Temperature difference MMA fixed bed anti-blocking method and device

Abstract

The invention discloses a temperature difference MMA fixed bed anti-blocking method and a temperature difference MMA fixed bed anti-blocking device. In the method and the device, at least one section of heating belt and a pressure gauge are arranged on a pipeline at the front end of a feed port of an MMA fixed bed reactor. In a liquid raw material for preparing MMA through condensation of methyl propionate and formaldehyde, methanol and formaldehyde form hemiacetal, and methanol is excessive. Hemiacetal is decomposed when the temperature reaches a certain temperature, released formaldehyde is self-polymerized to form a plugging block, and the plugging block is gradually dissolved by newly entering methanol gas to form hemiacetal to enter. According to the method and the device provided by the invention, the temperature of the heating belt is dynamically adjusted, and the precipitation position of the polyformaldehyde is changed by dynamically adjusting the precipitation-redissolution process, so that the pipeline is prevented from being blocked. According to the method and the device, the anti-blocking effect is remarkable, the operation time of the reactor is prolonged to 650-1770 hours, and high reaction performance can be maintained; the problem of pressure rise can be solved on line without stopping by adjusting the heating belt or the cold tracing device in a segmented mode, and production energy consumption and cost are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical equipment, and in particular to a method for preventing an MMA fixed bed reactor from being blocked at the front end of a preheating section or a heating section due to the precipitation of polyoxymethylene, and a device for implementing the method. Background Art

[0002] In the fixed-bed catalytic synthesis process of methyl methacrylate (MMA), blockage of the reactor feed port and pipeline is a key problem that restricts production efficiency and equipment life. Traditional fixed-bed reaction systems usually adopt a constant temperature heating method (such as heating at 175°C throughout the process), but during long-term operation, materials (such as methyl propionate, formaldehyde, methanol) are prone to polymerization, coking or crystallization on the catalyst surface or the inner wall of the pipeline, resulting in a continuous increase in the pressure before the column and eventually causing pipeline blockage. In the existing technology, a single heating method is usually used, which cannot effectively prevent blockage, resulting in short reactor operation time and low production efficiency. The current conventional means to deal with the blockage problem include regular shutdown and cleaning, increasing the reaction temperature or replacing the catalyst, but these methods have the following defects: 1) Regular shutdown and cleaning leads to reduced production efficiency, increased energy consumption and cost; 2) Increasing the reaction temperature may aggravate side reactions and reduce MMA selectivity; 3) Replacing the catalyst cannot fundamentally solve the problem of material deposition in the pipeline.

[0003] Therefore, how to achieve long-term stable operation of fixed-bed reactors and reduce the frequency of blockage through process optimization has become a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0004] The present invention aims to provide a method for preventing blockage in a MMA fixed-bed reactor. In the liquid feedstock used to prepare MMA by condensing methyl propionate and formaldehyde, methanol and formaldehyde form hemiacetal, resulting in an excess of methanol. At a certain temperature, the hemiacetal decomposes, releasing methanol that vaporizes and enters the reactor. The released formaldehyde then self-polymerizes to form a blockage, which is then gradually dissolved by newly entering methanol gas, forming hemiacetal that enters the reactor. This is a temperature-controlled process. By dynamically adjusting the temperature of the heating zone and the precipitation-redissolution process, the precipitation location of the polyoxymethylene is altered, thereby preventing pipeline blockage.

[0005] Technical Solution

[0006] A method for preventing clogging of an MMA fixed bed reactor, wherein at least one heating belt or a cooling circulation device is provided on the front pipeline of the reactor feed port, and the specific steps are as follows:

[0007] Step 1. Initial heating stage: The reaction conditions are as follows: the heating zone is heated to 150-190° C., the MMA synthesis reaction is carried out at a material molar ratio of methyl propionate: formaldehyde: methanol of 3-5:1:0.5-7.5, a liquid hourly mass space velocity of 1.3 to 4.0 h⁻¹, and a reaction temperature of 250 to 380° C.

