BN, or BPO4), and then ground using a ball mill to ensure uniform mixing. The grinding time is controlled at 4-8 hours, yielding one or more of B2O3 / SiO2, B2O3 / BN, BPO4 / SiO2, BPO4 / BN, and BPO4 / B2O3.

[0053] Test conditions:

[0054] (1) Gas chromatography analysis was performed using Fuli chromatography (F-60), with a SE-30 column, an injection port temperature of 220 °C, a detector temperature of 260 °C, and a column temperature of 60 °C for 1 min, followed by a temperature increase to 225 °C at 25 °C / min and a holding time of 8 min.

[0055] (2) Thermogravimetric analysis was performed using a PerkinElmer STA 6000 analyzer. Approximately 10 mg of the sample to be tested was placed in a crucible and heated from room temperature to 800 °C in an air atmosphere at a heating rate of 10 °C / min.

[0056] (3) XRD analysis was performed using a D8 Advance X-ray powder diffractometer (Bruker GmbH, Germany) to analyze the crystal structure of the sample. The test conditions were: Cu target Kα rays, tube voltage 40 kV, tube current 40 mA, scanning range 10-80°, step size 0.02°, and scanning rate 0.2 sec / step.

[0057] The first aspect of this application protects a method for synthesizing methacrylonitrile, which uses methacrylic acid and / or alkyl methacrylate as raw materials, which are vaporized and then reacted with ammonia under the action of a catalyst to generate methacrylonitrile;

[0058] The catalyst is a boron-based catalyst. As a mild Lewis acidic center, the boron-based catalyst can not only effectively catalyze the nitrification reaction of methacrylic acid (or alkyl methacrylate) with ammonia, but also mitigate the carbocation polymerization process caused by the protonation of the C=C double bond, thereby inhibiting the formation of coke. Since the catalyst does not contain any metal components, it avoids the hydrogenation side reaction of methyl methacrylate and methacrylonitrile, inhibiting the formation of methyl isobutyrate and isobutyronitrile from the source, thus solving the problem of byproduct interference with subsequent separation and purification in traditional processes.

[0059] In some embodiments, the boron-based catalyst is one or more of B2O3, BPO4, B2O3 / SiO2, B2O3 / BN, BPO4 / SiO2, BPO4 / BN, and BPO4 / B2O3.

[0060] In some embodiments, the reaction is carried out in a fluidized bed reactor or a fixed bed reactor; preferably, the reaction is carried out in a fixed bed reactor. Fixed bed reactors have advantages such as low catalyst wear and loss, lower requirements for catalyst mechanical strength, no need for fluidizing gas, low overall cost, and simple operation.

[0061] In some embodiments, when loading the catalyst, it is necessary to uniformly mix the catalyst with an equal mass of inert filler such as quartz sand or silicon carbide; after loading the catalyst, it needs to undergo N2 purging pretreatment at a temperature of 300-500 °C for a time of not less than 2 hours, which can effectively remove moisture and impurities from the catalyst surface.

[0062] In some embodiments, the vaporization of the raw material is carried out in a vaporization chamber, where the raw material is pumped into the vaporization chamber by a high-pressure liquid pump at a flow rate of 0.001-0.1 mL / min, and the vaporization temperature is 120-250 ºC, so as to vaporize the alkyl methacrylate raw material, which is then mixed with the system atmosphere.

[0063] In some embodiments, the alkyl group of the alkyl methacrylate is C10. n H 2n+1 If n=1-4, the alkyl chain is too long, the melting point will increase, and the alkyl chain will undergo side reactions such as cracking and isomerization during the reaction.

[0064] In some embodiments, the reaction temperature is 300-500 ºC and the reaction pressure is 10-500 kPa. Too low a temperature results in poor reaction activity; too high a temperature leads to more side reactions and coke buildup. The reaction itself is at atmospheric pressure, and a pressure drop occurs during the reaction. The pressure is controlled at 10-500 kPa; excessively high pressure will increase the occurrence of hydrogenation side reactions and reverse reactions. Preferably, the reaction temperature is 420 ºC and the reaction pressure is 100 kPa.

[0065] In some embodiments, the molar ratio of ammonia to methacrylic acid and / or alkyl methacrylic acid esters is (2-15):1. When the molar ratio is less than 2, the conversion rate is low; when the molar ratio is greater than 15, excess ammonia may promote side reactions such as amidation, polymerization or degradation of methacrylic acid or esters, generating undesirable byproducts, reducing product purity, and high concentrations of ammonia may corrode equipment and affect the stability of subsequent neutralization, washing or distillation processes.

