Recovery device of p-toluic acid

Abstract

The utility model discloses a p-toluic acid (PT acid) recovery device which comprises a mother liquor extraction tower, a mother liquor stripping tower, a condensate extraction tower, a condensate stripping tower and an extraction agent regeneration tower. P-xylene (PX) is adopted as an extraction agent, so that efficient recovery of PT acid in PTA refined mother liquor and refined condensate is realized at the same time. The device is provided with a mother liquor heater and an extractant heater to maintain operation temperature and prevent organic acid crystallization; the extraction agent regeneration tower realizes PX cyclic utilization; and first and second energy recovery devices are arranged to recover heat of the system. The device enables the PT acid recovery rate to reach more than 90%, raffinate can be directly used as product washing water, and the device has the characteristics of high recovery efficiency, low energy consumption, stable operation and the like, and is suitable for resource recovery of PT acid in the PTA production process.

Description

Technical Field

[0001] This utility model relates to the field of p-methylbenzoic acid separation technology, and more specifically, it relates to a p-methylbenzoic acid recovery device. Background Technology

[0002] Purified terephthalic acid (PTA) is one of the important basic organic chemical raw materials, mainly used in the production of polyester fibers and polyester films. In the production of PTA, the raw material p-xylene (PX) reacts with oxygen in acetic acid solvent to produce crude terephthalic acid (TA) with a purity of about 99.7% (CTA). Impurities mainly exist in the form of the intermediate p-carboxybenzaldehyde (4-CBA). However, TA and 4-CBA are not easily separated, and the quality of CTA cannot meet the requirements of downstream processes, so TA needs to be purified by a refining unit.

[0003] The refining unit mixes CTA with process water to form a slurry, which is then heated and pressurized to form a CTA aqueous solution. 4-CBA is selectively hydrogenated and reduced to p-methylbenzoic acid (PT acid). At the same time, colored impurities are converted into colorless soluble impurities. The difference in solubility of TA and PT acid in water is then utilized to achieve TA purification to over 99.98% through TA crystallization and solid-liquid separation.

[0004] During the TA purification process, the flash vapor generated in the TA crystallization section, containing various organic acids such as PT acid, TA, and benzoic acid (BA), is converted into a refined condensate after heat recovery. This condensate is then recycled within the refining system as a refining solvent. The presence of PT acid and other organic acids increases the difficulty of TA purification. The solid-liquid separation process generates a large amount of refined mother liquor containing TA, PT acid, 4-CBA, and BA, with PT acid having the highest content. PT acid is an intermediate product of the PX oxidation process. Recovering PT acid from the refined mother liquor can not only improve the PTA yield but also purify the PTA mother liquor, reducing the difficulty of subsequent mother liquor processing.

[0005] Currently, the main methods for recovering PT acid from refining systems are physicochemical methods, including crystallization, distillation, and extraction.

[0006] Chinese Patent Publication No. CN219848256U, published on October 20, 2023, describes an invention entitled "PT Acid Separation Device in Refined Coagulant." This device employs a static mixing method between PX and refined condensate to extract PT acid from the condensate into PX. After decantation, PX and PT acid are separated and returned to the oxidation reaction system. However, to avoid PT acid precipitation, this device uses a static mixing method for extraction, resulting in a low PT acid recovery rate due to limited contact mass transfer time. Utility Model Content

[0007] This invention overcomes the following shortcomings in the prior art: (1) Due to the flow rate limitation of raw material PX, the currently operating PTA production equipment only extracts one of the media in the refined mother liquor and refined condensate, and does not achieve a large-scale recovery of PT acid in the refined system; (2) The mother liquor extraction and stripping temperature is relatively low, which easily causes TA and PT acid to crystallize and precipitate, affecting the safe and stable operation of the equipment; a p-methylbenzoic acid recovery device is provided, which can simultaneously extract the refined mother liquor and refined condensate, thereby achieving a large-scale recovery of PT acid in the refined system; the stripping temperature is guaranteed during the extraction process to ensure that the organic acid is always in a dissolved state, and to avoid abnormalities such as blockage in the mother liquor extraction system caused by crystal precipitation.

