Method for producing aldehydes

Abstract

To provide a method for producing aldehydes, which enables, without stopping a hydroformylation reaction, recovering in high efficiency a highly active complex catalyst from a reaction liquid taken out of a reaction zone and reusing the same for producing aldehydes.SOLUTION: Provided is a method for producing aldehydes, comprising the following steps (1) to (3): (1) taking out a part or all of a reaction mixture from a hydroformylation reaction zone while carrying out the hydroformylation reaction; (2) oxidizing the reaction mixture taken out by contacting the mixture with an oxygen-containing gas under an environment of a total pressure of 0.8 MPaA or less and an oxygen partial pressure ratio of 10% or less; and (3) supplying the oxidized reaction mixture to the hydroformylation reaction zone while maintaining a state where the catalyst is dissolved or dispersed in the reaction mixture.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing an aldehyde. More specifically, the present invention relates to a method for producing an aldehyde, which comprises hydroformylating an olefin with hydrogen and carbon monoxide in the presence of a catalyst to produce an aldehyde. [Background technology]

[0002] A method for producing an aldehyde is known, which comprises subjecting an olefin to a hydroformylation reaction with a gas containing hydrogen and carbon monoxide in the presence of a long-form Group 8 to 10 metal of the periodic table (hereinafter, sometimes simply referred to as a "Group 8 to 10 metal")-organophosphorus complex catalyst. This hydroformylation reaction is also called the "oxo reaction", and the mixed gas of hydrogen (H2) and carbon monoxide (CO) used in the reaction is called "oxo gas".

[0003] The catalyst used in the hydroformylation reaction of olefins contains an expensive Group 8 to 10 metal such as rhodium, and therefore it is ideal to use the catalyst semi-permanently. Therefore, a method is used in which the reaction product is separated from the reaction liquid, and the reaction liquid containing the catalyst, which is a distillation residue, is supplied to or circulated in the reaction zone for reuse, or the reaction product is distilled away from the reaction zone by gas stripping and separated, and the reaction liquid containing the catalyst is left in the reaction zone and reacted continuously.

[0004] However, in the hydroformylation reaction, the catalyst is deactivated during the reaction and accumulates in the reaction liquid, and therefore methods for recovering and reusing such catalyst have been proposed.

[0005] For example, Patent Document 1 discloses a method for reactivating a deactivated catalyst by treating an alkylphosphine produced by partially substituting a ligand such as a triarylphosphine with an alkyl group of an α-olefin with oxygen gas to convert it into the corresponding phosphine oxide.

[0006] Patent Document 2 describes a method in which a hydroformylation reaction solution containing a Group 8 metal complex having a tertiary organophosphorus compound such as triphenylphosphine as a ligand is contacted with an oxidizing agent in the presence of a free tertiary organophosphorus compound, a polar organic solvent, water, and a basic substance to crystallize and recover a solid complex catalyst of a Group 8 metal.

[0007] Patent Document 3 describes a method in which a poor solvent and hydrogen are mixed with a hydroformylation reaction liquid in which high-boiling by-products have accumulated, and a rhodium-phosphine complex catalyst coordinated with hydrogen is crystallized and recovered.

[0008] Patent Document 4 describes a method in which an alkyl-substituted phosphine produced when a ligand such as triphenylphosphine is partially substituted with the alkyl group of an α-olefin is oxidized, and then a poor solvent and hydrogen are mixed to crystallize and recover a rhodium-phosphine complex catalyst in which hydrogen is coordinated by a crystallization method. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 57-87845 [Patent Document 2] Japanese Patent Application Publication No. 57-72995 [Patent Document 3] JP 2006-151826 A [Patent Document 4] International Publication No. 2019 / 098242 Summary of the Invention [Problem to be solved by the invention]

[0010] In the method described in Patent Document 1, the activation treatment of the inactive metal catalyst, whose catalytic activity has been impaired, is carried out within the reactor, so that the hydroformylation reaction must be stopped once, resulting in poor productivity. The method described in Patent Document 2 requires an operation of recovering the complex catalyst from the crystallized product using a solid-liquid separation method, which makes the process complicated. Moreover, the method described in Patent Document 2 does not allow sufficient recovery of the complex catalyst. The method described in Patent Document 3 also requires an operation of recovering the complex catalyst from the crystallized product using a solid-liquid separation method, which makes the process complicated. Moreover, the method described in Patent Document 3 does not allow sufficient recovery of the complex catalyst. The method described in Patent Document 4 requires a hydrogen reduction step, a crystallization step, and a solid-liquid separation step after the oxidation step, and a step of dissolving the solid catalyst recovered by the solid-liquid separation in an appropriate solvent and then supplying it to a reaction zone, which poses problems in terms of production cost and facility management. Moreover, Patent Document 4 does not allow sufficient recovery of the complex catalyst.

[0011] An object of the present invention is to provide a method for producing an aldehyde, which enables a highly active complex catalyst to be recovered with high efficiency from a reaction solution discharged outside a reaction zone without terminating a hydroformylation reaction, and to be reused in the production of an aldehyde. [Means for solving the problem]

[0012] The present inventors have discovered that by contacting the reaction liquid after the hydroformylation reaction with an oxygen-containing gas and supplying the oxidized catalyst liquid to the hydroformylation reaction zone, it is possible to recover and reuse a highly active complex catalyst with high efficiency in a simple process compared to conventional methods.

[0013] The present invention relates to the following.

[0014] [1] A method for producing an aldehyde, comprising hydroformylating an olefin with a gas containing hydrogen and carbon monoxide in the presence of a catalyst, A method for producing an aldehyde, comprising the following steps (1) to (3): (1) While the hydroformylation reaction is being carried out, a part or the whole of the reaction liquid is withdrawn from the hydroformylation reaction zone. (2) The withdrawn reaction liquid is oxidized by contacting it with an oxygen-containing gas under an atmosphere with a total pressure of 0.8 MPaA or less and an oxygen partial pressure ratio of 10% or less. (3) The oxidized reaction liquid is fed to the hydroformylation reaction zone while maintaining the catalyst dissolved or dispersed in the reaction liquid.

[0015] [2] A method for producing an aldehyde, comprising hydroformylating an olefin with a gas containing hydrogen and carbon monoxide in the presence of a catalyst, A method for producing an aldehyde, comprising the following steps (1A), (2) and (3): (1A) A part or all of the reaction liquid is withdrawn from the hydroformylation reaction zone. (2) The withdrawn reaction liquid is oxidized by contacting it with an oxygen-containing gas under an atmosphere with a total pressure of 0.8 MPaA or less and an oxygen partial pressure ratio of 10% or less. (3) The oxidized reaction liquid is fed to the hydroformylation reaction zone while maintaining the catalyst dissolved or dispersed in the reaction liquid.

[0016] [3] The method for producing an aldehyde according to [1] or [2], wherein in step (2), the reaction liquid is oxidized by contacting with the oxygen-containing gas in an atmosphere having an oxygen partial pressure of 0.009 MPaA or less.

[0017] [4] The method for producing an aldehyde according to any one of [1] to [3], wherein in step (2), oxidation is carried out so that the ratio of the alkyl-substituted phosphine to the organophosphorus ligand compound in the reaction solution is 0.068 or less.

[0018] [5] The method for producing an aldehyde according to any one of [1] to [4], wherein in step (3), the reaction liquid oxidized in step (2) is supplied to the hydroformylation reaction zone while maintaining the reaction liquid in a non-slurry liquid state.

[0019] [6] The method for producing an aldehyde according to any one of [1] to [5], wherein in step (3), the reaction liquid oxidized in step (2) is reduced with hydrogen in an atmosphere containing carbon monoxide and then supplied to the hydroformylation reaction zone.

[0020] [7] The method for producing an aldehyde according to any one of [1] to [5], wherein in step (3), the reaction liquid oxidized in step (2) is supplied to the hydroformylation reaction zone, and is first reduced with hydrogen in the reaction zone.

[0021] [8] The method for producing an aldehyde according to any one of [1] to [7], wherein the catalyst is a long-form Group 8 to 10 metal-organophosphorus complex catalyst.

[0022] [9] The method for producing an aldehyde according to [8], wherein the metal of Groups 8 to 10 of the periodic table is rhodium.

[0023]

[10] The method for producing an aldehyde according to any one of [1] to [9], wherein in the step (2), an alkyl-substituted phosphine in the reaction solution is converted into an alkyl-substituted phosphine oxide by the oxidation.

