DE102013000648A1 - Providing reactor system for preparing phthalic anhydride, involves performing gas phase oxidation of aromatic hydrocarbons at catalyst, and providing a tube bundle reactor with a number of tubes having diameter, tube length and tube wall - Google Patents

Abstract

Providing a reactor system for preparing phthalic anhydride, comprises: performing a gas phase oxidation of aromatic hydrocarbons at at least one catalyst (A m , n) comprising a catalyst body containing a vanadium-containing active material; providing a tube bundle reactor with a number b of tubes, which have a diameter (D), a tube length (L), and a tube wall; providing a catalyst phase in the tubes of at least one layer (L m); and feeding a reaction gas forming a gas phase through the tubes, where the reaction gas contains at least one reaction component. Providing a reactor system for preparing phthalic anhydride, comprises: performing a gas phase oxidation of aromatic hydrocarbons at at least one catalyst (A m , n) comprising a catalyst body containing a vanadium-containing active material; providing a tube bundle reactor with a number b of tubes, which have a diameter (D), a tube length (L), and a tube wall, which is flowed around by a coolant having an average coolant temperature (T k); providing a catalyst phase in the tubes of at least one layer (L m), where the layer (L m) is provided by the catalyst (A m , n), where m is an integer of 1 and assumes the maximum number of layer, n is an index of 1-n that identifies a specific catalyst, and an active mass loading (M m, n) is provided in the layer (L m) of the catalyst (A m , n); feeding a reaction gas forming a gas phase through the tubes, where the reaction gas contains at least one reaction component; providing a model for the tube bundle reactor for the gas phase and the catalyst phase in the tubes of the tube bundle reactor; describing a heat balance and a material balance for each of the gas phase and the catalyst phase, a mass transfer in a catalyst body, and reaction kinetics for the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons; determining operating conditions of the tube bundle reactor in which at least one certain flow of the reaction gas per tube, a predetermined concentration of the reaction component in the reaction gas and a certain average coolant temperature (T k) of the refrigerant are adjusted; determining a performance feature, which accepts values (W n); determining a difference (delta ) with the model in which (a) an intrinsic difference (delta G) of a value is assigned, (b) a first active material loading (M m, 1) in the layer (L m) with a first catalyst (A m, 1) is provided and a first value (W 1) of the performance feature is determined under the operating conditions of the tube bundle reactor, (c) the active mass loading of the layer (L m) is changed in which a second active mass loading (M m, 2) is provided by a second catalyst (A m, 2), (d) a second value (W 2) of the performance feature is determined with the model for the second catalyst (A m, 2) under the operating conditions of the tube bundle reactor, and (e) the first and second values are compared and the difference (delta ) is determined, where the steps (B)-(E) are repeated with the catalysts (A m , n) until the difference (delta ) of amount below the marginal difference (delta G); providing a catalyst (A m, g) value determined from the intrinsic difference (delta G); and providing the layer (L m) of the catalyst phase formed from the catalyst (A m, g) in the tubes of the reactor.

Description

The invention relates to a process for providing a reactor system for the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons on at least one catalyst of a vanadium-containing active material.

The large-scale production of phthalic anhydride is carried out by catalytic gas phase oxidation of o-xylene and / or naphthalene. For this purpose, a catalyst suitable for the reaction, generally a vanadium-containing contact, is provided in a reactor and a reaction gas passed over the catalyst. Preference is given to using, as reactors, so-called tube bundle reactors, in which a multiplicity of tubes is arranged in parallel, around which a coolant flows. The coolant used is generally a molten salt, for example a eutectic mixture of NaNO ₂ and KNO ₃ .

The catalyst is introduced into the tubes in the form of catalyst bodies. In the simplest case, use a homogeneous bed. About the bed then a reaction gas is passed, which contains a mixture of an oxygen-containing gas, usually air, and the hydrocarbon to be oxidized, usually o-xylene or naphthalene.

The oxidation of the hydrocarbon is highly exothermic, so that a strong heat development can be observed especially in the area of the reactor inlet. In order to achieve a high productivity of the reactor, it has begun to use structured catalyst beds, wherein in the tubes layers of catalysts of different activity are arranged one above the other.

Currently, three-layer catalyst beds are generally used, with a relatively low activity catalyst layer on the side of the reactor inlet, followed by catalyst layers of progressively increased activity. The catalyst layer with the highest activity is thus arranged on the side of the reactor outlet. Such systems are for example from the EP 1 082 317 B1 , of the EP 1 084 115 B1 or the WO 2004/103944 (A1) known.

Recently, it has begun to use catalyst systems with four or more layers, with a relatively thin layer of a catalyst of higher activity is initially arranged at the reactor inlet side. This higher activity site is followed by a lower activity, followed by further layers where the catalyst activity increases again. Such catalyst systems are for example in the WO 2007/134849 A1 or the WO 2011/032658 known.

In the oxidation of o-xylene or naphthalene in addition to the desired product phthalic anhydride still a number of undesirable by-products, such as carbon monoxide, carbon dioxide, benzoic acid, maleic anhydride or Citraconsäureanhydrid. Furthermore, the desired product may still be contaminated by compounds that result from incomplete reaction of the starting materials. Examples of such intermediates are o-tolualdehyde and phthalide. Desired is the highest possible selectivity of the oxidation to phthalic anhydride with the lowest possible levels of by-products or intermediates in the final product at the same time high conversion of the starting product.

At present, molar selectivities of phthalic anhydride of up to 81 mole% are achieved. In order to further increase the selectivity of the oxidation of o-xylene or naphthalene to phthalic anhydride, various parameters of the catalyst system can be varied. Thus, the composition of the catalyst can be varied or the properties of the bed of the catalyst. For this purpose, for example, the arrangement and length of the individual catalyst layers can be varied.

An empirical improvement of the catalyst or the catalyst bed, however, is associated with a very high experimental effort. This is especially true for multi-layer systems, in which the individual layers of the system must be optimized and matched. Here, even with a lot of time, only a very rough picture of the influence of the individual parameters on the entire system can be obtained.

The invention therefore an object of the invention to provide a method for providing a reactor system for the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons on at least one vanadium-containing active material, which is easy to perform and allows rapid optimization of such a reactor system.

This object is achieved by a method having the features of patent claim 1. Advantageous embodiments of the method are the subject of the dependent claims.

In the method according to the invention, a model is used which is based on a heat balance of the catalyst and the gas phase, a respectively prepared for the gas phase and the catalyst phase material balance and taking into account the mass transport in the catalyst body and a reaction kinetics for the production of phthalic anhydride by gas phase oxidation aromatic Hydrocarbons a statement about the influence of the change of the active mass loading M _{m, n} a layer L _{m of} the catalyst phase or of a catalyst A _{m, n} in the position L _m provided active mass loading M _{m, n} on a performance parameter, such as the selectivity of Reaction with respect to phthalic anhydride. With the model, the active mass loading M _{m, n of} a catalyst layer L _m , systematically varied and the influence on the one performance parameters are systematically recorded. In this way, the active mass loading M _{m, n of} a layer L _{m of} the catalyst phase or the active mass loading M _{m, n} provided by the catalyst A _{m, n} in the position L _m can be optimized for the performance parameter. The catalyst phase determined with the model may then be provided in a reactor, thereby providing an optimized reactor system having, for example, improved selectivity to phthalic anhydride.

• – ein Rohrbündelreaktor bereitgestellt wird,
• – mit einer Anzahl b von Rohren, welche
• – einen Durchmesser D, sowie
• – eine Rohrlänge L aufweisen; wobei die Rohre eine Rohrwand mit einer bestimmten Rohrwanddicke aufweisen, welche von einem Kühlmittel umströmt wird, welches eine mittlere Kühlmitteltemperatur T_K aufweist;
• – in den Rohren eine zumindest eine Lage L_m umfassende Katalysatorphase bereitgestellt wird, wobei die Lage L_m einen Katalysator A_m,n umfasst, wobei m einen ganzzahligen Wert zwischen 1 und der maximalen Anzahl der Lagen annimmt und n ein Index von 1 bis n ist, welcher einen bestimmten Katalysator kennzeichnet, und in der Lage L_m von dem Katalysator A_m,n eine Aktivmassenbeladung M_m,n bereitgestellt wird; und
• – durch die Rohre ein eine Gasphase bildendes Reaktionsgas geleitet wird, welches zumindest eine Reaktionskomponente enthält;
• – ein Modell bereitgestellt wird, welches für den Rohrbündelreaktor für die Gasphase und die Katalysatorphase in den Rohren des Rohrbündelreaktors
• – eine Wärmebilanz und
• – jeweils für die Gasphase und die Katalysatorphase eine Stoffbilanz, sowie
• – einen Stofftransport im Katalysatorkörper, und
• – eine Reaktionskinetik für die Herstellung von Phthalsäureanhydrid durch Gasphasenoxidation aromatischer Kohlenwasserstoffe beschreibt;
• – Betriebsbedingungen des Rohrbündelreaktors festgelegt werden, indem zumindest
• – ein bestimmter Durchfluss des Reaktionsgases pro Rohr;
• – eine bestimmte Konzentration der zumindest einen Reaktionskomponente im Reaktionsgas und
• – eine bestimmte mittlere Kühlmitteltemperatur T_k des Kühlmittels eingestellt werden;
• – ein Leistungsmerkmal bestimmt wird, welches Werte W_n annehmen kann;
• – mit dem Modell eine Differenz Δ ermittelt wird, indem
• a) einer Grenzdifferenz Δ_G ein Wert zugewiesen wird;
• b) in der Lage L_m mit einem ersten Katalysator A_m,1 eine erste Aktivmassenbeladung M_m,1 bereitgestellt und unter den Betriebsbedingungen des Rohrbündelreaktors ein erster Wert W₁ des Leistungsmerkmals bestimmt wird;
• c) die Aktivmassenbeladung der Lage L_m verändert wird, indem durch einen zweiten Katalysator A_m,2 eine zweiten Aktivmassenbeladung M_m,2 in der Lage L_m bereitgestellt wird;
• d) mit dem Modell für den zweiten Katalysator A_m,2 unter den Betriebsbedingungen des Rohrbündelreaktors ein zweiter Wert W₂ des Leistungsmerkmals bestimmt wird;
• e) der erste Wert W₁ und der zweite Wert W₂ verglichen und die Differenz Δ ermittelt wird; und die Schritte b bis e mit Katalysatoren A_m,n solange wiederholt werden, bis die Differenz Δ dem Betrag nach die Grenzdifferenz Δ_G unterschreitet;
• – ein aus der Grenzdifferenz Δ_G ermittelter Katalysator A_m,G bereitgestellt wird, und
• – in den Rohren des Reaktors die aus dem Katalysator A_m,G gebildete zumindest eine Lage L_m der Katalysatorphase bereitgestellt wird.

The invention is therefore directed to a process for providing a reactor system for the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons on at least one catalyst A _{m, n} , comprising catalyst bodies containing a vanadium-containing active material, wherein:

• A tube bundle reactor is provided,
• With a number b of tubes, which
• - a diameter D, as well
• - Have a tube length L; wherein the tubes have a tube wall with a certain tube wall thickness, which is surrounded by a coolant, which has an average coolant temperature T _K ;
• - In the tubes at least one layer L _m comprehensive catalyst phase is provided, wherein the layer L _m comprises a catalyst A _{m, n} , where m takes an integer value between 1 and the maximum number of layers and n is an index of 1 to n which identifies a particular catalyst and in the position L _m of the catalyst A _{m, n} an active mass loading M _{m, n is} provided; and
• - Passing through the tubes a gas phase forming reaction gas containing at least one reaction component;
• A model is provided which is suitable for the tube bundle reactor for the gas phase and the catalyst phase in the tubes of the tube bundle reactor
• - a heat balance and
• - in each case for the gas phase and the catalyst phase, a material balance, as well
• A mass transport in the catalyst body, and
• Describes a reaction kinetics for the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons;
• - Operating conditions of the tube bundle reactor are set by at least
• A certain flow of the reaction gas per tube;
• A certain concentration of the at least one reaction component in the reaction gas and
• - Setting a certain average coolant temperature T _{k of} the coolant;
• A feature is determined which can take values W _n ;
• - With the model, a difference Δ is determined by
• a) is an intrinsic difference Δ _G is assigned a value;
• b) in the position L _m with a first catalyst A _{m, 1} a first active mass loading M _{m, 1} provided and under the operating conditions of the tube bundle reactor _, a first value W _{1 of} the feature is determined;
• c) the active mass loading of the layer L _{m is} changed by providing a second active mass loading M _{m, 2} in the layer L _m by a second catalyst A _{m, 2} ;
• d) with the model for the second catalyst A _{m, 2} under the operating conditions of the tube bundle reactor, a second value W _{2 of} the feature is determined;
• e) the first value W ₁ and the second value W _{2 are} compared and the difference Δ is determined; and the steps b to e with catalysts A _{m, n are} repeated until the difference Δ in the amount below the limit difference Δ _G ;
• - a value determined from the intrinsic difference Δ _G Catalyst A _{m, G} is provided, and
• - In the tubes of the reactor from the catalyst A _{m, G} formed at least one layer L _{m of} the catalyst phase is provided.