[0066] In some embodiments, the reaction system atmosphere comprises a mixture of nitrogen and hydrogen. Nitrogen acts as a carrier gas and dilution gas in the reaction, while the addition of a small amount of hydrogen suppresses the coking process initiated by the dehydrogenation of organic matter from a thermodynamic equilibrium perspective; at the same time, hydrogen can undergo a methanation reaction with the surface carbon layer, further reducing coking accumulation and significantly improving the stability of the catalyst.

[0067] In some embodiments, the volume ratio of nitrogen to hydrogen is (3-30):1. A volume ratio greater than 30 results in insignificant suppression of coking; a volume ratio less than 3 increases the amount of hydrogen involved, increasing production costs and the risk of subsequent catalyst regeneration in air. Preferably, the volume ratio of nitrogen to hydrogen is 6:1.

[0068] Preferably, the liquid hourly space velocity (LHSV) of the feedstock is 0.06-27 mL·g. -1 ·h -1 The total gas hourly space velocity (GHSV) of the reaction was 126-90000 mL·g. -1 ·h -1 .

[0069] In some embodiments, the gas after the reaction is filtered to retain the byproduct solid methacrylamide; the filtered gas is then condensed by a condenser to obtain a crude product liquid mixture containing methacrylonitrile, alkyl methacrylate, alcohol and water.

[0070] The second aspect of this application protects a methacrylonitrile prepared according to a method for synthesizing methacrylonitrile.

[0071] Example 1

[0072] (1) 2.0 g of B2O3 / SiO2 catalyst was mixed with an equal amount of quartz sand and packed into a fixed bed reactor and pretreated with nitrogen at 400°C for 2 h.

[0073] (2) Using methyl methacrylate as raw material, the liquid hourly space velocity was 1.35 mL·g. -1 ·h -1 The temperature of the vaporization chamber is 200°C.

[0074] (3) Ammonia and nitrogen flow rates were set using a gas mass flow meter and mixed with the vaporized methyl methacrylate before entering the reactor bed, so that the total gas hourly space velocity of the reaction was 2250 mL·g -1 ·h -1 .

[0075] (4) The temperature of the fixed bed reactor is 420 °C and the pressure is 100 kPa.

[0076] (5) Collect the liquid product and perform gas chromatography analysis to calculate the conversion rate and yield.

[0077] Example 2

[0078] The catalyst was replaced with a BPO4 / SiO2 catalyst, and the other conditions were the same as in Example 1.

[0079] Example 3

[0080] The catalyst was replaced with a BPO4 catalyst, and the other conditions were the same as in Example 1.

[0081] Example 4

[0082] The catalyst was replaced with a BPO4 / B2O3 catalyst, and the other conditions were the same as in Example 1.

[0083] Example 5

[0084] Ammonia, nitrogen, and hydrogen flow rates were set using gas mass flow meters, with a nitrogen to hydrogen volumetric flow rate ratio of 6:1. The nitrogen gas was mixed with vaporized methyl methacrylate before entering the reactor bed, resulting in a total gas hourly space velocity (GHSV) of 2400 mL·g⁻¹. -1 ·h -1 The remaining conditions are the same as in Example 4.

[0085] Example 6

[0086] Ammonia, nitrogen, and hydrogen flow rates were set using gas mass flow meters, with a nitrogen to hydrogen volumetric flow rate ratio of 3:1. The nitrogen gas was mixed with vaporized methyl methacrylate before entering the reactor bed, resulting in a total gas hourly space velocity (GHSV) of 2550 mL·g⁻¹. -1 ·h -1 The remaining conditions are the same as in Example 4.

[0087] Example 7

[0088] Ammonia, nitrogen, and hydrogen flow rates were set using gas mass flow meters, with a nitrogen to hydrogen volumetric flow rate ratio of 30:1. The nitrogen gas was mixed with vaporized methyl methacrylate before entering the reactor bed, resulting in a total gas hourly space velocity (GHSV) of 2280 mL·g⁻¹. -1 ·h -1 The remaining conditions are the same as in Example 4.

[0089] Comparative Example 1

[0090] The catalyst was replaced with a commercially available TiO2 catalyst, and the other conditions were the same as in Example 1.

