JPH0413026B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention involves catalytic gas phase oxidation of durene or tetraalkylbenzene containing an alkyl group having 4 or less carbon atoms using air or a molecular oxygen-containing gas to produce pyromellitic acid or its anhydride. The present invention provides a catalyst for manufacturing.

Prior Art One of the methods for industrially producing pyromellitic acid or its anhydride is the catalytic oxidation method of durene or tetraalkylbenzene, but although there are many catalysts proposed for this process, they have some unsatisfactory performance. There are many. That is, for example, Tokko Akira
49-20302, Japanese Patent Publication No. 49-31972, etc., there is a statement that pyromellitic anhydride can be obtained from Duurene in a relatively high yield, but looking at the reaction conditions,
From an energy-saving perspective, it is very uneconomical to send a large amount of mixed gas with a very low Duurene concentration of 0.1 to 0.3% by volume to the catalyst layer for oxidation, and it is difficult to improve the ability to withstand reactions with high concentration gas. Therefore, a catalyst with a similar structure was desired.

Problems to be Solved by the Invention One of the reasons for adopting the above-mentioned usage condition of passing a gas containing a low concentration of oxidizable substance through the catalyst layer to obtain pyromellitic anhydride is due to the heat resistance of the above-mentioned known catalyst. This is probably due to the low level. When pyromellitic anhydride is synthesized by catalytic gas phase oxidation of Durene or tetraalkylbenzene, heat is generated by the reaction with secondary carbon monoxide, carbon dioxide (COx), trimellitic acid, dimethyl phthalic anhydride, etc. If you include this in your calculations, the amount of heat generated will be extremely large.

In addition, since the reaction rate from Durene to pyromellitic anhydride and by-products is very fast, a significant hot spot locally occurs in a portion of the front half of the catalyst layer.

The generation of such a large amount of heat and its local concentration promotes thermal deterioration of the catalyst in that area.

It is thus an object of the present invention to provide a catalyst with good thermal durability which makes it possible to operate the oxidation reaction at higher duurene or tetraalkylbenzene concentrations.

Means for Solving the Problems The present inventors conducted various studies in order to improve the heat resistance strength of the catalyst, and as a result, they developed a catalytically active material in which a specific additive was added as a co-catalyst to a mixture of vanadium oxide and zirconium oxide. The inventors have completed the present invention by discovering that a catalyst supported on an inert carrier, particularly an inert inorganic porous carrier, is suitable for the purpose of the present invention.

They also discovered that replacing a portion of zirconium oxide with titanium oxide and/or tin oxide has similarly excellent effects, and also added a specific amount of antimony oxide to these catalyst systems. It has been found that the catalyst can operate effectively at a lower temperature, which is more advantageous in terms of catalyst life.

The invention is thus specified as follows.

(1) Vanadium component is 1 to 20 parts by weight as V ₂ O ₅ ,
The zirconium component or the zirconium component and the titanium component and/or tin component are Z _r O ₂ +
99 to 80 parts by weight as TiO ₂ + SnO ₂ , and the phosphorus component is P ₂ O ₅ for the total 100 parts by weight of these components.
0.02 to 10 parts by weight as a niobium component, 0.01 to 5 parts by weight as Nb ₂ O ₅ , and 0.1 to 5 parts as an oxide of at least one component selected from the group consisting of potassium, cesium, rubidium, and thallium.
It is made of a catalytically active material that further contains 0 to 10 parts by weight of an antimony component as Sb ₂ O ₅ , and has an average particle diameter of 0.01 to 1 micron and a specific surface area of 5 to 100 m ² /g as a zirconium component. A catalyst for producing pyromellitic anhydride by catalytic gas phase oxidation of durene or tetraalkylbenzene, comprising a catalytically active substance prepared using ZnO ₂ powder as a starting material supported on an inert carrier.

(2) The weight ratio of zirconium component to titanium component and/or tin component is (TiO ₂ +SnO ₂ )/ZrO ₂
The catalyst according to (1) above, characterized in that =4 or less.

