JP7635592B2 - Aldehyde Recovery Method - Google Patents

Description

The present invention relates to a method for recovering aldehydes, which is useful for separating and recovering higher aldehydes and rhodium complex catalysts from the reaction product of a hydroformylation reaction in which a higher olefin is hydroformylated with carbon monoxide and hydrogen in the presence of a rhodium complex catalyst to produce a higher aldehyde.

The reaction of an ethylenically unsaturated compound with carbon monoxide and hydrogen in the presence of a metal complex catalyst formed by complexing a Group VIII metal compound with a phosphorus compound to convert it into an aldehyde is called a hydroformylation reaction or an oxo reaction, and the production of an aldehyde utilizing this reaction is of great industrial value.
In the industrial production of aldehydes by hydroformylation, a rhodium complex catalyst consisting of a rhodium compound and a phosphorus compound is mainly used. This catalyst is very expensive, and for industrial use, it is essential to recover it in high yield after the hydroformylation reaction and reuse it.

Conventionally, in the hydroformylation reaction of lower aldehydes, the reaction product of the hydroformylation reaction is distilled to separate and obtain the aldehyde and unreacted ethylenically unsaturated compounds, and the catalyst is recovered as the evaporation residue (evaporation separation method). However, when producing higher aldehydes or aldehydes having functional groups, the evaporation separation method is not used. This is because these aldehydes have high boiling points, making it necessary to increase the distillation temperature, and because aldehydes are sensitive to heat, during distillation some of the aldehyde turns into high-boiling by-products that are difficult to separate from the catalyst, reducing the aldehyde yield. In addition, rhodium complex catalysts are thermally unstable and easily decompose during distillation at high temperatures, making it impossible to recover and reuse the catalyst.

As a method for recovering aldehydes from hydroformylation reaction products using a rhodium complex catalyst, a method of extracting and separating the aldehyde with water or alcohol is also known. For example, in JP-T-06-501958, a dialdehyde having 10 carbon atoms is extracted from the reaction product into an aqueous layer using a polar solvent phase such as water/methanol, and the rhodium complex catalyst is recovered in an oil layer. However, although this method can recover the dialdehyde having 10 carbon atoms at a high recovery rate of 80% or more, it is necessary to add a carboxylate salt in order to recover the rhodium complex catalyst at a high recovery rate in the oil layer. In this case, further separation from the aldehyde is required, which is disadvantageous for industrial production.

Special Publication No. 06-501958

The object of the present invention is to provide a method for recovering aldehydes, which can easily and efficiently separate and recover aldehydes and rhodium complex catalysts from the reaction product in a hydroformylation reaction of an olefin to produce aldehydes in the presence of a rhodium complex catalyst.

As a result of extensive research conducted by the inventors to solve the above problems, they discovered that higher aldehydes can be easily and efficiently separated and recovered as solids by adding an aromatic hydrocarbon and a poor solvent to the reaction product and crystallizing it.

That is, the gist of the present invention is as follows:

[1] A method for recovering an aldehyde, comprising separating the aldehyde from a mixture containing a saturated linear or saturated branched aldehyde having a melting point of −5° C. or higher and a hydroformylation catalyst containing rhodium and an organophosphorus compound by sequentially carrying out the following steps (i) to (iv):
(i) adding an aromatic hydrocarbon and a poor solvent to the mixture;
(ii) Heat to homogenize.
(iii) cooling to precipitate the aldehyde;
(iv) Recovering the precipitated aldehyde.

[2] The method for recovering aldehyde described in [1], characterized in that the poor solvent is a primary alcohol having 1 to 3 carbon atoms.

[3] The method for recovering aldehyde described in [1], characterized in that the poor solvent is an amide compound having 1 to 5 carbon atoms.

[4] The method for recovering aldehyde described in [1], characterized in that the poor solvent is a cyclic ether having 4 to 6 carbon atoms.

[5] The method for recovering an aldehyde according to any one of [1] to [4], characterized in that the recovery rate of the aldehyde and the recovery rate of rhodium in the hydroformylation catalyst are 60% or more.

