| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | January 30, 2001 |
| PATENT TITLE |
Method of producing aromatic carboxylic acids by oxidizing alkyl aromatic compounds or partially oxidized intermediates thereof with carbon dioxide containing gas |
| PATENT ABSTRACT | An improved production method of aromatic carboxylic acid products of significantly improved yield and quality, the method including oxidizing alkyl aromatic substrates or their partially oxidized intermediates in a catalyst system containing a conventional catalyst and, if deemed necessary, additional components such as a transition metal or lanthanide series metal, in an acetic acid medium, with a feed gas containing both oxygen and carbon dioxide. Since carbon dioxide functions as a co-oxidant along with oxygen in the oxidation reaction, the oxidation reaction proceeds more selectively to produce the carboxylic acid product much faster under milder reaction conditions as compared to the conventional oxidation. The present invention also can be utilized as an effective purification process to produce highly pure terephthalic acid or isophthalic acid by oxidation of impurities such as 4-carboxybenzaldehyde and para-toluic acid or 3-carboxybenzaldehyde and meta-toluic acid which are contaminated in crude terephthalic acid and isophthalic acid products, respectively |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | December 3, 1999 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT REFERENCES CITED |
J. Yoo, "Selective Gas-Phase Oxidation at Oxide Nanoparticles on Microporous Materials," Catalysis Today, vol. 41 (1998), pp. 409-432. J. Yoo, "Gas Phase Oxygen Oxidation of Alkylaromatics over CVD Fe/Mo/Borosilicate Molecular Sieve, Fe/Mo/DBH. VII. Oxidative Dehydrogenation of Alkylaromatics," Applied Catalysis A: General, vol. 142 (1996), pp. 19-29. J. Yoo, "The CVD Fe/Mo/DBH (Deboronated Borosilicate Molecular Sieve)--Catalyzed Oxidation Reactions," Applied Catalysis A: General, vol. 143 (1996), pp. 29-51. J. Yoo, "Gas-Phase Oxygen Oxidations of Alkylaromatics over CVD Fe/Mo/Borosilicate Molecular Sieve. VI. Effects of para-Substituents in Toluene Derivatives," Applied Catalysis A: General, vol. 135 (1996), pp. 261-271. J. Yoo, et al., "Gas-Phase Oxygen Oxidations of Alkylaromatics over CVD Fe/Mo/Borosilicate Molecular Sieve. II. The Role of Carbon Dioxide as a Co-Oxidant," Applied Catalysis A: General, vol. 106 (1993), pp. 259-273. G. Zajac, et al., "Characterization and Oxidation Catalysis of Alkylaromatics over CVD Fe/Mo/Borosilicate Molecular Sieve: Fe/Mo/DBH," Journal of Catalysis, vol. 151, No. 2, Feb. 1995, pp. 338-348. W. Partenheimer, "Methodology and Scope of Metal/bromide Autoxidation of Hydrocarbons," J. Chem Soc. Chem. Commun., vol. 23 (1995), pp. 69-158. M. Aresta, et al., "Carbon Dioxide as Modulator of the Oxidative Properties of Dioxygen in the Presence of Transition Metal Systems," J. Chem. Soc. Chem. Commun., 1992, pp. 315-317. |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A method of producing an aromatic carboxylic acid, said method comprising the steps of: oxidizing an alkyl aromatic compound or a partially oxidized intermediate thereof, with a gas comprising oxygen and at least 4% by volume of the gas of carbon dioxide, using a catalyst comprising cobalt, manganese, and bromine. 2. A method according to claim 1, wherein the catalyst is dissolved in a solvent comprising an aliphatic carboxylic acid having 1 to 6 carbon atoms. 3. A method according to claim 2, wherein the solvent further comprises 2% to 25% by weight of water. 4. A method according to claim 1, wherein the catalyst further comprises another transition metal or a lanthanide metal. 5. A method according to claim 4, wherein the another transition metal or the lanthanide metal is selected from the group consisting of zirconium, hafnium, cerium, molybdenum, chromium, iron, and tungsten. 6. A method according to claim 1, wherein the gas comprises 4% to 80% by volume of the gas of carbon dioxide. 7. A method according to claim 6, wherein the gas comprises 5% to 50% by volume of the gas of carbon dioxide. 8. A method according to claim 7, wherein the gas lacks an inert diluent. 9. A method according to claim 1, wherein the alkyl aromatic compound is selected from the group consisting of para-xylene, meta-xylene, ortho-xylene, pseudocumene (1,2,4-trimethylbenzene), mesitylene (1,3,5-trimethylbenzene), durene (1,2,4,5-tetramethylbenzene), pentamethylbenzene, hexamethylbenzene, dimethylnaphthalene, 4,4'-dimethylbiphenyl, and toluene. 