WO2024003044A2

WO2024003044A2 - Catalyst system for preparing terephthalic acid

Info

Publication number: WO2024003044A2
Application number: PCT/EP2023/067466
Authority: WO
Inventors: Mohammed Rafiq Hussain Siddiqui; Waheed A. Al-Masry; Syed Azhar Hashmi; Syed Farooq ADIL; Mujeeb KHAN; Asif MAHMOOD; Sajjad Haider
Original assignee: Sabic Global Technologies B.V.
Priority date: 2022-06-30
Filing date: 2023-06-27
Publication date: 2024-01-04
Also published as: WO2024003044A3

Abstract

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

Description

CATALYST SYSTEM FOR PREPARING TEREPHTHALIC ACID

BACKGROUND

[0001] Terephthalic acid is a commodity chemical and can be used as raw material for various industrial processes. For example, terephthalic acid is a precursor to polyethylene terephthalate (PET), which can be used in clothing materials and plastic bottles. Some current commercially available processes for producing terephthalic acid typically rely on the oxidation of p-xylene with oxygen. However, such processes tend to produce 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 catalysts for making terephthalic acid, these attempts have the potential to create additional problems and may not solve the problems associated with the production of the aforementioned unwanted impurities. For example, bromine, which can be included in catalysts for making terephthalic acid, can be corrosive, especially for the equipment used in the terephthalic acid production process. Additionally, the limited coordination of metal ions used may limit catalyst effectivity and increase side reactions and impurities.

[0003] U.S. Patent No. 5,453,538 discloses a process for the manufacture of aromatic dicarboxylic acids is disclosed using a low bromine to metals ratio facilitated by the use of cerium along with the cobalt and manganese catalyst. Aromatic dicarboxylic acids such as terephthalic acid are useful in the manufacture of fiber, films, bottles and molded products.

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

[0005] Current catalysts for making terephthalic acid can include dissolved ions (e.g., manganese, cobalt, bromine, or combinations thereof). Some current catalysts for making terephthalic acid can be economically inefficient for large scale terephthalic acid production, can be corrosive to the equipment used in such processes, and/or can lead to unwanted production of impurities such as 4-CBA, p-toluic acid, and/or other colored impurities. These and other inefficiencies and opportunities for improvement are addressed and/or overcome by the systems, methods and processes of the present disclosure. BRIEF DESCRIPTION

[0006] As described above, conventional practice provides for use of bromine-containing catalysts in processes for preparing terephthalic acid. However, bromine-containing catalysts for preparing terephthalic acid may suffer from a number of disadvantages, such as undesirable impurities in the terephthalic acid product. Additionally, as described above, conventional practice provides catalysts with metal salts and not ligand coordinated metals. The lack of ligands for metal coordination may decrease the oxidation state flexibility and, therefore, may cause unwanted side reactions and increase impurities in the products. Thus, while catalysts for preparing terephthalic acid exist, there are many opportunities for improvement, which are addressed by the catalyst systems, processes, and methods of the present disclosure. A solution to address the deficiencies of conventional catalysts for preparing terephthalic acid has been discovered. Accordingly, disclosed, in various embodiments, are catalyst systems for preparing terephthalic acid, methods of forming a catalyst system for preparing terephthalic acid, and processes for producing terephthalic acid. The disclosed catalyst system may include a decreased amount of bromine (e.g., in an embodiment may not include bromine). Additionally, the catalyst system may include a chelating ligand such as an amino polycarboxylic acid, the chelating ligand may have a hexacoordinate chelate effect, which may assist in the coordination of substrate, activation of oxygen, and/or change in the oxidation state of plausible intermediates. Individually and in combination, the reduced bromine and chelating ligand may advantageously provide for decreased impurity levels in the terephthalic acid product, such as decreased levels of 4-CBA levels in the terephthalic acid product. Decreased levels of 4-CBA can lead to a decreased in the production costs associated with terephthalic acid and subsequently, PET.

[0007] Disclosed herein is catalyst system for preparing terephthalic acid including a first complexation of a manganese salt and a first multidentate ligand (e.g., a first amino polycarboxylic acid); and a second complexation of a cobalt salt and a second multidentate ligand (e.g., a second amino polycarboxylic acid).

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

[0009] Disclosed herein is a process for producing terephthalic acid including combining the 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 to produce the terephthalic acid.

