CN111574369B - Method for preparing methyl methacrylate by condensing methyl propionate and formaldehyde aldol and multistage reaction system - Google Patents
Method for preparing methyl methacrylate by condensing methyl propionate and formaldehyde aldol and multistage reaction system Download PDFInfo
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- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 title claims abstract description 99
- 238000000034 method Methods 0.000 title claims abstract description 85
- VVQNEPGJFQJSBK-UHFFFAOYSA-N Methyl methacrylate Chemical compound COC(=O)C(C)=C VVQNEPGJFQJSBK-UHFFFAOYSA-N 0.000 title claims abstract description 36
- HSJKGGMUJITCBW-UHFFFAOYSA-N 3-hydroxybutanal Chemical compound CC(O)CC=O HSJKGGMUJITCBW-UHFFFAOYSA-N 0.000 title claims abstract description 26
- RJUFJBKOKNCXHH-UHFFFAOYSA-N Methyl propionate Chemical compound CCC(=O)OC RJUFJBKOKNCXHH-UHFFFAOYSA-N 0.000 title claims abstract description 24
- 229940017219 methyl propionate Drugs 0.000 title claims abstract description 24
- 238000003541 multi-stage reaction Methods 0.000 title claims abstract description 24
- 238000005575 aldol reaction Methods 0.000 title description 2
- 239000003054 catalyst Substances 0.000 claims abstract description 70
- 238000006555 catalytic reaction Methods 0.000 claims abstract description 68
- 238000006243 chemical reaction Methods 0.000 claims abstract description 58
- 239000007795 chemical reaction product Substances 0.000 claims abstract description 55
- 238000011065 in-situ storage Methods 0.000 claims abstract description 40
- 230000000694 effects Effects 0.000 claims abstract description 33
- 238000004519 manufacturing process Methods 0.000 claims abstract description 25
- 239000002994 raw material Substances 0.000 claims abstract description 25
- 239000000203 mixture Substances 0.000 claims abstract description 16
- 239000000047 product Substances 0.000 claims abstract description 11
- 230000009471 action Effects 0.000 claims abstract description 5
- 230000008929 regeneration Effects 0.000 claims description 85
- 238000011069 regeneration method Methods 0.000 claims description 85
- 230000008569 process Effects 0.000 claims description 55
- 239000007789 gas Substances 0.000 claims description 35
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 33
- IJGRMHOSHXDMSA-UHFFFAOYSA-N nitrogen Substances N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 11
- 229910052757 nitrogen Inorganic materials 0.000 claims description 7
- 238000005882 aldol condensation reaction Methods 0.000 claims description 5
- 239000002904 solvent Substances 0.000 claims description 4
- BGJSXRVXTHVRSN-UHFFFAOYSA-N 1,3,5-trioxane Chemical group C1OCOCO1 BGJSXRVXTHVRSN-UHFFFAOYSA-N 0.000 claims description 3
- 229930040373 Paraformaldehyde Natural products 0.000 claims description 3
- NKDDWNXOKDWJAK-UHFFFAOYSA-N dimethoxymethane Chemical compound COCOC NKDDWNXOKDWJAK-UHFFFAOYSA-N 0.000 claims description 3
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 claims description 3
- 229920002866 paraformaldehyde Polymers 0.000 claims description 3
- 238000000926 separation method Methods 0.000 abstract description 6
- 238000002156 mixing Methods 0.000 abstract description 2
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 19
- 239000003546 flue gas Substances 0.000 description 18
- 239000000945 filler Substances 0.000 description 7
- 239000000571 coke Substances 0.000 description 6
- 238000005516 engineering process Methods 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 230000015572 biosynthetic process Effects 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- 238000003786 synthesis reaction Methods 0.000 description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- 208000035484 Cellulite Diseases 0.000 description 2
- VGGSQFUCUMXWEO-UHFFFAOYSA-N Ethene Chemical compound C=C VGGSQFUCUMXWEO-UHFFFAOYSA-N 0.000 description 2
- 239000005977 Ethylene Substances 0.000 description 2
- VQTUBCCKSQIDNK-UHFFFAOYSA-N Isobutene Chemical compound CC(C)=C VQTUBCCKSQIDNK-UHFFFAOYSA-N 0.000 description 2
- 206010049752 Peau d'orange Diseases 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 230000036232 cellulite Effects 0.000 description 2
- 238000002485 combustion reaction Methods 0.000 description 2
- 230000009849 deactivation Effects 0.000 description 2
- MWFMGBPGAXYFAR-UHFFFAOYSA-N 2-hydroxy-2-methylpropanenitrile Chemical compound CC(C)(O)C#N MWFMGBPGAXYFAR-UHFFFAOYSA-N 0.000 description 1
- 239000000853 adhesive Substances 0.000 description 1
- 230000001070 adhesive effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 230000006315 carbonylation Effects 0.000 description 1
- 238000005810 carbonylation reaction Methods 0.000 description 1
- 239000013064 chemical raw material Substances 0.000 description 1
- 238000004939 coking Methods 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 208000012839 conversion disease Diseases 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000003973 paint Substances 0.000 description 1
- 229920003229 poly(methyl methacrylate) Polymers 0.000 description 1
- 239000004926 polymethyl methacrylate Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C67/00—Preparation of carboxylic acid esters
- C07C67/30—Preparation of carboxylic acid esters by modifying the acid moiety of the ester, such modification not being an introduction of an ester group
