METHOD FOR IMPROVED CONTROL OF ISOMER RATIO IN HYDROFORMYLATIONS

Description

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

[0002] In hydroformylation reactions, olefins are converted to aldehydes containing an additional carbon atom compared to the olefin using a synthesis gas mixture of carbon monoxide and hydrogen in the presence of a metal complexed with organic ligands. This reaction principle was developed in Germany by Otto Roelen in the last century and represents a fundamental reaction in the field of homogeneous catalysis. The resulting aldehydes can be further processed, for example, by oxidizing them to carboxylic acids, hydrogenating them to alcohols, or undergoing other conversion reactions. The aldehydes themselves and the other reaction products are important industrial feedstocks and are widely used, for example, as solvents, additives, raw materials for plasticizers, and lubricants.

[0003] The hydroformylation process is inherently nonspecific with respect to regioselectivity and yields a mixture of linear (n-) and branched (iso) product aldehydes for 1- or alpha-olefins. Due to a lack of industrially viable alternative synthetic routes for isoselective reactions, the fundamental preservation of isomeric mixtures in this large-scale reaction was accepted. This compromise may be justified by the fact that, from a chemical perspective, stereoselective hydroformylation at the C2 carbon position is challenging, as unsubstituted, linear 1-olefins do not exhibit any electronic or steric advantages. The obtainable isomer ratio is a complex function of the prevailing reaction conditions, with the catalyst used, and in particular the formation of the catalyst's ligand sphere, having a significant influence on the isomeric product composition.In recent years, the majority of industrial interest has focused on process optimization to increase the yield of n-aldehydes. Only recently has there been a growing demand for the corresponding branched aldehydes, whereby, in addition to pure stereoselectivity, the economic viability of the entire conversion process, in terms of high selectivities and sufficient conversion rates, must also be considered as boundary conditions.

[0004] Patent literature also contains a large number of process descriptions which are intended to allow special influence on the isomer ratio for hydroformylation reactions.

[0005] For example, WO 2013 181 188 A1 discloses a process for the preparation of aldehydes, comprising: a) contacting a catalyst composition and a first olefin under hydroformylation conditions to prepare a catalyst ligand composition; and b) contacting a second olefin, hydrogen and carbon monoxide in the presence of the catalyst ligand composition to produce aldehydes, wherein the second olefin is propylene, wherein the first olefin has a longer carbon chain than the second olefin, and wherein the catalyst ligand composition comprises tris(3-pyridyl)phosphine, a magnesium-centered tetraphenylporphyrin coordination complex and a ligand formed in situ by insertion of the first olefin into a rhodium carbonyl bond.

[0006] In another patent document, EP 3 156 127 A1, catalyst compositions are described. The catalyst composition comprises: special monodentate phosphite ligands; special monodentate phosphine ligands; and a transition metal catalyst represented by the following formula 3: M(L 1< ) x (L 2< ) y (L 3< ) zwherein the total content of the entire ligand, including the monodentate phosphite ligand and the monodentate phosphine ligand, is 1 to 33 mol, based on 1 mol of the transition metal catalyst, wherein the catalyst ligands R1, R2, R3, R'1, R'2 and R'3 each independently represent: a substituted or unsubstituted cycloalkyl or cycloalkenyl group with 5 to 20 carbon atoms; or a substituted or unsubstituted aryl group with 6 to 36 carbon atoms; and if R1, R2, R3, R'1, R'2 and R'3 are substituted by a substituent that is nitro (-NO₂), fluorine (-F), chlorine (-CI), bromine (-Br) or an alkyl group with 1 to 20 carbon atoms; where 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);L1<, L2< and L3< each independently represent one selected from the group consisting of hydrogen, carbonyl (CO), cyclooctadiene, norbornene, chlorine, triphenylphosphine (TPP) and acetylacetonato (AcAc), and x, y and z each independently represent 0 to 5, with the proviso that not all x, y and z are zero, wherein 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, wherein a mixing ratio of the monodentate phosphite ligand and the monodentate phosphine ligand is 5:1 to 1:5, on a weight basis.

[0007] WO 2009 / 035204 A1 describes a catalyst composition comprising a triphenylphosphine ligand, a monodentate phosphine ligand, a monodentate phosphine oxide ligand, and a transition metal catalyst, as well as a hydroformylation process using the same. In the hydroformylation process using the catalyst composition according to the present invention, high catalytic activity can be obtained and the selectivity (n / iso-selectivity) with respect to normal or isoaldehyde can be desirably controlled.

