JP4245775B2 - Continuous production method of polyester - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for continuously producing a polyester from an aromatic dicarboxylic acid or a lower alkyl ester thereof and a glycol component containing 1,4-butanediol as a main component. More specifically, the present invention relates to a method for continuously producing polyester, in which tetrahydrofuran produced as a by-product in producing the polyester can be efficiently recovered outside the system.
[0002]
[Prior art]
Conventionally, polyesters containing 1,4-butanediol as the main glycol, especially polybutylene terephthalate, has its excellent physical and chemical properties, so it can be used in various applications such as fibers, films, and other molded articles. Widely used in Moreover, since it is excellent in mechanical properties such as strength and elastic modulus, heat resistance, etc., it is widely used especially as an engineering plastic.
[0003]
In general, a direct polymerization method or a transesterification method is used as a method for producing polybutylene terephthalate used in such various applications.
[0004]
Here, in the former direct polymerization method, a polyester precursor is first formed by directly esterifying an acid component and a diol component, and then the polyester precursor is polycondensed under reduced pressure to obtain polybutylene terephthalate. It is a manufacturing method. On the other hand, the latter transesterification method is a method in which a lower alkyl ester of an acid component and a diol are transesterified to form a polyester precursor, and then the polyester precursor is polycondensed under reduced pressure.
[0005]
In the case of polymerization of such a polyester, a batch method has been conventionally used. However, in recent years, a change to a continuous method has been promoted in order to produce a polyester at low cost by taking advantage of scale merit. . This is because the merits such as yield reduction, quality improvement, uniformity of polymerization degree, improvement in operability, etc. are extremely large by adopting the continuous method.
[0006]
In general, most of the production methods by continuous polymerization of polyester are performed by a process in which a plurality of transesterification reactors or esterification reactors and polycondensation reactors are combined. For example, a raw material is supplied to a transesterification reactor or an esterification reactor to produce a monomer or oligomer, and the obtained monomer or oligomer is supplied to an initial polycondensation reactor to react under reduced pressure. In this method, a low polymer is produced and supplied to a polycondensation reactor to produce an intermediate polymer and a high polymer under reduced pressure.
[0007]
Usually, when polybutylene terephthalate is produced, tetrahydrofuran is by-produced by a dehydration cyclization reaction of 1,4-butanediol used as a part of the raw material. Further, during the reaction, tetrahydrofuran is by-produced by thermal decomposition of the hydroxy terminal of polybutylene terephthalate. Thus, much of the tetrahydrofuran produced as a by-product in the transesterification or esterification reaction stage and the polycondensation stage is discharged out of the system together with methanol and / or water as a distillate at the top of the attached distillation column. In such a process, since the loss of 1,4-butanediol due to the by-product of tetrahydrofuran is disadvantageous in terms of production cost, many proposals for suppressing the by-product of tetrahydrofuran have been made. It is difficult to eliminate this completely.
[0008]
In general, a polyester production facility has a recovery process for recovering a distillate generated from the process, and the purified glycol component is reused as a raw material.
[0009]
As such a method, Japanese Patent Laid-Open No. 60-163918 discloses a direct polymerization method of polyethylene terephthalate obtained by condensing a gas mainly composed of ethylene glycol generated from a polycondensation reactor with a wet condenser. There has been proposed a method in which the condensate is sent to a distillation column attached to an esterification reactor to remove impurities having a low boiling point and then returned to a slurry mixing tank.
[0010]
In addition, Japanese Patent Publication No. 7-100734 discloses an example in which, in the direct polymerization method of polybutylene terephthalate, condensate from a decompression apparatus containing tetrahydrofuran and water is introduced into a tower of an esterification reactor. .
[0011]
Such a polyester production method is an effective method from the viewpoint that it is possible to reduce the operating cost and to simplify the apparatus without the need to newly install a rectifying apparatus as an incidental facility. No consideration has been given to the method of recovering tetrahydrofuran from the top distillate of the distillation column attached to the reactor or the transesterification reactor.
[0012]
Furthermore, in a method for separating tetrahydrofuran from a mixture of methanol and / or water containing tetrahydrofuran, JP-B-62-911 supplies tetrahydrofuran containing alcohol to a distillation column, and a specific amount from the top of the supply position. A method has been proposed in which water is supplied and is subjected to extractive distillation in countercurrent contact with a tetrahydrofuran stream to easily separate alcohol from tetrahydrofuran.
