A method for extending the single-pass service life of an MMA catalyst

Abstract

This invention provides a method for extending the single-pass lifespan of an MMA catalyst. During a long period of maintaining a stable space velocity, the space velocity is slightly changed at short intervals to alter the feed conversion rate, thereby changing the atmosphere ratio in the catalyst bed and generating gas turbulence disturbance. This causes rapid flushing and exchange of materials within the catalyst's fine pores, thereby reducing carbon buildup and extending the catalyst's single-pass lifespan.

Description

Technical Field

[0001] This invention relates to the field of catalyst application technology, and in particular to a method for extending the single-pass life of an MMA catalyst. Background Technology

[0002] Methyl methacrylate (MMA) is an important organic chemical raw material, mainly used to produce plexiglass (polymethyl methacrylate, PMMA). It is also used to manufacture other resins, plastics, coatings, adhesives, lubricants, impregnating agents for wood and cork, impregnating agents for motor coils, paper varnishes, printing and dyeing auxiliaries, and insulating potting materials, etc., with a wide range of applications.

[0003] Traditional methods for synthesizing MMA mainly include the acetone cyanohydrin (ACH) method, the isobutylene method, and the ethylene method. Later, the Alpha method emerged, whose main raw materials are ethylene, CO, methanol, formaldehyde, and water, all of which can be produced using coal chemical processes. my country possesses abundant coal resources, and with the commissioning of coal-to-olefins plants in the market, the shortage of low-carbon olefins production will be significantly alleviated. Compared with the existing acetone cyanohydrin or isobutylene methods, the Alpha method, which utilizes coal chemical raw materials to produce MMA, can reduce MMA production costs by 40%. It has advantages such as being environmentally friendly, safe, having a mild reaction process, less corrosive equipment, and lower production costs, enriching the technology for manufacturing bulk chemical products via non-petroleum routes, and is of great significance.

[0004] The Alpha process mainly consists of two steps: First, ethylene, methanol, and CO react to produce methyl propionate; second, methyl propionate reacts with formaldehyde to produce MMA and water. A proprietary heterogeneous catalyst is used. The Alpha process involves multiple variables and factors interacting with each other, making variable adjustment complex. Currently, the biggest problem is the decrease in catalyst activity due to carbon buildup, resulting in a short single-pass lifespan. Summary of the Invention

[0005] The purpose of this invention is to provide a method for extending the single-pass lifespan of an MMA catalyst.

[0006] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0007] This invention provides a method for extending the single-pass life of an MMA catalyst (particularly a catalyst used in the reaction of formaldehyde and methyl propionate to produce methyl methacrylate), comprising the following steps:

[0008] In the process of producing methyl methacrylate from formaldehyde and methyl propionate using MMA catalyst, the initial feed liquid hourly space velocity (LHSV) is set to SV0. After reaction time H1, the LHSV is adjusted to SV1, and after another reaction time h1, it is adjusted back to SV0±d. The reaction continues for another H2, after which the LHSV is adjusted to SV2, and after another H2, it is adjusted back to SV0±d; ..., the reaction continues for another H... n Then adjust the liquid hourly mass hourly space velocity to SV. n Reaction time h n Then adjust the liquid hourly mass hourly space velocity back to SV0±d, where d is the value of 0-1% SV0 (e.g., 0.5% SV0), and n is an integer greater than 2 (e.g., 3, 4, 5, 6, 7, 8, 9, 10), preferably 3, 4, 5, etc.

[0009] The single-pass lifespan of an MMA catalyst refers to the time during which the catalyst can be used after each activation. The test method is to stop when the mass percentage of MMA in the product solution drops to 90% of the initial value, and the time elapsed is recorded as the single-pass lifespan of the MMA catalyst.

[0010] Liquid hourly mass hourly space velocity (LIHSV) refers to the mass of liquid reactants processed per unit mass of MMA catalyst per hour, i.e., the total feed mass of liquid materials such as methyl propionate, formaldehyde source, and methanol per unit mass of MMA catalyst per hour.

[0011] According to one embodiment of this disclosure, SV0 is 0.01-20h. -1 Preferably, it is 0.5-10.5h. -1 For example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 8, 9, 10, 12, 15, 16, 18h -1 .

[0012] According to one embodiment of this disclosure, SV1, SV2...SV n Each is independently SV0±D, where D is a value of 5%-20% SV0, for example, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 15%, 16%, 18%, 20% SV0.

