DE102005044916A1 - Procedure for determining tortuosity of porous catalyst carrier material, comprises determining self-diffusion of gas or liquid and self-diffusion of free gas and/or free liquid and calculating the quotient - Google Patents

Abstract

Procedure for the determination of tortuosity of a porous catalyst carrier material, comprises determining a self-diffusion (D) of a gas or a liquid in the carrier material and self-diffusion (D0) of free gas and/or free liquid and calculating the quotient of D/D0. Independent claims are included for: (1) a catalyst carrier material from the porous carrier material with a tortuosity coefficient (tau ) of 1.5-4; (2) a dehydrogenation catalyst with improved deactivation characteristics, comprising one or more active metals in elementary form and/or oxidic form on the catalyst carrier material; (3) a dehydrogenation catalyst (tau of 1.5 to 4) consisting of a porous carrier body with an applied active mass; (4) heterogeneously catalyzed dehydrogenation of a reaction gas mixture containing one or more dehydrogenatable 2-30C-hydrocarbons, comprising contacting the reaction gas mixture containing the dehydrogenatable hydrocarbons with the dehydrogenation catalyst; (5) determination of the tortuosity of a catalyst comprising the porous carrier material with an applied active mass, comprising determining the self-diffusion (D) of a gas or a liquid in the catalyst and the self-diffusion (D 0) of the free gas and/or the free liquid and calculating the quotient (D/D 0); and (6) a catalyst comprising a porous carrier material and the applied active mass with a tortuosity coefficient of 1.5-4.

Description

The invention relates to a catalyst support, a dehydrogenation catalyst and a process for the heterogeneously catalyzed dehydrogenation of C ₂ -C ₃₀ -hydrocarbons, preferably of C ₂ -C ₁₅ -, more preferably of C ₂ -C ₈ - and most preferably of C ₃ - and C ₄ hydrocarbons. Hydrocarbons are preferably understood as meaning chemical compounds which are composed exclusively of C and H. Particularly advantageous is the heterogeneously catalyzed dehydrogenation of saturated hydrocarbons according to the invention. Furthermore, the invention relates to a method for determining the tortuosity of a porous catalyst support.

dehydrated Hydrocarbons are used as starting materials for numerous industrial processes in big Quantities needed. For example, find dehydrogenated hydrocarbons in the production detergents, knock-proof gasoline and pharmaceutical products Use. Likewise, many plastics are polymerized produced by olefins.

For example, acrylonitrile, acrylic acid or C ₄ -oxo alcohols are produced from propylene. Propylene is currently produced predominantly by steam cracking or by catalytic cracking of suitable hydrocarbons or hydrocarbon mixtures such as naphtha.

propylene can over it also prepared by heterogeneously catalyzed dehydrogenation of propane become.

Around acceptable conversions also in heterogeneously catalyzed dehydrogenations to achieve even with a single reactor passage, must in the Usually work at relatively high reaction temperatures. typical Reaction temperatures for heterogeneously catalyzed gas-phase dehydrogenations are at 300 to 700 ° C. Hydrocarbon per molecule As a rule, one molecule of hydrogen is generated.

The Dehydrogenation of hydrocarbons proceeds endothermically (a subordinate or simultaneous combustion of the hydrogen formed can for a heat balance to care). The for the setting of a desired Needed sales dehydrogenation must either the reaction gas in advance and / or in the course of the catalytic Dehydration fed become. In most known dehydrogenation process, the Dehydrierwärme outside produced from the reactor and fed to the reaction gas from the outside. This requires elaborate Reactor and process concepts and leads to high sales steep temperature gradients in the reactor, with the risk of increased by-product formation. So can For example, several adiabatic catalyst beds in succession switched annular gap reactors are arranged. The reaction gas mixture is on its way from one catalyst bed to the next catalyst bed overheated by heat exchanger and cool on the subsequent reactor passage again. To deal with one To catch such a reactor concept too high turnover must be the number the series-connected reactors or the reactor inlet temperature of the gas mixture increases be. The resulting overheating inevitably leads to a reinforced By-product formation by cracking reactions. It is also known that Arrange catalyst bed in a tubular reactor and the dehydrogenation heat through increasing the price of combustible gases outside the tubular reactor generate and over couple the tube wall into the interior of the reactor. In these Reactors lead high sales too steep temperature gradient between the wall and the interior of the reaction tube.

A Alternatively, the generation of dehydrogenation heat directly in the reaction gas mixture dehydrogenation by oxidation of dehydrogenation or additionally supplied Hydrogen or hydrocarbons contained in the reaction gas mixture with oxygen. This is the reaction gas mixture either already before the first catalyst bed or before subsequent catalyst beds an oxygen-containing gas and optionally hydrogen is added. The heat of reaction liberated during the oxidation prevents even at high temperatures sales size Temperature gradients in the reactor. At the same time, the waiver on the indirect reactor heating a very simple process concept realized.

Catalysts for heterogeneously catalyzed dehydrogenations are normally solid bodies which consist of an inert basic body (carrier) and of an active mass applied to this (in particular to its inner surface). One speaks also of supported catalysts. The carrier usually differs from the active material in that it is unable to catalyze the dehydration. That is, in its presence or in its absence under otherwise identical Dehydrierbedin Dehydration conversions (in mol% of the starting compound) are usually different from one another by less than 5 mol% points, preferably by less than 3 mol% points and more preferably by less than 1 mol% point.

US 4,788,371 describes a process for the water vapor dehydrogenation of dehydrogenatable hydrocarbons in the gas phase in conjunction with an oxidative re-heating of the intermediates, wherein the same catalyst for the selective oxidation of hydrogen and the Wasserdampfdehydrierung is used. In this case, hydrogen can be supplied as a co-feed. The catalyst used contains a Group VIII noble metal, an alkali metal, and another Group B, Ga, In, Ge, Sn, and Pb metal on an inorganic oxide support such as alumina. The process can be carried out in one or more stages in a fixed or moving bed.

WHERE 94/29021 describes a catalyst which is a substantially consisting of a mixed oxide of magnesium and aluminum Mg (Al) O carrier contains and a Group VIII noble metal, preferably platinum, a metal Group IVA, preferably tin, and optionally an alkali metal, preferably cesium. The catalyst is used in the dehydrogenation of hydrocarbons used, being carried out in the presence of oxygen can.

US 5,733,518 describes a process for the selective oxidation of hydrogen with oxygen in the presence of hydrocarbons such as n-butane over a catalyst containing a phosphate of germanium, tin, lead, arsenic, antimony or bismuth, preferably tin. The combustion of the hydrogen generates the heat of reaction necessary for the endothermic dehydrogenation in at least one reaction zone.

EP-A 0 838 534 describes a catalyst for the steam-free dehydrogenation of alkanes, especially isobutane, in the presence of oxygen. The catalyst used comprises a platinum group metal which on a carrier is applied from tin oxide / zirconium oxide with at least 10% tin. The oxygen content in the dehydrogenation feedstream is adjusted that generated by combustion of hydrogen with oxygen heat the same for needed the dehydration heat is.