[6] The method for recovering aldehyde described in [2], characterized in that the primary alcohol having 1 to 3 carbon atoms is methanol and/or ethanol.

[7] The method for recovering aldehyde described in [3], characterized in that the amide compound having 1 to 5 carbon atoms is N,N-dimethylformamide.

[8] The method for recovering aldehyde described in [4], characterized in that the cyclic ether having 4 to 6 carbon atoms is 1,4-dioxane.

According to the present invention, the aldehyde can be efficiently separated and recovered as a solid from a mixture containing an aldehyde, which is a reaction product of a hydroformylation reaction, and a rhodium complex catalyst by a simple procedure called crystallization.
In conventional methods, the aldehyde and rhodium complex catalyst were separated and recovered as a liquid phase, which required steps such as removing the solvent to turn the recovered aldehyde into a product and solvent replacement to convert it to the next step. However, according to the present invention, the aldehyde can be obtained as a solid by a simple operation such as filtration, making it possible to shorten the production process.
In addition, since the rhodium complex catalyst can be efficiently recovered and reused, the hydroformylation reaction can also be carried out in a homogeneous system, and the hydroformylation reaction can be carried out at a high conversion rate without the addition of other additives.
In particular, by improving the recovery and reuse efficiency of the rhodium complex catalyst, it becomes possible to use, as the ligand of the rhodium complex catalyst, a ligand suitable for obtaining linear aldehydes with high commercial value, thereby making it possible to obtain aldehydes with high linear selectivity.

The present invention will be described in detail below.

In the method for recovering an aldehyde of the present invention, the aldehyde and the hydroformylation catalyst containing rhodium and an organophosphorus compound are separated from a mixture containing a saturated linear or saturated branched aldehyde having a melting point of −5° C. or higher and the hydroformylation catalyst containing rhodium and an organophosphorus compound by sequentially carrying out the following steps (i) to (iv) to recover the aldehyde and the hydroformylation catalyst.
(i) adding an aromatic hydrocarbon and a poor solvent to the mixture;
(ii) Heat to homogenize.
(iii) cooling to precipitate the aldehyde;
(iv) The precipitated aldehyde is separated and recovered.

In the present invention, the mixture to be separated, which contains a saturated linear or branched aldehyde having a melting point of -5°C or higher and a hydroformylation catalyst containing rhodium and an organophosphorus compound, is not particularly limited as long as it contains this aldehyde and a hydroformylation catalyst, but the present invention is preferably applied to the reaction product produced when an aldehyde is produced by the hydroformylation reaction of an ethylenically unsaturated compound in the presence of a rhodium complex catalyst.

In the case of aldehydes having a melting point of less than −5° C., a large amount of cooling energy is required when carrying out the process on an industrial scale, and therefore, in the present invention, aldehydes having a melting point of −5° C. or higher are separated and recovered. From the viewpoint of the crystallization effect, aldehydes having a melting point of −2° C. or higher, particularly 10° C. or higher, are preferred as the aldehydes to be separated and recovered.
Aldehydes having such a melting point are generally higher aldehydes having 11 or more carbon atoms, and specific examples thereof include saturated linear or branched higher aldehydes having 11 to 40 carbon atoms, such as undecanal, tridecanal, pentadecanal, heptadecanal, nonadecanal, etc. Therefore, as the raw material ethylenically unsaturated compound for the hydroformylation reaction, the above-mentioned ethylenically unsaturated compounds serving as raw materials for higher aldehydes are used.
The present invention is also effective in terms of the fact that, as described above, the evaporation separation method cannot be applied to such higher aldehydes.

On the other hand, the rhodium complex catalyst to be separated and recovered is not particularly limited as long as it contains rhodium and an organic phosphorus compound as a ligand, and examples of such catalysts include rhodium complex catalysts used in general hydroformylation reactions.