Although the present invention has been specified as above, more preferred embodiments are as follows.

That is, as mentioned above, even if a part of ZrO ₂ is replaced with TiO ₂ and/or SnO ₂ , a high-quality catalyst can be obtained, but in this case, _{the two} types of TiO have a particle size of substantially 0.4 to Specific surface area is 0.7 micron
Porous anatase TiO ₂ of 10-60 m ² /g is
_{The two} types of SnO preferably have a particle size of 0.01 to 1 micron and a specific surface area of 5 to 100 m ² /g, particularly 8 to 60 m ² /g, and TiO ₂ and/or
_SnO2 can be substituted from 0 to 80% by weight of the amount of _ZrO2 in the aforementioned catalyst composition.

Furthermore, the present inventors prepared _{the above-mentioned V2O5 - ZrO2} , or _{V2O5 - ZrO2} / _TiO2 , or _{V2O5 - ZrO2} /
0 to 0 in multicomponent catalysts with specified promoters added to SnO ₂ or V ₂ O ₅ -ZrO ₂ /TiO ₂ /SnO ₂ systems.
The catalyst obtained by adding 10 parts by weight, especially 0.5 to 5 parts by weight of Sb ₂ O ₃ , was compared to the catalyst without addition.
It was discovered that the optimum reaction temperature could be reduced by 20 to 30°C, and a catalyst that was advantageous in terms of catalyst life was completed.

Each component constituting the catalytically active substance is appropriately prepared from raw materials that can be decomposed by heating and converted into the respective oxides, such as nitrates, carbonates, sulfates, ammonium salts, and organic halide salts. However, it is preferable that the starting material for ZrO ₂ is a ZrO ₂ powder obtained by preliminarily calcining a zirconium salt such as zirconyl nitrate, zirconium hydroxide, or zirconium carbonate at an appropriate temperature and pulverizing it. Particularly preferably, ZrO ₂ obtained by firing zirconyl nitrate at 600 to 900°C for 2 to 10 hours is finely pulverized to give a particle size of 0.01 to 1 micron and a specific surface area of 5 to 100 m ² /g, especially 8 to 60 m ² /g is used as catalyst raw material.

Similarly, the SnO ₂ source is preferably SnO ₂ powder obtained by pre-calcining tin salt at high temperature, and in particular tinnous sulfate is preferably used.
Obtained by firing at a temperature of 600-900℃ for 2-10 hours
Finely pulverized SnO ₂ with a particle size of 0.01 to 1 micron and a specific surface area of 5 to 100 m ² /g, particularly 8 to 60 m ² /g is suitable.

As the titanium raw material, it is preferable to use TiO ₂ powder obtained by heat-treating a titanium compound in advance, and it is particularly preferable to use hydrated titanium oxide obtained by dissolving ilmenite in sulfuric acid and introducing heated steam thereto to precipitate it. The TiO ₂ obtained by firing at a temperature of 900℃ for 2 to 10 hours is finely pulverized to a particle size of 0.4 to 0.7 microns.
Specific surface area is 5 to 100 m ² /g, especially 10 to 60 m ² /g
A porous material having a porous structure is preferably used.

As the carrier, any ordinary inert carrier can be used, but preferably the apparent porosity is 5 to 5.
50%, a specific surface area of 5 m ² /g or less, especially 1 m ² /g or less, an aluminum content of 10 wt % or less as Al ₂ O ₃ , preferably 3 wt % or less, and a SiC content of
An inorganic porous carrier of 50% by weight or less, particularly 80% by weight or more is used, and a self-sintering carrier with a SiC purity of about 98% by weight is also suitably used.

The shape of the carrier is not particularly limited, but it may be ball, ring, cylinder, cone, or saddle shape with an apparent outer diameter of 3 to 3.
A diameter of about 15 mm is used as appropriate.

