JP2001059020A - Production of polytetramethylene ether glycol - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for economically advantageously producing polytetramethylene ether glycol excellent in quality by which the separation and recovery of an unreacted lower alcohol included in the reaction liquid can be efficiently achieved in a short residence time. SOLUTION: This method for producing polytetramethylene ether glycol by carrying out an ester exchange of polytetramethylene ether glycol diacetate with a lower aliphatic alcohol in the presence of an oxide, a hydroxide or an alkoxide of an alkali metal or an alkaline earth metal, comprises treating the reaction liquid after the ester-exchange reaction by passing the reaction liquid through an evaporator and a gas-liquid contactor for counter-currently contacting the reaction liquid with an inert gas to separate and recover the lower aliphatic alcohol of an unreacted raw material in the reaction liquid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing polytetramethylene ether glycol (hereinafter sometimes abbreviated as PTMG). Specifically, polytetramethylene ether glycol diacetate (hereinafter, PT
(May be abbreviated as ME)) with a lower alcohol in the presence of an alkali metal or alkaline earth metal catalyst to produce a PTMG. P
TMG is used as a soft segment of polyester resin, urethane resin and the like, and is processed into industrial products such as rolls, shoe soles, elastic fibers for clothing (spandex and the like), and widely used in daily life.

[0002]

2. Description of the Related Art Various methods have been disclosed for the production of PTMG. Among them, tetrahydrofuran (hereinafter sometimes abbreviated as THF) may be used to prepare a solid acid catalyst and a carboxylic acid anhydride such as, for example, THF. A method of obtaining PTME by ring-opening polymerization in the presence of acetic anhydride and then transesterifying the PTME with a lower alcohol, for example, methanol in the presence of a basic catalyst to obtain PTMG is a method with less waste and an excellent method. is there. As solid acid catalysts, ion exchange resins, bleaching earths, zeolites and the like have been proposed.

In the transesterification of PTME, PTMG is obtained by transesterification with a lower alcohol, generally methanol, in the presence of a basic catalyst such as sodium methoxide. A mixture of the transesterification reaction solution, PTMG and methanol is subjected to a usual method such as neutralization or adsorption to remove the catalyst, and then methanol is separated and recovered. Since residual methanol has a great effect on the use of PTMG, as industrial raw materials are required to be as small as possible. PTMG is used as a soft segment for polyester elastomers and polyurethane elastomers. These elastomers are produced by condensation polymerization of PTMG and a dicarboxylic acid (for example, terephthalic acid) or dicarboxylic acid ester (for example, dimethyl terephthalate), or addition polymerization of PTMG and a diisocyanate (for example, diphenylmethane diisocyanate). In these condensation polymerization or addition polymerization, hydroxyl groups at both ends of PTMG react,
In order to obtain a high polymer, it is necessary that a monohydric monoalcohol, which causes end capping, be removed as much as possible. When a large amount of monoalcohol is present, it becomes unsuitable as an industrial raw material, for example, the volatile content during polymerization increases, or it becomes difficult to obtain a high molecular weight polymer.

[0004] Taking the production of polyurethane resin as an example,
For example, in PTMG obtained using methanol (molecular weight: 32) as an alcohol, PTMG having a methanol content of 0.1% by weight and an average molecular weight of 2,000 (about three hydroxyl-based sealing parts per 100 hydroxyl groups) is used, and diphenylmethane is used. When an adduct with a diisocyanate (molecular weight 250) is prepared, the maximum molecular weight of the polymer theoretically obtained is 75,000, but the methanol content is 0.01.
When an adduct is similarly prepared using PTMG having a weight% of 2000 and an average molecular weight of 2000, the maximum molecular weight of the polymer theoretically obtained is 750,000, and the residual amount of monoalcohol is large for the polymer formation reaction. You can see the effect. Further, when trying to produce a polymer having a higher molecular weight, PTMG in which a monoalcohol remains remains.
Cannot be used as a raw material. Therefore, PTMG used as an industrial raw material is required to have as little monoalcohol as possible.

As a method for separating and recovering the unreacted lower alcohol from the transesterification reaction liquid, for example, there is a method using a batch evaporator. However, in order to obtain a large amount of products, the equipment becomes large and is not practical. For this reason, a continuous distillation method using an evaporator equipped with a heating tube or a falling film evaporator is conventionally used.

