Aldehyde production method

Abstract

To provide a method for producing aldehyde by subjecting a raw material olefin to a hydroformylation reaction with H2 and CO in the presence of a catalyst, the method enabling aldehyde to be produced under low pressure conditions such as the atmospheric pressure, and also enabling an increase in the hydroformylation reaction rate.SOLUTION: A method for producing aldehyde includes subjecting a raw material olefin to a hydroformylation reaction with a gas including hydrogen and carbon monoxide in the presence of a catalyst. The method includes reacting at least part of the gas with the raw material olefin in the form of fine bubbles.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing an aldehyde. [Background technology]

[0002] A hydroformylation reaction is widely known in which a starting olefin is reacted with hydrogen and carbon monoxide in the presence of a metal complex catalyst derived from a transition metal of Groups 8 to 10 of the long-form periodic table, which has an organophosphorus compound as a ligand, to produce an aldehyde (for example, Patent Document 1).

[0003] 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."

[0004] Known examples of the metal complex catalyst include rhodium complex catalysts, and known techniques include those using a rhodium-based compound such as rhodium acetate as the transition metal source and using triphenylphosphine, tris(2,4-di-tert-butylphenyl)phosphite (hereinafter sometimes abbreviated as "DBPO"), cyclodiphenylphosphine, or the like as the organophosphorus compound (Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-188413 [Patent Document 2] Special Publication No. 2017-521402 [Patent Document 3] International Publication No. 2017 / 010618 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the techniques disclosed in Patent Documents 2 and 3, the carbonylation reaction of a rhodium-based compound (rhodium acetate) is carried out under high-pressure conditions, which poses a problem of increased costs due to the need for production equipment and utilities for pressure control. In other words, there has been a demand for a technique for producing aldehydes under low-pressure conditions, such as atmospheric pressure.

[0007] Furthermore, because rhodium is an expensive metal, reducing the amount of catalyst required relative to the amount of raw olefin used as the substrate was an issue. In other words, there was a need for a technology that would enable the production of aldehydes using a smaller amount of catalyst than conventional methods by improving the reaction rate.

[0008] The present invention aims to solve these problems. That is, an object of the present invention is to provide a method for producing an aldehyde by subjecting a raw material olefin to a hydroformylation reaction with H and CO in the presence of a catalyst, which method is capable of producing an aldehyde under low-pressure conditions such as atmospheric pressure, and which is capable of improving the reaction rate of the hydroformylation reaction. [Means for solving the problem]

[0009] That is, the present invention provides the following <1> ~ <13> It is related to. <1> A method for producing an aldehyde, comprising subjecting a raw material olefin and a gas containing hydrogen and carbon monoxide to a hydroformylation reaction in the presence of a catalyst, A method for producing an aldehyde, comprising reacting at least a portion of the gas in the form of fine bubbles with the raw material olefin. <2> The fine bubbles include at least either microbubbles or ultrafine bubbles. <1> A method for producing the aldehyde described in <3> The hydroformylation reaction is carried out in the presence of an organic solvent. <1> or <2> A method for producing the aldehyde described in <4> The organic solvent comprises an aromatic hydrocarbon. <3> A method for producing the aldehyde described in <5> The organic solvent has a viscosity of 0.68 cp or more at 25°C as measured using an Ubbelohde viscometer. <3> or <4> A method for producing the aldehyde described in <6> The aromatic hydrocarbon includes an aromatic hydrocarbon having an alkyl group on a side chain. <4> or <5> A method for producing the aldehyde described in <7> The method for producing an aldehyde according to <6>, wherein the aromatic compound having an alkyl group on a side chain is at least one selected from the group consisting of toluene, o-xylene, m-xylene, p-xylene, mesitylene, durene, ethylbenzene, and cuumene. <8> The hydroformylation reaction is carried out under atmospheric pressure. <1> ~ <7> 10. The method for producing an aldehyde according to claim 9, wherein the aldehyde is a hydroxybenzoate. <9> the catalyst comprises a transition metal compound; <1> ~ <8> 10. The method for producing an aldehyde according to claim 9, wherein the aldehyde is a hydroxybenzoate. <10> The catalyst contains a long-form transition metal compound of Groups 8 to 10 of the periodic table and an organophosphorus ligand compound. <1> ~ <9> 10. The method for producing an aldehyde according to claim 9, wherein the aldehyde is a hydroxybenzoate. <11> The Group 8 to 10 transition metal compound includes a monovalent or more and trivalent or less rhodium compound. <10> A method for producing the aldehyde described in <12> the rhodium compound comprises rhodium acetate; <11> A method for producing the aldehyde described in <13> The catalyst includes a rhodium complex catalyst having an organophosphorus ligand compound as a ligand. <1> ~ <12> 10. The method for producing an aldehyde according to claim 9, wherein the aldehyde is a hydroxybenzoate. [Effects of the Invention]

[0010] According to the method for producing aldehyde of the present invention, aldehyde can be produced under low pressure conditions, particularly under atmospheric pressure. As a result, production equipment and utilities for pressure control are not required, which makes it possible to reduce production costs and improve production efficiency.

[0011] Furthermore, the process for producing an aldehyde of the present invention can improve the reaction rate of the hydroformylation reaction, thereby improving production efficiency and reducing production costs by reducing the amount of catalyst used. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a fine bubble generator used in the aldehyde production method of the present invention. [Figure 2] FIG. 1 is a schematic diagram of a reaction apparatus including a fine bubble generator, a reaction vessel, and a reactor used in the examples. [Figure 3] 1 is a graph showing the change over time in the number concentration and bubble size of ultrafine bubbles and microbubbles in a reaction system in Experimental Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below, but the present invention is not limited to the following description and can be practiced in any modified form without departing from the gist of the present invention.

