EP4308530A1 - Process and system for preparing a target compound - Google Patents

Abstract

The invention relates to a process for preparing a target compound, in which an ethane-containing feed mixture (A) is distributed across a plurality of parallel reaction tubes (10) of a tube reactor (100) and subjected to an oxidative catalytic conversion of the ethane in the reaction tubes (10), wherein the catalytic conversion is carried out by means of catalysis zones (11, 12, 13), having different activity, arranged one behind the other in the reaction tubes (10), and wherein in each case one or more catalytically active materials and one or more catalytically inactive materials are provided in the catalysis zones (11, 12, 13). The different activity of the catalysis zones (11, 12, 13) is brought about by providing the one or more catalytically active materials with an identical or substantially identical basic formulation, wherein the one or more catalytically active materials is or are prepared using different calcination intensities. The invention also relates to a corresponding system.

Description

description

Process and plant for the production of a target compound

The present invention relates to a method and a plant for the production of a target compound according to the preambles of the corresponding independent patent claims.

Background of the Invention

The principle of the oxidative dehydrogenation (ODH) of paraffins having two to four carbon atoms is known. In the ODH, the paraffins mentioned are reacted with oxygen to form the respective olefins and water, among other things. The present invention relates to the oxidative dehydrogenation of ethane to ethylene, also referred to below as ODHE.

ODH(E) may offer advantages over more established olefin production processes such as steam cracking or catalytic dehydrogenation. Due to the exothermic nature of the reactions involved and the practically irreversible formation of water, there is no thermodynamic equilibrium limitation. The ODH(E) can be carried out at comparatively low reaction temperatures. In principle, the catalysts used do not need to be regenerated, since the presence of oxygen enables or causes in-situ regeneration. Finally, in contrast to steam cracking, smaller amounts of worthless by-products such as coke are formed.

For further details regarding the ODH(E), please refer to relevant literature, e.g. Ivars, F. and Lopez Nieto, JM, Light Alkanes Oxidation: Targets Reached and Current Challenges, in: Duprez, D. and Cavani, F. (eds.) , Handbook of Advanced Methods and Processes in Oxidation Catalysis: From Laboratory to Industry, London 2014: Imperial College Press, pages 767-834, or Gärtner, CA et al., Oxidative Dehydrogenation of Ethane: Common Principles and Mechanistic Aspects, ChemCatChem, Vol 5, No. 11, 2013, pages 3196 to 3217, and X. Li, E. Iglesia, Kinetics and Mechanism of Ethane Oxidation to Acetic Acid on Catalysts Based on Mo-V-Nb Oxides, J. Phys. Chem. C, 2008, 112, 15001-15008. In particular, MoVNb-based catalyst systems have turned out to be promising for the ODH(E), as for example by F. Cavani et al. , "Oxidative dehydrogenation of ethane and propane: How far from commercial Implementation?", Catal. Today, 2007, 127, 113-131. Catalyst systems additionally containing Te can also be used. If a "MoVNb-based catalyst system" or a "MoVTeNb-based catalyst system" is mentioned here, this is understood to mean a catalyst system which has the elements mentioned as a mixed oxide, also expressed as MoVNbO _x or MoVTeNbO _x . The specification of Te in parentheses stands for its optional presence. The invention is used in particular with such catalyst systems.

Significant amounts of the respective carboxylic acids of the paraffins used, in particular acetic acid in the case of ODHE, are formed as by-products in the ODH, particularly when using MoVNb(Te)0^-based catalysts under industrially relevant reaction conditions. Coproduction of olefins and the carboxylic acids when using the type of catalyst described is therefore generally unavoidable for economical plant operation, but preferential formation of olefins is desirable.

According to the prior art, the ODH(E) is preferably carried out in fixed bed reactors, in particular in cooled tube bundle reactors, e.g. with molten salt cooling. The use of a reactor bed with a plurality of zones is generally known for strongly exothermic reactions, ie in particular oxidative reactions, which also include ODH(E). The basics are described, for example, in WO 2019/243480 A1 by the applicant. This document discloses the principle that different catalyst beds or corresponding reaction zones which have different catalyst loadings and/or catalyst activities per unit volume are used.

The measures mentioned serve in particular to enable temperature and selectivity control in an ODH(E) reactor for practical technical implementation. The object of the present invention is to improve corresponding measures. Disclosure of Invention

The aforementioned object is achieved by a method and a system for producing a target compound with the features of the respective independent patent claims. Preferred configurations are the subject matter of the dependent patent claims and the following description.

WO 2019/243480 A1 discloses, as mentioned, the use of catalyst beds or corresponding reaction zones with different catalyst loadings and / or catalyst activities per unit space, layers with variable catalyst activity being used, which are provided by the fact that the proportion of inert material, for example in the catalyst particles, is changed. However, the formulation of the active catalyst material itself is kept the same for all catalyst beds or reaction zones. In particular, this recipe includes all steps of the manufacturing process, including steps such as drying and calcination, which are therefore carried out in a uniform manner and under the same conditions. In this way a catalytically active material with identical properties is obtained, diluted by the use of catalytically inactive material (binder, support...) in order to obtain an adjustment of the catalyst activity.

With regard to the terms “basic recipe” and “recipe”, reference is also made to the explanations for FIG. A preparation of an active catalyst material for use in the present invention comprises one or more first preparation steps, a calcination subsequent to these first preparation steps, and one or more second preparation steps following the calcination. The basic recipe includes the first production steps in an identical or essentially identical form, but not necessarily a calcination that is carried out identically or essentially identically. In contrast, the term recipe is intended to identify identically or essentially identically carried out first production steps as well as identically or essentially identically carried out calcination. In the terminology used here, materials with an identical basic recipe or recipe are produced from identical or essentially identical starting materials. Materials with an identical basic recipe or Recipe are characterized in particular by an identical composition of elements.

For example, for an "identical basic recipe", starting components, in particular metals, can be provided in the same form, i.e. in particular in the form of the same soluble metal salts or in the form of the same metal oxides, and these - apart from any fluctuations that are unavoidable due to production or that are irrelevant with regard to the catalyst properties - in the Substantially be used in equal amounts or proportions. Furthermore, the production process, for example by hydrothermal synthesis, is identical or essentially identical here, apart from in particular the calcination conditions or other parameters influencing the activity, such as the temperature or duration of certain production steps.

The term "substantially identical" is understood here in particular to mean an identity within the technical tolerance limits of a corresponding method or that a certain effect or a certain result can be achieved within a certain tolerance by several method steps carried out "substantially identically". Such a result can in particular be a conversion-selectivity behavior.

The “conversion-selectivity behavior” in the language used here denotes a connection between a conversion of a starting compound, in the present case ethane, and a selectivity for the target compound, in the present case ethylene, which are each expressed as a percentage. The conversion denotes the proportion of the starting compound which is converted into any other compound, and the selectivity denotes the proportion of the target compounds in all such compounds. An “essentially identical” conversion-selectivity behavior is present in the terminology understood here if—with essentially the same conversions of the one starting compound, in particular conversions of the ethane—essentially the same selectivities for the respective target compounds are obtained. Substantially the same conversions are present if the conversions of the different catalytically active materials are not more than 2 percentage points, preferably not more than 1.5 percentage points, particularly preferably not more than 1 percentage point, or not more than 6%, preferably by no more than 4%, particularly preferably by no more than 2.5% relative to one another. Substantially the same selectivities for a target compound are present if the selectivities for the one target compound of the different catalytically active materials - with essentially the same conversions - by no more than 1 percentage point, preferably by no more than 0.7 percentage points, particularly preferably by by no more than 0.5 percentage points or by no more than 7%, preferably by no more than 5% and particularly preferably by no more than 3% relative to one another.