The active substance is supported on the carrier by a conventionally known method.
That is, the active substance is supported by an impregnation method, a spray loading method, etc., but preferably by spraying a catalyst liquid or slurry onto a carrier heated to a temperature of 150 to 250°C.

The active substance is 3 to 3 to 100 c.c. of the apparent volume of the carrier.
50g, preferably 5-15g is supported. The support thus obtained was heated at 300 to 650°C under air circulation.
In particular, the catalyst is obtained by calcining at a temperature of 400 to 600°C for 1 to 10 hours, preferably 2 to 6 hours.

A hot spot often occurs in the first half of the catalyst layer.
Conventionally known methods are appropriately adopted as a measure to reduce the temperature of the catalyst as much as possible to increase selectivity and extend the catalyst life.

In other words, the amount of reaction at that part is suppressed by diluting the first half of the catalyst layer with a carrier, reducing the amount of catalytically active material supported, increasing the diameter of the catalyst, or suppressing the catalytic activity as described below. A catalyst may be used to reduce the temperature of the hot spot. Catalytic activity can be controlled by changing the vanadium content, alkali metal content, and phosphorus content within the above composition range of the catalytically active substance, or by reducing the specific surface area of ZrO ₂ , SnO ₂ , and TiO ₂ used. This can be done as appropriate.

Function and effectiveness The catalyst obtained in this way is used by filling a multitubular reaction tube surrounded by a heat medium such as a molten salt, and the temperature of the heat medium is 340 to 440℃, especially 360 to 400℃.
℃ and the tube used has an inner diameter of 15 to 40 mm, especially 20 to 30 mm.

The catalyst is packed to a bed height of 1 to 3.5 meters, especially 1.5 to 3 meters, and added to a molecular oxygen-containing gas consisting of air or an oxygen concentration of 10 to 21% by volume, water vapor of 0 to 15% by weight, and the balance being an inert gas. Mix alkylbenzene at a ratio of 20 to 60 g/NM ³ and preheat the gas to 120 to 160°C at a space velocity of 3000.
Conduct catalytic oxidation at ~6000Hr ^-1 . Pyromellitic anhydride can be obtained stably over a long period of time from Duurene at a yield of 115 to 120% by weight. The effectiveness will be explained in more detail with examples.

Example 1 Zirconium nitrate was thermally decomposed at 750°C for 3 hours to obtain ZrO ₂ with a specific surface area of 25 m ² /g. This was finely pulverized to obtain particles with an average particle diameter of 0.2 microns, which was used as a catalyst raw material.

200 g of oxalic acid was dissolved in 6400 c.c. of water, and 96.7 g of ammonium metavanadate, 9.1 g of monoammonium phosphate, 22.9 g of niobium chloride and 3.47 g of potassium hydroxide were added thereto and thoroughly stirred. 1800 g of the above ZrO ₂ was added to this, and a catalyst slurry was prepared using an emulsifier.

Al ₂ O 3 content 2% by weight, SiO ₂ with an apparent porosity of 45%, a specific surface area of 0.2 m ² /g, an average inner diameter of 4 mm, an average outer diameter of 6 mm and an average length of 6 mm in an externally heated rotary furnace _.
A ring-shaped carrier of 2000 c.c. containing 6% by weight and 92% by weight of SiC was placed and preheated to a temperature of 150 to 200°C. After spraying the catalyst slurry above to support 180g of the active substance, the mixture was heated to 540°C under air circulation.
A catalyst was obtained by firing at a temperature of 6 hours.

Internal diameter immersed in a molten salt bath held at 400℃
The above catalyst was placed in a 25 mm, 3.5 meter long iron reaction tube.
It was filled to a bed height of 2.5 meters.

From the top of the reaction tube, the ratio of Duurene/air is 25g/
Preheat the mixed gas of NM ³ to 140℃ and increase the space velocity.
When the mixture was run at 4000 Hr ^-1 (STP), pyromellitic anhydride was obtained with an initial yield of 114.5% by weight, and the temperature of the hot spot was 465°C. The reaction was continued under these conditions and the hot spot temperature and yield were measured after 3 and 6 months, and stable catalytic activity was obtained as 466°C, 114.1% by weight and 461°C, 113.3% by weight, respectively. Ta.

