WO2009149808A1

WO2009149808A1 - Method for producing maleic anhydride

Info

Publication number: WO2009149808A1
Application number: PCT/EP2009/003497
Authority: WO
Inventors: Evin Hizaler Hoffmann; Leslaw Mleczko; Ralf Schellen; Stephan Schubert
Original assignee: Bayer Technology Services Gmbh
Priority date: 2008-05-29
Filing date: 2009-05-16
Publication date: 2009-12-17
Also published as: DE102008025834A1

Abstract

The invention relates to a method for producing maleic anhydride by catalytic gas phase oxidation of butane with oxygen, the reaction being carried out under adiabatic conditions in 10 to 60 reaction zones that are arranged in series. The invention further relates to a reactor system for carrying out said method.

Description

Process for the preparation of maleic anhydride

The present invention relates to a process for the preparation of maleic anhydride by catalytic gas phase oxidation of butane with oxygen, wherein the reaction is carried out in 10 to 60 successive reaction zones under adiabatic conditions, and a reactor system for carrying out the method.

Maleic anhydride is generally subject to the catalytic influence of metal oxide catalysts e.g. Vanadium phosphorus oxide (cf., for example, EP 0 071 140 B1) is prepared from gaseous butane and oxygen in an exothermic, catalytic reaction according to formula (I):

C ₄ H ₁₀ (g) + 3.5 O ₂ (g) → _o J ^) ^ (g) + 4 H ₂ O; ΔH = -1260 kJ / mol (I)

The maleic anhydride prepared by the reaction of formula (I) forms an essential starting material for many other syntheses in the chemical industry. In particular, maleic anhydride is used in the production of unsaturated polyesters and for the synthesis of surfactants, insecticides, herbicides, fungicides and the like. One part is reduced to 1,4-butanediol and to tetrahydrofuran.

The removal and use of the heat of reaction is important in the performance of maleic anhydride synthesis. An uncontrolled increase in temperature can lead to permanent damage to the catalytic converter. In addition, at high temperatures there is the potential for side reactions to produce more or less large amounts of carbon monoxide and carbon dioxide. It is therefore advantageous to keep the temperature of the reaction zones controlled in the course of the process at a level which allows a rapid conversion while minimizing the side reactions and / or catalyst inactivation.

EP 0 326 536 B1 discloses a process for the preparation of maleic anhydride in which a reaction of a non-aromatic hydrocarbon having 4 to 10 carbon atoms with oxygen is carried out in a reaction zone at temperatures of 300 ^° C. to 600 ^° C. The reaction zone is further characterized by having in it the catalyst diluted with inert material, also disclosing the presence of various dilutions of the catalyst in the reaction zone. It is further disclosed that the reaction zone is in a fixed bed tubular reactor which is cooled. The inlet pressure of the disclosed method is disclosed at 1 to 3.45 bar. Preferably, the highest dilution of the catalyst or the smallest amount of catalyst in the reaction zone should be at the location of the "hot spot." The "hot spot" is disclosed as the location in the reaction zone where the highest temperature prevails and where usually the highest rate of oxidation of the non-aromatic hydrocarbon to maleic anhydride is present. According to the invention, the non-aromatic hydrocarbon is supplied to the reaction zone at proportions of 1 to 10 mol% of the process gas.

It is not disclosed that more than one reaction zone would be useful in the process.

The method disclosed in EP 0 326 536 B1 is disadvantageous in that it operates at a constant maximum cooling rate dictated by geometry and heat exchange medium. If, during operation of the method, the disclosed "hot spot" is no longer in the position of the highest catalyst dilution due to external influences, such as incorrect metering of the starting materials, overheating which can no longer be compensated for and at least undesired by-products of the reaction occur, in the worst case, operating safety parameters which can lead to a standstill or destruction of the system in which the disclosed method is carried out., Precise temperature control of the method is excluded for the reasons just mentioned, since a "hot spot" is deliberately tolerated and thus at least portions of the reaction zone are operated under adverse conditions, resulting in disadvantageous selectivity.

