JP3849360B2 - Process for producing polytetramethylene ether glycol - Google Patents

Description

【００２４】
実施例１
電磁誘導撹拌機、蒸留留去ユニットを付した１Ｌ丸底四ツ口フラスコにポンプを用い、原料溶液を１ｋｇ／ｈｒで吐出すると同時に、フラスコ底部よりポンプを用いて、内液を６２０ｇ／ｈｒにて連続抜き出しすることにより連続蒸留を実施した。蒸留条件は、常圧、オイルバス温度１００℃、撹拌５００ｒｐｍにて操作した。フラスコ内液（第一段缶出液）は、１３０℃に温調した熱交換器を経て、内径５０ｍｍの塔内にサイズ５ｍｍのラシヒリングを６００ｍｍ充填した理論段６段の充填塔に仕込み、塔下部より１３０℃に加熱した窒素を通気した。窒素仕込量は、予熱前マスフローにて５．６Ｌ／ｈｒに設定した。抜き出された塔缶出液（第二段缶出液）は、メタノール含量ＧＣ検出下限２０ｐｐｍ（重量）以下、ＧＰＣで測定した分子量１９４０のＰＴＭＧであった。色相はＡＰＨＡ単位（ＪＩＳ Ｋ１５５７−１９７０による）で１０以下であった。
【００２５】
比較例１
回分による蒸留を実施した。即ち、２Ｌ丸底四ツ口フラスコに原料溶液１ｋｇを秤取し、常圧下１００℃のオイルバスに３時間浸漬し、大部分のメタノールを留去後、オルイバス温度を２００℃に上げ、更に３時間蒸留を行った。得られた缶出液中のメタノール含量は、ＧＣ検出下限２０ｐｐｍ（重量）以下であったが、色相はＡＰＨＡ単位で３０であり、着色が見られた。
【００２６】
比較例２
実施例１において、蒸発器処理を行わず、直接充填塔に缶出液１ｋｇ／ｈｒを通液した。塔上部留出部の発泡が観察され、塔留出部及び塔缶出部の分離ができなかった。
【００２７】
【発明の効果】
本発明によれば、エステル交換反応によりＰＴＭＧを製造する方法において、エステル交換反応液を蒸発器及び不活性気体を向流接触させる気液接触装置を用いて二段で処理することにより、反応液中に含まれる未反応の低級アルコールの分離、回収を短い滞留時間で効率的に達成することができ、これにより経済的に有利に且つ品質の優れたＰＴＭＧを製造することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing polytetramethylene ether glycol (hereinafter sometimes abbreviated as PTMG). More specifically, the present invention relates to an improvement in a method for producing PTMG by transesterifying polytetramethylene ether glycol diacetate (hereinafter sometimes abbreviated as PTME) with a lower alcohol in the presence of an alkali metal or alkaline earth metal catalyst. .
PTMG is used as a soft segment such as a polyester resin and a urethane resin, and is processed into industrial products such as rolls, shoe soles, elastic fibers for clothes (spandex, etc.), etc., and is widely useful in daily life.
[0002]
[Prior art]
Various methods for producing PTMG have been disclosed. Among them, tetrahydrofuran (hereinafter sometimes abbreviated as THF) is used in the presence of a solid acid catalyst and a carboxylic acid anhydride such as acetic anhydride. Ring-opening polymerization to obtain PTME, and then PTMG is transesterified with a lower alcohol such as methanol in the presence of a basic catalyst to obtain PTMG, which is an excellent method with little waste.
As solid acid catalysts, ion exchange resins, bleaching earths, zeolites and the like have been proposed.
[0003]
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. The mixture of the transesterification reaction solution, PTMG and methanol removes the catalyst by a usual method such as neutralization or adsorption, and then separates and recovers the methanol.
If methanol remains, it has a great influence on the intended use of PTMG, so that as little as possible is required as an industrial raw material. PTMG is used as a soft segment such as polyester elastomer and polyurethane elastomer. These elastomers are produced by condensation polymerization of PTMG and dicarboxylic acid (for example, terephthalic acid) or dicarboxylic acid ester (for example, dimethyl terephthalate), or addition polymerization of PTMG and diisocyanate (for example, diphenylmethane diisocyanate), respectively. In these condensation polymerization or addition polymerization, hydroxyl groups at both ends of PTMG react, but in order to obtain a highly polymerized product, it is necessary to remove as much as possible the mono-alcohol monohydroxy which causes end-capping. . When a large amount of monoalcohol is present, the amount of volatile components at the time of polymerization increases, or it becomes difficult to obtain a polymer having a high molecular weight.