10. A method according to claim 1, wherein the partially oxidized alkyl aromatic intermediate is selected from the group consisting of para-toluic acid, meta-toluic acid, ortho-toluic acid, para-tolualdehyde, meta-tolualdehyde, ortho-tolualdehyde, 4-carboxybenzaldehyde, 3-carboxylbenzaldehyde, and 2-carboxybenzaldehyde. 11. A method according to claim 10, wherein the partially oxidized alkyl aromatic intermediate is selected from the group consisting of para-toluic acid, meta-toluic acid, 4-carboxybenzaldehyde, and 3-carboxybenzaldehyde. 12. A method according to claim 1, wherein the aromatic carboxylic acid is selected from the group consisting of terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydride, naphthalene dicarboxylic acid, trimellitic acid, trimellitic anhydride, trimesic acid, pyromellitic dianhydride, benzene pentacarboxylic acid, benzene hexacarboxylic acid, 4,4'-biphenyldicarboxylic acid, and benzoic acid. 13. A method according to claim 12, wherein the aromatic carboxylic acid is selected from the group consisting of terephthalic acid, isophthalic acid, and phthalic anhydride. 14. A method according to claim 1, wherein the carbon dioxide is added with a gas sparging device into one or more zones of a reactor in a gas phase or liquid phase either periodically, intermittently, or in a continuous manner. 15. A method according to claim 1, wherein the carbon dioxide is mixed into the gas, which is a feed gas. 16. A method according to claim 1, wherein carbon dioxide remaining in reaction vent gas is recovered by condensation and is recycled to provide the carbon dioxide required for the oxidation reaction. 17. A method according to claim 1, wherein the alkyl aromatic compound para-xylene is used to produce the aromatic carboxylic acid terephthalic acid, and the catalyst is prepared by combining cobalt acetate tetrahydrate, manganese acetate tetrahydrate, and hydrogen bromide. 18. A method according to claim 1, wherein the alkyl aromatic compound meta-xylene is used to produce the aromatic carboxylic acid isophthalic acid, and the catalyst is prepared by combining cobalt acetate tetrahydrate, manganese acetate tetrahydrate, and hydrogen bromide. 19. A method according to claim 1, wherein the alkyl aromatic compound ortho-xylene is used to produce the aromatic carboxylic acid phthalic acid or phthalic anhydride, and the catalyst is prepared by combining cobalt acetate tetrahydrate, manganese acetate tetrahydrate, and hydrogen bromide. 20. A method of producing an aromatic carboxylic acid, said method comprising the steps of: oxidizing an alkyl aromatic compound or a partially oxidized intermediate thereof, with a gas comprising oxygen and an effective amount of carbon dioxide, the effective amount being an amount sufficient to exhibit action by the carbon dioxide as a co-oxidant, using a catalyst comprising at least one transition metal. 21. A process of purifying crude terephthalic acid or crude isophthalic acid products containing, as an impurity, a partially oxidized intermediate of an alkyl aromatic compound, to obtain substantially pure terephthalic acid or isophthalic acid using the method according to claim 10. 22. A process according to claim 21, wherein the partially oxidized intermediate of an alkyl aromatic compound is selected from the group consisting of 4-carboxybenzaldehyde and 3-carboxybenzaldehyde. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention discloses an improved process for oxidizing alkyl aromatic hydrocarbons and/or their partially oxidized intermediates to produce aromatic carboxylic acids. The process involves the liquid phase oxidation in the presence of a catalyst of cobalt-manganese-bromine in an aliphatic carboxylic acid having 1-6 carbon atoms such as acetic acid as a solvent with a gas containing oxygen and carbon dioxide. Furthermore, an additional transition metal or lanthanide series metal is introduced to the cobalt-manganese-bromine catalyst system, when deemed necessary. The rate of the oxidation reaction of an alkyl aromatic substrate was remarkably increased in the present process over the conventional oxidation process. The yield and quality of the carboxylic acid products were also significantly improved in the process. Thus, for example, terephthalic acid and isophthalic acid of improved yield and purity are produced by carrying out the oxidation of para-xylene and meta-xylene, respectively, in the co-presence of carbon dioxide and oxygen under relatively mild reaction conditions. 