JP7803697B2 - Aldehyde production method - Google Patents

Description

The present invention relates to a method for producing aldehydes.

The hydroformylation reaction, 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 periodic table and which uses an organophosphorus compound as a ligand, to produce an aldehyde, is widely known (see, for example, Patent Document 1).

This hydroformylation reaction is also called the "oxo reaction," and the mixed gas of hydrogen (H ₂ ) and carbon monoxide (CO) used in the reaction is called "oxo gas."

For example, rhodium complex catalysts are known as the metal complex catalyst. For example, a technology is known that uses a rhodium-based compound such as rhodium acetate as the transition metal source and 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).

JP 2012-188413 A Special table 2017-521402 publication International Publication No. 2017/010618

However, the technologies disclosed in Patent Documents 2 and 3 involve carrying out the carbonylation reaction of a rhodium-based compound (rhodium acetate) under high-pressure conditions, which poses an issue of increased costs due to the need for production equipment and utilities for pressure control. In other words, there is a need for a technology that can produce aldehydes under low-pressure conditions, such as atmospheric pressure.

Furthermore, because rhodium is an expensive metal, reducing the amount of catalyst used relative to the substrate, or raw olefin, was an issue. In other words, there was a need for a technology that could produce aldehydes using a smaller amount of catalyst than conventional methods by improving the reaction rate.

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 _H2 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.

That is, the present invention relates to the following items <1> to <13>.
<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 method for producing an aldehyde according to <1>, wherein the fine bubbles include at least either microbubbles or ultrafine bubbles.
<3> The method for producing an aldehyde according to <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 <3>, wherein the organic solvent contains an aromatic hydrocarbon.
<5> The method for producing an aldehyde according to <3> or <4>, 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 <4> or <5>, wherein the aromatic hydrocarbon includes an aromatic hydrocarbon having an alkyl group on a side chain.
<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 method for producing an aldehyde according to any one of <1> to <7>, wherein the hydroformylation reaction is carried out under atmospheric pressure.
<9> The method for producing an aldehyde according to any one of <1> to <8>, wherein the catalyst contains a transition metal compound.
<10> The method for producing an aldehyde according to any one of <1> to <9>, wherein the catalyst contains a transition metal compound of Groups 8 to 10 of the long form periodic table and an organophosphorus ligand compound.
<11> The method for producing an aldehyde according to <10>, wherein the Group 8 to 10 transition metal compound includes a rhodium compound having a valence of 1 to 3.
<12> The method for producing an aldehyde according to <11>, wherein the rhodium compound includes rhodium acetate.
<13> The method for producing an aldehyde according to any one of <1> to <12>, wherein the catalyst contains a rhodium complex catalyst having an organophosphorus ligand compound as a ligand.

The aldehyde production method of the present invention allows aldehyde to be produced under low-pressure conditions, particularly atmospheric pressure. As a result, production equipment and utilities for pressure control are no longer required, making it possible to reduce production costs and improve production efficiency.

Furthermore, the aldehyde production method of the present invention can improve the reaction rate of the hydroformylation reaction. As a result, it is possible to improve production efficiency and reduce production costs by reducing the amount of catalyst used.

FIG. 1 is a schematic diagram of a fine bubble generator used in the aldehyde production method of the present invention. 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. 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.

The present invention is described in detail below, but the present invention is not limited to the following description and can be modified and implemented as desired without departing from the spirit of the present invention.

Unless otherwise specified, numerical ranges expressed using "~" in this specification mean a range that includes the numbers written before and after "~" as the lower and upper limits, and "A~B" means greater than or equal to A and less than or equal to B.

[Method for producing aldehyde]
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.

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

The raw material compound for the catalyst preferably contains a transition metal compound. Examples of transition metal compounds contained in the raw material compound include long-form Group 8-10 transition metal compounds (hereinafter referred to as "Group 8-10 transition metal compounds"). Long-form Group 8-10 transition metals (hereinafter referred to as "Group 8-10 transition metals") are transition metals belonging to Groups 8 to 10 of the long-form periodic table. Among these, ruthenium, cobalt, rhodium, palladium, and platinum are preferred due to their high activity when used as catalysts, with rhodium being even more preferred due to its particularly high activity.

