JP3899340B2 - Method for producing polybutylene terephthalate - Google Patents

Description

  The present invention relates to a method for producing polybutylene terephthalate. More specifically, the present invention relates to an improved polybutylene terephthalate that can stabilize production by stabilizing the conversion rate during esterification or transesterification and stabilizing the amount of foreign matter mixed in polybutylene terephthalate. It relates to the manufacturing method.

  Polybutylene terephthalate resin, a typical engineering plastic among thermoplastic polyester resins, is easy to mold, mechanical properties, heat resistance, chemical resistance, aroma retention, other physical and chemical properties Because of its excellent characteristics, it is widely used in automobile parts, electrical / electronic parts, precision equipment parts, and the like.

  Polybutylene terephthalate is produced through an esterification reaction when the raw material is terephthalic acid, and transesterification when the raw material is dialkyl terephthalate. Recently, it has been continuously used to stabilize quality, improve production efficiency, and improve energy efficiency. In particular, a so-called continuous polymerization method in which raw materials are continuously supplied, esterification or transesterification reaction is continuously performed, and subsequent steps are also continuously attracting attention.

  However, a high-temperature, high-vacuum post-process (polycondensation process) while the conversion rate of the esterification reaction or transesterification reaction (esterification rate in the case of esterification reaction, transesterification rate in the case of transesterification reaction) remains low. The unreacted monomer clogs the valves and pumps in the transfer piping and volatilizes in the vent system of the polycondensation reaction tank to induce clogging of the piping, etc., as well as recovering 1,4-butanediol. In addition, there was a problem of causing contamination with tetrahydrofuran (THF) and the like. Therefore, from this point of view, it is preferable that the conversion rate at the outlet of the esterification reaction or transesterification reaction tank is high, and generally the reaction conditions are selected until 90% or more.

  As a method for increasing the conversion rate, a method for increasing the catalyst concentration and the reaction temperature as well as a method for increasing the reaction time are known. For example, an esterification reaction under conditions of high catalyst concentration, high temperature and low pressure is performed. (For example, refer to Patent Document 1). However, in this method, a high temperature and a high catalyst concentration lead to an increase in side reactions, resulting in a decrease in the quality of the product polymer, or a conversion of 1,4-butanediol to THF, resulting in a decrease in raw material unit. There was a problem. The lower pressure setting has also caused problems such as an increase in 1,4-butanediol discharged out of the system as a distillate and excessive equipment.

  On the other hand, there is a method for suppressing the generation of foreign substances derived from a catalyst by regulating the molar ratio of 1,4-butanediol and terephthalic acid and suppressing the concentration of the organic titanium compound to a value calculated using the molar ratio. Although it has been proposed (see, for example, Patent Document 2), the basis of this technique is to compensate for the decrease in catalytic activity caused by setting the concentration of the organic titanium compound low with the organic tin compound. There is a problem that the problem based on the high catalyst concentration seen in the above is not solved at all. Moreover, the reaction temperature setting lower than that of Patent Document 1 results in an increase in the esterification reaction time, and a significant improvement has been demanded from the viewpoint of productivity.

  As described above, various attempts have been made to increase the conversion rate in the esterification or transesterification reaction stage in the production of polybutylene terephthalate. However, when the reaction temperature is increased, the esterification or transesterification rate increases. In addition, there is a dilemma that the side reaction rate increases more than that, and there is a dilemma that when the metal compound catalyst is increased, foreign substances in the product increase or the thermal stability of the product decreases.

  Although a low reaction pressure setting is effective from the viewpoint of removing reaction products such as water from the system, it also promotes volatilization of unreacted 1,4-butanediol. -To reduce butanediol and maintain the conversion rate, it is necessary to supply more 1,4-butanediol, resulting in side reactions such as THF conversion of 1,4-butanediol and energy loss. Was invited. In particular, in the direct polymerization method using terephthalic acid as a raw material, the conventional method has a problem that foreign substances based on the metal compound catalyst are easily generated.

  By the way, when reducing the foreign matter of polybutylene terephthalate produced by the continuous polymerization method and stabilizing the quality, the conversion rate (esterification rate or esterification rate) of the initial esterification reaction (or transesterification reaction) The exchange rate is required to be stabilized. In particular, under the conditions of high temperature and low pressure, 1,4-butanediol, water, THF, and the like evaporate vigorously, and the generated vapor is condensed to 1,4-butanediol. As shown in Patent Document 1 and Patent Document 2, simply specifying the molar ratio of 1,4-butanediol to the raw terephthalic acid component and returning it to the reactor, It became difficult to strictly control the concentration of 1,4-butanediol, and as a result, the fluctuation of the conversion rate was sometimes increased.

  That is, as is well known, in the production of polybutylene terephthalate, an excess of 1,4-butanediol is used relative to terephthalic acid or dialkyl terephthalate, and 1,4-butanediol is used in the esterification reaction or transesterification reaction. Evaporates. Therefore, in a general production process, 1,4-butanediol gas generated from the reaction vessel is agglomerated and recovered, separated from by-product light boiling components and then circulated to the reaction vessel. Is connected. However, the amount of 1,4-butanediol gas generated from the reaction vessel varies greatly under conditions such as high temperature and reduced pressure, and as a result, the amount of 1,4-butanediol circulated varies with a slight time delay. To do. As a result, the molar ratio of terephthalic acid and 1,4-butanediol varies despite the fact that the amount of terephthalic acid supplied into the reaction vessel is controlled to be constant.

  At this time, control is performed such that the circulation amount of 1,4-butanediol is changed so that the liquid amount of the aggregated 1,4-butanediol is constant, as in the general reflux control. In some cases, the fluctuation of the conversion rate (esterification rate) is caused, and in some cases, the fluctuation is amplified by the phase difference between the fluctuation of 1,4-butanediol gas generation and the liquid volume fluctuation of the aggregated 1,4-butanediol. This results in instability of quality.

