Process for preparing c5 aldehydes

Abstract

To provide a process for hydroformylation in which the degradation reaction of ligands is reduced or avoided entirely.SOLUTION: A process for preparing C5 aldehydes involves hydroformylation of butenes with synthesis gas in the presence of a homogeneous catalyst system and a solvent. It is a feature of the process that the aldehyde concentration in the reaction mixture is limited.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a process for preparing C5 aldehydes by hydroformylating butenes with synthesis gas in the presence of a homogeneous catalyst system and a solvent. The process is characterized by the limited concentration of aldehyde in the reaction mixture. [Background technology]

[0002] Hydroformylation of olefins is a known chemical reaction for preparing aldehydes. The global chemical industry uses the hydroformylation reaction to produce millions of tons of aldehydes annually. In hydroformylation, olefins are reacted with synthesis gas (a mixture of CO and H2) to produce aldehydes in the presence of a homogeneous catalyst system, which may contain a transition metal such as rhodium or cobalt and a ligand.

[0003] Some hydroformylation processes are carried out as so-called recycle gas processes, in which a product-containing gaseous output is removed from the reaction zone. The recycle gas process is generally used for the hydroformylation of shorter olefins, i.e., olefins having up to five carbon atoms, since the aldehydes formed are sufficiently volatile to leave the reaction zone in the gas phase.

[0004] The challenge with the recycle gas process is the potential for ligand decomposition due to the conditions prevailing in hydroformylation. The decomposition reactions that destroy the ligands are various processes, such as hydrolysis, oxidation, Abramov reaction, and transesterification, which may occur in parallel with one another. As a result, ligands are continuously lost during hydroformylation. In such cases, the ligands must be continuously replenished to continue operating economically, i.e., with sufficient reaction conversion. Summary of the Invention [Problem to be solved by the invention]

[0005] The problem that the present invention aims to solve was to provide a hydroformylation process in which ligand decomposition reactions are reduced or completely avoided.A further problem that the present invention aims to solve was to provide a process that does not require very complex preparation or chemical engineering to achieve the goal, i.e., reduction or avoidance of ligand decomposition reactions. [Means for solving the problem]

[0006] Surprisingly, it was found that lowering the aldehyde concentration in the reaction phase allows for smaller ligand replenishment amounts and still allows the process to be carried out economically. Ligand decomposition reactions are significantly reduced. This problem is solved by the method according to claim 1. Preferred embodiments are set forth in the dependent claims. Therefore, the present invention is a method for preparing a C5 aldehyde by hydroformylation of butene, reacting butenes with synthesis gas in the presence of a homogeneous catalyst system and a solvent in at least one reaction zone; removing a cycle gas comprising the product aldehydes, unconverted butenes, and at least a portion of the butanes from the reaction zone; The aldehyde concentration in the liquid reaction mixture in the reactor is maintained at less than 15% by weight by means of a recycle gas.

[0007] In the present context, the reduction of the aldehyde concentration is achieved by increasing the recycle gas rate. However, other means are technically possible. Increasing the recycle gas rate can achieve the effect that the product aldehyde produced is removed more quickly from at least one reaction zone. Furthermore, the above-mentioned ligand decomposition reaction is reduced. Therefore, the process according to the present invention can be operated with a lower ligand replenishment amount compared to conventional processes with similar conversion rates. Therefore, the process is more resource-efficient than comparable processes. Furthermore, costs are saved, which means that the process according to the present invention can be carried out with greater overall economic feasibility.

[0008] The reactants used in the hydroformylation according to the present invention are butenes, i.e., linear butenes (n-butenes, i.e., 1-butene and 2-butene) and / or branched butenes (isobutene), which are then reacted with synthesis gas (a mixture of CO and H) in the presence of a homogeneous catalyst to produce the desired C5 aldehydes. The butenes to be hydroformylated may be provided in pure form or in the form of industrially available mixtures as a feed mixture for the hydroformylation according to the present invention. The term "feed mixture" should be understood to refer to any type of butene-containing mixture containing butenes in an amount that allows for the economical implementation of the hydroformylation. Such a feed mixture may contain not only butenes but also the corresponding alkanes, i.e., butanes.