In the method according to the invention, first a tube bundle reactor is provided. In this case, conventional tube bundle reactors can be used, as they are known for the Phthalsäureanhydridherstellung. Such tube bundle reactors comprise, for example, up to 20,000 tubes which are arranged parallel to one another in a coolant space through which a coolant can flow. It is also possible to carry out the process for a reactor comprising only a single tube. For an industrial application, the number b of tubes is chosen up to 50,000, according to one embodiment up to 15,000. According to one embodiment, the number of tubes is selected greater than 1,000.

The tubes have a diameter D, wherein reference is here made to the inner diameter of the tube. Preferably, the diameter D of the tube is selected in the range of 10 to 50 mm, more preferably 20 to 40 mm. The tubes have a tube length L, which is also selected in the usual ranges. The tube length corresponds to the length of the tube which is filled with the catalyst phase. Portions of the tube which are filled with an inert material for setting the pressure, for preheating the reaction gas or for adjusting the filling level or are empty, are not taken into account in determining the tube length L. If several tubes are arranged in a reactor, the arithmetic mean values of the tube diameter and the tube length are used in each case. The tube length L is preferably selected in the range of 1 to 10 m, more preferably in the range of 2 to 5 m.

In most cases, the parameters number b of tubes, diameter D of the tube and tube length L are given by the already existing reactor which is to be filled with the catalyst A _{m, n} , for example as a replacement for a spent catalyst.

The tubes are arranged at a standard distance from each other in the coolant space. The horizontal distance between two tubes may for example be 1 to 5 cm, according to one embodiment 2 to 4 cm. Conventional internals may be provided in the coolant space, for example baffles, in order to ensure effective mixing of the coolant and thus efficient heat dissipation.

The tubes have a tube wall which separates the catalyst bed or in the sense of the invention the catalyst phase from the coolant surrounding the tubes and via which a heat transfer takes place in order to dissipate the heat produced during the oxidation of the aromatic hydrocarbons. The tubes are made of a conventional material, such as steel, and have a certain pipe wall thickness, which is selected in the range of a conventional wall thickness for such pipes, for example 1 to 5 mm. A heat exchange between the catalyst phase or gas phase arranged in the interior of the tube and the coolant which flows around the tubes is possible via the wall of the tubes. The coolant used are customary coolants, for example a molten salt, such as the eutectic already mentioned in the introduction of NaNO ₂ and KNO ₃ . The coolant has an average coolant temperature T _K. In itself, a spatially resolved temperature profile of the coolant could be used in the method according to the invention. However, this would considerably increase the effort required to carry out the process. As the mean coolant temperature T _K , a temperature is used which is representative of the coolant temperature. It can be determined by averaging from one or more measuring points which are suitably arranged in the coolant space of the reactor. The mean coolant temperature T _k can be determined, for example, by measuring the temperature of the coolant in the coolant supply and in the coolant discharge of the coolant space of the reactor and from this the arithmetic mean is formed. However, it is also possible to provide a plurality of measuring points in the reactor, at which the temperature of the coolant is measured in each case, in order then to form the arithmetic mean from these values, for example.

A catalyst phase is then provided in the tubes. The catalyst phase is formed from at least one layer L _{m of} a catalyst A _{m, n} . The layer L _m has an active mass loading M _{m, n} , which is provided by the catalyst A _{m, n} .

In the simplest case, the catalyst phase is formed from a single layer L _{1 of} the catalyst A _{1, n} .

According to one embodiment, the catalyst phase comprises at least two layers L _m of catalysts A _{m, n} . However, the catalyst phase is preferably formed from a plurality of layers L _m , preferably at least three layers L _m , according to a further embodiment formed from at least four layers L _m . According to one embodiment, the catalyst phase comprises less than 6 layers L _m , according to a further embodiment less than 5 layers L _m .

According to one embodiment, the catalyst phase is formed from exactly three layers L _m , according to a further embodiment of exactly four layers L _m . The index m correspondingly assumes integer values between 1 and the maximum number of layers. If the catalyst phase comprises three layers, the index m can assume the values 1, 2 and 3, where each value designates a position within the catalyst phase. If the catalyst phase comprises four layers, the index m can assume the values 1, 2, 3 and 4 accordingly. Within one layer, the properties of the catalyst A _{m, n are} preferably homogeneous, ie, the catalyst A _{m, n} has, for example, a homogeneous bed and a constant composition, so that the catalyst A _{m, n} within a layer L _m within normal technical fluctuations provides homogeneous activity.

Each layer L _{m, n} is in each case formed from a catalyst A _{m, n} , where m can assume the values defined above and n represents an index which can assume values from 1 to n and in each case denotes a specific catalyst which is capable L _{m is} arranged. An active mass loading M _{m, n is} provided by the catalyst A _{m, n} in the position L _m .

The catalyst A _{m, n} comprises catalyst bodies which contain a vanadium-containing active material. According to one embodiment, the catalyst A _{m, n is formed} by a bed of catalyst bodies. A bed of catalyst bodies, which has a certain extent in the longitudinal direction of the tube within the tube, forms a layer L _m in the sense of the invention. At least one layer L _m , according to one embodiment several layers L _m , then form a catalyst phase in the sense of the invention.

If the catalyst phase comprises several layers L _m , the layers L _m differ by their active mass loading M _{m, n} , which is provided by the catalysts A _{m, n} .

Active mass loading M _{m, n of} the layer L _m is understood as meaning the amount of active mass provided by the catalyst A _{m, n} within the layer L _m .

The active mass loading M _{m, n of} the layer L _m can be modified by changing the amount of active mass provided by a catalyst A _{m, n} . This can be achieved, for example, by diluting the catalyst with various amounts of inert material.

The activity of the catalyst A _{m, n} is understood to mean the ability of the catalyst A _{m, n} , within a defined volume (= balance space), for example of a reaction tube of defined length and inside diameter (eg 25 mm internal diameter, 1 m length) given reaction conditions (temperature, pressure, concentration, residence time) react an educt. A catalyst accordingly has a higher activity than another catalyst if it achieves a higher educt conversion in this given volume and under the same reaction conditions. In the case of o-xylene or naphthalene as starting material, the catalyst activity is thus measured on the basis of the amount of conversion of o-xylene or naphthalene to the oxidation products.

The layers L _m can, measured in the longitudinal direction, ie in the flow direction of the gas phase, have the same or a different length.

The length of a particular catalyst layer L _m is constant according to one embodiment of the method and is therefore not changed in carrying out the method according to the invention.

According to one embodiment, the catalyst phase has at least two layers L _m , according to one embodiment at least three layers L _m and according to a further embodiment at least four layers L _m . The active mass loading M _{m, n of} the individual layers L _m or the charge M _{m, n} of active mass provided by the catalyst A _{m, n} is determined by the method according to the invention.

In itself, a bed of catalyst would be possible in which the activity of the catalyst phase changes continuously in the longitudinal direction along the reactor axis.

Through the tubes, a gas phase forming reaction gas is then passed, which contains at least one reaction component. A reaction component is first understood to mean any compound which occurs during the oxidation of the hydrocarbon, for example o-xylene or naphthalene, ie arises or is consumed.

The reaction component may be a starting product, for example, o-xylene or naphthalene or oxygen, an intermediate, a by-product or a final product.

An intermediate is understood as meaning a compound which is formed from the starting product or a further intermediate and is converted into the end product as a result of the reaction, if appropriate via further intermediates. An intermediate is, for example, o-tolualdehyde or phthalide.

A by-product is understood as meaning a compound which is formed from the starting product or an intermediate, but which is not converted into an end product as a consequence of the further reaction, if appropriate via further intermediates or by-products. By-products usually contain fewer carbon atoms than the final product. Exemplary by-products are maleic anhydride, carbon dioxide or carbon monoxide.

The final product corresponds to phthalic anhydride.

• – eine Wärmebilanz und
• – jeweils für die Gasphase und die Katalysatorphase eine Stoffbilanz, sowie
• – einen Stofftransport im Katalysatorkörper und
• – eine Reaktionskinetik für die Herstellung von Phthalsäureanhydrid durch Gasphasenoxidation aromatischer Kohlenwasserstoffe beschreibt.

Furthermore, a model is provided which is suitable for the tube bundle reactor for the gas phase and the catalyst phase in the tubes of the tube bundle reactor

• - a heat balance and
• - in each case for the gas phase and the catalyst phase, a material balance, as well
• - a mass transport in the catalyst body and
• - describes a reaction kinetics for the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons.

The model can be set up by means of measurements carried out on a reference reactor and ultimately replaces measurements on a reactor system different from the reference reactor. Thus, the model replaces a spatially resolved measurement of temperature and composition of matter on a reactor system other than the reference reactor. This is made possible according to the invention since, in addition to the heat and material balance, the mass transfer in the catalyst body and the reaction kinetics are taken into account.

In the reference reactor, spatially resolved temperatures and concentrations of reaction components are measured. The measured temperatures enable the preparation of a heat balance for the specific state of the reference reactor. The measured concentrations allow the preparation of the material balance for this state as well as the reaction kinetics for this state. The parameters of the reaction kinetics are included in the heat balance as well as in the material balance.

In this case, according to one embodiment, only the concentration of reaction components which arise from the aromatic hydrocarbon, but not the concentration of oxygen, is taken into account for the model. According to a further embodiment, in addition to the concentration of the reaction components involved in the reaction, only the aromatic hydrocarbon added to the reaction gas at the reactor inlet, for example o-xylene, is considered for all partial reactions.

Based on the data set of the reference reactor, it is possible with the model to make statements about spatially resolved measurements of the temperature and the concentration of reaction components, ie ultimately to replace these measurements. Moreover, in the case of a reactor that is the same or different from the reference reactor, it is possible to replace the spatially resolved measurement of temperatures and concentrations which are effected under changed operating conditions of the reactor by the model.

Based on the data measured at the reference reactor, the model can therefore be used to refer to states of a reactor system that differ in at least one parameter from the reference reactor. In the process according to the invention, the catalyst parameter to be optimized is the active mass loading M _{m, n} provided by the catalyst A _{m, n} in the position L _m . The change in the active mass loading M _{m, n} causes a change in the conversion of reaction components. This change in sales leads to a change in the material and heat balance. According to the invention was now recognized that by considering the reaction kinetics a significant improvement of the model can be achieved and a much more accurate optimization of the active mass loading M _{m, n is} possible.

The heat balance describes the amount of energy supplied to a balancing room, the amount of energy dissipated from the balancing room and the amount of energy generated or consumed in the balancing room.

The model is determined according to one embodiment by creating it on a reference reactor.

• – ein Referenzreaktor bereitgestellt wird, mit
• – einer Anzahl a von Rohren, welche
• – einen Durchmesser d, sowie
• – eine Rohrlänge l aufweisen; wobei die Rohre eine Rohrwand aufweisen, welche von einem Kühlmittel umströmt wird, welches eine mittlere Kühlmitteltemperatur T_K' aufweist;
• – in den Rohren eine aus zumindest einem Katalysator a_M gebildete Katalysatorphase bereitgestellt wird, welche zumindest eine Lage l_M des Katalysators a_M umfasst, wobei M einen ganzzahligen Wert zwischen 1 und der maximalen Anzahl der Lagen annimmt, wobei der Katalysator a_M Katalysatorkörper umfasst, welche ein vanadiumhaltiges Aktivmaterial enthalten;
• – durch die Rohre ein eine Gasphase bildendes Reaktionsgas geleitet wird, welches zumindest ein Ausgangsprodukt enthält;
• – Betriebsbedingungen des Referenzreaktors festgelegt werden, indem zumindest
• – ein bestimmter Durchfluss des Reaktionsgases pro Rohr;
• – eine Eintrittstemperatur des Reaktionsgases bei Eintritt in das Reaktionsrohr,
• – eine bestimmte Konzentration des zumindest einen Ausgangsprodukts im Reaktionsgas und
• – eine bestimmte mittlere Kühlmitteltemperatur T_K' eingestellt werden;
• – für den Referenzreaktor mit der Katalysatorphase bei den Betriebsbedingungen
• – die Wärmebilanz;
• – die Stoffbilanz für die Gasphase und die Katalysatorphase;
• – der Stofftransport im Katalysatorkörper, und
• – die Reaktionskinetik ermittelt wird, und daraus das Modell erstellt wird.

The model may be provided according to one embodiment by:

• - A reference reactor is provided with
• A number a of pipes, which
• - a diameter d, as well
• - Have a tube length l; wherein the tubes have a tube wall, which is surrounded by a coolant, which has an average coolant temperature T _{K '} ;
• In the tubes, a catalyst _phase formed from at least one catalyst a _{M is} provided which comprises at least one layer l _{M of} the catalyst a _M , where M assumes an integer value between 1 and the maximum number of layers, the catalyst comprising a _M catalyst body containing a vanadium-containing active material;
• - Passing through the tubes a gas phase forming reaction gas containing at least one starting material;
• - Operating conditions of the reference reactor are set by at least
• A certain flow of the reaction gas per tube;
• An inlet temperature of the reaction gas when entering the reaction tube,
• A certain concentration of the at least one starting product in the reaction gas and
• A certain mean coolant temperature T _{K 'is} set;
• For the reference reactor with the catalyst phase at the operating conditions
• - the heat balance;
• - the material balance for the gas phase and the catalyst phase;
• - The mass transport in the catalyst body, and
• - The reaction kinetics is determined, and from the model is created.

