Method for improved control of isomer ratio in hydroformylation

Abstract

The present invention relates to a process for the hydroformylation of 1-olefins in the presence of hydrogen and carbon monoxide on a rhodium-containing complex catalyst comprising a mixture of phosphorus-containing organic complex ligands, in which the reaction is carried out in a solvent selected from the group of solvents having a boiling point of ≧180° C. and ≦250° C. at a rhodium concentration of ≧50 ppm and ≦250 ppm in a catalyst complex having at least two different complex ligands selected from the group consisting of arylphosphines and cycloalkylphosphines. The present invention further relates to the use of the process according to the invention within the framework of a two-stage hydroformylation reaction cascade.

Description

[Technical field]

[0001] The present invention relates to a process for the hydroformylation of 1-olefins in the presence of hydrogen and carbon monoxide over a rhodium-containing complex catalyst comprising a mixture of phosphorus-containing organic complex ligands, in which the reaction is carried out in a solvent selected from the group of solvents having a boiling point of ≧180° C. and ≦250° C., at a rhodium concentration of ≧50 ppm and ≦250 ppm in a catalyst complex having at least two different complex ligands selected from the group consisting of arylphosphines and di- or tri-cycloalkylphosphines. The present invention further relates to the use of the process according to the invention within the framework of a two-stage hydroformylation reaction cascade. [Background technology]

[0002] In the hydroformylation reaction, olefins are converted by a synthesis gas mixture of carbon monoxide and hydrogen in the presence of metals complexed with organic ligands into aldehydes that have additional carbon compared to the olefins. This reaction principle was developed by the German Otto Roelen in the last century and constitutes a fundamental reaction in the field of homogeneous catalysis. The resulting aldehydes can be oxidized, for example, to carboxylic acids or hydrogenated to alcohols or otherwise converted in further processing steps. The aldehydes themselves and other reaction products form important industrial starting materials and are used on a large scale, for example, as raw materials for solvents, additives, softeners and lubricants.

[0003] The hydroformylation process is non-specific with regard to the regioselectivity itself, leading to a mixture of linear (n-) and branched (iso)-product aldehydes with respect to 1- or α-olefins. In the absence of an industrially suitable alternative synthetic route for the isoselective reaction, it was accepted in principle to maintain the isomeric mixture in this large-scale reaction. This compromise may be due to the fact that, from a chemical point of view, stereoselective hydroformylation at the C2 carbon position is difficult, since unsubstituted linear 1-olefins do not have electronically or sterically favorable characteristics. The obtained isomer ratio is a complex function of the prevailing reaction conditions, with respect to the catalyst used, and here in particular the formation of the ligand sphere of the catalyst has a significant influence on the isomeric product composition. In recent years, a large part of the industrial interest has been in process optimization aimed at increasing the yield of n-aldehydes. Only recently has there been an increasing need for the corresponding branched aldehydes, where in addition to pure stereoselectivity, the economy of the overall reaction in terms of high selectivity and sufficient conversion must of course also be taken into account as boundary conditions.

[0004] The patent literature also contains many process procedures which aim to specifically influence the isomer ratio for hydroformylation reactions.

[0005] For example, WO2013 181188A1 (Patent Document 1) discloses a method for producing an aldehyde, comprising: a) contacting a catalyst composition with a first olefin under hydroformylation conditions to produce a catalyst ligand composition; and b) contacting a second olefin, hydrogen and carbon monoxide in the presence of the catalyst ligand composition to produce an aldehyde, wherein the second olefin is propylene and the first olefin has a longer carbon chain than the second olefin, and the catalyst ligand composition comprises tris(3-pyridyl)phosphine, a magnesium-centered tetraphenylporphyrin coordination complex and a ligand, the ligand being formed in situ by insertion of the first olefin into a rhodium carbonyl bond.

[0006] Another patent document, EP3156127A1 (Patent Document 2), describes a catalyst composition comprising: a specific monodentate phosphite ligand; a specific monodentate phosphine ligand; and a transition metal catalyst represented by the following formula 3:

