WO2011045051A1

WO2011045051A1 - Reactor array for catalytic gas phase oxidation

Info

Publication number: WO2011045051A1
Application number: PCT/EP2010/006268
Authority: WO
Inventors: Hans-Jörg WÖLK; Gerhard Mestl; Harald Dialer
Original assignee: Süd-Chemie AG
Priority date: 2009-10-13
Filing date: 2010-10-13
Publication date: 2011-04-21
Also published as: DE102009049173A1

Abstract

The present invention relates to a reactor array, consisting of a primary reactor and a secondary reactor, wherein the secondary reactor contains at least one catalyst, and wherein the catalyst comprises a porous carrier that is provided with a solid SiC sponge. A catalytically active mass containing TiO₂ and at least one transition metal oxide is applied to the porous carrier, and the TiO₂ used has a bulk density of less than 1.0 g/ml. The present invention further relates to the use of the secondary reactor in the production of phthalic anhydride by means of gas phase oxidation. Additionally, the invention relates to a method for producing the secondary reactor according to the invention.

Description

REACTOR ARRANGEMENT FOR THE C AT A L Y T I S C H E N

GAS PHASE OXIDATION

The present invention relates to a reactor arrangement consisting of a main reactor and a post-reactor, wherein the post-reactor contains at least one catalyst and wherein the catalyst comprises a porous support having a solid SiC sponge, wherein on the porous support

catalytically active mass is applied, the Ti0 ₂ and

contains at least one transition metal oxide, and wherein the Ti0 _{2 used has} a bulk density of less than 1.0 g / ml. In addition, the present invention relates to

Use of the postreactor in the production of

Phthalic anhydride by gas phase oxidation. Furthermore, the invention relates to a method for producing the

according to the invention. The large-scale production of oxygen-containing

Intermediates in the chemical industry is usually produced by the catalytic gas-phase oxidation of aliphatics,

Olefins, or (alkyl) aromatics performed. For example, the production of phthalic anhydride is carried out by

catalytic gas phase oxidation of o-xylene and / or naphthalene. For this purpose, a suitable catalyst for each reaction in a reactor, preferably a so-called tube bundle reactor, filled and from above or below with a mixture of the hydrocarbon and an oxygen-containing gas, for example air, flows through.

Due to the strong heat generation in such

Oxidation reactions, it is necessary to the reaction tube to

Preventing so-called hot spots ("hot spots") with a heat transfer medium to rinse and the resulting

Dissipate heat. As a heat transfer medium is usually used a molten salt, preferably a eutectic mixture of NaN0 ₂ and K 0 _3rd Likewise one can oppress the

unwanted hot spots fill a structured catalyst in the reaction tube, which means that the gas inlet side, where the highest educt concentration prevails, a catalyst layer of lower activity is arranged and the activity is increased via the reaction tube, depending on the number of filled layers. Such systems have already been described in EP 1082317 Bl or in EP 1084115 Bl.

As catalysts, so-called coated catalysts have been proven. This is an inert non-porous carrier made of quartz (Si0 ₂ ), magnesium silicate (steatite), silicon carbide (Sic),

Tin oxide, porcelain, etc., which has a shape and expression suitable for the particular reactor used, e.g. Spheres, rings, extrudates, spirals, stars coated with one or more layers of catalytically active mass. For a maximum

Yield of the desired oxidation product here has the task to raise these layers of the active catalysts highly uniformly and homogeneously on all carrier particles. In the prior art, various apparatuses are described for this purpose. Usually, organic and often inorganic binders are used in mounting the catalyst layers in such devices. As binders are various organic

Adhesive, e.g. Vinyl acetate / ethylene adhesive.

In the field of partial oxidation catalysts for the

Production of oxygenates from aliphatics, olefins or

(Alkyl) aromatics is a variety of different catalysts known. These are often catalyst systems containing as one of the catalytically essential constituents of the oxides of vanadium and titanium. Such

Catalysts are described, for example, in EP 0964744 B1. Usually, a variety of promoter elements are used to increase the productivity of these

Catalysts to achieve, which often too complex

Catalyst systems leads. Such promoters include, among others, the alkali, alkaline earth metals, thallium, antimony, phosphorus, iron, niobium, cobalt, molybdenum, silver, tungsten, tin, zirconium, lead and bismuth (A. Bielanski et al., Ap. Catal. A: Gen. 157, 223 (1997)).

As a carrier for the catalytically active mass of the catalysts, JP 2006-000850 describes the use of porous

Silicon carbide. In this case, a porosity of the carrier between 16 and 20% is disclosed as particularly advantageous, since at a higher porosity, for example of more than 35%, undesired reactions occur on the surface of the carrier. The same problem occurs when the surface of the carrier is greater than 0.3 m ² / g.

Nowadays, for the oxidation of o-xylene and / or

Naphthalene to phthalic anhydride (PSA)

Multi-layer catalyst systems used. The aim here is to adapt the activity of the individual catalyst layers to the course of the reaction along the reactor axis. This makes it possible to obtain a high yield of PSA and at the same time the lowest possible yield of undesired intermediates, e.g.

Phthalide, to achieve. Such multi-layer catalyst systems are described, for example, in EP 1 084 115 B1, in DE 103 23 818 A1, in DE 103 23 461 A1, in DE 103 23 817 A1 and in US Pat

WO 2006/092304 described.

In order to further increase the yield of the gas-phase oxidation, downstream post-reactors (also called post reactors) can be used in addition to the reactors (main reactors) described above. The catalysts serve To remove suboxidation products from the reaction gas or to further convert to product and to convert secondary oxidation products to C0 ₂ and thus to increase the product purity.

With the help of the postreactor, the loading of the main reactor with organic starting material can be further controlled by the design of the

Main reactor to be increased. Moreover, it is no longer necessary to reduce sales in the main reactor by loss of

Selectivity of the oxidation reaction to maximize, as the

Product yield in the secondary reactor is further increased. Thus, higher selectivities can be achieved. The postreactors can be honeycomb catalysts, as described in the

EP 1 181 097 A1 are described. The catalysts can also be applied to ceramic rings. The support of the catalytically active material on ceramic rings has the disadvantage that it causes the back pressure in

Main reactor increased. This disadvantage can be reduced by the use of honeycomb bodies. However, honeycomb bodies have the disadvantage that they are used for so-called "runaway"

(uncontrollable, exothermic temperature increase and

Burn through the honeycomb body). This leads to a chain reaction, because the channels of the honeycomb body become clogged with dust and due to the congestion of the honeycomb

Reaction gas in the channels a rise in temperature and the channel ignites.

