JP2002234883A - Method for purifying tetrahydrofuran - Google Patents

Abstract

PROBLEM TO BE SOLVED: To collect high-purity tetrahydrofuran by refining a hydrous tetrahydrofuran containing dihydrofuran and <=3C aldehydes. SOLUTION: The objective high-purity tetrahydrofuran is collected by the following steps: a hydrous tetrahydrofuran is contacted with a strongly acidic cation exchange resin to convert dihydrofuran in the hydrous tetrahydrofuran into hydroxytetrahydrofuran, and the resultant reaction liquid is put to high- boiling separatory distillation and low-boiling separatory distillation into an aqueous tetrahydrofuran solution, which is then subjected to dehydrating distillation comprising removing water therefrom by its azeotrope with tetrahydrofuran.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying hydrated tetrahydrofuran containing dihydrofuran and aldehydes having 3 or less carbon atoms. In particular, the present invention
The present invention relates to a method for efficiently purifying hydrated tetrahydrofuran, which is a by-product in the process of producing a polyester from 1,4-butanediol and an aromatic dicarboxylic acid or a reactive derivative thereof.

[0002]

2. Description of the Related Art Various methods for producing tetrahydrofuran are known, such as catalytic hydrogenation of furan, dehydration cyclization of 1,4-butanediol, and deesterification cyclization of diacetoxybutane. Since tetrahydrofuran obtained by these methods generally contains dihydrofuran, aldehydes and the like, methods for removing these impurities have been studied. For example, Tokuho 6-29
No. 280 describes a method for purifying tetrahydrofuran obtained by deesterification cyclization of diacetoxybutane. This tetrahydrofuran contains impurities such as dihydrofuran and butyraldehyde, acetic acid, and water, which are first brought into contact with a strongly acidic cation exchange resin to convert dihydrofuran into hydroxytetrahydrofuran or acetoxytetrahydrofuran. Conversion reaction solution was distilled, resulting hydroxytetrahydrofuran and acetoxy tetrahydrofuran, to flow out from the bottom together with water and acetic acid. Tetrahydrofuran, which is distilled off along with a small amount of water from the top of the column, is hydrogenated in the presence of a ruthenium catalyst to convert the contained butyraldehyde into butanol, and then distilled to evaporate water with tetrahydrofuran to form an azeotrope. It is distilled and tetrahydrofuran containing butanol is discharged from the bottom of the column. Finally, the tetrahydrofuran is distilled to distill the purified tetrahydrofuran from the top. This method is considered an excellent purification method when the main impurities are dihydrofuran and butyraldehyde.

[0003]

Recently, the production of polyesters known as polybutylene terephthalate, in which 1,4-butanediol is the main alcohol component and terephthalic acid is the main carboxylic acid component, is increasing. Accordingly, the amount of the aqueous tetrahydrofuran solution by-produced has also increased. This by-product aqueous solution of tetrahydrofuran contains a considerable amount of dihydrofuran and also contains aldehydes having 3 or less carbon atoms such as acetaldehyde, propionaldehyde, and acrolein. The use of tetrahydrofuran containing these impurities is significantly limited. For example, in the production of polytetramethylene ether glycol, which is one of the main uses of tetrahydrofuran, if tetrahydrofuran containing the above aldehydes is used, an increase in the acid value or coloring occurs, and it cannot be used as a raw material for resin or fiber. . Therefore, methods for removing these aldehydes have been conventionally studied. For example, JP-A-56-104881 describes a method in which an aqueous tetrahydrofuran solution as a by-product is treated with an alkali metal hydroxide and then distilled. Japanese Patent Application Laid-Open No. 57-1
No. 54179 describes a method in which an aqueous tetrahydrofuran by-product is treated with an alkali metal borohydride and then distilled. However, since these chemical treatments are complicated, there is a need for a method for purifying by-product tetrahydrofuran that does not require these chemical treatments. Accordingly, the present invention is as a byproduct in the process of manufacturing a polybutylene terephthalate, from aqueous tetrahydrofuran containing dihydrofuran and having 3 or less of aldehydes carbon, without treatment with an alkali metal hydroxide or alkali metal borohydrides Another object is to provide a method for removing these impurities.