EP 1 007 499 B1 discloses a process in which maleic anhydride is produced in the gas phase from n-butane using high oxygen contents in the process gas in the presence of a phosphorus-vanadium mixed oxide catalyst. The disclosed reaction temperatures are in the range of 300 ⁰ C to 550 ⁰ C, while the pressures at the beginning of the reaction zone are between 2.03 and 6.03 bar. The process is characterized by an at least partial reuse of the process gases after leaving the reaction zone, as well as by a high proportion of carbon dioxide and carbon monoxide in the process gases.

It is a reaction zone for conversion to maleic anhydride, a subsequent cooling of the process gases for the absorption of maleic anhydride in a solution means, washing, compression of the remaining process gases, partial venting of inert gases and carbon oxides, subsequent washing thereof with an organic solvent, and recycling together with fresh n-butane to the reaction zone. There is disclosed no further reaction zone for conversion to maleic anhydride and no means for controlling the reaction temperature.

The method disclosed in EP 1 007 499 B1 is disadvantageous because a high expenditure in terms of apparatus and process engineering is required. The expense is largely due to the low sales and the high proportion of process gases not involved in the reaction according to formula (I). The disclosed high selectivity of the overall process is opposed by a low yield and a low conversion, as well as a high energy consumption for the individual separation and purification steps, which further makes the method economically disadvantageous.

US Pat. No. 6,194,587 B1 discloses a process similar to that of EP 1 007 499 B1. In a first reaction zone, which is cooled, air is reacted with 0.5 to 3 mol% of n-butane to form maleic anhydride. The process gas exiting the reaction zone is cooled to condense and / or absorb in water portions of the maleic anhydride formed. The remaining process gas is fed to another reaction zone together with further n-butane. It is further disclosed that this combination of reaction zone with cooling and absorbing, and subsequent metered addition of further n-butane in the remaining process gas can also be performed more than twice in succession. It should also be noted that more than 3 mol% of n-butane content causes explosion hazards; only 4 to 5 mol% are possible in fluidized bed reactors. In the same context, it is disclosed that the process should be operated at a maximum temperature difference between the cooling medium and the reaction temperature of 100 ^° C. The reaction temperature can be between 365 ° C and 550 ⁰ C. It is further disclosed that the reaction temperature should not exceed a value of 475 ° C for longer times, otherwise loss of yield and losses of catalyst activity must be feared.

The process disclosed in US Pat. No. 6,194,587 B1 is disadvantageous for reasons similar to those already discussed in connection with the disclosure of EP 1 007 499 Bl, although it is already known from the simplified procedure Represents improvement. The fact that the reaction zone is operated analogously to the disclosure of EP 0 326 536 B1 at a constant maximum cooling rate, which is given by geometry and heat exchange medium, but leads to the same disadvantages as have already been set out there.

EP 1 251 951 (B1) discloses a device and the possibility of carrying out chemical reactions in the device, wherein the device is characterized by a cascade of reaction zones in contact with one another and heat exchanger devices which are arranged in a composite with one another. The method to be carried out here is thus characterized by the contact of the various reaction zones with a respective heat exchanger device in the form of a cascade. There is no disclosure as to the usability of the apparatus and method for the synthesis of maleic anhydride from gaseous oxygen and butane. Thus, it remains unclear how, starting from the disclosure of EP 1 251 951 (B1), such a reaction should be carried out by means of the device and the method carried out therein. Further, for the sake of uniformity, it is to be understood that the method disclosed in EP 1 251 951 (B1) is carried out in a device the same as or similar to the disclosure regarding the device. As a result, by the large-area contact of the heat exchange zones according to the disclosure with the reaction zones, a significant amount of heat takes place by heat conduction between the reaction zones and the adjacent heat exchange zones. The disclosure regarding the oscillating temperature profile can therefore only be understood as meaning that the temperature peaks ascertained here would be stronger if this contact did not exist. Another indication of this is the exponential increase in the disclosed temperature profiles between the individual temperature peaks. These indicate that there is some heat sink of appreciable but limited capacity in each reaction zone which can reduce the temperature rise in it. It can never be ruled out that a certain dissipation of heat (eg by radiation) takes place. However, a reduction of the possible heat removal from the reaction zone would indicate a linear or degressive temperature gradient, since no further addition of educts is envisaged and thus, after an exothermic reaction, the reaction becomes slower and thus the heat of reaction produced would decrease. Thus, EP 1 251 951 (B1) discloses multi-stage processes in cascades of reaction zones from which heat in undefined Quantity is dissipated by heat conduction. Accordingly, the disclosed method is disadvantageous in that accurate temperature control of the process gases of the reaction is not possible.

