Method for continuously synthesizing methacrylonitrile and catalyst used in method

Abstract

The invention provides a method capable of continuously preparing methacrylonitrile, raw materials including methacrylic acid, methyl methacrylate or methacrylamide and an ammonia source react with a catalyst in a continuous reactor to obtain methacrylonitrile, and the catalyst is a metal modified molecular sieve catalyst. The method provided by the invention has the characteristics of simple composition of the used catalyst, high raw material conversion rate, high methacrylonitrile selectivity and the like; meanwhile, the catalyst continuously reacts for about 500 hours, the conversion rate and the selectivity are not obviously reduced, and the catalyst is particularly suitable for industrial production.

Description

Technical Field

[0001] This application relates to the field of chemical synthesis, and more specifically, to a method for the continuous synthesis of methacrylonitrile and the catalyst used therein. Background Technology

[0002] Methacrylonitrile ( Methacrylonitrile (MAN), also known as isobutylene nitrile, is a colorless liquid, slightly soluble in water and chloroform, and miscible with propanol, diethyl ether, acetone, octane, and toluene. Methacrylonitrile is mainly used in the production of polymethacrylamide (PMI) and methyl methacrylate (MMA). In recent years, with the development of industries such as aerospace, vehicles, and shipbuilding, core layers made primarily of PMI foam have gained market favor, becoming a significant driving force for the development of the methacrylonitrile industry. Advances in industries such as acrylic glass and coatings have also contributed to the development of the MMA industry, thus benefiting the MAN industry.

[0003] Currently, the main production technologies for MAN include the acetone cyanohydrin (ACH) method, the isobutylene ammoxidation method, and the mixed C4 direct ammoxidation method. The ACH method uses acetone and hydrogen cyanide (HCN) as raw materials to produce ACH, which is then dehydrated to produce MAN, with a final MAN yield of approximately 80%. However, hydrogen cyanide is a highly toxic chemical, causing serious environmental pollution problems, and its storage, transportation, and use are subject to strict management requirements, increasing production costs and hindering large-scale industrial production. The isobutylene ammoxidation method is divided into one-step and two-step methods based on the reaction process. The one-step method uses isobutylene, ammonia, and air as raw materials, and synthesizes the product MAN in the next step under the action of a catalyst. Currently, the industrial production of methacrylonitrile (MAN) from isobutylene is a high-temperature gas-phase reaction process with a reaction temperature of 350–550 °C and a reaction pressure generally below 0.3 MPa. The ratio of raw material n(isobutylene):n(NH3):n(air) is 1:(0.8–1.4):(7–12). Under the action of Mo-Bi-Fe catalysts (CN1302796A, US462202), Zn, Mg, Cu, Ni, Fe, K, Mo composite catalysts (CN115322117A), or Mg, Ni, Fe, K, Mo, Bi, X, Y composite catalysts (X is at least one element among zinc, calcium, barium, and cobalt, and Y is at least one element among copper, cerium, samarium, and niobium, CN112121811A), the MAN yield can still be maintained between 70% and 80%. Sohio Chemicals in the US and Asahi Kasei in Japan use this method, which has low investment and readily available raw materials, but suffers from low product selectivity, numerous byproducts, and difficult processing. In recent years, to address these issues, researchers have developed a stepwise ammonia oxidation method for isobutylene, also known as a two-step method. This process divides the ammonia oxidation process into two steps: the first step involves mixing isobutylene, an oxidant, and a catalyst to produce methacrolein; the second step involves mixing methacrolein, ammonia, an oxidant, and a catalyst to prepare MAN. A catalyst with Mo-Bi as the main component can selectively oxidize methacrolein to achieve a yield of up to 94%. CN109772298A and CN116135308A disclose the use of a composite manganese-based catalyst, with methacrolein as the substrate, in the presence of a solvent, under oxygen and ammonia atmosphere, and mild conditions of 0-100℃, achieving a methacrylonitrile yield of up to 92% in a batch reactor, with an overall two-step yield of up to 80%. CN113996288A discloses an improved manganese-based catalyst, doped with at least one of Fe, Ce, Ni, Cu, and Mo, which accelerates the reaction rate and achieves a methacrylonitrile yield of up to 95%. Currently, the technology for preparing methacrolein from isobutylene is mature, but the catalysts for the ammoxidation of methacrolein to methacrylonitrile suffer from a series of problems, including complex structures, the need for many different elements, cumbersome manufacturing methods, and high costs. Furthermore, existing technologies for preparing methacrylonitrile from isobutylene often struggle to achieve continuous production.The direct ammonia oxidation of mixed C4 uses cracked mixed components as raw materials. Under suitable reaction conditions and in an ammonia / oxygen atmosphere, MAN can be obtained directly through catalysis. In the reaction process, alkanes are inert components. Isobutene is ammoniated to generate MAN, and n-butene is oxidized and dehydrogenated to generate butadiene. The Shanghai Institute of Petrochemical Technology (Petrochemical Technology, 1981, 10(1):1-8) first developed a phosphorus, molybdenum, bismuth, iron, and potassium impregnated catalyst for this process. Under the process conditions of a reaction temperature of 390℃ and a raw material ratio of n(mixed C4):n(NH3):n(air):n(H2O) = 3:1.67:30:5.6, the device operated stably for 500 hours, and the single-pass yield of MAN remained stable between 60% and 62%. Moreover, the catalyst preparation process was simple and had good reproducibility. However, due to the complex composition of the cracked C4 raw materials, the selectivity of this process is low, and there are many types of by-products that are difficult to separate. Although patents have been published at home and abroad, there have been no reports of industrialization to date.

