JP2001226480A - Method for producing polyoxytetramethyleneglycol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing polyoxytetramethyleneglycol having an excellent color tone. SOLUTION: This method for producing the polyoxytetramethyleneglycol produced by the ring-opening polymerization of tetrahydrofuran in the presence of acetic anhydride and an acid catalyst, characterized by carrying out the ring-opening polymerization using the acetic anhydride having a diketene concentration of <=10 ppm. Thereby, the polyoxytetramethyleneglycol having improved transparency and an excellent color tone can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing polyoxytetramethylene glycol produced by subjecting tetrahydrofuran to ring-opening polymerization in the presence of acetic anhydride and an acid catalyst.

[0002]

2. Description of the Related Art Polyoxytetramethylene glycol (hereinafter abbreviated as PTMG) is a main raw material of polyurethane, polyetherester, polyether (ester) amide used for spandex, elastomer, artificial leather and the like, and a surfactant. It is an industrially useful polymer used for pressure fluids and the like. In recent years, it has attracted attention as an engineering material, a medical polymer material and the like mainly in the field of elastomers.

There are various methods for producing PTMG, and usually, polyoxytetramethylene glycol diester is obtained by ring-opening polymerization of tetrahydrofuran (hereinafter abbreviated as THF) in the presence of acetic anhydride and a solid acid catalyst. (Hereinafter abbreviated as PTMGAC), and then
A method for producing PTMG by hydrolysis or transesterification with a lower alcohol in the presence of an alkali catalyst is known (for example, see JP-A-4-306228).

[0004]

By the way, the conventional PTMG manufactured by the above-described method has a hue evaluation result which is an important index of the quality, for example, the APHA value is not always good, and the color is somewhat colored. However, there is a problem that PTMG is easily generated. The present invention has been made in view of the above problems, and an object of the present invention is to provide a production method capable of producing high-quality PTMG having excellent hue.

[0005]

Means for Solving the Problems In order to achieve the above object, the present inventor has conducted intensive studies on various factors affecting the quality of PTMG, and as a result, diketene contained in acetic anhydride has been found to reduce the quality of the product. The inventors have found that they have a great effect, and have accomplished the present invention.

That is, the method for producing PTMG of the present invention is a method for producing PTMG produced by subjecting THF to ring-opening polymerization in the presence of acetic anhydride and an acid catalyst, wherein acetic anhydride having a diketene concentration of 10 ppm or less is produced. The above-mentioned ring-opening polymerization is carried out to produce PTMG.

In this case, if acetic anhydride having a diketene concentration of 2 ppm (detection limit) or less and containing almost no diketene is used, PTMG having further excellent hue can be produced.

[0008] As described above, the diketene concentration is 2 ppm.
(Detection limit) The following acetic anhydride can be produced, for example, by distilling crude acetic anhydride and then treating it with an ozone-containing gas.

[0009]

Next, an embodiment of the present invention will be described in detail. In the method for producing PTMG of the present invention, PTGMAC is produced by subjecting THF to ring-opening polymerization in the presence of acetic anhydride and an acid catalyst, and then hydrolyzed or reacted with a lower alcohol and an ester in the presence of an alkali catalyst in substantially the same manner as described above. In exchange, PTMG is manufactured.

In this case, first, as the acetic anhydride used in ring-opening polymerization of THF, the diketene concentration is 10%.
Less than ppm of acetic anhydride is used. The method for producing such acetic anhydride is not particularly limited, but acetic anhydride obtained by subjecting crude acetic anhydride to ozone treatment and then distillation can be used. By such a purification treatment, purified acetic anhydride having a diketene concentration of about 5 ppm can be obtained.

The method for producing crude acetic anhydride is not particularly limited. For example, ketene is generated by thermally decomposing acetic acid, and the ketene is allowed to undergo an absorption reaction with acetic acid.
There are a method of obtaining acetic anhydride (ketene method) and a method of reacting carbon monoxide with methyl acetate or dimethyl ether to obtain acetic anhydride. The crude acetic anhydride obtained by these methods is applied.

