JP3904576B2 - Heat exchanger cleaning method and polyester manufacturing method - Google Patents

Description

  The present invention relates to a heat exchanger cleaning method and a polyester manufacturing method. More specifically, the present invention effectively uses a washing method of a condenser or a heat exchanger for stably performing a polycondensation reaction of a polyester having 1,4-butanediol as one monomer component, and resources, and The present invention relates to a method for producing a polyester having stable quality.

Polyester is easy to mold, mechanical properties, heat resistance, chemical resistance, fragrance retention, and other physical and chemical properties, so it is used in various fields such as fibers, molded parts, and films. It has been.
Above all, polybutylene terephthalate consisting of terephthalic acid component and 1,4-butanediol component is one of engineering plastics with mechanical properties and heat resistance that can replace metal materials. It has been widely used for injection molded products such as equipment parts, and in recent years, it has been widely used in the fields of films, sheets, monofilaments, fibers and the like by taking advantage of its excellent properties.

Polyester is generally subjected to esterification reaction or transesterification reaction between a dicarboxylic acid or its ester derivative and a diol, and then a low molecular weight product such as diol or water is usually removed from the system under reduced pressure of 10 kPa or less. While removing, a polycondensation reaction is performed for production.
At this time, most of the low molecular weight components are removed from the system in a gaseous state, then cooled by a condenser, and usually recovered in a liquid form. On the other hand, a small amount of low boiling point components that are not condensed by the condenser are directed to a deaeration device such as a vacuum pump or an ejector. In the case of a polyester having 1,4-butanediol as one monomer component, the main low molecular weight components generated in the polycondensation reaction are 1,4-butanediol, water, and tetrahydrofuran produced by side reactions, Under a polycondensation condition of a high temperature of 200 ° C. or higher and a reduced pressure of 10 kPa or lower, these are discharged out of the system as a gas and collected by a condenser. However, under such high-temperature and high-vacuum polycondensation reaction conditions, oligomers containing 1,4-butanediol as a monomer component are volatilized in a small amount, and these oligomers having a high melting point and low solubility are converted into the condenser itself. Or the heat exchanger attached to the condenser is clogged, the pressure of the polycondensation reactor fluctuates, and the quality of the resulting polyester such as the intrinsic viscosity fluctuates.

In order to solve this problem, for example, in the production of polybutylene terephthalate, solid components such as oligomers contained in condensed 1,4-butanediol can be added by adding alkali components such as alkali alkoxide and alkali hydride. There is an attempt to solubilize (see, for example, Patent Document 1). However, in this method, 1,4-butanediol and oligomers collected by the condenser are contaminated with alkali components. Therefore, when these recovered 1,4-butanediol and the like are to be reused as raw materials and the like, there has been a problem that an operation for removing and refining the alkali component is required, resulting in excessive facilities. Further, when the recovered 1,4-butanediol or the like is reused as a raw material, for example, when distillation is performed as a method for removing or purifying alkali components, the treatment of alkaline waste liquid in the distillation residue and the aspect of running cost are required. There was also a need for improvement.
Japanese Examined Patent Publication No. 62-9094

  The present invention has been made with the object of providing a method for producing a polyester of stable quality and a method for washing a heat exchanger to achieve the method.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that fluctuations in quality such as intrinsic viscosity of a polyester having 1,4-butanediol as one monomer component are caused by pressure in the polycondensation process. Find out that it is largely related to fluctuations, and that the pressure fluctuations are due to oligomer blockage in the condenser or heat exchanger attached to the condenser in the polycondensation process and wash them under specific conditions As a result, it was found that stable quality polyester can be obtained, and the present invention has been completed.

That is, the gist of the present invention is to use 1,4-butanediol as one monomer component, in a molten state, using a polycondensation catalyst, at a pressure of 10 kPa or less, using at least one horizontal reaction vessel, and 210-245. 50 in the step of continuously producing a polyester by polycondensation reaction at a temperature of 50 ° C., a condenser for condensing the gas distilled from the horizontal reaction tank or a heat exchanger for cooling the condensed liquid of the distilled gas. The present invention resides in a condenser or heat exchanger washing method characterized by washing at ˜300 ° C., and another gist of the present invention is 1,4-butanediol as one monomer component in a molten state. using a polycondensation catalyst at pressures 10 kPa, continuously by polycondensation reaction with at least one horizontal reactor temperature was used and two hundred and ten to two hundred forty-five ° C., in the step of producing a polyester, Condenser for condensing the mold distilled gas from the reaction vessel, or distilled out of the heat exchanger for cooling the condensate of the gas is washed with a liquid containing 1,4-butanediol of 50 to 300 ° C., the washing A polyester production method is characterized in that at least a part of the liquid containing 1,4-butanediol used is used as part or all of the raw material 1,4-butanediol for the production of polyester.

