Terephthalic acid and preparation method thereof

Abstract

The invention discloses terephthalic acid and a preparation method thereof, and belongs to the field of fine chemical engineering. The method comprises the following steps: adding a catalyst, a co-catalyst and a solvent into p-xylene, blending, pumping into a reaction kettle, introducing oxidizing gas, inert gas and a co-catalyst gas at the same time, carrying out an oxidation reaction, and after the reaction is finished, carrying out cooling crystallization, centrifugal filtration, washing and drying to obtain terephthalic acid, the catalyst is cobalt acetate, manganese acetate and hydrobromic acid; the promoter is nickel acetate; the assistant gas is CO2. In order to reduce the use amount and the cost of a terephthalic acid oxidation catalyst, reduce the generation amount of byproducts, improve the product quality and the like, the invention provides the preparation method which takes nickel acetate and CO2 as cocatalysts and cobalt acetate, manganese acetate and hydrobromic acid as catalysts, so that the yield and the purity of terephthalic acid can be effectively improved, the content of p-carboxybenzaldehyde is reduced, and the production cost is reduced. The reaction time is shortened, the purification cost is saved, and industrial production of the process is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of fine chemicals, and in particular relates to terephthalic acid and a preparation method thereof. Background Art

[0002] Terephthalic acid is currently the world's most produced dicarboxylic acid, primarily used in the production of polyethylene terephthalate (PET). PET has a wide range of applications, including spinning into polyester fibers for clothing and textiles; forming thin films for recording, video, and film substrates, insulation films, and product packaging; blowing plastics into various bottles, such as cola and mineral water bottles; and manufacturing electrical components, bearings, and gears.

[0003] The liquid-phase oxidation of p-xylene is the core of the purified terephthalic acid (PTA) production process. It involves an oxidation reaction using acetic acid as the solvent, cobalt acetate, manganese acetate, and bromide as catalysts, and oxygen as the oxidant. The p-xylene oxidation process is a complex, coupled dissolution-reaction-crystallization-solvent evaporation-heat transfer process, with the primary and secondary reactions following the free radical chain reaction mechanism of hydrocarbon liquid-phase oxidation. The reaction occurs under high temperature and pressure, with a very high reaction rate and a large amount of heat released during the reaction, approximately 1.3×10 6 J / kg. This reaction is characterized by high conversion, high yield, and low impurity content, the main impurity being p-carboxybenzaldehyde. Conventionally produced terephthalic acid cannot be directly used in the production of polyethylene terephthalate and must be further purified to reduce the p-carboxybenzaldehyde content to less than 100 ppm.

[0004] This reaction process has been extensively researched worldwide. With the increasing maturity of oxidation technology and intensified competition in the terephthalic acid industry, optimizing reaction conditions to produce high-quality terephthalic acid more efficiently and energy-efficiently is a topic of considerable interest. Summary of the Invention

[0005] In order to overcome the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a terephthalic acid and a preparation method thereof, so as to solve the technical problem of high content of the impurity p-carboxybenzaldehyde in the existing terephthalic acid preparation method.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The invention discloses a method for preparing terephthalic acid, comprising the following steps: adding a catalyst, a catalyst promoter and a solvent to p-xylene; after the mixture is prepared, injecting the mixture into a reaction kettle; and simultaneously introducing an oxidizing gas, an inert gas and a catalyst promoter to carry out an oxidation reaction; after the reaction is completed, cooling and crystallizing, centrifuging, filtering, washing and drying to obtain terephthalic acid; The catalyst is cobalt acetate, manganese acetate and hydrobromic acid; the co-catalyst is nickel acetate; and the co-catalyst gas is CO2.

[0007] Preferably, the mass ratio of p-xylene, cobalt acetate, manganese acetate, hydrobromic acid and nickel acetate is (50-100): (0.1-0.2): (0.1-0.2): (0.4-0.8): (0.1-0.3).

[0008] Preferably, the solvent is acetic acid; the mass ratio of p-xylene to acetic acid is (50-100): (300-1200).

[0009] Preferably, the intake concentration of CO2 is 20%-60%.

[0010] Preferably, the oxidizing gas is oxygen, and the intake concentration of oxygen is 21%.

[0011] Preferably, the temperature of the oxidation reaction is 180-200° C.; and the time of the oxidation reaction is 1-3 h.

[0012] Preferably, the reactor is a high-temperature and high-pressure titanium reactor; the reactor adopts continuous operation, and the feed rate is 0.5-1.0 ml / min.

