JPH10265417A - Purification of alcohol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for purifying an alcohol, enabling to efficiently separate off ethers and branched alcohols, the by-produced impurities of a hydrogenation reaction, to obtain the purified linear alcohol in high purity. SOLUTION: This method for purifying an alcohol comprises distilling the crude alcohol containing 2nC ethers and nC branched alcohols as impurities and obtained by hydrogenating a nC aldehyde [(n) is an integer of 3-6]. Therein, the distillation operation is carried out by distilling at 100-500 mmHg (absolute pressure) in a reflux ratio of >=20 in a distillation tower, distilling out the linear alcohol enriched with the ethers and the branched alcohols from the overhead and extracting the linear alcohol reduced in the contents of the ethers and the contents of the branched alcohols from the bottom or a side flow.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for purifying alcohol. More specifically, the present invention relates to a method for purifying a crude alcohol containing by-products such as ether obtained by hydrogenating an aldehyde.

[0002]

2. Description of the Related Art A process for obtaining a product alcohol by subjecting an aldehyde obtained by hydroformylation of a monoolefin to a crude alcohol by a hydrogenation (hydrogenation) reaction and subsequent purification by distillation is well known as an industrial production method of alcohol. Have been. The hydrogenation reaction is usually performed using a nickel-based or copper-based catalyst, but in the case of using any of the catalysts, various side reactions occur to generate various side reaction products, and the selectivity of the reaction is reduced. It is a cause of decline.

The main problems as side reactions are the production of various hydrocarbons by the hydrocracking of aldehyde groups and the production of acetal and ether. Among them, the production of hydrocarbons can be suppressed to some extent by lowering the reaction temperature, but the production of acetal and ether can hardly be suppressed, which greatly affects the purity of alcohol. It is considered that these acetals and ethers are formed by the reactions of the following formulas (1) and (2).

[0004]

Embedded image (However, R is an alkyl group.)

That is, according to the above formula (1), one molecule of unreacted aldehyde reacts with two molecules of alcohol produced by the hydrogenation reaction to form an acetal, which is hydrolyzed according to the formula (2) to form an ether. And alcohol.

As a method for suppressing the formation of the acetal and ether, for example, i) a method of performing a hydrogenation reaction in the presence of water in a raw material aldehyde or a reaction zone (Journal of Petroleum Institute, Vol. 15, No. 6, (197)
2), pp. 453-458), ii) A method of performing a hydrogenation reaction using a nickel-based catalyst containing an alkaline earth metal salt (Japanese Patent Publication No. 44-171).
No. 27), and iii) a method of adding an aliphatic tertiary amine to a reaction system to carry out a hydrogenation reaction (Japanese Patent Publication No. 3-59885).

[0007]

Although each of the above methods relates to suppressing the by-products of acetal and ether during the hydrogenation reaction, the use of these methods does not necessarily result in the formation of acetal and ether. It is difficult to suppress it sufficiently. Therefore, in order to obtain a high-purity alcohol as a product, it is necessary to further separate and purify a crude alcohol containing these by-products. As the purification method, a distillation purification method is generally used. Above all, alcohols having 6 or less carbon atoms have a low boiling point, and industrially, distillation operation is usually performed under atmospheric pressure or slight pressure.

However, in this alcohol distillation operation, the by-product ether forms an azeotropic mixture with the alcohol, and the azeotropic mixture has a boiling point very close to that of the alcohol. Requires a relatively high theoretical number of distillation columns and a large amount of energy. For example, in a hydrogenation reaction of normal (hereinafter referred to as "n-") butyraldehyde, which is a linear aldehyde having 4 carbon atoms, a large amount of di-n-butyl ether is generated. Although di-n-butyl ether itself has a higher boiling point than n-butyl alcohol, both form a low-boiling azeotrope with a composition of about 20% by weight of di-n-butyl ether and about 80% by weight of n-butyl alcohol. At a concentration below this azeotropic composition, di-n-butyl ether behaves as a light boiling component. Since this azeotropic mixture has a boiling point very close to that of n-butyl alcohol, a distillation column having a high theoretical plate number is required to obtain high-purity n-butyl alcohol by distilling the reaction mixture. There is a problem that leads to loss of data.