- C07C67/333—Preparation of carboxylic acid esters by modifying the acid moiety of the ester, such modification not being an introduction of an ester group by isomerisation; by change of size of the carbon skeleton
- C07C67/343—Preparation of carboxylic acid esters by modifying the acid moiety of the ester, such modification not being an introduction of an ester group by isomerisation; by change of size of the carbon skeleton by increase in the number of carbon atoms
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
- B01J8/02—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with stationary particles, e.g. in fixed beds
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/584—Recycling of catalysts
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
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Abstract
The invention provides a method for preparing methyl methacrylate by condensing methyl propionate and formaldehyde aldol and a multi-stage reaction system, wherein the multi-stage reaction system at least comprises three stages of reactors; the raw material gas can enter each section of reactor respectively and react under the action of the catalyst to generate methyl methacrylate. In the production process, at least two sections of reactors are used for catalytic reaction, and the generated products can respectively enter a reaction product main pipe at the same time; at least one section of the reactor is in-situ regenerated; when the activity of the catalyst in the reactor drops to a preset percentage, the reactor is regenerated in situ. The mole fraction of methyl methacrylate of the product generated by the multistage reactor after entering the reaction product main pipeline for mixing is 5.0-7.5%. The method and the system can effectively reduce the variation amplitude of the composition of the reaction product at the initial stage and the final stage of the reaction, ensure the stability of the product quality and reduce the operation load of the subsequent separation process.
Description
Technical Field
The invention belongs to the technical field of methyl methacrylate synthesis, and particularly relates to a method for preparing methyl methacrylate by condensing methyl propionate and formaldehyde aldol and a multistage reaction system for the method.
Background
Methyl Methacrylate (MMA) is an important organic chemical raw material and is mainly applied to multiple production fields of organic glass (PMMA), resin, paint, adhesive and the like. The most dominant MMA production technology of acetone cyanohydrin method (ACH method) at present has a tendency of gradually being eliminated because the waste liquid produced by the method has serious environmental pollution after the process is lagged. The newly developed MMA preparation technology comprises an isobutene oxidation method of Mitsubishi, an ethylene method of Basoff, an alpha method of cellulite and the like, and the common characteristics of the technology are relatively simple process flow, safety and environmental protection. The synthetic route of the alpha method of the cellulite is divided into two steps: firstly, synthesizing methyl propionate by the carbonylation of ethylene, carbon monoxide and methanol, and secondly, preparing MMA by condensing methyl propionate and formaldehyde. The alpha method has the advantages of easily available and cheap raw materials, greatly shortens the process flow by two-step synthesis, is environment-friendly in production process and has great development potential. However, the technology is monopoly abroad, the synthesis process is poorly known from the outside, domestic researches are less, and the technology is mainly focused on the research and development of aldol catalysts, such as CN102962062A, CN102350336B, CN109999922A and the like.
MMA synthesis from methyl propionate and formaldehyde is performed at high temperature under a base catalyst, the conversion rate of raw materials in the reaction process is low, the catalyst is easy to be carbonized and deactivated, and the service life of the catalyst is short. For this reason, the catalyst must be subjected to charcoal-burning regeneration to restore activity. Aiming at the reaction characteristics of preparing MMA by an aldol method, a common strategy is a mode of multiple fixed bed switching reaction regeneration or a mode of circulating fluidized bed reaction regeneration. The adoption of the circulating fluidized bed has the advantages that the pulverization and the running loss of the catalyst are serious, the annual consumption of the catalyst is huge, the characteristics of low reaction conversion rate and easy coking of the catalyst are combined, the production and operation costs are directly high, the circulating fluidized bed has a complex structure and high equipment cost, and the circulating fluidized bed is not suitable for preparing MMA by an aldol method from the economical aspect. The fixed bed switching reaction regeneration mode has the defects that the composition of reaction products is greatly changed in the initial stage and the final stage along with the increase of the deactivation degree of the catalyst, certain challenges are brought to the subsequent separation operation, and the long-period stable operation of the device is also unfavorable.
