JP3837966B2 - Process for producing polytetramethylene ether glycol - Google Patents

Description

[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 transesterification of PTMG diacetate (hereinafter sometimes abbreviated as PTME) with a lower aliphatic alcohol in the presence of an alkali metal catalyst.
PTMG is used as a soft segment such as polyester resin and polyurethane resin, and is widely used in daily life after being processed into industrial products such as rolls and elastic fibers for clothing such as shoe soles and spandex.
[0002]
[Prior art]
Various methods for manufacturing PTMG have been disclosed. Among them, tetrahydrofuran (hereinafter sometimes abbreviated as THF) is subjected to ring-opening polymerization in the presence of a solid acid catalyst and a carboxylic acid anhydride such as acetic anhydride to obtain PTME, and then this PTME is present in the presence of a basic catalyst. A method for obtaining PTMG by transesterification with a lower alcohol such as methanol is an excellent method with little waste.
[0003]
As the solid acid catalyst, super strong acid ion exchange resin (Japanese Patent Publication No. 61-111969), bleaching earth (Japanese Patent Publication No. 62-19452), zeolite (Japanese Patent Laid-Open No. 7-228684) and the like have been proposed. . The solid acid catalyst can be used in either a suspended bed or a fixed bed, and when used in a fixed bed flow reaction, it is not particularly necessary to perform a separate operation for the catalyst, which is particularly preferable.
[0004]
Regarding the transesterification of PTME, PTMG is usually produced by transesterification with a lower alcohol such as methanol in the presence of a basic catalyst such as sodium methoxide.
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. 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.
[0005]
The reactive distillation for producing PTMG from PTME is proposed in, for example, WO 97/23559.
In this method, a mixture of PTME, catalyst and lower alcohol is supplied from the center of the distillation column to remove methyl acetate generated simultaneously with the transesterification, and heated methanol vapor is supplied from the bottom of the distillation column to complete the reaction. It is something to be made.
However, in this method, since the amount of PTME supplied to the distillation column is large, there is a problem that the distillation column becomes large in order to complete the reaction.
[0006]
[Problems to be solved by the invention]
As described above, in order to obtain a sufficient conversion rate in the transesterification, in the case of a batch reactor, it is necessary to enlarge the reactor or to use a plurality of reactors in parallel. In the case of a reactive distillation column, there is a problem that the distillation column becomes large.
An object of this invention is to provide the method of obtaining sufficient conversion, and making a reactor small, when manufacturing PTMG from PTME by transesterification.
[0007]
[Means for Solving the Problems]
As a result of intensive studies in view of such circumstances, the present inventors have conducted a two-stage reaction in a process for producing PTMG by transesterifying PTME with a lower aliphatic alcohol in the presence of an alkali metal or alkaline earth metal catalyst. In other words, the transesterification reaction is first performed in the reactor to near the equilibrium composition, and then the reaction mixture obtained is supplied to the reactive distillation column, and the remaining reaction is performed, so that the load on the reactive distillation column is increased. It has been found that the distillation column can be reduced, the conversion rate of PTME can be improved, the amount of unreacted substances can be reduced, and by-products can be efficiently removed, and the present invention has been completed.
[0008]
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 hydroxide or alkoxide to obtain polytetramethylene ether glycol. In the manufacturing method,
a. The reactor is charged with polytetramethylene ether glycol diacetate, lower aliphatic alcohol and alkali metal or alkaline earth metal hydroxide or alkoxide, and 85% of the equilibrium conversion of polytetramethylene ether glycol diacetate Transesterified to obtain the above, and then b. The obtained reaction mixture was supplied to a reactive distillation column, unreacted lower aliphatic alcohol and acetic acid ester of the generated lower aliphatic alcohol were distilled from the top of the column, and the lower fat of polytetramethylene ether glycol was distilled from the bottom of the column. Further transesterification while allowing the group alcohol solution to come out,
It is in the manufacturing method of the polytetramethylene ether glycol characterized by the above-mentioned.
