Reaction system and method for preparing 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-diisopropylnaphthalene

Abstract

The present invention provides a reaction system and method for preparing 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-diisopropylnaphthalene. The system includes: an oxidation reactor, and a solid-liquid mixing unit disposed inside the oxidation reactor and capable of conducting material flow with the oxidation reactor. The solid-liquid mixing unit is arranged such that solid and liquid inside the mixing unit can be dynamically mixed. The length, width, and height of the solid-liquid mixing unit are all smaller than those of the oxidation reactor. The oxidation reactor includes: a gas inlet, a 2,6-diisopropylnaphthalene raw material inlet, a main catalyst inlet, a crude 2,6-naphthalenedicarboxylic acid slurry outlet, and a tail gas outlet. By adopting the technology of the method of the present invention, the purity of the target product, 2,6-naphthalenedicarboxylic acid, can be effectively increased (from 97.14 wt% in the prior art to 99.24 wt%), and at the same time, the content of key impurities can be significantly reduced (the content of 2-methyl-6-naphthoic acid drops from 1224.31 ppm in the prior art to 872.13 ppm, and the content of 2-acetyl-6-naphthoic acid drops from 461.85 ppm in the prior art to 307.51 ppm). By adopting the present invention, better technical effects are achieved.

Description

Technical Field

[0001] The present invention relates to a reaction system and method for preparing 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-diisopropylnaphthalene. Background Art

[0002] Polyethylene 2,6-naphthalenedicarboxylate (PEN) is a new variety of polyester that began to be commercialized in the 1990s. Compared with other polyester materials, it has more excellent properties: higher physical and mechanical properties, gas barrier properties, chemical stability, and heat resistance, ultraviolet resistance, radiation resistance, etc. Like polyethylene terephthalate (PET), it can be processed into films, fibers, hollow containers, sheets, etc. However, due to its more excellent comprehensive properties and broader potential market, it has attracted continuous and extensive attention from the polyester industries around the world.

[0003] PEN is a high-end polyester material, and there are mainly two production methods: transesterification and polycondensation of dimethyl 2,6-naphthalenedicarboxylate (2,6-NDC) and ethylene glycol (EG); polymerization of 2,6-naphthalenedicarboxylic acid (2,6-NDCA) and EG. The liquid-phase oxidation method of 2,6-dialkylnaphthalene has become the focus of research and development due to mild reaction conditions and simple process routes.

[0004] Moreover, 2,6-diisopropylnaphthalene (2,6-DIPN) is easy to separate and purify from raw materials (isomer mixture), and the operating cost is relatively low. Therefore, in the long run, the liquid-phase oxidation method of 2,6-DIPN is a highly competitive process route.

[0005] N101244997A discloses a method for preparing 2,6-naphthalenedicarboxylic acid, using a stirred bubble reactor for preparing 2,6-naphthalenedicarboxylic acid.

[0006] CN106179135A discloses a reactor for gas-liquid phase continuous reaction for producing trimellitic acid, with bottom feeding in the annular gap reaction zone and bottom discharging in the internal reaction zone. Summary of the Invention

[0007] The purpose of the present invention is to improve the purity of crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0008] According to the first aspect of the present invention, the present invention provides a reaction system for preparing 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-diisopropylnaphthalene. The system includes: an oxidation reactor, and a solid-liquid mixing unit disposed inside the oxidation reactor and capable of conducting material flow with the oxidation reactor. The solid-liquid mixing unit is arranged such that the solid and liquid inside the mixing unit can be dynamically mixed. The length, width, and height of the solid-liquid mixing unit are all smaller than those of the oxidation reactor. The oxidation reactor includes: a gas inlet, a 2,6-diisopropylnaphthalene raw material inlet, a main catalyst inlet, a crude 2,6-naphthalenedicarboxylic acid slurry outlet, and a tail gas outlet.

[0009] According to the second aspect of the present invention, the present invention provides a method for preparing 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-diisopropylnaphthalene. The method is carried out in the reaction system of the present invention. Wherein, the method includes: the 2,6-diisopropylnaphthalene raw material and the catalyst enter the oxidation reactor and / or the solid-liquid mixing unit from their respective inlets. Under the action of the solid-liquid mixing unit, they fully contact with the oxygen in the air entering from the gas inlet and react. The unreacted air, water vapor, and gaseous products generated by oxidation leave the oxidation reactor through the tail gas outlet, and the crude 2,6-naphthalenedicarboxylic acid slurry leaves the oxidation reactor through the crude 2,6-naphthalenedicarboxylic acid slurry outlet.

[0010] In the method of the present invention, under the combined action of a solid-liquid mixing unit such as a stirrer and a draft tube, the flow state of the reaction fluid in the oxidation reactor changes from the completely mixed flow state in the prior art to a state close to plug flow, that is, the liquid-phase reactants first rise to the top of the draft tube inside the draft tube, and then descend to the bottom of the reactor kettle through the channel between the outer wall of the draft tube and the kettle wall of the reactor. Part of the reaction liquid leaves the oxidation reactor as a reaction product through the crude 2,6-naphthalenedicarboxylic acid slurry outlet, and the remaining reaction liquid continues the above-mentioned circulating flow. The oxygen in the gas-phase reactants dissolves and reacts while flowing, and rises to the top of the draft tube inside the draft tube together with the liquid-phase reactants. The unreacted gas, the gas generated by the reaction, and the unreacted and undissolved oxygen form tail gas, which is discharged from the oxidation reactor through the tail gas outlet. The dissolved oxygen continues to descend to the bottom of the reactor kettle with the reaction liquid through the channel between the outer wall of the draft tube and the kettle wall of the reactor and continues to react. It is speculated that since the oxidation of 2,6-diisopropylnaphthalene to 2,6-naphthalenedicarboxylic acid is a multi-stage series process, the oxidation of the first isopropyl group on the naphthalene ring is relatively easy and complete, while the oxidation of the second isopropyl group is relatively difficult and incomplete, which results in different requirements for the catalyst composition at different positions during the progress of this reaction.

[0011] The technology adopting the method of the present invention can effectively increase the purity of the target product, 2,6-naphthalenedicarboxylic acid (from 97.14 wt% in the prior art to 99.24 wt%), and at the same time can also significantly reduce the content of key impurities (the content of 2-methyl-6-naphthoic acid drops from 1224.31 ppm in the prior art to 872.13 ppm, and the content of 2-acetyl-6-naphthoic acid drops from 461.85 ppm in the prior art to 307.51 ppm). By adopting the present invention, good technical effects are achieved.

[0012] Compared with the reactor for the gas-liquid phase continuous reaction for producing trimellitic acid disclosed in CN106179135A, which feeds at the bottom of the annular gap reaction zone and discharges at the bottom of the internal reaction zone (i.e., inside the draft tube of the present technology), the present technology is used for producing 2,6-naphthalenedicarboxylic acid, feeds at the bottom of the draft tube and discharges at the side of the annular gap. By setting the catalyst draft tube inlet and the catalyst inlet between the draft tube and the reactor side wall in the reactor, it is beneficial to improve the purity of crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0013] Compared with the preparation method of 2,6-naphthalenedicarboxylic acid disclosed in CN101244997A, which uses a stirred bubble reactor for preparing 2,6-naphthalenedicarboxylic acid, in the present invention technology, a draft tube is arranged in the reaction kettle, and a flow field state conducive to achieving better reaction effects (improving the purity of crude 2,6-naphthalenedicarboxylic acid and reducing the impurity content) is formed in the reaction kettle. Description of the Drawings

[0014] Figure 1 It is a schematic diagram of the reaction system of the implementation mode of the prior art.