Examples of the raw material compound (Rh source) of the rhodium complex catalyst include one or more of rhodium acetate [Rh(OAc) ₃ ], acetylacetonatodicarbonylrhodium [Rh(acac)(CO) ₂ ], acetylacetonatocarbonyltriphenylphosphinerhodium [Rh(acac)(CO)(TPP)], and hydridocarbonyltri(triphenylphosphine)rhodium [HRh(CO)(TPP) ₃ ]. Among these, raw material compounds that do not have phosphine or phosphite ligands, such as rhodium acetate [Rh(OAc) ₃ ] and acetylacetonatodicarbonylrhodium [Rh(acac)(CO) ₂ ], are preferred because they can prepare a rhodium complex catalyst with excellent catalytic activity.

As the organophosphorus compound serving as a ligand for forming a rhodium complex catalyst, any trivalent organophosphorus compound commonly used to function as a monodentate or polydentate ligand for rhodium can be used. Among these, an example of an organophosphorus compound serving as a monodentate ligand is a tertiary triorganophosphine represented by the following formula [I].

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

The monovalent hydrocarbon group represented by R typically includes an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 3 to 12 carbon atoms, an aryl group having 3 to 12 carbon atoms, an alkylaryl group having 6 to 24 carbon atoms, and an arylalkyl group having 6 to 24 carbon atoms. That is, the above triorganophosphine is, for example, a trialkylphosphine, a triarylphosphine, a tricycloalkylphosphine, an alkylarylphosphine, a cycloalkylarylphosphine, or an alkylcycloalkylphosphine.

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

Specific examples of triorganophosphines include, for example, tributylphosphine, trioctylphosphine, triphenylphosphine, tritolylphosphine, tricycloalkylphosphine, monobutyldiphenylphosphine, dipropylphenylphosphine, cyclohexyldiphenylphosphine, etc. The most preferred triorganophosphine is triphenylphosphine.

Other examples of trivalent organic phosphorus compounds that can be used include trivalent phosphite compounds represented by 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 be substituted.)

The optionally substituted monovalent hydrocarbon groups of R ¹ to R ³ include an alkyl group, an aryl group, and a cycloalkyl group.

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

<Trivalent phosphite compound represented by formula (2)>

(In formula (2), ^R4 represents an optionally substituted divalent hydrocarbon group, and ^R5 represents an optionally substituted monovalent hydrocarbon group.)

Examples of the divalent hydrocarbon group which may be substituted for ^R4 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 alkylene group or an atom such as oxygen, nitrogen or sulfur; and a divalent aromatic group bonded to an alkylene group directly or via an atom such as oxygen, nitrogen or sulfur.
Examples of the monovalent hydrocarbon group for ^R5 include an alkyl group, an aryl group, and a cycloalkyl group.

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.

<Trivalent phosphite compound represented by formula (3)>

(In formula (3), R ¹⁰ has the same meaning as R ⁵ in formula (2) above; Ar ¹ and Ar ² each independently represent an optionally substituted aryl group; 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 trivalent phosphite 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 cyclic or non-cyclic trivalent hydrocarbon group which may be substituted.)

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.

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

(In formula (5), R ⁷ has the same meaning as R ⁴ in formula (3), R ⁸ and R ⁹ each independently represent a hydrocarbon group which may be substituted, 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).)

Among the compounds represented by formula (5), preferred examples include the compounds represented by the following formula (6), and also include the compounds described in JP-A-62-116535 and JP-A-62-116587.

(In formula (6), X represents a divalent group selected from the group consisting of alkylene, arylene, and ^-Ar1- ( _CH2 )x-Qn-( _CH2 )y- ^Ar2- , and ^Ar1 , ^Ar2 , Q, x, y, and n are the same as ^Ar1 , ^Ar2 , Q, x, y, and n in formula (3) above.)

<Trivalent phosphite compound represented by formula (7)>

(In formula (7), X, Ar ¹ , Ar ² , Q, x, y, and n are the same as X, Ar ¹ , Ar ² , Q, x, y, and n in formula (3) above, and R ¹⁸ is the same as R ⁴ in formula (2) above.)