[0007] [ka] wherein the total content of the ligands, including the monodentate phosphite ligand and the monodentate phosphine ligand, is 1 to 33 moles based on 1 mole of the transition metal catalyst, and the ligands R1, R2, R3, R'1, R'2 and R'3 of the catalyst each independently represent the following: a substituted or unsubstituted cycloalkyl- or cycloalkenyl group having 5 to 20 carbon atoms; or a substituted or unsubstituted aryl group having 6 to 36 carbon atoms; when R1, R2, R3, R'1, R'2 and R'3 are substituted by a substituent, the substituent is nitro (-NO 2 ), fluorine (-F), chlorine (-Cl), bromine (-Br), or an alkyl group having 1 to 20 carbon atoms; M is selected from the group consisting of cobalt (Co), rhodium (Rh), iridium (Ir), ruthenium (Ru), iron (Fe), nickel (Ni), palladium (Pd), platinum (Pt), and osmium (Os); L 1 , L 2 and L 3 each independently represents one member selected from the group consisting of hydrogen, carbonyl (CO), cyclooctadiene, norbornene, chlorine, triphenylphosphine (TPP), and acetylacetonate (AcAc); x, y, and z each independently represent 0 to 5, with the proviso that x, y, and z are not all zero; the content of each of the monodentate phosphite ligand and the monodentate phosphine ligand is 0.5 to 32.5 mol based on 1 mol of the transition metal catalyst; and the mixing ratio of the monodentate phosphite ligand and the monodentate phosphine ligand is 5:1 to 1:5 by weight.

[0008] WO2009 / 035204A1 (Patent Document 3) describes a catalyst composition containing a triphenylphosphine ligand, a monodentate phosphine ligand, a monodentate phosphine oxide ligand and a transition metal catalyst, and a hydroformylation method using the same. In the hydroformylation method using the catalyst composition according to the invention, high catalytic activity can be obtained, and the selectivity for normal- or isoaldehyde (n / iso-selectivity) can be controlled as desired.

[0009] Such solutions known from the prior art may still offer the potential for further improvement, in particular with regard to controlling the desired isomer ratio whilst maintaining the boundary conditions of high conversion and high yield. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] WO2013 181188A1 [Patent Document 2] EP3156127A1 [Patent Document 3] WO2009 / 035204A1 Summary of the Invention [Problem to be solved by the invention]

[0011] The object of the present invention is therefore to at least partially overcome the drawbacks known from the prior art. In particular, the object of the present invention is to provide a process which allows the control of the isomer ratio, in particular the production of a high proportion of isoaldehyde, at high conversions and yields. Furthermore, the object of the present invention is to provide an efficient use of said process, which allows an improved overall process sequence for the flexible production of various amounts of aldehyde isomers by coupling the process according to the invention with upstream process steps. [Means for solving the problem]

[0012] Said problem is solved by the features of the independent claims, which are directed to the method according to the invention and to the use according to the invention of said method in the context of a multi-step production. Preferred embodiments of the invention are set out in the dependent claims, the description or the drawings, whereby further features mentioned or shown in the dependent claims, the description or the drawings can form the subject of the invention individually or in any combination, unless the context clearly indicates otherwise.

[0013] According to the present invention, the above problem is solved by a process for the hydroformylation of 1-olefins by reacting them in the presence of hydrogen and carbon monoxide over a rhodium-containing complex catalyst comprising a mixture of phosphorus-containing organic complex ligands, the reaction being carried out in a pressure range from 0.5 MPa to 5 MPa and in a solvent selected from the group of solvents having a boiling point from 180° C. to 250° C., at a rhodium concentration of 50 ppm to 250 ppm in the catalyst complex having at least two different ligands selected from the group consisting of arylphosphines and di- or tri-cycloalkylphosphines, the proportion of cycloalkylphosphines in the total amount of organic phosphorus ligands being 1 mol % to 67 mol %, and the molar ratio of organic phosphorus ligand to rhodium, expressed as the molar amount of organic phosphorus ligand divided by the molar amount of rhodium, being 85 or less.

[0014] Surprisingly, it has been found that the process sequence according to the invention allows the production of particularly large amounts of branched aldehydes from 1-olefins, in comparison with the features of processes normally available in the prior art, while a high proportion of isoaldehydes must be obtained without a decrease in olefin conversion or a decrease in selectivity towards aldehydes as a whole. The reaction can thus advantageously be carried out at high rates, high conversions and very little undesirable by-products, which of course affects the economics of the overall process. Without being bound by theory, this is believed to be due in particular to the advantageous combination of the specific ligand environment of the catalyst, the amount of catalyst used as a whole, combined with the solvent selection, which on the one hand allows unhindered access of synthesis gas and on the other hand, due to the steric shaping of the catalytic environment, leads to high amounts of isoaldehydes without loss of productivity. Although the basic effect of the individual ligands on the isomer ratio is known, the shift towards iso isomers has come at the expense of a significant loss of productivity. So far, it has not been possible to create process conditions suitable for efficient production while at the same time leading to a high iso proportion. Furthermore, the process according to the invention is advantageous since the improved process procedure can be achieved in the low pressure range and with relatively low catalyst amounts, which further contributes to improving the overall process economics in terms of investment and running costs.

