JPH0629280B2 - Purification method of crude tetrahydrofuran - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for purifying crude tetrahydrofuran (hereinafter, abbreviated as crude THF).

More specifically, it relates to a method for obtaining high-purity tetrahydrofuran (hereinafter abbreviated as THF) by treating crude THF with a strongly acidic cation exchange resin and then hydrogenating it in the THF purification step.

THF is an extremely useful substance as an organic solvent or a raw material for producing a polymer compound such as polytetramethylene glycol (hereinafter abbreviated as PTMG).

[Conventional technology]

Conventionally, various methods for producing THF have been proposed,
For example, a method of catalytically hydrogenating furan obtained by decarbonylation of furfural, a method of cyclodehydrating 1,4-butanediol, or a diacetic acid ester of 1,4-butanediol in the presence of an acid catalyst is treated with water. There is a method of reacting.
The THF obtained by these methods contains various impurities such as dihydrofuran (hereinafter abbreviated as DHF), butyraldehyde (hereinafter abbreviated as NBD), propionaldehyde, and crotonaldehyde, depending on the production method. .
The presence of these impurities, even in a small amount, makes them unusable as raw materials for resins, fibers, etc. when used in PTMG, which is the main use of THF, because of the increase in acid value or due to the coloring tower. Value is significantly reduced. However, since these impurities, especially DHF and NBD, have a boiling point close to that of THF, it requires a high number of stages and high reflux when separated by an ordinary separation means such as distillation, which requires expensive equipment and a large amount of heat. Needed and not economical.

[Problems to be solved by the invention]

In view of the above circumstances, the inventors of the present invention have made extensive studies on a method for purifying crude THF containing impurities that are difficult to separate by distillation, and as a result,
Impurities contained in the crude THF by treatment of the crude THF with a strongly acidic cation exchange resin and hydrogenation treatment,
The inventors have found that highly pure THF can be obtained by converting it into THF or a compound that can be easily distilled and separated from THF, and completed the present invention.

[Means for solving problems]

The gist of the present invention is that (1) crude tetrahydrofuran containing at least one of dihydrofuran and butyraldehyde is added to (a) water and / or water in a reaction zone consisting of a strongly acidic cation exchange resin.
Alternatively, at least a part of dihydrofuran is converted into hydroxytetrahydrofuran and / or acetoxytetrahydrofuran by contacting with acetic acid, and (b) the reaction liquid from the reaction zone of the above (a) is supplied to an acetic acid separation column, and hydroxyl is introduced from the bottom of the column. A water-acetic acid bottoms solution containing tetrahydrofuran and / or acetoxytetrahydrofuran is withdrawn, and a water-tetrahydrofuran mixture containing butyraldehyde and / or dihydrofuran is distilled from the top of the column, and (c) the water-tetrahydrofuran mixture is used as a noble metal catalyst. Of butyraldehyde and / or dihydrofuran to n-butanol and / or tetrahydrofuran by hydrogenation in the presence of (d), and (d) the hydrogenation reaction product liquid of (c) above is supplied to the dehydration tower through the liquid phase portion after gas-liquid separation. Then, the water-tetrahydrofuran azeotrope is distilled from the top of the tower, and the bottom of the tower is distilled. Was out cans tetrahydrofuran containing boiling substances consists in bottoms were fed to the product column, the purification method of the crude tetrahydrofuran which comprises bringing distilled highly pure tetrahydrofuran from the top of the (e) (d).

Hereinafter, the present invention will be described in more detail.

The crude THF purified by the present invention includes DHF and NBD.
Is not particularly limited as long as it contains at least one of the above, a method of catalytic hydrogenation of furan, a method of cyclodehydration of 1,4-butanediol, or a diacetic acid of 1,4-butanediol. Although it may be produced by any method such as a method of reacting an ester with water in the presence of an acid catalyst, the following is produced by hydrolyzing a diacetic acid ester of 1,4-butanediol: The case of dehydration cyclization of 4-butanediol will be described.