In the language used here, “calcination” means in particular heating a corresponding material to temperatures of at least 400 °C (“calcination temperature”) in an atmosphere essentially containing nitrogen or pure nitrogen for a predetermined period of time (“calcination time”). The calcination time and calcination temperature define in particular the calcination intensity, with a lower calcination temperature possibly being offset or compensated for by a longer calcination time and vice versa. In particular in the context of the exemplary embodiments described below, calcination is also referred to synonymously as “activation”.

For reasons of clarity, a distinction is always made below between a "catalytically active material", the actual catalyst, and a "catalytically inactive material", which itself does not have a catalytic effect but is provided together with the catalyst. The catalytically inactive material can be, for example, silica (S1O2), alumina (AI2O3), silicon carbide (SiC) or graphite. In particular, silicon carbide and graphite are very advantageous inert materials for (strongly) exothermic reactions such as the oxidation of alkanes, especially ODHE, since, in addition to the effect of dilution, they are particularly good thermal conductors and thus also contribute to effective heat management of the reaction. Wax is also required to shape (tablet) the catalysts, but this is burned out once the shape has been completed. The wax is therefore no longer present in the actual catalyst, but instead leaves behind corresponding pores that are important for the accessibility of the reactants to the catalytically active centers. The inert materials mentioned above can be used for tableting or as framework materials for suitable shaped catalyst bodies of any type, or they can be other materials that are not catalytically active equipped bodies act. A catalytically inactive material is also referred to below as “inert material”.

As explained below, the catalyst beds or reaction zones produced according to embodiments of the invention offer advantages over such a prior art method, which include in particular an improved service life or durability of the catalyst, since it has a more homogeneous activity distribution. In addition, a further unexpected advantage results from the initially supposedly disadvantageous lower activity of catalytic zones provided according to embodiments of the invention.

If different activity levels are produced in the manner known from the prior art, i.e. by (i) dilution by physical mixing of active unsupported shaped catalyst bodies and inert shaped bodies within a layer or (ii) by shaped catalyst bodies which already contain the diluting inert fraction in the shaped body itself , this can result in a decisive disadvantage: Such layers (i) or layers of such diluted shaped bodies (ii) always consist on the one hand of more or less large areas that are either inert and therefore inactive for the reaction, and on the other hand of areas that have maximum (full) catalytic activity. The catalytic activity is therefore not distributed homogeneously. The reaction therefore takes place exclusively in these fully active areas. Thus, these areas are subject to very high local thermal stress with local temperature hotspots. On the one hand, this leads to faster aging of the catalyst (comprising the catalytically active material and the catalytically inactive material), e.g. due to sintering or, in extreme cases, to a loss of mechanical stability of a shaped catalyst body due to the (very local) thermal stress. On the other hand, the selectivity is negatively influenced, ie in particular the total oxidation of the starting material used, such as an alkane, in particular of ethane, is promoted at too high a temperature. These effects are amplified the larger the range of such inhomogeneities in the distribution of catalyst activity (dilution with inert particles versus dilution within a catalyst particle).

Even if the measures proposed in the prior art initially result in a simple and apparently relatively inexpensive production method that uses the same recipe (i.e. with identical or essentially identical calcination conditions), the further disadvantages mentioned and those mentioned below remain:

1. Nevertheless, there is a very high level of activity on the active particle and thus local stress and temperature increase. This leads to corresponding losses in selectivity and possibly also to accelerated aging of the catalyst.

2. The introduction of inert material is often limited, e.g. due to difficulties in shaping, stability and durability of the final shaped catalyst bodies.

3. Although the inert material is not catalytically active, it can also have a pore structure, which is then also subject to aging. The changing internal diffusion can have different aging kinetics than the chemical aging of the catalytically active material and thus make uniform, predictable aging more difficult. This can make calculating the service life and predicting the end of life of the catalyst bed considerably more difficult. However, such a predetermination is necessary in practice in order to be able to plan maintenance intervals with catalyst changes in a large commercial plant in good time.

4. In addition, the catalytically inactive material occupies available reactor volume that could be filled with catalytically active material. With such a solution, one typically always loses reaction space and thus space-time productivity.

5. Due to the aforementioned different aging characteristics, aging of the inert material can also occur, which makes it necessary to change the catalyst, although the actual catalytically active material is still sufficiently active and selective.

The present invention minimizes or avoids the use of inert material to dilute the active catalyst mass, i.e. the catalytically active material with catalytically inactive material, but typically a certain (but in particular constant) proportion of catalytically inactive material (to form of shaped bodies, ie tabletting) is used. In the context of this invention, it is proposed to produce tailor-made catalysts with a specifically adjusted conversion-selectivity behavior and a specifically adjusted activity per volume, which can be used in a particularly efficient process, in particular for the production of olefins by means of oxidative dehydrogenation of ethane.

Overall, within the scope of the present invention, a process for the preparation of a target compound is proposed in which an ethane-containing feed mixture is distributed over a large number of reaction tubes of a tube bundle reactor arranged in parallel and is subjected to an oxidative catalytic conversion of the ethane in the reaction tubes, the catalytic conversion being carried out by means of Reaction tubes of catalytic zones arranged one behind the other with different activities is carried out, and wherein one or more catalytically active materials and one or more catalytically inactive materials are provided in each of the catalytic zones. The different activity of the catalytic zones is brought about according to the invention by providing the one or more catalytically active materials with an identical basic recipe and in particular an identical elemental composition. In particular, the activity can increase from zone to zone, i.e. it can be more than 10%, 20% or 25% higher in a subsequent zone than in the respective preceding zone. A proportion of the one or more catalytically inactive materials in the respective catalysis zones in a total filling of the respective catalysis zones differs in particular by no more than 25%, 20%, 15%, 10% or 5% between the catalysis zones. In embodiments of the present invention, the catalytic activity is adjusted exclusively or primarily by influencing the activity, in particular due to the different calcination conditions and in particular due to the different calcination intensity.

In other words, within the scope of the present invention, in contrast to the prior art, neither (exclusively) the use of catalyst materials with different elemental compositions nor (exclusively) the use of differently diluted catalyst materials is provided. This leads to the advantages already explained in detail above. The one or at least one of the plurality of catalytically active materials has or have at least the metals molybdenum, vanadium, niobium and optionally tellurium. The one or at least one of the plurality of catalytically active materials is or are also in particular at least partially produced from the oxides of the metals mentioned. This catalytically active material can thus be produced from precursors that are commercially available in large quantities and at low prices. The disadvantages of production from (water) soluble precursors of the metals, such as ammonium heptamolybdate or vanadyl sulfate, can be avoided in this way. Instead of telluric acid, tellurium oxide can be used. In particular, the catalytically active material can (entirely) be prepared using the oxides M0O3, V2O5, Nb ₂ O ₅ and TeO ₂ .

As explained below with reference to specific exemplary embodiments of the invention, a catalytically active material produced on the basis of the metal oxides (as described, for example, in example 1 of DE 102017000 861 A1) can have a lower activity than a catalytically active material produced on the basis of the soluble precursors . However, in the conversion of ethane with a comparable overall selectivity to the commercial valuable products ethylene and acetic acid, a higher selectivity to ethylene can be observed for a catalytically active material of the corresponding type produced on the basis of the metal oxides. The same is to be expected in the implementation of other alkanes.

