Catalyst system for preparing terephthalic acid

Abstract

A catalyst system for preparing terephthalic acid includes a first complex of a manganese salt and a first multidentate ligand; and a second complex of a cobalt salt and a second polydentate ligand wherein the first polydentate ligand is a tridentate ligand, a tetradentate ligand, a pentadentate ligand or a hexadentate ligand and the second polydentate ligand is a tridentate ligand, a tetradentate ligand, a pentadentate ligand or a hexadentate ligand.

Description

Background Art

[0001] Terephthalic acid is a commodity chemical that is used as a feedstock for a variety of industrial processes. For example, terephthalic acid is a precursor to polyethylene terephthalate (PET), which is used in clothing materials and plastic bottles. Some of the processes currently available for the production of terephthalic acid generally rely on the oxidation of p-xylene with oxygen. However, this process often produces unwanted impurities such as 4-carboxybenzaldehyde (4-CBA), p-toluic acid and / or other colored impurities.

[0002] While attempts have been made to produce more efficient terephthalic acid catalysts, these attempts are likely to create additional problems and may not address the issues associated with the generation of the above-mentioned unwanted impurities. For example, bromine, which may be contained in terephthalic acid catalysts, may be corrosive, particularly to equipment used in the terephthalic acid production process. In addition, the limited coordination of the metal ions used may limit the effectiveness of the catalyst and increase side reactions and impurities.

[0003] US Patent No. 5,453,538 discloses a process for producing aromatic dicarboxylic acids by using cerium and cobalt and manganese catalysts to reduce the ratio of bromine to metal. Aromatic dicarboxylic acids such as terephthalic acid can be used to make fibers, films, bottles and molded products.

[0004] WO 2020 / 144517 discloses a method for oxidizing a dimethyl aromatic compound, comprising reacting a dimethyl aromatic compound and an oxidant in a solvent in the presence of a catalyst and a co-catalyst to produce a reaction product containing an aromatic dicarboxylic acid.

[0005] Catalysts currently used to make terephthalic acid may include dissolved ions (e.g., manganese, cobalt, bromine, or combinations thereof). Certain catalysts currently used to make terephthalic acid may not be economically viable in large-scale terephthalic acid production, may be corrosive to equipment used in such processes, and / or may result in the production of undesirable impurities, such as 4-CBA, p-toluic acid, and / or other colored impurities. The systems, methods, and processes of the present disclosure address and / or overcome these and other inefficiencies and opportunities for improvement. Summary of the invention

[0006] As mentioned above, conventional practice stipulates that bromine-containing catalysts are used in the process of preparing terephthalic acid. However, there may be many disadvantages in the bromine-containing catalysts used to prepare terephthalic acid, such as impurities that are not desirable in the terephthalic acid product. In addition, as mentioned above, conventional practice is to provide metal salt catalysts rather than ligand-coordinated metal catalysts. The lack of metal-coordinated ligands may reduce the flexibility of the oxidation state, and therefore may cause unnecessary side reactions and increase impurities in the product. Therefore, although there are catalysts for preparing terephthalic acid, there are still many opportunities for improvement, and the catalyst system, process and method disclosed in the present invention can solve these problems. Solutions to the defects of conventional catalysts for preparing terephthalic acid have been found. Therefore, in various embodiments, a catalyst system for preparing terephthalic acid, a method for forming a catalyst system for preparing terephthalic acid, and a process for producing terephthalic acid are disclosed. The disclosed catalyst system may include a relatively small amount of bromine (e.g., bromine may not be included in one embodiment). In addition, the catalyst system may also include a chelating ligand, such as aminopolycarboxylic acid, which may have a hexavalent chelating effect, which helps the coordination of the substrate, the activation of oxygen and / or the change of the oxidation state of the intermediate product. The use of reducing bromine and chelating ligands alone or in combination can effectively reduce the impurity content in the terephthalic acid product, such as reducing the content of 4-CBA in the terephthalic acid product. The reduction of 4-CBA content can reduce the production cost of terephthalic acid, thereby reducing the production cost of PET.

[0007] Disclosed herein is a catalyst system for preparing terephthalic acid, comprising a first complex of a manganese salt and a first multidentate ligand (such as a first aminopolycarboxylic acid); and a second complex of a cobalt salt and a second multidentate ligand (such as a second aminopolycarboxylic acid).

[0008] Disclosed herein is a process for producing a catalyst system, comprising forming a first complex by heating a first solution comprising a first multidentate ligand and a manganese salt; separating the first complex from the first solution; forming a second complex by heating a second solution comprising a second multidentate ligand and a cobalt salt; separating the second complex from the second solution; and combining the first complex and the second complex to produce the catalyst system.

[0009] Disclosed herein is a process for producing terephthalic acid, comprising combining a catalyst system, p-xylene, bromine and acetic acid to form a reaction mixture; and reacting the p-xylene in the presence of oxygen to convert the p-xylene into terephthalic acid.

