Multi-module reaction system and method for preparing methyl methacrylate

Abstract

The present application relates to a kind of multi-module reaction system, including n reactors, n≥3, in production process, multi-module reaction system can make m reactors form series reaction module to carry out catalytic reaction, n-m reactors form preparation module, m≥2, n-m≥1, when the change value of detecting the equilibrium conversion rate of raw material in corresponding reactor exceeds preset value, make corresponding reactor stop reaction, simultaneously make the reactor in preparation module series to reaction module and form new reaction module to carry out catalytic reaction, the catalyst in the reactor of stopping reaction carries out in situ regeneration, and the reactor after in situ regeneration is switched to preparation module and forms new preparation module.The present application also relates to a kind of preparation method of methyl methacrylate using the multi-module reaction system.The utilization rate of catalyst is high when using the multi-module reaction system of the present application to carry out catalytic reaction, and the stability time is long and the regeneration time is short, and the reaction selectivity is high, and the side reaction is less.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic synthesis, and particularly relates to a multi-module reaction system and a preparation method of methyl methacrylate. BACKGROUND

[0002] Methyl methacrylate (MMA) is an important fine chemical raw material, which can be used as a monomer for synthesizing polymethyl methacrylate (PMMA). PMMA is widely used in various industries, including paints, coatings, instrument and meter parts, etc. The demand for PMMA is growing at an annual rate of more than 5%.

[0003] The traditional industrial production technology of MMA is the acetone cyanohydrin method (ACH method), but in this process, toxic HCN is produced, a large amount of sulfuric acid is consumed in the reaction process, the equipment requirements are high, and a large amount of by-product NH4HSO4 (~1.2 kg / kg MMA) is produced, which needs to be sold as a fertilizer or processed to produce H2SO4, so additional equipment and investment are required. This process is long, has great environmental pressure, and has gradually been phased out.

[0004] Lucite International developed the Alpha process for synthesizing MMA. First, ethylene, CO and methanol react under the action of a Pd catalyst to produce methyl propionate, and then formaldehyde and methyl propionate are subjected to an aldol condensation reaction to obtain MMA. Compared with the traditional ACH method, the Alpha process has the advantages of being green, having good atom economy, simple process, low investment, low cost, no pollution, etc.

[0005] The synthesis of methyl propionate and formaldehyde to produce MMA is carried out at high temperature and under the action of a catalyst. The raw material conversion rate of this reaction process is low, the catalyst is easily coked and deactivated, and the service life of the catalyst is short. Therefore, the catalyst must be coked and regenerated to restore its activity. At present, from the perspective of the reactor, the circulating fluidized bed reaction regeneration method or the parallel switching regeneration method of multiple fixed beds is generally used to realize continuous production.

[0006] The circulating fluidized bed reaction regeneration method is adopted, such as CN102775302A of Beijing Xuyang Chemical Industry, which solves the problem of catalyst deactivation by coupling a fluidized bed reactor and a catalyst regenerator, and CN109293511A of Southwest Chemical Research and Design Institute, which solves the problem of rapid carbon deposition and deactivation of the catalyst by using an internal circulating fluidized bed reactor. However, compared with the fixed bed reactor, the use of the circulating fluidized bed has the problems of serious catalyst powdering and loss, high strength requirement for the catalyst, low reaction conversion rate, large catalyst consumption, and serious wear of the pipes and containers by the solid particle catalyst. Therefore, the circulating fluidized bed is not suitable for the preparation of MMA by the aldol method.

[0007] The continuous production mode is realized by adopting multiple fixed beds in parallel switching regeneration, such as CN111574369A of Beijing Xuyang Chemical Industry which adopts at least three reactors in parallel, wherein, during production, at least two reactors are used for catalytic reaction, and at least one reactor is used for in-situ regeneration. CN106674010A of Shanghai Pujing Chemical Industry adopts two reactor series in parallel to realize regeneration operation on the deactivated catalyst without stopping. The technical concept of the two patents is to enable the parallel fixed bed reactor when the catalyst is gradually deactivated to a certain extent, switch the raw material into the standby reactor for continuous reaction, and the deactivated catalyst is standby after in-situ regeneration. However, both patents use catalysts in parallel, and the reaction is carried out as a whole. Such a reaction process will result in low utilization rate of the catalyst, the main reason being that in order to ensure the stability of the reaction outlet, the lower layer or the rear end of the catalyst must be regenerated without being deactivated, that is, the utilization rate of the catalyst is low, and the catalyst is regenerated frequently. At the same time, with the increase of the number of regeneration, the type of carbon deposition of the catalyst changes, resulting in gradual extension of the catalyst regeneration time and continuous reduction of the stable reaction time, which may eventually result in longer regeneration time than reaction time; although the above patents emphasize the stability of the outlet conversion rate, the reaction stability cannot be achieved, for example, the by-product 3-pentanone gradually increases with the reaction, and the by-product is difficult to separate due to its similar boiling point with MMA.

[0008] Therefore, the present application is proposed. SUMMARY

[0009] Based on this, it is necessary to provide a multi-module reaction system and a preparation method of methyl methacrylate, which has high utilization rate of catalyst, long stable time of catalyst and shortened regeneration time, high reaction selectivity and less side reactions when the multi-module reaction system is used to prepare methyl methacrylate.

[0010] A multi-module reaction system, comprising n reactors, n≥3, the reactors being used to load catalysts and perform catalytic reactions;

[0011] Each reactor is provided with a raw material inlet and a product outlet, and the opening and closing of the first valve is controlled. The opening and closing control of the first valve can make m reactors form a series reaction module to perform catalytic reaction, and n-m reactors form a standby module, m≥2, n-m≥1.

[0012] The product outlet of each reactor is provided with a first on-line detector for detecting the equilibrium conversion rate of the raw material in the corresponding reactor, and when the first on-line detector detects that the change value of the equilibrium conversion rate of the raw material in the corresponding reactor exceeds a preset value, the corresponding reactor is stopped from reacting by controlling the first valve, and the reactors in the standby module are connected in series to form a new reaction module for catalytic reaction.

[0013] Each reactor is further provided with a regeneration gas inlet and a tail gas outlet for flowing the regeneration gas into the reactor, and the tail gas outlet is controlled by a second valve for in-situ regeneration of the catalyst in the reactor stopped from reacting, and the reactor after the in-situ regeneration of the catalyst is switched to the standby module to form a new standby module.

