Patent Publication Number: US-11384042-B2

Title: Process for hydroformylation of short-chain olefins in the gas phase

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage entry under § 371 of International Application No. PCT/EP2019/076413, filed on Sep. 30, 2019, and which claims the benefit of European Application No. 18198794.2, filed on Oct. 5, 2018. The content of each of these applications is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     The project which led to this patent application was financed in conjunction with grant agreement no. 680395 of the European Union Horizon 2020 Research and Innovation Programme. 
     FIELD OF THE INVENTION 
     The present invention relates to a process for hydroformylating short-chain olefins, especially C2 to C5 olefins, in which the catalyst system is present in heterogenized form on a support of a porous ceramic material, and to plants for performing this process. 
     DESCRIPTION OF RELATED ART 
     Hydroformylation is one of the most important reactions in industrial scale chemistry, having an annual global production capacity of several million tonnes. This involves reacting alkenes (olefins) with a mixture of carbon monoxide and hydrogen (also: synthesis gas or syngas) using a catalyst to give aldehydes, which are important and valuable intermediates in the production of chemical bulk products such as alcohols, esters or plasticizers. 
     Hydroformylation is conducted exclusively under homogeneous catalysis on the industrial scale. The soluble transition metal catalyst systems are typically based on cobalt or rhodium, which is often used together with phosphorus-containing ligands, for example phosphines or phosphites, for the hydroformylation of comparatively short-chain olefins. 
     There are various problems in the known processes, and these problems are especially linked to the fact that both rhodium and cobalt and compounds thereof are comparatively costly. There is a high level of energy expenditure and complex chemical engineering in order to very substantially avoid losses of catalyst during the hydroformylation process, for example by catalyst recycling steps, some of them very complex. Moreover, product purification steps are becoming more complex in order to ensure that as far as possible no catalyst residues remain in the product. 
     Further problems with the known homogeneously catalysed processes are the stability of the ligands, which have to withstand the hydroformylation conditions, such as temperature, pressure, pH etc., and consumption of the solvent used during the process, which can be compensated for by replenishment. 
     In order to get round the aforementioned problems in the homogeneously catalysed hydroformylation, there has been development of hydroformylation methods in which the catalyst is heterogenized, especially by immobilization on a support material (cf. introductory discussion in WO 2015/028284 A1). The terms “heterogenization” and “immobilization” should accordingly be understood such that the catalyst is immobilized by formation of 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 there is no reaction solution in the conventional sense in which the catalyst is homogeneously dissolved. 
     With regard to the immobilization/heterogenization, the already mentioned WO 2015/028284 A1 discloses what are called SILP systems (SILP=Supported Ionic Liquid Phase), in which the catalyst system is immobilized with rhodium, iridium or cobalt as central atom, especially on a porous silicon dioxide support using an ionic liquid. 
     However, the problem with the known SILP systems is that, after a certain service life, a distinct decreasing catalyst activity and hence a reduction in conversion can be observed. This may be attributable to various effects, for example condensation of the products in the pores and corresponding further reactions such as aldol condensations, or the formation of water that can lead to deactivation of the ligands, the formation of by-products and/or the flooding of the pores, as a result of which the catalyst may be discharged. 
     SUMMARY OF THE INVENTION 
     The problem addressed by the present invention was therefore that of providing a process for hydroformylating olefins that does not have the aforementioned problems and especially leads to an increase in the conversion and lifetime of the catalyst. 
     This problem is solved according to the description below, in that a catalyst system is used in the hydroformylation, where the catalyst system is in heterogenized form on a support which is in the form of a powder, in the form of a granular material or in the form of pellets and composed of a porous ceramic material. 
     The present invention thus provides a process for hydroformylating C2 to C5 olefins in a reaction zone using a heterogenized catalyst system, wherein the process is characterized in that 
     a gaseous feed mixture containing the C2 to C8 olefins is passed together with synthesis gas over a support 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, a stabilizer and optionally an ionic liquid is in heterogenized form; and 
     the support, which is in the form of a powder, in the form of a granular material or in the form of pellets and consists of a carbidic, nitridic or silicidic material or mixtures thereof, to which is applied a washcoat of the same or another ceramic material with respect to the ceramic material of the support. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The first feed mixture used may be any mixture comprising C2 to C5 olefins, especially ethene, propene, 1-butene, 2-butene, 1-pentene or 2-pentene, as reactants. The amount of olefins in the feed mixtures should naturally be high enough to be able to economically conduct a hydroformylation reaction. This especially includes technical mixtures from the petrochemical industry, for example raffinate streams (raffinate I, II or III) or crude butane. According to the present invention, crude butane comprises 5% to 40% by weight of butenes, preferably 20% to 40% by weight of butenes (the butenes are composed of 1% to 20% by weight of 1-butene and 80% to 99% by weight of 2-butene), and 60% to 95% by weight of butanes, preferably 60% to 80% by weight of butanes. 
     The reaction zone comprises at least one reactor in which the hydroformylation according to the invention is conducted, and in which the support with the heterogenized catalyst system is disposed. In a further embodiment of the present invention, the reaction zone comprises multiple reactors which can be connected in parallel or in series. Preferably, in this case the reactors are connected in parallel and are used alternately. This involves using at least one reactor (a) for the hydroformylation, i.e. the reactor is in operation. At least one further reactor (b) is in the wait state, where no hydroformylation is conducted therein. This is understood to mean that, as soon as catalyst activity is found to no longer be sufficient in reactor (a) which is in operation, the stream of the feed mixture is switched from this reactor (a) to the next reactor (b) In the wait state and this reactor (b) is put into operation therewith. Reactor (a) is then transferred to a regeneration mode, where the catalyst system is regenerated as described below or the support is newly impregnated, and then transferred into the wait position until the reactor is put back into operation. This principle can also be applied to 3 or more reactors, where at least one reactor is in operation, one or more reactors are simultaneously in the wait state and one or more reactors are simultaneously in regeneration mode. 
     The hydroformylation is preferably conducted under the following conditions: The temperature in the hydroformylation should be in the range from 65 to 200° C., preferably 75 to 175° C. and more preferably 85 to 150° C. The pressure should not exceed 35 bar, preferably 30 bar, more preferably 25 bar, during the hydroformylation. 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 alkanes present in technical hydrocarbon streams. 
     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, especially iron, ruthenium, iridium, cobalt or rhodium, more preferably cobalt or rhodium, at least one organic phosphorus-containing ligand, a stabilizer and optionally an ionic liquid. 
     The stabilizer is preferably an organic amine compound, more preferably an organic amine compound containing at least one 2,2,6,6-tetramethylpiperidine unit of formula (I): 
     