Without being bound to theory, this fact, as explained in connection with the exemplary embodiments, can result in a flatter temperature profile that can be determined when using a corresponding catalytically active material. This effect makes it possible to reduce the risk of thermal runaway of the catalyst bed or part of the catalyst bed or a reaction zone in a reactor. A higher catalyst bed inlet temperature can be used to achieve the same conversion.

Surprisingly, the alleged disadvantage of a lower activity, in particular of a catalyst produced using the pure oxides, turns out to be particularly advantageous in the sense of the invention, since the reduced activity means that the process can be operated at slightly higher temperatures or should. This in turn leads to an increased yield of the particularly preferred product of value ethylene.

In the method proposed according to the invention, one or at least one of the plurality of catalytically active materials is produced in particular using hydrothermal synthesis, as is also already known in principle from the aforementioned DE 102017 000861 A1.

In contrast to WO 2019/243480 A1, a different activity of the one or at least one of the several catalytically active materials in the reaction zones is brought about within the scope of the present invention by different calcination intensities. In other words, the one or more catalytically active materials are produced in the different reaction zones using the identical basic recipe but different calcination intensities. These therefore have different activities, as is utilized according to the invention, even without different inert fractions.

The basic recipe has a decisive influence on the conversion-selectivity behavior of a corresponding catalytically active material. The activity of the catalytically active material can be adapted for a specific base recipe, as has been recognized according to the invention, by choosing suitable calcination conditions. The calcination conditions include in particular the selection of the calcination process technology, i.e. continuous or discontinuous calcination, and the choice of the calcination intensity (the calcination intensity is defined in particular by a calcination temperature and/or a calcination time). Further details are also explained below with reference to a specific embodiment. As was recognized according to the invention and is proven by the exemplary embodiments, in particular the calcination intensity (temperature and duration) alone represents a suitable parameter for bringing about the different activity of the one or at least one of the several catalytically active materials. Other parameters can, but do not have to, be changed.

In other words, in one embodiment, the present invention makes use of the fact that the activity of a specific catalyst material, and associated other parameters such as the light-off temperature, changes the production and in particular can be influenced by a single production step. It has been found, in particular for the MoVNb(Te)O 4 catalysts advantageously used according to the invention, that the calcination conditions and in particular the calcination intensity have a direct influence on their respective activity. Increased activity is also accompanied by a reduced starting temperature. In principle, the composition of the catalytically active material remains the same and can in particular be taken from the same synthesis approach and (apart from calcination) the same synthesis and production processes, which corresponds to the basic recipe defined above.

In the context of the invention, it was surprisingly found that the physicochemical properties, in particular in the form of the BET surface area and/or the specific pore volume.

A greater calcination intensity leads to a reduction in the BET surface area and - more significantly - to a reduction in the specific pore volume. Furthermore, it was surprisingly found that the relationship between the BET surface area and - more significantly - between the specific pore volume and the catalytic activity in the catalyst materials produced in this way (i.e. identical basic recipe, different calcination intensity) shows that the catalytic activity increases with increasing specific pore volume (or higher BET surface) increases.

The specific pore volume or the BET surface area is therefore suitable as a guide variable for the production of the catalyst materials.

As just explained, a higher pore volume and/or a higher BET surface area is usually associated with a higher activity. As illustrated in the exemplary embodiments, what is meant here is the pore volume or the BET surface area of the catalyst material before shaping, ie after calcination. The BET surface area represents the mass specific surface area calculated from experimental data according to known methods and is usually given in units of square meters per gram (m ² g ^-1 ). The BET measurement is known to the competent person from relevant textbooks and standards, for example DIN ISO 9277:2003-05, "Determination of the specific surface area of solids by gas adsorption according to the BET Process (ISO 9277:1995) ", known. But this is not a necessary mandatory requirement for the implementation of the present invention, but relates to a possible embodiment. The specific pore volume of a catalyst can, for example, using nitrogen physisorption measurements, ie basically with the using the same measuring method that is also used to determine the BET surface area, whereby the part of the sorption isotherm at relative pressures of approx. 1 p/po is used to determine the specific pore volume.

In a corresponding embodiment, a pore volume and/or a BET surface area differ in at least two of the catalysis zones, with deviations of 15 to 60% being possible, i.e. the pore volume or the BET surface area of the catalyst material of the first catalysis zone by 15 to 60% less than the pore volume or BET surface area of the second catalytic zone (as stated above, the pore volume or BET surface area relates to the catalyst material after calcination before shaping). As just stated, the pore volume can be used in particular as a measure of the catalyst activity.

Advantageously, the one or at least one of the plurality of catalytically active materials in one of the catalysis zones can have a different calcination intensity that is more than 10% higher in activity than the one or at least one of the plurality of catalytically active materials in another of the catalysis zones . The activity can also be, for example, 20%, 30%, or 40% higher.

In the method proposed according to the invention, at least two different layers of catalyst are advantageously used, each with (substantially) the same proportion of binder or support (ie catalytically inactive material), but with different activity of the catalytically active material. In other words, a proportion of the one or more catalytically inactive materials in the different catalytic zones advantageously differs relative to one another by no more than 25%, 15%, 10% or 5%, and in particular only within the scope of dosing or manufacturing tolerances . As mentioned, the present invention is used in connection with an ODH of ethane (ODHE), so that the feed mixture contains oxygen and ethane as paraffin and the oxidative reaction is carried out as an oxidative dehydrogenation of the ethane. In all cases in which an “oxidative reaction” is mentioned in connection with embodiments of the invention, this is therefore understood to mean an oxidative dehydrogenation of ethane.

The oxidative reaction is advantageously carried out at a catalyst temperature in a range between 240 and 500.degree. C., preferably between 280 and 450.degree. C., in particular between 300 and 400.degree.

The starting mixture is advantageously fed to the reactor at a pressure in a pressure range from 1 to 10 bar (absolute), in particular from 2 to 6 bar (absolute). It is therefore a process that works at comparatively low pressure and in which advantages of the invention arise in a special way. A reduction in catalytically inactive material reduces the pressure loss in a corresponding reaction tube, which is particularly advantageous for corresponding “low-pressure” processes.

Within the scope of the present invention, it is particularly advantageous to set a water content in the feed mixture of between 5 and 95% by volume, in particular between 10 and 50% by volume and more particularly between 14 and 35% by volume. As also disclosed, for example, in the applicant's EP 3 558910 B1, at least one parameter can also be determined, for example, which indicates an activity of the or one of the catalysts, and on this basis a quantity of water in the reaction feed stream based on the at least one determined parameter to be set.

In particular, an embodiment can be advantageous in which the starting mixture contains ethane and in which the molar ratio of water to ethane in the starting mixture is at least 0.23.

The invention can be used independently of the routing of the cooling medium (ie co-current or counter-current). A particular additional advantage can be achieved when the cooling medium - in particular a molten salt - is guided in countercurrent, since the heat of reaction from the catalysis zones can be partially utilized here, for example in a preheating zone. Likewise, different cooling circuits in combination with different catalyst layers are conceivable (as also specified in more detail in WO 2019/243480 A1).

