Method for preparing methacrylic acid with high selectivity

Abstract

The invention discloses a method for preparing methacrylic acid with high selectivity, which comprises the following steps: sequentially carrying out deep acid treatment and silanization modification treatment on a molecular sieve to obtain a modified molecular sieve catalyst, taking a methacrylamide aqueous solution as a raw material, introducing the methacrylamide aqueous solution into a reactor loaded with the catalyst, and carrying out hydrolysis reaction to obtain the methacrylic acid with high selectivity. Methacrylamide is hydrolyzed to prepare methacrylic acid, and the methacrylic acid prepared by the method is high in selectivity; the method is easy to industrially amplify and has a relatively good application prospect.

Description

Technical Field

[0001] This invention relates to the field of methacrylic acid preparation technology, and more specifically, to a method for highly selectively preparing methacrylic acid. Background Technology

[0002] Methacrylic acid is an important chemical raw material. It possesses two functional groups: a carbon-carbon double bond and a carboxylic acid group, allowing it to undergo polymerization and esterification reactions. It can be used to prepare methyl methacrylate, coatings, synthetic rubber, adhesives, fabric treatment agents, resins, polymer additives, and functional polymers. It is a colorless, transparent liquid at room temperature. It is readily soluble in hot water, ethanol, and most organic solvents. It is an important organic chemical raw material and a polymer intermediate.

[0003] (Meth)acrylic acid is typically prepared by gas-phase oxidation of compounds such as propane, propylene, and (meth)acrylaldehyde in the presence of a catalyst. For example, in a reactor, propane, propylene, etc., are converted to (meth)acrylic acid via gas-phase oxidation of (meth)acrylaldehyde in the presence of a suitable catalyst. A mixed gas is obtained in the later stage of the reactor, containing (meth)acrylic acid, unreacted propane or propylene, (meth)acrylaldehyde, inert gas, carbon dioxide, water vapor, and various organic byproducts (such as acetic acid, low-boiling byproducts, and high-boiling byproducts). However, this method suffers from low product selectivity, numerous byproducts, and difficulty in processing them. CN101538197A discloses a method for preparing methacrylic acid by hydrolysis of methacrylamide, but this method uses 30-65 wt% sulfuric acid and 0-5 wt% additives, which is not conducive to separation during production.

[0004] Therefore, there is a need to develop a novel method for the hydrolysis of methacrylamide to produce methacrylic acid. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a method for preparing methacrylic acid with high selectivity. The method utilizes the hydrolysis of methacrylamide to prepare methacrylic acid, and the methacrylic acid prepared by this method has high selectivity; it is easy to scale up industrially and has good application prospects.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A method for highly selectively preparing methacrylic acid, the method comprising the following steps: mixing methacrylamide with water to obtain an aqueous solution of methacrylamide; passing the aqueous solution of methacrylamide into a reactor carrying a solid acid catalyst for hydrolysis reaction to obtain methacrylic acid; wherein the solid acid catalyst is a modified molecular sieve catalyst.

[0007] Optionally, the solid acid catalyst is a modified molecular sieve catalyst that has undergone deep acid treatment and organosilane treatment.

[0008] Optionally, the preparation method of the solid acid catalyst includes the following steps: S1. The molecular sieve is subjected to deep acid treatment to obtain precursor I; S2. Treat the precursor I with an organosilane to obtain precursor II; S3. The precursor II is calcined to obtain the solid acid catalyst.

[0009] Optionally, the preparation method of the solid acid catalyst includes the following steps: (1) Add the molecular sieve to a three-necked flask containing an acid solution, turn on the stirrer, and reflux at 60-80°C for 4-24 hours. After the reaction is complete, cool to room temperature, filter the resulting mixture, and wash the filter cake repeatedly with deionized water until the filtrate is neutral (pH≈7). Place the treated filter cake in an oven at 110°C and dry overnight for 12 hours to obtain precursor I. This step can be repeated once or multiple times. (2) The precursor I was activated in a Schlenk flask and treated at 120°C and <0.1 mmHg vacuum for 2 h to obtain the activated molecular sieve; under glove box or inert gas protection, 100 ml of anhydrous toluene was added to another dry flask, and then silane reagent was slowly added to obtain silane-toluene solution; the activated molecular sieve was quickly added to the silane-toluene solution, and the entire system was continuously purged with inert gas protection. The stirring was turned on, and the reaction system was heated to 110°C and reacted for 12-24 h, and then cooled to room temperature; the mixture was filtered under inert gas protection and washed with anhydrous toluene and anhydrous ethanol in sequence; the washed solid was vacuum dried at 60°C for 6-12 h to obtain the hydrophobically modified precursor II; (3) The precursor II is heated to 350-650°C at a heating rate of 1-5°C / min in air or N2 atmosphere, and kept at this temperature for 4-8h to obtain the solid acid catalyst.