[0008] Furthermore, WO2009 035 204 A1 describes a catalyst composition containing a triphenylphosphine ligand, a monodentate phosphine ligand, a monodentate phosphine oxide ligand and a transition metal catalyst, as well as a hydroformylation process using the same.

[0009] Such solutions, known from the prior art, can still offer further potential for improvement. This applies in particular to controlling the desired isomer ratio while maintaining the constraints of high conversion and high yield.

[0010] It is therefore an object of the present invention to at least partially overcome the disadvantages known from the prior art. In particular, it is an object of the present invention to provide a process which enables high conversion rates and yields, allowing for control of the isomer ratio and, in particular, the production of a high proportion of iso-aldehydes. Furthermore, it is an object of the present invention to provide efficient use of the process, whereby the coupling of the process according to the invention to an upstream process step enables improved overall process control for the flexible production of different quantities of aldehyde isomers.

[0011] The problem is solved by the features of the independent claims, which relate to the inventive method and the inventive use of the method in a multi-step manufacturing process. Preferred embodiments of the invention are specified in the dependent claims, the description, or the figures, wherein further features described or shown in the dependent claims, the description, or the figures may, individually or in any combination, constitute subject matter of the invention, unless the context clearly indicates otherwise.

[0012] According to the invention, the problem is solved by a process for the hydroformylation of 1-olefins by reacting them over a rhodium-containing complex catalyst comprising a mixture of phosphorus-containing organic complex ligands with the addition of hydrogen and carbon monoxide, wherein the reaction is carried out in a pressure range of greater than or equal to 0.5 MPa and less than or equal to 5 MPa and in a solvent selected from the group of solvents with a boiling point of greater than or equal to 180°C and less than or equal to 250°C, with a rhodium concentration of greater than or equal to 50 ppm and less than or equal to 250 ppm, and in catalyst complexes with at least two different complex ligands selected from the group consisting of arylphosphines and tri-cycloalkylphosphines.wherein the proportion of cycloalkylphosphines in the total organophosphorus ligand amount is greater than or equal to 1 mol% and less than or equal to 67 mol%, and the molar organophosphorus ligand to rhodium ratio, expressed as molar amount of organophosphorus ligand divided by molar amount of rhodium, is less than or equal to 85.

[0013] Surprisingly, it has been shown that, compared to the process parameters typically available in the prior art, the process according to the invention allows for the production of particularly large quantities of branched aldehydes from 1-olefins, whereby the high proportion of iso-aldehydes does not require a reduction in olefin conversion or a decrease in overall selectivity towards the aldehydes. The reaction can therefore advantageously be carried out at high rates, with high conversions, and with very low amounts of undesired byproducts, which naturally improves the economic efficiency of the entire process.Without being bound by theory, this appears to be primarily due to a favorable combination of the specific ligand environment of the catalyst, the total amount of catalyst used, and the choice of solvent. This combination allows, on the one hand, unimpeded access of the synthesis gas and, on the other hand, leads to high quantities of iso-aldehydes without productivity losses due to the steric design of the catalyst environment. Although the fundamental effect of individual ligands on the isomer ratio is known, the shift towards the iso-isomer has been achieved at the cost of significant productivity losses. So far, it has not been possible to create process conditions that enable efficient production while simultaneously producing high iso-aldehyde fractions.Furthermore, the process according to the invention is advantageous because the improved process control can be achieved in low pressure ranges and with relatively small amounts of catalyst, which additionally contributes to the improved economic efficiency of the entire process with regard to investment and operating costs.

[0014] The process according to the invention is a process for the hydroformylation of 1-olefins. 1- or alpha-olefins are substituted or unsubstituted aliphatic or aromatic hydrocarbons that have at least one terminal double bond in the 1-position of the hydrocarbon. The double bond is not part of an aromatic system. Possible carbon numbers of the 1-olefins can be, for example, up to 15, preferably up to 10, and more preferably up to 8. Mixtures of different 1-olefins can also be reacted, each olefin then having a corresponding terminal double bond. Possible representatives of this group include, for example, ethene, propene, 1-butene, 1-pentene, 1-hexene, 1-octene, or styrene.The corresponding olefin starting materials can carry further functional groups at other locations on the olefin skeleton, provided that these do not prevent the hydroformylation according to the invention from being carried out.