[0013] According to one embodiment of this disclosure, H1, H2...H n Each is independently rated from 20 to 800 hours, for example, 24, 36, 48, 60, 72, 84, 100, 200, 300, 400, 500, 600, 700h, and 800h.

[0014] According to one embodiment of this disclosure, h1, h2...h nEach is independently 0.08-0.5 hours, for example 0.1, 0.15, 0.2, 0.25, 0.3, 0.5h.

[0015] Under acceptable fluctuations in post-process distillation conditions, this invention maintains a stable space velocity over a long period of time, then slightly alters the space velocity at short intervals to change the feed conversion rate. This changes the atmosphere ratio in the catalyst bed, generating gas turbulence and driving rapid scouring and exchange of materials within the catalyst's fine pores (using concentration difference turbulence to rapidly scouring and exchange materials), thereby reducing carbon buildup and extending the catalyst's single-pass lifespan.

[0016] This method is particularly effective for the Alpha method of MMA preparation, which involves multiple variables and factors, resulting in a significant reduction in catalyst carbon deposition rate, an increase in product yield, and thus an extension of the catalyst's single-pass lifespan.

[0017] According to one embodiment of this disclosure, the MMA catalyst is a supported catalyst, comprising a support, an active component, and an active promoter. The support is selected from one or more of SiO2, TiO2, and Al2O3, preferably SiO2. The active component is an oxide of Cs, and the active promoter is an oxide selected from at least one of Na, K, Mg, Ca, Zr, Cu, Fe, Au, and Ce, such as Cs-Ce-Zr / SiO2, Cs-Zr / SiO2, Cs-Cu-Zr / Al2O3, Cs-Fe-Zr / Al2O3-SiO2, etc.

[0018] MMA catalysts are commercially available or can be prepared using existing known methods.

[0019] According to one embodiment of this disclosure, the reaction of formaldehyde and methyl propionate to produce methyl methacrylate is carried out in a fixed-bed reactor containing an MMA catalyst using an MMA catalyst. The raw materials, methyl propionate and formaldehyde source, are dissolved in methanol and fed into the reactor via a micro-metering pump for reaction.

[0020] Formaldehyde sources can include, but are not limited to, formaldehyde, paraformaldehyde, triformaldehyde, methylal, etc.

[0021] Preferably, the molar ratio of methyl propionate to formaldehyde source is 1:5 to 10:1, and the molar ratio of methanol to formaldehyde source is 0.5:1 to 10:1.

[0022] Preferably, the water content of methanol is 0.1-0.5%.

[0023] According to one embodiment of this disclosure, the reaction temperature is 300-450°C and the pressure is 0.1-1.0 MPa.

[0024] The reaction products can be analyzed by gas chromatography.

[0025] Beneficial effects:

[0026] 1. This invention provides a method for extending the single-pass lifespan of an MMA catalyst by altering the space velocity. In the Alpha process for MMA preparation, while maintaining a stable space velocity for an extended period, the space velocity is slightly altered at short intervals to change the feed conversion rate, thereby changing the atmosphere ratio in the catalyst bed. This generates gas turbulence, driving rapid scouring and exchange of material within the catalyst's fine pores, thus reducing carbon buildup and extending the catalyst's single-pass lifespan. The catalyst's single-pass lifespan exceeds 1000 hours.

[0027] 2. This invention is simple to operate, does not require additional process equipment, has high industrial application value, and can be applied to the production of methyl methacrylate from formaldehyde and methyl propionate.

[0028] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments.

[0029] Unless otherwise expressly stated, numerical ranges throughout the application include any subranges therein and any numerical values ​​incremented by the smallest subunit of a given value. Unless otherwise expressly stated, numerical values ​​throughout the application represent approximate measures or limitations on the range of embodiments including minor deviations from a given value and having approximately the mentioned value as well as having the mentioned precise value. Except in the detailed description of the working embodiments provided at the end, all numerical values ​​of parameters (e.g., quantities or conditions) in this application (including the appended claims) should in all cases be understood to be modified by the term “approximately,” regardless of whether “approximately” actually precedes the numerical value. “Approximately” indicates that the stated numerical value allows for slight inaccuracies (some close to precision at that value; approximately or reasonably close to the value; approximate). If the inaccuracy provided by “approximately” is not understood in this common sense in the art, then “approximately” as used herein at least indicates a variation that can be produced by common methods of measuring and using these parameters. For example, “approximately” can include variations less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less than or equal to 0.5%. Detailed Implementation

[0030] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0031] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0032] Raw materials: Methanol (99.5% purity), paraformaldehyde (95% purity), trioxymethylene (AR), formalin (formaldehyde content 37wt%, methanol content 10-15wt%), and methyl propionate (99% purity) were all from McLean Company.