An important parameter that leads to an improvement of the

Product yield leads to the suppression of the unwanted total oxidation products CO and C0 ₂ . The proportion of this

By-products can be reduced by the

various catalyst layers in the reactor with regard to their function optimized (activity, selectivity, layer length). In particular, the layer thicknesses of the catalytically active Layers on the non-porous, ceramic support structures are precisely controlled.

In addition to the yield, quality and purity of the obtained

Product is also the life or service life of the product

Catalysts in the main and secondary reactors of crucial importance and there is therefore a constant need for

improved catalysts.

An object of the present invention is therefore to provide a post-reactor which does not generate a high back pressure in the main reactor. Furthermore, no laminar flows, for example in honeycomb bodies, should be set in the after-reactor in order to suppress the diffusion limitation.

In addition, the catalytically active layer on the

Carrier sponge have a homogeneous layer thickness and within the catalyst layer must not express micropores, whereas acropores are desirable. Excessive layer thicknesses and micropores lead to diffusion limitation and

Total oxidation within the catalyst and thus too

Product loss.

In addition, the carrier of the post-catalyst should be able to exothermic by a high thermal conductivity

To transfer reaction enthalpy optimally to the reaction vessel and a possible cooling medium. In this way, the adiabatic temperature increase in the postreactor can be minimized and, moreover, distributed throughout the reactor volume, which in turn leads to an improved product yield.

Another object of the invention was to provide a

improved post-reactor, and a method for its

Preparation, wherein the post-catalyst a high Lifespan and service life and allows a high yield of good quality product.

In a first aspect of the invention, this object is achieved by a reactor arrangement consisting of a

A main reactor and a post-reactor, wherein the post-reactor comprises at least one catalyst, wherein the catalyst comprises a porous support having a solid Sic sponge, wherein on the porous support, a catalytically active composition is applied, which contains Ti0 ₂ and at least one transition metal oxide, and wherein the TiO _{2 used has} a bulk density of less than 1.0 g / ml.

Preferred embodiments are specified in the subclaims.

Surprisingly, with the inventive

Post-reactors, in contrast to the known post-reactors comprising, for example, catalysts with honeycomb bodies or ceramic support bodies, an uncontrolled "runaway" of the reactors and an increased back pressure in the main reactor can be avoided.

It has been found that the use of a porous carrier comprising a Sic sponge, among the special

Conditions in secondary reactors, including in terms of

catalytic properties is particularly advantageous. Contrary to the known problems with the use of porous SiC carriers could unexpectedly just with the inventive porous Sic- carrier sponges on the one catalytically active

Mass is applied, the Ti0 ₂ and at least one

Transition metal oxide, wherein the Ti0 _{2 has} a bulk density of less than 1.0 g / ml, the best catalytic

Properties in the implementation of the product gas from the

Main reactor can be achieved. Advantageously, SiC Sponges spew on only a small amount of impurities that could act as catalyst poisons.

The use of a Sic sponge invention with

irregular pore structure allows a turbulent

Mixing of the reaction gas in the secondary reactor and thus increased heat conduction to adjacent catalyst / reactor zones and to the reactor wall. As a result, for example, the adiabatic temperature increase (hot spot) in the postreactor is lower because the course of the reaction spreads over a larger volume range of the postreactor and thus the reactor can be operated more easily. Due to the thus improved temperature control can be achieved with improved quality of the product with the post-reactors according to the invention, compared to known post-reactors, a higher product yield. In addition, in comparison with the conventional post-reactors with honeycomb bodies, no depletion zones are formed in the post-reactor according to the invention, as in the laminar gas streams of the honeycomb body channels.

In addition, it has been found that the catalytic

Properties can be further improved if the

Pore structure is designed as uniform as possible within the catalyst layers. This allows for a better one

Reaction control. A uniform pore structure can

For example, be generated by using templates. For example, to produce SiC sponges

Polystyrene sponges are used.

The postreactor according to the invention contains at least one

A catalyst, wherein the catalyst comprises a porous support having a solid SiC sponge, wherein on the porous support, a catalytically active composition is applied, which contains Ti0 ₂ and at least one transition metal oxide, and wherein the used Ti0 _{2 has} a bulk density of less than 1.0 g / ml.

A "post-reactor" in the context of the present invention is a reactor downstream of the main reactor, which is the in the

Main reactor for the most part already implemented

Reaction mixture further converted into product. The expression

"Downstream" thus means that the reaction gas first the main reactor and then in the secondary reactor

flows through. The postreactor has a reaction space which is charged with catalyst. In contrast, show

Main reactors on several reaction rooms. During the

Main reactor usually containing bulk catalysts charged tube bundles are preferably used in the novel reactor according to catalysts with monolithic carriers comprising SiC sponges. Postreactors are therefore not tube reactors. In addition, inventive

Post-reactors unlike main reactors not cooled. For the purposes of the present invention, the reactors are used for the catalytic gas-phase oxidation of organic compounds, in particular of aliphatics, olefins, or (alkyl) aromatics.

The postreactor according to the invention can have any desired construction. For example, it may be attached to the main reactor, such as a shell and tube reactor, as a "piggyback reactor." The catalyst (s) of the postreactor are conventionally incorporated into the reactor so as to optimally contact the reaction gas It is preferred to use a hexagonal post-reactor, in which case it is preferable to use the carrier with a triangular cross-section

train. In another preferred embodiment, postcatalysts of square cross section are used in which quadrangular supports are used. Preferably, the postreactor according to the invention comprises at least one, more preferably at least two, even more preferably at least three, different catalyst (s).

Preferably, the catalysts comprise a porous support of a single monolithic support body or of two or more separate support bodies, which are preferably fixedly or movably connected to one another. If the

Catalyst consists of two or more separate carrier bodies, it is particularly preferred that between the individual carrier body is at least partially not filled with carrier material space. The term "catalyst" as used herein refers to a porous carrier having thereon

applied catalytically active mass. Two different catalysts differ in the properties of the porous supports and / or the properties of the catalytically active material. Between the various catalysts may be at least partially not filled with carrier material space, the catalysts are optionally fixed or movable together.