[0013] Preferably, the pressure in the reactor is 2.0-2.5 MPa.

[0014] Preferably, the temperature of cooling crystallization is 10-20°C; the washing condition is to use hot acetic acid at 60-70°C for washing; and the drying condition is to dry at 100-120°C for 2-3h.

[0015] The present invention also discloses terephthalic acid, which is prepared by the above preparation method, wherein the yield of terephthalic acid is 95.6%-98.3%, the purity of terephthalic acid is 99.2%-99.5%, and the content of p-carboxybenzaldehyde does not exceed 0.5%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a method for preparing terephthalic acid, namely, a method for preparing terephthalic acid by liquid-phase oxidation of p-xylene. The method increases the reaction rate, shortens the reaction time, improves the synergistic activity of the Co-Mn-Br ternary catalyst, and improves the yield and purity of the terephthalic acid product by adding a certain amount of co-catalysts, nickel acetate and CO2. The problem of high p-carboxybenzaldehyde content in the terephthalic acid product can be effectively reduced, and the method is suitable for industrial application, which can effectively save the purification cost of terephthalic acid and promote the development and application of high-performance polyethylene terephthalate materials. In the co-catalyst used in the present invention, CO2 can form peroxycarbonate in the solution to promote Co 2+ and Mn2+ Oxidation to generate Co 3+ 、Mn 3+ Thereby accelerating the reaction rate of the free radical chain. The Ni ions of nickel acetate can form a weak complex with Co, redistribute the balance of Co-Mn dimer and monomer, and strengthen the synergistic reduction effect of Co and Mn. The simultaneous use of CO2 and Ni can play a synergistic promoting role, accelerate the reaction rate, increase the degree of reaction, and thus improve the yield and purity of the product. The present invention provides a method for preparing terephthalic acid by liquid-phase oxidation of p-xylene using CO2 and nickel acetate as co-catalysts. The reaction time of traditional methods for liquid-phase oxidation of p-xylene to terephthalic acid is generally 3-5 hours. The reaction time of this method is 1-3 hours, which greatly shortens the reaction time, improves product production capacity, saves energy consumption in the reaction process, and has great economic benefits and commercial value. 2. The yield and purity of the product are high.

[0017] Furthermore, excessive CO2 inlet concentration reduces the contact area between oxygen and para-xylene, resulting in a reduced oxidation rate and incomplete oxidation. Excessive Ni ions can affect the formation of Co-Mn dimers, reducing catalyst activity and thus the reaction rate.

[0018] The present invention also discloses terephthalic acid produced by the above-mentioned preparation method, wherein the yield of the terephthalic acid is 95.6%-98.3%, the purity is 99.2%-99.5%, and the content of p-carboxybenzaldehyde does not exceed 0.5%. Compared with the yield of 92.3%-95.4% and the purity of 95.8%-98.2% in the current technology, the yield is significantly improved, the p-carboxybenzaldehyde content in the terephthalic acid product is effectively reduced, and the industrial application of the method and the promotion of high-performance polyester materials are facilitated. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a diagram of the device for preparing terephthalic acid by liquid-phase oxidation of p-xylene disclosed in the present invention; Figure 2 This is the high performance liquid chromatogram of terephthalic acid disclosed in Example 1 of the present invention; Among them, 1-needle valve; 2-temperature sensor; 3-pressure sensor; 4-stirring motor; 5-pressure reducing valve; 6-gas flow meter; 7-metering pump; 8-high performance liquid chromatograph; 9-condensation tank; 10-gas buffer tank; 11-exhaust gas absorption bottle; 12-exhaust gas analyzer; 13-vent. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0021] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0022] The present invention is described in further detail below with reference to the accompanying drawings: The production of terephthalic acid from the liquid-phase oxidation of p-xylene has always been plagued by high levels of p-carboxybenzaldehyde in the product, necessitating purification of the terephthalic acid for use in the production of polyethylene terephthalate, a high-performance polyester material. By adjusting the catalyst ratio and adding a suitable amount of a co-catalyst, the reaction time can be shortened while increasing product yield and purity. This significantly improves production efficiency, reduces production and purification costs, and promotes the development of high-performance polyester materials.

[0023] The present invention discloses a method for preparing terephthalic acid, and the steps are as follows: The liquid phase oxidation method of terephthalic acid is as follows: p-xylene is used as the reaction raw material, and an oxidation reaction occurs with oxygen under the synergistic action of a catalyst and a catalyst promoter. After the reaction is completed, the obtained mixture is cooled and crystallized, centrifuged and filtered, and vacuum dried to obtain terephthalic acid crystals.