The reference reactor may have a different configuration than the reactor system, which is filled or provided by means of the method according to the invention.

For example, the reference reactor may comprise only a single tube (a = 1).

The tubes of the reference reactor have a diameter d and a length l. The diameter d corresponds to the inner diameter of the tube and the length l to the portion of the tube which is filled with the catalyst phase. The diameter d may be equal to or different from the diameter D and the length l may be equal to or different from the length L. Preferably, d and l are chosen within the ranges given for D and L. Thus, according to one embodiment, d is selected in the range of 10 to 50 mm, in another embodiment in the range of 20 to 40 mm. The length l is selected according to an embodiment in the range of 1 to 10 m, according to another embodiment in the range of 2 to 5 m. The tubes are constructed from conventional materials and have a conventional wall thickness, as has already been explained for the reactor system to be provided by the method according to the invention.

The reference reactor may have one or more sampling points located along the longitudinal direction of the tube. With the help of the sampling points, the composition of the reaction gas and from it the reaction kinetics can be determined.

The tube or the tubes of the reference reactor are flowed around by a coolant, which has an average coolant temperature T _{K '} . The mean coolant temperature T _{K '} may be the same or different than the average coolant temperature T _K selected. It is preferably selected within the ranges specified for the average coolant temperature T _K and is determined analogously to the manner described in the determination of the mean coolant temperature T _K.

In the tubes or in the tube of the reference reactor, a catalyst _phase formed from the at least one catalyst a _{M is} provided which comprises at least one layer l _{M of} the catalyst a _M , where M assumes an integer value between 1 and the maximum number of layers.

The catalyst a _M has a known composition. The catalyst a _M may be the same or different than the catalyst Am. The catalyst is chosen similarly to the catalyst A _{m, n} , so is also a vanadium-containing catalyst for the gas phase oxidation of aromatic hydrocarbons for the production of phthalic anhydride. Similarly, the catalyst a _M in the process according to the invention could also be used as catalyst A _{m, n} .

The catalyst a _M comprises catalyst bodies containing a vanadium-containing active material. The catalyst bodies and the vanadium-containing active material may be the same or different from the catalyst bodies and the active material present in the reactor system provided by the process of the present invention.

If the catalyst phase comprises several layers 1 _M , a model is set up separately for each layer. When measuring the parameters for setting up the model, however, it is preferable to use a catalyst phase comprising all the layers. The composition of the reaction gas at the beginning or at the end of the layer, the temperature, etc. can be determined by sampling at appropriately arranged sampling points or by temperature measurement at the reference reactor.

Through the tubes or the tube of the reference reactor, a reaction gas is then passed, which contains at least one starting product. Preferably, the reaction gas contains o-xylene or naphthalene or a mixture of these compounds and an oxygen-containing gas, for example air. As such, the composition of the reaction gas used in the reference reactor essentially corresponds to the composition of the reaction gas as used in the reactor system. The concentration of o-xylene or naphthalene or the mixture of the two compounds is preferably selected in the range of 0.01 to 4 vol .-%.

Operating conditions of the reference reactor are then determined by setting a specific flow rate of the reaction gas per tube, a certain concentration of the starting components in the reaction gas, a specific mean coolant temperature T _{K '} and a certain inlet temperature of the reaction gas entering the reaction tube.

The operating conditions are chosen to be similar to the operating conditions used after providing the model for carrying out the method of the invention for providing the reactor system. The operating conditions of the reference reactor are preferably selected such that a statement about the values determined using the reactor system provided according to the invention is possible from the values determined using the reference reactor.

Preferably, in the reference reactor, the flow rate of the reaction gas per tube is in the range of 0.1 to 10 Nm ³ / h, the inlet temperature in the range of 150 to 400 ° C, the concentration of the starting product, preferably of the aromatic hydrocarbon, in the range of 0.1 to 4% by volume and the average coolant temperature T _{K '} in the range of 300 to 500 ° C set.

Then, if necessary after a start-up phase for setting a stationary state, parameters for setting up the model are measured at the reference reactor. The parameters are preferably selected from a spatially resolved concentration of the reaction components and a spatially resolved temperature profile. Preferably, said parameter set is determined in its entirety.

Based on the parameters measured at the reference reactor, the model is then created by conventional methods, for example numerical methods.

In the model used in the process according to the invention, in addition to the heat balance and mass balance usually considered, the mass transport in the catalyst body and the reaction kinetics for the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons are also taken into account.

Surprisingly, it has been found that by taking into account the mass transport in the catalyst body and the reaction kinetics for the production of phthalic anhydride by gas phase oxidation aromatic hydrocarbons can be made much better statement on the effect of changes of catalyst parameters on a performance feature in the preparation of the model.

The significance of the model and thus the performance of the method according to the invention can be further improved by further differentiation in the preparation of the heat balance and the material balance. In the preferred embodiments of the method according to the invention described below, corresponding features are also taken into account in the reference reactor and the installation of the model.

According to a preferred embodiment, the heat balance comprises a heat balance for the catalyst phase and a heat balance for the gas phase.

The heat balance for the catalyst phase may in turn comprise a heat balance for the at least one layer L _{m of} the catalyst A _{m, n} , the heat balance of the catalyst phase being formed from the entirety of the heat balances of the individual layers L _m .

The heat balance for the at least one layer L _{m of} the catalyst A _{m, n} comprehensive catalyst phase comprises according to a preferred embodiment, at least one heat conduction in the catalyst body and a heat production by at least one reaction.

The heat conduction in the catalyst body is described by the thermal coefficient λ. The radial heat conduction λ _s in the catalyst body preferably enters into the heat balance. A radial heat conduction is understood to mean the heat conduction in the direction from the center of a catalyst body to the periphery of the catalyst body.

Gleichung 1 wobei bedeutet: r_p radiale Variable im Katalysatorkörper (m) λ_s Wärmeleitfähigkeit im Katalysatorkörper (W/mK) ΔH_R Reaktionsenthalpie (J/mol) ν stöchiometrischer Koeffizient (–) r Reaktionsrate ((mol/sg_cat) ρ_cat Dichte des Katalysators (kg/m³) i ein Index welcher eine bestimmte Reaktionskomponente bezeichnet (–) j ein Index, welcher eine bestimmte Reaktion bezeichnet (–) T eine Temperatur (K) The heat conduction in the catalyst body can be described by:

Equation 1 where: r _p radial variable in the catalyst body (m) λ _s Thermal conductivity in the catalyst body (W / mK) ΔH _R Reaction enthalpy (J / mol) ν stoichiometric coefficient (-) r Reaction rate ((mol / sg _cat ) _cat Density of the catalyst (kg / m ³ ) i an index which denotes a specific reaction component (-) j an index which denotes a specific reaction (-) T a temperature (K)

The first term describes the heat conduction in the radial direction within a catalyst body, ie from the center of the catalyst body in the direction of the periphery of the catalyst body. The second term describes the heat production by a reaction j.

The heat balance of the gas phase preferably comprises a radial heat transfer in the tube and the heat transfer between the gas phase and the catalyst phase.

A radial heat transport in the pipe is understood as meaning a heat conduction in the pipe from the location of the longitudinal axis of the pipe in the direction perpendicular to the wall.

The catalyst A _{m, n} or the catalyst body A _{m, n} forming catalyst body has a first interface to the gas phase, wherein at the first interface, a first heat transfer between the gas phase and catalyst A _{m, n} is carried out, which preferably in the heat balance of the gas phase received.

The amount of heat supplied to a balance space is, according to a preferred embodiment, composed of a heat fraction fed with the flow of the reaction gas and a heat fraction supplied via the pipe wall.

The amount of heat removed from a balance chamber is preferably composed of a heat component removed with the flow of the gas phase and a heat component removed via the pipe wall.

Gleichung 2 wobei der erste Term den axialen Wärmetransport im Rohr, der zweite Term den radialen Wärmetransport im Rohr beschreibt und der dritte Term den Wärmeübergang zwischen Katalysator A_m,n und Gasphase.The heat balance for the gas phase can be described by:

Equation 2 wherein the first term describes the axial heat transfer in the pipe, the second term the radial heat transfer in the pipe, and the third term the heat transfer between catalyst A _{m, n} and gas phase.

Where: u _z the axial velocity (m / s) c _p the heat capacity of the gaseous phase (J / kgK) ρ _f the density of the gaseous phase (kg / m ³ ) T _f Temperature of the gaseous phase (K) T _s Temperature of the solid phase (K) z an axial variable (m) λ _{r, f} the radial thermal conductivity in the gaseous phase (m ² / s) h _f a coefficient for the heat transfer between gaseous and solid phase (W / m ² K) a _v the first interface (m ² / m ³ ) provided in a volume element r a radial variable (m)

The material balance for a specific reaction component i comprises the quantity of the reaction component i supplied to the balance space, the quantity of reaction component i discharged from the balance space, and the amount of reaction component i converted or formed by reaction in the balance space and the amount of reaction component i remaining in the balance space.

The material balance is set up according to a preferred embodiment in each case for the gas phase and for the catalyst phase.

The material balance can be established for each individual reaction component, in which case the material balance for the gas phase or for the catalyst phase is formed from all or part of the material balances prepared for the reaction components.

The material balance of the gas phase preferably comprises a radial transport of a reaction component i in the tube and the transition of the reaction component from the gas phase into the catalyst phase. Radial transport of a reaction component means a transport of the reaction component perpendicular to the longitudinal axis of the tube.

The mass transfer of the reaction component between the gas phase and the catalyst takes place at the first interface.

Gleichung 3 wobei bedeutet: u_z die axiale Geschwindigkeit (m/s) ε eine Porosität (–) D_r ein radialer Diffusionskoeffizient (m²/s) k_f ein Stoffübergangskoeffizient zwischen gasförmiger und fester Phase Cⁱ die Konzentration eine Komponente i in der gasförmigen Phase (mol/m³) Cⁱ _s eine Konzentration eine Komponente i an der Oberfläche der festen Phase (mol/m³) a_v die in einem Volumenelement bereitgestellte erste Grenzfläche (m²/m³) r eine radiale Variable (m) z eine axiale Variable (m) The material balance of the gas phase can preferably be described by:

Equation 3 where: u _z the axial velocity (m / s) ε a porosity (-) D _r a radial diffusion coefficient (m ² / s) k _f a mass transfer coefficient between gaseous and solid phase C ⁱ the concentration of a component i in the gaseous phase (mol / m ³ ) C ⁱ _s a concentration of a component i on the surface of the solid phase (mol / m ³ ) a _v the first interface (m ² / m ³ ) provided in a volume element r a radial variable (m) z an axial variable (m)

The first term describes the radial diffusion of the reaction component and the second term describes the transition of the reaction component from the gas phase into the catalyst A _{m, n} .

According to a further embodiment, the material balance in the catalyst A _{m, n} comprises the diffusion or mass transport of the at least one reaction component in the catalyst body and the reaction of the reaction component i.

Gleichung 4 The material balance of the reaction component i in the catalyst body can preferably be described by:

Equation 4

The first term describes the diffusion of the reaction component i in the catalyst body and the second term the reaction of the reaction component i.

Where: r _p a radial variable in the catalyst body (m) D _eff ⁱ the effective diffusion coefficient of component i (m ² / s) ΔH _R a reaction enthalpy (J / mol) _i stoichiometric coefficient of component i (-) r _j the reaction rate of the reaction j ((mol / sg _cat ) _cat the density of the catalyst (kg / m ³ ) i an index which denotes a specific reaction component (-) j an index which denotes a specific reaction (-) C _s ⁱ the concentration of component i in the solid phase (mol / m ³ )

wobei die Variablen folgende Bedeutung haben: r_p eine radiale Variable im Katalysatorkörper (m) D_eff ⁱ der effektiver Diffusionskoeffizient der Komponente i (m²/s) r eine radiale Variable (m) z eine axiale Variable (m) r_j die Reaktionsrate der Reaktion j (mol/sg_cat) ρ_f die Dichte der gasförmigen Phase (kg/m³) i ein Index welcher eine bestimmte Reaktionskomponente bezeichnet (–) j ein Index, welcher eine bestimmte Reaktion bezeichnet (–) C_s ⁱ die Konzentration der Komponente i in der festen Phase (mol/m³) C_f ⁱ die Konzentration der Komponente i in der gasförmigen Phase (mol/m³) T₀ die Temperatur des eintretenden Gases (K) T_s die Temperatur der festen Phase (K) T_f die Temperatur der gasförmigen Phase (K) T_in die Temperatur des inerten Trägermaterials (K) T_W die Temperatur der Rohrwand (K) h_f einen Koeffizienten für den Wärmeübergang zwischen gasförmiger und fester Phase (W/m²K) k_f ein Stoffübergangskoeffizient zwischen gasförmiger und fester Phase (m/s) M_z,tot,0 der Massenstrom des eintretenden Gases bezogen auf die Reaktor Querschnittsfläche (kg/sm²) λ_r,f die radiale Wärmeleitfähigkeit in der gasförmigen Phase (W/mK) λ_r,s die radiale Wärmeleitfähigkeit in der festen Phase (W/mK) λ_s die radiale Wärmeleitfähigkeit im Katalysatorkörper (W/mK) α_W,s der Wärmeübergangskoeffizient von der festen Phase zur Wand (W/m²K) α_W,f der Wärmeübergangskoeffizient von der gasförmigen Phase zur Wand (W/m²K) a die in einem Volumenelement bereitgestellte erste Grenzfläche (m²/m³) λ_s die Wärmeleitfähigkeit im Katalysatorformkörper (W/mK) R der Radius des (zylindrischen) Rohrs (m) R_p der Radius des Katalysatorkörpers (m) The boundary conditions are preferably included in the heat balance and the material balance. Where: (Equation 5)