1,4-Butanediol diacetate ester is obtained by hydrogenating 1,4-diacetoxybutene obtained by reacting butadiene and acetic acid with molecular oxygen in the presence of a palladium-based catalyst in the presence of a hydrogenation catalyst. It is obtained by doing. The reaction product is a mixture of 1,4-diacetoxybutane and 1,2-diacetoxybutane, and further contains water, acetic acid, butyl acetate, high-boiling aldehydes, and a small amount of acetals, but is particularly purified. No need. The diacetoxybutane mixture is supplied together with water to a reactor filled with a strongly acidic cation exchange resin, and a hydrolysis reaction is carried out at 40 to 80 ° C. The reaction solution is distilled to remove water and acetic acid, and the liquid phase portion consisting of 1,2- and 1,4-butanediol, mono- and acetic acid ester is 1,2-butanediol in the isomer separation column. The mono- and di-acetic acid ester was distilled off, and the bottoms containing 1,4-butanediol and the mono- and di-acetic acid ester were further fed to a high boiling point separation column to separate the high boiling point product. ,Four
-Butanediol is obtained. The crude 1,4-butanediol is supplied to a THF-forming reactor filled with a strongly acidic cation exchange resin, and the reaction is carried out at 40 to 90 ° C. The reaction product liquid is mainly composed of water, acetic acid and THF by distillation. The distillate is distilled off, and the distillate is further fed to a distillation column operated under normal pressure to distill off the water-THF azeotrope. The water
The THF azeotrope contains at least one of DHF and NBD as impurities, and satisfies the requirement of the raw crude THF to be purified in the present invention.

The amount of DHF and NBD contained in the crude THF to be purified is not particularly limited, and is an amount contained in the crude THF produced by various known methods. 500 ppm and NBD are about 0 to 1000 ppm.

According to the present invention, by subjecting such crude THF to hydrogenation treatment, DHF contained in the crude THF is converted into THF,
It is possible to convert NBD into n-butanol to facilitate separation from THF and obtain high-purity THF. However, in the present invention, prior to the hydrogenation treatment, the crude THF as the raw material of the present invention is converted to water. And / or by reacting with acetic acid, at least a part of the impurity DHF is converted into THF.
It is converted to hydroxytetrahydrofuran and / or acetoxytetrahydrofuran which are easily separated by distillation.
This reaction is carried out in the presence of a solid acid catalyst such as a strongly acidic cation exchange resin, preferably a sulfonic acid type cation exchange resin. When the raw material crude THF and water and / or acetic acid are contact-reacted with the solid acid catalyst, the reaction temperature is 30 to 80 ° C., LH
The SV (liquid space velocity) is about 0.5 to 5 hr ^-1 .

The reaction solution is supplied to an acetic acid separation column (third distillation column), a water-THF azeotrope mixture containing butyraldehyde and a part of dihydrofuran is distilled from the top of the column, and hydroxytetrahydrofuran and / or acetoxytetrahydrofuran from the bottom of the column. And a liquid phase portion containing water and / or acetic acid as a main component is extracted as a bottom liquid. The third distillation column is operated at atmospheric pressure,
Number of theoretical plates 8-15, bottom temperature 100-110 ° C, reflux ratio
It is about 0.5 to 2.0. The water-THF azeotrope distilled from the top of the column is then fed to the hydrogenation step.

The overhead fraction from the third distillation column is subjected to hydrogenation treatment in the presence of a noble metal hydrogenation catalyst supported on a carrier in a hydrogenation step, so that a trace amount of DHF and NBD can be treated with T, respectively.
Convert to HF and n-butanol. As the hydrogenation catalyst, a catalyst having an ability to reduce aldehydes to alcohols and / or a noble metal catalyst having an ability to hydrogenate a carbon-carbon unsaturated double bond is used, and specifically,
A noble metal catalyst such as ruthenium, palladium or platinum can be used. These hydrogenation catalysts have sufficient action alone, but two or more types can be used in combination. Nickel catalysts known as hydrogenation catalysts are active at relatively high temperatures, but at high temperatures the hydrogenolysis of THF increases, so the temperature must be selected appropriately. In the invention of the present application, it is also possible to use a palladium or platinum catalyst and a ruthenium catalyst, one layer each.