Disclosure of Invention
In view of the foregoing problems in the prior art, embodiments of the present invention provide a method for preparing methyl methacrylate by condensing methyl propionate with formaldehyde aldol, which can reduce the variation range of the reaction product composition at the initial stage and the final stage, and reduce the operation load of the subsequent separation process.
In order to solve the above problems, the technical solution provided by the embodiment of the present invention is:
a method for preparing methyl methacrylate by condensing methyl propionate and formaldehyde aldol, which utilizes a multi-stage reaction system, wherein the multi-stage reaction system at least comprises three stages of parallel reactors;
The mixture of methyl propionate and formaldehyde source as raw material gas can enter each section of reactor respectively, aldol condensation reaction is carried out under the action of catalyst to generate methyl methacrylate, and the products generated by the reaction in each section of reactor can enter a reaction product main pipe respectively; the regenerated gas can enter each section of reactor respectively so as to carry out in-situ regeneration on the catalyst in the reactor;
In the production process, at least two sections of reactors are used for catalytic reaction, and at least one section of reactors is used for in-situ regeneration; when the activity of the catalyst in the reactor in the catalytic reaction is reduced to a preset percentage, the catalytic reaction is cut off, in-situ regeneration is carried out, so that the mole fraction of the methyl methacrylate in the product generated by the reaction of the reactor in the multiple stages participating in the catalytic reaction after entering the reaction product main pipeline is 5.0-7.5%.
In some embodiments, the preset percentage is 10% -50%.
In some embodiments, the reactors include n sections, wherein 3.ltoreq.n.ltoreq.10, and n is a positive integer, and the n sections are a first section reactor, a second section reactor, a third section reactor …, an n-1 section reactor, and an n section reactor, respectively; the first stage reactor is started to perform catalytic reaction, when the activity of the catalyst of the first stage reactor is reduced to 1/(n-1), the second stage reactor is started to perform catalytic reaction, when the activity of the catalyst of the second stage reactor is reduced to 1/(n-1), the third stage reactor is started to perform catalytic reaction …, and so on, and when the nth stage reactor is started to perform catalytic reaction, at least the first stage reactor is in an in-situ regeneration process.
In some embodiments, the reactors include n sections, wherein 3.ltoreq.n.ltoreq.10, and n is a positive integer, and the n sections are a first section reactor, a second section reactor, a third section reactor …, an n-1 section reactor, and an n section reactor, respectively;
When n is more than or equal to 3 and less than or equal to 5, firstly starting the first-stage reactor to perform catalytic reaction, when the activity of the catalyst of the first-stage reactor is reduced to 1/2, starting the second-stage reactor to perform catalytic reaction, when the activity of the catalyst of the second-stage reactor is reduced to 1/2, starting the third-stage reactor to perform catalytic reaction, and when the third-stage reactor is started to perform catalytic reaction, the first-stage reactor is in an in-situ regeneration process, and the cycle is repeated;
When n is more than or equal to 6 and less than or equal to 10, the first-stage reactor and the second-stage reactor are started to perform catalytic reaction, when the activity of the catalyst of the first-stage reactor and the second-stage reactor is reduced to 1/2, the third-stage reactor and the fourth-stage reactor are started to perform catalytic reaction, when the activity of the catalyst of the third-stage reactor and the fourth-stage reactor is reduced to 1/2, the fifth-stage reactor and the sixth-stage reactor are started to perform catalytic reaction, and when the fifth-stage reactor and the sixth-stage reactor are started to perform catalytic reaction, at least the first-stage reactor and the second-stage reactor are in an in-situ regeneration process, and the cycle is repeated.
In some embodiments, the process conditions for catalytic reactions in each of the reactors are: the reaction temperature is 300-380 ℃, the reaction pressure is 50-600 KPa, and the weight hourly space velocity is 0.5-10/h.
In some embodiments, the regeneration gas for in situ regeneration of each segment of the reactor is nitrogen and air; the process conditions are as follows: the regeneration temperature is 340-450 ℃, the regeneration pressure is 100-800 KPa, and the volume airspeed is 300-3000/h.
In some embodiments, the formaldehyde source is one or more of trioxymethylene, paraformaldehyde, methylal, formaldehyde;
the feed gas further comprises methanol as a solvent; the molar ratio of methyl propionate to formaldehyde source is 1:5-10:1, and the molar ratio of formaldehyde source to methanol is 1:10-2:1.