       
         
         
             
             
         
       
     
     In a particularly preferred embodiment of the present invention, the stabilizer is selected from the group consisting of the compounds of the following formulae (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 is a C6- to C20-alkyl group. 
           
         
       
    
     The ionic liquid optionally present, in the context of the present invention, is a virtually anhydrous liquid (water content &lt;1.5% by weight based on the overall ionic liquid) which is in liquid form at standard pressure (1.01325 bar) and preferably at 25° C. The ionic liquid preferably consists to an extent of more than 98% by weight of ions. 
     In a preferred embodiment, the anion of the ionic liquid is selected from the group consisting of tetrafluoroborate [BF4] − ; hexafluorophosphate [PF6] − ; dicyanamide [N(CN) 2 ] − ; bis(trifluoromethylsulfonyl)imide [NTf 2 ] − ; tricyanomethide [C(CN) 3 ] − ; tetracyanoborate [B(CN) 4 ] − ; halides, especially Cl − , Br − , F − , I − ; hexafluoroantimonate [SbF 6 ] − ; hexafluoroarsenate [AsF 6 ] − ; sulfate [SO 4 ] 2− ; tosylate [C 7 H 7 SO 3 ] − ; triflate CF 3 SO 3   − ; nonaflate [C 4 F 9 SO 3 ] − ; tris(pentafluoroethyl)trifluorophosphate [PF 3 (C 2 F 5 ) 3 ] − ; thiocyanate [SCN] − ; carbonate [CO 3 ] 2− ; [RA-COO] − ; [RA-SO 3 ] − ; [RA-SO 4 ] − ; [RAPO 4 RB]— and [(RA-SO 2 ) 2 N] − , where RA and RB may be the same or different and are each a linear or branched, aliphatic or alicyclic alcyl group having 1 to 12 carbon atoms, a perfluoroalcyl group or a C5-C18-substituted aryl group that may be substituted by one or more halogen atoms. 
     The cation of the ionic liquid is preferably selected from the group consisting of quaternary ammonium cations of the general formula [NR 1 R 2 R 3 R 4 ] +  where R 1 , R 2 , R 3 , R 4  each independently represent a C1-C8-alkyl group; phosphonium cations of the general formula [PR 1 R 2 R 3 R 4 ] +  where R 1 , R 2 , R 3 , R 4  each independently represent a C1-C8-alkyl group; imidazolium cations of the general formula (II) 
     