[0015] The process according to the invention is a process for the hydroformylation of 1-olefins. The 1- or α-olefins are substituted or unsubstituted aliphatic or aromatic hydrocarbons having at least one terminal double bond in the 1-position of the hydrocarbon. Said double bond is not incorporated in an aromatic system. The possible carbon number of the 1-olefins can be, for example, up to 15, preferably up to 10, more preferably up to 8. Mixtures of different 1-olefins can also be reacted, in which case each of the olefins has a corresponding terminal double bond. Possible representatives of this group can be, for example, ethene, propene, 1-butene, 1-pentene, 1-hexene, 1-octene or styrene. Suitable olefin starting materials can have further functional groups in other positions of the olefin skeleton, as long as these do not interfere with the hydroformylation of the invention.

[0016] The hydroformylation is carried out by conversion of 1-olefins over a rhodium-containing complex catalyst containing a mixture of phosphorus-containing organic complex ligands in the presence of hydrogen and carbon monoxide. Olefins are hydroformylated, i.e. reacted in a reaction zone in the presence of synthesis gas consisting essentially of hydrogen and carbon monoxide, with the olefinic groups being converted to aldehyde groups on the catalyst. The resulting aldehydes have one more C atom than the starting olefins. The process according to the invention can be carried out in any suitable reaction vessel. Suitable reaction vessels include, for example, gas-sparged reactors, reactors with liquid outlets, tank reactors with stirrers, so-called trickle-bed reactors, etc. The amount of synthesis gas fed and its composition can vary within wide limits. Typically, the ratio of hydrogen to carbon monoxide can range from 0.5:1 to 10:1, more preferably from 1:1 to 6:1.

[0017] The reaction of olefins to aldehydes is carried out by rhodium metal catalysts, where the rhodium is not present as such but complexed with organic ligands as well as with carbon monoxide and hydrogen and therefore represents the catalytically active center. The exact composition of the complex, here in particular the stoichiometry of the ligands, including the synthesis gas components, is a function of the prevailing reaction conditions. To produce an active catalyst, a rhodium salt is usually introduced into the reaction zone, where it undergoes conversion into the actual active catalytic complex. However, it is also possible to preform the catalyst under similar reaction conditions at another location outside the reaction zone, i.e. to convert it into the active species. Non-preformed rhodium components are, for example, rhodium(I) dicarbonylacetonylacetonate, rhodium(II) 2-ethylhexanoate, rhodium(II) acetate, rhodium(0) carbonyl (e.g. Rh 6 (CO)l 6 , Rh 4 (CO)l 2 ), HRh(CO)(Ph 3 P) 3 (wherein Ph represents a phenyl group). Mixtures of two or more of these rhodium salts can also be used. It has been found that rhodium 2-ethylhexanoate can be preferably used.

[0018] The active catalyst complex, in the reaction zone, in any case has in its coordination sphere a phosphorus-containing organic complexing ligand, where the phosphorus-containing complexing ligand is a hydrocarbon having at least one phosphorus atom throughout the hydrocarbon backbone, preferably having cyclic groups, although the phosphorus atom does not necessarily have to be incorporated into one of the cyclic groups. The phosphorus-containing organic complexing ligand may, for example, conform to the following formula:

[0019] [ka] In the formula, R 1 , R 2 and R 3can each, independently of one another, be selected from the group consisting of substituted or unsubstituted alkyl groups having 1 to 20 carbon atoms; substituted or unsubstituted cycloalkyl or cycloalkenyl groups having 5 to 20 carbon atoms; substituted or unsubstituted aryl groups having 6 to 36 carbon atoms; substituted or unsubstituted heteroalkyl groups having 1 to 20 carbon atoms; substituted or unsubstituted heteroaryl groups having 4 to 36 carbon atoms, in the case of a substitution of one of said groups, this substitution can have one or more atoms from the group consisting of N, O and S. Possible representatives of these groups are, for example, triorganophosphines, such as triarylphosphines, trialkylphosphines, dialkylarylphosphines, dicycloalkylarylphosphines and tricycloalkylphosphines.

[0020] The reaction is carried out in the pressure range of 0.5 MPa or more and 5 MPa or less. The pressures in the above range can contribute to economically attractive reaction rates while increasing isoselectivity, and at these relatively low reaction pressures, the costs for reactor equipment are relatively low, because the reactor to be designed is correspondingly less labor-intensive and less costly, and the need for additional compressor capacity is reduced.