[0010] Optionally, in step (1), the acid in the acid solution is selected from at least one of hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, oxalic acid, acetic acid, citric acid and p-toluenesulfonic acid.

[0011] Optionally, in step (1), the molecular sieve is selected from at least one of MWW molecular sieve, FER molecular sieve, MTT molecular sieve, MFI molecular sieve, MEL molecular sieve, MOR molecular sieve, FAU molecular sieve, CHA molecular sieve and BEA molecular sieve; preferably, the molecular sieve is selected from at least one of MCM-22 molecular sieve, mordenite molecular sieve, ZSM-35 molecular sieve, ZSM-23 molecular sieve, ZSM-5 molecular sieve, ZSM-11 molecular sieve, Y molecular sieve, SAPO-34 molecular sieve and β molecular sieve.

[0012] Optionally, in step (1), the atomic ratio of silicon to aluminum in the molecular sieve is Si / Al = 2 to 500.

[0013] Optionally, in step (1), the concentration of the acid solution is 0.1~1.0 mol / L.

[0014] Optionally, in step (1), the mass-to-volume ratio of the molecular sieve to the acid solution is 1 / 5 to 1 / 30.

[0015] Optionally, in step (2), the inert gas is selected from at least one of N2 and Ar.

[0016] Optionally, in step (2), the silane reagent is selected from at least one of trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, octyltrichlorosilane, octadecyltrichlorosilane, methyltrimethoxysilane, trimethylmethoxysilane, dimethyldimethoxysilane, n-octyltriethoxysilane, hexadecyltrimethoxysilane, octadecyltrimethoxysilane, phenyltrimethoxysilane, and trimercaptopropyltrimethoxysilane.

[0017] Optionally, in step (2), the mass ratio of the silane reagent to the molecular sieve is 1:5 to 1:20.

[0018] Optionally, in step (2), the washing with anhydrous toluene is performed 3 times and the washing with anhydrous ethanol is performed 2 times.

[0019] Optionally, the particle size of the solid acid catalyst is 20-40 mesh.

[0020] Optionally, the reactor may consist of one or more reactors connected in series and / or in parallel.

[0021] Optionally, the mass ratio of the methacrylamide to the water is 10:90 to 80:20.

[0022] Optionally, the hydrolysis reaction is carried out at a temperature of 100–400°C, a pressure of 0.1–10 MPa, and a reaction time of 2–8 h, and the mass hourly space velocity (WHSV) of the methacrylamide aqueous solution is 0.1–10 h⁻¹.-1 Preferably, the hydrolysis reaction is carried out at a temperature of 150–350°C, a pressure of 0.1–5 MPa, and a reaction time of 2–8 h, with the mass hourly space velocity (MSV) of the methacrylamide aqueous solution being 0.5–5.0 h⁻¹. -1 .

[0023] Optionally, the reactor is selected from at least one of a batch reactor, a fixed bed reactor, a moving bed reactor, and a fluidized bed reactor.

[0024] Implementing the embodiments of the present invention will have the following beneficial effects: This invention involves subjecting molecular sieves to deep acid treatment and silanization modification to obtain a modified molecular sieve catalyst. Aqueous solutions of methacrylamide are then introduced into a reactor containing the modified molecular sieve catalyst for hydrolysis, enabling the preparation of methacrylic acid via the hydrolysis of methacrylamide. This method produces methacrylic acid with high selectivity, is easily scaled up for industrial applications, and has promising application prospects. Detailed Implementation

[0025] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0026] Example 1 Catalyst preparation: 10 g of ZSM-5 (Si / Al = 30) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L nitric acid solution; stirring was started, and the mixture was refluxed at 80°C for 6 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once to obtain precursor I.

[0027] Precursor I was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 1.0 g of trimethylchlorosilane reagent to obtain a silane-toluene solution. The activated molecular sieve was rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 24 h. After the reaction was complete, it was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h to obtain the hydrophobically modified precursor II.

