U.S. patent application number 09/963402 was filed with the patent office on 2002-03-28 for process for producing pyromellitic anhydride.
This patent application is currently assigned to NIPPON SHOKUBAI CO., LTD.. Invention is credited to Emoto, Yasuhisa, Matsunami, Etsushige, Takahashi, Tsukasa.
Application Number | 20020038039 09/963402 |
Document ID | / |
Family ID | 26600996 |
Filed Date | 2002-03-28 |
United States Patent
Application |
20020038039 |
Kind Code |
A1 |
Takahashi, Tsukasa ; et
al. |
March 28, 2002 |
Process for producing pyromellitic anhydride
Abstract
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 present invention relates to a production method of
pyromellitic anhydride comprising a step for catalytic gas-phase
oxidation of a 2,4,5-trialkylbenzaldehyde with a molecular
oxygen-containing gas in which said step for catalytic gas-phase
oxidation is carried out in the presence of a catalyst such that a
specific surface area of the catalytic active component thereof is
not greater than 50 m.sup.2/g or in the presence of a catalyst
containing vanadium as well as molybdenum and/or tungsten as a
catalytic active component.
Inventors: |
Takahashi, Tsukasa;
(Himeji-shi, JP) ; Emoto, Yasuhisa; (Ibo-gun,
JP) ; Matsunami, Etsushige; (Himeji-shi, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN,
MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3213
US
|
Assignee: |
NIPPON SHOKUBAI CO., LTD.
|
Family ID: |
26600996 |
Appl. No.: |
09/963402 |
Filed: |
September 27, 2001 |
Current U.S.
Class: |
549/239 |
Current CPC
Class: |
C07C 63/307 20130101;
C07C 51/235 20130101; C07C 51/235 20130101 |
Class at
Publication: |
549/239 |
International
Class: |
C07D 493/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2000 |
JP |
2000-297040 |
Sep 28, 2000 |
JP |
2000-297101 |
Claims
1. 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.sup.2/g.
2. The production method of a pyromellitic anhydride according to
claim 1 wherein said catalytic active component contains
vanadium.
3. The production method of a pyromellitic anhydride according to
claim 2 wherein said catalytic active component contains at least
one element selected from the group consisting of molybdenum,
tungsten, phosphorus, boron, silver, antimony, sulfur, niobium,
alkaline earth metal and rare earth element.
4. 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
molybdenum and/or tungsten as a catalytic active component.
5. The production method of a pyromellitic anhydride according to
claim 4 wherein said catalytic active component contains at least
one element selected from the group consisting of phosphorus,
boron, silver, antimony, sulfur, niobium, alkaline earth metal and
rare earth element.
6. The production method of a pyromellitic anhydride according to
claim 2 or 4 wherein said catalytic active component contains at
least one inorganic oxide powder selected from the group consisting
of TiO.sub.2, ZrO.sub.2 and SnO.sub.2.
Description
FIELD OF THE INVENTION
[0001] 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
[0002] Pyromellitic anhydride is in broad use as a starting
material of polyimide resin, a plasticizer, and a polyester resin
modifying agent, among other uses, and its importance as an
industrial material has been increasing steadily in recent
years.
[0003] 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.
[0004] 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.
[0005] 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.
[0006] 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 periodic table 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
[0007] 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.
[0008] 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.sup.2/g or (2) a catalyst the essential catalytic active
component of which is vanadium as well as molybdenum and/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.
[0009] 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
[0010] 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.sup.2/g.
[0011] 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
[0012] wherein said step for catalytic gas-phase oxidation is
carried out in the presence of a catalyst containing vanadium as
well as molybdenum and/or tungsten as a catalytic active
component.
DETAILED DESCRIPTION OF THE INVENTION
[0013] In the following, the present invention is now described in
detail.
[0014] 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.
[0015] 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.sup.2/g (hereinafter referred to sometimes as catalyst (1)) or
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.