[0015] Hydroformylation is carried out by reacting 1-olefins over a rhodium-containing complex catalyst comprising a mixture of phosphorus-containing organic complex ligands in the presence of hydrogen and carbon monoxide. The olefins are hydroformylated, i.e., they are reacted in a reaction zone over a catalyst in the presence of synthesis gas consisting essentially of hydrogen and carbon monoxide, converting the olefinic group to an aldehyde group. The resulting aldehyde has one more carbon atom than the starting olefin. 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 a liquid overflow, tank reactors with an agitator, so-called trickle-bed reactors, etc. The quantities and composition of the synthesis gas supplied can vary considerably.Typically, the ratios of hydrogen to carbon monoxide can range from 0.5:1 to 10:1, and more preferably from 1:1 to 6:1.

[0016] The reaction of olefins to aldehydes proceeds via rhodium metal catalysis, whereby the rhodium is not present as such, but complexed with organic ligands, carbon monoxide, and hydrogen, thus constituting the catalytically active center. The precise composition of the complex, and in particular the stoichiometry of the ligands including the synthesis gas components, is a function of the prevailing reaction conditions. To produce the active catalyst, a rhodium salt is typically introduced into the reaction zone, where it undergoes conversion into the actual active catalyst complex. However, it is also possible for the catalyst to be preformed, i.e., converted into the active species, under similar reaction conditions at a different location, outside the reaction zone.Non-preformed rhodium components can be, for example, rhodium compounds selected from the group consisting of rhodium(I) dicarbonylacetonylacetonate, rhodium(II) 2-ethylhexanoate, rhodium(II) acetate, rhodium(0) carbonyls (e.g., Rh₆(CO)I₆, Rh₄(CO)I₂), HRh(CO)(Ph₃P)₃, where Ph₃ represents a phenyl group. Mixtures of two or more of these rhodium salts can also be used. Rhodium 2-ethylhexanoate has been found to be preferentially used.

[0017] The active catalyst complex in the reaction zone always contains phosphorus-containing organic complex ligands in its coordination sphere. These phosphorus-containing complex ligands are hydrocarbons, preferably having cyclic groups, which contain at least one phosphorus atom in the entire hydrocarbon skeleton, whereby the phosphorus atom need not be incorporated into one of the cyclic groups. The phosphorus-containing organic complex ligands can, for example, correspond to the following formula: wherein R 1< , R 2< and R 3< may each be independently selected from the group consisting of substituted or unsubstituted alkyl groups with 1 to 20 C atoms; substituted or unsubstituted cycloalkyl groups or cycloalkenyl groups with 5 to 20 C atoms; substituted or unsubstituted aryl groups with 6 to 36 C atoms; substituted or unsubstituted heteroalkyl groups with 1 to 20 C atoms; substituted or unsubstituted heteroaryl groups with 4 to 36 C atoms, wherein in the case of substitution of one of the groups this substitution may include one or more atoms from the group consisting of N, O, and S. Possible representatives of these groups include, for example, the triorganophosphines such as triarylphosphine, trialkylphosphine, dialkylarylphosphine, dicycloalkylarylphosphine, and tricycloalkylphosphine.

[0018] The reaction is carried out in a pressure range of 0.5 MPa or greater than or equal to 5 MPa. Pressures in this range can contribute to economically attractive reaction rates with increased iso-selectivities. At these relatively low reaction pressures, the costs for the reactor system are relatively moderate, as the reactor design is correspondingly less complex and the need for additional compressor capacity is reduced.

[0019] The reaction takes place in a solvent selected from the group of solvents with a boiling point greater than or equal to 180°C and less than or equal to 250°C. The conversion of the olefins to the aldehydes occurs within an inert solvent, which dissolves the aforementioned rhodium complex catalysts as a solvent during the reaction, wherein the boiling point of the solvent under standard pressure lies within the range specified above. Suitable solvents may be selected from the group of alcohols, acetals, or alkanes with a chain length greater than or equal to C8, or mixtures thereof. Suitable solvents that meet the boiling point criterion of the invention may, for example, be selected from the group consisting of 2-ethylhexanol, 1-octanol, 1-decanol, higher aldehyde condensation products of one or more specific hydroformylations, or mixtures of at least two components from this list.The higher aldehyde condensation products of hydroformylation are the bottoms products of the reaction, which form in the reactor during the course of the reaction. These higher condensation products contain a complex mixture of different components and are also referred to as thick oils. The aldehyde products are themselves reactive and slowly undergo condensation reactions. This reaction occurs even in the absence of catalysts and is caused by the process parameters. The liquid condensation products naturally have higher boiling points than the reactant aldehydes. The condensation products can be formed, for example, by an aldol condensation. Other reaction pathways include Tischshenko reactions, transesterifications, and dismutation reactions. The condensation products are oligomers of the aldehydes and may also contain additional functional groups such as alcohol or ester groups.