[0014] In one embodiment, the multi-module reaction system further comprises a main feed pipe and a main discharge pipe, the raw material inlet of each reactor is connected to the main feed pipe through a feed branch pipe, the product outlet of the first to the n-1th reactor is further connected to the raw material inlet of the reactor arranged behind and adjacent to it through a connecting pipe, the product outlet of the nth reactor is further connected to the raw material inlet of the first reactor through a connecting pipe, the product outlet of each reactor is connected to the main discharge pipe through a discharge branch pipe, the first on-line detector is arranged on the discharge branch pipe, the first valve is arranged on each feed branch pipe, each connecting pipe and each discharge branch pipe, and the first valve is arranged on the main feed pipe between adjacent two feed branch pipes and on the main discharge pipe between adjacent two discharge branch pipes.

[0015] In one embodiment, the connecting pipe is connected to the discharge branch pipe, and the first valve on the discharge branch pipe is arranged between the connecting pipe and the main discharge pipe.

[0016] In one embodiment, the first valve is also arranged on the discharge branch pipe between the connecting pipe and the product outlet.

[0017] In one embodiment, the main discharge pipe is further provided with a second on-line detector, and the second on-line detector is arranged away from the discharge branch pipe and close to the outlet position of the main discharge pipe.

[0018] In one embodiment, the main feed pipe is further provided with a third on-line detector, and the third on-line detector is arranged away from the feed branch pipe and close to the inlet position of the main feed pipe.

[0019] In one embodiment, the first on-line detector, the second on-line detector and the third on-line detector are selected from an on-line Raman spectrum detector or a gas chromatography on-line monitor.

[0020] In one embodiment, the tail gas outlet of each reactor is provided with a first on-line gas chromatograph for detecting the composition of the tail gas.

[0021] In one of the embodiments, the multi-module reaction system further comprises a main gas inlet pipe and a main gas outlet pipe, the regeneration gas inlet of each reactor is connected to the main gas inlet pipe through a gas inlet branch pipe, the tail gas outlet of each reactor is connected to the main gas outlet pipe through a gas outlet branch pipe, the first online gas chromatograph is arranged on the gas outlet branch pipe, the second valve is arranged on each gas inlet branch pipe and each gas outlet branch pipe, and the second valve is arranged on the main gas inlet pipe between two adjacent gas inlet branch pipes and on the main gas outlet pipe between two adjacent gas outlet branch pipes.

[0022] In one of the embodiments, the second online gas chromatograph is arranged on the main gas inlet pipe, away from the gas inlet branch pipe and close to the inlet of the main gas inlet pipe, for detecting the composition of the regeneration gas in the main gas inlet pipe.

[0023] The reaction system can modularize n reactors for catalytic reaction in the production process, thereby effectively improving the utilization rate of the catalyst in each reactor, and significantly reducing the carbon deposition content of the catalyst, prolonging the stable time of the catalyst and shortening the regeneration time of the catalyst.

[0024] In addition, the catalytic reaction in the reactor is stable, which effectively improves the selectivity of the reaction and reduces the occurrence of side reactions.

[0025] A preparation method of methyl methacrylate, which adopts a multi-module reaction system, comprising the following steps:

[0026] providing raw materials, the raw materials comprising methyl propionate and a formaldehyde source; and

[0027] making the raw materials enter each reactor of the reaction module for catalytic reaction and output a product containing methyl methacrylate;

[0028] when the first online detector detects that the change value of the equilibrium conversion rate of methyl propionate in the corresponding reactor is greater than or equal to 10%, the corresponding reactor is stopped by the first valve, and the reactors in the standby module are connected in series to the reaction module to form a new reaction module for catalytic reaction, and the catalyst in the stopped reactor is regenerated in situ by the second valve, and the reactor after the in-situ regeneration of the catalyst is switched to the standby module to form a new standby module.

[0029] In one of the embodiments, the molar ratio of methyl propionate to the formaldehyde source in the raw materials is 1:1-15:1.

[0030] In one of the embodiments, the reaction conditions in each reactor include: temperature of 320-400 DEG C, pressure of normal pressure to 1.0 MPa.

[0031] In one of the embodiments, the catalyst in each reactor is an alkali metal catalyst, which includes a carrier and an active component supported on the carrier, wherein the active component includes one or more of K, Na and Cs, the carrier includes one or more of silica, alumina, molecular sieve and titanium dioxide, and the mass fraction of the active component in the alkali metal catalyst is 4-20%.

[0032] In one of the embodiments, the conditions for in-situ regeneration of the catalyst include: temperature of 330-450 DEG C, pressure of normal pressure to 0.5 MPa, and the regeneration gas includes a mixture of N2 and O2, wherein the volume fraction of O2 is 1-10%.

[0033] In one of the embodiments, a first online gas chromatograph is arranged at the tail gas outlet of each reactor, and when the first online gas chromatograph detects that the composition of the tail gas is consistent with that of the regeneration gas during the step of in-situ regeneration of the catalyst, the in-situ regeneration is stopped, nitrogen or inert gas is filled into the reactor, and the reactor after in-situ regeneration of the catalyst is switched to the standby module to form a new standby module.

[0034] When the multi-module reaction system is used to prepare methyl methacrylate, since the multiple reactors are connected in series to form a reaction module, and the first online detector arranged in each reactor can detect the real-time reaction result in the corresponding reactor, the catalyst in the reactor can be selectively regenerated in-situ according to the detection result, and thus the catalyst utilization rate can be effectively improved, unnecessary regeneration can be reduced, and the service life of the catalyst can be prolonged. Meanwhile, when the reaction module is formed by the multiple reactors connected in series, the carbon deposition of the catalyst can be understood, the change of the carbon deposition type of the catalyst can be reduced, and the carbon deposition type of the catalyst in each reactor can be more clear, so that the regeneration program can be flexibly changed according to the carbon deposition type of the catalyst in each reactor.

[0035] In addition, when the reaction module is formed by the multiple reactors connected in series, the reaction conditions of the next reactor in series can be changed according to the outlet composition of the reactor, so that the catalyst activity is stable, the selectivity is improved, and the production of methyl isobutyrate and 3-pentanone, two by-products, is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 The figure is a schematic diagram of the multi-module reaction system according to an embodiment of the application.