[0091] Comparative Example 2

[0092] The catalyst was replaced with a commercially available TiO2 catalyst, and the other conditions were the same as in Example 5.

[0093] From the appendix Figure 4-7 It can be seen that, under the same conditions, Example 4, using BPO4 / B2O3 as a catalyst, achieved the highest conversion rate of methyl methacrylate and the highest yield of methacrylonitrile.

[0094] From the appendix Figure 8-10It can be seen that when using BPO4 / B2O3 as the catalyst, the overall performance of the catalyst is best when the volume ratio of nitrogen to hydrogen is 6:1. When the hydrogen content is low, such as the 30:1 used in Example 7, the effect of hydrogen on improving the stability of the catalyst is not significant, mainly because its effect on inhibiting the dehydrogenation reaction during coking is weak. When the hydrogen content is high, such as the 3:1 used in Example 6, the effect is not much different from that of 6:1. Considering the cost of hydrogen and the safety of subsequent catalyst regeneration in air, controlling the volume ratio of nitrogen to hydrogen at 6:1 is more appropriate.

[0095] From the appendix Figure 11 It can be seen that, using BPO4 / B2O3 as a catalyst, under optimal reaction conditions, the catalyst still exhibits good stability after running for 1000 hours in a pilot-scale reactor, and the yield of methacrylonitrile remains at around 90%.

[0096] From the appendix Figure 12 It can be seen that the catalyst in Comparative Example 1 (commercially available TiO2) showed good initial activity, but the conversion rate of methyl methacrylate and the yield of methacrylonitrile continued to decline, reaching less than 30% after about 40 hours of reaction. This is mainly due to the strong acidity of the metal oxide catalyst, resulting in severe coking and rapid coverage of the active sites on the catalyst surface by coke. Comparing the thermogravimetric curves of the catalysts after the reaction, it can be seen that the coke content on the surface of the metal oxide catalyst is higher than that of the boron-based catalyst (see attached figure). Figure 14 ).

[0097] From the appendix Figure 13 It can be seen that the catalyst of Comparative Example 1 (commercially available TiO2) still showed good activity in the initial stage of the reaction after the introduction of a hydrogen atmosphere, but the yield of methacrylonitrile was low. This is mainly because the metal oxide catalyst itself has a certain hydrogenation performance, causing the product to undergo a hydrogenation reaction to generate isobutyronitrile. In addition, both the conversion rate and yield decreased significantly, which is also attributed to the strong acidity of the catalyst, severe coking reaction, and rapid coverage of the surface active sites by coking.

[0098] From the appendix Figure 15 It can be confirmed that a dehydrogenation reaction occurs during the nitrification reaction of methyl methacrylate with ammonia, and the detection of hydrogen in gas chromatography provides direct evidence of this. This dehydrogenation process leads to the gradual conversion of organic matter into coking precursors and further coking, thereby causing catalyst deactivation.

[0099] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0100] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for synthesizing methacrylonitrile, characterized in that, Methacrylonitrile is produced by reacting methacrylic acid and / or alkyl methacrylates with ammonia gas after vaporization in the presence of a catalyst. The catalyst is a boron-based catalyst.

2. The method according to claim 1, characterized in that, The boron-based catalyst is one or more of B2O3, BPO4, B2O3 / SiO2, B2O3 / BN, BPO4 / SiO2, BPO4 / BN, and BPO4 / B2O3.

3. The method according to claim 1, characterized in that, The alkyl group of the alkyl methacrylate is C. n H 2n+1 , n=1-4.

4. The method according to claim 1, characterized in that, The reaction temperature is 300-500 ºC, and the reaction pressure is 10-500 kPa.

5. The method according to claim 1, characterized in that, The molar ratio of ammonia to methacrylic acid and / or alkyl methacrylate is (2-15):

1.

6. The method according to claim 1, characterized in that, The reaction system atmosphere includes a mixture of nitrogen and hydrogen.

7. The method according to claim 6, characterized in that, The volume ratio of nitrogen to hydrogen is (3-30):

1.

8. The method according to claim 7, characterized in that, The volume ratio of nitrogen to hydrogen is 6:

1.

9. The method according to claim 1, characterized in that, The liquid hourly space velocity of the feedstock is 0.06-27 mL·g. -1 ·h -1 The total gas hourly space velocity of the reaction is 126-90000 mL·g -1 ·h -1 .

10. Methacrylonitrile prepared by the method according to any one of claims 1-9.

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