Preferably, the main reactor has at least one first catalyst layer located toward the gas inlet side, a second one located closer to the gas outlet side

Catalyst layer and a third, even closer to or at the gas outlet side towards the catalyst layer, wherein the catalyst layers are composed differently and preferably each containing an active material containing Ti0 _2nd

so that the catalyst activity of the first

Catalyst layer is higher than the catalyst activity of the second catalyst layer. Particularly suitable multilayer catalysts for the main reactor are described, for example, in WO 2006/092304. In a preferred embodiment, the BET surface area increases from the first to the gas inlet side

located catalyst layer to the catalyst outlet to the gas outlet side (in particular the third or fourth catalyst layer) to. As a result, surprisingly good catalyst performance can be achieved. Preferred BET surface areas are 15 to 25 m ² / g for the first

Catalyst layer and 25 to 45 m ² / g for the third (resp.

last) catalyst layer.

Preferably, the Ti0 _{2 used} (anatase modification) has a content of alkali in all catalyst layers,

in particular to Na of less than 0.3 wt .-%, in particular less than 0.2 wt .-%, preferably less than 0.15 wt .-%, more preferably less than 0.02 wt .-% and am most preferably less than 0.015% by weight. Preferably, the above limits for Na and K. apply. According to a further preferred aspect of the invention, the proportion of

Alkali impurities (total alkali content) of the TiO _{2 used} determined as the sum of the lithium, sodium, potassium, rubidium and cesium impurities, less than 1000 ppm, in particular less than 500 ppm, more preferably less than 300 ppm. A method for determining the proportion of alkali impurities of the Ti0 _{2 used} is carried out in accordance with DIN ISO 9964-3. The preferred total alkali content allows a more accurate adjustment of the alkali promoter content of the

Catalyst.

The post-reactor catalysts used according to the invention comprise "porous supports" on which a catalytically active composition is applied

Cell structure on. The individual cells are with theirs

adjacent cells connected by holes in the cells. The Cells have adjacent to all spatial directions

Cells (see Figure 1). The cells can ideally be described as pentagonal dodecahedra whose edges form the webs of the lattice structure. The ratio of big

Cell diameter to small diameter of a

Pentagon dodecahedron is theoretically 1.6. In contrast to the porous supports according to the invention, supports with honeycomb structures, channel structures or cross-channel structures in post-reactors have hitherto been used.

The porous support of the catalyst according to the invention therefore preferably has no honeycomb structure or cross-channel structure and preferably has fractal or non-ordered, open pore structures.

The porous support is preferably more than 90% by weight, more preferably more than 95% by weight, even more preferably more than 97% by weight, and most preferably at least 99% by weight of silicon carbide , The silicon carbide content can be determined by X-ray diffractometry in the usual way. Suitable Sic sponges are, for example, silicon carbide ceramic composite sponges. In a particularly preferred embodiment of the invention, the porous support is a pure silicon carbide sponge.

The porous carrier of the postreactor preferably has no honeycomb structure or cross channel structure. More preferably, the porous support has fractal or non-ordered structures. Whether a fractal structure is present can be determined by the method described in WO2005 / 003758.

The porous support may be cylindrical, cube-shaped, cuboid, prismatic, or any other suitable form or

Dimensioning be formed. Preferably, the porous Carrier on a cylindrical shape. The dimensions (height, length,

Width) of the porous supports are preferably between 0.5 cm and 30 cm, in particular 10 cm and 30 cm, more preferably between 10 cm and 20 cm, and more preferably between 10 cm and 15 cm. In addition, the compression strength of the porous supports is more than 0.2 MPa. The determination of the compression strength is described below in the Methods section.

Preferably, the pore volume of the porous support is between 0.01 cm ³ / g and 0.6 cm ³ / g for pores having a

Pore diameter of less than 1 μτη, and between 0.01 cm ³ / g and 0.2 cm ³ / g for pores having a diameter between 1000 and 1 μπι.

Besides the pores, the porous support preferably has a density of the open macroporous structure (channel system) of 1-100 ppi (pores per inch), preferably 10-50 ppi.

Preferably, the porous support has open pore structures with an open pore diameter between 500 μm and 5 mm, more preferably between 800 μm and 5 mm, more preferably between 0.9 mm and 5 mm, even more preferably between 2 mm and 5 mm and most preferably between 3 mm and 5 mm, on.

In addition to the open pore structure, the SiC sponge is further characterized by cell diameters of 0.1 to 10 μm,

preferably 1 to 5 μm.

The specific surface area of the porous support according to BET is preferably 1-20 m ² / g, more preferably 1-10 m / g, even more preferably between 1-5 m ² / g. The determination of the BET surface area is described in the Methods section. Additionally preferably, the porous support has an apparent density between 0.05 and 0.5 g / cm ³ , more preferably between 0.14 and 0.36 g / cm ³ and most preferably from 0.1 to 0.4 g / cm ³ up. The determination of the apparent density of the support is described below in the Methods section. The calculation of the apparent density of the porous support is based on the total volume of the porous support minus the open pores

The term porosity as used herein refers to the open porosity of the support, i. only the open pores, which are accessible to the reaction gas and are decisive for the catalytic properties, are considered.

When determining the porosity by means of water penetration method (see method section), the liquid can penetrate into the open pores. The porosity (P) is then given as follows:

P = [volume / volume-porous carrier] * 100 Preferably, the porous carrier of the inventive

Subsequent reactor has a porosity of 70 to 98%, more preferably between 70 and 95%, more preferably between 80 and 95%, more preferably between 85 and 95% and even further

preferably between 88 and 95%. The determination of

Porosity is described below in the Methods section. The

Preparation of porous supports is known to the person skilled in the art. The preparation of porous supports having the properties according to the invention is described below. Here, for example, of silicon powder and

Phenol resins / polyurethane sponges are assumed.