[0028] The hydrophobically modified precursor II powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare the methacrylamide hydrolysis catalyst. Catalyst evaluation: Methacrylamide and water were mixed at a mass ratio of 20:80 to obtain an aqueous solution of methacrylamide. 4.0 g of the above-mentioned methacrylamide hydrolysis catalyst was packed into a fixed-bed reactor. The aqueous solution of methacrylamide was fed into the fixed-bed reactor by a micro-plunger pump for hydrolysis reaction. The feed rate of the aqueous solution of methacrylamide was 20.0 g / h, the reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0029] Example 2 Catalyst preparation: 10 g of MCM-22 (Si / Al = 20) molecular sieve was placed in a three-necked flask containing 200 ml of 0.2 mol / L sulfuric acid solution; stirring was started, and the mixture was refluxed at 80°C for 6 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0030] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 1.0 g of methyltrichlorosilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 24 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0031] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0032] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0033] Example 3 Catalyst preparation: 10 g of MOR (Si / Al = 17) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L hydrochloric acid solution; stirring was started, and the mixture was refluxed at 80°C for 6 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0034] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of dimethyldichlorosilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 24 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0035] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0036] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0037] Example 4 Catalyst preparation: 10 g of ZSM-23 (Si / Al = 62) molecular sieve was placed in a three-necked flask containing 200 mL of 0.3 mol / L phosphoric acid solution; stirring was started, and the mixture was refluxed at 60°C for 8 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0038] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of octyltrichlorosilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 24 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0039] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0040] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0041] Example 5 Catalyst preparation: 10 g of Y (Si / Al = 17) molecular sieve was placed in a three-necked flask containing 200 ml of 0.3 mol / L p-toluenesulfonic acid solution; stirring was started, and the mixture was refluxed at 60°C for 8 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0042] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of octadecyltrichlorosilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 24 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0043] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0044] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0045] Example 6 Catalyst preparation: 10 g of magnesium alkali zeolite (Si / Al = 62) molecular sieve was placed in a three-necked flask containing 200 ml of 0.8 mol / L citric acid solution; stirring was started, and the mixture was refluxed at 70°C for 8 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0046] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of methyltrimethoxysilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0047] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0048] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0049] Example 7 Catalyst preparation: 10 g of Beta (Si / Al = 46) molecular sieve was placed in a three-necked flask containing 200 mL of 0.5 mol / L acetic acid solution; stirring was started, and the mixture was refluxed at 60°C for 8 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0050] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of trimethylmethoxysilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0051] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0052] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0053] Example 8 Catalyst preparation: 10 g of SAPO-34 (Si / Al = 30) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L oxalic acid solution; stirring was started, and the mixture was refluxed at 60°C for 8 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0054] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of dimethyldimethoxysilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0055] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0056] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0057] Example 9 Catalyst preparation: 10 g of ZSM-11 (Si / Al = 25) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L hydrofluoric acid solution; stirring was started, and the mixture was refluxed at 60°C for 8 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0058] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 0.8 g of n-octyltriethoxysilane reagent. The activated molecular sieve was then rapidly added to a silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0059] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0060] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0061] Example 10 Catalyst preparation: 10 g of ZSM-5 (Si / Al = 30) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L nitric acid solution; stirring was started, and the mixture was refluxed at 80°C for 6 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0062] The acid-treated and dried molecular sieves were activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 0.8 g of hexadecyltrimethoxysilane reagent. The activated molecular sieves were then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0063] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0064] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0065] Example 11 Catalyst preparation: 10 g of MCM-22 (Si / Al = 20) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L oxalic acid solution; stirring was started, and the mixture was refluxed at 80°C for 4 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0066] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of octadecyltrimethoxysilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0067] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0068] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0069] Example 12 Catalyst preparation: 10 g of magnesium alkali zeolite (Si / Al = 62) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L nitric acid solution; stirring was started, and the mixture was refluxed at 70°C for 6 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0070] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of phenyltrimethoxysilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0071] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0072] Catalyst evaluation: The above-mentioned 4.0 g catalyst was packed into a fixed bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis reaction. The mass ratio of methacrylamide to water was 20:80, and the feed rate of methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0073] Example 13 Catalyst preparation: 10 g of MOR (Si / Al = 17) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L acetic acid solution; stirring was started, and the mixture was refluxed at 60°C for 16 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0074] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of trimercaptopropyltrimethoxysilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0075] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0076] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0077] Example 14 Catalyst preparation: 10 g of ZSM-23 (Si / Al = 62) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L acetic acid solution; stirring was started, and the mixture was refluxed at 60°C for 16 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0078] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 1.0 g of methyltrichlorosilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0079] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0080] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0081] Example 15 Catalyst preparation: 10 g of Beta (Si / Al = 46) molecular sieve was placed in a three-necked flask containing 200 mL of 0.5 mol / L p-toluenesulfonic acid solution; stirring was started, and the mixture was refluxed at 60°C for 16 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0082] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 1.0 g of methyltrichlorosilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0083] The hydrophobically modified molecular sieve powder was heated to 450°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain 20-40 mesh particles to prepare a methacrylamide hydrolysis catalyst.

