A continuous production process and device for methyltetrahydrophthalic anhydride

Abstract

The present application relates to a kind of methyl tetrahydrophthalic anhydride continuous production process and device, the present application adopts piperylene segmented feed, isoprene is first with a part of piperylene and maleic anhydride pre-synthesis reaction at low temperature, then continue to react with another part of piperylene at higher temperature, reduce isoprene self-polymerization, using column tube heat exchanger to improve synthesis efficiency, heater and mixer are set on external circulation pipeline to carry out temperature control to reactor, using the method that reactor synthesis product carries fresh raw material and circulates into reactor to prevent fresh carbon five and anhydride aggregation self-polymerization to reduce side reaction, no high polymer slag is generated.

Description

Technical Field

[0001] This invention belongs to the field of methyltetrahydrophthalic anhydride preparation, and specifically relates to a continuous production process and apparatus for methyltetrahydrophthalic anhydride. Background Technology

[0002] Methyltetrahydrophthalic anhydride, also known as methyltetrahydrophthalic anhydride (MeTHPA), is a compound obtained by the Diels-Alder reaction and isomerization of maleic anhydride with isoprene / isoprene. It has a molecular weight of 166.17, is a pale yellow, transparent, oily liquid with a relative density of 1.20-1.22, a freezing point <-20℃, a boiling point of 115-155℃, a viscosity (25℃) of 40-80 mPa·s, a refractive index of 1.4960-1.4980, anhydride content ≥40%, a neutralization equivalent of 81-85, and a flash point of 137-150℃. It is soluble in acetone, ethanol, toluene, etc., and exhibits good stability in air, rarely crystallizing. It is also low in toxicity. Methyltetrahydrophthalic anhydride is mainly used as a curing agent for epoxy resins. It undergoes a ring-opening reaction with epoxy resins to form anhydride esters. These anhydride esters then undergo nucleophilic addition reactions with oxygen atoms in the epoxy resin to form epoxy and ester groups. These reactions will continue until the epoxy resin is completely cured.

[0003] Currently, the main method for producing methyltetrahydrophthalic anhydride in China is the batch process. For example, in patent CN116535372A, a method for preparing methyltetrahydrophthalic anhydride, maleic anhydride is stirred and melted at 60-70℃, and then a C5 solution is added dropwise while the temperature is controlled at 55-60℃. After the addition is completed, the reaction is kept at this temperature for 1-1.5 hours. After the reaction is completed, the remaining C5 solution and polymerization inhibitor are evaporated under reduced pressure to obtain the methyltetrahydrophthalic anhydride solution, which is a common process at present.

[0004] In recent years, the process for batch preparation of methyltetrahydrophthalic anhydride in industrial plants has been continuously optimized. For example, patent CN109158067A proposes a process device for chemical synthesis, isomerization, molecular distillation, and purification of methyltetrahydrophthalic anhydride. The process involves using a raw material ratio of maleic anhydride:isoprene:imrene (1:0.967:0.367) in an ultrasonic synthesis reactor to synthesize methyltetrahydrophthalic anhydride for 60 minutes. After the synthesis reactor is heated to 70°C for 2 hours, C5 is removed and recovered at 150°C. The crude methyltetrahydrophthalic anhydride is then fed into a magnetic isomerization reactor for isomerization under the action of a catalyst. The isomerized product is then purified in a short-path molecular distillation apparatus to obtain a methyltetrahydrophthalic anhydride product with a lighter color and better stability.

[0005] Of course, with the continuous development of industry in recent years, certain achievements have been made in the development of continuous methods for preparing methyltetrahydrophthalic anhydride. For example, the patent CN215250523U methyltetrahydrophthalic anhydride continuous production system proposes to pump a quantitative mixture of C5 and maleic anhydride into a tower reactor for diene synthesis reaction at a fixed residence time. After removing unreacted C5, the product enters a fixed bed containing isomerization catalyst for fixed bed isomerization reaction. The isomerized product then enters an adiabatic evaporator to remove heavy components to obtain isomerized liquid methyltetrahydrophthalic anhydride product.