       
         
         
             
             
         
       
     
     where R 1 , R 2 , R 3  and R 4  each independently represent H or a C1 to C8-alkyl group, a C1 to C6-alkoxy group, an optionally substituted C1 to C6-aminoalkyl group or an optionally substituted C5 to C12-aryl group;
         pyridinium cations of the general formula (III)       

     
       
         
         
             
             
         
       
     
     where R 1  and R 2  each independently represent H or a C1 to C8-alkyl group, a C1 to C8-alkoxy group, an optionally substituted C1 to C8-aminoalkyl group or an optionally substituted C5 to C12-aryl group; 
     pyrazolium cations of the general formula (IV) 
     
       
         
         
             
             
         
       
     
     where R 1  and R 2  each independently represent H or a C1 to C8-alkyl group, a C1 to C6-alkoxy group, an optionally substituted C1 to C6-aminoalkyl group or an optionally substituted C5 to C12-aryl group; 
     triazolium cations of the general formula (V) 
     
       
         
         
             
             
         
       
     
     where R 1  and R 2  and/or R 3  each independently represent H or a C1 to C8-alkyl group, a C1 to C6-alkoxy group, an optionally substituted C1 to C6-aminoalkyl group or an optionally substituted C5 to C12-aryl group. 
     In a preferred embodiment, the cation of the ionic liquid is an imidazolium cation of the above general formula (II) with corresponding definition of the R 1  to R 4  radicals. In a particularly preferred embodiment, the ionic liquid is selected from the group consisting of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium ethylsulfate, trioctylmethylammonium bis(trifluoromethylsulfonyl)imide and 1-butyl-3-methylimidazolium octylsulfate. 
     The ionic liquid optionally present, in the catalyst system according to the invention, serves as carrier solution for the transition metal catalyst with ligands and the stabilizer. It is important here that the ionic liquid can take up, i.e. dissolve, the reactants (feed olefins and synthesis gas) to a sufficient degree and has a comparatively low vapour pressure in order that the catalyst system is present as a liquid reservoir at high temperatures as well. However, it has been found that, surprisingly, the stabilizer can also form a stable liquid film in the pores of the support and hence is capable of partly or completely replacing the ionic liquid. In a preferred embodiment, the catalyst system does not comprise any ionic liquid. 
     For all film-forming components, i.e. In this case the ionic liquid and/or the stabilizer, the gas solubility for the reactants should be better than the gas solubility of the products. In that way alone, it is possible to achieve partial physical separation between reactant olefins used and product aldehydes formed. In principle, other film-forming substances would also be conceivable for the purpose, but it should be ensured that there is no elevated high boiler formation and/or that the resupply of the reactant olefins is restricted. 
     The organic phosphorus-containing ligand for the catalyst system according to the invention preferably has the general formula (VI)
 