Based on the prior art, it would therefore be advantageous to provide a method that can be carried out in simple reaction devices and that allows accurate, simple temperature control, so that it allows high conversions with the highest possible purity of the product. Such simple reaction devices would be easily scaled up and are inexpensive and robust in all sizes.

For the catalytic gas-phase oxidation of butane with oxygen to maleic anhydride, as described above, neither suitable reactors have yet been described, nor are suitable processes disclosed which permit them.

It is therefore the object of the invention to provide a process for the catalytic gas-phase oxidation of butane and oxygen to maleic anhydride, which can be carried out under precise temperature control in simple reaction apparatuses and which thereby permits high conversions at high purities of the product, the heat of reaction either in favor of the reaction or otherwise used.

It has surprisingly been found that a process for the preparation of maleic anhydride from butane and oxygen in the presence of heterogeneous catalysts, characterized in that it comprises 10 to 60 successive reaction zones with adiabatic conditions, is capable of solving this problem.

Butane in the context of the present invention refers to a process gas which is introduced into the process according to the invention and comprises butane. The proportion of butane in the process gases supplied to the process is usually between 1 and 5 mol%, preferably between 1 and 3 mol%.

Oxygen in the context of the present invention refers to a process gas which is introduced into the process according to the invention and which comprises oxygen. The proportion of oxygen in the process gases supplied to the process is usually between 10 and 60 mol%, preferably between 15 and 50 mol%. In addition to the essential components of the process gases butane and oxygen, these can also include secondary components. Non-exhaustive examples of minor components that may be included in the process gases include argon, nitrogen, carbon dioxide, carbon monoxide, and / or water.

Generally, in the context of the present invention, process gases are understood as gas mixtures which comprise oxygen and / or butane and / or maleic anhydride and / or secondary components.

According to the invention, carrying out the process under adiabatic conditions essentially means that the reaction zone is neither actively supplied with heat nor heat withdrawn from the outside. It is well known that complete isolation against heat input or discharge is possible only by complete evacuation, excluding the possibility of heat transfer by radiation. Therefore, in the context of the present invention, adiabat means that no heat supply or removal measures are taken.

In an alternative embodiment of the method according to the invention, however, e.g. by isolation by means of well-known isolation means, e.g. Polystyrene insulating materials, or by sufficiently large distances to heat sinks or heat sources, wherein the insulating agent is air, a heat transfer can be reduced.

An advantage of the adiabatic driving method according to the invention of the 10 to 60 successive reaction zones compared to a non-adiabatic mode of operation is that in the reaction zones no means for heat removal must be provided, which entails a considerable simplification of the construction. This results in particular simplifications in the manufacture of the reactor and in the scalability of the process and an increase in reaction conversions. In addition, the heat generated in the course of the exothermic reaction progress can be utilized in the single reaction zone to increase the conversion in a controlled manner.

Another advantage of the method according to the invention is the possibility of very accurate temperature control, due to the close staggering of adiabatic reaction zones. It can thus be set and controlled in each reaction zone advantageous in the reaction progress temperature. The catalysts used in the process according to the invention are usually catalysts which consist of a material which, in addition to its catalytic activity for the reaction according to formula (I), is characterized by sufficient chemical resistance under the conditions of the process and by a high specific surface area. Catalyst materials characterized by such chemical resistance under the conditions of the process are, for example, catalysts comprising vanadium and phosphorus supported on alumina.