Japanese Patent Laid-Open No. 62-195017 Japanese Patent Laid-Open No. 10-330469

  The present invention has been made in view of the above circumstances, and its purpose is to stabilize the conversion rate during the esterification or transesterification reaction and to stabilize the amount of foreign matter mixed in the polybutylene terephthalate. An object of the present invention is to provide a process for producing polybutylene terephthalate which is improved so that production is possible.

  The present inventors have obtained the knowledge that the above-mentioned object can be easily achieved if a special method is employed for controlling the circulation amount of 1,4-butanediol, and the present invention has been completed.

  That is, the first gist of the present invention is to provide esterification by continuously supplying terephthalic acid and excess 1,4-butanediol to terephthalic acid in the presence of a metal compound in an esterification reaction vessel. In the process for producing polybutylene terephthalate having a process for carrying out the reaction, the molar ratio of terephthalic acid and 1,4-butanediol supplied to the esterification reaction tank per unit time (number of moles of 1,4-butanediol / terephthalate) The present invention resides in a method for producing polybutylene terephthalate, characterized in that the number of moles of acid is controlled to be constant.

  The second gist of the present invention is to continuously supply dialkyl terephthalate and excess 1,4-butanediol to dialkyl terephthalate in the presence of a metal compound in a transesterification reactor. In the method for producing polybutylene terephthalate having a step of performing a transesterification reaction, the molar ratio of dialkyl terephthalate and 1,4-butanediol supplied to the transesterification reaction tank per unit time (moles of 1,4-butanediol) Number / mole number of dialkyl terephthalate) is controlled to be kept constant.

  According to the present invention, the conversion of polybutylene terephthalate improved so that stable conversion can be achieved by stabilizing the conversion rate during esterification or transesterification and stabilizing the amount of foreign matter mixed in polybutylene terephthalate. A manufacturing method is provided.

  Hereinafter, the present invention will be described in detail. The polybutylene terephthalate in the present invention is a polymer having a structure in which a terephthalic acid unit and a 1,4-butanediol unit are ester-bonded, and 50 mol% or more of dicarboxylic acid units are composed of terephthalic acid units. That whose 50 mol% or more consists of a 1, 4- butanediol unit is said. The proportion of terephthalic acid units in all dicarboxylic acid units is usually 70 mol% or more, preferably 80 mol% or more, more preferably 95 mol% or more. On the other hand, the proportion of 1,4-butanediol units in the diol units is usually 70 mol% or more, preferably 80 mol% or more, more preferably 95 mol% or more. When the amount of terephthalic acid units or 1,4-butanediol units is less than 50 mol%, the crystallization rate of polybutylene terephthalate is lowered, and the moldability is deteriorated.

  In the present invention, the dicarboxylic acid component other than terephthalic acid is not particularly limited. For example, phthalic acid, isophthalic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 4,4′-benzophenone. Aromatic dicarboxylic acids such as dicarboxylic acid, 4,4′-diphenoxyethanedicarboxylic acid, 4,4′-diphenylsulfone dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3- Aliphatic dicarboxylic acids such as cyclohexanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid, aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid I can list them.

  The above dicarboxylic acid component 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 used as a mixture of a dicarboxylic acid and a dicarboxylic acid alkyl ester. The alkyl group of the dicarboxylic acid alkyl ester is not particularly limited. However, if the alkyl group is long, the alkyl alcohol produced during the transesterification reaction will increase in boiling point and will not evaporate from the reaction solution, resulting in the end-stopper acting as a result. In order to inhibit polymerization, it is usually an alkyl group having 4 or less carbon atoms, preferably a methyl group.

  In the present invention, the diol component other than 1,4-butanediol is not particularly limited. For example, ethylene glycol, diethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3-propanediol, polypropylene glycol, polytetra Methylene glycol, dibutylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, aliphatic diols such as 1,8-octanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol , 1,1-cyclohexanedimethylol, 1,4-cyclohexanedimethylol and other alicyclic diols, xylylene glycol, 4,4′-dihydroxybiphenyl, 2,2-bis (4-hydroxyphenyl) propane, bis ( 4 Aromatic diols such as hydroxyphenyl) sulfone and the like.

  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 polyfunctional components such as trimethylolpropane, glycerol and pentaerythritol can be used as the copolymerization component.

  The intrinsic viscosity of the polybutylene terephthalate of the present invention measured at 30 ° C. using a mixed solvent of phenol / tetrachloroethane (weight ratio 1/1) is usually 0.5 to 1.5 dL / g, preferably 0. .6 to 1.4 dL / g, more preferably 0.7 to 1.3 dL / g. If the intrinsic viscosity is less than 0.5 dL / g, the mechanical strength of the molded product may be insufficient. When the intrinsic viscosity exceeds 1.5 dL / g, the melt viscosity is increased, the fluidity is deteriorated, and the moldability may be deteriorated.

  The production method of polybutylene terephthalate is roughly divided into a so-called direct polymerization method using a dicarboxylic acid as a main raw material and a transesterification method using a dialkyl dicarboxylate as a main raw material. 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, The direct polymerization method is preferred from the viewpoint of height and the improvement effect of the present invention.

  As an example of the direct polymerization method, the dicarboxylic acid component containing terephthalic acid as a main component and the diol component containing 1,4-butanediol as a main component are mixed in a raw material preparation tank to form a slurry, and one or a plurality of esters In the chemical reaction tank, in the presence of a metal compound, the temperature is usually 180 to 260 ° C., preferably 200 to 245 ° C., more preferably 210 to 235 ° C., and usually 10 to 133 kPa, preferably 13 to 101 kPa, The esterification reaction is preferably carried out continuously under a pressure of 60 to 90 kPa, usually for 0.5 to 5 hours, preferably 1 to 4 hours. The number average molecular weight of the oligomer as the obtained esterification reaction product is usually 300 to 3000, preferably 500 to 1500.