[0024]

[11] The method for producing an aldehyde according to

[10] , wherein the oxidation rate of the alkyl-substituted phosphine is 5.0 to 60.0%.

[0025]

[12] A method for producing an aldehyde according to any one of [1] to

[11] , comprising removing high-boiling by-products from the reaction liquid discharged from the hydroformylation reaction zone in step (1) or step (1A), and then oxidizing the reaction liquid with the oxygen-containing gas in step (2).

[0026]

[13] distilling the reaction liquid withdrawn from the hydroformylation reaction zone in step (1) or step (1A) to obtain a non-distillate fraction containing a high-boiling point component containing rhodium; and subjecting the obtained non-distillate fraction to step (2) and oxidizing it by contacting it with the oxygen-containing gas.

[0027]

[14] In step (3), the reaction liquid oxidized in step (2) is distilled to obtain a non-distillate fraction containing the obtained high-boiling point component containing rhodium; and supplying the obtained non-distillate fraction to the hydroformylation reaction zone. Effect of the Invention

[0028] According to the present invention, in a method for producing an aldehyde, which comprises subjecting an olefin to a hydroformylation reaction with a gas containing hydrogen and carbon monoxide in the presence of a catalyst, it is possible to efficiently recover a highly active complex catalyst, in particular an expensive Group 8 to 10 metal in the complex catalyst, from a reaction solution discharged outside a reaction zone without terminating the hydroformylation reaction, and reuse the recovered catalyst in the production of an aldehyde. According to the present invention, the highly active complex catalyst contained in the reaction solution can be efficiently recovered and reused using relatively simple equipment. As a result, the amount of expensive Group 8 to 10 transition metal used can be reduced, and an increase in production costs can be suppressed. Furthermore, a high reaction yield of aldehyde can be maintained during long-term continuous operation, resulting in excellent productivity. [Brief description of the drawings]

[0029] [Figure 1] FIG. 1 is a graph showing the relationship between the ratio of alkyl-substituted phosphines to organophosphorus ligand compounds ("PPh2(n-Pr) / TPP ratio") and the reaction rate of the recovered catalyst. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] The present invention will be described in detail below. The present invention is not limited to the following description, and can be modified in any manner without departing from the gist of the present invention.

[0031] Unless otherwise specified, in this specification, a numerical range expressed with "~" means a range including the numerical values ​​before and after "~" as the lower and upper limits. For example, "A~B" means A or more and B or less.

[0032] [Method for producing aldehyde] A first embodiment of the method for producing an aldehyde of the present invention is a method for producing an aldehyde by subjecting an olefin to a hydroformylation reaction with a gas containing hydrogen and carbon monoxide in the presence of a catalyst described later, the method comprising the following steps (1) to (3): (1) While the hydroformylation reaction is being carried out, a part or the whole of the reaction liquid is withdrawn from the hydroformylation reaction zone. (2) The withdrawn reaction liquid is oxidized by contacting it with an oxygen-containing gas under an atmosphere with a total pressure of 0.8 MPaA or less and an oxygen partial pressure ratio of 10% or less. (3) The oxidized reaction liquid is fed to the hydroformylation reaction zone while maintaining the catalyst dissolved or dispersed in the reaction liquid.

[0033] In this specification, the term "hydroformylation reaction zone" refers to a zone including a reactor for carrying out a hydroformylation reaction and reactor peripheral equipment associated with the reactor, such as a gas-liquid separator.

[0034] A second embodiment of the method for producing an aldehyde of the present invention is a method for producing an aldehyde, which comprises subjecting an olefin to a hydroformylation reaction with a gas containing hydrogen and carbon monoxide in the presence of a catalyst described later, and which comprises the following steps (1A), (2), and (3): (1A) A part or all of the reaction liquid is withdrawn from the hydroformylation reaction zone. (2) The withdrawn reaction liquid is oxidized by contacting it with an oxygen-containing gas under an atmosphere with a total pressure of 0.8 MPaA or less and an oxygen partial pressure ratio of 10% or less. (3) The oxidized reaction liquid is fed to the hydroformylation reaction zone while maintaining the catalyst dissolved or dispersed in the reaction liquid.

[0035] First, the hydroformylation reaction according to the first and second embodiments of the method for producing an aldehyde of the present invention (hereinafter, these may be collectively referred to as "the present invention") will be described, and then each of steps (1), (1A), (2) and (3) will be described.

[0036] [Hydroformylation reaction] [catalyst] In the present invention, the catalyst used in the hydroformylation reaction is not particularly limited as long as it has a catalytic effect on the hydroformylation reaction of olefins. As the catalyst used in the hydroformylation reaction, it is preferable to use a Group 8 to 10 metal-organic phosphorus complex catalyst because of its excellent reaction activity.

[0037] In the present invention, the Group 8 to 10 metals are metals that belong to Groups 8 to 10 of the long-form periodic table. Among them, ruthenium, cobalt, rhodium, palladium, and platinum are preferred because of their high activity when used as catalysts, and rhodium is particularly preferred because of its high activity.

[0038] As the organophosphorus ligand compound for forming the Group 8 to 10 metal-organophosphorus complex catalyst, any trivalent organophosphorus compound that functions as a monodentate or polydentate ligand for a Group 8 to 10 metal can be used. Among these, an example of the organophosphorus compound that serves as a monodentate ligand is a tertiary triorganophosphine represented by the following formula [I].

[0039] [ka]

[0040] (In formula [I], each R independently represents a substituted or unsubstituted monovalent hydrocarbon group.)

[0041] Examples of the monovalent hydrocarbon group represented by R include an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, an aryl group having 3 to 12 carbon atoms, an alkylaryl group having 6 to 24 carbon atoms, and an arylalkyl group having 6 to 24 carbon atoms. That is, the above-mentioned triorganophosphine is, for example, a trialkylphosphine, a triarylphosphine, a tricycloalkylphosphine, an alkylarylphosphine, a cycloalkylarylphosphine, and an alkylcycloalkylphosphine.

[0042] Substituents that the monovalent hydrocarbon group may have include, but are not limited to, alkyl groups, alkoxy groups, and the like.

[0043] Specific examples of triorganophosphines include tributylphosphine, trioctylphosphine, triphenylphosphine, tritolylphosphine, tricycloalkylphosphine, monobutyldiphenylphosphine, dipropylphenylphosphine, cyclohexyldiphenylphosphine, etc. Among these, triphenylphosphine is preferred because it is chemically stable due to its low activity and is easily available.

[0044] Other examples of the trivalent organic phosphorus compound that can be used include trivalent phosphite compounds represented by the following formulas (1) to (10).

[0045] <Trivalent phosphite compound represented by formula (1)>

[0046] [ka]

[0047] (In formula (1), R 1 ~R 3 each independently represents a monovalent hydrocarbon group which may have a substituent.

[0048] R 1 ~R 3Examples of the monovalent hydrocarbon group represented by the formula (1) which may have a substituent include an alkyl group, an aryl group, and a cycloalkyl group.

[0049] Specific examples of the compound represented by formula (1) include trialkyl phosphites such as trimethyl phosphite, triethyl phosphite, n-butyl diethyl phosphite, tri-n-butyl phosphite, tri-n-propyl phosphite, tri-n-octyl phosphite, and tri-n-dodecyl phosphite; triaryl phosphites such as triphenyl phosphite and trinaphthyl phosphite; and alkylaryl phosphites such as dimethylphenyl phosphite, diethylphenyl phosphite, and ethyldiphenyl phosphite. In addition, bis(3,6,8-tri-t-butyl-2-naphthyl)phenyl phosphite and bis(3,6,8-tri-t-butyl-2-naphthyl)(4-biphenyl)phenyl phosphite described in JP-A-6-122642 may be used. Among these, triphenyl phosphite is the most preferable.

[0050] <Trivalent phosphite compound represented by formula (2)>

[0051] [ka]

[0052] (In formula (2), R 4 R represents a divalent hydrocarbon group which may have a substituent. 5 represents a monovalent hydrocarbon group which may have a substituent.