Specific surface area in the context of the present invention refers to the area of the catalyst material that can be reached by the process gases based on the mass of catalyst material used.

A high specific surface area is a specific surface area of at least 10 m ² / g, preferably of at least 20 m ² / g.

The catalysts of the invention are each in the reaction zones and can be used in all known forms, e.g. Fixed bed, fluidized bed, fluidized bed present.

Preferred are the forms of fixed bed and fluidized bed.

The fixed bed arrangement comprises a catalyst bed in the true sense, d. H. loose, supported or unsupported catalyst in any form and in the form of suitable packings. The term catalyst bed as used herein also encompasses contiguous areas of suitable packages on a support material or structured catalyst supports. These would be e.g. to be coated ceramic honeycomb carrier with comparatively high geometric surfaces or corrugated layers of metal wire mesh on which, for example, catalyst granules is immobilized. As a special form of packing, in the context of the present invention, the presence of the catalyst in monolithic form is considered.

If a fixed-bed arrangement of the catalyst is used, the catalyst is preferably present in beds of particles having mean particle sizes of 1 to 10 mm, preferably 1.5 to 8 mm, particularly preferably 2 to 6 mm. Also preferably, the catalyst is in a fixed bed arrangement in monolithic form. In the case of a fixed-bed arrangement, a monolithic catalyst which consists of a vanadium-phosphorus mixed oxide supported on aluminum oxide is particularly preferred.

When a catalyst in monolithic form is used in the reaction zones, in a preferred further development of the invention the monolithic catalyst is provided with channels through which the process gases flow. Usually, the channels have a diameter of 0.1 to 3 mm, preferably a diameter of 0.2 to 2 mm, more preferably from 0.5 to 1.5 mm.

A monolithic catalyst with channels of the specified diameter is particularly advantageous, since this explosion protection can be ensured. This is done by absorbing the enthalpy through the wall of the monolith and thus suppressing further propagation of flames.

If a fluidized bed arrangement of the catalyst is used, the catalyst is preferably present in loose beds of particles, as have also previously been described for the fixed bed arrangement.

Beds of such particles are advantageous because the size of the particles have a high specific surface area of the catalyst material compared to the process gases oxygen and butane and thus a high conversion rate can be achieved. Thus, the mass transport limitation of the reaction by diffusion can be kept low. At the same time, however, the particles are not yet so small that disproportionately high pressure losses occur when the fixed bed flows through. The ranges of the particle sizes given in the preferred embodiment of the process, comprising a reaction in a fixed bed, are thus an optimum between the achievable conversion from the reaction according to formula (I) and the pressure drop produced when the process is carried out. Pressure loss is coupled in a direct manner with the necessary energy in the form of compressor performance, so that a disproportionate increase in the same would result in an inefficient operation of the method.

A preferred embodiment of the process according to the invention comprises 12 to 50, particularly preferably 14 to 40 reaction zones connected in series under adiabatic conditions. A preferred further embodiment of the method is characterized in that the process gas emerging from at least one reaction zone is subsequently passed through at least one heat exchange zone downstream of said reaction zone.

In a particularly preferred further embodiment of the process, after each reaction zone is at least one, preferably exactly one heat exchange zone, through which the process gas leaving the reaction zone is passed.

The reaction zones can either be arranged in a reactor or arranged divided into several reactors. The arrangement of the reaction zones in a reactor leads to a reduction in the number of apparatuses used.

The individual reaction zones and heat exchange zones can also be arranged together in a reactor or in any combination of reaction zones with heat exchange zones in several reactors.

If reaction zones and heat exchange zones are present in a reactor, in an alternative embodiment of the invention there is a heat insulation zone between them in order to be able to obtain the adiabatic operation of the reaction zone.