2. Description of the Related Art As discussed below, methods of manufacturing aromatic carboxylic acids are well known and widely used commercially. For example, the method of manufacturing of aromatic carboxylic acids such as terephthalic acid (TPA), isophthalic acid (IPA), phthalic acid, phthalic anhydride, naphthalene dicarboxylic acid, trimellitic acid, trimellitic anhydride, trimesic acid, pyromellitic dianhydride, 4,4'-biphenyldicarboxylic acid and benzoic acid by oxidizing alkylaromatic compounds or the oxidized intermediates thereof, in the presence of cobalt-manganese-bromine, from such alkylaromatic compounds as para-xylene, para-tolualdehyde, para-toluic acid, 4-carboxybenzaldehyde (4-CBA), meta-xylene, meta-tolualdehyde, meta-toluic acid, 3-carboxybenzaldehyde, ortho-xylene, dimethylnaphtalene, pseudocumene (1,2,4-trimethylbenzene), mesitylene (1,3,5-trimethylbenzene), durene (1,2,4,5-tetramethylbenzene), 4,4'-dimethylbiphenyl and toluene is well known (for example, U.S. Pat. Nos. 2,833,816 and 5,183,933). Such aromatic carboxylic acids are used as raw materials for manufacturing polyester after appropriate purification such as hydrogenation, etc. (U.S. Pat. No. 3,584,039). Also, polyester is widely used as a synthetic fiber, film, etc. There were continuous endeavors to develop a catalyst system with high efficiency and enhanced reactivity to manufacture aromatic carboxylic acids. The newly developed technologies, however, were not practical due to the increase in side reactions, price of catalyst, difficulty of operation, precipitation of catalyst, etc. Improvements in the efficiency of the reaction for manufacturing of aromatic carboxylic acids are very significant because they may improve productivity, quality and cost competitiveness due to the reduction in the reaction time and side reactions. In other words, it is highly desirable to develop a technology to increase the efficiency of the oxidation reaction of alkyl aromatic compounds and the oxidized intermediates thereof by means of an improvement in the reaction processes. There were many attempts to increase the efficiency by adding a third metal catalyst to the cobalt-manganese-bromine catalyst system which is the basic catalyst system, to enhance the catalyst efficiency during the manufacturing of aromatic carboxylic acids. The added metals were mainly transition metals, and by adding, for example, hafnium, zirconium, molybdenum, etc., the reactivity therein was increased (U.S. Pat. No. 5,112,992). On the other hand, an oxygen containing gas such as air was mainly used as an oxidant during the manufacturing of aromatic carboxylic acids. Carbon dioxide was not used as an oxidant due to its chemical stability. Yet, in the research for improving the process efficiency, there was a case in which chemically stable carbon dioxide, recycled from the reaction vent gas, was injected to the reactor to increase the stability in the process by mitigating the problematic possibilities of explosion due to oxygen when using pure oxygen or gas containing pure oxygen or oxygen enriched gas as an oxidant (U.S. Pat. No. 5,693,856). Nevertheless, the case is not known in which carbon dioxide was added to improve the reaction efficiency and the effects of the concentration of added carbon dioxide on oxidation. In summary, the basic oxidation technology for manufacturing carboxylic acids, especially for TPA manufacture, has been extensively developed. The basic process technology is now approaching a point of diminishing returns, and further major breakthroughs i.e., new catalyst systems, raw materials, and basic unit operations, are not anticipated. The leading producers are expected to have greater optimization and energy integration across the entire production complex with more advanced control schemes. However, surpassing the current general expectation, the present invention have made a remarkable breakthrough to achieve the improved catalyst activity and selectivity toward aromatic carboxylic acids, especially for terephthalic acid and isophthalic acid, in the aforementioned catalyst composition under milder oxidation conditions. SUMMARY OF THE INVENTION As a result of research for resolving the above problems, the inventors herein added an appropriate amount of carbon dioxide to the oxygen containing gas, which was supplied as an oxidant in the oxidation reaction, in the manufacturing of aromatic carboxylic acids in the catalyst of cobalt-manganese-bromine, in which a transition metal or lanthanide metal was added as deemed necessary. The reactivity not only dramatically increased but the side reactions also decreased. Based on such findings, the present invention has been thus perfected. In view of the foregoing, in one aspect, the present invention relates to a method of producing an aromatic carboxylic acid, the method comprising the steps of oxidizing an alkyl aromatic compound or a partially oxidized