METHOD FOR MAINTAINING ACTIVITY WHEN HYDROFORMYRATION IS STOPPED

Description

[0001] The project leading to this patent application received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 869896.

[0002] The present invention relates to a process for the hydroformylation of short-chain olefins, in particular C2 to C5 olefins, in at least one reactor, in which the catalyst system is heterogenized on a support made of a porous ceramic material and wherein, when the process is shut down, process steps a) to c) are carried out according to claim 1.

[0003] With an annual global production capacity of several million tons, hydroformylation is one of the most important reactions in industrial-scale chemistry. In this process, alkenes (olefins) are converted into aldehydes using a mixture of carbon monoxide and hydrogen (also known as synthesis gas or syngas) and a catalyst. These aldehydes are important and valuable intermediates in the production of bulk chemicals such as alcohols, esters, or plasticizers.

[0004] Hydroformylation is carried out exclusively under homogeneous catalysis on an industrial scale. Soluble transition metal catalyst systems are typically based on cobalt or rhodium, which is often used with phosphorus-containing ligands, such as phosphines or phosphites, for the hydroformylation of relatively short-chain olefins.

[0005] The problems with the known processes are manifold, particularly related to the comparatively expensive nature of both rhodium and cobalt, and their compounds. High energy and process engineering expenditures are required to minimize catalyst losses during the hydroformylation process, for example, through sometimes very complex catalyst recycling steps. Furthermore, product purification steps are becoming more complex to ensure that as few catalyst residues as possible remain in the product.

[0006] Further problems with the known homogeneously catalyzed processes are the stability of the ligands, which must withstand the conditions of hydroformylation, such as temperature, pressure, pH, etc., and the consumption of the solvent used during the process, which must be compensated by additional dosing.

[0007] To circumvent the aforementioned problems in homogeneously catalyzed hydroformylation, hydroformylation processes have been developed in which the catalyst system is heterogenized, in particular by immobilization on a support material. The terms "heterogenization" and "immobilization" are therefore to be understood as meaning that the catalyst is immobilized by forming a thin liquid film with the aid of an ionic liquid on the surface and / or in the pores of a solid support material, and that no reaction solution in the classical sense is present in which the catalyst is homogeneously dissolved. Hydroformylation processes in which the catalyst is heterogenized on a support material are disclosed, for example, in WO 2015 / 028284 A1, EP 3 632 885 A1, EP 3 744 707 A1, EP 3 632 886 A1, or EP 3 736 258 A1.

[0008] When conducting such chemical reactions on an industrial scale, it may be necessary to shut down the plant, even for extended periods, for example, due to assembly or maintenance work. During such a shutdown, the reaction is first stopped and the reactor is then purged with an inert material, such as nitrogen. This allows the products present in the reactor to be removed and prevents subsequent reactions with the remaining products. After such a shutdown procedure, problems may arise that make it impossible to restart the reaction. This could be due to a significantly reduced catalyst activity, which would require a costly catalyst replacement.

[0009] The object of the present invention was therefore to provide a process for the hydroformylation of olefins, which comprises steps for shutting down at least one reactor, but does not have the aforementioned disadvantages. In particular, the catalyst activity should not be significantly reduced after restarting the reaction, but rather the activity should be maintained as far as possible.

[0010] This object is achieved according to claim 1 in that the at least one reactor is purged with synthesis gas during shutdown and is left standing in a synthesis gas atmosphere during subsequent storage. Preferred embodiments are specified in the subclaims.

[0011] The present invention thus provides a process for the hydroformylation of C2- to C8-olefins in at least one reactor using a heterogenized catalyst system, wherein a gaseous feed mixture containing the C2 to C8 olefins is passed together with synthesis gas in at least one reactor over a support made of a porous ceramic material arranged in the at least one reactor, on which the catalyst system, which comprises a metal from group 8 or 9 of the Periodic Table of the Elements, at least one organic phosphorus-containing ligand, and a stabilizer, is heterogenized; wherein the support is a monolith, i.e. a block made of a ceramic material, or is in the form of a powder, in the form of granules, or in the form of shaped bodies, and the support consists of a carbide, nitride, silicide material, or mixtures thereof, and wherein the hydroformylation is carried out at a temperature in the at least one reactor of 65 to 200°C;characterized in that the process comprises the following steps for shutting down and storing the at least one reactor: a) shutting down the supply of gaseous feed mixture while synthesis gas continues to be fed into the at least one reactor; b) lowering the temperature in the at least one reactor to ambient temperature; c) shutting down the supply of synthesis gas and storing the at least one reactor under a synthesis gas atmosphere until the hydroformylation process is restarted. A characteristic feature of the present invention is the purging of the at least one reactor with synthesis gas when shutting down the reaction and the storage under a synthesis gas atmosphere. This makes it possible to run the process in normal operation again after the reaction has been restarted.