[0013]
Japanese Patent Publication No. 63-10928 discloses that crude tetrahydrofuran containing methanol is purified by operating both columns continuously under different pressures in a system of at least two columns, and does not contain methanol or water. A method for obtaining high purity tetrahydrofuran in high yield has been proposed.
[0014]
Such a method for separating tetrahydrofuran from a mixture of methanol and / or water containing tetrahydrofuran can easily separate tetrahydrofuran from a mixture of methanol and / or water containing tetrahydrofuran, and can produce tetrahydrofuran in a high yield. However, it is disadvantageous in terms of construction cost and running cost because the equipment is large in size.
[0015]
[Problems to be solved by the invention]
In view of the problems described above, the problem to be solved by the present invention is “manufacturing a polyester comprising an aromatic dicarboxylic acid or a lower alkyl ester thereof and a glycol component mainly composed of 1,4-butanediol. It is an object of the present invention to provide a continuous production method of polyester that can efficiently recover by-produced tetrahydrofuran out of the system.
[0016]
[Means for Solving the Problems]
Here, according to this invention, the following continuous manufacturing method of polyester is provided.
First, as the present invention according to claim 1, “aromatic dicarboxylic acid or aromatic dicarboxylic acid dimethyl ester and a glycol component in which 50 mol% or more is 1,4-butanediol based on the total glycol component are esterified. In the method for continuously producing a polyester by sequentially passing through a reaction step or a transesterification reaction step and a polycondensation reaction step, the distillate from the polycondensation reaction step is converted into an esterification reaction step or a transesterification step. The distillate containing tetrahydrofuran distilled from the top of the distillation column is temporarily stored and then fed to the second distillation column of the batch type. A series of polyesters characterized in that tetrahydrofuran is recovered from the top of the column and methanol and / or water is withdrawn from the bottom. Production method "is provided.
[0017]
Further, as the present invention according to claim 2, the continuous production according to claim 1, wherein the distillate from the top of the second distillation column contains 10% by weight or more of tetrahydrofuran based on the distillate. Method "is provided.
[0018]
Further, as the present invention according to claim 3, “the continuous production method according to claim 1, wherein the tetrahydrofuran content in methanol and water extracted from the bottom of the second distillation column is 0.5 wt% or less”. Provided.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
First, examples of the aromatic dicarboxylic acid used in the present invention include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid, and the like. Examples of the lower alkyl ester of aromatic carboxylic acid include dimethyl terephthalate and dimethyl isophthalate.
[0020]
In the present invention, the “main” of the glycol constituting the polyester means that the component occupies 50 mol% or more, preferably 80 mol% or more, based on the total glycol component.
[0021]
Examples of glycol components other than 1,4-butanediol include ethylene glycol, neopentyl glycol, 1,2-propanediol, 1,3-propanediol (trimethylene glycol), 1,3-butanediol, 1, 5-pentadiol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, propylene glycol, etc. These glycol components can be used alone or in combination of two or more, as long as 1,4-butanediol accounts for 50 mol% or more based on the total diol components. Well, 1,4-butanediol is Call component may account for 100 mol% based on.
[0022]
The polyester of the present invention can be copolymerized with a trifunctional or higher polyfunctional compound such as trimellitic acid, pyromellitic acid or glycerol, or a monofunctional compound such as benzoic acid or phenyl isocyanate.
[0023]
Furthermore, in the present invention, the polyester may be produced in the presence or absence of a catalyst. When using a catalyst, a well-known catalyst can be used, for example, an antimony compound, a manganese compound, a titanium compound, a tin compound, a zinc compound, a magnesium compound etc. can be used. The supply position and supply method of such a catalyst are not particularly limited, and may be appropriately determined according to the manufacturing conditions. In addition, in the method for producing a polyester of the present invention, a catalyst or additive that is effective for suppressing the by-production of tetrahydrofuran and that is commonly used can be used.
[0024]
Furthermore, if necessary, one or more of other commonly used thermoplastic resins, additives, inorganic fillers, organic fillers and the like are added to the reactor of the present invention as they are or together with the diol component. Alternatively, it can be directly kneaded with a molding machine, an extruder, a mixer or the like on the exit side of the reactor.
[0025]
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 exemplifies a flow chart for carrying out the present invention, and will be described when the polyester of the present invention is continuously produced by a transesterification method.