[0016] 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 a catalyst
obtained by molding a catalytic active component and, any of the
known molding techniques such as extrusion method and compression
molding method and so forth can be utilized. The catalytic active
component of such a catalyst means a substance having catalytic
activity in the composition of a catalyst and the substance which
does not satisfy this definition can be mentioned as the carrier of
a supported catalyst. A molded catalyst, except in special cases,
may be regarded as a catalyst consisting solely by the active
substance. As for special cases, an inert inorganic powder is added
as a diluent to suppress the catalytic activity.
[0017] The catalyst (1) which can be used in the present invention
is a catalyst the catalytic active component of which has a
specific surface area of not greater than 50 m.sup.2/g, preferably
within the range of 1 to 40 m.sup.2/g, more preferably within the
range of 5 to 30 m.sup.2/g. When the specific surface area of the
catalytic active component is greater than 50 m.sup.2/g, the
combustion activity is increased to lower the yield of pyromellitic
anhydride and it is not preferable. The specific surface area of
the catalytic active component can be easily controlled by
adjusting the specific surface area of the inorganic oxide powder
used for dispersing the catalytic active substance, for example.
However, this inorganic oxide powder is not essential and a control
within the preferred range can be attained even in the absence of
an inorganic oxide powder by modulating the constituent elements of
the catalyst or the catalytic calcinating temperature. The specific
surface area is the value found by the BET (Brunaer-Emmett-Teller)
method.
[0018] The catalyst (1) in the invention need only be a catalyst
the catalytic active component of which has the above-defined
specific surface area but preferably contains vanadium as the
catalytic active component, more preferably additionally contains
at least one element (hereinafter referred to sometimes as Group A
element) selected from the group consisting of molybdenum,
tungsten, phosphorus, boron, silver, antimony, sulfur, niobium,
alkaline earth metal, and rare earth elements. Addition of the
Group A element in an appropriate amount improves a yield. On the
other hand, the use of the Group A element in an excessive amount
may lead to a decrease in catalytic activity or an increase in
combustion. Therefore, this element is preferably used within the
range not over 3, more preferably, not over 2 atomic ratio of the
Group A element based on vanadium.
[0019] The catalyst (2) which can be used in the invention is the
oxide comprising vanadium as an essential element and at least one
element selected from the group consisting of molybdenum and
tungsten (hereinafter referred to sometimes as Group B element).
Containing molybdenum and/or tungsten in addition to vanadium
improves a yield of pyromellitic anhydride but if the amount is
small, the yield-improving effect is not appreciable and if added
excessively, the amount of byproducts such as trimellitic acid are
increased. The preferred level of addition is within the range of
0.01 to 2, more preferably, the range of 0.01 to 1 atomic ratio of
the Group B element based on vanadium.
[0020] The optional but preferred additional constituent element of
the catalyst (2) of the invention is at least one element selected
from phosphorus, boron, silver, antimony, sulfur, niobium, alkaline
earth metal, and rare earth elements (hereinafter referred to
sometimes as Group C element) . Thus, it is more preferable that
the catalytic active component of this catalyst (2) further contain
the Group C element. Use of such Group C element in an appropriate
amount improves a yield but when it is used excessively, a decrease
in catalytic activity or an increase in combustion occur to depress
the yield of pyromellitic anhydride. Therefore, the amount of use
is preferably within the range not over 1 atomic ratio of the Group
C element based on vanadium.
[0021] The catalyst (1) and catalyst (2) according to the invention
may each be optionally supplemented with at least one inorganic
oxide selected from titanium oxide, zirconium oxide and tin oxide.