[0053] R 4Examples of the divalent hydrocarbon group which may have a substituent include an alkylene group which may contain an oxygen, nitrogen, sulfur atom, etc. in the middle of the carbon chain; a cycloalkylene group which may contain an oxygen, nitrogen, sulfur atom, etc. in the middle of the carbon chain; a divalent aromatic group such as phenylene and naphthylene; a divalent aromatic group in which a divalent aromatic ring is bonded directly or via an alkylene group or an atom such as oxygen, nitrogen or sulfur; and a divalent aromatic group and an alkylene group bonded directly or via an atom such as oxygen, nitrogen or sulfur.

[0054] R 5 Examples of the monovalent hydrocarbon group include an alkyl group, an aryl group, and a cycloalkyl group.

[0055] Examples of the compound represented by formula (2) include the compounds described in US Pat. No. 3,415,906, such as neopentyl (2,4,6-t-butyl-phenyl) phosphite and ethylene (2,4,6-t-butyl-phenyl) phosphite.

[0056] <Trivalent phosphite compound represented by formula (3)>

[0057] [ka]

[0058] (In formula (3), R 10 is R in the above formula (2) 5 Synonymous with Ar 1 and Ar 2 Each of x and y independently represents an aryl group which may have a substituent. Each of Q and y independently represents 0 or 1. Q is -CR 11 R 12 -, -O-, -S-, -NR 13 -, -SiR 14 R 15 and -CO-. 11 and R 12 R each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a phenyl group, a tolyl group, or an anisyl group.13 , R 14 and R 15 each independently represents a hydrogen atom or a methyl group; and n represents 0 or 1.

[0059] Specific examples of the trivalent phosphite compound represented by formula (3) include compounds described in U.S. Pat. No. 4,599,206, such as 1,1'-biphenyl-2,2'-diyl-(2,6-di-t-butyl-4-methylphenyl) phosphite, and compounds described in U.S. Pat. No. 4,717,775, such as 3,3'-di-t-butyl-5,5'-dimethoxy-1,1'-biphenyl-2,2'-diyl(2-t-butyl-4-methoxyphenyl) phosphite.

[0060] <Trivalent phosphite compound represented by formula (4)>

[0061] [ka]

[0062] (In formula (4), R 6 represents a trivalent hydrocarbon group which may have a cyclic or acyclic substituent.

[0063] Examples of the compound represented by formula (4) include compounds described in US Pat. No. 4,567,306, such as 4-ethyl-2,6,7-trioxa-1-phosphabicyclo-[2,2,2]-octane.

[0064] <Trivalent phosphite compounds represented by formulas (5) and (6)>

[0065] [ka]

[0066] (In formula (5), R 7 is R in the above formula (3). 4 Synonymous with R. 8 and R 9each independently represents a hydrocarbon group which may have a substituent. a and b each represent an integer of 0 to 6. The sum of a and b is 2 to 6. X represents a hydrocarbon group having a valence of (a+b).

[0067] Among the compounds represented by formula (5), preferred examples include compounds represented by the following formula (6): Also included are the compounds described in JP-A-62-116535 and JP-A-62-116587.

[0068] [ka]

[0069] (In formula (6), X is alkylene, arylene, or -Ar 1 -(CH2)x-Qn-(CH2)y-Ar 2 - represents a divalent group selected from the group consisting of Ar 1 , Ar 2 , Q, x, y, and n are Ar in the above formula (3). 1 , Ar 2 , Q, x, y, n.)

[0070] <Trivalent phosphite compound represented by formula (7)>

[0071] [ka]

[0072] (In formula (7), X, Ar 1 , Ar 2 , Q, x, y, and n are X, Ar in the above formula (3). 1 , Ar 2 , Q, x, y, n. 18 is R in the above formula (2) 4 is equivalent to

[0073] <Trivalent phosphite compound represented by formula (8)>

[0074] [ka]

[0075] (In formula (8), R 19 and R 20 each independently represents an aromatic hydrocarbon group, and at least one of the aromatic hydrocarbon groups has a hydrocarbon group on a carbon atom adjacent to a carbon atom to which an oxygen atom is bonded. m represents an integer of 2 to 4. 19 )(OR 20 ) groups may be different from each other. X represents an m-valent hydrocarbon group which may have a substituent.

[0076] Of the compounds represented by formula (8), for example, the compounds described in JP-A-5-178779 are preferred.

[0077] <Trivalent phosphite compound represented by formula (9)>

[0078] [ka]

[0079] (In formula (9), R 21 ~R 24 R each independently represents a hydrocarbon group which may have a substituent. 21 and R 22 , R 23 and R 24 may be bonded to each other to form a ring. W represents a divalent aromatic hydrocarbon group which may have a substituent. L represents a saturated or unsaturated divalent aliphatic hydrocarbon group which may have a substituent.

[0080] As the compound represented by formula (9), for example, the compound described in JP-A-8-259578 can be used.

[0081] <Trivalent phosphite compound represented by formula (10)>

[0082] [ka]

[0083] (In formula (10), R 25 ~R 28 R represents a monovalent hydrocarbon group which may have a substituent. 25 and R 26 , R 27 and R 28 may be bonded to each other to form a ring. A and B each independently represent a divalent hydrocarbon group which may have a substituent. n represents an integer of 0 or 1.

[0084] R 25 ~R 28 Examples of the monovalent hydrocarbon group represented by the formula (1) and which may have a substituent include an alkyl group, an aryl group, a cycloalkyl group, etc. The divalent hydrocarbon group represented by A and B and which may have a substituent may be any of aromatic, aliphatic, and alicyclic.

[0085] These organophosphorus ligand compounds may be used alone or in combination of two or more, but usually only one is used.

[0086] As the organophosphorus ligand compound, from the viewpoint of the oxo reaction, a triorganophosphine represented by the above formula (I) is preferred, and triphenylphosphine is particularly preferred.

[0087] The Group 8 to 10 metal-organic phosphorus complex catalyst can be easily prepared from a long-form Group 8 to 10 metal compound of the periodic table (hereinafter referred to as "Group 8 to 10 metal compound") and an organic phosphorus ligand compound by a known complex formation method. The Group 8 to 10 metal compound and the organic phosphorus ligand compound may be supplied to a reaction zone to form a complex in the reaction zone. In this case, the organic phosphorus ligand compound may be introduced into the reaction zone as it is, but considering ease of handling, it is preferable to introduce it after dissolving it in the reaction medium.

[0088] Examples of the Group 8 to 10 metal compounds include water-soluble inorganic salts or inorganic complex compounds such as rhodium chloride, palladium chloride, ruthenium chloride, platinum chloride, rhodium bromide, rhodium iodide, rhodium sulfate, rhodium nitrate, palladium nitrate, rhodium ammonium chloride, and sodium rhodium chloride; water-soluble organic acid salts such as rhodium formate, rhodium acetate, palladium acetate, rhodium propionate, palladium propionate, and rhodium octanoate; and the like. Also, complex species of each metal may be used. Among them, it is preferable to use rhodium acetate from the viewpoint of excellent reaction activity and catalyst cost.

[0089] [Hydroformylation reaction process] The hydroformylation reaction is carried out by reacting an olefin with hydrogen and carbon monoxide in the presence of a catalyst such as a Group 8 to 10 metal-organophosphorus complex catalyst. The olefin is not particularly limited, and examples thereof include olefins having a carbon number of 2 to 20. Examples of the olefins having a carbon number of 2 to 20 include α-olefins such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, and 1-octene, and internal olefins such as 2-butene, 2-pentene, 3-hexene, and 4-octene.

[0090] The reaction medium for the hydroformylation reaction is preferably a solvent that dissolves the raw material olefin and the catalyst such as a Group 8 to 10 metal-organic phosphorus complex catalyst, has a higher boiling point than the aldehyde produced, and does not inhibit the reaction. Examples of solvents that can be used in the hydroformylation reaction include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane and octane; esters such as butyl acetate and butyl butyrate; and ketones.

[0091] The concentration of the catalyst in the reaction medium is usually 1 ppm by mass to 10% by mass in terms of metal atoms such as metals of Groups 8 to 10. An organophosphorus ligand compound such as phosphine used as a ligand is usually present in an excess amount in the reaction medium in order to increase the stability of the complex catalyst, etc.