As the carrier, activated carbon, silica gel, silica alumina,
Examples include clay, bauxite, magnesia, diatomaceous earth, and pumice stone. Hydrogen does not necessarily have to be pure, and may be diluted with an inert gas, saturated hydrocarbon or the like. The hydrogen partial pressure can be implemented if it is 1 kg / cm ² or more, but the use of high pressure requires expensive equipment.
If the pressure is too low, a large amount of catalyst is required,
Hydrogen partial pressure of 5kg / cm ² ~20kg / cm ² is preferred. The reaction temperature is in the range of 30 to 200 ° C., but the hydrogenolysis of THF is remarkable on the high temperature side, and a large amount of catalyst is required on the low temperature side, so 50 to 120 ° C. is preferable.

By the hydrogenation reaction, DHF and / or NBD in crude THF are converted into THF and n-butanol, etc., respectively.

The reaction product is transferred to a gas-liquid separator maintained at normal pressure, and after separating the gas-phase exhaust gas, the liquid phase part is supplied to the first distillation column which is a dehydration column, and water-THF coexists from the top of the column. The boiling mixture is distilled off, and dehydrated THF containing a high boiling point is removed from the bottom of the column.

When the crude THF contains NBD, the n-butanol produced by the hydrogenation reaction is removed from the first distillation column together with the high boiling substances. Since the water-THF mixture forms an azeotrope with an increased water mole fraction under pressure, the first distillation column is preferably operated under pressure. The operating conditions of the first distillation column are 10 to 20 theoretical plates and 5 to 15 kg / cm ^{2 of} pressure.
G, the bottom temperature is 130 to 180 ° C, and the reflux ratio is about 0.1 to 1.0. The bottoms of the first distillation column are further supplied to the second distillation column which is a product column, and the high boiling substance containing about 10 to 50% of THF and optionally n-butanol is discharged from the bottom of the column and the high purity THF is collected from the top of the column. To get. The second distillation column is operated at a theoretical plate number of 15 to 30, a pressure of 760 to 1000 Torr, a column bottom temperature of 60 to 125 ° C., and a reflux ratio of about 0.1 to 1.5.
The water-THF azeotrope from the top of the first distillation column can be circulated and mixed with the raw material THF after separating water by distillation, if necessary.

The THF thus obtained from the second distillation column has a purity of 99.9.
It has a very high purity of at least%.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

Incidentally, the crude T used as a raw material in the following examples and comparative examples
HF is obtained by hydrogenating 1,4-diacetoxybutene obtained by acetoxylation of butadiene to 1,4-diacetoxybutane, and further hydrolyzing it to cyclize 1,4-butanediol. The manufactured one was used. Further, in the following description, "%" and "part" represent "wt%" and "part by weight", respectively.

Example 1 Containing 250 ppm of DHF and 550 ppm of NBD, water 9.9
%, Acetic acid 23.0%, THF 67.1% as a mixture of sulfonic acid type strong acid cation exchange resin DIAION SK1
715 parts / in a reaction tower filled with B (manufactured by Mitsubishi Kasei Co., Ltd.)
It was introduced at hr and reacted. Reaction tower at 50 ℃, 2kg / cm
I drove at ² G. The liquid flowing out of the reaction tower contains 185 ppm of hydroxytetrahydrofuran, 190 ppm of acetoxytetrahydrofuran, and 540 ppm of NBD, and DHF is 1
It was 0 ppm or less. The reaction tower effluent was supplied to water and an acetic acid separation tower (third distillation tower) together with 394 parts / hr of the first distillation tower distillate, and a bottoms containing water and acetic acid as main components was discharged from the bottom of the tower to 2 times.
It was withdrawn at 35 parts / hr, and a distillate composed of water (5.9%) and tetrahydrofuran (94.0%) was distilled at 874 parts / hr from the top of the column.

The content of DHF, hydroxytetrahydrofuran and acetoxytetrahydrofuran in the distillate is 10 pp.
It was below m and NBD was 450 ppm. Distillate is R
U was fed to a reactor packed with a catalyst in which activated carbon was supported together with 0.5 part / hr of hydrogen. Hydrogenation reaction temperature is 100
℃, pressure 9.5kg / cm ² , residence time 0.5hr (empty cylinder standard)
I did it in.