[0012] In the context of the present invention, ambient temperature is understood as a temperature achieved without heating or cooling. A more precise definition is impossible because the prevailing temperature can vary significantly depending, for example, on the season.

[0013] In the first step a) of the shutdown and storage steps, the feed of feed mixture is shut off. This stops the reaction. At the same time, the synthesis gas stream continues to be fed to the at least one reactor. This allows any hydrocarbons still present in the reactor to be flushed out. In a preferred embodiment of the present invention, the synthesis gas feed is increased when the feed of gaseous feed mixture is shut off in step a). This ensures that a similar or identical volume flow continues to be passed through the at least one reactor. In a particularly preferred embodiment, the feed of gaseous feed mixture is therefore completely replaced by synthesis gas.

[0014] In the subsequent step b), the temperature in the at least one reactor is reduced to ambient pressure. This can be done actively by cooling, whereby the cooling only takes place up to the point where the ambient temperature is reached in the at least one reactor. Cooling can also be done passively, i.e. without active cooling. In a preferred embodiment of the present invention, the pressure in the at least one reactor is reduced after and / or during the temperature reduction in step b). This makes it possible to remove any high boilers still present in the reactor that could not be removed by purging in step a).

[0015] In a further preferred embodiment of the present invention, the synthesis gas feed in step b) can be reduced. This may be necessary under certain circumstances to achieve a pressure reduction in the at least one reactor. Furthermore, this can save synthesis gas.

[0016] In step c) of the shutdown and storage steps of the process according to the invention, the supply of synthesis gas is shut off, and the at least one reactor is stored in a synthesis gas atmosphere until the hydroformylation is restarted. In a preferred embodiment, the pressure in the at least one reactor can be increased again before shutting off the supply of synthesis gas in step c). If the pressure was reduced in the previous step b), this may make the pressure increase necessary.

[0017] The at least one reactor can be stored under a synthesis gas atmosphere for a specific period of time, for example, for days, weeks, months, or years. In a preferred embodiment, the at least one reactor is stored under a synthesis gas atmosphere for at least 24 hours.

[0018] All mixtures comprising C2 to C8 olefins, preferably C2 to C5 olefins, in particular ethene, propene, 1-butene, 2-butene, 1-pentene, or 2-pentene, as reactants can be used as the feed mixture. The amount of olefins in the feed mixtures should understandably be high enough to enable a hydroformylation reaction to be carried out economically. The feed mixtures usable in the process according to the invention also include, in particular, technical mixtures from the petrochemical industry, such as raffinate streams (raffinate I, II, or III) or crude butane. According to the present invention, crude butane comprises 5 to 40 wt.% butenes, preferably 20 to 40 wt.% butenes (the butenes are composed of 1 to 20 wt.% 1-butene and 80 to 99 wt.% 2-butene) and 60 to 95 wt.% butanes, preferably 60 to 80 wt.% butanes.

[0019] The process according to the invention is carried out in at least one reactor in which the hydroformylation according to the invention takes place. The support with the heterogenized catalyst system is arranged in the at least one reactor. In a further embodiment of the present invention, the process can also be carried out in a plurality of reactors, which may be connected in parallel or in series. If a plurality of reactors are present, these reactors are preferably connected in parallel and used alternately.

[0020] The hydroformylation is preferably carried out under the following conditions: The temperature during the hydroformylation is in the range from 65 to 200 °C, preferably from 75 to 175 °C, and particularly preferably from 85 to 150 °C. The temperature can be adjusted using a suitable cooling device, for example a cooling jacket. The pressure during the hydroformylation should be at least 1 bar and not greater than 35 bar, preferably not greater than 30 bar, and particularly preferably not greater than 25 bar. The molar ratio between synthesis gas and the feed mixture should be between 6:1 and 1:1, preferably between 5:1 and 3:1. Optionally, the feed mixture can be diluted with inert gas, for example with the alkanes present in industrial hydrocarbon streams.