[0006] For example, patent CN112973612A, a system and method for continuous synthesis of methyltetrahydrophthalic anhydride, proposes to achieve continuous and controllable production through the cooperation of a reaction device and a mixing device. Mixed C5 and maleic anhydride are introduced into the reaction device through a first storage tank (C5 storage tank) and a second storage tank (maleic anhydride storage tank), respectively. After the reaction, reaction products and unreacted mixed C5 are obtained. The mixed C5 enters the mixing device and is mixed with maleic anhydride again for synthesis reaction. This not only realizes the recycling of products, but also enables continuous operation of the equipment, improves the conversion rate of the reaction, enhances the reaction efficiency, and shortens the reaction time. However, the process does not explicitly mention how to remove the heat of reaction in the reactor in a timely manner and control the reaction temperature. Furthermore, after continuous recycling, the effective components of the mixed C5, isoprene and trans-isoprene, are converted into methyltetrahydrophthalic anhydride. The accumulation of inert C5 components such as cis-isoprene, which do not react with maleic anhydride, will increase and cannot be discharged from the system. This leads to a decrease in the contact probability between active C5 and maleic anhydride, which will increase the probability of C5 self-polymerization, reduce the single-pass conversion rate, and result in slightly poor long-term operation of the device.

[0007] As can be seen from the aforementioned methyltetrahydrophthalic anhydride synthesis process, both batch and continuous methods provide rather vague descriptions of the process. Feedback from actual production indicates that the density of C5 monomers is approximately 0.63 g / ml, while that of maleic anhydride is 1.484 g / ml, a significant density difference. Furthermore, the synthesis reaction of both monomers is a Diels-Alder reaction, which is highly exothermic, making it difficult to control the reactor temperature during synthesis. From a reaction mechanism perspective, three reactions coexist during the methyltetrahydrophthalic anhydride synthesis: C5 self-polymerization, generating C10 and higher self-polymers; maleic anhydride self-polymerization, generating polymaleic anhydride; and the main reaction involving the synthesis of C5 and maleic anhydride, which produces polymer residues as a side reaction. Controlling the reaction temperature and increasing the mixing of C5 and maleic anhydride to prevent self-aggregation of the two monomers are key to suppressing these side reactions. Moreover, improving the single-pass conversion rate of the two monomers without causing excessive side reactions remains a challenge. The existing process involves maleic anhydride or C5 first entering the synthesis reactor, then heating it with hot water. Once the preset temperature is reached, another raw material (liquid anhydride or C5) is added dropwise. The reactor is then refluxed by a C5 condenser at the top and circulated with water through the jacket to control the temperature. This method is difficult to control, with the synthesis temperature fluctuating between 60-80°C. When the temperature is too high, the only way to control the temperature inside the reactor is to stop feeding and control the heat released during synthesis. At the same time, as the concentration of methyltetrahydrophthalic anhydride increases during synthesis, the viscosity of the material system increases, making heat transfer inside the reactor more difficult and causing local overheating. This leads to the self-polymerization of C5 and maleic anhydride solvents, forming polymers. This reduces product yield and generates more byproducts, resulting in low product conversion and low product yield. Furthermore, a large amount of polymer residue tends to accumulate inside the synthesis reactor, requiring intermittent production shutdowns and the addition of alkali solution to clean the reactor, which affects production efficiency and generates a large amount of wastewater during reactor cleaning. The generated polymer residue remains in the synthesis reactor as slag and is periodically removed. The residue with a slightly lower degree of polymerization remains in the methyltetrahydrophthalic anhydride product as a heavy component. After isomerization of methyltetrahydrophthalic anhydride, it is removed along with the isomerization catalyst by removing the heavy component, becoming a heavy fraction. This process reflects that the polymer residue formed in the synthesis stage not only affects production efficiency but also increases the production steps in the isomerization stage, resulting in significant energy consumption. How to reasonably prevent the formation of polymers and optimize the isomerization stage process is of great research significance.

[0008] The aforementioned C5 fraction is a mixture, comprising crude isoprene and isoprene fractions. The specific composition of the crude isoprene fraction is as follows:

[0009] composition content / % isopentane 0.39 1,4-Pentadiene 0.04 1-Pentene 0.18 2-Methyl-1-butene 0.24 n-Pentane 2.2 Isoprene 0.34 trans-2-pentene 1.13 cis-2-pentene 1.19 2-Methyl-2-butene 6.5 trans-1,3-pentadiene 40.54 cyclopentadiene 0.14 cis-1,3-pentadiene 23.42 1,2-Pentadiene 0.14 2,3-Pentadiene 0.23 cyclopentene 20.04 4-Methyl-1-pentene 0.04 Cyclopentane 2.92 .

[0010] Isoprene is 99.5% pure, and the ratio of the two is 2:8 to 8:2. In the reaction process, only the synthesis of isoprene and trans-1,3-pentadiene with maleic anhydride is the main reaction, which produces methyltetrahydrophthalic anhydride. However, it is rich in other C5 atoms, and is rich in dienes and monoolefins. Self-polymerization and the synthesis reaction with maleic anhydride are side reactions.