[0024] Specifically, by mass, the air in the reactor is replaced with nitrogen at room temperature. After the air is completely replaced, the temperature is gradually raised to 180°C. Nitrogen is continued to be introduced and pressurized to 2 MPa. CO2 and oxygen are then introduced, with the CO2 inlet concentration controlled at 20%-60% and the oxygen inlet concentration at 21%. The remaining inlet concentration is compensated by nitrogen. 50-100 parts of p-xylene, 0.1-0.2 parts of cobalt acetate, 0.1-0.2 parts of manganese acetate, 0.4-0.8 parts of hydrobromic acid, 0.1-0.3 parts of nickel acetate, and 300-1200 parts of acetic acid are taken. Part of the solvent, catalyst, and co-catalyst are added to the reactor. After the air replacement, temperature increase, and pressurization operations are completed, p-xylene is dissolved in the remaining solvent and pumped into the reactor using metering pump 7 at a certain feed rate of 0.5-1.0 ml / min. During the feeding process, the reactor temperature is maintained at 180-200°C and the pressure at 2.0-2.5 MPa. After the feeding is completed, the reaction is allowed to proceed for 1-3 hours to obtain a mixture containing terephthalic acid crystals. The mixture containing terephthalic acid crystals is cooled and crystallized at 10-20°C. After centrifugation and filtration, it is washed three times with hot acetic acid at 60-70°C and dried at 100-120°C for 2-3 hours to obtain terephthalic acid crystals.

[0025] See also Figure 1This diagram illustrates the apparatus for producing terephthalic acid by liquid-phase oxidation of p-xylene disclosed in the present invention. As can be seen, the system receives gases from various sources, such as CO2, N2, and O2, which enter the system through separate pipelines. A needle valve 1, located at the beginning of the gas pipeline, precisely controls the flow of gas entering the system, ensuring stability and accuracy during subsequent processing. A temperature sensor 2 and a pressure sensor 3, located immediately after needle valve 1, monitor the gas temperature and pressure in real time, respectively, ensuring safe and appropriate gas entry into the system. A stirring motor 4, located in the gas mixing area, thoroughly mixes the different gases or gas and liquid, ensuring a homogeneous sample and providing a reliable foundation for subsequent analysis. During gas flow, the pressure is first adjusted to a suitable level for system analysis by a pressure reducing valve 5. A gas flowmeter 6 then accurately measures the flow rate to ensure accurate analysis. Before entering the analysis area, the gas is cooled in a condenser 9 to remove any condensate. The gas then enters a gas buffer tank 10 to stabilize the gas pressure and ensure uniform gas supply to the analytical instruments. The metering pump 7, as a key component of gas delivery, is responsible for accurately delivering the treated gas to the high-performance liquid chromatograph 8 for analysis. The high-performance liquid chromatograph 8 is the core part of the system, using high-performance liquid chromatography technology to separate and analyze the various components in the gas and provide detailed analysis data. After the analysis is completed, the exhaust gas first enters the exhaust gas absorption bottle 11 for preliminary treatment to absorb or convert harmful components and reduce environmental pollution. The exhaust gas analyzer 12 further monitors the exhaust gas composition to ensure that the discharged gas meets environmental protection standards and protects the ecological environment. Finally, the treated exhaust gas is safely and environmentally friendly discharged into the atmosphere through the vent 13, completing the cycle of the entire gas analysis system.

[0026] The invention discloses a method for preparing terephthalic acid, which uses p-xylene as a raw material, undergoes an oxidation reaction with oxygen of a certain intake concentration under the action of a Co-Mn-Br ternary catalyst and a catalyst promoter, and obtains the product terephthalic acid after cooling, crystallization, centrifugal filtration and drying after the reaction is completed.

[0027] The catalyst is nickel acetate and CO2; the CO2 inlet concentration is 20-60%.

[0028] The mass ratio of cobalt acetate: manganese acetate: hydrobromic acid and nickel acetate is (0.1-0.2): (0.1-0.2): (0.4-0.8): (0.1-0.3).

[0029] The solvent used in the oxidation reaction is acetic acid, and the mass ratio of p-xylene to the solvent is (50-100): (300-1200).

[0030] The oxidation reaction temperature is 180-200°C, the oxidation reaction time is 1-3 h, and the intake oxygen concentration is 21%.

[0031] The oxidation reaction pressure is 2.0-2.5 MPa, and the continuous feed rate of the reactor is 0.5-1.0 ml / min.