[0021] The catalyst system used in the hydroformylation process according to the invention preferably comprises a transition metal from group 8 or 9 of the Periodic Table of the Elements, in particular iron, ruthenium, iridium, cobalt or rhodium, further preferably cobalt and rhodium, particularly preferably rhodium, at least one organic phosphorus-containing ligand and a stabilizer.

[0022] The stabilizer is preferably an organic amine compound, particularly preferably an organic amine compound containing at least one 2,2,6,6-tetramethylpiperidine unit according to formula (I):

[0023] In a particularly preferred embodiment of the present invention, the stabilizer is selected from the group consisting of the compounds of the following formulas (I.1), (I.2), (I.3), (I.4), (I.5), (I.6), (I.7) and (I.8). where n is an integer from 1 to 20; where n is an integer from 1 to 12; where n is an integer from 1 to 17; where R represents a C6 to C20 alkyl group.

[0024] For all film-forming components, i.e., in this case, the stabilizer, the gas solubility of the reactants should be better than the gas solubility of the products. This alone can achieve partial separation between the reactant olefins used and the product aldehydes formed. In principle, other film-forming substances would also be conceivable for this purpose, but care must be taken to ensure that this does not lead to increased high-boiling component formation and / or to restrict the supply of reactant olefins.

[0025] The organic phosphorus-containing ligand for the catalyst system according to the invention can be selected from those known for hydroformylation. A large number of suitable ligands are known to the person skilled in the art from the patent and technical literature, for example mono- or biphosphite ligands. The organic phosphorus-containing ligand preferably has a biphosphite structure according to the general formula (II) R'-AR"-AR‴ (II) where R', R", and R‴ are each organic radicals and both A's are each a bridging -OP(-O) 2 group, with two of the three oxygen atoms -O- being bonded to the radical R' and the radical R‴, with the proviso that R' and R‴ are not identical. The organic radicals R', R", and R‴ preferably do not contain a terminal trialkoxysilane group.

[0026] In a preferred embodiment, R', R" and R‴ in the compound of formula (VI) are preferably selected from substituted or unsubstituted 1,1'-biphenyl, 1,1'-binaphthyl and ortho-phenyl groups, in particular from substituted or unsubstituted 1,1'-biphenyl groups, with the proviso that R' and R‴ are not identical. Particularly preferably, the substituted 1,1'-biphenyl groups in the 3,3'- and / or 5,5'-position of the 1,1'-biphenyl base structure have an alkyl group and / or an alkoxy group, in particular a C1-C4 alkyl group, particularly preferably a tert-butyl and / or methyl group and / or preferably a C1-C5 alkoxy group, particularly preferably a methoxy group.

[0027] According to the invention, the aforementioned catalyst system is heterogeneously supported on a support made of a porous ceramic material. For the purposes of the present invention, the term "heterogenized on a support" is to be understood as meaning that the catalyst system is immobilized by forming a thin, solid or liquid film on the inner and / or outer surface of the support with the aid of the stabilizer. The film can also be solid at room temperature and liquid under reaction conditions.

[0028] The inner surface of the solid support material includes, in particular, the inner surface of the pores. Immobilization conceptually encompasses both the case where the catalyst system and / or the catalytically active species are dissolved in the solid or liquid film, as well as the cases where the stabilizer acts as an adhesion promoter or where the catalyst system is adsorbed onto the surface but not chemically or covalently bound to the surface.

[0029] According to the invention, there is therefore no reaction solution in the classical sense in which the catalyst is homogeneously dissolved, but rather the catalyst system is dispersed on the surface and / or in the pores of the support.

[0030] The porous support material is preferably selected from the group consisting of a nitridic ceramic, a carbide ceramic, a silicide ceramic and mixtures thereof, for example carbonitride materials.

[0031] The nitridic ceramic is preferably selected from silicon nitride, boron nitride, aluminum nitride, and mixtures thereof. The carbide ceramic is preferably selected from silicon carbide, boron carbide, tungsten carbide, or mixtures thereof. Mixtures of carbide and nitride ceramics, so-called carbonitrides, are also conceivable. The silicide ceramic is preferably molybdenum disilicide. The support according to the present invention, to which the catalyst system is applied, preferably consists of a carbide ceramic, particularly preferably silicon carbide.