Suitable production methods are, for example, in

US6217841, US5958831, US6251819, and US10963604. By using a suitable polyurethane sponge, the desired sponge structure can be produced in this case. The SiC sponges according to the invention preferably consist of β-silicon carbide. Here, the ß-silicon carbide and the absence of other silicon carbide modifications, for example α-silicon carbide, by means of

Pulverdiffraktometrie be determined in the usual way. The catalytically active composition which is applied to the porous support of the postreactor according to the invention is described below. This catalytically active mass of the catalyst of the post-reactor can also be used for the catalyst of the main reactor. According to the invention, any TiO ₂ modification can be used, with TiO ₂ in the anatase form being preferred. Additionally preferably, the TiO _{2 used has} a BET surface area of at least 15 m ² / g, preferably between 15 and 60 m ² / g, in particular between about 15 and 45 m ² / g and particularly preferably between 15 and 40 m ² / g on. Continue

preferably that at least 30%, in particular at least 40% and up to 80%, preferably up to 75%, in particular up to 70% of the total pore volume of Ti0 _{2 are formed} by pores having a radius between 60 and 400 nm. The determination of the pore volumes or proportions stated herein takes place, unless stated otherwise, by means of

Mercury porosimetry (according to DIN 66133). The indication of the total pore volume refers in the present description in each case to the entire means

Mercury porosimetry measured pore volume between 7500 and 3.7 nm pore radius size. Pores with a radius of more than 400 nm are preferably less than about 30%,

especially less than about 22%, particularly preferably less than 20% of the total pore volume of the TiO _{2 used} . It is further preferred that about 50 to 75%, in particular about 50 to 70%, particularly preferably 50 to 65% of the total pore volume of the TiO _{2 are formed} by pores having a radius of 60 to 400 nm, and preferably about 15 to 25% of the total pore volume by pores having a radius of more than 400 nm. With respect to the smaller pore radii, it is preferred that less than 30%,

In particular, less than 20% of the total pore volume of Ti0 _{2 are formed} by pores having a radius of 3.7 to 60 nm. A particularly preferred range for this pore size is about 10 to 30% of the total pore volume, in particular 12 to 20%. According to a further preferred embodiment, the TiO _{2 used has} the following particle size distribution: The Dio value is preferably 0.5 μπι or less; the D ₅₀ value (ie the value at which each half of the

Particle has a larger or smaller particle diameter) is preferably at 1.5 μπι or less; of the

D ₉₀ value is preferably 4 pm or below. The D ₉₀ value of the TiO ₂ used is preferably between about 0.5 and 20 μπι, in particular between about 1 and 10 μπι, more preferably between about 1 and 5 μηι. In

Electron micrographs, the Ti0 ₂ used in the invention preferably has an open-pored, sponge-like structure, wherein primary particles or crystallites to more than 30%, in particular more than 50%, to open porous

Agglomerates are joined together. It is believed, without the invention being limited to this assumption, that this particular structure of the TiO _{2 used} , which is reflected in the pore radius distribution, makes it especially

favorable reaction conditions for the gas phase oxidation are created. In a further preferred embodiment, the

Primary crystallites of the titanium dioxide used at least partially connected to agglomerates, eg in

electron micrographs are easily recognizable. In a particularly preferred embodiment, the

Primary crystallites of Ti0 ₂ to more than 30%, in particular more than 50%, to agglomerates, in particular to open-pore agglomerates, joined together.

In a further preferred embodiment, TiO 2 having a primary crystallite size (primary particle size) of more than at least 210 angstroms to at most 900 angstroms, preferably more than at least 250 angstroms to at most 600 angstroms, more preferably more than at least 300

Angström to at most 500 angstroms, in particular more than at least 350 angstroms and most preferably more than at least 390 angstroms used. Primary crystallites having this preferred primary crystallite size enable the preparation of particularly advantageous catalysts by allowing the formation of a not too compact but open-pored structure of the titanium dioxide in the catalyst. A method for determining the primary crystallite size.

The determination of primary crystallite sizes

(Primary particle sizes) was carried out by means of powder

X-ray diffractometry. The analysis was carried out with a device from Bruker, DE, type BRUKER AXS-D4 Endeavor. The obtained Röntgendiffraktogramme were with the

Software package "DiffracPlus D4 Measurement" recorded according to the manufacturer's instructions and the half width of the

100% Reflexes was analyzed with the software "DiffracPlus Evaluation" according to the Debey-Scherrer formula according to the data of the

The manufacturer evaluated to determine the primary crystallite size. In a further preferred embodiment, TiO _{2 is used} with a bulk density of less than 0.8 g / ml, more preferably less than 0.6 g / ml. Most

preferred is TiO ₂ having a bulk density of not more than 0.55 g / ml. The lower the bulk density of the Ti0 _{2 used} , the better the structure of the catalyst in the

Provided Ti0 ₂ -Oberflache for the purpose of the invention.

In a further preferred embodiment, the TiO _{2 used has} a particle size distribution with a Di ₀ value of at most 0.5 μm and / or a D ₅₀ value of

at most l, 5pm and / or a D ₉₀ value of at most 4 μπι on. Particularly preferably, the D ₉₀ value of the TiO _{2 used is} between 0.5 and 20 μm, in particular between 1 and 10 μm, particularly preferably between 2 and 5 μm. The TiO ₂ is particularly preferably present in the anatase modification.

According to the invention, the catalytically active composition comprises at least one transition metal oxide selected from the group consisting of vanadium oxide, antimony oxide, chromium oxide, niobium oxide, tantalum oxide, molybdenum oxide, tungsten oxide, manganese oxide, iron oxide or their atomic mixtures; The catalytically active composition particularly preferably comprises at least vanadium oxide as the transition metal oxide. Preferably, the catalytically active composition contains at least one, more preferably at least two, and most preferably at least three of the aforementioned transition metal oxides. In a particularly preferred embodiment of the invention, the transition metal oxides V ₂ 0 ₅ and / or Sb ₂ 0 ₃ , preferably V ₂ 0 ₅ and Sb ₂ 0 ₃ are used. Preferably, this is

crystalline V ₂ 0 ₅ used. For example, in the

DE 21 59 441 A describes a catalyst, in addition to

Titanium dioxide of anatase modification from 1 to 30% by weight

Vanadium pentoxide and zirconium dioxide. Preferably, the catalyst is layered, wherein the actual carrier oxide Ti0 _{2 is} coated with a monoatomic to several atomic layers thick layer of one or more of the aforementioned transition metal oxides.

Additionally preferably, the catalytically active composition contains at least one promoter. The promoter is preferred

selected from the group consisting of P, Sb, Bi, Li, Cs, Sr, Ba, Ni, Co, Fe, b, Mo, W, Sn and noble metals selected from the group consisting of Cu, Ag, Au, Pt, Pd , and Rh.