[0009]
In the present invention, by carrying out the reaction and distillation under a pressurized condition of atmospheric pressure or higher, the reaction temperature is increased, the reaction rate is increased, and the amount of catalyst used is reduced. Can be made small.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
(A. First stage reaction)
The raw material PTME used in the present invention is usually obtained by subjecting THF to ring-opening polymerization using an acid catalyst in the presence of acetic anhydride. As the acid catalyst, a solid acid such as super strong acid ion exchange resin, activated clay, zeolite, silica alumina is used. Solid acids are easy to separate and are suitable for fixed bed flow reactions.
[0011]
About reaction conditions, although it changes with the molecular weight of the target PTMG, and the kind of acid catalyst, normally, acetic anhydride and a catalyst are 0.5-30 weight% and 0.1-30 weight respectively in the reaction liquid. %, The reaction temperature is usually in the range of 20 to 80 ° C., the reaction time is usually in the range of 0.5 to 10 hours, and the molar ratio of THF and acetic anhydride is adjusted. Thus, the molecular weight of the produced polymer can be adjusted. Since the obtained polymerization reaction liquid contains unreacted THF and acetic anhydride, these are distilled off under normal pressure or reduced pressure to obtain PTME. The THF and acetic anhydride distilled off can be purified and reused as necessary.
[0012]
The obtained PTME is mixed with a lower aliphatic alcohol, transesterified in the presence of a transesterification catalyst, and converted to PTMG. Since the reaction rate of the transesterification reaction depends on the alcohol concentration, the more alcohol there is, the easier the progress, and the transesterification reaction has an equilibrium, so that the carboxylic acid ester of the lower aliphatic alcohol to be produced is removed appropriately. It is preferred to do so.
As the lower aliphatic alcohol, an alcohol having 1 to 4 carbon atoms is used, and methanol is particularly preferable. Methanol is preferably used because it has a small molecular weight, allows a large mole with PTME even at the same weight, and has a higher relative volatility with the produced methyl acetate than other compounds.
[0013]
The ratio of alcohol to PTME is preferably 1: 1 to 1: 3 by weight. If the amount of alcohol is small, the viscosity is high and the reaction is slow. On the other hand, if the amount is too large, the apparatus becomes large, and the cost increases due to the removal of excess alcohol. Further, since the raw material alcohol forms an azeotrope with the by-product lower alcohol carboxylic acid ester and may be removed from the reaction system, the raw material alcohol may be appropriately replenished.
[0014]
As transesterification catalysts, hydroxides or alkoxides of alkali metals such as sodium and potassium, alkaline earth metals such as calcium and barium are usually used. Among these, alkali metal hydroxides or alkoxides are used. Alkali metal alkoxides are preferred, and sodium alkoxides are preferred because of their high reaction rate, high solubility in alcohol, easy handling, and the like. Sodium methoxide is particularly preferred.
Hereinafter, the case where methanol is used as the alcohol and sodium methoxide is used as the catalyst in the transesterification reaction of PTME will be described.
[0015]
In this case, a mixture of PTME, methanol and sodium methoxide is reacted in the reactor and transesterification is carried out, but the reaction rate is higher as the temperature is higher, the catalyst is higher, and the equilibrium is increased to PTMG as the methanol is higher. It is close. However, if the temperature is high, the vapor pressure of methanol becomes high, the reaction becomes high pressure, and the reactor needs to have a pressure resistance, and if there are a lot of methanol and catalyst, a large facility and utility are required for removal in a later process. I need. Therefore, in practicing the present invention, 20 to 300 mol times, preferably 50 to 100 mol times of methanol and sodium methoxide are added in a solution in a reactor installed in front of the distillation column. The transesterification is performed at 0.5 to 5 MPa, preferably 1 to 3 MPa, and a temperature of 100 to 250 ° C. using 0.005 to 1 wt%, preferably 0.01 to 0.5 wt%.
