Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-09-27
2002-09-17
Dentz, Bernard (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C502S242000, C502S247000, C502S248000
Reexamination Certificate
active
06452021
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a catalyst for use in the production of pyromellitic anhydride and a production method of pyromellitic anhydride. More particularly, the invention relates to a catalyst system suitable for the production method of pyromellitic anhydride by the catalytic gas-phase oxidation of a 2,4,5-trialkylbenzaldehyde and a production method of pyromellitic anhydride with the aid of said catalyst system.
BACKGROUND OF THE INVENTION
Pyromellitic anhydride is in broad use as a starting material of polyimide resin, a plasticizer, and apolyester resin modifying agent, among other uses, and its importance as an industrial material has been increasing steadily in recent years.
The production method of pyromellitic anhydride can be roughly classified into the liquid-phase oxidation method and the gas-phase oxidation method. As regards the liquid-phase oxidation method, the process for nitric acid oxidation of 1,2,4,5-tetramethylbenzene (hereinafter referred to sometimes as “durene”) and the process for liquid-phase air oxidation of 2,4,5-trimethylbenzaldehyde are known. But these processes do not give pyromellitic anhydride directly and require conversion of the produced pyromellitic acid to the anhydride. This conversion to the anhydride form is a step entailing a large energy consumption. Moreover, these liquid-phase oxidation processes generate large quantities of waste liquor and cause a substantial corrosion of the equipment so that they have much to be improved not only in economic terms but also in environmental terms.
On the other hand, the gas-phase oxidation method is superior in that it can give pyromellitic anhydride directly, does not require the costly step of conversion to the anhydride, nor does it generate an appreciable amount of waste liquor. However, compared with the liquid-phase oxidation method, the gas-phase method has a drawback of low selectivity and a large number of reports have been made mainly concerning improvement of the catalyst system.
The commonest production method of pyromellitic anhydride by catalytic gas-phase oxidation is the method using durene as a starting material but other examples are also reported using pentaalkylbenzene, hexaalkylbenzene (Japanese Kokai Publication Sho-55-122787), pentaalkylphenol, tetraalkylphenol (Japanese Kokai Publication Sho-55-154966), tetraethylbenzene (Japanese Kokai Publication Hei-3-284646, Japanese Kokai Publication Hei-3-109387, Japanese Kokai Publication Hei-3-284645), anthracene (Japanese Kokai Publication Sho-56-8388), 1-ethyl-2,4,5-triisopropylbenzene (Japanese Kokai Publication Hei-8-119969), or 2,4,5-trialkylbenzaldehyde (Japanese Kokai Publication Hei-7-2864, U.S. Pat. No. 5,387,699) as a starting material.
However, none of these technologies provide pyromellitic anhydride of high purity at low cost. The technology disclosed in Japanese Kokai Publication Hei-7-2864 and U.S. Pat. No. 5,387,699, for instance, is a production method of pyromellitic anhydride which comprises subjecting either a 2,4,5-trialkyl benzaldehyde or a 2,4,5-trialkyl benzaldehyde and 1,2,4,5-tetraalkyl benzene to heterogeneous catalytic oxidation in gas phase with a molecular oxygen-containing gas in the presence of a catalyst comprising the oxide or oxides of one or more transition metals of IV subgroup of the periodic table of the elements, the oxide or oxides of one or more transition metals of V subgroup of the periodic table of the elements, the oxide or oxides of one or more elements of I main-group of the periodic table of the elements and/or the oxide or oxides of one or more elements of III, IV and V main-groups and elements of IV and VII subgroups of the periodictable of the elements in a specified weight ratio. Here, the reaction yield is only as low as 90 mass % (61 mole %) at best and it is not satisfactory. Therefore, there has been room for further studies for a method of producing pyromellitic anhydride of high purity in good yield and at low cost.
SUMMARY OF THE INVENTION
In light of the above state of the art, the present invention has for its object to provide a production method of pyromellitic anhydride of high purity in good yield at low cost by catalytic gas-phase oxidation of a 2,4,5-trialkylbenzaldehyde with the aid of a suitable catalyst system.
The inventors of the present invention investigated the technologies for producing pyromellitic anhydride of high purity at low cost and found that when (1) a catalyst the catalytic active component of which has a specific surface area of not greater than 50 m
2
/g or (2) a catalyst the essential catalytic active component of which is vanadium as well as molybdenumand/or tungsten is used in the production of pyromellitic anhydride by catalytic gas-phase oxidation of a 2,4,5-trialkylbenzaldehyde, pyromellitic anhydride can be produced in high yield at low cost, thus giving a neat solution to the above problems. They found also that pyromellitic anhydride of high purity can be produced more positively when the catalytic active component contains certain metal elements or metal oxides and have accordingly perfected the present invention.
The present invention, therefore, is concerned with a production method of a pyromellitic anhydride comprising a step for catalytic gas-phase oxidation of a 2,4,5-trialkylbenzaldehyde with a molecular oxygen-containing gas
wherein said step for catalytic gas-phase oxidation is carried out in the presence of a catalyst such that a specific surface area of a catalytic active component thereof is not greater than 50 m
2
/g.
The present invention further relates to a production method of a pyromellitic anhydride comprising a step for catalytic gas-phase oxidation of a 2,4,5-trialkylbenzaldehyde with a molecular oxygen-containing gas
wherein said step for catalytic gas-phase oxidation is carried out in the presence of a catalyst containing vanadium as well as molybde num and/or tungsten as a catalytic active component.
DETAILED DESCRIPTION OF THE INVENTION
In the following, the present invention is now described in detail.
The production method of pyromellitic anhydride according to the invention comprises a step for catalytic gas-phase oxidation of a 2,4,5-trialkylbenzaldehyde with a molecular oxygen-containing gas. As the process for producing pyromellitic anhydride thus comprises a step for catalytic gas-phase oxidation using a molecular oxygen-containing gas, the step for conversion to the anhydride can be omitted and there is no substantial formation of waste liquor so that the process is advantageous not only in economic terms but also in environmental terms. Moreover, because a 2,4,5-trialkylbenzaldehyde is used as a starting material for production, the process is advantageous in terms of the cost and stable supply of the starting material.
The above-mentioned step for catalytic gas-phase oxidation is carried out in the presence of a catalyst the catalytic active component of which has a specific surface area of not greater than 50 m
2
/g (hereinafter referred to sometimes as catalyst (1)) o r in the presence of a catalyst containing vanadium as well as molybdenum and/or tungsten as a catalytic active component (hereinafter referred to sometimes as catalyst (2)). It should be understood that some of the catalysts which can be used in the present invention satisfy both the above requirement of said catalyst (1) and that of said catalyst (2). These catalysts may be used each independently or two or more of them may be used together. Moreover, these catalysts may be used in a suitable combination.
The morphology of the catalyst for use in the present invention is not particularly restricted but may be a supported catalyst or a molded catalyst. The supported catalyst means a catalyst obtained by coating an inert carrier with a catalytic active component and, any of the known coating techniques such as spray coating method, dipping method, rotary granulation method, and so forth can be utilized. The molded catalyst is acatalyst obtained by molding a catalytic active component and, any of the k
Emoto Yasuhisa
Matsunami Etsushige
Takahashi Tsukasa
Dentz Bernard
Nippon Shokubai Co. , Ltd.
Sughrue & Mion, PLLC
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