[0008] Step 2. Pressure monitoring and temperature differential adjustment stage: When the pressure in front of the fixed bed reactor column rises to 0.01-0.04 MPa during the reaction, the temperature differential control mechanism is activated: the heating belt is powered off / heated in sections: the power supply of the heating belt is disconnected, or a specific heating belt (such as the third heating belt) is heated to 56-80°C, so that the temperature of the outer wall of the reaction tube inlet is maintained at 40-80°C. The material is continuously fed for 1-2 hours until the pressure returns to zero;

[0009] Step 3. When the temperature at the front end of the feed inlet of the fixed bed reactor is too high, for example, higher than 300°C, start the cooling cycle control: open the cooling circulating water pipe at the front end of the feed inlet to reduce the temperature of the outer wall of the reaction tube inlet to about 50°C, and pass the material until the pressure returns to zero, or close the cooling cycle to allow the temperature to rise to restore the pressure balance.

[0010] Step 4. Cyclic control phase: Repeat steps 2 and 3 above to perform temperature difference adjustment operations according to pressure changes until the catalyst life ends. The total operating time can reach 650-1770 hours.

[0011] Preferably, the heating belt is set to 3 to 5 sections, each section covers a length of about 5 cm of the pipeline, and gradient temperature difference control is achieved by sequentially cutting off power or increasing temperature.

[0012] Preferably, the catalyst is a Cs-Ce-Zr / SiO2 composite carrier catalyst, wherein the Cs loading is 6.5-9.5wt%, and the molar ratio of Ce to Zr is 0.1-0.3:0.25.

[0013] Preferably, the material molar ratio of methyl propionate:formaldehyde:methanol is preferably 5:1:7.5, the liquid hourly mass space velocity is preferably 4.0h-1, and the reaction temperature is preferably 330°C.

[0014] A device for preventing an MMA fixed bed reactor from being blocked comprises at least one heating belt arranged on a pipeline at the front end of a feed port of the MMA fixed bed reactor, and a pressure gauge arranged at the front ends of the three heating belts.

[0015] Preferably, the heating belt is provided with 3 to 5 sections, and each section covers a length of about 5 cm of the pipeline.

[0016] Preferably, the heating belt is provided with a temperature monitoring meter for understanding the actual temperature of the heating belt.

[0017] Preferably, a cooling circulating water pipe is provided near the front end of the feed inlet of the MMA fixed bed reactor to control the material temperature.

[0018] Beneficial effects

[0019] Compared with the prior art, the present invention has the following significant advantages:

[0020] 1) Significant anti-blocking effect: By regulating the temperature difference, the reactor operation time is extended from 260 hours of the traditional technology to 650-1770 hours, which is extended by 2.5-6.8 times (for example, the total operation time of Example 2 is 1770 hours, compared with 260 hours of Comparative Example 1).

[0021] 2) Maintaining high reaction performance: During the anti-blocking process, the single-pass conversion rate of methyl propionate was maintained at 13.3%-16.1%, and the MMA selectivity reached 90.02%-93%. The reaction efficiency did not decrease due to temperature adjustment.

[0022] 3) Easy and controllable operation: By adjusting the heating belt or cooling device in sections, the pressure increase problem can be solved online without stopping the machine, reducing production energy consumption and costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 is a schematic diagram showing an apparatus according to the present invention.

[0025] Figure 2 This is the reaction detection diagram of Example 1. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below. Before describing, it should be understood that the terms used in this specification and the appended claims should not be interpreted as limited to the general meaning and dictionary meaning, but should be interpreted according to the meaning and concept corresponding to the technical aspects of the present invention on the basis of the principle that allows the inventor to appropriately define the terms for the best interpretation. Therefore, the descriptions presented here are merely preferred examples for illustrative purposes and are not intended to limit the scope of the present invention. It should be understood that other equivalents or improvements can be obtained therefrom without departing from the spirit and scope of the present invention.