[0020] Hydroformylation is carried out with a rhodium concentration of ≥ 50 ppm and ≥ 250 ppm. The concentration of rhodium present in the reaction zone is expressed as the weight ratio of rhodium to the total weight of the solution in the reaction zone. This concentration value refers to the ratio of the pure metal weight (without ligands) to the total weight of the solution, including any other components such as dissolved ligands. Lower concentrations can be disadvantageous because the reaction rate will be too slow. Higher concentrations can reduce the proportion of isoaldehyde in the product and, considering the cost of catalyst use, result in only disproportionately small increases in the reaction rate.

[0021] The catalyst complexes comprise at least two different complex ligands selected from the group consisting of arylphosphines and di- or tri-cycloalkylphosphines. The composition of the ligands has proven particularly important for controlling the n / iso-aldehyde ratio while maintaining the highest possible reaction rate. High conversions and selectivities can be achieved especially under certain mixing ratios of arylphosphines and di- or tri-cycloalkylphosphines. Arylphosphines are, for example, compounds of the following formula: where the individual aryl groups can still exist independently substituted from one another. The group of di- or tri-cycloalkylphosphines includes, for example, the following C6 cycloalkyl compounds: The individual cycloalkyl and / or aryl groups can each independently carry further functional groups as specified above. The cycloalkyl groups can be, for example, C3-C8 cycloalkanes, preferably C4-C7 cycloalkanes.

[0022] The proportion of cycloalkylphosphines in the total amount of organophosphorus ligands is greater than or equal to 1 mol% and less than or equal to 67 mol%. This narrow range of the cycloalkylphosphine ratio has proven particularly suitable for controlling the improved isomer ratio according to the invention while maintaining a high reaction rate. The molar proportion of cycloalkylphosphine is calculated as the quotient of the molar amount of cycloalkylphosphine divided by the total amount of organophosphorus compounds, for example, the sum of the compounds with the formulas given above from the group of aryl and cycloalkylphosphines. The amount of cycloalkylphosphine can be quantitatively determined, for example, using 31< P methods. The ligands can be placed directly in the reaction zone or introduced into the reaction solution by adding a preformed metal complex.To clarify, the amount of non-organophosphorus ligands of rhodium in the reaction zone, for example introduced by the catalyst salt components acetate, ethylhexanoate, CO, etc., is not included in the calculation of the molar fraction of the cycloalkylphosphines.

[0023] The molar ligand-to-rhodium ratio, expressed as the molar amount of organophosphorus ligands divided by the molar amount of rhodium, is less than or equal to 85. Despite the reduced thermal stability of cycloalkylphosphines, it has proven effective to operate with only a relatively small excess of organophosphorus ligands relative to the molar amount of rhodium. This ligand fraction is capable of providing the required n / iso ratio, leads to high conversions, and, surprisingly, is stable over long production periods in the specified solvents.

[0024] In a preferred embodiment of the process, the hydroformylation can be carried out in a temperature range of greater than or equal to 80°C and less than or equal to 140°C. Within this temperature range of the reaction zone, sufficient reaction rates can be achieved, and in particular, a preferred isomer ratio is obtained even at these conversions, which, compared to conventional prior art processes, is characterized by a higher proportion of iso-isomers.

[0025] In a further preferred embodiment of the process, the molar ratio of arylphosphine to cycloalkylphosphine ligands, expressed as the molar amount of arylphosphine divided by the molar amount of cycloalkylphosphine ligands, can be greater than or equal to 0.5 and less than or equal to 75. This ratio between arylphosphine and cycloalkylphosphine ligands can provide a significantly increased iso-isomer ratio with only a very slight reduction in conversion. In a further preferred embodiment, the ratio can be greater than or equal to 15 and less than or equal to 70, and more preferably greater than or equal to 20 and less than or equal to 60.

[0026] In a further preferred aspect of the process, the molar ratio of arylphosphine ligands to rhodium can be greater than or equal to 5 and less than or equal to 75. The amount of arylphosphine ligands, in addition to the isomer ratio, can also significantly influence the productivity of the overall reaction. Within this molar ratio, sufficiently high amounts of isomers can be obtained with high conversions. The molar ratio can also preferably be greater than or equal to 35 and less than or equal to 65, and further preferably greater than or equal to 45 and less than or equal to 55.

