A system and method for recovering waste anhydride in a n-butane method maleic anhydride production

Abstract

This invention discloses a waste anhydride recovery system and method in maleic anhydride production using the n-butane process. The system includes a maleic anhydride storage tank, the output of which is connected to the input of a mixer via a first crude anhydride transfer pump. The storage tank also contains a heat exchange coil for melting the maleic anhydride into a liquid state, facilitating system operation. The mixer is connected to a dehydration tower, the output of which is connected to the mixer input via a circulation conduit. Compared with existing technologies, this waste anhydride recovery system and method in maleic anhydride production using the n-butane process offers the following advantages: The device reprocesses the waste anhydride to obtain a qualified product, reducing waste generation and increasing company profits; the invention achieves maleic anhydride recovery and recycling of the circulating solvent in the dehydration tower, improving the utilization rate of the circulating solvent; the two refining routes in the refining tower further improve the recovery quality and yield of maleic anhydride; and the device can operate stably for a long period.

Description

Technical Field

[0001] This invention relates to the field of maleic anhydride production technology, specifically to a waste anhydride recovery system and method in the production of maleic anhydride using the n-butane process. Background Technology

[0002] Maleic anhydride is an important basic raw material in the organic chemical industry, ranking third in consumption after acetic anhydride and phthalic anhydride. Its main use is in the production of unsaturated polyester resins. Maleic anhydride is also used in coatings, inks, lubricant additives, agricultural chemicals, paper sizing agents, textile finishing agents, and surfactants. From maleic anhydride, a series of important fine chemical products can also be produced, including γ-butyrolactone, tetrahydrofuran, fumaric acid, and tetrahydrophthalic anhydride.

[0003] During the production of maleic anhydride, a certain amount of material is discharged during sampling, flake production, and maintenance of pipelines and equipment. These materials undergo oxidation and other reactions upon contact with air or water, resulting in inconsistent quality and making them unsellable as normal products. Previously, these waste materials were directly treated as waste, becoming real slag, causing waste and increasing the company's operating costs. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the existing defects and provide a waste anhydride recovery system and method in the production of maleic anhydride using the n-butane method, which can effectively solve the problems in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a waste anhydride recovery system in maleic anhydride production using the n-butane process, comprising a maleic anhydride storage tank, the output end of which is connected to the input end of a mixer via a first crude anhydride transfer pump, and a heat exchange coil installed inside the maleic anhydride storage tank for melting maleic anhydride into a liquid state to facilitate the operation of the system; the mixer is connected to a dehydration tower, and an auxiliary gas device is installed outside the dehydration tower; the output end of the dehydration tower is connected to the input end of the mixer via a circulation conduit; the other output end of the dehydration tower is connected to a desorption tower, the output end of which is connected to the input end of a purification tower, and the output end of the purification tower is connected to the input end of the desorption tower via a remelting line.

[0006] Furthermore, a first pressure gauge is installed on the outside of the maleic anhydride storage tank, and a first thermometer for detecting water temperature is installed on the heat exchange coil. The first pressure gauge is used to detect the pressure inside the maleic anhydride storage tank, and the first thermometer detects that the water temperature inside the heat exchange coil is between 60-100°C, so that the maleic anhydride is in a liquid state.

[0007] Furthermore, a second thermometer is provided on one side of the dehydration tower, and the auxiliary gas device is a ventilation pipe. The ventilation pipe is used to transport hot air with an external temperature of 140-180°C. A third thermometer is also provided on the outer side of the ventilation pipe. In order to improve the quality of dehydration, hot air at a temperature of 140-180°C is used to keep the temperature inside the dehydration tower at 110-140°C, so as to complete the dehydration of the mixed solvent in the dehydration tower.

[0008] Furthermore, the desorption tower is equipped with a second pressure gauge and a fourth thermometer, and the purification tower is equipped with a third pressure gauge and a fifth thermometer.

[0009] Furthermore, a second crude anhydride transfer pump is provided between the dehydration tower and the desorption tower, and a fourth crude anhydride transfer pump is provided between the desorption tower and the refining tower.

[0010] Furthermore, of the two reflux lines from the refining tower to the desorption tower, one is connected via a gas-liquid separator, and the other is connected via a third crude anhydride transfer pump.

[0011] Furthermore, the dehydration tower is equipped with a tray material pan, and several tray material pans are arranged sequentially from top to bottom, the arrangement of which is determined according to the material concentration inside the tower.

[0012] Furthermore, a circulating distillation tank is also installed on the closed-loop pipeline formed by the gas-liquid separator and the recirculation from the refining tower to the desorption tower. The gas-liquid separator is connected to the circulating distillation tank.