WO 96/33151 describes a process for the dehydrogenation of a C ₂ -C ₅ alkane in the absence of oxygen over a dehydrogenation catalyst containing Cr, Mo, Ga, Zn or a Group VIII metal with simultaneous oxidation of hydrogen formed on a reducible metal oxide such as the oxides of Bi, In, Sb, Zn, Tl, Pb or Te. The dehydration must be interrupted regularly to reoxidize the reduced oxide with an oxygen source. In US 5,430,209 a corresponding method is described in which the dehydrogenation step and the oxidation step take place one after the other and the associated catalysts are spatially separated from one another. Oxides of Bi, Sb and Te and their mixed oxides are used as catalysts for the selective hydrogen oxidation.

WO 96/33150 finally describes a process in which, in a first stage, a C ₂ -C ₅ alkane is dehydrogenated on a dehydrogenation catalyst, the exit gas of the dehydrogenation stage is mixed with oxygen and in a second stage via an oxidation catalyst, preferably Bi ₂ O. ₃ , wherein the hydrogen formed is selectively oxidized to water, and in a third stage, the second-stage source gas is again passed through a dehydrogenation catalyst.

US 5,565,775 describes a method for the nondestructive determination of bound and free, ie producible, liquid fractions in porous materials (especially on reservoir rocks), which is based on a two-component decomposition of the pulsed field gradient (PFG) NMR technique measured self-diffusion behavior of pore liquids trapped in the pore space ,

The used catalyst system must in terms of recoverable alkane conversion, selectivity for education of alkenes, mechanical stability, thermal stability, coking behavior, Deactivation behavior, regenerability, stability in the presence oxygen and insensitivity to catalyst poisons such as CO, Sulfur and chlorine containing compounds, alkynes, etc. and cost-effectiveness meet high requirements.

task The invention is to provide dehydrogenation catalysts with improved To provide properties. The object of the invention is in particular Dehydrogenation catalysts with improved deactivation behavior to provide.

The object is achieved by a catalyst support made of a support material with a Tortuositätskennzahl τ of 1.5 to 4, preferably 1.5 to 3 and more preferably 2 to 3. Conveniently, this Tortuositätskennzahl in this document, unless explicitly stated otherwise to a determination at 25 ° C and 1 bar using H ₂ O as the probe molecule. This is because H ₂ O is able to simulate the diffusion behavior of the relevant reactants in a good approximation.

Particularly according to the invention However, preference is given to catalyst supports whose tortuosity index determined with the dehydrogenating, (for example, propane or a Butane such as iso-butane) hydrocarbon (at 25 ° C, 1 bar) 1.5-4, preferably 1.5-3, more preferably 2-3. Very particularly preferred are catalyst carriers, their tortuosity indicator, determined with the hydrocarbon to be dehydrogenated, but in the temperature used for dehydration and that used for dehydration Pressure, 1.5-4, preferably 1.5-3, more preferably 2-3.

Yet more advantageous are catalyst supports their tortuosity ratio determined with the unsaturated formed by the dehydrogenation (e.g., propene or a butene, e.g., isobutene) hydrocarbon (at 25 ° C, 1 bar) 1.5-4, preferably 1.5-3, more preferably 2-3. All particularly preferred are catalyst supports whose tortuosity index, determined with the unsaturated hydrocarbon formed by the dehydrogenation, however, at the temperature used for dehydration and that for Dehydration applied pressure, 1.5-4, preferably 1.5-3, especially preferably 2-3.

Regarding the carrier geometry exist according to the invention no Restrictions. Especially frequent Geometries are solid cylinders, hollow cylinders (rings), balls, cones, Pyramids and cubes. The different geometries can e.g. obtained by tableting or extrusion. The extrusion is particularly suitable for the design of strands, wagon wheels, stars, Monoliths or rings. Also split carrier (carrier split) can be used come. The longest extent (longest direct connecting line of two points located on the support surface) such carrier is many times 0.5 mm to 100 mm, often 1.5 mm to 80 mm, and many times 3 mm to 50 mm, or up to 20 mm. For in Wirbelbettreaktoren to be used catalysts carrier beads to be used is this longitudinal extension appropriate 0.01 mm to 1 mm, preferably 0.02 to 0.2 mm. For monoliths and foams, the e.g. be used with advantage in low pressure loss reactors, can this longitudinal extension up to 1000 mm.

Is solved the task further by a dehydrogenation catalyst containing one or more active compositions on a catalyst support (in particular on its inner surface by appropriate impregnation) from a carrier material with an above-mentioned Tortuositätskennzahl (determined with water or the hydrocarbon to be dehydrogenated, or the unsaturated hydrocarbon formed in the dehydrogenation) τ of 1.5 to 4, preferably 1.5-3, more preferably 2-3. The active mass contains usually at least one active metal in elemental form, they but also exclusively be of oxidic nature.

The tortuosity index τ of a catalyst support material is determined according to a further aspect of the invention by determining the self-diffusion D (self-diffusion coefficient, hereinafter referred to as "self-diffusion") of a probe gas or a probe liquid in the support material and the self-diffusion D _{0 of} the free gas or the free liquid as a quotient τ = D / D ₀ under the corresponding boundary conditions (25 ° C, 1 bar) determined (see below).

Under a free gas or a free liquid becomes a gas or a liquid understood, whose extent is much larger than the middle free path length of the molecules and opposite their extent surface effects neglected can be.

preferred Support according to the invention for dehydrogenation catalysts contained as carrier material a metal oxide, e.g. selected from the group consisting of zirconia, alumina, silica, Titanium dioxide, magnesium oxide, lanthanum oxide and cerium oxide and mixtures thereof. The mixtures may be physical mixtures or also chemical mixed phases such as magnesium or zinc-aluminum oxide mixed oxides act. In principle, as carrier materials, both (e.g. the aforementioned) metal oxides per se, as well as mixtures of metal oxides or mixed metal oxides into consideration. Particularly suitable dehydrogenation catalysts according to the invention contained on the carrier according to the invention at least an element of the VIII. subgroup, or at least one element of the I. or II. Main group, or at least one element of III. or IV. Main group, or at least one element of III. Subgroup, including the lanthanides and actinides, each in metallic and / or chemically bound form.

All Particularly preferred dehydrogenation catalysts contain at least on the support according to the invention an element of VIII. subgroup, at least one element of I. and / or II. Main group, at least one element of III. and or IV. Main group and at least one element of III. Subgroup, including the lanthanides and actinides, in metallic or chemically bound Shape. Preferably, of the aforementioned elements lie the Elements of the VIII. Subgroup and the IV. Main group in elementary Form and the rest Elements in oxidic form before.

The invention further provides a process for the heterogeneously catalyzed dehydrogenation of one or more dehydrogenatable C ₂ -C ₃₀ hydrocarbons, preferably one or more C ₂ -C ₁₅ hydrocarbons, more preferably one or more C ₂ -C ₈ hydrocarbons and very particularly preferably one or more C ₃ and C ₄ hydrocarbons in a reaction gas mixture containing them, in which the reaction gas mixture containing the dehydrogenatable hydrocarbon (s) is brought into contact with at least one dehydrogenation catalyst according to the invention.

