Continuous anhydride formation of pyromellitic acid

Abstract

The application discloses a continuous phthalic anhydride device in the field of chemical production equipment, which comprises a horizontal shell, a feeding port for raw material phthalic acid is arranged at one end of the upper side of the shell, a gas phase outlet is arranged at the middle position of the upper side of the shell, a discharging port for phthalic anhydride liquid is arranged at the lower side of the other end of the shell, the shell comprises a double-layered outer shell and an inner shell, a heating medium cavity is arranged between the outer shell and the inner shell, two parallel main shafts are arranged in the shell, the axes of the two main shafts are located at the same horizontal position, outer spiral propeller blades with the same height are arranged on the two main shafts, the bottom of the outer shell and the inner shell is in the shape of omega which is consistent with the shape of the outer spiral propeller blades, a semicircular gas phase cavity is left above the outer spiral propeller blades, and the gas phase outlet is connected with a vacuum condenser and a vacuum air extraction device. The device has low working energy consumption, less material residue and provides technical support for large-scale industrial production of phthalic anhydride.

Description

TECHNICAL FIELD

[0001] The application relates to a chemical production device, in particular to a device for preparing pyromellitic dianhydride from pyromellitic anhydride. BACKGROUND

[0002] Pyromellitic acid is a white to slightly yellow powder crystal, with a melting point of 281-284.5 DEG C, a relative density of 1.79 g / cm 3 . Pyromellitic acid is easily soluble in ketone and alcohol, slightly soluble in diethyl ether and water, and can be sublimed; high-temperature dehydration can generate pyromellitic dianhydride. Pyromellitic acid is a main raw material for synthesizing polyimide, pyromellitic acid tetraoctyl ester and extinction curing agent.

[0003] The structural formula is as follows:

[0004] Description: Description: Description: Description: C:\Users\dxd\AppData\Roaming\Tencent\Users\306088938\QQ\WinTemp\RichOle\I]97)HOKB6M~O2Q1MKOJ]HP.png

[0005] Pyromellitic dianhydride, abbreviated as anhydride, is a white or slightly yellow crystal, with a melting point of 284-288 DEG C, a boiling point of 397-400 DEG C, a flash point of 380 DEG C, and a specific gravity of 1.68 g / cm 3 . When exposed to humid air, pyromellitic dianhydride can absorb water in the air and be hydrolyzed into pyromellitic acid. Pyromellitic dianhydride is soluble in acetone, dimethyl sulfoxide, dimethylformamide, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, acetonitrile and other organic solvents, and is insoluble in diethyl ether, chloroform and benzene. Pyromellitic dianhydride is mainly used for manufacturing polyimide resin and film, high-grade electrical insulation materials, high-temperature-resistant electrical insulation paint, curing agent of epoxy resin and polyester resin, extinction agent and crosslinking agent, high-temperature-resistant plasticizer, high-grade lubricating oil base oil, phthalocyanine blue dye and the like.

[0006] The structural formula is as follows:

[0007]

[0008] At present, the gas phase oxidation method is generally used in industry, a mixture of durene and air is introduced into a fixed bed after heating, the reaction is cooled by molten salt circulation heat exchange, and pyromellitic dianhydride is obtained through collection, hydrolysis crystallization and sublimation.

[0009] CN112390808A discloses a method for capturing and purifying pyromellitic dianhydride, comprising the following steps: after the vaporization of durene, it is mixed with air and enters a fixed bed reactor filled with catalyst for reaction, and the reacted gas is captured in a condenser filled with porous boron nitride nanosheet packing; the obtained porous boron nitride nanosheet packing loaded with crude pyromellitic dianhydride; the above-mentioned porous boron nitride nanosheet packing loaded with crude pyromellitic dianhydride is placed in a fixed bed vaporizer, inert gas hot stream is introduced into one end of the fixed bed vaporizer, and the gas coming out of the fixed bed vaporizer is condensed and captured in a columnar trap to obtain pyromellitic dianhydride. The method has high efficiency, and the prepared pyromellitic dianhydride has high purity.