  According to the present invention, a stable reduced pressure state can be maintained, and a method for producing a polyester with stable quality can be provided.

Hereinafter, the present invention will be described in detail.
The polyester in the present invention is a polymer having a structure in which a dicarboxylic acid unit and a diol unit are ester-bonded. Specific examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, 4,4′-diphenyldicarboxylic acid, 4, Aromatic dicarboxylic acids such as 4'-diphenyl ether dicarboxylic acid, 4,4'-benzophenone dicarboxylic acid, 4,4'-diphenoxyethane dicarboxylic acid, 4,4'-diphenylsulfone dicarboxylic acid, 2,6-naphthalenedicarboxylic acid Cycloaliphatic dicarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, Examples include aliphatic dicarboxylic acids such as azelaic acid and sebacic acid. Among the aromatic dicarboxylic acids, terephthalic acid, isophthalic acid, and aliphatic dicarboxylic acids are preferably succinic acid and adipic acid from the viewpoints of mechanical properties, wide application, and availability of raw materials. . These can be used by mixing different kinds.

  These dicarboxylic acid components can be donated to the reaction as a dicarboxylic acid or as an alkyl ester of a dicarboxylic acid, preferably a dialkyl ester, and may be a mixture of a dicarboxylic acid and a dicarboxylic acid alkyl ester. There are no particular restrictions on the alkyl group of the dicarboxylic acid alkyl ester, but if the alkyl group is long, the boiling point of the alkyl alcohol produced during the transesterification reaction will increase, and the reaction solution will not volatilize, resulting in polymerization as a terminator. In view of this, an alkyl group having 4 or less carbon atoms is preferable, and a methyl group is particularly preferable.

  Specific examples of the diol component include ethylene glycol, diethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3-propanediol, polypropylene glycol, 1,4-butanediol, polytetramethylene glycol, dibutylene glycol, 1 Aliphatic diols such as 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethylol Such as alicyclic diols such as 1,4-cyclohexanedimethylol, xylylene glycol, 4,4′-dihydroxybiphenyl, 2,2-bis (4-hydroxyphenyl) propane, bis (4-hydroxyphenyl) sulfone, etc. Aromatic Geo Etc. can be mentioned Le, it can also be used by mixing different types of things, in the present invention, as an essential component 1,4-butanediol. Among them, the improvement effect of the present invention is remarkable in the polyester in which 50 mol% or more of the diol units is 1,4-butanediol.

  In the present invention, a hydroxycarboxylic acid such as lactic acid, glycolic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 6-hydroxy-2-naphthalenecarboxylic acid, p-β-hydroxyethoxybenzoic acid, alkoxycarboxylic acid, etc. Monofunctional components such as acid, stearyl alcohol, benzyl alcohol, stearic acid, benzoic acid, t-butylbenzoic acid, benzoylbenzoic acid, tricarbaric acid, trimellitic acid, trimesic acid, pyromellitic acid, gallic acid, trimethylolethane Trifunctional or higher polyfunctional components such as trimethylolpropane, glycerol and pentaerythritol can be used as the copolymerization component.

  Among them, 70 mol% or more of dicarboxylic acid units, preferably 80 mol% or more, particularly preferably 95 mol% or more are composed of terephthalic acid units, and 70 mol% or more of diol units, preferably 80 mol% or more, particularly preferably. In polybutylene terephthalate in which 95 mol% or more is composed of 1,4-butanediol units, the amount of oligomer volatilization during the polycondensation reaction is large, so the improvement effect in the present invention is great.

  The intrinsic viscosity of the polyester of the present invention is usually 0.50 to 3.00 dL / g, preferably 0.60 to 2.00 dL / g, and more preferably 0.70 to 1.50 dL / g. When the intrinsic viscosity is less than 0.50 dL / g, the mechanical strength of the molded product becomes insufficient, and when it exceeds 3.00 dL / g, the melt viscosity becomes high, the fluidity deteriorates, and the moldability deteriorates. There is a tendency. The intrinsic viscosity is a value measured at 30 ° C. using a mixed solution of phenol / tetrachloroethane (weight ratio 1/1) as a solvent.