[0037] In the diagram: 10a-10e, reactor; 11, main feed pipe; 12, main discharge pipe; 13, main air inlet pipe; 14, main exhaust pipe; 15a-15e, first online detector; 16, second online detector; 17, third online detector; 18a-18e, first online gas chromatograph; 19, second online gas chromatograph; 20, feed branch pipe; 21, discharge branch pipe; 22, connecting pipe; 23, air inlet branch pipe; 24, exhaust branch pipe; 25a-25z and 27a-27b, first valve; 26a-26t, second valve. Detailed Implementation

[0038] The following will further explain the multi-module reaction system and the preparation method of methyl methacrylate provided by the present invention.

[0039] like Figure 1 As shown, a multi-module reaction system according to an embodiment of the present invention includes n reactors, n≥3, wherein the reactors are used to load catalysts and carry out catalytic reactions.

[0040] In one embodiment, n is an integer such as 3, 4, 5, or 6, and the reactor is preferably selected from fixed-bed reactors, such as isothermal fixed-bed reactors or adiabatic fixed-bed reactors.

[0041] Each reactor is equipped with a raw material inlet and a product outlet, and the on / off state is controlled by a first valve. Each reactor is equipped with a first online detector at the product outlet to detect the equilibrium conversion rate of the raw material in the corresponding reactor, thereby determining whether the catalyst in the corresponding reactor has been deactivated based on the equilibrium conversion rate of the raw material.

[0042] Since the feed inlet and product outlet of each reactor can be controlled by a first valve, during production, m reactors connected in series can form a catalytic reaction module, and nm reactors can form a preparatory module, where m ≥ 2 and nm ≥ 1. For example, when n is 3, m is 2 and nm is 1; when n is 4, m is 2 and nm is 2, or m is 3 and nm is 1; when n is 5, m is 4 and nm is 1, or m is 3 and nm is 2, or m is 2 and nm is 3.

[0043] To improve reactor utilization and production efficiency per unit time, it is understood that more reactors should be grouped into reaction modules as much as possible. For example, when n is 5, m is preferably 4 and nm is 1, or m is 3 and nm is 2.

[0044] When the first on-line detector detects that the change value of the equilibrium conversion rate of the raw material in the corresponding reactor exceeds the preset value, the first valve of the raw material inlet and the product outlet of the corresponding reactor is closed, the reaction of the corresponding reactor is stopped through the first valve control, and the first valve of the raw material inlet and the product outlet of the reactor in the standby module is opened, so that the reactor in the standby module is connected in series to the reaction module to form a new reaction module for catalytic reaction.

[0045] When the number of the reactors stopped reacting is 1, the number of the reactors in the standby module connected in series to the reaction module is also preferably 1, so that the total number of the reactors in the reaction module remains the same.

[0046] It should be noted that the change value of the equilibrium conversion rate of the raw material = (initial conversion rate of the raw material in the reactor - real-time detected conversion rate of the raw material in the reactor) / initial conversion rate of the raw material in the reactor.

[0047] Please continue to refer to Figure 1 The multi-module reaction system further comprises a main raw material inlet pipe 11 and a main product outlet pipe 12, the main raw material inlet pipe 11 is used to supply raw material to the reactors, and the product obtained after the raw material is subjected to catalytic reaction in the reactors is collected through the main product outlet pipe 12.

[0048] Specifically, the raw material inlet of each reactor is communicated with the main raw material inlet pipe 11 through a raw material inlet branch pipe 20, the product outlet of the first to the (n-1)th reactor is further communicated with the raw material inlet of the reactor arranged behind and adjacent to it through a connecting pipe 22, the product outlet of the nth reactor is further communicated with the raw material inlet of the first reactor through the connecting pipe 22, the product outlet of each reactor is communicated with the main product outlet pipe 12 through a product outlet branch pipe 21, and the first on-line detector is arranged on the product outlet branch pipe 21. Wherein, the first valve is arranged on each raw material inlet branch pipe 20, each connecting pipe 22 and each product outlet branch pipe 21, and the first valve is arranged at the position between adjacent two raw material inlet branch pipes 20 of the main raw material inlet pipe 11, and the first valve is arranged at the position between adjacent two product outlet branch pipes 21 of the main product outlet pipe 12.

[0049] More specifically, the connecting pipe 22 is communicated with the product outlet branch pipe 21, and the first valve on the product outlet branch pipe 21 is arranged between the connecting pipe 22 and the main product outlet pipe 12.

[0050] Therefore, each of the reactors can serve as a starting reactor in the reaction module, and the products after catalytic reaction in the first to the n-1th reactors can enter the reactors arranged in the rear and adjacent to the reactors through the cooperation of the connecting pipes 22, the branch pipes 21 and the main discharge pipe 12, and then enter the nth reactor for catalytic reaction and output to the main discharge pipe 12; and the product after catalytic reaction in the nth reactor can enter the first reactor for catalytic reaction through the connecting pipe 22.

[0051] Optionally, the first valve is also arranged on the branch pipe 21 between the connecting pipe 22 and the product outlet, so as to control the pressure of the reactor while controlling the direction of the product in the corresponding reactor.

[0052] In an embodiment, the main discharge pipe 12 is further provided with a second online detector 16, which is arranged away from the branch pipe 21 and close to the outlet position of the main discharge pipe 12, and is used to detect the equilibrium conversion rate of the raw material in the main discharge pipe 12.

[0053] When the second online detector 16 detects that the change value of the equilibrium conversion rate of the raw material in the main discharge pipe 12 exceeds the preset value, the reactor with the largest change value of the equilibrium conversion rate of the raw material in the reaction module is stopped through the first valve, and the reactors in the standby module are connected in series to the reaction module to form a new reaction module for catalytic reaction, so as to better control the stability of the product collected from the main discharge pipe 12.

[0054] Generally, when the first online detector detects that the change value of the equilibrium conversion rate of the raw material in the corresponding reactor exceeds the preset value and switches to in-situ regeneration, the second online detector 16 detects that the change value of the equilibrium conversion rate of the raw material in the main discharge pipe 12 does not exceed the preset value. At this time, the second online detector 16 can be used to detect whether there is a problem in the reaction system, i.e., if the change value of the equilibrium conversion rate of the raw material in the main discharge pipe 12 exceeds the preset value, the reaction system needs to be stopped for inspection.