[0014] Unless otherwise specified, in this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits, and "A to B" means A or more and B or less.

[0015] [Method for producing aldehydes] The method for producing an aldehyde of the present invention comprises subjecting a raw material olefin and a gas containing hydrogen and carbon monoxide (hereinafter also referred to as "raw material gas") to a hydroformylation reaction in the presence of a catalyst, and reacting at least a portion of the gas with the raw material olefin in the form of fine bubbles.

[0016] The catalyst used in the method for producing an aldehyde of the present invention can be obtained, for example, by chemically reacting a raw material compound with a raw material gas.

[0017] The raw material compound for the catalyst preferably contains a transition metal compound. Examples of the transition metal compound contained in the raw material compound include a long-form Group 8 to 10 transition metal compound of the periodic table (hereinafter referred to as "Group 8 to 10 transition metal compound"). A long-form Group 8 to 10 transition metal of the periodic table (hereinafter referred to as "Group 8 to 10 transition metal") is a transition metal belonging to Groups 8 to 10 of the long-form periodic table. Among these, ruthenium, cobalt, rhodium, palladium, and platinum are preferred because they have high activity when used as a catalyst, and rhodium is more preferred because it has particularly high activity.

[0018] Examples of the Group 8 to 10 transition metal compound 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, ammonium rhodium chloride, and sodium rhodium chloride, as well as water-soluble organic acid salts such as rhodium formate, rhodium acetate, palladium acetate, rhodium propionate, palladium propionate, and rhodium octanoate. Complex species of each metal may also be used.

[0019] As the Group 8 to 10 transition metal compound, it is preferable to use a rhodium compound having a valence of 1 to 3 among the above, and it is more preferable to use rhodium acetate among them from the viewpoint of excellent reaction activity and catalyst cost.

[0020] Furthermore, as the rhodium compound, for example, carbonyl complexes such as hydridotetracarbonylrhodium, octacarbonyldirhodium, dicarbonylacetylacetonatorhodium, dodecacarbonyltetrarhodium, and hexadecacarbonylhexarhodium can also be used.

[0021] In a typical hydroformylation reaction using a rhodium complex catalyst, a rhodium recovery process is provided to minimize catalyst loss, and rhodium is recovered after the reaction for regeneration and reuse. However, by reducing the amount of catalyst used relative to the substrate as in the present invention, this rhodium recovery process can be omitted, thereby reducing the effort, cost, and time required for recovery.

[0022] The raw material compounds for the catalyst preferably further contain an organic phosphorus-based ligand compound. The organic phosphorus-based ligand compound may be a monodentate ligand or a polydentate ligand. Such an organic phosphorus-based ligand compound can be coordinated to a Group 8 to 10 transition metal as a monodentate or polydentate ligand to form a complex catalyst.

[0023] The organophosphorus compounds that serve as monodentate ligands include triorganophosphines represented by the following general formula:

[0024] [ka]

[0025] (In the above general formula, each R independently represents a monovalent hydrocarbon group which may have a substituent.)

[0026] 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, examples of triorganophosphines include trialkylphosphines, triarylphosphines, tricycloalkylphosphines, alkylarylphosphines, cycloalkylarylphosphines, and alkylcycloalkylphosphines.

[0027] Substituents that the monovalent hydrocarbon group may have include, but are not limited to, alkyl groups, alkoxy groups, and the like.

[0028] 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.

[0029] Other examples of the organic phosphorus-based ligand compound that can be used include trivalent phosphite compounds represented by any of the following formulas (1) to (10).

[0030] <Trivalent phosphite compound represented by formula (1)>

[0031] [ka]

[0032] (In formula (1), R 1 ~R 3 each independently represents a monovalent hydrocarbon group which may have a substituent.

[0033] In formula (1), R 1 ~R 3 Examples of the monovalent hydrocarbon group represented by the formula (I) which may have a substituent include an alkyl group, an aryl group, and a cycloalkyl group.

[0034] Specific examples of the compound represented by formula (1) include trialkyl phosphites such as trimethyl phosphite, triethyl phosphite, n-butyldiethyl 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. Furthermore, bis(3,6,8-tri-t-butyl-2-naphthyl)phenyl phosphite and bis(3,6,8-tri-t-butyl-2-naphthyl)(4-biphenyl) phosphite, as described in JP-A-6-122642, may also be used. Among these, triphenyl phosphite is the most preferred.

[0035] <Trivalent phosphite compound represented by formula (2)>

[0036] [ka]

[0037] (In formula (2), R 4 represents a divalent hydrocarbon group which may have a substituent, and R 5 represents a monovalent hydrocarbon group which may have a substituent.

[0038] In formula (2), R 4 Examples of the divalent hydrocarbon group represented by the formula (I) 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 or naphthylene; a divalent aromatic group in which a divalent aromatic ring is bonded directly or via an atom such as an alkylene group, oxygen, nitrogen, or sulfur; and a divalent aromatic group and an alkylene group bonded directly or via an atom such as an oxygen, nitrogen, or sulfur. 5Examples of the monovalent hydrocarbon group represented by the formula (I) which may have a substituent include an alkyl group, an aryl group, and a cycloalkyl group.

[0039] Specific examples of the compound represented by formula (2) include compounds described in U.S. Pat. No. 3,415,906, such as neopentyl(2,4,6-t-butyl-phenyl)phosphite and ethylene(2,4,6-t-butyl-phenyl)phosphite.

[0040] <Trivalent phosphite compound represented by formula (3)>

[0041] [ka]

[0042] (In formula (3), R 10 is R in equation (2) 5 is synonymous with Ar 1 and Ar 2 each independently represents an arylene group which may have a substituent; x and y each independently represent 0 or 1; Q represents -CR 11 R 12 -,-O-,-S-,-NR 13 -,-SiR 14 R 15 and —CO—, R 11 and R 12 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, and R 13 , R 14 and R 15 each independently represents a hydrogen atom or a methyl group, and n represents 0 or 1.