[0033] Silica from Davicat Grace 57.

[0034] Test methods and equipment:

[0035] The stainless steel fixed-bed reactor was purchased from Tuochuan Technology Co., Ltd.

[0036] Qualitative and quantitative analyses of the product were performed using an Agilent 7890A gas chromatograph, a gas chromatography-mass spectrometer, and an Agilent Varian 660 infrared spectrometer.

[0037] Methyl propionate conversion rate φ g :

[0038]

[0039] Wherein, moles of unreacted MP is the number of unreacted methyl propionate moles, obtained by gas chromatography with internal standard quantification of the reaction product liquid; Produced PA is the number of propionic acid moles produced in the reaction, obtained by gas chromatography with internal standard quantification of the reaction product liquid, originating from the product of methyl propionate hydrolysis in the catalyst bed; and Moles of MP fed is the total number of methyl propionate moles in the pumped liquid material.

[0040] Methyl propionate selectivity S:

[0041]

[0042] Wherein, MMA is the number of moles of methyl methacrylate produced in the reaction, obtained by quantitative analysis of the reaction product liquid by gas chromatography with internal standard; MAA is the number of moles of methacrylic acid produced in the reaction, obtained by quantitative analysis of the reaction product liquid by gas chromatography with internal standard, and its source is the product of hydrolysis of methyl methacrylate in the catalyst bed; Moles of MP fed is the total number of moles of methyl propionate in the pumped liquid material.

[0043] Example

[0044] Example 1

[0045] The catalyst is cesium and cerium-zirconium supported on silica, wherein the cesium content is 15 wt%, and the cerium and zirconium content is 1 wt% respectively. First, the nitrates of cesium and cerium-zirconium are dissolved in water to form a solution, which is then loaded onto silica by impregnation. After drying at 120°C for 12 hours, the solution is calcined at 350°C for 6 hours to obtain the catalyst Cs-Ce-Zr / SiO2.

[0046] A stainless steel fixed-bed reactor with an inner diameter of 8-10 mm was loaded with 3g of catalyst Cs-Ce-Zr / SiO2. The molar ratio of methyl propionate (MP):paraformaldehyde:methanol was 5:1:7.5, and the total liquid material liquid hourly space velocity was 3.5 h⁻¹. -1 Methyl methacrylate was prepared at 330℃ and 0.13 MPa. The initial MMA concentration in the effluent was 10.75%. After 48 h of reaction, the single-pass conversion of methyl propionate was 14.1%, the selectivity of methyl methacrylate was 90.2%, and the MMA concentration in the effluent was 10.7%. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 3.85 h⁻¹. -1 Continue running for 6 minutes, then adjust the total liquid material mass hourly space velocity back to 3.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 10.7% in the outlet liquid, a single-pass conversion rate of methyl propionate of 14.1%, and a selectivity of methyl methacrylate of 90.2%. After 600 hours of operation, with the reaction temperature maintained constant, the total liquid hourly space velocity (LHSV) was adjusted to 3.75 h⁻¹. -1 Continue running for 20 minutes, then adjust the total liquid material mass hourly space velocity back to 3.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 10.47% in the outlet liquid, a single-pass conversion of methyl propionate of 13.7%, and a methyl methacrylate selectivity of 90.2%. This process was repeated for another 800 hours. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 3.75 h⁻¹. -1 Continue running for 20 minutes, then adjust the total liquid mass hourly space velocity back to 3.5 h. -1 After 1 hour, the system stabilized, with an outlet MMA concentration of 10.19%, a single-pass conversion rate of methyl propionate of 13.5%, and a methyl methacrylate selectivity of 90.4%. After another 400 hours of operation, the outlet MMA concentration reached 9.67%, at which point the experiment was stopped. The total operating time was approximately 1800 hours.

[0047] Example 2

[0048] The catalyst is the same as in Example 1.