Further, the reaction mixture also contains a branched alcohol which is an isomer of the desired linear alcohol, and it is necessary to separate the branched alcohol in order to obtain a high-purity linear alcohol. Therefore, from an industrial viewpoint, development of a method for more efficiently producing a high-purity linear alcohol has been awaited. That is, an object of the present invention is to provide a method for efficiently separating impurities such as ether and a branched chain alcohol from a crude alcohol obtained by hydrogenating an aldehyde to obtain a highly purified purified linear alcohol. It is in.

[0010]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have conducted a distillation operation under reduced pressure (100 to 500 mmHg (absolute pressure)) to obtain a distillation column. The ether and the branched-chain alcohol are concentrated at the top of the column to obtain a straight-chain alcohol fraction rich in these components, while the straight-chain alcohol having a reduced ether and branched-chain alcohol content from the bottom or side stream Was obtained, and it was found that a purified linear alcohol having high purity was efficiently obtained, and the present invention was reached.

That is, the gist of the present invention is that the carbon number n (where n
Is an integer of 3 to 6). The distillation operation is carried out at 100 to 500 mmHg for distilling and purifying a crude alcohol containing ether having 2 n carbon atoms and branched alcohol having n carbon atoms as impurities obtained by hydrogenating an aldehyde of 3 to 6).
(Absolute pressure) and the reflux ratio of the distillation column is set to 20 or more to distill straight-chain alcohols rich in ether and branched-chain alcohol from the top of the column, and ether and branched-chain from the bottom or side stream. A method for purifying an alcohol, characterized by obtaining a linear alcohol having a reduced alcohol content. In the present invention, the “top” of the distillation column includes the top of the distillation column and a distillation stage in the vicinity thereof.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The aldehyde used as a raw material of the alcohol in the present invention is an aldehyde having 3 to 6 carbon atoms, and specific examples thereof include propionaldehyde, butyraldehyde, and valeraldehyde.

As the hydrogenation catalyst, any conventionally known hydrogenation catalyst for aldehydes can be used. For example, a carrier such as diatomaceous earth or celite carrying an active component such as nickel or copper (usually nickel) can be used. In the hydrogenation reaction of the aldehyde, the hydrogenation catalyst as described above is used, usually at a normal pressure to 2
Reaction conditions at a temperature of 50-200 ° C. under pressure up to 00 atm are employed. In this hydrogenation reaction, high-boiling components such as ether having 2 carbon atoms and acetal having 3 carbon atoms, for example, ether having 8 carbon atoms and acetal having 12 carbon atoms when the raw material is butyraldehyde are produced.

In the present invention, a crude alcohol containing an ether component by-produced by the above-mentioned hydrogenation reaction, usually at a ratio of 5% by weight or less, is subjected to distillation treatment under reduced pressure, whereby the ether and the branched-chain alcohol are enriched. A purified straight-chain alcohol is obtained by distilling the straight-chain alcohol fraction from the top or near the top of the column and removing the straight-chain alcohol having a reduced content of ether and branched-chain alcohol from the bottom or a side stream.

FIG. 1 is a flowchart showing an example of the configuration of a distillation system for carrying out the method of the present invention. In FIG. 1, a crude alcohol containing ether and a branched-chain alcohol produced by the above hydrogenation reaction is supplied to the middle stage of the distillation column 1 from a flow path 5 and distilled under reduced pressure. Via 6 the straight-chain alcohols rich in ethers and branched alcohols are distilled off. Then, a straight-chain alcohol component having a reduced content of ether and branched-chain alcohol is obtained from the bottom of the tower or a side stream via a flow passage 9.

With respect to the distillation pressure, in the case of alcohol purification, in the case of alcohols having 3 to 6 carbon atoms, which is the object of the present invention, it is common practice to carry out normal pressure or pressure distillation because the boiling point is not high. It is a target. However, in the purification of the alcohol containing an ether component, the separation pressure is remarkably increased by setting the operating pressure of the distillation column in the range of 100 to 500 mmHg (absolute pressure), so that the ether component can be efficiently separated by distillation. it can. Therefore, by using the method of the present invention, the reflux ratio can be reduced, and the cost required for operation can be reduced.