[0021] The reaction is carried out in a solvent selected from the group of solvents having a boiling point of ≧180° C. and ≦250° C. The conversion of olefins to aldehydes is carried out in an inert solvent that dissolves the above-mentioned rhodium complex catalyst as a solvent during the reaction, the boiling point of said solvent under standard pressure being within the above-mentioned range. Possible solvents can be selected from the group of alcohols, acetals or alkanes with a chain length of C8 or more, or mixtures thereof. Possible solvents that meet the boiling point criteria according to the invention can be selected, for example, from the group consisting of 2-ethylhexanol, 1-octanol, 1-decanol, higher aldehyde condensation products of hydroformylation or of this particular hydroformylation, or a mixture of at least two components from this list. Here, higher aldehyde condensation products of hydroformylation are understood as bottom products of hydroformylation that are formed in the reactor in the course of the reaction. These higher condensation products contain a complex mixture of various components and are also called thick oils (Dickoele). The aldehyde products are themselves reactive and slowly undergo condensation reactions. This reaction occurs even in the absence of a catalyst and is caused by the operation of the process. The liquid condensation products naturally have a higher boiling point than the starting aldehydes. The condensation products may be formed, for example, by aldol condensation. Further reaction pathways include the Tischshenko reaction, transesterification, and disproportionation reactions. The condensation products are oligomers of aldehydes and may also have other functional groups, such as alcohol- or ester groups.

[0022] The hydroformylation is carried out at a rhodium concentration of 50 ppm or more and 250 ppm or less. The concentration of rhodium present in the reaction zone is expressed by the weight ratio of rhodium to the total weight of the solution in the reaction zone. Here, this concentration statement is directed to the ratio of the weight of the pure metal (without ligands) to the total weight of the solution including any further components (such as dissolved ligands, etc.). Lower concentrations may be disadvantageous, since in that case the reaction rate is too slow. Higher concentrations may result in a decrease in the proportion of isoaldehyde in the product and only a small percentage increase in the reaction rate that is not commensurate with the cost of using the catalyst.

[0023] The catalyst complex has at least two different complex ligands selected from the group consisting of arylphosphines and di- or tricycloalkylphosphines. It has been found that the composition of the ligands is particularly important in order to control the n / iso-aldehyde ratio while maintaining as high a reaction rate as possible. In particular, at a given mixing ratio of arylphosphines and di- or tricycloalkylphosphines, high conversions and selectivities can occur. Arylphosphines are, for example, compounds of the formula:

[0024] [ka] wherein each of the individual aryl groups may be further substituted, independently of the other. Examples of di- or tri-cycloalkylphosphines include the following C6-cycloalkyl compounds:

[0025] [ka] In the formula, each of the individual cycloalkyl- and / or aryl groups may, independently of one another, also have other functional groups as described above. The cycloalkyl group may be, for example, a C3-C8 cycloalkane, preferably a C4-C7 cycloalkane.

[0026] The proportion of cycloalkylphosphines in the total amount of organophosphorus ligands is ≧1 mol % and ≦67 mol %. It has been found that this narrow range of cycloalkylphosphine ratios is particularly suitable for the improved inventive control of the isomer ratio while maintaining a high conversion. The molar proportion of cycloalkylphosphines is obtained as the quotient of the molar amount of cycloalkylphosphines divided by the total amount of organophosphorus compounds, for example the sum of compounds having the above formula from the group of aryl- and cycloalkylphosphines. The amount of cycloalkylphosphines can be, for example, 31 The molar proportion of cycloalkylphosphines can be quantitatively determined by the P method. Here, the ligand can be introduced into the reaction zone purely or can be introduced into the reaction solution by adding a preformed metal complex. For clarity, the amount of non-organophosphorus ligand of rhodium in the reaction zone, introduced for example by the catalyst salt components acetate, ethylhexanoate, CO, etc., is not included in the calculation of the molar proportion of cycloalkylphosphines.

[0027] The molar ratio of ligand to rhodium, expressed as the molar amount of organophosphorus ligand divided by the molar amount of rhodium, is less than or equal to 85. Despite the reduced thermal stability of cycloalkylphosphines, it has been demonstrated to be advantageous to operate with only a relatively small excess of organophosphorus ligand, based on the molar amount of rhodium. This ratio of ligands can provide the required n / iso ratio to result in high conversions, and is surprisingly stable over long production periods in the abovementioned solvents.

[0028] In a preferred embodiment of the process, the hydroformylation can be carried out in a temperature range of at least 80° C. and not more than 140° C. Within this temperature range of the reaction zone, sufficient reaction rates can be provided, and in particular, these reactions also give favorable isomer ratios, characterized by a higher proportion of iso-isomers, as compared to typical prior art processes.