On the other hand, if the crude acetic anhydride obtained as described above is subjected to a purification step of first performing distillation and then performing ozone treatment, the diketene concentration is 2 ppm (detection limit) or less, and almost no diketene can be obtained. It is possible to obtain purified acetic anhydride free of acetic anhydride. A method for purifying acetic anhydride in this case will be described.

First, there is no particular limitation on the type of distillation column used for the primary purification by distilling the crude acetic anhydride, and it can be freely selected. Generally, it is possible to use one or more selected from tray columns such as sheave trays, bubble cap trays and valve trays, and packed towers such as interlock saddles, pole rings and sulzer packs.

In the case of a plate tower, it is preferable to use about 20 to 80 trays, and in the case of a packed tower, it is preferable to use a tray having a filling height corresponding thereto. Acetic anhydride to be purified is introduced from the middle part of the distillation column. The introduction position must be higher than the recovery position of the product acetic anhydride, and preferably the upper part is selected from the center of the distillation column. The product acetic anhydride is recovered by steam or liquid from below the raw material introduction stage, preferably below the center of the distillation column.

The operating pressure of the distillation column is not particularly limited. If the pressure is too high, an undesirable reaction may occur due to an increase in the temperature in the column. Conversely, if the pressure is too low, the vapor Difficult to condense. Therefore, the desired operating pressure is 100 mmH
g to normal pressure.

A part of the condensate of the vapor at the top is returned to the top as a reflux liquid.
The so-called reflux ratio is determined by the composition of the raw material liquid, the required product quality, and the like. Usually, it can be selected from a range of about 1 to 1,000.

Next, the primary purification is performed using the distillation column as described above.
A place for secondary purification of the crude acetic anhydride produced by ozone treatment
In this case, the ozone-containing gas used for this purpose is not particularly limited.
Industrially, generally air or oxygen is used as raw material,
A method of generating ozone by discharging is used. Through
Usually, in the case of air raw material, the concentration of ozone is 10 to 20 g / m
^ThreeIt is. The proportion of ozone in contact with acetic anhydride
The reaction is completely completed, taking into account its own decomposition reaction.
It is better to add a little excess ozone to make it work. Practical
Above is more suitable for experiments considering gas-liquid contact efficiency, purification rate, etc.
It is necessary to make an appropriate decision.
~ 300g-O_Three/ T, preferably 90 to 270
g-O_Three/ T.

The type of the reactor for ozone treatment is not particularly limited as long as the contact between ozone and acetic anhydride can be performed well, but in practice, a bubble column system and a stirring tank system are preferable. Further, the contact time may be set to an appropriate time within a range of several tens of seconds to several tens of minutes. The reaction temperature is suitably around room temperature, preferably about 20 to 30 ° C. If the temperature is too low, the reaction rate decreases, and if the temperature is too high, ozone itself is easily decomposed, which is not preferable.

According to such a purification method, purified acetic anhydride having a diketene concentration of 2 ppm (detection limit) or less can be obtained.

On the other hand, the acid catalyst used in the ring-opening polymerization of THF is not particularly limited, and any known acid catalyst can be used. For example, a solid acid catalyst such as a super strong acid cation exchange resin, bleaching earth, zeolite and the like can be mentioned. Liquid acids such as perchloric acid can also be used, but this is industrially disadvantageous because the process of neutralizing and / or separating the acid after ring-opening polymerization is complicated. It is preferable to use a solid acid catalyst because the catalyst can be easily separated. The solid acid catalyst comprises a suspension bed,
Although any of fixed beds can be used, it is particularly preferable to use it in a fixed bed flow reaction because there is no need to separately perform a catalyst separation operation.

The reaction conditions for the ring-opening polymerization of THF vary depending on the molecular weight of the target PTMG and the type of acid catalyst used, but are usually 0.1 to 50% by weight as the concentration of the acid catalyst in the reaction solution. 0.1 concentration of acetic anhydride
It is used at about 30% by weight.