<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 a carbon atom adjacent to a carbon atom to which an oxygen atom is bonded, m represents an integer from 2 to 4, each -O-P(OR ¹⁹ )(OR ²⁰ ) group may be different from the other, and X represents an optionally substituted m-valent hydrocarbon group.)

Among the compounds represented by formula (8), for example, the compounds described in JP-A-5-178779 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 be substituted, 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.)

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

<Trivalent phosphite compound represented by formula (10)>

(In formula (10), R ²⁵ to R ²⁸ represent an optionally substituted monovalent hydrocarbon group, 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 optionally substituted divalent hydrocarbon group, and n represents an integer of 0 or 1.)

The monovalent hydrocarbon groups which may be substituted for R ²⁵ to R ²⁸ include an alkyl group, an aryl group, a cycloalkyl group, etc. The divalent hydrocarbon groups which may be substituted for A and B may be any of aromatic, aliphatic, and alicyclic.
As the compound represented by formula (10), for example, those described in JP-A-10-45776 can be used.

As the organophosphorus compound, from the viewpoint of linear chain selectivity, a triorganophosphine represented by the above formula (10) is preferred.
These organic phosphorus compounds may be used alone or in combination of two or more, but usually only one is used.

The ratio of phosphorus to rhodium in the organophosphorus compound is usually, in terms of molar ratio, P/Rh = 1 to 10,000, preferably P/Rh = 1 to 1,000, and more preferably 1 to 100. If there is too little organophosphorus compound, the amount coordinated to rhodium will be small, and the rhodium may not be sufficiently stabilized, while if there is too much, the catalyst cost will increase and the product price will become high.

The rhodium complex catalyst can be prepared prior to the hydroformylation reaction or within the hydroformylation reaction system according to conventional methods.

The hydroformylation reaction to obtain a reaction product containing an aldehyde and a rhodium complex catalyst can be carried out according to a conventional method.

The reaction product obtained from the hydroformylation reaction usually contains 60 to 99% by weight of the target aldehyde, 0.05 to 5% by weight of the rhodium complex catalyst, and the remainder is a liquid olefin that has been internally isomerized with the raw olefin, although this varies depending on the reaction conditions and the rhodium complex catalyst used.

In the present invention, the reaction product is subjected to the following steps (i) to (iv) in order to separate and recover the aldehyde and the rhodium complex catalyst. Note that, since there is a risk of catalyst deactivation due to oxygen in the following steps (i) to (iv), it is preferable to carry out the operations under an inert gas atmosphere such as nitrogen gas.

<Step (i)>
In the present invention, an aromatic hydrocarbon and a poor solvent are added to such a reaction product.

The aromatic hydrocarbon may be a good solvent for the aldehyde in the reaction product, and may dissolve the aldehyde at a concentration of usually 30% by weight or more, preferably 50% by weight or more, at 60°C. Examples of the aromatic hydrocarbon include toluene, xylene, ethylbenzene, propylbenzene, and isopropylbenzene. These aromatic hydrocarbons may be used alone or in combination of two or more.

By using aromatic hydrocarbons as good solvents for aldehydes, and especially when bidentate phosphines or bidentate phosphites having aromatic groups as ligands are used because of their high linear chain selectivity, separation of the aldehyde and the hydroformylation catalyst is improved from the viewpoint of the affinity between aromatic groups.

The poor solvent is preferably a poor solvent for the aldehyde in the reaction product, in which the solubility of the aldehyde under a condition of 60° C. is usually 10% by weight or less, particularly 5% by weight or less. Examples of the poor solvent include primary alcohols having 1 to 3 carbon atoms, such as methanol, ethanol, and propanol; amide compounds having 1 to 5 carbon atoms, such as formamide, N-methylformamide, N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; and cyclic ethers having 4 to 6 carbon atoms, such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxane, 1,4-dioxane, and 4-methylhydropyrane.
These poor solvents may be used alone or in combination of two or more.