[0029] In a further preferred embodiment of the process, the molar ratio of arylphosphine ligand to cycloalkylphosphine ligand, expressed as the molar amount of arylphosphine ligand divided by the molar amount of cycloalkylphosphine ligand, can be 0.5 or more and 75 or less. This ratio between arylphosphine ligand and cycloalkylphosphine ligand can provide a significantly increased iso-isomer ratio with only a very slight decrease in conversion. In a further preferred embodiment, said ratio can be 15 or more and 70 or less, more preferably 20 or more and 60 or less.

[0030] In a further preferred embodiment of the process, the molar ratio of arylphosphine ligand to rhodium can be 5 or more and 75 or less. The amount of arylphosphine ligand can have a significant effect on the isomer ratio as well as the overall reaction productivity. Within this molar ratio, a sufficiently high amount of iso-isomer can be provided with high conversion. The molar ratio can be more preferably 35 or more and 65 or less, more preferably 45 or more and 55 or less.

[0031] In a further preferred embodiment of the process, the molar ratio of cycloalkylphosphine ligand to rhodium can be ≧1 and ≦10. The amount of cycloalkylphosphine ligand can have a significant effect on the isomer ratio, in particular on the iso proportion of aldehydes formed. In the case of smaller ratios, the effect of cycloalkylphosphine ligand on increasing the proportion of isoaldehydes is too small. Higher ratios can be disadvantageous in these cases, since they can significantly reduce the olefin conversion. The molar ratio can be more preferably ≧2 and ≦8, more preferably ≧4 and ≦6.

[0032] In a preferred embodiment of the method, the arylphosphine can be triphenylphosphine. The use of triarylphosphine (TPP) as the arylphosphine can contribute to a particularly high yield and to a particularly long service life of the catalyst solution. Here, an excess of TPP can in particular stabilize rhodium in the solution. Moreover, TPP can also act as a ligand reservoir when cycloalkylphosphine ligand is damaged.

[0033] In a preferred embodiment of the method, the cycloalkylphosphine can be tricyclohexylphosphine.In particular, the use of tricyclohexylphosphine can contribute to a particularly efficient shift of aldehyde isomer ratio towards iso isomer.This is likely achieved by the increased space requirement of the ligand.The shift of isomer ratio towards isoaldehyde occurs even in the above-mentioned solvents at concentrations that do not adversely affect the possible achievable reaction rate.In this respect, this ligand can contribute more efficiently than cycloalkylphosphines that only have two cycloalkyl groups.

[0034] In a further preferred embodiment of the process, the 1-olefin can be selected from the group consisting of C3-C8 olefins or mixtures thereof. In particular, the average olefin can be converted in the direction of the isoaldehyde isomers by the process according to the invention without significant loss of conversion. Without being bound by theory, this effect is caused by the special orientation of the olefin in the catalyst complex, which depends on the ligand composition and the solvent, for the "average" olefin.

[0035] In a preferred embodiment of the present invention, (H 2The molar ratio of syngas to 1-olefin, expressed as molar amount of syngas + molar amount of CO, can be greater than or equal to 1:1 and less than or equal to 5:1. Within this range of relationship between olefin and syngas, the claimed solvents can be provided with sufficiently high concentrations of reactants which, together, result in high conversions and only a few undesirable side reactions.

[0036] The invention furthermore relates to the use of the process according to the invention for the hydroformylation of 1-olefins over a complex catalyst, wherein the hydroformylation is carried out in two steps, in which in a first process step the reaction is carried out in a solvent selected from the group of alcohols, acetals or alkanes with a chain length of at least C10 or mixtures thereof in the presence of a rhodium-containing complex catalyst comprising an arylphosphine ligand and not a cycloalkylphosphine ligand, and in which in a second process step a further solvent with a boiling point of at least 180° C. and at most 250° C. and additionally a cycloalkylphosphine ligand are added to the reaction mixture of the first process step.

[0037] Surprisingly, it has been shown that the method according to the invention can be used very advantageously within the framework of a two-step hydroformylation cascade. In this two-step process, several advantages can be achieved by adjusting the reaction conditions according to the invention only in the second step. By providing a second step, the reaction solution in the reaction zone of the first step can also be used in principle, and the adjustment of the conditions according to the invention can be achieved by simply adding ligand and solvent. Costly and laborious separation operations, and even the exchange of the entire reaction solution, can be avoided. By linking the two process steps, the desired isomer ratio can also be adjusted overall over the two process steps, the ratio profile also following the adjustment and profile of the second step. Furthermore, advantageously, the thick oil formed in the first step can also be used, and some of the addition of solvents with very high boiling points can be omitted, since these are already at least partially present in the reaction zone.