  Next, the above oligomer is transferred to a polycondensation reaction tank, and in the presence of a metal compound, preferably continuously in the presence or absence of a metal compound in one or a plurality of polycondensation reaction tanks, usually 210 to 280 ° C, preferably 220 to 265 ° C. And a method of performing a polycondensation reaction under stirring under a reduced pressure of usually 27 kPa or less, preferably 20 kPa or less, more preferably 13 kPa or less, usually for 2 to 10 hours, preferably 2 to 5 hours.

  In addition, the resin obtained by the polycondensation reaction is usually extracted from the bottom of the polycondensation reaction tank, transferred to a die and shaped into a strand, while being cooled with water or after being cooled with water, and then cut with a cutter to form a pellet, It is a granular material such as a chip.

  On the other hand, as an example of the transesterification method, the dicarboxylic acid ester component mainly composed of a dialkyl ester of terephthalic acid and the diol component mainly composed of 1,4-butanediol are mixed in a raw material mixing tank. Alternatively, in a plurality of esterification reaction vessels, in the presence of a metal compound, the temperature is usually 110 to 260 ° C., preferably 140 to 245 ° C., more preferably 180 to 220 ° C., and usually 10 to 133 kPa, preferably 13 The transesterification is carried out continuously under a pressure of ˜120 kPa, more preferably 60 to 101 kPa, usually for 0.5 to 5 hours, preferably 1 to 3 hours. The molecular weight of the oligomer as the obtained transesterification product is usually 300 to 3000, preferably 500 to 2000.

  Next, the above oligomer is transferred to a polycondensation reaction tank, and in the presence of a metal compound, preferably continuously in the presence or absence of a metal compound in one or a plurality of polycondensation reaction tanks, usually 210 to 280 ° C, preferably 220 to 265 ° C And a method of performing a polycondensation reaction under stirring under a reduced pressure of usually 27 kPa or less, preferably 20 kPa or less, more preferably 13 kPa or less, usually for 2 to 12 hours, preferably 3 to 10 hours.

  The improvement effect of the present invention is great when the esterification reaction or transesterification reaction is carried out at a temperature equal to or higher than the boiling point of 1,4-butanediol. The boiling point of 1,4-butanediol depends on the reaction pressure, but is 230 ° C. at 101.1 kPa (atmospheric pressure) and 205 ° C. at 50 kPa.

  As the esterification or transesterification reaction catalyst, a metal compound is used, and among these, a titanium compound is preferably used. Specific examples of titanium compounds include inorganic titanium compounds such as titanium oxide, titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate, and tetrabutyl titanate, titanium phenolates such as tetraphenyl titanate, and the like. Of these, organic titanium compounds are preferred, and tetrabutyl titanate is particularly preferred.

  In addition to titanium, tin may be used as a catalyst. Tin is usually used as a tin compound, and specific examples thereof include dibutyltin oxide, methylphenyltin oxide, tetraethyltin, hexaethylditin oxide, cyclohexahexylditin oxide, didodecyltin oxide, triethyltin hydroxide. , Triphenyltin hydroxide, triisobutyltin acetate, dibutyltin diacetate, diphenyltin dilaurate, monobutyltin trichloride, tributyltin chloride, dibutyltin sulfide, butylhydroxytin oxide, methylstannic acid, ethylstannic acid, butylstannic acid Is mentioned.

  In addition to titanium, 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 In addition to calcium compounds such as calcium hydrogen phosphate, antimony compounds such as antimony trioxide, germanium compounds such as germanium dioxide and germanium tetroxide, manganese compounds, zinc compounds, zirconium compounds, cobalt compounds, orthophosphoric acid, phosphorous acid, hypochlorous acid Reaction aids such as phosphoric acid, polyphosphoric acid, phosphorus compounds such as esters and metal salts thereof, sodium hydroxide and sodium benzoate may be used.

  The catalyst and reaction aid may be added in portions when the esterification reaction (or transesterification reaction) consists of a plurality of tanks, or may be added in the subsequent polycondensation reaction.

  In the present invention, the amount of the metal compound used in the esterification or transesterification reaction is not particularly limited, but is usually 5 to 2000 μmol, preferably 50 to 1000 μmol, more preferably as a metal atom with respect to 1 mol of the terephthalic acid component. 100 to 500 μmol, particularly preferably 100 to 300 μmol. When there are too many metal compounds, the side reaction is promoted and foreign substances tend to increase, and further, the thermal stability of the finally obtained polymer is deteriorated. When the amount of the metal compound is too small, not only does the reaction rate decrease and polybutylene terephthalate having a desired molecular weight cannot be obtained, but the conversion of 1,4-butanediol to THF tends to increase. The amount of these metals can be measured using a method such as atomic emission, atomic absorption, or Inducted Coupled Plasma (ICP) after recovering the metal in the polymer by a method such as wet ashing.

  In the present invention, as a supply mode of each component in the esterification reaction tank or the transesterification reaction tank, a specific mode, that is, at least a part of 1,4-butanediol is converted into an esterification reaction tank (independent of terephthalic acid) ( Or 10% by weight or more of 1,4-butanediol supplied to the esterification reaction tank (or transesterification reaction tank) independently of terephthalic acid. It is preferable to employ a mode in which 10% by weight or more of the metal compound is supplied to the liquid phase part of the reaction tank independently of terephthalic acid.

  By adopting the above specific embodiment, the conversion rate during the esterification or transesterification reaction can be increased, foreign matters can be reduced, and loss due to side reaction of 1,4-butanediol can be prevented. In addition, according to the present invention, it is possible to stabilize the conversion rate during the esterification or transesterification reaction, stabilize the amount of foreign matter mixed in the polybutylene terephthalate, and perform stable production.

  The liquid phase part of the reaction tank indicates the liquid phase side of the gas-liquid interface in the esterification reaction tank or the transesterification reaction tank. To supply the liquid phase part of the reaction tank, use a pipe or the like. This means that the compound is supplied directly to the liquid phase part without going through the gas phase part of the reactor.