[0008] To solve the above-mentioned technical problems, this utility model adopts the following technical solution: A p-methylbenzoic acid recovery device, comprising:

[0009] The mother liquor extraction tower uses PX extraction to refine PT acid from the mother liquor;

[0010] The mother liquor stripping tower removes PX carried by the PT acid during the process of removing purified mother liquor from the mother liquor extraction tower;

[0011] The condensate extraction tower uses PX extraction to refine PT acid in the condensate.

[0012] The condensate stripping tower removes PX carried by the purified condensate from the condensate extraction tower during the process of removing PT acid;

[0013] The extractant regeneration tower regenerates the PX that has already been extracted with PT acid in the mother liquor extraction tower, and continues to extract and refine the condensate.

[0014] This application achieves simultaneous extraction of refined mother liquor and refined condensate, enabling the recovery of a large amount of PT acid in the refining system. The extractant can be recycled during the extraction process, reducing usage costs. In addition, the refined mother liquor and extractant in this application are heated by a mother liquor heater and an extractant heater, respectively. The purpose of heating is to ensure that the multi-element organic acids remain in a dissolved state throughout the extraction process, avoiding crystallization and precipitation that could lead to blockage or other abnormalities in the mother liquor extraction tower, thus ensuring the smooth operation of the entire device.

[0015] Preferably, the system also includes a first energy recovery device, through which the PX regenerated in the extractant regeneration tower enters the lower part of the condensate extraction tower.

[0016] The regenerated PX flows through the first energy recovery unit to achieve heat recovery.

[0017] Preferably, the upper and lower parts of the mother liquor extraction tower are respectively provided with a first mother liquor inlet and a second mother liquor inlet;

[0018] The first mother liquor inlet is connected to the mother liquor heater. After passing through the mother liquor heater, the refined mother liquor enters the mother liquor extraction tower through the first mother liquor inlet.

[0019] The second mother liquor inlet is connected to the extractant heater. After passing through the extractant heater, the extractant enters the mother liquor extraction tower from the second mother liquor inlet.

[0020] The refined mother liquor and extractant are heated by the mother liquor heater and extractant heater, respectively. The purpose of heating is to ensure that the multi-organic acids remain in a dissolved state throughout the extraction process, to avoid crystallization and precipitation that could cause blockages in the mother liquor extraction tower, and to ensure the smooth operation of the entire device.

[0021] Preferably, the upper part of the mother liquor stripping tower is provided with a first mother steam inlet, which is connected to the second mother extract outlet at the bottom of the mother liquor extraction tower; the lower part of the mother liquor stripping tower is provided with a mother liquor stripping tower reboiler.

[0022] The residual mother liquor collected from the bottom of the mother liquor extraction tower enters the mother liquor stripping tower through the first mother liquor steam inlet from the second mother liquor extraction outlet.

[0023] Preferably, the mother liquor stripping tower is provided with a second mother steam inlet at the top and a second mother steam outlet at the top; the second mother steam outlet is connected to the decanter, and the aqueous phase separated from the decanter enters the mother liquor stripping tower from the second mother steam inlet.

[0024] After removing residual extractant (PX) in the mother liquor stripping tower, the raffinate mother liquor flows out of the stripping tower and enters subsequent energy recovery and deep mother liquor treatment before being recycled back to the purification system. The steam generated in the mother liquor stripping tower flows out from the second steam outlet at the top of the tower, passes through the second energy recovery device, and enters the decantation tank. The aqueous phase separated in the decantation tank enters the mother liquor stripping tower through the second steam inlet, while the organic phase separated in the decantation tank enters the oxidation reaction system for further reaction.

[0025] Preferably, the upper part of the condensate stripping tower is provided with a first condensate inlet, which is connected to the second condensate outlet at the bottom of the condensate extraction tower; the lower part of the condensate stripping tower is provided with a condensate stripping tower reboiler.

[0026] The condensate collected from the bottom of the condensate extraction tower flows out from the second condensate outlet and then enters the condensate stripping tower from the first condensate inlet. After removing the residual extractant in the condensate stripping tower, the refined condensate flows out directly.

[0027] Preferably, the upper part of the condensate stripping tower is provided with a second condensate inlet, and the top of the condensate stripping tower is provided with a second condensate outlet; the second condensate outlet is connected to the decanter, and the aqueous phase separated from the decanter enters the condensate stripping tower from the second condensate inlet.