It has been found that catalysts based on the catalyst support according to the invention with the specified tortuosity a very cheap Have deactivation behavior, ie during the reaction especially be deactivated slowly.

wobei der geometrische Abstand der Punkte groß gegenüber charakteristischen Abmessungen des Porenraumes wie z.B. Poren- oder Korndurchmesser ist. Daraus folgt, dass die Tortuosität eines porösen Materials größer als oder gleich 1 ist.The tortuosity coefficient (or "labyrinth factor") of a porous material closely approximates the square of the ratio of the length (L) of the shortest connection between two points in the pore space that runs completely through the pore space to the geometric distance of these points (L ₀ ). (Equation 1):

wherein the geometric distance of the points is large compared to characteristic dimensions of the pore space such as pore or grain diameter. It follows that the tortuosity of a porous material is greater than or equal to 1.

For transport processes that run through the pore space, the tortuosity describes the square of the extension of the transport path due to the geometric hindrance at the pore / matrix interface. In addition to the porosity (Φ), the tortuosity thus represents an important parameter that determines transport parameters in porous materials. In transport diffusion processes, for example, it is expected that the diffusion coefficient of a fluid in the porous material (D _{t, eff} ) is reduced by the quotient of porosity and tortuosity compared to the free fluid (D _t, ) (equation 2):

Observing the self-diffusion of fluids in the pore space over distances that are large compared to the pore size, one finds that the self-diffusion coefficient in the pore space (D) compared to the value measured in the free liquid (D _0), just to reduces tortuosity (Equation 3):

The self-diffusion coefficients of the free liquid D ₀ and the same liquid in a porous material D can be measured directly, for example, by means of pulsed field gradient nuclear magnetic resonance (PFG) NMR. Alternatively, tracers (eg radioactives) can also be used. The ratio D ₀ / D then gives the tortuosity of the porous material.

The greater the tortuosity of the transport pores in the catalyst particles, the longer the reactant and product molecules require to exchange by diffusion between the catalytically active centers at the pore / matrix interface of the catalyst particles and the reaction medium flowing around the catalyst particles. If the residence time of reactant and product molecules in the catalyst particles has an influence on the catalytic properties, such as selectivity, activity and deactivation behavior, changes in the tortuosity of the transport pore system of the catalyst particles may lead to changes in the catalytic properties with otherwise identical properties of the catalyst matrix. the reason for this is the influence of tortuosity on the mean residence time t _{e / p of} the reactant and product molecules, which can be estimated from the diffusion coefficient under reaction conditions (D _{e / p} ) and the radius R of spherical catalyst particles (equation 4):

For non-spherical (e.g. cylindrical) Catalyst particle R in equation (4) denotes the corresponding equivalent radius.

According to the invention advantageous are therefore dehydrogenation catalysts in which the active composition is so on the inner surface of the carrier was applied to the tortuosity of the finished catalyst essentially corresponds to that of the carrier used. preferred Catalysts are therefore also those with corresponding Tortuositätskennzahlen (determined with water or the hydrocarbon to be dehydrogenated, or the unsaturated hydrocarbon formed during the dehydrogenation) from 1.5-4, preferably 1.5-3, more preferably 2-3.

The PFG NMR allows the non-destructive investigation of self-diffusion, ie the thermally induced Brownian molecular motion of free gases and liquids, of macromolecular solutions and melts as well as of adsorbed molecules and liquids in the pore space of porous materials. The prerequisite is that the molecules of the substances to be investigated (gases or liquids) contain in their molecular structure at least one atom with a non-vanishing nuclear spin / and thus with the magnetic nuclear magnetic resonance (NMR) transitions between the Zeeman energy levels of the nuclear spins / in a strong external magnetic field (B ₀ ) can be observed.

Principle, execution and application of PFG NMR measurements are in the following references described: (1) E.O. Stejskal, J.E. Tanner, J. Chem. Phys. 42 288-292 (1965). (2) Stallmach, F., Seiffert, G., Kärger, J., Kaess, U., and Majer, G., J. Magn. Reson. 151, 260-268 (2001); (3) Kärger, J., Papadakis, Ch. M., and Stallmach, F. Structure Mobility Relations of Molecular Diffusion in Interface Systems, in Lecture Notes in Physics, vol. 634, publisher: R. Stanarius, A. Pöppel, R. Haberlandt and D. Michel, Springer Verlag, 2004; (4) Stable, F., and Kärger, J., Adsorption 5, 117-133 (1999); (4) Kärger, J. and M.D. Ruthven, Diffusion in Zeolites and other Microporous Solids, Wiley-Interscience, New York, 1992, and Callaghan, P.T., Principles of Nuclear Magnetic Resonance Microscopy, Clarendon Press, Oxford, 1991.

In PFG NMR, a so-called spin echo of the nuclear spins is first generated by means of short-frequency magnetic field pulses (RF pulses). The intensity of this spin-echo NMR signal is proportional to the number of resonant nuclear spins in the examination volume and is the time between the excitation to the spin echo maximum by the first RF pulse (t _e) by spin-lattice (T ₁₎ and spin-spin ( T ₂ ) relaxation processes damped. In 1a By way of example, three different pulse programs for the generation of such spin echo NMR signals are shown. In the time intervals of the pulse sequences b (stimulated spin echo, STE) and c (13-interval pulse train) marked with Δ ', the nuclear spins are subject to the T ₁ relaxation. During all other times and in the pulse sequence a (Hahn's spin echo, SE), they are only subject to T ₂ relaxation.

For the measurement of the self-diffusion, a local magnetic field of the form B _inh (z) = gz is superimposed on the external magnetic field B ₀ during these pulse sequences, where g and z correspond to the pulsed magnetic field gradients (narrow: pulsed field gradient) Represent location coordinate. The necessary magnetic field gradient pulses are thereby generated via current pulses synchronized to the HF pulse sequence, which flow through a suitable magnet coil combination (the gradient coils). Because, during the duration of the field gradient pulses, the resonance condition for the nuclear spins is location dependent and the probe molecules diffuse to another location between successive field gradient pulses due to self-diffusion, the amplitude of the observed spin echo is attenuated. This spin echo attenuation Ψ as a function of the duration (δ), intensity (g) and the interval spacing (Δ) of the magnetic field gradients is the observed variable in the PFG NMR. From this follows the self-diffusion coefficient D (Δ) of the molecules according to equation (5)

The size b depends on the pulse train used. It is calculated from the measurement parameters of the respective PFG NMR pulse train. For the example in 1 shown pulse sequence results in the size b to:

In this case, γ denotes the gyromagnetic ratio of the observed nuclear spins. The term dependent on the pulse sequence in the parenthesis in Eq. (6) is the effective diffusion time. It is for short field gradient pulses of the time Δ, so the distance of the field gradient pulses of the same polarity (see 1 ) dominates and in the PFG NMR experiment is a known and variable size from the pulse sequence.

