A catalyst for preparing malononitrile, a preparation method thereof, and an application thereof

Abstract

The application discloses a catalyst for preparing malononitrile, a preparation method of the catalyst and a method for preparing malononitrile by using the catalyst. The catalyst is a solid catalyst, which is an acidic catalyst loaded with rare earth metal oxide. The method for preparing malononitrile is that cyanoacetic acid or cyanoacetate or cyanoacetamide and an ammonia source are subjected to ammoniation dehydration reaction in a continuous reactor to prepare malononitrile according to a certain molar ratio. Then, vacuum distillation (20 torr-25 torr) is carried out, and a fraction collected at 110 DEG C-120 DEG C is malononitrile product. The ammonia source can be ammonia gas, ammonia water, ammonium carbonate or urea. The method for preparing malononitrile can reduce production cost, improve production safety, reduce the discharge amount of three wastes in the preparation of malononitrile by using an existing process, and improve product quality, and is a sustainable and green synthesis route.

Description

Technical fields:

[0001] This application belongs to the field of pharmaceutical and chemical intermediates and related chemical technologies. Specifically, it relates to a catalyst for preparing malononitrile, a method for preparing the catalyst, and a method for preparing malononitrile using the catalyst. Background technology:

[0002] Malononitrile (chemical name 1,3-cyano-methane, also known as dicyanomethane or cyanoacetonitrile) is a colorless solid (<25℃), with a melting point of 32℃~34℃, a boiling point of 220℃, and a flash point of 112℃. It is readily soluble in water and soluble in organic solvents such as benzene and alcohols. Malononitrile is toxic, capable of causing central nervous system disorders, and is corrosive and explosive. It is an important raw material for organic synthesis and a crucial intermediate in the synthesis of pharmaceuticals (such as vitamin B1, triamterene, and adenine) and pesticides (such as oxadiazon, propionoxam, and thiamethoxam). Malononitrile also has important applications in the synthesis of dyes, metal corrosion inhibitors, and resin crosslinking agents.

[0003] There are many methods for synthesizing malononitrile, including the cyanoacetamide dehydration method, the propadiene oxidation ammonolysis method, the acetonitrile-ammonia-cyanide gas-phase method, the acetonitrile high-temperature pyrolysis method, and the acrylonitrile and aminoacetonitrile method. Except for the cyanoacetamide dehydration method, all other methods require high temperature and pressure, resulting in large equipment investments and stringent requirements. Gas-phase reactions, in particular, produce highly toxic cyanide, chlorine, and hydrogen cyanide, posing significant environmental challenges. The cyanoacetamide dehydration method is a commonly used method for synthesizing malononitrile due to its simple route, readily available and inexpensive raw materials, mild reaction conditions, low process requirements, simple equipment, and few byproducts. In the preparation of malononitrile via the cyanoacetamide dehydration method, commonly used dehydrating agents are phosphorus oxychloride, phosphorus pentachloride, and phosphorus pentoxide. However, the use of these dehydrating agents generates large amounts of phosphorus-containing solid waste during the reaction process.

[0004] To cope with increasingly stringent environmental regulations, domestic malononitrile producers have been upgrading their technologies and optimizing their processes, replacing phosphorus oxychloride with phosgene or solid phosgene (CN112724041A, CN103044286A, CN111440090A, CN104387290A, etc.), thereby significantly reducing phosphate formation. However, due to the low solubility of phosgene or solid phosgene in the solvents used and its high volatility, the reaction is less efficient, and the yield is generally lower than when phosphorus oxychloride is used as a dehydrating agent. Furthermore, phosgene is expensive, corrosive, and toxic, requiring strict control over production equipment and operations, and necessitating careful treatment of exhaust gas and wastewater. Furthermore, patent CN114057605A reports a gas-phase dehydration reaction of amides to nitriles in a tubular reactor in the presence of a solid bulk catalyst or a supported catalyst such as CoCl2 / activated carbon. While this solves the problem of traditional amide dehydration requiring large amounts of dehydrating agents and generating significant waste, it still suffers from high reaction temperatures, high energy consumption, and demanding equipment requirements. Additionally, the patent's claimed 100% malonamide conversion rate and over 99% malononitrile selectivity appear difficult to achieve.

[0005] To further reduce costs, researchers first prepared cyanoacetamide by amination of methyl (ethyl) cyanoacetate, and then dehydrated it to obtain malononitrile. CN1250773A describes adding an organic solvent to methyl cyanoacetate and introducing ammonia at a controlled temperature of 10℃–60℃ to generate cyanoacetamide, which is then collected. The cyanoacetamide is then reacted with an organic solvent and the dehydrating agent phosphorus oxychloride in a reactor, under the presence of a composite catalyst composed of diethylamine hydrochloride, anhydrous aluminum trichloride, and pyridine. The reaction product is collected to obtain crude malononitrile, which is then dissolved in anhydrous ethanol, cooled, crystallized, centrifuged, and distilled under reduced pressure to obtain high-purity malononitrile with a yield of 85%. CN104945278A and CN1264701A also report similar methods. However, these methods also require dehydrating agents such as phosphorus oxychloride, and still present serious waste problems.