[0026]
First, methanol containing tetrahydrofuran, water and the like distilled from a transesterification reactor (not shown) is supplied from a pipe (2 in FIG. 1) to the first distillation column (1 in FIG. 1). In addition, 1,4-butanediol containing tetrahydrofuran, water, methanol and the like, which is a distillate from a polycondensation reactor (not shown), is also supplied from the piping (3 in FIG. 1) to the first distillation column (in FIG. 1). 1). Here, it is preferable that the distillate from the polycondensation reactor is supplied to the upper stage from the distillate from the transesterification reactor in terms of preventing clogging of the first distillation column due to scattered matter.
[0027]
Further, the vapor mainly composed of methanol distilled from the top of the first distillation column (1 in FIG. 1) is once supplied to the fraction tank (7 in FIG. 1) through the pipe (6 in FIG. 1). The Here, in order to control the temperature at the top of the first distillation column (1 in FIG. 1), the vapor rising to the top of the distillation column is condensed by a condenser (4 in FIG. 1), and a part of it is condensed. It is preferable to reflux to the top of the column and supply the remaining condensate to the fraction tank (7 in FIG. 1) via a pipe (6 in FIG. 1). The effluent containing 1,4-butanediol as the main component at the bottom of the column is reused as a part of the raw material for the transesterification reaction through a pipe (8 in FIG. 1).
[0028]
In addition, a batch-type second distillation column (9 in FIG. 1) having a plate or a packed column has a valve (11 in FIG. 1) and a pipe (12 in FIG. 1) and a fraction tank (7 in FIG. 1). The condensate from the condenser (4 in FIG. 1) stored in the fraction tank is charged periodically. Further, the vapor mainly composed of methanol and / or water and tetrahydrofuran rising to the top of the second distillation column (9 in FIG. 1) is condensed in the condenser (10 in FIG. 1) and partly the second. Refluxed to a double distillation column (9 in FIG. 1), a part thereof was withdrawn out of the system through a pipe (13 in FIG. 1), and the effluent containing methanol and / or water as main components was pipe (14 in FIG. 1). ) To be discharged outside the system.
[0029]
A method of continuously producing polybutylene terephthalate by the transesterification method in the present apparatus configured as described above will be described in more detail with reference to FIG.
[0030]
First, the raw materials dimethyl terephthalate and 1,4-butanediol are supplied to a transesterification reactor (not shown). Here, the molar ratio of the 1,4-butanediol to the dimethyl terephthalate is preferably in the range of (1.1: 1) to (1.8: 1), particularly preferably (1.3: 1). To (1.7: 1). The temperature in the transesterification reactor is set to 150 to 200 ° C., and the supplied raw material undergoes transesterification under normal pressure. During this time, by-product steam containing methanol as a main component is led from the pipe (2 in FIG. 1) to the first distillation column (1 in FIG. 1). On the other hand, the main product in the transesterification reaction is subsequently transferred to a polycondensation reactor (not shown) and subjected to a polycondensation reaction at a reaction temperature of 200 to 260 ° C. under reduced pressure.
[0031]
Here, the number of transesterification reactors and polycondensation reactors, and the type of reactor are not particularly limited. Further, the operation pressure and temperature are not limited, and these reactions may be performed in an inert gas atmosphere as necessary. Further, the finally obtained polybutylene terephthalate polymer is pelletized in a granulation step or the like, and further made high molecular weight by solid phase polymerization as necessary.
[0032]
Here, by-product steam mainly composed of 1,4-butanediol generated from each polycondensation reactor is condensed in a condenser (not shown), and the condensed distillate is a pipe (3 in FIG. 1). And then sent to the first distillation column (1 in FIG. 1). Note that the condensate containing 1,4-butanediol as a main component contains impurities such as sticky scattered matter, and therefore, before being supplied to the first distillation column (1 in FIG. 1), a wire mesh filter or a centrifuge is used. It is preferable to remove the sticking scattered matter with a separator or the like. Further, it may be supplied by heating in advance.
[0033]
As described above, the distillate from the polycondensation reactor is supplied to the first distillation column (1 in the figure) attached to the transesterification reactor through the pipe (3 in FIG. 1). The first distillation column (1 in FIG. 1) is obtained by distilling by-product steam containing methanol as a main component guided from a transesterification reactor (not shown) and a polycondensation reactor (not shown). It is also used for distillation of the distillate. In addition, when a mechanical booster pump is used as the vacuum device of the polycondensation reactor, the vapor of low boiling point substances such as methanol and tetrahydrofuran distilled into the vacuum system is condensed and supplied to the first distillation column (1 in FIG. 1). Thus, it can also be used for these distillations.