[0015] Figure 2 It is a schematic diagram of the reaction system according to an implementation mode of the present invention.

[0016] Figure 3 It is a schematic diagram of the reaction system according to an implementation mode of the present invention.

[0017] Figure 4 It is a schematic diagram of the reaction system according to an implementation mode of the present invention.

[0018] Figure 5 It is a schematic diagram of the reaction system according to an implementation mode of the present invention.

[0019] Description of the Reference Numerals

[0020] Figures 1 to 5 In which:

[0021] 1b and 1d are catalyst draft tube inlets;

[0022] 2, 2a, 2b, 2c, and 2d are air inlets;

[0023] 3, 3a, 3b, 3c, 3d are the inlets for 2,6 - diisopropylnaphthalene raw materials;

[0024] 4, 4a, 4b, 4c, 4d are the main inlets for the catalyst;

[0025] 5, 5a, 5b, 5c, 5d are the outlets for the crude 2,6 - naphthalenedicarboxylic acid slurry;

[0026] 6, 6a, 6b, 6c, 6d are the stirring paddles;

[0027] 7c, 7d are the inlets for the catalyst between the draft tube and the reactor side wall;

[0028] 8a, 8b, 8c, 8d are the draft tubes;

[0029] 9, 9a, 9b, 9c, 9d are the tail gas outlets. Detailed implementation manners

[0030] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0031] The present invention provides a reaction system for preparing 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-diisopropylnaphthalene. The system includes an oxidation reactor and a solid-liquid mixing unit disposed inside the oxidation reactor and capable of material circulation with the oxidation reactor. The solid-liquid mixing unit is arranged such that the solid and liquid inside the mixing unit can be dynamically mixed. The length, width, and height of the solid-liquid mixing unit are all smaller than those of the oxidation reactor. The oxidation reactor includes a gas inlet, a 2,6-diisopropylnaphthalene raw material inlet, a main catalyst inlet, a crude 2,6-naphthalenedicarboxylic acid slurry outlet, and a tail gas outlet. In the method of the present invention, under the action of the solid-liquid mixing unit, the flow state of the reaction fluid in the oxidation reactor changes from the well-mixed flow state in the prior art to a state close to plug flow, that is, the liquid-phase reactants first rise to the top of the solid-liquid mixing unit inside the solid-liquid mixing unit, and then descend to the bottom of the reactor kettle through the channel between the outer wall of the solid-liquid mixing unit and the reactor kettle wall. Part of the reaction liquid leaves the oxidation reactor as a reaction product through the crude 2,6-naphthalenedicarboxylic acid slurry outlet, and the remaining reaction liquid continues the above-mentioned circulating flow. The oxygen in the gas-phase reactants dissolves and reacts while flowing, and together with the liquid-phase reactants, it first rises to the top of the solid-liquid mixing unit inside the solid-liquid mixing unit. The unreacted gas, the gas generated by the reaction, and the unreacted and undissolved oxygen form tail gas, which is discharged from the oxidation reactor through the tail gas outlet. The dissolved oxygen continues to descend to the bottom of the reactor kettle with the reaction liquid through the channel between the outer wall of the solid-liquid mixing unit and the reactor kettle wall and continues to react. Thereby, it is possible to improve the purity of the crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0032] According to a preferred embodiment of the present invention, the solid-liquid mixing unit includes a device having an accommodation space capable of material circulation with the oxidation reactor and a dynamic stirring device for dynamically mixing the device having the space.

[0033] According to a preferred embodiment of the present invention, preferably, the solid-liquid mixing unit includes a draft tube and a stirrer capable of material circulation with the oxidation reactor. The stirrer includes a stirring paddle and a stirring shaft, and the stirring paddle is disposed inside the draft tube. By adopting the foregoing preferred setting, it is possible to improve the purity of the crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0034] According to a preferred embodiment of the present invention, the oxidation reactor is provided with a catalyst mixing unit inlet for supplying a catalyst to the solid-liquid mixing unit; preferably, the height at which the catalyst mixing unit inlet is provided is between the lower end face of the solid-liquid mixing unit and the upper end face of the oxidation reactor.

[0035] According to a preferred embodiment of the present invention, preferably, the height at which the catalyst mixing unit inlet is provided is between the upper end face of the stirring paddle and the upper edge of the draft tube. By adopting the foregoing preferred setting, it is possible to improve the purity of the crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0036] According to a preferred embodiment of the present invention, preferably, the catalyst main inlet and the catalyst mixing unit inlet are arranged such that the weight ratio of the flow rate at the catalyst main inlet to the flow rate at the catalyst mixing unit inlet is 4 to 49:1, preferably 6 to 38:1, more preferably 8 to 19:1. Thereby, it is possible to improve the purity of crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0037] According to a preferred embodiment of the present invention, preferably, the oxidation reactor is provided with a catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor for introducing the catalyst into the gap space between the solid-liquid mixing unit and the oxidation reactor. By adopting this preferred arrangement, it is possible to improve the purity of crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0038] According to a preferred embodiment of the present invention, preferably, the height of the catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor is located between the lower edge and the upper edge of the solid-liquid mixing unit, preferably at a position close to the upper edge between the lower edge and the upper edge of the solid-liquid mixing unit, more preferably at a position close to the upper edge between the lower edge and the upper edge of the draft tube. By adopting this preferred arrangement, it is possible to improve the purity of crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0039] According to a preferred embodiment of the present invention, the arrangement of the catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor is such that the weight ratio of the flow rate at the catalyst main inlet to the flow rate at the catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor is 4 to 49:1, preferably 6 to 38:1, more preferably 15 to 17:1. Thereby, it is possible to improve the purity of crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0040] According to a preferred embodiment of the present invention, the gas inlet is provided at the bottom of the oxidation reactor.

[0041] According to a preferred embodiment of the present invention, the 2,6-diisopropylnaphthalene raw material inlet is provided at the bottom of the oxidation reactor.

[0042] According to a preferred embodiment of the present invention, the catalyst main inlet is provided at the bottom of the oxidation reactor.

[0043] According to a preferred embodiment of the present invention, preferably, the gas inlet, the 2,6-diisopropylnaphthalene raw material inlet and the catalyst main inlet are provided at the bottom of the oxidation reactor and point to the lower opening of the solid-liquid mixing unit. By adopting this preferred arrangement, it is possible to improve the purity of crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0044] According to a preferred embodiment of the present invention, preferably, the outlet of the crude 2,6-naphthalenedicarboxylic acid slurry is arranged at the middle and lower part of the oxidation reactor; preferably, the height at which the outlet of the crude 2,6-naphthalenedicarboxylic acid slurry is arranged is between the lower edge and the upper edge of the solid-liquid mixing unit; more preferably, the height at which the outlet of the crude 2,6-naphthalenedicarboxylic acid slurry is arranged is at a position close to the lower edge between the lower edge and the upper edge of the solid-liquid mixing unit. By adopting this preferred arrangement, it is possible to improve the purity of the crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0045] According to a preferred embodiment of the present invention, preferably, the tail gas outlet is arranged at the top of the oxidation reactor.