[0010] The above described features and other features are exemplified by the following figures and detailed description.

[0011] Embodiments of the invention may be in any combination or arrangement.Other advantageous features, functions and applications of the catalyst systems, processes and methods of the present disclosure will be apparent from the following description, particularly when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The following drawings are exemplary embodiments.

[0013] Exemplary embodiments of the present disclosure are further described with reference to the accompanying drawings. It should be noted that the various features, steps, and combinations of features / steps described below can be arranged and organized in different ways to produce embodiments that are still within the scope of the present disclosure. To assist those of ordinary skill in the art in making, using, and practicing the disclosed catalyst systems, methods, and processes, please refer to the accompanying drawings, in which:

[0014] Figure 1 is a schematic diagram of an example of a terephthalic acid production process disclosed in the present invention;

[0015] Figure 2 The Fourier transform infrared spectrum (FTIR) of ethylenediaminetetraacetic acid (EDTA) and manganese-EDTA complex prepared in the embodiment of the present invention is shown;

[0016] Figure 3 FTIR spectra of EDTA and cobalt-EDTA complex prepared in the examples are shown;

[0017] Figure 4 Thermogravimetric analysis (TGA) curves of EDTA and manganese-EDTA complex prepared in the examples are shown;

[0018] Figure 5 The TGA curves of EDTA and cobalt-EDTA complex prepared in the examples are shown;

[0019] Figure 6 The UV-visible absorption spectra of EDTA and manganese-EDTA complex prepared in the examples are shown;

[0020] Figure 7 The UV-visible absorption spectra of EDTA and cobalt-EDTA complex prepared in the examples are shown;

[0021] Figure 8 The X-ray diffraction (XRD) patterns of EDTA and EDTA manganese complex prepared in the examples are shown;

[0022] Fig. 9 shows the XRD patterns of EDTA and cobalt-EDTA complex prepared in the examples; and

[0023] Fig.10is a graph of intensity (arbitrary units (au)) versus time (minutes (min)) showing a high performance liquid chromatography (HPLC) analysis of the solid phase recovered in Example 1; and

[0024] Fig.11 is a graph of intensity (au) versus time (min) showing the HPLC analysis of the liquid recovered in Example 1. DETAILED DESCRIPTION

[0025] The exemplary embodiments disclosed herein illustrate advantageous catalyst systems for preparing terephthalic acid, methods for forming catalyst systems for preparing terephthalic acid, and processes for producing terephthalic acid. However, it should be understood that the disclosed embodiments are merely exemplary of the present disclosure, which may be embodied in various forms. Therefore, the details disclosed herein with reference to exemplary catalyst systems, methods, and processes should not be construed as limiting, but merely as a basis for those skilled in the art to understand advantageous catalyst systems, methods, and processes of the present disclosure.

[0026] Advantages of using the disclosed metal multidentate ligand (e.g., aminopolycarboxylic acid) complex in a catalyst system for preparing terephthalic acid include reducing the amount of bromine used as a promoter in the reaction mixture, which can reduce corrosion and extend the service life of the reactor. In addition, using the disclosed metal multidentate ligand (e.g., aminopolycarboxylic acid) complex in a catalyst system can improve the overall yield and selectivity of the process for preparing terephthalic acid while reducing catalyst deactivation and the formation of by-products.

[0027] In one embodiment, the catalyst system for preparing terephthalic acid includes a first complex of a manganese salt and a first multidentate ligand (such as a first aminopolycarboxylic acid), and a second complex of a cobalt salt and a second multidentate ligand (such as a second aminopolycarboxylic acid). Based on the total weight of the catalyst system, the catalyst system may include less than 400 parts by weight of bromine, or less than 100 parts by weight of bromine, or less than 50 parts by weight of bromine. Based on the total weight of the catalyst system, the catalyst system may include 0 parts by weight of bromine. In one embodiment, based on the total weight of the catalyst system, the catalyst system includes greater than 1 part by weight of bromine, or greater than 20 parts by weight of bromine, or greater than 40 parts by weight of bromine.

[0028] As used herein, the term "complexation" of a first material and a second material refers to a complex formed by the first material and the second material. In one embodiment, the complex formed does not include each of the first and second materials because during the formation of the complex, one of the first and second materials (e.g., a ligand, such as an aminopolycarboxylic acid) can coordinate with the other of the materials (e.g., a metal salt) to form a complex, which may include protonation or deprotonation of amine, carboxylic acid and / or alcohol functional groups. In certain embodiments, the first material or the second material is a metal salt, such as MnCl2, Mn(NO3)2, manganese acetate, CoCl2, Co(NO3)2, cobalt acetate.