On the other hand, with respect to the distillation separation of the branched alcohol, even if the operating pressure is changed, the separation efficiency does not change much, and the reflux ratio cannot be reduced to a certain level or less. This relationship can be explained from the relationship between the specific volatility of the ether and the branched alcohol relative to the straight-chain alcohol and the pressure.
FIG. 2 shows the relationship between the specific volatility of the ether and the branched-chain alcohol with respect to the straight-chain alcohol and the pressure.

In the figures, "α _DNBE " is the relative volatility of di-n-butyl ether with respect to n-butyl alcohol, and "α _IBA " is the relative volatility of i-butyl alcohol with respect to n-butyl alcohol. As apparent from FIG. 2, the relative volatility of the ether with respect to the straight-chain alcohol sharply increases with a decrease in pressure, suggesting that the separation efficiency is improved by distillation under reduced pressure. The relative volatility is not significantly affected by changes in pressure, indicating that pressure has little effect on separation efficiency.

That is, in order to separate the ether from the linear alcohol, the efficiency can be improved by lowering the pressure, and the reflux ratio can be lowered. Becomes insufficient and the reflux ratio cannot be lowered. Further, the distillation pressure is, for example, 100 mm
If the temperature is too low, such as Hg (absolute pressure), the condensation temperature of the distillate component also decreases, and the temperature difference with the refrigerant decreases, so the required heat transfer area of the heat exchanger increases or the temperature of the refrigerant decreases. It becomes necessary to further lower the flow rate, or the volume flow rate of the steam in the tower increases, and the diameter of the tower must be increased, which increases the equipment cost.

In the method of the present invention, the distillation operation is
By performing the reaction in the range of ~ 500 mmHg (absolute pressure) and setting the reflux ratio at that time to 20 or more, preferably 20 to 50, a high-purity straight-chain alcohol having a low content of either ether or branched-chain alcohol can be obtained. Obtainable. When the operating pressure is less than 100 mmHg (absolute pressure), the above-described problems occur. On the other hand, when the operating pressure is more than 500 mmHg (absolute pressure), the ether separation efficiency is insufficient even if the reflux ratio is increased. Become. When the reflux ratio is 20
If it is less than 1, the separation of the branched-chain alcohol becomes insufficient. It is more preferable to set the distillation pressure to 200 to 400 mmHg (absolute pressure) from the viewpoint of equipment cost and distillation efficiency.
The distillation column used in the method of the present invention is usually 10 theoretical plates.
A packed tower or a tray tower having up to 40 stages is used. The column top temperature and the column bottom temperature may be operated under conditions corresponding to the type of alcohol to be distilled and the selected column top operating pressure.

[0021]

EXAMPLES Specific examples of the present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the invention.
In the examples, “pressure” means “absolute pressure” and “%”
Represents "% by weight", respectively.

Examples 1 to 3 N-butyraldehyde obtained by distilling aldehyde obtained by hydroformylation of propylene with a rhodium catalyst was subjected to hydrogenation using a nickel-based solid catalyst. Hydrogenation reaction is pressure 5
The test was performed under the conditions of 0 kg / cm ² G and a temperature of 100 ° C. The concentration of di-n-butyl ether in the resulting crude alcohol was 0.3% by weight, and the concentration of isobutyl alcohol of the isomer that was a branched alcohol was 0.03% by weight. The above crude alcohol was distilled using a distillation system having the structure shown in FIG.
Continuous distillation was performed at each pressure of mmHg, 300 mmHg, and 500 mmHg. That is, the crude alcohol is supplied to the middle stage of a perforated plate distillation column 1 having 18 actual plates, and an alcohol component in which di-n-butyl ether is concentrated is distilled off from the top of the column. Purified n-butyl alcohol with a reduced alcohol component was obtained.
The resulting top distillate and bottom bottoms were analyzed by gas chromatography. The results are shown in Table 1.

<Comparative Example 1> Continuous distillation was carried out in the same manner as in Example 1 except that the pressure at the top of the column was 760 mmHg. The results are shown in Table 1.

[0024]

[Table 1] However,

[0025]

(Equation 1)

As shown in Table 1, when the pressure is increased under the condition that the reflux ratio is kept constant, the separation efficiency in the distillation column 1 becomes n
The separation efficiency of i-butyl alcohol, which is an isomer of -butyl alcohol, is almost constant (cut rate around 70%), whereas the separation efficiency of di-n-butyl ether as a by-product deteriorates to about 30%. Product purity tends to decrease, and it is clear that lower pressure enables more efficient ether separation.