[0032] In this case, the support can be in the form of a monolith, i.e. a block of a ceramic material, or in the form of a powder, in the form of granules or in the form of shaped bodies.

[0033] If the support is a monolith, it consists of a block (a three-dimensional object) made of the porous ceramic material. The block can be formed as a single piece or consist of several, i.e., at least two, individual parts that can be joined together to form the block and / or are firmly or detachably connected to each other.

[0034] The support made of the porous ceramic material is preferably a three-dimensionally extending component, the cross-section of which can, in principle, have any geometric shape, for example, round, angular, square, or similar. In a preferred embodiment, the three-dimensionally extending component, which can be used as a support, has a longitudinal direction (direction of the longest extent) in the main flow direction (direction in which the feed mixture and the synthesis gas flow from the inlet to the outlet of the at least one reactor).

[0035] The support monolith formed in this way from the porous ceramic material has at least one continuous channel in the main flow direction. However, the channel(s) can also be designed such that they are not completely continuous, but have a closure at the end opposite the inlet of the at least one reactor, or the channel is closed towards this end. The support monolith can also have at least two or more channels. The diameter of the channels can be in the range from 0.25 to 50 mm, preferably in the range from 1 to 30 mm, more preferably in the range from 1.5 to 20 mm, and particularly preferably in the range from 2 to 16 mm. If multiple channels are present, the diameters of the channels can be the same or different from one another. The diameter of the channels, in comparison to the or one of the diameters of the entire support, is to be selected in particular such that the mechanical stability is not impaired.

[0036] Furthermore, the support monolith made of the ceramic material is porous, i.e., it has pores. The catalyst system according to the invention is also located in these pores, particularly in the solid or liquid film. The pore diameter is preferably in the range of 0.9 nm to 30 µm, preferably in the range of 10 nm to 25 µm, and particularly preferably in the range of 70 nm to 20 µm. The pore diameter can be determined by nitrogen adsorption or mercury porosimetry according to DIN 66133 (version: 1993-06).

[0037] In a preferred embodiment, the support monolith has at least partially continuous pores that extend from the surface to the channels and / or from one channel to the nearest channel(s). It is also possible for several pores to be interconnected, thus forming a single continuous pore.

[0038] According to the invention, the support can also be in the form of a powder, in the form of granules, or in the form of shaped bodies such as pellets, rings, spheres, or the like. The average particle diameter (d50) of the support can be from 0.1 mm to 7 mm, preferably 0.3 to 6 mm, particularly preferably from 0.5 mm to 5 mm. The average particle diameter can be determined using imaging techniques, in particular by the methods specified in the standards ISO 13322-1 (as of December 1, 2004) and ISO 13322-2 (as of November 1, 2006). The support can be produced in the form of a powder, in the form of granules, or in the form of shaped bodies using methods known to those skilled in the art. For example, it could be achieved by mechanically crushing a monolith of the carbide, nitride, silicide material or mixtures thereof, for example with a jaw crusher, and adjusting the particle size of the resulting crushed granulate by means of sieving.

[0039] Like the support monolith, the particles of the powder, granules, or shaped bodies made of the ceramic material are porous, i.e., they have pores. The catalyst system according to the invention is also present, in particular, in the solid or liquid film in these pores. The pore diameter is preferably in the range of 0.9 nm to 30 µm, preferably in the range of 10 nm to 25 µm, and particularly preferably in the range of 70 nm to 20 µm. The pore diameter can be determined by nitrogen adsorption or mercury porosimetry according to DIN 66133 (version: 1993-06).

[0040] The production of the support, regardless of whether it is a monolith, powder, granulate, or molded body, is carried out as described below: A so-called washcoat can additionally be applied to the provided powder, granulate, or pellet-shaped support made of the ceramic material. This washcoat can be made of the same or a different ceramic material, preferably silicon oxide, relative to the ceramic material of the support. The washcoat itself can be porous or non-porous; preferably, the washcoat is non-porous. The particle size of the washcoat is preferably 5 nm to 3 µm, more preferably 7 nm to 700 nm. The washcoat is used to introduce or generate the desired pore size and / or to increase the surface area of ​​the support. The washcoat can be applied in particular by immersion (dip coating) in a washcoat solution containing the ceramic material of the washcoat, optionally also as a precursor.The amount of washcoat present on the support is ≤ 20 wt.%, preferably ≤ 15 wt.%, particularly preferably ≤ 10 wt.%, based on the total amount of the support. In a preferred embodiment of the present invention, however, the support has no washcoat.