[0004]
Taking polyurethane resin as an example, for example, PTMG obtained using methanol (molecular weight 32) as alcohol, PTMG having a methanol content of 0.1% by weight and an average molecular weight of 2000 (methanol-derived sealing for 100 hydroxyl groups) When an adduct with diphenylmethane diisocyanate (molecular weight 250) is produced using about 3 parts), the theoretical maximum molecular weight of the polymer is 75,000, but the methanol content is 0.01% by weight, the average When an adduct is produced in the same manner using PTMG having a molecular weight of 2000, the theoretically obtained maximum molecular weight of the polymer is 750,000, and the residual amount of monoalcohol may greatly affect the polymer formation reaction. I understand. Further, when attempting to produce a polymer having a higher molecular weight, PTMG in which the monoalcohol 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.
[0005]
As a method for separating and recovering the unreacted lower alcohol from the transesterification reaction solution, for example, there is a method using a batch evaporator. However, in order to obtain a large amount of product, the equipment becomes large and is not practical.
For this reason, the method of distilling off continuously using the evaporator provided with the heating tube and the falling film type evaporator is used conventionally.
[0006]
[Problems to be solved by the invention]
However, in this method, the viscosity of the treatment liquid increases with the concentration of the polymer, and the deaeration transfer speed gradually decreases. When a single evaporator is used to remove the lower alcohol concentration in PTMG to a trace level, it takes a long time to obtain the final polymer from the initial polymer dilution solution, which only reduces productivity. In addition, when the polymer is exposed to a heating condition for a long time, there is a problem in that quality deterioration represented by hue is caused.
[0007]
In the method for producing PTMG by transesterification, the present invention solves the problem of a large amount of energy consumption and quality deterioration which are problematic when recovering lower alcohol which is an unreacted raw material after transesterification. It aims at providing the method of manufacturing excellent PTMG industrially advantageously.
[0008]
[Means for Solving the Problems]
As a result of intensive studies in view of such circumstances, the present inventors have processed the transesterification reaction solution in two stages using a vapor-liquid contact device that countercurrently contacts an evaporator and an inert gas, thereby producing a reaction solution. It has been found that the separation and recovery of unreacted lower alcohol contained therein can be efficiently achieved with a short residence time, and this makes it possible to produce PTMG that is economically advantageous and excellent in quality. It came to be completed.
[0009]
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 oxide, hydroxide or alkoxide of an alkali metal or alkaline earth metal. In the method for producing glycol, after the transesterification reaction, the reaction solution is processed through an evaporator and a gas-liquid contact device that makes an inert gas contact countercurrently to separate lower aliphatic alcohol as an unreacted raw material in the reaction solution. And a method for producing polytetramethylene ether glycol, which is recovered.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
(Manufacture of PTMG)
The 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, 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.
[0011]
The reaction conditions vary depending on the molecular weight of the target PTMG and the type of acid catalyst used, but the molar ratio of acetic anhydride / THF is usually 0.001 to 0.3, and acetic anhydride and catalyst in the reaction solution. The raw materials are charged so that the concentrations are 0.5 to 30% by weight and 0.1 to 30% by weight, the reaction temperature is usually in the range of 20 to 80 ° C., and the reaction pressure is normal pressure. Polymerization is carried out in the range of usually 0.5 to 10 hours under slightly increased pressure, and the molecular weight of the produced polymer can be adjusted by adjusting the molar ratio of THF and acetic anhydride.
Since the polymerization reaction solution thus obtained contains unreacted THF and acetic anhydride in addition to the target PTME, these unreacted raw materials are usually distilled off under normal pressure or reduced pressure. The distilled THF and acetic anhydride can be purified as necessary and reused in the reaction.