Among them, when the polyester is polybutylene terephthalate, it is usually 0.60 to 2.00 dL / g, preferably 0.70 to 1.70 dL / g, more preferably 0.80 to 1.50 dL / g, particularly preferably. Is 0.80 to 0.90 dL / g.
In the present invention, an antimony compound such as antimony trioxide, a germanium compound such as germanium dioxide or germanium tetraoxide, a manganese compound, a zinc compound, a zirconium compound, a cobalt compound, a titanium compound, or a tin compound may be used as a polycondensation catalyst. it can. Among these, when the polyester is polybutylene terephthalate, the catalyst is preferably used from the stage of esterification reaction or transesterification reaction. In this case, the catalyst can be added all at once or dividedly at the stage of the esterification reaction or transesterification reaction.

When a catalyst is used in the esterification reaction or transesterification reaction, the same catalyst can be used subsequently as a polycondensation catalyst, or it may be added additionally at the stage of polycondensation.
The polycondensation catalyst is preferably a titanium compound. Specific examples of titanium compounds include inorganic titanium compounds such as titanium oxide and titanium tetrachloride, titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate and tetrabutyl titanate, and tetraphenyl titanate. And titanium phenolate. Among these, tetraalkyl titanate is preferable, and among them, tetrabutyl titanate is preferable.

  In addition to the above catalyst, magnesium compounds such as magnesium acetate, magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium alkoxide, magnesium hydrogen phosphate, calcium acetate, calcium hydroxide, calcium carbonate, calcium oxide, calcium alkoxide. Side, calcium hydrogen phosphate and other calcium compounds, orthophosphoric acid, phosphorous acid, hypophosphorous acid, polyphosphoric acid, phosphorus compounds such as esters and metal salts thereof, and reaction aids such as sodium hydroxide and sodium benzoate are used. May be.

  Furthermore, in addition to the catalyst and reaction aid, 2,6-di-t-butyl-4-octylphenol, pentaerythrityl-tetrakis [3- (3 ′, 5′-t-butyl-4′-hydroxyphenyl) Phenol compounds such as propionate], thioether compounds such as dilauryl-3,3′-thiodipropionate, pentaerythrityl-tetrakis (3-laurylthiodipropionate), triphenyl phosphite, tris (nonylphenyl) phosphite Antioxidants such as phosphorus compounds such as tris (2,4-di-t-butylphenyl) phosphite, paraffin wax, microcrystalline wax, polyethylene wax, long chain fatty acids represented by montanic acid and montanic acid ester, and Other additives such as release agents such as esters and silicone oil It may be Zaisa.

  In the present invention, the lower limit of the amount of the metal catalyst used when the polycondensation catalyst is composed of a metal compound is 1 ppm, preferably 3 ppm, more preferably 5 ppm, particularly preferably 5 ppm, particularly as a metal atom derived from the catalyst with respect to the polyester usually obtained. Preferably it is 8 ppm, more preferably 15 ppm. On the other hand, the upper limit is preferably 250 ppm, more preferably 150 ppm, and still more preferably 100 ppm as a metal atom derived from the catalyst with respect to the obtained polyester. In particular, when the catalyst contains titanium, the upper limit of the amount of titanium is preferably 100 ppm, more preferably 70 ppm, more preferably 50 ppm, and particularly preferably 35 ppm. When the metal atom content derived from the catalyst is more than 250 ppm, the color tone, hydrolysis resistance, transparency, moldability and the like are deteriorated and foreign matter tends to increase. Moreover, since the production | generation rate of the oligomer which volatilizes and has a bad influence on a condenser also increases, the improvement effect of this invention is impaired. On the other hand, when it is less than 1 ppm, the polymerizability may be deteriorated.

The content of metal atoms such as titanium atoms can be measured using a method such as atomic emission, atomic absorption, Inductively Coupled Plasma (ICP) after recovering the metal in the polymer by a method such as wet ashing. .
The polyester production method of the present invention is based on a conventional production method. These known methods are roughly divided into a so-called direct polymerization method using dicarboxylic acid and diol as main raw materials, and dicarboxylic acid dialkyl ester and diol as main raw materials. There are transesterification methods used. The former has the difference that water is produced in the initial esterification reaction, and the latter produces alcohol in the initial transesterification reaction, but the availability of raw materials, ease of distillate treatment, From the standpoint of superiority and the improvement effect of the present invention, the direct polymerization method is preferred.