[0049] A stainless steel fixed-bed reactor with an inner diameter of 8-10 mm was loaded with 3 g of catalyst Cs-Ce-Zr / SiO2. The molar ratio of formaldehyde to methanol in methyl propionate:formaldehyde:methanol was 5:1:4.5, and the total liquid material liquid hourly space velocity was 3.5 h⁻¹. -1 Methyl methacrylate was prepared at 350℃ and 0.14 MPa. The initial MMA concentration in the effluent was 11.32%. After 48 h of reaction, the single-pass conversion of methyl propionate was 14.3%, the selectivity of methyl methacrylate was 90.0%, and the MMA concentration in the effluent was 11.27%. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 3.85 h⁻¹. -1 Continue running for 6 minutes, then adjust the total liquid material mass hourly space velocity back to 3.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 11.31% in the outlet liquid, a single-pass conversion of methyl propionate of 14.3%, and a methyl methacrylate selectivity of 90.0%. After 700 hours of operation, with the reaction temperature maintained constant, the total liquid hourly space velocity (LHSV) was adjusted to 3.75 h⁻¹. -1 Continue running for 20 minutes, then adjust the total liquid mass hourly space velocity back to 3.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 10.9% in the outlet liquid, a single-pass conversion rate of methyl propionate of 13.7%, and a methyl methacrylate selectivity of 90.0%. This process was repeated for another 800 hours. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 3.75 h⁻¹. -1 Continue running for 20 minutes, then adjust the total liquid mass hourly space velocity back to 3.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 10.2% in the outlet liquid, a single-pass conversion rate of methyl propionate of 12.8%, and a selectivity of methyl methacrylate of 90.1%. The experiment was then stopped, with a total runtime of approximately 1500 hours.

[0050] Example 3

[0051] The catalyst is cesium and zirconium supported on silica, wherein the cesium content is 15 wt% and the zirconium content is 1 wt%. First, the cesium and zirconium nitrates are dissolved in water to form a solution, which is then loaded onto silica by impregnation. After drying at 120°C for 12 hours, the solution is calcined at 350°C for 6 hours to obtain the catalyst Cs-Zr / SiO2.

[0052] A stainless steel fixed-bed reactor with an inner diameter of 8-10 mm was loaded with 3g of catalyst Cs-Zr / SiO2. The molar ratio of methyl propionate:paraformaldehyde:methanol was 5:1:7.5, and the total liquid material liquid hourly space velocity was 2.5 h⁻¹. -1Methyl methacrylate was prepared at 330℃ and 0.14 MPa. The initial MMA concentration in the effluent was 11.01%. After 48 h of reaction, the single-pass conversion of methyl propionate was 14.5%, the selectivity of methyl methacrylate was 90.1%, and the MMA concentration in the effluent was 11.0%. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 2.75 h⁻¹. -1 Continue running for 15 minutes, then adjust the total liquid material mass hourly space velocity back to 2.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 11.01% in the outlet liquid, a single-pass conversion of methyl propionate of 14.5%, and a methyl methacrylate selectivity of 90.1%. After 500 hours of operation, with the reaction temperature maintained constant, the total liquid hourly space velocity (LHSV) was adjusted to 2.65 h⁻¹. -1 Continue running for 30 minutes, then adjust the total liquid material mass hourly space velocity back to 2.5 h. -1 After 1 hour, the system stabilized, with an outlet MMA concentration of 10.68%, a single-pass conversion of methyl propionate of 14.5%, and a methyl methacrylate selectivity of 90.1%. This process was repeated for another 800 hours. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 2.2 h⁻¹. -1 Continue running for 20 minutes, then adjust the total liquid material mass hourly space velocity back to 2.5 h. -1 After 1 hour, the operation stabilized, with an MMA concentration of 10.51% in the outlet liquid, a single-pass conversion rate of methyl propionate of 13.8%, and a selectivity of methyl methacrylate of 90.1%. This process was repeated for another 500 hours, maintaining a constant reaction temperature, while adjusting the total liquid hourly space velocity (LHSV) of the liquid feedstock to 2.85 h⁻¹. -1 Continue running for 10 minutes, then adjust the total liquid material mass hourly space velocity back to 2.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 10.17% in the outlet liquid, a single-pass conversion rate of methyl propionate of 13.8%, and a selectivity of methyl methacrylate of 90.1%. After another 100 hours of operation, the MMA concentration in the outlet liquid reached 10%, at which point the experiment was stopped. The total operating time was approximately 1900 hours.

[0053] Example 4

[0054] The catalyst is the same as in Example 3.