[0006]

However, in the case of this method, the viscosity of the treatment liquid increases with the concentration of the polymer,
The deaeration movement speed gradually decreases. If a single evaporator is used to remove the lower alcohol concentration in PTMG to a trace level, it will take a long time to obtain the final polymer from the initial polymer diluent solution, which only lowers productivity. In addition, there is a problem that when the polymer is exposed to the heating condition for a long time, the quality represented by the hue is deteriorated.

The present invention solves the problem of a large amount of energy consumption and quality deterioration, which are problems when recovering a lower alcohol which is an unreacted raw material after a transesterification reaction in a method for producing PTMG by transesterification, An object of the present invention is to provide a method for industrially advantageously producing PTMG excellent in quality.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in view of the above circumstances, and have found that the transesterification reaction solution is provided in two stages by using an evaporator and a gas-liquid contact device for bringing an inert gas into countercurrent contact. By the treatment, the separation and recovery of the unreacted lower alcohol contained in the reaction solution can be efficiently achieved with a short residence time, thereby producing a PTMG which is economically advantageous and excellent in quality. Find out what you can do,
The present invention has been completed.

That is, the gist of the present invention is that polytetramethylene ether glycol diacetate is transesterified with a lower aliphatic alcohol in the presence of an alkali metal or alkaline earth metal oxide, hydroxide or alkoxide. In the method for producing tetramethylene ether glycol, after the transesterification reaction, the reaction solution is treated through an evaporator and a gas-liquid contacting device in which an inert gas is brought into countercurrent contact, and a lower aliphatic material as unreacted raw material in the reaction solution is obtained. A method for producing polytetramethylene ether glycol, which comprises separating and recovering an alcohol.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. (Production of PTMG) PTME used in the present invention is usually obtained by ring-opening polymerization of THF in the presence of a solid acid catalyst and acetic anhydride. As the catalyst, an ion exchange resin, bleaching earth, zeolite, silica alumina or the like is used. Solid acid catalysts are easy to separate and are suitable for fixed bed flow reactions.

Regarding the reaction conditions, the desired PTMG
The molar ratio of acetic anhydride / THF is usually 0.001 to 0.001 depending on the molecular weight of
0.3, the raw materials are charged so that the concentrations of acetic anhydride and the catalyst in the reaction solution are 0.5 to 30% by weight and 0.1 to 30% by weight, respectively, and the reaction temperature is usually 2%.
In the range of 0 to 80 ° C., the reaction pressure is atmospheric pressure or slightly under pressure, and the reaction time is usually 0.5 to 10 hours. The polymerization is carried out, and the molar ratio between THF and acetic anhydride is adjusted. Thereby, the molecular weight of the produced polymer can be adjusted. The polymerization reaction solution thus obtained contains the desired PT
Since unreacted THF and acetic anhydride are contained in addition to ME, these unreacted raw materials are usually distilled off under normal pressure or reduced pressure. The evaporated THF and acetic anhydride can be purified as necessary and reused in the reaction.

Next, a transesterification catalyst and an alcohol are added to the obtained polymer to carry out a transesterification reaction. As the transesterification catalyst, oxides, hydroxides or alkoxides of alkali metals such as sodium and potassium, and alkaline earth metals such as calcium and barium are preferably used. In particular, alkoxides of alkali metals, especially sodium, are preferably used because they have a high reaction rate and a high solubility in alcohols, and are easy to handle. As the lower alcohol, a lower alcohol having 1 to 4 carbon atoms is usually used. In particular, methanol is preferably used because it has a small molecular weight and a large molar ratio with PTME even with the same weight. The transesterification is carried out by using a catalyst in an amount of 0.001 to 1% by weight and a lower alcohol in a molar ratio of 5 to 50 times with respect to the acetate ester of PTMG. The reaction may be performed in the presence of a small amount of water.
Since the transesterification reaction is an equilibrium reaction, in order to obtain PTMG whose terminals are all hydroxyl groups, it is necessary to carry out the reaction while removing the acetic acid ester of the lower alcohol which is generated in some form. As a method therefor, there is a method in which a batch reactor equipped with a distillation facility is used, but the facility becomes large in order to obtain a large amount of products, which is not practical. A continuous transesterification method is desirable, and a method using a reactor equipped with a distillation facility is also conceivable, but the facility is expensive.