[0027] In a further preferred embodiment of the process, the molar ratio of cycloalkylphosphine ligands to rhodium can be greater than or equal to 1 and less than or equal to 10. The amount of cycloalkylphosphine ligands can have a significant influence on the isomer ratio and, in particular, on the iso-content of the aldehydes formed. At lower ratios, the influence of the cycloalkylphosphine ligands on increasing the iso-aldehyde content is too small. Higher ratios can be disadvantageous, as the olefin conversion rates can be significantly reduced in these cases. The molar ratio can also preferably be greater than or equal to 2 and less than or equal to 8, and further preferably greater than or equal to 4 and less than or equal to 6.

[0028] Within a preferred aspect of the process, the arylphosphine can be triphenylphosphine. The use of triarylphosphine (TPP) as the arylphosphine can contribute to particularly high yields and especially long catalyst solution lifetimes. Excess TPP is particularly effective at stabilizing the rhodium in the solution. Furthermore, TPP can also act as a ligand reservoir in case of damage to the cycloalkylphosphine ligand.

[0029] Within a preferred aspect of the process, the cycloalkylphosphine can be tricyclohexylphosphine. In particular, the use of tricyclohexylphosphine can contribute to a particularly efficient shift of the aldehyde isomer ratio towards the iso-isomers. This is most likely achieved due to the increased steric bulk of the ligand. The shift of the isomer ratio towards iso-aldehydes occurs in the specified solvents even at concentrations that do not yet adversely affect the achievable reaction rate. Therefore, this ligand can contribute more efficiently than cycloalkylphosphines with only two cycloalkyl groups.

[0030] 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. The intermediate olefins, in particular, can be converted more extensively towards the iso-aldehyde disomers using the process according to the invention without significant losses in conversion. While not limited by theory, this effect arises for the "intermediate" alpha-olefins due to the specific orientation of the olefin at the catalyst complex, which is determined by the ligand composition and the solvent.

[0031] In a preferred embodiment of the process, the molar ratio of synthesis gas to 1-olefin, expressed as (molar amount of H₂ + molar amount of CO) divided by the molar amount of 1-olefin, can be greater than or equal to 1:1 and less than or equal to 5:1. Within this ratio between olefin and synthesis gas, sufficiently high concentrations of reactants can be provided in the claimed group of solvents, which together lead to high conversions and only a small number of undesired side reactions.

[0032] Furthermore, according to the invention, the process according to the invention is used for the hydroformylation of 1-olefins on a complex catalyst, wherein the hydroformylation is carried out in two steps, wherein in a first process step the reaction is carried out in the presence of a rhodium-containing complex catalyst comprising arylphosphine and without cycloalkylphosphine ligands in a solvent selected from the group consisting of alcohols, acetals or alkanes with a chain length greater than or equal to C10 or a mixture thereof, and wherein in a second process step a further solvent with a boiling point greater than or equal to 180°C and less than or equal to 250°C and additionally tri-cycloalkylphosphine ligands are added to the reaction mixture of the first process step.

[0033] Surprisingly, it has been found that the process 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 initiating the second step, the reaction solution in the reaction zone of the first step can essentially be reused, whereby adjusting it to the conditions according to the invention can be accomplished simply by adding ligands and solvent. Complex separation operations or even a complete exchange of the reaction solution are unnecessary. Furthermore, by coupling the two process steps, a desired isomer ratio can be achieved overall across both process steps, with the position of the ratio also being determined by the adjustment and the timing of the second step.In addition, the thick oils formed in the first step can advantageously also be used, and some of the solvents with very high boiling points can be omitted, since these are, at least partially, already present in the reaction zone.

[0034] In the application according to the invention, the hydroformylation is carried out in two steps. In a first process step, the reaction is performed in the presence of a rhodium-containing complex catalyst comprising arylphosphine ligands and excluding cycloalkylphosphine ligands in a solvent selected from the group consisting of alcohols, acetals, or alkanes with a chain length greater than or equal to C10, or a mixture thereof. Thus, the first process step of the cascade does not proceed according to the invention without the presence of cycloalkyl ligands. In this process step, n-aldehydes are formed in greater quantities. Thick oils, resulting from the self-condensation of the produced aldehydes, are also naturally formed in this step. The process conditions in this step cannot correspond to those of the process according to the invention., that, for example, the rhodium concentrations in the reaction zone may be higher than claimed in the process according to the invention.

