JPS5848558B2 - Tetrahydrofuran separation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for separating tetrahydrofuran and methanol or a water-containing mixture thereof.

Tetrahydrofuran and methanol are an azeotrope (composition:
Tetrahydrone 69wt% (weight%: same below),
Tetrahydrofuran and methanol cannot be separated by simple distillation because methanol (31 wt%, boiling point 60.7°C) is formed.

Therefore, methanol (or methanol and water) must be separated using appropriate chemicals, and the following methods are known.

(1) A method of selectively adsorbing only methanol using a molecular sieve with a specific molecular structure.

(Japanese Patent Publication No. 49-5338) (2) A method of separating tetrahydrofuran by reacting sodium hydride with methanol and converting the methanol into an alcoholate and distilling it.

(Japanese Unexamined Patent Publication No. 49-30353) (3) A method of separating water-containing alcohol-containing tetrahydrofuran by distilling it together with sulfamic acid, an organic base and an alkali metal hydroxide after vigorously heating the reflux.

(Japanese Unexamined Patent Publication No. 49-43963) However, in method (1), it is necessary to regenerate the molecular sieve that has adsorbed methanol by heating it to 250 to 500°C with heated air, and in addition, tetrahydrofuran containing a high concentration of methanol Not available.

In method (2), sodium hydride used as a reagent is expensive and reacts with methanol to turn into alcoholate and hydrogen, which cannot be recovered and reused.

Also, special care must be taken in handling.

In method (3), three types of reagents including sulfamino acid must be used for dehydration and dealcoholization, and the operation is complicated.

As described above, the conventional methods are very complicated to operate, use expensive reagents, and are not industrially practicable.

As a result of various tests and intensive studies, we have found that tetrahydrofuran can be extracted from tetrahydrofuran by an economically cheap and simple method of contacting a mixture of methanol and tetrahydrofuran or a water-containing mixture thereof with an aqueous alkali metal hydroxide solution and extracting methanol. The present invention was completed by discovering that tetrahydrofuran can be concentrated more than the azeotropic composition of methanol.

In carrying out the present invention, a mixing tank and a static fixing tank are used as devices.

The extractor may be either a batch type or a continuous type, and the flow of the aqueous alkali metal hydroxide solution and tetrahydrofuran solution may be either cocurrent or countercurrent.

For example, a mixture of methanol and tetrahydrofuran, or a water-containing mixture thereof, is sufficiently mixed with an aqueous alkali metal hydroxide solution in a mixing tank, then transferred to a stabilization tank and separated into two layers, and the upper tetrahydrofuran layer is separated. do.

To remove methanol more completely, if the tetrahydrofuran after methanol extraction is distilled, a very small amount of an azeotropic mixture of methanol and tetrahydrofuran will be distilled out at the top of the column, and only pure tetrahydrofuran will be obtained at the bottom of the column.

As the alkali metal hydroxide, sodium hydroxide is practically used, but potassium hydroxide can also be used satisfactorily.

For alkali metal carbonates such as sodium carbonate and potassium carbonate, sodium chloride, and sodium acetate, even if a saturated aqueous solution is used, methanol and tetrahydrofuran mixture (composition 3)
The methanol and water concentrations of the tetrahydrofuran layer after methanol extraction from 1wt% and 69wt% are respectively 15
wt%, more than 8 wt%, the extraction rate of methanol is low, and a considerable amount of water is dissolved in the tetrahydrofuran layer.
In addition, saturated aqueous solutions of potassium chloride and sodium sulfate cannot be used because they separate into two liquid layers even when they come into contact with a mixture of methanol and tetrahydrofuran, resulting in staleness.

The extraction rate of methanol is closely related to the concentration of alkali metal hydroxide, and the higher the concentration is, the higher the extraction rate of methanol becomes.

Taking sodium hydroxide aqueous solution as an example, methanol and tetrahydrofuran mixture (composition: 31 wt%, 69 wt%
) and the same weight of sodium hydroxide aqueous solution are mixed and separated, the methanol remaining in the upper tetrahydrofuran layer,
To form water, the sodium hydroxide aqueous solution before mixing is 46wt.
% is 4. Owt%, 0.58wt%, 5.8wt% for 40wt%, 7.9w for 1.1wt%, 35wt%
t%, 1.9wt%: 10.4wt% at 30wt%,
3.3wt%: 12.1wt% at 25wt%, 5.6
It is wt%.

However, even with a low concentration sodium hydroxide aqueous solution, the amount of methanol and water remaining in the tetrahydrofuran layer can be reduced by increasing the number of extraction stages.

When methanol is extracted from an azeotropic mixture of the same weight of methanol and tetrahydrofuran using a 30 wt% aqueous sodium hydroxide solution in a countercurrent contact method, the composition of methanol and water remaining in the upper tetrahydrofuran layer is 10.4 wt%, 3.3 wt% for 1 extraction stage, 5.2 wt%, 4 wt%, 3 extraction stages for 2 extraction stages
When the number of extraction stages is 4, it decreases to 2.9 wt% and 0.57 wt%, and when the number of extraction stages is 4, it decreases to 1.6 wt% and 0.29 wt%.