[0027] As used herein, the terms "comprises," "includes," "has," "contains" or any other similar terms are open conjunctions that are intended to cover non-exclusive inclusions. For example, a composition or article containing multiple elements is not limited to the elements listed herein, but may also include other elements that are not explicitly listed but are generally inherent to the composition or article. In addition, unless expressly stated to the contrary, the term "or" refers to an inclusive "or" rather than an exclusive "or." For example, any of the following situations satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and both A and B are true (or exist). In addition, as used herein, the terms "comprises," "includes," "has," and "contains" should be interpreted as specifically disclosed and simultaneously cover closed or semi-closed conjunctions such as "consisting of" and "consisting essentially of."

[0028] Throughout this document, all features or conditions defined as numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered to encompass and specifically disclose all possible subranges and individual values ​​within those ranges, particularly integer values. For example, a description of a range "1 to 8" should be considered to specifically disclose all possible subranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, and so forth, particularly those defined by all integer values, and should be considered to specifically disclose individual values ​​within those ranges such as 1, 2, 3, 4, 5, 6, 7, and 8. Unless otherwise indicated, the foregoing interpretation applies to all of the present disclosure, regardless of whether the ranges are comprehensive or not.

[0029] If a quantity or other value or parameter is expressed as a range, a preferred range, or a series of upper and lower limits, it should be understood that all ranges consisting of any upper limit or preferred value of the range and any lower limit or preferred value of the range have been specifically disclosed herein, regardless of whether these ranges are disclosed separately. In addition, when a numerical range is mentioned herein, unless otherwise specified, the range should include its endpoints and all integers and fractions within the range.

[0030] In this document, numerical values ​​should be understood to have the accuracy of the number of significant digits of the numerical value, provided that the purpose of the invention can be achieved. For example, the number 40.0 should be understood to cover the range from 39.50 to 40.49.

[0031] Liquid products were analyzed using an Agilent 7890AGC gas chromatograph with n-heptane as the internal standard. Chromatographic analysis was performed using a DB-624 column (capillary column, 6% cyanopropylbenzene, 94% dimethylsiloxane, 30 m (length) × 0.25 mm (inner diameter) × 1.4 μm (film thickness)) and a flame ionization detector (FID). Unless otherwise stated, the reagents and solvents disclosed below were purchased from Inokai Chemical Reagent Co., Ltd.

[0032] The following examples are merely examples of embodiments of the present invention and do not constitute any limitation thereto. Those skilled in the art will appreciate that modifications without departing from the spirit and scope of the present invention fall within the scope of protection of the present invention. Unless otherwise specified, the reagents and instruments used in the following examples are commercially available products.

[0033] Example 1

[0034] A small-scale MMA fixed-bed reactor was prepared. Three heating bands were placed in front of the feed port, all heated to 175°C. Each band covered approximately 5 cm of the pipe. A 50 cm long, 8-10 mm inner diameter stainless steel fixed-bed reactor was loaded with 3 g of MMA catalyst (9.5 wt% Cs-Ce-Zr / SiO2). The reactor was heated to 4.0 h at a liquid hourly mass space velocity (LHV) of 4.0 h in a methyl propionate:formaldehyde:methanol molar ratio of 5:1:7.5. -1 Methyl methacrylate was prepared at 330°C. After 180 hours of reaction, the single-pass conversion of methyl propionate was 16.1%, the selectivity for methyl methacrylate was 90.02%, and the column head pressure rose to 0.03 MPa. The first heating zone was disconnected, and the feed was continued for 2 hours, allowing the pressure to return to zero. After 300 hours of feed, the pressure gauge rose to 0.02 MPa. The second heating zone was disconnected, and the pressure returned to zero after approximately 1 hour. After 800 hours of feed, the pressure gauge rose to 0.02 MPa. The third heating zone was disconnected, and the pressure returned to zero after approximately 1 hour. After 600 hours of feed, the pressure gauge rose to 0.04 MPa. The first heating zone was then turned on, and the pressure returned to zero after approximately 1 hour. The reaction continued until the end of the catalyst life. The total run time was 1880 hours.

[0035] Figure 2 This is the reaction detection diagram of Example 1. Figure 2 It can be seen that the MP conversion rate and MMA selectivity remained relatively stable during the total operating time of 1880 hours, and there was no problem of reduced reaction efficiency due to reactor blockage or other phenomena.