R′-A-R″-A-R′″  (VI)
 
     where R′, R″ and R′″ are each organic radicals and each A is a bridging —O—P(—O) 2 — group, where two of the three oxygen atoms —O— are each bonded to 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 any terminal trialkoxysilane group. 
     In a preferred embodiment, R′, R″ and R′″ in the compound of the formula (VI) are preferably selected from substituted or unsubstituted 1,1′-biphenyl, 1,1′-binaphthyl and ortho-phenyl groups, especially from substituted or unsubstituted 1,1′-biphenyl groups, with the proviso that R′ and R′″ are not identical. More preferably, the substituted 1,1′-biphenyl groups in the 3,3′ and/or 5,5′ positions of the 1,1′-biphenyl base skeleton have an alkyl group and/or an alkoxy group, especially a C1-C4-alkyl group, more preferably a tert-butyl and/or methyl group, and preferably a C1-C5-alkoxy group, more preferably a methoxy group. 
     According to the invention, the aforementioned catalyst system is in heterogenized form on a support of a porous ceramic material. In the context of the present invention, the expression “heterogenized on a support” Is understood to mean that the catalyst system is immobilized via formation of a thin, solid or liquid film with the aid of a stabilizer and/or, optionally, of the ionic liquid on the inner and/or outer surface of a solid support material. The film may also be solid at room temperature and liquid under reaction conditions. 
     The inner surface of the solid support material especially comprises the inner surface area of the pores. The concept of immobilization includes both the case that the catalyst system and/or the catalytically active species is in dissolved form in the solid or liquid film and the case that the stabilizer acts as an adhesion promoter or the catalyst system is adsorbed on the surface but is not chemically or covalently bound to the surface. 
     According to the invention, there is thus no reaction solution in the conventional sense in which the catalyst is homogeneously dissolved; instead, the catalyst system is dispersed on the surface and/or in the pores of the support. 
     The porous support material is preferably selected from the group consisting of a nitridic ceramic, a carbidic ceramic, a silicidic ceramic and mixtures thereof, for example carbonitridic materials. 
     The nitridic ceramic is preferably selected from silicon nitride, boron nitride, aluminium nitride and mixtures thereof. The carbidic ceramic is preferably selected from silicon carbide, boron carbide, tungsten carbide or mixtures thereof. Also conceivable are mixtures of carbidic and nitridic ceramic, called the carbonitrides. The silicidic ceramic is preferably molybdenum silicide. The support according to the present invention to which the catalyst system is applied preferably consists of a carbidic ceramic, more preferably or silicon carbide. 
     According to the invention, the support is preferably in the form of a powder, in the form of a granular material or in the form of pellets. The median particle diameter (d50) of the support may have from 0.1 mm to 7 mm, preferably 0.3 to 6 mm, more preferably from 0.5 mm to 5 mm. The median particle diameter can be ascertained by means of imaging methods, especially by the methods specified in standards ISO 13322-1 (date: 2004 Dec. 1) and ISO 13322-2 (date: 2006 Nov. 1). The support can be produced in the form of a powder, in the form of a granular material or in the form of pellets by methods known to those skilled in the art. For example, this could be done by mechanically comminuting a monolith of the carbidic, nitridic or silicidic material or mixtures thereof, for example with a jaw crusher, and adjusting the particle size of the crushed granular material obtained by means of sieving. 
     Furthermore, the support or the particles of the powder, of the granular material or the pellet particles of the ceramic material is/are porous, i.e. the support has pores. The catalyst system according to the invention is especially also in the liquid or solid film in these pores. The pore diameter is preferably in the range from 0.9 nm to 30 μm, preferably in the range from 10 nm to 25 μm and more preferably in the range from 70 nm to 20 μm. Pore diameter can be determined by means of nitrogen adsorption or mercury porosimetry to DIN 66133 (1993-06 version). 
     In a preferred embodiment, the support has at least partly continuous pores that extend from one surface to another surface. It is also possible that multiple pores are connected to one another and hence overall form a single continuous pore. 
     The production of the support from a porous ceramic material on which the catalyst system is in heterogenized form is effected as described below: additionally applied to the support provided, which is composed of the ceramic material and is in the form of a powder, a granular material or pellets, is what is called a washcoat which, with respect to the the ceramic material of the support, of the same or a different ceramic material, preferably silicon oxide. The washcoat itself may be porous or nonporous; the washcoat is preferably nonporous. The particle size of the washcoat is preferably 5 nm to 3 μm, preferably 7 nm to 700 nm. The washcoat is used to introduce or to generate the desired pore size and/or to increase the surface area of the support. The washcoat can especially be applied by means of dipping (dip-coating) into a washcoat solution containing the ceramic material of the washcoat, possibly also as a precursor. The amount of washcoat present on the support is ≤20% by weight, preferably ≤15% by weight, more preferably ≤10% by weight, based on the total amount of the support. 