  In addition, the above metal compound can be directly supplied to the liquid phase part of the reaction tank of the esterification reaction tank or the transesterification reaction tank without being dissolved or diluted in a solvent or the like, but the supply amount is stabilized. In order to reduce adverse effects such as heat denaturation from the heat medium jacket of the reactor, it is preferable to dilute with a solvent such as 1,4-butanediol. The concentration at this time is determined as appropriate, but generally the metal compound concentration relative to the metal compound solution or the entire slurry is generally 0.01 to 20% by weight, preferably 0.05 to 10% by weight, more preferably 0.08 to 8% by weight.

  Among these, from the viewpoint of reducing foreign matters, the metal compound is supplied as a 1,4-butanediol solution of 0.01 to 20% by weight (preferably 1 to 10% by weight), and the water concentration in the solution is 0.00. It is preferable that it is 05-1.0 weight%. In addition, the metal compound or the metal compound solution is preferably mixed and supplied with 1,4-butanediol supplied independently from terephthalic acid or dialkyl terephthalate from the viewpoint of preventing deterioration, preventing precipitation, and suppressing foreign matter.

  In the specific embodiment, some of the metal compounds used in the esterification reaction or transesterification reaction may not be supplied to the liquid phase part of the reaction tank independently of terephthalic acid or dialkyl terephthalate. As a method for supplying the metal compound in that case, (a) a method in which the metal compound is supplied alone via the gas phase part of the reactor, and (b) a gas phase part obtained by mixing the metal compound with 1,4-butanediol. And (c) a method in which a metal compound, terephthalic acid or dialkyl terephthalate, and 1,4-butanediol are mixed and supplied from a gas phase part or a liquid phase part. From the viewpoint of reducing foreign substances, the metal compound is preferably not mixed with terephthalic acid or dialkyl terephthalate before being supplied to the reactor.

  The production of polybutylene terephthalate usually uses a plurality of reaction vessels, preferably 2 to 5 reaction vessels, and sequentially increases the molecular weight. However, the esterification reaction step according to the production method of the present invention or The transesterification reaction step is a step performed in a reaction vessel to which an initial raw material terephthalic acid component is supplied when a plurality of reaction vessels are used. In order to obtain polyethylene terephthalate having a predetermined molecular weight, a polycondensation reaction is performed following the esterification reaction or transesterification reaction.

  As the polycondensation reaction catalyst, the metal compound added during the esterification or transesterification reaction may be used as a polycondensation reaction catalyst, and no new metal compound may be added. The amount used in this case is not particularly limited, but if it is too much, the above-mentioned problems occur. Therefore, it is usually 1000 μmol or less, preferably 500 μmol or less, more preferably, relative to 1 mol of the terephthalic acid component. 400 μmol or less. Further, for example, an antimony compound such as antimony trioxide, a germanium compound such as germanium dioxide, germanium tetroxide, or the like, which is different from the metal compound added during the esterification reaction or transesterification reaction, may be newly added.

  Further, in the esterification reaction, transesterification reaction, and polycondensation reaction, in addition to the above metal compounds, phosphoric compounds such as orthophosphoric acid, phosphorous acid, hypophosphorous acid, polyphosphoric acid, their esters and metal salts, water Reaction aids such as alkali metal or alkaline earth metal compounds such as sodium oxide, sodium benzoate, magnesium acetate, calcium acetate, 2,6-di-t-butyl-4-octylphenol, pentaerythrityl-tetrakis [3- Phenol compounds such as (3 ′, 5′-t-butyl-4′-hydroxyphenyl) propionate], dilauryl-3,3′-thiodipropionate, pentaerythrityl-tetrakis (3-laurylthiodipropionate) Thioether compounds such as 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 the like Other additives such as release agents such as esters and silicone oils may be present.

  In addition, as the esterification or transesterification reaction tank, known ones can be used, and any of types such as a vertical stirring complete mixing tank, a vertical heat convection mixing tank, a tower type continuous reaction tank, etc. Also, a single tank or a plurality of tanks in which the same kind or different kinds of tanks are connected in series may be used. Among them, a reaction tank having a stirring device is preferable, and as a stirring device, a turbine stator type high-speed rotating stirrer, a disk mill type stirrer, a rotor mill type stirrer in addition to a normal type including a power unit, a bearing, a shaft, and a stirring blade. A type that rotates at high speeds can also be used.

  There is no limitation on the form of stirring, and in addition to the usual stirring method of stirring the reaction solution in the reaction tank directly from the top, bottom, side, etc. of the reaction tank, a part of the reaction solution is piped outside the reactor. It is also possible to take the reaction liquid and circulate the reaction liquid by stirring with a line mixer or the like.

  Known types of stirring blades can be selected, and specific examples include propeller blades, screw blades, turbine blades, fan turbine blades, disk turbine blades, fiddler blades, full-zone blades, and Max blend blades.

  In the present invention, in the case of the direct polymerization method, the molar ratio of terephthalic acid and 1,4-butanediol preferably satisfies the following formula.

  Among them, BM / TM = 2.0 to 4.0, more preferably 2.5 to 3.8, and particularly preferably 2.7 to 3.5. When BM / TM is smaller than 1.6, the conversion rate is lowered, and when it is larger than 4.5, not only the thermal efficiency is lowered, but also by-products such as THF tend to increase.

  On the other hand, in the case of transesterification, the molar ratio of dialkyl terephthalate and 1,4-butanediol preferably satisfies the following formula.

  Especially, BM / DM = 1.1-1.8, Furthermore, 1.2-1.5 are preferable. When BM / DM is smaller than 1.1, the conversion rate decreases, and when it is larger than 2.5, not only the thermal efficiency decreases but also by-products such as THF tend to increase.

  In the specific embodiment, the 1,4-butanediol supplied to the reaction vessel is, in addition to 1,4-butanediol supplied together with terephthalic acid or terephthalic acid dialkyl ester, as a raw slurry or solution. 1,4-butanediol supplied independently (hereinafter, the 1,4-butanediol may be referred to as “separately supplied 1,4-butanediol”), 1,4 used as a solvent for metal compounds -Total of 1,4-butanediol, such as butanediol, which enters the reaction vessel from the outside of the reaction vessel.

