KR20130131306A - Catalyst for the oxidation of o-xylene and/or naphthalene to phthalic anhydride - Google Patents

Abstract

The present invention is a catalyst for the oxidation of o-xylene and / or naphthalene to phthalic anhydride, comprising a plurality of antimony trioxides prepared in series in a reaction tube and comprising a significant amount of valerianite. It relates to a catalyst having catalyst zones. The present invention further relates to a gas phase oxidation process comprising passing a gas stream comprising one or more hydrocarbons and oxygen molecules through a catalyst prepared using antimony trioxide comprising a significant amount of valerianite.

Description

Catalyst for the oxidation of o-xylene and / or naphthalene to phthalic anhydride {CATALYST FOR THE OXIDATION OF O-XYLENE AND / OR NAPHTHALENE TO PHTHALIC ANHYDRIDE}

The present invention provides a catalyst for the oxidation of o-xylene and / or naphthalene to phthalic anhydride, a plurality of catalysts prepared by using antimony trioxide arranged in series in a reaction tube and containing a significant amount of valentinite. It relates to a catalyst having bands. The invention further relates to a gas phase oxidation process comprising passing a gas stream comprising one or more hydrocarbons and oxygen molecules through a catalyst made using antimony trioxide comprising a significant amount of valentinite.

Many carboxylic acids and / or carboxylic anhydrides are industrially produced by catalyzed gas phase oxidation of hydrocarbons such as benzene, xylene, naphthalene, toluene or durene in a fixed bed reactor. In this way it is possible to obtain, for example, benzoic acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid or pyromellitic anhydride. In general, the mixture of starting material and oxygen-comprising gas to be oxidized is passed through a tube in which the catalyst layer is present. In order to control the temperature, the tube is surrounded by a heat transfer medium, for example a salt melt.

Coated catalysts in which the catalytically active composition is applied in the form of a sheath for an inert support material, for example steatite, have been found to be useful as catalysts for such oxidation reactions. In general, the catalyst has an active composition layer which has an essentially homogeneous chemical composition and is applied in the form of an envelope. In addition, two or more different layers of the active composition may be applied successively to the support. It is therefore referred to as a two-layer or multilayer catalyst (see for example DE 19839001 A1).

Catalytically active constituents of the catalytically active composition of such coated catalysts generally consist of titanium dioxide and vanadium pentoxide. In addition, small amounts of many other oxidative compounds (cesium oxide, phosphorus oxide and antimony oxide) that act as promoters that affect the activity and selectivity of the catalyst may be present in the catalysis active composition.

According to EP 1636161, catalysts can be obtained that give particularly high PAn yields when a certain V ₂ O ₅ / Sb ₂ O ₃ ratio is set and the antimony trioxide has a defined average particle size.

The presence of antimony oxide provides an increase in PAn selectivity and the effect is considered to be the separation of the vanadium moiety.

The antimony oxides used in the active composition of the catalyst can be various antimony (III), antimony (IV) and antimony (V) compounds, antimony trioxide or antimony pentoxide are generally used. EP 522871 describes the use of antimony pentoxide and US 2009/306409 and EP 1636161 describe the use of antimony trioxide.

Compared to antimony trioxide and antimony pentoxide, antimony trioxide has the ability to disperse well on titanium dioxide, thereby significantly improving the distribution of the catalyst. Antimony trioxide is typically used as a pure cenamontite phase (cf. Schubert, U.-A. et al., Topics in Catalysis, 2001, vol. 15 (2-4), pages 195 to 200). Reference). In addition to the cube cenamontite, there are also tetragonal modifications of antimony trioxide, known as valentinites (see Golunski, S. E. et al., Appl. Catal., 1989, vol. 48, pages 123-135).

There is a continuing need for catalysts for gas phase oxidation, in which catalysts provide very high conversions with high selectivity.

It is an object of the present invention to provide a catalyst for the oxidation of o-xylene and / or naphthalene to phthalic anhydride, which enables a high phthalic anhydride with low o-xylene and phthalide contents at low salt bath temperatures. To develop.

This object is achieved by a catalyst for the oxidation of o-xylene and / or naphthalene to phthalic anhydride, prepared using antimony trioxide comprising significant amounts of valentinite.