[0011] The main reactions that occur during the synthesis are as follows:

[0012] Summary of the Invention

[0013] The technical problem to be solved by the present invention is to provide a continuous production process and apparatus for methyltetrahydrophthalic anhydride. This process can realize the continuous operation of the synthesis reaction and isomerization reaction of methyltetrahydrophthalic anhydride. At the same time, it adopts stepwise synthesis, efficient blending and temperature control, novel high-efficiency isomer catalyst, and cyclic reuse of isomer catalyst, which results in fewer by-products, no polymer formation, high product purity, and high yield.

[0014] This invention provides a continuous production process for methyltetrahydrophthalic anhydride, comprising the following steps:

[0015] (1) Part of the isoprene, isoprene and maleic anhydride are fed into the first dynamic mixer for premixing, and then fed into the shell and tube heat exchanger for pre-reaction; part of the pre-reaction product, another part of the isoprene and recycled material A are mixed in the second dynamic mixer and then fed into the first reactor for further reaction; wherein, the recycled material A refers to the material whose temperature is controlled by the first external circulation heater, which is a part of the reaction product of the first reactor and another part of the pre-reaction product.

[0016] (2) Another portion of the reaction product from the first reactor is mixed with the recycled material B in the third dynamic mixer and then fed into the second reactor to continue the reaction; wherein, the recycled material B refers to the material whose temperature is controlled by the second external circulation heater for a portion of the reaction product from the second reactor.

[0017] (3) Another part of the reaction product of the second reactor is sent to the C5 separation tower to remove C5 after temperature control by the first heat exchanger, and then sent to the fore-fraction separation tower to remove the fore-fraction after temperature control by the second heat exchanger.

[0018] (4) The material processed in step (3) is fed into the first isomerization vessel for reaction under the action of the catalyst. Part of the reaction product is recycled to the first isomerization vessel for further reaction, and the other part of the reaction product is collected and sent to the second isomerization vessel for reaction. The reaction product of the second isomerization vessel is collected into the cyclone separator. The catalyst is separated to the bottom by the cyclone separator and part of it is sent back to the first isomerization vessel. The other part is discharged as waste catalyst. The isomerized product in the cyclone separator is collected from the middle side to the product storage tank to obtain the isomerized methyltetrahydrophthalic anhydride.

[0019] In step (1), the weight percentage of isoprene fed into the first dynamic mixer is 20-50%, and the weight percentage of isoprene fed into the second dynamic mixer is 50-80%.

[0020] The heat exchange medium in the shell-and-tube heat exchanger in step (1) is hot water at a temperature of 40-70℃, and the material temperature inside the tubes is maintained at 30-65℃.

[0021] In step (1), the weight percentage of the pre-reaction product fed into the first reactor is 20-80%, and the weight percentage of the pre-reaction product passing through the first external circulation heater is 20-80%.

[0022] In step (1), the weight percentage of the reaction product passing through the first reactor via the first external circulation heater is 30-80%; in step (2), the weight percentage of the reaction product fed into the first reactor via the third dynamic mixer is 20-70%.

[0023] The temperature of the first reactor in step (1) is 60-80℃; the temperature of the second reactor in step (2) is 60-80℃. The first and second reactors have a large number of wound microchannels inside, and the material reacts inside the microchannels. Cooling water is present in the space between the microchannels and the reactor wall to control the temperature.

[0024] In step (2), the weight percentage of the reaction product passing through the second reactor via the second external circulation heater is 20-80%; in step (3), the weight percentage of the reaction product fed into the second reactor via the C5 separation tower is 20-80%.

[0025] The circulating hot water temperature of both the first and second external circulation heaters is 40-90℃.

[0026] The temperature of the first heat exchanger is 80-150℃; the temperature of the second heat exchanger is 90-140℃.

[0027] The vacuum degree of the pre-fractionation tower in step (3) is -0.08 to -0.095 MPa.

[0028] The catalyst in step (4) is Na / CH3COONa / γ-Al2O3, and the amount added is 0.01-0.5% of the material (isomeric raw material), preferably 0.02-0.1%.