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

[0011] Any combination or permutation of embodiments is envisioned. Additional advantageous features, functions and applications of the disclosed catalyst systems, processes, and methods of the present disclosure will be apparent from the description which follows, particularly when read in conjunction with the appended figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The following figures are exemplary embodiments.

[0013] Exemplary embodiments of the present disclosure are further described with reference to the appended figures. It is to be noted that the various features, steps, and combinations of features/steps described below can be arranged and organized differently to result in embodiments, which 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, reference is made to the appended figures, wherein:

[0014] FIG. 1 is a schematic of an example process of the present disclosure to product terephthalic acid;

[0015] FIG. 2 shows Fourier-transform infrared spectroscopy (FTIR) spectra of ethylenediaminetetraacetic acid (EDTA) and a manganese-EDTA complex prepared in the examples;

[0016] FIG. 3 shows FTIR spectra of EDTA and a cobalt-EDTA complex prepared in the examples;

[0017] FIG. 4 shows thermogravimetric analysis (TGA) profiles of EDTA and the manganese-EDTA complex prepared in the examples;

[0018] FIG. 5 shows TGA profile of EDTA and the cobalt-EDTA complex prepared in the examples; [0019] FIG. 6 shows ultraviol et-visible(UV-vis) absorption spectra of EDTA and the manganese-EDTA complex prepared in the examples;

[0020] FIG. 7 shows UV-vis absorption spectra of EDTA and the cobalt-EDTA complex; prepared in the examples;

[0021] FIG. 8 shows X-ray diffraction (XRD) patterns of EDTA and the manganese-EDTA complex prepared in the examples;

[0022] FIG. 9 shows XRD pattern of EDTA and the cobalt-EDTA complex prepared in the example; and

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

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

DETAILED DESCRIPTION

[0025] The exemplary embodiments disclosed herein are illustrative of advantageous catalyst systems for preparing terephthalic acid, methods of forming a catalyst system for preparing terephthalic acid, and processes for producing terephthalic acid. It should be understood, however, that the disclosed embodiments are merely exemplary of the present disclosure, which may be embodied in various forms. Therefore, details disclosed herein with reference to exemplary catalyst systems, methods, and processes are not to be interpreted as limiting, but merely as the basis for teaching one skilled in the art the advantageous catalyst systems, methods, and processes of the present disclosure.

[0026] Advantages of use of the disclosed metal-multidentate ligand (e.g., amino polycarboxylic acid) complex in a catalyst system for preparing terephthalic acid include use of a decreased amount of bromine as a promoter in the reaction mixture, which can decrease corrosion and increase reactor lifetime. Additionally, use of the disclosed metal-multidentate ligand (e.g., amino polycarboxylic acid) complex in a catalyst system can improve overall yield and selectivity of a process for preparing terephthalic acid with reduced catalyst inactivation and by-product formation. [0027] In an embodiment, a catalyst system for preparing terephthalic acid includes a first complexation of a manganese salt and a first multidentate ligand (e.g., a first amino polycarboxylic acid) and a second complexation of a cobalt salt and a second multidentate ligand (e.g., a second amino polycarboxylic acid). The catalyst system can include 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, of bromine, based on a total weight of the catalyst system. The catalyst system can include 0 parts per million by weight bromine, based on a total weight of the catalyst system. In an embodiment, the catalyst system includes 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 a total weight of the catalyst system.

[0028] As used herein, the term “complexation” of a first material and a second material refers to a complex formed from the first material and the second material. In an embodiment, the formed complex does not include each of the first and second materials, as one of the first and second materials (e.g., a ligand such as an amino polycarboxylic acid) can coordinated to the other of the materials (e.g., a metal salt) during formation of the complexation process to form the complex, this may include protonation or deprotonation of amines, carboxylic acids, and/or alcohol functional groups. In some embodiments, the first material or the second material are a metal salt such as MnCh, Mn(NOs)2, manganese acetate, C0CI2, Co(NOs)2, cobalt acetate.

[0029] Each of the first material and the second material can independently include a multidentate ligand, i.e., a tridentate ligand, tetradentate ligand, pentadentate ligand, or hexadentate ligand such as N,N,N',N'-tetrakis(2-pyridinylmethyl)-l,2-ethanediamine, ethylenediaminetetraacetic acid, 2.2.2-cryptand, or a combination thereof. In an embodiment, the first material is a first amino carboxylic acid. In an embodiment, the second material is a second amino carboxylic acid. In an 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 use of a multidentate ligand, e.g., a hexadentate ligand such as ethylenediaminetetraacetic acid, in the catalyst system can provide an advantageous chelating effect; for example, the chelate arms can activate oxygen or the metal ion, and the oxidation state of intermediates can be changed.