[0084] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 260℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0085] Example 16 Catalyst preparation: 10 g of SAPO-34 (Si / Al = 30) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L p-toluenesulfonic acid solution; stirring was started, and the mixture was refluxed at 60°C for 16 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0086] The acid-treated and dried molecular sieves were activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of octadecyltrichlorosilane reagent. The activated molecular sieves were then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0087] The hydrophobically modified molecular sieve powder was heated to 450°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample, thus preparing a methacrylamide hydrolysis catalyst.

[0088] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 300℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0089] Example 17 Catalyst preparation: 10 g of ZSM-11 (Si / Al = 25) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L hydrofluoric acid solution; stirring was started, and the mixture was refluxed at 70°C for 8 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0090] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of n-octyltriethoxysilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0091] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0092] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 40:60, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 260℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0093] Example 18 Catalyst preparation: 10 g of ZSM-5 (Si / Al = 30) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L nitric acid solution; stirring was started, and the mixture was refluxed at 70°C for 8 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0094] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of hexadecyltrimethoxysilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0095] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0096] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 1000 h. The results are shown in Table 1.

[0097] Example 19 Catalyst preparation: 10 g of MCM-22 (Si / Al = 20) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L oxalic acid solution; stirring was started, and the mixture was refluxed at 70°C for 8 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0098] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of octadecyltrimethoxysilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0099] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0100] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. The raw materials were fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 40:60, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 300℃, the reaction pressure was 1.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0101] Example 20 Catalyst preparation: 10 g of magnesium alkali zeolite (Si / Al = 62) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L nitric acid solution; stirring was started, and the mixture was refluxed at 70°C for 8 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0102] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of phenyltrimethoxysilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 12 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0103] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0104] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump for hydrolysis. The mass ratio of methacrylamide to water was 40:60, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 150℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0105] Comparative Example 1 Catalyst preparation: 10 g of ZSM-5 (Si / Al = 30) molecular sieve was placed in 200 ml of 0.5 mol / L nitric acid aqueous solution and treated at 60 °C for 3 h. After filtration and washing, the above acid treatment process was repeated twice after drying. The sample obtained above was calcined at 550 °C for 4 h in air atmosphere. The calcined solid powder was pressed into tablets, crushed and sieved to 20-40 mesh to obtain the methacrylamide hydrolysis catalyst.

[0106] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 30.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0107] Comparative Example 2 Catalyst preparation: 10 g of ZSM-5 (Si / Al = 30) molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of trimethylchlorosilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 24 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0108] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0109] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0110] Comparative Example 3 Catalyst preparation: 10 g of ZSM-5 (Si / Al = 30) molecular sieve was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 h. The calcined solid powder was pressed into tablets, crushed, and sieved to 20-40 mesh to obtain a methacrylamide hydrolysis catalyst.

[0111] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0112] Comparative Example 4 Catalyst preparation: 10 g of ZSM-5 (Si / Al = 30) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L nitric acid solution; stirring was started, and the mixture was refluxed at 80°C for 24 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0113] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of trimethylchlorosilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 24 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0114] The hydrophobically modified molecular sieve powder was heated to 300°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain 20-40 mesh particles to prepare a methacrylamide hydrolysis catalyst.