[0055] A stainless steel fixed-bed reactor with an inner diameter of 8-10 mm was loaded with 5 g of catalyst Cs-Zr / SiO2. The molar ratio of methyl propionate:paraformaldehyde:methanol was 5:1:3, and the total liquid material liquid hourly space velocity was 2.5 h⁻¹. -1Methyl methacrylate was prepared at 330℃ and 0.14 MPa. The initial MMA concentration in the effluent was 12.4%. After 48 h of reaction, the single-pass conversion of methyl propionate was 16.5%, the selectivity of methyl methacrylate was 85%, and the MMA concentration in the effluent was 12.20%. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 2.75 h⁻¹. -1 Continue running for 10 minutes, then adjust the total liquid material mass hourly space velocity back to 2.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 12.3% in the outlet liquid, a single-pass conversion of methyl propionate of 16.5%, and a methyl methacrylate selectivity of 85%. After 800 hours of operation, with the reaction temperature maintained constant, the total liquid hourly space velocity (LHSV) was adjusted to 2.85 h⁻¹. -1 Continue running for 10 minutes, then adjust the total liquid material mass hourly space velocity back to 2.5 h. -1 After 1 hour, the system stabilized, with an outlet MMA concentration of 11.7%, a single-pass conversion of methyl propionate of 16.5%, and a methyl methacrylate selectivity of 85%. This process was repeated for another 200 hours. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 2.15 h⁻¹. -1 Continue running for 20 minutes, then adjust the total liquid material mass hourly space velocity back to 2.5 h. -1 After 1 hour, the operation stabilized, with an MMA concentration of 11.6% in the outlet liquid, a single-pass conversion rate of methyl propionate of 15.6%, and a selectivity of methyl methacrylate of 88%. This process was repeated for another 200 hours, maintaining a constant reaction temperature, while adjusting the total liquid hourly space velocity (LHSV) to 2.9 h⁻¹. -1 Continue running for 20 minutes, then adjust the total liquid material mass hourly space velocity back to 2.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 11.4% in the outlet liquid, a single-pass conversion rate of methyl propionate of 15.1%, and a selectivity of methyl methacrylate of 89%. After running for another 200 hours, the MMA concentration in the outlet liquid reached 11.2%, at which point the experiment was stopped. The total runtime was approximately 1400 hours.

[0056] Example 5

[0057] The catalyst is cesium and copper zirconium supported on commercially available alumina spheres (2-3 mm in diameter), with cesium content of 7 wt% and copper and zirconium content of 4 wt% respectively. First, the nitrates of cesium and copper zirconium are dissolved in water to form a solution, which is then loaded onto alumina by impregnation. After drying at 120°C for 12 hours, the solution is calcined at 350°C for 6 hours to obtain the catalyst Cs-Cu-Zr / Al2O3.

[0058] A stainless steel fixed-bed reactor with an inner diameter of 8-10 mm was loaded with 6 g of catalyst Cs-Cu-Zr / Al2O3. The molar ratio of methyl propionate:paraformaldehyde:methanol was 5:1:7.5, and the total liquid material liquid hourly space velocity was 4.2 h⁻¹. -1 Methyl methacrylate was prepared at 330℃ and 0.14 MPa. The initial MMA concentration in the effluent was 10.13%. After 100 h of reaction, the single-pass conversion of methyl propionate was 13.8%, the selectivity of methyl methacrylate was 90.3%, and the MMA concentration in the effluent was 10.08%. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 3.78 h⁻¹. -1 Continue running for 30 minutes, then adjust the total liquid mass hourly space velocity back to 4.2 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 10.09% in the outlet liquid, a single-pass conversion rate of methyl propionate of 13.8%, and a selectivity of methyl methacrylate of 90.3%. After 600 hours of operation, with the reaction temperature maintained constant, the total liquid hourly space velocity (LHSV) was adjusted to 4.8 h⁻¹. -1 Continue running for 10 minutes, then adjust the total liquid material mass hourly space velocity back to 4.2 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 10.05% in the outlet liquid, a single-pass conversion rate of methyl propionate of 13.8%, and a methyl methacrylate selectivity of 90.3%. This process was repeated for another 200 hours. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 3.5 h⁻¹. -1 Continue running for 20 minutes, then adjust the total liquid material mass hourly space velocity back to 4.2 h. -1 After 1 hour, the operation stabilized, with an MMA concentration of 9.9% in the outlet liquid, a single-pass conversion rate of methyl propionate of 13.5%, and a selectivity of methyl methacrylate of 90.1%. This process was repeated for another 800 hours, maintaining a constant reaction temperature, while adjusting the total liquid hourly space velocity (LHSV) to 4.6 h⁻¹. -1 Continue running for 20 minutes, then adjust the total liquid mass hourly space velocity back to 4.2 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 9.29% in the outlet liquid, a single-pass conversion rate of methyl propionate of 12.5%, and a methyl methacrylate selectivity of 90.0%. After another 200 hours of operation, the MMA concentration in the outlet liquid reached 9.2%, at which point the experiment was stopped. The total operating time was approximately 1900 hours.