Example 2 450 g of oxalic acid was dissolved in 6400 c.c. of water, and 201.4 g of ammonium metavanadate, 23.8 g of niobium pentachloride, 9.5 g of monoammonium phosphate and 3.38 g of cesium nitrate were added thereto and thoroughly stirred. In addition to this, particles with a particle diameter of 0.2 microns and a specific surface area of 25 m ² /g obtained by the same method as in Example 1 were added.
ZrO ₂ 980g, particle size 0.5 micron and specific surface area 20
820 g of porous anatase-type TiO ₂ of m ² /g was added to form a catalyst slurry liquid using an emulsifier.

Apparent porosity 43 in a rotary furnace that can be heated from the outside
%, specific surface area 0.3 m ² /g, Al ₂ O ₃ content 2 wt %, SiO ₂ content 4 wt % and SiC content 94
Porous carrier consisting of % by weight (average diameter 6 mm spheres)
2000 c.c. was added and heated to a temperature of 150-200°C. Spray the above catalyst slurry onto this to add catalytically active material to 180%
After supporting G, catalyst A was obtained by calcining at a temperature of 520° C. for 4 hours.

Separately, average particle size 0.3 microns, specific surface area 12
Catalyst-B was obtained in the same manner as Catalyst-A except that ZrO ₂ of m ² /g and a porous anatase type having an average particle size of 0.6 microns and a specific surface area of 13 m ² /g were used.

Inner diameter immersed in molten salt held at a temperature of 400℃
First, add 1.5 liters of catalyst-A to a 25 mm, 3.5 meter long tube.
A bed height of 1 meter was filled, followed by catalyst-B to a bed height of 1 meter.

From the top of the reaction tube, the ratio of Duurene/air is 35g/
A mixed gas of NM ³ has a space velocity of 4000Hr ^-1 (STP)
As a result, pyromellitic anhydride was obtained in a stable yield of 115.6% by weight over a long period of time.

Example 3 900 g of oxalic acid was dissolved in 6400 c.c. of water, and 408.6 g of ammonium vanadate and 4.3 g of niobium pentachloride were dissolved in the solution.
g, 27.4 g of monoammonium phosphate, 21.3 g of thallium nitrate, and 42.4 g of powdered Sb ₂ O ₃ were added and thoroughly stirred. This was supplemented with 720 g of the same ZrO ₂ and TiO ₂ used in the preparation of catalyst-A in Example 2.
A catalyst slurry liquid was prepared by adding 1080 g using an emulsifier.

A self-sintered SiC carrier (average diameter 6 mm) with an apparent porosity of 38% and a specific surface area of 0.2 m ² /g was placed in an externally heated rotary furnace.
2,000 c.c. (sphere) was put therein and the above catalyst liquid was sprayed while heating to a temperature of 150 to 200°C, so that 170 g of the catalytically active substance was supported. The support obtained in this way was calcined at a temperature of 580°C for 3 hours under air circulation to obtain catalyst-C.
I got it.

Separately, rubidium nitrate is used instead of thallium nitrate.
Catalyst-D was obtained in the same manner as Catalyst-C except that 6.68g was added.

Internal diameter immersed in a molten salt bath held at 375°C
A 25 mm, 3.5 meter long iron reaction tube was first filled with Catalyst-D to a height of 1.25 meters, and then Catalyst-C was packed thereon to a bed height of 1.25 meters.

Duurene/molecular oxygen-containing gas (oxygen 12% by volume, water vapor 10% by volume, nitrogen 78% by volume) is introduced from the top of the reaction tube.
The space velocity of a mixed gas with a ratio of 40g/NM ³ is
When the mixture was heated at 3500 Hr ^-1 (STP), pyromellitic anhydride was obtained with an initial yield of 117.1% by weight, and the temperature of the hot spot was 457°C.