[0006] With increasingly stringent safety policies and stringent environmental protection requirements in chemical production, the synthesis of malononitrile faces significant challenges. Traditional malononitrile synthesis processes are cumbersome and generate substantial amounts of waste, making them unsuitable for modern applications. Therefore, there is a need to develop new, more economical, and environmentally friendly processes for preparing malononitrile to address these shortcomings. Summary of the Invention:

[0007] To address the shortcomings of the existing technology, this application aims to provide a catalyst for preparing malononitrile, a method for preparing the same, and a method for preparing malononitrile using the catalyst. The catalyst is a solid catalyst, specifically an acidic catalyst supported on rare earth metal oxides. The method for preparing malononitrile involves ammoniation and dehydration reaction of cyanoacetic acid, cyanoacetic acid ester, or cyanoacetamide with an ammonia source at a specific molar ratio in a continuous reactor. The product is then subjected to vacuum distillation (20 to 25 torr), and the fraction collected at 110°C to 120°C is the malononitrile product. The ammonia source can be ammonia gas, ammonia water, ammonium carbonate, or urea. This method reduces production costs, decreases the amount of waste generated during malononitrile preparation using existing processes, and improves product quality.

[0008] According to one aspect of the present invention, an object of the present invention is to provide a catalyst for the preparation of malononitrile, said catalyst being an acidic catalyst supported on rare earth metal oxides, in solid form, comprising an acidic support and rare earth metal oxides as active components, said rare earth metal oxides accounting for 0.1% to 20% of the total mass of the acidic support, preferably 1% to 10%.

[0009] The acidic support is selected from at least one of SiO2, Al2O3, or molecular sieves, and is in the form of microspheres with a particle size of 30 μm to 280 μm. Preferably, the particle size is 75 μm to 200 μm; the specific surface area of ​​the acidic support is 250 m². 2 / g-500m 2 / g, pore size 1nm-15nm.

[0010] Preferably, the rare earth metal oxide is selected from one or more of the oxides of lanthanide rare earth elements, Sc2O3, Y2O3, etc., in any proportion; more preferably, the rare earth metal oxide is one or more of the oxides of CeO2, La2O3, Sm2O3, Sc2O3, Y2O3, etc., in any proportion; more preferably, the rare earth metal oxide is La2O3.

[0011] Preferably, the molecules are screened from at least one of ZSM-5, Hβ, SAPO-34, and HY.

[0012] According to another aspect of the present invention, another object of the present invention is to provide a method for preparing the catalyst for preparing malononitrile, the method comprising the following steps:

[0013] 1) Completely dissolve the precursor of rare earth metal oxides in an aqueous solution;

[0014] 2) Add the acidic support to an aqueous solution containing the rare earth metal oxide precursor and ultrasonically impregnate for 8 to 48 hours;

[0015] 3) Then place it in a drying oven at 120℃ for 12 hours; calcine it at 400℃~800℃ for 2 hours~6 hours to obtain a catalyst supported on rare earth metal oxides;

[0016] 4) Soak the catalyst loaded with rare earth metal oxides in an aqueous solution of organic or inorganic acid for 5-12 hours, then centrifuge and wash with water until neutral.

[0017] 5) After filtration, place the sample in a drying oven at 120°C for 12 hours to obtain the acidic catalyst supported on rare earth metal oxides.

[0018] Preferably, the precursor of the rare earth metal oxide in step 1) is selected from soluble salts of rare earth metals such as nitrates and acetylacetone salts, and is preferably a nitrate.

[0019] Preferably, the concentration of the aqueous solution of the organic or inorganic acid in step 4) is 0.05 mol / L to 0.5 mol / L, the organic acid is one of citric acid, tartaric acid, formic acid or acetic acid, the inorganic acid is one of hydrochloric acid, nitric acid, sulfuric acid or phosphoric acid, and the ratio of the acidic carrier to the aqueous solution of the organic or inorganic acid is 1 g: 8 mL to 15 mL.

[0020] Preferably, the preparation method of the acidic catalyst uses an aqueous solution of an inorganic acid for impregnation; more preferably, the aqueous solution of the inorganic acid is an aqueous solution of phosphoric acid.

[0021] According to another aspect of the invention, another object of the invention is to provide a method for preparing malononitrile using said catalyst, said method being shown in reaction formula 1 below:

[0022]

[0023] Malononitrile is prepared by ammoniation and dehydration reaction of cyanoacetic acid, cyanoacetic acid ester, or cyanoacetamide with an ammonia source in a continuous reactor at a specific molar ratio. The raw materials, cyanoacetic acid or cyanoacetamide, are solids and are quantitatively fed into the continuous reactor via a solid feeder, or heated to a molten state or dissolved in an inert solvent and quantitatively fed into the continuous reactor. The cyanoacetic acid ester is liquid and can be pumped into the reactor. The reaction of each raw material with the ammonia source yields a mixture containing malononitrile. The continuous reactor is equipped with the catalyst described according to the present invention. The malononitrile-containing mixture is then subjected to vacuum distillation at 20-25 torr, and the fraction collected at 110°C to 120°C is the malononitrile product.