[0013] A method for recovering waste anhydride in maleic anhydride production using the n-butane process comprises the following steps:

[0014] S1): Maleic anhydride is melted in hot water at 60-100°C under the action of heat exchange coils;

[0015] S2): Maleic anhydride is delivered to the mixer by the first crude anhydride transfer pump to achieve mixing. The solvent circulates continuously in the loop formed by the mixer and the dehydration tower. The low-concentration circulating solvent in the dehydration tower is returned to the mixer. The concentration of the mixture is close to the concentration of the material in the 24 trays of the tower. It is dehydrated by hot nitrogen gas stripping at 140-180°C. After a second purification and distillation process, the qualified product is purified.

[0016] The specific steps of the first purification are as follows: The solvent after treatment in S2) is transported to the desorption tower, and the first purification is carried out in the desorption tower under the conditions of a pressure of 5-15 kPa (A) and a tower top temperature of 78-85°C.

[0017] The specific steps of distillation are as follows: The solvent processed in the first purification is sent to the purification column, and distillation is carried out under the conditions of a pressure of 5-15 kPa (A) and a column top temperature of 110-130°C to achieve the purification of qualified products.

[0018] Furthermore, the concentration of the material in the mixer is 4-16% of the concentration of the material in the 24 trays of the tower.

[0019] Compared with existing technologies, the waste anhydride recovery system and method in maleic anhydride production via the n-butane process has the following advantages:

[0020] 1. This device reprocesses waste anhydride to obtain qualified products, reducing waste generation and increasing company profits;

[0021] 2. This invention realizes the recovery of maleic anhydride and the recycling of circulating solvent in the dehydration tower, thereby improving the utilization rate of circulating solvent. The two recycling routes in the refining tower further improve the recovery quality and yield of maleic anhydride, and the device can operate stably for a long time. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention.

[0023] In the diagram: 1 First pressure gauge, 2 First thermometer, 3 Maleic anhydride storage tank, 4 First crude anhydride transfer pump, 5 Mixer, 6 Second thermometer, 7 Dehydration tower, 8 Third thermometer, 9 Ventilation pipe, 10 Fourth thermometer, 11 Second pressure gauge, 12 Desorption tower, 13 Third crude anhydride transfer pump, 14 Fourth crude anhydride transfer pump, 15 Fifth thermometer, 16 Refining tower, 17 Third pressure gauge, 18 Circulating distillation tank, 19 Gas-liquid separator, 20 Second crude anhydride transfer pump, 21 Heat exchange coil. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In the description of this invention, if directional descriptions are involved, such as "up," "down," "front," "back," "left," "right," etc., indicating directional or positional relationships, they are based on the appendix. Figure 1The orientations or positional relationships shown are for the convenience of describing the invention and simplifying the description only, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. When a feature is referred to as "set", "fixed", or "connected" to another feature, it can be set, fixed, or connected to the other feature directly, or it can be set, fixed, or connected to the other feature indirectly.

[0026] Please see Figure 1 This invention provides a technical solution: a waste maleic anhydride recovery system in the production of maleic anhydride using the n-butane method, comprising a maleic anhydride storage tank 3, wherein a heat exchange coil 21 is also provided inside the maleic anhydride storage tank 3. The maleic anhydride storage tank 3 contains substandard maleic anhydride that will undergo oxidation or other reactions upon contact with air or water. In order to achieve the recycling of waste maleic anhydride, hot water at 60-100°C is introduced into the heat exchange coil 21 connected to the maleic anhydride storage tank 3, so that the temperature inside the maleic anhydride storage tank 3 is higher than the melting point of maleic anhydride, thereby melting the solid maleic anhydride into a liquid state. A first pressure gauge 1 is installed on it to facilitate the detection of pressure changes inside, prevent gas from escaping from the tank, and ensure its sealing.

[0027] To improve the quality of maleic anhydride recovery, the product needs to be dehydrated. The molten material in the maleic anhydride storage tank 3 is transported to the mixer 5 by the first crude anhydride transfer pump 4 for mixing. The mixer 5 contains a mixing agent from the dehydration tower 7. The mixing agent is preferably dibutyl phthalate, and its concentration in the dehydration tower 7 is set in a gradient. This solvent is mixed with the molten maleic anhydride waste to dissolve it, making it easier to recover later.