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

[0031] A 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. The catalyst system can include, based on a total weight of the catalyst system 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 can include MnCh, Mn(N0s)2, manganese acetate, or a combination thereof. In an embodiment, the manganese salt includes manganese acetate.

[0033] The cobalt salt can include C0CI2, Co(NOs)2, cobalt acetate, or a combination thereof. In an embodiment, the cobalt salt includes cobalt acetate.

[0034] A process for producing the catalyst system for preparing terephthalic acid can include forming a first complexation by heating a first solution including a first material (e.g., a first multidentate ligand, such as a first an amino carboxylic acid) and a manganese salt to form the first complexation; separating the first complexation from the first solution; forming a second complexation by heating a second solution including a second material (e.g., a second multidentate ligand, such as a second amino polycarboxylic acid), and a cobalt salt to form the second complexation; separating the second complexation from the second solution; and combining the first complexation and the second complexation to produce the catalyst system.

[0035] A molar ratio of the manganese salt to the first multidentate ligand (e.g., a first amino polycarboxylic 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. A molar ratio of the cobalt salt to the second multidentate ligand (e.g., a second amino polycarboxylic 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] A process for producing terephthalic acid includes combining the 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 to produce the terephthalic acid.

[0037] The process can 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 a total weight of the reaction mixture including bromine. In an embodiment, bromine can be added to the reaction mixture in an amount of 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 a total weight of the catalyst system. As used herein, bromine added to the reaction mixture is a promoter, which is a separate component from the catalyst system added to the reaction mixture.

[0038] With reference to FIG. 1, a stream 10 including p-xylene can be fed to oxidation reactor 100. A gaseous stream 20 including oxygen (e.g., O2) can be fed to oxidation reactor 100. The gaseous stream 20 can include 19 to 25 volume percent (vol%) of oxygen, based on a total volume of the gaseous stream 20, or at least any one of, equal to any one of, or between any two of 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%, of oxygen, based on a total volume of the gaseous stream 20. In an embodiment, the gaseous stream 20 can be air. A liquid stream 30 including acetic acid and the disclosed catalyst can be fed to oxidation reactor 100.

[0039] In the oxidation reactor 100, the p-xylene can be oxidized, e.g., by O2, in presence of the disclosed catalyst system to form terephthalic acid. The p-xylene oxidation reaction condition can include (1) a temperature of 180 to 195 °C or at least any one of, equal to any one of, or between any two 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 and/or (2) a pressure 5 to 20 bar (500 to 2,000 kilopascals (kPa)) or 10 to 14 bar or at least any one of, equal to any one of, or between any two 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.

[0040] Product streams can include a gaseous effluent stream 40, a liquid stream, 50, solids 60, or a combination thereof, which can be subjected to HPLC analysis. In an embodiment, at least two of the gaseous effluent stream 40, a liquid stream, 50, and solids 60 can be withdrawn from the oxidation reactor 100 together, and thereafter separated.

[0041] Residence time of the reaction mixture in the oxidation reactor 100 can be 0.5 to 3 hours (hr) or at least any one of, equal to any one of, or between any two 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, 3 hr.

[0042] The oxidation reactor 100 can have a relatively inert inner surface. In an embodiment, the oxidation reactor 100 can be a platinum line reactor. [0043] In an embodiment, the p-xylene and oxygen can be fed to the oxidation reactor 100 at a molar ratio 1 :3 to 1 :5 or at least any one of, equal to any one of, or between any two 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.

[0044] In an embodiment, the p-xylene conversion can be 95 to 100 mole percent (mol%), based on a total number of moles of p-xylene fed to the reactor, or at least any one of, equal to any one of, or between any two of 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%, based on a total number of moles of p-xylene fed to the reactor. As used herein, the term “conversion” refers to the mole fraction (i.e., percent) of a reactant (e.g., p-xylene) converted to a product or products.

[0045] In an embodiment, the terephthalic acid yield (e.g., mol%) from the reaction between p-xylene and oxygen can be 90 to 100 mol%, based on a total number of moles of reaction products, or at least any one of, equal to any one of, or between any two of 90 mol%, 91 mol%, 92 mol%, 93 mol%, 94 mol%, 95 mol%, 96 mol%, 97 mol%, 98 mol%, 99 mol%, and 100 mol%, based on a total number of moles of reaction products. As used herein, the term “yield” refers to the mole fraction (i.e., percent) of a specified product (e.g., terephthalic acid) in a total product stream.