Of these poor solvents, alcohols with fewer carbon atoms are preferred from the standpoint of aldehyde recovery rate and rhodium complex catalyst recovery rate, and linear alcohols are more preferred than branched alcohols. In addition, N,N-dimethylformamide and 1,4-dioxane also show high recovery rates.

The amounts of aromatic hydrocarbon and poor solvent added to the reaction product are preferably 0.1 to 5 mL, particularly 0.5 to 1.5 mL, of the aromatic hydrocarbon per 1 g of the reaction product, and 0.01 to 1.5 mL, particularly 0.15 to 0.3 mL of the poor solvent per 1 g of the reaction product, with the aromatic hydrocarbon:poor solvent (volume ratio) being preferably 10 to 1:1.
If the aromatic hydrocarbon is less than the above range, the recovery rate of the rhodium catalyst will decrease, and if it is more than the above range, the recovery rate of the aldehyde will decrease. Also, if the poor solvent is less than the above range, the recovery rate of the aldehyde will decrease, and if it is more than the above range, the recovery rate of the rhodium catalyst will decrease.

The aromatic hydrocarbon and the poor solvent may be added to the reaction product simultaneously or separately. If they are added separately, either one may be added first.

<Step (ii)>
In the step (ii), the liquid obtained by adding the aromatic hydrocarbon and poor solvent to the reaction product in the step (i) is heated and homogenized.
If the heating temperature is too high, the solvent may volatilize and the optimum solvent ratio may not be obtained, whereas if the heating temperature is too low, homogenization may be difficult. Therefore, although it varies depending on the aldehyde and the solvent, it is preferable to set the heating temperature in the range of 40 to 120°C, particularly 60 to 90°C.

The heating time is usually about 15 to 120 minutes. Stirring may be performed during this heating process if necessary.

<Step (iii)>
In the step (iii), the liquid that has been heated and homogenized in the step (ii) is cooled to precipitate the aldehyde as a solid.
The cooling temperature is not particularly limited as long as it is a temperature at which the aldehyde precipitates, but it is preferably about −5 to 10° C. If the cooling temperature is too high, the aldehyde precipitates less efficiently.

<Step (iv)>
In the step (iv), the aldehyde precipitated in the step (iii) is separated and recovered as a solid.
As a method for solid-liquid separation during this separation and recovery, filtration, reduced pressure filtration, pressure filtration, membrane separation, etc. can be used, with filtration or reduced pressure filtration being preferred due to its simple operation.

The aldehyde separated and recovered in the step (iv) can be dried to obtain a product.
Furthermore, since the rhodium complex catalyst is contained in the residual liquid after recovery of the aldehyde, by removing the rhodium complex catalyst with a solvent, the rhodium complex catalyst can be recovered and reused in the hydroformylation reaction.
According to the method for recovering aldehyde of the present invention, the aldehyde and the rhodium complex catalyst serving as a hydroformylation catalyst can both be separated and recovered at a high recovery rate of at least 60%, preferably at least 70%.

The following examples will explain the present invention in more detail.

[Reference Example 1]
26.6 mg (0.049 mmol) of rhodium acetate 1,5-cyclooctadiene dimer ([Rh(cod)(OAc)]2) was weighed out into a glass vessel, and 200 mL of 1-hexadecene, the substrate, was added and dissolved under a nitrogen atmosphere. 1.1 g of the bisphosphite (A) described below, which corresponds to a rhodium:ligand molar ratio of 1:10, was added to a separately prepared stainless steel autoclave, and the solution in the glass vessel was transferred to the autoclave under a nitrogen atmosphere. After sealing the autoclave, it was heated to 80°C in an electric furnace, and then hydrogen/carbon monoxide mixed gas (mixing ratio: 1/1) was quickly introduced from the gas inlet valve up to 3 MPa, and the mixture was reacted for 2 hours while stirring with a vertical stirrer. The mixture was then heated to 150°C in an electric furnace, and further reacted for 2 hours.
After the reaction was completed, the mixture was cooled to room temperature, and the residual gas was released, and the reaction results were analyzed by gas chromatography. As a result, the yield of heptadecanal (melting point 34-39°C) was 88.4%. In addition, the linear selectivity of heptadecanal (ratio (L/B) of linear aldehyde (L) to branched aldehyde (B)) was 12.5.