[0024] The ammonia source is ammonia gas, ammonia water, ammonium carbonate, urea, etc., with ammonia gas being preferred. Ammonia gas can be controlled by a flow meter to enter the reactor through a preheater, and ammonia water can be controlled by a pump to enter the reactor through a preheater. Ammonium carbonate or urea can be mixed evenly with cyanoacetic acid at a certain molar ratio and then fed into the reactor by a solid feeder.

[0025] The inert solvent is acetonitrile, tetrahydrofuran, dichloromethane, dichloroethane, etc., preferably acetonitrile;

[0026] The reaction temperature for the method of preparing malononitrile is 200℃~400℃, preferably 250℃~350℃;

[0027] The reaction pressure is atmospheric pressure to 0.1 MPa;

[0028] The molar ratio of cyanoacetic acid or cyanoacetic acid ester or cyanoacetamide to the ammonia source (calculated based on the amount of ammonia that can be provided) is 1:1 to 1:20, preferably 1:2 to 1:10, wherein the amount of ammonia that can be provided is calculated based on 1 mole of ammonia water providing 0.25 moles of ammonia, 1 mole of ammonium carbonate providing 2 moles of ammonia, and 1 mole of urea providing 2 moles of ammonia.

[0029] The reaction space velocity is 0.01 h⁻¹. -1 ~100h -1 The preferred reaction space velocity is 0.1 h⁻¹. -1 ~1h -1 .

[0030] The reaction is carried out in a continuous reactor, which is either a fixed-bed reactor or a fluidized-bed reactor, preferably a fluidized-bed reactor.

[0031] When the continuous reactor is a fluidized bed reactor, the fluidizing gas used is selected from one or more of nitrogen, hydrogen and helium, preferably nitrogen.

[0032] Beneficial effects

[0033] The preparation method according to the present invention employs a specific solid acid catalyst to directly prepare malononitrile from cyanoacetic acid, cyanoacetic acid ester, or cyanoacetamide and an ammonia source. This method effectively reduces production costs, improves production safety, reduces the amount of waste generated during malononitrile preparation using existing processes, and improves product quality. It represents a sustainable and green synthetic route. Detailed Implementation

[0034] 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.

[0035] In this document, the terms “comprising,” “including,” “having,” “containing,” or any similar terms are open-ended transitional phrases intended to encompass non-exclusive inclusions. For example, a composition or article containing a plural element is not limited to the elements listed herein, but may also include other elements not explicitly listed but typically inherent to the composition or article. Furthermore, unless explicitly stated otherwise, 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 encompassing closed or semi-closed transitional phrases such as “composed of” and “substantially composed of.”

[0036] 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.

[0037] 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.

[0038] In this application, the preparation method employs a specific solid acid catalyst, enabling continuous processing. The main product after the reaction is malononitrile, and the main byproducts using cyanoacetic acid or cyanoacetic acid esters as raw materials are cyanoacetamide and high-boiling-point polymers. Cyanoacetamide can be removed by reducing the space velocity or increasing the reaction temperature. The main byproduct using cyanoacetamide as a raw material is a high-boiling-point polymer.

[0039] The catalytic activity of the catalyst for preparing malononitrile according to the present invention is affected by factors such as the composition, particle size, type of support, and loading of the active component used as the catalyst.

[0040] The catalyst for preparing malononitrile according to the present invention is an acidic catalyst supported on rare earth metal oxides, comprising an acidic support and rare earth metal oxides as the active component, wherein the rare earth metal oxides account for 0.1% to 20% of the total mass of the acidic support, preferably 1% to 10%. If the loading of rare earth metal oxides is too low, for example less than 0.1%, the conversion of cyanoacetic acid is incomplete, resulting in an increase in the intermediate product cyanoacetamide. As the loading increases, cyanoacetic acid is completely converted; however, as the loading continues to increase, the amount of cyanoacetamide increases. This may be because the increased loading reduces the specific surface area, thus decreasing the catalytic activity.