[0038] In the use according to the invention, the hydroformylation is carried out in two steps, in the first process step the reaction is carried out in the presence of a rhodium-containing complex catalyst containing an arylphosphine ligand and not having a cycloalkylphosphine ligand, in a solvent selected from the group of alcohols, acetals or alkanes with a chain length of C10 or more or mixtures thereof. The first process step of the cascade is therefore carried out without the invention, excluding the cycloalkyl ligand. In this process step, n-aldehydes are formed in increasing amounts. In this step, of course, thick oils are formed, resulting from the self-condensation of the aldehydes formed. The process conditions in this step may not correspond to those of the process according to the invention, i.e. the rhodium concentration in the reaction zone may for example be higher than required in the process according to the invention.

[0039] Within the second process step, a further solvent with a boiling point of ≧180° C. and ≦250° C. and additionally a cycloalkylphosphine ligand are added to the reaction mixture of the first process step. The addition of the higher boiling further solvent adjusts the reaction solution of the first process step to the composition according to the invention of the method according to the invention. By dilution and addition of further ligand species, reaction conditions are obtained which produce a higher proportion of iso-isomers without significant loss of conversion and productivity. This is advantageously possible, with the use of part of the reaction environment of the first step resulting in an efficient utilization of the reaction solution. Furthermore, depending on the need for isomers, the proportion of isomers obtained can advantageously be controlled by the length of the individual process steps. Overall, an overall process is obtained which acts synergistically with each other.

[0040] In a further preferred embodiment of the use, the solvent in the second process step can be selected from the group consisting of alcohols with a chain length of C8 or more, acetals with a chain length of C13 or more, alkanes with a chain length of C10 or more, or a mixture of at least two components from this group. This group of solvents additionally used in the second process step can contribute to obtaining an improved catalyst service life, especially for the second process step, at high conversions.

[0041] According to a preferred feature of said use, the weight ratio of the solvent added in the second process step to the amount of solvent in the first process step can be ≧4 and ≦20. It has been found that the above-mentioned mixing ratio of the two solvents is particularly suitable to obtain the most efficient possible solvent mixture of the high-boiling solvent formed in the first process step and the high-boiling solvent added in the second process step. In the second process step, a long catalyst life, a high conversion rate and a high iso-isomer proportion for the aldehyde are obtained.

[0042] In a further preferred embodiment of the use, the concentration of arylphosphine ligand in the first process step can be 10% by weight or more and 30% by weight or less, based on the total weight of the process solution. It has been found that this concentration of arylphosphine ligand in the first process step is particularly suitable for adjusting the ligand ratio according to the invention in the second process step particularly efficiently. This concentration provides a stable conversion with relatively little catalyst deactivation in the first process step, but at the same time is low enough to prevent too much catalyst being added and wasted in the second process step. In addition to the proper control of the n / iso ratio, an efficient overall process is obtained over the two process steps, which also shows an overall high conversion rate.

[0043] In a preferred embodiment of the use, the concentration of cycloalkylphosphines added in the second process step can be 0.01% by weight or more and 1% by weight or less, based on the total weight of the process solution.It has been shown that for the economy of the process and for the efficient increase of the iso proportion in the product, only a relatively small amount of cycloalkylphosphine needs to be added to the reaction solution of the second process step.In particular, the addition of cycloalkylphosphine increases the formation of isoaldehyde, and depending on the reaction conditions selected, it is possible to avoid a large decrease in conversion in the second process step compared to the first process step.

[0044] In the preferred embodiment of the use, the entire amount of rhodium can be added in the first process step.In order to simplify the process procedure, in order to obtain a favorable high iso ratio of the aldehyde formed and for high conversion, it has been found to be suitable for the entire addition of metal complex catalyst to be carried out in the scope of the first process step.This is surprising, because in the second process step, due to the changed ligand supply, the equilibrium must first be adjusted, which would be expected to occur more quickly when adding fresh catalyst, due to the changed equilibrium position.Surprisingly, this is not the case.

[0045] Further details, features and advantages of the subject matter of the invention emerge from the dependent claims and from the following description of the drawings and the associated examples. [Brief description of the drawings]

[0046] FIG. 1 shows the proportion of iso-aldehyde and 1-butene consumption (1-Butenaufnahme) of the reaction solution using 2-ethylhexanol as the solvent as a function of the tricyclohexylphosphine / rhodium molar ratio.

[0047] FIG. 2 shows the proportion of iso-aldehyde and consumption of 1-butene in the reaction solution using 2-ethylhexanol as the solvent as a function of the proportion of the organophosphorus ligand tricyclohexylphosphine.

[0048] FIG. 3 shows the iso-aldehyde percentage and 1-butene consumption of the Rh-triphenylphosphine catalyzed reaction solution as a function of rhodium concentration after dilution with 2-ethylhexanol as the solvent in the absence of tricyclohexylphosphine.