[0055] In an embodiment, the main feed pipe 11 is further provided with a third online detector 17, which is arranged away from the feed branch pipe 20 and close to the inlet position of the main feed pipe 11, and is used to detect the composition of the raw material in the main feed pipe 11, so as to ensure the stability of the raw material and make the catalytic reaction more stable.

[0056] Optionally, the first, second and third online detectors are selected from online Raman spectroscopy detectors or gas chromatography online monitors.

[0057] Please continue to see Figure 1 Each of the reactors is further provided with a regeneration gas inlet and a tail gas outlet for flowing regeneration gas into the reactor, and the on-off of the tail gas outlet is controlled by a second valve, so as to regenerate the catalyst in the reactor in situ when the reaction is stopped, and the reactor after the catalyst is regenerated in situ is switched to the standby module to form a new standby module, and the cycle is repeated.

[0058] Therefore, the multi-module reaction system can effectively improve the utilization rate of the catalyst in each reactor, significantly reduce the carbon deposition content of the catalyst, prolong the stable time of the catalyst, and shorten the regeneration time of the catalyst.

[0059] In addition, the catalytic reaction in the reactor is stable, which can effectively improve the selectivity of the reaction and reduce the occurrence of side reactions.

[0060] In an embodiment, a first online gas chromatograph is arranged at the tail gas outlet of each reactor to detect the composition of the tail gas, and the regeneration process of the catalyst in the corresponding reactor and whether the regeneration is completed are controlled based on the composition of the tail gas.

[0061] Please continue to see Figure 1 The multi-module reaction system further comprises a main gas inlet pipe 13 and a main gas outlet pipe 14, the regeneration gas inlet of each reactor is connected to the main gas inlet pipe 13 through a gas inlet branch pipe 23, the tail gas outlet of each reactor is connected to the main gas outlet pipe 14 through a gas outlet branch pipe 24, and the first online gas chromatograph is arranged on the gas outlet branch pipe 24.

[0062] Each of the gas inlet branch pipes 23 and the gas outlet branch pipes 24 is provided with the second valve, and the main gas inlet pipe 13 is provided with the second valve at the position between two adjacent gas inlet branch pipes 23, and the main gas outlet pipe 14 is provided with the second valve at the position between two adjacent gas outlet branch pipes 24. Therefore, the catalyst in each reactor can be regenerated in situ independently by controlling the second valve.

[0063] In an embodiment, the main air inlet pipe 13 is further provided with a second online gas chromatograph 19, which is arranged away from the air inlet branch pipe 23 and close to the inlet position of the main air inlet pipe 13, for detecting the composition of the regeneration gas in the main air inlet pipe 13. At the same time, the regeneration process of the catalyst in the corresponding reactor and whether the regeneration is completed can be better controlled by comparing the detection results of the second online gas chromatograph and the first online gas chromatograph.

[0064] Optionally, the first online gas chromatograph and the second online gas chromatograph are selected from oxygen detectors.

[0065] Specifically, please refer to Figure 1 , the multi-module reaction system includes five reactors 10a, 10b, 10c, 10d and 10e, wherein the reactors 10a-10e are connected to the main feed pipe 11 through the feed branch pipe 20, the reactors 10a-10e are connected to the main discharge pipe 12 through the discharge branch pipe 21, the discharge branch pipes 21 of the reactors 10a-10e are provided with first online detectors 15a-15e, and the adjacent two reactors are connected in series through the connecting pipe 22, and the reactor 10e is connected in series with the reactor 10a through the connecting pipe, so that the reaction product in the reactor 10e can enter the reactor 10a through the connecting pipe.

[0066] At the same time, the reactors 10a-10e are connected to the main air inlet pipe 13 through the air inlet branch pipe 23, and the reactors 10a-10e are connected to the main exhaust pipe 14 through the exhaust branch pipe 24, and the exhaust branch pipes 24 of the reactors 10a-10e are provided with first online gas chromatographs 18a-18e.

[0067] During production, any three reactors in the multi-module reaction system are connected in series to form a reaction module to continuously perform catalytic reaction, and two reactors form a standby module to ensure the replacement and regeneration of the catalyst in the reactor. Specifically as follows:

[0068] First, the reactor 10a, the reactor 10b and the reactor 10c are warmed up to a preset temperature, the first valve 25a and the first valve 25b are opened, and the rest of the first valves are in a closed state. The raw material enters the reactor 10a through the main feed pipe 11 and the feed branch pipe 20 for catalytic reaction, and the first online detector 15a detects the equilibrium conversion rate of the raw material in the reactor 10a. When the preset reaction pressure is reached, the first valve 25e and the first valve 25h are opened, so that the product in the reactor 10a enters the reactor 10b for catalytic reaction, and the first online detector 15b detects the equilibrium conversion rate of the raw material in the reactor 10b. When the preset reaction pressure is reached, the first valve 25k and the first valve 25n are opened, so that the product in the reactor 10b enters the reactor 10c for catalytic reaction, and the first online detector 15c detects the equilibrium conversion rate of the raw material in the reactor 10c. When the preset reaction pressure is reached, the first valve 25o, the first valve 25r, the first valve 25w and the first valve 25z are opened, and the second online detector 16 detects the equilibrium conversion rate of the raw material in the final product obtained in the main discharge pipe 12. At this time, the reactor 10a, the reactor 10b and the reactor 10c are connected in series to form a reaction module, and the reactor 10d and the reactor 10e form a standby module.

[0069] When the first online detector 15a detects that the equilibrium conversion rate of the raw material in the reactor 10a exceeds the preset value, it is considered that the catalyst in the reactor 10a is close to deactivation. At this time, the first valve 25a and the first valve 25b are closed, the first valve 25d and the first valve 25g are opened, and the reaction starts from the reactor 10b. At the same time, the first valve 25o and the first valve 25r are closed, and the first valve 25q, the first valve 25t and the first valve 25u are opened, so that the reactor 10d reaching the preset temperature enters the reaction state, and is connected with the reactor 10b and the reactor 10c to form a new reaction module.