[0046] According to a preferred embodiment of the present invention, preferably, the oxidation reactor is provided with a catalyst guide cylinder inlet and a catalyst inlet between the guide cylinder and the side wall of the oxidation reactor.

[0047] According to a preferred embodiment of the present invention, preferably, the height at which the catalyst guide cylinder inlet is arranged is between the upper end face of the stirring paddle and the upper edge of the guide cylinder. Thereby, it is possible to improve the purity of the crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0048] According to a preferred embodiment of the present invention, preferably, the height of the catalyst inlet between the guide cylinder and the side wall of the oxidation reactor is between the lower edge and the upper edge of the guide cylinder, preferably at a position close to the upper edge between the lower edge and the upper edge of the guide cylinder. Thereby, it is possible to improve the purity of the crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0049] According to a preferred embodiment of the present invention, preferably, the settings of the main catalyst inlet, the catalyst inlet between the guide cylinder and the side wall of the oxidation reactor, and the main catalyst inlet are such that the weight ratio of the flow rate of the main catalyst inlet to the flow rate of the catalyst guide cylinder inlet is 6 to 38:1, preferably 8 to 19:1, the weight ratio of the flow rate of the main catalyst inlet to the flow rate of the catalyst inlet between the guide cylinder and the reactor side wall is 6 to 38:1, preferably 15 to 17:1, and the weight ratio of the flow rate of the catalyst guide cylinder inlet to the flow rate of the catalyst inlet between the guide cylinder and the reactor side wall is 0.5 to 2:1, preferably 0.6 to 0.98:1. Thereby, it is possible to improve the purity of the crude 2,6-naphthalenedicarboxylic acid and reduce the impurity content.

[0050] Using the reaction system of the present invention for the oxidation of 2,6 - diisopropylnaphthalene to prepare 2,6 - naphthalenedicarboxylic acid has the advantages of improving the purity of crude 2,6 - naphthalenedicarboxylic acid and reducing the impurity content. There are no special requirements for its oxidation method. For the present invention, a method for the oxidation of 2,6 - diisopropylnaphthalene to prepare 2,6 - naphthalenedicarboxylic acid is provided. This method is carried out in the reaction system described in the present invention. Among them, this method includes: The raw material of 2,6 - diisopropylnaphthalene and the catalyst enter the oxidation reactor and / or the solid - liquid mixing unit from their respective inlets. Under the action of the solid - liquid mixing unit, they fully contact with the oxygen in the air entering from the gas inlet and react. The unreacted air, water vapor, and the gaseous products generated by oxidation leave the oxidation reactor through the tail gas outlet, and the slurry of crude 2,6 - naphthalenedicarboxylic acid leaves the oxidation reactor through the outlet of the slurry of crude 2,6 - naphthalenedicarboxylic acid.

[0051] According to the present invention, preferably, the catalyst contains cobalt acetate, manganese acetate, bromide, potassium acetate, and acetic acid. According to a more preferred embodiment of the present invention, the molar ratio of cobalt acetate to manganese acetate is 0.25 - 4:1, preferably 0.5 - 2:1.

[0052] According to the present invention, preferably, the catalyst at the main inlet of the catalyst contains cobalt acetate, manganese acetate, bromide, potassium acetate, and acetic acid.

[0053] According to the present invention, preferably, the catalyst at the catalyst inlet between the draft tube and the side wall of the oxidation reactor contains cobalt acetate, manganese acetate, optionally bromide, optionally potassium acetate, and acetic acid, preferably contains cobalt acetate, manganese acetate, and acetic acid.

[0054] According to the present invention, preferably, the catalyst at the inlet of the catalyst mixing unit contains cobalt acetate, manganese acetate, optionally bromide, optionally potassium acetate, and acetic acid, preferably contains cobalt acetate, manganese acetate, and acetic acid.

[0055] According to the present invention, preferably, the bromide is one or more of potassium bromide, tetrabromoethane, and ammonium bromide, preferably potassium bromide.

[0056] According to the present invention, in normal industrial production, the catalyst is replenished according to the amount of mother liquor withdrawn (5 - 10%).

[0057] According to the present invention, the amount of gas (usually air) is controlled according to the oxygen content in the exhaust gas not being higher than 8% (by volume), and it is in excess relative to the theoretical requirement of the reaction. Generally, it is not particularly limited.

[0058] According to the preferred embodiment of the present invention, the flow rate of air ensures that the oxygen is in excess relative to the reaction theory and the oxygen content in the exhaust gas is not higher than 8% by volume.

[0059] According to the present invention, preferably, the reaction conditions include: the reaction temperature is 150 to 240 °C, preferably 180 to 210 °C.

[0060] According to the present invention, preferably, the reaction conditions include: the reaction pressure is 1.5 to 6.0 MPa, preferably 3.0 to 5.0 MPa.

[0061] According to the present invention, preferably, the reaction conditions include: the residence time of 2,6 - diisopropylnaphthalene raw material in the oxidation reactor is 0.5 to 2.0 h, preferably 0.75 to 1.5 h.

[0062] According to the preferred embodiment of the present invention, the weight ratio of the flow rate at the main catalyst inlet to the flow rate at the catalyst draft tube inlet is 6 to 38:1, preferably 8 to 19:1.

[0063] According to the preferred embodiment of the present invention, the weight ratio of the flow rate at the main catalyst inlet to the flow rate at the catalyst inlet between the draft tube and the reactor side wall is 6 to 38:1, preferably 15 to 17:1.

[0064] According to the preferred embodiment of the present invention, the weight ratio of the flow rate at the catalyst draft tube inlet to the flow rate at the catalyst inlet between the draft tube and the reactor side wall is 0.5 to 2:1, preferably 0.6 to 0.98:1.

[0065] According to the preferred embodiment of the present invention, the catalyst includes: a first catalyst, a second catalyst, and a third catalyst. The present invention finds that the components in the compositions of the first, second, and third catalysts can be the same, only the ratio of the main catalysts cobalt acetate and manganese acetate is different. Whether the second and third catalysts contain bromides such as potassium bromide and potassium acetate has little effect on the reaction results. Of course, preferably, the first catalyst includes cobalt acetate, manganese acetate, potassium bromide, potassium acetate, and acetic acid. Acetic acid is a solvent and continuous feeding is essential. The second and third catalysts include cobalt acetate, manganese acetate, and acetic acid.

[0066] According to the preferred embodiment of the present invention, the first catalyst contains: cobalt acetate, manganese acetate, potassium bromide, potassium acetate, and acetic acid. Based on the total weight of the first catalyst, cobalt acetate is 1 - 3 wt%, manganese acetate is 3 - 5 wt%, potassium bromide is 2 - 4 wt%, potassium acetate is 4 - 6 wt%, acetic acid is 80 - 90 wt%, and the weight ratio of cobalt acetate to manganese acetate is 0.4 - 0.6.