[0032] The yield of terephthalic acid obtained by the above preparation method is 95.6%-98.3%, the purity of terephthalic acid is 99.2%-99.5%, and the content of p-carboxybenzaldehyde does not exceed 0.5%.

[0033] To reduce the usage and cost of a terephthalic acid oxidation catalyst, lower the amount of by-products generated, and improve product quality, the present invention provides a preparation method using nickel acetate and CO2 as catalyst promoters and cobalt acetate, manganese acetate, and hydrobromic acid as catalysts. The method can effectively improve the yield and purity of terephthalic acid, reduce the content of p-carboxybenzaldehyde, shorten the reaction time, save purification costs, and facilitate industrial production of the process.

[0034] The technical solution of the present invention is described in detail below through specific embodiments: Example 1 This embodiment provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.25 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 0.5 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 195°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 40%. Maintain these conditions for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain the mixed material.

[0035] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0036] The yield and purity were determined by weighing and using an Agilent 1260 high performance liquid chromatograph. The external standard method was used. The mobile phase consisted of methanol, water containing 0.1% (volume fraction) phosphoric acid, and acetonitrile. The mobile phase volume was 1 mL / min, the column temperature was 30°C, and the elution gradient was as shown in Table 1 below: Table 1 Mobile phase elution gradient for high performance chromatography analysis

[0037] See also Figure 2 This is a HPLC chromatogram of terephthalic acid disclosed in Example 1 of the present invention. As can be seen from the figure, the terephthalic acid peak appears around 4 minutes, the peak of its impurity, p-carboxybenzaldehyde, appears at 3.5 minutes, and the remaining peaks are solvent peaks. The figure clearly shows that the terephthalic acid in the product is very pure, and the content of the p-carboxybenzaldehyde impurity is very low, approximately less than 0.5%. This indicates that high-purity terephthalic acid has been successfully produced.

[0038] The yield calculation formula of terephthalic acid is:

[0039] The yield and purity of terephthalic acid crystals are shown in the following table: Table 2 Yield and purity of 2,6-NDA crystals obtained in Example 1 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 97.2% 99.32% 0.35% Example 2 This embodiment provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.18 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 0.5 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 195°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 25%. Maintain these conditions for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain the mixed material.

[0040] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0041] The yield and purity of the product terephthalic acid were determined by the method shown in Example 2. The results are shown in the following table: Table 3 Yield and purity of terephthalic acid crystals obtained in Example 2 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 97.5% 99.42% 0.27% Example 3 This embodiment provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.175 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 0.5 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 190°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 35%. Maintain these conditions for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain the mixed material.

[0042] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0043] The yield and purity of the product terephthalic acid were determined by the method shown in Example 3. The results are shown in the following table: Table 4 Yield and purity of terephthalic acid crystals obtained in Example 3 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 98.3% 99.5% 0.18% Example 4 This embodiment provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.175 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 0.5 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 190°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 60%. Maintain this condition for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain the mixed material.

[0044] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0045] The yield and purity of the product terephthalic acid were determined by the method shown in Example 4. The results are shown in the following table: Table 5 Yield and purity of terephthalic acid crystals obtained in Example 4 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 96.8% 99.35% 0.38% Example 5 This embodiment provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.175 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 0.5 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 190°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 50%. Maintain these conditions for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain the mixed material.

[0046] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0047] The yield and purity of the product terephthalic acid were determined by the method shown in Example 5. The results are shown in the following table: Table 6 Yield and purity of terephthalic acid crystals obtained in Example 5 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 97.1% 99.38% 0.32% Example 6 This embodiment provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.175 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 0.5 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 185°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 35%. Maintain these conditions for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain the mixed material.

[0048] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0049] The yield and purity of the product terephthalic acid were determined by the method shown in Example 6. The results are shown in the following table: Table 7 Yield and purity of terephthalic acid crystals obtained in Example 6 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 96.3% 99.25% 0.41% Example 7 This embodiment provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.175 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 0.5 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 200°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 35%. Maintain these conditions for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain the mixed material.

[0050] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0051] The yield and purity of the product terephthalic acid were determined by the method shown in Example 7. The results are shown in the following table: Table 8 Yield and purity of 2,6-NDA crystals obtained in Example 7 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 95.9% 99.3% 0.34% Example 8 This embodiment provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.285 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 1 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 200°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 35%. Maintain this condition for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain a mixed material.