[0070] Alternatively, when the second online detector 16 detects that the equilibrium conversion rate of the raw material in the main discharge pipe 12 exceeds the preset value, the reactor corresponding to the largest change value of the equilibrium conversion rate of the raw material detected by the first online detector 15a to the first online detector 15c is stopped. Generally, the change value of the equilibrium conversion rate of the raw material of the reactor 10a which has the longest reaction time is the largest, so that the reactor 10a is stopped as described above, and the reactor 10d enters the reaction state.

[0071] After the reactor 10a stops the reaction, the catalyst in the reactor 10a is regenerated in situ. During the regeneration, the second valve 26a, the second valve 26b, the second valve 26c, the second valve 26e, the second valve 26i, the second valve 26m, the second valve 26q and the second valve 26t are opened, so that the regeneration gas regenerates the catalyst in the reactor 10a in situ, and the regeneration progress is monitored by the first online gas chromatograph 18a.

[0072] Taking the synthesis of methyl methacrylate by using the multi-module reaction system as an example, the regeneration process includes: first, setting the temperature of the reactor 10a to 330°C, then opening the above-mentioned second valves, and purging the reactor 10a with nitrogen gas with 0% oxygen content detected by the second online gas chromatograph 19, after purging for 1 h at a nitrogen flow rate of 500 mL / min, increasing the oxygen content in the regeneration gas to 5%, and detecting the oxygen and carbon dioxide contents in the tail gas by the first online gas chromatograph 18a, until the oxygen content in the tail gas detected by the first online gas chromatograph 18a is consistent with that detected by the second online gas chromatograph 19, increasing the temperature of the reactor 10a to 380°C, and continuing to detect the oxygen and carbon dioxide contents in the tail gas, until the oxygen content in the tail gas detected by the first online gas chromatograph 18a is consistent with that detected by the second online gas chromatograph 19. Purging the reactor 10a with nitrogen gas with 0% oxygen content again, after purging until the oxygen content in the tail gas detected by the first online gas chromatograph 18a is 0%, closing the second valve 26a, the second valve 26b, the second valve 26c, the second valve 26e, the second valve 26i, the second valve 26m, the second valve 26q and the second valve 26t, decreasing the temperature of the reactor 10a to the preset temperature for the next reaction, and storing the nitrogen gas in the reactor 10a, and the reactor 10a and the reactor 10e form a new standby module.

[0073] It can be understood that the specific regeneration process can be adjusted according to the type of catalyst.

[0074] When the catalyst in the reactor 10b is deactivated, the reactor 10e enters the reaction state, and at the same time the reactor 10b is regenerated, the process of which can be referred to the above-mentioned conversion; when the catalyst in the reactor 10c is deactivated, the reactor 10a enters the reaction state, and at the same time the reactor 10c is regenerated, the process of which can be referred to the above-mentioned conversion; when the catalyst in the reactor 10d is deactivated, the reactor 10b enters the reaction state again, the process of which can be referred to the above-mentioned conversion; when the catalyst in the reactor 10e is deactivated, the reactor 10c enters the reaction state again, the process of which can be referred to the above-mentioned conversion; and the cycle continues.

[0075] It can be understood that when starting the reaction, it is not necessary to connect the reactor 10a, the reactor 10b and the reactor 10c in series to form a reaction module, and any three reactors can be connected in series to form a reaction module for reaction.

[0076] Based on the above, the application further provides a preparation method of methyl methacrylate using the multi-module reaction system, which comprises the following steps:

[0077] S1, providing raw materials, wherein the raw materials comprise methyl propionate (MP) and a formaldehyde source;

[0078] S2, allowing the raw materials to enter each reactor of the reaction module for catalytic reaction and outputting a product containing methyl methacrylate (MMA);

[0079] When the first online detector detects that the change value of the equilibrium conversion rate of methyl propionate in the corresponding reactor is greater than or equal to 10%, the first valve is controlled to stop the reaction of the corresponding reactor, the reactor in the standby module is connected in series to the reaction module to form a new reaction module for catalytic reaction, the second valve is controlled to in-situ regenerate the catalyst in the reactor stopped for reaction, and the reactor after in-situ regeneration of the catalyst is switched to the standby module to form a new standby module.

[0080] In step S1, the formaldehyde source comprises one or more of formaldehyde, formalin, a formaldehyde-methanol mixture, trioxane and paraformaldehyde, and is preferably formaldehyde.

[0081] In step S2, the reactor is preferably an isothermal fixed-bed reactor, each reactor is equipped with the same catalyst, the catalyst is an alkali metal catalyst, the catalyst comprises a carrier and an active component supported on the carrier, the mass fraction of the active component in the alkali metal catalyst is 4%-20%, the active component comprises one or more of K, Na and Cs, the carrier comprises one or more of silicon dioxide, aluminum oxide, molecular sieve and titanium dioxide, and is preferably Cs / SiO2.

[0082] In the step of allowing the raw materials to enter each reactor of the reaction module for catalytic reaction, the molar ratio of methyl propionate to the formaldehyde source in the raw materials is 1:1-15:1, and is preferably 5:1-10:1; the reaction conditions in each reactor include that the temperature is 320°C to 400°C and the pressure is normal pressure to 1.0 MPa.

[0083] In the reaction module, the temperature of each reactor can be the same, or the temperature of the next reactor in series can be changed by detecting the product ratio of the previous reactor to change the temperature of the next reactor in series for reaction. In an embodiment, in the reaction module, the temperature of the reactor gradually increases along with the movement of the raw materials.

[0084] The in-situ regeneration conditions of the catalyst include: temperature of 330-450 DEG C, pressure of normal pressure to 0.5 MPa, and the regeneration gas including the mixed gas of N2 and O2, wherein the volume fraction of O2 is 1-10%. In the step of in-situ regeneration of the catalyst, when the first online gas chromatograph detects that the composition of the tail gas is consistent with that of the regeneration gas, the in-situ regeneration is stopped, nitrogen or inert gas is filled into the reactor, and the reactor after in-situ regeneration of the catalyst is switched to the standby module to form a new standby module.

[0085] In combination Figure 1 As shown in the figure, the catalytic reaction is continuously carried out in the reaction module composed of any three reactors in series in the multi-module reaction system, and the catalyst in the reactor is replaced and regenerated in the standby module composed of two reactors.