  In the specific embodiment, 30% by weight or more, further 50% by weight or more, particularly 80% by weight or more of “separately supplied 1,4-butanediol” is returned to the liquid phase part of the reaction vessel. 90% by weight or more is optimal. If “separately supplied 1,4-butanediol” returned directly to the liquid phase part of the reaction vessel is less than 10% by weight, the conversion effect during the esterification or transesterification reaction is not seen, and side reactions increase. There is a tendency for foreign matter to increase.

  The liquid phase part of the reaction tank referred to in the present invention indicates the liquid phase side of the gas-liquid interface in the esterification reaction tank or the transesterification reaction tank, and returning to the liquid phase part of the reaction tank uses piping or the like. This means that “separately supplied 1,4-butanediol” is directly supplied to the liquid phase portion without passing through the gas phase portion.

  A feature of the present invention is that, in the method for producing polybutylene terephthalate as described above, terephthalic acid (or alkyl terephthalate) supplied to an esterification reaction tank (or transesterification reaction tank) per unit time and 1,4- It is in the point which controls so that the molar ratio of butanediol may be kept constant. The means for controlling the molar ratio is not particularly limited, but cascade control is preferable.

  As a suitable example of the above cascade control, 1,4-butanediol is a main component of 1,4-butanediol-containing gas component distilled from the esterification reaction tank (or transesterification reaction tank) in the rectification column. Provided with a step of separating the high boiling component and the low boiling component, and the rectifying column of the step includes a line for circulating the separated high boiling component to the rectifying column, and a branch from the circulation line. And a line for supplying high-boiling components to the reaction tank and an extraction line branched from the circulation line and discharging high-boiling components to the outside of the system, so that the liquid level at the bottom of the rectification column is constant. Similarly, there is a method of adjusting the discharge amount of the high boiling component from the extraction line. A specific example will be described with reference to FIG.

  In addition, as another preferred example of the cascade control described above, a 1,4-butanediol-containing gas component distilled from the esterification reaction tank is used in a rectification column to increase the amount of 1,4-butanediol as a main component. A process for separating the boiling component and the low boiling component is provided, and the rectifying column of the process is divided into a line for circulating the separated high boiling component to the rectifying column, and a reaction branched from the circulation line. A line for supplying high boiling components to the tank and an extraction line for branching out from the circulation line and discharging the high boiling components to the outside of the system are provided, and a tank for retaining the high boiling components is provided in the circulation line. A method of adjusting the discharge amount of the high boiling component from the extraction line so that the liquid level of the liquid is constant. A specific example will be described with reference to FIG.

  The above-described molar ratio control in the present invention is preferably performed even in a transition period of condition change during so-called “Rate up” or “Rate down”. That is, when changing the production amount or the like, if the supply amount of the terephthalic acid component is increased and the circulation amount of 1,4-butanediol is not increased, the above molar ratio is lowered and the conversion rate is lowered. Invite. On the other hand, if the supply amount of the terephthalic acid component is decreased and the circulation amount of 1,4-butanediol is not decreased, the above molar ratio increases and the conversion rate increases, but side reactions such as generation of THF increase. And incurs energy loss. Therefore, in the transition period of the condition change, the change is followed so that the molar ratio of terephthalic acid or dialkyl terephthalate and 1,4-butanediol supplied to the esterification reaction tank or transesterification reaction tank becomes constant. To control.

  The high-boiling component (high-boiling component mainly composed of 1,4-butanediol) supplied to the reaction tank is part or all of the “separately supplied 1,4-butanediol” in the specific embodiment. Although it corresponds, it may be referred to as “recycled 1,4-butanediol” in particular. In addition, said low boiling component is components, such as water, alcohol, and THF.

  In the present invention, the temperature of the high boiling point component ("separately supplied 1,4-butanediol") supplied to the reaction vessel is usually 50 to 220 ° C, preferably 100 to 200 ° C, more preferably 150 to 190. ° C. If the temperature is too high, the amount of by-product of THF tends to increase. If the temperature is too low, the heat load increases, so that energy loss tends to be caused.

  In the present invention, 1,4-butanediol gas generated from the reaction tank is agglomerated and recovered, separated from the by-product light boiling component, and then circulated into the reaction tank. And by the said specific control means, the fluctuation | variation of the circulation amount with respect to the reaction tank of 1, 4- butanediol is suppressed, and the terephthalic acid (or transesterification reaction tank) supplied per unit time (or transesterification reaction tank) Alternatively, the molar ratio of alkyl terephthalate) to 1,4-butanediol is controlled to be constant. In addition, unlike 1,4-butanediol circulated in the reaction tank, the method of supplying terephthalic acid (or alkyl terephthalate) to the reaction tank, in which the supply amount to the reaction tank does not particularly vary, is not particularly limited. However, a method of supplying a constant amount of 1,4-butanediol slurry (or solution) with a constant molar ratio to the esterification reactor is preferable.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. 1 and 2 are illustrations of preferred embodiments of the present invention, including the specific delivery modes described above.

  In FIG. 1, terephthalic acid as a raw material is usually mixed with 1,4-butanediol in a raw material mixing tank (not shown), and supplied to the reaction tank (A) in the form of slurry from the raw material supply line (1). The In the case of terephthalic acid dialkyl ester, it is usually supplied to the reaction vessel (A) without being mixed with 1,4-butanediol. On the other hand, the titanium catalyst is preferably supplied from a catalyst supply line (3) after being made into a solution of 1,4-butanediol in a catalyst adjustment tank (not shown). FIG. 1 shows a mode in which the catalyst supply line (3) is connected to the recycle 1,4-butanediol supply line (2), and both are mixed and then supplied to the liquid phase part of the reaction tank (A). .