Preferably, the catalytically active composition comprises at least one, more preferably at least two, and most preferably at least three of the above-mentioned promoters. By using promoters, the activity and selectivity of the catalysts can be influenced, in particular by

Lowering or increasing the activity. To the the

Selectivity increasing promoters include, for example, the alkali metal oxides and oxidic phosphorus compounds,

in particular phosphorus pentoxide.

The components of the catalytically active composition are preferably used in the following amounts (see Table 1). The components not listed in the table are preferably used in proportions of between 1 and 10% by weight, more preferably between 1 and 7% by weight, more preferably between 1 and 2% by weight. Table 1.

In addition to the above ingredients, the remainder of the catalytically active material is TiO ₂ . More preferably, the catalytically active composition is at least 70 wt .-%, more preferably at least 80 wt .-%, even more preferably at least 90 wt% of Ti0 _second In a preferred

Embodiment of the invention, the active composition comprises 80-90 wt .-% Ti0 ₂ , 9.5-19.9 wt .-% V ₂ 0 ₅ and 0.1 - 0.5 wt .-% P, more preferably consists of the active composition of the abovementioned constituents. In a further preferred

Embodiment of the invention, the active material consists of 85.80 wt .-% of Ti0 ₂ , 14 wt .-% V ₂ 0 ₅ and 0.2 wt -.% P.

Preferably, the amount of active mass in the catalyst is between 5 and 15% by weight, more preferably between 6 and 12% by weight, and most preferably between 7 and 11% by weight. In a particularly preferred embodiment of the invention contains the catalytically active material of the catalyst

(i) Ti0 ₂ in the anatase modification

(ii) at least one, preferably two transition metal oxide (s) selected from the group consisting of vanadium oxide,

Antimony oxide, chromium oxide, niobium oxide, tantalum oxide, molybdenum oxide, tungsten oxide, manganese oxide, iron oxide or their atomic

mixtures thereof; and or

(iii) at least one, preferably two, promoter (s) selected from the group consisting of P, Sb, Bi, Li, Cs, Sr, Ba, Ni, Co and noble metals selected from the group consisting of Cu, Ag, Au, Pt, Pd and Rh.

In addition, the catalytically active composition of the postreactor according to the invention preferably additionally comprises an organic binder, preferably a vinyl acetate-ethylene copolymer, or a decomposition product of the abovementioned during calcination

Binders or copolymers. Furthermore, the catalytically active composition preferably has an inorganic binder in the form of a sol, metal alkoxide (of Si0 ₂ sol or its precursors, Al ₂ 0 ₃ sol or its precursors, Zr0 ₂ sol or its precursors, Ti0 ₂ sol, Ce0 ₂ sol or its precursors, water glass, MgO, etc).

Furthermore, the present invention relates to a process for producing a post-reactor according to the invention, comprising the following steps: (i) providing a catalytically active composition as defined herein, at least containing TiO ₂ , wherein the TiO 2 is a

Bulk density of less than 1.0 g / ml, and at least one transition metal oxide; (ii) providing a porous support having a solid SiC-Schwamtn;

(iii) applying the catalytically active composition obtained under (i) to the porous support from step (ii).

(iv) drying at 120 ° C of the product obtained in step iii)

Catalyst at a temperature of more than 400 ° C, preferably at a temperature of 440 ° to 450 ° C; and

(v) incorporating the catalyst obtained in step (iv) into a post-reactor. In a preferred embodiment, the

methods according to the invention further the steps:

(VI) calcining the catalyst obtained in step v) at a temperature of more than 200 ° C, preferably at a

Temperature from 240 ° to 350 ° C; (vii) activating the catalyst obtained in step vi) at a temperature of more than 350 ° C, preferably at a

Temperature from 370 to 350 ° C using the product gas stream from the main reactor.

The catalytically active layer is preferably by immersion and extraction, by purging, by

Soak, or applied by spraying. Furthermore, the method according to the invention is preferred for producing a reactor arrangement comprising a

Main reactor and a secondary reactor according to the invention

used. Here, first, the inventive

Afterreactor are prepared and then in the usual manner a main reactor can be connected. The provision of the catalytically active material in step (i) of the

Manufacturing process can be carried out in the usual manner, for example, a suspension of titanium oxide,

preferably in the anatase modification, vanadium pentoxide, diantimony trioxide, with a suitable organic and an inorganic binder, for example vinyl acetate-ethylene copolymer, a Ti0 ₂ sol and suitable promoters

getting produced.

In the method according to the invention, preference is given to

catalytically active composition provided in the form of an aqueous suspension. Preferably, the suspension contains

at least one suitable binder. Suitable binders include organic binders known to the person skilled in the art, preferably copolymers, advantageously in the form of an aqueous dispersion, of vinyl acetate / vinyl laurate, vinyl acetate / acrylate, styrene / acrylate, vinyl acetate / maleate and vinyl acetate / ethylene. Particularly preferred is an organic polymeric or copolymeric adhesive, especially a vinyl acetate copolymer adhesive, most preferably a vinyl acetate-ethylene copolymer as

Binder used. The binder used is added in conventional amounts of the catalytically active composition, preferably with 10 to 25 wt .-%, more preferably with 20 to 25 wt .-%, based on the solids content of the catalytically active material. In this regard, reference may be made, for example, to EP 744 214.

The preparation of the porous support in step (ii) is carried out as described above. It can too

commercially available porous supports are used.

In step (iii), the suspension from step (i) can then be applied by single or multiple impregnation, spraying, or by suction, In particular, by applying in. The application of a thin layer of 50 to 500 \ x of the catalytically active material on the porous support, for example, by spraying a

Suspension to the heated support at 80 to 200 ° C. In this regard, for example, reference is made to EP-A 744214, EP 1 181097, DE 197 09 589 and DE 21 06 796.

As far as the application of the catalytically active material takes place at elevated temperatures of about 150 ° C, as known from the prior art, an application to the

Carrier also possible without organic binders. Useful coating temperatures when using the abovementioned binders are according to DE 21 06 796

for example between about 50 and 450 ° C. The binders used burn when the catalyst is heated

Commissioning of the filled reactor within a short time. The binders serve primarily to enhance the adhesion of the catalytically active material to the carrier.