[0086] When the first online detector 15a detects that the change value of the equilibrium conversion rate of methyl propionate in the reactor 10a is greater than or equal to 10%, it is considered that the catalyst in the reactor 10a is close to deactivation, at this time, the reactor 10d reaching the preset temperature is put into the reaction state, and the reactors 10b and 10c are connected in series to form a new reaction module, and so on, so that the reactors 10a-10e are used in circulation.

[0087] Alternatively, when the second online detector 16 detects that the change value of the equilibrium conversion rate of methyl propionate in the main discharge pipe 12 is greater than or equal to 2%, the reactor corresponding to the change value of the equilibrium conversion rate of the raw material detected by the first online detector 15a to the first online detector 15c is stopped. Generally, the change value of the equilibrium conversion rate of the raw material of the reactor 10a with the longest reaction time is the largest, so that the reactor 10a is stopped to carry out the reaction, the reactor 10d is put into the reaction state, and so on, so that the reactors 10a-10e are used in circulation.

[0088] In an embodiment, when the second online detector 16 is further arranged on the main discharge pipe 12, when the second online detector 16 detects that the change value of the equilibrium conversion rate of methyl propionate in the main discharge pipe 12 is greater than or equal to 2%, the reaction system needs to be stopped for inspection.

[0089] When the multi-module reaction system is used to prepare methyl methacrylate, the multiple reactors are connected in series to form a reaction module, and the first online detector arranged in each reactor can detect the real-time reaction result in the corresponding reactor, so that the catalyst in the reactor can be selectively regenerated in situ according to the detection result, and the catalyst in all reactors does not need to be regenerated in situ, so that the utilization rate of the catalyst can be effectively improved, unnecessary regeneration is reduced, and the service life of the catalyst can be prolonged. At the same time, when the reaction module is composed of multiple reactors connected in series, the carbon deposition of the catalyst can be decomposed, the type of carbon deposition of the catalyst in each reactor is more clear, and the regeneration program can be flexibly changed according to the type of carbon deposition of the catalyst in each reactor.

[0090] In addition, when the reaction module is composed of multiple reactors connected in series, the reaction conditions of the next reactor in series can be changed according to the outlet of the reactor, so that the selectivity is improved while the activity of the catalyst is stable, and the production of methyl isobutyrate and 3-pentanone, two by-products, is reduced.

[0091] Hereinafter, the multi-module reaction system and the preparation method of methyl methacrylate will be further described through the following specific examples.

[0092] Example 1-3

[0093] Reference Figure 1 In the multi-module reaction system, the reactor is an electric heating isothermal fixed bed made of stainless steel, the length of each reactor is 100 cm, the inner diameter is 12 mm, and a catalyst with a height of 50 cm is arranged therein. The catalyst is an alkali metal catalyst Cs / SiO2, and the metal Cs is loaded on the carrier SiO2. The mass fraction of the metal Cs in the Cs / SiO2 is 10%.

[0094] In the generation process, the four reactors of the multi-module reaction system are connected in series to form a reaction module, and one reactor is used as a preparation module. First, the temperature of the reactors 10a-10d is set, and the preset reaction pressure is controlled through the pressure gauge connected to the rear end of the reactor. A certain molar ratio of methyl propionate and formaldehyde enters the reactor 10a, is directly detected by the first online Raman spectrum detector, and then enters the reactor 10b, the reactor 10c, and the reactor 10d. The reaction process conditions are set according to the process parameters in Table 1, wherein the feed air speed is calculated according to the total amount of the catalysts in the reactors 10a-10d. The content of the substances in the outlet of each reactor is detected, and the MP conversion rate and the MMA selectivity are calculated.

[0095] Table 1

[0096]

[0097] Comparative Example 1-3

[0098] The above experiment was carried out by using a single tube fixed bed reactor, which was also an electrically heated isothermal fixed bed made of stainless steel, the length of the reactor was 100 cm, the inner diameter was 12 mm, and a catalyst with the same as that in Example 1 was arranged in the reactor with a height of 50 cm. The reaction process conditions were set according to the process parameters in Table 2, wherein the content of the substances in the reactor outlet was detected, and the MP conversion rate and the MMA selectivity were calculated.

[0099] Table 2

[0100]

[0101] It can be seen from the comparison results of Examples 1-3 and Comparative Examples 1-3 that under the same ratio and the same conversion rate, the selectivity obtained by the multi-module reaction system of the present application is obviously higher than that of the single tube reactor, and after stable reaction for 96 h, only reactor 1 needs to be regenerated in the multi-module reaction system, while all the catalysts in the single tube reactor are regenerated, that is, only 1 / 4 of the catalysts affect the stability of the catalyst, but due to the problem of the single tube, the catalyst must be regenerated.

[0102] The deactivated catalysts in Examples 1-3 and Comparative Example 1 were respectively detected by thermogravimetry to obtain the corresponding carbon deposition contents.

[0103] Then, the catalysts in each reactor and the single tube reactor were regenerated by using the following regeneration process: the temperature of the reactor 10a was set to 320 ℃, the reactor 10a was first purged with nitrogen at a flow rate of 500 mL / min for 1 h, then the oxygen content in the regeneration gas was increased to 5%, and the content of oxygen and carbon dioxide in the tail gas was detected by the first online gas chromatograph 18a (online oxygen detector), until the oxygen content in the tail gas detected by the first online gas chromatograph 18a was consistent with that detected by the second online gas chromatograph 19 (online oxygen detector), the temperature of the reactor 10a was increased to 380 ℃, and the content of oxygen and carbon dioxide in the tail gas was continuously detected, until the oxygen content in the tail gas detected by the first online gas chromatograph 18a was consistent with that detected by the second online gas chromatograph 19.

[0104] The regeneration time was monitored by using the same regeneration process, and the comparison results are shown in Table 3.

[0105] Table 3

[0106]

[0107] As can be seen from Table 3, the stable reaction of the multi-module reaction system of the present application not only makes the selectivity of the catalyst relatively higher than that of the single tube fixed bed reactor, but also significantly reduces the carbon deposition content of the catalyst, shortens the regeneration time of the catalyst, and prolongs the stable time of the catalyst.

[0108] The contents of two by-products, 3-pentanone and methyl isobutyrate, which have higher contents and affect the separation, in the reaction products of Examples 1-3 and Comparative Example 1 were detected, respectively, and the results are shown in Table 4.