[0067] According to the preferred embodiment of the present invention, the second catalyst contains: cobalt acetate, manganese acetate, optionally potassium bromide, optionally potassium acetate, and acetic acid. Based on the total weight of the second catalyst, cobalt acetate is 4 - 10 wt%, manganese acetate is 3.5 - 6 wt%, potassium bromide is 3 - 5 wt%, potassium acetate is 4 - 6 wt%, acetic acid is 80 - 90 wt%, and the weight ratio of cobalt acetate to manganese acetate is 1.1 - 2.2.

[0068] According to a preferred embodiment of the present invention, the third catalyst contains: cobalt acetate, manganese acetate, optionally potassium bromide, optionally potassium acetate and acetic acid. Based on the total weight of the third catalyst, cobalt acetate is 8-15% by weight, manganese acetate is 3.5-6% by weight, potassium bromide is 3-5% by weight, potassium acetate is 4-6% by weight, and acetic acid is 80-90% by weight. The weight ratio of cobalt acetate to manganese acetate is 2.22-2.55.

[0069] According to a preferred embodiment of the present invention, preferably, the first catalyst enters from the main catalyst inlet, the second catalyst enters from the catalyst draft tube inlet, and the third catalyst enters from the catalyst inlet between the draft tube and the reactor side wall.

[0070] According to a preferred embodiment of the present invention, preferably, the flow weight ratio of the first catalyst, the second catalyst, and the third catalyst is 9-18:0.5-2:1, preferably 15-17:0.6-0.98:1.

[0071] The present invention provides a method for preparing 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-diisopropylnaphthalene, which includes an oxidation reactor. The oxidation reactor includes a stirrer composed of a stirring paddle and a stirring shaft, a draft tube, an air inlet, a 2,6-diisopropylnaphthalene raw material inlet, a main catalyst inlet, a crude 2,6-naphthalenedicarboxylic acid slurry outlet, and a tail gas outlet. The stirring paddle is arranged inside the draft tube. The air inlet, the 2,6-diisopropylnaphthalene raw material inlet, and the main catalyst inlet are located at the bottom of the reactor and point to the lower opening of the draft tube. The height at which the crude 2,6-naphthalenedicarboxylic acid slurry outlet is arranged is between the lower edge and the upper edge of the draft tube. The 2,6-diisopropylnaphthalene raw material and the catalyst supplemented with a catalyst, a cocatalyst, and a solvent enter the oxidation reactor from the 2,6-diisopropylnaphthalene raw material inlet and the main catalyst inlet respectively. Under the combined action of the stirrer and the draft tube, they fully contact with the oxygen in the air entering from the air inlet and react. The unreacted air, water vapor, and gaseous products generated by oxidation leave the oxidation reactor through the tail gas outlet, and the crude 2,6-naphthalenedicarboxylic acid slurry leaves the oxidation reactor through the crude 2,6-naphthalenedicarboxylic acid slurry outlet.

[0072] According to a preferred embodiment of the present invention, preferably, the height at which the crude 2,6-naphthalenedicarboxylic acid slurry outlet is arranged is at a position close to the lower edge between the lower edge and the upper edge of the draft tube.

[0073] According to a preferred embodiment of the present invention, preferably, the oxidation reactor is provided with a catalyst draft tube inlet.

[0074] According to a preferred embodiment of the present invention, preferably, the height at which the catalyst draft tube inlet is arranged is between the upper end face of the stirring paddle and the upper edge of the draft tube.

[0075] According to a preferred embodiment of the present invention, preferably, the weight ratio of the flow rate at the main catalyst inlet to the flow rate at the catalyst inlet of the draft tube is 4 to 49:1, preferably 6 to 38:1, and preferably 8 to 19:1.

[0076] According to a preferred embodiment of the present invention, preferably, the oxidation reactor is provided with a catalyst inlet between the draft tube and the reactor side wall.

[0077] According to a preferred embodiment of the present invention, preferably, the height of the catalyst inlet between the draft tube and the reactor side wall is located between the lower edge and the upper edge of the draft tube, preferably at a position close to the upper edge between the lower edge and the upper edge of the draft tube.

[0078] According to a preferred embodiment of the present invention, preferably, the weight ratio of the flow rate at the main catalyst inlet to the flow rate at the catalyst inlet between the draft tube and the reactor side wall is 6 to 38:1, preferably 15 to 17:1.

[0079] According to a preferred embodiment of the present invention, preferably, the oxidation reactor is provided with a catalyst inlet of the draft tube and a catalyst inlet between the draft tube and the reactor side wall.

[0080] According to a preferred embodiment of the present invention, preferably, the height at which the catalyst inlet of the draft tube is provided is located between the upper end face of the stirring paddle and the upper edge of the draft tube, and the height of the catalyst inlet between the draft tube and the reactor side wall is located between the lower edge and the upper edge of the draft tube, preferably at a position close to the upper edge between the lower edge and the upper edge of the draft tube.

[0081] According to a preferred embodiment of the present invention, preferably, the weight ratio of the flow rate at the main catalyst inlet to the flow rate at the catalyst inlet of the draft tube is 6 to 38:1, preferably 8 to 19:1; the weight ratio of the flow rate at the main catalyst inlet to the flow rate at the catalyst inlet between the draft tube and the reactor side wall is 6 to 38:1, preferably 15 to 17:1; and the weight ratio of the flow rate at the catalyst inlet of the draft tube to the flow rate at the catalyst inlet between the draft tube and the reactor side wall is 0.5 to 2:1, preferably 0.6 to 0.98:1.

[0082] According to a preferred embodiment of the present invention, preferably, the catalyst entering the main catalyst inlet, the catalyst inlet between the reactor side walls, and the catalyst inlet between the draft tube and the reactor side wall contains cobalt acetate, manganese acetate, potassium bromide, potassium acetate, and acetic acid, and the molar ratio of cobalt acetate to manganese acetate therein is 0.25 to 4:1, preferably 0.4 to 3:1.

[0083] According to a preferred embodiment of the present invention, preferably, the reaction temperature is 150 to 240 °C, preferably 180 to 210 °C.

[0084] According to a preferred embodiment of the present invention, preferably, the reaction pressure is 1.5 to 6.0 MPa, preferably 3.0 to 5.0 MPa.

[0085] According to a preferred embodiment of the present invention, the residence time of the 2,6 - diisopropylnaphthalene raw material in the oxidation reactor is preferably 0.5 to 2.0 h, more preferably 0.75 to 1.5 h.

[0086] The advantages of the present invention are illustrated by the following examples, but the present invention is not limited thereto.

[0087] Example 1

[0088] Adopt Figure 2 the system shown.

[0089] Prepare the catalyst: Based on a total amount of 100 g, 2.22 g of cobalt acetate tetrahydrate, 4.04 g of manganese acetate tetrahydrate, 3.64 g of potassium bromide, 4.50 g of potassium acetate, and 85.60 g of acetic acid. After fully stirring the above catalyst, pre - heat it to 150 °C to make it in a solution state. Pre - heat a certain amount of 2,6 - diisopropylnaphthalene to 150 °C to melt it into a liquid state.