[0004] Other novel process routes include the synthesis of methacrylonitrile from methacrylic acid or methyl methacrylate (MMA) via amination and dehydration reaction, and the synthesis of methacrylonitrile from methacrylamide via dehydration. Patent DE102008035261Al uses methacrylic acid or MMA as a raw material and alumina as a catalyst, achieving a methacrylonitrile yield of 85-90%, with the main byproducts being n-propionitrile, isobutyronitrile, and methacrylonitrile dimers. Patent JP 4818525B2 uses methacrylic acid / methyl methacrylate as a raw material and gallium oxide-supported silicon dioxide, iron silicate, or borosilicate as a catalyst, achieving a methacrylonitrile yield of up to 92%. However, according to the patent terms, the actual methacrylonitrile yield in practice is only 70%. Patent CN110511160A uses methacrylamide as a raw material. First, methacrylamide is dissolved in a solvent and dehydrated in a homogeneous system under the action of a polyionic liquid acid-binding agent. Then, a mesoporous organometallic palladium catalyst is used for secondary catalytic dehydration in a reaction bed, achieving a methacrylonitrile yield of 90%. However, the dehydrating agent preparation process is complex, methacrylamide has low solubility, resulting in low production efficiency, and methacrylamide is expensive.

[0005] Currently, the source of methacrylonitrile is limited by the monopoly of international companies, and there are few channels for importing methacrylonitrile, resulting in high prices. The main domestic MMA production processes are the ACH method (accounting for 74.5% of the capacity) and the isobutylene method. In the past five years, MMA production has steadily increased, and the market as a whole is in a situation of oversupply, with overcapacity becoming increasingly serious (Chemical Industry, 2024, 42(3):76-82). Strengthening the development of downstream MMA products and expanding the product chain is particularly important. The advantages of the amination and dehydration process using methacrylic acid or methyl methacrylate and methacrylamide as raw materials are becoming increasingly apparent. Developing efficient, economical, and stable catalysts will be the key to the success or failure of the process. Summary of the Invention

[0006] Technical issues

[0007] To address the problems existing in the prior art, this application provides a method for the continuous synthesis of methacrylonitrile, which uses a continuous reactor and has milder reaction conditions and higher production efficiency than the ammonia oxidation method.

