Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acids and salts thereof
Reexamination Certificate
2000-08-22
2002-03-12
Killos, Paul J. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acids and salts thereof
Reexamination Certificate
active
06355834
ABSTRACT:
FIELD OF INVENTION
This invention generally relates to oxidation and disproportionation/isomerization reactions. More particularly, this invention is related to catalysts, conditions, and media used to combine oxidation and disproportionation/isomerization reactions to form aromatic diacids. Still more particularly, this invention is a novel process for making aromatic diacids in one step from aromatic methyl compounds using a single catalyst system. The examples demonstrate the manufacture of 2,6-naphthalene dicarboxylic acid (2,6-NDA) in one step using the catalyst system of the present invention.
BACKGROUND OF THE INVENTION
Aromatic dicarboxylic acids are highly useful organic compounds. They are often used as monomers for the preparation of polymeric materials. 2,6-naphthalene dicarboxylic acid (2,6-NDA) is a particularly useful aromatic carboxylic acid, because it can be reacted with ethylene glycol to prepare poly(ethylene-2,6-naphthalate), PEN. Fibers and films manufactured from PEN display improved strength and superior thermal properties compared with other polyester materials such as polyethylene terephthalate. High strength fibers made from PEN can be used to make tire cords, and films made from PEN are advantageously used to manufacture magnetic recording tape and components for electronic applications.
All of the processes in the art for producing aromatic dicarboxylic acids, including 2,6-NDA, require multiple separate steps, including oxidation and isomerization. The catalyst for each of these steps is distinct and the catalysts for the various steps are incompatible.
Currently, the most common process for making 2,6-NDA starts with relatively expensive o-xylene and butadiene feedstocks, as discussed, for example, in U.S. Pat. No. 5,510,563 and U.S. Pat. No. 5,329,058. The 2,6-NDA is formed from the xylene and butadiene by a complex set of reactions terminating in a solid acid catalyzed isomerization of a family of dimethyl napthalene isomers to the 2,6-NDA form. The 2,6 dimethyl naphthalene is then oxidized to 2,6-NDA by means of a cobalt/manganese catalyst system in a liquid organic solvent. Besides the numerous steps, the process requires extensive purification.
In the 1970s Teijin briefly operated a type of Henkel process in which a dialkyl naphthalene was oxidized to 1,8-naphthoic dicarboxylic acid anhydride, or other naphthoic acid derivatives, using catalysts similar to those used in the second step of the process of U.S. Pat. No. 5,510,563 and U.S. Pat. No. 5,329,058. The acids were subsequently converted to potassium salts and isomerized in a disproportionation reaction using a completely different catalyst under a set of conditions distinct from previous steps.
It would constitute a vast improvement over anything currently available in the art if it were possible to effect isomerization and oxidation simultaneously, with one catalyst system. For example, this would make it possible to take a mixture of methyl naphthalenes or dimethyl naphthalenes, and convert them directly, using a single catalyst system in one step, to 2,6-NDA or its salts.
It is known in the art that catalysts other than cobalt/manganese will oxidize aromatic methyl groups to aromatic acids. For example, phthalic anhydride is commercially manufactured by air oxidation of ortho-xylene over vanadium pentoxide catalysts, usually supported on titania or other infusible supports. However, 2,6-NDA cannot be manufactured by this method, nor can terephthalic acid (TPA), since while phthalic anhydride (PA) is volatile (bp 163° C.) at the reaction temperature (typically near 300° C.), neither TPA nor 2,6-NDA is appreciably volatile, and, therefore, if a mixture of, for example, para-xylene and ortho-xylene is fed to the PA process, the result is PA from the ortho-xylene, and complete combustion or decarboxylation of the paraxylene, which is held up on the vanadia titania catalyst until it is burned to water and CO
2
.