The embodiment of the invention also provides a multi-stage reaction system, which comprises at least three stages of parallel reactors, wherein the upper part of each stage of the reactors is provided with an inlet, the inlet is connected with a raw material pipeline and a regeneration gas pipeline, so that when the reactors are in a catalytic reaction process, reaction raw materials are input into the reactors, and after the activity of the catalyst in the reactors is reduced to 10-50% and is switched to a regeneration process, regeneration gas is input into the reactors so as to perform in-situ regeneration; in the production process, at least two sections of reactors are in a catalytic reaction process, and at least one section of reactors is in an in-situ regeneration process;
The lower part of each section of the reactor is provided with an outlet, the outlet is connected with a reaction product pipeline and a flue gas pipeline, the reaction product pipeline of each section of the reactor is connected to a reaction product total pipeline so as to lead all reaction products of the reactor in the catalytic reaction process to be converged to the reaction product total pipeline through the reaction product pipeline, so that the mole fraction of methyl methacrylate generated by a plurality of sections of the reactor after entering the reaction product total pipeline for mixing is 5.0-7.5%, and the flue gas generated by the reactor in the in-situ regeneration process enters the flue gas pipeline.
In some embodiments, each section of the reactor is identical in structure and is an adiabatic fixed bed reactor of vertical cylindrical structure; a support grid is arranged in the reactor, and a first inert filler layer, a catalyst bed layer and a second inert filler layer are sequentially loaded on the support grid from top to bottom; and a feeding distributor is arranged above the first inert filler layer.
In some embodiments, the raw material pipeline and the regeneration gas pipeline of each section of the reactor are respectively provided with an inlet valve, and the reaction product pipeline and the flue gas pipeline of each section of the reactor are respectively provided with an outlet valve so as to control the reactor to switch between the catalytic reaction process and the in-situ regeneration process.
Compared with the prior art, the embodiment of the invention has the beneficial effects that: the method and the multistage reaction system can effectively reduce the variation amplitude of the composition of the reaction products at the initial stage and the final stage of the reaction, ensure the stability of the product quality and reduce the operation load of the subsequent separation process.
Drawings
FIG. 1 is a schematic structural diagram of a multistage reaction system according to an embodiment of the present invention.
Reference numerals illustrate:
1-a first stage reactor; 2-a second stage reactor; 3-a third stage reactor; 4-inlet; 5-a raw material pipeline; 6-a regeneration gas pipeline; 7-outlet; 9-a flue gas pipeline; 10-a reaction product main line; 11-a first inlet valve; 12-a second inlet valve; 13-a first outlet valve; 14-a second outlet valve.
Detailed Description
In order to enable those skilled in the art to better understand the technical solutions of the embodiments of the present invention, the present invention is described in detail below with reference to the accompanying drawings and detailed description.
The embodiment of the invention provides a method for preparing methyl methacrylate by condensing methyl propionate and formaldehyde aldol, which uses methyl propionate, a formaldehyde source and methanol (the methanol is taken as a solvent and does not participate in the reaction basically) as reaction raw materials, and adopts a multi-stage reaction system shown in figure 1, wherein the multi-stage reaction system at least comprises three stages of parallel reactors; the reaction raw materials can respectively enter each section of reactor at the same time, and methyl propionate and formaldehyde generate aldol condensation reaction in the reactor under the action of a catalyst to generate methyl methacrylate (METHYL METHACRYLATE, MMA for short); the reaction products generated by the reaction in each section of the reactor can respectively enter a reaction product main pipeline 10; the regeneration gas can enter each section of reactor respectively so as to regenerate the catalyst in the reactor in situ.
In the production process, at least two sections of reactors are used for catalytic reaction, and at least one section of reactors is used for in-situ regeneration; when the activity of the catalyst in the reactor in the catalytic reaction is reduced to a preset percentage, the catalytic reaction is cut off, in-situ regeneration is carried out, the regenerated reactor is continuously used for the catalytic reaction, and the cycle is carried out so that the mole fraction of methyl methacrylate in the reaction product generated by the reaction of the multiple sections of the reactor participating in the catalytic reaction after entering the total reaction product pipeline 10 is 5.0-7.5%.
According to the method provided by the embodiment of the invention, carbon is formed on the surface of the catalyst during the reaction (in the reaction process), so that the catalyst performance is reduced, when the catalyst activity of a certain section of reactor is reduced to a preset percentage, the section of reactor needs to be cut out of the reaction system for in-situ regeneration instead of the catalyst being completely deactivated, and in the production process, the whole multi-section reaction system always has one section of reactor in the in-situ regeneration process, so that the relative stability of the composition of the reaction product at the initial stage and the final stage of the reaction is ensured, and particularly, the mole fraction of MMA can be controlled within the range of 5.0-7.5%, so that the operation load of a subsequent separation process is favorably reduced.
It should be noted that when the production is just started, each section of reactor is started gradually, and one section of reactor may be started first, or multiple sections of reactors may be started simultaneously; likewise, each reactor is gradually stopped at the end of production; thus, the production process refers to the stage when the multistage reaction system is operated to form a cyclic production, the whole multistage reaction system always has one stage of reactor in an in-situ regeneration process, and at least two stages of reactors in a catalytic reaction process are not suitable for starting production and ending production.