[0008] Technical solution

[0009] According to one aspect of the present invention, an object of the present invention is to provide a method for the continuous synthesis of methacrylonitrile, wherein a raw material, methacrylic acid, methyl methacrylate or methacrylamide, and an ammonia source are reacted with a catalyst in a continuous reactor to obtain methacrylonitrile, wherein the catalyst is a metal-modified molecular sieve catalyst, and the reaction formula is as follows:

[0010]

[0011] R = CH3, H.

[0012] The method for continuous synthesis of methacrylonitrile includes the following steps:

[0013] (1) Add metal-modified molecular sieve catalyst to a continuous reactor, introduce carrier gas, and heat to the reaction temperature;

[0014] (2) After the temperature stabilizes, the raw materials and ammonia source are introduced into the continuous reactor along with the carrier gas to carry out the reaction.

[0015] (3) The product is purified by condensation and gas-liquid separation, and then by distillation to obtain methyl acrylonitrile.

[0016] Preferably, the continuous reactor in step (1) is selected from any one of the following reactors: continuous stirred tank reactor, plug flow reactor, fixed bed reactor, and fluidized bed reactor, or a mixed reactor consisting of two or more of these reactors connected together. It is more preferably a fluidized bed reactor or a fixed bed reactor.

[0017] Preferably, the reaction temperature in step (1) is in the range of 150-500℃, and more preferably 250-450℃; if it is below 150℃, the raw material conversion rate is low; if it is above 500℃, there are more by-products such as propionitrile and isobutyronitrile, and the amount of methacrylonitrile polymer increases, resulting in high energy consumption.

[0018] Preferably, the raw materials in step (2) are selected from methacrylic acid, methyl methacrylate, and methacrylamide;

[0019] Preferably, the ammonia source in step (2) is selected from one or more of ammonia gas, ammonia water, urea, ammonium bicarbonate, ammonium carbonate, and ammonia methanol solution;

[0020] Preferably, the air velocity of the raw material in step (2) is 0.01-3.00 h⁻¹. -1 More preferably 0.05-0.80h -1 ;

[0021] Preferably, the reaction in step (2) is carried out at atmospheric pressure to 2 MPa, and more preferably at atmospheric pressure to 0.5 MPa. If the pressure is higher than 2 MPa, the requirements for the equipment will be higher and the cost will be higher.

[0022] Preferably, in step (2), the raw material reacts in the presence of a solvent or without a solvent, wherein the solvent is selected from one or more of tetrahydrofuran, 1,4-dioxane, benzonitrile, N-methylpyrrolidone, and 1,3-dimethyl-2-imidazolinone, preferably N-methylpyrrolidone or 1,3-dimethyl-2-imidazolinone; if a solvent is present, the raw material is first dissolved in the solvent and then fed into a continuous reactor, wherein the mass concentration of the raw material is 5wt-100wt%, preferably 5wt-50wt%.

[0023] Preferably, the molar ratio of raw materials and ammonia source in step (2) is 1:2-1:100, preferably 1:5-1:50. If it is lower than 1:2, the raw material conversion rate is low. If it is higher than 1:100, there are more by-products, high ammonia consumption, and serious waste of ammonia.

[0024] Preferably, when using methacrylamide as a raw material, an ammonia source may not be added.

[0025] Preferably, the carrier gas in step (2) is selected from one or more of nitrogen and helium, and more preferably nitrogen.

[0026] Preferably, the distillation purification in step (3) is atmospheric distillation purification with 50-55 plates, a bottom temperature of 100-130℃, a head temperature of 75-95℃, and a reflux ratio of 1:1-1:10.

[0027] According to another aspect of the present invention, another object of the present invention is to provide a metal-modified molecular sieve catalyst, wherein the metal-modified molecular sieve catalyst is a supported catalyst, wherein the support is a molecular sieve, the active component is an oxide of a modified metal, and based on the total weight of the metal-modified molecular sieve catalyst, the content of the support is 50-98%, preferably 70-95%, and the content of the active component is 2-30%, preferably 5-20%.