[0041] The acidic support is selected from at least one of SiO2, Al2O3, or molecular sieves, and is microspheres with a particle size of 30 μm to 280 μm, preferably 75 μm to 200 μm; the specific surface area of ​​the acidic support is 250 m² / g. 2 / g~500m 2 / g, pore size 1nm~15nm. Catalytic activity is most economical when the particle size, specific surface area, and pore size of the acidic support are controlled within the above range. For example, if the particle size is less than 30μm, although the specific surface area can be increased, the pore size in the support may be greatly reduced, which is not conducive to the penetration of the active ingredient precursor into the pores, and thus not conducive to the loading of the active ingredient. If the pore size of the support is increased, for example, to greater than 15nm, although the loading of the active ingredient and the specific surface area can be effectively increased, the mechanical strength of the support may decrease, and as the reaction time increases, phenomena such as catalyst pulverization may occur, resulting in a shortened reaction cycle. Therefore, controlling the particle size, specific surface area, and pore size of the support within the above range can achieve optimal catalyst performance.

[0042] Preferably, the rare earth metal oxide is selected from one or more of the oxides of lanthanide rare earth elements, Sc2O3, Y2O3, etc., in any proportion; more preferably, the rare earth metal oxide is one or more of the oxides of CeO2, La2O3, Sm2O3, Sc2O3, Y2O3, etc., in any proportion; more preferably, the rare earth metal oxide is La2O3.

[0043] Preferably, the molecules are screened from at least one of ZSM-5, Hβ, SAPO-34, and HY.

[0044] The method for preparing the catalyst for preparing malononitrile according to the present invention includes the following steps:

[0045] 1) Completely dissolve the precursor of rare earth metal oxides in an aqueous solution;

[0046] 2) Add the acidic support to an aqueous solution containing the rare earth metal oxide precursor and ultrasonically impregnate for 8 to 48 hours;

[0047] 3) Then place it in a drying oven at 120℃ for 12 hours; calcine it at 400℃~800℃ for 2 hours~6 hours to obtain a catalyst supported on rare earth metal oxides;

[0048] 4) Soak the catalyst loaded with rare earth metal oxides in an aqueous solution of organic or inorganic acid for 5-12 hours, then centrifuge and wash with water until neutral.

[0049] 5) After filtration, place the sample in a drying oven at 120°C for 12 hours to obtain the acidic catalyst supported on rare earth metal oxides.

[0050] Preferably, the precursor of the rare earth metal oxide in step 1) is selected from soluble salts of rare earth metals such as nitrates and acetylacetone salts, and is preferably a nitrate.

[0051] Preferably, the acid treatment in step 4) involves immersing the catalyst supported on rare earth metal oxides in an aqueous solution of an organic or inorganic acid, washing it with water until neutral, and then drying it. The concentration of the aqueous solution of the organic or inorganic acid is 0.05 mol / L to 0.5 mol / L. The organic acid is one of citric acid, tartaric acid, formic acid, or acetic acid; the inorganic acid is one of hydrochloric acid, nitric acid, sulfuric acid, or phosphoric acid. The ratio of the support to the aqueous solution of the organic or inorganic acid is 1 g: 8 mL to 15 mL. A certain degree of acid treatment can increase the specific surface area, pore volume, and pore size, thereby shortening the product diffusion path, weakening the pore confinement effect, reducing side reactions, and increasing selectivity. At the same time, acid treatment can expose more active sites, thereby improving the conversion rate of raw materials. If the acid concentration is too high, the acid radicals will remain in the system, forming additional acidic sites. Too many acidic sites can lead to side reactions such as cyano polymerization, affecting the selectivity of malononitrile.

[0052] Preferably, the preparation method of the acidic catalyst uses an aqueous solution of an inorganic acid for impregnation; more preferably, the aqueous solution of the inorganic acid is an aqueous solution of phosphoric acid.

[0053] According to the present invention, a method for preparing malononitrile using the catalyst is shown in reaction formula 1 below:

[0054]

[0055] Malononitrile is prepared by ammoniation and dehydration reaction of cyanoacetic acid, cyanoacetic acid ester, or cyanoacetamide with an ammonia source in a continuous reactor at a specific molar ratio. The raw materials, cyanoacetic acid or cyanoacetamide, are solids and are quantitatively fed into the continuous reactor via a solid feeder, or heated to a molten state or dissolved in an inert solvent and quantitatively fed into the continuous reactor. The cyanoacetic acid ester is liquid and can be pumped into the reactor. The reaction of each raw material with the ammonia source yields a mixture containing malononitrile. The continuous reactor is equipped with the catalyst described according to the present invention. The malononitrile-containing mixture is then subjected to vacuum distillation at 20-25 torr, and the fraction collected at 110°C to 120°C is the malononitrile product.

[0056] The ammonia source is ammonia gas, ammonia water, ammonium carbonate, urea, etc., with ammonia gas being preferred. Ammonia gas can be controlled by a flow meter to enter the reactor through a preheater, and ammonia water can be controlled by a pump to enter the reactor through a preheater. Ammonium carbonate or urea can be mixed evenly with cyanoacetic acid at a certain molar ratio and then fed into the reactor by a solid feeder.