Experimentally, one usually measures the spin echo damping curves for a fixed interval distance Δ and a fixed duration δ of the field gradient pulses and varies their intensity g. The self-diffusion coefficient D (Δ) for the associated diffusion time Δ results according to Eq. (5) from the slope of a plot of In Ψ versus -b. Using Einstein's equation, the mean square displacement during diffusion time can be calculated from D (Δ) (Equation 7): ⟨r 2 (Δ)⟩ = 6D (Δ) Δ (7)

• (i) ein Gas oder eine Flüssigkeit, enthaltend Moleküle mit mindestens einem Atom mit nicht verschwindendem Kernspin I („Sondenmoleküle"), in den Porenraum einer Probe des Trägermaterials eingebracht wird,
• (ii) ein äußeres Magnetfeld B₀ am Ort der Probe des Trägermaterials erzeugt wird,
• (iii) durch Einstrahlung von kurzen hochfrequenten Magnetfeldimpulsen ein Spinecho der Kernspins I in der Probe erzeugt wird,
• (iv) während mehrerer kurzer Zeitintervalle δ dem externen Magnetfeld B₀ ein ortsabhängiges Magnetfeld B als Feldgradientenimpuls überlagert wird, wodurch die Amplitude des beobachteten Spinechos gedämpft wird und so eine Spine chodämpfung Ψ als Funktion der Impulsdauer δ, der Intensität g und des zeitlichen Abstands Δ der Feldgradientenimpulse gemessen wird,
• (v) aus der Spinechodämpfung Ψ der Selbstdiffusionskoeffizient D der Gas- bzw. Flüssigkeitsmoleküle in der Probe bestimmt wird,
• (vi) die Schritte (i) bis (v) mit einer Probe des freien Gases bzw. der freien Flüssigkeit durchgeführt werden, wobei ein Selbstdiffusionskoeffizient D₀ der Moleküle des freien Gases bzw. der freien Flüssigkeit ermittelt wird,
• (vii) die Tortuositätskennzahl τ als Quotient aus dem Selbstdiffusionskoeffizient D₀ des freien Gases bzw. der freien Flüssigkeit und dem Selbstdiffusionskoeffizient D des Gases bzw. der Flüssigkeit in dem Trägermaterial τ = D₀/D erhalten wird.

The present invention also provides a method for determining the tortuosity of a catalyst support material by determining the self-diffusion D of a gas or a liquid in the support material and the self-diffusion D _{0 of} the free gas or the free liquid, in which expediently

• (i) a gas or a liquid containing molecules having at least one atom with non-vanishing nuclear spin I ("probe molecules") is introduced into the pore space of a sample of the carrier material,
• (ii) an external magnetic field B _{0 is} generated at the location of the sample of the carrier material,
• (iii) generating a spin echo of the nuclear spins I in the sample by irradiation of short high-frequency magnetic field pulses,
• (iv) superimposed on the external magnetic field B ₀ a field-dependent magnetic field B as a field gradient pulse during several short time intervals δ, whereby the amplitude of the observed spin echo is damped and thus a spin damping Ψ as a function of the pulse duration δ, the intensity g and the time interval Δ the field gradient pulses are measured,
• (v) from the spin echo damping Ψ the self-diffusion coefficient D of the gas or liquid molecules in the sample is determined,
• (vi) carrying out steps (i) to (v) with a sample of the free gas or the free liquid, whereby a self-diffusion coefficient D _{0 of} the molecules of the free gas or of the free liquid is determined,
• (vii) the tortuosity factor τ is obtained as the quotient of the self-diffusion coefficient D _{0 of} the free gas or of the free liquid and the self-diffusion coefficient D of the gas or of the liquid in the carrier material τ = D ₀ / D.

A preferred probe liquid, which in step (i) is introduced into the pore space of the sample of the carrier material, for example by soaking the sample, is, as already mentioned, water. Alternatively, liquids other than water can also be used as "probe molecules" for tortuosity measurement with PFG NMR: they only need to have atoms with a nuclear spin detectable by NMR (eg, ¹ H, ¹⁹ F, ¹³ C) and wet the porous support material In addition, the vapor pressure of the liquid used should be high enough so that the catalysts do not dry out during the NMR measurement, which can take several hours Other liquids are, for example, cyclooctanes or other linear or cyclic alkanes having 5 or more carbon atoms, but the tortuosity can also be determined using gaseous probe molecules contained in the carrier material (eg propane, butane). the result achieved is essentially independent of the choice of probe molecule ängig.

The support according to the invention generally consists of a (preferably heat-resistant) oxide or mixed oxide (eg steatite). It preferably contains a metal oxide which is selected from the group consisting of zirconium dioxide, zinc oxide, aluminum oxide, silicon dioxide, titanium dioxide, magnesium oxide, lanthanum oxide, cerium oxide and mixtures thereof. The mixtures may be physical mixtures or chemical mixed phases such as magnesium or zinc-aluminum oxide mixed oxides. The tortuosity of said metal oxides can vary widely. Among them, a carrier having suitable tortuosity is selected. However, the tortuosity can also be adjusted in a targeted manner by allowing (in particular finely divided) non-oxidic or even oxidic carrier starting materials (usually metals containing compounds which decompose upon thermal treatment and convert to metal oxides, at least in thermal decomposition in air) in the presence of pore formers formed (eg by tableting or extrusion) and then thermally treated ,

In a preferred embodiment contains the dehydrogenation catalyst according to the invention at least one element of subgroup VIII, at least one element the I. and / or II. Main group, at least one element of the III. and / or IV. Main group and at least one element of III. subgroup including the lanthanides and actinides.

When Element of VIII. Subgroup contains the active material of the dehydrogenation catalysts preferably platinum and / or palladium, more preferably platinum.

When Elements of the I. and / or II. Main group contains the active material of the dehydrogenation catalysts according to the invention preferably potassium and / or cesium.

When Elements of the III. Subgroup including the lanthanides and actinides contains the active material the dehydrogenation catalysts according to the invention preferably lanthanum and / or cerium.

When Elements of the III. and / or IV. Main group contains the active composition of the dehydrogenation catalysts according to the invention preferably one or more elements selected from the group consisting of Boron, gallium, silicon, germanium, tin and lead, particularly preferred Tin. Most preferably, the active composition contains a dehydrogenation catalyst according to the invention in each case at least one member of the aforementioned groups of elements.

The catalytic hydrocarbon dehydrogenation can in principle be carried out in all reactor types and modes of operation known from the prior art. A comparatively comprehensive description of dehydrogenation processes suitable according to the invention also contains "Catalytica® ^® Studies Division, Oxidative Dehydrogenation and Alternative Dehydrogenation Processes" (Study Number 4192 OD, 1993, 430 Ferguson Drive, Mountain View, California, 94043-5272, USA).