[0028] Preferably, the molecules are screened from one or more of H-ZSM5, H-ZSM11, HY, Hβ, HMOR, and SAPO-34; preferably, the molecules are screened from H-ZSM5.

[0029] Preferably, the active ingredient is selected from one or more oxides of iron, zinc, tungsten, titanium, gallium, lanthanum, cerium, zirconium, and ytterbium.

[0030] According to another aspect of the present invention, another object of the present invention is to provide a method for preparing the aforementioned metal-modified molecular sieve catalyst, the method comprising the following steps:

[0031] a. Calcine the molecular sieve powder at 400-600℃ for 5-10 hours;

[0032] b. Mix the calcined molecular sieve powder with the modified metal salt solution, stir, and let stand for 3-10 hours, then filter.

[0033] c. Dry the filtered molecular sieve at 100-120℃ for 8-15 hours, calcine it at 500-600℃ for 5-10 hours, add water and binder to the treated molecular sieve in proportion, mix them evenly to form a suspension, shear the suspension at high speed until 90% of the particles in the suspension are smaller than 8 micrometers, and spray granulate to form microspheres, wherein the binder is aluminum sol and / or silica sol.

[0034] d. Dry the shaped material at 100-120℃ for 8-15 hours, and then calcine it at 500-600℃ for 5-12 hours to obtain the catalyst.

[0035] Preferably, step b is carried out as follows: the molecular sieve powder and the modified metal salt solution are in a solid-liquid mass ratio of 1:10. After standing at 80°C for 5 hours, the solid is separated. Then the above method is repeated at least twice. Finally, the mixture is washed with 5-10 times the volume of the modified metal salt solution of deionized water and then filtered.

[0036] Preferably, the molecules are screened from one or more of H-ZSM5, H-ZSM11, HY, Hβ, HMOR, and SAPO-34; preferably, the molecules are screened from H-ZSM5.

[0037] The modified metal is one or more of the elements selected from iron, zinc, tungsten, titanium, gallium, lanthanum, cerium, zirconium, and ytterbium.

[0038] Preferably, the modified metal salt solution in step b is selected from the hydrochloride, nitrate, sulfate, or carbonate solution of the metal.

[0039] Preferably, in the spray molding process described in step c, the binder is preferably in the range of 5-30%, and the suspension solid content is 20-60%.

[0040] Beneficial effects

[0041] This invention provides a method for the continuous preparation of methacrylonitrile, which features a simple catalyst composition, high raw material conversion rate, and high selectivity for methacrylonitrile. Furthermore, the catalyst can be continuously reacted for approximately 500 hours without a significant decrease in conversion rate and selectivity, making it particularly suitable for industrial production. Attached Figure Description

[0042] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0043] Figure 1 This is a schematic diagram of a continuous reaction fluidized bed reactor.

[0044] Figure 2 The results show the stability evaluation of catalyst 1 obtained in Example 1 in a fluidized bed reactor. Detailed Implementation

[0045] The present invention will now be described in detail. Before proceeding with the description, it should be understood that the terminology used in this specification and the appended claims should not be construed as limited to its general or dictionary meaning, but rather should be interpreted according to the meaning and concept corresponding to the technical aspects of the invention, based on the principle that the inventors are allowed to appropriately define the terms for the best interpretation. Therefore, the description presented herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the invention. It should be understood that other equivalents or modifications can be obtained from it without departing from the spirit and scope of the invention.

[0046] The following embodiments are merely examples illustrating implementations of the present invention and do not constitute any limitation on the present invention. Those skilled in the art will understand that modifications made without departing from the spirit and concept of the present invention fall within the protection scope of the present invention. Unless otherwise specified, the reagents and instruments used in the following embodiments are commercially available products.

