A system and process for extracting aromatic acids from oxidation residues of PTA production

Abstract

This invention discloses a system and process for extracting aromatic acids from the oxidation residue of PTA production. The system includes a residue dryer, a primary mill, a secondary mill, a first collector for collecting benzoic acid, and a second collector for collecting isophthalic acid. The primary mill has a conical shell that is wider at the top and narrower at the bottom. A vertical rotating shaft is installed at the center of the conical shell, and several grinding wheels distributed from top to bottom are mounted on the vertical rotating shaft. The top of the conical shell has a feed pipeline connected to a drying tank and a first gas phase pipeline connected to the first collector. The bottom of the conical shell has a second slag discharge pipeline connected to the secondary mill. This invention, by using a primary and secondary mill and employing a sublimation grinding method to extract benzoic acid and isophthalic acid, ensures extraction purity, improves sublimation efficiency, and increases the extraction yield of benzoic acid and isophthalic acid. The process described in this invention is simple, has low input and operating costs, reliable performance, and high purity.

Description

Technical Field

[0001] This invention relates to a PTA production apparatus, and more particularly to a system and process for extracting aromatic acids from the oxidation residue of PTA production. Background Technology

[0002] During PTA production, because the raw materials p-xylene and toluene are homologues, benzoic acid is produced as a byproduct during the oxidation reaction. Benzoic acid, as an important organic chemical raw material, is widely used in pharmaceuticals, dye carriers, plasticizers, fragrances, and preservatives. In previous PTA production plants, the treatment of benzoic acid in the oxidation residue involved two methods: one was extraction by distillation crystallization. This method involved numerous equipment, a complex process, high energy consumption, and was prone to clogging and wall formation, making continuous operation difficult. The other method, without recycling, involved adding sodium hydroxide to neutralize benzoic acid, terephthalic acid, and other organic compounds before external treatment. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a system for extracting aromatic acids from the oxidation residue of PTA production that is reasonably designed, has low operating cost, and high extraction efficiency, in order to overcome the shortcomings of the prior art.

[0004] Another technical problem to be solved by the present invention is to provide a simple and fast process for extracting aromatic acids from the oxidation residue of PTA production, which addresses the shortcomings of the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A system for extracting aromatic acids from oxidation residues of PTA production, characterized in that the system includes a residue dryer, a primary mill, a secondary mill, a first collector for collecting benzoic acid, and a second collector for collecting isophthalic acid.

[0007] The residue dryer is equipped with a drying tank. The top of the drying tank is provided with a feed inlet for receiving the oxidized residue after distillation in the PTA unit, and the bottom of the drying tank is provided with a first slag discharge pipeline connected to the first-stage mill.

[0008] The primary mill is equipped with a conical shell that is larger at the top and smaller at the bottom. A vertical rotating shaft is installed at the center of the conical shell, and several grinding wheels are installed on the vertical rotating shaft from top to bottom. The axis of the grinding wheel shaft coincides with the axis of the rotating shaft, and the rim of the grinding wheel is consistent with the shape of the side of the conical shell. The top of the conical shell is equipped with a feed pipeline connected to the drying tank and a first gas phase pipeline connected to the first collector. The bottom of the conical shell is equipped with a second slag discharge pipeline connected to the secondary mill.

[0009] The secondary grinding mill has a conical shell that is wider at the top and narrower at the bottom. An electric heating wire is wound around the outside of the conical shell. A horizontal rotating shaft is located inside the conical shell, and grinding wheels are mounted on the horizontal rotating shaft. The upper part of the conical shell has a slag inlet connected to the second slag discharge pipeline and a second gas phase pipeline connected to the second collector. The bottom of the conical shell has a third slag discharge pipeline.

[0010] Both the primary and secondary grinding mills are equipped with variable frequency motors for easy control of grinding speed, and both are connected to nitrogen pipelines.