[0028] The mixer 5 is connected to the dehydration tower 7. The output end of the dehydration tower 7 is connected to the input end of the mixer 5 through a circulation conduit. The mixer 5 and the dehydration tower 7 form a circulation loop. The maleic anhydride storage tank 3 continuously transports unqualified products into the mixer 5, while the low-concentration circulating solvent at the top of the dehydration tower 7 continuously mixes with the material in the mixer 5, achieving uninterrupted continuous feeding. The flow rate is controlled by selecting a high-head, low-flow jacketed centrifugal pump.

[0029] The material processed in the dehydration tower 7 is conveyed to the desorption tower 12 for a first desorption distillation to obtain a crude product. The crude product then enters the refining tower 16 for a second distillation to obtain a refined product. At the same time, the refining tower 16 is also equipped with two return lines connected to the desorption tower 12 to increase the yield of the refined product.

[0030] A first pressure gauge 1 is installed on the outside of the maleic anhydride storage tank 3, and a first thermometer 2 for detecting water temperature is installed on the heat exchange coil 21. The first pressure gauge 1 is used to detect the pressure inside the maleic anhydride storage tank 3, and the first thermometer 2 detects that the water temperature inside the heat exchange coil 21 is between 60-100°C, so that the maleic anhydride is in a liquid state.

[0031] A second thermometer 6 is installed on one side of the dehydration tower 7. The dehydration tower 7 is connected to a ventilation pipe 9. A third thermometer 8 is installed on the outer side of the ventilation pipe 9. Hot nitrogen gas at 140-180°C is introduced into the ventilation pipe 9 as an auxiliary gas for dehydration, thereby improving the quality of the product. The third thermometer 8 is used to detect the gas temperature in the ventilation pipe 9, and the second thermometer 6 is used to detect the temperature inside the dehydration tower 7, so that the temperature inside the dehydration tower 7 meets the dehydration requirements of maleic acid impurities, thereby achieving the purpose of removing impurities and extraction.

[0032] The desorption tower 12 is equipped with a second pressure gauge 11 and a fourth thermometer 10, and the purification tower 16 is equipped with a third pressure gauge 17 and a fifth thermometer 15. The fifth thermometer 15 and the fourth thermometer 10 are used to detect the water temperature in the purification tower 16 and the desorption tower 12, respectively. When the water temperature in the desorption tower 12 is too low, the condenser of the desorption tower 12 is easily blocked because maleic anhydride is prone to solidification. When the water temperature is too high, it will increase the load on the pump. At the same time, the second pressure gauge 11 and the third pressure gauge 17 constantly monitor the pressure in the desorption tower 12 and the purification tower 16 to prevent the internal pressure from changing and decreasing, control the temperature at the top of the tower, and thus remove some impurities in the desorption tower 12. The main components of the impurities are acrylic acid and acetic acid.

[0033] A second crude anhydride transfer pump 20 is provided between the dehydration tower 7 and the desorption tower 12, and a fourth crude anhydride transfer pump 14 is provided between the desorption tower 12 and the refining tower 16.

[0034] Of the two reflux lines from the refining tower 16 to the desorption tower 12, one is connected via a gas-liquid separator 19, and the other is connected via a third crude anhydride transfer pump 13.

[0035] The gas-liquid separator 19 is used to ensure that the pressure inside the purification tower 16 is in a negative pressure state. If the purification tower 16 is not in a negative pressure state, the heat accumulated inside the tower cannot be released in a short time, which can easily lead to flooding. In severe cases, it can cause blockage of the condenser at the top of the desorption tower 12 and some pipelines, which seriously affects production. Its continuous operation will extract the gas inside the purification tower 16 and keep its internal pressure in the working state.

[0036] The dehydration tower 7 is equipped with a tray material tray, and several tray material trays are arranged from top to bottom, the arrangement of which is determined according to the material concentration in the tower.

[0037] The refining tower 16 is refluxed to the desorption tower 12 and forms a closed loop through the gas-liquid separator 19. A circulating distillation tank 18 is also installed on the pipeline of the vacuum pump inside the tower, and the vacuum pump is connected to the circulating distillation tank 18.

[0038] A method for recovering waste anhydride in maleic anhydride production via the n-butane process comprises the following steps:

[0039] S1): Maleic anhydride is melted in hot water at 60-100°C under the action of heat exchange coil 21;

[0040] S2): Maleic anhydride is delivered to mixer 5 by the first crude anhydride transfer pump 4 to achieve mixing. The solvent continuously circulates in the loop formed by mixer 5 and dehydration tower 7. The low-concentration circulating solvent in dehydration tower 7 is returned to mixer 5. The concentration of the mixture is close to the concentration of the material in the 24 trays of the tower. It is dehydrated by hot gas stripping at 140-180°C. After a second purification and distillation process, qualified product is obtained.