[0109] Table 4

[0110] Reaction system 3-pentanone selectivity % isobutyric acid methyl ester selectivity % Comparative Example 1 2.64 0.93 Example 1 0.28 0.11 Example 2 0.24 0.07 Example 3 0.35 0.18

[0111] From Table 4, it can be seen that the by-products produced by the multi-module reaction system of the present application are significantly less than those produced by the single-tube reactor.

[0112] Example 4

[0113] The multi-module reaction system of Example 1 was used for continuous operation, and the reaction of the reactor was carried out according to the molar ratio of MP to FA of 5 / 1 in Example 1, and the feed airspeed was 1.1.

[0114] The reaction stage of the first group of reaction modules was carried out by the reaction modules of reactor 10a, reactor 10b, reactor 10c and reactor 10d in series, and reactor 10e was used as a standby module and did not react. After about 96 hours of reaction, the change value of the conversion rate of MP in reactor 10a reached 10%, and it was considered that the catalyst in reactor 10a was close to deactivation. At this time, by controlling the first valve, reactor 10a ended the reaction, reactor 10b started the reaction, and reactor 10e reached the preset temperature and entered the reaction state to form the second group of reaction modules in series with reactor 10b, reactor 10c and reactor 10d to enter the reaction stage, and at the same time, the second valve was controlled to start the regeneration of reactor 10a.

[0115] The reaction stage of the second group of reaction modules was carried out by the reaction modules of reactor 10b, reactor 10c, reactor 10d and reactor 10e in series, and reactor 10a started regeneration to be used as a new standby module for the next catalytic reaction. After about 96 hours of reaction, the change value of the conversion rate of MP in reactor 10b reached 10%, and it was considered that the catalyst in reactor 10b was close to deactivation. At this time, by controlling the first valve, reactor 10a reached the preset temperature and entered the reaction state to form the third group of reaction modules in series with reactor 10c, reactor 10d, reactor 10e and reactor 10a to enter the reaction stage, and at the same time, the second valve was controlled to start the regeneration of reactor 10b.

[0116] The reaction stage of the third group of reaction modules was carried out by the reaction modules of reactor 10c, reactor 10d, reactor 10e and reactor 10a in series, and reactor 10b started regeneration to be used as a new standby module for the next catalytic reaction.

[0117] The long period experiment was repeated in this way, and the results are shown in Table 5.

[0118] Table 5

[0119]

[0120] The long period reaction of 2000h was carried out by using the multi-module reaction system of Example 1 and the single tube reactor of Comparative Example 1, wherein the long period reaction of 2000h was carried out by using the single tube reactor of Comparative Example 1, and 2000h is the cumulative reaction time of the single tube reactor, excluding the regeneration time.

[0121] The composition of the reactor outlet material after 2000h was monitored, and the composition was calculated, and the results are shown in Table 6 and Table 7, respectively. The carbon deposition amount, regeneration time and selectivity of two by-products 3-pentanone and methyl isobutyrate are shown in Table 8 and Table 9, respectively.

[0122] During the long period experiment, the catalyst of the multi-module reaction system needs to be regenerated every 96h. It can be known by comparing Table 1 and Table 6 that after running for 2000h, the activity of the reaction system will decrease, the reaction temperature needs to be increased in order to maintain the conversion rate of MP, and the reaction selectivity decreases, and the selectivity of MMA in the outlet changes from 86.7% at the beginning to 85.9%.

[0123] During the long period experiment, the catalyst of the single tube reaction system needs to be regenerated every 72h. It can be known by comparing Table 2 and Table 7 that after running for 2000h, the activity of the reaction system will decrease, the reaction temperature needs to be increased in order to maintain the conversion rate of MP, and the reaction selectivity decreases, and the selectivity of MMA in the outlet changes from 83.5% at the beginning to 79.8%.

[0124] It can be known by combining Table 3 and Table 8 that after running for 2000h, when a reactor of the multi-module reaction system of Example 1 needs to be replaced, the carbon deposition amount increases from 4.6% to 6.4%, and the regeneration time extends from 18h to 24h, while when the single tube reactor needs to be replaced, the carbon deposition amount increases from 9.2% to 15.1%, and the regeneration time extends from 48h to 68h. It can be seen that after the long period running of the single tube reactor, the regeneration time of the catalyst is greatly improved, the catalyst continues to be used for too long through regeneration, and the regeneration effect is not good (part of the catalyst cannot be regenerated), and new catalyst needs to be replaced. The regeneration time of the multi-module reaction system in the present application does not change too much, and the performance of the catalyst is maintained in a relatively stable range through regeneration.

[0125] From Table 4 and Table 9, it can be seen that after 2000h of operation, the selectivity of by-product 3-pentanone is increased from 0.28% to 0.39% and the selectivity of methyl isobutyrate is increased from 0.11% to 0.19% by using the multi-module reaction system of Example 1; while after 2000h of operation, the selectivity of by-product 3-pentanone is increased from 2.64% to 4.85% and the selectivity of methyl isobutyrate is increased from 0.93% to 1.98% by using the single-tube reactor, which shows that the performance of the catalyst is obviously decreased and the selectivity of the two by-products is obviously increased after long-period operation by using the single-tube reactor, while the selectivity of the two by-products is increased to some extent but within an acceptable range by using the multi-module reaction system of the application, which also reflects that the multi-module reaction system can maintain the performance of the catalyst within a relatively stable range.

[0126] From the comparison results in the long-period experiment, it can be seen that the reaction temperature needs to be increased in both reaction systems with the decrease of the activity of the catalyst, which also leads to the decrease of the reaction selectivity, but the reaction conditions and results of the multi-module reaction system of the application change less compared with the single-tube reactor, and the corresponding coke content / regeneration time and the selectivity of the two by-products are consistent.

[0127] Table 6

[0128]

[0129] Table 7

[0130]

[0131] Table 8

[0132]

[0133] Table 9

[0134]

[0135] The technical features of the above-described embodiments can be combined in any manner. In order to make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not exist in contradiction, they shall be considered as the scope of the description.

[0136] The above-described embodiments only express several implementation manners of the application, and the description is relatively specific and detailed, however, it shall not be understood as the limitation on the scope of the patent. It should be pointed out that, for the ordinary skilled in the art, several modifications and improvements can be made without departing from the concept of the application, which shall be within the protection scope of the application. Therefore, the protection scope of the patent of the application shall be subject to the appended claims.