[0041] The catalyst system is applied to the support with or without a washcoat. For this purpose, a catalyst solution is first prepared by mixing, particularly at room temperature and ambient pressure. The catalyst solution comprises at least one organic phosphorus-containing ligand, at least one metal precursor, for example chlorides, oxides, or carboxylates of the respective metal, at least one stabilizer, and at least one solvent. Optionally, an ionic liquid can be used in the preparation of the catalyst system; however, the catalyst solution can also be prepared explicitly without an ionic liquid. The catalyst solution should be prepared in an inert environment, e.g., a glove box. In this case, an inert environment means an atmosphere that is as free from water and oxygen as possible.

[0042] The solvent can be selected from all solvent classes (protic, aprotic, polar, or nonpolar). The prerequisite for the solvent is the solubility of the catalyst system (ligand, metal precursor, stabilizer, and optionally the ionic liquid) and preferably also of the high boilers formed during hydroformylation. The solubility can be increased during the immobilization step by heating.

[0043] The solvent is preferably aprotic and polar, such as acetonitrile and ethyl acetate, or aprotic and nonpolar, such as THF and diethyl ether. Chlorinated hydrocarbons such as dichloromethane or aldehydes can also be used as solvents.

[0044] The catalyst solution thus prepared is then brought into contact with the support (optionally including the washcoat), for example by immersion (dip coating) or by filling a pressure vessel, for example, directly in the at least one reactor (in-situ impregnation). If the catalyst solution is applied outside the reactor, the support must, of course, be reinserted into the reactor after the solvent has been removed. Preferably, the catalyst solution is applied directly to the support with the washcoat in the reactor, as this can avoid potentially time-consuming installation and removal steps as well as potential catalyst contamination.

[0045] The reactor can be filled with the catalyst solution via the standard inlets and outlets, for example, using a pump. Liquid distributors or nozzles within the reactor can ensure even distribution of the catalyst liquid, as can optionally be installed to reduce pressure or regulate the dosing rate.

[0046] After applying the catalyst system, the solvent is separated. First, the remaining catalyst solution is drained through the reactor outlet. Any solvent residues remaining in the reactor are then evaporated by adjusting the pressure or increasing the temperature. Alternatively, the pressure can be adjusted while simultaneously increasing the temperature. Depending on the solvent, the temperature can be between 20 and 150 °C. Depending on the solvent, the pressure can be adjusted to a high vacuum (10 -3 < to 10 -7 < mbar), but depending on the solvent and temperature, overpressures of a few mbar to several bar are also conceivable.

[0047] The stabilizer and the optionally present ionic liquid remain heterogenized on the support with the catalyst made of the transition metal, in particular cobalt or rhodium, and the organic phosphorus-containing ligand.

[0048] The catalyst system can be applied to the support either directly in the reactor (in situ) or outside the reactor. If the catalyst system is applied outside the reactor, the support must always be transported under the exclusion of air, which can be achieved, for example, with a nitrogen countercurrent. In a preferred embodiment of the present invention, the catalyst system is applied directly in the reactor, i.e., in situ. After the solvent has been removed, the reactor can be used immediately and charged with the feed mixture. This has the advantage that no time-consuming installation and removal steps are necessary, which would result in a prolonged reactor downtime. Furthermore, the size of the support is then no longer limited by the availability of suitable rooms with inert environments of a certain size. The size of the support can be freely selected depending on the reactor design.

[0049] After the catalyst system has been applied to the support and the solvent has been removed, the plant, especially the reactor, can be started up, i.e., put into operation, using a two- or multi-stage start-up procedure. A suitable start-up procedure is described, for example, in EP 3 632 887.

[0050] From the reaction zone in which the hydroformylation according to the invention is carried out, a gaseous output containing at least a portion of the product aldehydes formed and at least a portion of the unreacted olefins is preferably withdrawn continuously. The gaseous output can be subjected to one or more separation steps in which the gaseous output is separated into at least one phase rich in unreacted olefins and at least one product aldehyde-rich phase.