In addition, each of the series-connected reaction zones can be replaced or supplemented independently of one another by one or more reaction zones connected in parallel. The use of reaction zones connected in parallel allows in particular their replacement or supplementation during ongoing continuous operation of the process.

Parallel and successive reaction zones may in particular also be combined with one another. However, the process according to the invention particularly preferably has exclusively reaction zones connected in series.

The reactors preferably used in the process according to the invention can consist of simple containers with one or more reaction zones, as described, for example, in Ulimann's Encyclopedia of Industrial Chemistry (Fifth, Completely Revised Edition, VoI B4, pages 95-104, pages 210-216), wherein in each case between the individual reaction zones and / or heat exchange zones heat insulation zones can be additionally provided. In an alternative embodiment of the method, there is thus at least one heat-insulating zone between a reaction zone and a heat exchange zone. Preferably, there is a heat isolation zone around each reaction zone.

The catalysts or the fixed beds thereof are mounted in a manner known per se on or between gas-permeable walls comprising the reaction zone of the reactor. Especially with thin fixed beds can in the flow direction before the

Catalyst beds technical devices for uniform gas distribution can be attached. These can be perforated plates, bubble-cap trays, valve trays or other internals which, by producing a small but uniform pressure loss, cause a uniform entry of the process gas into the fixed bed.

In a particular embodiment of the process according to the invention, preference is given to using a substance excess of between 0 and 300 mol% of oxygen, based on the mass flow rate of butane, before entering the first reaction zone. By increasing the ratio of oxygen per butane, on the one hand the reaction can be accelerated and thus the space-time yield (amount of produced maleic anhydride per mass of catalyst material) can be increased, on the other hand a composition of the process gas is achieved which is further removed from the critical boundary composition for an explosion ,

In a particularly preferred embodiment of the method, the inlet temperature of the process gas entering the first reaction zone is from 10 to 360 ° C., preferably from 50 to 39O ⁰ C, particularly preferably from 100 to 410 ° C.

In yet another particularly preferred embodiment of the process, the absolute pressure at the inlet of the first reaction zone is between 1 and 7 bar, preferably between 1, 5 and 6 bar, more preferably between 2 and 5 bar.

In a further particularly preferred embodiment of the process, the residence time of the process gas in a reaction zone is between 0.1 and 30 s, preferably between 0.2 and 15 s, particularly preferably between 0.5 and 7 s.

The butane and the oxygen are preferably fed only before the first reaction zone. This has the advantage that the entire process gas can be used for the absorption and removal of the heat of reaction in all reaction zones. In addition, through Such a procedure, the space-time yield can be increased, or the necessary catalyst mass can be reduced. However, it is also possible before one or more of the reaction zones following the first reaction zone to meter in butane and / or oxygen as required into the process gas. In addition, the temperature of the conversion can be controlled via the supply of gas between the reaction zones.

In a particularly preferred embodiment of the method according to the invention, the process gas is cooled after at least one of the reaction zones used, more preferably after each of the catalyst beds used. For this purpose, the process gas is passed after exiting a reaction zone through one or more of the above-mentioned heat exchange zones, which are located behind the respective reaction zones. These may be used as heat exchange zones in the form of heat exchangers known to those skilled in the art, e.g. Rohrbündel- be, plate, Ringnut-, spiral, finned tube, micro heat exchanger be executed. The heat exchangers are preferably microstructured heat exchangers.

In the context of the present invention, microstructured means that the heat exchanger for the purpose of heat transfer comprises fluid-carrying channels, which are characterized in that they have a hydraulic diameter between 50 μm and 5 mm. The hydraulic diameter is calculated as four times the flow cross-sectional area of the fluid-conducting channel divided by the circumference of the channel.

In a particular embodiment of the method, steam is generated during cooling of the process gas in the heat exchange zones by the heat exchanger.

Within this further embodiment, it is preferable in the heat exchangers, which include the heat exchange zones, to carry out evaporation on the side of the cooling medium, preferably partial evaporation.