[0028] After removing residual extractant in the condensate stripping tower, the purified condensate flows out directly and is returned to the purification system to replace the demineralized water as product washing water. The steam generated at the top of the condensate stripping tower recovers heat through a second energy recovery device and then enters a decantation tank. The aqueous phase, which is efficiently separated in the decantation tank, is returned to the condensate stripping tower, while the organic phase separated in the decantation tank enters the oxidation reaction system for further reaction.

[0029] Preferably, the extractant regeneration tower is provided with a first regeneration inlet, which is connected to the first mother extract outlet at the top of the mother liquor extraction tower; the lower part of the extractant regeneration tower is provided with an extractant regeneration tower reboiler.

[0030] The raffinate collected from the top of the mother liquor extraction tower enters the extractant regeneration tower through the first regeneration inlet from the first mother liquor outlet, where PX containing PT acid is purified by distillation.

[0031] Preferably, the bottom of the extractant regeneration tower is provided with a second regeneration outlet, which is connected to the oxidation reaction system.

[0032] The bottom of the extractant regeneration tower contains a PX solution concentrated with PT acid, which then enters the oxidation reaction system from the second regeneration outlet to carry out the reaction.

[0033] Preferably, the upper part of the condensate extraction tower is provided with a first condensate outlet, and the lower part of the condensate extraction tower is provided with a first condensate inlet, which is connected to the first regeneration outlet at the top of the extractant regeneration tower.

[0034] The refined condensate with a temperature higher than 160℃ is pressurized by a pump and enters the upper part of the condensate extraction tower through the second condensation inlet. The regenerated PX distilled from the top of the extractant regeneration tower is pressurized and enters the lower part of the condensate extraction tower through the first condensation inlet. The refined condensate and the regenerated PX flow counterclockwise through the extraction packing in the condensate extraction tower to fully contact each other, extracting the PT acid in the refined condensate into the regenerated PX. The regenerated PX extract is drawn out from the top of the condensate extraction tower, and the raffinate flows out from the bottom of the condensate extraction tower through the second condensation outlet. During this process, the temperature of the condensate extraction tower is higher than the dissolution temperature of the polybasic organic acid, so the polybasic organic acid will not precipitate.

[0035] Compared with the prior art, the beneficial effects of this utility model are:

[0036] This application utilizes an added extractant regeneration tower to simultaneously extract both the refined mother liquor and the refined condensate while maintaining a high extractant-to-source ratio. The PT acid content in the refined mother liquor and refined condensate is reduced from 1500 ppm and 650 ppm to less than 50 ppm, respectively, with recovery rates exceeding 95% and 90%, significantly improving product yield and quality. The high-temperature raffinate, after extractant removal in a condensate stripping tower, can be directly used as product washing water to replace demineralized water, saving steam consumed in heating the product washing water. The heat input from the condensate stripping tower, mother liquor stripping tower, and extractant regeneration tower is efficiently recovered through a first energy recovery device and a second energy recovery device. Attached Figure Description

[0037] Figure 1 This is a simplified structural diagram of the present invention.

[0038] Figure 2 yes Figure 1 A partial schematic diagram of region I in the middle.

[0039] Figure 3 yes Figure 1 A partial schematic diagram of region II.

[0040] In the diagram: 1. Mother liquor extraction tower; 11. First mother liquor inlet; 12. Second mother liquor inlet; 13. First mother liquor outlet; 14. Second mother liquor outlet.

[0041] 2. Mother liquor stripping tower; 21. First mother steam inlet; 22. Second mother steam inlet; 23. First mother steam outlet; 24. Second mother steam inlet; 25. Mother liquor stripping tower reboiler.

[0042] 3. Extractant regeneration tower; 31. First regeneration inlet; 32. First regeneration outlet; 33. Second regeneration outlet; 34. Extractant regeneration tower reboiler;

[0043] 4. Condensate extraction tower, 41. First condensate inlet, 42. Second condensate inlet, 43. First condensate outlet, 44. Second condensate outlet;

[0044] 5. Condensate stripping tower; 51. First condensate inlet; 52. Second condensate inlet; 53. First condensate outlet; 54. Second condensate outlet; 55. Condensate stripping tower reboiler.

[0045] 6. Mother liquor heater;

[0046] 7. Extractant heater;

[0047] 8. Decanter. Detailed Implementation

[0048] The technical solution of this utility model will be further described in detail below through specific embodiments and with reference to the accompanying drawings:

[0049] Example 1: Refer to Figures 1 to 3 As shown, a p-methylbenzoic acid recovery device includes:

[0050] Mother liquor extraction tower 1 extracts PT acid (p-methylbenzoic acid) from the PTA refining mother liquor using PX (p-xylene).