  The gas distilled from the reaction tank (A) is separated into a high-boiling component and a low-boiling component in the rectifying column (C) through the distillation line (5). Usually, the main component of the high boiling point component is 1,4-butanediol, and the main component of the low boiling point component is water and tetrahydrofuran in the case of the direct polymerization method, and alcohol, tetrahydrofuran and water in the case of the transesterification method. .

  The high boiling component separated in the rectification column (C) is extracted from the extraction line (6), passed through the pump (D), and partly circulated from the supply line (2) to the reaction tank (A), A part is returned from the feed line (7) to the rectification column (C). Further, the surplus is extracted outside from the extraction line (8). On the other hand, the light boiling components separated in the rectification column (C) are extracted from the gas extraction line (9), condensed in the condenser (G), and temporarily passed through the condensate line (10) to the tank (F). Accumulated. Part of the light boiling components collected in the tank (F) is returned to the rectification column (C) via the extraction line (11), the pump (E) and the supply line (12), and the remainder is extracted. It is extracted outside through the line (13). The condenser (G) is connected to an exhaust device (not shown) via a vent line (14). The oligomer produced | generated within the reaction tank (A) is extracted through an extraction pump (B) and an extraction line (4).

  In the process shown in FIG. 1, the catalyst supply line (3) is connected to the supply line (2), but both may be independent. Moreover, the raw material supply line (1) may be connected to the liquid phase part of the reaction vessel (A).

  In the process shown in FIG. 1, a flow control valve (J) and a flow control valve (K) are provided in the supply line (2) and the extraction line (8), respectively. A control device (L) for detecting the liquid level and adjusting the opening of the flow control valve (K) based on the detection signal to adjust the liquid level of the rectifying column (C) to be constant is provided. . The liquid level at the bottom of the rectification column (C) is the temperature fluctuation of the reaction tank (A), the fluctuation of the distillate gas amount and the distillate gas composition, the fluctuation of the feed rate, and the temperature fluctuation of the rectification tower (C). 1, the extraction amount from the extraction line (8) is adjusted by the liquid level fluctuation at the bottom of the rectification column (C), and the supply line (2 The recirculation amount from) is kept constant.

  The process shown in FIG. 2 is provided with a flow control valve (J) and a flow control valve (K) in the supply line (2) and the extraction line (8), respectively, compared to the process shown in FIG. A tank (N) and a reboiler (M) for retaining high-boiling components are provided in the line (6) and the supply line (7), respectively, and the supply line (7) is supplied downstream from the reboiler (H). A line (15) is provided to detect the liquid level of the tank (N) and adjust the opening of the flow control valve (K) based on the detection signal to adjust the liquid level of the tank (N) to be constant. Is different in that a control device (L) is provided. The process shown in FIG. 2 has the same improvement effect as the process shown in FIG. The process shown in FIG. 2 reveals that a signal based on the liquid level fluctuation of the tank (N) can be used as an input signal to the control device (L).

  In the present invention, the high-boiling component circulation line provided in the rectification column (C) includes the extraction line (6), the supply line (7), the column bottom of the rectification column (C), and the pump (D). Therefore, for example, the supply line (2) is not limited to the embodiment shown in FIG. 1 branched from the supply line (7), and may be an embodiment branched from the tank (N).

  The type of the polycondensation reaction tank used in the present invention is not particularly limited, and examples thereof include a vertical stirring polymerization tank, a horizontal stirring polymerization tank, and a thin film evaporation polymerization tank. The number of polycondensation reaction tanks can be one, or a plurality of tanks in which a plurality of tanks of the same or different types are connected in series can be used. In any case, it is preferable to select a horizontal stirring polymerization machine having a thin film evaporation function excellent in interface renewal property, plug flow property, and self-cleaning property in the latter stage of the polycondensation in which the viscosity of the reaction solution increases.

  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) Water concentration in the catalyst solution:
It was determined with a Karl Fischer moisture meter (“CA-03” manufactured by Mitsubishi Kasei Co., Ltd.).

(2) Esterification rate of oligomer:
It calculated using the acid value and saponification value which were calculated | required as follows.
[Acid value]
The oligomer was dissolved in dimethylformamide and titrated using a 0.1N KOH / methanol solution.
[Saponification value]
The oligomer was hydrolyzed with a 0.5N KOH / ethanol solution and titrated with 0.5N hydrochloric acid.

(3) Amount of foreign matter in oligomer:
10 g of the oligomer was dissolved in hexafluoroisopropanol / chloroform = 2/3 (volume ratio) at a concentration of 10 wt%, filtered through a polytetrafluoroethylene membrane filter having a pore diameter of 5 μm and a diameter of 47 mm, and then thoroughly washed with the above solvent. The foreign matters remaining on the filter were observed with an optical microscope, and the number of foreign matters having a size of 10 μm or more was counted.

[Example 1]
FIG. 1 is a flowchart of this embodiment. A polybutylene terephthalate having an esterification rate of 99% is prepared in advance from a slurry preparation tank through a line (1) with a slurry at 60 ° C. prepared at a ratio of 2.00 mol of 1,4-butanediol to 1.00 mol of terephthalic acid. The mixture was continuously supplied to an esterification reaction tank A equipped with a max blend type stirrer filled with oligomer and a baffle so as to be 51.8 kg / h. The fluctuation of the supply amount was 0.1 kg / h or less. At the same time, the bottom component of the rectifying column C at 185 ° C. was supplied from the line (2) at 15.0 kg / h, and the flow rate was fixed. The fluctuation of the flow rate was 0.1 kg / h or less. On the other hand, from the line (3), pure water was added to a 6.0 wt% 1,4-butanediol solution of tetrabutyl titanate at 65 ° C. as a catalyst to obtain a 0.39 kg solution having a water concentration of 0.20 wt%. / H (460 μmol as titanium atoms with respect to 1 mol of terephthalic acid). The fluctuation of the supply amount was 0.01 kg / h or less.