The bath temperature was intentionally maintained at 387°C, 12°C higher than the optimum temperature so that the temperature at the hot spot was 500°C, and the oxidation reaction of the above mixed gas was carried out for one month.
When the temperature was returned to 375°C, the temperature of the hot spot was 452°C, and 116.2% by weight of pyromellitic anhydride was obtained, with almost no damage caused by heat being observed.

Example 4 200 g of oxalic acid was dissolved in 6400 c.c. of water, and 96.5 g of ammonium metavanadate and niobium pentachloride were added to the solution.
7.6g, diammonium phosphate 36.4g, cesium nitrate 20.7g and powdered antimony trioxide 18.8g
g was added and thoroughly stirred. To this were added 940 g of ZrO ₂ as obtained in Example 1, 470 g of TiO ₂ as used in the preparation of Example 2 Catalyst-B and
Average particle size 0.13 microns, specific surface area 26 obtained by pulverizing tin after thermally decomposing it at a temperature of 700℃ for 4 hours.
A catalyst slurry liquid was prepared by adding 390 g of SnO ₂ of m ² /g using an emulsifier.

An interlocked saddle shape with an apparent porosity of 45%, a specific surface area of 0.4 m ² /g, an average outer circumference length of 12 mm, an average inner circumference of 6 mm, an average outer diameter of 5 mm, and an average thickness of 1 mm in an externally heated rotary furnace. SiC80wt%, MgO6wt%
and a porous carrier consisting of 14% by weight of SiO ₂ 2000 c.c.
and preheated to a temperature of 150-200℃. Spray the above catalyst slurry onto this to support 160g of active substance,
The catalyst was calcined for 4 hours at a temperature of 520° C. under air circulation to obtain catalyst-E.

Separately, except for not adding cesium nitrate, the catalyst was
Catalyst-F was prepared in the same manner as E.

A tube with an inner diameter of 20 mm and a height of 4.5 meters maintained at 380 DEG C. was first filled with Catalyst-F to a height of 2.0 meters, and then filled with Catalyst-E to a height of 2.0 meters.

When a mixed gas containing 4-isopropylsoid cumene/air at a ratio of 40 g/NM ³ was passed through the upper part of the reaction tube at a space velocity of 3500 Hr ^-1 , pyromellitic anhydride was obtained stably over a long period of time with a yield of 98.7% by weight. Ta.

Effects of the Invention As shown in Examples 1 to 4, the catalyst of the present invention withstood severe heat loads at hot spots, making it possible to oxidize durene under industrially advantageous high gas concentration conditions. .

Claims (1)

[Claims] 1. The vanadium component is 1 to 20 parts by weight as V ₂ O ₅ ,
The zirconium component or the zirconium component and the titanium component and/or tin component are Z _r O ₂ + TiO ₂ +
99 to 80 parts by weight as SnO ₂ , and 0.02 parts by weight of phosphorus component as P ₂ O ₅ for a total of 100 parts by weight of these components
~10 parts by weight, niobium component is 0.01~5 as Nb ₂ O ₅
0.1 to 1.2 parts by weight of at least one component selected from the group consisting of potassium, cesium, rubidium and thallium as an oxide, and 0 to 10 parts by weight of an antimony component as Sb ₂ O ₅ . It consists of an active substance with an average particle size of 0.01 to 1 micron and a zirconium component of 5 to 1 micron.
Catalyst for producing pyromellitic anhydride by catalytic gas phase oxidation of durene or tetraalkylbenzene, comprising a catalytically active material prepared using ZnO ₂ powder with a specific surface area of 100 m ² /g as a starting material supported on an inert carrier. . 2 The weight ratio of the zirconium component to the titanium component and/or tin component is (TiO ₂ +SnO ₂ )/ZrO ₂ =
Claim 1 characterized in that the number is 4 or less.
Catalysts as described.