[0011] Both the first collector and the second collector are equipped with a conical tank that is larger at the top and smaller at the bottom. The upper part of the conical tank is provided with an air inlet that is connected to the gas phase pipeline mentioned above. A filter screen is installed at the air inlet. The bottom of the conical tank is provided with a discharge port. Vibrators are symmetrically installed on both sides of the conical tank. An axial flow fan is installed inside the conical tank to introduce cold air into the conical tank for cooling the sublimated benzoic acid or isophthalic acid.

[0012] The technical problem to be solved by the present invention can also be achieved by the following technical solution: a material dispersing mechanism is installed in both the residue dryer, the first collector, and the second collector.

[0013] The technical problem to be solved by the present invention can also be achieved by the following technical solution: the bulk material mechanism includes a rotating baffle for bulk material distribution, a plurality of bulk material distribution holes are provided on the rotating baffle, and horizontal rotating shafts are symmetrically provided on both sides of the rotating baffle. The ends of the horizontal rotating shafts are mounted on the inner walls of the drying tank, the first collector and the second collector through bearings. One end of the horizontal rotating shaft is connected to a drive motor installed on the drying tank, the first collector and the second collector.

[0014] The technical problem to be solved by the present invention can also be achieved by the following technical solution: the gap between the upper grinding wheel rim and the conical shell of the first-stage mill is greater than the gap between the lower grinding wheel rim and the conical shell.

[0015] The technical problem to be solved by the present invention can also be achieved by the following technical solution: the first-stage mill has three grinding wheels, which are equally spaced from top to bottom along the axis of rotation.

[0016] The technical problem to be solved by the present invention can also be achieved by the following technical solution: the rim of the grinding wheel of the first-stage mill is provided with a number of grooves that are inclined along the grinding wheel axis. The grooves are evenly arranged along the circumference of the grinding wheel and are used to lift the oxide residue or slow down the falling speed of the oxide residue when the grinding wheel rotates.

[0017] The technical problem to be solved by the present invention can also be achieved by the following technical solution: the conical tank is provided with an air-cooled jacket, and the air-cooled jacket is connected to the fan through an air circulation pipe.

[0018] The technical problem to be solved by the present invention can also be achieved through the following technical solution: a high-temperature interlock protection mechanism is installed on both the primary and secondary mills. The high-temperature interlock protection mechanism includes a high-temperature interlock protection controller, a water-cooled jacket sleeved on the feed pipeline, an infrared temperature measuring device installed on the feed pipeline / second slag discharge pipeline, and a water supply device connected to the water-cooled jacket. A cooling water pipe connected to the water supply device is connected to the water-cooled jacket. A water pump is installed on the cooling water pipe. The water pump and the infrared temperature measuring device are both connected to the high-temperature interlock protection controller.

[0019] A process for extracting aromatic acids from oxidation residues of PTA production, characterized in that the process employs the aforementioned system for extracting aromatic acids from oxidation residues of PTA production, and the process includes the following steps.

[0020] (1) The mother liquor is extracted from the oxidation residue of the PTA production unit, filtered and distilled, and then put into the residue dryer for drying. The drying temperature is 150℃-180℃. The acetic acid content in the residue is controlled between 8% and 15%. The dried oxidation residue is then discharged into the first-stage mill.

[0021] (2) The oxidation residue is ground in a primary mill. Nitrogen gas is introduced at the same time to control the temperature in the primary mill at 180℃-210℃ and the pressure at 0.1-1kpa, so that the benzoic acid in the oxidation residue sublimates rapidly to form benzoic acid gas. The benzoic acid gas enters the first collector through the first gas phase pipeline. The benzoic acid gas accumulates in the first collector. Cold air is introduced into the benzoic acid collector by an axial flow fan to cool the benzoic acid gas in the benzoic acid collector and form scaly or needle-shaped benzoic acid crystals. Under the action of the cyclone thrust and gravity formed by the axial flow fan, the benzoic acid crystals accumulate at the bottom of the benzoic acid collector. Under the action of the vibrator, the benzoic acid is recovered.