By adding any of them in an appropriate-amount, it becomes possible
to improve the yield of pyromellitic anhydride and the heat
resistance of the catalyst. Thus, more preferably said catalytic
active component additionally contains at least one inorganic oxide
powder selected from the group consisting of TiO.sub.2, ZrO.sub.2
and SnO.sub.2. The preferred level of addition of such inorganic
oxide may for example be such that, based on the total sum of moles
of vanadium, a Group A or Group B element, and Group C element as
constitution elements of said catalyst, the surface area of the
inorganic oxide powder so added will be greater than 0 and up to
1.times.10.sup.5 m.sup.2/mole, more preferably 1.times.10.sup.2 to
1.times.10.sup.5 m.sup.2/mole, most preferably up
to1.times.10.sup.2 to 4.times.10.sup.4 m.sup.2/mole.
[0022] The surface area (m.sup.2/mole) of the inorganic oxide
powder to be added is the value found by multiplying the weight (g)
of the used oxide powder by the specific surface area (m.sup.2/g)
of said oxide and dividing the product by the total sum of moles of
used vanadium, a Group A or Group B element, and Group C element
each in terms of metal. The specific surface area mentioned just
above is also found by the BET method.
[0023] The preparation method and the raw materials for such
catalysts are not particularly restricted but the conventional
techniques and materials can be utilized. Referring to the raw
materials, the inorganic salts, such as nitrates, sulfates,
hydrochlorides, phosphates, carbonates, etc., the organic acid
salts, such as oxalates, citrates, tartrates, etc., the complex
salts, or the oxides of the elements to be used can be employed. By
the calcinating operation for catalyst preparation, these are
thought to become the corresponding oxides or complex oxides in the
catalyst. As to titanium oxide, zirconium oxide and tin oxide,
commercial oxide powders or oxide powders prepared from the
corresponding salts can be employed and those having BET specific
surface areas in the range of 5 to 100 m.sup.2/g can be used
preferably.
[0024] In preparing said catalyst, the starting compounds of
respective elements are blended as evenly as possible. Thus, the
compounds are blended by stirring in a dispersant such as water to
give a liquid, a slurry or a clay-like artifact. It is also
advantageous to increase the strength of the catalyst by
incorporating whiskers or other fibrous matter at the same
time.
[0025] For imparting a definite shape to said catalyst, the
hitherto-known techniques can be used. For example, the bake-on
method which comprises spray-coating a pre-heated heat-resistant
carrier with the slurry, the rotary granulation method and the
dipping method, among other supporting methods, or the extrusion
molding method, etc. can be utilized.
[0026] When said supporting method is used, a material for the
carrier to be used is not particularly restricted but any of the
inert carriers in general use as a catalyst carrier which are
stable in a high-temperature oxidizing atmosphere, such as silicon
carbide, silica, alumina, steatite, earthenware, porcelain, or the
like can be employed. The preferred is made of silicon carbide, and
a carrier made of high-purity silicon carbide with a purity of not
less than 95% can be employed with particular advantage. The shape
of the carrier is not particularly restricted but granular forms
such as beads, rings, hemi-rings, cylinders, cones, saddles, etc.
can be used with advantage. More preferably, carriers with an
apparent outer diameter of about 3 to 15 mm on the average are
used.
[0027] The reaction starting material for use in the invention,
namely 2,4,5-trialkylbenzaldehyde, may have an alkyl group of any
arbitrary kind. However, the larger the number of carbon atoms of
the alkyl group is, the greater the amount of heat generated in the
oxidation reaction is. Therefore, the number of carbon atoms of the
alkyl group is preferably as few as possible. Thus, a compound
having alkyl groups of 1 to 3 carbon atoms can be used with
advantage. Particularly, 2,4,5-trimethylbenzaldehyde can be
produced with high yield by the carbonylation of
1,2,4-trimethylbenzene (hereinafter referred to sometimes as
pseudocumene), which gives rise to only a small amount of heat in
oxidation reaction and is comparatively inexpensive, with carbon
monoxide (CO) at atmospheric temperature in the presence of
HF--BF.sub.3, HSO.sub.3F--SbF.sub.5, CF.sub.3SO.sub.3H or the like
and, therefore, is particularly advantageous as a starting material
for low-cost production of pyromellitic anhydride.