[0016]
In this case, PTME may be reacted at 85% or more, preferably 87 to 99% of the equilibrium conversion rate. If the reaction is carried out to a very high conversion rate, a large amount of catalyst is used, and the subsequent catalyst treatment is burdened, the reaction conditions such as temperature and pressure become severe, and the residence time becomes long. is not. The equilibrium conversion rate refers to the conversion rate when the esterification reaction reaches equilibrium under the reaction conditions.
The progress of the reaction can be checked by analyzing the ester content remaining in the reaction system by a conventional method such as chemical analysis or infrared analysis.
[0017]
The reactor should just be what can be used continuously, and a stirring tank, a circulation type reaction tank, a tube type reactor, etc. are used. In the tank reactor, there is reverse mixing in which part of the liquid moves in the direction opposite to the main flow direction. Therefore, the reaction type in which the flow is close to the piston flow is suitable, and the use of the tube type reactor is simple and Since reaction efficiency is also good, it is used suitably. In the tube type reactor, the transesterification is carried out only to the equilibrium composition or a state close to the equilibrium composition in a residence time of 4 to 10 minutes, so that no equipment for separating the produced methyl acetate is required.
The composition of the mixture withdrawn from the reactor is, for example, PTME 50% by weight, methanol 50% by weight, catalyst 0.01% by weight, the equilibrium composition under the conditions of 2 MPa, 160 ° C., PTME 0.5% by weight, PTMG 47.5 wt%, methyl acetate 3.6 wt%, methanol 48.5 wt%.
[0018]
(B. Second stage reaction)
The mixture produced here is sent to a distillation column to remove methyl acetate, and at the same time, unreacted PTME is further transesterified to form PTMG.
The distillation column is operated at a lower pressure than the reactor. One reason is that the raw material can be supplied without special equipment using the pressure of the reactor, but the separation of methanol and methyl acetate also depends on the lower pressure. However, if the pressure is lowered too much, the temperature of the distillation column is lowered, and the transesterification rate is decreased, which is not preferable. Accordingly, the distillation column is operated at 0.5 to 2 MPa, preferably 1 to 1.5 MPa, and a temperature of 100 to 170 ° C. The residence time is 10 to 30 minutes.
[0019]
Since separation and reaction occur simultaneously in the distillation column, time is required for the reaction in the lower part of the charging stage and in the distillation column recovery part. Accordingly, as the type of distillation column, the recovery section is preferably a shelf that can greatly hold up the liquid, and a bubble tray, a perforated plate tray, a valve tray, or the like is used. The bubble tray has a wide stable operation range but is expensive due to its complicated structure, while the perforated plate tray has the disadvantages of simple structure and low pressure loss but narrow stable operation range. A bubble tray is preferred. Above the preparation stage, the distillation column concentrating section does not require any special devices and can be used with ordinary distillation equipment. The aforementioned shelf, for example, a tray such as a sieve tray, or irregular packing such as a Raschig ring or a ball ring, and low pressure loss. Regular packing can be used in the rectification section. The reflux ratio varies depending on the molar ratio of PTME and methanol used and the number of concentration stages, but a reflux ratio of 0.5 to 20 is usually used. An excessive reflux ratio is disadvantageous for the transesterification because the catalyst concentration of the liquid on the tray is lowered, the reaction rate is reduced, and the residence time on the tray is shortened. Distillation is suitably carried out with a concentration unit of 1 to 10 stages, a recovery unit of 5 to 30 stages, and a reflux ratio of 1 to 10.
[0020]
The tower bottom liquid is a mixture of PTMG and methanol, 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.
The methyl acetate and methanol thus distilled are sent to a methanol recovery tower, and an azeotropic mixture of methyl acetate and methanol is distilled from the top of the tower. The methanol is recovered from the bottom and used as a raw material for transesterification of PTME. . If the purity of methanol recovered at this time is about 95% or more, it can be used without any problem.