[0029] The preparation method of Na / CH3COONa / γ-Al2O3 includes:

[0030] Add Al2O3·nH2O to the reactor, start stirring, and continuously introduce nitrogen gas into the reactor to maintain a nitrogen atmosphere. Increase the temperature at 2℃ / min-4℃ / min to 300-600℃, preferably 450-480℃, and hold for 1-6 hours, preferably 2.5 hours. Then, reduce the temperature to 420-440℃ and add sodium acetate (15-50% by mass of Al2O3·nH2O, preferably 24%-28%). Continue stirring for 1-5 hours, preferably 1.5-2.5 hours, while maintaining a constant temperature. Add metallic sodium (2-8% by mass of Al2O3·nH2O, preferably 4-6 times) in 2-8 portions. Then add metallic sodium (3-5% by mass of Al2O3·nH2O) and continue stirring for 50-90 minutes. After cooling, discharge the material to obtain the target catalyst. The final effective element mass contents are Na 5-15%, Al 42%-60%, and O 35-53%.

[0031] In step (4), the weight percentage of the reaction product recycled to the first isomer reactor for further reaction is 20-80% (preferably 65%), and the weight percentage of the reaction product sent to the second isomer reactor for reaction is 20-80% (preferably 35%).

[0032] In step (4), the temperature of the first isomer reactor is 80-200℃, preferably 100-130℃; the temperature of the second isomer reactor is 70-220℃, preferably 105-140℃.

[0033] The present invention also provides a continuous production process apparatus for methyltetrahydrophthalic anhydride;

[0034] It includes a tubular heat exchanger, a first synthesis vessel, a second synthesis vessel, a C5 separation tower, a pre-fraction separation tower, a first isomerization vessel, and a second isomerization vessel, which are connected in sequence by pipelines.

[0035] The top of the shell-and-tube heat exchanger is provided with a first dynamic mixer, the top of the first synthesis vessel is provided with a second dynamic mixer, and the top of the second synthesis vessel is provided with a third dynamic mixer.

[0036] The bottom of the shell-and-tube heat exchanger is connected to the first dynamic mixer;

[0037] The first synthesis vessel is externally connected to a first external circulation heater, and the second synthesis vessel is externally connected to a second external circulation heater;

[0038] The bottom of the second synthesis vessel is connected to the C5 separation tower via a first heat exchanger, and the bottom of the C5 separation tower is connected to the fore-fraction separation tower via a second heat exchanger.

[0039] The bottom of the pre-fractionation tower is connected to the middle of the first isomeric vessel, and the bottom of the first isomeric vessel is connected to the top of the second isomeric vessel.

[0040] The bottom of the second isomerization vessel is connected to a cyclone separator; the isomerization product is collected from the middle of the cyclone separator, and the catalyst is collected from the bottom of the cyclone separator. Part of the catalyst is sent back to the first isomerization vessel, and the other part of the catalyst is discharged as waste catalyst.

[0041] Preferably, all materials in the equipment are extracted using extraction pumps.

[0042] This invention employs two reactors and one tubular heat exchanger in the synthesis stage. All three devices participate in the synthesis reaction. The tubular heat exchanger is used for the first synthesis reaction, at a temperature slightly lower than the reactors, allowing for partial synthesis. The discharged material, along with a portion of fresh C5, enters the two reactors for further synthesis at slightly higher temperatures. Simultaneously, both reactors are equipped with external circulation pipelines and heaters to circulate and mix the reactants, ensuring uniform material distribution and a constant temperature. This significantly reduces the amount of polymer generated during the synthesis stage, eliminating the formation of polymer residue.

[0043] Two spray towers are used in the separation stage to remove C5 and the fore fraction. The C5 tower operates at atmospheric or slightly positive pressure, while the fore fraction tower operates at negative pressure.

[0044] In the isomerization stage, a superbase catalyst supported by γ-alumina is used. Two isomerization reactors are connected in series, and the output is controlled to achieve continuous operation. At the same time, the catalyst is separated from the product by a cyclone separator. The catalyst is collected from the bottom of the cyclone separator and recycled to the first isomerization reactor. The isomerized product is extracted by side extraction. The isomerized product does not contain heavy fractions and catalyst, and does not need to be separated into heavy components before entering the product tank for storage and sale.

[0045] Beneficial effects

[0046] 1. The synthesis reactor in this invention is a reactor with a spiral tube microchannel, which greatly enhances the heat removal capacity of the material inside the reactor, reduces hot spots, prevents self-polymerization of acid anhydride or C5 due to overheating, and prevents the formation of C5 polymers.

[0047] 2. In this invention, the mixed C5 segmented feed is used. Since isoprene has higher activity than isoprene and stronger ability to form self-polymers, the reaction involves partially isoprene and isoprene first undergoing a synthesis reaction with maleic anhydride in a shell-and-tube heat exchanger at a lower temperature. In the shell-and-tube heat exchanger, the anhydride is in excess, which reduces the formation of C5 polymers. The main reaction is the synthesis of 4-methyltetrahydrophthalic anhydride from isoprene and maleic anhydride.