[0028] In the present invention, the reaction may optionally be
carried out using a 2,4,5-trialkylbenzaldehyde and
1,2,4,5-tetraalkylbenzene mixture as the starting material and, in
that case, the proportions of the component compounds may be
arbitrary.
[0029] The reaction according to the invention is preferably
carried out in a fixed-bed type reactor packed with the catalyst
and passing a feed gas composed of either a
2,4,5-trialkylbenzaldehyde or a 2,4,5-trialkylbenzaldehyde and
1,2,4,5-tetraalkylbenzene mixture and a molecular oxygen-containing
gas through the catalyst bed in the tubular reactor held in a heat
medium controlled at a predetermined temperature. For industrial
production, a heat-exchange type multi-tubular reactor, which is
commonly used for gas-phase oxidation reaction, comprising a
plurality of tubular reactors sharing in the feed gas inlet space
and outlet space and held in a heat medium can be used with
advantage. The diameter of the tubular reactor is not particularly
restricted but tubes having inside diameters in the range of 15 mm
to 30 mm, which are used for catalytic gas-phase oxidation
reactions in general, can be employed.
[0030] In the production method according to the invention, such a
tubular reactor is packed with the oxide catalyst the catalytic
active component of which has a specific surface area of not
greater than 50 m.sup.2/g (catalyst (1)) or the oxide catalyst
containing vanadium as well as molybdenum and/or tungsten (catalyst
(2)) and the feed gas is passed through to carry out a catalytic
gas-phase oxidation reaction. When the catalyst (2) is used, it is
not necessary to use a catalyst containing molybdenum and/or
tungsten throughout the entire catalyst bed but a high yield can be
obtained by dividing the catalyst bed in two and using a catalyst
containing molybdenum and/or tungsten only at the side of the feed
gas outlet. Moreover, a similar effect can be obtained by using the
reactor packed with catalysts of increasing molybdenum and/or
tungsten contents from the feed gas inlet toward the gas outlet up
to the point of substantial completion of the pyromellitic
anhydride-producing reaction where the catalyst bed is divided into
a larger number of zones.
[0031] In the present invention, the reaction conditions are not
particularly restricted but the space velocity is preferably 500 to
10000 h.sup.-1, particularly 1000 to 8000 h.sup.-1. The reaction
temperature is 300 to 500.degree. C., preferably 350 to 450.degree.
C., in terms of the temperature of the heat medium. The
concentration of the feed gas in mass per m.sup.3 of the molecular
oxygen-containing gas (g/m.sup.3, standard condition) is 10 to 100
g/m.sup.3, preferably 10 to 50 g/m.sup.3.
[0032] The molecular oxygen-containing gas may be air, oxygen or a
mixture gas composed of a reaction-indifferent inert gas, such as
nitrogen or carbon dioxide, and oxygen.
[0033] In accordance with the production method of the invention,
constituted as above, pyromellitic anhydride of high purity can be
produced at low cost by the catalytic gas-phase oxidation of a
2,4,5-trialkylbenzaldehyde or a 2,4,5-trialkylbenzaldehyde and
1,2,4,5-tetraalkylbenzene mixture in the presence of a catalyst of
the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0034] The following examples illustrate the present invention in
further detail without defining the scope of the invention.
[0035] It is to be understood that the pyromellitic anhydride yield
(mole %) values given in the following examples and comparative
examples are those measured by liquid chromatography and the yield
is defined by the following expression. [(number of moles of
pyromellitic anhydride produced)/(number of moles of starting
material fed)].times.100
CATALYST PREPARATION
[0036] Catalyst A
[0037] In 400 ml of deionized water was dissolved 240 g of oxalic
acid, and 100 g of ammonium metavanadate was added and uniformly
dissolved therein. Then, 3.07 g of ammonium dihydrogen phosphate
was added and mixed evenly. To this mixture, 214 g of anatase type
titanium oxide with a specific surface area of 20 m.sup.2/g and 17
g of silicon carbide whiskers were added and the whole mixture was
thoroughly stirred to give 600 ml of a homogeneous slurry of
catalyst components. An external heating-type rotary furnace was
charged with 200 ml of ring-formed silicon carbide carrier having
an outer diameter of 7 mm, an inner diameter of 4 mm and a length
of 7 mm and the carrier was preheated to 200 to 350.degree. C. This
heated carrier was spray-coated with the catalyst component slurry
prepared above to support 10 g of the catalyst substance on the
carrier while keeping the carrier temperature at 180 to 250.degree.