[0004]

According to the present invention, the following steps (a) and (b) are performed on hydrous tetrahydrofuran containing dihydrofuran and an aldehyde having 3 or less carbon atoms, and then the step (c) is performed. By performing the above, hydrous tetrahydrofuran can be easily purified. (B) step; the aqueous tetrahydrofuran is contacted with a strongly acidic cation exchange resin, after conversion of dihydrofuran in tetrahydrofuran hydroxytetrahydrofuran, drained an aqueous solution containing hydroxytetrahydrofuran from the bottom was distilled conversion reaction, A dihydrofuran removal step of distilling off tetrahydrofuran together with water from the top of the tower.

Step (b): an aldehyde removing step in which hydrated tetrahydrofuran is distilled off to distill aldehydes having 3 or less carbon atoms from the top of the column together with some tetrahydrofuran, and the remaining tetrahydrofuran flows out together with water from the bottom of the column. Step (c): dihydrofuran and hydrated tetrahydrofuran having a reduced concentration of aldehydes having 3 or less carbon atoms are distilled to distill water as an azeotrope with tetrahydrofuran from the top of the column and dehydrated tetrahydrofuran from the bottom of the column Draining step.

In the present invention, usually, after performing the step (a),
It is preferable to perform the step (b), but this order can be reversed if desired. In addition, since the conversion reaction from dihydrofuran to hydroxytetrahydrofuran is an equilibrium reaction, when the content of dihydrofuran in the hydrated tetrahydrofuran to be purified is large, it is preferable to perform step (a) a plurality of times. In this case, perform (a) step may be carried out continuously, and (b) after step performed (b) step may be performed further (b) step. Furthermore, (a)
After contacting the aqueous tetrahydrofuran distilled from the top of the column with the strongly acidic cation exchange resin, at least a part of the tetrahydrofuran is returned to the distillation column in the step (a), and the remainder is supplied to the step (b). Good. In this case, when the step (a) is repeated, it is preferable to return the mixture to the distillation column in the immediately preceding step (a). Further, the dehydrated tetrahydrofuran obtained in the step (c) can be further distilled to distill the further purified tetrahydrofuran from the top of the column.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The object of purification in the present invention is
Hydrous tetrahydrofuran containing dihydrofuran and aldehydes having 3 or less carbon atoms as impurities. For example, 1,4-butanediol as a main diol component and hydrous tetrahydrofuran by-produced in the process of producing a polyester having an aromatic dicarboxylic acid such as terephthalic acid as a main dicarboxylic acid component are preferred objects of the present invention. is there. This hydrated tetrahydrofuran has a tetrahydrofuran concentration of 10 to 50% (% by weight,% and ppm in this specification are by weight unless otherwise specified) depending on the reaction conditions, and may have several thousand ppm as an impurity. Up to 10-1000 with dihydrofuran
aldehydes having 3 or less carbon atoms in ppm.

In the present invention, dihydrofuran is converted into hydroxytetrahydrofuran and separated by distillation from tetrahydrofuran, and aldehydes are separated from tetrahydrofuran by distillation at a high reflux ratio. Usually, it is preferable to remove the aldehydes after removing dihydrofuran at least once. Because a significant amount of water is removed at the same time when dihydrofuran is removed,
This is because the amount of hydrous tetrahydrofuran used for removing aldehydes can be reduced.

[0009] The removal of dihydrofuran is described in JP-B-6-29.
According to the method described in Japanese Patent Publication No. 280, a strongly acidic cation exchange resin may be brought into contact with hydrous tetrahydrofuran.
The most commonly used sulfonated styrene-divinylbenzene cross-linked copolymer may be used as the strongly acidic cation exchange resin. For example, Diaion SK1B, SK104, SK112, PK208, P
K212, PK228 and the like can be used (Diaion is a registered trademark of Mitsubishi Chemical Corporation). Normally, dihydrofuran is converted into hydroxytetrahydrofuran by passing hydrated tetrahydrofuran at 20 to 80 ° C. and a LHSV (liquid hourly space velocity) of 0.01 to 5 hr ^-1 through a reaction tower filled with these strongly acidic cation exchange resins. Can be converted.