  The internal temperature of the esterification reaction tank A is 230 ° C. and the pressure is 78 kPa. The generated water, THF, and excess 1,4-butanediol are distilled from the line (5), and the high boiling component in the rectifying column C is obtained. And separated into low boiling components. The high-boiling component at the bottom of the column after the system is stabilized is 98% by weight or more of 1,4-butanediol, so that the liquid level of the rectifying column C is constant, and the valve K is changed according to the liquid level fluctuation. And a part of it was extracted to the outside through the line (8). The flow rate of the line (8) was 4.1 kg / h on average, and the flow rate variation was ± 4.0 kg / h.

  At this time, 1,4-butanediol supplied to the esterification reaction tank A from the outside is via line (1) (raw slurry), via line (2) (“recycled 1,4-butanediol”), The ratio of the total amount of 1,4-butanediol and the amount of terephthalic acid supplied as a slurry from the line (1) per unit time (BM) (via the line (3) (catalyst solvent)) / TM) was 3.14 mol / mol. Moreover, the fluctuation | variation was 0.01 mol / mol or less.

  On the other hand, the low boiling component was extracted from the top of the column in the form of gas, condensed by the condenser G, and extracted from the line (13) to the outside so that the liquid level of the tank F was constant.

  Further, a certain amount of the oligomer produced in the reaction tank A was extracted using the pump B, and the liquid level was controlled so that the average residence time of the liquid in the reaction tank A was 2 hr. The extracted oligomer was sent through a line (4) to a polycondensation reaction tank (not shown). After the system was stabilized, the oligomer was collected 12 times every 2 hours, and the esterification rate and the amount of foreign matter were measured. As a result, the average esterification rate of the oligomer was 96.5%, and the standard deviation was 0.16. The average amount of foreign matter was 27, and the standard deviation was 6.9. The results are summarized in Table 1.

[Example 2]
In Example 1, “recycled 1,4-butanediol” supplied to the reaction tank A from the line (2) was fixed at 5.0 kg / h, and condensed 1,4-butanediol extracted from the line (8) The same procedure as in Example 1 was performed except that the average flow rate was 4.4 kg / h and the fluctuation was ± 4.0 kg / h. The average esterification rate of the oligomer collected in the same manner as in Example 1 was 94.9%, and the standard deviation was 0.36. The average amount of foreign matter was 27, and the standard deviation was 6.9. The results are summarized in Table 1.

[Comparative Example 1]
In Example 1, it changed into the apparatus shown in FIG. 3 changed so that the valve | bulb J might be controlled by the control apparatus L, and the quantity of the condensed 1, 4- butanediol extracted from a line (8) is 4.1 kg / h. The amount of “recycled 1,4-butanediol” supplied to the reaction tank A from the line (2) is adjusted so that the bottom liquid level of the rectifying column C is fixed and the liquid level fluctuation is fixed. This was performed in the same manner as in Example 2 except that absorption was performed. The average flow rate of “recycled 1,4-butanediol” fed to the reaction tank A from the line (2) is 15.0 kg / h, the fluctuation is ± 4.0 kg / h, and the fluctuation of BM / TM is ± It was 0.30 mol / mol. The average esterification rate of the oligomer collected in the same manner as in Example 1 was 95.8%, the standard deviation was 0.70, and the variation in the esterification rate was large. Further, the average amount of foreign matter was 40, the standard deviation was 32.9, there were many foreign matters, and the number variation was large. The results are summarized in Table 1.

[Comparative Example 2]
In Example 2, the apparatus is changed to the apparatus shown in FIG. 3, the amount of condensed 1,4-butanediol extracted from the line (8) is fixed at 4.4 kg / h, and the bottom liquid level of the rectifying column C is kept constant. As in Example 2, except that the fluctuation in the liquid level was absorbed by adjusting the amount of “recycled 1,4-butanediol” supplied to the reaction tank A from the line (2). went. The average flow rate of “recycled 1,4-butanediol” supplied to the reaction tank A from the line (2) is 5.0 kg / h, the fluctuation is ± 4.0 kg / h, and the fluctuation of BM / TM is ± It was 0.30 mol / mol. The average esterification rate of the oligomers collected in the same manner as in Example 1 was as low as 93.0%, the standard deviation was 1.02, and the variation in the esterification rate was large. In addition, the average amount of foreign matter was 114, the standard deviation was 71.7, there were many foreign matters, and the number variation was large. The results are summarized in Table 1.

[Example 3]
The amount of slurry supplied in Example 1 was gradually increased over 12 hours from 51.8 kg / h to 57.0 kg / h. At the same time, the supply amount of the catalyst solution is adjusted so that the titanium atom is constant at 460 μmol with respect to 1 mol of terephthalic acid, and supplied from the line (2) so that the fluctuation of BM / TM becomes 0.01 mol / mol or less. The amount of “recycled 1,4-butanediol” was adjusted. The other conditions were the same as in Example 7. The oligomer was sampled 12 times every hour, and the esterification rate and the amount of foreign matter were measured. As a result, the average esterification rate of the oligomer was 96.0%, and the standard deviation was 0.16.

[Comparative Example 3]
In Example 1, with the amount of “recycled 1,4-butanediol” supplied from the line (2) kept constant at 15.0 kg / h, the amount of slurry and catalyst solution supplied was the same as in Example 1. Increased. The average esterification rate of the oligomer measured in the same manner as in Example 1 was 95.0%, and the standard deviation was 0.95. Further, the esterification rate after 12 hours was as low as 94.5%.