[0010] CN101735232A discloses a production method of pyromellitic dianhydride, comprising the following steps: 1. oxidation, using durene and air as raw materials, carrying out oxidation reaction at a higher molten salt temperature through a catalyst to obtain a gas phase mixture, and recovering a crude anhydride semi-finished product through three connected cooling traps; 2. discharging, cleaning and raking out the crude anhydride in the trap; 3. hydrolysis and centrifugation, melting the obtained crude anhydride into a liquid in a soft water hydrolysis kettle through steam heating, hydrolyzing into tetramethylbenzene-4,4'-dicarboxylic acid, recrystallizing after decolorization through activated carbon and hot filtration, and obtaining qualified tetramethylbenzene-4,4'-dicarboxylic acid and crude tetraacid crystals through centrifugation; 4. dehydration and sublimation, obtaining refined pyromellitic dianhydride product.

[0011] CN1245171A discloses a production method of pyromellitic dianhydride, characterized in that durene or 5-isopropyl-m-xylylene is used as raw material, vaporized, mixed with air at a proportion of 0.0023-0.35 volume, and then introduced into a tube reactor filled with catalyst to be catalytically oxidized into high-temperature reaction gas at 430-450 DEG C, and then the gas is passed through a heat exchanger and a grading trap to obtain crude pyromellitic dianhydride product, which is heated to 85-95 DEG C, dissolved, decolorized, filtered, cooled to room temperature, and centrifuged to obtain pyromellitic acid, and then vacuum dehydration and sublimation are carried out to obtain refined pyromellitic dianhydride with purity greater than 98.5%.

[0012] The deficiencies are as follows: the existing production process of pyromellitic dianhydride is a batch process, including durene gas phase oxidation one-step anhydride or hydrolysis of the captured material to obtain pyromellitic acid, and stirring tank or baking dehydration to obtain anhydride process.

[0013] 1) The durene gas phase oxidation one-step anhydride process obtains crude anhydride, and the content of anhydride in the captured material gradually decreases (from 98% to 80% or even to 50%) in the first, second, third and fourth captured materials.

[0014] 2) After the hydrolysis of the collected material, the stirred tank or baking dehydration of pyromellitic acid to obtain anhydride is obtained, and finally, recrystallization or sublimation can be used to obtain higher purity of refined anhydride.

[0015] The above two processes are both batch anhydride formation: the anhydride formation process is to send the wet material into the anhydride formation tank to dehydrate to anhydride. Anhydride formation is a chemical reaction, dehydration to anhydride, which is related to pressure and temperature. If the temperature and pressure are too high, by-products will be produced; if the temperature and pressure are too low, the yield of pyromellitic dianhydride will be reduced.

[0016] The batch anhydride formation process makes the equipment unstable and the process indicators difficult to control. For example, repeated temperature and pressure changes during the anhydride formation process can cause the equipment to be easily damaged, increase the corrosion of the equipment pipes, and reduce the service life of the equipment. At the same time, by-products are easy to appear, which cannot improve the product quality and product yield. The entire production process cannot be carried out stably, the production adaptability is not high, the production cannot be greatly improved, and it is not suitable for large-scale production. SUMMARY

[0017] The purpose of the present application is to provide a continuous anhydride formation device for pyromellitic acid, so as to realize the continuous anhydride formation of pyromellitic dianhydride from pyromellitic acid, which has low energy consumption and less material residue, and provides technical support for large-scale industrial production of pyromellitic dianhydride.

[0018] In order to achieve the purpose of the present application, the continuous anhydride formation device for pyromellitic acid provided by the present application comprises a horizontal shell, a feed inlet for feeding pyromellitic acid raw materials is arranged at one end of the upper side of the shell, and a feed valve is arranged at the feed inlet; a gas phase outlet is arranged at the middle position of the upper side of the shell, and a discharge outlet for discharging pyromellitic dianhydride liquid is arranged at the lower side of the other end of the shell, and a discharge valve is arranged at the discharge outlet; the shell comprises an outer shell and an inner shell in a double-layer structure, a heating medium cavity is arranged between the outer shell and the inner shell, two main shafts parallel to each other are arranged in the shell, the axis lines of the two main shafts are located at the same horizontal position, outer helical propelling blades with consistent heights are arranged on the two main shafts, the bottom of the outer shell and the inner shell is in the shape of omega which is consistent with the shape of the outer helical propelling blades, a semicircular gas phase cavity is arranged above the outer helical propelling blades and connected to the two sides of the omega shape; the gas phase outlet is connected with a vacuum condenser and a vacuum air extraction device.