C. The coated carrier was fired in a furnace at 500.degree. C. for
6 hours to give Catalyst A. The supported catalytic active
substance powder was stripped off and recovered and the specific
surface area was measured with 4-SOAP U2C, product of Yuasa-Ionics.
The result was 14.5 m.sup.2/g.
[0038] Catalyst B
[0039] Using titanium oxide with a specific surface area of 64
m.sup.2/g in lieu of the above titanium oxide with a specific
surface area of 20 m.sup.2/g, Catalyst B was prepared in otherwise
the same manner as Catalyst A. The supported catalytic active
substance powder was stripped off and recovered and the specific
surface area was measured. The result was 52 m.sup.2/g.
[0040] Catalyst C
[0041] In 400 ml of deionized water was dissolved 240 g of oxalic
acid, and 100 g of ammonium metavanadate and 15.1 g of ammonium
paramolybdate were added and evenly admixed. Then, 3.07 g of
ammonium dihydrogen phosphate and 6.53 g of silver nitrate
dissolved in a small quantity of deionized water in advance were
added and evenly admixed. To this mixture, 214 g of anatase type
titanium oxide with a specific surface area of 20 m.sup.2/g and 17
g of silicon carbide whiskers were added and the whole mixture was
thoroughly stirred to give 600 ml of a homogeneous slurry of
catalyst components. An external-heating type rotary furnace was
charged with 200 ml of ring-formed silicon carbide carrier 7 mm in
outer diameter and 7 mm long and the carrier was preheated to 200
to 350.degree. C. Then, the carrier was spray-coated with the
catalyst component slurry prepared above to support 10 g of the
catalyst substance on the carrier while keeping the carrier
temperature at 260 to 310.degree. C.
[0042] Then, the coated carrier was fired in a furnace at
500.degree. C. for 6 hours to give Catalyst C. The supported
catalytic active substance powder was stripped off and recovered
and the specific surface area was measured. The result was 18.4
m.sup.2/g.
[0043] Catalyst D
[0044] Except that the use of 214 g of anatase type titanium oxide
with a specific surface area of 20 m.sup.2/g was omitted, Catalyst
D was prepared in otherwise the same manner as Catalyst C. The
supported catalytic active substance powder was stripped off and
recovered and the specific surface area was measured. The result
was 16.7 m.sup.2/g.
[0045] Catalyst E
[0046] Except that the use of ammonium paramolybdate was omitted,
Catalyst E was prepared in otherwise the same manner as Catalyst C.
The supported catalytic active substance powder was stripped off
and recovered and the specific surface area was measured. The
result was 14.6 m.sup.2/g.
[0047] Catalyst F
[0048] Using 19.8 g of ammonium metatungstate with a tungsten oxide
content of 50 weight % in lieu of ammonium paramolybdate, Catalyst
F was prepared in otherwise the same manner as Catalyst C. The
supported catalytic active substance powder was stripped off and
recovered and the specific surface area was measured. The result
was 19.8 m.sup.2/g.
EXAMPLE 1
[0049] A stainless steel tubular reactor 25 mm in inside diameter
and 400 mm long was packed with Catalyst A to prepare a 200 mm-long
catalyst bed and further with glass beads having an average
diameter of 5 mm to prepare an approximately 100 mm-long preheating
zone.
[0050] The reaction was carried out by passing a substrate mixture
gas composed of 30 g/m.sup.3 of 2,4,5-trimethylbenzaldehyde and the
balance of air through the catalyst bed at a flow rate of 6.3
L/min.