where the variables have the following meaning: r _p a radial variable in the catalyst body (m) D _eff ⁱ the effective diffusion coefficient of component i (m ² / s) r a radial variable (m) z an axial variable (m) r _j the reaction rate of the reaction j (mol / sg _cat ) ρ _f the density of the gaseous phase (kg / m ³ ) i an index which denotes a specific reaction component (-) j an index which denotes a specific reaction (-) C _s ⁱ the concentration of component i in the solid phase (mol / m ³ ) C _f ⁱ the concentration of component i in the gaseous phase (mol / m ³ ) T ₀ the temperature of the incoming gas (K) T _s the temperature of the solid phase (K) T _f the temperature of the gaseous phase (K) T _in the temperature of the inert carrier material (K) T _W the temperature of the pipe wall (K) h _f a coefficient for the heat transfer between gaseous and solid phase (W / m ² K) k _f a mass transfer coefficient between gaseous and solid phase (m / s) M _{z, dead, 0} the mass flow of the incoming gas based on the reactor cross-sectional area (kg / sm ² ) λ _{r, f} the radial thermal conductivity in the gaseous phase (W / mK) λ _{r, s} the radial thermal conductivity in the solid phase (W / mK) λ _s the radial thermal conductivity in the catalyst body (W / mK) α _{W, s} the heat transfer coefficient from the solid phase to the wall (W / m ² K) α _{W, f} the heat transfer coefficient from the gaseous phase to the wall (W / m ² K) a the first interface (m ² / m ³ ) provided in a volume element λ _s the thermal conductivity in the shaped catalyst body (W / mK) R the radius of the (cylindrical) tube (m) R _p the radius of the catalyst body (m)

At the reactor inlet (z = 0) (Equation 5 (a)), the temperature in the gas phase and the catalyst are the same and correspond to an initial temperature T ₀ .

The concentration of a reaction component i in the gas phase (C _f ) at the reactor inlet corresponds to the concentration of the introduced gas C _{f, 0} and the concentration of the component i is constant in the radial direction. The axial velocity u _z is determined from the incoming mass flow and the gas density.

In the middle of the reactor (r = 0) (Equation 5 (b)), both the axial flow rate, and thus the temperature of the gas phase and the solid phase, preferably find a minimum or a maximum.

On the outer tube wall (r = R) (Equation 5 (c)), the heat transfer from the gaseous phase to the tube wall corresponds to the added or removed heat in the gaseous phase, as well as the heat transfer from the solid phase into the tube wall. or removed heat in the solid phase. Preferably, no mass transfer takes place with the pipe wall.

When a shell catalyst is used as the catalyst body, the temperature at the inner periphery of the active layer (r _p = 0) (Equation 5 (d)) of the catalyst body corresponds to the temperature of the inert support material. A Stoffaustauch with the inert carrier material does not take place.

At the outer periphery of the catalyst body (r _p = R _p ) (Equation 5 (e)), the heat transferred from the gas phase or an adjacent catalyst body corresponds to the heat transferred or removed in the catalyst body. The mass flow of a component i transferred from the gas phase corresponds to the mass flow of a component i transported in or removed from the catalyst body.

The active mass loading of the catalyst A _{m, n is} determined by the resulting volume of the active composition, the catalyst geometry and the density of the active composition and the volume and density of the inert core. From this, the active mass loading M _{m, n is derived from} a position L _{m of} the catalyst phase.

During start-up or shutdown of a reactor or in dynamic states, the material balance and the heat balance change over time.

Preferably, however, a state is used for the provision of the reactor system in which the heat balance and the material balance are measured constant over time. This corresponds to a stable operating state of the reactor.

The balance space is formed in each case by a volume element of a certain size. The balance space may, for example, be the entire volume of a catalyst phase arranged in a pipe, the volume of a layer L _m within the catalyst phase, or else a possibly infinitesimal small volume within a layer L _m or within a catalyst body.

The balance space may for example be formed from a volume element which extends over a certain length along the longitudinal axis of the reaction tube and over the entire cross section of the interior of the tube. However, the balance space can also be formed by a hollow cylinder extending in the direction of the longitudinal axis of the reaction tube over the length of the catalyst phase or the length of a layer L _m and in the direction of the cross section of the tube via an annular portion having a certain inner radius and a certain outer radius extends. But it is also possible to provide a balance space with an annular shape which extends in the direction of the longitudinal axis of the tube over a certain length and having a certain inner radius and a certain outer radius. Preferably, a plurality of balancing chambers formed from the volume elements are provided, which preferably adjoin one another, so that the heat balance or the material balance can be established via a layer L _m or the catalyst phase arranged in the tube.

Further, the model comprises a reaction kinetics for the gas phase oxidation of aromatic hydrocarbons to produce phthalic anhydride.

Preferred aromatic hydrocarbons are o-xylene and / or naphthalene.

The reaction kinetics in the simplest embodiment describes the conversion of the aromatic hydrocarbon, preferably o-xylene or naphthalene, into phthalic anhydride.

According to one embodiment, other reaction components which occur during the oxidation of the aromatic hydrocarbon to phthalic anhydride are also taken into account in the reaction kinetics.

During the oxidation of the aromatic hydrocarbon to phthalic anhydride, several intermediates are passed through. Furthermore by-products are formed. In these reactions, at least one further reaction component is formed in each case from a first reaction component. The formation of this at least one further reaction component from the first reaction component can be described by a partial reaction kinetics, wherein the reaction kinetics for the gas phase oxidation of aromatic hydrocarbons for the production of phthalic anhydride is determined from the partial reaction kinetics.

The reaction kinetics preferably describe the reaction rate of the formation of the at least one further reaction component from the first reaction component as a function of the temperature.

It is further preferred that the reaction kinetics be independent of the partial pressure of the oxygen.

• – ein bestimmter Durchfluss des Reaktionsgases pro Rohr;
• – eine bestimmte Konzentration der zumindest einen Reaktionskomponente im Reaktionsgas und
• – eine bestimmte mittlere Kühlmitteltemperatur T_k des Kühlmittels

eingestellt.Furthermore, operating conditions of the tube bundle reactor are determined. At least

• A certain flow of the reaction gas per tube;
• A certain concentration of the at least one reaction component in the reaction gas and
• A certain mean coolant temperature T _{k of} the coolant

set.

According to one embodiment, an inlet temperature of the reaction gas is further defined upon entry into the reaction tube.

Preferably, the inlet temperature is selected in a range of 150 to 250 ° C.

A specific flow rate, a specific concentration and a specific average coolant temperature T _K are understood to mean specific numerical values, so that the operating conditions of the tube bundle reactor are determined.

These parameters are essentially predetermined by the reactor used. For example, the cross section and the length of the tubes affect the flow of the reaction gas. Becomes the coolant used, for example, to generate steam, a certain mean coolant temperature T _{k of} the coolant may be required to produce a certain amount of steam. The concentration of the at least one reaction component in the reaction gas can be predetermined, for example, by explosion limits of the mixture of the reaction components.

The person skilled in the art will therefore suitably select the operating conditions of the tube bundle reactor on the basis of his knowledge.

Preferred ranges for the flow of the reaction gas per tube are, for example, 0.1 to 10 Nm ³ / h, according to one embodiment 2 to 4.5 Nm ³ / h. The unit "Nm ³ " refers to a volume under standard conditions, ie 1013 hPa and 25 ° C. Such a range relates in particular to a pipe diameter of 20 to 30 mm.

The concentration of the at least one reaction component in the reaction gas depends strongly on the considered reaction component. The starting concentration for o-xylene and / or naphthalene is preferably in the range of 0.01 to 4% by volume in an embodiment in the range of 1.5 to 3.5% by volume, according to another embodiment in the range of 2, 0 to 2.5 vol.% Selected.

In addition to the starting component, preferably o-xylene and / or naphthalene, the reaction gas comprises an oxygen-containing gas, preferably air.

The mean coolant temperature T _{k of} the coolant is selected according to an embodiment in the range of 300 to 500 ° C, more preferably in the range of 350 to 450 ° C.

Furthermore, a feature is determined which can take values W _n .

A feature is understood to be a parameter that allows an assessment of the performance of the catalyst phase. The feature can be arbitrarily selected as long as it allows an assessment of the performance of the catalyst phase. The performance feature can be selected so that the highest possible value of high performance corresponds to the catalyst phase. Such a feature is, for example, the concentration of phthalic anhydride in the reaction gas discharged from the reactor. However, the performance feature may also be selected such that the lowest possible value corresponds to a high performance of the catalyst phase. In this case, the performance feature may be, for example, the concentration of a by-product in the reaction gas discharged from the reactor.

The feature can take on values W _n . The value W _n can in each case be assigned to a specific catalyst A _{m, n} .

With the model, a difference Δ is then determined.

To a cutoff difference Δ _G is first assigned a value.

The limit difference Δ _G results from the degree to which the optimization of the feature is performed. Corresponds to the difference in value of the feature which is determined in two steps with the model to the amount according to the limit difference Δ _G or falls below this the amount by which optimization of the performance feature is terminated. Two catalysts A _{m, n} , the performance of which differs in magnitude less than the limit difference Δ _G are considered in the context of the invention in the reaction conditions as equivalent, since it makes no difference in terms of the value of the feature, which catalyst is used.

In the next step, for a first catalyst A _{m, 1} which provides an active mass loading M _{m, 1} in the position L _m , a first value W _{1 of} the feature is determined under the operating conditions of the tube bundle reactor. This can be determined by means of a reactor. However, it is also possible to use the model for this.

Next, the active mass loading of the layer L _{m is} changed, whereby a second catalyst A _{m, 2 is} obtained, which in the position L _m provides an active mass loading M _{m, 2} . With the model is then for the second catalyst A _{m, 2} under the operating conditions of the tube bundle reactor, a second Value W _{2 of} the feature determined. The first value W ₁ and the second value W ₂ are then compared and the difference Δ determined.

Falls below the difference Δ with a value of the boundary difference Δ _G, the active mass loading M _m, the layer L _{m n is} not further modified and a catalyst A _{m, G} determined. This accordingly provides an optimized active mass loading M _{m, G.} The index "G" in each case characterizes the state optimized by the method according to the invention. This active mass loading M _{m, G} corresponds either to the active mass charge M _{m, n} in the position L _m ready from the first or the second catalyst or an active mass charge between the first and the second catalyst. As already explained, are catalysts or catalyst phases, the value of the feature differs by less than the threshold difference Δ _G viewed in the context of the invention in terms of the feature as equivalent.

If the difference Δ in magnitude but greater than the limit difference Δ _G is the active mass loading M _{m, n} further modified so that a third catalyst A _{m, 3} is obtained which provides able L _m is an active mass loading M _{m, n.} Now, a value W _{3 of} the feature and, in turn, a difference Δ to the second value W _{2 is} determined, which is compared with the limit difference Δ _G. This process is continued for as long are found to two catalysts A _{m, n,} which differ in their feature by more than the limit difference Δ _G. On reaching or falling below the limit difference Δ _G to obtain a catalyst A _{m, G,} which is optimized with respect to the provided in a position _m L active mass loading M _{m, G.}

According to one embodiment, in the variation of the active mass loading M _{m, n of} the layer L _m , the active mass loading is initially changed in larger steps and the approximate position of the maximum or the minimum of the active mass loading in relation to the performance feature is determined therefrom. If the amount of the difference Δ is smaller compared to the previous measurement, the maximum or minimum is moved. If the difference Δ increases in comparison to the previous measurement, one moves away from the maximum or minimum.

Within an area around the maximum or the minimum of the performance feature, the steps are then reduced with which the active mass loading M _{m, n of} the position L _m or the active mass loading M _{m, n} provided by the catalyst A _{m, n} is changed, so that finally two catalysts A _{m, n} can be determined, where the value of the performance characteristic is different by less than the limit difference Δ _G.

The catalyst A _{m, G} determined from the limiting difference Δ _G is prepared and filled into the tubes of the reactor in order to provide a layer L _m with optimized active mass loading M _{m, G} and thus to obtain an optimized catalyst phase.

The catalyst A _{m, G} corresponds to the catalyst provided in a layer L _{m of} the catalyst phase, which provides the optimized active mass loading M _{m, G of} the layer L _m .

The performance feature which is used for optimizing the active mass loading M _{m, n of} the layer L _m or the charge of active mass and therefore the catalyst phase provided by the catalyst A _{m, n} can be selected as desired.

• – Selektivität in Bezug auf eine Produktkomponente;
• – Ausbeute einer Produktkomponente;
• – Umsatz einer Reaktionskomponente;
• – Konzentration eines Nebenprodukts im aus dem Reaktor austretenden Produktstrom.

According to one embodiment, the feature is preferably selected from

• Selectivity with respect to a product component;
• - yield of a product component;
• - conversion of a reaction component;
• Concentration of a by-product in the product stream leaving the reactor.

According to a preferred embodiment, the model comprises a momentum balance.