[0090] Pre - add 1000.00 g of 2,6 - diisopropylnaphthalene and 8176.92 g of the above catalyst to the oxidation reactor (such as Figure 2, (20.0 L), start the stirrer paddle 6a in the draft tube 8a and set its rotation speed to 60 rpm. When the temperature is raised to 160 °C, introduce air into the oxidation reactor through the air inlet 2a. The air flow rate is 10.0 L / min (standard state), the partial pressure of air is controlled at 0.5 MPa, and the pressure in the reaction kettle is controlled at 4.0 MPa by the back pressure valve behind the tail gas outlet 9a. Continuously discharge the tail gas generated by the reaction through the tail gas outlet 9a. The reaction temperature is controlled at 200 °C. After reacting for 30 minutes, add liquid 2,6 - diisopropylnaphthalene and the catalyst to the bottom position of the oxidation reactor at rates of 10.00 g / min and 81.77 g / min respectively through the 2,6 - diisopropylnaphthalene raw material inlet 3a and the catalyst main inlet 4a. After reacting for 30 minutes, continuously discharge the material from the crude 2,6 - naphthalenedicarboxylic acid slurry outlet 5a at a rate of 91.77 g / min (crude 2,6 - naphthalenedicarboxylic acid oxidation slurry), and collect the crude 2,6 - naphthalenedicarboxylic acid oxidation slurry. Based on 100 g of the above - mentioned crude 2,6 - naphthalenedicarboxylic acid oxidation slurry, perform the following treatments in sequence: directly pressure - filter for 10 min at a pressure difference of 0.5 MPa to obtain filter cake 1; add 50 g of acetic acid to filter cake 1, mix well, and then pressure - filter for 5 min at a pressure difference of 0.2 MPa to obtain filter cake 2; add 25 g of acetic acid to filter cake 2 and then pressure - filter for 5 min at a pressure difference of 0.2 MPa to obtain filter cake 3; add 50 g of pure water to filter cake 3 and then pressure - filter for 5 min at a pressure difference of 0.2 MPa to obtain filter cake 4; add 25 g of pure water to filter cake 4 and then pressure - filter for 5 min at a pressure difference of 0.2 MPa to obtain filter cake 5; place filter cake 5 in an oven at 120 °C for 24 h to dry, and send the dried sample for analysis. The analysis results are shown in Table 1.

[0091] Example 2

[0092] Use Figure 3 the system shown.

[0093] Prepare the catalyst: Catalyst 1 (based on a total of 100 g, 2.22 g of cobalt acetate tetrahydrate, 4.04 g of manganese acetate tetrahydrate, 3.64 g of potassium bromide, 4.50 g of potassium acetate, 85.60 g of acetic acid) and Catalyst 2 (based on a total of 100 g, 4.38 g of cobalt acetate tetrahydrate, 3.95 g of manganese acetate tetrahydrate, 3.56 g of potassium bromide, 4.40 g of potassium acetate, 83.72 g of acetic acid). After fully stirring the above - mentioned catalysts, pre - heat them to 150 °C to make them in a solution state. Pre - heat a certain amount of 2,6 - diisopropylnaphthalene to 150 °C to make it melt into a liquid state.

[0094] Pre - add 1000.00 g of 2,6 - diisopropylnaphthalene and 8176.92 g of the above - mentioned Catalyst 1 to the oxidation reactor (such as Figure 3, (20.0 L), start the stirrer 6b in the draft tube 8b and set its rotation speed to 60 rpm. When the temperature is raised to 160 °C, introduce air into the oxidation reactor through the air inlet 2b. The air flow rate is 10.0 L / min (standard state), and the partial pressure of air is controlled at 0.5 MPa. The pressure in the reaction kettle is controlled at 4.0 MPa by the back pressure valve behind the tail gas outlet 9b, and the tail gas generated by the reaction is continuously discharged through the tail gas outlet 9b. The reaction temperature is controlled at 200 °C. After reacting for 30 minutes, liquid 2,6 - diisopropylnaphthalene, catalyst 1, and catalyst 2 are respectively added to the oxidation reactor through the 2,6 - diisopropylnaphthalene raw material inlet 3b, the main catalyst inlet 4b, and the catalyst draft tube inlet 1b at a rate of 10.00 g / min, 73.59 g / min, and 8.36 g / min. After reacting for 30 minutes, continuously discharge the material from the crude 2,6 - naphthalenedicarboxylic acid slurry outlet 5b at a rate of 91.95 g / min, and collect the crude 2,6 - naphthalenedicarboxylic acid oxidation slurry. Based on 100 g of the above - mentioned crude 2,6 - naphthalenedicarboxylic acid oxidation slurry, the following treatments are carried out in sequence: directly pressure - filter for 10 min at a pressure difference of 0.5 MPa to obtain filter cake 1; add 50 g of acetic acid to filter cake 1, mix well, and then pressure - filter for 5 min at a pressure difference of 0.2 MPa to obtain filter cake 2; add 25 g of acetic acid to filter cake 2 and then pressure - filter for 5 min at a pressure difference of 0.2 MPa to obtain filter cake 3; add 50 g of pure water to filter cake 3 and then pressure - filter for 5 min at a pressure difference of 0.2 MPa to obtain filter cake 4; add 25 g of pure water to filter cake 4 and then pressure - filter for 5 min at a pressure difference of 0.2 MPa to obtain filter cake 5; place filter cake 5 in an oven and dry it at 120 °C for 24 h. Send the dried sample for analysis, and the analysis results are shown in Table 1.

[0095] Example 3

[0096] Adopt Figure 4 the system shown for the experiment.

[0097] Prepare the catalysts: Catalyst 1 (based on a total of 100 g, 2.22 g of cobalt acetate tetrahydrate, 4.04 g of manganese acetate tetrahydrate, 3.64 g of potassium bromide, 4.50 g of potassium acetate, 85.60 g of acetic acid) and Catalyst 2 (based on a total of 100 g, 8.40 g of cobalt acetate tetrahydrate, 3.78 g of manganese acetate tetrahydrate, 3.41 g of potassium bromide, 4.22 g of potassium acetate, 80.19 g of acetic acid). After fully stirring the above - mentioned catalysts, pre - heat them to 150 °C to make them in a solution state. Pre - heat a certain amount of 2,6 - diisopropylnaphthalene to 150 °C to make it melt into a liquid state.