[0019] In operation, the raw material of pyromellitic acid is continuously fed into the inner shell from the feed inlet, the main shaft is driven to rotate by the motor, the outer helical propelling blade pushes the material towards the discharge outlet, at the same time, the heating medium is introduced into the heating medium cavity, and the heating medium can also be directly heated by electric heating, the heating medium is heated to above the melting point of pyromellitic acid, vacuum is continuously extracted outside through the gas phase outlet, pyromellitic acid is gradually melted by heating, and after dehydration into anhydride, it flows out of the discharge outlet, and the white powder product of pyromellitic dianhydride is obtained after cooling to room temperature, and is packaged in a sealed manner. The two sets of helical propelling blades can play a good stirring and propelling effect, avoid the adhesion of the material on the inner wall of the inner shell, and reduce the energy consumption of the anhydride, while providing sufficient gas phase space, the heat dissipation area is small, and the working energy consumption is low. The present application provides technical support for large-scale industrial production of pyromellitic dianhydride.

[0020] Further, an overflow baffle is arranged in the inner shell above the discharge outlet, and the height of the overflow baffle is flush with the upper edge of the main shaft. This structure enables the pyromellitic dianhydride above the overflow baffle to overflow out of the device, realizes discharging from the discharge outlet, so that the liquid level in the inner shell is maintained below the upper edge of the main shaft, and when the helical propelling blade rotates, the liquid adhered to the exposed liquid surface has a large evaporation area in the gas phase space, which promotes rapid anhydride formation.

[0021] Further, the radius of gyration of the outer helical propelling blade is 200-800mm, the radius of the main shaft is 50%-75% of the radius of gyration of the outer helical propelling blade, and the distance between the lower half of the outer helical propelling blade and the inner bottom of the inner shell is 8-12mm.

[0022] As a further improvement of the present application, the shell is divided into a feeding section, an anhydride forming section and a discharging section in the length direction, the corresponding main shaft of the anhydride forming section is a partially hollow structure, a plurality of through-flow holes are arranged on the main shaft to connect the inside and outside of the main shaft, and inner helical propelling blades are arranged on the inner wall of the main shaft, the inner helical propelling blades are opposite in rotation direction to the outer helical propelling blades on the main shaft. In this structure, the pyromellitic acid raw material is gradually heated to melt in the feeding section, the anhydride forming section mainly functions to form anhydride, and the water is continuously removed, in the process of material propelling, the material in the anhydride forming section is propelled to the discharging direction under the action of the outer helical propelling blades, at the same time, the material entering the inside of the main shaft through the through-flow holes is propelled to the feeding port direction in the opposite direction, so that a convection is formed in the anhydride forming section, the material in the inside of the main shaft flows to the outside, and the material in the outside also flows to the inside, so that a stirring action is formed, the exchange of the inside and outside materials makes the evaporation effect better, at the same time, the outer helical propelling blades and the inner helical propelling blades can form a larger evaporation surface, and a large amount of material is anhydrized here. In the discharging section, the material is unidirectionally propelled, the material which has been anhydrized a large amount is propelled to the outlet of the discharging section from the starting point of the discharging section, at the same time, the evaporated water vapor is continuously removed to make the material further anhydrized, part of the material also flows back from the gap at the bottom and the outside of the outer helical propelling blades, and then is repeatedly propelled to the discharging port, a small circulation is formed in the discharging section, the concentration of pyromellitic dianhydride of the material in the discharging section is higher than that in the anhydride forming section, and the product purity is further improved.

[0023] Further, the temperature gradually rises from 240 DEG C to 285 DEG C from the feeding section to the anhydride forming section; the temperature of the anhydride forming section is 285-295 DEG C; and the temperature gradually reduces from the end of the anhydride forming section to 283 DEG C in the discharging section, and then the material is discharged from the discharging port.