Gleichung 6 wobei bedeutet: P ein Druck (Pa) z eine axiale Variable (m) u_z eine Fließgeschwindigkeit (m/s) d_p die Partikelgröße eines Katalysatorformkörpers (m) η_f eine dynamische Viskosität der Gasphase (Pas) ρ_f die Dichte der gasförmigen Phase (kg/m³) ε eine Porosität (–) Preferably, the momentum balance can be described by:

Equation 6 where: P a pressure (Pa) z an axial variable (m) u _z a flow rate (m / s) d _p the particle size of a shaped catalyst body (m) η _f a dynamic viscosity of the gas phase (Pas) ρ _f the density of the gaseous phase (kg / m ³ ) ε a porosity (-)

According to one embodiment, the catalyst phase comprises at least two layers L _m of catalysts A _{m, n} wherein the active mass loads M _{m, n} provided by the catalysts A _{m, n} in the at least two layers L _m are different.

According to one embodiment, the catalyst phase comprises at least three layers L _m of catalysts A _{m, n} wherein the active mass loads M _{m, n} provided by the catalysts A _{m, n} in the at least three layers L _m are different.

More preferably, the catalyst phase comprises at least four layers L _m of catalysts A _{m, n} wherein the provided by the catalysts A _{m, n} in the at least four layers L _{m active} mass loading M _{m, n is} different.

According to one embodiment, the catalyst phase comprises exactly three layers L _m of catalysts A _{m, n} and, according to yet another embodiment, exactly four layers L _m of catalysts A _{m, n} .

In a catalyst phase with more than two layers, the active mass loading M _{m, n of} all layers L _m can be varied simultaneously or in each case the active mass loading M _{m, n} for only one layer L _m .

In carrying out the method according to the invention, in the case where the catalyst phase comprises more than one layer L _m , preference is given to varying the active mass loading M _{m, n} in only one layer L _m while the other layers remain unchanged. Preferably, therefore, the different layers of the catalyst phase are optimized individually. In this case, it is also possible to proceed in such a way that a certain position L _{m is} optimized several times by the method according to the invention.

According to one embodiment, only the active mass loading M _{m, n of} the individual layers L _{m of} the catalyst phase is varied, while all other catalyst parameters are kept constant. In this embodiment of the method, therefore, the length of the layers of the catalyst phase is kept constant, for example, while the active mass loading M _{m, n of} the catalyst layer L _m and thus the active mass loading provided by the catalyst A _{m, n} is varied.

In one embodiment of the method according to the invention, a catalyst phase comprises more than 2 layers L _m , where m can assume the values 1, 2,... M. The individual layers L _m each contain different catalysts A _{1, n} , A _{1, n} ,..., A _{m, n} . The composition of the active composition of the catalysts A _{1, n} , A _{2, n} ,... A _{m, n} may be the same or different for the different layers L _m . The catalysts A _{1, n} , A _{2, n} ,... A _{m, n} each provide a different active mass loading M _{1, n} , M _{2, n} ,..., M _{m, n} . The catalyst A _{1, n} provides an active mass loading M _{1, n} , the catalyst A _{2, n} an active mass loading M _{2, n} , and the catalyst A _{3, n} an active mass loading M _{3, n} ready.

The index n of the catalyst A _{m, n} would then correspond to different amounts of the catalyst A _{m, n} provided load of active mass or different active mass loading M _{m, n} the situation L _m .

In the situation L ₁ , the catalyst A _1,1 , which is contained in the first layer L _{1 of} the catalyst phase, provides a first active mass loading M _1,1 in the position L ₁ . The catalyst A _1,2 would then provide a second active mass loading M _1,1 in the layer L ₁ built up from the catalyst A _1,2 , etc.

For the second and third layer analogously applies that these are composed of catalysts A _{2, n} or A _{3, n} and the index n each have a certain active mass loading M _{m, n} the position L _m or a certain by the catalyst A _{m , n} provided load with active mass.

The optimized active mass loading M _{m, G of} the individual layers L _{m of} the catalyst phase or the active mass loading M _{m, n} provided by the catalysts A _{m, G} in the individual layers L _m are determined sequentially according to one embodiment.

In this embodiment, therefore, first the active mass loading M _{1, G of} the first layer L _{1 is} determined with the inventive method, wherein the first layer L _{1 is} preferably arranged on the gas inlet side of the tube. This is done using a first performance parameter. This gives a first active mass loading M _{1, G} , which is provided by a catalyst A _{1, G.}

Subsequently, if provided, the active mass loading M _{m, G of} a second layer L _{2 of} the catalyst phase is determined by the method according to the invention, wherein the second layer L _{2 is} preferably arranged downstream of the first layer L ₁ . For this purpose, the same performance parameter can be used as in the determination of the active mass loading M _{1, G of} the first layer L ₁ , or a different performance parameter. This gives the active mass loading M _{2, G} , which is provided by the catalyst A _{2, G} , so that a total of one catalyst phase with the downstream successively arranged layers L ₁ , L ₂ with the catalysts A _{1, G} , A _{2, G is} obtained.

If the catalyst phase comprises further layers, the process according to the invention is carried out again and the active mass loading M _{3, G of} a third layer L ₃ arranged downstream of the second layer is determined, so that a catalyst phase with the layers L ₁ , L ₂ , L ₃ arranged downstream one after the other Catalysts A _{1, G} , A _{2, G} , A _{3, G is} obtained.

To determine the active mass loading M _{3, G of} the third layer L _{3, it is} possible to use a performance parameter which is the same or different from the performance parameters used to determine the active mass loading M _{1, G} or M _{2, G of} the first and second layer L, respectively ₁ , L _{2 were} used.

The determination of the active mass loading M _{m, G} further downstream layers is carried out analogously to the determination of the active mass loading of the first, second and third layer.

In one embodiment of the method, it would therefore be assumed, for example, of a three-layer system in which the catalyst phase thus comprises three catalyst layers L ₁ , L ₂ , and L ₃ . The individual catalyst layers would be formed by catalysts A _{1, n} , A _{2, n} , or A _{3, n} . In the initial state, the catalyst layers have a certain active mass loading M _{m, 1} , so that the catalyst phase comprises catalysts A _1,1 , A _2,1 and A _3,1 .

In the first step, the active mass loading M _{1, G of} the first layer L _{1 is} determined. For this purpose, the layer L _{1 is} provided from the catalyst A _1,1 and the value of a performance parameter W ₁ determined, that is to say, for example, the concentration of o-xylene in the exhaust gas flow, which exits from the first layer of the catalyst phase.

The active mass loading M _{1,1 of} the layer L ₁ is then changed by providing it by a catalyst A _1,2 . The catalyst A _1.2 provides a different active mass loading M _1.2 to the catalyst A _1.1 . This can be achieved when using shell catalysts, for example, by a different layer thickness of the shell. The value of the performance parameter W ₂ is then determined again. This is done in one embodiment using the model.

In the next step, the difference Δ = W ₁ -W ₂ is now determined and compared with the previously defined limit difference Δ _G. This limit difference can be, for example, a concentration difference of phthalic anhydride in the exhaust gas stream of + 0.05%.

If the sign of the difference Δ does not correspond to the sign of the limit difference Δ _G , the active mass loading of the layer L _{1 is changed} in the opposite direction, for example by the active mass loading M _{m, n being} lowered after it has been increased in the previous step. A value W _{3 of} the performance parameter is then determined.

The difference Δ = W ₁ -W ₃ is now determined and compared with the previously defined limit difference Δ _G.

If the amount of the difference Δ is greater than the amount of the limit difference Δ _G , the active mass loading of the catalyst layer is further changed, so that a layer L ₁ with the catalyst A _{1,4 is} obtained, which provides an active mass loading M _1,4 . There is then a performance parameters W ₄ determined W = _3, the difference Δ - W ₄ determined and compared to the amount according to the difference Δ _G boundary. This process is repeated until the difference Δ in magnitude smaller than the limit difference Δ _G.

A catalyst phase is then obtained, in which the active mass loading M _{1, G of} the first layer L _{1 is} determined, which is provided by the catalyst A _{1, G.}

In the next step, the active mass loading M _{2, G of} the second layer L _{2 of} the catalyst phase is determined, which adjoins the first layer L ₁ downstream. For this purpose, a suitable performance parameter is selected, for example the concentration of phthalic anhydride in the exhaust gas stream leaving the reactor. As described in the determination of the active mass loading M _{1, G of} the first layer L _{1 of} the catalyst phase, the active mass loading M _{2, G of} the second layer L _{2 is} determined. The first layer remains unchanged in this embodiment of the method. This gives a catalyst phase which comprises the layers L ₁ and L ₂ with the catalysts A _{1, G} , A _{2, G.}

In the next step, the active mass loading M _{3, G of} the third layer of the catalyst phase is determined. For this purpose, a suitable performance parameter is first selected, for example the concentration of a by-product, such as phthalide, in the exhaust gas stream, which leaves the third layer of the catalyst phase. Further, an intrinsic difference Δ _G is set.

To determine the active mass loading M _{3, G of} the third layer L ₃ is assumed by a catalyst phase with the layers L ₁ , L ₂ , L ₃ with the catalysts A _{1, G} , A _{2, G} , A _3.1 and the corresponding performance parameters W ₁ determined. In the next step, the active mass loading of the layer L ₃ , which is provided by the catalyst A _{3, n} , changed, so that a catalyst phase with the layers L ₁ , L ₂ , L ₃ with the catalysts A _{1, G} , A _{2, G} , A _{3.2 is} obtained, to which in turn the value of the power parameter W _{2 is} determined.

It is then determined, the difference Δ and compared in magnitude with the limit difference Δ _G. The intrinsic difference Δ _G can be the amount by identical or different to the boundary difference Δ _G, which was used in the determination of the active mass loading of the layers L _1, L _2, which are provided by the catalysts A _{1, G,} A _{2, G.}

Analogously to the above-described determination of the catalysts A _{1, G} , A _{2, G} , the catalyst A _{3 , G} is then determined so that a catalyst phase with the layers L ₁ , L ₂ , L ₃ with the catalysts A _{1, G} , A _{2 , G} , A _{3, G is} obtained. This composition of the catalyst phase is then provided as a reactor system for the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons.

If the catalyst phase comprises further layers, for example a fourth layer L ₄ , the active mass loading M _{4, G of} this layer is described as in the determination of the active mass loading of the first, second or third layer.

According to a further embodiment, the at least one catalyst A _{m, n is formed} as a shell catalyst having an inert core and at least one shell surrounding the inert core. The shell contains the active material. By changing the layer thickness, the active mass loading of a layer L _{m can be} changed.

The inert core can in itself have any geometry and, for example, take the form of rings, balls, solid cylinders or hollow cylinders. Rings and hollow cylinders are preferred.

The inert core may consist of conventional materials which are inert under the reaction conditions of phthalic anhydride production. Suitable materials for the inert support are, for example, quartz (SiO ₂ ), porcelain, magnesium oxide, tin dioxide, silicon carbide, rutile, alumina (Al ₂ O ₃ ), aluminum silicate, magnesium silicate (steatite), zirconium silicate or cerium silicate, or mixtures of the above materials.

The inert core according to one embodiment has a maximum diameter of 10 mm, according to another embodiment of at most 5 mm, according to another embodiment of the highest 4 mm.

According to a further embodiment, the inert core has a maximum diameter of at least 1 mm, according to a further embodiment of at least 2 mm.

On the inert carrier, a shell of the active material is applied. The shell may be composed of a single layer or of several layers, wherein the individual layers may also have different compositions.

The thickness of the shell is according to one embodiment 10 to 1000 microns, according to another embodiment 50 to 500 microns. The thickness of the shell is measured perpendicular to the surface of the inert support.

According to a preferred embodiment, a second interface is formed between the inert core and the shell surrounding the inert core, and a second heat transfer occurs between the inert core and the shell, wherein in the model the heat conduction in the catalyst comprises the second heat transfer.

Most preferably, the core is non-porous, d. H. there is no diffusion of reaction components in the core. Accordingly, it is provided in this embodiment in the model that no mass transfer takes place via the second interface.

In the model, a reaction kinetics is considered, which describes the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons.

In the simplest case, the reaction kinetics describes the conversion of the starting product, preferably o-xylene and / or naphthalene, into phthalic anhydride.

However, the reaction kinetics preferably also take into account further reaction components which form during the oxidation of the starting product to the desired product, ie intermediate or by-products.

The reaction kinetics can be set up according to one embodiment for the entire catalyst phase.

According to one embodiment, the reaction kinetics are set up individually for each layer L _m within the catalyst phase.

The reaction kinetics results according to one embodiment from the reaction kinetics of partial reactions in which one reaction component is converted into another reaction component. The partial reactions in the oxidation of the hydrocarbon to phthalic anhydride can be described by a network comprising the partial reactions for the conversion of the individual reaction components in the other reaction components.

The various reaction components occur during the reaction of the aromatic hydrocarbon, preferably o-xylene or naphthalene, to phthalic anhydride in different concentrations, wherein the individual partial reactions have a different influence on the reaction kinetics of the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons.