[0022] (3) The oxidized residue solid after benzoic acid extraction enters the secondary mill. Nitrogen gas is introduced during milling. Under the action of electric heating components, the temperature continues to rise to 280℃-330℃, and the pressure is controlled at 0.1-1kpa. Nitrogen gas protection is carried out during the production and extraction of isophthalic acid. At this temperature, the isophthalic acid solid gradually sublimates and accumulates in the second collector. Under the action of axial flow fan and vibrator, isophthalic acid is recovered.

[0023] The technical problem to be solved by the present invention can also be achieved by the following technical solution: the oxidized residue after grinding is pushed into the residue collection tank in the secondary grinding mill, water is added to the residue collection tank to make slurry, the slurry enters the rotary filter for separation, the separated liquid enters the catalyst recovery unit, the filtered solid enters the receiving tank, is mixed with the external wastewater, and discharged into the sewage unit.

[0024] Compared with the prior art, the present invention has the following technical effects:

[0025] First, by setting up a primary and a secondary grinding mill, the oxidation residue is ground to increase the surface area of ​​the benzoic acid solid, thereby improving the sublimation efficiency of benzoic acid in the oxidation residue and increasing the extraction yield of benzoic acid and isophthalic acid in the PTA production unit. The residual heat of the oxidation residue and the frictional heat generated during the grinding process are used to promote the sublimation of benzoic acid and isophthalic acid into the gas phase, thus achieving the extraction of benzoic acid and isophthalic acid from the oxidation residue. Based on the sublimation characteristics of benzoic acid and isophthalic acid, the gaseous benzoic acid is introduced into the first collector, thereby completing the rapid extraction of benzoic acid and isophthalic acid from the oxidation residue.

[0026] In addition, based on the easy sublimation of benzoic acid, solid benzoic acid was extracted by controlling the temperature at 150~210℃ to increase the surface area of ​​benzoic acid and the sublimation time by 20~40 minutes; similarly, based on the easy sublimation of isophthalic acid, solid isophthalic acid was extracted by controlling the temperature at 260~310℃ to increase the surface area of ​​isophthalic acid and the sublimation time by 20~40 minutes.

[0027] Secondly, based on the physical property that benzoic acid and isophthalic acid are easily sublimated, gaseous benzoic acid and isophthalic acid are introduced into the corresponding collectors for crystallization and cooling to extract benzoic acid and isophthalic acid from the oxidation unit residue of the PTA production process; by using an axial flow fan to introduce cold air, the benzoic acid gas and isophthalic acid gas are introduced into the corresponding collectors through the flow of rotating air, which accelerates the crystallization of benzoic acid gas and isophthalic acid gas, shortens the extraction time of benzoic acid and isophthalic acid, and reduces costs;

[0028] Third, a vibrator is installed on the aforementioned collector to increase the downward gravity of benzoic acid and isophthalic acid, thereby accelerating the accumulation of benzoic acid crystals and isophthalic acid crystals at the bottom of the corresponding collector.

[0029] This invention uses the sublimation method to extract benzoic acid, which is simple, has low input and operating costs, reliable performance, and high benzoic acid content. Attached Figure Description

[0030] Figure 1 This is a process flow diagram of the system for extracting aromatic acids from the oxidation residue of PTA production according to the present invention;

[0031] Figure 2 This is a structural diagram of the grinding wheel in a primary grinding mill.

[0032] In the diagram: 1-Residue dryer, 2-First-stage mill, 3-Second-stage mill, 4-First collector, 5-Second collector, 6-Residue collection tank, 7-Axial flow fan, 8-Vibrator, 9-Rotary filter, 10-Receiving tank. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0034] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0035] Reference Figure 1 and Figure 2 A system for extracting aromatic acids from oxidation residues of PTA production, comprising a residue dryer 1, a primary mill 2, a secondary mill 3, a first collector 4 for collecting benzoic acid, and a second collector 5 for collecting isophthalic acid.