The reaction temperature is usually selected from the range of 0.5 to 10 hours. Since the obtained polymerization reaction solution contains PTMGAC and unreacted raw materials, the unreacted TH is usually used.
F and acetic anhydride are distilled off under normal pressure or reduced pressure. By such a manufacturing method, PTMGAC is manufactured from THF. Then, the production of PTMG from this PTMGAC,
Usually, in the presence of an alkali catalyst, the terminal ester group is converted to a hydroxyl group by hydrolysis or alcoholysis.

First, the case of producing PTMG by hydrolysis in the presence of an alkali catalyst will be described. The alkali hydrolysis is a method in which an aqueous alkali solution is added in the presence of an organic solvent and the mixture is heated to replace the terminal ester group with a hydroxyl group. As the organic solvent, compounds that separate from water, such as aromatic hydrocarbons such as benzene, toluene, and xylene, aliphatic alcohols such as n-butanol, and aliphatic ethers such as di-isopropyl ether are used.

As the alkali catalyst, hydroxides of alkali metals and alkaline earth metals such as sodium hydroxide, potassium hydroxide and calcium hydroxide are used. These hydroxides are usually used as an aqueous solution. This aqueous solution is usually used at a concentration of 1 to 50% by weight.

The amount of the aqueous solution depends on the PTMG used.
Depending on the weight of water relative to AC, usually PT
The weight of water with respect to MGAC is 0.1 to 10 times, and P
It is used in such a range that the alkali concentration in the total weight of TMGAC, water and alkali is 0.01 to 40% by weight. The alkali hydrolysis temperature varies depending on the alkali concentration and the type of alkali used, but is usually 50 to 1%.
It is performed in the range of 50 ° C. The alkali hydrolysis time also varies depending on the alkali concentration, the type of alkali used and the hydrolysis temperature, but is usually in the range of 0.1 to 20 hours.

The reaction crude liquid containing water after the completion of the alkaline hydrolysis is separated into an organic layer and an aqueous layer by, for example, a centrifugal separator, and the collected organic layer is subjected to evaporation with a short residence time such as a thin film evaporator. The product PTMG is obtained by evaporating the organic solvent and water using a vessel.

Next, a case where PTMG is produced from PTMGAC by replacing the terminal ester group with a hydroxyl group by alcoholysis in the presence of an alkali catalyst will be described.

Alcolysis is a method for producing PTMG using an aliphatic alcohol such as methanol while removing a by-produced carboxylic acid ester by azeotropic distillation with the alcohol by reactive distillation. As the alcohol, ethanol, butanol, or the like is used in addition to methanol. Among them, methanol is most preferable in terms of cost, reactivity, and separability between the ester formed by the reaction and the starting alcohol.

As the alkali catalyst, an alkaline earth metal oxide or an alkali metal or an alkaline earth metal alcoholate is used. As the alkaline earth metal oxide, magnesium oxide, calcium oxide, and strontium oxide are preferable. This catalyst is usually used in the form of a powder, but may be used in the form of a tablet, and may be appropriately selected depending on the reaction system and the method of separating the catalyst.

The amount of the catalyst used is usually from 0.1 to 10% by weight, more preferably from 0.5 to 3% by weight, based on the catalyst concentration in the reaction crude liquid. When the catalyst is a powder, the catalyst concentration may be low because the contact surface area per unit weight of the catalyst with the reaction crude liquid is large, but in the case of a tablet-formed catalyst, the contact area per unit weight of the catalyst is small. The higher the catalyst concentration, the more preferable.

On the other hand, when an alkali metal or alkaline earth metal alcoholate is used as the alcoholysis catalyst, the catalyst concentration varies depending on the type of the catalyst.
It is used in the range of ３3% by weight. Moreover, it is usually used in the form of an alcohol solution in terms of ease of handling.