[0057] The solvent is acetonitrile, tetrahydrofuran, dichloromethane, dichloroethane, etc., preferably acetonitrile;

[0058] The reaction temperature for the method of preparing malononitrile is 200℃~400℃, preferably 250℃~350℃;

[0059] The reaction pressure is atmospheric pressure to 0.1 MPa;

[0060] The molar ratio of cyanoacetic acid or cyanoacetic acid ester or cyanoacetamide to an ammonia source (calculated based on the amount of ammonia that can be provided, i.e., 1 mole of ammonia water provides 0.25 moles of ammonia, 1 mole of ammonium carbonate provides 2 moles of ammonia, and 1 mole of urea provides 2 moles of ammonia) is 1:1 to 1:20, preferably 1:2 to 1:10.

[0061] The reaction space velocity is 0.01 h⁻¹. -1 ~100h -1 The preferred reaction space velocity is 0.1 h⁻¹. -1 ~1h -1 .

[0062] The reaction is carried out in a continuous reactor, which is either a fixed-bed reactor or a fluidized-bed reactor, preferably a fluidized-bed reactor.

[0063] When the continuous reactor is a fluidized bed reactor, the fluidizing gas used is selected from one or more of nitrogen, hydrogen and helium, preferably nitrogen.

[0064] The method for preparing malononitrile according to the present invention features continuous process, high reactant selectivity and product conversion rate, and is simple, efficient, easy to operate, can be run continuously, is green and environmentally friendly, and produces less industrial waste. It is a sustainable, economical and green synthetic route.

[0065] 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.

[0066] In the following embodiments, the following detection instruments were used for analysis:

[0067] Quantitative testing: SHIMADZU HPLC-2010Plus liquid chromatograph;

[0068] Product identification: SHIMADZU-QP-2010-Ultra liquid chromatography-mass spectrometry.

[0069] Example

[0070] Example 1

[0071] In this embodiment, organic acids (citric acid, tartaric acid, acetic acid) and inorganic acids (phosphoric acid, hydrochloric acid, nitric acid) were used to treat SiO2 (average particle size 100 μm, specific surface area 380 m²). 2 SiO2 particles (8 nm pore size) were modified with an acid concentration of 0.3 mol / L for 10 h. The modification method involved immersing the SiO2 particles in the acid solution at a ratio of 1 g:10 mL for 10 h, followed by centrifugation and water washing until neutral. After filtration, the particles were dried in a drying oven at 120 °C for 12 h to obtain SiO2 particles modified with different acids. These modified SiO2 particles were then used to catalyze the synthesis of malononitrile from cyanoacetic acid and ammonia.

[0072] The method for synthesizing malononitrile using these modified SiO2 catalysts specifically includes the following steps: Solid cyanoacetic acid is fed into a continuous fluidized bed reactor via a high-precision solid feeder. Ammonia gas, used as the ammonia source, is preheated by a preheater and precisely controlled by a flow meter before entering the fluidized bed reactor. The molar ratio of cyanoacetic acid to ammonia gas is 1:3. The fluidized bed reactor is a straight tube made of quartz or stainless steel, and the reaction tube is packed with 300g of the various modified SiO2 catalysts prepared above, with a space velocity of 0.2h⁻¹. -1 The reaction was carried out at a controlled temperature of 300℃. After the conditions stabilized, the material flowing out of the fluidized bed reactor was collected to obtain malononitrile and other products. The product was then subjected to vacuum distillation (20 torr-25 torr), and the fraction collected at 110℃~120℃ was the malononitrile product. The reaction results were analyzed using liquid chromatography.

[0073] The reaction performance test results are shown in Table 1. As can be seen from Table 1, the catalytic activities of SiO2 modified with different acids vary considerably. The catalytic activities of SiO2 modified with organic acids (citric acid, tartaric acid, acetic acid) are basically equivalent to those of unmodified SiO2, while the catalytic activities of SiO2 modified with inorganic acids (phosphoric acid, hydrochloric acid, nitric acid) are all greater than those of unmodified SiO2. Among these, for phosphoric acid-modified SiO2, the conversion rate of cyanoacetic acid increased from 85.5% to 93.2% of unmodified SiO2, while the selectivity of malononitrile increased from 90.6% to 91.7%, indicating a better catalytic effect (effectiveness). Therefore, SiO2 modified with phosphoric acid among inorganic acids exhibits the best catalytic effect.

[0074] Table 1

[0075]

[0076] Example 2

[0077] In this embodiment, phosphoric acid was used to treat γ-Al₂O₃, ZSM-5, Hβ, SAPO-34, and HY (where γ-Al₂O₃ has an average particle size of 125 μm and a specific surface area of ​​280 m²). 2 / g, pore size 7nm; ZSM-5 average particle size 150μm, specific surface area 260m² 2 / g, pore size 12nm; Hβ average particle size 150μm, specific surface area 450m² 2 / g, pore size 5nm, average particle size of SAPO-34 150μm, specific surface area 480m² 2 / g, pore size 2nm; HY average particle size 150μm, specific surface area 300m² 2 The carrier particles (with a pore size of 10 nm) were modified with an acid concentration of 0.3 mol / L for 10 h. The modification method involved immersing the carrier particles in the acid solution at a ratio of 1 g:10 mL for 10 h, followed by centrifugation and washing with water until neutral. After filtration, the mixture was dried in a drying oven at 120 °C for 12 h to prepare catalysts with different phosphoric acid modifications. These modified catalysts were then used to catalyze the synthesis of malononitrile from cyanoacetic acid and ammonia, using the same method as in Example 1.