Also, when using the same weight of alkali metal hydroxide,
Using a small amount of a high-concentration alkali metal hydroxide aqueous solution provides better results in terms of demethanol and dehydration than using a large amount of a low-concentration alkali metal hydroxide aqueous solution.

The concentration of sodium hydroxide dissolved in the tetrahydrofuran layer is 0.1 wt % or less and usually does not pose a problem.

Furthermore, the amount of tetrahydrofuran that dissolves into the lower water layer and is lost is affected by the methanol concentration before extraction, and increases as the methanol concentration increases.

For example, when methanol is extracted from a mixture of the same weight of methanol and tetrahydrofuran with a 40 wt% aqueous sodium hydroxide solution, if the methanol concentration is 10 wt%, the loss of tetrahydrofuran is 0.1 wt% and 31 wt%.
So 6. Owt%, 60wt% becomes 27wt%.

Therefore, if the concentration of methanol in the mixture of methanol and tetrahydrofuran before methanol separation is higher than the azeotropic introduction of methanol and tetrahydrofuran, first methanol and tetrahydrofuran are added from the top of the column by distillation.
The azeotrope of lahydrofuran is distilled off, leaving only methanol at the bottom of the column.

The loss of tetrahydrofuran can be reduced by extracting methanol from the distillate with an aqueous alkali metal hydroxide solution and separating the tetrahydrofuran.

However, the tetrahydrofuran dissolved in the aqueous layer can be recovered as an azeotrope with methanol by simple distillation, so if this operation is carried out, there is no need to distill it before extraction with methanol as described above.

Conversely, if the methanol and tetrahydrofuran mixture has a concentration below the azeotropic composition and the amount of the tetrahydrofuran mixture to be treated with the alkali metal hydroxide aqueous solution is small, methanol is directly extracted with the alkali metal hydroxide aqueous solution.

However, even if the methanol concentration is low, if the mixture of methanol and tetrahydrofuran to be treated with an aqueous alkali metal hydroxide solution is large, methanol and tetrahydrofuran can be separated by distillation.
- If the azeotropic mixture of lahydrofuran is distilled and methanol is extracted only from the distillate, the amount of the tetrahydrofuran mixture to be treated with the aqueous alkali metal hydroxide solution will be reduced, and the extraction equipment can be small.

The lower the temperature and the higher the concentration of the alkali metal hydroxide aqueous solution when extracting methanol, the lower the concentration of methanol and water remaining in the tetrahydrone run after extraction, which is desirable. However, if the temperature is too low, the alkali metal hydroxide The viscosity of the aqueous solution increases, and in the case of a concentrated solution, there is a risk of solidification.Also, it is possible to achieve a high alkaline concentration by operating at high temperature under pressure, but the equipment such as extraction equipment and pumps This requires a pressurized type, which causes operational inconvenience.

Therefore, it is usually operated at normal temperature and pressure.

Next, the present invention will be explained in detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Tetrahydrofuran solution i containing 31 wt% methanol
oooy and 48wt% sodium hydroxide aqueous solution 100
0'? is continuously supplied to a mixing tank (2t) with an agitator,
After thorough mixing, the mixture was transferred to a static tank (2 tons) and separated into two layers.

The average residence time of the aqueous sodium hydroxide solution in the stabilization tank was 60 minutes.

Then, after extraction, methanol 3.5wt%, water 0.2wt%
681 g of tetrahydrofuran solution containing 1.5%
c1rL, length 50 (11771 glass tube with diameter 41
It was distilled using a distillation apparatus equipped with a packed column filled with 1 lrIL of Fenske, and 90 g of a tetrahydrofuran solution containing 26 wt% methanol and 0.8 wt% water was poured from the top of the column.
At the bottom of the tower, only water is added at 0.1. 591 g of tetrahydrofuran containing wt% was obtained.

Also, during extraction, the tetrahydrofuran dissolved in the aqueous layer is 6.0% of the tetrahydrofuran before extraction. It was 0 wt%.

Example 2 A tetrahydrofuran solution containing 10 wt% methanol and a 48 wt% aqueous sodium hydroxide solution were continuously supplied at a weight ratio of 1:1 to the apparatus used in Example 1, methanol was extracted, and tetrahydrofuran was extracted. was separated.

The average residence time of the aqueous sodium hydroxide solution in the stabilization tank was 60 minutes.

The concentration of methanol in tetrahydrofuran after extraction is 2
5wt%, the concentration of water is 0.2wt%, and the tetrahydrofuran dissolved in the water layer is 0% of the tetrahydrofuran before extraction.
．． It was 1wt%.