As catalyst for the oxidation of o-xylene and / or naphthalene to phthalic anhydride, at 2-theta = 28.4 ° to the sum of the signal heights of the X-ray powder diffraction pattern at 2-theta = 27.7 ° and 28.4 ° It is an object of the present invention to provide a catalyst prepared using antimony trioxide having a ratio of signal height of X-ray powder diffraction pattern of at least 0.02.

The signal at 2-theta = 27.7 ° is a feature of cenamontite (see ASTM Index 5-0534 / 7) and the signal at 2-theta = 28.4 ° relates to Valentinite (ASTM Index 11- 689). The signal height is provided by the difference between the maximum intensity and the background value of the individual signal measured.

In a preferred embodiment of the present invention, the catalyst is characterized by the fact that the X-ray powder diffraction pattern at 2- It is prepared using antimony trioxide having a signal height ratio of at least 0.03, particularly preferably at least 0.05.

Antimony trioxide having a significant valentinite content that can be used in accordance with the present invention can be used to prepare one or more catalyst zones. In a preferred embodiment of the invention, the catalyst has three, four or five zones, wherein antimony trioxide having a significant valentinite content is used to prepare one or more zones.

The catalyst of the present invention may be used with suitable upstream and / or downstream beds and also with intermediate zones, for example to eliminate high hot spot temperatures, but upstream and / or downstream Beds and intermediate zones may comprise materials that are generally inert or less active in terms of catalysis.

The catalyst of the present invention is generally a coated catalyst wherein the catalytically active composition is applied in the form of a sheath for an inert support material.

Inert support materials include all support materials in the art, for example quartz (SiO ₂ ), porcelain, magnesium, which are advantageously used in the preparation of coated catalysts for oxidizing aromatic hydrocarbons to aldehydes, carboxylic acids and / or carboxylic anhydrides. It is possible to use oxides, tin dioxides, silicon carbide, rutiles, alumina (Al ₂ O ₃ ), aluminum silicates, steatites (magnesium silicates), zirconium silicates, cerium silicates or mixtures of these support materials. The catalyst support can be used, for example, in the form of spheres, rings, pellets, spirals, tubes, extrudates or ground materials. The size of such catalyst support corresponds to the catalyst support generally used to prepare coated catalysts for the gas phase reaction of aromatic hydrocarbons. Preferably, a ring having a diameter of 3 to 6 mm, or an outer diameter of 5 to 9 mm and a length of 3 to 8 mm and a wall thickness of 1 to 2 mm is used.

The catalyst of the present invention comprises a catalytically active composition comprising at least vanadium oxide and titanium dioxide and can be applied in one or more layers to the support material. In this case, the various layers may differ in terms of their chemical makeup.

The catalytically active composition preferably comprises 1 to 40% by weight of vanadium oxide (calculated as V ₂ O ₅ ) and 60 to 99% by weight of titanium dioxide (TiO ₂ ), based on the total amount of the catalytically active composition. Calculated). In a preferred embodiment, the catalytically active composition comprises up to 1% by weight cesium compound, up to 1% by weight phosphorus compound (calculated as P), and up to 10% by weight antimony oxide (calculated as Sb ₂ O ₃ ). It includes. All figures relating to the chemical composition of the catalytically active composition are based on calcination of the catalyst at a later calcined state, for example at 450 ° C. for 1 hour.

Titanium dioxide is commonly used in the form of anatase in catalytically active compositions. The BET surface area of titanium dioxide is preferably 15 to 60 m ² / g, more specifically 15 to 45 m ² / g, and particularly preferably 13 to 28 m ² / g. The titanium dioxide used may be individual titanium dioxide or a mixture of titanium dioxide. In the latter case, the size of the weight averaged BET surface area determines the distribution of the individual titanium dioxide. The titanium dioxide used is advantageously a mixture of TiO ₂ with a BET surface area of 5 to 15 m ² / g and TiO ₂ with a BET surface area of 15 to 50 m ² / g, for example.

Suitable vanadium sources are in particular vanadium pentoxide or ammonium metavanadate. Suitable antimony sources are various antimony trioxides with significant valenceite content. Possible phosphorus sources are, in particular, phosphoric acid, phosphorous acid, hypophosphorous acid, ammonium phosphate or phosphoryl esters, in particular ammonium dihydrogenphosphate. Suitable sources of cesium are oxides or hydroxides, or carboxylates, in particular acetates, malonates, or salts that can be converted to oxides by heat, such as oxalates, carbonates, hydrogencarbonates, sulfates or nitrates to be.