[0048] 3. In this invention, an external circulation pipeline is added from the bottom of the reactor to the side of the reactor to circulate hot water to control the temperature of the circulating material. This not only improves the mixing of the material but also facilitates heat transfer, prevents local overheating, and reduces polymer formation.

[0049] 4. The present invention uses a preheating method before entering the tower and a material spraying method to separate the material quickly and efficiently.

[0050] 5. The isomerization catalyst of this invention uses a special superbase Na / CH3COONa / γ-Al2O3 catalyst. Its high isomerization activity enables isomerization of methyltetrahydrophthalic anhydride at a lower temperature, preventing the formation of polymer polyanhydrides at low temperatures. At the same time, the catalyst is separated by a cyclone separator and reused. The isomerized product contains no light or heavy components and can be directly used as a product in the isomerized product storage tank. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the device structure of the present invention. Detailed Implementation

[0052] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0053] This invention provides a specific embodiment of a continuous production process for methyltetrahydrophthalic anhydride, comprising the following steps:

[0054] (1) Part of the isoprene, isoprene and maleic anhydride are fed into the first dynamic mixer 1 for premixing, and then fed into the shell and tube heat exchanger 2 for pre-reaction; part of the pre-reaction product, another part of the isoprene and the recycled material A are mixed in the second dynamic mixer 3 and then fed into the first reactor 4 for further reaction; wherein, the recycled material A refers to the material in the first reactor 4 whose temperature is controlled by the first external circulation heater 5, which is part of the reaction product and another part of the pre-reaction product.

[0055] (2) Another part of the reaction product of the first reactor 4 is mixed with the recycled material B in the third dynamic mixer 6 and then sent to the second reactor 7 to continue the reaction; wherein, the recycled material B refers to the material whose temperature is controlled by the second external circulation heater 8 for part of the reaction product of the second reactor 7.

[0056] (3) Another part of the reaction product of the second reactor 7 is sent to the C5 separation tower 10 to remove C5 after temperature control by the first heat exchanger 9, and then sent to the fore-fraction separation tower 12 to remove the fore-fraction after temperature control by the second heat exchanger 11.

[0057] (4) The material processed in step (3) is fed into the first isomerization vessel 13 for reaction under the action of the catalyst. Part of the reaction product is recycled to the first isomerization vessel 13 for further reaction, and the other part of the reaction product is collected and sent to the second isomerization vessel 15 for reaction. The reaction product of the second isomerization vessel 15 is collected into the cyclone separator 14. The catalyst is separated to the bottom by the cyclone separator 14 and part of it is sent back to the first isomerization vessel 13. The other part is discharged as waste catalyst. The isomerized product in the cyclone separator 14 is collected from the middle side to the product storage tank, thus obtaining the methyltetrahydrophthalic anhydride isomerization product.

[0058] The present invention also provides a specific embodiment of a continuous production process apparatus for methyltetrahydrophthalic anhydride.

[0059] It includes a tubular heat exchanger 2, a first synthesis vessel 4, a second synthesis vessel 7, a C5 separation tower 10, a pre-fraction separation tower 12, a first isomerization vessel 13, and a second isomerization vessel 15, which are connected in sequence by pipelines.

[0060] The top of the shell and tube heat exchanger 2 is provided with a first dynamic mixer 1, the top of the first synthesis vessel 4 is provided with a second dynamic mixer 3, and the top of the second synthesis vessel 7 is provided with a third dynamic mixer 6.

[0061] The bottom of the shell-and-tube heat exchanger 2 is connected to the first dynamic mixer 1;

[0062] The first synthesis vessel 4 is externally connected to a first external circulation heater 5, and the second synthesis vessel 7 is externally connected to a second external circulation heater 8;

[0063] The bottom of the second synthesis vessel 7 is connected to the C5 separation tower 10 through the first heat exchanger 9, and the bottom of the C5 separation tower 10 is connected to the fore-fraction separation tower 12 through the second heat exchanger 11.

[0064] The bottom of the pre-fractionation tower 12 is connected to the middle of the first isomeric vessel 13, and the bottom of the first isomeric vessel 13 is connected to the top of the second isomeric vessel 15.

[0065] The bottom of the second isomerization vessel 15 is connected to the cyclone separator 14; the isomerization product is collected from the middle of the cyclone separator 14, and the catalyst is collected from the bottom of the cyclone separator 14. Part of the catalyst is sent back to the first isomerization vessel 13, and the other part of the catalyst is discharged as waste catalyst.

[0066] Preferably, all materials in the equipment are extracted using extraction pumps.