[0036] The residue dryer 1 is equipped with a drying tank. The top of the drying tank is provided with a feed inlet for receiving the oxidized residue after distillation in the PTA unit, and the bottom of the drying tank is provided with a first slag discharge pipeline connected to the first-stage mill.

[0037] The primary grinding mill 2 has a conical shell that is wider at the top and narrower at the bottom. A vertical rotating shaft 12 is installed at the center of the conical shell, and several grinding wheels 11 are installed on the vertical rotating shaft 12, arranged horizontally from top to bottom. The axis of the grinding wheel 11 coincides with the axis of the rotating shaft 12, and the rim of the grinding wheel 11 matches the shape of the side of the conical shell, so as to achieve full grinding of the material by the grinding wheel 11. The gap between the rim of the upper grinding wheel 11 and the conical shell is larger than the gap between the rim of the lower grinding wheel 11 and the conical shell, so as to achieve gradual grinding from top to bottom and ensure the grinding effect. There are three grinding wheels 11, arranged along the rotating shaft 12. The axis is set at equal intervals from top to bottom, and the material is fed and ground at the same time; the rim of the grinding wheel 11 is provided with a number of grooves 13 that are inclined along the wheel axis. The grooves 13 are evenly arranged along the circumference of the grinding wheel and are used to lift the oxide residue or slow down the falling speed of the oxide residue when the grinding wheel rotates, so as to further improve the grinding efficiency. The gap between the rim of the grinding wheel 11 and the conical shell and the size of the grooves are set according to the usage requirements and are not specifically described. The top of the conical shell is provided with a feed pipeline connected to the drying tank and a first gas phase pipeline connected to the first collector. The bottom of the conical shell is provided with a second slag discharge pipeline connected to the secondary grinding mill.

[0038] The secondary grinding mill 3 has a conical shell that is wider at the top and narrower at the bottom. An electric heating wire is wound around the outside of the conical shell. A horizontal rotating shaft is located inside the conical shell, with bearings at both ends mounted on the conical shell. Grinding wheels are installed on the horizontal rotating shaft. The upper part of the conical shell has a slag inlet connected to the second slag discharge pipeline and a second gas phase pipeline connected to the second collector. The bottom of the conical shell has a third slag discharge pipeline.

[0039] Both the primary mill 2 and the secondary mill 3 are equipped with variable frequency motors for easy control of the milling speed, and both the primary mill 2 and the secondary mill 3 are connected to nitrogen pipelines.

[0040] Both the first collector 4 and the second collector 5 are equipped with a conical tank that is wider at the top and narrower at the bottom. An air inlet connected to the aforementioned gas phase pipeline is located at the top of the conical tank, and a filter screen is installed at the air inlet. A discharge port is located at the bottom of the conical tank. Vibrators 8 are symmetrically installed on both sides of the conical tank. An axial flow fan 7 is installed inside the conical tank to introduce cold air for cooling the sublimated benzoic acid or isophthalic acid. In addition, the system described in this application also includes a frame for mounting the aforementioned residue dryer 1, mill 2, first collector 4, and second collector. Since the frame is configured according to usage requirements, its structure, dimensions, and location are not described in detail.

[0041] A material dispersing mechanism is installed in the residue dryer 1, the first collector 4, and the second collector 5. The material dispersing mechanism includes a rotating baffle for dispersing material. The rotating baffle has several material dispersing holes. Horizontal rotating shafts are symmetrically arranged on both sides of the rotating baffle. The ends of the horizontal rotating shafts are mounted on the inner walls of the drying tank, the first collector, and the second collector through bearings. One end of the horizontal rotating shaft is connected to a drive motor installed on the drying tank, the first collector, and the second collector.