[0024] As a further improvement of the present application, the outer helical propelling blades on the two main shafts are arranged in interlaced manner, and the outer edges of the outer helical propelling blades on any one main shaft abut against the other main shaft. Further, the shortest distance between the outer edge of the outer helical propelling blades on any one main shaft and the other main shaft is 8-12 mm.

[0025] As a further improvement of the present application, the outer helical propelling blades on the two main shafts are arranged in interlaced manner, and the outer edges of the outer helical propelling blades on any one main shaft abut against the other main shaft. Further, the shortest distance between the outer edge of the outer helical propelling blades on any one main shaft and the other main shaft is 8-12 mm.

[0026] When working, the vacuum pressure in the gas phase cavity is 0.01-0.09 Mpa. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a structural schematic view of the present application.

[0028] Figure 2 It is a top view of the present application. Figure 1 It is a top view of the present application.

[0029] Figure 3 for Figure 2 The left view.

[0030] Figure 4 This is a structural schematic diagram of Comparative Embodiment 1 of the present invention.

[0031] Figure 5 This is a structural schematic diagram of Comparative Embodiment 2 of the present invention.

[0032] Figure 6 This is a schematic diagram of the mechanism of Comparative Embodiment 3 of the present invention.

[0033] Figure 7 This is another structural schematic diagram of the present invention.

[0034] Figure 8 This is another structural diagram of the main axis.

[0035] In the diagram, 1 is the feed inlet, 2 is the outer shell, 3 is the inner shell, 4 is the gas phase cavity, 5 is the heating medium cavity, 6 is the outer spiral propeller blade, 7 is the main shaft, 8 is the discharge port, 9 is the gas phase outlet, 10 is the overflow baffle, 11 is the condenser, 12 is the vacuum pump, 13 is the flow passage, 14 is the inner spiral propeller blade, L1 is the length of the feed section, L2 is the length of the anhydride formation section, and L3 is the length of the discharge section. Detailed Implementation

[0036] Example 1

[0037] like Figures 1-3 The diagram shows a continuous pyromellitic dianhydride production apparatus, comprising a horizontal shell. One end of the shell has an inlet 1 for feeding pyromellitic dianhydride raw material, with a feed valve at inlet 1. A gas outlet 9 is located at the middle of the upper side of the shell, and an outlet 8 for discharging pyromellitic dianhydride liquid from the lower side of the other end of the shell, with a discharge valve at outlet 8. Both the feed valve and the discharge valve are one-way valves. The shell includes a double-layered outer shell 2 and an inner shell 3, with a heating medium chamber 5 between the outer shell 2 and the inner shell 3. Two parallel main shafts 7 are located inside the shell. The axes of the two main shafts 7 are located at the same horizontal position. The two main shafts 7 are equipped with external helical propulsion blades 6 of the same height. The bottom of the outer shell 2 and the inner shell 3 are ω-shaped, which matches the shape of the external helical propulsion blades 6. A semi-circular gas phase cavity 4 is left above the external helical propulsion blades 6, which connects to the two sides of the ω-shape. That is, the diameter of the semi-circle is slightly larger than the maximum horizontal distance between the outer edges of the two external helical propulsion blades 6, so that the external helical propulsion blades 6 do not touch the inner wall of the inner shell 3 during rotation. The gas phase outlet 9 is connected to the vacuum pump 12 via the vacuum condenser 11.

[0038] An overflow baffle 10 is provided inside the inner shell 3 on the upper side of the discharge port 8. The height of the overflow baffle 10 is flush with the upper edge of the main shaft 7.

[0039] In this embodiment, the revolution radius of the outer helical propeller blade 6 is 500 mm, and the radius of the main shaft 7 is 75% of the revolution radius of the outer helical propeller blade 6; the distance between the lower half of the outer helical propeller blade 6 and the inner bottom of the inner shell 3 is 10 mm.

[0040] The shell is divided into a feeding section, an anhydride forming section and a discharging section in the length direction, and the length ratio is L1:L2:L3=1:2:1.5. The effective working length of the main shaft is 6 m, i.e. L1+L2+L3=6 m. During working, the temperature gradually rises from 240℃ to 285℃ from the feeding section to the anhydride forming section; the temperature of the anhydride forming section is 285-295℃; and the temperature gradually decreases from the end of the anhydride forming section to 283℃ in the discharging section, and then the material is discharged from the discharge port.