On the other hand, the reactive distillation in which the reaction and the separation are simultaneously performed in the distillation column is advantageous because the equipment is small. Reactive distillation to produce PTMG from PTME
For example, it is described in WO97 / 23559.
In this method, a mixture of PTME, a catalyst and a lower alcohol is supplied from the center of a distillation column to remove methyl acetate produced at the same time as transesterification. Further, heated methanol vapor is supplied from the lower part of the distillation column to complete the reaction. In this method, the PTM supplied to the distillation column is
Since the amount of E is large, the distillation column becomes large in order to complete the reaction. On the other hand, a method in which the raw material mixture charged in the distillation column is subjected to a transesterification reaction in advance to have a composition close to the equilibrium composition, thereby reducing the amount of PTME reacted in the distillation column and making the distillation column small, is economically advantageous. And is preferably used. The bottom liquid is a mixture of PTMG and a lower alcohol, but if the concentration of PTMG is increased, the viscosity increases and the thermosiphon of the reboiler does not work. . Further, as the viscosity increases, the flow of the liquid in the reboiler deteriorates. Therefore, it is preferable to flow the liquid in the reboiler by a pump as necessary.

(Separation and Recovery of Unreacted Lower Alcohol) In the present invention, the transesterification reaction solution from which the catalyst has been removed is treated using an evaporator and a gas-liquid contacting device for bringing an inert gas into countercurrent contact. And separating and recovering a lower alcohol contained in the reaction solution.

The evaporator to be used in the present invention is not particularly limited, but a jacket-type evaporator having a heating jacket outside the tank, and a Fos as an evaporator having heating tubes arranged horizontally.
ter-Wheeler can, Buffalo can, Yar
Standard evaporators, basket-type evaporators, Kestner evaporators, etc., evaporators with heating tubes arranged upright, inclined-tube evaporators, coils (coil tubes) as evaporators with heating tubes arranged diagonally, such as yan cans Examples of evaporators suitable for fluids having large viscosity, such as a mold evaporator and a plate (plate) evaporator, include a falling thin film evaporator and a forced circulation evaporator. Above all, a falling-film evaporator and a forced circulation evaporator are used for P
It is preferable to handle the TME polymerization reaction solution. Furthermore,
A forced circulation evaporator is particularly preferred because it has a high film heat transfer coefficient, has good evaporation efficiency, and can be installed at low cost. A forced circulation evaporator is a flash drum that supplies latent heat of evaporation with the sensible heat of the stock solution to perform equilibrium flash separation, a circulation pump that sends concentrated viscous liquid from the flash drum to a heating pipe,
An evaporator comprising a heating tube for heating the concentrated viscous liquid.

When the transesterification reaction solution is treated using a forced circulation evaporator, the operating conditions are as follows:
Although depending on the amount of processing, the processing temperature is usually 60 to 20.
0 ° C., the treatment time is usually 15 to 60 minutes, preferably 150 ° C. or lower, and 90 to 9 minutes of unreacted lower alcohol.
It is operated at 9%, more preferably below 100 ° C., to recover 92-98% of the unreacted lower alcohol. The composition of the mixture withdrawn from the evaporator is, for example,
When 60% by weight of PTMG and 40% by weight of methanol are used, 97% by weight of PTMG and 3% by weight of methanol under the conditions of normal pressure and 75 ° C.

The bottom mixture extracted from the evaporator is further processed in a gas-liquid contact device. The gas-liquid contact device for countercurrently contacting the inert gas used in the present invention is not particularly limited as long as it is a gas-liquid contact device having a function as a stripping tower.
As a gas-liquid contact device of the type for dispersing a liquid in a gas continuous phase, a packed tower, a spray tower, a scrubber, a wet wall tower, etc., as a gas-liquid contact device of a type for dispersing a gas in a liquid continuous phase, a bubble column, A step tower, a bubble stirring tank, and the like are included. An inert gas is used as the gas, and a type in which the bottom mixture and the inert gas are brought into countercurrent contact with each other, for example, an inert gas is passed from the bottom of the tower to lower the partial pressure of volatile substances in the bottom mixture A stripping tower is preferably used.

In the case of a stripping tower, the bottom mixture is sent to the upper part of the tower, and residual methanol is removed by an inert gas passed from the lower part of the tower. The stripping tower can be operated at normal pressure without any problem because the partial pressure of the volatile substance should be reduced, but it is more advantageous to operate at reduced pressure. Therefore, the stripping tower is 10 to 200 kPa,
It is preferably operated at 50 to 100 kPa. Since volatile components are separated by gas-liquid contact in the stripping tower, it is advantageous that the liquid viscosity is low, and the temperature is 100 to 2 which is hard to be deteriorated by heating.
It is operated at 50C, preferably at 130-230C. In addition, the type of the stripping tower is preferably a packed tower, a spray tower, or a scrubber capable of increasing the gas-liquid contact area, and among these, a packed tower that can shorten the residence time and is easily controlled is preferable.