[0051] The substance separation can be carried out using known substance separation methods such as condensation, distillation, centrifugation, nanofiltration or a combination of several of them, preferably condensation or distillation.

[0052] In the case of a multi-stage separation, the product aldehyde-rich phase formed in the first separation can be fed to a second separation, in particular a subsequent aldehyde separation, in which the product aldehyde is separated from the other substances present in this phase, frequently alkanes and reactant olefins. The unreacted olefin-rich phase can be recycled to the hydroformylation step or, in the case of a multi-stage configuration, to one of the hydroformylation steps in order to hydroformylate the olefins contained therein to the product aldehyde.

[0053] During the separation process, in addition to the aforementioned phases, a purge gas stream can also be removed, which has a composition at least similar or identical to that of the unreacted olefin-rich phase. The purge gas stream can also be passed to the second separation process or aldehyde separation process to separate the product aldehydes contained therein and to remove impurities (e.g., nitrogen in the synthesis gas) or inert substances (e.g., alkanes in the feed mixture) from the system. The impurities or inert substances can usually be removed during the second separation process as volatile substances, for example, at the top of a column.

[0054] Even without further elaboration, it is assumed that a person skilled in the art can utilize the above description to the fullest extent possible. The preferred embodiments and examples are therefore to be considered merely descriptive and not in any way limiting disclosure.

[0055] The present invention is explained in more detail below using examples.

[0056] Example 1 (Comparative Example) SiC pellets (SIKAT SarL) were used as the starting material for the support. The SiC pellets were placed into a 20 cm long, round reactor sleeve with a diameter of one inch (approximately 2.54 cm), with glass beads of a similar size placed above and below the granules. The SiC pellets were then treated with a catalyst solution containing Rh(acac)(CO)2, bisphephos (ligand), bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (stabilizer), and pentanal as a solvent. For this purpose, the catalyst solution was flushed with nitrogen and then introduced into the reactor at a slight overpressure. After removing the solvent from the reactor by venting and evaporation, the catalyst system heterogenized on the support granules was used for hydroformylation.

[0057] A hydrocarbon stream containing 15 wt.% butenes and 85 wt.% butanes was used as the feed mixture for the experiments. The feed mixture was fed into the reactor for hydroformylation together with synthesis gas (molar ratio of synthesis gas to feed mixture = 3.5:1) at a gas flow rate of 390 ml / min. The hydroformylation was carried out at a temperature of 120-130 °C and a pressure of 17 bar.

[0058] During the experiment, the reactant flow was interrupted for several extended periods (stand time). During this stand time, the reactor, still heated to 120 °C, was purged with a nitrogen stream at a pressure of 17 bar. Conversion and yield were determined before and after the stand time using gas chromatography on the output stream. Table 1: Results of Example 1 Example 1 yield Sales volume Previously 24,5% 45,8% afterward 11% 30,8% Example 2

[0059] SiC pellets (SIKAT SarL) were used as the starting material for the support. The SiC pellets were placed into a 20 cm long, round reactor sleeve with a diameter of one inch (approximately 2.54 cm), with glass beads of similar size placed above and below the granules. The SiC pellets were then treated with a catalyst solution containing Rh(acac)(CO)2, bisphephos (ligand), bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (stabilizer), and pentanal as a solvent. For this purpose, the catalyst solution was flushed with nitrogen and introduced into the reactor at a slight overpressure. After removing the solvent from the reactor by venting and evaporation, the catalyst system heterogenized on the support granules was used for hydroformylation.

[0060] A hydrocarbon stream containing 15 wt.% butenes and 85 wt.% butanes was used as the feed mixture for the experiments. The feed mixture was fed into the reactor for hydroformylation together with synthesis gas (molar ratio of synthesis gas to feed mixture = 3.5:1) at a gas flow rate of 390 ml / min. The hydroformylation was carried out at a temperature of 120-130 °C and a pressure of 17 bar.

[0061] During the experiment, a reactor shutdown was simulated. For this purpose, the flow of reactants was interrupted for extended periods, the reactor was cooled to ambient temperature, and then restarted after a standstill period of 23 days. During storage, the reactor was pressurized with synthesis gas.

[0062] In the first step, the flow of the hydrocarbon stream was stopped and at least partially replaced with synthesis gas. After a prolonged purge phase near reaction temperature, the pressure in the reactor was reduced to expel further product residues. The system was then cooled to room temperature and finally pressurized to reaction pressure with synthesis gas for storage, and the system was closed.