[0067] The preparation methods of the catalyst Na / CH3COONa / γ-Al2O3 include:

[0068] Add 30g of Al2O3·nH2O to the reactor, start stirring, and continuously introduce nitrogen gas into the reactor to maintain a nitrogen atmosphere. Increase the temperature to 450℃ at 3℃ / min and hold for 2.5 hours. Then, reduce the temperature to 420℃, add 9g of sodium acetate, and continue stirring for 2 hours while keeping the temperature constant. Add 1.5g of metallic sodium in 5 portions, reduce the temperature to 400℃, add another 0.5g of metallic sodium, continue stirring for 60 minutes, and then cool down to discharge the material to obtain the target catalyst.

[0069] Comparative Example 1

[0070] A continuous batch reactor was used for synthesis. Maleic anhydride and C5 were added dropwise to the reactor simultaneously, with a C5:maleic anhydride molar ratio of 1.05:1. Heat was extracted via a jacket, and the synthesis temperature fluctuated between 68-74℃. The residence time was 3 hours. C5 was removed by rotary evaporation at 120℃, and the fore-distillate was removed by rotary evaporation at 135℃ and a pressure of -0.093 MPa. The product was analyzed for yield, color number, purity, residual maleic anhydride, fore-distillate, and heavy fraction.

[0071] Example 1

[0072] Using the process of this invention, maleic anhydride and C5 are fed in two separate streams, with a total feed C5:maleic anhydride molar ratio of 1.05:1. Isoprene and 40% isoprene and maleic anhydride enter the shell-and-tube heat exchanger 2 through the first dynamic mixer 1. Hot water at 60°C is circulated through the shell-and-tube heat exchanger 2 to maintain the material temperature at approximately 50°C. The remaining 60% of isoprene is fed through the outlet pipe of the shell-and-tube heat exchanger 2 and enters the first reaction vessel 4 through the second dynamic mixer 3. The material temperature in the first reaction vessel 4 is 70°C. The ratio of the amount of material circulating outside reactor 4 to the amount of material collected to the second reactor 7 is 6:4. The temperature of the material inside the second reactor 7 is 70℃. The ratio of the amount of material circulating outside reactor 7 to the amount of material collected to the C5 separation tower 10 is 6:4. The temperature of the heater before the C5 separation tower 10 is 110℃. The temperature of the heater before the pre-distillate separation tower 12 is 130℃. The pressure is -0.093 MPa. The product is analyzed for yield, color number, purity, maleic anhydride residue, pre-distillate, and heavy distillate.

[0073] Example 2

[0074] Using the process of this invention, maleic anhydride and C5 are fed in two separate streams, with a total feed C5:maleic anhydride molar ratio of 1.05:1. Isoprene and 40% isoprene and maleic anhydride enter the shell-and-tube heat exchanger 2 through the first dynamic mixer 1. Hot water at 60°C is circulated through the shell-and-tube heat exchanger 2 to maintain the material temperature at approximately 50°C. The remaining 60% isoprene is fed through the outlet pipe of the shell-and-tube heat exchanger 2 and enters the first reaction vessel 4 through the second dynamic mixer 3. The material temperature in the first reaction vessel 4 is 60°C. The ratio of the amount of material circulating outside reactor 4 to the amount of material collected to the second reactor 7 is 6:4. The temperature of the material inside the second reactor 7 is 63℃. The ratio of the amount of material circulating outside reactor 7 to the amount of material collected to the C5 separation tower 10 is 6:4. The temperature of the heater before the C5 separation tower 10 is 110℃. The temperature of the heater before the pre-distillate separation tower 12 is 130℃. The pressure is -0.093 MPa. The product is analyzed for yield, color number, purity, maleic anhydride residue, pre-distillate, and heavy distillate.

[0075] Example 3

[0076] Using the process of this invention, maleic anhydride and C5 are fed in two separate streams, with a total feed C5:maleic anhydride molar ratio of 1.02:1. Isoprene and 40% isoprene and maleic anhydride enter the shell-and-tube heat exchanger 2 through the first dynamic mixer 1. Hot water at 60°C is circulated through the shell-and-tube heat exchanger 2 to maintain the material temperature at approximately 50°C. The remaining 60% of isoprene is fed through the outlet pipe of the shell-and-tube heat exchanger 2 and enters the first reaction vessel 4 through the second dynamic mixer 3. The material temperature in the first reaction vessel 4 is 60°C. The ratio of the amount of material circulating outside reactor 4 to the amount of material collected to the second reactor 7 is 6:4. The temperature of the material inside the second reactor 7 is 63℃. The ratio of the amount of material circulating outside reactor 7 to the amount of material collected to the C5 separation tower 10 is 6:4. The temperature of the heater before the C5 separation tower 10 is 110℃. The temperature of the heater before the pre-distillate separation tower 12 is 130℃. The pressure is -0.093 MPa. The product is analyzed for yield, color number, purity, maleic anhydride residue, pre-distillate, and heavy distillate.