[0092] The hydroformylation reaction can be carried out under known conditions. For example, when a Group 8 to 10 metal-organophosphorus complex catalyst, particularly a rhodium-phosphine complex catalyst, is used, the reaction conditions are usually appropriately selected within the following ranges. Hydrogen partial pressure: 0.01 to 20 MPaG Carbon monoxide partial pressure: 0.01 to 20 MPaG Total pressure: 0.02MPaG~30MPaG Hydrogen partial pressure / carbon monoxide partial pressure: 0.1 to 10 Reaction temperature: 60~200℃ Rh (rhodium) concentration: several ppm to several percent by mass P (free organic phosphorus ligand) / Rh: 2-10,000 (molar ratio) Reaction time: several minutes to several tens of hours

[0093] In the hydroformylation reaction, an aldehyde having a carbon number of n+1 can be obtained from a raw material olefin having a carbon number of n (n is, for example, an integer of 2 to 20). Examples of such aldehydes include propionaldehyde, butylaldehyde, pentylaldehyde, hexylaldehyde, heptylaldehyde, octylaldehyde, nonylaldehyde, and decylaldehyde. In general, the aldehyde is obtained as a mixture of linear and branched aldehydes.

[0094] The hydroformylation reaction is usually carried out under the above reaction conditions using a flow reactor, but a batch reactor can also be used.

[0095] The main types of flow reaction (reaction using the above-mentioned flow reactor) are the stripping method and the liquid circulation method.

[0096] The stripping method is a method in which a reaction liquid containing a catalyst is held in a reactor, an olefin and an oxo gas are continuously supplied, and the aldehyde produced by the reaction is vaporized in the reactor and removed from the system.

[0097] The liquid circulation system is a method in which a reaction medium containing an olefin, an oxo gas, and a catalyst is continuously supplied to a reactor, and a reaction liquid containing the produced aldehyde, the catalyst, the reaction medium, etc. is continuously withdrawn from the reactor. The reaction liquid withdrawn from the reactor is separated into the produced aldehyde and the reaction liquid containing the catalyst by a separation operation such as stripping with unreacted gas or distillation. The resulting produced aldehyde is withdrawn from the system, and the reaction liquid containing the catalyst (in the present invention, this reaction liquid corresponds to the reaction liquid withdrawn in step (1) or step (1A)) is returned to the reactor and recycled.

[0098] In the case of the stripping method, high-boiling by-products, which are by-products of the hydroformylation reaction, accumulate in the reaction liquid containing the catalyst held in the reactor, and therefore, usually, a part of the reaction liquid containing the catalyst (in the present invention, this reaction liquid corresponds to the reaction liquid withdrawn in step (1) or step (1A)) is intermittently withdrawn from the reaction zone. In the case of the liquid circulation method, if the reaction liquid containing the catalyst is continuously recycled, high boiling point by-products accumulate in the reaction zone, so that a part of the reaction liquid containing the catalyst (in the present invention, this reaction liquid corresponds to the reaction liquid withdrawn in step (1) or step (1A)) is withdrawn from the reaction zone continuously or intermittently. The amount of the reaction liquid discharged from the hydroformylation reaction zone, i.e., the reactor, may be appropriately determined depending on the amount of high-boiling by-products produced.

[0099] Usually, when the reaction solution is withdrawn from the reaction zone, a catalyst is newly supplied to the reaction zone in an amount corresponding to the catalyst contained in the withdrawn reaction solution. In the present invention, the amount of catalyst newly supplied can be reduced by subjecting the withdrawn reaction solution to step (2) and returning it to the reaction zone. In particular, the reaction can be maintained without replenishment for Group 8 to 10 metals.

[0100] The high-boiling by-products are, for example, aldehyde condensates produced by condensation of aldehyde, which is the target product of the hydroformylation reaction.

[0101] When a Group 8 to 10 metal-phosphine complex catalyst is used as the catalyst, phosphine, alkyl-substituted phosphine (hereinafter, alkyl-substituted phosphine is referred to as "alkyl-substituted phosphine"), etc. are present in the reaction liquid in which the above-mentioned high-boiling point by-products have accumulated.

[0102] Taking the example of using rhodium as the Group 8 to 10 metal, the following rhodium complexes (a) to (e) are present in the reaction liquid in which the above-mentioned high-boiling by-products have accumulated. (a) Rhodium-phosphine complex For example, the complex RhH(PPh3)4, in which triphenylphosphine (PPh3) is coordinated to rhodium (Rh), (b) Complexes of rhodium with carbon monoxide and phosphine For example, RhH(CO)(PPh3)3 (c) Complexes of rhodium with carbon monoxide and alkyl-substituted phosphines For example, RhH(CO)(PPh3)(PPh2R)2 or RhH(CO)(PPh2R)3 (R represents an alkyl group). (d) A rhodium cluster complex in which multiple rhodium atoms are bonded to carbon monoxide and phosphine. (e) A rhodium cluster complex in which an alkyl-substituted phosphine is coordinated to the rhodium cluster complex.

[0103] Among these, complexes in which alkyl-substituted phosphines are coordinated to rhodium and rhodium cluster complexes have low activity as complex catalysts. Furthermore, complexes in which alkyl-substituted phosphines are coordinated (including cluster complexes) have higher solubility in poor solvents than complexes in which alkyl-substituted phosphines are not coordinated, and are less likely to crystallize. Moreover, complexes in which alkyl-substituted phosphines are not coordinated to rhodium, and at least hydrogen and phosphine are coordinated, have high activity and work well as complex catalysts for hydroformylation reactions. Although rhodium has been used as an example in the above explanation, the same applies to other Group 8 to 10 metals.

[0104] [Step (1) and Step (1A)] The step (1) is a step in which a part or the whole of the reaction liquid is withdrawn from the hydroformylation reaction zone while the hydroformylation reaction is being carried out as described above. Step (1A) is a step of withdrawing a part or the whole of the reaction liquid from the hydroformylation reaction zone as described above. Step (1A) does not necessarily have to be carried out while the hydroformylation reaction is being carried out, and may be a step of withdrawing a part or the whole of the reaction liquid from the hydroformylation reaction zone of another hydroformylation reaction series. Specifically, each of the steps (1) and (1A) is a step of withdrawing a reaction liquid containing an aldehyde produced by the hydroformylation reaction, a catalyst, a reaction medium, and the like, from a reactor.

[0105] The reaction liquid in the hydroformylation reaction zone contains about 40 to 80 mass % of high-boiling by-products. By subjecting this reaction liquid containing high-boiling by-products to the next step (2), the catalyst recovery rate can be increased compared to the conventional method of recovering the catalyst using a solid-liquid separation method after crystallization treatment.

[0106] Alternatively, in step (1) or step (1A), if necessary, the hydroformylation reaction liquid extracted from the hydroformylation reaction zone may be supplied to step (2) after removing low-boiling components therefrom, and then oxidized by contacting with an oxygen-containing gas. To remove the light-boiling components from the reaction liquid, a known separation operation such as distillation can be used.

[0107] Alternatively, in step (1) or step (1A), the hydroformylation reaction liquid extracted from the hydroformylation reaction zone may be optionally supplied to step (2) after removing high-boiling by-products therein, and then oxidized by contacting with an oxygen-containing gas. To remove the high-boiling by-products from the reaction liquid, a known separation operation such as distillation may be used.

[0108] Alternatively, in step (1) or step (1A), if necessary, the hydroformylation reaction liquid withdrawn from the hydroformylation reaction zone may be distilled to obtain a non-distillate containing a high-boiling point component containing rhodium, and the non-distillate thus obtained may be supplied to step (2) and oxidized by contacting with an oxygen-containing gas. A known distillation method may be used for distilling the hydroformylation reaction liquid.

[0109] Alternatively, in step (3), the reaction liquid oxidized in step (2) may be distilled to obtain a non-distillate fraction containing high boiling components containing rhodium, and the non-distillate fraction may be supplied to the hydroformylation reaction zone. A known distillation method may be used for distilling the hydroformylation reaction liquid.

[0110] When a rhodium-phosphine complex catalyst is used as the catalyst, the reaction liquid extracted in step (1) or step (1A), i.e., the reaction liquid before the oxidation treatment, usually has the following composition: This reaction liquid is subjected to the next step (2).

[0111] (Composition of the reaction solution withdrawn in step (1) or step (1A)) Alkyl-substituted phosphines: 0.5 to 10% by mass Alkyl-substituted phosphine oxide: 0.1 to 5% by mass Phosphine: 5 to 50% by mass Phosphine oxide: 0.5 to 8% by mass Other components (various complexes, high boiling point by-products, etc.): 40 to 80% by mass

[0112] The "various complexes" contained in the "other components" refer to the various rhodium complexes contained in the reaction liquid in which high-boiling by-products have accumulated, as described above in the section [Hydroformylation Reaction Step].