[0010] Conversion reaction solution was distilled, the most and the resulting hydroxytetrahydrofuran water was drained from the bottom, distilling from the column top of tetrahydrofuran as azeotrope with water. This distillation is preferably carried out using a distillation column having 20 to 40 theoretical plates under normal pressure at a column bottom temperature of 90 to 110 ° C. and a reflux ratio of 0.5 to 3.0. In addition, since the formation reaction of hydroxytetrahydrofuran by hydration of dihydrofuran is an equilibrium reaction, when the content of dihydrofuran in hydrous tetrahydrofuran subjected to the hydration reaction is large,
It may be included noted above the allowable level dihydrofuran in aqueous tetrahydrofuran obtained from the column top. In this case, the above-mentioned treatment with a strongly acidic cation exchange resin and distillation may be repeated. Although the conversion reaction proceeds sufficiently even when the water content of the hydrous tetrahydrofuran used for the treatment with the strongly acidic cation exchange resin is about 5%, the water content of the hydrous tetrahydrofuran distilled off from the top of the column by the above-mentioned distillation is usually about 10%. It is preferable that the mixture be passed through a reaction column filled with a strongly acidic cation exchange resin and then distilled. If desired, this strong acid cation exchange resin treatment-distillation can also be performed after the removal of aldehydes by distillation as described below.

In the case where the aqueous tetrahydrofuran distilled from the top of the distillation column in step (a) is brought into contact with a strongly acidic cation exchange resin, and the resulting conversion reaction solution is returned to the distillation column in step (a), return ratio can be arbitrarily set in accordance with dihydrofuran concentration of the reaction solution obtained in contact with a strongly acidic cation exchange resin. Usually, 20 to 80% by weight, preferably 30 to 70% by weight of the reaction solution is returned. If the return ratio is as low as 20% by weight or less, the effect of this treatment is likely to be insufficient. Not a target.

In the present invention, the removal of aldehydes having 3 or less carbon atoms from hydrous tetrahydrofuran is carried out by distillation. In this distillation, aldehydes are distilled off along with a small amount of a tetrahydrofuran-water azeotrope from the column, and most of the remaining tetrahydrofuran and water are discharged from the column bottom. This distillation is preferably performed at a bottom temperature of 60 to 90 ° C. under normal pressure using a distillation column having 20 to 50 theoretical plates. In this distillation, 100 parts of aldehydes are sufficiently removed by distilling a small amount of tetrahydrofuran.
It is preferable to perform distillation at the above high reflux ratio. Usually, distillation is performed at a reflux ratio of 100 to 200.

Dihydrofuran and hydrated tetrahydrofuran from which aldehydes having 3 or less carbon atoms have been removed are supplied to a dehydration distillation column, water is distilled off from the top as an azeotrope with tetrahydrofuran, and dehydrated tetrahydrofuran is recovered from the bottom of the column. Spill. The number of theoretical plates is 1 for this dehydration distillation column.
It is preferable to use one having about 0 to 20 stages and operate under pressure so that a tetrahydrofuran-water azeotrope having a large ratio of water is distilled off from the tower top. For example, 0.5
1.5 MPa, bottom temperature 130 to 180 ° C., the reflux ratio of 0.
Distill at 1-1.0. The tetrahydrofuran-water azeotrope distilled from the top may be supplied to the distillation column in the dihydrofuran removal step, if desired. The dehydrated tetrahydrofuran flowing out from the bottom of the column can be usually used as it is for various uses. If higher purity tetrahydrofuran is desired, it is obtained by distilling it further to distill off further purified tetrahydrofuran from the top. The impure tetrahydrofuran flowing out from the bottom of the column can be recycled to, for example, a distillation column in a dihydrofuran removal step. The distillation for high purification is carried out with a theoretical plate number of 15 to
Pressure of 0.1 to 0.13MP using about 30 steps
a, the reaction may be performed at a tower bottom temperature of 60 to 120 ° C. and a reflux ratio of about 0.1 to 1.5.

[0014]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to the following examples. In addition, the analysis in an Example was performed according to the following method. (1) Moisture Concentration in Hydrous Tetrahydrofuran Approximately 30 μl of hydrated tetrahydrofuran was precisely weighed, and then the water content (μg) was measured using a Karl Fischer moisture meter (manufactured by Mitsubishi Chemical Corporation) and calculated as a percentage of the sample amount. .

[0015] (2) the ingredients DB-WAX in aqueous tetrahydrofuran by gas chromatography using as column, a peak area corresponding to each component, a modified area percentage method content ratio (A%) of each component demand,
Based on the water concentration (w%) obtained in (1), the content (C%) was calculated by correcting as follows. ("%" Used herein may be read as "ppm" according to the component content.)