intermediate thereof, with a gas (e.g., a feed gas or a reaction gas) comprising oxygen and carbon dioxide, using a catalyst comprising cobalt, manganese, and bromine. Preferably, the carbon dioxide is present in the gas in an amount of at least 4% by volume of the gas. In another aspect, the present invention relates to a method of producing an aromatic carboxylic acid, the method comprising the steps of oxidizing an alkyl aromatic compound or a partially oxidized intermediate thereof, with a gas comprising oxygen and an effective amount of carbon dioxide, the effective amount being an amount sufficient to exhibit action by the carbon dioxide as a co-oxidant (e.g., an amount greater than that present in air, or as in the examples hereinbelow), using a catalyst comprising at least one transition metal. Preferably, the carbon dioxide is present in the gas phase in an amount of at least 1% by volume of the gas phase, or at least 4% by volume, or at least 7% by volume, or at least 14% by volume, or at least 50% by volume. In another aspect, the present invention relates to a method of liquid phase O.sub.2 oxidation of alkylaromatics such as p-, m-, and o-xylenes to the corresponding terephthalic acid, isophthalic acid, and phthalic anhydride with the MC-type catalyst, Co--Mn--Br, in the co-presence of CO.sub.2, e.g., ##STR1## In a still further aspect, the present invention relates to a process of purifying crude terephthalic acid products or crude isophthalic acid products containing, as an impurity, a partially oxidized intermediate of an alkyl aromatic compound, to obtain substantially pure terephthalic acid or isophthalic acid by using an above-discussed method. In still further aspects, the present invention relates to (a) an aromatic carboxylic acid prepared by an above-discussed method, (b) polyester made using the aromatic carboxylic acid, and (c) a product made using the polyester. These and other aspects, objects, advantages, and features of the present invention will become apparent from the following detailed description of preferred embodiments thereof. Unless otherwise stated, in this application, the concentration of gas is in volume %, the concentration of the catalyst is in weight ppm (by total weight of the reaction mixture), and the concentration of the product, and any other unspecified %, is in weight %. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a production method of aromatic carboxylic acids, wherein alkylaromatic compounds or the oxidized intermediates thereof are oxidized by an oxygen containing gas, with an aliphatic carboxylic acid having 1-6 carbon atoms as a solvent, in the presence of a catalyst of cobalt-manganese-bromine, with addition of a transition metal or lanthanide metal as deemed necessary. In the process, an appropriate amount of carbon dioxide is added to the oxygen containing gas, which is supplied as an oxidant. Starting substances, i.e., alkylaromatic compounds or the oxidized intermediates thereof, to be oxidized in the present invention are preferably the compounds of benzene, naphthalene or similar aromatic compounds having one or more than one substituted alkyl groups (or a functional group having an oxidized alkyl group), such as para-xylene, para-tolualdehyde, para-toluic acid, 4-carboxybenzaldehyde, meta-xylene, meta-tolualdehyde, meta-toluic acid, 3-carboxybenzaldehyde, ortho-xylene, dimethylnaphthalene, pseudocumene (1,2,4-trimethylbenzene), mesitylene (1,3,5-trimethylbenzene), durene (1,2,4,5-tetramethylbenzene), pentamethylbenzene, hexamethylbenzene, 4,4'-dimethylbiphenyl, and toluene. The intended substances of the present invention i.e., aromatic carboxylic acids, are preferably the compounds of benzene, naphthalene or similar aromatic compounds having one or more than one substituted carboxylic acid groups (or anhydrides with the removal of water by condensation of the carboxylic groups), such as terephthalic acid, isophthalic acid, phthalic acid, phthalic anhydrides, naphthalene dicarboxylic acid, trimellitic acid, trimellitic anhydrides, trimesic acid, pyromellitic dianhydride, 4,4'-biphenyldicarboxylic acid, and benzoic acid. As for the basic catalyst in the present invention, a cobalt-manganese-bromine catalyst system was used. If deemed necessary, a transition metal or lanthanide metal component may be added. In the basic catalyst, the atomic weight ratio of manganese/cobalt is preferably 0.1.about.10, or more preferably 0.5.about.5. The atomic weight ratio of bromine/(manganese+cobalt) is preferably 0.1.about.10, or more preferably 0.5.about.2. The concentration of cobalt is preferably 20.about.10,000 ppm of the weight of the reactants (i.e., the substrate (the starting substance to be oxidized such as the alkylaromatic compound), the solvent, and the catalyst), or more preferably 50.about.10,000 ppm. As for the source of bromine, it could be a bromine compound, such as hydrogen bromide, tetrabromoethane, etc. As for the source of manganese and cobalt, a compound which is soluble in solvents, such as acetate, carbonate, acetate tetrahydrate, bromide, etc. can be used, or more preferably, sources of cobalt, manganese, and bromine are cobalt acetate tetrahydrate, manganese acetate tetrahydrate, and hydrogen bromide, respectively. Compounds of Ce, Zr, Hf, Mo, Cr, Fe, W, etc. are preferred for transition metals or lanthanide metals, which are added if necessary. The weight ratio of the added transition metal or lanthanide metal/manganese is preferably 0.001.about.1. Further, the present invention can be applied to an oxidation reaction by a cobalt-manganese catalyst without bromine as well as to the oxidation reaction by a nickel-manganese-bromine catalyst. The solvent used in the present invention can be any aliphatic acids of C.sub.1.about.C.sub.6, such as formic acid, acetic acid, propionic acid, n-butyric acid, isobutyric acid, pentanoic acid, hexanoic acid, trimethylacetic acid, etc, or more preferably acetic acid or the mixture of acetic acid and water. Preferably, the solvent comprises from 2% to 25%, by weight, of water. The amount of solvent should be 1.about.10 times the weight of an alkylaromatic compound or the oxidized intermediate compound thereof. Further, the present invention can be applied to the oxidation reaction with water as a solvent. As for the reaction gas used in the present invention, oxygen, or a gas mixture of oxygen and an inert gas such as nitrogen can be used, or more preferably, a gas mixture of oxygen and carbon dioxide can be used. Preferably, the reaction gas or feed gas lacks an inert diluent. The minimal pressure of the reaction is such that some portions of an alkylaromatic compound or the oxidized intermediate thereof and the solvent are maintained as liquid. The reaction pressure is appropriately 0.about.35 atm in terms of the gauge pressure or more preferably 8.about.30 atm. The amount of carbon dioxide should be 1.about.80% by volume of the gas, or more preferably 5-50% by volume. As for the method of adding carbon dioxide, it can be supplied in the gas phase at the upper part of the reactor or in the reactants of liquid phase, either periodically or continuously. (For example, carbon dioxide may be added with a gas sparging device into one or more zones of a reactor in a gas phase or liquid phase either periodically, intermittently, or in a continuous manner.) As for the method of supplying carbon dioxide to the reactor, carbon dioxide can be mixed into the reaction gas. Alternatively, the method of recycling the reacted vent gas to the reaction gas can be used for the purpose of utilization of the carbon dioxide and oxygen remaining in the vent gas. (For example, carbon dioxide remaining in the reaction vent gas may be recovered by condensation and recycled to provide carbon dioxide required for the oxidation reaction). When it is supplied to the reactants in liquid, a dip tube, etc. can be used for supplying via bubbling or sparging. The production method of aromatic carboxylic acids of the present invention could be carried out by a batch type process or a continuous process. The appropriate reaction temperature should be 100.about.255.degree. C., or more preferably 175.about.235.degree. C., or most preferably 180.about.210.degree. C. If the reaction temperature is too low, it is impractical since the reaction rate is too slow. On the other hand, if the reaction temperature is too high, it is non-economical due to the excessive side reactions. As a reactor, general CSTR (continuous stirred tank reactor) or LOR (liquid oxygen reactor) specially designed to mix liquid oxygen and liquid hydrocarbon substrates without appreciable loss of unreacted oxygen into the overhead vapor space can be used. According to the present invention, the reaction time is decreased at the same reaction temperature for obtaining the same conversion. At the same reaction time, the present invention requires a lower reaction temperature for a given conversion. The productivity and quality such as chemical impurities can be improved due to the decreased side reactions with the present invention. The present invention is explained in detail by examples below. Nevertheless, the examples are illustrative only and should not be deemed to limit the present invention. |
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