Although the reaction temperature of the alcoholysis is not particularly limited, it is usually carried out at normal pressure at a temperature of 30 to 120 ° C. If a reaction with an alcohol having a reaction temperature exceeding 120 ° C. under normal pressure is carried out, the hue of the final product deteriorates.
It is preferable to carry out the reaction under reduced pressure so as to reach 20 ° C. Conversely, if the reaction temperature is too low, it takes too much time until the reaction becomes simple, which is not preferable. Furthermore, when low-boiling alcohols such as methanol and ethanol are used,
The reaction may be carried out under pressure in order to raise the reaction temperature of the kettle of the distillation column and to shorten the time until the reaction is completed.

The alcoholysis may be performed in a batch mode or a continuous mode. In the case of the batch mode, the catalyst and the PTM are placed in a batch distillation tower equipped with a reflux device.
GAC and alcohol were charged and reactive distillation was performed.
After distilling off the carboxylic acid ester formed in the kettle by azeotropic distillation with the alcohol, the reaction is carried out until the top temperature reaches the boiling point of the alcohol to complete the alcoholysis.

In the case of a continuous method, a catalyst, PTMGA
C and the alcohol are continuously charged into a continuous distillation column so that a residence time for completing the reaction can be obtained, and the carboxylic acid ester formed from the top of the continuous distillation column is continuously converted in the form of an azeotrope with the starting alcohol. And the unreacted alcohol, the generated PTMG and the catalyst are continuously withdrawn from the kettle. The distillation column in this case differs depending on the type, filler, and distillation method (continuous distillation and batch distillation), but it is preferable to use a distillation column having 20 to 100 theoretical plates.

When a distillation column having a low theoretical plate number is used, it becomes difficult to separate the azeotropic mixture of the starting alcohol and the produced carboxylic acid ester from the starting alcohol. Usually, the azeotropic mixture of the raw material alcohol and the generated carboxylic acid ester is incinerated, and if the azeotropic mixture of the raw material alcohol and the generated carboxylic acid ester and the raw material alcohol are poorly separated, the use amount of the raw material alcohol increases. Is not preferred. Conversely, if a distillation column with a high theoretical plate number is used, an azeotropic mixture of the raw material alcohol and the generated carboxylic acid ester and more stages required for separating the raw material alcohol will be stacked, and the equipment cost will increase. In addition, running costs also increase.

The reaction time (residence time) of alcoholysis is as follows:
Catalyst concentration, reaction temperature, raw material alcohol and PTMGA
Although it is determined by the molar ratio of C and the like, it is usually carried out in the range of 1 to 10 hours. If the reaction time is too long, there is an extra residence time even though the reaction is over, resulting in a decrease in PTMG production. Conversely, if the reaction time is too short, PTMG due to alcoholysis of PTMGAC will result. Is not completed. Note that P
Since ester residues in TMG degrade the quality of products such as polyurethane produced from PTMG, PTMGAC
It is necessary to complete the reaction for producing PTMG from the product.

The molar ratio between PTMGAC and alcohol used in alcoholysis varies depending on the number average molecular weight and degree of dispersion of PTMGAC, but the molar ratio of alcohol to PTMGAC is usually selected from the range of 3 to 100. Here, if the molar ratio of the alcohol to PTMGAC is too low, the alcoholysis becomes very slow, and the reaction time is prolonged, and the reaction may not be completed. Conversely, if the molar ratio of alcohol to PTMGAC is too high, the energy cost required for alcoholysis and the amount of alcohol to be flushed after alcoholysis increase, which is not preferable because the energy cost increases.

In the presence of an alkaline earth metal oxide catalyst, P
When there is an insoluble catalyst in the crude reaction liquid from the bottom of the distillation column produced by the alcoholysis of TMGAC, the catalyst is usually separated and removed by filtration or centrifugation to recover and recycle the unreacted alcohol. Flash using a flash device with a short residence time such as a thin film evaporator.