[0016]

(Equation 1)

As the correction coefficient of each component used in the modified area percentage method, the following values obtained from the available carbon number based on tetrahydrofuran were used.

[0018]

Table 1 Acetaldehyde 1.833 Propionaldehyde 1.208 Acrolein 1.228 Dihydrofuran 1.109 Hydroxytetrahydrofuran 1.629 Isopropanol 1.111 Example 1 Terephthalic acid and 1,4-butanediol 1: 1.8.
(Molar ratio) to prepare a slurry. The esterification reaction vessel, 0.0 to the above slurry and the slurry
474% of tetra-n-butyl titanate was supplied and reacted under stirring at 230 ° C. and 0.1 MPa for 3 hours 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 carried out at 0.1 MPa and a top temperature of 90 to 100 ° C. to distill hydrated tetrahydrofuran. The amount of hydrated tetrahydrofuran distilled was 18.8% of the slurry supplied to the esterification reactor, and the tetrahydrofuran concentration was 3%.
At 2.6%, dihydrofuran 350 ppm, acetaldehyde 10 ppm, propionaldehyde 20 ppm,
It contained 20 ppm of acrolein.

The above-mentioned hydrated tetrahydrofuran is emptied into a hydration reaction tower filled with Diaion SK1B (a product of Mitsubishi Chemical Corporation, Diaion is a registered trademark of Mitsubishi Chemical Corporation) which is a sulfonic acid type strongly acidic cation exchange resin. Speed (LH
SV) 0.2 / hr. Reaction tower is 50 ℃, 0.
It was maintained at 2 MPa. The composition of the effluent of the hydration reaction tower was as follows.

[0020]

Table 2 Tetrahydrofuran 32.6% Dihydrofuran <10 ppm Acetaldehyde 10 ppm Propionaldehyde 20 ppm Acrolein 20 ppm Hydroxytetrahydrofuran 0.19% Others 1.21% Water 66.0% The above-mentioned hydration reaction is carried out in a distillation column having 30 theoretical plates. The column effluent and the top distillate of the dehydration distillation column are supplied and distilled under normal pressure at a column bottom temperature of about 100 ° C. and a reflux ratio of 2.9, and a column bottom liquid mainly composed of water is discharged from the column bottom. A hydrated tetrahydrofuran having a tetrahydrofuran concentration of 94.7% was distilled off from the top of the column. The weight ratio of the bottom effluent to the top distillate was 67:54. The overhead distillate contained acetaldehyde 19
ppm, propionaldehyde 37 ppm and acrolein 37 ppm.

The top distillate is supplied to a light boiling distillation column having 25 theoretical plates, and distilled at a bottom temperature of about 68 ° C. and a reflux ratio of 150, and aldehydes are azeotropically distilled from the top of the column with tetrahydrofuran-water. Together with tetrahydrofuran 9 from the bottom of the column.
A 4.7% tetrahydrofuran-water mixture was drained. The weight ratio between the top distillate and the bottom effluent was 1:53. The content of acetaldehyde, propionaldehyde and acrolein in the bottom effluent was 1
It was less than 0 ppm.

The bottom distillate of the light boiling distillation column has a theoretical plate number of 14
Is fed to the dehydration distillation column of the stage, and distilled at a top pressure of 0.84 MPa, a bottom temperature of about 150 ° C. and a reflux ratio of 0.5, and from the top of the column, 87.2% of tetrahydrofuran and 12.6% of water are contained. Was distilled off, and dehydrated tetrahydrofuran was discharged from the bottom of the column. The purity was 99.95% or more, and dihydrofuran and aldehyde having 3 or less carbon atoms were each 10 ppm or less. Further, 20 ppm of isopropanol was contained. The weight ratio between the top distillate and the bottom effluent was 21:32.

Example 2 Example 1 was repeated using hydrated tetrahydrofuran as in Example 1 except that the dihydrofuran content was 0.3%.
As a result, the composition of the effluent of the reaction tower was as follows.

[0024]

Table 3 Tetrahydrofuran 32.3% Dihydrofuran 30ppm Acetaldehyde 10ppm Propionaldehyde 20ppm Acrolein 20ppm Hydroxytetrahydrofuran 0.68% Others 1.02% Water 66% A reaction obtained from the second hydration reaction column described later in this liquid. After a part of the liquid was added, distillation was performed in the same manner as in Example 1. At this time, the weight ratio between the bottom effluent and the top distillate was 6
7: 104, and the top distillate contained 19 ppm of acetaldehyde, 37 ppm of propionaldehyde, 37 ppm of acrolein, and 29 ppm of dihydrofuran.