Partial evaporation referred to in the context of the present invention, an evaporation in which a gas / liquid mixture of a substance is used as a cooling medium and in which there is still a gas / liquid mixture of a substance after heat transfer in the heat exchanger. The carrying out of evaporation is particularly advantageous because in this way the achievable heat transfer coefficient from / to process gases on / from the cooling / heating medium becomes particularly high and thus efficient cooling can be achieved.

Performing a partial evaporation is particularly advantageous because the absorption / release of heat by the cooling medium thereby no longer results in a temperature change of the cooling medium, but only the gas / liquid equilibrium is shifted. This has the consequence that over the entire heat exchange zone, the process gas is cooled to a constant temperature. This in turn safely prevents the occurrence of temperature profiles in the flow of process gases, thereby improving control over the reaction temperatures in the reaction zones and, in particular, preventing the formation of local overheating by temperature profiles.

In an alternative embodiment, instead of evaporation / partial evaporation, a mixing zone can also be provided upstream of the entrance of a reaction zone in order to standardize the temperature profiles in the flow of process gases which may arise during cooling by mixing transversely to the main flow direction.

In a preferred embodiment of the process, the reaction zones connected in series are operated at an average temperature increasing or decreasing from reaction zone to reaction zone. This means that within a sequence of reaction zones, the temperature can be both increased and decreased from reaction zone to reaction zone. This can be adjusted, for example, via the control of the heat exchange zones connected between the reaction zone.

The thickness of the flow-through reaction zones can be chosen to be the same or different and results according to laws generally known in the art from the residence time described above and the process gas quantities enforced in the process. The mass flows of product gas (maleic anhydride) which can be carried out according to the invention by the method, and from which the amounts of process gas to be used, are usually between 0.01 and 35 t / h, preferably between 0.1 and 30 t / h, more preferably between 1 and 25 t / h. The maximum outlet temperature of the process gas from the reaction zones is usually in a range from 370 ° C to 500 ° C, preferably from 400 ° C to 485 ° C, more preferably from 420 ⁰ C to 470 ⁰ C. The control of the temperature in the reaction zones is preferably carried out by at least one of the following measures: dimensioning of the adiabatic reaction zone, control of heat dissipation between the reaction zones, addition of gas between the reaction zones, molar ratio of the reactants / excess of oxygen used, addition of inert gases, in particular nitrogen, carbon dioxide, before and / or between the reaction zones.

The composition of the catalysts in the reaction zones according to the invention may be identical or different. In a preferred embodiment, in each

Reaction zone uses the same catalysts. However, it is also advantageous to use different catalysts in the individual reaction zones. Thus, especially in the first reaction zone, when the concentration of the reaction educts is still high, a less active catalyst can be used and in the further reaction zones the activity of the catalyst can be increased from reaction zone to reaction zone. The control of catalyst activity can also be achieved by dilution with

Inert materials or carrier material take place. Also advantageous is the use of a catalyst in the first and / or second reaction zone, which is particularly stable against deactivation at the temperatures of the process in these reaction zones.

0.01 kg / h to 1 kg / h, preferably 0.03 kg / h to 0.5 kg / h, particularly preferably 0.05 kg / h to 0.2 kg / per 1 kg of catalyst with the method according to the invention be prepared maleic anhydride.

The inventive method is thus characterized by high space-time yields, combined with a reduction of the apparatus sizes and a simplification of

Apparatuses or reactors. This surprisingly high space-time yield is made possible by the interaction of the inventive and preferred embodiments of the new method. In particular, the interaction of staggered, adiabatic

Reaction zones with interposed heat exchange zones and the defined residence times allows precise control of the process and the resulting high space-time yields, as well as a reduction of the formed

By-products, such as CO ₂ and water. Another object of the invention is a reactor system for the reaction of butane and oxygen to maleic anhydride, characterized in that it comprises feed lines (Z) for a process gas comprising butane and oxygen or for at least two process gases, of which at least one butane and at least one oxygen and 10 comprises up to 60 reaction zones (R) connected in series in the form of fixed beds of a heterogeneous catalyst, heat insulation zones (I) in the form of insulating material and between these heat exchange zones (W) in the form of plate heat exchangers between the reaction zones. and discharges for the process gases are connected and include the supply and discharge lines for a cooling medium.