Since the crude PTMG discharged from the thin film evaporator contains catalyst components dissolved in the reaction crude liquid, water and crude PTM are used to remove these catalyst components and oligomers.
TMG and TMG are charged into a stirring tank and stirred for several hours while heating. After completion of the stirring and washing, the liquid is separated by a centrifugal separator, then separated into an aqueous layer and an organic layer, and the organic layer is collected.The organic solvent and water are separated using an evaporator having a short residence time such as a thin film evaporator. Evaporate to obtain the product PTMG.

According to the above-mentioned production method, in particular, as the acetic anhydride used in the step of producing PTMGAC by first performing ring-opening polymerization of THF, a diketene concentration of 10 pp
By using purified acetic anhydride of m or less, preferably 2 ppm or less, PTMG excellent in hue can be obtained.

[0041]

The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

First, as a product acetic anhydride used for the production of PTMG, three types of product acetic anhydride were obtained by changing the purification method as in the following experiments No. 1 to No. 3.

[Experiment No. 1 (purification method: distillation + ozone treatment)] Ketene obtained by thermal decomposition of acetic acid was absorbed into acetic acid through a ketene furnace to obtain crude acetic anhydride. Were passed through a de-boiling tower and a de-boiling tower each at normal pressure to carry out a primary purification treatment. Then, the crude acetic anhydride subjected to the primary purification was treated as shown in FIG.
The ozone treatment was performed using the experimental apparatus shown in FIG.

In FIG. 1, 1 is an ozone generator,
2 is a packed tower. Ozone is generated by the ozone generator 1 using air as a raw material, and the ozonized air (mixed gas of ozone and air) emitted from the ozone generator 1 has an inner diameter of 5 mm ×
It was introduced into the packed tower 2 loaded with a 5 mm high Raschig ring from below. The amount of ozonized air at this time is 42 NL
/ H, ozone concentration 19.0 g / Nm ³ , ozone inflow 38.
3 mol / H. On the other hand, the crude acetic anhydride which had been subjected to the primary purification treatment by distillation as described above was charged from the upper part of the packed tower 2 and brought into countercurrent contact with ozone to perform ozone treatment. The ozone-treated product acetic anhydride was withdrawn from the lower part of the packed tower 2 and collected. At this time, the charged flow rate of acetic anhydride was 6006 g / H, and the ozone usage rate was 13%.
A 4.3g-O ₃ / T. The diketene concentration of the crude acetic anhydride was 76 ppm. The diketene concentration in the obtained product acetic anhydride was below the detection limit (2 ppm).

[Experiment No. 2 (purification method: ozone treatment + distillation)] In the apparatus shown in FIG. 1, the ozone concentration was 20 g / Nm.
³ ozonated air was introduced at a rate of 150 NL / H from the lower part of the packed tower 2. On the other hand, crude acetic anhydride was charged from the upper part of the packed tower 2 at 6000 g / H, and brought into countercurrent contact with ozone to perform ozone treatment. The ozone-treated acetic anhydride extracted from the lower part of the packed tower 2 is continuously introduced at 400 g / H into the 13th stage from the top of a distillation column (40 mm in diameter, made of glass) having 30 stages of sieve trays, and the reflux ratio is set. The operation was performed at 200 at the top pressure of 1 atm. The concentrated low-boiling material was continuously withdrawn at 2 g / H from the condensate at the top of the column, and the purified acetic anhydride was continuously withdrawn at a rate of 392 g / H from the 27th stage from the top by steam side cut. Also, acetic anhydride containing a high-boiling substance was continuously extracted at a rate of 6 g / H from the bottom of the column. 27
The diketene concentration of the purified acetic anhydride extracted from the stage is 7p
pm.

[Experiment No. 3 (purification method: distillation only)] Crude acetic anhydride was continuously supplied to a 13-stage surface of a distillation column (40 mm in diameter, made of glass) having 400 stages of sieve at 400 g / H. The reactor was operated at a reflux ratio of 200 and a top pressure of 1 atm. The concentrated low-boiling material was continuously withdrawn at 2 g / H from the condensate at the top of the column, and the purified acetic anhydride was continuously withdrawn at a rate of 392 g / H from the 27th stage from the top by steam side cut. Also, acetic anhydride containing a high-boiling substance was continuously extracted at a rate of 6 g / H from the bottom of the column. The diketene concentration of the purified acetic anhydride extracted from the 27th stage was 98 ppm.