[0078] The reaction performance test results are shown in Table 2. Table 2 shows that phosphoric acid-modified γ-Al₂O₃ and HY exhibit poor catalytic activity, low cyanoacetic acid conversion, and high cyanoacetamide content. Phosphoric acid-modified ZSM-5, Hβ, and SAPO-34 show higher catalytic activity and better cyanoacetic acid conversion than phosphoric acid-modified SiO₂, but their malononitrile selectivity is slightly lower than that of phosphoric acid-modified SiO₂. However, the prices of ZSM-5, Hβ, and SAPO-34 are significantly higher than those of SiO₂.

[0079] Table 2

[0080]

[0081]

[0082] Example 3

[0083] This embodiment first provides an acidic catalyst supported on rare earth metal oxides, which is prepared through the following steps:

[0084] 37.85 g of cerium nitrate (Ce(NO3)3·6H2O) was added to 500 mL of aqueous solution and stirred to dissolve. Then, 300 g of SiO2 (average particle size 100 μm, specific surface area 380 m²) was added. 2 / g (pore size 8nm), ultrasonically impregnated for 12h. Drying in a drying oven at 120℃ for 12h, followed by calcination at 600℃ for 5h, yields a catalyst supported on rare earth metal oxides. The supported catalyst is then added to 3L of a 0.3mol / L phosphoric acid solution and soaked for 10h. Water is removed by suction filtration, and the solution is washed with water until neutral. It is then dried at 120℃ to obtain an acidic catalyst supported on rare earth metal oxides: 5% CeO2 / phosphoric acid modified SiO2. Here, "5%" refers to the CeO2 content in the final catalyst product being approximately 5% of the phosphoric acid modified SiO2 support.

[0085] 5% La2O3 / phosphoric acid modified SiO2, 5% Sm2O3 / phosphoric acid modified SiO2, 5% Sc2O3 / phosphoric acid modified SiO2, and 5% Y2O3 / phosphoric acid modified SiO2 were prepared as catalysts using similar methods.

[0086] These modified catalysts were used to catalyze the synthesis of malononitrile from cyanoacetic acid and ammonia, respectively, using the same method as in Example 1.

[0087] Table 3 shows the catalytic performance of malononitrile synthesis from cyanoacetic acid and urea using 5% CeO2 / phosphoric acid modified SiO2, 5% La2O3 / phosphoric acid modified SiO2, 5% Sm2O3 / phosphoric acid modified SiO2, 5% Sc2O3 / phosphoric acid modified SiO2, and 5% Y2O3 / phosphoric acid modified SiO2 as catalysts. The comparison shows that loading rare earth metal oxides onto the catalyst can further improve the conversion rate of cyanoacetic acid, maintain the malononitrile selectivity above 91%, and further improve the malononitrile yield. Among these, La2O3 / phosphoric acid modified SiO2 showed the best catalytic effect.

[0088] Table 3

[0089]

[0090]

[0091] Example 4

[0092] In this embodiment, the catalyst selected is the La2O3 / phosphoric acid modified SiO2 catalyst from Example 3, and the raw material is methyl cyanoacetate or cyanoacetamide. Ammonia gas is the ammonia source. Solid cyanoacetamide is quantitatively fed into the continuous fluidized bed reactor via a solid feeder, methyl cyanoacetate is pumped into the fluidized bed reactor, and ammonia gas is preheated by a preheater and then enters the fluidized bed reactor under precise flow meter control. The molar ratio of methyl cyanoacetate or cyanoacetamide to ammonia gas is 1:3. Other conditions are the same as in Example 1. The product is distilled under reduced pressure (20 torr-25 torr), and the fraction collected at 110℃~120℃ is the malononitrile product. The reaction results are analyzed using liquid chromatography.

[0093] Table 4 shows the reaction performance test results of methyl cyanoacetate or cyanoacetamide with ammonia in the preparation of malononitrile using 5% La2O3 / phosphoric acid modified SiO2 as a catalyst. With methyl cyanoacetate as the raw material, the conversion rate was lower than that of cyanoacetic acid under the same reaction conditions, while the selectivity was basically the same. With cyanoacetamide as the raw material, the malononitrile yield reached 94.8%, but the price of cyanoacetamide was relatively high.