[0113] [Process (2)] In step (2), the reaction liquid withdrawn in step (1) or (1A) is oxidized by contacting it with an oxygen-containing gas in an atmosphere having a total pressure of 0.8 MPaA or less and an oxygen partial pressure ratio of 10% or less.

[0114] For example, when a Group 8 to 10 metal-phosphine complex is used as the hydroformylation catalyst, in step (2), it is preferable to oxidize the alkyl-substituted phosphine by contacting the reaction liquid in which high-boiling by-products such as the above-mentioned aldehyde condensation by-products have accumulated with an oxygen-containing gas, thereby converting the alkyl-substituted phosphine to the corresponding alkyl-substituted phosphine oxide. This conversion suppresses the formation of a complex in which the alkyl-substituted phosphine is coordinated, and prevents a decrease in the reaction activity as a complex catalyst and a decrease in the recovery rate of the Group 8 to 10 metal-phosphine complex. Alkyl-substituted phosphines have a higher affinity for Group 8 to 10 metals than phosphines and are easily oxidized.

[0115] In step (2), it is preferable to decompose the complex or cluster complex in which the alkyl-substituted phosphine is coordinated by oxidation. Furthermore, the complex obtained by this decomposition can be recovered as a highly active complex catalyst by supplying the reaction solution from step (2) to a hydroformylation reaction zone in step (3).

[0116] The reaction liquid after step (2), i.e., the reaction liquid after the oxidation treatment, usually has the following composition.

[0117] (Composition of reaction solution after step (2)) Alkyl-substituted phosphines: 0.1 to 6% by mass Alkyl-substituted phosphine oxide: 0.1 to 10% by mass Phosphine: 5 to 40% by mass Phosphine oxide: 1 to 10% by mass Other components (various complexes, high boiling point by-products, etc.): 40 to 80% by mass

[0118] When rhodium is used as the Group 8 to 10 metal, examples of the highly active complex catalyst include RhH(CO)(PPh3)3 and RhH(PPh3)4.

[0119] Preferred examples of the oxygen-containing gas used in step (2) include oxygen, air, and air plus an inert gas such as nitrogen.

[0120] In step (2), the total pressure is 0.8 MPaA or less, and the oxygen partial pressure ratio is 10% or less.

[0121] The upper limit of the total pressure in step (2) is 0.8 MPaA or less, since oxidation of phosphine is suppressed and the activity of the recovered Group 8 to 10 metal-phosphine complex catalyst is increased. The total pressure is preferably 0.6 MPaA or less, and more preferably 0.4 MPaA or less. On the other hand, the lower limit of the total pressure is not particularly limited, but if the total pressure is excessively low, the amount of the complex having the alkyl-substituted phosphine coordinated thereto in the reaction liquid cannot be sufficiently reduced, and the activity of the recovered Group 8 to 10 metal-phosphine complex catalyst decreases. Therefore, the total pressure is usually preferably 0.01 MPaA or more, more preferably 0.02 MPaA or more, and even more preferably 0.05 MPaA or more. The above upper and lower limits can be combined in any combination. That is, the total pressure in step (2) is preferably from 0.01 to 0.8 MPaA, more preferably from 0.02 to 0.6 MPaA, and further preferably from 0.0.05 to 0.4 MPaA.

[0122] The upper limit of the oxygen partial pressure ratio in step (2) is 10% or less, since oxidation of phosphine is suppressed and the activity rate of the recovered Group 8 to 10 metal-phosphine complex catalyst is high. The oxygen partial pressure ratio is more preferably 9% or less, and even more preferably 8% or less. On the other hand, the lower limit of the oxygen partial pressure ratio is not particularly limited, but if the oxygen partial pressure ratio is too low, the amount of the complex coordinated with the alkyl-substituted phosphine in the reaction solution cannot be sufficiently reduced, and the activity rate of the recovered Group 8 to 10 metal-phosphine complex catalyst decreases, so that an oxygen partial pressure ratio of 2% or more is usually preferred, and in particular 4% or more is more preferred. The above upper and lower limits can be combined in any combination. That is, the oxygen partial pressure ratio in step (2) is preferably 2 to 10%, more preferably 4 to 9%, and further preferably 4 to 8%.

[0123] In step (2), the upper limit of the oxygen partial pressure is not particularly limited, but is preferably 0.009 MPaA or less, more preferably 0.008 MPaA or less, and even more preferably 0.007 MPaA or less, since the above total pressure and oxygen partial pressure ratio are satisfied, oxidation of phosphine is suppressed, and the activity rate of the recovered Group 8 to 10 metal-phosphine complex catalyst is high. On the other hand, the lower limit of the oxygen partial pressure is not particularly limited, but if the oxygen partial pressure is too low, the amount of the complex coordinated with an alkyl-substituted phosphine in the reaction solution cannot be sufficiently reduced, and the activity rate of the recovered Group 8 to 10 metal-phosphine complex catalyst decreases, so that it is usually preferably 0.001 MPaA or more, more preferably 0.002 MPaA or more, and even more preferably 0.004 MPaA or more. The above upper and lower limits can be combined in any combination. That is, the oxygen partial pressure in step (2) is preferably from 0.001 to 0.009, more preferably from 0.002 to 0.008, and even more preferably from 0.004 to 0.007.

[0124] In step (2), the upper limit of the ratio of the alkyl-substituted phosphine to the organophosphorus ligand compound in the extracted reaction solution (hereinafter, sometimes referred to as "alkyl-substituted phosphine / phosphine ratio") is not particularly limited, but since oxidation of the phosphine is suppressed and the activity rate of the recovered Group 8 to 10 metal-phosphine complex catalyst is increased, it is preferable to oxidize to 0.068 or less, more preferably 0.060 or less, even more preferably 0.058 or less, and particularly preferably 0.052 or less. On the other hand, the lower limit of the alkyl-substituted phosphine / phosphine ratio is not particularly limited, but since the amount of the complex coordinated with the alkyl-substituted phosphine in the reaction solution is reduced and the activity rate of the recovered Group 8 to 10 metal-phosphine complex catalyst can be well maintained, it is preferably 0.010 or more, more preferably 0.015 or more, even more preferably 0.020 or more, and particularly preferably 0.025 or more. The above upper and lower limits can be combined in any combination. That is, the alkyl-substituted phosphine / phosphine ratio is preferably 0.010 to 0.068, more preferably 0.015 to 0.060, even more preferably 0.020 to 0.058, and particularly preferably 0.025 to 0.052.

[0125] In order to effect the oxidation treatment so that the alkyl-substituted phosphine / phosphine ratio falls within the above-mentioned range, for example, a method can be mentioned in which the reaction liquid is extracted from the reaction zone, and then the extracted reaction liquid is oxidized by contacting it with an oxygen-containing gas, and known conditions such as the oxygen concentration, oxygen partial pressure, oxidation time, oxidation temperature, etc. are adjusted.

[0126] When a Group 8 to 10 metal-phosphine complex is used as the hydroformylation reaction catalyst, the oxidation rate of the alkyl-substituted phosphine in step (2) is preferably 5.0 to 60.0%, more preferably 10.0 to 55.0%, and even more preferably 15.0 to 50.0%.

[0127] If the oxidation rate is equal to or higher than the lower limit of the above range, the amount of the complex with the alkyl-substituted phosphine coordinated in the reaction solution is reduced, and the recovery rate of the Group 8 to 10 metal-phosphine complex catalyst is increased, which is preferable. If the oxidation rate is equal to or lower than the upper limit of the above range, the oxidation of the phosphine is suppressed, and the amount of the phosphine reused in the reaction zone is not reduced, which is preferable.

[0128] Here, the oxidation rate (%) of the alkyl-substituted phosphine is represented by the following formula. {(amount of alkyl-substituted phosphine in reaction solution before oxidation treatment-amount of alkyl-substituted phosphine in reaction solution after oxidation treatment) / amount of alkyl-substituted phosphine in reaction solution before oxidation treatment}×100 The change in the amount of the alkyl-substituted phosphine or the like before and after oxidation can be detected by a conventional analytical method such as gas chromatography.