[0036] Example 2

[0037] A small-scale MMA fixed-bed reactor was prepared. Three heating bands were placed in front of the feed port, with only the first band heated to 160°C. Each band covered approximately 5 cm of the pipeline. A 50 cm long, 8-10 mm inner diameter stainless steel fixed-bed reactor was loaded with 3 g of MMA catalyst (9.5 wt% Cs-Ce-Zr / SiO2). The reactor was heated in a methyl propionate:formaldehyde:methanol molar ratio of 2:1:4 at a liquid hourly mass space velocity of 4.0 h / min. -1 Methyl methacrylate was produced at 330°C. After 170 hours of reaction, the single-pass conversion of methyl propionate was 16.1%, the selectivity for methyl methacrylate was 90.02%, and the column head pressure rose to 0.03 MPa. The first heater was then disconnected, and the second heater was turned on and heated to 56°C. Feed was continued for 2 hours, and the pressure returned to zero. After 200 hours of feed, the pressure gauge rose to 0.02 MPa. The second heater was then disconnected, and the third heater was turned on and heated to 80°C. After approximately 1 hour, the pressure returned to zero. After 800 hours of feed, the pressure gauge rose to 0.02 MPa. All three heaters were disconnected, and the pressure returned to zero approximately 1 hour later. After 600 hours of feed, the pressure gauge rose to 0.04 MPa. The first heater was then turned on, and the pressure returned to zero approximately 1 hour later. The reaction continued until the end of the catalyst life. The total run time was 1770 hours.

[0038] Example 3

[0039] A small-scale MMA fixed-bed reactor was prepared. A heating tape was placed in front of the feed port and heated to 160°C. The tape covered approximately 5 cm of the pipe. A stainless steel fixed-bed reactor, 50 cm long and with an inner diameter of 8-10 mm, was loaded with 3 g of MMA catalyst (9.5 wt% Cs-Ce-Zr / SiO2). The reactor was stirred at a molar ratio of methyl propionate: formaldehyde: methanol of 3:1:4.5 and a liquid hourly mass space velocity of 2.0 h. -1 Methyl methacrylate was prepared at 250°C. After 200 hours of reaction, the single-pass conversion of methyl propionate was 14.1%, the selectivity for methyl methacrylate was 92%, and the column head pressure rose to 0.01 MPa. The heating tape was then disconnected, and the temperature of the reaction tube inlet outer wall was maintained at 60°C. Feed was continued for 2 hours, and the pressure returned to zero. After 300 hours of feed, the pressure gauge rose to 0.02 MPa. The heating tape was then removed, and the temperature of the reaction tube inlet outer wall was maintained at 40°C. After approximately 1 hour, the pressure returned to zero. After 800 hours of feed, the pressure gauge rose to 0.02 MPa. The heating tape was then turned on again, and the pressure returned to zero approximately 1 hour later. The reaction continued until the end of the catalyst life. The total run time was 1300 hours.

[0040] Example 4

[0041] A small-scale MMA fixed-bed reactor was prepared. Two sections of retractable heating tubular furnace chambers were installed in front of the feed port and heated to 90°C. Each section covered approximately 8 cm of tubing. A stainless steel fixed-bed reactor, 50 cm long and with an inner diameter of 8-10 mm, was loaded with 5 g of MMA catalyst (5.5 wt% Cs-Zr / SiO2). The reactor was heated to 1.3 h at a liquid hourly mass space velocity (LHV) of 1.3 h in a methyl propionate:formaldehyde:methanol molar ratio of 4:1:0.5. -1 Methyl methacrylate was prepared at 380°C. After 100 hours of reaction, the single-pass conversion of methyl propionate was 13.3%, the selectivity for methyl methacrylate was 93%, and the column pressure rose to 0.01 MPa. The first furnace chamber was powered off and cooled, maintaining the outer wall temperature of the reaction tube inlet at 80°C. Feeding continued for 2 hours, and the pressure returned to zero. After 300 hours of feeding, the pressure gauge rose to 0.02 MPa. The second furnace chamber was powered off and cooled, and the pressure returned to zero after approximately 1 hour. After 800 hours of feeding, the pressure gauge rose to 0.02 MPa. The first two furnace chambers were then closed and heated, and the pressure returned to zero after approximately 1 hour. The reaction continued until the end of the catalyst life. The total run time was 1200 hours.