[0021]
The mixture of PTMG and methanol extracted from the bottom of the column is operated under a high vacuum of 5 Torr or less after removing the catalyst by a conventional method such as neutralization or adsorption, and further removing methanol in the distillation column. Methanol is completely removed by a thin film evaporator to form PTMG, and the distilled methanol can be used as a raw material for transesterification.
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】
Hereinafter, the present invention will be described in detail by way of examples. However, the present invention is not limited to the examples unless it exceeds the gist.
(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 0.001 wt% and 0.0005 wt%, respectively. This was repeated three times to produce a raw material.
The composition of the transesterification reaction solution was carried out according to the following analysis method.
In order to deactivate the basic catalyst as a pretreatment, 1N hydrochloric acid was used, and 1N hydrochloric acid corresponding to 1.2 times the neutralization equivalent was prepared as a coating solution, and then sampling was performed.
[0023]
(Methyl acetate, methanol content analysis)
Gas chromatography: The sampling solution was collected in a 1 ml container and quantified by absolute calibration by automatic injection.
GC device: Shimadzu GC-14A
Column: NEUTRABOND-1 manufactured by GL Science Size 0.32 mmφ × 60 m Liquid film thickness df = 0.4 μm
Column temperature: 50 ° C Constant temperature Vaporization chamber temperature: 320 ° C
Detector temperature: 320 ° C
Detector: FID
[0024]
(PTME residual amount analysis)
Infrared analysis: Methyl acetate and methanol are distilled off to a trace amount by 100 Pa vacuum distillation of the sampling solution using a rotary evaporator. The distillation residue liquid is a mixture of the reaction product PTMG and unreacted PTME, which is diluted and dissolved with chloroform equivalent to 4 times the weight of the residue weighed. The diluted preparation solution was poured into a liquid measurement cell, and the absorbance of the carbonyl group characteristic absorption νC = 0 1732 cm ⁻¹ of PTME was determined. The PTME residual amount was determined from a calibration curve prepared separately.
[0025]
Example 1
A 50 kg / hr methanol solution containing 50 wt% PTME and 100 ppm sodium methoxide was passed through a tube reactor (inner diameter 20 mm, length 20 m) having an internal temperature of 160 ° C. and a pressure of 1.85 MPa as the first reactor. Analysis of the tube reactor outlet composition showed PTME 0.5 wt%, PTMG 47.5 wt%, methyl acetate 3.6 wt%, and methanol 48.5 wt%. The liquid passed through the tube reactor has an upper diameter of 0.20 m, which has a rectifying section of five theoretical stages filled with a ball ring at the upper part and a five-stage bubble tray at the lower part of the charging stage. The mixture was charged into a 1 MPa pressure distillation tower having a lower diameter of 0.5 m and operated at a reflux ratio of 4. A distillate consisting of 17% methyl acetate and 83% methanol was extracted from the top of the column at 7 kg / hr, and a bottoms consisting of 55% by weight PTMG, 44% by weight methanol and 1% by weight methyl acetate was extracted from the bottom of the column. After cooling the bottoms, 1% by weight of water is added and introduced into a column packed with a sulfonic acid type strongly acidic ion exchange resin (Mitsubishi Chemical Corporation SK1BH) to remove dissolved Na ions, and the solvent is distilled off. Distilled off to obtain PTMG. The average molecular weight of the obtained PTMG was 1965, and the residual amount of PTME was 0.5% by weight as a result of infrared analysis.
[0026]
Comparative Example 1
In Example 1, the operation was performed under the same conditions as in Example 1 except that the first reactor was not directly passed through the tube reactor and was directly introduced into the distillation column. When the residual amount of PTME in the obtained PTMG was measured by infrared analysis, it was 10.2% by weight.
[0027]
Comparative Example 2
In Example 1, the same conditions as in Example 1 except that the lower part of the distillation column preparation stage is added to the 15-stage bubble bell tray and introduced directly into the distillation column without passing through the tube reactor as the first reactor. Drove by. When the residual amount of PTME in the obtained PTMG was measured by infrared analysis, it was 1.8% by weight.