A suitable reactor form is the fixed bed tube or tube bundle reactor. In these, the catalyst is (dehydrogenation catalyst according to the invention and, when working with oxygen as a co-feed, optionally special oxidation catalyst) as a fixed bed in a reaction tube or in a bundle of reaction tubes. The reaction tubes are usually indirectly heated by the fact that in the space surrounding the reaction tubes, a gas, such as a hydrocarbon such as methane, is burned ver. It is advantageous to apply this indirect form of heating only to the first about 20 to 30% of the length of the fixed bed and to heat the remaining bed length by the released in the context of indirect heating radiant heat to the required reaction temperature. Typical reaction tube internal diameters are about 10 to 15 cm. A typical Dehydrierrohrbündelreaktor comprises about 300 to 1000 reaction tubes. The temperature inside the reaction tube usually moves in the range of 300 to 1200 ° C, preferably in the range of 500 to 1000 ° C. The working pressure is usually between 0.5 and 8 bar, often between 1 and 2 bar using a low water vapor dilution (according to the Linde process for propane dehydrogenation), but also between 3 and 8 bar when using a high water vapor dilution (corresponding to the so-called "steam active reforming process" (STAR process) for the dehydrogenation of propane or butane by Phillips Petroleum Co., see US 4,902,849 . US 4,996,387 and US 5,389,342 ). Typical catalyst loads (GHSV) are 500 to 2000 h ^-1 , based on the hydrocarbon used. The catalyst geometry can be, for example, spherical or cylindrical (hollow or full).

The non-oxidative catalytic hydrocarbon dehydrogenation can also, as in Chem. Eng. Sci. 1992 b, 47 (9-11) 2313, be carried out heterogeneously catalyzed in a fluidized bed. Conveniently, two fluidized beds are operated side by side, of which one is usually in a state of regeneration. Of the Working pressure is typically 1 to 2 bar, the dehydrogenation temperature usually 550 to 600 ° C. The for the dehydration required heat is introduced into the reaction system by the dehydrogenation catalyst is preheated to the reaction temperature. By the admixture An oxygen-containing co-feed may be on the preheater be dispensed with, and the heat needed directly in the reactor system by combustion of hydrogen and / or hydrocarbons be generated in the presence of oxygen. If necessary, can additionally a hydrogen-containing co-feed are mixed.

The non-oxidative catalytic hydrocarbon dehydrogenation can with or without oxygen-containing gas as co-feed in a tray reactor carried out become. This contains one or more consecutive catalyst beds. The number the catalyst beds may be 1 to 20, preferably 1 to 6, preferred 1 to 4 and especially 1 to 3 amount. The catalyst beds are preferably flowed through radially radially or axially from the reaction gas. In general Such a tray reactor is operated with a fixed catalyst bed. In the simplest case, the fixed catalyst beds are in a shaft furnace reactor axially or in the annular gaps of concentrically arranged cylindrical Gratings arranged. A shaft furnace reactor corresponds to one Horde. The implementation corresponding to dehydrogenation in a single shaft furnace reactor a preferred embodiment, where you can work with oxygenated co-feed. In a further preferred embodiment the dehydrogenation is in a tray reactor with 3 catalyst beds carried out. In a driving without oxygen-containing gas as a co-feed is the reaction gas mixture in the tray reactor on its way from a Catalyst bed to the next Catalyst bed subjected to reheating, e.g. by passing over with be called Gases heated heat exchanger surfaces or by passing through with hot Fuel gases heated pipes.

In a preferred embodiment the method according to the invention becomes the non-oxidative catalytic hydrocarbon dehydrogenation performed autothermally. For this purpose, the reaction gas mixture of the hydrocarbon dehydrogenation additionally oxygen is added in at least one reaction zone and the hydrogen contained in the reaction gas mixture and / or Hydrocarbon at least partially burned, causing at least a part of the needed dehydrogenation in the at least one reaction zone directly in the reaction gas mixture is produced.

in the Generally, the amount of the reaction gas mixture added selected oxygen-containing gas, that by the combustion of existing in the reaction gas mixture Hydrogen and optionally present in the reaction gas mixture Hydrocarbons and / or present in the form of coke carbon the for the dehydrogenation of the hydrocarbon required amount of heat is generated. In general is the total supplied Oxygen amount, based on the total amount of butane, 0.001 to 0.5 mol / mol, preferably 0.005 to 0.2 mol / mol, more preferably 0.05 to 0.2 mol / mol. Oxygen can either be pure oxygen or as an oxygen-containing gas in admixture with inert gases, for example in the form of air. The inert gases and the resulting Combustion gases generally additionally dilute and thus promote the heterogeneously catalyzed Dehydration.

The hydrogen burned to generate heat is the hydrogen formed during the catalytic hydrocarbon dehydrogenation and, if appropriate, the hydrogen gas additionally added to the reaction gas mixture as hydrogen. Preferably, sufficient hydrogen should be present so that the molar ratio H ₂ / O ₂ in the reaction gas mixture immediately after the introduction of oxygen is 1 to 10, preferably 2 to 5 mol / mol. This applies to multi-stage reactors for each intermediate feed of oxygen-containing and possibly hydrogen-containing gas.

The hydrogen combustion takes place catalytically. The dehydrogenation catalyst used generally also catalyzes the combustion of the hydrocarbons and of hydrogen with oxygen, so that in principle no special oxidation catalyst different from this one is required. In one embodiment, the reaction is carried out in the presence of one or more oxidation catalysts which selectively catalyze the combustion of hydrogen to oxygen in the presence of hydrocarbons. The combustion of these hydrocarbons with oxygen to CO, CO ₂ and water is therefore only to a minor extent. Preferably, the dehydrogenation catalyst and the oxidation catalyst are present in different reaction zones.

at multistage reaction procedure For example, the oxidation catalyst may be in one, more, or all Reaction zones are present.

Prefers is the catalyst that selectively oxidizes hydrogen catalyzed, placed at the sites where higher oxygen partial pressures prevail as elsewhere in the reactor, especially in the Near the Feed-in point for the oxygen-containing gas. The feed of oxygen-containing gas and / or hydrogen-containing gas may be at one or more points of the reactor.

In one embodiment of the process according to the invention, an intermediate feed of oxygen-containing gas and of hydrogen-containing gas takes place before each tray of a tray reactor. In a further embodiment of the method according to the invention, the feed of oxygen-containing gas and of hydrogen-containing gas takes place before each horde except the first horde. In one embodiment behind each feed point is a layer of a specific oxidation catalyst, followed by a layer of the dehydrogenation catalyst. In another embodiment, no special oxidation catalyst is present. The dehydrogenation temperature is generally 400 to 1100 ° C, the pressure in the last catalyst bed of the tray reactor generally 0.2 to 5 bar, preferably 1 to 3 bar. The load (GHSV) is generally 500 to 2000 h ^-1 , in high load mode also up to 100 000 h ^-1 , preferably 4000 to 16 000 h ^-1 .

One preferred catalyst which selectively combusts hydrogen catalyzed contains Oxides and / or phosphates selected from the group consisting of the oxides and / or phosphates of Germanium, tin, lead, arsenic, antimony or bismuth.

One Another preferred catalyst, the combustion of hydrogen catalyzed contains a noble metal of VIII. and / or I. subgroup.

The Hydrocarbon dehydrogenation is preferred in the presence of water vapor carried out. Of the added water vapor serves as a heat carrier and supports the Gasification of organic deposits on the catalysts, causing counteracted the coking of the catalysts and the life of the Catalysts increased becomes. The organic deposits in carbon monoxide, Converted carbon dioxide and optionally water.

Preferred C ₂ -C ₃₀ hydrocarbons which are dehydrogenated according to the invention are propane and butane.