[0012]
Next, a transesterification catalyst and alcohol are added to the obtained polymer to perform a transesterification reaction. As the transesterification catalyst, an alkali metal such as sodium or potassium, an oxide of an alkaline earth metal such as calcium or barium, a hydroxide or an alkoxide is preferably used. In particular, alkali metals, especially sodium alkoxides, are easy to handle because they have a high reaction rate and a high solubility in alcohols, and are therefore preferably used. As the lower alcohol, usually a lower alcohol having 1 to 4 carbon atoms is used, and methanol is particularly preferred because it has a small molecular weight and a large molar ratio with PTME even with the same weight. The transesterification is carried out using 0.001 to 1% by weight of the catalyst and 5 to 50 moles of the lower alcohol relative to the acetate ester of PTMG. Further, the reaction may be carried out in the presence of a small amount of water.
Since the transesterification reaction is an equilibrium reaction, in order to obtain PTMG having all hydroxyl groups at the ends, it is necessary to carry out the process while removing the acetic acid ester of the lower alcohol produced in some form. As a method therefor, there is a method in which a batch reactor equipped with a distillation facility is used. However, in order to obtain a large amount of products, the facility becomes large, which is not practical. A continuous transesterification method is desirable, and a method using a reactor equipped with distillation equipment is also conceivable, but the equipment is expensive.
[0013]
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 for producing PTMG from PTME is described, for example, in WO 97/23559. In this method, a mixture of PTME, catalyst and lower alcohol is supplied from the middle of the distillation column, and methyl acetate formed simultaneously with transesterification is removed. Furthermore, heating methanol vapor is supplied from the lower part of the distillation tower to complete the reaction. In this method, since the amount of PTME supplied to the distillation column is large, the distillation column becomes large in order to complete the reaction. On the other hand, a method in which the amount of PTME reacted in the distillation column can be reduced by reducing the amount of PTME reacted in the distillation column by subjecting the raw material mixture charged to the distillation column to a transesterification reaction in advance to make it close to the equilibrium composition is economically advantageous. And is preferably used.
The bottom liquid is a mixture of PTMG and lower alcohol, but if the concentration of PTMG is increased, the viscosity increases and the reboiler thermosyphon does not work, so a concentration of 30 to 70%, preferably 40 to 50% is suitable. . Moreover, since the flow of the liquid in the reboiler becomes worse as the viscosity increases, it is also preferable to flow the liquid in the reboiler with a pump as necessary.
[0014]
(Separation and recovery of unreacted lower alcohol)
In the present invention, the transesterification reaction liquid from which the catalyst has been removed is treated by using an evaporator and a gas-liquid contact device that makes an inert gas contact countercurrently to separate and recover a lower alcohol contained in the reaction liquid. It is characterized by doing.
[0015]
The evaporator used in the present invention is not particularly limited, but a jacket-type evaporator with a heating jacket outside the tank, a Foster-Wheeler can, a Baffalo can, a Yaryan can, etc. as an evaporator with a heating tube arranged horizontally. Standard evaporators, basket-type evaporators, Kestner-type evaporators, etc. as evaporators with tubes arranged upright, inclined tube-type evaporators, coil (snake tube) -type evaporators, plates as evaporators with diagonally arranged heating tubes Examples of the evaporator suitable for a fluid having a large viscosity, such as a (flat) evaporator, include a falling thin film evaporator and a forced circulation evaporator. Among these, a falling film evaporator and a forced circulation evaporator are preferable in order to handle a PTME polymerization reaction liquid having a high viscosity. Furthermore, a forced circulation evaporator is particularly preferable because it has a high film heat transfer coefficient, good evaporation efficiency, and can be installed at low cost. The forced circulation type evaporator is a flash drum that supplies latent heat of evaporation with sensible heat of the stock solution to perform equilibrium flash separation, a circulation pump that sends the concentrated viscous liquid from the flash drum can to the heating pipe, and a heating pipe that heats the concentrated viscous liquid. It is an evaporator.
[0016]
In addition, when processing a transesterification reaction liquid using a forced circulation type evaporator, although it depends on the processing amount, the processing temperature is usually 60 to 200 ° C., and the processing time is usually 15 to 60 minutes, preferably at 150 ° C. or less, 90 to 99% of the unreacted lower alcohol, more preferably at 100 ° C. or less, so that 92 to 98% of the unreacted lower alcohol can be recovered. .
The composition of the mixture extracted from the evaporator is, for example, when PTMG 60 wt% and methanol 40 wt% are used, PTMG 97 wt% and methanol 3 wt% under the conditions of normal pressure and 75 ° C.
[0017]
The bottom mixture extracted from the evaporator is further processed by a gas-liquid contact device.