[0009] Industrial mixtures containing butenes and butanes and that can be used as the feed mixture for the present process include petroleum ether fractions from refineries, C4 fractions from FC crackers or steam crackers, mixtures from Fischer-Tropsch synthesis, mixtures from butane dehydrogenation, and mixtures from metathesis reactions or other industrial processes. Butene mixtures suitable for the process of the present invention can also be obtained from C4 fractions from steam crackers, such as Raffinate I, Raffinate II, or Raffinate III. Another butene-containing mixture that can be used as the feed mixture in the present invention is crude butane. 1-Butene can also be used as the feed mixture. Preferred butene-containing mixtures for use as the feed mixture in accordance with the present invention are hydrocarbon streams containing at least 15 wt.% butene. In a preferred embodiment of the present invention, the butene-containing mixture used as the feed mixture is diene- and alkyne-free, i.e., the diene and alkyne contents are in each case less than 100 ppm, preferably less than 10 ppm, and more preferably less than 1 ppm.

[0010] The hydroformylation of butene according to the present invention can produce aldehydes having five carbon atoms (C5 aldehydes). C5 aldehydes include n-pentanal (valeraldehyde), isopentanal (isovaleraldehyde), sec-pentanal (2-methylbutanal), and tert-pentanal (pivalaldehyde). In a preferred embodiment of the present invention, the method described is for preparing n-pentanal (valeraldehyde).

[0011] The process according to the invention can also be carried out using a solvent in which the homogeneous catalyst system is dissolved. At least the solvent and the homogeneous catalyst system dissolved therein form a reaction mixture, which exists in at least one reactor as a liquid phase. In a preferred embodiment, the solvent has a higher boiling point than the butenes used and the product aldehyde. The solvent used can be any solvent known to those skilled in the art. The solvent used in the process according to the invention can be, in particular, INB (isononyl benzoate) or DINCH (diisononyl cyclohexane-1,2-dicarboxylate).

[0012] The catalytic system used in the process according to the present invention comprises or consists exclusively of a metal from group 8 or 9 of the periodic table and at least one organophosphorus-containing ligand. The metal is selected from iron, ruthenium, iridium, cobalt, and rhodium. Preferred metals for the catalytic system according to the present invention are cobalt and rhodium, with rhodium being particularly preferred. The ligand used is preferably a monophosphite or bisphosphite ligand, which are known in principle to those skilled in the art. Suitable ligands are disclosed, for example, in WO 2017 / 080690 A1, WO 2014 / 056732 A1, WO 2014 / 056735 A1, WO 2014 / 056736 A1, WO 2014 / 056737 A1 and DE 10 2008 002 187 A1. Particularly preferred ligands are compounds of formula (1):

[0013] [ka]

[0014] In a particularly preferred embodiment, the process according to the invention uses a catalyst system comprising rhodium and a ligand of formula (1) above.

[0015] The molar ratio of rhodium to monophosphite or bisphosphite ligands (ligand / rhodium ratio) is preferably in the range of 1 to 100. Thus, for every rhodium, there are 1 to 100 monophosphite or bisphosphite ligands. The ligand / rhodium ratio is also preferably in the range of 1 to 20, more preferably in the range of 1 to 2. The rhodium concentration in the liquid reaction mixture is in the range of 1 to 1,000 ppm by weight, in particular in the range of 20 to 300 ppm by weight, and very particularly in the range of 40 to 150 ppm by weight.

[0016] The homogeneous catalyst system is preferably prepared in situ, i.e., in the reactor, rather than being introduced into the process as a ready-to-use activated complex. For this purpose, an activated complex is prepared in at least one reactor from a rhodium compound as a precursor in the presence of a ligand. Suitable rhodium compounds for this purpose include, for example, rhodium(II) and rhodium(III) salts such as rhodium(III) chloride, rhodium(III) nitrate, rhodium(III) sulfate, potassium rhodium sulfate, rhodium(II) or rhodium(III) carboxylate, rhodium(II) and rhodium(III) acetate, rhodium(II) octoate, rhodium(II) nonanoate, rhodium(III) oxide, salts of rhodium(III) acid, and trisammonium hexachlororhodate(III). Rhodium complexes such as rhodium biscarbonylacetylacetonate and acetylacetonatobisethylenerhodium(I) are also suitable. Rhodium acetate, rhodium octoate, and rhodium nonanoate are particularly suitable.

[0017] In a particularly preferred embodiment of the present invention, the hydroformylation is further carried out in the presence of a stabilizer, which is preferably an organic amine compound, more preferably an organic amine compound comprising at least one 2,2,6,6-tetramethylpiperidine unit of formula (I).

[0018] [ka]

[0019] In a particularly preferred embodiment of the present invention, the stabilizer is selected from the group consisting of compounds of the following formulae (I.1), (I.2), (I.3), (I.4), (I.5), (I.6), (I.7) and (I.8):

[0020] [ka]

[0021] [ka]

[0022] In formula (I.2), n is an integer of 1 to 20.