[0059] Example 6

[0060] The catalyst is the same as in Example 5.

[0061] A stainless steel fixed-bed reactor with an inner diameter of 16-18 mm was loaded with 6 g of catalyst Cs-Cu-Zr / Al2O3. The molar ratio of methyl propionate:paraformaldehyde:methanol was 2:1:1, and the total liquid material liquid hourly space velocity was 4.0 h⁻¹. -1 Methyl methacrylate was prepared at 330℃ and 0.14 MPa. The initial MMA concentration in the effluent was 11.05%. After 800 h of reaction, the single-pass conversion of methyl propionate was 10.9%, the selectivity of methyl methacrylate was 90.0%, and the MMA concentration in the effluent was 10.3%. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 4.68 h⁻¹. -1 Continue running for 16 minutes, then adjust the total liquid material mass hourly space velocity back to 4.0 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 10.34% in the outlet liquid, a single-pass conversion rate of methyl propionate of 10.9%, and a selectivity of methyl methacrylate of 90.0%. After 100 hours of operation, with the reaction temperature maintained constant, the total liquid hourly space velocity (LHSV) was adjusted to 4.3 h⁻¹. -1 Continue running for 10 minutes, then adjust the total liquid material mass hourly space velocity back to 4.0 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 10.21% in the outlet liquid, a single-pass conversion of methyl propionate of 10.9%, and a methyl methacrylate selectivity of 90.0%. This process was repeated for another 200 hours. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 3.8 h⁻¹. -1 Continue running for 25 minutes, then adjust the total liquid material mass hourly space velocity back to 4.0 h. -1 After 1 hour, the operation stabilized, with an MMA concentration of 10.04% in the outlet liquid, a single-pass conversion rate of methyl propionate of 10.3%, and a methyl methacrylate selectivity of 90%. This process was repeated for another 300 hours, maintaining a constant reaction temperature, while adjusting the total liquid hourly space velocity (LHSV) to 3.2 h⁻¹. -1 Continue running for 15 minutes, then adjust the total liquid material mass hourly space velocity back to 4.0 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 10.2% in the outlet liquid, a single-pass conversion rate of methyl propionate of 9.9%, and a selectivity of methyl methacrylate of 91%. After another 200 hours of operation, the MMA concentration in the outlet liquid reached 10.0%, at which point the experiment was stopped. The total operating time was approximately 1600 hours.

[0062] Example 7

[0063] The catalyst is cesium and zirconium iron supported on commercially available kaolin, with cesium content of 20 wt% and iron and zirconium content of 3 wt% respectively. First, the nitrates of cesium and zirconium iron are dissolved in water to form a solution, which is then loaded onto kaolin by impregnation. After drying at 120°C for 12 hours, the solution is calcined at 350°C for 6 hours to obtain the catalyst Cs-Fe-Zr / Al2O3-SiO2.