[0034]
The bottom temperature of the first distillation column (1 in FIG. 1) is controlled by a reboiler (5 in FIG. 1). And the vapor | steam containing tetrahydrofuran and water which uses methanol as a main component from a tower top part is distilled through piping (6 in FIG. 1), and is supplied to a fraction tank (7 in FIG. 1). Further, glycol containing 1,4-butanediol as a main component is recovered from the bottom of the column and reused as at least a part of the glycol component which is a polyester starting material. At this time, it is preferable that the water content of the 1,4-butanediol to be reused is 0.5% by weight or less because the reactivity during the production of the polyester becomes particularly good.
[0035]
Further, the temperature at the top of the second distillation column (9 in FIG. 1) is controlled to 64 ° C. or less, preferably 63 ° C. or less as the reflux amount of the condenser (10 in FIG. 1). Most of the tetrahydrofuran supplied to the middle 9) is distilled off from the top of the tower via a pipe (13 in FIG. 1). At this time, from the viewpoint of recovery efficiency, it is desirable that 10% by weight or more of tetrahydrofuran is contained in the distillate. Further, a distillate containing methanol as a main component is extracted from the bottom of the column. In the second distillation column of the present invention (9 in FIG. 1), known extractive distillation methods and operating conditions in methanol and tetrahydrofuran or water and tetrahydrofuran can be applied. Furthermore, tetrahydrofuran may be recovered from the bottom of the second distillation column (9 in FIG. 1).
[0036]
If the method of the present invention described above is used, tetrahydrofuran produced as a by-product in the polyester production process can be recovered out of the system very efficiently using two distillation columns.
[0037]
【Example】
Next, although the Example of this invention is described concretely using the flow of FIG. 1, this invention does not receive any limitation by this.
[0038]
[Example 1]
Transesterification reactor at a feed rate of 40 kg / hr dimethyl terephthalate, 27 kg / hr 1,4-butanediol, and 0.03 kg / hr titanate titanate as starting materials for polyester The polybutylene terephthalate oligomer was obtained by continuously transesterifying the mixture and conducting a transesterification reaction at a temperature of 160 to 190 ° C. and normal pressure to distill 85% of the theoretical amount of methanol. Subsequently, the obtained oligomer was continuously supplied to the initial polycondensation reactor, and a polycondensation reaction was performed under the conditions of a temperature of 230 ° C. and a vacuum degree of 4.0 kPa to obtain a polybutylene terephthalate low polymer. Subsequently, the obtained low polymer was continuously supplied to the final polycondensation reactor, and a polycondensation reaction was performed under conditions of a temperature of 247 to 248 ° C. and a degree of vacuum of 0.2 kPa. The resulting polybutylene terephthalate polymer had an intrinsic viscosity (value calculated from melt viscosity measured in orthochlorophenol at 35 ° C.) of 0.63, which was taken out by a gear pump and pelletized in the granulation step.
[0039]
Further, by-product steam containing methanol as a main component containing 1% by weight of tetrahydrofuran from the transesterification reactor at a supply rate of 16 kg / hr is passed through the pipe (2 in FIG. 1) through the first distillation column (1 in FIG. 1). Supplied to. Transesterification of a distillate containing 1,4-butanediol as a main component containing 3% by weight of tetrahydrofuran from the initial polycondensation reactor and the final polycondensation reactor through a pipe (3 in FIG. 1) at 11 kg / hr. It was supplied to the first distillation column (1 in the figure) attached to the reactor. The top temperature of the first distillation column (1 in FIG. 1) was controlled at 64 ° C., and the bottom temperature was controlled at 180 ° C. by a reboiler (5 in FIG. 1). Then, a vapor containing tetrahydrofuran and water as a main component was distilled from the top of the tower and supplied to the fraction tank 7 via the pipe 6. At this time, 1,4-butanediol containing 0.5 wt% or less of water was recovered from the bottom of the first distillation column (1 in FIG. 1) through the pipe 8, and one glycol as a starting material was recovered. Reused as part. Further, methanol containing 23% by weight of tetrahydrofuran was recovered from the top of the second distillation column (9 in FIG. 1) through the pipe 13. Further, methanol containing almost no tetrahydrofuran was recovered from the bottom of the column via the pipe 14. The top temperature of the second distillation column (9 in FIG. 1) was controlled at 60 ° C. by the amount of reflux from the cooler 11.