[0051] Mother liquor stripping tower 2 removes PX carried by the purified mother liquor from the mother liquor extraction tower 1 during the process of removing PT acid;

[0052] Condensate extraction tower 4 uses PX to extract PTA to purify PT acid in the condensate;

[0053] Condensate stripping tower 5 removes PX carried by the purified condensate from PT acid in the condensate extraction tower 4;

[0054] Extractant regeneration tower 3 regenerates the PX that has already been extracted with PT acid in mother liquor extraction tower 1, and continues to extract and refine the condensate.

[0055] The upper and lower parts of the mother liquor extraction tower 1 are respectively provided with a first mother liquor inlet 11 and a second mother liquor inlet 12;

[0056] The first mother extract inlet 11 is connected to the mother liquor heater 6. After passing through the mother liquor heater 6, the refined mother liquor enters the mother liquor extraction tower 1 from the first mother extract inlet 11.

[0057] The second mother liquor inlet 12 is connected to the extractant heater 7. After passing through the extractant heater 7, the extractant enters the mother liquor extraction tower 1 from the second mother liquor inlet 12. PX is used as the extractant.

[0058] The refined mother liquor and extractant are heated by the mother liquor heater 6 and the extractant heater 7, respectively. The purpose of heating is to ensure that the multi-organic acids remain in a dissolved state throughout the extraction process, so as to avoid crystallization and precipitation that could cause blockage or other abnormalities in the mother liquor extraction tower 1, and to ensure the smooth operation of the entire device.

[0059] The extractant regeneration tower 3 is equipped with a first regeneration inlet 31, which is connected to the first mother extract outlet 13 at the top of the mother liquor extraction tower 1. A reboiler 34 is installed at the bottom of the extractant regeneration tower 3. The raffinate collected from the top of the mother liquor extraction tower 1 enters the extractant regeneration tower 3 through the first mother extract outlet 13 and the first regeneration inlet 31, where the PX containing PT acid is purified by distillation.

[0060] It also includes a first energy recovery device. The PX regenerated after distillation and purification in the extractant regeneration tower 3 flows out of the extractant regeneration tower 3 from the first regeneration outlet 32, and then enters the lower part of the condensate extraction tower 4 through the first energy recovery device. The condensate extraction tower 4 is provided with a first condensation inlet 41 at the bottom, and the regenerated PX enters the condensate extraction tower 4 from the first condensation inlet 41.

[0061] The bottom of the extractant regeneration tower 3 is equipped with a second regeneration outlet 33, which is connected to the oxidation reaction system. The bottom of the extractant regeneration tower 3 contains a PX solution concentrated with PT acid, which then enters the oxidation reaction system from the second regeneration outlet 33 to undergo the reaction.

[0062] A second condensation inlet 42 is provided at the top of the condensate extraction tower 4, through which the refined condensate enters the condensate extraction tower 4. A first condensation outlet 43 is provided at the top of the condensate extraction tower 4. The refined condensate with a temperature higher than 160°C is pressurized by a pump and enters the upper part of the condensate extraction tower 4 through the second condensation inlet 42. The regenerated PX distilled from the top of the extractant regeneration tower 3 is pressurized and enters the lower part of the condensate extraction tower 4 through the first condensation inlet 41. The refined condensate and the regenerated PX flow counterclockwise through the extraction packing in the condensate extraction tower 4 to fully contact each other, extracting the PT acid in the refined condensate into the regenerated PX. The regenerated PX extract is drawn from the top of the condensate extraction tower 4, and the raffinate flows out from the bottom of the condensate extraction tower 4 through the second condensation outlet 44. During this process, the temperature of the condensate extraction tower 4 is higher than the dissolution temperature of the polybasic organic acid, so the polybasic organic acid will not precipitate.

[0063] The upper part of the mother liquor stripping tower 2 is provided with a first mother steam inlet 21, which is connected to the second mother extract outlet 14 at the bottom of the mother liquor extraction tower 1; the lower part of the mother liquor stripping tower 2 is provided with a mother liquor stripping tower reboiler 25.