Examples of the Group 8 to 10 transition 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, 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.

Of the above, it is preferable to use a monovalent or greater and trivalent rhodium compound as the Group 8 to 10 transition metal compound, and it is particularly preferable to use rhodium acetate from the viewpoint of excellent reaction activity and catalyst cost.

Rhodium compounds that can be used include carbonyl complexes such as hydridotetracarbonylrhodium, octacarbonyldirhodium, dicarbonylacetylacetonatorhodium, dodecacarbonyltetrarhodium, and hexadecacarbonylhexarhodium.

Typically, in hydroformylation reactions using a rhodium complex catalyst, a rhodium recovery process is set up 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.

The catalyst raw material compounds preferably further contain an organophosphorus ligand compound. The organophosphorus ligand compound may be a monodentate or polydentate ligand compound. Such organophosphorus ligand compounds can be coordinated as monodentate or polydentate ligands to Group 8 to 10 transition metals to form a complex catalyst.

Organophosphorus compounds that serve as monodentate ligands include triorganophosphines represented by the following general formula:

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

Examples of the monovalent hydrocarbon group represented by R include alkyl groups having 1 to 12 carbon atoms, cycloalkyl groups having 3 to 12 carbon atoms, aryl groups having 3 to 12 carbon atoms, alkylaryl groups having 6 to 24 carbon atoms, and arylalkyl groups having 6 to 24 carbon atoms. Examples of triorganophosphines include trialkylphosphines, triarylphosphines, tricycloalkylphosphines, alkylarylphosphines, cycloalkylarylphosphines, and alkylcycloalkylphosphines.

Substituents that the monovalent hydrocarbon group may have include, but are not limited to, alkyl groups, alkoxy groups, etc.

Specific examples of triorganophosphines include tributylphosphine, trioctylphosphine, triphenylphosphine, tritolylphosphine, tricycloalkylphosphines, monobutyldiphenylphosphine, dipropylphenylphosphine, and cyclohexyldiphenylphosphine. Among these, triphenylphosphine is preferred because it is chemically stable due to its low activity and is readily available.

Other examples of organophosphorus ligand compounds that can be used include trivalent phosphite compounds represented by any of the following formulas (1) to (10):

<Trivalent phosphite compound represented by formula (1)>

(In formula (1), R ¹ to R ³ each independently represent a monovalent hydrocarbon group which may have a substituent.)

In formula (1), the monovalent hydrocarbon groups represented by R ¹ to R ³ and which may have a substituent include alkyl groups, aryl groups, and cycloalkyl groups.

Specific examples of compounds 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.

<Trivalent phosphite compound represented by formula (2)>

(In formula (2), ^R4 represents a divalent hydrocarbon group which may have a substituent, and ^R5 represents a monovalent hydrocarbon group which may have a substituent.)

In formula (2), examples of the divalent hydrocarbon group represented by ^R4 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, sulfur, etc.; and a divalent aromatic group and an alkylene group bonded directly or via an atom such as an oxygen, nitrogen, sulfur, etc. In formula (2), examples of the monovalent hydrocarbon group represented by ^R5 which may have a substituent include an alkyl group, an aryl group, a cycloalkyl group, etc.

Specific examples of compounds 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.

<Trivalent phosphite compound represented by formula (3)>

(In formula (3), R ¹⁰ has the same meaning as R ⁵ in formula (2); Ar ¹ and Ar ² each independently represent an arylene group which may have a substituent; x and y each independently represent 0 or 1; Q is a bridging group selected from the group consisting of —CR ¹¹ R ¹² —, —O—, —S—, —NR ¹³ —, —SiR ¹⁴ R ¹⁵ and —CO—; R ¹¹ and R ¹² each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, a phenyl group, a tolyl group or an anisyl group; R ¹³ , R ¹⁴ and R ¹⁵ each independently represent a hydrogen atom or a methyl group; and n represents 0 or 1.)

Specific examples of compounds 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.

<Trivalent phosphite compound represented by formula (4)>

(In formula (4), ^R6 represents a trivalent hydrocarbon group which may have a cyclic or acyclic substituent.)

Specific examples of compounds 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.

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

(In formula (5), ^R7 has the same meaning as ^R4 in formula (2), ^R8 and ^R9 each independently represent 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 an (a+b)-valent hydrocarbon group.)