[0035] In a second process step, a further solvent with a boiling point greater than or equal to 180°C and less than or equal to 250°C, along with cycloalkylphosphine ligands, is added to the reaction mixture of the first process step. The addition of this further high-boiling-point solvent adjusts the reaction solution of the first process step to the composition of the process according to the invention. Through dilution and the addition of the further ligand species, reaction conditions are obtained that produce a higher proportion of iso-isomers without significant losses in conversion and productivity. This is advantageously possible and, by utilizing a portion of the reaction environment from the first step, leads to efficient use of the reaction solution. Furthermore, depending on the isomer requirements, the proportion of obtainable isomers can advantageously be controlled by adjusting the lengths of the individual process steps.The result is a synergistically interacting overall process.

[0036] Within a further preferred aspect of the application, the solvent in the second process step can be selected from the group consisting of alcohols with a chain length greater than or equal to C8, acetals with a chain length greater than or equal to C13, alkanes with a chain length greater than or equal to C10, or mixtures of at least two components from this group. This group of additional solvents used in the second process step can contribute to improved catalyst lifetimes, particularly for the second process step, at high conversion rates.

[0037] According to a preferred characteristic of the application, the weight ratio of the solvent added in the second process step to the amount of solvent in the first process step can be greater than or equal to 4 and less than or equal to 20. To obtain the most efficient solvent mixture, consisting of the high-boiling solvent formed in the first process step and the high-boiling solvent added in the second process step, the mixing ratio of both solvents specified above has proven particularly suitable. In the second process step, long catalyst lifetimes, high conversions, and a high iso-isomer fraction for the aldehydes are obtained.

[0038] In a further preferred embodiment, the concentration of arylphosphine ligands in the first process step, based on the total weight of the process solution, can be greater than or equal to 10 wt.% and less than or equal to 30 wt.%. This concentration of arylphosphine ligands in the first process step has proven particularly suitable for achieving especially efficient adjustment of the ligand ratios according to the invention in the second process step. This concentration leads to stable conversion with relatively low catalyst deactivation in the first process step, while simultaneously being low enough to avoid wasting too much of the catalyst added in the second process step. Overall, an efficient process is obtained across both process steps, which, in addition to suitable control of the n / iso ratios, also exhibits high overall conversion rates.

[0039] Within a preferred application, the concentration of cycloalkylphosphine added in the second process step, based on the total weight of the process solution, can be greater than or equal to 0.01 wt% and less than or equal to 1 wt%. For process economy and to efficiently increase the iso-aldehyde content in the product, it has been shown that only relatively small amounts of cycloalkylphosphine need to be added to the reaction solution of the second process step. In particular, the addition of cycloalkylphosphine leads to increased formation of iso-aldehydes, while the selected reaction conditions prevent a significant decrease in conversion in the second process step compared to the first.

[0040] Within a preferred application, the entire amount of rhodium can be added in the first process step. For simplified process control, to obtain a preferred high iso ratio of the aldehydes formed, and for high conversions, it has proven suitable for the entire addition of the metallic complex catalyst to take place within the first process step. This is surprising, since in the second process step, due to the altered ligand availability, an equilibrium must first be established, which, as expected, should occur more quickly with the addition of fresh catalyst due to the changed equilibrium position. Surprisingly, this is not the case.

[0041] Further details, features and advantages of the subject matter of the invention will become apparent from the dependent claims and from the following description of the figures and the associated examples. It shows the: Fig. 1 The iso-aldehyde fraction and the 1-butene uptake of a reaction solution with 2-ethylhexanol as solvent as a function of the molar tricyclohexylphosphine / rhodium ratio; Fig. 2 The iso-aldehyde fraction and the 1-butene uptake of a reaction solution with 2-ethylhexanol as solvent as a function of the tricyclohexylphosphine fraction of organophosphorus ligands; Fig. 3 The iso-aldehyde fraction and the 1-butene uptake of a reaction solution with rh-triphenylphosphine catalyst after dilution with 2-ethylhexanol as solvent, in the absence of tricyclohexylphosphine, as a function of the rhodium concentration; Fig. 4 shows the iso-aldehyde fraction and the 1-butene uptake of a reaction solution with Rh-triphenylphosphine catalyst after dilution with 2-ethylhexanol as solvent, and with tricyclohexylphosphine, as a function of the rhodium concentration. Examples

[0042] All experiments were conducted in a batch reactor using a preformed catalyst phase (9 bar synthesis gas pressure (SynGas), temperature 120°C for 30 min). A 1:1 1-butene / SynGas mixture was continuously added at 13 bar and 120°C, with reaction times varying from 20 min to 2 h until a conversion of 25 g of 1-butene was achieved. In all experiments, the catalyst solution was transferred to the evacuated reactor under inert conditions, and the reaction was initiated with a continuous addition of 1-butene and synthesis gas. The resulting 1-butene uptake over time (system productivity) and the iso / n ratio of the C5 aldehydes were used to determine the 2-methylbutanal (2-MB) fraction.