[0064] The upper part of the mother liquor stripping tower 2 is provided with a second mother steam inlet 22, and the top of the mother liquor stripping tower 2 is provided with a second mother steam outlet 24; the second mother steam outlet 24 is connected to the decanter 8.

[0065] The raffinate from the bottom of mother liquor extraction tower 1 enters mother liquor stripping tower 2 through the second mother liquor extraction outlet 14 and the first mother steam inlet 21. After removing residual extractant (PX) in mother liquor stripping tower 2, the raffinate flows out of mother liquor stripping tower 2 through the first mother steam outlet 23 and enters subsequent energy recovery and mother liquor deep treatment before being recycled back to the purification system. The steam generated in mother liquor stripping tower 2 flows out from the second mother steam outlet 24 at the top of mother liquor stripping tower 2, passes through the second energy recovery device, and enters decanter 8. The aqueous phase separated in decanter 8 enters mother liquor stripping tower 2 through the second mother steam inlet 22, while the organic phase separated in decanter 8 enters the oxidation reaction system for further reaction.

[0066] The upper part of the condensate stripping tower 5 is provided with a first condensate inlet 51, which is connected to the second condensate extraction outlet 44 at the bottom of the condensate extraction tower 4; the lower part of the condensate stripping tower 5 is provided with a condensate stripping tower reboiler 55.

[0067] The upper part of the condensate stripping tower 5 is provided with a second condensate inlet 52, and the top of the condensate stripping tower 5 is provided with a second condensate outlet 54; the second condensate outlet 54 is connected to the decanter 8, and the aqueous phase separated from the decanter 8 enters the condensate stripping tower 5 from the second condensate inlet 52.

[0068] The condensate collected from the bottom of condensate extraction tower 4 flows out from the second condensate outlet 44, and then enters the condensate stripping tower 5 through the first condensate inlet 51. After removing the residual extractant in the condensate stripping tower 5, the purified condensate flows out directly from the first condensate outlet 53 and returns to the purification system to replace the demineralized water as product washing water. The steam generated at the top of the condensate stripping tower 5, after recovering its heat through the second energy recovery device, enters the decanter 8. The aqueous phase efficiently separated in the decanter 8 is returned to the condensate stripping tower 5, while the organic phase separated in the decanter 8 enters the oxidation reaction system for further reaction.

[0069] It should be noted that in this embodiment, the steam flowing out from the top of the mother liquor stripping tower 2 and the top of the condensate stripping tower 5 enters the second energy recovery device together. After the heat of the steam is recovered by the second energy recovery device, it enters the decanter 8. The aqueous phase separated from the decanter 8 enters the condensate stripping tower 5 and the mother liquor stripping tower 2 respectively, while the organic phase separated from the decanter 8 enters the oxidation reaction system for further reaction.

[0070] The working principle of this application is as follows, specifically including the following steps:

[0071] Step 1: Refined Mother Liquor Extraction. The refined mother liquor is pressurized by a pump and heated to 160-180℃ by the mother liquor heater 6, then enters the upper part of the mother liquor extraction tower 1 through the first mother liquor inlet 11. The extractant PX is heated to 125-150℃ by the extractant heater 7 and enters the lower part of the mother liquor extraction tower 1 through the second mother liquor inlet 12. The refined mother liquor and extractant PX flow counter-currently through the extraction packing in the mother liquor extraction tower 1 to fully contact each other, extracting the PT acid in the refined mother liquor into the extractant PX. The extract is drawn off from the top of the tower, and the remaining mother liquor is discharged from the bottom of the tower. The purpose of heating the refined mother liquor and extractant PX in this process is to ensure that the polyprotic organic acids remain in a dissolved state throughout the extraction process, avoiding abnormalities such as blockage in the mother liquor extraction tower 1 caused by crystallization. In specific operation, the operating pressure of the mother liquor extraction tower 1 is 0.8-1.0 MPaG, and the feed mass ratio of PX extractant to refined mother liquor is 1:3. The mass transfer element in mother liquor extraction tower 1 is made of anti-clogging packing material to avoid the abnormalities in the upstream section (such as RPF filter cloth damage causing increased TA content and increased solid content) from affecting the stable operation of the extraction system.