In addition to the optional addition of cesium and phosphorus, the catalytically active composition contains small amounts of many other oxidic compounds which act as promoters to affect the activity and selectivity of the catalyst, for example by reducing or increasing the catalytic activity. It may include. Examples of such promoters are alkali metals other than cesium, in particular lithium, potassium and rubidium, thallium (I) oxide, aluminum oxide, zirconium oxide, iron oxide, nickel oxide, which are generally used in the form of oxides or hydroxides. , Cobalt oxide, manganese oxide, tin oxide, silver oxide, copper oxide, chromium oxide, molybdenum oxide, tungsten oxide, iridium oxide, tantalum oxide, niobium oxide, arsenic oxide, antimontetoxide, antimony pentoxide and cerium oxide.

In addition, among the aforementioned accelerators, niobium and tungsten oxide as additives in amounts of 0.01 to 0.50% by weight based on the catalytically active composition are further preferred.

Application of the coated catalyst layer optionally comprises a source of the aforementioned promoter element TiO ₂ And by spraying a suspension of V ₂ O ₅ onto the fluidized support. Prior to coating, the suspension is preferably stirred for a sufficiently long time, for example 2 to 30 hours, in particular 12 to 25 hours, in order to break up the aggregates of suspended solids to obtain a homogeneous suspension. The solids content of the suspension is typically from 20 to 50% by weight. Suspension media are generally aqueous, for example water itself or aqueous-miscible organic solvents such as methanol, ethanol, isopropanol, formamide and the like.

In general, copolymers in the form of organic binders, preferably in the form of aqueous dispersions of acrylic acid-maleic acid, vinyl acetate-vinyl laurate, vinyl acetate-acrylate, styrene-acrylate, and vinyl acetate-ethylene, Is added to the suspension. The binder is commercially available as an aqueous dispersion with a solids content of, for example, 35 to 65% by weight. The amount of such binder dispersion used is generally from 2 to 45% by weight, preferably from 5 to 35% by weight and particularly preferably from 7 to 20% by weight, based on the weight of the suspension.

The support is fluidized in an ascending gas stream, in particular in air, in a fluidized bed device or a moving bed device. The apparatus generally comprises a conical or spherical vessel, in which the fluidizing gas is introduced under or over via a tube which is immersed. The suspension is dispersed via the nozzle from the foregoing to the side of the fluidized bed or to the fluidized bed. It is advantageous to use a vertical pipe arranged centrally or concentrically around the immersed tube. Higher gas velocities that move support particles upwards are advantageously used inside the vertical canal. At the outer ring, the gas velocity is only slightly higher than the slowed down velocity. As a result, the particles move vertically in a circular manner. Suitable fluidized bed installations are described, for example, in DE-A 4006935.

Coating temperatures of 20 to 500 ° C. are generally used for coating catalyst supports comprising catalytically active compositions, and the coating can be carried out at atmospheric or reduced pressure. In general, the coating is carried out at 0 ° C to 200 ° C, preferably 20 to 150 ° C, in particular 60 to 120 ° C.

The layer thickness of the catalysis active composition is generally 0.02 to 0.2 mm, preferably 0.05 to 0.15 mm. The content of the active composition in the catalyst is generally 5 to 25% by weight, generally 7 to 15% by weight.

The heat treatment at temperatures above 200 ° C. to 500 ° C. of the precatalyst obtained in this way results in the binder being released from the applied layer due to thermal decomposition and / or combustion. The heat treatment is preferably carried out in situ in a gas phase oxidation reactor.

The present invention further provides a method of gas phase oxidation, in which a gas stream comprising one or more hydrocarbons and oxygen molecules is characterized by an X-ray powder diffraction pattern at 2-theta = 27.7 ° and 28.4 °. Pass the catalyst prepared using antimony trioxide with a ratio of the signal height of the X-ray powder diffraction pattern at 2-theta = 28.4 ° to the sum of the signal heights of at least 0.02.

A preferred embodiment of the invention is a method of gas phase oxidation of o-xylene and / or naphthalene to phthalic anhydride, wherein the gas stream comprising o-xylene and / or naphthalene and oxygen molecules is 2-theta = 27.7. A catalyst prepared using antimony trioxide having a ratio of the signal height of the X-ray powder diffraction pattern at 2 theta = 28.4 ° to the sum of the signal heights of the X-ray powder diffraction pattern at ° and 28.4 ° was not less than 0.02. To pass.