The reactor system may also comprise 12 to 50, preferably 14 to 40 reaction zones in the form of fixed beds.

The insulating material of the heat insulating zones is preferably a material having a

Wärmeleitkoeffizient λ less than or equal to 0.08. Particularly preferred are about

Polystyrene, polyurethanes, glass wool or air.

The present invention will be elucidated with reference to the drawings without, however, being limited thereto.

1 shows a schematic representation of an embodiment of the reactor system according to the invention, the following reference numerals being used in the figures:

Z: supply line (s)

R: reaction zone (s)

I: thermal insulation zone (s)

W: Heat exchange zone (s) FIG. 2 shows reactor temperature (T), butane conversion (U) and maleic anhydride selectivity (Y) over a number of 21 reaction zones (S) with downstream heat exchange zones (according to Example 1). 3 shows reactor temperature (T), butane conversion (U) and maleic anhydride selectivity (Y) over a number of 24 reaction zones (S) with downstream heat exchange zones (according to Example 2).

The present invention will be further illustrated by the following Examples 1 and 2, without being limited thereto.

Examples

Example 1:

In this example, the process gas flows over a total of 21 fixed catalyst beds of vanadium phosphorous oxide, which is applied to a support of alumina, that is, through 21 reaction zones. Each after a reaction zone is a heat exchange zone in which the process gas is cooled before it enters the next reaction zone. The process gas used at the beginning of the first reaction zone contains 2 mol% of butane, 20 mol% of oxygen, and 78 mol% of inert gases (nitrogen, water vapor). The absolute inlet pressure of the process gas directly in front of the first reaction zone is 3.13 bar. The length of the fixed catalyst beds, ie the reaction zones, is always 0.23 m. There is no replenishment of gas before the individual catalyst stages. The total residence time in the system is 1, 6 seconds.

The results are shown in FIG. Here, the individual reaction zones are listed on the x-axis, so that a spatial course of developments in the process is visible. The temperature of the process gas is indicated on the left y-axis. The temperature profile across the individual reaction zones is shown as a thick, solid line. On the right y-axis the total conversion of butane, as well as the selectivity of maleic anhydride is given. The course of the conversion over the individual reaction zones is shown as a thick dashed line. The course of selectivity, as a thin solid line.

It can be seen that the inlet temperature of the process gas before the first reaction zone is about 405 ⁰ C. Due to the exothermic reaction to maleic anhydride under adiabatic conditions, the temperature in the first reaction zone rises to about 440 ° C, before the process gas is cooled in the downstream heat exchange zone again. The inlet temperature before the next reaction zone is about 400 ⁰ C. By exothermic adiabatic reaction, it rises again to about 440 ⁰ C. The sequence of heating and cooling continues. The inlet temperatures of the process gas upstream of the individual reaction zones changes in the course of the process to a value of about 420 ^° C. A conversion of butane of 80.3 mol% is obtained. The selectivity is obtained at 73.6 mol%. The achieved space-time yield based on the mass used

Catalyst is 0.07 kg maleic anhydride / kg cath

Example 2:

In this example, the process gas flows through a total of 24 reaction zones, in the form of monoliths with channel diameters of the monoliths of 1 mm, which are coated with the catalyst used in Example 1. Each after a reaction zone is a heat exchange zone in which the process gas is cooled before it enters the next reaction zone. The process gas used at the beginning now contains 2 mol% of butane, 48 mol% of oxygen and only 50 mol% of inert gases. The inlet pressure before the first reaction zone is identical to that of Example 1. The length of the reaction zones is constantly 0.2 m. The amount of catalyst coated according to Example 1 on the monoliths is 35 wt .-%. There is no replenishment of gas before the individual catalyst stages. The residence time in the system is a total of 5.2 seconds.