Example 4, Comparative Examples 2 to 5 n-butyraldehyde obtained by distilling aldehyde obtained by hydroformylating propylene with a rhodium catalyst was hydrogenated using a nickel-based solid catalyst. . The hydrogenation reaction was performed under the conditions of a pressure of 50 kg / cm ² G and a temperature of 100 ° C. The concentration of di-n-butyl ether in the resulting crude alcohol was 0.33% by weight, and the concentration of isobutyl alcohol in the isomer that was a branched alcohol was 0.04% by weight.

The above crude alcohol was distilled by using a distillation system having the structure shown in FIG. 1 and a top pressure of 760 mmHg (Comparative Example 2).
00 mmHg (Comparative Example 3), 500 mmHg (Example 4), 300 mmHg (Comparative Example 4, reflux ratio is out of range),
And 100 mmHg (Comparative Example 5, the same before), continuous distillation was performed. That is, the above crude alcohol is supplied from the flow path 5 to the middle stage of the perforated plate distillation column 1 having 35 actual plates, and the alcohol component in which di-n-butyl ether and isobutyl alcohol are concentrated is distilled from the top of the column via the flow channel 6. And a part of it was extracted from the flow channel 8. On the other hand, purified n-butyl alcohol having a reduced content of di-n-butyl ether and branched alcohol components was obtained from the bottom of the column via the flow path 9. The obtained top distillate and bottom bottoms were analyzed by gas chromatography, and the reflux ratio was adjusted so that the ratio of the di-n-butyl ether supplied to the top (cut ratio) to the supply amount was 70%. Was adjusted. Table 2 shows the results.

[0029]

[Table 2]

As is clear from the above table, when the pressure at the top of the column is high (Comparative Examples 2 and 3), an extremely large reflux ratio is required to remove the ether component, and both operating costs and equipment costs are enormous. Become. On the other hand, at the same time as reducing the overhead pressure by removing the ether component with the same efficiency,
If the reflux ratio is reduced (Comparative Examples 4 and 5), the cut rate of the branched alcohol component is reduced, and only a product having a large amount of impurities can be obtained. <Examples 5 to 7, Comparative Examples 6 and 7) Distillation treatment under the same conditions as in Example 4 and Comparative Examples 2 to 5 by adjusting the reflux ratio so that the cut rate of isobutyl alcohol would be 70%. Was done. The results are shown in Table-3.

[0031]

[Table 3]

From Table 3, it can be seen that when the distillation pressure is changed under the condition that the cut rate of the branched-chain alcohol is constant, the cut rate of dibutyl ether is 60 when the pressure is out of the range of the present invention.
%, Which indicates that the purification efficiency is still insufficient.

[0033]

By purifying the alcohol by the method of the present invention, the ether and the branched-chain alcohol as impurities can be efficiently separated to obtain a high-purity straight-chain alcohol.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an example of the configuration of a distillation system for carrying out the method of the present invention.

FIG. 2 is a graph showing the relationship between the specific volatility of dibutyl ether and a branched chain alcohol with respect to a linear product and the pressure in the case of butyl alcohol.

[Explanation of symbols]

1: distillation column 2: heat exchanger 3: reflux drum 4: reboiler 5, 6, 7, 8, 9: flow path α _DNBE : volatility of n- _butyl ether / volatility of n- _butyl alcohol α _IBA : Volatility of i-butyl alcohol / volatility of n-butyl alcohol

Claims (3)

[Claims] 1. A crude alcohol containing ethers having 2n carbon atoms and branched alcohols having n carbon atoms as impurities obtained by hydrogenating an aldehyde having n carbon atoms (where n is an integer of 3 to 6). In performing the distillation purification, the distillation operation is performed at 100 to 500 mmHg (absolute pressure) and the reflux ratio of the distillation column is set to 20 or more, thereby distilling straight-chain alcohol rich in ether and branched-chain alcohol from the top of the column. A method for purifying an alcohol, characterized in that a straight-chain alcohol having a reduced content of ether and branched-chain alcohol is obtained from a column bottom or a side stream. 2. The method for purifying an alcohol according to claim 1, wherein the distillation pressure is 200 to 400 mmHg (absolute pressure). 3. The method for purifying an alcohol according to claim 1, wherein the reflux ratio is 20 to 50.