The gas-liquid contact device for countercurrent contact with 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 diffusion tower. As a gas-liquid contact device of a type that disperses a liquid in a gas continuous phase, as a gas-liquid contact device of a type that disperses a gas in a liquid continuous phase, such as a packed tower, a spray tower, a scrubber, a wet wall tower, A column tower, a bubble stirring tank, etc. are mentioned. A type that uses an inert gas as the gas and counter-contacts the bottom mixture with the inert gas, for example, vents inert gas from the bottom of the tower to lower the partial pressure of volatile substances in the bottom mixture A stripping tower is preferably used.
[0018]
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 vented from the lower part of the tower.
The stripping tower can be operated without any problem at normal pressure because it is sufficient to lower the partial pressure of the volatile substance, but it is more advantageous to operate at a reduced pressure. Therefore, the stripping tower is operated at 10 to 200 kPa, preferably 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 it is operated at a temperature of 100 to 250 ° C., preferably 130 to 230 ° C., which is less susceptible to heat deterioration.
As the type of the stripping tower, a packed tower, a spray tower, and a scrubber that can increase the gas-liquid contact area are preferable, and among these, a packed tower that can shorten the residence time and is easy to control is preferable.
[0019]
In this case, the filling may be an irregular filling such as a Raschig ring or a pole ring or a regular filling. The charging volume ratio of the aeration gas to the charging liquid amount varies depending on the tower temperature and the number of stages in the tower, but a volume ratio of 1 to 100 is usually used. An excessive volume ratio is disadvantageous because it leads to loss of vent gas. Although the number of tower stages depends on the residence time, it is preferably carried out in 5 to 30 stages.
A method in which the canned mixture is charged directly into the stripping tower without passing through the first stage evaporator is also conceivable. However, a PTMG solution containing 30 to 50% by weight of methanol has a strong foaming property, and a foam is formed at the top of the tower. This is not preferable because the liquid content becomes wet or the distillation efficiency is lowered and the final product purity is lowered.
In the contact between the liquid and the inert gas in the stripping tower, it is usually preferable to use an inert gas having a flow rate of 1 to 100 Nl / min, preferably 5 to 50 Nl / min per 1 Nl of liquid.
[0020]
In this case, the inert gas is preferably at least one selected from nitrogen, carbon dioxide, and a saturated hydrocarbon having 1 to 4 carbon atoms , and among these, nitrogen is more preferable.
Regarding the stripping tower, the residual amount of the lower alcohol in the polymer is preferably 250 ° C. or less, and 0.1% by weight or less, more preferably 230 ° C. or less, and the residual amount is 0.01% by weight or less. To be driven.
[0021]
PTMG extracted from the column bottom is finally obtained as PTMG having a viscosity (40 ° C.) of 200 to 1400 mPa · sec by distilling off the lower alcohol.
Usually, industrially, PTMG having a number average molecular weight of 500 to 3000 is obtained by the above-mentioned method and used as a raw material for polyurethane elastic fiber, polyurethane elastomer or polyester elastomer.
[0022]
【Example】
EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited to an Example, unless the summary is exceeded.
In addition,% and ppm in the preparation of the following raw materials and examples represent weight% and weight ppm, respectively.
(Preparation of raw materials)
100 parts of THF, 5.6 parts of acetic anhydride, and 0.2 part of acetic acid were reacted with 3.5 parts of zirconia silica catalyst at 40 ° C. for 5 hours. After removing the catalyst by filtering the reaction product, most of the unreacted product is distilled off by batch distillation at normal pressure, and then batch distillation is carried out at a reduced pressure of 10 Torr to distill off the remaining acetic anhydride and acetic acid. A small amount of nitrogen was introduced below to remove volatile matter, and 37 parts of PTME having a molecular weight of 2100 measured by GPC was obtained. The remaining acetic anhydride and acetic acid were 0.01% and 0.005%, respectively.
It had a rectifying section with 8 stages of theoretical plates filled with a pole ring at the top and 50 kg / hr of a methanol solution containing 35% PTME and 0.2% calcium hydroxide, and a 10-stage bubble tray at the bottom of the charging stage. The mixture was charged in an atmospheric distillation tower having an upper diameter of 0.20 m and a lower diameter of 0.5 m, and operated at a reflux ratio of 15. The operation was performed so that the methyl acetate concentration at the bottom of the column was 30 ppm. A distillate consisting of 20% methyl acetate and 80% methanol was extracted from the top of the column at 87 kg / hr, and a bottoms consisting of 60% PTMG and 40% methanol was extracted from the bottom of the column. After cooling the bottoms, calcium hydroxide was filtered and introduced into a tower filled with a sulfonic acid type strongly acidic ion exchange resin (Mitsubishi Chemical Corporation SK1BH) to remove dissolved Ca ions.