[0063] After a shutdown period of 23 days, the system was restarted. To restart, the reactor was first flushed with synthesis gas, pressurized to 10 bar, and heated to a reaction temperature of 120°C. The hydrocarbon stream was metered in in several stages (as described in EP 3 632 887 A1). Before and after shutdown and storage, the reactor performance was determined based on conversion, yield, and selectivity using gas chromatography of the output stream. Table 2: Results of Example 2 Example 2 Sales (total butenes) n / iso selectivity yield Before decommissioning 17% 96% 15% After storage and storage 18% 96% 15%

[0064] It can be seen that after the shutdown and storage according to the invention, the conversion, selectivity, and yield are almost identical to the values ​​before the shutdown. Consequently, the catalyst activity remained almost constant and did not drop sharply as in Example 1, even though only nitrogen was used for purging in Example 1.

Claims

1. Process for hydroformylating C2 to C8 olefins in at least one reactor using a heterogenized catalyst system, wherein a gaseous feed mixture containing the C2 to C8 olefins is passed together with synthesis gas in at least one reactor over a support which is arranged in the at least one reactor and is composed of a porous ceramic material on which the catalyst system, which comprises a metal from group 8 or 9 of the periodic table of the elements, at least one organic phosphorus-containing ligand and a stabilizer, is present in heterogenized form; wherein the support is a monolith, i.e. a block of a ceramic material, or is in the form of a powder, in the form of a granular material or in the form of shaped bodies and the support consists of a carbidic material, nitridic material, silicidic material or mixtures thereof, and wherein the hydroformylation is conducted at a temperature in the reactor of 65 to 200°C; characterized in that the process comprises the following steps for shutdown of the at least one reactor: a) shutting down the feed of gaseous feed mixture while synthesis gas is still being fed into the at least one reactor; b) lowering the temperature in the at least one reactor to ambient temperature; c) shutting down the feed of synthesis gas and keeping the at least one reactor under synthesis gas atmosphere until the hydroformylation process is restarted.

2. Process according to Claim 1, wherein the synthesis gas feed rate is increased when the feed of gaseous feed mixture is shut down in step a).

3. Process according to Claim 1 or 2, wherein the pressure in the at least one reactor is reduced after and / or during the lowering of the temperature in step b).

4. Process according to Claim 3, wherein the synthesis gas feed rate is already reduced in step b).

5. Process according to any of the preceding claims, wherein, before the synthesis gas feed is shut down in step c), the pressure in the reactor is increased again.

6. Process according to any of the preceding claims, wherein the organic phosphorus-containing ligand of the hydroformylation catalyst system preferably has the general formula (II)         R'-A-R''-A-R‴     (II) where R', R'' and R‴ are each organic radicals, with the proviso that R' and R‴ are nonidentical, and the two A are each a bridging -O-P(-O)2- group, wherein two of the three oxygen atoms -O- are attached respectively to radical R' and to the radical R‴.

7. Process according to any of the preceding claims, wherein the stabilizer is an organic amine compound containing at least one 2,2,6,6-tetramethylpiperidine unit of formula (I):

8. Process according to any of the preceding claims, wherein the nitridic ceramic is selected from silicon nitride, boron nitride, aluminium nitride and mixtures thereof; the carbidic ceramic is selected from silicon carbide, boron carbide, tungsten carbide or mixtures thereof; and the silicidic ceramic is molybdenum silicide.

9. Process according to Claim 8, wherein the support consists of a carbidic ceramic.

10. Process according to Claim 9, wherein the support consists of silicon carbide.

11. Process according to any of Claims 1 to 7, wherein the hydroformylation is conducted at a temperature in the range from 75 to 175°C, preferably in the range from 85 to 150°C.

12. Process according to any of the preceding claims, wherein the pressure in the hydroformylation is at least 1 bar and not greater than 35 bar, preferably not greater than 30 bar, more preferably not greater than 25 bar.

13. Process according to any of the preceding claims, wherein the catalyst system does not comprise an ionic liquid.

14. Process according to any of the preceding claims, wherein C4 olefins are used in the hydroformylation process.

15. Process according to any of the preceding claims, wherein rhodium is used as a metal from group 8 or 9 of the periodic table of the elements.