[0029] Each of the first material and the second material can independently include a multidentate ligand, i.e., a tridentate ligand, a tetradentate ligand, a pentadentate ligand, or a hexadentate ligand, such as N,N,N',N'-tetrakis(2-pyridylmethyl)-1,2-ethylenediamine, ethylenediaminetetraacetic acid, 2.2.2-cryptand, or a combination thereof. In one embodiment, the first material is a first aminocarboxylic acid. In one embodiment, the second material is a second aminocarboxylic acid. In one embodiment, each of the first multidentate ligand and the second multidentate ligand includes ethylenediaminetetraacetic acid. Without wishing to be bound by any theory, it is believed that the use of a multidentate ligand, such as a hexadentate ligand such as ethylenediaminetetraacetic acid, in a catalyst system can provide a favorable chelation effect; for example, the chelating arm can activate oxygen or metal ions, and the oxidation state of the intermediate product can be changed.

[0030] Each of the first material (e.g., the first aminocarboxylic acid) and the second material (e.g., the second aminocarboxylic acid) can independently include a non-six-position ligand. The first multidentate ligand (e.g., the first aminopolycarboxylic acid) can be different from or the same as the second multidentate ligand (e.g., the second aminopolycarboxylic acid).

[0031] The molar ratio of manganese in the catalyst system to cobalt in the catalyst system can be 3:1 to 1:3, or 2:1 to 1:2, or 1.5:1 to 1:1.5. Based on the total weight of the catalyst system, the catalyst system can include 1 to 20 weight percent, or 5 to 15 weight percent, or 7 to 9 weight percent of manganese; and 1 to 20 weight percent, or 5 to 15 weight percent, or 7 to 9 weight percent of cobalt.

[0032] The manganese salt may include MnCl2, Mn(NO3)2, manganese acetate, or a combination thereof. In one embodiment, the manganese salt includes manganese acetate.

[0033] The cobalt salt may include CoCl2, Co(NO3)2, cobalt acetate, or a combination thereof. In one embodiment, the cobalt salt includes cobalt acetate.

[0034] A process for producing a catalyst system for preparing terephthalic acid may include forming a first complex by heating a first solution including a first material (e.g., a first multidentate ligand, such as a first aminocarboxylic acid) and a manganese salt; separating the first complex from the first solution; forming a second complex by heating a second solution including a second material (e.g., a second multidentate ligand, such as a second aminopolycarboxylic acid) and a cobalt salt; separating the second complex from the second solution; and combining the first complexing agent and the second complexing agent to form the catalyst system.

[0035] The molar ratio of the manganese salt to the first multidentate ligand (e.g., the first aminopolycarboxylic acid) in the first solution can be 3:1 to 1:3, or 2:1 to 1:2, or 1.5:1 to 1:1.5. The molar ratio of the cobalt salt to the second multidentate ligand (e.g., the second aminopolycarboxylic acid) in the second solution can be 3:1 to 1:3, or 2:1 to 1:2, or 1.5:1 to 1:1.5.

[0036] The process for producing terephthalic acid comprises mixing a catalyst system, p-xylene and acetic acid to form a reaction mixture, and reacting the p-xylene in the presence of oxygen to convert the p-xylene into terephthalic acid.

[0037] The process may further include adding bromine to the reaction mixture in an amount of less than 400 parts per million by weight, or less than 100 parts per million by weight, or less than 50 parts per million by weight, based on the total weight of the reaction mixture including bromine. In one embodiment, bromine may be added to the reaction mixture in an amount greater than 1 part per million by weight, or greater than 20 parts per million by weight, or greater than 40 parts per million by weight, based on the total weight of the catalyst system. As used herein, bromine added to the reaction mixture is a promoter, which is a component separate from the catalyst system added to the reaction mixture.

[0038] refer to Figure 1, a gas stream 10 including paraxylene can be fed into an oxidation reactor 100. A gaseous stream 20 including oxygen (e.g., O2) can be fed into the oxidation reactor 100. The gaseous stream 20 can include 19 to 25 volume percent (vol%) oxygen based on the total volume of the gaseous stream 20, or the oxygen content based on the total volume of the gaseous stream 20 is 19 vol%, 19.2 vol%, 19.4 vol%, 19.6 vol%, 19.8 vol%, 20 vol%, 20.2 vol%, 20.4 vol%, 20.6 vol%, 20.8 vol%, 21 vol%, 21.2 vol%, 21.4 vol%, 21.6 vol%. %, 21.8 vol%, 22 vol%, 22.2 vol%, 22.4 vol%, 22.6 vol%, 22.8 vol%, 23 vol%, 23.2 vol%, 23.4 vol%, 23.6 vol%, 23.8 vol%, 24 vol%, 24.2 vol%, 24.4 vol%, 24.6 vol%, 24.8 vol% and 25 vol%, or equal to any one of them, or between any two of them. In one embodiment, gas stream 20 can be air. Liquid stream 30 includes acetic acid and a disclosed catalyst and can be fed into oxidation reactor 100.