In this case, the packing may be an irregular packing such as a Raschig ring or a pole ring, or an ordered packing. The ratio of the volume of charged gas to the charged liquid varies depending on the temperature in the column and the number of stages in the column.
Is used. An excessive volume ratio is disadvantageous as it leads to a loss of ventilation gas. The number of columns depends on the residence time, but is preferably 5 to 30 stages. A method in which the bottom mixture is directly charged to the stripping tower without passing through the first-stage evaporator may be considered. However, a PTMG solution containing 30 to 50% by weight of methanol has a strong foaming property, and foams are formed on the top of the tower. The resulting liquid is not preferable because it becomes wet or lowers the distillation efficiency and lowers the purity of the final product. In the contact between the liquid and the inert gas in the stripping tower, the liquid 1N
Usually, 1 to 100 Nl / min, preferably 5 to 5
It is preferable to use an inert gas at a flow rate of 0 Nl / min.

In this case, the inert gas includes nitrogen, carbon dioxide, a saturated hydrocarbon having 1 to 4 carbon atoms, and 1 to 4 carbon atoms.
At least one selected from aliphatic alcohols and dimethyl ether of the above is preferable, and among these, nitrogen is more preferable. In addition, about a stripping tower, Preferably 250 degreeC
Below, the residual amount of the lower alcohol in the polymer is 0.1
The operation is performed so that the residual amount is 0.01% by weight or less at a temperature of 230% by weight or less, more preferably 230 ° C or less.

The PTMG extracted from the bottom of the column is obtained by distilling the lower alcohol and finally having a viscosity (40 ° C.) of 200 to
Obtained as PTMG of 1400 mPa · s. Normal,
Industrially, the number average molecular weight is 500 to 3000 by the above method.
PTMG is obtained and used as a raw material for polyurethane elastic fiber, polyurethane elastomer or polyester elastomer.

[0022]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the examples unless it exceeds the gist thereof. In the preparation of the following raw materials and% and ppm in the examples, respectively,
% By weight and ppm by weight. (Preparation of raw materials) 100 parts of THF, 5.6 parts of acetic anhydride and 0.2 parts of acetic acid were added together with 3.5 parts of a zirconia silica catalyst to 40 parts.
The reaction was performed at 5 ° C. for 5 hours. After removing the catalyst by filtration, most of the unreacted substances were distilled off by batch distillation at normal pressure,
Next, acetic anhydride and acetic acid residues were distilled off by batch distillation at a reduced pressure of 10 Torr, a small amount of nitrogen was introduced under reduced pressure to remove volatile components, and PT of molecular weight 2100 measured by GPC.
37 parts of ME were obtained. The remaining acetic anhydride and acetic acid were 0.01% and 0.005%, respectively. PTME3
A 50 kg / hr methanol solution containing 5% and 0.2% calcium hydroxide was provided with an eight-stage theoretical rectification section filled with a pole ring at the top, and a 10-stage bubble bell tray at the bottom of the preparation stage. An atmospheric distillation column having an upper diameter of 0.20 m and a lower diameter of 0.5 m was charged and operated at a reflux ratio of 15. The operation was performed such that the methyl acetate concentration at the bottom of the column became 30 ppm. A distillate comprising 20% of methyl acetate and 80% of methanol was withdrawn at 87 kg / hr from the top of the column, and PTMG6 was removed from the bottom of the column.
A bottom liquid consisting of 0% and methanol 40% was withdrawn.
After the bottom liquid is cooled, calcium hydroxide is filtered, and a sulfonic acid type strongly acidic ion exchange resin (Mitsubishi Chemical Corporation SK1
BH) was introduced into the packed column to remove dissolved Ca ions.