[0129] In order to carry out the oxidation treatment so that the oxidation rate of the alkyl-substituted phosphine falls within the above range, for example, a method can be mentioned in which the reaction liquid is extracted from the reaction zone, and then the extracted reaction liquid is oxidized by contacting it with an oxygen-containing gas, and known conditions such as the oxygen concentration, oxygen partial pressure, oxidation time, oxidation temperature, etc. are adjusted.

[0130] The oxidation treatment in step (2) is preferably carried out at 85 to 180°C, more preferably at 90 to 180°C, even more preferably at 110 to 180°C, particularly preferably at 110 to 160°C, and most preferably at 110 to 150°C.

[0131] When the oxidation treatment temperature is equal to or higher than the lower limit of the above range, the conversion of the alkyl-substituted phosphine to the corresponding alkyl-substituted phosphine oxide is sufficient, and the recovery rate of the Group 8 to 10 metal-phosphine complex catalyst is higher, which is preferable. Also, when the oxidation temperature is equal to or lower than the upper limit of the above range, the oxidation of the phosphine is suppressed, and the amount of the phosphine reused in the reaction zone is not reduced, which is preferable. When the oxidation treatment temperature is 110 to 150° C., the decomposition of the cluster complex is further promoted, and the amount of highly active complexes of Groups 8 to 10 metals such as rhodium increases.

[0132] The time for the oxidation treatment in step (2) varies depending on other conditions such as temperature, but is usually about several minutes to several hours, and specifically, 1 to 5 hours is preferable.

[0133] The specific treatment method for step (2) is not particularly limited, but in order to realize the above-mentioned total pressure, oxygen partial pressure and its ratio, and oxidation treatment temperature, a method in which a continuous stirred tank reactor equipped with a jacket and stirring blades is usually used, into which the reaction liquid extracted in step (1) or step (1A) and an oxygen-containing gas are continuously supplied, and the oxidation treatment is performed using the stirring blades at a predetermined temperature and for a predetermined residence time can be mentioned.

[0134] [Process (3)] In the step (3), the reaction liquid subjected to the oxidation treatment in the step (2) is supplied to the hydroformylation reaction zone while maintaining the catalyst in a dissolved or dispersed state in the reaction liquid. Here, "while maintaining the catalyst dissolved or dispersed in the reaction liquid" means that the reaction liquid after oxidation treatment to be supplied to the hydroformylation reaction zone is in a liquid state containing the catalyst. In step (3), the reaction liquid after oxidation treatment in step (2) is preferably supplied to the hydroformylation reaction zone in a non-slurry liquid state, in other words, while maintaining the catalyst in a solution state without being precipitated.

[0135] If the reaction liquid after the oxidation treatment supplied to the hydroformylation reaction zone in step (3) is in the form of a slurry, i.e., a slurry containing crystallized material and mother liquor, when the catalyst-containing crystallized material in the reaction liquid is recovered by a known separation method such as solid-liquid separation, the crystallized material is lost, resulting in an insufficient recovery rate of the catalyst. For this reason, in the present invention, a non-slurry, preferably a solution, reaction liquid is supplied to or circulated in the hydroformylation reaction zone, thereby eliminating the loss of the catalyst-containing crystallized material and increasing the recovery rate of the catalyst.

[0136] In order to supply or circulate the reaction liquid in a non-slurry state, preferably in a solution state, to the hydroformylation reaction zone, the reaction liquid need not be converted into a slurry state by a crystallization method which requires a solid-liquid separation method, but rather the reaction liquid may be oxidized under specific oxidation conditions, and the non-slurry state, preferably in a solution state, may be supplied or circulated to the hydroformylation reaction zone.

[0137] In step (3), the reaction liquid oxidized in step (2) may be optionally reduced with hydrogen in an atmosphere containing carbon monoxide and then fed to the hydroformylation reaction zone. Also, in step (3), the reaction liquid oxidized in step (2) may be optionally fed directly to the hydroformylation reaction zone and subjected to hydrogen reduction only in the reaction zone.

[0138] That is, in the reaction solution oxidized in step (2), the alkyl-substituted phosphines are converted to the corresponding alkyl-substituted phosphine oxides by oxidation, but some of the alkyl-substituted phosphines are not oxidized and remain as complexes in which the alkyl-substituted phosphines are coordinated to rhodium or as rhodium cluster complexes. These complexes do not exhibit high catalytic activity as hydroformylation reaction catalysts. Therefore, in step (3), prior to supplying the reaction liquid oxidized in step (2) to the hydroformylation reaction zone, a complex in which rhodium is coordinated with an alkyl-substituted phosphine or a rhodium cluster complex may be optionally reduced with hydrogen in an atmosphere containing carbon monoxide to enhance the catalytic activity, and then the reaction liquid may be supplied to the hydroformylation reaction zone.

[0139] In the step (3), hydrogen reduction in an atmosphere containing carbon monoxide can be carried out under known conditions. For example, when a rhodium-phosphine complex catalyst is used, the reaction conditions for hydrogen reduction are usually appropriately selected within the following ranges. Hydrogen partial pressure: 0.01 to 20 MPaG Carbon monoxide partial pressure: 0.01 to 20 MPaG Total pressure: 0.02MPaG~30MPaG Hydrogen partial pressure / carbon monoxide partial pressure: 0.1 to 10 Reaction temperature: 60~200℃ Reaction time: several minutes to several tens of hours

[0140] However, since the hydroformylation reaction zone is supplied with hydrogen and carbon monoxide to create a reducing atmosphere, if the reaction liquid oxidized in step (2) is directly supplied to the hydroformylation reaction zone without being subjected to a separate hydrogen reduction as described above, it will be reduced with hydrogen within this reaction zone, and therefore hydrogen reduction treatment of the reaction liquid is not necessarily required.

[0141] In the present invention, the reaction liquid extracted in step (1) or step (1A) is subjected to oxidation treatment in step (2), and then in step (3), the oxidation-treated reaction liquid is supplied to a hydroformylation reaction zone with the catalyst components contained in the oxidation reaction liquid as they are, without carrying out operations such as crystallization, etc. Therefore, the catalyst components, particularly expensive Group 8 to 10 metals such as rhodium, can be reused in the hydroformylation reaction with a recovery rate of substantially 100% without loss.

[0142] In the present invention, the reaction liquid is continuously withdrawn in step (1) or step (1A), and the withdrawn reaction liquid is continuously oxidized in step (2). In step (3), the oxidized reaction liquid may be recycled to the hydroformylation reaction zone while retaining the catalyst components in the oxidation reaction liquid as they are, without being subjected to an operation such as crystallization.

[0143] The activity rate of the catalyst in the oxidation reaction liquid supplied to the hydroformylation reaction zone in step (3) can be determined by comparing the hydroformylation reaction rate A obtained when the hydroformylation reaction is carried out using the catalyst with the reaction rate B obtained when the same hydroformylation reaction is carried out using a fresh catalyst. Specifically, the activity rate (%) is expressed by the following formula: Activity rate (%) = (reaction rate A / reaction rate B) x 100

[0144] The activity can also be determined by comparing the reaction rate of the catalyst immediately before and after the oxidation treatment in step (2). The reaction rate can be observed as the reduction rate of the raw material olefin, carbon monoxide, or hydrogen.

[0145] According to the present invention, the reaction liquid extracted from the hydroformylation reaction zone is oxidized under predetermined conditions and then fed to the hydroformylation reaction zone, thereby making it possible to increase the catalyst recovery rate and activity rate as compared with the case where the oxidation treatment is performed under conditions other than the predetermined conditions. According to the present invention, the recovery rate of the catalyst can be increased as compared with the case where crystallization of the catalyst is carried out after the oxidation treatment. EXAMPLES

[0146] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples as long as it does not depart from the gist of the present invention.

[0147] (Oxidation rate of alkyl-substituted phosphines) The oxidation rate of the alkyl-substituted phosphine was calculated by the following formula: In this example, n-propyldiphenylphosphine was used as the alkyl-substituted phosphine.

[0148]

number

[0149] (Oxidation rate of organophosphorus ligand compounds) The oxidation rate of the organophosphorus ligand compound was calculated by the following formula: In this example, triphenylphosphine, which is an organophosphorus ligand compound, and triphenylphosphine oxide, which is obtained by converting triphenylphosphine through oxidation, were measured.