Example 3 A tetrahydrofuran solution containing 31 wt% methanol and 6 wt% water and a 48 wt% aqueous sodium hydroxide solution were continuously supplied to the apparatus used in Example 1 at a weight ratio of 1:1 to extract methanol. was carried out to separate tetrahydrofuran.

The average residence time of the aqueous sodium hydroxide solution in the stabilization tank was 60 minutes.

The concentration of methanol in tetra and dorofuran after extraction is 4
．． The concentration of water was 0.5 wt%, and the tetrahydrofuran dissolved in the lower aqueous layer was 6.0 wt% of the tetrahydrofuran before extraction.

Example 4 In the apparatus used in Example 1, a tetrahydrofuran solution containing 31 wt% methanol and a 40 wt% aqueous sodium hydroxide solution were mixed at various weight ratios as shown in the table below, methanol was extracted, and tetrahydrofuran was separated. did.

The table below shows the concentrations of methanol and water in the tetrahydrofuran after extraction and the ratio of tetrahydrofuran dissolved in the aqueous layer to the tetrahydrofuran before extraction.

Example 5 Tetrahydrofuran solution 1 containing 60 wt% methanol
o00f was distilled using a distillation apparatus equipped with a glass tube having a diameter of 1.5 crrL and a length of 80 crrL and a packed column filled with Fenske of 4 mm in diameter to obtain a tetrahydrofuran solution 566i containing 30 wt% of methanol.

Next, this solution and a 48 wt% aqueous sodium hydroxide solution 6
0 (l) was continuously fed into the apparatus used in Example 1, methanol was extracted, and tetrahydrofuran was separated.

The average residence time of the aqueous sodium hydroxide solution in the stabilization tank was 60 minutes.

After extraction, the concentration of methanol in tetrahydrofuran is 3
．． 5 wt%, the water concentration is 0.2 wt%, and the tetrahydrofuran dissolved in the water layer is 6.5 wt% of the tetrahydrofuran after distillation. It was Owt%.

Reference example Tetrahydrofuran solution J containing 60 wt% methanol
- 0 0 0 P and 4-8 wt% sodium hydroxide 6
0 (l) was continuously fed into the apparatus used in Example 1, methanol was extracted, and tetrahydrofuran was separated.

The average residence time of the aqueous sodium hydroxide solution in the stabilization tank was 60 minutes.

After the extraction, the concentration of methanol in TeI-Rahydrofuran is 9wt%, the concentration of water is 1.5wt%, and the tetrahydrofuran dissolved in the aqueous layer is 3% of the tetrahydrofuran before extraction.
It was 0wt%.

Example 6 A tetrahydrofuran solution containing 31 wt% methanol and a 55 wt% potassium hydroxide aqueous solution were continuously supplied at a weight ratio of 1:1 to the apparatus used in Example 1, methanol was extracted, and tetrahydrofuran was separated. did.

The average residence time of potassium hydroxide in the static tank is 120
It was a minute.

The methanol concentration in tetrahydrofuran after extraction is 38
wt%, the concentration of water is 0.2wt%, and the tetrahydrofuran dissolved in the aqueous layer is 7% of the tetrahydrofuran before extraction.
It was 0wt%.

Comparative Example: Tetrahydrofuran solution containing 10% by weight of ethanol
oooy and 40% by weight aqueous sodium hydroxide solution 100
Of was continuously supplied to a mixing tank (2t) with a stirrer, and after sufficient mixing, it was transferred to a static tank (2t) and separated into two layers.

The average residence time of the aqueous sodium hydroxide solution in the stabilization tank was 60 minutes.

The composition of the tetrahydrofuran solution after extraction was 9.8% by weight of ethanol, 89.3% by weight of tetrahydrofuran, and 0.9% by weight of water.

Claims (1)

[Claims] 1. A method for separating tetrahydrofuran, which comprises contacting a mixture of methanol and tetrahydrofuran or a water-containing mixture thereof with an aqueous alkali metal hydroxide solution to extract methanol. 2. The method according to claim 1, wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide. 3. The method according to claim 1 or 2, wherein the azeotropic composition distillate obtained by distilling a mixture of methanol and tetrahydrofuran in which the methanol concentration is higher than the azeotropic composition is a mixture of methanol and tetrahydrofuran. 4. A mixture of methanol and tetrahydrofuran or a water-containing mixture thereof is brought into contact with an aqueous alkali metal hydroxide solution to extract and separate methanol, and the resulting concentrated tetrahydrofuran is distilled to distill off an azeotrope of methanol and tetrahydrofuran. A method for separating pure tetrahydrofuran. 5. The method according to claim 4, wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide. 6. The method according to claim 4 or 5, wherein the azeotropic composition distillate obtained by distilling a mixture of methanol and tetrahydrofuran whose methanol concentration is higher than the azeotropic value is a mixture of methanol and tetrahydrofuran.