Of the Dehydrogenation catalyst according to the invention can be regenerated in a conventional manner. So can that Reaction gas mixture can be added to steam or from time to time Time an oxygen-containing gas at elevated temperature over the catalyst bed and the deposited carbon are burned off. By dilution with steam, the equilibrium becomes the products of dehydration postponed. Optionally, the catalyst becomes after regeneration reduced with a hydrogen-containing gas.

The inventive method is particularly advantageous if that via the dehydrogenation catalyst guided Reaction gas mixture already contains dehydrogenated hydrocarbon as is e.g. in the methods of the publications DE-A 102005009885, DE-A 102005022798, WO 01/96270, WO 01/96271, WO 03/011804, WO 03/76370, DE-A 10245585, DE-A 10246119, DE-A 10316039, DE-A 102004032129, DE-A 102005010111, DE-A 102005013039 and DE-A 102005009891 described in detail is. In all mentioned in these documents dehydrogenation are inventive catalysts particularly suitable.

The Invention will be explained in more detail by the following examples. The subsequent carrier are good catalyst carriers especially if the pore volume in the range of 0.12-0.4 ml / g (measured by Hg porosimetry) lies. The pore radius distribution can be unimodal, bimodal or polymodal be.

The inventive method is particularly advantageous in that the determination of tortuosity in very much easier than in the past, the selection of suitable carrier or dehydrogenation catalysts allows. In the past, this always involved elaborate dehydrogenation tests required.

Examples 1-6

In The following catalyst supports were used in the experiments described below:

Preparation of a ZrO ₂ spray powder:

72.6 kg of concentrated aqueous nitric acid (69% by weight of HNO ₃ ) were initially introduced into a 500 l kettle and 58.7 kg of Zr (IV) carbonate were uniformly stirred in with stirring (20 rpm) over the course of 2 h ( Company MEL, Luxfer Group Company, about 43% by weight ZrO ₂ ). A zirconyl nitrate solution containing about 19% by weight ZrO ₂ and a density of 1.59 kg / l was obtained. In a stirred tank (1000 l) 135.8 kg of ammonia water (12.5 wt .-% NH ₃ ) were submitted. For this purpose, the zirconyl nitrate solution was pumped in uniformly with stirring within 2 h. The pH of the precipitation reached was 5.2 at 25 ° C. After 6 h stirring time, the suspension was pumped to a filter press and over a period of 14 h with a total of 15 washed m ³ of demineralized water until the conductivity of the washing water at 25 ° C of less than 20 cm was .mu.S /. There were obtained 85.6 kg of wet filter paste. The filter paste was spread on sheets (layer height 10 cm) and dried in a box furnace from Naber at 450 ° C for 8 h under air. (Alternatively, the heat treatment may be carried out under N ₂ O steam (1 bar), and the resulting ZrO ₂ powders are then used in Examples 1-11 and Comparative Example, respectively, and a rotary kiln may be used instead of a Neber furnace through which air or water vapor is passed in countercurrent to the dry material The resulting ZrO ₂ powders are then used analogously in Examples 1-11 and Comparative Example). The material had an ignition loss of 2.31% by weight at 900 ° C. in air. The XRD measurement showed a proportion of 73% monoclinic and 27% tetragonal ZrO ₂ . Unless otherwise stated, the above steps were carried out at room temperature.

The ZrO ₂ powder (particle diameter <500 μm) was used to prepare supports 1-6 according to Examples 1-6. The tortuosity data are mean values from 2 measurements.

Instead of Of the polyethylene oxide used in each case, other polyethylene oxides with molecular weights in the range of 100,000-8 million. g / mol lying be used. In the sense of the invention is particularly favorable but the use of the specified polyethylene oxides.

example 1

3000 g of ZrO ₂ powder were mixed in a Koller with 90 g of polyethylene oxide (Alkox ^® E 100, KOWA American Cooperation) and treated with 90 g of concentrated aqueous nitric acid (69 wt .-% HNO ₃ ). To this was added 317 g Silres MSE 100 ^® (Wacker, 70 wt .-% strength SiO ₂ solid solution) and 500 ml of water. After 5 minutes of rinsing, an additional 150 ml of water were added. After further 20 minutes of mulling at room temperature, the kneading material was pressed in an extruder at a pressure of 280 bar to strands with a diameter of 1.5 mm. After 16 h of drying at 120 ° C in air, the strands were annealed for 4 h at 560 ° C in air. The support thus obtained had a tortuosity of 2.15, measured with H ₂ O at 25 ° C and 1 bar pressure.

Example 2

3000 g of ZrO ₂ powder and 120 g of polyethylene oxide (Alkox E 100, KOWA American Cooperation) were mixed in a Koller and mixed with 90 g of concentrated aqueous nitric acid (69 wt .-% HNO ₃ ). To this was added 350 g of Silres MSE 100 (Wacker, 70% strength by weight SiO ₂ solution) and 500 ml of water. After rinsing for 5 minutes, an additional 250 ml of water were added. After a further 30 minutes of mulling at room temperature, the kneading material was pressed in an extruder at a pressure of 280 bar into strands with a diameter of 1.5 mm. After 16 h of drying at 120 ° C in air, the strands were annealed for 4 h at 600 ° C in air. The support thus obtained had a tortuosity of 2.55, measured with H ₂ O at 25 ° C and 1 bar pressure.

Example 3

In a muller 3000 g of ZrO ₂ powder were mixed with 150 g of polyethylene oxide (Alkox E 100, company Kowa American Corporation) and mixed with 120 g of concentrated aqueous nitric acid (69 wt .-% HNO _3). To this was added 500 g Siles MSE 100 (Wacker, 70% strength by weight SiO ₂ solution) and 500 ml water. After rinsing for 5 minutes, an additional 250 ml of water were added. After a further 30 minutes of mulling at room temperature, the kneading material was pressed in an extruder at a pressure of 280 bar into strands with a diameter of 1.5 mm. After 16 h of drying at 120 ° C in air, the strands were annealed for 4 h at 600 ° C in air. The support thus obtained had a tortuosity of 2.95, measured with H ₂ O at 25 ° C and 1 bar pressure.

Example 4

In a muller 3000 g of ZrO ₂ powder were mixed with 100 g cellulose ether (Optamix ^® AT 100, Zschimmer & Schwarz GmbH & Co KG) and 120 g of concentrated aqueous nitric acid (69 wt .-% HNO ₃₎ was added. To this was added 300 g of Silres MSE 100 (Wacker, 70% strength by weight SiO ₂ solution) and 500 ml of water. After rinsing for 5 minutes, an additional 250 ml of water were added. After a further 30 minutes of mulling at room temperature, the kneading material was pressed in an extruder at a pressure of 280 bar to strands with a diameter of 1.5 mm. After 16 h of drying at 120 ° C in air, the strands were annealed for 4 h at 600 ° C in air. The support thus obtained had one Tortuosity of 5.45, measured with H ₂ O at 25 ° C and 1 bar pressure.