[0042] Both the primary and secondary mills are equipped with high-temperature interlock protection mechanisms. These mechanisms include a high-temperature interlock protection controller, a water-cooled jacket fitted onto the feed pipeline, an infrared thermometer installed on the feed pipeline / second slag discharge pipeline, and a water supply device connected to the water-cooled jacket. The water-cooled jacket is connected to a cooling water pipe connected to the water supply device, and a water pump is installed on the cooling water pipe. Both the water pump and the infrared thermometer are connected to the high-temperature interlock protection controller. The high-temperature interlock protection controller can be any device, module, or system with control functions disclosed in the prior art.

[0043] A process for extracting aromatic acids from oxidation residues of PTA production, employing the aforementioned system for extracting aromatic acids from oxidation residues of PTA production, includes the following steps.

[0044] (1) The mother liquor is extracted from the oxidation residue of the PTA production unit, filtered and distilled, and then put into the residue dryer for drying. The drying temperature is 150℃-180℃. The acetic acid content in the residue is controlled between 8% and 15%. The dried oxidation residue is then discharged into the first-stage mill.

[0045] (2) The oxidation residue is ground in a primary mill. Nitrogen gas is introduced during grinding. By controlling the temperature at 150℃-210℃, the surface area of ​​benzoic acid and the sublimation time of benzoic acid are increased by 20min~40min. The pressure is controlled at 0.1-1kpa, so that the benzoic acid in the oxidation residue is rapidly sublimated to form benzoic acid gas. The benzoic acid gas enters the first collector through the first gas phase pipeline. The benzoic acid gas accumulates in the first collector. Cold air is introduced into the benzoic acid collector by using an axial flow fan, so that the benzoic acid gas is cooled in the benzoic acid collector and forms scaly or needle-shaped benzoic acid crystals. Under the action of the cyclone thrust and gravity formed by the axial flow fan, the benzoic acid crystals accumulate at the bottom of the benzoic acid collector. Under the action of the vibrator, the benzoic acid is recovered.

[0046] The metal catalyst is also fully dispersed during the grinding process, which can improve the precipitation and neutralization efficiency of the metal catalyst in the catalyst recovery unit;

[0047] (3) The oxidized residue solid after benzoic acid extraction enters the secondary mill. Nitrogen gas is introduced during milling. Under the action of electric heating wire, the temperature is further raised to 280℃-330℃ to increase the surface area of ​​isophthalic acid and the sublimation time of benzoic acid by 20min~40min. The pressure is controlled at 0.1-1kpa. Nitrogen gas protection is carried out during the production and extraction of isophthalic acid. At this temperature, the isophthalic acid solid gradually sublimates and accumulates in the second collector. Under the action of axial flow fan and vibrator, the recovery of isophthalic acid is realized.

[0048] The metal catalyst is further dispersed during the grinding process, improving the precipitation efficiency of the metal catalyst in the catalyst recovery unit. The extracted and collected solid benzoic acid and isophthalic acid can be analyzed by ultraviolet spectroscopy and used in other industrial production or further purified to produce high-purity solid benzoic acid and isophthalic acid.

[0049] (4) The oxidized residue after grinding is pushed into the residue collection tank 6 in the secondary mill. Water is added to the residue collection tank 6 to make slurry. The slurry enters the rotary filter 9 for separation. The separated liquid enters the catalyst recovery unit, and the filtered solid enters the receiving tank 10. It is mixed with the external wastewater and discharged into the sewage unit.

[0050] According to the extraction process described in this invention, mother liquor is extracted from the oxidation residue of a PTA production unit. After filtration and distillation, a solid residue is obtained. Conventional analysis reveals that the benzoic acid content in the solid residue is 30%-31%, the isophthalic acid content is 28%-30%, and the remaining 69%-70% is other non-sublimable PTA. The solid residue is then divided into three batches, with 100 kg of oxidation residue taken from each batch. Analysis of the benzoic acid and isophthalic acid content in the three batches of oxidation residue is performed. Each batch is then processed according to the benzoic acid extraction process for PTA unit oxidation residue described in this invention. After 30 minutes, solid benzoic acid and solid isophthalic acid are extracted. The processing data are as follows.