Specific examples of compounds 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.

Specific examples of compounds represented by formula (5) include compounds represented by formula (6) below.

(In formula (6), X represents a divalent group selected from the group consisting of alkylene, arylene, and ^-Ar1- ( _CH2 )x-Qn-( _CH2 )y- ^Ar2- ; ^R16 and ^R17 each independently represent a hydrocarbon group which may have a substituent; ^{and Ar1} , ^Ar2 , Q, x, y, and n are defined as in formula (3).)

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

<Trivalent phosphite compound represented by formula (7)>

(In formula (7), X, Ar ¹ , Ar ² , Q, x, y, and n are defined as in formula (6), and R ¹⁸ is defined as R ⁴ in formula (2).)

<Trivalent phosphite compound represented by formula (8)>

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

Among the compounds represented by formula (8), compounds such as those described in JP-A-5-178779 and those 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.

<Trivalent phosphite compound represented by formula (9)>

(In formula (9), R ²¹ to R ²⁴ each independently represent a hydrocarbon group which may have a substituent, R ²¹ and R ²² , and 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.)

Examples of compounds represented by formula (9) include compounds described in JP-A-8-259578.

<Trivalent phosphite compound represented by formula (10)>

(In formula (10), R ²⁵ to R ²⁸ each independently represent a monovalent hydrocarbon group which may have a substituent, R ²⁵ and R ²⁶ , and 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.)

The optionally substituted monovalent hydrocarbon groups represented by R ²⁵ to R ²⁸ include alkyl groups, aryl groups, cycloalkyl groups, etc. The optionally substituted divalent hydrocarbon groups represented by A and B may be aromatic, aliphatic or alicyclic.

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

From the viewpoint of oxo reaction, the above-mentioned triorganophosphines are preferred as organophosphorus ligand compounds, with triphenylphosphine being particularly preferred.

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, H ₂ /CO=0.1 to 10, more preferably 0.5 to 6, and even more preferably 0.8 to 1.2.

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 typically 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, based on 100 mol% of the total amount of feed gas. Alternatively, the feed gas may be a mixed gas consisting essentially of hydrogen and carbon monoxide.

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 not all of the solute in this catalyst mixture needs to be dissolved; some may remain dispersed and not dissolved.

The organic solvent in the catalyst mixture is preferably at least one selected from alcohols and aromatic hydrocarbons.

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 standpoint of solubility, it is preferable to use methanol.

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, but if the concentration is too high, crystals may precipitate, while if it is too low, it will be less economical. Therefore, a concentration of 0.3 to 15% by mass is preferred, and 1 to 5% by mass is more preferred.

Aromatic hydrocarbons include, for example, benzene, toluene, xylene, and mesitylene. These may be used alone or in combination of two or more. From the standpoint of solubility, it is preferable to use xylene.

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

The lower limit of the concentration of Group 8 to 10 transition metals such as rhodium in the catalyst mixture is not particularly limited, but is typically 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 Group 8 to 10 transition metals such as rhodium in the catalyst mixture is not particularly limited, but is typically 10% by mass or less, preferably 1% by mass or less, and more preferably 1000 ppm by mass or less. If the concentration of Group 8 to 10 transition metals such as rhodium is too low, the reaction rate will be slow and the reaction may not proceed sufficiently. If the concentration of Group 8 to 10 transition metals such as rhodium is too high, they will be withdrawn entrained during purging of high boiling points, resulting in significant loss of expensive Group 8 to 10 transition metals such as rhodium.

The above upper and lower limits can be combined in any manner. For example, the concentration of Group 8 to 10 transition metals 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 1,000 ppm by mass.

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 = 1-10,000, preferably P/Group 8-10 transition metal = 1-1,000, and more preferably 1-100. 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 it will be withdrawn entrained when high boiling points are purged, resulting in significant loss.

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 liquid temperature is preferably 130°C or lower, more preferably 127°C or lower, and even more preferably 125°C or lower. If the liquid temperature is below 90°C, the effects of the present invention may not be fully achieved, while if the liquid temperature exceeds 130°C, the catalyst may be deactivated.

The above upper and lower limits can be combined in any way. 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.