In the present invention we have unexpectedly discovered a method of addressing the deficiency characteristic of a vanadium catalyst in the V
2
O
5
oxidation of para-substituted dimethyl aromatics, and have discovered a means for applying the use of a vanadium-containing catalyst system to the manufacture of 2,6-NDA from monomethyl naphthalenes. Furthermore, we have discovered a process for manufacturing 2,6-NDA in one step, using a single reactor.
SUMMARY
In accordance with the foregoing the present invention comprises:
A process for manufacturing an aromatic diacid in one step with a single catalyst system which comprises:
a) Introducing into a reactor an aromatic hydrocarbon containing the number of rings desired in the product diacid with one or more alkyl groups attached to the rings;
b) Reacting said aromatic hydrocarbon in the presence of an oxidant supply and a catalyst system comprising at least one catalyst selected from Group IB, IIB, VB, or VIIB of the Periodic Table, or a mixture thereof, in a reaction medium capable of stabilizing the aromatic acids formed against further oxidation to water and CO
2
or decarboxylation to aromatic hydrocarbons, and also capable of allowing the isomerization of the acids so formed to the desired diacids; and
c) Reacting said hydrocarbon feed with said oxidant in the presence of said catalyst and medium system until a desired amount of said feed is oxidized to carboxylic acids and isomerized to the desired diacid product.
DETAILED DESCRIPTION OF THE INVENTION
The hydrocarbon feed in the present invention comprises one containing the aromatic rings desired in the final diacid, with one or more alkyl groups attached to the rings, in mixture or in single isomers. Hydrocarbons which are suitable as starting materials in the present invention include aromatic hydrocarbons containing one or more benzene rings, including, but not limited to benzene, toluene, xylene, and tetralin, and condensed aromatic hydrocarbons such as naphthalene, anthracene, phenanthrene, etc.,with one or more alkyl groups attached to the rings, or a mixture thereof, or a fraction containing one or more of them.
The catalyst used in the present invention comprises a compound selected from Group IB, IIB, VB, or VIIB of the Periodic Table. Suitable catalysts include compounds of vanadium, zinc, manganese, and cobalt in the form of, for example, oxides, halides, sulfates, carbonates, and carboxylates of these metals. Suitable vanadium catalysts include vanadium catalysts known in the art, including supported vanadium catalysts, as described, for example in U.S. Pat. No. 4,931,572, incorporated by reference herein in the entirety.
The vanadium metal oxide source may be vanadium pentoxide or may be a vanadium compound such as an ammonium metavanadate, vanadyl sulfate, vanadyl halide (e.g., vanadyl chloride, vanadyl dichloride), vanadyl oxyhalide (e.g., vanadyl oxychloride), metavanadic acid, pyrovanatic acid, vanadium hydroxide, and vanadyl carboxylates such as formate, tartrate, salicylate and oxalate, which can then become vanadium oxide at the calcining temperature.
Suitable zinc compounds include zinc halides such as zinc fluoride, zinc chloride, zinc bromide, and zinc iodide; zinc carboxylates such as zinc naphthoate and zinc naphthalene-dicarboxylate; zinc oxide, zinc carbonate; zinc sulfate and mixtures thereof.
The preferred catalysts are vanadium pentoxide and zinc oxide.
The catalyst can optionally be on a support. Where the catalyst is on a support, the support may be selected from Groups II, III, IV, or V of the Periodic Table. Supported catalysts for use in either fixed or fluidized bed operations employ carriers including alumina, silica, silica gel, silica-alumina, silicon carbide, magnesium oxide, titania and titania-silica zirconia, zeolites such as zeolite Y as well as mixtures thereof. Where a support is used in the present invention, the preferred support is titania.
In the present invention it is desirable to employ a medium which is capable of stabilizing the aromatic acids formed against further oxidation to water and CO
2
, or carboxylation to arom
Brownscombe Thomas Fairchild
King William Larry
Pfrehm Susan Secor
Killos Paul J.
Shell Oil Company
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