[0043] Specific examples of the 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.

[0044] <Trivalent phosphite compound represented by formula (4)>

[0045] [ka]

[0046] (In formula (4), R 6 represents a trivalent hydrocarbon group which may have a cyclic or acyclic substituent.

[0047] Specific examples of the compound represented by formula (4) include compounds described in U.S. Pat. No. 4,567,306, such as 4-ethyl-2,6,7-trioxa-1-phosphabicyclo-[2,2,2]-octane.

[0048] <Trivalent phosphite compounds represented by formulas (5) and (6)>

[0049] [ka]

[0050] (In formula (5), R 7 is R in equation (2) 4 is synonymous with R 8 and R 9 each 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, and X represents a hydrocarbon group having a valence of (a+b).

[0051] Specific examples of the compound represented by formula (5) include compounds described in JP-A-2-231497, such as 6,6'-[[3,3',5,5'-tetrakis(1,1'-dimethylethyl)-[1,1'-biphenyl]-2,2'-diyl]bis(oxy)]bis-benzo[d,f][1,3,2]dioxaphosphebin.

[0052] Specific examples of the compound represented by formula (5) include the compound represented by the following formula (6).

[0053] [ka]

[0054] (In formula (6), X represents alkylene, arylene, or -Ar 1 -(CH2)x-Qn-(CH2)y-Ar 2 -, and R 16 and R 17 each independently represents a hydrocarbon group which may have a substituent. 1 , Ar 2 , Q, x, y, and n are the same as in formula (3).

[0055] Specific examples of the compound represented by formula (6) include the compounds described in JP-A Nos. 62-116535 and 62-116587.

[0056] <Trivalent phosphite compound represented by formula (7)>

[0057] [ka]

[0058] (In formula (7), X, Ar 1 , Ar 2 , Q, x, y, n are the same as in equation (6), and R 18 is R in equation (2) 4 is equivalent to

[0059] <Trivalent phosphite compound represented by formula (8)>

[0060] [ka]

[0061] (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; and each -OP(OR 19 )(OR 20 ) groups may be different from each other, and X represents an m-valent hydrocarbon group which may have a substituent.

[0062] Among the compounds represented by formula (8), for example, compounds described in JP-A-5-178779 and compounds described in JP-A-10-45776, such as 2,2'-bis(di-1-naphthylphosphite)-3,3',5,5'-tetra-t-butyl-6,6'-dimethyl-1,1'-biphenyl, are preferred.

[0063] <Trivalent phosphite compound represented by formula (9)>

[0064] [ka]

[0065] (In formula (9), R 21 ~R 24 each independently represents a hydrocarbon group which may have a substituent, and R 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, and L represents a saturated or unsaturated divalent aliphatic hydrocarbon group which may have a substituent.

[0066] Examples of the compound represented by formula (9) include compounds described in JP-A-8-259578.

[0067] <Trivalent phosphite compound represented by formula (10)>

[0068] [ka]

[0069] (In formula (10), R 25 ~R 28 each independently represents a monovalent hydrocarbon group which may have a substituent, and R 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 aromatic hydrocarbon group which may have a substituent, and n represents an integer of 0 or 1.

[0070] R 25 ~R 28 Examples of the optionally substituted monovalent hydrocarbon group represented by include an alkyl group, an aryl group, a cycloalkyl group, etc. The optionally substituted divalent hydrocarbon group represented by A and B may be aromatic, aliphatic, or alicyclic.

[0071] These organic phosphorus ligand compounds may be used alone or in combination of two or more, but usually only one is used.

[0072] As the organophosphorus ligand compound, the above-mentioned triorganophosphines are preferred from the viewpoint of the oxo reaction, and triphenylphosphine is particularly preferred.

[0073] The raw material gas for the catalyst preferably contains hydrogen and carbon monoxide. When the raw material gas contains hydrogen and carbon monoxide, the ratio of hydrogen to carbon monoxide is not particularly limited, and is usually, in molar ratio, H2 / CO=0.1 to 10, more preferably 0.5 to 6, and even more preferably 0.8 to 1.2.

[0074] When the feed gas contains hydrogen and carbon monoxide, the total content of hydrogen and carbon monoxide in the feed gas is not particularly limited, and is usually 50 mol % or more, preferably 70 mol % or more, more preferably 80 mol % or more, even more preferably 90 mol % or more, and particularly preferably 95 mol % or more, relative to 100 mol % of the total amount of the feed gas. Alternatively, the feed gas may be a mixed gas consisting essentially of hydrogen and carbon monoxide.

[0075] To chemically react a raw material compound with a raw material gas when producing a catalyst, for example, a catalyst mixture containing the raw material compound and an organic solvent is first prepared. The organic solvent is used to dissolve the raw material compound. Note that it is not necessary for all solutes in this catalyst mixture to be dissolved; some may be dispersed without being dissolved.

[0076] The organic solvent in the catalyst mixture is preferably at least one selected from, for example, alcohols and aromatic hydrocarbons.

[0077] Examples of alcohols include lower alcohols having 1 to 10 carbon atoms, such as methanol, ethanol, isopropanol, and 2-propylhexanol. These may be used alone or in combination of two or more. From the viewpoint of solubility, it is preferable to use methanol.

[0078] In an alcohol solution in which a Group 8 to 10 transition metal compound such as rhodium acetate is dissolved in alcohol, there are no particular restrictions on the concentration of the Group 8 to 10 transition metal compound such as rhodium acetate. However, if the concentration of the Group 8 to 10 transition metal compound is too high, crystals may precipitate, whereas if it is too low, economic efficiency decreases. Therefore, the concentration is preferably 0.3 to 15 mass%, more preferably 1 to 5 mass%.