[0094] Table 4

[0095]

[0096] Example 5

[0097] In this embodiment, the catalyst selected is the La2O3 / phosphoric acid modified SiO2 catalyst from Example 3. The ammonia source differs in the malononitrile preparation method. The ammonia sources are ammonia water, ammonium carbonate, and urea. 25% ammonia water is precisely controlled by a pump and enters the reactor via a preheater. Ammonium carbonate monohydrate or urea is mixed uniformly with cyanoacetic acid at a specific molar ratio and then quantitatively fed into the reactor via a solid feeder. The molar ratio of cyanoacetic acid to ammonia source is controlled at 1:3. Other conditions are the same as in Example 1. The product is distilled under reduced pressure (20 torr-25 torr), and the fraction collected at 110℃~120℃ is the malononitrile product. The reaction results are analyzed using liquid chromatography.

[0098] Table 5 shows the reaction performance test results of malononitrile synthesis from cyanoacetic acid and different ammonia sources using 5% La2O3 / phosphoric acid modified SiO2 as a catalyst. Ammonia water, as an ammonia source, partially inhibits the dehydration reaction of cyanoacetamide due to the presence of a large amount of water, resulting in lower malononitrile selectivity. Ammonium carbonate and urea, as ammonia sources, may have incomplete decomposition issues, similarly leading to a decrease in product selectivity.

[0099] Table 5

[0100]

[0101] Example 6

[0102] In this embodiment, phosphoric acid-modified NaY molecular sieve and 5A molecular sieve catalysts were prepared according to Examples 2 and 3. Phosphoric acid-modified SiO2 supported catalysts were prepared using MgO, Fe2O3, NiO, and ZnO as active components. These modified catalysts were then used to catalyze the synthesis of malononitrile from cyanoacetic acid and ammonia, respectively. The preparation method of malononitrile was the same as in Example 1.

[0103] Table 6 shows the catalyst evaluation results. Basic molecular sieves NaY and 5A have a relatively small effect on the dehydration reaction of cyanoacetamide, resulting in lower malononitrile selectivity. The reaction of cyanoacetic acid with ammonia to form cyanoacetamide is a non-catalytic reaction; because the cyanoacetamide fails to react and move out in time, the conversion rate of cyanoacetic acid is reduced. The phosphoric acid-modified SiO2 catalyst supported on MgO, Fe2O3, NiO, and ZnO is slightly worse than that of phosphoric acid-modified SiO2, possibly because the loading of other metals affects the acidity of the catalyst.

[0104] Table 6

[0105]

[0106]

[0107] The specific embodiments described above are merely preferred embodiments for explaining this application and are not intended to limit this application. Those skilled in the art can make modifications without creative contribution as needed after reading this specification. However, any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A catalyst for preparing malononitrile, said catalyst being an acidic catalyst supported on rare earth metal oxides, in solid form, comprising an acidic support and rare earth metal oxides as the active component, said rare earth metal oxides accounting for 0.1% to 20% of the total mass of the acidic support; The acidic support is selected from at least one of SiO2, Al2O3, or molecular sieves, and is microspheres with a particle size of 30 μm to 280 μm; the specific surface area of ​​the acidic support is 250 m². 2 / g -500m 2 / g, pore size 1nm-15nm, the molecules are screened from at least one of ZSM-5, Hβ, SAPO-34, and HY; The rare earth metal oxide is one or a mixture of two or more of CeO2, La2O3, Sm2O3, Sc2O3, and Y2O3 in any proportion; The method for preparing the catalyst includes the following steps: 1) Completely dissolve the rare earth metal oxide precursor in an aqueous solution; 2) Add the acidic support to the aqueous solution containing the rare earth metal oxide precursor and ultrasonically impregnate for 8h~48h; 3) Then place it in a drying oven at 120℃ for 12 hours; calcine it at 400℃~800℃ for 2 hours~6 hours to obtain a catalyst supported on rare earth metal oxides; 4) Soak the catalyst loaded with rare earth metal oxides in an aqueous solution of organic or inorganic acid for 5-12 hours, then centrifuge and wash with water until neutral. 5) After filtration, place the sample in a drying oven at 120°C for 12 hours to obtain the acidic catalyst supported on rare earth metal oxides. The concentration of the aqueous solution of the organic or inorganic acid mentioned in step 4) is 0.05 mol / L to 0.5 mol / L. The organic acid is one of citric acid, tartaric acid, formic acid or acetic acid, and the inorganic acid is one of hydrochloric acid, nitric acid, sulfuric acid or phosphoric acid. The ratio of the acidic carrier to the aqueous solution of the organic or inorganic acid is 1 g : 8 mL to 15 mL.

2. The catalyst for preparing malononitrile according to claim 1, characterized in that, The rare earth metal oxides account for 1% to 10% of the total mass of the acidic carrier.

3. The catalyst for preparing malononitrile according to claim 1 or 2, characterized in that, The acidic carrier has a particle size of 75μm to 200μm.

4. The catalyst for preparing malononitrile according to claim 1 or 2, characterized in that, The rare earth metal oxide is La2O3.