Example 5

In a Koller, 3000 g of ZrO ₂ powder were mixed with 150 g of polyethylene oxide (Alkox E 100, KOWA American Cooperation) and admixed with 120 g of concentrated aqueous nitric acid (69% by weight of HNO ₃ ). To this was added 500 mg of Silres MSE 100 (Wacker, 70% strength by weight SiO ₂ solution) and 500 ml of water. After rinsing for 5 minutes, an additional 250 ml of water were added. After a further 30 minutes of mulling at room temperature, the kneading material was pressed in an extruder at a pressure of 280 bar into strands with a diameter of 3 mm. After 16 h of drying at 120 ° C in air, the strands were annealed for 4 h at 600 ° C in air. The catalyst support was crushed to chippings to obtain a sieve fraction of 1.6-2 mm. The support thus obtained had a tortuosity of 2.8, measured with H ₂ O at 25 ° C and 1 bar pressure.

Example 6

3000 g of ZrO ₂ powder were mixed in a Koller with 90 g of polyethylene oxide (Alkox E 100, KOWA American Cooperation) and treated with 90 g of concentrated aqueous nitric acid (69 wt .-% HNO ₃ ). To this was added 317 g of Silres MSE 100 (Wacker, 70% strength by weight SiO ₂ solution) and 500 ml of water. After 5 minutes of rinsing, an additional 150 ml of water were added. After a further 20 minutes of mulling at room temperature, the kneading material was pressed in an extruder at a pressure of 280 bar into strands with a diameter of 3 mm. After 16 h of drying at 120 ° C, the strands were annealed for 4 h at 560 ° C in air. The catalyst support was crushed to chippings to obtain a sieve fraction of 1.6-2 mm. The support thus obtained had a tortuosity of 2.3, measured with H ₂ O at 25 ° C and 1 bar pressure.

Perform PFG NMR self-diffusion measurements to the water-saturated catalyst supports 1-6:

The NMR measurements were carried out at 25 ° C and 1 bar at 125 MHz ¹ H resonant frequency with the NMR spectrometer FEGRIS NT at the Faculty of Physics and Earth Sciences of the University of Leipzig. As a pulse program for the PFG NMR self-diffusion studies, the stimulated spin echo with pulsed field gradients according to 1b used. For each sample, the spin echo attenuation curves were measured at up to six different diffusion times (Δ / ms = 20, 40, 80, 160, 240, 320) by stepwise increasing the field gradient intensity (g _max = 4 T / m). From the spin echo damping curves, the time dependence of the self-diffusion coefficient of the pore water was determined by means of equations (2) and (3).

Calculation of tortuosity:

Using equation (7), the time dependence of the mean square displacement ⟨r ² (Δ)⟩ was calculated from the self-diffusion coefficients D (Δ) determined in this way. In 2 For the catalyst supports 1 to 7, these data are plotted twice logarithmically together with the corresponding results for free water. Also shows 2 in each case the straight line from the linear fit of ⟨r ² (Δ)⟩ as a function of the diffusion time Δ. Its rise corresponds to the value 6D according to equation (7), whereby D corresponds to the self-diffusion coefficient averaged over the diffusion time interval. According to equation (6), the tortuosity then results from the ratio of the thus determined mean self-diffusion coefficient of the free water to the corresponding value of the mean self-diffusion coefficient in the catalyst support.

The thus determined tortuosity values are for the catalyst supports 1-6 summarized in Table 1, wherein each catalyst support two independently prepared from each other Samples from the same batch were measured.

Table 1:

Examples 7 to 11 and Comparative Example C1

Preparation of the catalysts 1 to 6 based on the catalyst supports 1 to 6:

The catalyst supports 5 and 6 were crushed to chippings, whereby a sieve fraction of 1.6-2 mm was obtained. The catalyst supports 1-4 were used as 1.5 mm strands (natural fracture). The support materials were coated with the active components Pt / Sn / K / Cs and La according to the method described below: 0.1814 g H ₂ PtCl ₆ .6H ₂ O and 0.2758 g SnCl ₂ .2H ₂ O were in Dissolved 138 ml of ethanol and added at 25 ° C in a rotary evaporator to 23 g of the carrier material. The supernatant ethanol was stripped off on a rotary evaporator while rotating in a water jet pump vacuum (20 mbar) at a water bath temperature of 40.degree. The mixture was then dried under standing air initially at 100 ° C. for 15 h and then calcined at 560 ° C. (under stagnant air) for 3 h. Thereafter, the dried solid with a solution of 0.1773 g CsNO ₃ was 0.3127 g KNO ₃ and 2.2616 g La (NO _{3) 3} · 6H ₂ O poured in 55 ml H ₂ O at 25 ° C. The supernatant water was removed from the rotavapor while rotating in a water pump vacuum (20 mbar) at a water bath temperature of 85.degree. The mixture was then dried under standing air initially at 100 ° C. for 15 h and then calcined at 560 ° C. under stagnant air for 3 h.

It became so from the catalyst carriers 1-6 obtained the catalysts 1-6. The catalysts thus obtained were installed in a test reactor and activated.

Catalyst activation:

• Reaktorlänge: 520 mm;
• Wanddicke: 2 mm;
• Innendurchmesser: 20 mm;
• Reaktormaterial: innen alonisiertes, d.h. mit Aluminiumoxid beschichtetes Stahlrohr;
• Beheizung: elektrisch auf einer längsmittigen Länge von 450 mm;
• Länge der Katalysatorschüttung: 60 mm;
• Position der Katalysatorschüttung: längsmittig;
• Befüllung des Reaktorrestvolumens nach oben und unten mit Steatitkugeln eines Durchmessers von 4-5 mm als Inertmaterial, unten auf einem Kontaktstuhl aufsitzend.

With 20 ml of the obtained catalyst precursor, a vertically standing tube reactor was charged.

• Reactor length: 520 mm;
• Wall thickness: 2 mm;
• Inner diameter: 20 mm;
• Reactor material: internally alanized, ie coated with alumina steel tube;
• Heating: electrically on a longitudinal center length of 450 mm;
• Length of catalyst bed: 60 mm;
• Position of the catalyst bed: longitudinally centered;
• Fill the reactor residual volume upwards and downwards with steatite balls of 4-5 mm diameter as inert material, sitting down on a contact chair.

Subsequently, the reaction tube was charged at an outside wall temperature along the heating zone of 500 ° C with 9.3 Nl / h of hydrogen for 30 min. Subsequently, the hydrogen flow was maintained at a constant wall temperature for 30 minutes by a stream of 23.6 Nl / h from 80 vol .-% nitrogen and 20 vol .-% air and then for another 30 minutes by an equal stream of pure air replaced. While maintaining the wall temperature was then flushed with an equal current of N ₂ 15 min long and finally reduced again for 30 minutes with 9.3 Nl / h of hydrogen. This completed the activation of the catalyst precursor.

Catalyst Testing:

in the Following activation, the catalysts were tested, by placing in the same reactor with a mixture of 20 Nl / h Raw propane, 18 g / h steam and 1 Nl / h nitrogen applied were. For this purpose, crude propane by means of a mass flow controller dosed while Initially metered liquid into an evaporator by means of an HPLC pump, evaporated in this and then mixed with the crude propane and nitrogen. The gas mixture was over passed the catalyst. The wall temperature was 622 ° C.

through a located at the reactor outlet pressure control was the Output pressure of the reactor set to 1.5 bar absolute.