There is a particular advantage if the reactor is designed in such a way that the reactor is explicitly additionally cooled differently in certain areas, ie there is the possibility of a separate cooling circuit (with possibly even a different coolant flow direction). This results in the advantage of a targeted temperature and thus activity adjustment in certain zones. As a result, these zones can also be explicitly “switched on” by means of a corresponding heat input or, if not needed or only slightly, “switched off” by specifically exceeding or falling below the light-off temperatures of the catalytically active materials.

In other words, in one embodiment, the present invention proposes that the reaction tubes be cooled using one or more cooling media flowing around the reaction tubes. Different pipe sections can be cooled with particular advantage using different cooling media, the same cooling medium in different cooling medium circuits, and/or the same or different cooling media in different or the same flow directions.

The invention also extends to a plant for the production of a target compound with a tube bundle reactor which has a multiplicity of reaction tubes arranged in parallel, the plant having means which are set up to distribute an ethane-containing feed mixture to the reaction tubes and in the reaction tubes to an oxidative subject to catalytic conversion of the ethane, being provided for the catalytic conversion in the reaction tubes arranged in series catalysis zones with different activities, and wherein one or more catalytically active materials and one or more catalytically inactive materials are provided in the catalysis zones.

According to the invention, the different activity of the catalytic zones is mitigated by providing the one or more catalytically active materials identical basic recipe (ie also with identical elemental composition), wherein the one or more catalytically active materials is or are produced using different calcination intensities.

With regard to further features and advantages of the system proposed according to the invention, reference is expressly made to the above explanations. In corresponding configurations, the system is set up in particular for carrying out a method as has already been explained above, likewise in different configurations. The explanations apply accordingly.

Overall, as mentioned, the invention creates a method for the targeted production of tailor-made catalysts (in particular with regard to their selectivity). A process for the production of catalytically active materials for use in the oxidative dehydrogenation of ethane can therefore also be the subject of the invention. The method comprises providing catalyst components of the type explained above, in particular metals in the form of the metal oxides mentioned, and subjecting them to a catalyst synthesis, in particular a hydrothermal synthesis, after the preparation of aqueous solutions or slurries, and subjecting a raw material obtained in the process to calcination under different calcination conditions. The different calcination conditions include, in particular, different calcination temperatures and/or calcination times. The catalytically active materials obtained are introduced together with one or more catalytically inactive materials as supports or binders into catalytic zones of a reactor, the proportion of the one or more catalytically inactive materials being essentially the same in particular.

The invention includes an improved production procedure for the catalytically active component of the catalyst, ie the active material of a catalyst (shaped body), in the form of using the pure oxides as raw materials. This leads to an increased selectivity, for example to ethylene, already in the catalytically active component of the catalyst. Furthermore, a targeted gradation of the catalyst activity is achieved by different calcination intensities, so that different layers of different activity can be generated via different calcination intensities. Overall, in this way, the use of significantly cheaper raw materials available in the required quantities allows, and ensures easy scalability of the catalyst production on an industrial scale.

The combination of the catalysts produced in this way, in particular in an ODH(E) process with a reactor system having a plurality of reaction zones, leads to a significant increase in the catalyst life and improved selectivities or product yields compared to a reactor system known from the prior art having a plurality of reaction zones in which the reaction zones are created by diluting the layers with inert material or diluting the shaped catalyst bodies themselves with inert components.

Overall, the invention allows a significant intensification of the process by using the specifically tailored catalysts or catalytically active materials in a reactor system with a plurality of reaction zones.

exemplary embodiments

The invention is explained in more detail below using examples that correspond to configurations of the invention and comparative examples that are not according to the invention, as well as associated figures and tables.

FIG. 1A illustrates selectivities and conversions obtained with catalysts according to exemplary embodiments of the invention.

FIG. 1B illustrates temperature profiles obtained with catalysts according to embodiments of the invention.

FIG. 2 illustrates a plant according to an embodiment of the present invention in a simplified schematic representation.

FIG. 3 illustrates a reactor according to an embodiment of the present invention in a simplified schematic representation.

FIG. 4 illustrates the production of a catalytically active material according to one embodiment of the present invention in a simplified schematic representation. The present invention minimizes or avoids the use of inert material (catalytically inactive material) to dilute the active catalyst mass (catalytically active material). As explained and documented below, it is possible to produce tailor-made catalysts (hereinafter the term "catalyst" is used in particular for the catalytically active material) with a specifically adjusted conversion selectivity behavior and a specifically adjusted activity per volume, so that these can be used in a particularly efficient Methods, in particular for the production of olefins by means of oxidative dehydrogenation of alkanes, in particular of ethane, can be used.

As mentioned, the present invention makes use of the fact that the activity of a specific catalyst material can be influenced by the production. The composition of the catalytically active material remains the same in principle and can in particular be taken from the same synthesis batch. This surprising effect was found in a catalytic testing of MoVNb(Te)O ^ catalyst material of the same synthesis approach and thus the same stoichiometry (composition of elements), but different calcination temperatures. As explained below, an essential (and in particular the only necessary) influencing factor is the calcination intensity, which results from the calcination temperature and calcination time.

The specific pore volume and/or the BET surface area can serve as a characteristic feature for the catalytically active materials. As a rule, these variables depend on the parameters of the synthesis recipe, calcination intensity and composition.

Raw materials and synthesis processes

In principle, different synthesis recipes, different calcination methods, different calcination intensities and different tellurium contents (each individually or in a defined combination) could lead to the establishment of different activities of catalytically active materials that can be used according to the invention. Various synthesis recipes are known for the production of corresponding catalytically active materials. A synthesis of MoVNbTe mixed oxide catalysts by combining solutions and spray drying and calcining is described in JP H07-053414 A, for example. Significantly improved syntheses with a very high content of the catalytically active M1 phase and thus higher selectivity and activity were subsequently described by hydrothermal synthesis in an autoclave from the soluble precursors (see, for example, A. Celaya Sanfiz et al., "Preparation of Phase- Pure M1 MoVTeNb Oxide Catalysts by Hydrothermal Synthesis-Influence of Reaction Parameters on Structure and Morphology", Top. Catal. 50, 2008, 1 -32).

An alternative newer synthesis method starts from the metal oxides of the respective metals instead of correspondingly soluble compounds of the respective metals. The metal oxides are subjected to a hydrothermal synthesis in the presence of oxo ligands, as specified, for example, in DE 102017 000861 A1. In this synthesis, crucial parameters are the temperature and heating method of the autoclave synthesis and the crystallization time. For example, DE 102017000861 A1 describes crystallization in an autoclave with a heating jacket, while similar syntheses using other raw materials to give MoVNbTe catalysts with an M1 phase at 175° C. in microwave heating are described. (e.g. WO 2013/021034 A1). It is also described that the activity of the catalyst can be influenced by the length of the synthesis time in the autoclave. For example, maximum activity (but not maximum selectivity) can be achieved after a synthesis time of 3.5 hours (see D. Melzer et al., "Design and synthesis of highly active MoVTeNb-oxides for ethane oxidative dehydrogenation", Nature Commun. 10 , 2019, 4012, figure 11).

