JP2003089694A - Method for purifying tetrahydrofuran - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover highly pure tetrahydrofuran (THF) from a THF aqueous solution recovered on the production of PBT from 1,4-butanediol and terephthalic acid. SOLUTION: This method for purifying the tetrahydrofuran (THF) comprises bringing the THF aqueous solution into contact with a strongly acidic ion exchange resin to hydrate an impure substance, i.e., dihydrofuran, distilling the hydration product solution to obtain THF as an overhead product, distilling the overhead product to remove <=3C aldehydes and simultaneously obtain THF as a bottom product, mixing the obtained THF with an acetic acid- containing THF aqueous solution obtained by acetic acid removal and cyclization of the 1,4-butanediol monoacetate-containing solution, bringing the obtained mixture into contact with a strongly acidic ion exchange resin to hydrate the dihydrofuran, distilling the hydration product solution to obtain THF as an overhead product, hydrogenating the overhead product, and then distilling the hydrogenation product to remove water by an azeotrope together with THF and simultaneously obtain the purified THF as a bottom product.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying tetrahydrofuran by a combination of a series of steps. According to the present invention, tetrahydrofuran produced as a by-product in the esterification reaction using 1,4-butanediol as a raw material can be easily recovered as high-purity tetrahydrofuran.

[0002]

2. Description of the Related Art Tetrahydrofuran is an important compound as a solvent and a raw material for polytetramethylene ether glycol. There are several known methods for producing tetrahydrofuran. One of them is the reaction of butadiene with acetic acid to give diacetoxybutene, which is hydrogenated to give diacetoxybutane and then hydrolyzed to give 1,4-diacetoxybutane. When producing butanediol, there is a method of co-producing it with 1,4-butanediol. In this method, a solution containing 1,4-butanediol monoacetate is deacetic acid-cyclized to produce tetrahydrofuran. High-purity tetrahydrofuran is recovered from the thus obtained tetrahydrofuran containing acetic acid and the like through a series of purification steps.

Recently, the production of polyesters from 1,4-butanediol and polycarboxylic acids has become popular. A typical example is the production of polybutylene terephthalate from 1,4-butanediol and terephthalic acid. In the production of this polyester, 1,4-
Tetrahydrofuran is by-produced from butanediol. The by-produced tetrahydrofuran is also gaseous together with water by-produced in the reaction and flows out from the esterification reactor, so that it is condensed and recovered as an aqueous tetrahydrofuran solution. This tetrahydrofuran aqueous solution contains dihydrofuran, aldehydes, alcohols, etc., and its use is extremely limited.

[0004]

Various methods for recovering tetrahydrofuran with high purity from an aqueous tetrahydrofuran solution by-produced in the esterification step have been investigated. As a typical example thereof, an aldehyde removal method by an alkali treatment is known. However, with such a purification method, it is difficult to industrially recover high-purity tetrahydrofuran that can be used for the production of polytetramethylene ether glycol from the by-produced tetrahydrofuran aqueous solution. Therefore, the present invention is intended to provide a method for industrially recovering highly pure tetrahydrofuran from this by-produced tetrahydrofuran aqueous solution.

[0005]

According to the present invention, 1,4 by a purification method including the following steps (a) to (f)
-Deacetic acid of a solution containing butanediol monoacetate
High-purity tetrahydrofuran can be easily obtained from the hydrous tetrahydrofuran produced by cyclization and the by-produced tetrahydrofuran aqueous solution.

Step (a): An aqueous tetrahydrofuran solution (B) containing dihydrofuran by-produced in the step of reacting 1,4-butanediol and a carboxylic acid and an aldehyde having 3 or less carbon atoms is treated with a strongly acidic cation exchange resin. Dihydrofuran is hydrated to hydroxytetrahydrofuran by contacting with, and the obtained hydration reaction liquid is distilled to distill tetrahydrofuran from the top of the tower together with a part of water to recover it, and from the bottom of the tower, hydroxytetrahydrofuran Drain with water.

Step (b): Tetrahydrofuran containing water obtained from the top of the step (b) is distilled to distill off an aldehyde having 3 or less carbon atoms from the top of the tower together with a part of tetrahydrofuran, and then from the bottom of the tower. The rest of the tetrahydrofuran is flushed out with water. Step (c): Hydrous tetrahydrofuran (A) containing acetic acid and the like produced by deacetic acidification / cyclization of 1,4-butanediol monoacetate is distilled to distill tetrahydrofuran together with water and acetic acid from the top of the column. The boiling material is discharged from the bottom of the column.