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 approximately 1 to 10 MPa, the total pressure in the vessel is adjusted to, for example, 1 to 10 MPa, and the mixture is stirred for approximately 0.5 to 5 hours while maintaining the liquid temperature within the above range.

The vessel into which the catalyst mixture is charged may be separate from, or the same as, the reactor in which the hydroformylation reaction described below is carried out. If 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 withdrawn from the vessel and poured into the reactor. If the vessel into which the catalyst mixture is charged and the reactor in which the hydroformylation reaction is carried out are the same, after production of the metal complex catalyst, the production of aldehyde can be carried out directly by the hydroformylation reaction.

In the aldehyde production method of the present invention, for example, a feed olefin is subjected to a hydroformylation reaction with a gas containing hydrogen and carbon monoxide in the presence of a catalyst produced by the above-mentioned method.

The raw material olefin typically used is a linear or branched α-olefin or internal olefin, preferably an olefin having 2 to 8 carbon atoms, such as ethylene, propylene, 1-butene, 1-hexene, 1-octene, 1-dodecene, or 1-tetradecene, with ethylene, propylene, 1-butene, and 1-octene being more preferred. Propylene and 1-octene are particularly preferred.

In addition, in the aldehyde production method of the present invention, at least a portion of the gas containing hydrogen and carbon monoxide is reacted with the feed olefin in the form of fine bubbles. There is no particular lower limit for the proportion of the feed gas in the form of fine bubbles, and it 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 feed gas. Alternatively, 100 mol% of the total feed gas may be essentially fine bubbles.

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, H ₂ /CO=0.1 to 10, more preferably 0.5 to 6, and even more preferably 0.8 to 1.2.

Furthermore, when the feed gas contains hydrogen and carbon monoxide, the total content of hydrogen and carbon monoxide in the feed gas is typically 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, based on 100 mol% of the total amount of feed gas. Alternatively, the feed gas may be a mixed gas consisting essentially of hydrogen and carbon monoxide.

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

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 raw gas bubbles are in the form of millibubbles, i.e., millibubbles with a diameter of 1 mm or more, in a relatively low-viscosity liquid such as water, the millibubbles rise rapidly and burst at the liquid surface, disappearing. In contrast, when the raw gas bubbles are in the form of fine bubbles, the rising speed of fine bubbles in water is very 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 by supplying the raw gas in the form of fine bubbles, the residence time of the raw gas in the liquid is significantly increased.

(2) Increased 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 is negatively charged. This charge causes the bubbles to repel each other, preventing the bubbles 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.

(3) The liquid phase can be supersaturated with gas. The surface tension acting on the interface between the fine bubbles of the raw gas and the liquid phase reduces the surface area, thereby pressurizing the gas inside the bubbles. At this time, the pressure inside each raw gas bubble is balanced 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 raw 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 raw gas bubbles are in the form of normal millibubbles, i.e., millibubbles with a diameter _{of 1} mm or more, creating a supersaturated state.

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 aldehyde can be produced with a reduced catalyst amount. The reason for this is believed to be that when the feed gas is supplied in the form of millibubbles as in the conventional hydroformylation reaction, gas diffusion becomes the reaction rate-limiting factor, resulting in insufficient efficiency of the hydroformylation reaction. However, when the feed gas is supplied in the form of fine bubbles, the fine bubbles possess the above-mentioned characteristics (1) to (3), allowing efficient contact between the gas phase (feed gas) and the liquid phase over a wide interface for a long period of time and maintaining the supersaturated state of the feed gas in the liquid phase for a long period of time. This significantly improves the reaction rate of the hydroformylation reaction at and near the gas-liquid interface.

From the perspective 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 contain" means that the target microbubbles and/or ultrafine bubbles account for 95% or more of the total number of fine bubbles (100%).

Fine bubble production methods include, for example, the swirling liquid flow method, the pressurized dissolution/decompression method, and the micropore method, all of which are well-known fine bubble production methods.

In the swirling liquid flow method, liquid is injected into a cylindrical container at high speed, creating a high-speed swirling flow inside, generating a pressure drop zone at the center. Here, gas is introduced through small holes at the bottom of the cylindrical container and discharged through small holes at the top, producing fine bubbles.