[0052] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0053] The yield and purity of the product terephthalic acid were determined by the method shown in Example 8. The results are shown in the following table: Table 9 Yield and purity of terephthalic acid crystals obtained in Example 8 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 95.66% 99.2% 0.48% Example 9 This embodiment provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.175 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 1 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 200°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 35%. Maintain this condition for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain a mixed material.

[0054] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0055] The yield and purity of the product terephthalic acid were determined by the method shown in Example 9. The results are shown in the following table: Table 10 Yield and purity of terephthalic acid crystals obtained in Example 9 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 95.84% 99.31% 0.42% Example 10 This embodiment provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 75g of p-xylene, 300g of acetic acid, 0.1g of cobalt acetate, 0.1g of manganese acetate, 0.4g of hydrobromic acid, and 0.1g of nickel acetate. Open the lid of the titanium reactor and add 100g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the reactor to heat up to 180℃. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 0.75 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 180℃, the pressure to 2MPa, and the CO2 inlet concentration to 20%. Maintain this condition for 3 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain a mixed material.

[0056] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 15°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 65°C hot acetic acid, filtered, and placed in a vacuum oven set at 110°C for 3 hours to obtain terephthalic acid crystals.

[0057] The yield and purity of the product terephthalic acid were determined by the method shown in Example 10. The results are shown in the following table: Table 11 Yield and purity of terephthalic acid crystals obtained in Example 10 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 95.6% 99.20% 0.5% Example 11 This embodiment provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 100 g of p-xylene, 1200 g of acetic acid, 0.2 g of cobalt acetate, 0.2 g of manganese acetate, 0.8 g of hydrobromic acid, and 0.3 g of nickel acetate. Open the lid of the titanium reactor and add 600 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 0.5 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 200°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 40%. Maintain this condition for 1 hour and terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain a mixed material.

[0058] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 20°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 70°C hot acetic acid, filtered, and placed in a vacuum oven set at 120°C for two hours to obtain terephthalic acid crystals.

[0059] The yield and purity of the product terephthalic acid were determined by the method shown in Example 11. The results are shown in the following table: Table 12 Yield and purity of terephthalic acid crystals obtained in Example 11 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 95.91% 99.32% 0.43% Comparative Example 1 This comparative example provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.175 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 1 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 210°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 70%. Maintain this condition for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain a mixed material.

[0060] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0061] The yield and purity of the product terephthalic acid were measured using the method shown in Comparative Example 1. The results are shown in the following table: Table 13 Yield and purity of terephthalic acid crystals obtained in Comparative Example 1 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 92.78% 97.15% 1.24% Comparative Example 2 This comparative example provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.52 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 3.5 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 200°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 35%. Maintain this condition for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain the mixed material.

[0062] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0063] The yield and purity of the product terephthalic acid were determined by the method shown in Example 1. The results are shown in the following table: Table 14 Yield and purity of terephthalic acid crystals obtained in Comparative Example 2 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 93.15% 97.38% 1.12% Comparative Example 3 This comparative example provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.35 g of cobalt acetate, 0.35 g of manganese acetate, 1.44 g of hydrobromic acid, and 0.35 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 0.5 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 200°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 35%. Maintain this condition for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain a mixed material.

[0064] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0065] The yield and purity of the product terephthalic acid were determined by the method shown in Example 1. The results are shown in the following table: Table 15 Yield and purity of terephthalic acid crystals obtained in Comparative Example 3 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 92.80% 96.64% 1.83% Comparative Example 4 This comparative example provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.175 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 1.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 1 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 200°C, the pressure to 1.5 MPa, and the CO2 inlet concentration to 35%. Maintain this condition for 2 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain a mixed material.

[0066] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0067] The yield and purity of the product terephthalic acid were determined by the method shown in Example 1. The results are shown in the following table: Table 16 Yield and purity of terephthalic acid crystals obtained in Comparative Example 4 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 94.13% 98.23% 1.06% Comparative Example 5 This comparative example provides a method for preparing terephthalic acid, comprising the following steps: (1) Take 50 g of p-xylene, 500 g of acetic acid, 0.175 g of cobalt acetate, 0.175 g of manganese acetate, 0.72 g of hydrobromic acid, and 0.175 g of nickel acetate. Open the lid of the titanium reactor and add 200 g of cobalt acetate, manganese acetate, hydrobromic acid, nickel acetate, and acetic acid into the reactor. After closing the lid, open the nitrogen valve of the reactor, replace the air in the reactor with nitrogen, and pressurize it to 2.0 MPa. Then close the nitrogen valve and control the temperature of the reactor to 180°C. Dissolve the raw material p-xylene in the remaining acetic acid solvent. After the mixture is prepared, use metering pump 7 to pump it into the reactor at a feed rate of 1 ml / min. At the same time, open the oxygen valve, nitrogen valve, and CO2 valve, adjust the oxygen inlet concentration to 21%, control the reactor temperature to 160°C, the pressure to 2.5 MPa, and the CO2 inlet concentration to 35%. Maintain this condition for 3 hours and then terminate the reaction. Close the oxygen valve and CO2 valve, cool down, and obtain a mixed material.