Step (d): A tetrahydrofuran containing water obtained from the bottom of the step (b) and a tetrahydrofuran containing water obtained from the top of the step (c) are mixed to obtain a strongly acidic cation exchange resin. Contact with
The contained dihydrofuran is hydrated to hydroxytetrahydrofuran, the obtained hydration reaction liquid is distilled to distill tetrahydrofuran from the top of the tower together with a part of water, and acetic acid and hydroxytetrahydrofuran from the bottom of the tower to the remaining water. Drain with.

Step (e): Tetrahydrofuran containing water obtained from the top of the step (d) is supplied to a reactor containing a noble metal catalyst together with hydrogen, and n-butyl contained in the tetrahydrofuran is supplied. The aldehyde is converted to n-butanol. Step (f): The tetrahydrofuran containing n-butanol and water obtained in the step (e) is distilled to distill water from the column top as an azeotrope with a part of tetrahydrofuran,
The dehydrated tetrahydrofuran is recovered from the bottom of the column.

In one of the preferred embodiments of the present invention,
Tetrahydrofuran obtained from the column bottom in the above step (f) is further distilled to distill higher purity tetrahydrofuran from the column top, and tetrahydrofuran containing n-butanol is discharged from the column bottom.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a by-product is produced by an esterification reaction using 1,4-butanediol as an alcohol component, particularly an esterification reaction for producing polybutylene terephthalate from terephthalic acid and 1,4-butanediol. Is used as one of the purification raw materials. The composition of this tetrahydrofuran aqueous solution differs depending on the esterification reaction method and the method for recovering the tetrahydrofuran aqueous solution from it, but in general, the tetrahydrofuran concentration is 10 to 50% by weight, and it is used for dihydrofuran, aldehydes and esterification reaction. Alcohol derived from the catalyst was also included. The ratio of these impurities to tetrahydrofuran also differs depending on the esterification reaction method and the method for recovering the tetrahydrofuran aqueous solution, but generally 10 to several thousand parts by weight of dihydrofuran and 10 to several parts by weight of aldehydes and alcohols with respect to 10 ⁶ parts by weight of tetrahydrofuran. It is 1000 parts by weight. In the present invention, first, in the step (a), this tetrahydrofuran aqueous solution is brought into contact with a strongly acidic cation exchange resin to hydrate dihydrofuran to hydroxytetrahydrofuran. This hydration reaction is known as described in, for example, Japanese Patent Publication No. 29280/1994, and a reactor filled with a sulfonic acid type cation exchange resin is charged with 20 to 80.
It can be easily carried out by passing an aqueous tetrahydrofuran solution at a temperature of about 0.01 to 5 hr ^{−1 at} LHSV (liquid hourly space velocity).

The hydration reaction liquid is distilled to distill tetrahydrofuran from the top of the column together with a part of water, and to discharge hydroxytetrahydrofuran from the bottom of the column together with the remaining water.
In this distillation, a distillation column having a theoretical plate number of 20 to 40 is used, and the column bottom temperature is 90 to 110 ° C and the reflux ratio is 0.5 to under normal pressure.
It is preferable to carry out at 3. Dihydrofuran may remain in the tetrahydrofuran recovered from the top of the column. This hydration reaction is considered to be an equilibrium reaction.Therefore, when the concentration of dihydrofuran in the starting tetrahydrofuran aqueous solution used for the hydration reaction is high, the tetrahydrofuran aqueous solution recovered from the top of the column is contacted with the strongly acidic cation exchange resin again. It is preferable to hydrate the remaining dihydrofuran. The produced hydroxytetrahydrofuran is contained in this hydration reaction liquid, but since it can be separated from tetrahydrofuran by distillation in the subsequent step and included in the bottom liquid of the column and discharged to the outside of the system, the hydration reaction liquid is It can be directly supplied to the next step. In one of the preferred embodiments of the present invention, a part of the hydration reaction liquid is circulated to the distillation column in step (a),
The rest is supplied to the step (b). By doing so, both dihydrofuran and hydroxytetrahydrofuran supplied to the step (b) can be reduced.