[0115] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0116] Comparative Example 5 Catalyst preparation: 10 g of ZSM-5 (Si / Al = 30) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L nitric acid solution; stirring was started, and the mixture was refluxed at 90°C for 16 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0117] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of trimethylchlorosilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 24 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0118] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0119] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 100℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0120] Comparative Example 6 Catalyst preparation: 10 g of ZSM-5 (Si / Al = 30) molecular sieve was placed in a three-necked flask containing 200 ml of 0.5 mol / L nitric acid solution; stirring was started, and the mixture was refluxed at 40°C for 6 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH ≈ 7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0121] The acid-treated and dried molecular sieve was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under a glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of trimethylchlorosilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 24 h. After the reaction was complete, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0122] The hydrophobically modified molecular sieve powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0123] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0124] Comparative Example 7 Catalyst preparation: 10 g of alumina was calcined at 550 °C for 4 h in air atmosphere. The calcined solid powder was pressed into tablets, crushed, and sieved to obtain 20-40 mesh to prepare a methacrylamide hydrolysis catalyst.

[0125] Catalyst evaluation: 4.0 g of catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0126] Comparative Example 8 Catalyst preparation: 10 g of alumina was placed in a three-necked flask containing 200 ml of 0.5 mol / L nitric acid solution; stirring was started, and the mixture was refluxed at 80°C for 6 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH≈7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0127] Acid-treated and dried alumina was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 h. Under glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of trimethylchlorosilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 24 h. After the reaction, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 h.

[0128] Hydrophobically modified alumina powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0129] Catalyst evaluation: 4.0 g of catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0130] Comparative Example 9 Catalyst preparation: 10 g of silica was calcined at 550 °C for 4 h in air atmosphere. The calcined solid powder was pressed into tablets, crushed, and sieved to obtain 20-40 mesh to prepare a methacrylamide hydrolysis catalyst.

[0131] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, and the reaction pressure was 2.0 MPa. The reaction results are shown in Table 1.

[0132] Comparative Example 10 Catalyst preparation: 10 g of silica was placed in a three-necked flask containing 200 ml of 0.5 mol / L nitric acid solution; stirring was started, and the mixture was refluxed at 80°C for 6 h; after the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was repeatedly washed with a large amount of deionized water until the filtrate was neutral (pH≈7); the filter cake was then dried in an oven at 110°C overnight for 12 h. The above steps were repeated once.

[0133] Acid-treated and dried silica was activated in a Schlenk flask and treated under vacuum (<0.1 mmHg) at 120°C for 2 hours. Under glove box or inert gas protection, 100 mL of anhydrous toluene was added to another dry flask, followed by the slow addition of 2.0 g of trimethylchlorosilane reagent. The activated molecular sieve was then rapidly added to the silane-toluene solution. The entire system was continuously purged with N2, stirred, and heated to 110°C for 24 hours. After the reaction, the mixture was cooled to room temperature. The mixture was filtered under N2 protection, washed three times with anhydrous toluene, and then twice with anhydrous ethanol. The resulting solid was dried under vacuum at 60°C for 8 hours.

[0134] Hydrophobically modified silica powder was heated to 550°C at a rate of 2°C / min under air or N2 atmosphere and held at this temperature for 8 hours. The calcined solid powder was then pressed into tablets, crushed, and sieved to obtain a 20-40 mesh sample to prepare a methacrylamide hydrolysis catalyst.

[0135] Catalyst evaluation: 4.0 g of the above catalyst was packed into a fixed-bed reactor. A methacrylamide aqueous solution was fed into the reactor by a micro-plunger pump. The mass ratio of methacrylamide to water was 20:80, and the feed rate of the methacrylamide aqueous solution was 20.0 g / h. The reaction temperature was 200℃, the reaction pressure was 2.0 MPa, and the reaction time was 24 h. The results are shown in Table 1.

[0136] Table 1

[0137] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A process for the highly selective preparation of methacrylic acid, characterized in that, The method comprises the following steps: The methyl acrylamide is mixed with water to obtain an aqueous solution of methyl acrylamide, and the aqueous solution of methyl acrylamide is introduced into a reactor loaded with a solid acid catalyst to perform a hydrolysis reaction, so as to obtain methyl acrylate; The solid acid catalyst is a modified molecular sieve catalyst.

2. The process for the highly selective preparation of methacrylic acid according to claim 1, characterized in that, The solid acid catalyst is a modified molecular sieve catalyst subjected to deep acid treatment and organic silane treatment.