[0041] The first purification is as follows: The solvent after treatment in S2) is sent to the desorption tower 12 and purified in the desorption tower 12 under the conditions of a pressure of 5-15 kPaA and a tower top temperature of 78-85°C.

[0042] Temperature is regulated by high-pressure steam at the bottom of the tower. If the temperature is too high, the solvent will undergo hydrolysis in the negative pressure environment, decomposing into phthalic anhydride and butanol. This will cause the solvent to completely lose its ability to absorb maleic anhydride, leading to increased solvent consumption. If the temperature of desorption tower 12 is too low, the maleic anhydride in the rich solvent will not have enough heat for complete desorption. The increased anhydride content in the solvent at the bottom of the tower will cause maleic anhydride to convert into fumaric acid byproduct at high temperatures. The increase in fumaric acid will clog the structured packing of desorption tower 12. Moreover, the fumaric acid clogged in the packing is difficult to clean, which will seriously affect the desorption effect. At the same time, the increased anhydride content in the solvent will also cause maleic anhydride polymerization reaction at high temperatures. The polymer adheres to the tube wall of the reboiler at the bottom of the tower, seriously affecting the heat exchange performance, resulting in a vicious cycle and causing blockage of the heat exchanger and pipelines.

[0043] During production operation, the temperature at the bottom of desorption tower 12 should be kept as close as possible to 180℃ and not exceed 200℃. At the same time, the solvent circulation flow rate of the reboiler should be increased to minimize the residence time of the solvent at the bottom of the tower and ensure the desorption effect.

[0044] If the tower pressure is too high, maleic anhydride cannot be fully desorbed from the solvent, leading to the accumulation of maleic anhydride in the solvent and causing side reactions. If the tower pressure is too low, it will increase the load on the evacuation system and damage the equipment. The pressure of the desorption tower should be controlled so that the pressure inside the tower is set in a gradient from the bottom, middle and top of the tower.

[0045] The temperature at the top of the column is maintained at 78-85°C. Acrylic acid and acetic acid precipitate from the stripping column 12, removing impurities.

[0046] The distillation operation is as follows: The solvent processed in S3) is sent to the purification column 16, and distillation is carried out under the conditions of pressure of 5-15 kPaA and column top temperature of 110-130°C to achieve the purification of qualified products.

[0047] In the refining tower 16, the light solvent is refluxed from the top of the refining tower 16 to the stripping tower 12 for secondary refining through the gas-liquid separator 19, while the rich solvent deposited at the bottom is also refluxed to the stripping tower 12 for secondary refining through the third crude anhydride transfer pump 13. The qualified product is discharged from the middle of the refining tower 16. After two refining processes, the recovery efficiency is effectively improved.

[0048] The concentration of the material in the mixer 5 is 4-16% of the concentration of the material in the 24 trays of the tower. At this time, the solvent is in an unsaturated state, ensuring that it does not precipitate in the circulating solvent.

[0049] In use: Substandard maleic anhydride is placed into the maleic anhydride storage tank 3. The heat exchange coil 21 inside operates, raising the temperature of the storage tank 3 to 80°C. At this point, the substandard maleic anhydride in the storage tank 3 begins to melt, becoming molten maleic anhydride. This molten maleic anhydride is then transported to the mixer 5 by the first crude anhydride transfer pump 4 and mixed with the circulating solvent from the dehydration tower 7. This allows the molten maleic anhydride to dissolve in the circulating solvent. The solvent in the mixer 5 is unsaturated. The mixed solvent then enters the dehydration tower 7, where the temperature is 120°C. The C4H4O4 entering the dehydration tower 7 is dehydrated, becoming C4H2O. 3， The kinetic energy brought by the saturated hot air causes the gas in dehydration tower 7 to flow, carrying out the light components of the gas. The dehydrated material then enters desorption tower 12 via the second crude anhydride transfer pump 20 for rectification. External circulation heating is used, and the pressure inside desorption tower 12 is 5-15 kPa. The crude anhydride product is distilled off at a top temperature of 78-85°C. This crude anhydride product is then transported to refining tower 16 by the fourth crude anhydride transfer pump 14. Refining tower 16 also uses external circulation heating, with a pressure of 5-15 kPa. Under conditions of aA and a column top temperature of 110-130°C, distillation is carried out to distill off the refined anhydride product. The distillate in the column is cooled by the column top condenser and separated by the gas-liquid separator 19 before being discharged. The gas phase in the gas-liquid separator 19 is discharged from the top of the separator, while the liquid phase of the gas-liquid separator 19 is returned to the desorption column 12. The rich solvent deposited at the bottom is also returned to the stripping column 12 for secondary refining via the third crude anhydride transfer pump 13. The qualified product is discharged from the middle of the refining column 16. Through two refining processes, the recovery quality is effectively improved.