In step (iv), the catalyst is subsequently dried, incorporated in a post reactor and in the usual way

temperature treated or calcined (conditioned). It has been found to be advantageous if the catalyst for at least 24 hours at least 250 ° C, especially between 24 and 72 hours at 350 ° C, in a 0 ₂ -containing gas, especially in air, is calcined. The temperature should preferably not exceed 500 ° C, especially 470 ° C

exceed. Basically, however, are others

Calcination conditions that are suitable to those skilled in the art

appear, not excluded.

The conditioning of the post-catalyst takes place by means of the product gas stream from the main reactor at temperatures between 250 and 350 ° C, preferably between 370 and 350 ° C. However, such high temperatures can not be achieved in situ in the post-reactor, since, for example, the o-xylene content in the feed and the operating temperature are too low. That is, the catalyst for the post-reactor must before installation in a reactor arrangement, for example in a tray oven at the top

calcined temperatures in the air stream for at least 24 hours in order to burn out the organic adhesive advantageously completely.

In step (v), the shaped catalyst bodies are so

layered incorporated into the post reactor that no

Voids arise and also the catalysts are sealed against the reactor wall, so that the reaction gas is passed through the catalysts. Optionally, different catalysts can be incorporated into the post-reactor. In addition, the catalysts can be interconnected.

Furthermore, the present invention relates to the use of a secondary reactor according to the invention and a reactor arrangement according to the invention for the gas phase oxidation of organic

Starting compounds such as aliphatics, olefins, or

(Alkyl) aromatics, in particular for the production of

Phthalic anhydride by gas phase oxidation of o-xylene and / or naphthalene.

In general, when using the postreactor according to the invention for the production of phthalic anhydride, a mixture of a molecular oxygen-containing gas, for example air, and the starting material to be oxidized (in particular o-xylene and / or naphthalene) by a

Main reactor, for example, a tube bundle reactor with catalyst bed, and then by a

passed downstream downstream reactor according to the invention. Suitable conditions for carrying out a process for the preparation of phthalic anhydride from o-xylene and / or naphthalene are familiar to the person skilled in the art equally from the prior art. In particular, reference is made to the summary in K. Towae, W. Enke, R. Jaeckh, N. Bhargana

"Phthalic Acid and Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry Vol. A. 20, 1992, 181 and hereby incorporated by reference. For example, the boundary conditions known from the above reference WO-A 98/37967 or WO 99/61433 can be selected for the stationary operating state of the oxidation.

For this purpose, first the catalysts in the reaction tubes of the main reactor, which are thermostated from the outside to the reaction temperature, for example by means of molten salts, filled. About the thus prepared catalyst bed, the reaction gas at temperatures of generally 250 to

430 ° C, preferably 270 to 410 ° C, and more preferably from 280 to 400 ° C and at an overpressure of generally 0.1 to 2.5, preferably from 0.3 to 1.5 bar with a

The space velocity is generally from 1000 to 50,000 h.sup.- ¹ . Subsequently, the reaction mixture is passed through the after-reactor according to the invention

Inlet temperature of the reaction gas is adjusted by a gas cooler before the postreactor.

The reaction gas supplied to the catalyst is in

Generally, by mixing a molecular oxygen-containing gas which is still suitable in addition to oxygen

Reaction moderators and / or diluents such as vapor, carbon dioxide and / or nitrogen may contain, produced with the aromatic hydrocarbon to be oxidized, wherein the molecular oxygen-containing gas is generally 1 to 100, preferably 2 to 50 and particularly preferably 10 to 30 mol% of oxygen, 0 to 30, preferably 0 to 10 mol% of water vapor and 0 to 50, preferably 0 to 1 mol% of carbon dioxide, balance nitrogen. To generate the reaction gas, the gas containing the molecular oxygen is generally charged with 30 to 150 g per Nm ^{3 of} gas of the aromatic hydrocarbon to be oxidized.

The temperature management in the gas phase oxidation of o-xylene or naphthalene to phthalic anhydride is well known to those skilled in the art, with reference being made, for example, to DE 100 40 827 A1. CHARACTERS

The invention is explained in more detail below with reference to figures and examples. Figures and examples serve only

for illustrative purposes without intending to be limiting. Show it:

Figure 1 is a schematic illustration of cells as they are arranged in a sponge. The numbers in the cells indicate the number of adjacent cells.

2 shows an illustration of a postreactor 1 according to the invention, in which the catalysts according to the invention, in the form of cylindrical cores, can be used. During operation of the postreactor 1, reaction gas containing the

Main reactor has passed through the inlet 2 in the

Reaction space 6, which contains the catalyst, introduced into the secondary reactor 1. Through the outlet 5, the reaction gas is passed out of the secondary reactor 1. Terminals 3 and 4 are used to connect thermocouples to measure the adiabatic T increase in the reactor. METHODS

For determining the parameters of the invention

Catalysts are used the following methods. If properties of the finished catalyst are to be measured, the catalyst or a part thereof can be pulverized and the determination of the parameters of this powder

(porous support and catalytically active layer) are performed. If properties of the porous support without

catalytically active layer to be measured, the catalytically active layer can be removed manually, for example by shaking or scraping. The remaining porous support can then be pulverized and examined again. Similarly, the manually removed catalytically active layer can be examined.

1. BET surface

The determination is made according to the BET method according to DIN 66131; a publication of the BET method can also be found in J. Am. Chem. Soc. 60, 309 (1938).

2. Pore radius distribution / pore diameter / pore volumes The determination of the pore radius distribution of the porous support and the Ti0 _{2 was} carried out by

Mercury porosimetry according to DIN 66133; maximum pressure: 2,000 bar, Porosimeter 4000 (Porotec, DE), according to the manufacturer. The determination of the pore volumes or

shares also takes place by means of mercury porosimetry. 3. Particle sizes

The determination of the particle sizes took place after the

Laser diffraction method with a Fritsch particle sizer

Analysette 22 Economy (Fritsch, DE) according to the manufacturer's instructions, also with regard to sample pretreatment: the Sample is dissolved in deionized water without addition of

Homogenized and treated with ultrasound for 5 minutes.