An economically producible catalyst should be able to be prepared from precursors that are commercially available in large quantities and at the lowest possible prices. For the elements Mo, V, Nb and Te these are the metal oxides M0O3, V2O5, Nb ₂ 0s and TeC> ₂ . Therefore, earlier production methods of MoVNbTeO^ materials, which are based on the (water) soluble precursors of the metals such as ammonium heptamolybdate or vanadyl sulfate, are less advantageous. It is also advantageous to replace telluric acid, which is soluble but not commercially available in large quantities, so tellurium oxide is advantageously used, as described in DE 102017000848 A1 (example 2). In Example 2 of DE 102017000848 A1, 3.3 L dist. Submitted water and heated to 80 ° C with stirring. Meanwhile, 725.58 g of ammonium heptamolybdate tetrahydrate was added and dissolved (hereinafter referred to as AHM solution). In two beakers, each with a volume of 5 L, 1.65 L dist. Water is also heated to 80 °C while stirring on a magnetic stirrer with temperature control. 405.10 g of vanadyl sulfate hydrate (V content: 21.2%) and 185.59 g of ammonium niobium oxalate (Nb content: 20.6%) were then added to these beakers and dissolved (hereinafter referred to as V solution and Nb solution). designated). 65.59 g Te0 ₂ were distilled in 200 g the day before 3 hours. Water ground using a ball mill and diluted with 1.45 L dist. Water transferred to a beaker (hereinafter referred to as Te suspension). The V solution was pumped into the AHM solution one after the other, then the Te suspension ground the day before was added, stirring was continued for 1 h at 80 °C and finally the Nb solution was pumped into the AHM solution using a peristaltic pump. The pumping time for the V solution was 5 min at 290 rpm (tube diameter: 8×5 mm) and for the Nb solution 5 min at 275 rpm (tube diameter: 8×5 mm). The resulting suspension was then stirred for a further 10 min at 80° C., the speed of the stirrer during precipitation was 90 rpm. It was then blanketed with nitrogen by building up a pressure of up to about 6 bar with nitrogen in the autoclave and opening the drain valve to this extent that the autoclave was flowed through with nitrogen under pressure (5 min). At the end, the pressure was released via the vent valve to a residual pressure of 1 bar. The hydrothermal synthesis in the autoclave was carried out at 175° C. for 20 h (heating time 3 h) using an anchor stirrer at a stirrer speed of 90 rpm. After the synthesis, it was filtered using a vacuum pump with a blue band filter and the filter cake was diluted with 5 L dist. water washed. Drying took place at 80° C. in a drying cabinet for 3 days and was then ground in an impact mill, with a solids yield of 0.8 kg being achieved. The calcination took place at 280° C. for 4 h in a stream of air (heating rate 5° C./min, air volume 1 L/min). The activation took place in the retort at 600 °C for 2 h in a stream of nitrogen (heating rate 5 °C/min, amount of nitrogen 0.5 L/min).

A particularly advantageous base manufacturing process for a catalyst from the metal oxides is also already in the because of its economy mentioned DE 102017000861 A1 (Example 1). It leads to an exemplary catalyst with the stoichiometry MoVo _, 3Nbo _,i Teo _,i O _x . In the context of the present invention, the catalyst material can be produced in principle as described in the cited example of DE 102017 000861 A1. The metal oxides that are suitable in each case can be subjected to a hydrothermal synthesis.

In the method used in Example 1 of DE 102017000861 A1, TeC>2 was suspended in 200 g of distilled water and ground in a planetary ball mill with balls 1 cm in diameter (ZrC>2). The portion containing 500 ml of distilled water was then transferred to a beaker. Nb ₂ 0s was slurried in 200 g distilled water and ground in the same ball mill. The portion containing 500 ml of distilled water was then transferred to a beaker. The next morning, the mixture was heated to 80° C., 107.8 g of oxalic acid dihydrate were added to the Nb ₂ 0s suspension and the mixture was stirred for about 1 hour. 6 L of distilled water were placed in the autoclave (40 L) and heated to 80° C. with stirring (stirrer speed 90 rpm). When the water has reached the temperature, 61.58 g citric acid, 19.9 g ethylene glycol, 615.5 g MOO3, 124.5 g V2O5, the ground TeC>2 and the ground Nb ₂ 0s in oxalic acid were added one after the other. 850 mL of distilled water was used to transfer and rinse the vessels.

The total amount of water in the autoclave was 8.25 L. It was then blanketed with nitrogen. A hydrothermal synthesis was carried out in a 40 L autoclave at 190° C./48 h. After the synthesis, it was filtered off using a vacuum pump with a blue band filter, and the filter cake was washed with 5 L of distilled water.

Drying took place at 80° C. in a drying cabinet for 3 days and the product was then ground in an impact mill. A solids yield of 0.8 kg was achieved. The subsequent precalcination took place at 280° C. for 4 h in air (heating rate 5° C./min air: 1 L/min). The activation or calcination took place in a retort at 600° C. for 2 h (heating rate 5° C./min nitrogen: 0.5 L/min).

For example and in particular by reducing the tellurium content in the catalytically active material, the activity can be increased, as described in WO2018/141652 A1 and by Melzer et al. (above) described. pilot plants

In the context of the examples explained below, different test systems were used, which are initially explained below.

A test reactor designed as a double tube (fixed bed, max. total length of the bed 0.9 m, inner diameter of the reaction space 10 mm) was used in the test plant designated "Test Plant 1". The heating or cooling takes place with the aid of a thermal oil bath, the thermal oil being pumped through the exterior of the reactor and thus heating or simultaneously cooling the interior or the reaction zone (the reaction is an exothermic reaction).

The test plant designated "Test Plant 2" comprises a tubular reactor with a usable length of 1 m and an internal diameter of 25 mm. The heating and at the same time also the cooling took place by means of a salt bath, in which the reactor is immersed. For technical reasons, air was used as the oxidizing agent instead of pure oxygen, and this experimental plant 2 could only be operated under atmospheric pressure. The other test conditions included a catalyst amount of 337 g, a composition of the reaction feed from ethane to nitrogen to oxygen to water (vapor) of 11.1 to 46.7 to 6.8 to 35.4 (each mol%), GHSV of 412 (NLGas/h)/Lcatalyst. The test results are shown in Table 4.

Example 1 - Influence of the basic recipe on the activity-selectivity behavior

A catalyst designated "catalyst A" was produced on the basis of the soluble precursors and TeÜ2 (basically as described in Example 2 of DE 102017000848 A1, see above). A catalyst designated "Catalyst B" was produced on the basis of the metal oxides (basically as in Example 1 of DE 102017 000861, see above).

The investigation was carried out in the test facility 1 described above. The exact test conditions are listed in Table 1 below. The different activities are summarized in Table 2. Table 1

Table 2

Catalyst B showed an activity that was about 19% lower than catalyst A, i.e. there is a lower ethane conversion at the same catalyst bed inlet temperature or the same coolant temperature. The activity test was carried out at the same coolant temperature (oil bath temperature) of 298° C. (see Table 1).

With the same conversion, catalyst B based on the pure oxides compared to catalyst A based on the soluble precursors and TeO2 has an approximately 5 percentage point higher selectivity for ethylene with the same overall selectivity of over 96% for the commercial valuable products ethylene and acetic acid ( and correspondingly 5 percentage points lower selectivity for acetic acid), namely approx. 83% vs. approx. 78% selectivity for ethylene (catalyst B vs. catalyst A) and approx. 13% vs. approx. 18% selectivity for acetic acid ( Catalyst B vs. Catalyst A). This fact is illustrated in Figure 1A, in which the selectivities (left vertical axis; cross-hatching: ethylene, diagonal hatching: acetic acid, without filling: carbon oxides) and conversions (right vertical axis; triangles) of the catalysts according to the experimental points A, B1 and shown in Table 1 B2 are shown.