[0039] In oxidation reactor 100, para-xylene may be oxidized in the presence of the disclosed catalyst system, for example, by O2, to produce terephthalic acid. The para-xylene oxidation reaction conditions may include (1) a temperature of 180 to 195°C or at least any one of 180°C, 181°C, 182°C, 183°C, 184°C, 185°C, 186°C, 187°C, 187.5°C, 188°C, 188.5°C, 189°C, 189.5°C, 190°C, 190.5°C, 191°C, 192°C, 193°C, 194°C, and 195°C, or equal to the above. any one of, or between any two of them; and / or (2) the pressure is from 5 to 20 bar (500 to 2,000 kilopascals (kPa)) or from 10 to 14 bar, or at least any one of 5 bar, 6 bar, 7 bar, 8 bar, 9 bar, 10 bar, 11 bar, 12 bar, 13 bar, 14 bar, 15 bar, 16 bar, 17 bar, 18 bar, 19 bar and 20 bar, or equal to any one of them, or between any two of them.

[0040] The product stream may include gaseous effluent 40, liquid effluent 50, solid effluent 60, or a combination thereof, which may be subjected to HPLC analysis. In one embodiment, at least two of gaseous effluent 40, liquid effluent 50, and solid 60 may be withdrawn from oxidation reactor 100 together and then separated.

[0041] The residence time of the reaction mixture in oxidation reactor 100 can be 0.5 to 3 hours (hr), or at least any one of 0.5 hr, 0.6 hr, 0.7 hr, 0.8 hr, 0.9 hr, 1 hr, 1.1 hr, 1.2 hr, 1.3 hr, 1.4 hr, 1.5 hr, 1.6 hr, 1.7 hr, 1.8 hr, 1.9 hr, 2 hr, 2.1 hr, 2.2 hr, 2.3 hr, 2.4 hr, 2.5 hr, 2.6 hr, 2.7 hr, 2.8 hr, 2.9 hr and 3 hr, or equal to any one of them, or between any two of them.

[0042] The oxidation reactor 100 may have a relatively inert interior surface. In one embodiment, the oxidation reactor 100 may be a platinum wire reactor.

[0043] In one embodiment, paraxylene and oxygen can be added to the oxidation reactor 100 in a molar ratio of 1:3 to 1:5, or a molar ratio of at least any one of 1:3, 1:31, 1:32, 1:33, 1:34, 1:35, 1:36, 1:37, 1:38, 1:39, 1:4, 1:41, 1:42, 1:43, 1:44, 1:45, 1:46, 1:47, 1:48, 1:49 and 1:5, or equal to any one of them, or between any two of them.

[0044] In one embodiment, based on the total moles of p-xylene added to the reactor, the p-xylene conversion rate can be 95 to 100 mole percent (mol%); or based on the total moles of p-xylene added to the reactor, at least 95 mol%, 95.5 mol%, 96 mol%, 96.5 mol%, 97 mol%, 97.5 mol%, 98 mol%, 98.5 mol%, 99 mol%, 99.5 mol% and 100 mol%, or equal to any one of them, or between any two of them. As used herein, the term "conversion rate" refers to the mole fraction (i.e., percentage) of a reactant (such as p-xylene) converted into one or more products.

[0045] In one embodiment, the terephthalic acid yield (e.g., mol%) of the reaction of para-xylene with oxygen can be 90 to 100 mol%, based on the total moles of the reaction products, or at least any one of 90 mol%, 91 mol%, 92 mol%, 93 mol%, 94 mol%, 95 mol%, 96 mol%, 97 mol%, 98 mol%, 99 mol% and 100 mol%, or equal to any one of them, or between any two of them, based on the total moles of the reaction products. The term "yield" as used herein refers to the mole fraction (i.e., percentage) of a specific product (e.g., terephthalic acid) in the total product stream.

[0046] In one embodiment, the selectivity of terephthalic acid in the reaction of para-xylene with oxygen can be greater than or equal to 93 mol%, or greater than or equal to 94 mol%, or greater than or equal to 95 mol%, or at least any one of 93 mol%, 93.2 mol%, 93.4 mol%, 93.6 mol%, 93.8 mol%, 94 mol%, 94.2 mol%, 94.4 mol%, 94.6 mol%, 94.8 mol%, 95 mol%, 95.1 mol%, 95.7 mol%, 95.8 mol%, 95.9 mol% and 100 mol%, or equal to any one of them, or between any two of them. As used herein, the term "selectivity" refers to the mole fraction (i.e., percentage) of a reactant converted to a specific product, for example, the selectivity of terephthalic acid refers to the percentage of para-xylene converted to terephthalic acid.