[0028]
【The invention's effect】
According to the present invention, in a process for producing PTMG by transesterifying PTME with a lower aliphatic alcohol in the presence of an alkali metal or alkaline earth metal catalyst, the load on the reactive distillation column is reduced and the distillation column itself is made smaller. And the conversion rate of PTME is improved, the amount of unreacted substances is reduced, and by-products can be efficiently removed.

Claims (9)

In the method for producing polytetramethylene ether glycol by transesterifying a diacetate of polytetramethylene ether glycol with a lower aliphatic alcohol in the presence of an alkali metal or alkaline earth metal hydroxide or alkoxide,
a. The reactor is charged with polytetramethylene ether glycol diacetate, lower aliphatic alcohol and alkali metal or alkaline earth metal hydroxide or alkoxide, and 85% of the equilibrium conversion of polytetramethylene ether glycol diacetate Transesterified to obtain the above, and then b. The obtained reaction mixture was supplied to a reactive distillation column, unreacted lower aliphatic alcohol and acetic acid ester of the generated lower aliphatic alcohol were distilled from the top of the column, and the lower fat of polytetramethylene ether glycol was distilled from the bottom of the column. A process for producing polytetramethylene ether glycol, wherein the transesterification is further carried out while the aromatic alcohol solution is taken out. The process for producing polytetramethylene ether glycol according to claim 1, wherein the pressure of the reactor and the reactive distillation column is 0.5 to 5 MPa, and the temperature of the reactor is 100 to 250 ° C.   The lower aliphatic alcohol is methanol, the alkali metal or alkaline earth metal hydroxide or alkoxide is sodium methoxide, and the amount charged to these reactors is less than that of polytetramethylene ether glycol diacetate. The method for producing polytetramethylene ether glycol according to claim 1 or 2, wherein methanol is 0.5 to 5 times by weight and sodium methoxide is 0.005 to 1% by weight. Method for producing polytetramethylene ether glycol as claimed in any one of claims 1 to 3, wherein the reactor is a tube reactor. In a method for producing polytetramethylene ether glycol by transesterifying diacetate of polytetramethylene ether glycol with methanol in the presence of an alkali metal or alkaline earth metal hydroxide or alkoxide,
a. To the tube reactor, polytetramethylene ether glycol diacetate, and 20 to 300 moles of methanol, and alkali metal or alkaline earth metal hydroxide or alkoxide are continuously fed, Transesterification was performed at 0.5 to 5 MPa at 100 to 250 ° C. to obtain a reaction mixture that reached a transesterification rate of 85% or more of the equilibrium conversion of polytetramethylene ether glycol diacetate,
b. The obtained reaction mixture was supplied to a reactive distillation column, the top of the column was maintained at 0.5 to 2 MPa, 100 to 170 ° C., methanol and methyl acetate were distilled from the top of the column, and polytetramethylene was distilled from the bottom of the column. A process for producing polytetramethylene ether glycol, wherein transesterification is further performed while a methanol solution of ether glycol is taken out.   The method for producing polytetramethylene ether glycol according to any one of claims 1 to 5, wherein the recovery section of the reactive distillation column is a shelf.   The transesterification of polytetramethylene ether glycol according to any one of claims 1 to 6, characterized in that the transesterification is carried out in a reactor until it reaches 87 to 99% of the equilibrium reaction rate of polytetramethylene ether glycol diacetate. Production method.   The method for producing polytetramethylene ether glycol according to any one of claims 1 to 7, wherein the reactive distillation column is operated at a reflux ratio of 0.5 to 20.   9. The production of polytetramethylene ether glycol according to claim 1, wherein the reactive distillation column is operated so that the concentration of polytetramethylene ether glycol in the bottoms is 30 to 70% by weight. Method.