Example

Determination of Valentinite and Cenamontite Content in Antimony Trioxide

The measurement was performed by X-ray powder diffraction. For this purpose, antimony trioxide powder was measured on a "D5000 Theta / Theta" X-ray powder diffractometer from Siemens. Measurement parameters are as follows:

 The signal height is provided as the difference between the maximum intensity and the background value of each signal measured. To measure the valentinite content, signals were used at 2-theta = 27.7 ° (cenamontite, signal height a) and 28.4 ° (valentinite, signal height b). The valentinite content is b / (a + b) and the cenamontite content is a / (a + b).

Example 1 (Example according to the invention):

Catalyst zone CZ1:

3.38 g cesium carbonate, 459.3 g titanium dioxide (Fuji TA 100C, anatase, BET surface area 20 m ² / g), 196.9 g titanium dioxide (Fuji TA 100, anatase, BET surface area 7 m ² / g) and 51.4 g vanadium pentoxide and 13.2 g antimony trioxide (Merck Selectipur 7835, Valentinite content = 0.18, Cenamontite content = 0.82, 99.5% Sb ₂ O ₃ content, 300 ppm by weight As, 500 ppm by weight of Pb, 50 ppm by weight of Fe, average particle size 2 μm) was suspended in 1869 g of deionized water and stirred for 18 hours to achieve uniform distribution. To this suspension 78.4 g of an organic binder comprising a copolymer of vinyl acetate and vinyl laurate were added in the form of an aqueous dispersion of 50% strength by weight. In a fluidized bed apparatus, 820 g of this suspension was sprayed onto 2 kg of steatite (magnesium silicate) in the form of a ring having dimensions of 7 mm x 7 mm x 4 mm and dried. After calcining the catalyst at 450 ° C. for 1 hour, the amount of active composition applied to the steatite ring was 9.1%. The analyzed chemical composition of the active composition was 7.1% V ₂ O ₅ , 1.8% Sb ₂ O ₃ , 0.38% Cs, remaining amount of TiO ₂ .

Catalyst zone CZ2:

It was prepared similar to CZ1 except that the chemical composition of the suspension was changed. After calcination of the catalyst at 450 ° C. for 1 hour, the amount of active composition applied to the steatite ring was 8.5%. The analyzed chemical composition of the active composition included 7.95% V ₂ O ₅ , 2.7% Sb ₂ O ₃ , 0.31% Cs, remaining amount, TiO ₂ with an average BET surface area of 18 m ² / g.

Catalyst zone CZ3:

It was prepared similar to CZ1 except that the chemical composition of the suspension was changed. After calcination of the catalyst at 450 ° C. for 1 hour, the amount of active composition applied to the steatite ring was 8.5%. The analyzed chemical composition of the active composition included 7.1% V ₂ O ₅ , 2.4% Sb ₂ O ₃ , 0.10% Cs, remaining amount, TiO ₂ with an average BET surface area of 17 m ² / g.

Catalyst zone CZ4:

It was prepared similarly to CZ1 except that the chemical composition of the suspension was changed and Fuji TA 100CT, anatase (BET surface area 27 m ² / g) was used instead of Fuji TA 100C. After calcining the catalyst at 450 ° C. for 1 hour, the amount of active composition applied to the steatite ring was 9.1%. The analyzed chemical composition of the active composition included 20% of V ₂ O ₅ , 0.38% of P, remaining amount of TiO ₂ with an average BET surface area of 23 m ² / g.

Example 2 (Not in accordance with the present invention):

Catalyst zone CZ5:

Antimony trioxide grade with reduced valentinite content (e.g., Triox white from Antraco, valentinite content = 0.015, senamonite content = 0.985, 99.3% Sb ₂ O ₃ Content, 0.3 wt% As ₂ O ₃ , 0.18 wt% PbO, 0.02 wt% iron oxide, average particle size 1.5 μm), was prepared similarly to CZ1.

Catalyst zone CZ6:

Antimony trioxide grade with reduced valentinite content (e.g., triox white from anthraco, valentinite content = 0.015, cenamontite content = 0.985, 99.3% Sb ₂ O ₃ content, 0.3 wt% As ₂ O ₃ , 0.18 wt% PbO, 0.02 wt% iron oxide, average particle size 1.5 μm), was prepared similarly to CZ2.