  In the method for producing a polyester of the present invention, the oligomer obtained by the initial esterification reaction or transesterification reaction is subjected to a polycondensation reaction to further increase the molecular weight. When the polycondensation reaction is carried out by a batch method, usually, one polycondensation reaction tank is used, and the pressure is gradually lowered to increase the molecular weight. On the other hand, when the polycondensation reaction is carried out in a continuous process, usually a multi-stage polycondensation reactor is used to increase the molecular weight in order from the prepolymer to the polymer. There is no clear distinction between a prepolymer and a polymer. Generally, a polymer having a low molecular weight in a polycondensation stage is called a prepolymer, and a polymer having a practical mechanical strength is called a polymer. Polybutylene terephthalate In this case, the boundary is about an intrinsic viscosity of about 0.5.

  As an example of the continuous direct polymerization method, a dicarboxylic acid component and a diol component are usually 180 to 300 ° C., preferably 200 to 280 ° C., using an esterification reaction catalyst in a single or multi-stage esterification reaction tank. In particular, a temperature of 210 to 270 ° C., usually 10 to 250 kPa, preferably 13 to 133 kPa, particularly preferably 60 to 101 kPa, and a pressure of 0.5 to 6 hours, preferably 1 to 3 hours, The esterification reaction is performed continuously, and the resulting oligomer as an esterification reaction product is transferred to a polycondensation reaction tank, and continuously in a multistage polycondensation reaction tank using a polycondensation reaction catalyst. A temperature of 210 to 300 ° C., preferably 220 to 290 ° C., particularly preferably a temperature of 230 to 280 ° C. Among them, the final stage of polycondensation is preferable to the melting point of the polymer. Is 5 to 30 ° C., more preferably 5 to 20 ° C., particularly preferably 7 to 15 ° C., and usually 27 kPa or less, preferably 20 kPa or less, particularly preferably 13 kPa or less. Examples thereof include a polycondensation reaction under stirring at a reduced pressure of 2 kPa or less for 1 to 12 hours, preferably 2 to 10 hours.

When terephthalic acid is used as the dicarboxylic acid component and 1,4-butanediol is used as the diol component, the temperature is usually 180 to 260 ° C, preferably 200 to 250 ° C, particularly preferably 210 to 245 ° C, and usually 10 to 10 ° C. 133 kPa, preferably 13 to 101 kPa, particularly preferably 60 to 90 kPa, 0.5 to 6 hours, preferably 1 to 3 hours in an esterification reaction, and the resulting oligomer as an esterification reaction product It is transferred to a polycondensation reaction tank, and continuously in a multistage polycondensation reaction tank using a polycondensation reaction catalyst , 2 10 to 245 ° C , preferably 220 to 245 ° C, particularly preferably 220 to 245 ° C. Temperature, usually not more than 27 kPa, preferably not more than 20 kPa, particularly preferably not more than 13 kPa, in particular at least one polycondensation reactor Oite preferably the following vacuo 2 kPa, 1 to 12 hours under stirring, preferably 2 to 10 hours, and a method for the polycondensation reaction.

  On the other hand, as an example of the continuous transesterification method, a dicarboxylic acid dialkyl ester component and a diol component are usually used at a temperature of 110 to 300 ° C., preferably in a single or multi-stage transesterification reaction tank, using an esterification exchange catalyst. 140 to 280 ° C., particularly preferably 180 to 260 ° C., usually 10 to 250 kPa, preferably 13 to 133 kPa, particularly preferably 60 to 101 kPa, for 0.5 to 6 hours, preferably 1 to The transesterification reaction is continuously performed in 3 hours, and the resulting oligomer as the transesterification reaction product is transferred to a polycondensation reaction tank, and continuously in a multistage polycondensation reaction tank using a polycondensation reaction catalyst. The temperature is usually from 210 to 300 ° C, preferably from 220 to 290 ° C, particularly preferably from 230 to 280 ° C. The stage is a temperature higher than the melting point of the polymer, preferably 5 to 30 ° C., more preferably 5 to 20 ° C., particularly preferably 7 to 15 ° C., and usually 27 kPa or less, preferably 20 kPa or less, particularly preferably 13 kPa or less, In one polycondensation reaction tank, a polycondensation reaction is preferably performed under reduced pressure of 2 kPa or less and with stirring for 1 to 12 hours, preferably 2 to 10 hours.