Gleichung 7 wobei bedeutet: r die Reaktionsrate der Reaktion j ((mol/sg_cat) i ein Index welcher eine bestimmte Reaktionskomponente bezeichnet (–) j einen Index, welcher eine bestimmte Reaktion bezeichnet (–) p_i den Partialdruck der Komponente i (Pa) P_oX den Partialdruck der Komponente c-Xylol (Pa) K_oX ein zweiter Parameter der Reaktionsgeschwindigkeit (Pa^–1) k_j ein erster Parameter der Reaktionsgeschwindigkeit (mol/sg_catPa) In one embodiment, the kinetics of a partial reaction can be described by:

Equation 7 where: r the reaction rate of the reaction j ((mol / sg _cat ) i an index which denotes a specific reaction component (-) j an index, which denotes a certain reaction (-) p _i the partial pressure of the component i (Pa) P _oX the partial pressure of the component c-xylene (Pa) _COX a second parameter of the reaction rate (Pa ^-1 ) k _j a first parameter of the reaction rate (mol / sg _cat Pa)

According to a further embodiment, the kinetics of a partial reaction can be described by: r _j = _j k · p _i Equation 8 where: r _j Reaction rate of reaction j ((mol / sg _cat ) i an index which denotes a specific reaction component (-) j an index which denotes a specific reaction (-) p _i Partial pressure of component i (Pa) k _j a parameter of the reaction rate (mol / sg _cat Pa)

Gleichung 9 wobei bedeutet: k_0,j eine erste Konstante der Reaktionsgeschwindigkeit (mol/sg_catPa) E_A,j eine zweite Konstante der Reaktionsgeschwindigkeit (kJ/kmol) j ein Index, welcher eine bestimmte Reaktion bezeichnet (–) R allgemeine Gaskonstante (kJ/kmolK) T Temperatur (K) k_j ein Parameter der Reaktionsgeschwindigkeit (mol/sg_catPa) The temperature dependence of the reaction rate can be described according to one embodiment by:

Equation 9 where: k _{0, j} a first constant of the reaction rate (mol / sg _cat Pa) E _{A, j} a second constant of the reaction rate (kJ / kmol) j an index which denotes a specific reaction (-) R general gas constant (kJ / kmolK) T Temperature (K) k _j a parameter of the reaction rate (mol / sg _cat Pa)

In providing the model, the reaction kinetics are preferably established by consideration of reaction components selected from the group consisting of carbon monoxide, carbon dioxide, phthalaldehyde, acetic acid, m-xylene, naphthalene, naphthoquinone, p-xylene, o-xylene, Nonane, cumene, p-benzoquinone, o-tolualdehyde, maleic anhydride, citraconic anhydride, benzoic acid, o-toluic acid, benzaldehyde, benzene, phenol, hydroquinone, dimethylmaleic anhydride, phthalic anhydride, phthalic acid, phthalide, toluene, 2,3-dimethyl-p-benzoquinone, 2-methyl-p-benzoquinone.

As already explained, the reaction component may be a starting material, an intermediate, a by-product or a final product in the gas-phase oxidation of aromatic hydrocarbons to produce phthalic anhydride.

The aromatic hydrocarbon used as the starting material is preferably selected from o-xylene and naphthalene.

As already explained, the partial reactions have different effects on the reaction kinetics. According to one embodiment, only part of the intermediates or by-products are taken into account in establishing the reaction kinetics. This reduces the effort for carrying out the method for providing the reactor system.

When the reaction component is formed from an intermediate, according to one embodiment it is selected from a group formed from phthalaldehyde, naphthoquinone, o-xylene, o-tolualdehyde, o-toluic acid, phthalic acid and phthalide.

In a preferred embodiment, the intermediate is selected from the group formed from o-tolualdehyde and phthalide.

When the reaction component is formed by a minor component, in one embodiment the minor component is selected from the group consisting of carbon monoxide, carbon dioxide, acetic acid, p-benzoquinone, maleic anhydride, citraconic anhydride, benzoic acid, benzaldehyde, benzene, phenol, p-hydroquinone, toluene , 2,3-dimethyl-p-benzoquinone, and 2-methyl-p-benzoquinone.

The formation of the minor component is described in each case by a partial secondary reaction kinetics, which enters into the reaction kinetics.

In one embodiment, the minor component is selected from the group consisting of carbon monoxide, carbon dioxide, and maleic anhydride.

By reducing the consideration taken into account in the preparation of the reaction kinetics secondary components can also reduce the cost of implementing the method according to the invention.

As already explained above, the formation or consumption of starting products, intermediates and by-products in the formation of phthalic anhydride can be represented by a network comprising reaction paths which describe the formation of a reaction product from another reaction product.

Such a network comprises at least one reaction path which describes the conversion of a first reaction product into a second reaction product. The transfer is described by a partial reaction kinetics or a partial secondary reaction kinetics.

Preferably, the network comprises more than one reaction path. In one embodiment, the network comprises less than 30 reaction pathways.

In a preferred embodiment, the network does not involve direct oxidation of o-xylene to phthalic anhydride.

According to another embodiment, the by-product carbon monoxide and / or carbon dioxide and is formed in the network of o-xylene and / or phthalic anhydride.

According to a further embodiment, the by-product is maleic anhydride and is formed in the network from o-xylene, tolualdehyde and / or phthalic anhydride, preferably toluenoaldehyde.

• a) die Oxidation von o-Xylol zu Kohlenmonoxid, Kohlendioxid (2), Tolylaldehyd (1), oder zu 2,3-Dimethylbenzochinon (3);
• b) die Oxidation von Tolylaldehyd zu Phthaldialdehyd (8), Tolylsäure (5), Phthalid (4), oder Toluol (11);
• c) die Oxidation von Tolylsäure zu Phthalid (6);
• d) die Oxidation von Phthaldialdehyd zu Phthalsäure (9)
• e) die Oxidation von Toluol zu Benzaldehyd (19), 2-Methyl-p-Benzochinon (12);
• f) die Oxidation von Benzaldehyd zu Benzoesäure (20);
• g) die Oxidation von Benzoesäure zu Benzol (21);
• h) die Oxidation von Benzol zu Phenol (22);
• i) die Oxidation von Phenol zu Hydrochinon (23);
• j) die Oxidation von Hydrochinon zu Benzochinon (24);
• k) die Oxidation von Benzochinon zu Maleinsäureanhydrid (25);
• l) die Oxidation von 2-Methyl-p-Benzochinon zu Maleinsäureanhydrid (14);
• m) die Oxidation von 2-Methyl-p-Benzochinon zu Citraconsäureanhydrid (13);
• n) die Oxidation von Citraconsäureanhydrid zu Essigsäure (18);
• o) die Oxidation von Dimethylbenzochinon zu Dimethylmaleinsäureanhydrid (16) oder Maleinsäureanhydrid (15);
• p) die Oxidation von Dimethylmaleinsäureanhydrid zu Essigsäure (17);
• q) die Oxidation von Phthalid zu Phthalsäureanhydrid (7);
• r) die Überführung von Phthalsäure in Phthalsäureanhydrid (10); sowie
• s) die Oxidation von Phthalsäureanhydrid zu Benzoesäure (26)

In one embodiment, the network includes at least the following reaction pathways:

• a) the oxidation of o-xylene to carbon monoxide, carbon dioxide (2), tolualdehyde (1), or to 2,3-dimethylbenzoquinone (3);
• b) the oxidation of tolualdehyde to phthalaldehyde (8), toluic acid (5), phthalide (4), or toluene (11);
• c) the oxidation of toluic acid to phthalide (6);
• d) the oxidation of phthalaldehyde to phthalic acid (9)
• e) the oxidation of toluene to benzaldehyde (19), 2-methyl-p-benzoquinone (12);
• f) the oxidation of benzaldehyde to benzoic acid (20);
• g) the oxidation of benzoic acid to benzene (21);
• h) the oxidation of benzene to phenol (22);
• i) the oxidation of phenol to hydroquinone (23);
• j) the oxidation of hydroquinone to benzoquinone (24);
• k) the oxidation of benzoquinone to maleic anhydride (25);
• l) the oxidation of 2-methyl-p-benzoquinone to maleic anhydride (14);
• m) the oxidation of 2-methyl-p-benzoquinone to citraconic anhydride (13);
• n) the oxidation of citraconic anhydride to acetic acid (18);
• o) the oxidation of dimethylbenzoquinone to dimethylmaleic anhydride (16) or maleic anhydride (15);
• p) the oxidation of dimethylmaleic anhydride to acetic acid (17);
• q) the oxidation of phthalide to phthalic anhydride (7);
• r) the conversion of phthalic acid into phthalic anhydride (10); such as
• s) the oxidation of phthalic anhydride to benzoic acid (26)

The network is in 1 played.

Preferably, the network comprises only the above-mentioned reaction routes.

Preferably, the network comprises the smallest possible number of reaction paths, whereby the effort in carrying out the method according to the invention decreases.

If the catalyst phase comprises several layers, different networks may be preferred in the different layers.

According to a preferred first embodiment, the network comprises at least the following reaction pathways:

• a) the oxidation of o-xylene to carbon monoxide, carbon dioxide (3), and tolualdehyde (1);
• b) the oxidation of tolualdehyde to maleic anhydride (6), phthalic anhydride (7) and phthalide (4);
• c) the oxidation of phthalide to phthalic anhydride (5); and
• d) the oxidation of phthalic anhydride to carbon monoxide, carbon dioxide (10).

Preferably, the network comprises only the mentioned reaction pathways.

The network is in 2 played.

If the catalyst phase comprises a plurality of layers, the network of the first layer L _{1 is} preferably formed by the network according to the first embodiment.

According to a second embodiment, the network comprises at least the following reaction paths:

• a) the oxidation of o-xylene to carbon monoxide, carbon dioxide (3), and tolualdehyde (1);
• b) the oxidation of tolualdehyde to maleic anhydride (6), and phthalide (4);
• c) the oxidation of phthalide to phthalic anhydride (5); and
• d) the oxidation of phthalic anhydride to carbon monoxide, carbon dioxide (10).

Preferably, the network according to the second embodiment comprises only the said reaction pathways.

The network is in 3 played.

If the catalyst phase comprises a plurality of layers L _m , the network of the second layer L _{2 is} preferably determined by the network according to the second embodiment ( 3 ) educated.

In one embodiment, the activity provided by the catalyst A _{1, n} in the first layer L _m is lower than the activity provided by the catalyst A _{2, n} in the second layer.

According to a third embodiment, the network comprises at least the following reaction paths:

• a) the oxidation of o-xylene to tolualdehyde (1); b) the oxidation of tolylaldehyde phthalide (4);
• c) the oxidation of phthalide to phthalic anhydride (5); and
• d) the oxidation of phthalic anhydride to carbon monoxide, carbon dioxide (10) and maleic anhydride (6).

Preferably, the network according to the third embodiment comprises only the said reaction pathways.

The network is in 4 played.

If the catalyst phase comprises a plurality of layers, the network of the third layer is preferably formed by the network according to the third embodiment ( 4 ) educated.

According to one embodiment, a lower activity is thereby provided by the catalyst A _{1, n of} the first layer L ₁ than by the catalyst A _{2, n of} the second layer L ₂ and by the catalyst A _{3, n} is provided a higher activity in the layer L ₃ than from the catalyst A _{2, n of} the second layer L ₂ .

Is the activity provided by the catalyst A _{1, n} in the first layer L ₁ higher than the activity provided by the catalyst A _{2, n} in the second layer L ₂ and the activity provided by the catalyst A _{3, n of} the third layer L ₃ is higher than the activity provided by the catalyst A _{2, n of} the second layer L ₂ , the network of the first layer L ₁ and the second layer L ₂ according to an embodiment is determined by the network according to the first embodiment ( 2 ) and the network of the third layer L ₃ through the network of the second embodiment ( 3 ) educated. It is preferred that the length z _{1, n of} the first layer L _{1 is} less than 50% of the length z _{2, n of} the second layer L ₂ .

In a catalyst phase with 4 layers L _m , in which from the catalyst A _{1, n} in the first layer, a higher activity is provided than by the catalyst A _{2, n} in the second layer L ₂ , and that of the catalyst A _{3, n} in a higher activity is provided to the third layer than from the catalyst A _{2, n} in the second layer L ₂ , and further from the catalyst A _{4, n} in the fourth layer is provided a higher activity than from the catalyst A _{3, n} in the third layer L ₃ , according to one embodiment, the network of first and second layer L ₁ , L ₂ through the network according to the first embodiment ( 2 ), the network of the third layer L ₃ through the network of the second embodiment ( 3 ) and the network of the fourth layer L ₄ through the network according to the third embodiment ( 4 ) educated. It is provided according to an embodiment that the length z _{1, n of} the first layer L _{1 is} less than 50% of the length z _{2 of} the second layer L ₂ .

In one embodiment of a catalyst layer having four layers L _m , according to one embodiment, the network of the first layer of the network according to the first embodiment (FIG. 2 ), the network of the second layer L _{2 of} the network according to the second embodiment ( 3 ) and the network of third and fourth layer L ₃ , L _{4 of} the network of the third embodiment ( 4 ) educated. It is provided according to an embodiment that the length z _{4, n of} the fourth layer L _{4 is} less than 50% of the length z _{3 of} the third layer L ₃ .

The catalyst of a vanadium-containing material, or more precisely the active material of the catalyst, can per se have a known and customary composition from the prior art, wherein the specific composition of the catalyst can also be determined with the aid of the method according to the invention.