In some embodiments, in order to prevent frequent reactor switching to increase the running cost and to maximize the catalyst utilization efficiency, when the catalyst activity is reduced to 10% -50%, the in-situ regeneration process is switched in, so that the mole fraction of MMA in the mixture of reaction products of the multistage reactor can be controlled within the range of 5.0% -7.5%, and the production cost can be reduced.
The total number of the reactors in the multistage reaction system is preferably 3-10, namely, the reactors comprise n stages, wherein n is more than or equal to 3 and less than or equal to 10, n is a positive integer, and the n stages of the reactors are respectively a first stage reactor 1, a second stage reactor 2, a third stage reactor 3 …, an n-1 stage reactor and an n-th stage reactor; the first stage reactor 1 is started first to perform catalytic reaction, when the activity of the catalyst of the first stage reactor 1 is reduced to 1/(n-1), the second stage reactor 2 is started to perform catalytic reaction, when the activity of the catalyst of the second stage reactor 2 is reduced to 1/(n-1), the third stage reactor 3 is started to perform catalytic reaction …, and so on, and when the nth stage reactor is started to perform catalytic reaction, at least the first stage reactor 1 is in an in-situ regeneration process. The method of this example utilizes a multistage reaction system in which at least two stages of reactors are in the catalytic reaction process and at least one stage is in the regeneration process when they are in the production process, and the activity of the catalyst in the reactors in the catalytic reaction process is not less than 10%, so that the variation of the composition of the reaction product in the initial stage and the final stage of the reaction is not large, that is, the mole fraction of MMA after the reaction products of the respective reactors are mixed in the reaction product main pipe 10 is controlled to 5.0% to 7.5% in the whole reaction process including the initial stage and the final stage of the reaction. The product quality is stable, and the operation load of the subsequent separation process is reduced.
During the production run, the reactor sections may be subjected to a reaction switching operation sequentially, preferably in a sequential rotation, at certain time intervals. For example, first stage reactor 1 is started to react, when the catalyst activity is reduced to, for example, 50%, second stage reactor 2 is started, first stage reactor 1 continues to operate, and third stage reactor 3 is started to react when the catalyst activity of first stage reactor 1 is reduced to any value within 10% -50%, and at the same time, first stage reactor 1 is cut out to catalyze the reaction to perform in-situ regeneration. When the catalyst activity of the second-stage reactor 2 is reduced to any value within 10% -50%, the regenerated first-stage reactor 1 is started to react, and meanwhile, the second-stage reactor 2 is cut out for catalytic reaction, so that in-situ regeneration of the catalyst is performed.
The operation steps are circulated according to the reaction time interval of each section of the reactor, so that continuous and stable operation of the n sections of the reactor can be realized, the variation range of the composition of the reaction products is effectively reduced, and the fluctuation range of the composition of the reaction products is smaller when the number of the adopted sections is larger.
For example, when the total number of reactors in the multistage reaction system is small, such as 3 to 5 stages, only one stage of the reactors may be in the in-situ regeneration process and at least two stages of the reactors are in the catalytic reaction process. Specifically, when n is more than or equal to 3 and less than or equal to 5, the first-stage reactor 1 is started to perform catalytic reaction, when the activity of the catalyst in the first-stage reactor 1 is reduced to 1/2, the second-stage reactor 2 is started to perform catalytic reaction, when the activity of the catalyst in the second-stage reactor 2 is reduced to 1/2, the third-stage reactor 3 is started to perform catalytic reaction, and when the third-stage reactor 3 is started to perform catalytic reaction, the first-stage reactor 1 is in an in-situ regeneration process, and the cycle is repeated.
For example, when the total number of reactors in the multistage reaction system is more, for example, 6 to 10 stages, two stages of reactors can be in-situ regeneration process at the same time, and at least two stages of reactors are in catalytic reaction process. Specifically, when n is 6-10, the first stage reactor 1 and the second stage reactor 2 are started to perform catalytic reaction, when the activity of the catalyst of the first stage reactor 1 and the second stage reactor 2 is reduced to 1/2, the third stage reactor 3 and the fourth stage reactor are started to perform catalytic reaction, when the activity of the catalyst of the third stage reactor 3 and the fourth stage reactor is reduced to 1/2, the fifth stage reactor and the sixth stage reactor are started to perform catalytic reaction, and when the fifth stage reactor and the sixth stage reactor are started to perform catalytic reaction, at least the first stage reactor 1 and the second stage reactor 2 are in an in-situ regeneration process, and the cycle is repeated.