[0041] The outer helical propeller blades 6 on the two main shafts 7 have the same propelling direction and opposite rotation directions.

[0042] During working, the vacuum pressure in the gas phase cavity is 0.01-0.09 Mpa.

[0043] The outer shell 2 is provided with a heat preservation layer to avoid heat loss. The residence time of the material in the device is about 100-120 minutes.

[0044] Embodiment 2

[0045] As shown in Figure 7 The outer helical propeller blades 6 on the two main shafts 7 are arranged in a staggered manner, and the outer edge of the outer helical propeller blade 6 on any one main shaft 7 abuts against the other main shaft, and the shortest distance between the two is 8-12 mm.

[0046] Embodiment 3

[0047] The main shaft 7 corresponding to the anhydride forming section L2 is a partially hollow structure, and is provided with a plurality of flow-through holes 13 connecting the inside and outside of the main shaft 7. The inner helical propeller blade 14 is arranged on the inner wall of the main shaft 7, and the rotation direction of the inner helical propeller blade 14 is opposite to that of the outer helical propeller blade 6 on the same main shaft. In order to ensure that both the outer helical propeller blade 6 and the inner helical propeller blade 14 can form an evaporation surface, the overflow baffle 10 can not be arranged, or the height of the overflow baffle 10 is set to be lower, so that the upper part of the inner helical propeller blade 14 can be directly connected to the gas phase cavity 4 to form a larger evaporation surface.

[0048] In this structure, the pyromellitic acid raw material is gradually heated to the point of melting in the feeding section. It mainly plays the role of anhydride formation in the anhydride formation section. The water that is removed is continuously pumped away. During the material propulsion process, the material in the anhydride formation section is pushed towards the discharge direction under the action of the outer spiral propulsion blade 7. At the same time, the material that enters the main shaft 7 through the flow hole 13 is pushed in the opposite direction towards the feed port 8, thereby forming convection in the anhydride formation section. The material inside the main shaft 7 will flow to the outside, and the material outside will also flow to the inside, thereby forming a stirring effect. The exchange of materials inside and outside will make the evaporation effect better. At the same time, both the outer spiral propulsion blade 6 and the inner spiral propulsion blade 14 can form a larger evaporation surface, and a large amount of material will form anhydride here. In the discharge section, the material is propelled in one direction. A large amount of the material that has already formed anhydride is pushed from the starting point of the discharge section to the discharge port 8. At the same time, the evaporated water vapor is continuously drawn away, which promotes the material to form anhydride. Some material will also flow back from the gaps at the bottom and outside of the outer spiral propulsion blade 6, and then be repeatedly pushed to the discharge port 8, forming a small circulation in the discharge section. The concentration of pyromellitic dianhydride in this section is greater than that in the anhydride formation section, which further improves the purity of the product.

[0049] Comparative Example 1

[0050] The difference from Example 1 is that, as Figure 4 As shown, the cross-section of the gas phase cavity 4 is a flat elliptical structure, with its horizontal axis being the major axis and the ratio of the major axis to the minor axis being 3:2.

[0051] Comparative Example 2

[0052] The difference from Example 1 is that, as Figure 5 As shown, the cross-section of the gas phase cavity 4 is a highly elliptical structure, with its horizontal axis being the minor axis and the ratio of the major axis to the minor axis being 3:2.

[0053] Comparative Example 3

[0054] The difference from Example 1 is that, as Figure 6 As shown, the cross-section of the gas phase cavity 4 is a rectangular structure, and its height h is 2.5 times the radius of the outer helical propulsion blade.

[0055] The results of the experiments are shown in the table below.