[0098] Pre - add 1000.00 g of 2,6 - diisopropylnaphthalene and 8176.92 g of the above - mentioned Catalyst 1 to the oxidation reactor (such as Figure 4, (20.0 L), start the stirrer paddle 6c in the draft tube 8c and set its rotation speed to 60 rpm. When the temperature is raised to 160 °C, introduce air into the oxidation reactor from the air inlet 2c. The air flow rate is 10.0 L / min (standard state), and the partial pressure of air is controlled at 0.5 MPa. The pressure in the reaction kettle is controlled at 4.0 MPa by the back pressure valve behind the tail gas outlet 9c, and the tail gas generated by the reaction is continuously discharged through 9c. The reaction temperature is controlled at 200 °C. After reacting for 30 minutes, liquid 2,6 - diisopropylnaphthalene, catalyst 1, and catalyst 2 are respectively added to the oxidation reactor at a rate of 10.00 g / min, 73.59 g / min, and 8.73 / min through the 2,6 - diisopropylnaphthalene raw material inlet 3c, the main catalyst inlet 4c, and the catalyst inlet 7c between the draft tube 8c and the reactor side wall. After reacting for 30 minutes, continuously discharge the material from the crude 2,6 - naphthalenedicarboxylic acid slurry outlet 5c at a rate of 92.32 g / min, and collect the crude 2,6 - naphthalenedicarboxylic acid oxidation slurry. Based on 100 g of the above - mentioned crude 2,6 - naphthalenedicarboxylic acid oxidation slurry, perform the following treatments in sequence: directly filter press at a pressure difference of 0.5 MPa for 10 min to obtain filter cake 1; add 50 g of acetic acid to filter cake 1, mix well, and then filter press at a pressure difference of 0.2 MPa for 5 min to obtain filter cake 2; add 25 g of acetic acid to filter cake 2 and filter press at a pressure difference of 0.2 MPa for 5 min to obtain filter cake 3; add 50 g of pure water to filter cake 3 and filter press at a pressure difference of 0.2 MPa for 5 min to obtain filter cake 4; add 25 g of pure water to filter cake 4 and filter press at a pressure difference of 0.2 MPa for 5 min to obtain filter cake 5; place filter cake 5 in an oven at 120 °C for 24 h to dry, and send the dried sample for analysis. The analysis results are shown in Table 1.

[0099] Example 4

[0100] Adopt Figure 5 the system shown for the experiment.

[0101] Prepare the catalysts: Catalyst 1 (based on a total of 100 g, 2.22 g of cobalt acetate tetrahydrate, 4.04 g of manganese acetate tetrahydrate, 3.64 g of potassium bromide, 4.50 g of potassium acetate, 85.60 g of acetic acid), Catalyst 2 (based on a total of 100 g, 4.38 g of cobalt acetate tetrahydrate, 3.95 g of manganese acetate tetrahydrate, 3.56 g of potassium bromide, 4.40 g of potassium acetate, 83.71 g of acetic acid), and Catalyst 3 (based on a total of 100 g, 8.40 g of cobalt acetate tetrahydrate, 3.78 g of manganese acetate tetrahydrate, 3.41 g of potassium bromide, 4.22 g of potassium acetate, 80.19 g of acetic acid). After fully stirring the above - mentioned catalysts, pre - heat them to 150 °C to make them in a solution state. Pre - heat a certain amount of 2,6 - diisopropylnaphthalene to 150 °C to make it melt into a liquid state.

[0102] 1000.00 g of 2,6-diisopropylnaphthalene and 8176.92 g of the above catalyst 1 were pre-charged into an oxidation reactor (eg Figure 5 , 20.0L), the stirring paddle 6d in the guide tube 8d was turned on and set to a speed of 60rpm. When the temperature was raised to 160°C, air was introduced into the oxidation reactor from the air inlet 2d, with an air flow rate of 10.0L / min (standard state), and the air partial pressure was controlled at 0.5MPa. The pressure in the reactor was controlled to be 4.0MPa by the back pressure valve behind the tail gas outlet 9d, and the tail gas generated by the reaction was continuously discharged through the tail gas outlet 9d. The reaction temperature was controlled at 200°C. After reacting for 30 minutes, liquid 2,6-diisopropylnaphthalene, catalyst 1, catalyst 2 and catalyst 3 were added into the oxidation reactor at a rate of 10.00g / min, 73.59g / min, 4.18g / min and 4.36 / min respectively through the 2,6-diisopropylnaphthalene raw material inlet 3d, the catalyst main inlet 4d, the guide tube inlet 1d and the catalyst inlet 7d between the guide tube and the reactor side wall. After reacting for 30 minutes, the crude 2,6-naphthalene dicarboxylic acid slurry was continuously discharged at a rate of 92.13 g / min from the crude 2,6-naphthalene dicarboxylic acid slurry outlet 5d, and the crude 2,6-naphthalene dicarboxylic acid oxidation slurry was collected. 100 g of the above crude 2,6-naphthalenedicarboxylic acid oxidation slurry was sequentially treated as follows: direct pressure filtration at a pressure difference of 0.5 MPa for 10 min to obtain filter cake 1; 50 g of acetic acid was added to filter cake 1 and mixed thoroughly, and then pressure filtration was performed at a pressure difference of 0.2 MPa for 5 min to obtain filter cake 2; 25 g of acetic acid was added to filter cake 2 and then pressure filtration was performed at a pressure difference of 0.2 MPa for 5 min to obtain filter cake 3; 50 g of pure water was added to filter cake 3 and then pressure filtration was performed at a pressure difference of 0.2 MPa for 5 min to obtain filter cake 4; 25 g of pure water was added to filter cake 4 and then pressure filtration was performed at a pressure difference of 0.2 MPa for 5 min to obtain filter cake 5; filter cake 5 was placed in an oven at 120° C. for 24 h to dry, and the dried sample was sent for analysis. The analysis results are shown in Table 1.

[0103] Example 5

[0104] The method of Example 4 was followed, except that the three catalysts used were the same catalyst: 2.22 g of cobalt acetate tetrahydrate, 4.04 g of manganese acetate tetrahydrate, 3.64 g of potassium bromide, 4.50 g of potassium acetate, and 85.60 g of acetic acid, based on a total amount of 100 g. Filter cake 6 was obtained accordingly, and the filter cake 6 was placed in an oven at 120° C. for 24 hours for drying, and the dried sample was sent for analysis, and the analysis results are shown in Table 1.

[0105] Comparative Example 1

[0106] Preparation of catalyst: Based on a total amount of 100 g, 2.22 g of cobalt acetate tetrahydrate, 4.04 g of manganese acetate tetrahydrate, 3.64 g of potassium bromide, 4.50 g of potassium acetate, and 85.60 g of acetic acid. After fully stirring the above catalyst, it is preheated to 150 °C to make it in a solution state. A certain amount of 2,6-diisopropylnaphthalene is preheated to 150 °C to make it melt into a liquid state.