It can be seen that the inlet temperature of the process gas before the first reaction zone is about 395 ° C. Due to the exothermic reaction to maleic anhydride under adiabatic conditions, the temperature in the first reaction zone rises to about 470 ° C, before the process gas is cooled in the downstream heat exchange zone. The inlet temperature before the next reaction zone is about 425 ⁰ C. By exothermic adiabatic reaction, it rises again to about 470 ⁰ C. The sequence of heating and cooling continues. The inlet temperature of the process gas upstream of the individual reaction zones changes in the course of the process to a value of about 455 ° C. It can continue using a higher percentage of oxygen be worked without fear of explosion hazard, since the use of monoliths with the selected channel diameter are able to suppress this.

It is a conversion of 90.8% of the input of the first reaction zone butane, calculated from the remaining mass output of the last reaction zone obtained. The selectivity is about 71.6 mol% with respect to maleic anhydride. The space-time yield achieved based on the mass used catalyst

0.07 kg of maleic anhydride / kg of Kath.

Claims

claims

1. A process for the preparation of maleic anhydride from butane and oxygen in the presence of heterogeneous catalysts, characterized in that it comprises 10 to 60 successive reaction zones with adiabatic conditions.

2. The method according to claim 1, characterized in that it is 12 to 50, preferably

Comprises 14 to 40 consecutive reaction zones with adiabatic conditions.

3. The method according to claim 1 or claim 2, characterized in that the inlet temperature of the entering into the first reaction zone process gas 10 to 360 ⁰ C, preferably from 50 to 390 ⁰ C, more preferably from 100 to 410 ⁰ C.

4. The method according to claim 1 to 3, characterized in that the absolute pressure at the entrance of the first reaction zone is between 1 and 7 bar, preferably between 1.5 and 6 bar, more preferably between 2 and 5 bar.

5. The method according to any one of the preceding claims, characterized in that the

Residence time of the process gas in all reaction zones together between 0.1 and 30 s, preferably between 0.2 and 15 s, more preferably between 0.5 and 7 s.

6. The method according to claim 5, characterized in that the catalysts comprise supported on alumina vanadium-phosphorus mixed oxides.

7. The method according to any one of the preceding claims, characterized in that the catalysts are present in a fixed bed arrangement.

8. The method according to claim 7, characterized in that the catalysts are present as monoliths.

9. The method according to claim 8, characterized in that the monolith channels having a diameter of 0.1 to 3 mm, preferably from 0.2 to 2 mm, particularly preferably from 0.5 to 1.5 mm.

10. The method according to any one of claims 1 to 6, characterized in that the catalysts are in fluidized bed arrangement.

11. The method according to claims 7 or 10, characterized in that the catalysts are present in beds of particles having average particle sizes of 1 to 10 mm, preferably 1, 5 to 8 mm, particularly preferably from 2 to 6 mm.

12. The method according to any one of the preceding claims, characterized in that after at least one reaction zone is at least one heat exchange zone through which the process gas is passed.

13. The method according to claim 12, characterized in that after each reaction zone at least one, preferably a heat exchange zone is located, through which the process gas is passed.

14. The method according to any one of the preceding claims, characterized in that there is at least one heat insulation zone between a reaction zone and a heat exchange zone.

15. The method according to claim 14, characterized in that around each

Reaction zone is a heat insulation zone.

16. Reactor system for carrying out a method according to one of the preceding claims, characterized in that it comprises feed lines (Z) for a process gas comprising butane and oxygen or for at least two process gases, of which at least one butane and at least one oxygen and 10 to 60 in a row connected reaction zones (R) in the form of fixed beds of a heterogeneous catalyst, which are between the reaction zones heat insulation zones (I) in the form of insulating material and between these heat exchange zones (W) in the form of plate heat exchangers with the reaction zones via inlets and outlets for the process gases are connected and include the supply and discharge lines for a cooling medium.