It should be noted that the start-up sequence and the number of simultaneous starts of each stage reactor in the method of the present invention are not limited, so long as at least two stages of reactors are guaranteed to be in the catalytic reaction process and at least one stage of reactors is guaranteed to be in the regeneration process during the production operation, and when the activity of the catalyst in the reactors is reduced to 10% -50%, the catalytic reaction must be cut out and enter the regeneration process, and at the same time, the mole fraction of Methyl Methacrylate (MMA) in the reaction products produced by the multiple stages of reactors is guaranteed to be 5.0% -7.5% after the reaction products are mixed.
In order to ensure that the catalytic reaction is smoothly and stably carried out, the production process is continuously operated, and the technological conditions of the catalytic reaction carried out by each section of the reactor can be as follows: the reaction temperature is 300-380 ℃, the reaction pressure is 50-600 KPa, and the weight hourly space velocity is 0.5-10/h; the more preferable reaction temperature is 320-350 ℃, the more preferable reaction pressure is 100 KPa-350 KPa, and the more preferable weight hourly space velocity is 2-5/h.
The catalyst deactivation is mainly that coke is adhered to the surface of the catalyst in the reaction process, and the coke on the surface of the catalyst is burnt, namely, the coke is burnt, so that the catalyst is regenerated and revived, and the gas used for combustion, namely, the regenerated gas, is the mixed gas of nitrogen and oxygen. The regeneration process is started, firstly, nitrogen is introduced, then air is gradually introduced, the air introduction amount is gradually increased, and the nitrogen introduction amount is reduced until the nitrogen introduction is stopped, namely, the oxygen concentration is gradually increased from 0 to 21% (only air is introduced) along with the progress of the regeneration process, namely, the coke is burnt out and the regeneration process is a process of dynamically and gradually increasing the oxygen concentration. When the inlet 4 temperature of the reactor is the same as the temperature of the catalyst bed of the reactor (indicating that the coke has been completely combusted, no more heat can be generated, and the temperature of the catalyst bed is unchanged) and the flue gas oxygen concentration is 21% (because the coke is completely combusted, the introduced air is no longer involved in combustion and is directly discharged as flue gas), the in-situ regeneration is completed.
In some embodiments, the regeneration gas for in-situ regeneration of each section of the reactor is nitrogen and air, and when regeneration begins, the regeneration gas is firstly introduced; the process conditions of in-situ regeneration are as follows: the regeneration temperature is 340-450 ℃, the regeneration pressure is 100-800 KPa, and the volume airspeed is 300-3000/h. The more preferable regeneration temperature is 350-380 ℃, the more preferable regeneration pressure is 100 KPa-350 KPa, and the more preferable volume airspeed is 400-550/h.
The formaldehyde source used for aldol condensation with methyl propionate can be one or more of trioxymethylene, paraformaldehyde, methylal and formaldehyde. In addition, the raw material gas also comprises methanol as a solvent; the molar ratio of methyl propionate to formaldehyde source is 1:5-10:1, and the molar ratio of formaldehyde source to methanol is 1:10-2:1.
The embodiment of the invention also provides a multi-stage reaction system, as shown in figure 1, the multi-stage reaction system comprises at least three stages of parallel reactors, the upper part of each stage of reactor is provided with an inlet 4, the inlet 4 is connected with a raw material pipeline 5 and a regeneration gas pipeline 6, so that when the reactor is in a catalytic reaction process, the raw material is used for inputting reaction into the reactor, and after the activity of the catalyst in the reactor is reduced to 10% -50% and is switched to a regeneration process, the catalyst is used for inputting regeneration gas into the reactor, so as to perform in-situ regeneration; the lower part of each section of reactor is provided with an outlet 7, the outlet 7 is connected with a reaction product pipeline and a flue gas pipeline 9, and the reaction product pipeline of each section of reactor is connected to a reaction product total pipeline 10 so as to merge the reaction products of all the reactors in the catalytic reaction process to the reaction product total pipeline 10 through the reaction product pipeline.
Continuing to combine with FIG. 1, each section of reactor has the same structure and is an adiabatic fixed bed reactor with a vertical cylindrical structure; the reactor is provided with a support grid (not shown) which may be a metal mesh. The first inert filler layer, the catalyst bed layer and the second inert filler layer are sequentially loaded on the support grid from top to bottom. The feeding distributor is arranged above the first inert filler layer, so that the effect of uniform gas distribution can be achieved after the raw material gas or the regenerated gas passes through the gas distributor and the first inert filler layer.