Next, the production example of PTMG using the product acetic anhydride obtained in the above-mentioned experiment No. 1 will be described in Example 1 and Experiment N.
A production example of PTMG using the product acetic anhydride of Example No. 2 will be described as Example 2, and a production example of PTMG using the product acetic anhydride of Experiment No. 3 will be described as Comparative Example 1.

Example 1 2000 parts by weight of THF, experiment
332 parts by weight of acetic anhydride having a diketene concentration below the detection limit obtained in No. 1 was reacted at 40 ° C. for 8 hours in a reactor equipped with a stirrer using 100 parts by weight of zirconia-silica powder calcined at 800 ° C. as a catalyst. I let it. After completion of the reaction, the catalyst was filtered, and unreacted THF and acetic anhydride were distilled off from the colorless polymerization solution under reduced pressure to obtain PTMGAC. Then, this PT
A mixture of 1000 parts by weight of MGAC, 1000 parts by weight of methanol, and 1 part by weight of calcium hydroxide was charged into a reactor equipped with a distillation column having 20 theoretical plates, and stirred under stirring.
The mixture was heated by boiling for an hour, and transesterification was performed while distilling an azeotropic mixture of methanol / methyl acetate from the top of the distillation column.

After cooling, the reaction solution was filtered through a pressure filter equipped with a 1 μm filter to remove calcium hydroxide, thereby obtaining 1910 parts by weight of a colorless and transparent filtrate. The filtrate was passed through an adsorption tower at 30 ° C. filled with a sulfonic acid type strongly acidic cation exchange resin to remove dissolved calcium hydroxide.

After removing most of the methanol from the treatment liquid under normal pressure using an evaporator, the heating medium temperature was reduced to 25 at a reduced pressure of 10 torr.
Continuous treatment in a thin film evaporator operated at 0 ° C. yielded 870 parts by weight of PTMG substantially free of methanol.
Table 1 shows the hue evaluation results of the obtained PTMG.

Example 2 The diketene concentration obtained in Experiment No. 2 was 7 as the acetic anhydride used in the ring-opening polymerization of THF.
PTMG was produced in the same manner as in Example 1 except that ppm was used. Table 1 shows the hue evaluation results of the obtained PTMG.

[Comparative Example 1] The diketene concentration obtained in Experiment No. 3 was 9 as the acetic anhydride used in ring-opening polymerization of THF.
PTMG was produced in the same manner as in Example 1 except that 8 ppm was used. Table 1 shows the hue evaluation results of the obtained PTMG.

[0053]

[Table 1]

As shown in the table, as the acetic anhydride used in ring-opening polymerization of THF, if the diketene concentration is 10 ppm or less, the acetic anhydride having a higher diketene concentration is used. Compared with the PTMG, the color tone is greatly improved, and if acetic anhydride having a diketene concentration below the detection limit and containing almost no diketene is used, colorless and transparent high-quality PTMG can be obtained.

[0055]

As described above, according to the present invention, PTMG having excellent hue can be produced by using acetic anhydride having a low diketene concentration.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an apparatus used for performing ozone treatment on crude acetic anhydride.

[Explanation of symbols]

 1 ozone generator 2 packed tower

Claims (2)

[Claims] 1. A process for producing polyoxytetramethylene glycol, which is produced by subjecting tetrahydrofuran to ring-opening polymerization in the presence of acetic anhydride and an acid catalyst, the process comprising using acetic anhydride having a diketene concentration of 10 ppm or less. A method for producing polyoxytetramethylene glycol, comprising producing polyoxytetramethylene glycol by performing ring polymerization. 2. The method for producing polyoxytetramethylene glycol according to claim 1, wherein said diketene concentration is 2 ppm or less.