According to one embodiment, the catalyst comprises, in addition to vanadium oxide, further components, for example the components indicated in the following table, which are preferably present in the active mass in amounts within the ranges indicated: V ₂ O ₅ 0.5-30% by weight, in particular 1-30% by weight Sb ₂ O ₃ or Sb ₂ O ₅ 0-10% by weight Cs 0-2% by weight P 0-5% by weight Nb 0-5% by weight Other components such as Ba, W, Mo, Y, Ce, Mg, Sn, Bi, Fe, Ag, Co, Ni, Cu, Au, Sn, Zr, etc. 0-5% by weight TiO ₂ 40 to 99 wt .-%, in particular balance to 100 wt .-%

The percentages in each case relate to the total weight of the active composition.

Furthermore, promoters for modulating the activity of the catalysts can be present in the active mass. Suitable promoters are, for example, alkali metals and alkaline earth metals, thallium, antimony, phosphorus, iron, niobium, cobalt, molybdenum, silver, tungsten, tin, lead, zirconium, copper, gold and / or bismuth, and Mixtures of two or more of the above components. About the individual promoters, the activity and selectivity of the catalysts or the active composition can be influenced, in particular by lowering or increasing the activity. The selectivity increasing promoters include, for example, the alkali metal oxides, whereas oxidic phosphorus compounds, especially phosphorus pentoxide, can lower the activity of the catalyst at the expense of selectivity depending on the degree of promotion.

If the catalyst phase comprises several layers, the catalysts of the individual layers preferably differ in their composition.

According to one embodiment, the catalyst has an active composition content of between 7 and 12% by weight, preferably between 8 and 10% by weight. The active composition (catalytically active composition) preferably contains between 5 to 15% by weight of V ₂ O ₅ , 0 to 4% by weight of Sb ₂ O ₃ , 0.2 to 0.75% by weight of Cs, 0 to 3 Wt% Nb ₂ O ₅ . In addition to the above components, the remainder of the active composition is at least 90 wt .-%, preferably at least 95 wt .-%, more preferably at least 98 wt .-%, in particular at least 99 wt .-%, more preferably at least 99.5 wt. -%, In particular 100 wt .-% of TiO ₂ . Such a catalyst can be used, for example, advantageously in a two- or multi-layer catalyst as the first, to the gas inlet side located catalyst layer.

According to one embodiment, the BET surface area of the catalyst or the active composition is between 15 and about 25 m ² / g. Furthermore, it is preferred that such a first layer L _{1 of} the catalyst phase catalyst layer has a length fraction of about 40 to 60% of the total length of all existing catalyst layers layers of the catalyst phase (total length of the existing catalyst bed).

According to a further embodiment, the catalyst has an active composition content of about 6 to 11 wt .-%, in particular 7 to 9 wt .-% to. The active composition preferably contains 5 to 15 wt .-% V ₂ O ₅ , 0 to 4 wt .-% Sb ₂ O ₃ , 0.05 to 0.3 wt .-% Cs, 0 to 2 wt .-% Nb ₂ O ₅ and 0-2 wt% phosphorus. In addition to the above components, the remainder of the active composition consists of at least 90% by weight, preferably at least 95% by weight, more preferably at least 98% by weight, in particular at least 99% by weight, more preferably at least 99.5% by weight. %, in particular 100 wt .-% of TiO ₂ . Such a catalyst can be used, for example, as the second layer L _{2 of} the catalyst phase, ie downstream of the first layer L _{1 of} the catalyst phase located toward the gas inlet side. It is preferred that the catalyst or the active composition has a BET surface area between about 15 and 25 m ² / g. Furthermore, it is preferred that this second layer occupies a length fraction of about 10 to 30% of the total length of all existing catalyst layers.

According to a further embodiment, the catalyst has an active composition content of between about 5 and 10% by weight, in particular between 6 and 8% by weight. The active composition (catalytically active composition) preferably contains 5 to 15% by weight of V ₂ O ₅ , 0 to 4% by weight of Sb ₂ O ₃ , 0 to 0.1% by weight of Cs, 0 to 1% by weight. % Nb ₂ O ₅ and 0 to 2 wt% phosphorus. In addition to the above components, the remainder of the active composition is at least 90 wt .-%, preferably at least 95 wt .-%, more preferably at least 98 wt .-%, in particular at least 99 wt .-%, more preferably at least 99.5 wt. -%, In particular 100 wt .-% of TiO ₂ . Such a catalyst can be used, for example, as the third (or last) layer L _{3 of} the catalyst phase arranged downstream of the second layer L _{2 of} the catalyst phase described above. In this case, a BET surface of the catalyst or of the active composition which is slightly higher than that of the layers closer to the gas inlet side, in particular in the range between about 25 to about 45 m ² / g, is preferred. Furthermore, it is preferred that such a third layer L ₃ occupies a length fraction of about 10 to 50% of the total length of all existing catalyst layers.

If the catalyst phase comprises a plurality of layers L _m , their proportion of the total length of the catalyst phase or of the catalyst bed is selected according to an embodiment within certain ranges.

Thus, according to one embodiment, the first layer L _{1 of} the catalyst phase located toward the gas inlet side has a length fraction, based on the total length of the catalyst phase, of at least 40%, in particular at least 45%, particularly preferably at least 50%. According to one embodiment, the proportion of the first layer L _{1 of} the catalyst phase in the total length of the catalyst phase is between 40 and 70%, according to a further embodiment between 40 and 55%, and according to yet another embodiment between 40 and 52%. The second layer L ₂ according to one embodiment takes about 10 to 40%, according to another embodiment, about 10 to 30% of the total length of the catalyst phase. Furthermore, according to one embodiment, the ratio of the length z _{3, G of} the third layer L _{3 of} the catalyst phase to the length z _{2, G of} the second layer L ₂ between about 1 and 2, according to another embodiment between 1.2 to 1.7, selected according to yet another embodiment, between 1.3 and 1.6.

These regions find application in a three phase catalyst phase according to one embodiment. In this case, according to one embodiment, it is provided that the activity provided in the layers by the catalysts A _{m, n increases} stepwise from the first to the third position.

In a 4-layer catalyst, the first layer L _{1 of} the catalyst phase according to one embodiment has a length fraction, based on the total length of the catalyst phase or the catalyst phase, between about 10% and 20%. The length fraction of the second layer L _{2 of} the catalyst phase is according to one embodiment between about 40% and 60%, based on the total length of the catalyst phase. The length fraction of the third or fourth layer L ₃ , L _{4 of} the catalyst phase is according to one embodiment in each case between about 15% and 40%, based on the total length of the catalyst bed.

According to one embodiment, it is provided that the activity provided by the catalysts A _{m, n} initially drops from the first to the second layer and then increases towards the third or fourth position. It is provided according to an embodiment that the length z _{1, G of} the first layer L _{1 is} less than the length z _{2, G of} the second layer, according to one embodiment, less than 50% of the length z _{2, G of} the second layer L _2nd is.

By adjusting the length proportions of the individual catalyst layers influence on the positioning of the hot spot can be taken. Likewise, the temperature of the hot spot can be controlled so that a slower deactivation of the catalyst and thus a longer operating time of the reactor is made possible.

The activity profile of the catalyst phase, ie the activity of the individual layers within the catalyst phase, can be influenced, for example, by the content of the active mass of alkali metals. As a result, for example, an activity profile can be set at which the activity of the catalyst in the catalyst layers decreases from the gas inlet side to the gas outlet side.

According to one embodiment, the alkali content, preferably the Cs content (calculated as Cs), in the second layer L _{2 of} the catalyst phase is smaller than in the first layer L _{1 of} the catalyst phase, and in the third layer L ₃ smaller than in the second layer L ₂ (and according to one embodiment optionally to the third layer L ₃ following layers L _m ).

In one embodiment, the Cs content (calculated as Cs) in the catalyst phase decreases from layer to layer in the gas flow direction. According to a preferred embodiment, the third (and preferably also optionally subsequent layers) contains no Cs. Preferably: (Cs content) _{1st layer} > (Cs content) _{2nd layer} >...> Cs content _{last layer}

In one embodiment, the last layer L _{m of} the catalyst phase does not have Cs.

According to another embodiment, only the last layer L _{m of} the catalyst phase has phosphorus. In a further embodiment, no phosphorus is contained in the active composition in the first layer and in the second layer, and in a four-layer catalyst preferably also in the third layer L ₃ . (By "no phosphorus" is meant that in the preparation no P active was added to the active mass).

According to a further embodiment, in the case of three-layer or multi-layer catalyst phases, the active material content may decrease from the first layer located towards the gas inlet side to the layer located toward the gas outlet side. In this case, according to one embodiment, the first layer L _{1 of} the catalyst phase has an active material content between about 7 and 12 wt .-% according to one embodiment between about 8 and 11 wt .-%, the second layer L _{2 of} the catalyst phase has an active material content between about 6 and 11 wt .-% according to one embodiment between about 7 and 10 wt .-%, and the third layer L _{3 of} the catalyst phase has an active material content of between about 5 and 10 wt .-% according to one embodiment between about 6 and 9 wt .-%.

The terms first, second and third layer L _{m of} the catalyst phase are used as follows: the first layer L _{1 of} the catalyst phase is the layer which faces the gas inlet side. Towards the gas outlet side, two further layers may be contained in the catalyst phase, which are referred to as the second or third layer L ₂ , L _{3 of} the catalyst phase. The third layer is closer to the gas outlet side than the second layer.

In one embodiment, the catalyst phase has three or four layers. In a 3-layer catalyst phase, the third layer L _{3 is located} on the gas outlet side. However, the presence of additional layers of gas downstream from the first layer L ₁ is not excluded. For example, according to a further embodiment, the third layer L _{3 may} be followed by a fourth layer L ₄ (preferably with an identical or even lower active material content than the third layer L ₃ ).

To set the activity profile, according to one embodiment, the active material content between the first and the second layer L ₁ , L _{2 of} the catalyst phase and / or between the second and the third layer L ₂ , L _{3 of} the catalyst phase decrease. According to a further embodiment, the active material content decreases between the second and the third layer. In accordance with a further embodiment, the BET surface area increases from the first position L ₁ located toward the gas inlet side to the third position L ₃ located toward the gas outlet side. Suitable ranges for the BET surface area are, for example, 15 to 25 m ² / g for the first layer L ₁ , 15 to 25 m ² / g for the second layer L ₂ and 25 to 45 m ² / g for the third layer L ₃ the catalyst phase.

According to one embodiment, it is provided that the BET surface area of the first layer L _{1 of} the catalyst phase is less than the BET surface area of the third layer L ₃ . Suitable catalyst phases are also obtained when the BET surface areas of the first and second layers L ₁ , L _{2 are the} same, whereas the BET surface area of the third layer L _{3 is} larger. The catalyst activity to the gas inlet side is according to one embodiment less than the catalyst activity towards the gas outlet side. It can be provided according to an embodiment that at least 0.05 wt .-% of the catalytically active material by at least one alkali metal, calculated as alkali metal (s), is formed. In one embodiment, cesium is used as the alkali metal.

In addition, according to the results of the inventors, according to one embodiment, it is provided that the catalyst or the active composition contains a total of niobium in an amount of 0.01 to 2 wt .-%, in particular 0.5 to 1 wt .-% of the active composition.

The catalyst bodies of the catalysts A _{m, n} are prepared in the usual manner, wherein a thin layer of the active composition is applied to the inert support body. For this purpose, for example, a suspension of the active composition or a solution or suspension of precursor compounds, which can be converted into the components of the active composition, sprayed onto the inert carrier. This can be done, for example, at a temperature of 80 to 200 ° C in a fluidized bed. However, the active composition can also be applied, for example, in a coating drum to the inert carrier.

For the coating process, the aqueous solution or suspension of active components and an organic binder, preferably a copolymer of vinyl acetate / vinyl laurate, vinyl acetate / ethylene or styrene / acrylate, sprayed via one or more nozzles on the heated, fluidized carrier. It is particularly advantageous to give up the spray liquid at the place of the highest product speed, whereby the spray can be evenly distributed in the bed. The spraying process is continued until either the suspension has been consumed or the required amount of active components has been applied to the carrier. Active components are understood to mean components of the active composition, in particular metal compounds contained in the active composition. The active components can be used as oxides or in the form of precursor compounds. Precursor compounds are compounds which can be converted, for example by heating in air, into the components of the active composition, ie the oxides. Suitable precursor compounds are, for example, nitrates, carbonates, acetates or chlorides of the metals.

According to one embodiment, the active composition is applied in a fluidized bed or fluidized bed with the aid of suitable binders, so that a shell catalyst is produced. Suitable binders include organic binders known to the person skilled in the art, preferably copolymers, advantageously in the form of an aqueous dispersion, of vinyl acetate / vinyl laurate, vinyl acetate / acrylate, styrene / acrylate, vinyl acetate / maleate and vinyl acetate / ethylene. Particularly preferably, an organic polymeric or copolymeric adhesive, in particular a vinyl acetate copolymer adhesive, is used as the binder. The binder used is added in conventional amounts of the active composition, for example with about 10 to 20 wt .-% based on the solids content of the active composition. For example, on the EP 744 214 to get expelled.