[0042] Comparative Example 1

[0043] The difference from Example 2 is that no temperature differential polyoxymethylene regulating device is used before the reactor. A stainless steel fixed-bed reactor with a length of 50 cm and an inner diameter of 8-10 mm is loaded with 3 g of MMA catalyst 6.5 wt% Cs-Zr / SiO2, and a molar ratio of methyl propionate: formaldehyde: methanol of 5:1:7.5 and a liquid hourly mass space velocity of 4.0 h -1 Methyl methacrylate was produced at 330°C. After 180 hours of reaction, the single-pass conversion of methyl propionate was 16.1%, the selectivity for methyl methacrylate was 90.02%, and the column head pressure rose to 0.03 MPa. The reaction continued, and the column head pressure continued to rise. After approximately 260 hours, a line blockage occurred, and the reactor was shut down.

[0044] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preventing blockage of an MMA fixed-bed reactor, wherein at least one heating belt or cooling circulation device is provided on the front pipeline of the reactor feed port, and the specific steps are as follows: Step 1. The reaction conditions in the initial heating stage are as follows: the heating zone is heated to 150-190° C., the material molar ratio of methyl propionate: formaldehyde: methanol is 3-5:1:0.5-7.5, the liquid hourly mass space velocity is 1.3 to 4.0 h-1, and the reaction temperature is 250 to 380° C. to carry out the MMA synthesis reaction; Step 2. Pressure monitoring and temperature differential adjustment stage: When the pressure in front of the fixed bed reactor column rises to 0.01-0.04 MPa during the reaction, the temperature differential control mechanism is activated: the heating belt is powered off / heated in sections: the power supply of the heating belt is disconnected, or a specific heating belt (such as the third heating belt) is heated to 56-80°C, so that the temperature of the outer wall of the reaction tube inlet is maintained at 40-80°C. The material is continuously fed for 1-2 hours until the pressure returns to zero; Step 3. When the temperature at the front end of the feed inlet of the fixed bed reactor is too high, for example, above 300°C, start the cooling cycle control: open the cooling water pipe at the front end of the feed inlet to reduce the temperature of the outer wall of the reaction tube inlet to about 50°C, and pass the feed until the pressure returns to zero, or close the cooling cycle to allow the temperature to rise again to restore the pressure balance; Step 4. Cyclic control phase: Repeat steps 2 and 3 above to perform temperature difference adjustment operations according to pressure changes until the catalyst life ends. The total operating time can reach 650-1770 hours.

2. The method according to claim 1, characterized in that The heating belt is set to 3 to 5 sections, each section covers a length of about 5 cm of the pipeline, and gradient temperature difference control is achieved by sequentially cutting off power or increasing temperature.

3. The method according to claim 1, characterized in that The catalyst adopts a Cs-Ce-Zr / SiO2 composite carrier catalyst, wherein the Cs loading amount is 6.5-9.5wt%, and the molar ratio of Ce to Zr is 0.1-0.3:0.

25.

4. The method according to claim 1, wherein The material molar ratio of methyl propionate: formaldehyde: methanol is 5:1:7.5, the liquid hourly mass space velocity is 4.0h-1, and the reaction temperature is 330°C.

5. A device for preventing blockage of an MMA fixed-bed reactor, the device comprising at least one heating belt section provided on a pipeline at the front end of a feed port of the MMA fixed-bed reactor, and a pressure gauge provided at the front end of the heating belt section.

6. The device according to claim 5, characterized in that The heating belt is arranged into 3 to 5 sections, and each section covers a length of about 5 cm of the pipeline.

7. The device according to claim 5, characterized in that The heating belt is provided with a temperature monitoring meter for understanding the actual temperature of the heating belt.

8. The device according to claim 5, characterized in that A cooling circulating water pipe is provided near the front end of the feed inlet of the MMA fixed bed reactor to control the material temperature.

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