[0043] In the first series of experiments, the influence of tricyclohexylphosphine (TCHP) on the iso / n ratio of the C5 aldehydes formed and the 1-butene uptake was investigated using varying TCHP / Rh ratios. The results are shown in Table 1 and in the Figure 1 shown: Table 1: Hydroformylation of 1-Butene with TCHP in 2-Ethylhexanol (2-EHol) Exp. LM Rh (ppm) TPP / Rh TCHP / Rh TCHP (Vol.%) Convert % It. GC iso:n 1-Butene (g / h) 1. 2-EHol 50 65 0 0 99 24:76 43 2. 2-EHol 50 0 5 0,07 94 39:61 46 3. 2-EHol 50 0 10 0,14 92 38:62 33 4. 2-EHol 50 0 20 0,27 91 39:61 24 5. 2-EHol 50 0 50 0,68 82 39:61 15

[0044] From Table 1 and Figure 1It becomes apparent that TCHP, compared to TPP, increases the proportion of 2-MB in the product, thus leading to an increase in the iso / n ratio. Even at a low TCHP / Rh ratio, the ligand exerts a positive effect on the formation of the branched aldehyde. The large steric bulk of the TCHP ligand and the resulting change in the geometry and properties of the Rh complex likely alter the selectivity of the 1-butene hydroformylation. However, at higher TCHP / Rh ratios, the 1-butene uptake decreases, and consequently, the reaction rate of the overall system also declines. The reduced olefin uptake can probably be attributed to the high binding affinity of the TCHP ligand for rhodium.

[0045] In a further series of experiments, a ligand mixture of TCHP and triphenylphosphine (TPP) was used for the process according to the invention. Where available, a TCHP / Rh ratio of 50 was specified, and the amount of TPP in the reaction solution was varied. The other specific experimental conditions are given above. The results are presented in Table 2. Table 2: Hydroformylation of 1-butene with TCHP and TPP in 2-ethylhexanol (2-EHol) Exp. LM Rh (ppm) TPP / Rh TCHP / Rh TCHP (Vol.%) Convert % It. GC iso:n 1-Butene g / h 1. 2-EHol 50 65 0 0 99 24:76 43 5. 2-EHol 50 0 50 0,68 82 39:61 15 6. 2-EHol 50 100 50 0,68 76 33:67 19 7. 2-EHol 50 360 50 0,68 79 25:75 19 8. 2-EHol 50 360 0 0 87 19:81 31

[0046] The Figure 2This shows the dependence of the obtainable iso content and butene uptake as a function of the TCHP content of the total phosphorus(III) introduced by the ligands. Equivalent to the TCHP / Rh ratio, a higher iso content in the product is found with increasing TCHP content; however, the butene uptake and thus the reaction rate also decrease significantly. By using both TPP and TCHP ligands, under specific concentration and ratios between ligands and catalyst, and between the ligands themselves, the reaction can be carried out at high conversions and high iso ratios. The use of TPP leads to higher productivity, which is maintained even at higher TPP / Rh ratios. At the same time, a larger TPP excess stabilizes the catalyst system against deactivation, thus enabling long process times for the catalyst solution.The addition of a slight excess of TCHP relative to the molar amount of rhodium is able to increase the 2-MB content in the reaction solution while maintaining the same catalyst activity.

[0047] The Figure 3This figure shows the isoaldehyde fraction and the 1-butene uptake of a reaction solution with a rh-triphenylphosphine catalyst after dilution with 2-ethylhexanol as solvent, in the absence of tricyclohexylphosphine, as a function of rhodium concentration. The TPP / Rh ratio was 66 in all experiments. Due to the dilution of the catalyst solution with 2-ethylhexanol, a lower catalyst concentration results, which consequently leads to a lower 1-butene conversion. The linear regressions over the two parameters show the expected linear relationship between butene uptake and iso fraction and catalyst concentration when using a pure TPP ligand system. With increasing Rh concentration but a constant TPP / Rh ratio, the productivity of the catalyst system increases, while the iso fraction in the product decreases with the use of a pure TPP ligand system.To counteract the decreasing iso content and thus increase the formation of 2-MB, TCHP ligand is added to the Rh-TPP catalyst system in the process according to the invention.