The product gas, which had been expanded to atmospheric pressure behind the pressure control, was cooled, with the water vapor condensed out. The uncondensed residual gas was analyzed by GC (HP 6890 with Chem-Station, detectors: FID, WLD, separation columns: Al ₂ O ₃ / KCl (Chrompack), Carboxene 1010 (Supelco)). In a similar manner, the reaction gas [feed gas stream] had been analyzed.

Table 2 summarizes for the catalysts 1-6 the averaged tortuosity, the BET surface area determined by N ₂ adsorption, the activity (based on the propane conversion) and the deactivation of the catalysts.

Table 2:

The Deactivation of the catalyst is correlated with the average tortuosity (τ). The inner surface of the catalyst (BET surface area) correlates neither with the tortuosity nor with the deactivation. The indicated conversion represents the propane conversion at the beginning of the dehydrogenation test the decline in sales in % per hour is a measure of deactivation of the catalyst. As can be seen from the examples, the catalysts of the invention at substantially comparable BET surface area, a much lower one Deactivation opposite on the comparative catalyst.

Claims (25)

Method for determining the tortuosity of a porous catalyst support material by determining the self-diffusion D of a gas or a liquid into the carrier material and the self-diffusion D ₀ of the free gas and the free liquid and calculation of the ratio D / D = _0. A method according to claim 1, characterized in that (i) a gas or a liquid containing molecules having at least one atom with non-vanishing nuclear spin I, is introduced into the pore space of a sample of the carrier material, (ii) an external magnetic field B ₀ in place (iii) a spin echo of the nuclear spins 1 in the sample is generated by irradiation of short high-frequency magnetic field pulses, (iv) a spatially dependent magnetic field B is superposed as a field gradient pulse during a plurality of short time intervals δ the external magnetic field B ₀ the amplitude of the observed spin echo is attenuated and thus a spin echo damping Ψ is measured as a function of the pulse duration δ, the intensity g and the time interval Δ of the field gradient pulses, (v) from the spin echo damping Ψ the self-diffusion coefficient D of the gas or liquid particles in the sample is determined, (vi) the Step (i) to (v) are performed with a sample of the free gas or the free liquid, wherein a self-diffusion coefficient D _{0 of} the free gas or the free liquid is determined, (vii) the tortuosity index τ as a quotient of the self-diffusion coefficient D _{0 of} the molecules of the free gas or of the free liquid and the self-diffusion coefficient D of the molecules of the gas or of the liquid in the carrier material τ = D ₀ / D is obtained. Method according to claim 2, characterized in that that the gas or the liquid, in step (i) into the pore space of a sample of the carrier material is introduced, water is. catalyst support from a porous one support material with a Tortuositätskennzahl τ of 1.5 to 4. catalyst support according to claim 4 of a porous support material with a Tortuositätskennzahl τ of 1.5 to 3. catalyst support according to claim 5 of a porous support material with a tortuosity index τ from 2 to Third catalyst support according to one of the claims 4-6, characterized in that the carrier material is a metal oxide, selected from the group consisting of zirconia, alumina, silica, Titanium dioxide, magnesium oxide, lanthanum oxide and cerium oxide. Dehydrogenation catalyst with improved deactivation behavior, comprising one or more active metals in elemental form and / or oxidic form on a catalyst support according to one of claims 4 to 7th Dehydrogenation catalyst according to claim 8, characterized characterized in that it comprises at least one element of VIII. subgroup, at least one element of the I or II main group, at least one Element of the III. or IV. main group and at least one element the III. Subgroup, including the lanthanides and actinides, in elemental form and / or oxidic Mold on the catalyst support contains. Dehydrogenation catalyst according to claim 8 or 9, characterized in that it platinum and / or palladium in elementary Contains form. Dehydrogenation catalyst according to one of claims 8 to 10, characterized in that it cesium and / or potassium in oxidic Contains form. Dehydrogenation catalyst according to one of claims 8 to 11, characterized in that it lanthanum and / or cerium in oxidic Contains form. Dehydrogenation catalyst according to one of claims 8 to 12, characterized in that it contains tin. Dehydration catalyst consisting of a porous support body and an active mass applied to the same, characterized that it has a tortuosity index τ of 1.5 to 4 has. A process for the heterogeneously catalyzed dehydrogenation of one or more dehydrogenatable C ₂ -C ₃₀ hydrocarbons in a reaction gas mixture containing them, characterized in that the reaction gas mixture containing the dehydrogenatable hydrocarbon (s) in contact with a dehydrogenation catalyst according to any one of claims 8 to 14 is brought. Method according to claim 15, characterized in that that the dehydrogenation is carried out autothermally by at least one Part of the needed dehydrogenation in at least one reaction zone by combustion of hydrogen, the educt and / or product hydrocarbons and / or of carbon in the presence of an oxygen-containing gas directly is generated in the reaction gas mixture. A method according to claim 15 or 16, characterized in that the dehydrogenatable hydrocarbon substance is propane and / or butane. Method according to claims 15 to 17, characterized that the starting reaction gas mixture is already dehydrogenated hydrocarbon contains. A method for determining the tortuosity of a catalyst comprising a porous support material and an active mass applied thereto by determining the self-diffusion D of a gas or a liquid in the catalyst and the self-diffusion D _{0 of} the free gas or the free liquid and calculating the quotient D / D ₀ . A method according to claim 1, characterized in that (i) a gas or a liquid containing molecules having at least one atom with non-disappearing nuclear spin 1 is introduced into the pore space of a sample of the catalyst, (ii) an external magnetic field B ₀ in place (iii) a spin echo of the nuclear spins I in the sample is generated by irradiation of short high-frequency magnetic field pulses, (iv) a spatially dependent magnetic field B is superimposed as a field gradient pulse during a plurality of short time intervals δ the external magnetic field B ₀ the amplitude of the observed spin echo is damped and a spin echo attenuation Ψ as a function of the pulse duration δ, the intensity g and the time interval Δ of the field gradient pulses is measured, (v) from the spin echo damping Ψ the self-diffusion coefficient D of the gas or liquid particles in the sample is determined, (vi) the step (i) to (v) with a sample de s free gas or the free liquid are carried out, wherein a self-diffusion coefficient D _{0 of} the free gas or the free liquid is determined, (vii) the Tortuositätskennzahl τ as a quotient of the self-diffusion coefficient D _{0 of} the molecules of the free gas or the free liquid and the self-diffusion coefficient D of the molecules of the gas or the liquid in the carrier material τ = D ₀ / D is obtained. Method according to claim 2, characterized in that that the gas or the liquid, in step (i) into the pore space of a sample of the catalyst is introduced, water is. Catalyst comprising a porous support material and one on this applied active mass with a Tortuositätskennzahl τ of 1.5 to 4. A catalyst according to claim 22 comprising a porous support material and an active mass applied thereto having a tortuosity index τ of 1.5 to 3. Catalyst according to claim 23 comprising a support material and an applied on this active mass having a Tortuositätskennzahl τ of 2 to Third Catalyst according to one of Claims 22-24, characterized that the carrier material a metal oxide selected from the group consisting of zirconia, alumina, silica, Titanium dioxide, magnesium oxide, lanthanum oxide and cerium oxide.