     The catalyst system is applied to the ceramic support thus produced with the washcoat applied. For this purpose, a catalyst solution is first produced by mixing, especially at room temperature and ambient pressure, where the catalyst solution comprises at least one organic phosphorus-containing ligand, at least one metal precursor, for example chlorides, oxides, carboxylates of the respective metal, at least one stabilizer and at least one solvent. It is optionally possible to use an ionic liquid in the production of the catalyst system, but the catalyst solution can also explicitly be made up without ionic liquid. The catalyst solution should especially be prepared in an inert environment, for example a glovebox. “Inert environment” in this case means a very substantially water- and oxygen-free atmosphere. 
     The solvent may be chosen from all solvent classes (protic, aprotic, polar or nonpolar). A prerequisite for the solvent is the solubility of catalyst system (ligand, metal precursor, stabilizer and optionally the ionic liquid) and preferably also of the high boilers formed in the hydroformylation. Solubility can be increased within the immobilization step by heating. 
     The solvent is preferably aprotic and polar, for example acetonitrile and ethyl acetate, or else aprotic and nonpolar, for example THF and diethyl ether. It is also possible to use hydrochlorocarbons, for example dichloromethane, as solvent. 
     The catalyst solution thus prepared is then contacted with the support (optionally including washcoat), for example by dipping (dip-coating) or by filing a pressure vessel, for example directly in the reactor (in situ impregnation). If the catalyst solution is applied outside the reactor, the support must of course be installed 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 because this can avoid possibly time-consuming installation and deinstallation steps and possible contamination of the catalyst. 
     In the case of in situ impregnation, the reactor, prior to the filling, is purged with an inert gas, for example noble gases, alkanes or nitrogen. The purging can be conducted at 1 to 25 bar, preferably under a slightly positive pressure of 20 to 90 mbar, more preferably 30 to 60 mbar, above standard pressure. The reactor can be cooled down prior to the purging with inert gas in order to prevent the solvent in the catalyst solution to be introduced from evaporating immediately. However, if the solvent has a boiling temperature greater than the reactor temperature, the cooling of the reactor can be dispensed with. 
     After the purging with inert gas, the pressure present can be released, for example via the pressure control system, preferably until the reactor is unpressurized, i.e. at ambient pressure (i.e. 1 bar). Otherwise, it is also possible to generate a vacuum in the reactor, for example with a vacuum pump. In one configuration of the present invention, the reactor can again be purged with an inert gas as described above after the pressure has been released or after evacuation. This operation of releasing pressure/evacuating and purging again can be repeated as often as desired. 
     For the filing of the reactor, the catalyst solution is initially charged in a pressure vessel and preferably pressurized to a positive inert gas pressure of 1 to 25 bar, more preferably a slightly positive inert gas pressure of 20 to 90 mbar, preferably 30 to 60 mbar, above reactor pressure. The inert gas may be a noble gas, an alkane, for example butane, or nitrogen. The catalyst solution is then introduced into the reactor at said positive pressure to which the pressure vessel has been pressurized, especially in a pressure-driven manner. The pressure in the pressure vessel on filling should be higher than in the reactor. Temperatures may be in the range from 20 to 150° C., and pressure from 1 to 25 bar. 
     Another means of filing is that the reactor is kept under reduced pressure after purging with inert gas and the catalyst solution is drawn into the reactor by virtue of the reduced pressure. For the preparation of the catalyst solution, a solvent that bolls under the prevailing vacuum or reduced pressure and the prevailing temperatures should be used. 
     The reactor can be filled with the catalyst solution via the normal inlets/outlets. Liquid distributors or nozzles within the reactor can ensure homogeneous distribution of the catalyst liquid, as can pressure drop internals or regulators for the metering rate that are optionally present. 
     After the catalyst system has been applied, the solvent is removed. This involves firstly discharging the remaining catalyst solution via the reactor outlet. Thereafter, solvent residues remaining in the reactor are evaporated by adjusting the pressure or increasing the temperature. In another embodiment, the adjustment of the pressure can also be conducted with a simultaneous increase in temperature. Depending on the solvent, the temperature may be 20 to 150° C. Depending on the solvent, the pressure may be adjusted to a high vacuum (10 −3  to 10 −7  mbar), but according to the solvent and temperature, elevated pressures of a few mbar up to several mbar are also conceivable. 
     The stabilizer and the ionic liquid optionally present remain in heterogenized form on the support with the catalyst composed of the transition metal, especially cobalt or rhodium, and the organic phosphorus-containing ligand. 