[0077]

[0078] Analysis of Examples 1, 2, and 3 and Comparative Example 1 shows that the process of the present invention can achieve isothermal reaction control in the synthesis stage. Due to the low-temperature pre-synthesis in the shell-and-tube heat exchanger, the concentration of C5 and acid anhydride is reduced after the raw materials enter the synthesis kettle. The yield of the final synthesized product is slightly higher, the product color is lighter, the content of heavy distillate (polymer) in the product is very low, the purity of the target product methyltetrahydrophthalic anhydride is also very high, and the acid anhydride residue is low, indicating that the material conversion rate is high and the synthesis stage has obvious beneficial effects.

[0079] Comparative Example 2

[0080] The synthesized product from Comparative Example 1 was subjected to isomerization using a high-pressure reactor with electric heating. Potassium acetate was used as the catalyst at a dosage of 0.1%. The isomerization temperature was 170°C, and the isomerization time was 3 hours. After isomerization, heavy components and catalyst were removed by rotary evaporation at a heating temperature of 155°C. After discharge, the isomerization yield, color number, target isomer content, tetramethylamine purity, fore-distillate content, and heavy distillate content in the product were tested.

[0081] Comparative Example 3

[0082] The synthesis and decarbonylation process of the first isomerization vessel 13 was carried out using the conditions set in Example 2. After the product entered the first isomerization vessel 13, the temperature of the first isomerization vessel 13 was 160°C, the catalyst was potassium acetate catalyst, and the addition amount was 0.05%. The temperature of the second isomerization vessel 15 was 160°C. The total residence time of the two vessels was 3 hours. The isomerization yield, color number, target isomer content, tetramethyl methyl ether purity, the content of the first fraction and the content of the heavy fraction in the product were directly tested.

[0083] Example 4

[0084] The synthesis and decarbonylation process of the first isomerization vessel 13 was carried out under the conditions of Example 2. The product entered the first isomerization vessel 13 at a temperature of 160°C. The catalyst was Na / CH3COONa / γ-Al2O3 catalyst with an addition amount of 0.05%. The temperature of the second isomerization vessel 15 was 160°C. The total residence time of the two vessels was 3 hours. The isomerization yield, color number, target isomer content, tetramethylolamine purity, pre-distillate content, and heavy distillate content of the product were directly tested.

[0085] Example 5

[0086] The synthesis and decarbonylation process of the first isomerization reactor 13 was carried out under the conditions of Example 2. The product entered the first isomerization reactor 13 at a temperature of 145°C. The catalyst was Na / CH3COONa / γ-Al2O3 catalyst with an addition amount of 0.03%. The temperature of the second isomerization reactor 15 was 160°C. The total residence time of the two reactors was 3 hours. The isomerization yield, color number, target isomer content, tetramethylolamine purity, pre-fraction content, and heavy fraction content of the product were directly tested.

[0087] Example 6

[0088] The synthesis and decarbonylation of the fore-distillate were carried out using the conditions set in Example 2. After the product entered the first isomerization reactor 13, the temperature of the first isomerization reactor 13 was 140°C, and the catalyst was Na / CH3COONa / γ-Al2O3 catalyst, with an addition amount of 0.04%. The temperature of the second isomerization reactor 15 was 163°C. The total residence time of the two reactors was 3 hours. This scheme was continuously operated for about 72 hours. Theoretically, the catalyst was used 24 times. The final product was directly tested for isomer yield, color number, target isomer content, tetramethylolamine purity, fore-distillate content, and heavy distillate content.