[0079] Examples of aromatic hydrocarbons include benzene, toluene, xylene, and mesitylene. These may be used alone or in combination of two or more. From the viewpoint of solubility, xylene is preferably used.

[0080] The concentration of the organophosphorus ligand compound in an aromatic hydrocarbon solution in which the organophosphorus ligand compound is dissolved in an aromatic hydrocarbon is preferably 1 to 90 mass %, more preferably 5 to 50 mass %.

[0081] The lower limit of the concentration of the Group 8 to 10 transition metal such as rhodium in the catalyst mixture is not particularly limited, but is usually 1 ppm by mass or more, preferably 10 ppm by mass or more, and more preferably 50 ppm by mass or more. On the other hand, the upper limit of the concentration of the Group 8 to 10 transition metal such as rhodium in the catalyst mixture is not particularly limited, but is usually 10% by mass or less, preferably 1% by mass or less, and more preferably 1000 ppm by mass or less. If the concentration of the Group 8 to 10 transition metal such as rhodium is too low, the reaction rate will be slow and the reaction may not proceed sufficiently. If the concentration of the Group 8 to 10 transition metal such as rhodium is too high, it will be withdrawn entrained during purging of high boiling points, resulting in a large loss of the expensive Group 8 to 10 transition metal such as rhodium.

[0082] The above upper and lower limits can be combined in any desired manner. For example, the concentration of Group 8 to 10 transition metal such as rhodium in the catalyst mixture is preferably 1 ppm by mass to 10% by mass, more preferably 10 ppm by mass to 1% by mass, and even more preferably 50 to 1000 ppm by mass.

[0083] The ratio of phosphorus in the organophosphorus ligand compound to the Group 8-10 transition metal, such as rhodium (Rh), in the catalyst mixture is not particularly limited, and is typically a molar ratio of P / Group 8-10 transition metal = 1 to 10,000, preferably P / Group 8-10 transition metal = 1 to 1,000, and more preferably 1 to 100. If the amount of organophosphorus ligand compound is too small, the amount coordinated to the Group 8-10 transition metal, such as rhodium, will be small, and the Group 8-10 transition metal may not be sufficiently stabilized. If the amount of organophosphorus ligand compound is too large, the concentration in the reaction system will be high, and the compound will be withdrawn entrained when high boiling points are purged, resulting in significant loss.

[0084] In the present invention, the temperature of the catalyst mixture when it is brought into contact with the raw material gas to cause a chemical reaction is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 105°C or higher. On the other hand, the upper limit of the temperature is preferably 130°C or lower, more preferably 127°C or lower, and even more preferably 125°C or lower. If the temperature is lower than 90°C, the effects of the present invention may not be fully achieved, while if the temperature exceeds 130°C, the catalyst may be deactivated.

[0085] The above upper and lower limits can be combined in any combination. For example, the temperature of the catalyst mixture when it is brought into contact with the raw material gas to cause a chemical reaction is preferably 90 to 130°C, more preferably 100 to 127°C, and even more preferably 105 to 125°C.

[0086] To bring the catalyst mixture into contact with the raw material gas, the raw material gas is injected into a vessel containing the catalyst mixture at a pressure of about 1 to 10 MPa, so that the total pressure of the vessel is, for example, 1 to 10 MPa, and the mixture is stirred for about 0.5 to 5 hours while maintaining the liquid temperature within the above liquid temperature range.

[0087] The vessel into which the catalyst mixture is charged may be different from or the same as the reactor in which the hydroformylation reaction described below is carried out. When the vessel into which the catalyst mixture is charged and the reactor in which the hydroformylation reaction is carried out are different, the catalyst mixture can be extracted from the vessel and charged into the reactor. When the vessel into which the catalyst mixture is charged and the reactor in which the hydroformylation reaction is carried out are the same, after the production of the metal complex catalyst, the production of an aldehyde can be carried out directly by the hydroformylation reaction.

[0088] In the process for producing an aldehyde of the present invention, for example, a starting olefin is subjected to a hydroformylation reaction with a gas containing hydrogen and carbon monoxide in the presence of the catalyst produced by the above-mentioned method.

[0089] As the raw material olefin, a linear or branched α-olefin or internal olefin is usually used, preferably an olefin having 2 to 8 carbon atoms, specifically ethylene, propylene, 1-butene, 1-hexene, 1-octene, 1-dodecene, 1-tetradecene, etc., more preferably ethylene, propylene, 1-butene, 1-octene, and particularly preferably propylene and 1-octene.

[0090] In the aldehyde production method of the present invention, at least a part of the gas containing hydrogen and carbon monoxide is reacted with the raw material olefin in the form of fine bubbles. The lower limit of the proportion of the raw material gas in the form of fine bubbles is not particularly limited, and is usually 10 mol% or more, preferably 30 mol% or more, more preferably 50 mol% or more, and even more preferably 70 mol% or more, based on 100 mol% of the total amount of the raw material gas. Alternatively, 100 mol% of the total amount of the raw material gas may be substantially fine bubbles.

[0091] The gas contains hydrogen and carbon monoxide, and the ratio of hydrogen to carbon monoxide is not particularly limited, but is usually, in molar ratio, H2 / CO=0.1 to 10, more preferably 0.5 to 6, and even more preferably 0.8 to 1.2.

[0092] Furthermore, when the raw material gas contains hydrogen and carbon monoxide, the total content of hydrogen and carbon monoxide contained in the raw material gas is usually 50 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more, relative to 100 mol% of the total amount of the raw material gas. Alternatively, the raw material gas may be a mixed gas consisting essentially of hydrogen and carbon monoxide.