[0047] During the oxidation of p-xylene to terephthalic acid, 4-CBA, p-toluic acid, CO2, or a combination thereof may be formed as a byproduct. The catalyst systems, processes, and methods of the present disclosure may produce acceptable (e.g., desirable) amounts of terephthalic acid, 4-CBA, p-toluic acid, and CO2, as well as relatively low amounts of 4-CBA and p-toluic acid (compared to other catalysts / processes / methods).

[0048] For example, the total product of the oxidation reactor 100 may include less than 5 wt%, or less than 4 wt%, or less than 3 wt%, or less than 2 wt% of 4-CBA, based on the total weight of the total product of the oxidation reactor 100. The total product of the oxidation reactor 100 may include less than 5 wt%, or less than 4 wt%, or less than 3 wt%, or less than 2.9 wt%, or less than 2.8 wt%, or less than 2.7 wt% of p-toluic acid, based on the total weight of the total product of the oxidation reactor 100. The volume percentage of carbon dioxide (CO2) in the gaseous effluent 40 of the oxidation reactor 100 may be less than 5 Vol%, or less than 4 Vol%, or less than 3 Vol%, or less than 2.9 Vol%, or less than 2.8 Vol%, or less than 2.7 Vol%, based on the total weight of the gaseous effluent 40.

[0049] The present disclosure is further illustrated by the following non-limiting examples. Example Example 1

[0050] Prepare 100 milliliters (mL) of 0.1 molar (M) per liter of ethylenediaminetetraacetic acid (EDTA) and 0.1 M cobalt acetate and manganese acetate in a standard flask. Add ethylenediaminetetraacetic acid and metal salt solution to a round-bottom flask and a pressure equalizing funnel, respectively. The round-bottom flask is equipped with a reflux condenser and heated to 85°C. After reaching the desired temperature, the metal salt is added dropwise with a magnetic bar while stirring. After the addition of the metal salt solution is completed, the resulting mixture is stirred at high temperature for another 3 hours. After 3 hours, the heating is stopped and stirring is continued at room temperature overnight. The precipitate formed is collected by filtration, washed several times with ethanol, and then dried in a desiccator. Prepare a catalyst system, including the prepared EDTA cobalt complex and an EDTA manganese complex with a cobalt-manganese molar ratio of 1:1.

[0051] Ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to characterize the prepared materials and confirm the complex. Figure 2 FTIR spectra of EDTA and manganese-EDTA complex are shown; Figure 3 FTIR spectra of EDTA and cobalt-EDTA complex are shown; Figure 4 TGA curves of EDTA and manganese-EDTA complex are shown; Figure 5 TGA curves of EDTA and cobalt-EDTA complex are shown; Figure 6 Shows UV-Vis absorption spectrum. Figure 6 Shows the UV-visible absorption spectra of EDTA and manganese-EDTA complex; Figure 7 Shows the UV-visible absorption spectra of EDTA and cobalt-EDTA complex; Figure 8Shows the XRD patterns of EDTA and manganese-EDTA complex; Fig. 9 Shown are the XRD patterns of EDTA and cobalt-EDTA complex.

[0052] 2.3 g (1 mole percent (mol%)) of the prepared catalyst system was added to the reactor, and 46 parts per million by weight (ppm) of bromine promoter was added, the percentage (relative amount) being based on the total content of the reaction mixture including the catalyst (system). The reaction chamber was pressurized to 12 bar with 9 bar of N2 gas and 3 bar of O2 gas until the reactor temperature reached 190 degrees Celsius. After reaching the desired temperature, p-xylene was injected into the reactor at a flow rate of 1 ml / min, while the atmosphere in the reactor was replaced with oxygen and oxygen was released periodically in the reactor chamber while the pressure was maintained at 12 bar. The reaction lasted for 2 hours. A total of 46.5 ml (0.377 mole (mol)) of p-xylene and 142.9 ml (2.498 mol) of acetic acid were added to the reactor. The reactor was cooled and the solid terephthalic acid (TPA) formed was separated by filtration.

[0053] 125 ml of liquid and 57 g of solid were recovered. The purity of the formed product was analyzed by high performance liquid chromatography (HPLC). Fig.10 (Recovered Solids) and Fig.11 (Recovered liquid) shown. Comparative Example 1

[0054] A catalyst system including 400 ppm Co, 220 ppm Mn and 460 ppm Br was added to the reactor. The reactor chamber was pressurized to 12 bar with 9 bar of N2 gas and 3 bar of O2 gas until the reactor temperature reached 190°C. After reaching the desired temperature, p-xylene was injected into the reactor at a flow rate of 1 ml / min, while the atmosphere in the reactor was replaced with oxygen and oxygen was released periodically in the reactor chamber while the pressure was maintained at 12 bar. The reaction lasted for 1 hour. A total of 46.5 ml (0.377 mol) of p-xylene and 142.9 ml (2.498 mol) of acetic acid were added to the reactor. The reactor was cooled and the solid TPA formed was separated by filtration. Comparative Example 2