[0047] In this document, the terms “comprising,” “including,” “having,” “containing,” or any other similar terms are open-ended conjunctions intended to cover non-exclusive inclusions. For example, a composition or article containing a plurality of elements is not limited to those listed herein, but may also include other elements not explicitly listed but typically inherent to the composition or article. Furthermore, unless explicitly stated to the contrary, the term “or” is inclusive, not exclusive. For example, the condition “A or B” is satisfied in any of the following cases: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); A and B are both true (or exist). Moreover, in this document, the terms “comprising,” “including,” “having,” and “containing” should be interpreted as specifically disclosed and simultaneously cover closed or semi-closed conjunctions such as “composed of” and “substantially composed of.”

[0048] In this document, all features or conditions defined in the form of numerical ranges or percentage ranges are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible secondary ranges and individual values ​​within those ranges, particularly integer values. For example, a range description of "1 to 8" should be considered as specifically disclosing all secondary ranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, etc., particularly secondary ranges defined by all integer values, and should be considered as specifically disclosing individual values ​​within those ranges such as 1, 2, 3, 4, 5, 6, 7, 8, etc. Unless otherwise specified, the foregoing interpretation applies to all content throughout this invention, regardless of its scope.

[0049] If a quantity or other numerical value or parameter is expressed as a range, a preferred range, or a series of upper and lower limits, it should be understood that this document has specifically disclosed all ranges consisting of any upper or preferred value of that range and the lower or preferred value of that range, regardless of whether such ranges are separately disclosed. Furthermore, when a range of numerical values ​​is mentioned herein, unless otherwise stated, the range shall include its endpoints and all integers and fractions within the range.

[0050] In this document, numerical values ​​are to be understood as having a precision with significant digits, provided that the purpose of the invention can be achieved. For example, the number 40.0 should be understood to cover a range from 39.50 to 40.49.

[0051] In the continuous synthesis method of methacrylonitrile according to the present invention, the product is obtained from methacrylic acid, methyl methacrylate, methacrylamide, and ammonia. The product is analyzed and detected by gas chromatography (GC), and the low-boiling-point product is qualitatively analyzed by GC-MS and GC retention time comparison with standards. The low-boiling-point substances are quantitatively determined using a Shimadzu-GC 2020 gas chromatograph, and quantitative analysis is performed by comparing the retention time with that of standards and the peak area. The relevant calculation formulas are as follows:

[0052]

[0053]

[0054] The yield of methacrylonitrile = the conversion rate of the feedstock * the selectivity of methacrylonitrile

[0055]

[0056] The flow rate of the raw material is expressed in g / min, and the amount of catalyst is expressed in g.

[0057] This method utilizes a continuous reactor, preferably a fluidized bed reactor. Traditional batch reactors involve a large amount of feedstock and a small amount of catalyst in contact, limiting the contact time and area between the feedstock and catalyst, thus hindering the conversion rate of the feedstock with a small amount of catalyst. This method, using a fluidized bed reactor, allows for continuous feed and discharge. By adjusting the space velocity of the feedstock entering the fluidized bed, the contact time between the feedstock and catalyst can be flexibly changed, allowing a small amount of feedstock to contact a large amount of catalyst. Appropriate reaction conditions can be matched to different requirements, thereby improving the conversion rate of the feedstock and the yield of the product. Using two or more sets of fluidized beds or circulating fluidized beds allows a certain amount of catalyst to be reused for a long time and regenerated within the fluidized bed, reducing production and labor costs, reducing waste generation, and making it more environmentally friendly. Furthermore, compared to fixed-bed reactors, fluidized beds offer more uniform temperature and lower bed pressure drop, effectively preventing the polymerization of the feedstock and product, methacrylonitrile. The continuous production mode of the continuous reactor improves production efficiency.

[0058] Traditional ammonia oxidation requires the use of ammonia and a large amount of air for the reaction, necessitates a large reactor volume, and results in a small proportion of carbon-based raw materials in the system, leading to low production efficiency and high reaction temperatures. In contrast, this method uses less gaseous raw materials, has a larger proportion of carbon-based raw materials in the system, offers milder reaction conditions, a higher safety factor, and higher production efficiency.