[0093] In the present invention, "fine bubbles" refers to raw material gas bubbles having a diameter of less than 100 μm, "microbubbles" refers to raw material gas bubbles having a diameter of 1 μm or more and less than 100 μm among the fine bubbles, and "ultrafine bubbles" refers to raw material gas bubbles having a diameter of less than 1 μm among the fine bubbles.

[0094] The production method of the present invention has the following features by using at least a part of the raw material gas in the form of fine bubbles. (1) Slow rising speed in liquid When the source gas bubbles are in the form of millibubbles, i.e., millibubbles with a diameter of 1 mm or more, they rise rapidly in a relatively low-viscosity liquid such as water, bursting at the liquid surface and disappearing. In contrast, when the source gas bubbles are in the form of fine bubbles, the rate at which fine bubbles rise in water is extremely slow, only about 2 mm / hour for bubbles with a diameter of 1 μm. This is a characteristic that appears because the buoyancy of fine bubbles is minimal. A similar tendency is observed in liquids other than water, and supplying the source gas in the form of fine bubbles significantly increases the residence time of the source gas in the liquid.

[0095] (2) Increase in the gas-liquid interface When the same volume of gas is introduced into a liquid phase as bubbles, the smaller the bubble diameter, the larger the gas-liquid interface area in the liquid. Furthermore, measurements of the surface charge of fine bubbles have revealed that the surface of fine bubbles carries a negative charge. This charge causes the bubbles to repel each other, preventing the bubbles of the raw gas from bonding together and preventing the gas-liquid interface from decreasing due to the coarsening of the bubbles. Therefore, the significantly enlarged interface between the gas phase and the liquid phase of the raw gas can be maintained for a long period of time.

[0096] (3) The liquid phase can be supersaturated with gas. The surface tension acting on the interface between the fine bubbles of the source gas and the liquid phase reduces the surface area, pressurizing the gas inside the bubbles. At this time, the pressure inside each bubble of the source gas is in balance with the sum of the pressure component p1 due to surface tension and the pressure component p2 due to the depth in the liquid. Since the solubility of gas in liquid increases with increasing pressure, when the source gas bubbles are in the form of fine bubbles, the dissolution of the gas inside the fine bubbles into the liquid phase is promoted by p1 compared to when the source gas bubbles are in the form of regular millibubbles, i.e., millibubbles with a diameter of 1 mm or more, creating a state of supersaturation.

[0097] In the aldehyde production method of the present invention, by converting at least a portion of the gas containing hydrogen and carbon monoxide into fine bubbles, the reaction rate of the hydroformylation reaction can be improved under low-pressure conditions, particularly atmospheric pressure, and the amount of catalyst can be reduced to produce aldehyde. The reason for this is presumably that, in the hydroformylation reaction, when the raw material gas is supplied in the form of millibubbles as in the past, gas diffusion becomes the reaction rate-limiting factor, resulting in insufficient efficiency of the hydroformylation reaction. However, when the raw material gas is supplied in the form of fine bubbles, the fine bubbles have the above-mentioned characteristics (1) to (3), so that the gas phase (raw material gas) and the liquid phase can be efficiently contacted over a wide interface for a long period of time, and the supersaturated state of the raw material gas in the liquid phase can be maintained for a long period of time, resulting in a significant improvement in the reaction rate of the hydroformylation reaction at the gas-liquid interface and its vicinity.

[0098] From the viewpoint of producing a metal complex catalyst with excellent catalytic activity, the fine bubbles in the present invention preferably contain at least either microbubbles or ultrafine bubbles. That is, the fine bubbles in the present invention may contain both microbubbles and ultrafine bubbles, or may contain substantially only microbubbles, or may contain substantially only ultrafine bubbles. "Substantially containing" means that the target microbubbles and / or ultrafine bubbles account for 95% or more of the total number of fine bubbles (100%).

[0099] Examples of methods for producing fine bubbles include known fine bubble production methods such as a swirling liquid flow method, a pressurized dissolution / decompression method, and a micropore method.

[0100] In the swirling liquid flow method, liquid is forced into a cylindrical container at high speed, creating a high-speed swirling flow inside, and a pressure drop occurs in the center.Fine bubbles are produced by introducing gas through small holes at the bottom of the cylindrical container and discharging it through small holes at the top.

[0101] In the pressurized dissolution and reduced pressure method, gas is pressurized and dissolved in liquid. Then, by suddenly ejecting the liquid into a liquid at reduced or normal pressure, the dissolved gas can be precipitated as fine bubbles.

[0102] In the micropore type, gas is ejected into the liquid through nano-level micropores.

[0103] A schematic diagram of a fine bubble generator that can be used in the aldehyde production method of the present invention is shown in Figure 1. As shown in Figure 1, liquid 1 and gas 2 are supplied to a fine bubble generator 100, pass through a nozzle housing 3, and fine bubbles 5 are discharged from nozzle holes 4.

[0104] In the process for producing an aldehyde of the present invention, the above-mentioned raw material olefin and the above-mentioned gas are subjected to a hydroformylation reaction.

[0105] The hydrogen and carbon monoxide in the gas may be supplied separately to the reactor, or may be premixed as an oxo gas and supplied together to the reactor before being supplied to the reactor. For example, gas generated by a reforming furnace or the like, or hydrogen and carbon monoxide separated from such gas, may be supplied to the reactor.

[0106] As reaction conditions for hydroformylation, the hydrogen partial pressure is usually 0.0001 MPa or more, preferably 0.01 MPa or more, more preferably 0.1 MPa or more, and usually 20 MPa or less, preferably 10 MPa or less, more preferably 5 MPa or less. If the hydrogen partial pressure is too low, the reaction rate will decrease, and if it is too high, the production of by-products will increase.