[0023] [ka]

[0024] [ka]

[0025] [ka]

[0026] In formula (I.5), n is an integer of 1 to 12.

[0027] [ka]

[0028] In formula (I.6), n is an integer of 1 to 17.

[0029] [ka]

[0030] [ka]

[0031] In formula (I.8), R is a C6 to C20 alkyl group.

[0032] Most preferably, the organic amine is di-4-(2,2,6,6-tetramethylpiperidinyl) sebacate, available, for example, under the brand name Tinuvin® 770DF. The molar ratio of ligand to stabilizer is preferably in the range of 0.1:10 to 10:1, in particular in the range of 5:10 to 10:5, and very particularly in the range of 0.8:1 to 1:0.8.

[0033] The process according to the invention is carried out in at least one reaction zone, preferably in a single reaction zone. A reaction zone in the context of this specification comprises at least one reactor, preferably a plurality of reactors. The individual reactors within a reaction zone may be connected in parallel or in series. In a particularly preferred embodiment, the reaction zone comprises at least two reactors connected in parallel.

[0034] A liquid phase is present in at least one reactor, which contains at least a solvent and a homogeneous catalyst system dissolved therein. If a stabilizer is present, it is also present in the liquid phase in at least one reactor. At least one reactor also contains a gas phase. However, since the catalyst system is present in the liquid phase, the reaction also occurs in the liquid phase. The reactants or a feed mixture containing butenes and butanes and synthesis gas are preferably added to the bottom of the reactor via a suitable device known to those skilled in the art, such as a nozzle. In a particularly preferred embodiment of the present invention, the addition is quantitatively controlled.

[0035] The hydroformylation process described herein may in principle be carried out continuously or batchwise. However, the process is preferably carried out continuously.

[0036] Typical conditions for hydroformylation are known to those skilled in the art. The hydroformylation is preferably carried out at a temperature ranging from 65° C. to 200° C., more preferably from 75° C. to 175° C., and even more preferably from 85° C. to 135° C. The pressure for the hydroformylation is preferably from 10 to 200 bar, more preferably from 12.5 to 100 bar, and even more preferably from 15 to 25 bar.

[0037] As described above, in the process according to the present invention, a circulating gas containing at least a portion of the product aldehyde, unconverted butenes, and butanes is removed from the reaction zone or at least one reactor. The removed circulating gas can then be sent to an aerosol separator to remove suspended particles of liquid entrained in the circulating gas from the circulating gas. The liquid mixture separated from the circulating gas in the aerosol separator can be recycled to the reaction zone or reactor. The structure and operation mode of aerosol separators are well known to those skilled in the art. To improve the deposition of aerosols, these separators may contain a scrubbing liquid or use a corresponding scrubbing column, which is also known to those skilled in the art.

[0038] Downstream of the aerosol separator, the circulating gas is sent to a condenser, which at least partially condenses the product aldehydes, unconverted butenes, butanes, and solvent present in the circulating gas. The condenser is preferably operated at a temperature lower than the reaction temperature. The temperature in the condenser can be 30 to 100°C. A temperature of 70 to 90°C is particularly preferred. The synthesis gas remains in the gas phase and is not condensed. In that case, the condenser contains a liquid phase containing at least partially condensed components, unconverted butenes, butanes, and solvent, and a gas phase containing synthesis gas.

[0039] The condensed liquid phase and the gas phase may be separated from each other in a phase separator. The resulting gas phase is preferably recycled to the reaction zone or reactor via a cycle gas compressor. The condensed liquid phase is preferably subjected to crude product removal, which may consist of one or more distillation columns. This separates unconverted butenes and butanes (residual C4) from the crude product. The crude product contains at least the aldehydes formed and any high-boiling by-products and / or solvents. Those skilled in the art are familiar with the conditions for distillation. The crude product may then be used in downstream reaction steps.

[0040] When INB is used as a solvent, further solvent removal may be advantageous and necessary to completely remove the solvent. INB is relatively volatile, so increasing the recycle gas rate increases INB emissions via the recycle gas. However, INB needs to be removed because it can cause problems in downstream processes or reaction steps. A solvent removal system that can be used for this purpose consists of at least one distillation column. The crude product from the crude product removal is used here to separate the solvent and any high-boiling by-products from the C5 aldehyde. The solvent may then be recycled to the reactor. If high-boiling by-products are present, it may be advantageous to purge, i.e., discharge a portion of the recycle, to prevent high-boiling by-products from accumulating in the reactor.

[0041] Alternatively, crude product removal and solvent removal can be carried out in a single distillation column, for example, by a dividing wall column that can obtain residual C4 at the top, solvent and any high-boiling by-products at the bottom, and remove C5 aldehydes in between.