  Among these, when dimethyl terephthalate is used as the dicarboxylic acid dialkyl ester component and 1,4-butanediol is used as the diol component, the temperature is usually 110 to 260 ° C, preferably 140 to 245 ° C, particularly preferably 180 to 220 ° C. Moreover, it was usually obtained by carrying out a transesterification reaction continuously under a pressure of 10 to 133 kPa, preferably 13 to 101 kPa, particularly preferably 60 to 90 kPa for 0.5 to 6 hours, preferably 1 to 3 hours. The oligomer as the transesterification reaction product is transferred to a polycondensation reaction tank, and continuously in a multistage polycondensation reaction tank using a polycondensation reaction catalyst, usually 210 to 260 ° C, preferably 220 to 250 ° C. Particularly preferably, the temperature is 220 to 245 ° C., usually 27 kPa or less, preferably 20 kPa or less, particularly preferably 1 There is a method in which a polycondensation reaction is carried out under a reduced pressure of 3 kPa or less, particularly in at least one polycondensation reaction tank, preferably under a reduced pressure of 2 kPa or less, with stirring for 1 to 12 hours, preferably 2 to 10 hours.

  In the polycondensation step of the present invention, it is essential to have a condenser that condenses the distilled gas, and as the condenser, a known type such as a surface type or a direct contact type may be used. Among them, a direct contact type, a so-called wet capacitor, which has good heat exchange efficiency and is less likely to be blocked by an oligomer or the like is preferable. Some wet-type capacitors have a spray type in which the liquid is made into small droplets in order to obtain a large gas-liquid contact interface. However, in order to prevent the clogging, a shelf type is preferable. In addition, a plurality of condensers can be arranged in series to improve condensation efficiency and reduce clogging. Usually, at least one of these condensers is controlled to a temperature of less than 50 ° C. in order to condense the distilled gas component.

  For oligomers volatilized from the polycondensation reaction tank, especially cyclic oligomers with a high melting point and low solubility, in the case of surface type condensers, the liquid is circulated on the heat exchange surface where the distilled gas is condensed, a wet condenser, etc. If this occurs, it gradually accumulates on the heat exchange surface of the heat exchanger that cools the liquid, which not only lowers the heat exchange efficiency, but eventually causes blockage. In particular, when the polyester is polybutylene terephthalate, this phenomenon becomes more prominent when the polycondensation reaction conditions are 230 ° C. or higher and 1 kPa or lower.

Such a situation fluctuates the condensing capacity of the low molecular weight compound distilled from the polycondensation reaction tank, which in turn causes pressure fluctuations in the polycondensation reaction tank. Therefore, in the present invention, the heat attached to the condenser or the condenser is used. It is essential to wash the exchanger at 50-300 ° C. If the temperature for washing is higher than 300 ° C., there is an increased risk of deterioration of the obstruction and damage due to thermal expansion of the condenser and heat exchanger, and if it is lower than 50 ° C., the washing effect is reduced. The washing temperature is preferably 70 to 230 ° C, more preferably 90 to 200 ° C, particularly preferably 100 to 180 ° C, and particularly preferably 110 to 160 ° C.

There are no restrictions on the type of heat exchanger attached to the wet condenser, and known types such as a multi-tube type, plate type, plate fin type, spiral type, block type can be used. In a heat exchanger such as a plate type, plate fin type, or block type that can take a large amount, blockage or the like is likely to occur, so the improvement effect of the present invention is great.
There is no limitation on the method of cleaning the condenser or the heat exchanger attached to the condenser, but there are a method of temporarily raising the temperature of the heat medium, a method of directly flowing or spraying a gas, liquid, or the like at the temperature. Among them, a method of heating 1,4-butanediol having a relatively high boiling point and using this as a heat medium and a method of washing with a liquid containing 1,4-butanediol are preferable. In the present invention, the “liquid containing 1,4-butanediol” used for washing means a liquid in which a part or all of the liquid is 1,4-butanediol. At least a part of the liquid containing 1,4-butanediol and 1,4-butanediol after use can be reused as a part or all of 1,4-butanediol, which is a raw material for producing polyester. The washing time is usually 0.1 to 720 hours, preferably 1 to 240 hours, more preferably 3 to 72 hours.