[0107] The carbon monoxide partial pressure is usually 0.0001 MPa or more, preferably 0.01 MPa or more, more preferably 0.1 MPa or more, and usually 20 MPa or less, preferably 10 MPa or less, more preferably 5 MPa or less. If the carbon monoxide partial pressure is too low, the reaction will not proceed, and if it is too high, the olefin partial pressure will decrease, and the reaction will not proceed.

[0108] The total pressure is usually 0.0001 MPaG or higher, and usually 50 MPaG or lower, preferably 30 MPaG or lower, and more preferably 20 MPaG or lower. If the total pressure is too low, the reaction rate will be slow and the reaction will not proceed sufficiently, while if the total pressure is too high, the design pressure of the reactor will be high, resulting in increased equipment costs. In the present invention, the hydroformylation reaction is most preferably carried out under atmospheric pressure (0.10 MPa).

[0109] The hydrogen partial pressure / carbon monoxide partial pressure ratio, i.e., the hydrogen / carbon monoxide molar ratio, is usually 0.1 to 10, preferably 0.5 to 6, and more preferably 0.8 to 1.2. If this partial pressure ratio is too low, the reaction will not proceed sufficiently, and if it is too high, the reaction will not proceed sufficiently or the production of by-products will increase.

[0110] The reaction temperature is usually 20° C. or higher, preferably 40° C. or higher, more preferably 50° C. or higher, and usually 200° C. or lower, preferably 150° C. or lower. If the reaction temperature is too low, the reaction will not proceed sufficiently, whereas if the reaction temperature is too high, the production of by-products may increase or the catalyst may be deactivated.

[0111] The reaction time is usually 1 minute or more, preferably 10 minutes or more, more preferably 20 minutes or more, and usually 24 hours or less, preferably 10 hours or less, more preferably 5 hours or less. If the reaction time is too short, the reaction does not proceed sufficiently, and if the reaction time is too long, high boiling point reaction occurs.

[0112] In the process for producing an aldehyde of the present invention, the hydroformylation reaction can be carried out in the presence of an organic solvent as a reaction medium in which the starting olefin and catalyst are dissolved, which has a boiling point higher than that of the aldehyde produced by the reaction and does not inhibit the reaction.

[0113] Examples of organic solvents that can be used in the hydroformylation reaction of the present invention include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as hexane and octane; alicyclic hydrocarbons such as cyclohexane; alcohols such as butanol, octanol, and polyethylene glycol; ethers such as triglyme; esters and ketones such as butyl acetate, butyl butyrate, and dioctyl phthalate. Among these organic solvents, aromatic hydrocarbons are particularly preferred.

[0114] In the aldehyde production method of the present invention, from the viewpoint of the reaction rate of the hydroformylation reaction, the lower limit of the viscosity of the organic solvent measured using an Ubbelohde viscometer at 25°C is not particularly limited, but is preferably 0.60 cp or more, more preferably 0.68 cp or more, and even more preferably 0.72 cp or more. The upper limit of the viscosity is not particularly limited, but is preferably 0.90 cp or less, more preferably 0.85 cp or less, and even more preferably 0.80 cp or less. If the viscosity is too low, the rise rate of the fine bubbles, which are the raw material gas, in the solution increases, shortening the residence time of the fine bubbles. As a result, the reaction time of the hydroformylation reaction is shortened, and the reaction does not proceed sufficiently. On the other hand, if the viscosity is too high, the diffusion of the raw material olefin or raw material gas becomes the reaction rate-limiting factor, and the reaction rate of the hydroformylation reaction decreases.

[0115] The upper and lower limits can be combined in any desired manner. For example, the viscosity of the organic solvent at 25° C. measured using an Ubbelohde viscometer is preferably 0.60 to 0.90 cp, more preferably 0.68 to 0.85 cp, and even more preferably 0.72 to 0.80 cp.

[0116] Measurement of viscosity using an Ubbelohde viscometer may be carried out according to a commonly used method, for example, in accordance with JIS Z8803:2011 or ISO 3105. The Ubbelohde viscometer may be a viscometer described in ISO 3105 or JIS K 2283.

[0117] In the method for producing an aldehyde of the present invention, the aromatic hydrocarbon preferably includes an aromatic hydrocarbon having an alkyl group on the side chain. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group.

[0118] Specific examples of aromatic compounds having an alkyl group in a side chain include at least one selected from the group consisting of toluene, o-xylene, m-xylene, p-xylene, mesitylene, durene, ethylbenzene, and cuumene. These may be used alone or in combination of two or more.

[0119] In addition, as the organic solvent inert to the aldehyde produced, the aldehyde produced in the reaction or its aldehyde condensation product such as a trimer or tetramer can also be used. Furthermore, paraffins having the same carbon number as the raw material olefin can also be used. For example, in the hydroformylation of propylene, it is preferable to use a mixture of toluene and butyl aldehyde or an aldehyde condensation product such as a trimer or tetramer.

[0120] The catalyst concentration in the reaction medium is usually 1 mass ppm to 10 mass % in terms of metal atoms constituting the complex catalyst. Furthermore, to increase the stability of the catalyst, an excess amount of an organophosphorus ligand compound can be present in the reaction medium.

[0121] The type of reactor used in the hydroformylation reaction is not particularly limited, and a stirred tank type, bubble column type, plate column type, tubular type, or gas stripping type can be used. Typically, the raw materials, olefin, oxo gas, and catalyst mixed solution are continuously fed into a continuous reactor, and the hydroformylation reaction is carried out under the above-mentioned reaction conditions. However, a batch reactor can also be used. Furthermore, in order to maintain a constant reaction temperature, the reactor may have an internal coil, jacket, external heat exchanger, or the like.