[0042] When DINCH is used as the solvent, no further solvent removal is necessary. DINCH has a higher boiling point and is less volatile than INB. If the recycle gas rate is increased, at least more solvent, if any, is emitted with the recycle gas.

[0043] In a preferred embodiment, the resulting product aldehyde can be subjected to downstream reaction steps such as hydrogenation, aldolization (aldol condensation), oxidation to a carboxylic acid, or conversion to an amine.

[0044] The present invention further provides a liquid mixture comprising an aldehyde, cobalt or rhodium, an organic phosphorus-containing ligand, and a solvent, wherein the aldehyde concentration is less than 15% by weight. The solvent used may be any solvent known to those skilled in the art. The solvent used in the process according to the present invention may be, in particular, INB (isononyl benzoate) or DINCH (diisononyl cyclohexane-1,2-dicarboxylate). The ligand used is preferably a phosphate ester compound, in particular a monophosphite or bisphosphite ligand known in principle to those skilled in the art. Suitable ligands have already been mentioned above, in particular the ligand of formula (1). This mixture is in particular a liquid reaction mixture from the process according to the present invention for preparing a C5 aldehyde.

[0045] FIG. 1 shows an example of the process according to the invention. The process is carried out in a reactor (1) in which a liquid reaction phase (I) consisting of a solvent and a homogeneously dissolved catalyst system is present. The reactor (1) also contains a free gas phase (II), which may be further heated or cooled by an internal heat exchanger (16). Synthesis gas (VI) and reactant (V), i.e., the olefin or olefin-containing hydrocarbon stream used, flow continuously into the reactor (1). Reactant (V) may be added either in gaseous or liquid form. Optionally, hydrogen (VII) can be further added to the synthesis gas (VI). Furthermore, to compensate for any losses, the reactor (1) may be supplied with a ligand solution (IV) and / or solvent (III) in liquid form.

[0046] In this diagram, a continuous gas stream is removed from the reaction vessel (1) via a gas circulation system consisting of a compressor (13), an aerosol separator (7), a condenser (8), a phase separation vessel (9), and a pipeline system (6, 11) connecting the components of the gas circulation system. This gas stream is generated by the compressor (13) and can be actively transformed. From the bottom, the gas stream is transferred to the liquid reaction phase (I). The supplied reactants (V) react with the synthesis gas (VI) in the liquid phase, producing the corresponding aldehydes. Due to their partial pressures, the formed products and unconverted reactants are converted into the gas phase (II) and leave the reaction vessel (1). The removed gas stream then passes through the aerosol separator (7), where the entrained fraction of the reaction phase (I) is separated and returned to the reaction vessel (1). The resulting gas stream then reaches the downstream condenser (8). In the condenser (8), the temperature is lowered to such an extent that the remaining reactants and products are at least partially condensed from the gas phase. The resulting liquid (product-containing) and gas phases are sent together to a phase separation vessel (9), where they are separated from each other. Via pipeline (10), the liquid crude product (IX) is sent to further workup. The gas phase from the phase separation vessel (9) is sent to the suction side of the compressor (13) and returned to the reaction vessel (1). The plant pressure can be adjusted by the off-gas (IIX) using pipeline (14).

[0047] The present invention will now be described with reference to examples which are merely illustrative of the invention and should not be construed as constituting a limitation thereof. [Brief explanation of the drawings]

[0048] [Figure 1] FIG. 1 shows an example of a method according to the invention. [Example]

[0049] Experimental Example 1 (Comparative Example) Before the start of the reaction, the entire system was inerted with nitrogen, then purged with synthesis gas to remove nitrogen (less than 5% N), and then synthesis gas was injected to 14 bar (absolute pressure). 3 of reaction phase was charged.

[0050] This was prepared in advance as follows: In both cases, 5 ml of isononyl benzoate (INB) was added to remove dissolved oxygen. 3 The mixture was purged with nitrogen for 5 hours in an inerted batch vessel. Next, 140 kg of Tinuvin 770DF, 130 kg of the ligand having the structure shown in formula (1), and 11 kg of acetylacetonato(dicarbonyl)rhodium(I) were added to the INB via a nitrogen-inerted powder lock. The mixture was heated to 60°C until the solids dissolved, and then the contents were poured into the reaction vessel. The ligand concentration in the reaction phase was monitored by sampling and analyzing by HPLC. This method also allowed for the determination of the oxidized fraction of the ligand. The oxidized fraction was less than 10% of the amount of ligand used.