Furthermore, from the viewpoint of securing productivity, it is preferable to install a plurality of condensers or heat exchangers, and switch between these to perform cleaning and use alternately.
When polyester is continuously polycondensed in a molten state, it is generally carried out using a multistage reaction vessel. Among them, at least one reaction vessel is a horizontal type having a rotating shaft of a stirring blade in a horizontal direction. The reaction tank (hereinafter sometimes abbreviated as a horizontal reaction tank) is preferable because a polyester with stable quality can be produced. On the other hand, horizontal reactors with excellent interfacial renewal ability also promote the volatilization of oligomers, so the above problems such as clogging tend to become larger.By applying the present invention, these problems are greatly reduced. Can be improved.

  There may be a plurality of horizontal reaction vessels, and the rotation shaft for rotating the stirring blades of the horizontal reaction vessel may be singular or plural. It is preferable that the structure has no support shaft. On the other hand, in the case of having a plurality of axes, each of them does not rotate in the same direction, but the combination of at least one axis preferably rotates in different directions. Among them, a preferable form is a reaction tank comprising a plurality of stirring blade blocks excellent in plug flow property and having two shafts having self-cleaning properties, and more preferably, the upper part is a prepolymer or a polymer. And the lower part rotates in a different direction to be the prepolymer or polymer entrainment direction.

By combining the above-described apparatus excellent in interface renewal and the cleaning method of the present invention, it becomes easy to sublimate at the time of molding and to remove the oligomer component in the polyester, which is a problem in food use.
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, (A) is a horizontal type polycondensation reaction tank having a plurality of rotor blades and having a rotating shaft of the stirring blade in the horizontal direction. It has a structure that does not have. (B) is a gear pump for extracting the polymer from the polycondensation reaction tank (A), (C) is a wet condenser, (D) is a pump for circulating liquid in the wet condenser, and (E) is circulated in the wet condenser. A heat exchange unit for cooling the liquid, (F) is a tank for temporarily storing the liquid extracted from the wet condenser, (G) is a dice head, and (H) is a rotary chip cutter. Also, (1) is a prepolymer supply line, (2) is a polymer extraction line, (3) is a vent line, (4) is a line connecting the wet condenser (C) and the tank (F), and both ends thereof. Preferably have a height difference of 10 m or more. (5) is a line connecting the pump (D) and the heat exchanging unit (E), (6) is a line connecting the heat exchanging unit (E) and the wet condenser (C), and (7) is disconnected from the wet condenser (C). A line connecting gas devices (not shown), (8) is a line for supplying liquid from the outside to the tank (F), and (9) is a liquid draining line to the outside.

  The prepolymer obtained by the initial polycondensation reaction is introduced into the horizontal polycondensation reaction tank (A) through the line (1), preferably continuously, and usually at a high temperature of 200 ° C. or higher and a reduced pressure of 10 kPa or lower. The polycondensation reaction proceeds further below. The obtained polymer is extracted in the form of a melted strand from the dice head (G) via the line (2), cooled with water, etc., and then cut into a pellet by a rotary cutter (H). On the other hand, low molecular weight components such as diol and water produced by the polycondensation reaction are led to a wet capacitor (C) through a line (3) together with a small amount of oligomer components. In the wet condenser (C), the liquid cooled in the heat exchange unit (E) is supplied from the line (6), and comes into contact with the distillate component introduced from the line (3). Condenses. The condensed component is guided to the tank (F) through the line (4) together with the circulating liquid, and the surplus is extracted to the outside through the line (9). The remaining liquid is introduced into the heat exchange unit (E) through the line (5), and is circulated to the wet condenser (C) through the line (6) again. At this time, since the liquid flowing through the line (5) may have insoluble matter, it is preferable to install a strainer or the like that removes the insoluble matter before entering the heat exchange unit (E). On the other hand, components not condensed in (C) are led to a vacuum deaerator through line (7). In addition, a liquid with a low boiling point is supplied from the line (8) to the tank (F) so that the condensation performance of the wet condenser (C) is not deteriorated. In a preferred embodiment of the present invention, the main component of the liquid circulating through the line (6) is 1,4-butanediol, and the liquid extracted through the line (9) is a part of the raw material 1,4-butanediol. Or recycle as a whole.