Catalyst zone CZ7:

Antimony trioxide grade with reduced valentinite content (e.g., triox white from anthraco, valentinite content = 0.015, cenamontite content = 0.985, 99.3% Sb ₂ O ₃ content, 0.3 wt% As ₂ O ₃ , 0.18 wt% PbO, 0.02 wt% iron oxide, average particle size 1.5 μm), was prepared similarly to CZ3.

Example 3 (oxidation of o-xylene to phthalic anhydride at model tube scale according to the present invention):

Catalytic oxidation of o-xylene to phthalic anhydride was performed in a salt bath cooled tube reactor with an inner diameter of 25 mm. From the reactor inlet to the reactor outlet, an iron tube of 3.5 m in length and 25 mm in diameter was introduced with 130 cm CZ1, 70 cm CZ2, 60 cm CZ3 and 60 cm CZ4. The iron tube includes a salt melt for controlling temperature; It is surrounded by a thermocouple with an outer diameter of 4 mm, and a built-in retractable component that serves to measure the catalyst temperature.

Air with a loading of 99.2% strength (by weight) of o-xylene of 30 to 100 g / standard m ³ , 4.0 standard m ³ / h, was passed through the tube from top to bottom. This shows the results summarized in Table 1 below (“PAn yield” is the amount of phthalic anhydride obtained in weight percent based on o-xylene of 100% strength).

Example 4 (oxidation of o-xylene to phthalic anhydride at model tube scale, not in accordance with the present invention):

See Example 3, with the exception of using a catalyst bed comprising 130 cm CZ5, 70 cm CZ6, 60 cm CZ7 and 60 cm CZ4 from the reactor inlet to the reactor outlet.

[Table 1]

Comparing Examples 3 and 4 in Table 1, it can be seen that the catalyst activity of the catalyst in Example 3 is higher than in Example 4. The salt bath temperature of Example 3 (according to the invention) can be further lowered for this reason and the PSn yield due to the low o-xylene and phthalide content is significantly higher than in Example 4 (not following the invention). high.

Example 5 (oxidation from industrial scale o-xylene to phthalic anhydride according to the invention)

Catalytic oxidation of o-xylene to phthalic anhydride was performed in a salt bath cooled tube reactor with an inner diameter of 25 mm. From the reactor inlet to the reactor outlet, 130 cm CZ1, 90 cm CZ2, 60 cm CZ3 and 60 cm CZ4 were introduced. In order to record the temperature profile, some reactor tubes were equipped with thermocouples. Air having an o-xylene loading (purity about 99% by weight) of 0 to 100 g / standard m ³ , 4.0 standard m ³ / h, was passed through the tube. PAn yield was measured at the reactor outlet gas and reported in weight percent in Table 2 based on 100% strength o-xylene (kg of PAn per kg of reacted o-xylene).

Example 6 (oxidation of industrial scale o-xylene to phthalic anhydride, not according to the present invention):

See Example 5, except that from the reactor inlet to the reactor outlet, a catalyst bed comprising 130 cm CZ5, 90 cm CZ6, 60 cm CZ7 and 60 cm CZ4 is used.

[Table 2]

Comparing Examples 5 and 6 in Table 2, it can be seen that the catalyst activity of the catalyst in Example 5 is higher than in Example 6. The salt bath temperature of Example 5 (according to the invention) can be further lowered for this reason, with PSn yields having a low o-xylene and phthalide content significantly higher than in Example 6 (not following the invention). high.

Claims (3)

As catalyst for the oxidation of o-xylene and / or naphthalene to phthalic anhydride, at 2-theta = 28.4 ° to the sum of the signal heights of the X-ray powder diffraction pattern at 2-theta = 27.7 ° and 28.4 ° A catalyst prepared using an antimony trioxide having a ratio of the signal height of the X-ray powder diffraction pattern of 0.02 or more. A gas stream comprising one or more hydrocarbon and oxygen molecules was subjected to X-ray powder diffraction at 2-theta = 28.4 ° relative to the sum of the signal heights of the X-ray powder diffraction pattern at 2-theta = 27.7 ° and 28.4 °. A gas phase oxidation method comprising passing a catalyst prepared using antimony trioxide having a signal height ratio of at least 0.02. 3. The method of claim 2,
Wherein said hydrocarbon is o-xylene and / or naphthalene.