The hydrated tetrahydrofuran is supplied to a second hydration reaction column filled with Diaion SK1B at a superficial velocity (L).
HSV) at 0.2 / hr. The reaction tower is at a temperature of 5
The temperature was maintained at 0 ° C. and 0.2 MPa. The dihydrofuran concentration in the reaction liquid flowing out of the second hydration reaction tower was less than 10 ppm. 50% of the reaction liquid flowing out of the second hydration reaction tower
Was returned to the distillation column, and the remainder was supplied to a light boiling distillation column having 40 theoretical plates. The light-boiling distillation column was operated under the conditions of a bottom temperature of 68 ° C. and a reflux ratio of 150, distilling aldehydes together with an azeotropic mixture of tetrahydrofuran-water from the top of the column, and having a tetrahydrofuran content of 94.7% from the bottom. Hydrous tetrahydrofuran was obtained. The weight ratio between the top distillate and the bottom effluent was 1:53. The contents of acetaldehyde, propionaldehyde, and acrolein in the bottom effluent were all less than 5 ppm.

The bottom effluent low-boiling distillation tower is supplied also to the dehydration distillation column as in Example 1, subjected to dehydration distillation under the same conditions, to obtain a column top distillate and dehydrated tetrahydrofuran having the same composition as in Example 1 Was. The purity of the obtained tetrahydrofuran is 99.
95% or more, and dihydrofuran and aldehydes having 3 or less carbon atoms were all 5 ppm or less. The content of isopropanol was 20 ppm. The weight ratio between the top distillate and the bottom effluent was 21:32.

Continued on the front page (72) Inventor Kazuyuki Okubo 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Chemical Corporation Yokkaichi Office (72) Inventor Teruo Yoshida 191-1, Shiojihama, Yokkaichi-shi, Mie Mitsubishi Chemical Engineering Co., Ltd. Engine center F term (reference) 4C037 BA05

Claims (7)

[Claims] 1. A method for purifying hydrated tetrahydrofuran containing dihydrofuran and aldehydes having 3 or less carbon atoms, wherein the step (a) and the step (b) are performed, and then the step (c) is performed. And how. (A) Step: After contacting hydrous tetrahydrofuran with a strongly acidic cation exchange resin to convert dihydrofuran in tetrahydrofuran into hydroxytetrahydrofuran, distilling the conversion reaction solution and flowing out an aqueous solution containing hydroxytetrahydrofuran from the bottom of the column; A dihydrofuran removal step of distilling off tetrahydrofuran together with water from the top of the tower. Step (b): an aldehyde removing step of distilling hydrated tetrahydrofuran to distill aldehydes having 3 or less carbon atoms from the top of the column together with some tetrahydrofuran, and flowing out the remaining tetrahydrofuran together with water from the bottom of the column. Step (c): dihydrofuran and hydrated tetrahydrofuran having a reduced concentration of aldehydes having 3 or less carbon atoms are distilled to distill water as an azeotrope with tetrahydrofuran from the top of the column and dehydrated tetrahydrofuran from the bottom of the column Draining step. 2. The method according to claim 1, wherein the step (b) is performed after the step (a). 3. The method according to claim 1, wherein the step (a) is performed twice, and then the step (b) is performed. 4. The method according to claim 1, wherein the step (a) is performed, the step (b) is performed, and the step (a) is performed again. 5. After bringing aqueous tetrahydrofuran distilled off from the top of the column in the step (a) into contact with a strongly acidic cation exchange resin, at least a part thereof is returned to the distillation column in the step (a), and the remainder is ( 2. The method according to claim 1, wherein the method is supplied to the step (b). 6. distilling the dehydrated tetrahydrofuran obtained in (c) step, claim, characterized in that distilling the further purified tetrahydrofuran from the top 1
Through method according to any one of 5. 7. The hydrated tetrahydrofuran to be purified is a by-product produced in the process of producing a polyester from 1,4-butanediol and an aromatic dicarboxylic acid or a reactive derivative thereof. Or 6
The method according to any of the above.