N-Butanol in the liquid flowing out from the reactor was 475 pp
m and NBD were 10 ppm or less. This reaction solution was supplied to a dehydration column (first distillation column) operated under the conditions of 14 theoretical plates, a pressure of 8.5 kg / cm ² , and a reflux ratio of 0.3, and water 1
Distillate consisting of 3.1% and THF 86.9% 394 parts / h
Distilled at r, and the distillate was recycled to the third distillation column.
Crude T containing 50ppm of water and 850ppm of butanol from the bottom of the tower
HF was extracted at 480 parts / hr and supplied to a product column (second distillation column) operated under the conditions of 19 theoretical plates, a pressure of 760 Torr and a reflux ratio of 0.6.

THF containing 8.2% butanol and high boiling point was withdrawn from the bottom of the column at a rate of 5 parts / hr, and the bottom liquid was separated from the high boiling point raw material crude T
Mix with HF and collect THF. Product TH from the top of the tower
F was distilled at 475 parts / hr. The product has a purity of 99.9%
Above, the DHF and NBD contents are both 10 pp
It was less than m.

Comparative Example 1 Crude THF having the same composition as in Example 1 (715 parts / hr) and the first distillation column distillate (394 parts / hr) were simultaneously supplied to a third distillation column operated under the same conditions as in Example 1, and water was supplied from the top of the column. 5.9%, T
A distillate consisting of HF94.0% was distilled at 874 parts / hr, and a bottom liquid containing water and acetic acid as main components was distilled from the bottom of the column to 23
It was extracted at 5 parts / hr. Distillate is NBD 450ppm,
It contained 200 ppm of DHF. The distillate was supplied to a dehydration column (first distillation column) operated under the same conditions as in Example 1, consisting of water (13.1%) and THF (86.9%) from the top, and NBD5
A distillate containing 394 parts / hr of 0 ppm and 200 ppm of DHF was distilled, and the distillate was recycled to the third distillation column.

From the bottom of the first distillation column, DHF 360ppm, NBD82
480 parts / hr of bottom liquid containing 0 ppm and 50 ppm of H ₂ O was withdrawn, and a product column operated under the same conditions as in Example 1 (second
It was supplied to a distillation column). From the top of the second distillation column, the product TH
F470 parts / hr was withdrawn and the NBD concentration was 1.
0% of THF 10 parts / hr was extracted. NB in the product
The D concentration was 620 ppm and the DHF was 350 ppm.

〔The invention's effect〕

According to the present invention, in the crude THF purification step, by treatment with a strongly acidic cation exchange resin and hydrogenation treatment,
Impurities such as DHF and NBD, which are difficult to separate from THF by distillation, can be converted into compounds that can be easily separated from THF. THF can be obtained.

The THF obtained by the method of the present invention preferably has a purity of 99.9%.
Because of the extremely high purity described above, it has high product value as a raw material for resins and fibers.

Claims (1)

[Claims] 1. A crude tetrahydrofuran containing at least one of dihydrofuran and butyraldehyde is mixed with water and / or in a reaction zone comprising (a) a strongly acidic cation exchange resin.
Alternatively, at least a part of dihydrofuran is converted into hydroxytetrahydrofuran and / or acetoxytetrahydrofuran by contacting with acetic acid, and (b) the reaction liquid from the reaction zone of the above (a) is supplied to an acetic acid separation column, and hydroxyl is introduced from the bottom of the column. The water-acetic acid bottoms containing tetrahydrofuran and / or acetoxytetrahydrofuran is withdrawn, the water-tetrahydrofuran mixture containing butyraldehyde and / or dihydrofuran is distilled off from the top of the column, and (c) the water-tetrahydrofuran mixture is used as a noble metal catalyst. Of butyraldehyde and / or dihydrofuran to n-butanol and / or tetrahydrofuran by hydrogenation in the presence of (d), and (d) the hydrogenation reaction product liquid of (c) above is supplied to the dehydration tower through the liquid phase portion after gas-liquid separation. Then, the water-tetrahydrofuran azeotrope is distilled from the top of the tower, and the bottom of the tower is distilled. Was out cans tetrahydrofuran containing boiling substances, (e) the bottom liquid of (d) is supplied to the product column, the crude tetrahydrofuran purification method, characterized in that distilling the high-purity tetrahydrofuran from the top of the tower.