[0055] A catalyst system including 560 ppm Co, 468 ppm Mn, 620 ppm Br and 50 ppm Cu was added to the reactor. The reactor chamber was pressurized to 12 bar with 9 bar of N2 gas and 3 bar of O2 gas until the reactor temperature reached 190°C. After reaching the desired temperature, p-xylene was injected into the reactor at a flow rate of 1 ml / min, while the atmosphere in the reactor was replaced with oxygen and oxygen was released periodically in the reactor chamber while the pressure was maintained at 12 bar. The reaction lasted for 1 hour. A total of 46.5 ml (0.377 mol) of p-xylene and 142.9 ml (2.498 mol) of acetic acid were added to the reactor. The reactor was cooled and the solid TPA formed was separated by filtration.

[0056] The products formed in Example 1 and Comparative Examples 1 and 2 are shown in Table 2 and summarized in Table 3. Table 2 Table 3 Comparative Example 1 Comparative Example 2 Example 1 TPA selectivity (mol%) 98.5 96.19 95.1 Yield (g) 58.5 62 57 <![CDATA[CO2 product (volume percentage)]]> 1.88 1.022 2.6

[0057] Example 1 increases conversion while still providing acceptable, eg, desirable, TPA selectivity, TPA production, CO2 production, 4-CBA production, and p-toluic acid production.

[0058] The present disclosure further includes the following aspects.

[0059] Aspect 1. A catalyst system for preparing terephthalic acid, comprising a first complex of a manganese salt and a first multidentate ligand; a second complex of a cobalt salt and a second multidentate ligand, wherein the first multidentate ligand is a tridentate ligand, a tetradentate ligand, a pentadentate ligand or a hexadentate ligand, and wherein the second multidentate ligand is a tridentate ligand, a tetradentate ligand, a pentadentate ligand or a hexadentate ligand.

[0060] Aspect 2. The catalyst system of aspect 1, wherein the catalyst system comprises less than 400 parts by weight of bromine, or less than 100 parts by weight of bromine, or less than 50 parts by weight of bromine, based on the total weight of the catalyst system.

[0061] Aspect 3. The catalyst system of aspect 2, wherein the catalyst system comprises greater than 1 part per million by weight, or greater than 20 parts per million by weight, or greater than 40 parts per million by weight of bromine based on the total weight of the catalyst system.

[0062] Aspect 4. The catalyst system of any of the preceding aspects, wherein the molar ratio of manganese in the catalyst system to cobalt in the catalyst system is from 3:1 to 1:3, or from 2:1 to 1:2, or from 1.5:1 to 1:1.5.

[0063] Aspect 5. The catalyst system of any of the preceding aspects, wherein the first multidentate ligand comprises a hexamer ligand; the second multidentate ligand comprises a hexamer ligand; or a combination thereof.

[0064] Aspect 6. A catalyst system according to any of the preceding aspects, wherein the first multidentate ligand comprises N,N,N',N'-tetrakis(2-pyridylmethyl)-1,2-ethylenediamine, ethylenediaminetetraacetic acid, 2.2.2-cryptand or a combination thereof; the second multidentate ligand comprises N,N,N',N'-tetrakis(2-pyridylmethyl)-1,2-ethylenediamine, ethylenediaminetetraacetic acid, 2.2.2-cryptand or a combination thereof; or a combination thereof.

[0065] 7. The catalyst system of any one of aspects 1 to 4, wherein the first multidentate ligand comprises a first aminopolycarboxylic acid; and the second multidentate ligand comprises a second aminopolycarboxylic acid.

[0066] Aspect 8. The catalyst system of any of the preceding aspects, comprising, based on the total weight of the catalyst system: 1 to 20 wt%, or 5 to 15 wt%, or 7 to 9 wt% manganese; and 1 to 20 wt%, or 5 to 15 wt%, or 7 to 9 wt% cobalt.

[0067] Aspect 9. The catalyst system of any of the preceding aspects, comprising zero parts per million by weight bromine, based on the total weight of the catalyst system.

[0068] Aspect 10. A process for producing the catalyst system of any of the preceding claims, the process comprising forming a first complex by heating a first solution comprising a first multidentate ligand and a manganese salt; separating the first complex from the first solution; forming a second complex by heating a second solution comprising a second aminopolycarboxylic acid and a cobalt salt; separating the second complex from the second solution; and combining the first complexing agent and the second complexing agent to produce the catalyst system.

[0069] Aspect 11. The process of aspect 10, wherein the first multidentate ligand comprises a hexamer ligand; the second multidentate ligand comprises a hexamer ligand; or a combination thereof.