3. The process for the highly selective preparation of methacrylic acid according to claim 1, characterized in that, The preparation method of the solid acid catalyst comprises the following steps: (1) molecular sieve is added into a three-necked flask loaded with an acid solution, stirring is started, and reflux treatment is performed at 60-80°C for 4-24h; after the reaction is completed, cooling is performed to room temperature, the obtained mixture is subjected to suction filtration, and the filter cake is repeatedly washed with deionized water until the filtrate is neutral; the treated filter cake is placed into an oven at 110°C and dried overnight for 12h to obtain a precursor I; (2) the precursor I is placed into a Schlenk flask and activated under the condition of 120°C and <0.1mmHg vacuum for 2h to obtain activated molecular sieve; under the protection of a glove box or inert gas, 100ml of anhydrous toluene is added into another dry flask, and then silane reagent is slowly added to obtain a silane-toluene solution; the activated molecular sieve is quickly added into the silane-toluene solution, inert gas protection is continuously introduced into the whole system, stirring is started, the reaction system is heated to 110°C, and reaction is performed for 12-24h, and then cooling is performed to room temperature; filtration is performed under the protection of inert gas, and washing is sequentially performed with anhydrous toluene and anhydrous ethanol; the washed solid is vacuum dried at 60°C for 6-12h to obtain a hydrophobically modified precursor II; (3) the precursor II is programmed to be heated to 350-650°C at a heating rate of 1-5°C / min under the protection of air or N2, and is kept at this temperature for 4-8h to obtain the solid acid catalyst.

4. The process for the highly selective preparation of methacrylic acid according to claim 3, characterized in that, In step (1), the acid in the acid solution is at least one selected from hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, oxalic acid, acetic acid, citric acid and p-toluene sulfonic acid; In step (1), the molecular sieve is at least one selected from MWW molecular sieve, FER molecular sieve, MTT molecular sieve, MFI molecular sieve, MEL molecular sieve, MOR molecular sieve, FAU molecular sieve, CHA molecular sieve and BEA molecular sieve; In step (1), the atomic ratio of silicon and aluminum in the molecular sieve is Si / Al=2-500; In step (1), the concentration of the acid solution is 0.1-1.0 mol / L; In step (1), the mass-volume ratio of the molecular sieve and the acid solution is 1 / 5-1 / 30.

5. The process for the highly selective preparation of methacrylic acid according to claim 3, characterized in that, In step (1), the molecular sieve is at least one selected from MCM-22 molecular sieve, mordenite molecular sieve, ZSM-35 molecular sieve, ZSM-23 molecular sieve, ZSM-5 molecular sieve, ZSM-11 molecular sieve, Y molecular sieve, SAPO-34 molecular sieve and β molecular sieve.

6. The process for the highly selective preparation of methacrylic acid according to claim 3, characterized in that, In step (2), the inert gas is at least one selected from N2 and Ar; In step (2), the silane reagent is selected from at least one of trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, octyltrichlorosilane, octadecyltrichlorosilane, methyltrimethoxysilane, trimethylmethoxysilane, dimethyldimethoxysilane, n-octyltriethoxysilane, hexadecyltrimethoxysilane, octadecyltrimethoxysilane, phenyltrimethoxysilane and mercaptopropyltrimethoxysilane; In step (2), the mass ratio of the silane reagent to the molecular sieve is 1:5 to 1:

20.

7. The process for the highly selective preparation of methacrylic acid according to claim 1, characterized in that, The reactor is composed of one or more reactors connected in series and / or in parallel. The mass ratio of the methacrylamide to the water is 10:90 to 80:

20. The reaction temperature of the hydrolysis reaction is 100-400℃, the reaction pressure is 0.1-10 MPa, the reaction time is 2-8 h, and the mass space velocity of the methacrylamide aqueous solution is 0.1-10 h -1 .

8. The process for the highly selective preparation of methacrylic acid according to claim 1, characterized in that, The reaction temperature of the hydrolysis reaction is 150-350℃, the reaction pressure is 0.1-5MPa, the reaction time is 2-8h, and the mass space velocity of the methacrylamide aqueous solution is 0.5-5.0h -1 .

9. The process for the highly selective preparation of methacrylic acid according to claim 1, characterized in that, The reactor is selected from at least one of a tank reactor, a fixed bed reactor, a moving bed reactor and a fluidized bed reactor.

10. The process for the highly selective preparation of methacrylic acid according to claim 1, characterized in that, The particle size of the solid acid catalyst is 20 to 40 mesh.

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