[Example 1]
20.0 g of the reaction product obtained by the above method (heptadecanal concentration 93.2 wt%, rhodium complex catalyst concentration 0.69 wt%) was placed in a glass eggplant flask and purged with nitrogen. 30 mL of toluene (aromatic hydrocarbon) and 10 mL of ethanol (poor solvent) were added to the flask and dissolved by heating and stirring at 60 ° C for 30 minutes. After cooling at room temperature, the solution was cooled in an ice bath (5 ° C) to precipitate a solid. The solid and filtrate were separated by vacuum filtration, and heptadecanal and Rh were analyzed by gas chromatography analysis and X-ray fluorescence analysis, respectively, to determine the recovery rate. The results are shown in Table 1.

[Examples 2 to 5, Comparative Examples 1 to 3]
The recovery operations and analyses of heptadecanal and rhodium complex catalyst were carried out in the same manner as in Example 1, except that the amount of the reaction product subjected to recovery, and the types and amounts of the aromatic hydrocarbon or other solvent used as the good solvent and the poor solvent were changed as shown in Table 1. The results are shown in Table 1.

From Table 1, it can be seen that according to the present invention, the aldehyde and the rhodium complex catalyst can be separated and recovered at high recovery rates from the reaction products of the hydroformylation reaction by the simple operation of crystallization.

[Comparative Example 1]
20.0 g of the reaction product obtained by the method of Reference Example 1 was transferred to a glass bottle in a glove box under a nitrogen gas flow, 59 mL of ethylene glycol and 57 mL of methylcyclohexane were added to the glass bottle, and the mixture was stirred vigorously and then allowed to stand until it separated into two layers. Each phase was separated and analyzed by glass chromatography, and the distribution coefficient Kp (=amount of heptadecanal in the ethylene glycol extraction layer)/(amount of heptadecanal in the methylcyclohexane layer) was 0.0003, which shows that in this method, most of the heptadecanal migrates to the methylcyclohexane layer side of the oil layer, which is the rhodium complex catalyst recovery layer, making it difficult to separate and recover it from the rhodium complex catalyst.

Claims (8)

A method for recovering an aldehyde, comprising the steps of: separating the aldehyde from a mixture containing a saturated linear or branched aldehyde having a melting point of -5°C or higher and a hydroformylation catalyst containing rhodium and an organophosphorus compound, by sequentially carrying out the following steps (i) to (iv):
(i) adding to the mixture an aromatic hydrocarbon and a poor solvent for the aldehyde ;
(ii) Heat to homogenize.
(iii) cooling to precipitate the aldehyde;
(iv) Recovering the precipitated aldehyde. The method for recovering aldehyde according to claim 1, characterized in that the poor solvent is a primary alcohol having 1 to 3 carbon atoms. The method for recovering aldehydes according to claim 1, characterized in that the poor solvent is an amide compound having 1 to 5 carbon atoms. The method for recovering aldehydes according to claim 1, characterized in that the poor solvent is a cyclic ether having 4 to 6 carbon atoms. The method for recovering aldehyde according to any one of claims 1 to 4, characterized in that the recovery rate of the aldehyde and the recovery rate of rhodium in the hydroformylation catalyst are 60% or more. The method for recovering aldehydes according to claim 2, characterized in that the primary alcohol having 1 to 3 carbon atoms is methanol and/or ethanol. The method for recovering aldehydes according to claim 3, characterized in that the amide compound having 1 to 5 carbon atoms is N,N-dimethylformamide. The method for recovering aldehydes according to claim 4, characterized in that the cyclic ether having 4 to 6 carbon atoms is 1,4-dioxane.