[0056] Serial number Capacity (kg / h) Specific energy consumption (kJ / kg) Product purity (%) Example 1 2000 4346.28 99.54 Example 2 2000 4350.53 99.86 Example 3 2000 4337.76 99.95 Comparative Example 1 1800 5533.94 97.47 Comparative Example 2 2000 5959.63 98.18 Comparative Example 3 2000 6598.17 97.82

[0057] As shown in the table above, the semi-circular structure of the gas phase cavity results in the lowest unit energy consumption and the best energy-saving effect. When the external helical propulsion blades are arranged in an alternating pattern, the product purity is higher; when using an internal helical propulsion blade structure, the product purity is the highest due to more thorough mixing. In Comparative Example 1, due to the relatively small gas phase cavity, there are more condensed products, including some pyromellitic acid raw material, leading to greater losses. Comparative Examples 2 and 3, due to their larger heat dissipation surfaces, have relatively higher energy consumption per unit output.

[0058] The revolution radius of the outer spiral propeller blade can be selected as 200-800mm, the radius of the main shaft is 50%-75% of the revolution radius of the outer spiral propeller blade; the interval between the lower half of the outer spiral propeller blade and the inner bottom of the inner shell is 8-12mm.

[0059] The application is not limited to the above-mentioned embodiments, and based on the technical solutions disclosed in the application, some substitutions and modifications can be made to some technical features by those skilled in the art without creative labor, and the substitutions and modifications are within the protection scope of the application.

Claims

1. A continuous device for preparing pyromellitic anhydride, comprising a horizontal shell, one end of the upper side of the shell is provided with a feed inlet for feeding raw pyromellitic acid, the feed inlet is provided with a feed valve; the middle of the upper side of the shell is provided with a gas phase outlet, the other end of the lower side of the shell is provided with a discharge outlet for discharging liquid pyromellitic dianhydride, the discharge outlet is provided with a discharge valve; the shell comprises a double-layered outer shell and an inner shell, and a heating medium cavity is arranged between the outer shell and the inner shell, characterized in that: The shell is provided with two parallel main shafts, the axes of which are located at the same horizontal position, and the outer helical propelling blades on the two main shafts have the same height; the bottom of the outer shell and the inner shell is in the shape of omega which is consistent with the shape of the outer helical propelling blades, and a semicircular gas phase cavity is left above the outer helical propelling blades which is connected with the two sides of the omega; the gas phase outlet is connected with the vacuum condenser and the vacuum air extraction device; the inner shell on the upper side of the discharge port is provided with an overflow baffle, the height of which is flush with the upper edge of the main shaft; the shell is divided into a feeding section, an anhydride forming section and a discharging section in the length direction, the main shaft corresponding to the anhydride forming section is a partially hollow structure, and a plurality of through holes are provided on the main shaft to connect the inside and outside of the main shaft, and the inner helical propelling blades are provided on the inner wall of the main shaft, and the rotation direction of the inner helical propelling blades is opposite to that of the outer helical propelling blades on the main shaft. ​ 2. A continuous device for the anhydridation of pyromellitic acid according to claim 1, characterized in that: The rotation radius of the outer helical propelling blades is 200-800mm, and the radius of the main shaft is 50%-75% of the rotation radius of the outer helical propelling blades; the distance between the lower half of the outer helical propelling blades and the inner bottom of the inner shell is 8-12mm.

3. A continuous device for preparing anhydrides of pyromellitic acid according to claim 1, characterized in that: During operation, the temperature gradually rises from 240℃ to 285℃ from the feeding section to the anhydride forming section; the temperature of the anhydride forming section is 285-295℃; and the temperature of the discharging section gradually decreases from the end of the anhydride forming section to 283℃, and then the material is discharged from the discharge port.

4. The continuous device for preparing pyromellitic anhydride according to claim 1, characterized in that: The outer helical propelling blades on the two main shafts are arranged in a staggered manner, and the outer edge of the outer helical propelling blades on any one main shaft abuts against the other main shaft.

5. A continuous device for the anhydridation of pyromellitic acid according to claim 4, characterized in that: The shortest distance between the outer edge of the outer helical propelling blades on any one main shaft and the other main shaft is 8-12mm.

6. A continuous pyromellitic anhydride production apparatus according to any one of claims 1 to 5, characterized in that: The propelling directions of the outer helical propelling blades on the two main shafts are the same, and the rotation directions are opposite.

7. A continuous pyromellitic anhydride production apparatus according to any one of claims 1 to 5, characterized in that: During operation, the vacuum pressure in the gas phase cavity is 0.01-0.09Mpa.

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