[0059] Example 1

[0060] The following steps are used to prepare microspherical metal-modified molecular sieve catalysts:

[0061] HZSM-5 raw powder (powder form, specific surface area 420m²) with a silicon-to-aluminum ratio of 80 was used. 2 / g, average pore size 5nm, pore volume 0.4cm³ 3 / g) was treated at 550℃ for 5h. 300g of calcined HZSM-5 was weighed and added to 3L of 1mol / L ferric nitrate solution. The mixture was allowed to stand at 90℃ for 3 hours, and the solid was separated by filtration. The above process was repeated twice. Finally, the filter cake was washed with 30L of deionized water, dried at 110℃ for 12 hours, and calcined at 550℃ for 5 hours to obtain the iron-modified HZSM-5 molecular sieve catalyst. 300g of the modified molecular sieve was weighed and added to 120g of water. The mixture was stirred for 1 hour and sheared at high speed for 15 minutes to form a molecular sieve suspension. 150g of silica sol (SiO2 mass percentage concentration 20%) and 150g of alumina sol (Al2O3 mass percentage concentration 20%) were added to the suspension. The mixture was stirred rapidly for 30 minutes and sheared at high speed for 30 minutes. Microspheres were obtained by spray granulation. Drying at 110℃ for 12 hours and calcining at 550℃ for 5 hours yielded iron-modified particles with an average particle size of 100 μm and a specific surface area of ​​400 m². 2 / g, ZSM-5 molecular sieve microsphere catalyst with an attrition index of 1.5%.

[0062] The catalyst prepared above is used to prepare methylacrylonitrile in a fluidized bed reactor through the following steps:

[0063] 300g of the above catalyst (sieved to 80-150 mesh) was packed into a fluidized bed reactor tube (upper section inner diameter 100mm, outer diameter 108mm, length 300mm; lower section inner diameter 40mm, outer diameter 48mm, length 200mm). The temperature was set at 360℃ and the space velocity was 0.1h. -1 The reaction was evaluated under conditions of ammonia to methacrylic acid molar ratio of 5:1, and the product was cooled to -10°C. After stabilization, the reaction was monitored by gas chromatography. The conversion rate of this batch of raw materials was 98.5%, and the selectivity for methacrylonitrile was 90.0%.

[0064] The catalyst prepared above is used to prepare methylacrylonitrile in a fixed-bed reactor via the following steps:

[0065] Take 20g of the above catalyst and pack it into a fixed-bed reaction tube (inner diameter 12mm, outer diameter 21mm, length 400mm). The reaction temperature is 360℃ and the space velocity is 0.1h. -1 The product was evaluated under the following conditions: it was cooled at -10℃, and the reaction was detected by gas chromatography after the operation was stable.

[0066] The following steps are used to separate methacrylonitrile:

[0067] 300g of the reaction product was transferred to a 500mL round-bottom flask and distilled at atmospheric pressure at 100-130℃. The distillation column was 25mm (ID) × 100cm (L) with φ2×2 stainless steel packing and a reflux ratio of 1:3. After distillation, 210g of methacrylonitrile with a purity >98% was obtained, with a separation yield of 85% (based on methacrylic acid).

[0068] Example 2

[0069] Molecular screening was performed on Hβ with a silicon-to-aluminum ratio of 30. Catalyst preparation, reaction, and separation conditions were as described in Example 1.

[0070] Example 3

[0071] Molecular screening was performed on HY with a silicon-to-aluminum ratio of 30. Catalyst preparation, reaction, and separation conditions were as described in Example 1.

[0072] Example 4

[0073] Molecular screening was performed using HMOR, and catalyst preparation, reaction, and separation conditions were as described in Example 1.

[0074] Example 5

[0075] Molecular screening was performed using SAPO-34, and catalyst preparation, reaction, and separation conditions were as described in Example 1.