[0150]

number

[0151] (oxidation rate ratio) As an index showing the regeneration efficiency of the catalyst contained in the reaction liquid after the hydroformylation reaction, the oxidation rate ratio (1) / (2) was calculated from the oxidation rate of the alkyl-substituted phosphine (n-propyldiphenylphosphine) (referred to as "oxidation rate (1)") and the oxidation rate of the organophosphorus ligand compound (triphenylphosphine) (referred to as "oxidation rate (2)") according to the following formula, and evaluated according to the following criteria. Oxidation rate ratio (1) / (2) = Oxidation rate (1) / Oxidation rate (2) A: Oxidation rate ratio (1) / (2) is 7.0 or more B: Oxidation rate ratio (1) / (2) is 5.5 or more and less than 7.0 C: Oxidation rate ratio (1) / (2) is less than 5.5

[0152] It can be seen that the larger the value of the oxidation rate ratio (1) / (2), the more the oxidation / decomposition of the alkyl-substituted phosphine (n-propyldiphenylphosphine) tends to be promoted, or the oxidation / decomposition of the organophosphorus ligand compound (triphenylphosphine) tends to be suppressed. In other words, the larger the value of the oxidation rate ratio (1) / (2), the more efficiently the inactivated catalyst contained in the reaction solution after the hydroformylation reaction is regenerated.

[0153] (Rh recovery rate) The amount of rhodium (in terms of rhodium atoms) in the reaction solution before the oxidation treatment and in the treated product (the reaction solution after the oxidation treatment or the crystallized product after crystallization, if crystallization was performed) was measured by X-ray fluorescence analysis, and the rhodium recovery rate was calculated using the following formula and evaluated according to the following criteria. Rh recovery rate (%) = amount of rhodium in treated material (unit: mg) / (amount of rhodium in reaction solution before oxidation treatment (unit: mg) × 100 A: Rh recovery rate is 90-100% B: Rh recovery rate is between 80% and 90% C: Rh recovery rate is less than 80%

[0154] [Example 1] A hydroformylation reaction of propylene was carried out using rhodium acetate as a Group 8-10 metal compound and triphenylphosphine as an organophosphorus ligand compound. The reaction liquid was then extracted from the hydroformylation reaction zone, and low boiling point components were removed by distillation. The composition of the reaction liquid after distillation and before being subjected to oxidation treatment was as follows: The liquid composition was determined by gas chromatography with an internal standard method.

[0155] (Composition of reaction solution before oxidation treatment) n-Propyldiphenylphosphine: 1.12% by mass n-Propyldiphenylphosphine oxide: 0.46% by mass Triphenylphosphine: 21.17% by mass Triphenylphosphine oxide: 1.31% by mass Other components (various complexes, high boiling point by-products, etc.): 75.94% by mass

[0156] Next, the extracted reaction liquid was transferred to a jacketed, impeller-equipped continuous stirred tank reactor (volume 250 mL) and air and nitrogen (N2) gas containing 6.0% by volume of oxygen were continuously supplied at a flow rate of 6.0 mL / min with an air supply rate of 0.09 L / min and an N2 gas supply rate of 0.21 L / min. The reaction liquid was subjected to oxidation treatment under the oxidation conditions shown in Table 1 while stirring at 500 rpm with the impeller. Analysis of the liquid composition of the reaction solution after the oxidation treatment (after oxidation) revealed that the oxidation rate of n-propyldiphenylphosphine was 21.6% by mass, and the oxidation rate of triphenylphosphine was 2.3% by mass, as shown in Table 1. Since the reaction solution after the oxidation treatment was a transparent amber color, it was confirmed that the catalyst was dissolved in the reaction solution and that the cluster complex was decomposed. Since no rhodium was extracted outside the hydroformylation reaction zone after the oxidation treatment, the rhodium recovery rate in Example 1 was 100% calculated as rhodium atoms.

[0157] In this embodiment, the "oxidation temperature" is the liquid temperature in the reactor. The "oxidation time" is the residence time of the reaction liquid in the reactor, calculated from the amount of liquid present in the reactor and the liquid supply rate.

[0158] [Comparative Example 1] A raw material solution having the following liquid composition was continuously supplied to a jacketed, impeller-equipped continuous stirred tank reactor (volume 342 mL) at a flow rate of 6.0 mL / min, and nitrogen gas containing 6% by volume of oxygen was continuously supplied at a flow rate of 0.35 L / min, and the mixture was stirred at 500 rpm using the impeller.

[0159] (Composition of raw solution before oxidation treatment) n-Propyldiphenylphosphine: 1.22% by mass n-Propyldiphenylphosphine oxide: 0.47% by mass Triphenylphosphine: 17.44% by mass Triphenylphosphine oxide: 1.06% by mass Other components (various complexes, high boiling point by-products, etc.): 79.81% by mass

[0160] Next, the reaction liquid was continuously extracted from the reactor and subjected to oxidation treatment under the same conditions as in Example 1, except that the oxidation conditions were as shown in Table 1. The liquid composition of the reaction liquid after the oxidation treatment is shown in Table 1.

[0161] Next, a mixed gas of hydrogen and carbon monoxide (hydrogen:carbon monoxide=1:1 (volume ratio)), 35 NL / hr, 34.7 g / hr of propylene, and the reaction liquid after the oxidation treatment were continuously supplied at a flow rate of 325 g / hr to a continuous stirred tank reactor (volume 250 mL) equipped with a jacket and an impeller under reaction conditions of a reaction temperature of 100° C., a reaction pressure of 2.0 MPaG, and a stirring speed of 630 rpm, to carry out a hydroformylation reaction. The reaction liquid was extracted from the continuous stirred tank reactor, and the light boiling point components were distilled off using a distillation method, and then returned to the continuous stirred tank reactor.

[0162] In Comparative Example 1, the "oxidation time" is the value obtained by dividing the amount of liquid present in the reactor in which the oxidation treatment is performed by the liquid supply rate, and is the integrated residence time of the reaction liquid in the reactor.

[0163] The reaction solution after the oxidation treatment for 7.44 hours was subjected to gas chromatography to measure the oxidation rate of n-propyldiphenylphosphine and the oxidation rate of triphenylphosphine. The results are shown in Table 1. Furthermore, 80 (g) of the reaction liquid after the oxidation treatment and 331 (g) of a mixed solvent of isopropyl alcohol and water (isopropyl alcohol:water = 65:35 (weight ratio)) were placed in a 0.5 L capacity autoclave equipped with an electromagnetic induction stirrer in an inert gas atmosphere. After sealing the autoclave, hydrogen gas was injected to a pressure of 0.9 MPaG at a temperature of 15°C while stirring at 600 rpm, and this pressure and temperature were maintained for 2 hours to precipitate the complex catalyst. Thereafter, the hydrogen gas was purged, and solid-liquid separation was performed by normal reduced pressure filtration. The amount of the separated rhodium complex was quantified, and the recovery rate of the rhodium complex was calculated to be 82.1% by mass in terms of rhodium atoms.

[0164] [Comparative Example 2] As shown in Table 1, the oxidation reaction and crystallization were carried out under the same conditions as in Comparative Example 1, except that the liquid composition of the raw material solution and the time of the oxidation crystallization treatment were shortened. The reaction solution after the oxidation treatment for 0.93 hours was subjected to gas chromatography to measure the oxidation rate of n-propyldiphenylphosphine and the oxidation rate of triphenylphosphine. The results are shown in Table 1. The amount of the rhodium complex separated by crystallization was quantified, and the recovery rate of the rhodium complex was calculated to be 72.9% by mass in terms of rhodium atoms.

[0165] [Comparative Example 3] Propylene hydroformylation was carried out using rhodium acetate as the Group 8-10 metal compound and triphenylphosphine as the phosphine ligand under the same conditions as in Example 1. The reaction solution was then extracted from the hydroformylation reaction zone, and low boiling point components were removed by distillation. The composition of the reaction solution after distillation and before being subjected to oxidation treatment was as follows: The liquid composition was determined by gas chromatography with an internal standard method.

[0166] (Liquid composition before oxidation treatment) n-Propyldiphenylphosphine: 1.21% by mass n-Propyldiphenylphosphine oxide: 0.56% by mass Triphenylphosphine: 27.08% by mass Triphenylphosphine oxide: 1.49% by mass Other components (various complexes, high boiling point by-products, etc.): 69.66% by mass

[0167] 10 L of the extracted reaction liquid was supplied to a jacketed complete mixing reactor (volume 20 L), and air and nitrogen (N2) gas containing 6% by volume of oxygen were supplied at the supply rates shown in Table 1. The oxidation treatment was carried out for 0.5 hours while stirring at 500 rpm using a stirring blade. The composition of the reaction solution after the oxidation treatment and the results of various evaluations are shown in Table 1.