Claims

1. A multi-module reaction system, characterized by, The multi-module reaction system comprises n reactors, n≥3, for loading catalysts and performing catalytic reactions; Each of the reactors is provided with a raw material inlet and a product outlet, and is controlled by a first valve to be on or off. The on-off control of the first valve enables m reactors to form a series of reaction modules to perform catalytic reactions, and enables n-m reactors to form a standby module, m≥2, n-m≥1. The product outlet of each reactor is provided with a first online detector for detecting the equilibrium conversion rate of the raw material in the corresponding reactor. When the first online detector detects that the change value of the equilibrium conversion rate of the raw material in the corresponding reactor exceeds a preset value, the corresponding reactor is stopped from reacting by the first valve control, and the reactors in the standby module are connected in series to the reaction module to form a new reaction module for catalytic reaction. Each of the reactors is also provided with a regeneration gas inlet and a tail gas outlet for flowing regeneration gas into the reactor, and is controlled by a second valve to be on or off, for in-situ regeneration of the catalyst in the reactor stopped from reacting. The reactor with the regenerated catalyst is switched to the standby module to form a new standby module. The multi-module reaction system further comprises a main feed pipe and a main discharge pipe. The main feed pipe is used to supply raw materials to the reactors, and the products obtained after the catalytic reaction of the raw materials in the reactors are collected by the main discharge pipe. The main discharge pipe is also provided with a second online detector, which is arranged away from the discharge branch pipe and close to the outlet position of the main discharge pipe, for detecting the equilibrium conversion rate of the raw material in the main discharge pipe.

2. The multi-module reaction system of claim 1, wherein, The raw material inlet of each reactor is connected to the main feed pipe through a feed branch pipe. The product outlet of the 1st to the n-1th reactor is also connected to the raw material inlet of the reactor arranged behind and adjacent to it through a connecting pipe. The product outlet of the n th reactor is also connected to the raw material inlet of the 1st reactor through a connecting pipe. The product outlet of each reactor is connected to the main discharge pipe through a discharge branch pipe. The first online detector is arranged on the discharge branch pipe. The first valve is arranged on each feed branch pipe, connecting pipe and discharge branch pipe. The first valve is also arranged between the adjacent two feed branch pipes of the main feed pipe, and between the adjacent two discharge branch pipes of the main discharge pipe.

3. The multi-module reaction system of claim 2, wherein, The connecting pipe is connected to the discharge branch pipe. The first valve on the discharge branch pipe is arranged between the connecting pipe and the main discharge pipe.

4. The multi-module reaction system of claim 3, wherein, The first valve is also arranged on the discharge branch pipe between the connecting pipe and the product outlet.

5. The multi-module reaction system of claim 1, wherein, The main feed pipe is also provided with a third online detector, which is arranged away from the feed branch pipe and close to the inlet position of the main feed pipe.

6. The multi-module reaction system of claim 5, wherein, The first, second and third online detectors are selected from online Raman spectrum detectors or gas chromatography online monitors.

7. The multi-module reaction system of claim 1, wherein, A first online gas chromatograph is arranged at the tail gas outlet of each reactor for detecting the composition of the tail gas.

8. The multi-module reaction system of claim 7, wherein, The multi-module reaction system further comprises a main gas inlet pipe and a main gas outlet pipe, the regeneration gas inlets of the reactors are connected to the main gas inlet pipe through gas inlet branch pipes, the tail gas outlets of the reactors are connected to the main gas outlet pipe through gas outlet branch pipes, the first online gas chromatographs are arranged on the gas outlet branch pipes, the second valves are arranged on each gas inlet branch pipe and each gas outlet branch pipe, and the second valves are arranged on the main gas inlet pipe between adjacent gas inlet branch pipes and on the main gas outlet pipe between adjacent gas outlet branch pipes.

9. The multi-module reaction system of claim 8, wherein, A second online gas chromatograph is arranged on the main gas inlet pipe, away from the gas inlet branch pipes and close to the inlet of the main gas inlet pipe, for detecting the composition of the regeneration gas in the main gas inlet pipe.

10. A process for the preparation of methyl methacrylate, characterized in that, The preparation method comprises the following steps: providing raw materials comprising methyl propionate and a formaldehyde source; and feeding the raw materials into each reactor of the reaction module for catalytic reaction and outputting a product containing methyl methacrylate; when the first online detector detects that the change value of the equilibrium conversion rate of the methyl propionate in the corresponding reactor is greater than or equal to 10%, the first valve is controlled to stop the reaction of the corresponding reactor, the reactors in the standby module are connected in series to the reaction module to form a new reaction module for catalytic reaction, and the second valve is controlled to in-situ regenerate the catalyst in the stopped reactor, and the reactor after in-situ regeneration of the catalyst is switched to the standby module to form a new standby module.

11. The method for preparing methyl methacrylate according to claim 10, characterized in that, The molar ratio of methyl propionate to the formaldehyde source in the raw materials is 1:1-15:

1.

12. The method for preparing methyl methacrylate according to claim 10, characterized in that, The reaction conditions in each reactor include a temperature of 320-400°C and a pressure of normal pressure to 1.0 MPa.

13. The method for preparing methyl methacrylate according to claim 10, characterized in that, The catalyst in each reactor is an alkali metal catalyst comprising a carrier and an active component supported on the carrier, wherein the active component comprises one or more of K, Na and Cs, the carrier comprises one or more of silicon dioxide, aluminum oxide, molecular sieve and titanium dioxide, and the mass fraction of the active component in the alkali metal catalyst is 4%-20%.

14. The method for preparing methyl methacrylate according to claim 13, characterized in that, The in-situ regeneration conditions of the catalyst include a temperature of 330-450°C, a pressure of normal pressure to 0.5 MPa, and a regeneration gas comprising a mixture of N2 and O2 with a volume fraction of O2 of 1%-10%.

15. The method for preparing methyl methacrylate according to claim 10, characterized in that, A first on-line gas chromatograph is arranged at the tail gas outlet of each reactor, and when the first on-line gas chromatograph detects that the composition of the tail gas is consistent with that of the regeneration gas during the step of in-situ regeneration of the catalyst, the in-situ regeneration is stopped, inert gas is filled into the reactor, and the reactor after the in-situ regeneration of the catalyst is switched to the standby module to form a new standby module.

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