[0040]
In the above continuous production method of polybutylene terephthalate, it was possible to efficiently recover tetrahydrofuran and methanol by-produced in the production process without using a large distillation apparatus by using two distillation columns.
[0041]
[Comparative Example 1]
Next, a comparative example of the present invention will be specifically described with reference to the flow of FIG.
A polybutylene terephthalate polymer was produced in the same manner as in Example 1, and by-product steam containing methanol as a component containing 1% by weight of tetrahydrofuran from the transesterification tank was passed through the pipe 16 at 16 kg / hr through the first distillation column (FIG. 2). 15). A distillate comprising 1,4-butanediol containing 3% by weight of tetrahydrofuran from the initial polycondensation reactor and the final polycondensation reactor as a component at 11 kg / hr via a pipe 16 is attached to the first transesterification reactor. It supplied to the distillation column (15 in FIG. 2). The top temperature of the first distillation column was controlled at 64 ° C., and the bottom of the column was controlled at 180 ° C. by the reboiler 19. And the vapor | steam containing tetrahydrofuran, water, etc. which made methanol the main component was distilled from the tower top part, and was continuously supplied to the 2nd distillation tower (22 in FIG. 2) through piping (FIG. 2). At this time, 1,4-butanediol having a water content of 0.5% by weight or less was recovered from the bottom of the first distillation column (15 in FIG. 2) via a pipe (21 in FIG. 2), and the starting material Recycled as part of the glycol. Further, methanol containing 7% by weight of tetrahydrofuran was recovered from the top of the second distillation column (22 in FIG. 2) through a pipe (24 in FIG. 2). On the other hand, methanol containing 3% by weight of tetrahydrofuran was recovered from the bottom of the column through a pipe (26 in FIG. 2). The second distillation column (22 in FIG. 2) had a large temperature fluctuation range, and stable operation was difficult.
[0042]
【The invention's effect】
According to the present invention, a process for reducing the amount of tetrahydrofuran produced as a by-product in the continuous production of polyester from an aromatic dicarboxylic acid or a lower alkyl ester thereof and a glycol component mainly composed of 1,4-butanediol. In addition, it is possible to efficiently recover the number, to reduce the operating cost and to simplify the equipment, and to provide a stable and inexpensive method for continuously producing polyester.
[Brief description of the drawings]
FIG. 1 is a flow diagram schematically illustrating one embodiment of the method of the present invention.
FIG. 2 is a flow diagram schematically illustrating one aspect of a prior art method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 First distillation column 2 Distillate supply piping of transesterification reactor 3 Distillate supply piping of polycondensation reactor 4 Condenser 5 Reboiler 6 Distillate supply piping of first distillation column 7 Distillation tank 8 First distillation Tower distillation liquid supply pipe 9 Second distillation tower 10 Condenser 11 Supply valve 12 Contents tank supply pipe 13 Distillate discharge pipe 14 of the second distillation tower Second distillation tower discharge pipe 15 First distillation Column 16 Distillate supply pipe 17 of the transesterification reactor 17 Distillate supply pipe 18 of the polycondensation reactor 18 Condenser 19 Reboiler 20 Distillate supply pipe 21 of the first distillation column Effluent supply pipe 22 of the first distillation column Distillation tower 23 Condenser 24 Distillate discharge pipe 25 of the second distillation tower Reboiler 26 Exhaust liquid discharge pipe of the second distillation tower

Claims (3)

Aromatic dicarboxylic acid or aromatic dicarboxylic acid dimethyl ester and a glycol component in which 50 mol% or more is 1,4-butanediol based on the total glycol component , esterification reaction step or transesterification reaction step, and polycondensation reaction In a method of continuously producing polyester by sequentially passing the steps,
The distillate from the polycondensation reaction step is supplied to the first distillation column attached to the esterification reaction step or the transesterification reaction step, and a distillate containing tetrahydrofuran distilled from the top of the distillation column is obtained. Once stored, fed to a batch-type second distillation column, tetrahydrofuran is recovered from the top of the second distillation column, and methanol and / or water is withdrawn from the bottom of the column, A continuous production method of polyester.   The continuous production method according to claim 1, wherein the distillate from the top of the second distillation column contains 10 wt% or more of tetrahydrofuran based on the distillate.   The continuous production method according to claim 1, wherein the content of tetrahydrofuran in methanol and water extracted from the bottom of the second distillation column is 0.5% by weight or less.

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