  FIG. 2 is a detailed view when the heat exchange unit (E) in FIG. 1 has two series of heat exchangers. In FIG. 2, (e1) and (e2) are heat exchanger bodies, (e3) is a heat exchanger for heating a heat medium for washing the heat exchangers (e1) and (e2), and (v1) (V8) is a valve, (5) and (6) are lines (5) and (6) in FIG. 1, and (21) to (40) are piping lines.

  Assuming that the heat exchanger (e1) is now in operation, the liquid introduced through the line (5) is cooled by the heat exchanger (e1) via the line (21), and the line (23), line ( It is circulated through the wet condenser (C) through 6). On the other hand, in the heat exchanger (e2) that is not operated in a switching manner, the heat medium introduced from the line (31) and heated by the heat exchanger (e3) is transferred to the lines (32) and (33). It is introduced and cleaned. The liquid after washing is extracted outside through the lines (34), (35) and (40). In a preferred embodiment of the present invention, the cleaning liquid is a liquid containing 1,4-butanediol, and further, 1,4-butanediol extracted through the line (40) is used as a part of the polyester production raw material. Is preferred.

After the washing, the heat exchanger (e2) is switched to the heat exchanger (e1) where the oligomer blockage has progressed at an appropriate timing, and then the heat exchanger (e1) in the same manner as the heat exchanger (e2). Perform cleaning.
In the present invention, since industrially stable polyester can be produced, the industrial utility value is great.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
In Examples and Comparative Examples, evaluation was performed as follows.
(1) Intrinsic viscosity (IV):
It calculated | required in the following way using the Ubbelohde type viscometer. That is, by using a mixed solution of phenol / tetrachloroethane (weight ratio 1/1) as a solvent, the polymer solution having a concentration of 1.0 g / dL and the number of seconds falling alone were measured at 30 ° C., and the following formula (5) I asked more.

Where η _sp = η / η ₀ −1, η is the polymer solution dropping time, η ₀ is the solvent dropping time, C is the polymer solution concentration (g / dL), and K _H is the Huggins constant. . K _H adopted the 0.33.

[Example 1]
FIG. 1 is a flowchart of this embodiment.
A polybutylene terephthalate oligomer obtained by continuously esterifying terephthalic acid and 1,4-butanediol in the presence of tetrabutyl titanate (30 ppm per polymer theoretical yield as the weight of titanium atom) has an internal temperature of 240 ° C. The liquid level was controlled such that the average residence time was 120 minutes by continuously supplying to a first polycondensation reaction tank (not shown) controlled at a pressure of 2.1 kPa. While extracting water, tetrahydrofuran and 1,4-butanediol from a vent line connected to a decompressor, an initial polycondensation reaction was performed to obtain a prepolymer. The obtained prepolymer was continuously supplied to the second polycondensation reaction tank (A). The intrinsic viscosity of the prepolymer at this time was 0.27.

In the second polycondensation reaction tank (A), the polymer was obtained by proceeding the polycondensation reaction at a pressure of 120 Pa, an average residence time of 90 minutes, and an internal temperature of 242 ° C. The obtained polymer was continuously extracted in the form of a strand via the extraction line (2) and the die head (G) by the extraction gear pump (B), and was chipped by the rotary cutter (H). .
At this time, the pressure control inside the second polycondensation reaction tank (A) was performed using a vacuum deaerator connected to the line (7). The liquid mainly composed of 1,4-butanediol, which is circulated and supplied to the wet condenser (C) via the line (6), is a heat exchanger (e1) of the heat exchange unit (E) shown in FIG. ) Was used, and 1,4-butanediol, water, tetrahydrofuran and the like distilled in a gaseous state were condensed from the vent line (3) with a wet condenser (C). At this time, water and tetrahydrofuran having a low boiling point partly distilled in the direction of the vacuum deaerator through the line (7) as a gas. On the other hand, the 1,4-butanediol component having a high boiling point and a small amount of the oligomer component were mostly condensed by the wet condenser (C). The liquid mainly composed of 1,4-butanediol condensed in the wet condenser (C) was temporarily stored in the tank (F) through the line (4). A liquid having a higher purity of 1,4-butanediol than the circulating liquid was introduced into the tank (F) from the outside through the line (8). On the other hand, using the pump (D), the liquid was extracted so that the liquid level of the tank was kept constant, and the excess liquid was discharged through the line (9) and used as a part of the raw material. The remaining liquid was cooled to 40 ° C. in the heat exchange unit (E) and then circulated through the wet condenser (C).