     The catalyst system can be applied to the support either directly in the reactor (in situ) or outside the reactor. A further problem is that the support must always be transported with exclusion of air, which is difficult to achieve on installation and deinstallation. In a preferred embodiment of the present invention, the catalyst system is therefore 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 deinstallation steps that would result in a prolonged reactor shutdown are needed. Moreover, the size of the support in that case is no longer limited in that suitable spaces with inert environments are available in a particular size. The size of the support can be chosen freely depending on the reactor design. 
     On completion of application of the catalyst system to the support and of removal of the solvent, the plant, especially the reactor, can be run up, i.e. put into operation, by a two-stage or multistage startup procedure. 
     The aim of the startup procedure is gentle activation of the catalyst system and attenuation of the maximum starting activity of the catalyst to prolong the service life of the catalyst system. Moreover, the startup procedure is intended to prevent the formation of a liquid phase since this can lead to deactivation, blocking and/or washout of the catalyst system. This is because, particularly in the case of startup of a freshly produced catalyst system (on the support) with concentrated reactant, it is possible to attain a reaction conversion maximum which is also associated with maximum formation of by-products (high boilers). If the proportion of the high-boiling by-products, depending on the operating conditions (pressure and temperature), exceeds a certain value, the result of this, owing to the vapour pressures of the individual components that are dependent on the mixture present, can be the formation of a liquid phase that can damage, block or wash out the catalyst system. 
     According to the invention, the activation or the catalyst system is preferably implemented with a rising conversion over a prolonged period of time. Thus, for any combination of pressure, temperature and composition of the feed mixture, it is possible to calculate a maximum permissible conversion for the formation of by-products that must not be exceeded in order not to allow the aforementioned problems to arise. The conversion for the formation of by-products can also be ascertained depending on the conversion for the formation of the product aldehydes (=depending on the aldehyde concentration), meaning that the startup procedure is guided by the maximum conversion of the feed olefins. 
     In the case of known long-term operating conditions of the reactor that enable a reliable degree of conversion of the feed olefins of 20% to 95%, preferably of 80%-95%, the startup procedure can be implemented in such a way that the composition of the feed mixture which is run into the reactor is altered stepwise without exceeding the maximum conversion of the feed olefins. 
     It is possible here to vary the composition of the feed mixture that ensures a reliable conversion of the olefins under long-term operating conditions in such a way that, at a constant volume flow rate, the olefin content and/or the synthesis gas content is raised in at least two stages, preferably more than three, especially four or more stages, without exceeding the maximum conversion of the feed olefins. For this purpose, the technical feed mixture and synthesis gas mixture may be supplied in the first stage(s) with inert gases, for example N 2 , argon, helium or the like. 
     Catalyst activity can decrease with increasing operating time, for example as a result of the enrichment of high boilers and/or the coverage or deactivation of active sites. The high boilers can lead to increased condensation in the pores, such that the pores are accessible to the reactant olefins more slowly, if at all. Secondly, some by-products can lead to breakdown of the catalyst system, which likewise decreases the activity of the catalyst. A decrease in catalyst activity can be ascertained, for example, from the drop in conversions or selectivities, especially via an appropriate analysis by means of Raman spectroscopy, gas chromatography or mass flow meters (MFMs). Another option would be model-based monitoring of the catalyst activity. This would be a method independent of the operating conditions for monitoring the catalyst activity, but also in order to extrapolate the progression and hence support review/regeneration planning. 
     In the case of inadequate catalyst activity, the catalyst system in heterogenized form on the porous ceramic support can be exchanged. For this purpose, the catalyst or support can be purged once or more than once with a solvent in the reactor. The purging can demobilize and remove the catalyst system. The solvent may be one of the solvents mentioned for the preparation of the catalyst solution. The temperature on solvent purging may be 20 to 150° C. The pressure on solvent purging may additionally be 1 to 25 bar. 
     After the purge, the support is reimpregnated once or more than once, especially by the above-described in situ impregnation of the support. The in situ impregnation is thus renewed and the heterogenized catalyst system is freshly applied. The in situ reimpregnation can be conducted under exactly the same conditions as described above for the first in situ impregnation. 