[0107] 1000.00 g of 2,6-diisopropylnaphthalene and 8176.92 g of the above catalyst are pre-added to an oxidation reactor (such as Figure 1 , 20.0 L). Start the stirring paddle 6 and set its rotation speed to 60 rpm. When the temperature is raised to 160 °C, air is introduced into the oxidation reactor through the air inlet 2, with an air flow rate of 10.0 L / min (standard state), the air partial pressure is controlled at 0.5 MPa, and the pressure in the reaction kettle is controlled at 4.0 MPa by the back pressure valve behind the tail gas outlet 9. The tail gas generated by the reaction is continuously discharged through the tail gas outlet 9. The reaction temperature is controlled at 200 °C. After reacting for 30 minutes, the liquid 2,6-diisopropylnaphthalene and the catalyst are respectively added to the bottom position of the oxidation reactor through the 2,6-diisopropylnaphthalene raw material inlet 3 and the catalyst main inlet 4 at a rate of 10.00 g / min and 81.77 g / min. After reacting for 30 minutes, continuous discharging is carried out from the crude 2,6-naphthalenedicarboxylic acid slurry outlet 5 at a rate of 91.77 g / min (crude 2,6-naphthalenedicarboxylic acid oxidation slurry), and the crude 2,6-naphthalenedicarboxylic acid oxidation slurry is collected. Based on 100 g of the above crude 2,6-naphthalenedicarboxylic acid oxidation slurry, the following treatments are carried out in sequence: direct pressure filtration for 10 min with a pressure difference of 0.5 MPa to obtain filter cake 1; add 50 g of acetic acid to filter cake 1, mix well, and then carry out pressure filtration for 5 min with a pressure difference of 0.2 MPa to obtain filter cake 2; add 25 g of acetic acid to filter cake 2 and carry out pressure filtration for 5 min with a pressure difference of 0.2 MPa to obtain filter cake 3; add 50 g of pure water to filter cake 3 and carry out pressure filtration for 5 min with a pressure difference of 0.2 MPa to obtain filter cake 4; add 25 g of pure water to filter cake 4 and carry out pressure filtration for 5 min with a pressure difference of 0.2 MPa to obtain filter cake 5; place filter cake 5 in an oven at 120 °C for 24 h for drying, and send the dried sample for analysis. The analysis results are shown in Table 1.

[0108] Table 1 Summary of analysis results of crude 2,6-naphthalenedicarboxylic acid oxidation slurry samples

[0109]

[0110] As can be seen from the results in Table 1 above, the reaction effect is improved to a certain extent by adding a draft tube compared with no draft tube (the purity of crude 2,6-naphthalenedicarboxylic acid is increased and the impurity content is reduced, the same below). The reaction effect is more significantly improved by using the catalyst inlet at the draft tube inlet or between the draft tube and the reactor side wall and adding a draft tube compared with no draft tube. The reaction effect is even more significantly improved by using the catalyst inlet at the draft tube inlet, the catalyst inlet between the draft tube and the reactor side wall, and adding a draft tube compared with no draft tube.

[0111] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A reaction system for preparing 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-diisopropylnaphthalene, characterized in that, the system comprises: an oxidation reactor, a solid-liquid mixing unit disposed inside the oxidation reactor and capable of material circulation with the oxidation reactor, the solid-liquid mixing unit being arranged such that the solid and liquid inside the mixing unit can be dynamically mixed, the length, width and height of the solid-liquid mixing unit being all smaller than those of the oxidation reactor, and the oxidation reactor comprising: a gas inlet, a 2,6-diisopropylnaphthalene raw material inlet, a main catalyst inlet, a crude 2,6-naphthalenedicarboxylic acid slurry outlet, and a tail gas outlet; the solid-liquid mixing unit comprises: a draft tube capable of material circulation with the oxidation reactor and a stirrer, the stirrer comprising a stirring paddle and a stirring shaft, and the stirring paddle being disposed inside the draft tube; the gas inlet is disposed at the bottom of the oxidation reactor; the 2,6-diisopropylnaphthalene raw material inlet is disposed at the bottom of the oxidation reactor; the main catalyst inlet is disposed at the bottom of the oxidation reactor; the crude 2,6-naphthalenedicarboxylic acid slurry outlet is disposed in the middle and lower part of the oxidation reactor; the tail gas outlet is disposed at the top of the oxidation reactor; the oxidation reactor is provided with a catalyst draft tube inlet and a catalyst inlet between the draft tube and the side wall of the oxidation reactor.

2. The reaction system according to claim 1, wherein, the oxidation reactor is provided with a catalyst mixing unit inlet for supplying a catalyst to the solid-liquid mixing unit.

3. The reaction system according to claim 2, wherein, the height at which the catalyst mixing unit inlet is disposed is between the lower end face of the solid-liquid mixing unit and the upper end face of the oxidation reactor.

4. The reaction system according to claim 3, wherein, the height at which the catalyst mixing unit inlet is disposed is between the upper end face of the stirring paddle and the upper edge of the draft tube.

5. The reaction system according to claim 2, wherein, the main catalyst inlet and the catalyst mixing unit inlet are arranged such that the weight ratio of the flow rate of the main catalyst inlet to the flow rate of the catalyst mixing unit inlet is 4 to 49:

1.

6. The reaction system according to claim 5, wherein, the main catalyst inlet and the catalyst mixing unit inlet are arranged such that the weight ratio of the flow rate of the main catalyst inlet to the flow rate of the catalyst mixing unit inlet is 6 to 38:

1.

7. The reaction system according to claim 6, wherein, the main catalyst inlet and the catalyst mixing unit inlet are arranged such that the weight ratio of the flow rate of the main catalyst inlet to the flow rate of the catalyst mixing unit inlet is 8 to 19:

1.

8. The reaction system according to claim 1, wherein, the oxidation reactor is provided with a catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor for introducing a catalyst into the gap space between the solid-liquid mixing unit and the oxidation reactor.

9. The reaction system according to claim 8, wherein, the height of the catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor is between the lower edge and the upper edge of the solid-liquid mixing unit.

10. The reaction system according to claim 9, wherein, the height of the catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor is at a position close to the upper edge between the lower edge and the upper edge of the solid-liquid mixing unit.

11. The reaction system according to claim 10, wherein, the height of the catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor is located at a position close to the upper edge between the lower edge and the upper edge of the draft tube.

12. The reaction system according to claim 8, wherein, the setting of the catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor is such that the weight ratio of the flow rate of the main catalyst inlet to the flow rate of the catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor is 4 to 49:

1.

13. The reaction system according to claim 12, wherein, the setting of the catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor is such that the weight ratio of the flow rate of the main catalyst inlet to the flow rate of the catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor is 6 to 38:

1.

14. The reaction system according to claim 13, wherein, the setting of the catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor is such that the weight ratio of the flow rate of the main catalyst inlet to the flow rate of the catalyst inlet between the solid-liquid mixing unit and the side wall of the oxidation reactor is 15 to 17:

1.

15. The reaction system according to claim 1, wherein, the gas inlet, the 2,6-diisopropylnaphthalene raw material inlet, and the main catalyst inlet are arranged at the bottom of the oxidation reactor and point to the lower opening of the solid-liquid mixing unit.

16. The reaction system according to claim 1, wherein, the height at which the crude 2,6-naphthalenedicarboxylic acid slurry outlet is arranged is between the lower edge and the upper edge of the solid-liquid mixing unit.

17. The reaction system according to claim 16, wherein, the height at which the crude 2,6-naphthalenedicarboxylic acid slurry outlet is arranged is at a position between the lower edge and the upper edge of the solid-liquid mixing unit, close to the lower edge of the solid-liquid mixing unit.