[0051] At a reaction temperature of 370.degree. C., pyromellitic
anhydride was obtained in the highest yield and the yield of
pyromellitic anhydride was 70.7 mole %.
COMPARATIVE EXAMPLE 1
[0052] Using Catalyst B in lieu of Catalyst A, the catalytic
gas-phase oxidation of 2,4,5-trimethylbenzaldehyde was carried out
in otherwise the same manner as in Example 1. At a reaction
temperature of 370.degree. C., pyromellitic anhydride was obtained
in the highest yield and the yield of pyromellitic anhydride was
66.4 mole %.
EXAMPLE 2
[0053] Using Catalyst C in lieu of Catalyst A, the catalytic
gas-phase oxidation of 2,4,5-trimethylbenzaldehyde was carried out
in otherwise the same manner as in Example 1. At a reaction
temperature of 390.degree. C., pyromellitic anhydride was obtained
in the highest yield and the yield of pyromellitic anhydride was
76.0 mole %.
EXAMPLE 3
[0054] Using Catalyst D in lieu of Catalyst A, the reaction was
carried out in otherwise the same manner as in Example 1. At a
reaction temperature of 390.degree. C., pyromellitic anhydride was
obtained in the highest yield and the yield of pyromellitic
anhydride was 76.5 mole %.
COMPARATIVE EXAMPLE 2
[0055] Using durene in lieu of 2,4,5-trimethylbenzaldehyde as the
reaction starting material, the reaction was carried out in
otherwise the same manner as in Example 3. At a reaction
temperature of 400.degree. C., pyromellitic anhydride was obtained
in the highest yield and the yield of pyromellitic anhydride was
59.6 mole %.
EXAMPLE 4
[0056] Using a mixture of 2,4,5-trimethylbenzaldehyde and durene
(1:1, mole ratio) as the reaction starting material, the reaction
was carried out in otherwise the same manner as in Example 2. As a
result, pyromellitic anhydride was obtained in a yield of 68.1 mole
%.
COMPARATIVE EXAMPLE 3
[0057] Using Catalyst B in lieu of Catalyst C, the reaction was
carried out in otherwise the same manner as in Example 4. As a
result, pyromellitic anhydride was obtained in a yield of 60.7 mole
%.
EXAMPLE 5
[0058] Using Catalyst E in lieu of Catalyst A, the catalytic
gas-phase oxidation reaction of 2,4,5-trimethylbenzaldehyde was
carried out in otherwise the same manner as in Example 1. At a
reaction temperature of 370.degree. C., pyromellitic anhydride was
obtained in the highest yield and the yield of pyromellitic
anhydride was 71.4 mole %.
COMPARATIVE EXAMPLE 4
[0059] Using durene in lieu of 2,4,5-trimethylbenzaldehyde as the
reaction starting material, the reaction was carried out in
otherwise the same manner as in Example 5. At a reaction
temperature of 370.degree. C., pyromellitic anhydride was obtained
in the highest yield and the yield of pyromellitic anhydride was
59.5 mole %.
EXAMPLE 6
[0060] Except that the bed length of Catalyst C was prepared to 150
mm and Catalyst E was packed to a 50 mm-long bed at the feed gas
inlet side, the catalytic gas-phase oxidation reaction of
2,4,5-trimethylbenzaldehyde was carried out in otherwise the same
manner as in Example 2. At a reaction temperature of 400 to
410.degree. C., pyromellitic anhydride was obtained in the highest
yield and the yield of pyromellitic anhydride was 75.3 mole %. The
hot spot representing the highest bed temperature was situated in
the catalyst bed comprised of Catalyst E.
EXAMPLE 7
[0061] Using Catalyst F in lieu of Catalyst A, the reaction was
carried out in otherwise the same manner as in Example 1. At a
reaction temperature of 400.degree. C., the highest yield was
attained and it was 75.1 mole %.
* * * * *