[0168] [Table 1]

[0169] [Examples 2 to 8] The oxygenation reaction and oxidation treatment were carried out under the same conditions as in Example 1, except that the temperature of the oxidation treatment, the flow rate of the supply gas, and the residence time of the reaction liquid in the reactor were changed as shown in Table 2. In all of Examples 2 to 8, the reaction liquid after the oxidation treatment was a transparent amber color, confirming that the catalyst was in a dissolved state in the reaction liquid. The results of Examples 2 to 8 are shown in Table 2.

[0170] [Table 2]

[0171] Under the conditions of Examples 1 to 8, the ratio of the oxidation rate of the alkyl-substituted phosphine to the oxidation rate of the organophosphorus ligand compound (oxidation rate ratio (1) / (2)) and the rhodium recovery rate were high. That is, the inactivated catalyst contained in the reaction solution after the hydroformylation reaction could be efficiently regenerated, and the highly active complex catalyst could be efficiently recovered.

[0172] On the other hand, in the conditions of Comparative Examples 1 and 2, the oxidation treatment of the present invention was not carried out, and instead, the crystallization treatment was carried out, so that the rhodium recovery rate was insufficient. Under the conditions of Comparative Example 3, the oxygen partial pressure ratio was high, so that the ratio of the oxidation rate of the alkyl-substituted phosphine to the oxidation rate of the organophosphorus ligand compound (oxidation rate ratio (1) / (2)) was low and insufficient. That is, the regeneration efficiency of the inactivated catalyst contained in the reaction solution after the hydroformylation reaction and the activity of the recovered complex catalyst were insufficient.

[0173] [Reference Example 1 and Experimental Examples 1 to 16] The following experiment was conducted to investigate the relationship between the ratio of alkyl-substituted phosphines to organophosphorus ligand compounds ("PPh2(n-Pr) / TPP ratio") after oxidation treatment and the activity of the recovered catalyst.

[0174] (Production of aldehydes) A hydroformylation reaction was carried out by continuously supplying a mixed gas of hydrogen and carbon monoxide (hydrogen:carbon monoxide=1:1 (volume ratio)) at 35 NL / hr, propylene at 34.7 g / hr, and the reaction liquid after oxidation treatment containing the catalyst described in Reference Example 1 of Table 3 at a flow rate of 325 g / hr to a continuous stirred tank reactor (volume: 250 mL) equipped with a jacket and an agitator under reaction conditions of a reaction temperature of 100° C., a reaction pressure of 2.0 MPaG, and an agitator rotation speed of 630 rpm.

[0175] The liquid compositions of the reaction liquid discharged from the outlet of the continuous stirred tank reactor before the hydroformylation reaction (Reference Example 1) and after the hydroformylation reaction (Experimental Examples 1 to 16) were analyzed. The results are shown in Table 3. In this Reference Example and this Experimental Example, since the liquid before the hydroformylation reaction does not contain aldehyde, the "aldehyde concentration" refers to the concentration (unit: mass %) of aldehyde produced in the hydroformylation reaction. "Residence time" is the time divided by the reactor volume relative to the outlet flow rate. "Reaction rate" refers to the rate of aldehyde production (unit: mol / L / hr). Aldehyde was quantified by gas chromatography internal standard method. "PPh2(n-Pr) / TPP ratio" is the ratio of alkyl-substituted phosphine to organophosphorus ligand compound in the reaction liquid at the reactor outlet. In this experiment, the ratio is the molar ratio of n-propyldiphenylphosphine to triphenylphosphine. Each compound was quantified by gas chromatography internal standard method.

[0176] [Table 3]

[0177] Next, the relationship between the ratio of alkyl-substituted phosphine to organophosphorus ligand compound ("PPh2(n-Pr) / TPP ratio") in Table 3 and the reaction rate of the recovered catalyst was plotted in Figure 1. FIG. 1 shows that the lower the ratio of alkyl-substituted phosphines to organophosphorus ligand compounds after oxidation treatment (the "PPh2(n-Pr) / TPP ratio"), the higher the reaction rate of the recovered catalyst, i.e., the activity of the recovered catalyst, tends to be.

[0178] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese patent application No. 2021-193373 filed on November 29, 2021, the entirety of which is incorporated by reference.

Claims

1. A process for producing an aldehyde, comprising subjecting an olefin to a hydroformylation reaction with a gas containing hydrogen and carbon monoxide in the presence of a catalyst, A method for producing an aldehyde, comprising the following steps (1) to (3): (1) While the hydroformylation reaction is being carried out, a part or the whole of the reaction liquid is withdrawn from the hydroformylation reaction zone. (2) The withdrawn reaction liquid is oxidized by contacting it with an oxygen-containing gas in an atmosphere having a total pressure of 0.8 MPaA or less and an oxygen partial pressure ratio of 10% or less. (3) The oxidized reaction liquid is fed to the hydroformylation reaction zone while maintaining the catalyst dissolved or dispersed in the reaction liquid.

2. 1. A process for producing an aldehyde, comprising hydroformylating an olefin with a gas containing hydrogen and carbon monoxide in the presence of a catalyst, A method for producing an aldehyde, comprising the following steps (1A), (2) and (3): (1A) A part or all of the reaction liquid is withdrawn from the hydroformylation reaction zone. (2) The withdrawn reaction liquid is oxidized by contacting it with an oxygen-containing gas in an atmosphere having a total pressure of 0.8 MPaA or less and an oxygen partial pressure ratio of 10% or less. (3) The oxidized reaction liquid is fed to the hydroformylation reaction zone while maintaining the catalyst dissolved or dispersed in the reaction liquid.

3. 3. The method for producing an aldehyde according to claim 1 or 2, wherein in the step (2), the reaction solution is oxidized by contacting with the oxygen-containing gas in an atmosphere having an oxygen partial pressure of 0.009 MPaA or less.

4. The method for producing an aldehyde according to any one of claims 1 to 3, wherein in the step (2), oxidation is carried out so that a ratio of the alkyl-substituted phosphine to the organophosphorus ligand compound in the reaction solution is 0.068 or less.

5. The method for producing an aldehyde according to any one of claims 1 to 4, wherein in the step (3), the reaction liquid oxidized in the step (2) is supplied to the hydroformylation reaction zone while maintaining the reaction liquid in a non-slurry liquid state.

6. The method for producing an aldehyde according to any one of claims 1 to 5, wherein in the step (3), the reaction liquid oxidized in the step (2) is reduced with hydrogen in an atmosphere containing carbon monoxide and then supplied to the hydroformylation reaction zone.

7. The method for producing an aldehyde according to any one of claims 1 to 5, wherein in the step (3), the reaction liquid oxidized in the step (2) is supplied to the hydroformylation reaction zone, and is first reduced with hydrogen in the reaction zone.

8. The method for producing an aldehyde according to any one of claims 1 to 7, wherein the catalyst is a long-form Group 8 to 10 metal-organophosphorus complex catalyst of the periodic table.

9. The method for producing an aldehyde according to claim 8, wherein the metal of Groups 8 to 10 of the periodic table is rhodium.

10. The method for producing an aldehyde according to any one of claims 1 to 9, wherein in the step (2), an alkyl-substituted phosphine in the reaction solution is converted into an alkyl-substituted phosphine oxide by the oxidation.

11. The method for producing an aldehyde according to claim 10, wherein the oxidation rate of the alkyl-substituted phosphine is 5.0 to 60.0%.

12. The method for producing an aldehyde according to any one of claims 1 to 11, comprising removing high-boiling by-products from the reaction liquid discharged from the hydroformylation reaction zone in step (1) or step (1A), and then oxidizing the reaction liquid with the oxygen-containing gas in step (2).

13. distilling the reaction liquid withdrawn from the hydroformylation reaction zone in step (1) or step (1A) to obtain a non-distillate fraction containing a high-boiling component containing rhodium; and subjecting the obtained non-distillate fraction to step (2) and oxidizing it by contacting it with the oxygen-containing gas.

14. In step (3), the reaction liquid oxidized in step (2) is distilled to obtain a non-distillate fraction containing the obtained high-boiling point component containing rhodium; and feeding the resulting non-distillate fraction to the hydroformylation reaction zone.

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