[0068] (2) Low-temperature heat transfer oil is introduced into the reactor coil to control the cooling crystallization temperature to 10°C. After the crystallization is complete, the reactor is opened to release the mixed material, and the solid product is obtained by centrifugation. The product is washed twice with 60°C hot acetic acid, filtered, and placed in a vacuum oven set at 100°C for two hours to obtain terephthalic acid crystals.

[0069] The yield and purity of the product terephthalic acid were determined by the method shown in Example 1. The results are shown in the following table: Table 17 Yield and purity of terephthalic acid crystals obtained in Comparative Example 5 Type of substance Yield purity p-Carboxybenzaldehyde content Terephthalic acid 94.53% 97.82% 1.41% According to the above Examples 1-11 and Comparative Examples 1-5, it can be seen that using nickel acetate and CO2 as catalyst promoters can effectively improve the yield and purity of terephthalic acid, and can effectively solve the shortcoming of the high content of p-carboxybenzaldehyde in the current p-xylene oxidation product. At the same time, this method can also accelerate the reaction rate, shorten the reaction time, increase production capacity and reduce energy consumption, and has broad industrial application prospects and commercial value.

[0070] In summary, the present invention discloses a method for preparing terephthalic acid. The method uses acetic acid as a solvent, nickel acetate and CO2 as co-catalysts based on a Co-Mn-Br ternary catalyst, shortens the reaction time, and can improve the yield and purity of the product, which is beneficial to the industrial application of the process and lays the foundation for the development of high-performance polyester materials.

[0071] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing terephthalic acid, characterized in that: The following steps are involved: Adding a catalyst, a catalyst promoter and a solvent to p-xylene, after the preparation is completed, injecting it into a reaction kettle, and introducing an oxidizing gas, an inert gas and a catalyst promoter gas at the same time to carry out an oxidation reaction. After the reaction is completed, cooling and crystallizing, centrifugal filtration, washing and drying are carried out to obtain terephthalic acid; The catalyst is cobalt acetate, manganese acetate and hydrobromic acid; the promoter is nickel acetate; and the promoter gas is CO2.

2. The method for preparing terephthalic acid according to claim 1, characterized in that: The mass ratio of p-xylene, cobalt acetate, manganese acetate, hydrobromic acid and nickel acetate is (50-100): (0.1-0.2): (0.1-0.2): (0.4-0.8): (0.1-0.3).

3. The method for preparing terephthalic acid according to claim 1, characterized in that: The solvent is acetic acid; the mass ratio of p-xylene to acetic acid is (50-100): (300-1200).

4. The method for preparing terephthalic acid according to claim 1, characterized in that: The intake concentration of CO2 is 20%-60%.

5. The method for preparing terephthalic acid according to claim 1, characterized in that: The oxidizing gas is oxygen, and the intake concentration of oxygen is 21%.

6. The method for preparing terephthalic acid according to claim 1, characterized in that: The temperature of the oxidation reaction is 180-200° C.; the time of the oxidation reaction is 1-3 h.

7. The method for preparing terephthalic acid according to claim 1, characterized in that: The reactor is a high-temperature and high-pressure titanium reactor; the reactor adopts continuous operation, and the feed rate is 0.5-1.0 ml / min.

8. The method for preparing terephthalic acid according to claim 1, characterized in that: The pressure in the reactor is 2.0-2.5 MPa.

9. The method for preparing terephthalic acid according to claim 1, characterized in that: The cooling crystallization temperature is 10-20°C; the washing condition is to use hot acetic acid at 60-70°C for washing; the drying condition is to dry at 100-120°C for 2-3h.

10. A terephthalic acid, characterized in that: The product is prepared by the preparation method according to any one of claims 1 to 8, wherein the yield of terephthalic acid is 95.6%-98.3%, the purity of terephthalic acid is 99.2%-99.5%, and the content of p-carboxybenzaldehyde is no more than 0.5%.

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