[0046] In an embodiment, the terephthalic acid selectivity from the reaction between p-xylene and 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, equal to any one of, or between any two 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%. As used herein, the term “selectivity” refers to the mole fraction (i.e., percent) of reactant converted to a specified product, for example, terephthalic acid selectivity is the percentage of p-xylene that was converted to terephthalic acid.

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

[0048] For example, a total product of the oxidation reactor 100 can 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 a total weight of the total product of the oxidation reactor 100. A total product of the oxidation reactor 100 can 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 a total weight of the total product of the oxidation reactor 100. Carbon dioxide (CO2) vol% in the gaseous effluent stream 40 from the oxidation reactor 100 can 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%, of CO2, based on a total weight of the gaseous effluent stream 40.

[0049] This disclosure is further illustrated by the following examples, which are non-limiting.

EXAMPLES

Example 1

[0050] Amounts of 100 milliliters (mL) of 0.1 moles per liter (molar (M)) ethylenediaminetetraacetic acid (EDTA) and 0.1 M cobalt acetate and manganese acetate are prepared in a standard flask. The solutions of EDTA and metal salts are added to a round-bottomed flask and pressure equalizer funnel, respectively. The round-bottomed flask is fitted with a reflux condenser and heated to 85 °C, upon attaining the desired temperature, the metal salt is added drop-wise while stirring using a magnetic bar. Upon completion of the addition of a metal salt solution, the resulting mixture stirred at the elevated temperature for another 3 hours. After completion of 3 hours, the heating is stopped and the stirring is continued overnight at room temperature. The precipitate formed is collected by filtration and washed several times with ethanol and dried in a desiccator. A catalyst system including the prepared cobalt-EDTA complex and manganese-EDTA complex having a molar ratio of cobalt to manganese of 1 : 1 is prepared.

[0051] The prepared material was characterized using ultraviolet-visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA), and complexation was confirmed. FIG. 2 shows FTIR spectra of EDTA and the manganese-EDTA complex; FIG. 3 shows FTIR spectra of EDTA and the cobalt-EDTA complex; FIG. 4 shows TGA profiles of EDTA and the manganese-EDTA complex; FIG. 5 shows TGA profile of EDTA and the cobalt-EDTA complex; FIG. 6 shows UV-vis absorption spectra of EDTA and the manganese-EDTA complex; FIG. 7 shows UV-vis absorption spectra of EDTA and the cobalt-EDTA complex; FIG. 8 shows XRD patterns of EDTA and the manganese-EDTA complex; and FIG. 9 shows XRD pattern of EDTA and the cobalt-EDTA complex.

[0052] An amount of 2.3 grams (g) (1 mole percent (mol%)) of the prepared catalyst system was added to a reactor and 46 parts per million by weight (ppm) of bromine promoter was added, percentages (relative amounts) based on a total content of the reaction mixture including catalyst (system). The reactor chamber is pressurized up to 12 bar with 9 bars of N2 gas and 3 bars of O2 gas until the reactor temperature of 190 °C is attained. Once the desired temperature is attained p-xylene is injected into the reactor at a flow rate of 1 millimeter per minute (mL/min), while the reactor atmosphere is replaced with O2 with a periodic release of O2 in the reactor chamber while the pressure is maintained at 12 bar. The reaction is carried out for 2 hours. In total, 46.5 mL (0.377 moles (mol)) of p-xylene and 142.9 mL (2.498 mol) acetic acid were fed to the reactor. The reactor is cooled and the solid terephthalic acid (TP A) formed is separated by filtration.

[0053] An amount of 125 mL of liquid was recovered, and 57 g of solid was recovered. The purity of the product formed is analyzed by high-performance liquid chromatography (HPLC) analysis, as shown in FIG. 10 (recovered solid) and FIG. 11 (recovered liquid).