[0051]

[0052] The extracted and sublimated benzoic acid was analyzed by ultraviolet spectroscopy, and the purity of the benzoic acid was above 99.0%, reaching the purity of industrial-grade benzoic acid.

[0053] The system and process described in this invention are a production process for extracting and recovering aromatic acids from the oxidation residue generated during the production of purified terephthalic acid. Compared with other oxidation residue treatment methods, the system and process described in this invention are simpler, have lower investment and consumption costs, and the target products are easier to obtain. This invention is based on the sublimation characteristics of benzoic acid and isophthalic acid at different temperatures, extracting the two products stepwise. Furthermore, through experimental comparison, benzoic acid can sublimate in the range of 150~220℃, while isophthalic acid can sublimate in the range of 260~310℃. The significant difference in the sublimation temperature ranges of the two products is more conducive to the implementation of the technical route.

Claims

1. A system for extracting aromatic acids from the oxidation residue of PTA production, characterized in that, The system includes a residue dryer, a primary mill, a secondary mill, a first collector for collecting benzoic acid, and a second collector for collecting isophthalic acid. The residue dryer is equipped with a drying tank. The top of the drying tank is provided with a feed inlet for receiving the oxidized residue after distillation in the PTA unit, and the bottom of the drying tank is provided with a first slag discharge pipeline connected to the first-stage mill. The primary mill is equipped with a conical shell that is larger at the top and smaller at the bottom. A vertical rotating shaft is installed at the center of the conical shell, and several grinding wheels are installed on the vertical rotating shaft from top to bottom. The axis of the grinding wheel shaft coincides with the axis of the rotating shaft, and the rim of the grinding wheel is consistent with the shape of the side of the conical shell. The top of the conical shell is equipped with a feed pipeline connected to the drying tank and a first gas phase pipeline connected to the first collector. The bottom of the conical shell is equipped with a second slag discharge pipeline connected to the secondary mill. The secondary grinding mill has a conical shell that is wider at the top and narrower at the bottom. An electric heating wire is wound around the outside of the conical shell. A horizontal rotating shaft is located inside the conical shell, and grinding wheels are mounted on the horizontal rotating shaft. The upper part of the conical shell has a slag inlet connected to the second slag discharge pipeline and a second gas phase pipeline connected to the second collector. The bottom of the conical shell has a third slag discharge pipeline. Both the primary and secondary grinding mills are equipped with variable frequency motors for easy control of grinding speed, and both are connected to nitrogen pipelines. Both the first collector and the second collector are equipped with a conical tank that is larger at the top and smaller at the bottom. The upper part of the conical tank is provided with an air inlet that is connected to the gas phase pipeline mentioned above. A filter screen is installed at the air inlet. The bottom of the conical tank is provided with a discharge port. Vibrators are symmetrically installed on both sides of the conical tank. An axial flow fan is installed inside the conical tank to introduce cold air into the conical tank for cooling the sublimated benzoic acid or isophthalic acid.

2. The system for extracting aromatic acids from the oxidation residue of PTA production according to claim 1, characterized in that, A material dispersing mechanism is installed in both the residue dryer, the first collector, and the second collector.

3. The system for extracting aromatic acids from the oxidation residue of PTA production according to claim 2, characterized in that, The material dispersing mechanism includes a rotating baffle for dispersing materials. The rotating baffle has several material dispersing holes. Horizontal rotating shafts are symmetrically arranged on both sides of the rotating baffle. The ends of the horizontal rotating shafts are mounted on the inner walls of the drying tank, the first collector, and the second collector via bearings. One end of the horizontal rotating shaft is connected to a drive motor installed on the drying tank, the first collector, and the second collector.