In order to achieve the same conversion, a higher catalyst bed inlet temperature and also a higher mean or minimum catalyst bed temperature are required because of the lower activity of a catalyst B, which is prepared via the pure oxides. Finally, the increased average catalyst bed temperature is also the reason for the increased selectivity to ethylene observed. The explanation for this can be found, for example, in WO 2019/243480 A1 on page 13,

Line 4 to page 14, line 2.

There is a flatter temperature profile (even at a higher catalyst bed inlet temperature) of catalyst B vs. catalyst A due to the lower activity and lower selectivity to acetic acid. One explanation is found in the fact that the oxidation of ethane to acetic acid is significantly more exothermic than the oxidation of ethane to ethylene (standard enthalpy of reaction ethane to ethylene - 105 kJ/mol, standard reaction enthalpy of ethane to acetic acid -590 kJ/mol). By this effect, a reduction in the risk of thermal runaway of the catalyst bed or a part of the catalyst bed or a reaction zone in a commercial reactor can be achieved. This circumstance is illustrated in Figure 1B, in which for measuring points before (measuring point 1) and after (measuring point 8) a catalyst bed of approx. 60 cm and measuring points (measuring points 2 to 7) within the catalyst bed on the horizontal axis the corresponding temperatures in °C are plotted on the vertical axis.

In order to achieve the same conversion, a higher catalyst bed inlet temperature and also a higher mean or minimum catalyst bed temperature are required because of the lower activity of a catalyst B, which is prepared via the pure oxides. Finally, the increased average catalyst bed temperature is also the reason for the increased selectivity to ethylene observed. A possible explanation for this can be found, without being bound by it, in WO 2019/243480 A1, page 13, line 4 to page 14, line 2.

Surprisingly, the supposed disadvantage of a lower activity of a catalyst produced via the pure oxides in the context of the invention turns out to be particularly advantageous, since the reduced activity means that the process can or should/must be operated at slightly elevated temperatures in the sense of the explanation from WO 2019/243480 A1 (see above) then leads to an increased yield of particularly preferred product of value ethylene.

Example 2 - Effect of calcination conditions

As described above, the basic recipe has a decisive influence on the conversion-selectivity behavior. However, the activity of a catalyst can be adjusted within a basic recipe by choosing suitable calcination conditions (calcination intensity). The calcination conditions include in particular the selection of the calcination process technology, ie continuous or discontinuous calcination, and the choice of the calcination intensity (determined in particular by the calcination temperature and calcination time). Surprisingly, it was found that the calcination intensity has a decisive influence on the activity of a catalyst. For a given calcination temperature, the calcination intensity is determined in particular by the length of the heating, holding and cooling time. Furthermore, the presence or absence of mixing of the calcined material and the layer thickness of the calcined material (eg fill level in a calcining bowl in discontinuous calcination or the layer thickness formed in continuous mixing in continuous calcination) also play a role.

It is therefore to be expected that the calcination intensity is also significantly determined by the choice of calcination process technology, i.e. in a discontinuous manner, e.g. in a retort or a muffle furnace, or in a continuous manner, e.g. in a rotary kiln. In discontinuous calcination, the calcined product cannot usually be mixed. Furthermore, the heating, holding and cooling times are longer in batch calcination than in continuous calcination. Continuous calcination, especially in a rotary kiln, is characterized by the fact that the material to be calcined is simultaneously mixed during calcination due to the forward transport of the material to be calcined through the tube rotating about its longitudinal axis, which means in particular a more uniform treatment of the material to be calcined. The calcination time, i.e. the overall heating, holding and cooling times, is much shorter in continuous calcination, especially in a rotary kiln: The heating-up phase is very short and only takes place to a small extent at the beginning of the (rotary) kiln. The holding time is mainly characterized by the kiln length and the transport speed (e.g. influenced by the kiln inclination in the case of a rotary kiln). Cooling time is minimal as the material exits the hot furnace directly into an ambient or room temperature receptacle. Thus, the calcined material usually experiences a significantly higher calcination intensity during discontinuous calcination.

At this point it should be expressly pointed out that the calcination intensity should generally be selected in such a way that the calcined material can form correspondingly stable crystal phases. In the case of catalysts or catalyst materials, this means above all that the reaction or Catalysis conditions - especially with regard to the temperatures prevailing during catalysis - Sufficient crystal phase stability, which is expressed in activity and selectivity that remain the same for the intended reaction.

An adapted calcination intensity (time and temperature), in particular the selection of the calcination temperature T (see examples below), thus contributes significantly to the properties of the catalytically active materials mentioned, with particular attention being paid to homogeneous calcination under inert gas. Homogeneous calcination in small quantities is also possible in a bowl in the furnace, but the calcination intensity is less homogeneous with large quantities and thick layers of powder. For large quantities, the material has to be moved, e.g. in a rotary kiln. It should be noted that a normal oven needs a certain amount of time to cool down before the material is removed. In a rotary kiln, on the other hand, the material falls directly from the hot tube into a cold container, so that reproducible and precisely definable conditions can be set. On the other hand, extremely long calcination times cannot be achieved with conventional technical tube lengths of a rotary kiln. To a limited extent, therefore, a shorter residence time in a continuous kiln, such as a rotary kiln, can be replaced by a higher calcination temperature. Therefore, the calcination intensity, which results from time and temperature, is decisive here.

Example 2a - Effect of calcination processing technique and calcination time

This effect was shown when testing two catalyst samples that were produced in exactly the same way using the same basic recipe, ie starting from the insoluble oxides (see above). The only difference is the choice of calcination process technology and thus the calcination intensity. A catalyst designated "Catalyst C" was batch calcined in a muffle furnace. A catalyst designated "Catalyst D" was calcined in a rotary kiln. As mentioned above, muffle kiln calcination is a batch process, while rotary kiln calcination is a continuous process. The calcination temperatures (i.e. the temperatures during the holding time) were the same for both calcination processes, namely 650°C, but the effects described above result in corresponding effects on the respective calcination intensity, ie a higher calcination intensity in the case of catalyst C and compared to catalyst C significantly lower Calcination intensity for catalyst D, due to the procedure. The sufficient calcination intensity for catalyst D was confirmed by a constant catalyst performance over a longer period. The catalyst samples Catalyst C and Catalyst D obtained via different calcination intensities were tested in the test facility 1 described above under exactly the same conditions for both samples (regarding the amount of catalyst introduced, system pressure, composition of the reaction feed). Table 3 shows the comparison of the activities at an oil bath temperature of 295° C. (which also corresponds to the catalyst bed inlet temperature).

From the data in Table 3 it can be seen that discontinuous calcination leads to a catalyst with lower activity, because this discontinuous calcination, carried out in the retort, is associated with a stronger calcination intensity - in the form of a longer effective calcination time (incl. heating - and cooling phase at the same temperature of 650°C during the holding time).

Table 3

The value marked with an asterisk * (the same also applies to the following tables) relates to the pure MoVNbTe oxide catalyst powder (before tableting). For tabletting, silica and wax are added as tableting aids, with the wax being burned out, as mentioned. The porosity of the silica also determines the porosity of the final shaped catalyst body, so that it differs. However, the specific pore volume of the actual catalyst powder correlates with the activity.

The behavior is the same for catalysts E and F. These catalyst samples were tested in test facility 2 described above. The other test conditions for testing catalysts E and F in test facility 2 included a catalyst quantity of 337 g, a composition of the reaction feed from ethane to nitrogen to oxygen to water (vapour) from 11.1 to 46.7 to 6.8 to 35.4 (each mol%), GHSV of 412 (N Lcas/hy atayzer. The test results are shown in Table 4 .