     Owing to the fact that the catalyst system is fully exchanged by purging and reapplication, these steps can constantly be repeated as soon as the catalyst activity drops again. A further advantage is that both high boilers and product aldehydes and breakdown products of the catalyst system can be discharged. However, it should be ensured that the properties of the support are not impaired by demobilization and in situ reimpregnation. Otherwise, exchange or the porous ceramic support would have to be conducted. 
     A further option is that the overall porous ceramic support on which the catalyst system is in heterogenized form is exchanged. The catalyst system in heterogenized form on the support (removed from the reactor) can then be exchanged as described above outside the reactor and stored until the next installation and use in the reactor. As mentioned above, an inert environment is required on application of the catalyst system, and therefore the handling and storage in the procedure mentioned of deinstallation and installation of the support should be effected under corresponding conditions. 
     A gaseous output comprising at least a portion of the product aldehydes formed and at least a portion of the unconverted olefins is preferably withdrawn continuously from the reaction zone in which the hydroformylation according to the invention is conducted. The gaseous output may be subjected to one or more physical separation step(s) in which the gaseous output is separated into at least one phase rich in unconverted olefins and at least one phase rich in product aldehyde. 
     The physical separation can be conducted by known physical separation methods such as condensation, distillation, centrifugation, nanofiltration or combinations of two or more of these, preferably condensation or distillation. 
     In the case of a multistage physical separation, the phase rich in product aldehyde which is formed in the first physical separation is sent to a second physical separation, especially a downstream removal of aldehyde, in which the product aldehyde is separated from the other substances present in this phase, frequently alkanes and reactant olefins. The phase rich in unconverted olefin can be recycled to the hydroformylatlon step or, in the case of a multistage configuration, to one of the hydroformylation steps in order to hydroformylate the olefins present therein to the product aldehyde as well. 
     In the physical separation, as well as the phases mentioned, it is also possible to withdraw a purge gas stream having a composition identical or at least similar to the phase rich in unconverted olefin. The purge gas stream can likewise be guided to the second physical separation or aldehyde removal in order to remove the product aldehyde present therein and in order to discharge 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 typically be removed in the second physical separation as volatile substances, for example at the top of a column. 
     The present invention also further provides a plant with which the present process can be conducted and which especially comprises a reactor in which the hydroformylation step according to the invention is conducted. In addition, the plant may comprise a physical separation unit with which the gaseous output from the hydroformylation step is separated into at least one phase rich in unconverted olefin and at least one phase rich in product aldehyde, where this physical separation unit is arranged downstream of the hydroformylation according to the invention. Downstream of the first physical separation, there may be a second physical separation unit, especially an aldehyde removal unit, with which the product aldehyde is removed. 
     Even without further elaboration it is assumed that a person skilled in the art will be able to utilize the description above to the greatest possible extent. The preferred embodiments and examples are therefore to be interpreted merely as a descriptive disclosure which is by no means limiting in any way whatsoever. 
     The present invention Is more particularly elucidated hereinbelow with reference to examples. Alternative embodiments of the present invention are obtainable analogously. 
     EXAMPLE 
     Experiment 1: Preparation and Analysis of a Catalyst System According to the Invention 
     The starting material used for the support was a monolith of silicon carbide having a length of about 20 cm and a diameter of about 25 mm. This monolith was comminuted with a jaw crusher having a gap width of 2 mm. The comminuted support was then sieved to a target grain size of 2 to 3.15 mm and pretreated with a washcoat (SiO 2 ). The granular material thus produced was then introduced into a round reactor sleeve of length 20 cm and having a diameter of one inch (about 2.54 cm), with glass beads of similar size introduced above and below the granular material. The granular material was then contacted with a catalyst solution containing Rh(acac)(CO) 2 , Bisphephos (ligand), bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate (stabilizer) and dichloromethane as solvent, prepared by mixing in an inert environment (glovebox). For this purpose, after the reactor had been purged with nitrogen, the catalyst solution was introduced into the reactor with a slightly positive pressure. After the solvent had been removed from the reactor by discharge and evaporation, the catalyst system heterogenized on the granular support material was used for hydroformylation. 
     The feed mixture used was a hydrocarbon stream having the following composition: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                   
                 Amount (% by wt.) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 1-butene/ 
                 19.14 
               