Comparative Example 1

[0054] A catalyst system including 400 ppm Co, 220 ppm Mn, and 460 ppm Br was added to a reactor. The reactor chamber is pressurized up to 12 bar with 9 bars of N2 gas and 3 bars of O2 gas until the reactor temperature of 190 °C is attained. Once the desired temperature is attained p-xylene is injected into the reactor at a flow rate of 1 mL/min, while the reactor atmosphere is replaced with O2 with a periodic release of O2 in the reactor chamber while the pressure is maintained at 12 bar. The reaction is carried out for 1 hour. In total, 46.5 mL (0.377 mol) of p-xylene and 142.9 mL (2.498 mol) acetic acid were fed to the reactor. The reactor is cooled and the solid TPA formed is 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 a reactor. The reactor chamber is pressurized up to 12 bar with 9 bars of N2 gas and 3 bars of O2 gas until the reactor temperature of 190 °C is attained. Once the desired temperature is attained p-xylene is injected into the reactor at a flow rate of 1 mL/min, while the reactor atmosphere is replaced with O2 with a periodic release of O2 in the reactor chamber while the pressure is maintained at 12 bar. The reaction is carried out for 1 hour. In total, 46.5 mL (0.377 mol) of p-xylene and 142.9 mL (2.498 mol) acetic acid were fed to the reactor. The reactor is cooled and the solid TPA formed is separated by filtration.

[0056] The products formed in Example 1 and Comparative Examples 1 and 2 are provided in Table 2, with a summary provided in Table 3.

Table 2

Table 3

[0057] Example 1 provided an improvement in conversion, while still providing acceptable, e.g., desirable, values for TPA selectivity, TPA yield, CO2 production, 4-CBA production, and p-toluic acid production.

[0058] This disclosure further encompasses the following aspects.

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

[0060] Aspect 2. The catalyst system of Aspect 1, wherein the catalyst system comprises 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, of bromine, based on a 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 a total weight of the catalyst system.

[0062] Aspect 4. The catalyst system of any of the preceding aspects, wherein a molar ratio of manganese in the catalyst system to cobalt in the catalyst system is 3: 1 to 1 :3, or 2: 1 to 1 :2, or 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 hexadentate ligand; the second multidentate ligand comprises a hexadentate ligand; or a combination thereof.

[0064] Aspect 6. The catalyst system of any of the preceding aspects, wherein the first multidentate ligand comprises N,N,N',N'-tetrakis(2-pyridinylmethyl)-l,2-ethanediamine, ethylenediaminetetraacetic acid, 2.2.2-cryptand, or a combination thereof; the second multidentate ligand comprises N,N,N',N'-tetrakis(2-pyridinylmethyl)-l,2-ethanediamine, ethylenediaminetetraacetic acid, 2.2.2-cryptand, or a combination thereof; or a combination thereof.

[0065] Aspect 7. The catalyst system of any of Aspects 1 to 4, wherein the first multidentate ligand comprises a first amino polycarboxylic acid; and the second multidentate ligand comprises a second amino polycarboxylic acid.

[0066] Aspect 8. The catalyst system of any of the preceding aspects, comprising, based on a total weight of the catalyst system: 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.

[0067] Aspect 9. The catalyst system of any of the preceding aspects, comprising 0 parts per million by weight bromine, based on a 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 the first complexation by heating a first solution comprising the first multidentate ligand and the manganese salt to form the first complexation; separating the first complexation from the first solution; forming the second complexation by heating a second solution comprising the second amino polycarboxylic acid and the cobalt salt to form the second complexation; separating the second complexation from the second solution; and combining the first complexation and the second complexation to produce the catalyst system.

[0069] Aspect 11. The process of Aspect 10, wherein the first multidentate ligand comprises a hexadentate ligand; the second multi dentate ligand comprises a hexadentate 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 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 of Aspects 10 to 13, wherein the catalyst system comprises, based on a total weight of the catalyst system: 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; or a combination thereof; and wherein a 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; a 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 of Aspects 1 to 9, /?-xylene, and acetic acid to form a reaction mixture; and reacting the /?-xylene in the presence of oxygen to convert the /?-xylene to produce the terephthalic acid.

[0074] Aspect 16. The process of Aspect 15, further comprising 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 a total weight of the reaction mixture including bromine.

[0075] Aspect 17. The process of Aspect 16, comprising adding bromine to the reaction mixture in an amount of 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 a total weight of the catalyst system.

[0076] Aspect 18. The process of any of Aspects 15 to 17, wherein a conversion 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 a total number of moles of p-xylene reacted; and wherein a yield of terephthalic acid is greater than or equal to 90 mol%, or 91 mol%, or 92 mol%, or 93 mol%, based on a total number of moles of reaction products; a 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 can alternatively comprise, consist of, or consist essentially of, any appropriate materials, steps, or components herein disclosed. The compositions, methods, and articles can additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any materials (or species), steps, or components, that are otherwise not necessary to the achievement of the function or objectives of the compositions, methods, and articles.