Specifically, as shown in fig. 1, the inlet 4 is disposed at the top of the reactor, and the raw material pipeline 5 and the regeneration gas pipeline 6 are connected and then connected to the inlet 4 through a common section, so that both the raw material gas and the regeneration gas can enter the reactor through the inlet 4. That is, the inlet 4 is shared by the raw material gas and the regeneration gas. The outlet 7 is arranged at the bottom of the reactor, and the reaction product pipeline and the flue gas pipeline 9 are connected and then connected into the outlet 7 through a shared section, so that both reaction products and the flue gas during regeneration can respectively enter the reaction product pipeline and the flue gas pipeline 9 through the outlet 7. The reaction product pipelines of the multi-stage reactor are converged and communicated to a reaction product main pipeline 10, so that the reaction products generated by the multi-stage reactor enter the reaction product main pipeline 10 to be mixed, the mole fraction of methyl methacrylate is 5.0-7.5%, and the flue gas generated by the reactor in the in-situ regeneration process enters a flue gas pipeline 9.
In some embodiments, inlet valves are provided on the feed line 5 and the regeneration gas line 6, respectively, of each reactor, and outlet valves are provided on the reaction product line and the flue gas line 9, respectively, of each reactor to control the reactor to switch between the catalytic reaction process and the in situ regeneration process.
Specifically, as shown in fig. 1, the multistage reaction system comprises three stages of reactors, namely a first stage reactor 1, a second stage reactor 2 and a third stage reactor 3. The inlet 4 at the top of the three-stage reactor is respectively communicated with a raw material pipeline 5 and a regenerated gas pipeline 6. The raw material pipeline 5 is respectively provided with a first inlet valve 11, and the regenerated gas pipeline 6 is provided with a second inlet valve 12; the outlet 7 at the bottom of the three-stage reactor is respectively communicated with a reaction product pipeline and a flue gas pipeline 9. The reaction product pipeline is provided with a first outlet valve 13; the flue gas pipeline 9 is provided with a second outlet valve 14. When the reactor is in the catalytic reaction process, the second inlet valve 12 is closed, the first inlet valve 11 is opened, so that the reaction raw materials are introduced into the reactor, and the regenerated gas is blocked from entering the reactor, so that the catalytic reaction is carried out in the reactor; the second outlet valve 14 is closed and the first outlet valve 13 is opened so that the reaction product generated in the reactor flows via the reaction product line into the reaction product header line 10. When the activity of the catalyst in the reactor is reduced to 10 to 50 percent, the first inlet valve 11 is closed, the second inlet valve 12 is opened, so that the regenerated gas is introduced into the reactor, the reaction raw materials are blocked from entering the reactor, and the catalyst in the reactor is regenerated; the first outlet valve 13 is closed, and the second outlet valve 14 is opened, so that the flue gas regenerated in the reactor enters the flue gas pipeline 9.
In the multi-stage reaction system of the embodiment of the invention, in the production process, the multi-stage reactors are connected in parallel, reaction raw materials can respectively enter each stage of reactor at the same time, methyl propionate and formaldehyde undergo aldol condensation reaction under the action of a catalyst to generate MMA, and outlet products generated by each stage of reactor can respectively enter a reaction product total pipeline 10 through respective reaction product pipelines. In the production process, at least two sections of reactors in the whole multi-section reaction system are used for catalytic reaction, and one section of reactor is always used for regeneration. In the production process, carbon is formed on the surface of a catalyst in a reactor, so that the performance of the catalyst is reduced, when the activity of the catalyst in a certain section of the reactor is reduced to 10% -50%, a multi-section reaction system is cut out from the section of the reactor to carry out in-situ regeneration, so that the relative stability of the composition of a reaction product at the initial stage and the final stage of the reaction can be ensured, and particularly, the mole fraction of MMA can be controlled to be in the range of 5.0% -7.5%. The product quality is stable, and the operation difficulty of the subsequent procedures is reduced.
Example 1
The multistage reactor process for preparing methyl methacrylate by condensing methyl propionate and formaldehyde by aldol method shown in figure 1 comprises a first stage reactor 1, a second stage reactor 2 and a third stage reactor 3, wherein two stages are used for reaction, and one stage is used for catalyst regeneration. The reaction process conditions are as follows: the weight hourly space velocity is 3/h, the reaction pressure is normal pressure, the reaction temperature is 330 ℃, the mole ratio of raw material methyl propionate to formaldehyde is 2:1, and the mole ratio of formaldehyde to methanol is 1:4; the regeneration process conditions are as follows: the volume space velocity is 600/h, the regeneration temperature is 400 ℃, and the regeneration pressure is normal pressure. The catalyst life was 336 hours, i.e., regeneration was required after 336 hours of reaction, each reactor was switched at 168 hours intervals, and the initial and final compositions of the reaction according to the above process conditions were shown in table 1.