The concentrated tetrahydrofuran solution obtained from the top of the column in step (a) and in which most of the dihydrofuran has been removed contains components having a boiling point lower than that of tetrahydrofuran, such as acetaldehyde and propionaldehyde. There is. In the step (b) of the present invention, this tetrahydrofuran aqueous solution is distilled to distill off an aldehyde having a carbon number of 3 or less, which is a low boiling point component, together with a part of the tetrahydrofuran from the top of the tower, and the remaining tetrahydrofuran from the bottom of the tower together with water. Drain. This distillation has 20 to 5 theoretical plates
Using a 0-stage distillation column, the column bottom temperature is 60 to 90 ° C. under normal pressure.
It is preferable to carry out. In this distillation, it is preferable to distill at a high reflux ratio of 100 or more so that the aldehydes can be sufficiently removed by distilling off a small amount of tetrahydrofuran. Usually, distillation is carried out at a reflux ratio of 100 to 200.

Most of the impurities in the tetrahydrofuran aqueous solution recovered from the esterification step using 1,4-butanediol as an alcohol component are removed in the above steps (a) and (b), but they are still considerable. It contains a certain amount of water and trace impurities. In the present invention, the water-containing tetrahydrofuran purified through the steps (a) and (b) is used to remove acetic acid from a solution containing 1,4-butanediol monoacetate, which is one of the typical production processes of tetrahydrofuran. -Adding to the purification step of hydrous tetrahydrofuran containing acetic acid and the like obtained by the method for producing tetrahydrofuran by cyclization, and further refining. Hydrous tetrahydrofuran obtained by deacetic acidification / cyclization of 1,4-butanediol monoacetate contains n-butyraldehyde and dihydrofuran in an amount of 100 to 5000 ppm and 10 to 500 ppm with respect to tetrahydrofuran, respectively.
The degree is included.

In step (c) of the present invention, the hydrous tetrahydrofuran containing acetic acid and the like is distilled to distill tetrahydrofuran from the top of the tower together with water and acetic acid.
4-diacetoxybutane and other high-boiling substances are discharged from the bottom of the column. The tetrahydrofuran aqueous solution recovered from the column top contains acetic acid, dihydrofuran, n-butyraldehyde and other impurities. That is, this distillation may be simple.

In the present invention, in the step (d), the tetrahydrofuran containing water recovered from the bottom of the step (b) and the tetrahydrofuran containing water and acetic acid recovered from the top of the step (c) are combined. The contained dihydrofuran is hydrated in tetrahydrofuran by contact with a strongly acidic cation exchange resin. This hydration reaction can be performed in the same manner as the hydration reaction in the step (a). Thus, by subjecting the tetrahydrofuran containing water recovered in the step (b) to the hydration reaction again in the step (d), the hydration reaction in the step (a) does not proceed to a desired degree for some reason. Even in such a case, it is possible to prevent dihydrofuran from being mixed into the tetrahydrofuran obtained as a product in excess of the allowable amount. The hydration reaction solution is distilled to distill tetrahydrofuran from the top of the column together with a part of water, and the remaining water containing acetic acid and hydroxytetrahydrofuran is discharged from the bottom of the column.

Tetrahydrofuran containing water obtained from the top of the column in step (d) contains unsaturated impurities such as aldehyde and a very small amount of dihydrofuran. One of the main ones is n-butyraldehyde derived from tetrahydrofuran from step (c). In the present invention, as the step (e), hydrogenation for saturating unsaturated bonds of impurities in the tetrahydrofuran containing water is performed. This hydrogenation reaction can be easily carried out by passing tetrahydrofuran containing water through a reactor filled with a noble metal catalyst and supplying hydrogen thereto. As the noble metal catalyst, it is preferable to use a carrier made of activated carbon, silica gel, silica-alumina, magnesia, diatomaceous earth or the like, on which a noble metal such as ruthenium, palladium or platinum is supported. The reaction temperature is usually 30 to 200 ° C,
Hydrogenation of tetrahydrofuran is likely to occur at high temperatures, and the reaction rate is slow at low temperatures, so hydrogenation at 50 to 120 ° C. is preferred. Hydrogen pressure is 0.1 MPa (gauge pressure)
Above, 0.5 to 2 MPa (gauge pressure) is particularly preferable.
As the hydrogen, hydrogen containing an inert gas other than pure hydrogen may be used. From the tetrahydrofuran used for the hydrogenation reaction,
Most of the unsaturated components such as dihydrofuran and aldehydes having 3 or less carbon atoms that were present in the raw material tetrahydrofuran aqueous solution have already been removed, so that the main hydrogenation reaction is n-butyraldehyde hydrogenation. It is the production of butanol, and the reaction is easy.