[0089]

[0090] The comparative results show that by arranging two isomerization reactors in series, the present invention allows for different temperature settings. In the initial stage of isomerization, when the concentration of methyltetrahydrophthalic anhydride is high, the first isomerization reactor 13 employs a low-temperature isomerization scheme. In the later stage of isomerization, when the concentration of methyltetrahydrophthalic anhydride is low, the second isomerization reactor 15 employs a slightly higher temperature isomerization. This reduces the self-polymerization of methyltetrahydrophthalic anhydride during the isomerization process, resulting in a significant decrease in the heavy fraction content of the product. Furthermore, since the formation of polymers is prevented during the synthesis stage, and the catalyst is reused via a cyclone separator, the product after isomerization does not require weighing, resulting in a 100% yield with high purity and significantly improved color. Comparative Examples 2 and 3 show that even using the same catalyst, Comparative Example 3, with its synthetic raw materials and isomerization process derived from the present invention, exhibits significantly lower fore- and heavy fraction contents compared to Comparative Example 2. Furthermore, a comparison between Example 4 and Comparative Example 3 demonstrates that the catalyst provided by the present invention has higher isomerization efficiency and a higher content of the target isomer. As can be seen in Example 6, the resin product can still remain stable after multiple catalyst reuses, indicating that the catalyst life is long. The isomerization efficiency, i.e., the content of the target isomer, decreases slightly, the product color increases slightly, and the fore fraction increases slightly, but the overall product indicators are still better than the comparative example, and this process still has obvious advantages.

Claims

1. A continuous production process for methyltetrahydrophthalic anhydride, comprising the following steps: (1) Part of the isoprene, isoprene, and maleic anhydride are fed into the first dynamic mixer (1) for premixing, and then fed into the shell-and-tube heat exchanger (2) for pre-reaction; part of the pre-reaction product, another part of the isoprene, and recycled material A are co-mixed in the second dynamic mixer (3) and then fed into the first synthesis vessel (4) for further reaction; wherein, The circulating material A refers to the material in which part of the reaction product of the first synthesis vessel (4) and another part of the pre-reaction product are temperature-controlled by the first external circulation heater (5); (2) The reaction product of another part of the first synthesis vessel (4) is mixed with the recycled material B in the third dynamic mixer (6) and then sent to the second synthesis vessel (7) to continue the reaction; wherein, the recycled material B refers to the material whose temperature is controlled by the second external circulation heater (8) for part of the reaction product of the second synthesis vessel (7); (3) The reaction product of another part of the second synthesis vessel (7) is sent to the C5 separation tower (10) to remove C5 after temperature control by the first heat exchanger (9), and then sent to the fore-fraction separation tower (12) to remove the fore-fraction after temperature control by the second heat exchanger (11). (4) The material processed in step (3) is fed into the first isomerization vessel (13) for reaction under the action of the catalyst. Part of the reaction product is recycled to the first isomerization vessel (13) for further reaction, and another part of the reaction product is collected and sent to the second isomerization vessel (15) for reaction. The reaction product in the second isomerization vessel (15) is collected into the cyclone separator (14). The catalyst is separated to the bottom by the cyclone separator (14), and part of it is sent back to the first isomerization vessel (13), and the other part is discharged as waste catalyst. The isomerized product in the cyclone separator (14) is collected from the middle side to the product storage tank, thus obtaining the isomerized product of methyltetrahydrophthalic anhydride. The catalyst is Na / CH3COONa / γ-Al2O3.

2. The production process according to claim 1, characterized in that: In step (1), the weight percentage of isoprene fed into the first dynamic mixer (1) is 20-50%, and the weight percentage of isoprene fed into the second dynamic mixer (3) is 50-80%.

3. The production process according to claim 1, characterized in that: The heat exchange medium of the shell-and-tube heat exchanger (2) in step (1) is hot water at a temperature of 40-70℃, and the temperature of the material inside the tube is maintained at 30-65℃.

4. The production process according to claim 1, characterized in that: In step (1), the weight percentage of the pre-reaction product fed into the first synthesis vessel (4) is 20-80%, and the weight percentage of the pre-reaction product passing through the first external circulation heater (5) is 20-80%.

5. The production process according to claim 1, characterized in that: In step (1), the weight percentage of the reaction product in the first synthesis vessel (4) passing through the first external circulation heater (5) is 30-80%; in step (2), the weight percentage of the reaction product in the first synthesis vessel (4) fed into the third dynamic mixer (6) is 20-70%.

6. The production process according to claim 1, characterized in that: The temperature of the first synthesis vessel (4) in step (1) is 60-80℃; the temperature of the second synthesis vessel (7) in step (2) is 60-80℃.

7. The production process according to claim 1, characterized in that: In step (2), the weight percentage of the reaction product in the second synthesis vessel (7) passing through the second external circulation heater (8) is 20-80%; in step (3), the weight percentage of the reaction product in the second synthesis vessel (7) fed into the C5 separation tower (10) is 20-80%.

8. The production process according to claim 1, characterized in that: In step (4), the weight percentage of the reaction product circulated to the first isomer reactor (13) for further reaction is 20-80%, and the weight percentage of the reaction product sent to the second isomer reactor (15) for reaction is 20-80%.

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