[0122] The reaction liquid containing the aldehyde produced in the hydroformylation reaction can be withdrawn from the reactor. The separation of the produced aldehyde from the reaction liquid withdrawn from the reactor can be carried out by any separation operation and apparatus, such as distillation, evaporation, gas stripping, gas absorption, or extraction. Among these, separation by distillation is preferred. In this case, a distillation column is used, and components containing the produced aldehyde as a main component can be distilled and separated from the top of the column. The distillation conditions are not particularly limited, but a column bottom temperature of 50 to 150°C is usually preferred. The pressure inside the column is also not particularly limited, but is usually preferably 0.01 to 0.1 MPa.

[0123] In the step of separating the produced aldehyde, any means and device for recovering unreacted olefin from the reaction liquid may be added. In this case, a countercurrent contact column or the like is preferably used. A gas-liquid separator or the like may be provided between each device as appropriate.

[0124] The catalyst solution, which is the residue after separating the produced aldehyde from the reaction solution as described above, is returned to the reactor and recycled. [Example]

[0125] The present invention will be described in more detail below with reference to examples and comparative examples.

[0126] The compounds used in the examples and comparative examples are as follows. Acetylacetonatodicarbonylrhodium (trade name: Rh(acac)(CO)2, manufactured by N.E. Chemcat Corporation) Tris(2,4-di-tert-butylphenyl)phosphite (trade name: DBPO, manufactured by Tokyo Chemical Industry Co., Ltd.) Triphenylphosphine (trade name: TPP, manufactured by Hokko Chemical Industry Co., Ltd.) o-Xylene (trade name: o-Xylene, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.; viscosity at 25°C: 0.76 cp) Mesitylene (trade name: Mesitylene, manufactured by Tokyo Chemical Industry Co., Ltd.; viscosity at 25°C: 0.66 cp)

[0127] [Example 1] Under a nitrogen gas atmosphere, 0.1148 g (0.445 mmol) of acetylacetonatodicarbonylrhodium (Rh(acac)(CO)2) and 2.878 g (4.45 mmol) of tris(2,4-di-tert-butylphenyl)phosphite (DBPO) were weighed into a dry 100 mL glass reaction vessel, and 65 g of o-xylene was added as an organic solvent and stirred for several minutes to dissolve the catalyst and ligand. Then, 2.500 g (22.28 mmol) of 1-octene, the reaction raw material, was added and the temperature was raised while stirring with a 22 mm diameter crosshead rotor.

[0128] (Hydroformylation reaction) Next, using an ultrafine bubble generator (manufactured by PMT Corporation, equipment name: FBG-OS Type 1), the internal liquid (catalyst mixture) in the reaction vessel was circulated at a rate of 40 mL / min. Oxo gas (hydrogen / carbon monoxide molar ratio: 1) was then introduced into the circulation line for circulating the internal liquid at a flow rate of 10 mL / min. The oxo gas was introduced so that the bubble diameter of the oxo gas in the internal liquid in the reaction vessel was within the range of 100–200 nm, i.e., so that the oxo gas maintained the form of ultrafine bubbles. This operation was carried out under atmospheric pressure in the reaction vessel. The internal liquid in the reaction vessel was then heated to 90°C. While maintaining the pressure in the reaction vessel at atmospheric pressure, oxo gas (hydrogen / carbon monoxide molar ratio: 1) was continuously introduced into the reaction vessel and stirred for 6 hours.

[0129] During the hydroformylation reaction, the liquid in the reaction vessel was sampled every two hours, and the amount of substrate lost was analyzed by gas chromatography to determine the conversion rate of 1-octene. Furthermore, the time required for the conversion rate of 1-octene to reach 60% (hereinafter referred to as "60% conversion rate") was calculated by plotting the conversion rate logarithmically against time, starting from the time when the temperature of the liquid in the reaction vessel reached 90°C. As a result, the time required for the conversion rate to reach 60% was 1.8 hours, and the reaction rate calculated from the conversion rate was 0.0093 [1 / min].

[0130] [Examples 2 and 3] A hydroformylation reaction was carried out under the same conditions as in Example 1, except that mesitylene or a mixture of o-xylene and mesitylene (o-xylene / mesitylene = 1.0 (mass ratio)) was used instead of o-xylene as the organic solvent. The evaluation results are shown in Table 1.

[0131] [Example 4] A hydroformylation reaction was carried out under the same conditions as in Example 1, except that triphenylphosphine (TPP) was used instead of DBPO as the catalyst ligand. The evaluation results are shown in Table 1.

[0132] [Comparative Example 1] The hydroformylation reaction was carried out under the same conditions as in Example 1, except that no ultrafine bubble generator was used, the circulation of the internal liquid (catalyst mixed liquid) in the reaction vessel was stopped, and oxo gas (hydrogen / carbon monoxide = 1 (molar ratio)) was introduced into the gas phase of the reaction vessel at a flow rate of 10 ml / min. The above operation was carried out with the reaction vessel under atmospheric pressure. The evaluation results are shown in Table 1.

[0133] [Comparative Examples 2 and 3] In the hydroformylation reaction, an ultrafine bubble generator was not used. The circulation of the internal liquid (catalyst mixture) in the reaction vessel was stopped, and oxo gas (hydrogen / carbon monoxide = 1 (molar ratio)) was introduced into the liquid phase of the reaction vessel at a flow rate of 10 ml / min through a 1.0 mm inner diameter stainless steel tube. The hydroformylation reaction was carried out under the same conditions as in Example 1, except that the oxo gas was introduced into the reaction vessel so that the bubble diameter of the oxo gas in the internal liquid of the reaction vessel was within the range of 1 to 2 mm, i.e., so that the oxo gas maintained the form of millibubbles. The above operation was carried out under atmospheric pressure in the reaction vessel. The evaluation results are shown in Table 1.

[0134] The results of the examples and comparative examples are shown in Table 1.