               
                   
                 isobutene 
                   
               
               
                   
                 cis-2-butene 
                 19.10 
               
               
                   
                 trans-2-butene 
                 28.40 
               
               
                   
                 n-butane 
                 30.80 
               
               
                   
                 isobutane 
                 0.02 
               
               
                   
                 2-methylbutane 
                 2.50 
               
               
                   
                   
               
            
           
         
       
     
     The feed mixture was guided into the reactor together with synthesis gas (molar synthesis gas:input mixture ratio=3.5:1) for hydroformylation at a gas volume flow rate of 390 ml/min. The hydroformylation was conducted at a temperature of 120° C. and a pressure of 10 bar. The total conversion of butenes (i.e. the conversion of all butenes present in the feed mixture) and the n/iso selectivity (ratio of linear to branched products) was ascertained by gas chromatography via the product composition. 
     After an experiment duration of 380 hours, total conversion of butenes was 35% and the n/iso selectivity 97%. 
     Experiment 2: Preparation and Analysis of an SILP Catalyst System not According to the Invention 
     The catalyst system was prepared analogously to the preparation of the catalytically active composition Rh(II) in WO 2015/028284 A1. 
     The feed mixture used was a hydrocarbon stream having the following composition: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                   
                 Amount (% by wt.) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 1-butene/ 
                 27.40 
               
               
                   
                 isobutene 
                   
               
               
                   
                 cis-2-butene 
                 15.00 
               
               
                   
                 trans-2-butene 
                 25.00 
               
               
                   
                 n-butane 
                 29.50 
               
               
                   
                 isobutane 
                 0.02 
               
               
                   
                 2-methylbutane 
                 3.00 
               
               
                   
                   
               
            
           
         
       
     
     The feed mixture was guided into the reactor together with synthesis gas (molar synthesis gas:feed mixture ratio=3.5:1) for hydroformylation at a gas volume flow rate of 390 ml/min. The hydroformylation was conducted at a temperature of 120° C. and a pressure of 10 bar. The total conversion of butenes (i.e. the conversion of all butenes present in the feed mixture) and the n/iso selectivity (ratio of linear to branched products) was ascertained by gas chromatography via the product composition. 
     After an experiment duration of 380 hours, total conversion or butenes was 25% and the n/iso selectivity 93%. 
     It is thus apparent from the series of experiments that the heterogenized catalyst systems according to the invention have the advantage over the known SILP systems that higher conversions and higher linearity of the products (n/iso selectivity) can be achieved therewith.