[0049] FIG. 4 shows the iso-aldehyde percentage and 1-butene consumption of the reaction solution as a function of rhodium concentration using the Rh-triphenylphosphine catalyst and using tricyclohexylphosphine after dilution with 2-ethylhexanol as the solvent. EXAMPLES

[0050] example All experiments were carried out in the reactor in batch mode with a preformed catalyst phase (9 bar synthesis gas pressure (SynGas), temperature 120 °C, 30 min). 1-Butene / SynGas 1:1 was added continuously at 120 °C and 13 bar and the reaction was carried out for various reaction times, from 20 min to 2 h, until the conversion of 25 g of 1-butene. In all experiments, the catalyst solution was transferred under inert conditions to a vacuum reactor and the reaction was started by the continuous metered addition of 1-butene and synthesis gas. The resulting 1-butene consumption over time (productivity of the system) and the iso / n ratio of C5 aldehydes were used as characteristic values ​​to determine the proportion of 2-methylbutanal (2-MB).

[0051] In a first series of experiments, the effect of tricyclohexylphosphine (TCHP) on the iso / n ratio of C5 aldehydes formed and on 1-butene consumption with different TCHP / Rh ratios was investigated, the results are shown in Table 1 and Figure 1:

[0052] [Table 1] From Table 1 and Figure 1, it can be seen that TCHP increases the proportion of 2-MB in the product compared to TPP, thus resulting in an increase in the iso / n ratio. Even at low TCHP / Rh ratios, the ligand has a positive effect on the formation of branched aldehydes. It is believed that the high space requirement of the TCHP ligand and the change in the geometry and properties of the resulting Rh complexes lead to a change in the selectivity of 1-butene-hydroformylation. However, at higher TCHP / Rh ratios, the consumption of 1-butene, and therefore the reaction rate of the entire system, also decreases. The reduced olefin consumption may possibly be due to the high binding affinity of the TCHP ligand to rhodium.

[0053] In a further series of experiments, a mixture of ligands, TCHP and triphenylphosphine (TPP), was used for the process according to the present invention. When present, the TCHP-Rh ratio was set to 50, and the amount of TPP in the reaction solution was varied. Further specific experimental conditions are as above. The results are shown in Table 2.

[0054] [Table 2] FIG. 2 shows the dependence of the resulting iso fraction and butene consumption as a function of the TCHP fraction in the total phosphorus(III) provided by the ligand. As the TCHP fraction increases, equivalent to the TCHP / Rh ratio, a higher iso fraction is found in the product, but the consumption of butenes and therefore also the reaction rate decreases significantly. By using TPP and TCHP ligands together, under certain concentration and ratio relationships between the ligand and the catalyst and between each ligand, the reaction can be carried out with high conversion and high iso ratio. The use of TPP leads to higher productivity, which is further maintained at higher TPP / Rh ratios. At the same time, a higher excess of TPP stabilizes the catalytic system against deactivation, so that longer process run times of the catalytic solution are possible. Here, the addition of a slight excess of TCHP compared to the molar amount of rhodium can increase the 2-MB fraction in the reaction solution with unchanged catalytic activity.

[0055] FIG. 3 shows the iso-aldehyde percentage and 1-butene consumption of the reaction solution using the Rh-triphenylphosphine catalyst as a function of rhodium concentration after dilution with 2-ethylhexanol as solvent in the absence of tricyclohexylphosphine. The TPP-Rh ratio was 66 in all experiments. Diluting the catalyst solution with 2-ethylhexanol results in a lower catalyst concentration and therefore a lower conversion of 1-butene. A linear regression over the two parameters results in the expected linear relationship between butene consumption and iso percentage of catalyst concentration when using a pure TPP ligand system. As the Rh concentration increases but the TPP / Rh ratio remains the same, the productivity of the catalyst system increases and the iso percentage in the product decreases with the use of a pure TPP ligand system. To counteract the decrease in iso percentage and thereby increase the formation of 2-MB, the process according to the invention adds a TCHP ligand to the Rh-TPP catalyst system.