4. BET surface area, porosity, apparent SiC density,

Pore volume, pore diameter, pore radius distribution or pore volume and particle size distribution

The determination of these parameters was carried out with respect to the SiC sponge and the titanium dioxide in each case at the, at 150 ° C in a vacuum dried, uncalcined material. In addition, microscopic examinations can be carried out. The statements in the present description with respect to the BET surface areas of the catalysts or catalyst layers also relate to the BET surface areas of each

used SiC sponge or Ti0 ₂ material (dried in vacuo at 150 ° C, uncalcined, see above). The proportion of active mass (proportion of the catalytically active composition, without binder) in each case refers to the proportion (in% by weight) of the catalytically active composition in the total weight of the catalyst, including support in the respective catalyst layer, measured after conditioning at 400 ° C. for 4 hours in air.

Determination of Apparent Density: The determination of the open porosity of the sintered samples is performed with the

Water penetration method according to DIN EN 623 Part 2 made. The principle is based on the fact that a porous body is a

Mass increase is experienced when its externally accessible

Pores are filled with liquid. (In the case of the materials reacting with the water (eg MgO etc.), other liquids, which nevertheless have lower vapor pressure (eg toluene) must be selected.) The same also changes Buoyancy related to the theoretical density of the material when closed pores are present. In order to be able to calculate the porosity, the dry mass (mt), the

Buoyancy mass (ma) and wet mass (mf) with a

Precision balance determined. Bulk density generally refers to the mass of a dry material by volume, including all pores. The basis for the raw density determination is DIN 1094. The

Volume is not determined according to the Archimedian principle by measuring the buoyancy in a liquid of known density, but determined by the Ausmessverfahren. This succeeds only on geometrically defined bodies. In this case, sealing in the surface area (wax, zapon varnish) can help, the volume also irregularly shaped porous

Determine body according to the principle of buoyancy. 5. Catalyst activity

Under activity of the catalyst in a catalyst layer according to the invention the ability of the catalyst is understood, within a defined volume (= balance space),

For example, a reaction tube of defined length and inner diameter (for example 25 mm inner diameter, 1 m length), at given reaction conditions (temperature, pressure,

Concentration, residence time) to react the starting material used. The considered catalyst accordingly has a higher

Activity as another catalyst when in this

given volume and under each same

Reaction conditions achieved a higher Eduktumsatz. In the case of o-xylene or naphthalene as starting material, the measures

Catalyst activity thus on the basis of the level of conversion of o-xylene or naphthalene to the oxidation products. Cause of a higher catalyst activity can either be optimized for the desired nature / quality of the active Centers (see, for example, "turn over frequency") or an increased number of active centers in the same balance area, which is given, for example, if a higher

Catalyst mass with otherwise identical properties in the balance room is present. 6. Compression strength

The determination of the compression strength is carried out according to DIN 53291. The compression strength in MPa corresponds to the value at 20% elongation of the test specimen.

7. Pore density (ppi)

The pore density is determined by counting the number of open pores that are in an area of one square inch.

B E I S P I E L E

Comparative Example 1 The comparative example relates to the use of a

Main reactor in combination with a secondary reactor. Of the

Main reactor, a 4-layer catalyst system with subsequent composition and layer length, was in a

salt bath cooled tubular reactor of 4m length filled with 25mm inner diameter. In the reaction tube was centrally arranged a 3 mm thermal sleeve with built-in tension element for temperature measurement.

To determine the catalytic performance of this reactor combination of 0 to a maximum of 100 g / Nm ³ (Nm ³ = standard cubic meters) o-xylene (purity 99.9%) at 4 Nm ³ air / h and passed the reaction gas after leaving the reaction tube through a condenser directed by all organic

Components of the reaction gas, except for the carbon monoxide and Carbon dioxide, deposit. The separated crude product is melted by means of superheated steam, collected and then weighed and analyzed. In addition, you can

Reaction gas samples are taken by means of a separate glass cold trap in an acetone / dry ice mixture directly after the output of the main and secondary reactor and analyzed.

The postreactor is downstream of the main reactor and is described below. The postreactor was constructed as shown in Figure 2 and contained 3 "cores" in the form of honeycomb catalysts

Post reactor was 292 ° C, the gas outlet temperature after the post reactor was 307 ° C. The

Post-reactor catalyst temperature was determined to be 309 ° C in the middle of the middle core. 236 g Ti0 ₂ (BET about 30m ² / g) with a middle

Particle diameter of about 1 μπι, 236 g Ti0 ₂ (BET about 20m ² / g) with an average particle diameter of about 1 μπ \, 120 g V ₂ 0 ₅ and 8.24 g of (NH ₄ ) ₂ HPO ₄ were suspended in 1400 ml of deionized water and stirred for 18 hours to achieve a homogeneous distribution. The solids content of the resulting suspension was 29.6 wt .-%. Thereafter, 60 g were added

organic binder, a copolymer of ethylene / vinyl acetate, added in the form of a 50 wt .-% aqueous dispersion. In this coating suspension was a monolithic ceramic carrier honeycomb of cordierite with a cell density of 200 cpsi and the dimensions described below

immersed and removed from the dipping bath after about 1 minute residence time. The remains of the channels located in the channels

Suspension were blown out with an air blower (at a maximum of 130 ° C). The complete drying of the coated honeycomb body was carried out for 12 h in a drying oven at 130 ° C. The amount of active mass applied was 20 g / l

Catalyst. Following were the coated ones

Honeycomb bodies calcined in air in a rack oven at 450 ° C for 24 h. The honeycomb bodies had a diameter of 55 mm and a length of 150 mm, with the 3 catalysts

were consecutively inserted into the postreactor, so that a total length of the cores of 450 mm resulted. The drill cores are located in the reaction space through which the reaction gas flows.

The crude yield is determined as follows. Max. Raw PSA yield [% by weight]

Balanced amount of crude PSA [g] x 100 / feed o-xylene [g] x

Purity o-xylene [% / 100]

The table below compares the reaction gas samples before and after the post reactor, which were obtained at an o-xylene loading of 80g / Nm ³ .