[0064] Nine g of catalyst Cs-Fe-Zr / Al2O3-SiO2 was packed into a stainless steel fixed-bed reactor with an inner diameter of 18-20 mm. The molar ratio of methyl propionate:paraformaldehyde:methanol was 3:1:3, and the total liquid material liquid hourly space velocity was 0.5 h⁻¹. -1 Methyl methacrylate was prepared at 330℃ and 0.1 MPa. The initial MMA concentration in the effluent was 12.7%. After 200 h of reaction, the single-pass conversion of methyl propionate was 13%, the selectivity of methyl methacrylate was 90.0%, and the MMA concentration in the effluent was 12.5%. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 0.6 h⁻¹. -1 Continue running for 30 minutes, then adjust the total liquid material mass hourly space velocity back to 0.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 12.68% in the effluent, a single-pass conversion of methyl propionate of 13%, and a methyl methacrylate selectivity of 90.0%. After 400 hours of operation, with the reaction temperature maintained, the total liquid hourly space velocity (LHSV) was adjusted to 0.4 h⁻¹. -1 Continue running for 13 minutes, then adjust the total liquid material mass hourly space velocity back to 0.5 h. -1 After 1 hour, the system stabilized, with an outlet MMA concentration of 12.25%, a single-pass conversion of methyl propionate of 13%, and a methyl methacrylate selectivity of 90.0%. This process was repeated for another 300 hours. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 0.55 h⁻¹. -1 Continue running for 30 minutes, then adjust the total liquid material mass hourly space velocity back to 0.5 h. -1 After 1 hour, the operation stabilized, with an MMA concentration of 11.95% in the outlet liquid, a single-pass conversion rate of methyl propionate of 12.4%, and a selectivity of methyl methacrylate of 90.0%. This process was repeated for another 400 hours, maintaining a constant reaction temperature, while adjusting the total liquid hourly space velocity (LHSV) of the liquid feedstock to 0.57 h⁻¹. -1 Continue running for 10 minutes, then adjust the total liquid material mass hourly space velocity back to 0.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 11.5% in the outlet liquid, a single-pass conversion rate of methyl propionate of 12.1%, and a methyl methacrylate selectivity of 90.2%. After another 200 hours of operation, the MMA concentration in the outlet liquid reached 11.48%, at which point the experiment was stopped. The total operating time was approximately 1500 hours.

[0065] Example 8

[0066] The catalyst is the same as in Example 3.

[0067] A stainless steel fixed-bed reactor with an inner diameter of 8-10 mm was loaded with 6 g of catalyst Cs-Zr / SiO2. The molar ratio of methyl propionate:paraformaldehyde:methanol was 3:1:3, and the total liquid material liquid hourly space velocity was 10.5 h⁻¹. -1 Methyl methacrylate was prepared at 330℃ and 0.14 MPa. The initial MMA concentration in the effluent was 10.7%. After 200 h of reaction, the single-pass conversion of methyl propionate was 11%, the selectivity of methyl methacrylate was 90.0%, and the MMA concentration in the effluent was 10.5%. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 11.2 h⁻¹. -1 Continue running for 30 minutes, then adjust the total liquid material mass hourly space velocity back to 10.5 h. -1 After 1 hour, the operation stabilized, with an MMA concentration of 10.68% in the outlet liquid, a single-pass conversion rate of methyl propionate of 11%, and a selectivity of methyl methacrylate of 90.0%. After continuing the reaction for another 175 hours, the total liquid hourly space velocity (LHSV) was adjusted to 9.9 h⁻¹. -1 Continue running for 20 minutes, then adjust the total liquid mass hourly space velocity back to 10.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 10.65% in the effluent, a single-pass conversion of methyl propionate of 11%, and a methyl methacrylate selectivity of 90.0%. After 400 hours of operation, with the reaction temperature maintained, the total liquid hourly space velocity (LHSV) was adjusted to 8.4 h⁻¹. -1 Continue running for 20 minutes, then adjust the total liquid mass hourly space velocity back to 10.5 h. -1 After 1 hour, the system stabilized, with an MMA concentration of 10.33% in the outlet liquid, a single-pass conversion rate of methyl propionate of 11%, and a methyl methacrylate selectivity of 90.0%. This process was repeated for another 400 hours. The reaction temperature was kept constant, and the total liquid hourly space velocity (LHSV) was adjusted to 12.5 h⁻¹. -1 Continue running for 30 minutes, then adjust the total liquid material mass hourly space velocity back to 10.5 h. -1 After 1 hour, the operation stabilized, with an MMA concentration of 10.12% in the outlet liquid, a single-pass conversion rate of methyl propionate of 10.4%, and a methyl methacrylate selectivity of 90.0%. This process was repeated for another 300 hours, maintaining a constant reaction temperature, while adjusting the total liquid hourly space velocity (LHSV) of the liquid feedstock to 11.65 h⁻¹. -1 Continue running for 10 minutes, then adjust the total liquid material mass hourly space velocity back to 10.5 h. -1After 1 hour, the system stabilized, with an MMA concentration of 9.9% in the outlet liquid, a single-pass conversion rate of methyl propionate of 10.1%, and a selectivity of methyl methacrylate of 90.1%. After another 200 hours of operation, the MMA concentration in the outlet liquid reached 9.7%, at which point the experiment was stopped. The total operating time was approximately 1675 hours.