[0023]
(PTMG analysis)
GPC (gel permeation chromatography): A POLYTETRAHYDROFURAN calibration kit manufactured by POLYMER LABORATORIES, UK was used for calibration.
(Methanol content analysis)
GC (gas chromatography): A sample was weighed, diluted with a solvent isopropylbenzene, and quantified by an internal standard method using toluene as an internal standard.

[0024]
Example 1
Using a pump to a 1 L round bottom four-necked flask equipped with a magnetic induction stirrer and a distillation distillation unit, the raw material solution is discharged at 1 kg / hr, and at the same time, the internal solution is reduced to 620 g / hr using a pump from the bottom of the flask. Continuous distillation was carried out by continuous extraction. The distillation conditions were normal pressure, oil bath temperature 100 ° C., and stirring 500 rpm. The liquid in the flask (first stage bottom liquid) passes through a heat exchanger whose temperature is adjusted to 130 ° C., and is charged into a packed column of 6 theoretical plates in which a 5 mm sized Raschig ring is packed in a 50 mm inner diameter column. Nitrogen heated to 130 ° C. was bubbled from the bottom. The nitrogen charge was set to 5.6 L / hr in the mass flow before preheating. The extracted tower bottom (second stage bottom) was PTMG having a methanol content GC detection lower limit of 20 ppm (weight) or less and a molecular weight of 1940 measured by GPC. The hue was 10 or less in APHA unit (according to JIS K1557-1970).
[0025]
Comparative Example 1
Batch distillation was performed. That is, 1 kg of the raw material solution was weighed in a 2 L round bottom four-necked flask and immersed in an oil bath at 100 ° C. under normal pressure for 3 hours. After most of methanol was distilled off, the Oliva bath temperature was raised to 200 ° C. Time distillation was performed. The methanol content in the resulting bottoms was below the GC detection lower limit of 20 ppm (weight), but the hue was 30 in APHA units, and coloring was observed.
[0026]
Comparative Example 2
In Example 1, the evaporator treatment was not performed, and 1 kg / hr of the bottoms was directly passed through the packed tower. Foaming of the tower upper distillation part was observed, and separation of the tower distillation part and the tower can outlet was not possible.
[0027]
【The invention's effect】
According to the present invention, in the method for producing PTMG by transesterification reaction, the transesterification reaction solution is treated in two stages using an evaporator and a gas-liquid contact device that countercurrently contacts an inert gas. Separation and recovery of the unreacted lower alcohol contained therein can be efficiently achieved in a short residence time, and thereby, PTMG having an economically advantageous and excellent quality can be produced.

Claims (7)

  In a method for producing polytetramethylene ether glycol by transesterifying polytetramethylene ether glycol diacetate with a lower aliphatic alcohol in the presence of an oxide, hydroxide or alkoxide of an alkali metal or alkaline earth metal, After the exchange reaction, the reaction solution is processed through an evaporator and a gas-liquid contact device that makes an inert gas counter-current contact to separate and recover the lower aliphatic alcohol that is an unreacted raw material in the reaction solution. A method for producing polytetramethylene ether glycol.   The method for producing polytetramethylene ether glycol according to claim 1, wherein the evaporator is a forced circulation evaporator.   The method for producing polytetramethylene ether glycol according to claim 1 or 2, wherein the contact between the liquid and the inert gas in the gas-liquid contact device is performed at 50 to 250 ° C.   The method for producing polytetramethylene ether glycol according to any one of claims 1 to 3, 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.   The method for producing polytetramethylene ether glycol according to any one of claims 1 to 4, wherein the contact between the liquid and the inert gas in the gas-liquid contact device is performed under atmospheric pressure.   6. The method for producing 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 liquid is used in the treatment in the gas-liquid contact device. The method for producing polytetramethylene ether glycol according to any one of claims 1 to 6, wherein the inert gas is at least one selected from nitrogen, carbon dioxide, and saturated hydrocarbon having 1 to 4 carbon atoms. .