[0070] Aspect 12. The process of aspect 10 or 11, wherein the first multidentate ligand comprises ethylenediaminetetraacetic acid; the second multidentate ligand comprises ethylenediaminetetraacetic acid; or a combination thereof.

[0071] Aspect 13. The process of any one of Aspects 10 to 12, wherein the manganese salt comprises manganese acetate; the cobalt salt comprises cobalt acetate; or a combination thereof.

[0072] Aspect 14. The process of any one of Aspects 10 to 13, wherein the catalyst system comprises 1 to 20 weight percent, or 5 to 15 weight percent, or 7 to 9 weight percent of manganese based on the total weight of the catalyst system; 1 to 20 weight percent, or 5 to 15 weight percent, or 7 to 9 weight percent of cobalt; or a combination thereof; wherein the molar ratio of the manganese salt to the first multidentate ligand in the first solution is 3:1 to 1:3, or 2:1 to 1:2, or 1.5:1 to 1:1.5; the molar ratio of the cobalt salt to the second multidentate ligand in the second solution is 3:1 to 1:3, or 2:1 to 1:2, or 1.5:1 to 1:1.5; or a combination thereof.

[0073] Aspect 15. A process for producing terephthalic acid, comprising: combining the catalyst system of any one of aspects 1 to 9, p-xylene, and acetic acid to form a reaction mixture; and reacting the p-xylene in the presence of oxygen to convert the p-xylene to produce terephthalic acid.

[0074] Aspect 16. The process of embodiment 15 further comprises adding bromine to the reaction mixture in an amount of less than 400 parts per million by weight, or less than 100 parts per million by weight, or less than 50 parts per million by weight, based on the total weight of the reaction mixture including bromine.

[0075] Aspect 17. The process of Aspect 16 comprises adding bromine to the reaction mixture, wherein the amount of bromine is greater than 1 part per million by weight, or greater than 20 parts per million by weight, or greater than 40 parts per million by weight, based on the total weight of the catalyst system.

[0076] Aspect 18. A process according to any one of Aspects 15 to 17, wherein the conversion of para-xylene is greater than or equal to 95 mol%, or 95.5 mol%, or 96 mol%, or 96.5 mol%, or 97 mol%, or 97.5 mol%, or 98 mol%, or 98.5 mol%, based on the total moles of para-xylene reacted; wherein the yield of terephthalic acid is greater than or equal to 90 mol%, or 91 mol%, or 92 mol%, or 93 mol% (based on the total moles of reaction products); the selectivity of terephthalic acid is greater than or equal to 93 mol%, or greater than or equal to 94 mol%, or greater than or equal to 95 mol%; or a combination thereof.

[0077] The compositions, methods and articles of the present invention may selectively include, consist of or consist essentially of any suitable material, step or component disclosed herein. In addition, the compositions, methods and articles may also be formulated to not contain or not contain essentially any material (or variety), step or component, which is not necessary for achieving the function or purpose of the compositions, methods and articles.

[0078] All ranges disclosed herein include endpoints, and the endpoints are independently combinable (e.g., the range of "up to 25 wt%, or more specifically, 5 wt% to 20 wt%" includes the endpoints and all intermediate values ​​of the range of "5 wt% to 25 wt%"). "Combination" includes blends, mixtures, alloys, reaction products, etc. The terms "one", "an" and "the" do not indicate a quantitative limitation and should be interpreted as including the singular and the plural, unless otherwise specified herein or clearly contradicted by the context. Unless otherwise expressly stated, "or" means "and / or". References to "some embodiments", "one embodiment", etc. throughout the specification refer to specific elements related to the embodiments that are included in at least one embodiment described herein, may be present in other embodiments, or may not be present in other embodiments. In addition, the described elements may be combined in various embodiments in any suitable manner. Its "combination" is open and includes any combination consisting of at least one listed component or property together with unlisted similar or equivalent components or properties.

[0079] Unless otherwise specified herein, all test standards are the most current standards in effect on the filing date of this application or, if priority is claimed, on the filing date of the earliest priority application in which the test standards appear.

[0080] Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs. All cited patents, patent applications and other references are incorporated herein by reference. However, if a term in this application contradicts or conflicts with a term in an incorporated reference, the term in this application takes precedence over the conflicting term in the incorporated reference.

[0081] Although particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are not presently foreseen or may not presently be foreseen may occur to applicants or other persons skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to encompass all such alternatives, modifications, variations, improvements, and substantial equivalents.

[0082] Although the processes and methods of the present disclosure have been described with reference to exemplary embodiments thereof, the present disclosure is not limited to these exemplary embodiments and / or implementations. On the contrary, the processes and methods of the present disclosure may have a variety of implementations and applications, which will be apparent to those skilled in the art. The present disclosure explicitly includes modifications, enhancements and / or changes to the disclosed embodiments. Since many modifications may be made to the above-described structures and many widely different embodiments of the present disclosure may be made without departing from the scope of the present disclosure, all matters contained in the drawings and descriptions should be interpreted as illustrative rather than restrictive. Other modifications, changes and substitutions are also included in the above disclosure. Therefore, it is appropriate to interpret the appended claims broadly and in accordance with the scope of the disclosure.