[0050] It is worth noting that maleic anhydride storage tank 3 is also equipped with two nitrogen split-range controls. Because maleic anhydride products are prone to condensation and sublimation, radar level gauges are used for liquid level detection inside.

[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A waste anhydride recovery system for maleic anhydride production using the n-butane process, comprising a maleic anhydride storage tank (3), characterized in that: The output end of the maleic anhydride storage tank (3) is connected to the input end of the mixer (5) through the first crude anhydride delivery pump (4). The maleic anhydride storage tank (3) is also equipped with a heat exchange coil (21). A first pressure gauge (1) is installed on the outside of the maleic anhydride storage tank (3). A first thermometer (2) for detecting water temperature is installed on the heat exchange coil (21). The mixer (5) is connected to a dehydration tower (7), and a second thermometer (6) is provided on one side of the dehydration tower (7). An auxiliary gas device is also provided on the outside of the dehydration tower (7). The auxiliary gas device is a ventilation pipe (9). The ventilation pipe (9) is used to transport hot air with an external temperature of 140-180℃. A third thermometer (8) is also provided on the outer side of the ventilation pipe (9). A second crude anhydride transfer pump (20) is provided between the dehydration tower (7) and the desorption tower (12). A fourth crude anhydride transfer pump (14) is provided between the desorption tower (12) and the refining tower (16). The dehydration tower (7) is equipped with a tower tray material tray, and there are several tower tray material trays arranged from top to bottom, which are arranged according to the material concentration in the tower. The output end of the dehydration tower (7) is connected to the input end of the mixer (5) through a circulation conduit. The other output end of the dehydration tower (7) is connected to a desorption tower (12). The output end of the desorption tower (12) is connected to the input end of the refining tower (16). The output end of the refining tower (16) is connected to the input end of the desorption tower (12) through a remelting line. The desorption tower (12) is equipped with a second pressure gauge (11) and a fourth thermometer (10), and the purification tower (16) is equipped with a third pressure gauge (17) and a fifth thermometer (15). The refining tower (16) has two reflux lines to the desorption tower (12), one of which is connected to a gas-liquid separator (19) and the other is connected to a third crude anhydride transfer pump (13). The refrigerant tower (16) flows back to the desorption tower (12) and forms a closed loop through the gas-liquid separator (19). A circulating distillation tank (18) is also provided on the loop, and the gas-liquid separator (19) is connected to the circulating distillation tank (18).

2. A method for recovering waste anhydride in maleic anhydride production using the n-butane process, characterized in that... The following steps are required: S1): Under hot water at 60-100°C, maleic anhydride is melted under the action of heat exchange coil (21), and the pressure in maleic anhydride storage tank (3) is detected by the first pressure gauge (1), and the water temperature in heat exchange coil (21) is detected by the first thermometer (2). S2): Maleic anhydride is transported to the mixer (5) under the action of the first crude anhydride transfer pump (4) to achieve mixing. The solvent circulates continuously in the loop formed by the mixer (5) and the dehydration tower (7). The circulating solvent with a lower concentration in the dehydration tower (7) is returned to the mixer (5). The concentration of the material in the mixer (5) is 4-16% of the concentration of the material in the 24 trays of the tower. The temperature in the dehydration tower (7) is detected by the second thermometer (6), and the gas temperature in the ventilation pipe (9) is detected by the third thermometer (8). Hot nitrogen gas is used for stripping and dehydration at 140-180°C. S3): The solvent processed in S2) is transported to the desorption tower (12). Under the conditions of a pressure of 5-15 kPa (A) and a tower top temperature of 78-85°C, a purification is carried out in the desorption tower (12). The pressure and temperature inside the desorption tower (12) are detected by the second pressure gauge (11) and the fourth thermometer (10). S4): The solvent processed in S3) is transported to the refining tower (16). Under the conditions of pressure of 5-15 kPa (A) and tower top temperature of 110-130°C, distillation is carried out to achieve the purification of qualified products. The pressure and temperature inside the refining tower (16) are detected by the third pressure gauge (17) and the fifth thermometer (15). The light solvent in the refining tower (16) is returned to the desorption tower (12) for secondary refining through the gas-liquid separator (19). The rich solvent deposited at the bottom of the refining tower (16) is returned to the desorption tower (12) for secondary refining through the third crude anhydride transfer pump (13).

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