Example 2
A multistage reactor for preparing methyl methacrylate by condensing methyl propionate and formaldehyde by an aldol method comprises a first stage reactor, a second stage reactor, a third stage reactor and a fourth stage reactor, wherein three stages of reactors are used for reaction, and one stage of reactors is used for regeneration of a catalyst. The reaction process conditions are as follows: the weight hourly space velocity is 3/h, the reaction pressure is normal pressure, the reaction temperature is 330 ℃, the mole ratio of raw material methyl propionate to formaldehyde is 2:1, and the mole ratio of formaldehyde to methanol is 1:4; the regeneration process conditions are as follows: the volume space velocity is 600/h, the regeneration temperature is 400 ℃, and the regeneration pressure is normal pressure. The catalyst life was 336 hours, i.e., regeneration was required after 336 hours of reaction, each reactor was switched at 112 hours intervals, and the initial and final compositions of the reaction according to the above process conditions were shown in table 1.
Comparative examples 1 and 2
For comparison with example 1 and example 2, the reaction was carried out using a single reactor under the same process conditions and catalyst as in example 1 and example 2, and the initial and final compositions of the reaction were shown in Table 1.
Table 1 reaction product composition:
The above embodiments are only exemplary embodiments of the present invention and are not intended to limit the present invention, the scope of which is defined by the claims. Various modifications and equivalent arrangements of this invention will occur to those skilled in the art, and are intended to be within the spirit and scope of the invention.
Claims (4)
1. A method for preparing methyl methacrylate by condensing methyl propionate and formaldehyde aldol, which is characterized by utilizing a multi-stage reaction system, wherein the multi-stage reaction system at least comprises three stages of parallel reactors;
The mixture of methyl propionate and formaldehyde source as raw material gas can enter each section of reactor respectively, aldol condensation reaction is carried out under the action of catalyst to generate methyl methacrylate, and the products generated by the reaction in each section of reactor can enter a reaction product main pipe respectively; the regenerated gas can enter each section of reactor respectively so as to carry out in-situ regeneration on the catalyst in the reactor;
In the production process, at least two sections of reactors are used for catalytic reaction, and at least one section of reactors is used for in-situ regeneration; when the activity of the catalyst in the reactor in the catalytic reaction is reduced to a preset percentage, cutting off the catalytic reaction, and performing in-situ regeneration so that the mole fraction of methyl methacrylate in the product generated by the reaction of the reactor in the multiple sections participating in the catalytic reaction after entering the reaction product main pipeline is 5.0-7.5%;
The reactors comprise n sections, wherein n is more than or equal to 3 and less than or equal to 10, n is a positive integer, and the n sections of the reactors are a first section of reactor, a second section of reactor, a third section of reactor …, an n-1 section of reactor and an n section of reactor respectively;
When n is more than or equal to 3 and less than or equal to 5, firstly starting the first-stage reactor to perform catalytic reaction, when the activity of the catalyst of the first-stage reactor is reduced to 1/2, starting the second-stage reactor to perform catalytic reaction, when the activity of the catalyst of the second-stage reactor is reduced to 1/2, starting the third-stage reactor to perform catalytic reaction, and when the third-stage reactor is started to perform catalytic reaction, the first-stage reactor is in an in-situ regeneration process, and the cycle is repeated;
When n is more than or equal to 6 and less than or equal to 10, the first-stage reactor and the second-stage reactor are started to perform catalytic reaction, when the activity of the catalyst of the first-stage reactor and the second-stage reactor is reduced to 1/2, the third-stage reactor and the fourth-stage reactor are started to perform catalytic reaction, when the activity of the catalyst of the third-stage reactor and the fourth-stage reactor is reduced to 1/2, the fifth-stage reactor and the sixth-stage reactor are started to perform catalytic reaction, and when the fifth-stage reactor and the sixth-stage reactor are started to perform catalytic reaction, at least the first-stage reactor and the second-stage reactor are in an in-situ regeneration process, and the cycle is repeated.
2. The method of claim 1, wherein the process conditions for catalytic reaction in each of the reactor sections are: the reaction temperature is 300-380 ℃, the reaction pressure is 50-600 KPa, and the weight hourly space velocity is 0.5-10/h.
3. The method of claim 1, wherein the regeneration gas for in situ regeneration of each segment of the reactor is nitrogen and air; the process conditions are as follows: the regeneration temperature is 340-450 ℃, the regeneration pressure is 100-800 KPa, and the volume airspeed is 300-3000/h.
4. The method of claim 1, wherein the formaldehyde source is one or more of trioxymethylene, paraformaldehyde, methylal, formaldehyde;
the feed gas further comprises methanol as a solvent; the molar ratio of methyl propionate to formaldehyde source is 1:5-10:1, and the molar ratio of formaldehyde source to methanol is 1:10-2:1.
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