[0072] Step 2: Stripping of the raffinate mother liquor. The raffinate mother liquor collected from the bottom of mother liquor extraction tower 1 flows out from the second mother liquor extraction outlet 14, and then enters the upper part of mother liquor stripping tower 2 through the first mother steam inlet 21. After removing residual extractant in mother liquor stripping tower 2, the raffinate mother liquor flows out from the first mother steam outlet 23 of the mother liquor stripping tower, enters the subsequent process for processing, and is recycled back to the purification system. In specific operation, the operating pressure of mother liquor stripping tower 2 is 0.1-0.3MPa, corresponding to a temperature of 120-143℃, ensuring that the organic acids in the raffinate mother liquor remain in a dissolved state under normal operating conditions. Anti-clogging trays are selected as mass transfer elements to avoid abnormalities in the upstream process affecting the normal operation of the stripping system. The steam generated at the top of the stripping tower recovers heat through an energy recovery device. After the condensate is cooled to 50℃, it is efficiently separated through a decanter 8. The aqueous phase flows back to the stripping tower from the second mother steam inlet 22 at the top of mother liquor stripping tower 2, and the organic phase is pumped to the oxidation reaction system for recycling.

[0073] Step 3: Extractant Regeneration. The extract collected from the top of mother liquor extraction tower 1 flows out of the first mother liquor outlet 13 and then enters the extractant regeneration tower 3 through the first regeneration inlet 31. The PX in the extract containing PT acid is purified by distillation. Pure PX vapor is distilled from the top of extractant regeneration tower 3 and flows out of the first regeneration outlet 32 ​​into the first energy recovery device for heat recovery. The resulting secondary regenerated PX condensate enters the condensate extraction tower 4 through the first condensate inlet 41 as extractant for secondary use. The bottom of extractant regeneration tower 3 contains a concentrated PX solution containing PT acid. The mass transfer element of extractant regeneration tower 3 is a conventional tray, with an operating pressure of 10 kPaG and a corresponding temperature of 144°C. The PT acid in the bottom of the tower remains in a dissolved state after concentration.

[0074] Step 4: Refined condensate extraction. The refined condensate, with a temperature above 160℃, is pressurized by a pump and enters the upper part of the condensate extraction tower 4 through the second condensation inlet 42. The regenerated PX, distilled from the top of the extractant regeneration tower 3, is pressurized and enters the lower part of the condensate extraction tower 4 through the first condensation inlet 41. The refined condensate and regenerated PX flow counter-currently through the extraction packing in the condensate extraction tower 4, ensuring thorough contact and extraction of PT acid from the refined condensate into the regenerated PX. The extract is drawn off from the first condensation outlet 43 at the top of the condensate extraction tower 4, and the raffinate is discharged from the second condensation outlet 44 at the bottom of the condensate extraction tower 4. During this process, the temperature of the condensate extraction tower 4 is higher than the dissolution temperature of the polybasic organic acids, preventing their precipitation. Specifically, the operating pressure of the condensate extraction tower 4 is 0.8-1.0 MPaG, the operating temperature is 162℃, and the feed mass ratio of PX to mother liquor is 1:3. The mass transfer element uses anti-clogging packing to avoid the impact of abnormalities in the upstream section (such as high liquid level in the refining crystallizer causing increased TA content and solid content in the condensate) on the stable operation of the condensate extraction system.

[0075] Step 5: Raffinate Stripping. The raffinate collected from the bottom of condensate extraction tower 4 is discharged from the second condensate outlet 44 and then enters condensate stripping tower 5 through the first condensate inlet 51. After removing residual extractant in condensate stripping tower 5, the purified condensate is discharged directly from the first condensate outlet 53 and returned to the purification system to replace demineralized water as product washing water. In specific operation, the condensate stripping operating pressure is 0.1-0.3 MPa, corresponding to a temperature of 120-143℃, ensuring that the organic acids in the raffinate remain in a dissolved state under normal operating conditions. Anti-clogging trays are selected as mass transfer elements to avoid abnormalities in the upstream section affecting the normal operation of the stripping system. The steam generated at the top of condensate stripping tower 5 recovers heat through an energy recovery device. After the condensate is cooled to 50℃, it is efficiently separated through decanter 8. The aqueous phase is refluxed back to the top of condensate stripping tower through the second condensate inlet 52, and the organic phase is pumped to the oxidation reaction system for recycling.

[0076] Step 6: PT acid recovery. The extract from the purification condensate extraction tower 4 is mixed with the concentrate from the bottom of the extractant regeneration tower 3 and then sent to the oxidation reaction system to recover PT acid.