[0078] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other (e.g., ranges of “up to 25 wt%, or, more specifically, 5 wt% to 20 wt%”, is inclusive of the endpoints and all intermediate values of the ranges of “5 wt% to 25 wt%,” etc.). “Combinations” is inclusive of blends, mixtures, alloys, reaction products, and the like. The terms “a” and “an” and “the” do not denote a limitation of quantity and are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. “Or” means “and/or” unless clearly stated otherwise. Reference throughout the specification to “some embodiments”, “an embodiment”, and so forth, means that a particular element described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, the described elements may be combined in any suitable manner in the various embodiments. A “combination thereof’ is open and includes any combination comprising at least one of the listed components or properties optionally together with a like or equivalent component or property not listed.

[0079] Unless specified to the contrary herein, all test standards are the most recent standard in effect as of the filing date of this application, or, if priority is claimed, the filing date of the earliest priority application in which the test standard appears.

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

[0081] While particular embodiments have been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace 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 such exemplary embodiments and/or implementations. Rather, the processes and methods of the present disclosure are susceptible to many implementations and applications, as will be readily apparent to persons skilled in the art from the disclosure hereof. The present disclosure expressly encompasses such modifications, enhancements and/or variations of the disclosed embodiments. Since many changes could be made in the above construction and many widely different embodiments of this disclosure could be made without departing from the scope thereof, it is intended that all matter contained in the drawings and specification shall be interpreted as illustrative and not in a limiting sense. Additional modifications, changes, and substitutions are intended in the foregoing disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure.

Claims

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

2. The catalyst system of Claim 1, wherein the catalyst system comprises less than 100 parts per million by weight, or less than 50 parts per million by weight, of bromine, based on a 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, or greater than 20 parts per million by weight, or greater than 40 parts per million by weight, of bromine, based on a total weight of the catalyst system.

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

5. The process of any of the preceding claims, wherein: the first multidentate ligand comprises a hexadentate ligand; the second multidentate ligand comprises a hexadentate ligand; or a combination thereof.

6. The catalyst system of any of the preceding claims, wherein: the first multidentate ligand comprises

N,N,N',N'-tetrakis(2-pyridinylmethyl)- 1 ,2-ethanediamine, ethylenediaminetetraacetic acid, 2.2.2-cryptand, or a combination thereof; the second multidentate ligand comprises

N,N,N',N'-tetrakis(2-pyridinylmethyl)- 1 ,2-ethanediamine, ethylenediaminetetraacetic acid, 2.2.2-cryptand, or a combination thereof; or a combination thereof.

7. The process of any of Claims 1 to 4, wherein: the first multidentate ligand comprises a first amino polycarboxylic acid; and the second multidentate ligand comprises a second amino polycarboxylic acid.

8. The catalyst system of any of the preceding claims, comprising, based on a total weight of the catalyst system:

1 to 20 weight percent of manganese; and

1 to 20 weight percent of cobalt.

9. The catalyst system of any of the preceding claims, comprising 0 parts per million by weight bromine, based on a total weight of the catalyst system.

10. A process for producing the catalyst system of any of the preceding claims, the process comprising: forming the first complexation by heating a first solution comprising the first multidentate ligand and the manganese salt to form the first complexation; separating the first complexation from the first solution; forming a second complexation by heating a second solution comprising the second multidentate ligand and the cobalt salt to form the second complexation; separating the second complexation from the second solution; and combining the first complexation and the second complexation to produce the catalyst system.

11. The process of Claim 10, wherein: the manganese salt comprises manganese acetate; the cobalt salt comprises cobalt acetate; or a combination thereof.

12. The process of Claim 10 or 11, wherein the catalyst system comprises, based on a total weight of the catalyst system:

1 to 20 weight percent of manganese; and

1 to 20 weight percent of cobalt; or a combination thereof; and wherein a 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; a 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.

13. A process for producing terephthalic acid comprising: combining the catalyst system of any of Claims 1 to 9, /?-xylene, and acetic acid to form a reaction mixture; and reacting the /?-xylene in the presence of oxygen to convert the /?-xylene to produce the terephthalic acid.

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

15. The process of any of Claims 12 to 14, wherein a conversion 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 a total number of moles of p-xylene reacted; and wherein a yield of terephthalic acid is greater than or equal to 90 mol%, or 91 mol%, or 92 mol%, or 93 mol%, based on a total number of moles of reaction products; a 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.