  72 hours after the start of the continuous polycondensation reaction, the pressure in the second polycondensation reaction tank (A) was stable, and the IV of the polymer obtained was always in the range of 0.84 to 0.86. At this time, the difference between the pressure near the inlet of the heat exchange unit (E) of the line (5) and the pressure near the outlet of the line (6) (hereinafter referred to as differential pressure) has doubled the initial value. When the heat exchanger was switched from (e1) to (e2), the differential pressure returned to the initial state. Subsequently, 1,4-butanediol heated to 120 ° C. was supplied to the heat exchanger (e1) separated from the process through a line (37) and washed for 6 hours. The 1,4-butanediol used for washing was mixed with the raw material 1,4-butanediol.

After 72 hours, the pressure and IV in the second polycondensation reactor were stable as described above, but since the differential pressure reached twice the initial pressure, the heat exchanger was cleaned from (e2) (e1). ) Returned to the initial differential pressure.
Subsequently, when this operation was repeated 5 times, the pressure and IV of the second polycondensation reaction tank were stable as described above.

[Comparative Example 1]
The same operation as in Example 1 was performed except that the operation of switching the heat exchanger was not performed. After 140 hours from the start of the polycondensation reaction, the pressure in the second polycondensation reaction tank could not be controlled, and IV decreased to 0.75.

[Comparative Example 2]
The same procedure as in Example 1 was conducted except that 1,4-butanediol at 45 ° C. was supplied through the line (37) and the heat exchanger (e1) was washed. After switching from the heat exchanger (e2) to the heat exchanger (e1) after washing, when this operation was repeated three times, the pressure in the second polycondensation reaction tank could not be controlled, and the IV was 0.78. It dropped to.

It is the schematic of the manufacturing apparatus of the polyester which is one preferable embodiment of this invention. It is the schematic of the heat exchange unit of the manufacturing apparatus of the polyester which is one preferable embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Prepolymer supply line 2 Polymer extraction line 3 Vent line 4 Extraction line from wet condenser 5 Supply line to heat exchange unit 6 Circulating fluid supply line to wet condenser 7 Line from wet condenser to deaerator 8 External 9 Feeding line from outside 21-24 Circulating fluid line 31-40 Washing fluid line A Polycondensation reaction tank B Gear pump C Wet condenser D Pump E Heat exchange unit F Tank G Die head H Chip cutter e1 to e3 Heat Exchanger v1-v8 valve

Claims (6)

Using 1,4-butanediol as one monomer component , continuously in a molten state using a polycondensation catalyst at a pressure of 10 kPa or less, using at least one horizontal reaction vessel, and a temperature of 210 to 245 ° C. In the step of producing polyester by polycondensation reaction, the condenser for condensing the gas distilled from the horizontal reaction tank or the heat exchanger for cooling the condensed liquid of the distilled gas is washed at 50 to 300 ° C. A method for cleaning a condenser or a heat exchanger.   The cleaning method according to claim 1, wherein a plurality of condensers or heat exchangers are installed, and these are switched to perform cleaning and use alternately.   The cleaning method according to claim 1 or 2, wherein the cleaning is performed using a liquid containing 1,4-butanediol at 50 to 300 ° C. Carried out in a wet capacitor using a liquid containing condensing 1,4-butanediol distilled gas, of claims 1 to 3 having a facility the liquid containing the 1,4-butanediol is cooled in heat exchanger The cleaning method according to any one of the above. Using 1,4-butanediol as one monomer component , continuously in a molten state using a polycondensation catalyst at a pressure of 10 kPa or less, using at least one horizontal reaction vessel, and a temperature of 210 to 245 ° C. In the step of producing polyester by polycondensation reaction, a condenser for condensing the gas distilled from the horizontal reaction tank or a heat exchanger for cooling the condensed liquid of the distilled gas is used at 1, 50 to 300 ° C. Washing with a liquid containing 4-butanediol, and using at least a part of the liquid containing 1,4-butanediol used for the washing as part or all of the raw material 1,4-butanediol for the production of polyester A feature of the polyester production method. The method for producing a polyester according to claim 5 , wherein the polyester is polybutylene terephthalate.

Images