The hydrogenation reaction liquid is subjected to gas-liquid separation and then distilled in the step (f) to distill the contained water as an azeotrope with a part of tetrahydrofuran from the top of the column and dehydrate it from the bottom of the column. The obtained high-purity tetrahydrofuran is obtained. For dehydration distillation, usually, a dehydration distillation column having 10 to 30 theoretical plates is used, a top pressure of 0.5 to 1.5 MPa, and a bottom temperature of 13
It is preferable to operate at 0 to 180 ° C. and a reflux ratio of about 0.1 to 1.0. Since n-butanol produced in the step (e) is contained in this tetrahydrofuran, if higher purity tetrahydrofuran is desired,
By distilling the tetrahydrofuran obtained in the step (f),
Tetrahydrofuran is distilled off from the top of the column to recover it, and tetrahydrofuran containing n-butanol is discharged from the bottom of the column.

[0019]

EXAMPLES The present invention will be described in more detail with reference to the examples in which tetrahydrofuran is purified according to the flow sheet of FIG. All ppm are on a weight basis. The analysis of water content was performed using a Karl Fischer water content meter. Analysis of organic components was performed by gas chromatography. DB-WAX was used as the column, and the content of each peak component was determined by the modified area percentage method. The coefficient of each peak was determined as follows based on the number of effective carbons with tetrahydrofuran as the reference.

Coefficients for Tetrahydrofuran Acetaldehyde 1.833 Propionaldehyde 1.208 Acrolein 1.228 Dihydrofuran 1.006 Hydroxytetrahydrofuran 1.629 n-Butanol 0.907 n-Butylaldehyde 1.000 Example 1 Terephthalic acid and 1, 4-butanediol with 1: 1.8
(Mole ratio) was mixed to obtain a slurry. In the esterification reactor, 0.0474 for this slurry and slurry
(Wt)% tetrabutyl titanate was supplied and reacted at 230 ° C and 0.1 MPa for 3 hours with stirring to obtain an oligomer having an esterification rate of 95%. The gas generated from the esterification reaction tank is introduced into the attached distillation column,
Distillation was performed at 0.1 MPa and a column top temperature of 90 to 100 ° C. to distill an aqueous tetrahydrofuran solution from the column top. The tetrahydrofuran concentration of this aqueous solution was 32.6% by weight, hydroxytetrahydrofuran 3000 ppm, dihydrofuran 3000 ppm, and acetaldehyde 10 p.
It contained pm, 20 ppm of propionaldehyde, and 20 ppm of acrolein.

Sulfonic acid type cation exchange resin (Diaion SKIB, Diaion is a registered trademark of Mitsubishi Chemical Corporation)
The aqueous tetrahydrofuran solution recovered above was passed through the first hydration reactor 1 filled with OH at 50 ° C. and 0.2 MPa at a liquid superficial velocity of 0.2 hr ⁻¹ to dihydrofuran to hydroxytetrahydrofuran. Hydrated. The tetrahydrofuran concentration of the hydration reaction liquid flowing out from the reactor was 3
Dihydrofuran 30 ppm, acetaldehyde 10 ppm, propionaldehyde 20 pp at 2.3% by weight
m, acrolein 20ppm, hydroxytetrahydrofuran 6800ppm, other impurities 1.02% by weight
Was included.

Using a distillation column 2 having 30 theoretical plates, this hydration reaction liquid is mixed with a circulating liquid from a second hydration reactor 3 described later under atmospheric pressure at a column bottom temperature of about 100 ° C. and a reflux ratio of 2. The mixture was distilled at 9, and substantially all of the tetrahydrofuran was distilled off from the top of the column. The distilled water-containing tetrahydrofuran had a tetrahydrofuran concentration of 94.7% by weight, and contained 30 ppm of acetaldehyde, 59 ppm of propionaldehyde, 59 ppm of acrolein and 50 ppm of dihydrofuran. From the bottom of the column, an aqueous solution containing water as a main component and containing hydroxytetrahydrofuran and other impurities having a high boiling point was discharged.