[0076] Example 6

[0077] The modified metal solution was titanium sulfate, and the catalyst preparation, reaction, and separation conditions were as described in Example 1.

[0078] Example 7

[0079] The modified metal solution was gallium nitrate, and the catalyst preparation, reaction, and separation conditions were as described in Example 1.

[0080] Example 8

[0081] The modified metal solution was zinc nitrate, and the catalyst preparation, reaction, and separation conditions were as described in Example 1.

[0082] Example 9

[0083] The modified metal solution was lanthanum nitrate, and the catalyst preparation, reaction, and separation conditions were as described in Example 1.

[0084] Comparative Example 10

[0085] The HZSM-5 raw powder with a silicon-to-aluminum ratio of 80 was treated at 550°C for 5 hours, without treatment with ferric nitrate solution as the active ingredient. The catalyst forming, reaction, and separation conditions were as described in Example 1.

[0086] Comparative Examples 11-15

[0087] Using the Fe / HZSM5 catalyst from Example 1, the reaction temperature, space velocity, ammonia / feed molar ratio, and feed type were varied, while other conditions were the same as in Example 1.

[0088] The evaluation conditions and results of the catalysts in each embodiment are shown in Table 1.

[0089] Table 1. Reaction results using different reactors, catalysts, and reaction conditions.

[0090]

[0091] Note: When using methacrylamide as a raw material, N-methylpyrrolidone is used as the solvent at a mass concentration of 20%.

[0092] The synthesis of methylacrylonitrile using metal-modified molecular sieve catalysis yielded a product separation yield of over 70% under optimal conditions, while the unmodified HZSM5 showed a lower separation yield. Changing the evaluation conditions—increasing the temperature to 400℃—increased the content of the byproduct propionitrile, leading to a decrease in product yield; increasing the space velocity to 0.2 h⁻¹... -1 The reduced conversion rate leads to a decrease in separation yield. (See attached image) Figure 2 The results show that after continuous operation of catalyst 1 obtained in preparation example 1 in a fluidized bed reactor for 500 hours, the feed conversion rate still remains above 95%, and the selectivity of the product methacrylonitrile is above 90%, indicating that the catalyst has good stability and long lifespan.

[0093] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. 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 be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for the continuous synthesis of methacrylonitrile, comprising reacting raw materials methacrylic acid, methyl methacrylate or methacrylamide and an ammonia source with a catalyst in a continuous reactor to obtain methacrylonitrile, wherein the catalyst is a metal-modified molecular sieve catalyst, and the reaction formula is as follows: Where R is CH3 or H; Includes the following steps: (1) Add metal-modified molecular sieve catalyst to a continuous reactor, introduce carrier gas, and heat to the reaction temperature; (2) After the temperature stabilizes, the raw materials and ammonia source are introduced into the continuous reactor along with the carrier gas to carry out the reaction. (3) The product is purified by condensation and gas-liquid separation, and then by distillation to obtain methyl acrylonitrile.

2. The method according to claim 1, characterized in that, Preferably, the continuous reactor in step (1) is selected from any one of the following reactors: continuous stirred tank reactor, plug flow reactor, fixed bed reactor, and fluidized bed reactor, or a mixed reactor consisting of two or more of these reactors connected together as a continuous reactor, preferably a fluidized bed reactor or a fixed bed reactor; Preferably, the reaction temperature in step (1) is in the range of 150-500℃, and more preferably 250-450℃.