5. A method for preparing a catalyst for preparing malononitrile according to any one of claims 1 to 4, the method comprising the following steps: 1) Completely dissolve the rare earth metal oxide precursor in an aqueous solution; 2) Add the acidic support to the aqueous solution containing the rare earth metal oxide precursor and ultrasonically impregnate for 8h~48h; 3) Then place it in a drying oven at 120℃ for 12 hours; calcine it at 400℃~800℃ for 2 hours~6 hours to obtain a catalyst supported on rare earth metal oxides; 4) Soak the catalyst loaded with rare earth metal oxides in an aqueous solution of organic or inorganic acid for 5-12 hours, then centrifuge and wash with water until neutral. 5) After filtration, place the sample in a drying oven at 120°C for 12 hours to obtain the acidic catalyst supported on rare earth metal oxides.

6. The preparation method according to claim 5, characterized in that, The precursors of rare earth metal oxides mentioned in step 1) are selected from rare earth metal nitrates and acetylacetone salts.

7. The preparation method according to claim 6, characterized in that, The precursor of the rare earth metal oxide mentioned in step 1) is nitrate.

8. The preparation method according to claim 5, characterized in that, The concentration of the aqueous solution of the organic or inorganic acid mentioned in step 4) is 0.05 mol / L to 0.5 mol / L. The organic acid is one of citric acid, tartaric acid, formic acid or acetic acid, and the inorganic acid is one of hydrochloric acid, nitric acid, sulfuric acid or phosphoric acid. The ratio of the acidic carrier to the aqueous solution of the organic or inorganic acid is 1 g : 8 mL to 15 mL.

9. The preparation method according to claim 5, characterized in that, The preparation method of the acidic catalyst uses an aqueous solution of inorganic acid for impregnation.

10. The preparation method according to claim 9, characterized in that, The aqueous solution of the inorganic acid is an aqueous solution of phosphoric acid.

11. A method for preparing malononitrile, the method being carried out as shown in reaction formula 1 below, and using the catalyst according to any one of claims 1 to 4. Reaction 1 Malononitrile is prepared by ammoniation and dehydration reaction of cyanoacetic acid, cyanoacetic acid ester, or cyanoacetamide and an ammonia source in a continuous reactor at a certain molar ratio. The ammonia source is ammonia gas, ammonia water, ammonium carbonate, or urea. The raw materials, cyanoacetic acid or cyanoacetamide, are solids and are quantitatively fed into the continuous reactor by a solid feeder, or they are heated to a molten state or dissolved in an inert solvent and quantitatively fed into the continuous reactor; cyanoacetic acid esters are liquids and can be controlled to enter the reactor by a pump. The raw material reacts with an ammonia source to obtain a mixture containing malononitrile. The continuous reactor is equipped with a catalyst according to any one of claims 1 to 4. The mixture containing malononitrile is subjected to vacuum distillation at 20 torr-25 torr, and the fraction collected at 110℃ to 120℃ is the malononitrile product.

12. The method for preparing malononitrile according to claim 11, characterized in that, The ammonia source is ammonia gas; ammonia gas is controlled by a flow meter to enter the reactor through the preheater, and ammonia water is controlled by a pump to enter the reactor through the preheater. Ammonium carbonate or urea and cyanoacetic acid are mixed evenly at a certain molar ratio and then fed into the reactor by a solid feeder. The inert solvent is acetonitrile, tetrahydrofuran, dichloromethane, or dichloroethane; The reaction temperature for the method of preparing malononitrile is 200℃~400℃; The reaction pressure is atmospheric pressure to 0.1 MPa; The molar ratio of cyanoacetic acid or cyanoacetic acid ester or cyanoacetamide to the ammonia source calculated based on the amount of ammonia that can be provided is 1:1 to 1:20, wherein the amount of ammonia that can be provided is calculated based on 1 mole of ammonia water providing 0.25 moles of ammonia, 1 mole of ammonium carbonate providing 2 moles of ammonia, and 1 mole of urea providing 2 moles of ammonia. The reaction space velocity was 0.01 h⁻¹. -1 ~100h -1 ; The reaction is carried out in a continuous reactor, which is either a fixed-bed reactor or a fluidized-bed reactor. When the continuous reactor is a fluidized bed reactor, the fluidizing gas used is selected from one or more of nitrogen, hydrogen and helium.

13. The method for preparing malononitrile according to claim 11, characterized in that, The inert solvent is acetonitrile; The reaction temperature for the method of preparing malononitrile is 250℃~350℃; The molar ratio of cyanoacetic acid or methyl cyanoacetate or cyanoacetamide to the ammonia source calculated based on the amount of ammonia available is 1:2 to 1:

10. The reaction space velocity is 0.1 h⁻¹. -1 ~1h -1 ; The continuous reactor is a fluidized bed reactor; When the continuous reactor is a fluidized bed reactor, nitrogen is used as the fluidizing gas.

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