Claims

1. A catalyst system for preparing terephthalic acid, comprising: a first complex of a manganese salt and a first multidentate ligand; and a second complex of the cobalt salt and the second multidentate ligand, wherein the first multidentate ligand is a tridentate ligand, a tetradentate ligand, a pentadentate ligand or a hexadentate ligand, and The second multidentate ligand is a tridentate ligand, a tetradentate ligand, a pentadentate ligand or a hexadentate ligand.

2. The catalyst system of claim 1, wherein the catalyst system comprises less than 100 parts per million or less than 50 parts per million by weight of bromine, based on the total weight of the catalyst system.

3. The catalyst system of claim 2, wherein the catalyst system comprises greater than 1 part per million by weight of bromine, or greater than 20 parts per million by weight of bromine, or greater than 40 parts per million by weight of bromine, based on the total weight of the catalyst system.

4. The catalyst system according to any one of the preceding claims, wherein the molar ratio of manganese to cobalt in the catalyst system is from 3:1 to 1:3, or from 2:1 to 1:2, or from 1.5:1 to 1:1.

5.

5. A method according to any one of the preceding claims, wherein: The first multidentate ligand comprises a hexadentate ligand; The second multidentate ligand comprises a hexadentate ligand; or Its combination.

6. The catalyst system according to any one of the preceding claims, wherein: The first multidentate ligand comprises N,N,N',N'-tetrakis(2-pyridylmethyl)-1,1-ethylenediamine, ethylenediaminetetraacetic acid, 2.2.2-cryptand or a combination thereof; The second multidentate ligand comprises N,N,N',N'-tetrakis(2-pyridylmethyl)-1,1-ethylenediamine, ethylenediaminetetraacetic acid, 2.2.2-cryptand or a combination thereof; or Its combination.

7. The method according to any one of claims 1 to 4, wherein: The first multidentate ligand comprises a first aminopolycarboxylic acid; and The second multidentate ligand includes a second aminopolycarboxylic acid.

8. The catalyst system according to any one of the preceding claims, comprising, based on the total weight of the catalyst system: 1 to 20 wt. % manganese; and 1 to 20 wt. % cobalt.

9. The catalyst system according to any one of the preceding claims, wherein the bromine content is zero parts per million based on the total weight of the catalyst system.

10. A method for producing the catalyst system according to any one of the preceding claims, the method comprising: heating a first solution comprising a first multidentate ligand and a manganese salt to form a first complex; separating the first complex from the first solution; heating a second solution comprising a second multidentate ligand and a cobalt salt to form a second complex; separating the second complex from the second solution; and The first complex and the second complex are combined to form the catalyst system.

11. The method according to claim 10, wherein: The manganese salt includes manganese acetate; The cobalt salt comprises cobalt acetate; or Its combination.

12. The method according to claim 10 or 11, Wherein, based on the total weight of the catalyst system, the catalyst system comprises: 1 wt % to 20 wt % manganese; and 1 to 20% by weight of cobalt; or combinations thereof; and in The molar ratio of the manganese salt to the first multidentate ligand in the first solution is 3:1 to 1:3, or 2:1 to 1:2, or 1.5:1 to 1:1.5; The molar ratio of the cobalt salt to the second multidentate ligand in the second solution is 3:1 to 1:3, or 2:1 to 1:2, or 1.5:1 to 1:1.5; or Its combination.

13. A method for producing terephthalic acid, comprising: mixing the catalyst system of any one of claims 1 to 9, para-xylene, and acetic acid to form a reaction mixture; as well as The para-xylene is reacted in the presence of oxygen to convert the para-xylene to produce terephthalic acid.

14. The method of claim 12, further comprising adding bromine to the reaction mixture in an amount less than 100 parts per million by weight, or less than 50 parts per million by weight, based on the total weight of the reaction mixture containing bromine.

15. The method according to any one of claims 12 to 14, wherein the conversion rate of the p-xylene is greater than or equal to 95 mol%, or 95.5 mol%, or 96 mol%, or 96.5 mol%, or 97 mol%, or 97.5 mol%, or 98 mol%, or 98.5 mol%, based on the total moles of the p-xylene reacted; and in Based on the total moles of the reaction product, the yield of terephthalic acid is greater than or equal to 90 mol%, or 91 mol%, or 92 mol%, or 93 mol%; The selectivity of terephthalic acid is greater than or equal to 93 mol%, or greater than or equal to 94 mol%, or is greater than or equal to 95 mol%; or Its combination.

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