It is clearly evident from Table 4 that a catalyst produced via a discontinuous calcination, referred to here as "catalyst E", ie the catalyst which was subjected to a higher calcination intensity, has a lower activity than a catalyst referred to as "catalyst F", which was produced via continuous calcination and was therefore subject to a lower calcination intensity. The lower activity of catalyst E compared to catalyst F can be seen from the fact that catalyst E required a 4 K higher reaction temperature to achieve the same ethane conversion. Table 4

Example 2b - Effect of calcination temperature

As described above, the basic recipe has a decisive influence on the conversion-selectivity behavior. However, the activity and thus also the light-off temperature of a catalyst can be adjusted within a basic recipe by choosing suitable calcination conditions.

This effect was found in a catalytic testing of MoVNbTeO ^ catalyst material of the same synthesis approach and thus the same stoichiometry (element composition), i.e. the identical basic recipe, but different calcination temperatures but the same calcination times.

The MoVTeNbOc materials were produced as described in DE 102017000861 (Example 2), except that the activation under inert gas was not carried out in a retort at 600° C., as in the section there [0049], but in a rotary kiln with a diameter of 10 cm one meter of heated length with a dwell time of 30 min, and an inlet temperature of 550° C. and with an outlet temperature which is given in Table 5 as the calcination temperature. Table 5

The activity of the catalysts produced in this way (catalysts "G", "D" and "H") was investigated in the test plant 1 described above under exactly the same conditions (amount of catalyst introduced, system pressure, composition of the reaction charge). At an oil bath temperature of 295°C, clear absolute and relative activity gradations of +21% and -23% (relative in each case) were found compared to the base case (standard calcination temperature of 650°C) of the differently calcined catalysts.

To determine the light-off temperature listed in Table 5, an Arrhenius plot, i.e., a plot of the natural logarithm of the reaction rate constant versus the reciprocal of the reaction temperature (in Kelvin), can be prepared for each of the catalyst samples. The person skilled in the art is generally familiar with the creation of an Arrhenius plot.

The Arrhenius plot provides a straight line with different parameters (slope and intercept) for each of the catalyst samples. With the help of the respective straight-line equation, the associated reaction rate constant for a given ethane conversion and the corresponding

Reaction temperature are determined. The corresponding reaction temperature, which was determined for an ethane conversion of 10%, is given in Table 5 in the line “Light-off temperature [° C.] (calculated)=temperature for 10% ethane conversion”. Based on the observed trends in terms of the activities and the light-off temperatures of the catalysts G, D and H as a function of the calcination temperature (cf. Figure 2 and Table 5), it is therefore reasonable to assume that the activity of the catalysts with a lower calcination temperature is at least within certain limits can be further increased as long as the temperature and duration of the calcination - i.e. the calcination intensity - is sufficient for a solid or crystal phase which is sufficiently stable for the catalysis to form. In fact, a further, significant increase in activity and thus also a further, significant shift in the light-off temperature to lower values was observed for a catalyst which had been calcined at 400°C (batchwise) instead of at 650°C ("catalyst I", see Table 6).

This catalyst was tested in test facility 2 using the test parameters specified above for test facility 2. For comparison, catalyst F (cf. Table 4) was also tested in this experimental plant 2 under the same conditions. The test results are shown in Table 6.

Table 6

A significantly higher activity of catalyst I compared to catalyst F (see also Table 4) is proven from the direct experimental comparison in test facility 2 (see Table 6): Catalyst F has an ethane conversion of approx. 67% at a salt bath temperature of 322° C on. Catalyst I, on the other hand, only requires a salt bath temperature of 302° C. for a conversion of 64% and at this temperature still has a significantly higher conversion than catalyst F at a higher temperature of 310° C. (ethane conversion of catalyst F of 53%).

In order to estimate the light-off temperature of catalyst I under the technically much more relevant conditions of test facility 1, the procedure was as follows: Using the ethane conversion determined at the salt bath temperature given in Table 6 and the other test conditions given, a reaction rate constant corresponding to this temperature was calculated. The procedure for this is generally known to the person skilled in the art.

This reaction rate constant served as a starting point for determining a corresponding Arrhenius line. Since only one measuring point was available for catalyst I, the same slope of the Arrhenius straight line was used as for the test conditions from test facility 1 (compare the results from Figure 2 and Table 5) was determined. With the help of these Arrhenius straight lines determined for catalyst I, taking into account the from this procedure resulting inaccuracy, a range for the light-off temperature of catalyst I of approx. Despite the relatively high degree of uncertainty regarding the light-off temperature for catalyst I under the technically relevant conditions, it can be seen that the range of the light-off temperature for catalyst I is well below the light-off temperature for catalyst G (cf. Table 5), catalyst I also shows accordingly the highest activity among the tested catalysts. Thus, the following activity series can be determined (in decreasing order): Catalyst I > Catalyst G > Catalyst D > Catalyst H.

Example 2c - Conversion-Selectivity Behavior

Surprisingly, however, it is found that catalysts of a basic recipe have almost the same conversion-selectivity behavior regardless of the chosen calcination process technology or calcination intensity (cf. Table 7).

Table 7

This is confirmed both for catalyst samples that come from one and the same autoclave synthesis batch (catalyst D and G) as well as from different autoclave synthesis batches (catalyst C). Thus, in a reactor or a reaction zone of a reactor or a respective reactor tube a tube bundle reactor, catalysts with a specific activity are used in a targeted manner, for example to achieve optimal activity of the catalyst bed and thus optimal balance between heat production by reaction and heat dissipation within a reactor or within a reaction zone of a reactor or reactor tube and thus to increase the productivity of a commercial reactor maximize or to use the reactor optimally.

Table 7 also underscores the above observations on the activity as a function of the different calcination intensity. According to what is described above, the grading of the calcination intensity in Table 7 is in descending order (from the highest to the lowest calcination intensity): calcination intensity catalyst C > calcination intensity catalyst D > calcination intensity catalyst G. Correspondingly, the activity increases in the reverse order, i.e.: activity catalyst C<activity of catalyst D<activity of catalyst G. This can be seen by comparing the conversions at the corresponding reaction temperatures: For a similar ethane conversion of approx. 34 to 35%, a reaction temperature which is 5 K higher than that for catalyst D is required for catalyst C. Catalyst G, in turn, is more active than catalyst D, because for an ethane conversion of approx. 40%, a reaction temperature that is 5 K lower than catalyst D is required for catalyst G. The above-mentioned independence of the selectivity from the calcination intensity for catalysts of the same basic recipe is confirmed by almost the same selectivity values with comparable conversion levels of approx. 34 to 35% for catalysts C and D and approx. 40% for catalysts D and G. It should be mentioned here that deviations in the selectivities of up to 0.3 percentage points are not to be regarded as significantly different (error analysis based on 10 independent repeated measurements on catalyst G).

Example 3 - plant and reactor

In FIG. 2, a plant for the production of olefins according to one embodiment of the invention is illustrated in the form of a greatly simplified plant diagram and is denoted overall by 1. The plant 1 is indicated only schematically. In particular, the basic arrangement of the catalytic zones in a tube bundle reactor 100 is shown. Although a system 1 for ODHE is described below, the present invention is also suitable, as mentioned, for Use in the ODH of higher hydrocarbons. In this case, the following explanations apply accordingly.