Into the second hydration reactor 3 filled with DIAION SKIB, 5 parts of the hydrous tetrahydrofuran obtained above was added.
The remaining dihydrofuran was hydrated by passing the solution at 0 ° C., 0.2 MPa and a liquid superficial velocity of 0.2 hr ⁻¹ . The concentration of dihydrofuran in the hydration reaction liquid flowing out from the reactor 3 is
It was reduced to less than 10 ppm. Half of this hydration reaction liquid was circulated to the immediately preceding distillation column 2, and the remaining half was supplied to the subsequent light boiling distillation column 4 having 40 theoretical plates. The light-boiling distillation column 4 is operated under normal pressure at a bottom temperature of about 68 ° C. and a reflux ratio of 150, and an aldehyde having a carbon number of 3 or less is distilled off together with an azeotrope of tetrahydrofuran-water from the top of the column, and a tetrahydrofuran concentration from the bottom of the column. 94.7 wt% hydrous tetrahydrofuran was discharged. The weight ratio of the top distillate and the bottom effluent is 1: 5.
It was 3. Further, the contents of acetaldehyde, propionaldehyde, acrolein and dihydrofuran in the hydrous tetrahydrofuran recovered from the column bottom were all less than 5 ppm.

1,4-Diacetoxybutane obtained by acetoxylation of butadiene and hydrogenation is hydrolyzed to obtain a hydrolyzate containing 1,4-butanediol and 1,4-butanediol monoacetate and diacetate. A decomposition liquid was generated. This is dehydrated or deacetic acid in the presence of an acid catalyst to produce tetrahydrofuran, and the reaction product solution is distilled in a distillation column 5 and tetrahydrofuran 59.
A distillate containing 1 wt%, 36.7 wt% acetic acid and 4.1 wt% water was obtained. This distillate is 20 pp of dihydrofuran
It contained 550 ppm of m and n-butyraldehyde. This distillate was mixed with hydrous tetrahydrofuran recovered from the bottom of the light-boiling distillation column 4 and tetrahydrofuran recovered from the bottom of the tetrahydrofuran purification column described later (weight mixing ratio 167: 53: 19), In the third hydration reactor 6 filled with Diaion SKIB, 50
The solution was allowed to pass under the conditions of ° C, 0.2 MPa and 0.2 hr ^-1 to cause the hydration reaction of dihydrofuran. The composition of the obtained hydration reaction liquid was as follows, and acetaldehyde, propionaldehyde, acrolein and dihydrofuran were all less than 10 ppm.

Tetrahydrofuran 70.3% by weight Acetic acid 25.6% by weight Water 4.0% by weight n-butyraldehyde 380 ppm Hydroxytetrahydrofuran 30 ppm This hydration reaction solution was mixed with the overhead distillate of the dehydration tower 10 described below. Distilling at a tower top temperature of about 107 ° C. and a reflux ratio of 1.4 in a distillation tower 7 at atmospheric pressure, a tetrahydrofuran-water azeotrope was distilled from the tower top, and acetic acid containing water was made to flow out from the tower bottom. . The weight ratio of the top distillate and the bottom effluent is 281: 70.
Met. The amount of n-butyraldehyde in the overhead distillate was 320 ppm.

The overhead distillate was then passed together with hydrogen into a hydrogenation reactor 8 having a hydrogenation catalyst in which activated carbon was loaded with ruthenium, and n-butyraldehyde was hydrogenated to n-butanol. The supply ratio of the overhead distillate and hydrogen to the hydrogenation reactor was 281: 0.3 (weight ratio), and the hydrogenation reaction was 1
It was carried out at 00 ° C, 0.94 MPa, and liquid superficial velocity of 0.5 hr ^-1 . The hydrogenation reaction liquid flowing out from the hydrogenation reactor was subjected to gas-liquid separation under normal pressure in the gas-liquid separation tank 9. Liquid phase n-butanol was 330 ppm and n-butyraldehyde was 10 ppm or less.

This liquid phase is used as a dehydration distillation column 1 having 21 theoretical plates.
0, the tower top pressure is 0.84 MPa, the tower bottom temperature is about 150 ° C.,
Distill at a reflux ratio of 0.5 to distill hydrated tetrahydrofuran containing 87.3% by weight of tetrahydrofuran and 12.7% by weight of water from the top of the column and circulate it in the distillation column 7 to recover dehydrated tetrahydrofuran from the bottom of the column. did. The weight ratio of the top distillate and the bottom effluent was 112: 169.