The yield of phthalic anhydride in the reaction gas sample after the main reactor was 114.7 wt .-%. The yield

Phthalic anhydride in the reaction gas sample after the

Post reactor was 115.5 wt%. example 1

This inventive example relates to the use of a main reactor, as described in Comparative Example 1, in combination with a post-reactor according to the invention. The postreactor according to the invention is the main reactor

downstream and is described below:

The secondary reactor was constructed as shown in Figure 2 and contained 3 "cores" in the form of catalysts according to the invention

Reaction space, which is traversed by the reaction gas. The gas inlet temperature into the post reactor was 292 ° C, the

Gas inlet temperature after the post reactor was 307 ° C. The post-reactor catalyst temperature was determined to be 305 ° C in the middle of the middle core. The catalysts comprised a porous support (Sic sponge with 110 ppi) with a diameter of 55 mm and a length of 150 mm, wherein the 3 catalysts in succession in the

Subsequent reactor were used, so that a total length of the cores of 450 mm resulted. The active mass became as above for the ceramic honeycombs

described applied to the SiC sponges. The catalytically active composition applied to the porous carrier contained: 79.8% by weight of TiO _{2 /} 20.0% by weight of V ₂ O ₅ , 0.2% by weight of P. In addition, 2.3% by weight of % of an organic binder

(Vinyl acetate / ethylene copolymer) used in the

Calcination at 450 ° C for 24h decomposed. The catalyst thus prepared had a BET surface area of about 32 m ² / g.

The yield of phthalic anhydride in the reaction gas sample after the main reactor was 114.4 wt .-%. The yield Phthalic anhydride in the reaction gas sample after the post-reactor according to the invention was 116, l-wt%.

A comparison of the product yields from Comparative Example 1 and Example 1 shows that the catalytic properties are improved in the reactor arrangement according to the invention. In addition to an increased yield of phthalic anhydride, the

Quality of the product can be improved, as by the

lower concentrations of by-products is indicated. The use of the reactor arrangement according to the invention also led to a turbulent mixing of the reaction gas in the post-reactor and thus a measurable reduced temperature in

Post reactor catalyst.

Claims

claims

Reactor arrangement consisting of a main reactor and a post-reactor, wherein the post-reactor at least one

Catalyst, wherein the catalyst comprises a porous support having a solid Sic sponge, wherein on the porous support, a catalytically active material is applied, the Ti0 ₂ and at least one

Transition metal oxide contains, and wherein the Ti0 _{2 used has} a bulk density of less than 1.0 g / ml.

Reactor assembly according to claim 1, wherein the porous support of the catalyst is not a honeycomb or

Cross channel structure has. 3. Reactor arrangement according to claim 1 or 2, wherein the porous support fractal or non-ordered, open

Owns pore structures.

4. Reactor arrangement according to one of claims 1 to 3, wherein the porous support of the catalyst pores with a

Pore diameter of 500 m to 5 mm.

The reactor assembly of any one of claims 1 to 4, wherein the porous support of the catalyst has 1-100 pores per inch (ppi).

6. Reactor arrangement according to one of claims 1 to 5, wherein the porous support of the catalyst has an apparent density of 0.1-0.4 g / cm ³ .

Reactor arrangement according to one of claims 1 to 6, wherein the porous support of the catalyst has a porosity of 70-98%. Reactor arrangement according to one of claims 1 to 7, wherein the porous support of the catalyst consists of a single monolithic carrier body or of two or more separate carrier bodies, between which there is a space not filled with carrier material.

Reactor arrangement according to claim 8, wherein the carrier bodies are fixedly or movably connected to one another.

Reactor arrangement according to one of claims 1 to 9, wherein the catalytically active material of the catalyst additionally contains one or more promoters.

Reactor arrangement according to one of claims 1 to 10, wherein in the catalytically active composition of the catalyst:

(i) Ti0 _{2 is present} in the anatase modification; and or

(ii) the transition metal oxides are selected from the group consisting of vanadium oxide, antimony oxide, chromium oxide, niobium oxide, tantalum oxide, molybdenum oxide, tungsten oxide, manganese oxide, iron oxide or their atomic mixtures; and or

(iii) the promoters are selected from the group

consisting of P, Sb, Bi, Li, Cs, Sr, Ba, Ni, Co and noble metals selected from the group consisting of Cu, Ag, Au, Pt, Pd and Rh.

Reactor arrangement according to one of claims 1 to 11, wherein the transition metal oxides of the catalytically active material V ₂ 0 ₅ and / or Sb ₂ 0 ₃ are. Reactor arrangement according to one of claims 1 to 12, wherein the catalytically active material of the catalyst comprises an organic binder.

14. Reactor arrangement according to claim 13, wherein the organic binder is a vinyl acetate-ethylene copolymer or a

calcined vinyl acetate-ethylene copolymer.

15. Reactor arrangement according to one of claims 1 to 14, wherein the Ti0 _{2 is used} in the form of primary crystallites, which are connected to at least 5% to agglomerates.

16. Reactor arrangement according to one of claims 1 to 15, wherein the Ti0 _{2 used has} a particle size distribution of

Dio ^ 0.5 μιτι and D _{50 has} 1.5 m.

17. Reactor arrangement according to one of claims 1 to 16, wherein the Ti0 _{2 used has} a content of alkali <0.3 wt .-%. 18. Reactor arrangement according to one of claims 1 to 17, wherein the Primärkristallitgröße of Ti0 used ₂ ^ 210 Ä.

19. Use of a as in any one of claims 1 to 18

defined postreactor in the production of

Phthalic anhydride by gas phase oxidation of o-xylene and / or naphthalene.

20. A process for producing a postreactor as defined in any one of claims 1 to 18, comprising the

subsequent steps of: (i) providing a catalytically active composition comprising TiO ₂ , wherein the TiO _{2 used has} a bulk density of less than 1.0 g / ml, and at least one transition metal oxide;

(ii) providing a porous support having a solid Sic sponge;

(iii) applying the catalytically active composition obtained under (i) to the porous support of step (ii);

(iv) drying at 120 ° C and calcining the in step

(iii) the obtained catalyst at a temperature higher than 400 ° C; and

(v) incorporating the product obtained in step (iv)

Catalyst in a post-reactor.

21. The method of claim 20, wherein the catalytically active composition is provided in the form of an aqueous suspension.

22. The method according to claim 19 or 20, wherein the catalytically active material from step (i) comprises an organic binder.

A process according to claim 22, wherein the organic binder is a vinyl acetate-ethylene copolymer or a calcined vinyl acetate-ethylene copolymer

24. The method according to any one of claims 21 to 23, wherein the catalytically active material by one or more times Soaking, spraying or sucking on the porous support is applied.