3. The method according to claim 1, characterized in that, Preferably, the raw materials in step (2) are selected from methacrylic acid, methyl methacrylate, and methacrylamide; Preferably, the ammonia source in step (2) is selected from one or more of ammonia gas, ammonia water, urea, ammonium bicarbonate, ammonium carbonate, and ammonia methanol solution; Preferably, the air velocity of the raw material in step (2) is 0.01-3.00 h⁻¹. -1 More preferably 0.05-0.80h -1 ; Preferably, the reaction in step (2) is carried out at atmospheric pressure to 2 MPa, and more preferably at atmospheric pressure to 0.5 MPa. Preferably, in step (2), the raw material reacts in the presence of a solvent or without a solvent, wherein the solvent is selected from one or more of tetrahydrofuran, 1,4-dioxane, benzonitrile, N-methylpyrrolidone, and 1,3-dimethyl-2-imidazolinone, preferably N-methylpyrrolidone or 1,3-dimethyl-2-imidazolinone; if a solvent is present, the raw material is first dissolved in the solvent and then fed into a continuous reactor, wherein the mass concentration of the raw material is 5wt-100wt%, preferably 5wt-50wt%. Preferably, the molar ratio of the raw material and the ammonia source in step (2) is 1:2-1:100, and more preferably 1:5-1:

50.

4. The method according to claim 1, characterized in that, The carrier gas mentioned in step (2) is selected from one or more of nitrogen and helium, more preferably nitrogen; Preferably, the distillation purification in step (3) is atmospheric distillation purification with 50-55 plates, a bottom temperature of 100-130℃, a head temperature of 75-95℃, and a reflux ratio of 1:1-1:

10.

5. The method according to claim 1, characterized in that, When using methacrylamide as a raw material, an ammonia source may or may not be added.

6. A metal-modified molecular sieve catalyst, wherein the metal-modified molecular sieve catalyst is a supported catalyst, wherein the support is a molecular sieve, the active component is an oxide of a modified metal, and based on the total weight of the metal-modified molecular sieve catalyst, the content of the support is 50-98%, preferably 70-95%, and the content of the active component is 2-30%, preferably 5-20%.

7. The metal-modified molecular sieve catalyst according to claim 6, characterized in that, The molecules are screened from one or more of H-ZSM5, H-ZSM11, HY, Hβ, HMOR, and SAPO-34; preferably, the molecules are screened from H-ZSM5.

8. The metal-modified molecular sieve catalyst according to claim 6, characterized in that, The active ingredient is selected from one or more oxides of iron, zinc, tungsten, titanium, gallium, lanthanum, cerium, zirconium, and ytterbium.

9. The method for preparing the metal-modified molecular sieve catalyst according to claim 6, wherein the method is carried out according to the following steps: a. Calcine the molecular sieve powder at 400-600℃ for 5-10 hours; b. Mix the calcined molecular sieve powder with the modified metal salt solution, stir, and let stand for 3-10 hours, then filter. c. Dry the filtered molecular sieve at 100-120℃ for 8-15 hours, calcine it at 500-600℃ for 5-10 hours, add water and binder to the treated molecular sieve in proportion, mix them evenly to form a suspension, shear the suspension at high speed until 90% of the particles in the suspension are smaller than 8 micrometers, and spray granulate to form microspheres, wherein the binder is aluminum sol and / or silica sol. d. Dry the shaped material at 100-120℃ for 8-15 hours, and then calcine it at 500-600℃ for 5-12 hours to obtain the catalyst.

10. The method for preparing the metal-modified molecular sieve catalyst according to claim 9, characterized in that, Preferably, step b is carried out as follows: the molecular sieve powder and the modified metal salt solution are in a solid-liquid mass ratio of 1:

10. After standing at 80°C for 5 hours, the solid is separated. Then the above method is repeated at least twice. Finally, the mixture is washed with 5-10 times the volume of the modified metal salt solution of deionized water and then filtered. Preferably, the molecules are screened from one or more of H-ZSM5, H-ZSM11, HY, Hβ, HMOR, and SAPO-34; preferably, the molecules are screened from H-ZSM5. The modified metal is one or more of the elements selected from iron, zinc, tungsten, titanium, gallium, lanthanum, cerium, zirconium, and ytterbium. Preferably, the modified metal salt solution in step b is selected from the hydrochloride, nitrate, sulfate, or carbonate solution of the metal; Preferably, in the spray molding process described in step c, the binder is preferably in the range of 5-30%, and the suspension solid content is 20-60%.

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