4. The system for extracting aromatic acids from the oxidation residue of PTA production according to claim 1, characterized in that, The gap between the upper roller rim and the conical shell of the primary mill is greater than the gap between the lower roller rim and the conical shell.

5. A system for extracting aromatic acids from oxidation residues of PTA production according to claim 4, characterized in that, The primary grinding mill has three grinding wheels, which are evenly spaced from top to bottom along the axis of rotation.

6. A system for extracting aromatic acids from oxidation residues of PTA production according to claim 1, characterized in that, The rim of the primary grinding mill is provided with several grooves that are inclined along the wheel axis. The grooves are evenly distributed along the circumference of the grinding mill and are used to lift the oxide residue or slow down the falling speed of the oxide residue when the grinding mill rotates.

7. A system for extracting aromatic acids from oxidation residues of PTA production according to claim 1, characterized in that, The conical tank is equipped with an air-cooled jacket, which is connected to a fan via an air circulation pipe.

8. A system for extracting aromatic acids from oxidation residues of PTA production according to claim 1, characterized in that, Both the primary and secondary mills are equipped with high-temperature interlock protection mechanisms. These mechanisms include a high-temperature interlock protection controller, a water-cooled jacket fitted onto the feed pipeline / second slag discharge pipeline, an infrared temperature measuring device installed on the feed pipeline, and a water supply device connected to the water-cooled jacket. The water-cooled jacket is connected to a cooling water pipe connected to the water supply device, and a water pump is installed on the cooling water pipe. Both the water pump and the infrared temperature measuring device are connected to the high-temperature interlock protection controller.

9. A process for extracting aromatic acids from the oxidation residue of PTA production, characterized in that, The process employs the system described in any one of claims 1-8 for extracting aromatic acids from the oxidation residue of PTA production, and includes the following steps. (1) The mother liquor is extracted from the oxidation residue of the PTA production unit, filtered and distilled, and then put into the residue dryer for drying. The drying temperature is 150℃-180℃. The acetic acid content in the residue is controlled between 8% and 15%. The dried oxidation residue is then discharged into the first-stage mill. (2) The oxidation residue is ground in a primary mill. Nitrogen gas is introduced at the same time to control the temperature in the primary mill at 180℃-210℃ and the pressure at 0.1-1kpa, so that the benzoic acid in the oxidation residue sublimates rapidly to form benzoic acid gas. The benzoic acid gas enters the first collector through the first gas phase pipeline. The benzoic acid gas accumulates in the first collector. Cold air is introduced into the benzoic acid collector by an axial flow fan to cool the benzoic acid gas in the benzoic acid collector and form scaly or needle-shaped benzoic acid crystals. Under the action of the cyclone thrust and gravity formed by the axial flow fan, the benzoic acid crystals accumulate at the bottom of the benzoic acid collector. Under the action of the vibrator, the benzoic acid is recovered. (3) The oxidized residue solid after benzoic acid extraction enters the secondary mill. Nitrogen gas is introduced during milling. Under the action of electric heating components, the temperature continues to rise to 280℃-330℃, and the pressure is controlled at 0.1-1kpa. Nitrogen gas protection is carried out during the production and extraction of isophthalic acid. At this temperature, the isophthalic acid solid gradually sublimates and accumulates in the second collector. Under the action of axial flow fan and vibrator, isophthalic acid is recovered.

10. A process for extracting aromatic acids from the oxidation residue of PTA production according to claim 9, characterized in that, The oxidized residue after grinding is pushed into the residue collection tank in the secondary mill. Water is added to the residue collection tank to make a slurry. The slurry enters the rotary filter for separation. The separated liquid enters the catalyst recovery unit, and the filtered solid enters the receiving tank. It is mixed with the discharged wastewater and discharged into the sewage unit.

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