[0077] This application utilizes an added extractant regeneration tower to simultaneously extract both the refined mother liquor and the refined condensate while maintaining a high extractant-to-source ratio. The PT acid content in the refined mother liquor and refined condensate is reduced from 1500 ppm and 650 ppm to less than 50 ppm, respectively, with recovery rates exceeding 95% and 90%, significantly improving product yield and quality. The high-temperature raffinate, after extractant removal in a condensate stripping tower, can be directly used as product washing water to replace demineralized water, saving steam consumed in heating the product washing water. The heat input from the condensate stripping tower, mother liquor stripping tower, and extractant regeneration tower is efficiently recovered through a first energy recovery device and a second energy recovery device.

[0078] The embodiments described above are merely preferred solutions of this utility model and are not intended to limit this utility model in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A device for recovering p-methylbenzoic acid, characterized in that, include: The mother liquor extraction tower uses PX extraction to refine PT acid from the mother liquor; The mother liquor stripping tower removes PX carried by the PT acid during the process of removing purified mother liquor from the mother liquor extraction tower; The condensate extraction tower uses PX extraction to refine PT acid in the condensate. The condensate stripping tower removes PX carried by the purified condensate from the condensate extraction tower during the process of removing PT acid; The extractant regeneration tower regenerates the PX that has already been extracted with PT acid in the mother liquor extraction tower, and continues to extract and refine the condensate.

2. The p-methylbenzoic acid recovery device according to claim 1, characterized in that, It also includes a first energy recovery device, through which the PX regenerated in the extractant regeneration tower enters the lower part of the condensate extraction tower.

3. The p-methylbenzoic acid recovery device according to claim 1, characterized in that, The mother liquor extraction tower is equipped with a first mother extract inlet and a second mother extract inlet at the top and bottom, respectively; The first mother liquor inlet is connected to the mother liquor heater. After passing through the mother liquor heater, the refined mother liquor enters the mother liquor extraction tower through the first mother liquor inlet. The second mother liquor inlet is connected to the extractant heater. After passing through the extractant heater, the extractant enters the mother liquor extraction tower from the second mother liquor inlet.

4. The p-methylbenzoic acid recovery apparatus according to any one of claims 1 to 3, characterized in that, The upper part of the mother liquor stripping tower is equipped with a first mother steam inlet, which is connected to the second mother extract outlet at the bottom of the mother liquor extraction tower; the lower part of the mother liquor stripping tower is equipped with a mother liquor stripping tower reboiler.

5. The p-methylbenzoic acid recovery device according to claim 4, characterized in that, The mother liquor stripping tower is equipped with a second mother steam inlet at the top and a second mother steam outlet at the top. The second mother steam outlet is connected to the decanter, and the aqueous phase separated from the decanter enters the mother liquor stripping tower through the second mother steam inlet.

6. The p-methylbenzoic acid recovery apparatus according to any one of claims 1 to 3, characterized in that, The upper part of the condensate stripping tower is equipped with a first condensate inlet, which is connected to the second condensate outlet at the bottom of the condensate extraction tower; the lower part of the condensate stripping tower is equipped with a condensate stripping tower reboiler.

7. The p-methylbenzoic acid recovery device according to claim 6, characterized in that, The upper part of the condensate stripping tower is provided with a second condensate inlet, and the top of the condensate stripping tower is provided with a second condensate outlet; the second condensate outlet is connected to the decanter, and the aqueous phase separated from the decanter enters the condensate stripping tower from the second condensate inlet.

8. The p-methylbenzoic acid recovery apparatus according to any one of claims 1 to 3, characterized in that, The extractant regeneration tower is equipped with a first regeneration inlet, which is connected to the first mother extract outlet at the top of the mother liquor extraction tower; the lower part of the extractant regeneration tower is equipped with an extractant regeneration tower reboiler.

9. The p-methylbenzoic acid recovery device according to claim 8, characterized in that, The bottom of the extractant regeneration tower is equipped with a second regeneration outlet, which is connected to the oxidation reaction system.

10. The p-methylbenzoic acid recovery device according to claim 9, characterized in that, The upper part of the condensate extraction tower is provided with a first condensate outlet, and the lower part of the condensate extraction tower is provided with a first condensate inlet. The first condensate inlet is connected to the first regeneration outlet at the top of the extractant regeneration tower.

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