Explanatory drawing of an example of the esterification reaction process or transesterification process employed in the present invention Explanatory drawing of another example of the esterification reaction step or transesterification reaction step employed in the present invention Explanatory drawing of the esterification reaction process employ | adopted by the comparative examples 1 and 2

Explanation of symbols

1: Raw material supply line 2: Supply line 3: Catalyst supply line 4: Extraction line 5: Distillation line 6: Extraction line 7: Supply line 8: Extraction line 9: Gas extraction line 10: Condensate line 11 : Extraction line 12: Supply line 13: Extraction line 14: Vent line
15: Recovery line 16: Bypass line 17: Extraction line A: Reaction tank B: Extraction pump C: Rectification tower D, E: Pump F, N: Tank G: Condenser H: Reboiler J, K: Valve L: Control device N: tank L1: extraction line L3, L5: extraction lines L2, L4, L6: vent line a: first polycondensation reaction tank d: second polycondensation reaction tank k: third polycondensation reaction tank c , E, m: gear pump for extraction f: filter g: dice head h: rotary cutter

Claims (13)

Production of polybutylene terephthalate having a process of continuously supplying terephthalic acid and excess 1,4-butanediol to terephthalic acid in the presence of a metal compound in an esterification reaction tank. In the method, control is performed so that the molar ratio of terephthalic acid and 1,4-butanediol supplied to the esterification reactor per unit time is kept constant (number of moles of 1,4-butanediol / number of moles of terephthalic acid). In doing so , a step of separating the 1,4-butanediol-containing gas component distilled from the esterification reaction tank into a high-boiling component and a low-boiling component mainly composed of 1,4-butanediol in a rectifying column. And a rectifying column for the process, a line for circulating the separated high boiling component to the rectifying column, and a line for branching from the circulation line and supplying the high boiling component to the reaction tank. And an extraction line that branches off from the circulation line and discharges the high boiling component to the outside of the system, so that the liquid level of the bottom of the rectification tower is constant, the high boiling component from the extraction line is method for producing a polybutylene terephthalate, characterized in that adjusting the amount of discharge. Production of polybutylene terephthalate having a process of continuously supplying terephthalic acid and excess 1,4-butanediol to terephthalic acid in the presence of a metal compound in an esterification reaction tank. In the method, control is performed so that the molar ratio of terephthalic acid and 1,4-butanediol supplied to the esterification reactor per unit time is kept constant (number of moles of 1,4-butanediol / number of moles of terephthalic acid). In doing so, a step of separating the 1,4-butanediol-containing gas component distilled from the esterification reaction tank into a high-boiling component and a low-boiling component mainly composed of 1,4-butanediol in a rectifying column. And a rectifying column for the process, a line for circulating the separated high boiling component to the rectifying column, and a line for branching from the circulation line and supplying the high boiling component to the reaction tank. And a discharge line that branches off from the circulation line and discharges a high boiling component to the outside of the system, and a tank that retains the high boiling component is provided in the circulation line so that the liquid level of the tank is constant. And a method for producing polybutylene terephthalate , characterized in that the amount of high-boiling components discharged from the extraction line is adjusted. The molar ratio of terephthalic acid and 1,4-butanediol fed to the esterification reaction vessel per unit time (1,4-butanediol / terephthalic acid) according to claim 1 or 1.6 to 4.5 the method according to 2. The production method according to any one of claims 1 to 3 , wherein terephthalic acid is supplied to the esterification reaction tank in a constant amount as 1,4-butanediol slurry having a constant molar ratio. Polybutylene terephthalate having a process of continuously supplying a dialkyl terephthalate and an excess of 1,4-butanediol to the dialkyl terephthalate in the presence of a metal compound in a transesterification reaction tank. In this production method, the molar ratio of dialkyl terephthalate and 1,4-butanediol supplied to the transesterification reactor per unit time (mole number of 1,4-butanediol / mole number of dialkyl terephthalate) is constant. upon controls to keep, 1,4-butanediol-containing gas component distilled from the transesterification reactor in a high boiling component and the low boiling component 1,4-butanediol in the rectification column is a main component A separation step, and a rectifying column of the step includes a line for circulating the separated high-boiling components to the rectification column, and a circulation line. A line for supplying high-boiling components to the reaction tank and a discharge line for branching from the circulation line and discharging high-boiling components to the outside of the system. A method for producing polybutylene terephthalate, characterized in that the amount of high-boiling components discharged from the extraction line is adjusted so as to be constant . Polybutylene terephthalate having a process of continuously supplying a dialkyl terephthalate and an excess of 1,4-butanediol to the dialkyl terephthalate in the presence of a metal compound in a transesterification reaction tank. In the production method, the molar ratio of dialkyl terephthalate and 1,4-butanediol supplied to the transesterification reactor per unit time (mole number of 1,4-butanediol / mole number of dialkyl terephthalate) is constant. When controlling to keep the 1,4-butanediol-containing gas component distilled from the transesterification reaction tank into a high-boiling component and a low-boiling component mainly composed of 1,4-butanediol in the rectification column. A separation step, and a rectifying column of the step includes a line for circulating the separated high-boiling components to the rectification column, and a circulation line. A line branched from the tank and supplying a high-boiling component to the reaction tank, and an extraction line branched from the circulation line and discharging the high-boiling component out of the system are provided, and the high-boiling component is retained in the circulation line. A method for producing polybutylene terephthalate , characterized in that a tank is provided and the amount of high-boiling components discharged from the extraction line is adjusted so that the liquid level in the tank is constant. The molar ratio of dialkyl terephthalate and 1,4-butanediol (1,4-butanediol / dialkyl terephthalate) fed to the transesterification reactor per unit time is 1.1 to 1.8. 5. The production method according to 5 or 6 . The production method according to any one of claims 5 to 7 , wherein dialkyl terephthalate is supplied to the esterification reaction tank in a constant amount as a 1,4-butanediol solution having a constant molar ratio. The method according to any one of claims 1 to 8 , wherein the metal compound is supplied to the esterification reaction tank in a constant amount as a 1,4-butanediol solution having a constant concentration in the range of 0.01 to 30% by weight. The production method according to claim 9 , wherein the 1,4-butanediol solution of the metal compound contains 0.05 to 1.0% by weight of water. The manufacturing method in any one of Claims 1-10 in which a metal compound contains an organic titanium compound. The production method according to any one of claims 1 to 11 , wherein a reaction temperature of the esterification reaction or the transesterification reaction is not less than the boiling point of 1,4-butanediol at the reaction pressure. The production method according to any one of claims 1 to 12 , further comprising a step of performing a polycondensation reaction following the esterification reaction or the transesterification reaction.