[0068] Comparative Example 1

[0069] The catalyst is the same as in Example 1.

[0070] A stainless steel fixed-bed reactor with an inner diameter of 8-10 mm was loaded with 3g of catalyst Cs-Ce-Zr / SiO2. The molar ratio of methyl propionate:paraformaldehyde:methanol was 5:1:7.5, and the total liquid material liquid hourly space velocity was 3.5 h⁻¹. -1 Methyl methacrylate was prepared under constant conditions of 330℃ and 0.13 MPa. The initial MMA concentration in the effluent was 10.75%. After 48 h of reaction, the single-pass conversion of methyl propionate was 14.0%, the selectivity of methyl methacrylate was 90.2%, and the MMA concentration in the effluent was 10.7%. When the MMA concentration in the effluent was 9.67%, the total running time was approximately 1100 h.

[0071] Comparative Example 2

[0072] The catalyst is the same as in Example 1.

[0073] A stainless steel fixed-bed reactor with an inner diameter of 8-10 mm was loaded with 3 g of catalyst Cs-Ce-Zr / SiO2. The molar ratio of formaldehyde to methanol in methyl propionate:formaldehyde:methanol was 5:1:4.5, and the total liquid material liquid hourly space velocity was 3.5 h⁻¹. -1 Methyl methacrylate was prepared under constant conditions of 350℃ and 0.14 MPa. The initial MMA concentration in the effluent was 11.32%. After 48 h of reaction, the single-pass conversion of methyl propionate was 14.0%, the selectivity of methyl methacrylate was 90.0%, and the MMA concentration in the effluent was 11.27%. When the MMA concentration in the effluent was 10.2%, the total running time was approximately 900 h.

[0074] For details of the embodiments and comparative examples, please refer to Table 1:

[0075] Table 1

[0076]

[0077] The above embodiments are merely illustrative of the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and substance defined by the claims of the present invention; and such modifications or substitutions are still within the scope defined by the claims of the present invention.

Claims

1. A method for extending the single-pass life of an MMA catalyst, comprising the following steps: In the process of producing methyl methacrylate from formaldehyde and methyl propionate using MMA catalyst in a fixed-bed reactor, the initial liquid hourly space velocity (LHSV) of the feed is set to SV0. After reaction time H1, the LHSV is adjusted to SV1, and after another reaction time h1, it is adjusted back to SV0±d. The reaction continues for another H2, after which the LHSV is adjusted to SV2, and after another reaction time h2, it is adjusted back to SV0±d. This process is repeated for another H2. n Then adjust the liquid hourly mass hourly space velocity to SV. n Reaction time h n Then adjust the liquid hourly mass hourly space velocity (LHSV) back to SV0 ± d, where d is the value of 0-1% SV0, n is an integer greater than 2, H1 is 20-100 hours, and H2 and H... n Each independently ranges from 20 to 800 hours, h1 is 0.08 to 0.15 hours, h2, h n Each independently lasts 0.08-0.5 hours. in, SV0 is 0.5-10.5h -1 , SV1, SV2, SV n Each is independently SV0±D, where D is 5%-20% of the value of SV0.

2. The method according to claim 1, wherein, The MMA catalyst is a supported catalyst, comprising a support, an active component, and an active promoter. The support is selected from one or more of SiO2, TiO2, and Al2O3. The active component is an oxide of Cs. The active promoter is an oxide selected from at least one of Na, K, Mg, Ca, Zr, Cu, Fe, Au, and Ce.

3. The method according to claim 1 or 2, wherein, The production of methyl methacrylate by reacting formaldehyde and methyl propionate with MMA catalyst is carried out in a fixed-bed reactor containing MMA catalyst. The raw materials, methyl propionate and formaldehyde source, are dissolved in methanol and fed into the reactor through a micro-metering pump for reaction.

4. The method according to claim 3, wherein, The formaldehyde source is selected from one of formaldehyde, paraformaldehyde, triformaldehyde, and methyl acetal.

5. The method according to claim 3, wherein, The molar ratio of methyl propionate to formaldehyde source is 1:5 to 10:1, and the molar ratio of methanol to formaldehyde source is 0.5:1 to 10:

1.

6. The method according to claim 3, wherein, The reaction temperature is 300-450℃ and the pressure is 0.1-1.0MPa.

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