[0056] FIG. 4 shows the isoaldehyde proportion and 1-butene consumption of the reaction solution with mixed Rh-TPP-TCHP catalyst as a function of the rhodium concentration in a dilution series with 2-ethylhexanol as solvent. The experiment therefore basically corresponds to the implementation described with reference to FIG. 4, only in this series a mixed ligand system of TPP and TCHP is used. Surprisingly, when using the ligand mixtures (TPP / Rh69 and TCHP / Rh2), there is both an increase in butene consumption and an increase in the proportion of isoaldehyde, with the catalyst metal concentration decreasing with dilution. Surprisingly, this process is therefore fundamentally different from the process with the pure TPP catalyst system, as explained with reference to FIG. 4. This relationship clearly shows that when using the ligand system of the invention consisting of two ligands (TPP / TCHP) in a solvent, with relatively low catalyst concentrations and a specific amount ratio between the two ligands to each other, surprisingly, both high conversions and high isoaldehyde proportions can be achieved. The particular advantage of the process according to the invention is based on the specific ratio of the two ligands. On the one hand, a low molar amount of TCHP ligand based on the rhodium metal is sufficient to increase the iso fraction in the product due to the ligand with high space requirements. Also, the catalytic activity is very high at this ligand ratio and at a low TCHP / Rh ratio. On the other hand, the molar amount of TPP ligand based on the rhodium metal was selected so that the rhodium-ligand-catalyst system is stabilized and the catalytic activity is maintained.

Claims

1. 1. A process for the hydroformylation of 1-olefins by reacting the 1-olefins in the presence of hydrogen and carbon monoxide over a rhodium-containing complex catalyst comprising a mixture of phosphorus-containing organic complexing ligands, wherein the reaction is carried out in a pressure range of 0.5 MPa to 5 MPa, inclusive, in a solvent selected from the group of solvents having a boiling point of 180°C to 250°C, at a rhodium concentration of 50 ppm to 250 ppm in a catalyst complex having at least two different complexing ligands selected from the group consisting of arylphosphines and di- or tri-cycloalkylphosphines, wherein the proportion of cycloalkylphosphines in the total amount of organic phosphorus ligands is 1 mol % to 67 mol %, and the molar ratio of organic phosphorus ligands to rhodium, expressed as the molar amount of organic phosphorus ligands divided by the molar amount of rhodium, is 85 or less.

2. 10. The process of claim 1, wherein the hydroformylation is carried out at a temperature ranging from 80°C to 140°C.

3. 3. The process of claim 1, wherein the molar ratio of arylphosphine ligand to cycloalkylphosphine ligand, expressed as the molar amount of arylphosphine ligand divided by the molar amount of cycloalkylphosphine ligand, is 0.5 or more and 75 or less.

4. 3. The process according to claim 1, wherein the molar ratio of arylphosphine ligand to rhodium is 5 or more and 75 or less.

5. 3. The process according to claim 1, wherein the molar ratio of cycloalkylphosphine ligand to rhodium is 1 or more and 10 or less.

6. 3. The method of claim 1, wherein the arylphosphine is triphenylphosphine.

7. 3. The method of claim 1 or 2, wherein the cycloalkylphosphine is tricyclohexylphosphine.

8. 3. The process of claim 1 or 2, wherein the 1-olefin is selected from the group consisting of C3 to C8 olefins or mixtures thereof.

9. 1-Divided by the molar amount of olefin (H ２ 3. The process of claim 1 or 2, wherein the molar ratio of synthesis gas to 1-olefin, expressed as molar amount of synthesis gas plus molar amount of CO, is greater than or equal to 1:1 and less than or equal to 5:

1.

10. 10. Use of the process according to claim 1 for the hydroformylation of 1-olefins over a complex catalyst, wherein the hydroformylation is carried out in two steps, in the first process step the reaction is carried out in a solvent selected from the group consisting of alcohols, acetals or alkanes with a chain length of at least C10 or mixtures thereof in the presence of a rhodium-containing complex catalyst comprising an arylphosphine ligand and no cycloalkylphosphine ligand, and in the second process step a further solvent having a boiling point of at least 180° C. and at most 250° C. and additionally a cycloalkylphosphine ligand is added to the reaction mixture of the first process step.

11. 11. The use according to claim 10, wherein the solvent in the second process step is selected from the group consisting of alcohols with a chain length of C8 or more, acetals with a chain length of C13 or more, alkanes with a chain length of C10 or more, or a mixture of at least two components from this group.

12. 12. Use according to claim 10 or 11, wherein the weight ratio of the amount of solvent added in the second process step to the amount of solvent in the first process step is ≧4 and ≦20.

13. 12. Use according to claim 10 or 11, wherein the concentration of arylphosphine ligand in the first process step is ≧10 wt. % and ≦30 wt. %, based on the total weight of the process solution.

14. 12. Use according to claim 10 or 11, wherein the concentration of cycloalkylphosphine added in the second process step is ≧0.01 wt. % and ≦1 wt. %, based on the total weight of the process solution.

15. 12. Use according to claim 10 or 11, wherein the entire amount of rhodium is added in the first process step.

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