[0048] The Figure 4 This shows the iso-aldehyde fraction and the 1-butene uptake of a reaction solution with a mixed Rh-TPP-TCHP catalyst in a dilution series with 2-ethylhexanol as solvent as a function of the rhodium concentration. The experiment is therefore essentially the same as for the Figure 4As described, this series uses a mixed ligand system of TPP and TCHP. Surprisingly, when using a ligand mixture (TPP / Rh 69 and TCHP / Rh 2), both an increase in butene uptake and an increase in the iso-aldehyde fraction are observed with decreasing dilution of the catalyst metal concentration. Thus, the behavior is surprisingly fundamentally different from that of a pure TPP catalyst system, as described in the Figure 4This relationship clearly demonstrates that, surprisingly, using a ligand system according to the invention consisting of two ligands (TPP / TCHP) in a solvent, with relatively low catalyst concentrations and a specific ratio of the two ligands to each other, both high conversions and high isoaldehyde fractions can be achieved. The particular advantages of the process according to the invention are based on the specific ratio of the two ligands. Firstly, only small molar amounts of TCHP ligands relative to the rhodium metal are sufficient to increase the isoaldehyde fraction in the product due to the spatially demanding nature of the ligand. The catalyst activity is also very high with this ligand and low TCHP / Rh ratio. Secondly, the molar amount of TPP ligands relative to the rhodium metal was selected to stabilize the rhodium-ligand catalyst system and maintain the catalyst activity.

Claims

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

2. The process according to claim 1, wherein the hydroformylation is carried out in a temperature range of greater than or equal to 80°C and less than or equal to 140°C.

3. The process according to any one of the preceding claims, wherein the molar ratio of arylphosphine to cycloalkylphosphine ligands, expressed as molar amount of arylphosphine divided by molar amount of cycloalkylphosphine ligands, is greater than or equal to 0.5 and less than or equal to 75.

4. The process according to any one of the preceding claims, wherein the molar ratio of the arylphosphine ligands to rhodium is greater than or equal to 5 and less than or equal to 75.

5. The process according to any one of the preceding claims, wherein the molar ratio of cycloalkylphosphine ligands to rhodium is greater than or equal to 1 and less than or equal to 10.

6. The process according to any one of the preceding claims, wherein the arylphosphine is triphenylphosphine.

7. The process according to any one of the preceding claims, wherein the cycloalkylphosphine is tricyclohexylphosphine.

8. The process according to any one of the preceding claims, wherein the 1-olefin is selected from the group consisting of C3-C8 olefins or mixtures thereof.

9. The process according to any one of the preceding claims, wherein the molar ratio of synthesis gas to 1-olefin, expressed as (molar amount of H2 + molar amount of CO) divided by molar amount of 1-olefin, is greater than or equal to 1:1 and less than or equal to 5:1.

10. Use of the process according to one of the preceding claims for the hydroformylation of 1-olefins on a complex catalyst, characterized in that the hydroformylation is carried out in two steps, wherein within a first process step the reaction is carried out in the presence of a rhodium-containing complex catalyst comprising arylphosphine ligands and without cycloalkylphosphine ligands in a solvent selected from the group consisting of alcohols, acetals or alkanes with a chain length greater than or equal to C10 or a mixture thereof, and wherein within a second process step a further solvent with a boiling point greater than or equal to 180°C and less than or equal to 250°C and additionally cycloalkylphosphine ligands are added to the reaction mixture of the first process step.

11. Use according to claim 10, wherein the solvent in the second process step is selected from the group consisting of alcohols having a chain length greater than or equal to C8, acetals having a chain length greater than or equal to C13, alkanes having a chain length greater than or equal to C10, or mixtures of at least two components of this group.

12. Use according to any one of claims 10 or 11, wherein the weight ratio of the solvent added in the second process step to the amount of solvent of the first process step is greater than or equal to 4 and less than or equal to 20.

13. Use according to any one of claims 10 to 12, wherein the concentration of the arylphosphine ligands in the first process step is greater than or equal to 10% by weight and less than or equal to 30% by weight based on the total weight of the process solution.

14. Use according to any one of claims 10 to 13, wherein the concentration of the cycloalkylphosphine added in the second process step is greater than or equal to 0.01% by weight and less than or equal to 1% by weight based on the total weight of the process solution.

15. Use according to any one of claims 10 to 14, wherein the total amount of rhodium is added in the first process step.