Tetrahydrofuran recovered from the bottom of the dehydration distillation column 10 is distilled in a purification column 11 having 19 theoretical plates at a column bottom temperature of about 67 ° C. and a reflux ratio of 0.5 under normal pressure, and then distilled from the top of the column. Purified tetrahydrofuran was distilled off. Tetrahydrofuran containing n-butanol was discharged from the bottom of the column and circulated in the third hydration reactor. The weight ratio of the top distillate to the bottom effluent was 150: 19. Further, the purity of tetrahydrofuran recovered from the top of the column was 99.95% or more, and dihydrofuran, aldehyde having 3 or less carbon atoms and alcohol were all 5 ppm or less.

[Brief description of drawings]

FIG. 1 is an example of a flow sheet for carrying out the present invention.

[Explanation of symbols]

1 first hydration reactor 2 distillation tower 3 second hydration reactor 4 Light boiling distillation column 5 distillation tower 6 3rd hydration reactor 7 distillation tower 8 Hydrogenation reactor 9 gas-liquid separation tank 10 dehydration distillation column 11 purification tower

Continued front page    (72) Inventor Kazuyuki Okubo             1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Chemical Corporation             Inside the company (72) Inventor Teruo Yoshida             191-1 Shiohama, Yokkaichi, Mie Prefecture Mitsubishi             Within Chemical Engineering Co., Ltd.

Claims (3)

[Claims] 1. Recovery of high-purity tetrahydrofuran from hydrous tetrahydrofuran (A) containing acetic acid and the like obtained by deacetic acidification / cyclization of a solution containing 1,4-butanediol monoacetate, and 1,4-butanediol. A method for purifying tetrahydrofuran, which is an integrated method of recovering high-purity tetrahydrofuran from an aqueous tetrahydrofuran solution (B) containing dihydrofuran by-produced in the step of reacting carboxylic acid with carboxylic acid, and an aldehyde having 3 or less carbon atoms. A method comprising the steps of: Step (a): The aqueous tetrahydrofuran solution (B) is brought into contact with a strongly acidic cation exchange resin to hydrate dihydrofuran to hydroxytetrahydrofuran, and the obtained hydration reaction liquid is distilled to remove tetrahydrofuran partially from the top of the column. It is distilled out together with water to be recovered, and hydroxytetrahydrofuran is allowed to flow out together with the balance of water from the bottom of the column. Step (b): Tetrahydrofuran containing water obtained in the step (a) is distilled to distill off an aldehyde having 3 or less carbon atoms together with a part of tetrahydrofuran from the top of the tower, and the remaining tetrahydrofuran from the bottom of the tower. With water. Step (c): Distill the hydrous tetrahydrofuran (A), distill tetrahydrofuran from the top of the column together with water and acetic acid, and let the high-boiling substance flow out from the bottom of the column. Step (d): Tetrahydrofuran containing water obtained from the bottom of step (b) and tetrahydrofuran containing water obtained from the top of step (c) are mixed and brought into contact with a strongly acidic cation exchange resin. Hydrate the dihydrofuran contained therein to hydroxytetrahydrofuran, distill the resulting hydration reaction liquid to distill off tetrahydrofuran with some water from the top of the column, and leave acetic acid and hydroxytetrahydrofuran at the bottom from the bottom. Drain with water. Step (e): Tetrahydrofuran containing water obtained from the top of the step (d) is supplied to a reactor containing a noble metal catalyst together with hydrogen, and n-butyraldehyde contained in the tetrahydrofuran is n. -Convert to butanol. Step (f): The tetrahydrofuran containing n-butanol and water obtained in the step (e) is distilled to distill water from the column top as an azeotrope with a part of tetrahydrofuran,
The dehydrated tetrahydrofuran is recovered from the bottom of the column. 2. Tetrahydrofuran recovered from the column bottom in step (f) is distilled to distill the purified tetrahydrofuran from the column top, and tetrahydrofuran containing n-butanol is discharged from the column bottom. The method of claim 1, wherein 3. The water-containing tetrahydrofuran obtained in the step (a) from the top of the column is brought into contact with a strongly acidic cation exchange resin to hydrate the contained dihydrofuran to hydroxytetrahydrofuran, and the resulting water is obtained. 3. The method according to claim 1, wherein a part of the sum reaction liquid is circulated to the distillation column in the step (a) and the rest is supplied to the step (b).