18. The reaction system according to claim 1, wherein, the height at which the catalyst draft tube inlet is arranged is between the upper end face of the stirring paddle and the upper edge of the draft tube; the height of the catalyst inlet between the draft tube and the side wall of the oxidation reactor is between the lower edge and the upper edge of the draft tube; the setting of the main catalyst inlet, the setting of the catalyst inlet between the draft tube and the side wall of the oxidation reactor, and the setting of the main catalyst inlet are such that the weight ratio of the flow rate of the main catalyst inlet to the flow rate of the catalyst draft tube inlet is 6 to 38:1, the weight ratio of the flow rate of the main catalyst inlet to the flow rate of the catalyst inlet between the draft tube and the reactor side wall is 6 to 38:1, and the weight ratio of the flow rate of the catalyst draft tube inlet to the flow rate of the catalyst inlet between the draft tube and the reactor side wall is 0.5 to 2:

1.

19. The reaction system according to claim 18, wherein, the height of the catalyst inlet between the draft tube and the side wall of the oxidation reactor is located at a position close to the upper edge between the lower edge and the upper edge of the draft tube; The setting of the main catalyst inlet, the setting of the catalyst inlet between the draft tube and the side wall of the oxidation reactor, and the setting of the main catalyst inlet make the weight ratio of the flow rate at the main catalyst inlet to the flow rate at the catalyst inlet of the draft tube 8-19:1, the weight ratio of the flow rate at the main catalyst inlet to the flow rate at the catalyst inlet between the draft tube and the reactor side wall 15-17:1, and the weight ratio of the flow rate at the catalyst inlet of the draft tube to the flow rate at the catalyst inlet between the draft tube and the reactor side wall 0.6-0.98:

1.

20. A method for preparing 2,6-naphthalenedicarboxylic acid by oxidizing 2,6-diisopropylnaphthalene, characterized in that, this method is carried out in the reaction system described in any one of claims 1-19, wherein this method includes: The 2,6-diisopropylnaphthalene raw material and the catalyst enter the oxidation reactor and / or the solid-liquid mixing unit from their respective inlets, and under the action of the solid-liquid mixing unit, they fully contact with the oxygen in the air entering from the gas inlet to react. The unreacted air, water vapor and the gaseous products generated by oxidation leave the oxidation reactor through the tail gas outlet, and the crude 2,6-naphthalenedicarboxylic acid slurry leaves the oxidation reactor through the crude 2,6-naphthalenedicarboxylic acid slurry outlet.

21. The method according to claim 20, wherein, the catalyst contains cobalt acetate, manganese acetate, bromide, potassium acetate and acetic acid, wherein the molar ratio of cobalt acetate to manganese acetate is 0.25-4:

1.

22. The method according to claim 21, wherein, the molar ratio of cobalt acetate to manganese acetate is 0.4-3:

1.

23. The method according to claim 20, wherein, in the reaction system, the catalyst at the main catalyst inlet contains cobalt acetate, manganese acetate, bromide, potassium acetate and acetic acid; in the reaction system, the catalyst at the catalyst inlet between the draft tube and the side wall of the oxidation reactor contains cobalt acetate, manganese acetate, bromide, potassium acetate and acetic acid; in the reaction system, the catalyst at the catalyst mixing unit inlet contains cobalt acetate, manganese acetate, bromide, potassium acetate and acetic acid; The reaction conditions include: the reaction temperature is 150-240 °C; and / or the reaction pressure is 1.5-6.0 MPa; and / or the residence time of the 2,6-diisopropylnaphthalene raw material in the oxidation reactor is 0.5-2 h; The flow rate of air ensures that the oxygen is in excess relative to the reaction theory and the oxygen content in the exhaust gas does not exceed 8% by volume.

24. The method according to claim 23, wherein, in the reaction system, the catalyst at the catalyst inlet between the draft tube and the side wall of the oxidation reactor contains cobalt acetate, manganese acetate and acetic acid; in the reaction system, the catalyst at the catalyst mixing unit inlet contains cobalt acetate, manganese acetate and acetic acid; the bromide is one or more of potassium bromide, tetrabromoethane and ammonium bromide; The reaction conditions include: the reaction temperature is 180-210 °C; and / or the reaction pressure is 3.0-5.0 MPa; and / or the residence time of the 2,6-diisopropylnaphthalene raw material in the oxidation reactor is 0.75-1.5 h.

25. The method according to claim 24, wherein, the bromide is potassium bromide.

26. The method according to claim 23, wherein, The weight ratio of the flow rate at the main catalyst inlet to the flow rate at the inlet of the catalyst guide cylinder is 6 to 38:1; and / or The weight ratio of the flow rate at the main catalyst inlet to the flow rate at the catalyst inlet between the guide cylinder and the reactor sidewall is 6 to 38:1; and / or The weight ratio of the flow rate at the inlet of the catalyst guide cylinder to the flow rate at the catalyst inlet between the guide cylinder and the reactor sidewall is 0.5 to 2:

1.

27. The method according to claim 26, wherein, The weight ratio of the flow rate at the main catalyst inlet to the flow rate at the inlet of the catalyst guide cylinder is 8 to 19:1; and / or The weight ratio of the flow rate at the main catalyst inlet to the flow rate at the catalyst inlet between the guide cylinder and the reactor sidewall is 15 to 17:1; and / or The weight ratio of the flow rate at the inlet of the catalyst guide cylinder to the flow rate at the catalyst inlet between the guide cylinder and the reactor sidewall is 0.6 to 0.98:

1.

28. The method according to claim 20, wherein, The catalyst includes: a first catalyst, a second catalyst, and a third catalyst; The first catalyst contains: cobalt acetate, manganese acetate, potassium bromide, potassium acetate, and acetic acid. Based on the total weight of the first catalyst, cobalt acetate is 1-3% by weight, manganese acetate is 3-5% by weight, potassium bromide is 2-4% by weight, potassium acetate is 4-6% by weight, acetic acid is 80-90% by weight, and the weight ratio of cobalt acetate to manganese acetate is 0.4-0.6; The second catalyst contains: cobalt acetate, manganese acetate, potassium bromide, potassium acetate, and acetic acid. Based on the total weight of the second catalyst, cobalt acetate is 4-10% by weight, manganese acetate is 3.5-6% by weight, potassium bromide is 3-5% by weight, potassium acetate is 4-6% by weight, acetic acid is 80-90% by weight, and the weight ratio of cobalt acetate to manganese acetate is 1.1-2.2; The third catalyst contains: cobalt acetate, manganese acetate, potassium bromide, potassium acetate, and acetic acid. Based on the total weight of the third catalyst, cobalt acetate is 8-15% by weight, manganese acetate is 3.5-6% by weight, potassium bromide is 3-5% by weight, potassium acetate is 4-6% by weight, acetic acid is 80-90% by weight, and the weight ratio of cobalt acetate to manganese acetate is 2.22-2.

55.

29. The method according to claim 28, wherein, The first catalyst enters from the main catalyst inlet, the second catalyst enters from the inlet of the catalyst guide cylinder, and the third catalyst enters from the catalyst inlet between the guide cylinder and the reactor sidewall; The weight ratio of the flow rates of the first catalyst, the second catalyst, and the third catalyst is 9-18:0.5-2:

1.

30. The method according to claim 29, wherein, The weight ratio of the flow rates of the first catalyst, the second catalyst, and the third catalyst is 15-17:0.6-0.98:1.

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