[0051] In the next step, the cycle gas compressor was started. The reaction phase was heated to 120°C. A control valve in the off-gas stream then brought the reaction pressure to 17 bar (absolute). In this way, excess pressure in the reaction system was dissipated during the heating stage.

[0052] Once the reaction temperature was reached, the metered addition of the reactants was started at 4,500 kg / h. The synthesis gas was flowed in at a stoichiometric ratio of 1:1.2 relative to the butene content in the reactants. The reactant used was a C4 stream with a composition of 35% butenes (a mixture of 1-butene and 2-butene) and 65% n-butane.

[0053] The volume of the reaction phase increases to 50m3 by adding and reacting the reactants. 3 The concentration increased to 1000 ppm. The circulation gas was adjusted accordingly to maintain a constant concentration. The proportion of uncomplexed ligand was determined by regular sampling and HPLC analysis, and the ligand decomposed by oxidation was replaced by metered addition of ligand. For this purpose, the ligand and Tinuvin 770DF were dissolved in crude C4-free aldehyde under inert conditions and poured into the reaction phase. This ensured a constant ratio of rhodium to uncomplexed ligand during the reaction.

[0054] Calculate the ligand utilization factor in kg per ton of aldehyde prepared from the amount of ligand replenished and the mass of aldehyde produced. The ligand utilization factor is calculated as follows:

[0055]

number

[0056] This is equal to 100% under these conditions in this example and serves as a reference for Example 2. At the same time, the aldehyde content in the reaction solution was measured from the sample by gas chromatography analysis. On average, the aldehyde content was 15% by mass.

[0057] The number of moles of aldehyde prepared per hour and the number of moles of butene used per hour were further used to calculate the yield by the following formula: A yield of 60% was obtained.

[0058]

number

[0059] Experimental Example 2 (Example) This experiment was set up and started in the same way as in Experiment 1, except that the recycle gas rate was set so that the aldehyde concentration in the reaction phase averaged 13%. The decrease in concentration was compensated for by replenishing the solvent (INB in ​​this case).

[0060] As in Example 1, the percentage of free ligand and the yield were measured in this example. As in Example 1, the ligand utilization factor in kg per ton of aldehyde prepared was measured. The ligand utilization factor was only 75% of that in Example 1. Table 1 provides a summary of the data obtained.

[0061] [Table 1]

Claims

1. This is a method for preparing C5 aldehydes by hydroformylation of butene. In at least one reaction zone, butene is reacted with synthesis gas in the presence of a homogeneous catalyst system and solvent. The circulating gas containing at least a portion of the product aldehyde, unconverted butene, and butane is removed from the reaction zone. A method for maintaining the aldehyde concentration in the liquid reaction mixture in the reactor at less than 15% by mass using the circulating gas.

2. The method according to claim 1, wherein the circulating gas removed from the reaction zone is first sent to an aerosol separator.

3. The method according to claim 2, wherein the downstream portion of the circulating gas of the aerosol separator is sent to a condenser, and the condenser condenses the product aldehyde, the unconverted butene, and the solvent present in the circulating gas.

4. The method according to claim 3, wherein the condensed liquid phase and gas phase are separated from each other in a phase separator.

5. The method according to claim 4, wherein the gas phase is recirculated to the reaction zone via a circulating gas compressor.

6. The method according to claim 4, wherein the condensed liquid phase is sent to a C4 / C5 separator having one or more distillation columns.

7. The method according to claim 6, wherein the previously removed product aldehyde and solvent are separated from each other by solvent removal, and the solvent is recycled back into the reactor.

8. The method according to claim 1, wherein the solvent has a higher boiling point than the product aldehyde.

9. The method according to claim 1, wherein the solvent is INB (isononylbenzoate) or DINCH (diisononylcyclohexane-1,2-dicarboxylate).

10. The method according to claim 1, wherein the hydroformylation in the reaction zone is further carried out in the presence of a stabilizer.

11. The aforementioned stabilizer is given by formula (I): 【Chemistry 1】 The method according to claim 10, wherein the organic amine compound comprises at least one 2,2,6,6-tetramethylpiperidine unit.

12. The method according to claim 1, wherein the homogeneous catalyst system comprises a metal of group 8 or group 9 of the periodic table and at least one organophosphorus-containing ligand.

13. The method according to claim 12, wherein the metal is iron, ruthenium, iridium, cobalt, or rhodium.

14. The homogeneous catalyst system comprises rhodium and formula (1): 【Chemistry 2】 The method according to claim 1, comprising a ligand having the structure.

15. A liquid mixture comprising an aldehyde, cobalt or rhodium, an organophosphorus-containing ligand, and a solvent, wherein the aldehyde concentration is less than 15% by mass.

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