As far as the application of the active composition takes place at elevated temperatures of about 150 ° C, it can be applied to the carrier without organic binders. Useful coating temperatures when using the above-mentioned binders are for example between about 50 and 450 ° C. The binders used burn when the catalyst is heated during commissioning of the catalyst filled reactor within a short time. The binders serve primarily to enhance the adhesion of the active composition to the support and to reduce abrasion during transport and filling of the catalyst bodies in the reactor.

According to a further embodiment, first of all a powder is prepared from a solution and / or a suspension of the active composition and / or its precursor compounds, optionally in the presence of auxiliaries for the preparation of the catalyst, which is then used for catalyst preparation on the inert support, optionally after conditioning and optionally after heat treatment to produce the catalytically active metal oxides cup-shaped applied and subjected to the thus coated carrier to a heat treatment to produce the active composition or a treatment for devolatilization.

The invention will be explained in more detail with reference to examples.

example

A 4-layer catalyst system with subsequent composition and layer lengths was filled in a salt bath cooled tube reactor with 25 mm inner diameter. In the reaction tube was centrally arranged a 3 mm thermal sleeve with built-in tension element for temperature measurement. Table 1: Composition of the active composition of the catalysts composition Location 1: Length 50 cm Position 2: length 100 cm Location 3: length 60 cm Position 4: length 90 cm V ₂ O ₅ / weight% 8.0 7.5 7.5 7.5 Sb ₂ O ₃ / weight% 3.2 3.2 3.2 3.2 Cs / wt .-% 0.4 0.4 0.2 0.1 P / wt .-% 0.2 0.2 0.2 0.2 TiO ₂ / weight% Rest to 100% Rest to 100% Rest to 100% Rest to 100% BET TiO ₂ / (m ² / g) 20 20 20 20 Proportion AM /% by weight 10 8th 7.5 7.5

The tube was surrounded over a length of 400 cm by a cooling jacket, which was flowed through by a cooling medium (eutectic mixture of NaNO ₂ and KNO ₃ ). The temperature of the cooling medium was measured at a height of 50 cm and 400 cm along the length of the pipe. The arithmetic mean of the temperatures was assumed to be the mean coolant temperature T _K.

Into the tube was charged a catalyst bed (catalyst phase) having a total length of 300 cm. The catalyst bed was arranged so that the entire catalyst bed is in the area of the cooled reaction tube.

At the outlet of the reaction tube, and at the transitions between the individual catalyst layers were measuring points for measuring the composition of the reaction gas.

3-4 Nm ^{3 of} air with a loading of 30-100 g o-xylene / Nm ³ air (purity o-xylene> 99%) and a total pressure of about 1450 mbar were passed through the tube from top to bottom every hour.

Temperatures in the thermal sleeve were recorded at subsequent operating conditions at a distance of 10 cm and the composition of the reaction gas at the outlet of the reactor was determined. Table 2: Operating conditions for determining the model

The diffusion and heat transport parameters were estimated according to known correlations, for example, according to VDI heat atlas.

With the measured temperature and concentration data, equations 1 to 5 were solved with the aid of the gPROMS ^® software, thus determining the reaction kinetics of the individual catalysts.

The determined reaction kinetics are composed of the following partial reaction kinetics for the different catalyst layers.

For site 1, the partial reaction kinetics were corresponding 2 described. The reaction kinetics parameters are given in Table 3. Table 3: Partial reaction kinetics of layer 1 Partial reaction no. k _{0, j} (molL ^-3 s ^-1 bar ^-2 ) E _{A, j} (kJ mol ^-1 ) 1 0.55 × 10 ¹³ 110 3 1.4 × 10 ¹⁰ 85 4 0.76 × 10 ¹¹ 85 5 0.31 × 10 ¹² 95 7 0.65 × 10 ¹² 110 10 0.5 × 10 ⁹ 96

The parameter K _oX assumes the value 1.5 bar ^-1 .

For site 2, the partial reaction kinetics were corresponding 2 described. The reaction kinetics parameters are given in Table 4. Table 4: Partial reaction kinetics of layer 2 Partial reaction no. k _{0, j} (molL ^-3 s ^-1 bar ^-2 ) E _{A, j} (kJ mol ^-1 ) 1 0.13 × 10 ¹³ 110 3 0.70 × 10 ¹⁰ 85 4 0.38 × 10 ¹¹ 85 5 0.18 × 10 ¹² 95 7 0.28 × 10 ¹² 110 10 0.84 × 10 ⁹ 96

The parameter K _oX assumes the value 1.5 bar ^-1 .

For layer 3, the partial reaction kinetics were corresponding 3 described. The reaction kinetics parameters are given in Table 5. Table 5: Partial reaction kinetics of layer 3 Partial reaction no. k _{0, j} (molL ^-3 s ^-1 bar ^-2 ) E _{A, j} (kJ mol ^-1 ) 1 0.13 × 10 ¹³ 110 3 0.70 × 10 ¹⁰ 85 4 0.38 × 10 ¹⁰ 85 5 0.18 × 10 ¹² 95 10 0.84 × 10 ⁹ 96

The parameter K _oX assumes the value 1.5 bar ^-1 .

For layer 4, the partial reaction kinetics were corresponding 4 described. The reaction kinetics parameters are given in Table 6. Table 6: Partial reaction kinetics of layer 4 Partial reaction no. k _{0, j} (molL ^-3 s ^-1 bar ^-2 ) E _{A, j} (kJ mol ^-1 ) 1 0.13 × 10 ¹³ 60 4 0.38 × 10 ¹⁰ 65 5 0.34 × 10 ¹² 62 6 0.85 × 10 ⁹ 95 10 1.2 × 10 ⁹ 110

The parameter K _oX assumes the value 1.5 bar ^-1 .

For a salt bath cooled tube reactor with 25 mm inner diameter, without thermowell, an optimized catalyst with subsequent composition and active mass loading was provided. Table 7: Compositions and Load Loads of the Optimized System composition Location 1: Length 50 cm Position 2: length 100 cm Location 3: length 60 cm Position 4: length 90 cm V ₂ O ₅ / weight% 8.0 7.5 7.5 7.5 Sb ₂ O ₃ / weight% 3.2 3.2 3.2 3.2 Cs / wt .-% 0.4 0.4 0.2 0.1 P / wt .-% 0.2 0.2 0.2 0.2 TiO ₂ / weight% Rest to 100% Rest to 100% Rest to 100% Rest to 100% BET TiO ₂ / (m ² / g) 20 20 20 20 Proportion AM /% by weight 7 6 5.5 4.5

• • Geringerer Gehalt an CO und CO im Reaktionsgas und ein höherer Anteil an Phthalsäureanhydrid
• • Geringere Umsetzung von Phthalsäureanhydrid zu CO und CO₂, da die Konzentration von Phthalsäureanhydrid in den ersten beiden Lagen eine gewisse Grenze nicht überschreitet.

From this, the following advantages for the optimized catalyst can be derived, which apply not only to this specific example but generally to the catalyst system:

• • Lower content of CO and CO in the reaction gas and a higher proportion of phthalic anhydride
• • Lower conversion of phthalic anhydride to CO and CO ₂ , as the concentration of phthalic anhydride in the first two layers does not exceed a certain limit.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1082317 B1 [0005]
• EP 1084115 B1 [0005]
• WO 2004/103944 A1 [0005]
• WO 2007/134849 A1 [0006]
• WO 2011/032658 [0006]
• EP 744214 [0252]

Claims (12)

A process for providing a reactor system for the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons on at least one catalyst A _{m, n} , comprising catalyst bodies containing a vanadium-containing active material, wherein: - a shell-and-tube reactor is provided, - having a number b of tubes, which Diameter D, and - have a tube length L; wherein the tubes have a tube wall, which is surrounded by a coolant, which has an average coolant temperature T _K ; - Provided in the tubes at least one layer L _m comprehensive catalyst phase, the layer L _{m is provided} by a catalyst A _{m, n} , where m assumes an integer value between 1 and the maximum number of layers and n is an index of 1 to n, which identifies a particular catalyst, and in the position L _m of the catalyst A _{m, n} an active mass loading M _{m, n is} provided; and - passing through the tubes a gas phase forming reaction gas containing at least one reaction component; A model is provided, which for the tube reactor for the gas phase and the catalyst phase in the tubes of the tube reactor - a heat balance and - each for the gas phase and the catalyst phase, a material balance, and - a mass transfer in the catalyst body and - a reaction kinetics for the production of Describes phthalic anhydride by gas phase oxidation of aromatic hydrocarbons; - Operating conditions of the tube bundle reactor are set by at least A certain flow of the reaction gas per tube; A specific concentration of the at least one reaction component in the reaction gas and a certain mean coolant temperature T _{k of} the coolant are set; A feature is determined which can take values W _n ; - With the model, a difference Δ is determined by a) a value is assigned to a limit difference Δ _G ; b) in the position L _m with a first catalyst A _{m, 1} a first active mass loading M _{m, 1} provided and under the operating conditions of the tube bundle reactor _, a first value W _{1 of} the feature is determined; c) the active mass loading of the layer L _{m is} changed by providing a second active mass loading M _{m, 2} by a second catalyst A _{m, 2} ; d) with the model for the second catalyst A _{m, 2} under the operating conditions of the tube bundle reactor, a second value W _{2 of} the feature is determined; e) the first value W ₁ and the second value W _{2 are} compared and the difference Δ is determined; and the steps b to e with catalysts A _{m, n are} repeated until the difference Δ in the amount below the limit difference Δ _G ; A catalyst A _{m, G} determined from the limiting difference Δ _{G is} provided, and in the tubes of the reactor the at least one layer L _{m of} the catalyst phase formed from the catalyst A _{m, G is} provided. The method of claim 1, wherein the model is provided by - providing a reference reactor comprising - a number a of tubes having - a diameter d, and - a tube length l; wherein the tubes have a tube wall, which is surrounded by a coolant, which has an average coolant temperature T _{K '} ; In the tubes, a catalyst _phase formed from at least one catalyst a _{M is} provided which comprises at least one layer l _{M of} the catalyst a _M , where M assumes an integer value between 1 and the maximum number of layers, and wherein the catalyst a _M catalyst body comprising a vanadium-containing active material; - Passing through the tubes a gas phase forming reaction gas containing at least one starting material; - Operating conditions of the reference reactor are determined by at least - a certain flow of the reaction gas per tube; - an inlet temperature of the reaction gas entering the reaction tube, - a certain concentration of the at least one starting product in the reaction gas and - a certain mean coolant temperature T _{K 'are} set; - for the reference reactor with the catalyst phase in the operating conditions - the heat balance; - the material balance for the gas phase and the catalyst phase; - The mass transfer in the catalyst body and - The reaction kinetics is determined, and from the model is created. The method of claim 1 or 2, wherein the heat balance comprises a heat balance for the at least one layer L _{m of} the catalyst A _m comprehensive catalyst phase and a heat balance for the gas phase. The method of claim 3, wherein the heat balance for the at least one layer L _{m of} the catalyst A _m comprehensive catalyst phase comprises at least one heat conduction in the catalyst body and a heat production by a reaction. The method of claim 3 or 4, wherein the heat balance of the gas phase comprises a radial heat transfer in the reaction tube and the heat transfer between the gas phase and the catalyst phase. Method according to one of claims 1 to 5, wherein the material balance of the gas phase comprises the radial transport of a reaction component in the reaction tube and the transition of the reaction component of the gas phase in the catalyst A _{m, n} . Method according to one of claims 1 to 6, wherein the material balance in the catalyst A _{m, n describes} the diffusion of the reaction component in the at least one catalyst body, and the reaction of the reaction component. Method according to one of the preceding claims, wherein the model comprises a momentum balance. A process according to any one of the preceding claims, wherein the catalyst body is formed as a shell catalyst having an inert core and a shell surrounding the inert core, the shell containing the active material. A process according to any one of the preceding claims wherein the reaction kinetics for the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons is formed from a network of partial reactions comprising the following reaction pathways: a) the oxidation of o-xylene to carbon monoxide, carbon dioxide (3), and tolualdehyde (1); b) the oxidation of tolualdehyde to maleic anhydride (6), phthalic anhydride (7) and phthalide (4); c) the oxidation of phthalide to phthalic anhydride (5); and d) the oxidation of phthalic anhydride to carbon monoxide, carbon dioxide (10); wherein the network preferably describes the first layer of the catalyst phase. A process according to any one of the preceding claims wherein the reaction kinetics for the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons is formed from a network of partial reactions comprising the following reaction pathways: a) the oxidation of o-xylene to carbon monoxide, carbon dioxide (3), and tolualdehyde (1); b) the oxidation of tolualdehyde to maleic anhydride (6), and phthalide (4); c) the oxidation of phthalide to phthalic anhydride (5); and d) the oxidation of phthalic anhydride to carbon monoxide, carbon dioxide (10); wherein the network preferably describes the second layer of the catalyst phase. A process according to any one of the preceding claims, wherein the reaction kinetics for the production of phthalic anhydride by gas phase oxidation of aromatic hydrocarbons is formed from a network of partial reactions comprising the following reaction pathways: a) the oxidation of o-xylene to tolualdehyde (1); b) the oxidation of tolylaldehyde phthalide (4); c) the oxidation of phthalide to phthalic anhydride (5); and d) the oxidation of phthalic anhydride to carbon monoxide, carbon dioxide (10) and maleic anhydride (6); wherein the network preferably describes the third layer of the catalyst phase.

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