As mentioned, the plant 1 has a tube bundle reactor 100 to which, in the example shown, an ethane-containing feed mixture A obtained in any desired manner is fed. The starting mixture A can contain, for example, hydrocarbons taken from a rectification unit (not shown). The feed mixture A can also be preheated, for example, and processed in some other way. The feed mixture A can already contain oxygen and, if appropriate, a reaction moderator such as steam, but corresponding media can also be added upstream or in the tube bundle reactor 100, as not shown separately. A product mixture B is removed from the tube bundle reactor 100 .

The tube bundle reactor 100, which is shown in detail in FIG. 3, has a multiplicity of reaction tubes 10 arranged in parallel (only partially designated), which run through several reaction zones 110, 120, 130, three in the example shown. A preheating zone 140 and a post-reaction zone 150 may be present upstream and downstream, respectively. The reaction tubes 10 are surrounded by a jacket area 20 through which a coolant C of the type explained is guided in the example. The representation is greatly simplified because, as mentioned, the reaction tubes 10 can optionally be cooled using a plurality of cooling media flowing around the reaction tubes 10 or different tube sections using different cooling media, the same cooling medium in different cooling medium circuits, and/or the same or different cooling media in same or different directions of flow can be cooled.

After being fed into the tube bundle reactor, the starting mixture A is distributed over the reaction tubes 10 in a suitable manner at a temperature in a first temperature range. The reaction tubes each have catalytic zones 11, 12 and 13, which are located in the reaction zones 110, 120 and 130.

A catalytic reaction takes place by means of the catalytic zones 11, 12 and 13 arranged one behind the other in the reaction tubes 10 with different activities, and in the catalytic zones 11, 12 and 13 one or more catalytically active materials and one or more catalytically inactive materials are provided. As explained, the different activity of the catalytic zones 11, 12 and 13 is effected by providing the one or more catalytically active materials with identical elemental composition and different activity.

Figure 4 illustrates the production of a catalytically active material according to one embodiment of the present invention in a simplified schematic representation or in the form of a schematic flowchart of a corresponding method 400.

The method here includes in particular production steps 410, 420 and 430 previously referred to as “first production steps”, a subsequent calcination 440, and one or more subsequent production steps 450, previously referred to as “second production steps”. Production step 410 represents in particular a suitable pretreatment of the starting materials used, which is followed by step 420 of a synthesis, for example an autoclave synthesis with crystallization (and optionally filtration). In particular, step 430 can include drying. Step 450 includes in particular shaping, including burning out the wax if necessary, as already explained above.

The term "recipe" used, for example, in WO 2019/243480 A1 has already been defined above and includes in particular steps 410 to 440.

In this case, these steps 410 to 440 up to and including the calcination 440 are therefore carried out identically or essentially identically. A catalytically active material is created with exactly one defined element composition, exactly one set of physicochemical properties (e.g. BET surface area and/or nitrogen pore volume) and therefore a specific activity. The process chain up to and including calcination 440 is therefore mainly the activity-determining factor for the finished shaped catalyst body (with the same proportion of binder).

The term “basic recipe” also defined above includes identical or essentially identical steps 410 to 430 up to and including drying, but not necessarily an identical or essentially identical calcination 440. In this way, a precursor or basic material with a precisely defined element composition. However, this material still has to be activated in the sense of calcination under nitrogen at temperatures of at least 400° C. so that the material is converted into the final catalytically active form. Different calcination intensities can be used here.

An activity setting for the respective catalyst layers carried out in embodiments of the present invention can be influenced by a targeted choice of the calcination conditions or, more precisely, the calcination intensity. Although the catalytically active materials formed can have the same chemical or elemental composition (“chemically identical”), they differ in terms of their physicochemical properties, namely at least in the form of the BET surface area and/or the nitrogen pore volume. The calcination intensity therefore determines the physicochemical properties or the materials differ with regard to these properties.

In step 450, an activity gradation can be made by adding different proportions of binder during shaping. The various catalytic layers are then distinguished by different proportions of binder. Thus, in absolute terms, the elemental composition is different for each catalytic layer (although the relative amounts of the catalytically active metals to one another do not change, since they are the same for all layers).

Claims

patent claims

1. A method for preparing a target compound, in which a

Ethane-containing feed mixture (A) is distributed over a large number of parallel reaction tubes (10) of a tube bundle reactor (100) and is subjected to an oxidative catalytic conversion of the ethane in the reaction tubes (10), the catalytic conversion being carried out by means of reaction tubes (10) arranged one behind the other Catalytic zones (11, 12, 13) is carried out with different activities, and in the catalytic zones (11, 12, 13) one or more catalytically active materials and one or more catalytically inactive materials are provided, characterized in that the different activity of the Catalytic zones (11, 12,

13) is effected by providing the one or more catalytically active materials with identical or substantially identical basic formulation, wherein the one or more catalytically active materials is or are prepared using different calcination intensities.

2. The method of claim 1, wherein the plurality of catalytic materials exhibit substantially equal conversion-selectivity behavior.

3. The method according to claim 1 or 2, wherein a proportion of the one or more catalytically inactive materials in the respective catalytic zones (11,

12, 13) at a total filling of the respective catalytic zones (11, 12, 13) differs by no more than 25% relative to each other.

4. The method according to any one of the preceding claims, wherein the one or at least one of the plurality of catalytically active materials contains at least the metals molybdenum, vanadium, niobium and optionally tellurium.

5. The method of claim 4, wherein the one or at least one of the plurality of catalytically active materials is at least partially made of the oxides of the metals.

6. The method according to any one of the preceding claims, wherein a pore volume and / or a BET surface area in at least two of the Catalytic zones differ from each other by 15 to 60% and in particular the pore volume is used as a measure of the catalyst activity.

7. The method according to any one of the preceding claims, in which the oxidative reaction is carried out at a temperature of the catalyst in a range between 240 and 500 ° C, preferably between 280 and 450 ° C, in particular between 300 and 400 ° C, and / or in which the starting mixture is fed to the reactor (100) at a pressure in a pressure range from 1 to 10 bar (absolute), in particular from 2 to 6 bar (absolute).

8. The process as claimed in any of the preceding claims, in which the starting mixture contains a water content which is adjusted to between 5 and 95% by volume, in particular 10 and 50% by volume, in particular 14 and 35% by volume.

9. The process of claim 8 wherein the molar ratio of water to ethane in the feed mixture is at least 0.23.

10. The method according to any one of the preceding claims, in which the reaction tubes are cooled using one or more cooling media flowing around the reaction tubes (10).

11. The method according to claim 10, in which tube sections of the reaction tubes (10) are cooled using different cooling media, the same cooling medium in different cooling medium circuits, and/or the same or different cooling media in different or the same flow directions.

12. Plant for the production of a target compound with a tube bundle reactor (10) which has a multiplicity of reaction tubes (10) arranged in parallel, the plant having means which are set up to direct an ethane-containing feed mixture (A) towards the reaction tubes (10). distributed and subjecting them to an oxidative catalytic reaction in the reaction tubes, with catalysis zones (11, 12, 13) arranged one behind the other in the reaction tubes (10) being provided with different activities, and with the catalysis zones (11, 12, 13 ) each one or several catalytically active materials and one or more catalytically inactive materials are provided, characterized in that the different activity of the catalytic zones (11, 12, 13) is brought about by providing the one or more catalytically active materials with an identical or essentially identical basic recipe wherein the one or more catalytically active materials is or are prepared using different calcination intensities.