In the pressurized dissolution/decompression method, gas is pressurized and dissolved in liquid. The liquid is then suddenly ejected into a liquid at reduced or normal pressure, causing the dissolved gas to precipitate as fine bubbles.

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

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 supplied to the fine bubble generator 100 pass through the nozzle housing 3, and fine bubbles 5 are discharged from the nozzle holes 4.

In the aldehyde production method of the present invention, the above-mentioned raw material olefin and the above-mentioned gas are subjected to a hydroformylation reaction.

The hydrogen and carbon monoxide in the gas may be supplied to the reactor separately, or they may be pre-mixed as 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.

The reaction conditions for hydroformylation are a hydrogen partial pressure of typically 0.0001 MPa or higher, preferably 0.01 MPa or higher, and more preferably 0.1 MPa or higher, and typically 20 MPa or lower, preferably 10 MPa or lower, and more preferably 5 MPa or lower. 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.

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; if it is too high, the olefin partial pressure will decrease, preventing the reaction from proceeding.

The total pressure is typically 0.0001 MPaG or higher, and typically 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. If the total pressure is too high, the reactor's design pressure will be high, increasing the cost of the equipment. In the present invention, the hydroformylation reaction is most preferably carried out at atmospheric pressure (0.10 MPa).

The hydrogen partial pressure/carbon monoxide partial pressure ratio, i.e., the hydrogen/carbon monoxide molar ratio, is typically 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, while if it is too high, the reaction will not proceed sufficiently or the production of by-products will increase.

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, while if the reaction temperature is too high, the production of by-products may increase or the catalyst may be deactivated.

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 will not proceed sufficiently, and if the reaction time is too long, high boiling point will occur.

In the aldehyde production method of the present invention, the hydroformylation reaction can be carried out in the presence of an organic solvent that dissolves the raw material olefin and catalyst, has a higher boiling point than the aldehyde produced in the reaction, and does not inhibit the reaction.

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.

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 rate at which fine bubbles (the raw material gas) rise 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.

The above upper and lower limits can be combined in any combination. 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.

Measuring viscosity using an Ubbelohde viscometer can be done according to a commonly used method, for example, in accordance with JIS Z8803:2011 or ISO 3105. The Ubbelohde viscometer can be one specified in ISO 3105 or JIS K 2283.

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.

Specific examples of aromatic compounds having an alkyl group on the 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.

Also, as organic solvents inert to the aldehyde produced, the aldehyde produced in the reaction or its aldehyde condensation products such as trimers and tetramers can be used. Furthermore, paraffins having the same number of carbon atoms as the raw 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.

The catalyst concentration in the reaction medium, calculated as the metal atoms that make up the complex catalyst, is typically 1 ppm to 10% by mass. Furthermore, to increase the stability of the catalyst, an excess amount of an organophosphorus ligand compound can also be present in the reaction medium.

There are no particular limitations on the type of reactor used in the hydroformylation reaction, and a stirred tank, bubble column, tray column, tubular, or gas stripping reactor can be used. Typically, the raw materials, olefin, oxo gas, and catalyst mixture are continuously supplied to a continuous reactor, and the hydroformylation reaction is carried out under the above-mentioned conditions. However, a batch reactor can also be used. Furthermore, to maintain a constant reaction temperature, the reactor may have an internal coil, jacket, external heat exchanger, or the like.

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 from the top of the column to separate the product. The distillation conditions are not particularly limited, but it is usually preferable that the column bottom temperature be 50 to 150°C. The pressure inside the column is also not particularly limited, but it is usually preferable that it be 0.01 to 0.1 MPa.

In this process for separating the produced aldehyde, any means and device for recovering unreacted olefins from the reaction liquid may be added. In this case, a countercurrent contact tower or the like is preferably used. Gas-liquid separators or the like may be installed between each device as appropriate.

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 circulated.

The present invention will be explained in more detail below with reference to examples and comparative examples.

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)

[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 as raw material compounds for the Rh complex catalyst, 65 g of o-xylene was added as an organic solvent, and the mixture was stirred for several minutes to dissolve the catalyst and ligand. Thereafter, 2.500 g (22.28 mmol) of 1-octene, a reaction raw material, was added, and the temperature was raised while stirring with a 22 mm diameter crosshead rotor.