[0135] [Table 1]

[0136] Under the production conditions of Examples 1 to 4, oxo gas is supplied in the form of fine bubbles into the reaction system during the hydroformylation reaction, so the reaction rate of the hydroformylation reaction is high and it is expected that aldehyde can be produced with a small amount of catalyst. Furthermore, aldehyde could be produced at a low temperature of 90°C and atmospheric pressure.

[0137] Under the production conditions of Comparative Example 1, in the hydroformylation reaction step, oxo gas was not supplied to the reaction system in the form of fine bubbles, but was simply introduced into the gas phase only, resulting in a low reaction rate of the hydroformylation reaction.

[0138] Under the production conditions of Comparative Examples 2 and 3, the oxo gas was supplied into the reaction system in the form of millibubbles rather than fine bubbles in the hydroformylation reaction step, and therefore the reaction rate of the hydroformylation reaction was low.

[0139] [Experimental Example 1] Using o-xylene as the organic solvent and the ultrafine bubble generator used in Example 1, the organic solvent in the reaction vessel was circulated at a circulation rate of 40 mL / min, while hydrogen gas was introduced into the circulation line for circulating the organic solvent at a flow rate of 10 mL / min. The hydrogen gas was introduced so that the bubble diameter of the hydrogen gas in the liquid inside the reaction vessel was within the range of 100 to 200 nm, i.e., so that the hydrogen gas maintained the form of ultrafine bubbles. The above operation was carried out under atmospheric pressure inside the reaction vessel.

[0140] Next, the temperature of the organic solvent in the reaction vessel was controlled to 30°C, and the pressure in the reaction vessel was maintained at atmospheric pressure, and the mixture was stirred for 90 to 240 minutes while continuing to introduce hydrogen gas.

[0141] For ultrafine bubbles in organic solvents, a nanoparticle analysis system (Malvern, instrument name: NanoSite LM10) was used to observe the particle size distribution and particle number concentration of nanoparticles with diameters of 20 to 1000 nm every 15 minutes using the nanotracking method. For microbubbles, a shape and particle size distribution measurement device (Microtrac-Bell, instrument name: Microtrac PartAn SI) was used to capture the sample dispersed in the sample circulator with a full-frame camera, measure particle size through image analysis, and observe the number concentration every 15 minutes. The observation results are shown in Figure 3(a) and Figure 3(c), respectively.

[0142] [Experimental Example 2] Except for using mesitylene instead of o-xylene as the organic solvent, the number concentrations and bubble sizes of ultrafine bubbles and microbubbles in the organic solvent were observed every 15 minutes under the same conditions as in Experimental Example 1. The observation results are shown in Figure 3(b) and Figure 3(d), respectively.

[0143] [Table 2]

[0144] As shown in Figures 3(a) and 3(c), when o-xylene, which has a high viscosity, was used as the organic solvent, ultrafine and microbubbles of hydrogen gas were observed in the early stages of the experiment.

[0145] On the other hand, when mesitylene, which has a low viscosity, was used as the organic solvent, ultrafine hydrogen gas bubbles were not observed, but microbubbles were, as shown in Figures 3(b) and 3(d). Comparing Figure 3(d) with Figure 3(c), which used o-xylene as the organic solvent, the initial number concentration of hydrogen gas microbubbles was low.

[0146] This is presumably because the higher the viscosity of the organic solvent, the slower the rate at which hydrogen gas rises in the reaction system, and the higher the concentration of microbubbles maintained. [Explanation of symbols]

[0147] 1 liquid 2. Gas 3 nozzle housing 4 nozzle holes 5 Fine Bubbles 10 Reaction vessel 11 Oxogas (H2 / CO) 12 Flow control section 13 Gas-liquid mixing section 14 Pump 15 Pressure Regulating Valve 100 Fine Bubble Generator

Claims

1. A method for producing an aldehyde, comprising subjecting a raw material olefin and a gas containing hydrogen and carbon monoxide to a hydroformylation reaction in the presence of a catalyst, reacting at least a portion of the gas in the form of fine bubbles with the raw material olefin; The method for producing an aldehyde, wherein the hydroformylation reaction is carried out under atmospheric pressure.

2. The method for producing an aldehyde according to claim 1, wherein the fine bubbles include at least either microbubbles or ultrafine bubbles.

3. The method for producing an aldehyde according to claim 1 or 2, wherein the hydroformylation reaction is carried out in the presence of an organic solvent.

4. The method for producing an aldehyde according to claim 3 , wherein the organic solvent comprises an aromatic hydrocarbon.

5. 5. The method for producing an aldehyde according to claim 3, wherein the organic solvent has a viscosity of 0.68 cp or more at 25°C as measured using an Ubbelohde viscometer.

6. The method for producing an aldehyde according to claim 4, wherein the aromatic hydrocarbon comprises an aromatic hydrocarbon having an alkyl group on a side chain.

7. The method for producing an aldehyde according to claim 6, wherein the aromatic compound having an alkyl group on a side chain is at least one selected from the group consisting of toluene, o-xylene, m-xylene, p-xylene, mesitylene, durene, ethylbenzene, and cuumene.

8. The method for producing an aldehyde according to any one of claims 1 to 7, wherein the catalyst comprises a transition metal compound.

9. The method for producing an aldehyde according to any one of claims 1 to 8, wherein the catalyst comprises a compound of a transition metal of Groups 8 to 10 of the long form periodic table and an organophosphorus ligand compound.

10. The method for producing an aldehyde according to claim 9, wherein the Group 8 to 10 transition metal compound includes a monovalent or more and trivalent or less rhodium compound.

11. The method for producing an aldehyde according to claim 10, wherein the rhodium compound comprises rhodium acetate.

12. The method for producing an aldehyde according to any one of claims 1 to 11, wherein the catalyst comprises a rhodium complex catalyst having an organophosphorus ligand compound as a ligand.

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