(PTMG analysis) GPC (gel permeation chromatography):
Calibration was performed at POLYMER LAB
ORATYRES POLYTETRAHYDRO
The FURAN calibration kit was used. (Methanol content analysis) GC (gas chromatography): After weighing a sample,
The solvent was diluted with isopropylbenzene and quantified by an internal standard method using toluene as an internal standard. GC apparatus: Shimadzu GC-14A Column: DB-1 0.53 mmφ × 30 m Liquid film thickness df = 1.5 μm Column temperature: Start at 100 ° C. Temperature rise 3 ° C./min → 121 ° C. Temperature rise 10 ° C./min → 150 ° C. Vaporization Room temperature: 160 ° C Detector temperature: 160 ° C

Example 1 Using a pump in a 1 L round bottom four-necked flask equipped with an electromagnetic induction stirrer and a distillation unit, a raw material solution was supplied at a rate of 1 kg / hr.
And at the same time, continuous distillation was carried out by continuously extracting the internal solution from the bottom of the flask at 620 g / hr using a pump. Distillation conditions were normal pressure, an oil bath temperature of 100 ° C., and stirring at 500 rpm. The liquid in the flask (first-stage bottoms) was charged through a heat exchanger controlled at 130 ° C. into a packed column of 6 theoretical stages in which a Raschig ring of 5 mm in size was filled with 600 mm in a column of 50 mm in inner diameter. Nitrogen heated to 130 ° C. was passed from the bottom.
The amount of nitrogen charged was set to 5.6 L / hr by mass flow before preheating. The extracted column bottoms (second stage bottoms)
Methanol content GC detection lower limit 20 ppm (weight) or less,
It was a PTMG having a molecular weight of 1940 as measured by GPC.
The hue was 10 or less in APHA units (according to JIS K1557-1970).

COMPARATIVE EXAMPLE 1 Batch distillation was carried out. That is, 1 kg of the raw material solution was weighed into a 2 L round-bottom four-necked flask, immersed in an oil bath at 100 ° C. under normal pressure for 3 hours, and most of the methanol was distilled off.
The temperature of the Olivas was raised to 200 ° C., and distillation was carried out for 3 hours. The methanol content in the bottom liquid obtained was lower than the GC detection lower limit of 20 ppm (weight) or less, but the hue was APH.
It was 30 in A unit and coloring was observed.

Comparative Example 2 In Example 1, 1 kg / hr of the bottom liquid was directly passed through the packed tower without performing the evaporator treatment. Bubbling was observed in the upper part of the tower, and the tower distillate and the tower can were not separated.

[0027]

According to the present invention, in a method for producing PTMG by a transesterification reaction, a transesterification reaction solution is treated in two stages by using an evaporator and a gas-liquid contacting device for bringing an inert gas into countercurrent contact. Thereby, the separation and recovery of the unreacted lower alcohol contained in the reaction solution can be efficiently achieved with a short residence time, whereby the economically advantageous and high-quality PTMG can be produced. it can.

Claims (7)

[Claims] 1. A polytetramethylene ether glycol is produced by transesterification of a polytetramethylene ether glycol diacetate with a lower aliphatic alcohol in the presence of an alkali metal or alkaline earth metal oxide, hydroxide or alkoxide. In the method, after the transesterification reaction, the reaction liquid is treated through an evaporator and a gas-liquid contact device for bringing an inert gas into countercurrent contact to separate and recover a lower aliphatic alcohol which is an unreacted raw material in the reaction liquid. A method for producing polytetramethylene ether glycol, comprising: 2. The method for producing polytetramethylene ether glycol according to claim 1, wherein the evaporator is a forced circulation evaporator. 3. The method for producing polytetramethylene ether glycol according to claim 1, wherein the contact between the liquid and the inert gas in the gas-liquid contact device is performed at 50 to 250 ° C. 4. The production of polytetramethylene ether glycol according to claim 1, wherein the contact between the liquid and the inert gas in the gas-liquid contact device is performed under a pressure of 10 to 200 kPa. Method. 5. The method for producing polytetramethylene ether glycol according to claim 1, wherein the contact between the liquid and the inert gas in the gas-liquid contact device is performed under atmospheric pressure. 6. The polytetramethylene ether glycol according to claim 1, wherein an inert gas having a flow rate of 10 to 100 Nl / min per 1 Nl of the liquid is used in the treatment in the gas-liquid contact device. Manufacturing method. 7. The method according to claim 1, wherein the inert gas is at least one selected from nitrogen, carbon dioxide, a saturated hydrocarbon having 1 to 4 carbon atoms, an aliphatic alcohol having 1 to 4 carbon atoms, and dimethyl ether. 7. The method for producing polytetramethylene ether glycol according to any one of 1 to 6.