(Hydroformylation Reaction)
Next, using an ultra-fine 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 circulation rate of 40 mL/min, while oxo gas (hydrogen/carbon monoxide = 1 (molar ratio)) was introduced at a flow rate of 10 mL/min into the circulation line for circulating the internal liquid. 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 to 200 nm, i.e., so that the oxo gas maintained the form of ultrafine bubbles. This operation was carried out with the reaction vessel under atmospheric pressure. The internal liquid in the reaction vessel was then heated to a temperature of 90°C, and while the pressure in the reaction vessel was maintained at atmospheric pressure, oxo gas (hydrogen/carbon monoxide = 1 (molar ratio)) was continuously introduced into the reaction vessel, and the mixture was stirred for 6 hours.

During the hydroformylation reaction, the liquid inside 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 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 inside 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 60% conversion rate was 0.0093 [1/min].

[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.

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

[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 under atmospheric pressure in the reaction vessel. The evaluation results are shown in Table 1.

[Comparative Examples 2 and 3]
In the hydroformylation reaction, no ultrafine bubble generator was 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 SUS 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.

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

Under the production conditions of Examples 1 to 4, oxo gas is supplied to the reaction system in the form of fine bubbles during the hydroformylation reaction. This increases the reaction rate of the hydroformylation reaction, 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.

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

Under the production conditions of Comparative Examples 2 and 3, the oxo gas was supplied to the reaction system in the form of millibubbles rather than fine bubbles during the hydroformylation reaction, resulting in a low reaction rate for the hydroformylation reaction.

[Experimental Example 1]
Using o-xylene as the organic solvent and the ultrafine bubble generator used in Example 1, hydrogen gas was introduced at a flow rate of 10 mL/min into the circulation line for circulating the organic solvent while circulating the organic solvent in a reaction vessel at a circulation rate of 40 mL/min. The hydrogen gas was introduced so that the hydrogen gas bubbles in the liquid inside the reaction vessel had a diameter in 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.

Then, the temperature of the organic solvent in the reaction vessel was controlled to 30°C, and the pressure inside the reaction vessel was maintained at atmospheric pressure while continuing to introduce hydrogen gas and stirring was continued for 90 to 240 minutes.

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

[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.

Figures 3(a) and 3(c) show that when o-xylene, a highly viscous organic solvent, was used, ultrafine and microbubbles of hydrogen gas were observed early in the experiment.

On the other hand, Figures 3(b) and 3(d) show that when mesitylene, which has a low viscosity, was used as the organic solvent, ultrafine hydrogen gas bubbles were not observed, but microbubbles were. 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 lower.

This is thought to be because the higher the viscosity of the organic solvent, the slower the rate at which hydrogen gas rises within the reaction system, maintaining a high concentration of microbubbles.

REFERENCE SIGNS LIST 1 Liquid 2 Gas 3 Nozzle housing 4 Nozzle hole 5 Fine bubbles 10 Reaction vessel 11 Oxo gas (H ₂ /CO)
12 Flow rate control unit 13 Gas-liquid mixing unit 14 Pump 15 Pressure regulating valve 100 Fine bubble generator

Claims (12)

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 . The method for producing aldehyde according to claim 1, wherein the fine bubbles include at least either microbubbles or ultrafine bubbles. 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. The method for producing an aldehyde according to claim 3, wherein the organic solvent comprises an aromatic hydrocarbon. The method for producing an aldehyde according to claim 3 or 4, wherein the organic solvent has a viscosity of 0.68 cp or more at 25°C as measured using an Ubbelohde viscometer. The method for producing an aldehyde according to claim 4 , wherein the aromatic hydrocarbon includes an aromatic hydrocarbon having an alkyl group on a side chain. The method for producing an aldehyde according to claim 6, wherein the aromatic compound having an alkyl group on the side chain is at least one selected from the group consisting of toluene, o-xylene, m-xylene, p-xylene, mesitylene, durene, ethylbenzene, and cuumene. The method for producing an aldehyde according to any one of claims 1 to 7 , wherein the catalyst comprises a transition metal compound. 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. 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. The method for producing an aldehyde according to claim 10 , wherein the rhodium compound comprises rhodium acetate. 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.