Dimethyl terephthalate composition and polyester

Abstract

To provide a dimethyl terephthalate composition capable of producing a polyester in a short time and in a large scale by shortening the time required for melting raw materials in the production of the polyester and suppressing bumping in the reaction, and to provide a polyester using the dimethyl terephthalate composition.SOLUTION: The dimethyl terephthalate composition contains a methyl alkyl terephthalate represented by formula (1) in an amount of 0.0001 mass% or more and 1 mass% or less based on dimethyl terephthalate. The polyester is obtained by reacting the dimethyl terephthalate composition with a diol component. (In the above formula (1), R1 represents an optionally branched hydrocarbyl group having 2 to 10 carbon atoms. ) SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a dimethyl terephthalate composition and a polyester using the dimethyl terephthalate composition. More specifically, the present invention relates to a dimethyl terephthalate composition that has a short melting time and suppresses bumping during polyester production, thereby improving the efficiency of polyester production, and to a polyester obtained by reacting the dimethyl terephthalate composition with a diol component. [Background technology]

[0002] Polyesters are widely used in applications such as fibers, films, and molded articles due to their excellent strength, thermal stability, and chemical resistance. Dimethyl terephthalate is commonly used as a raw material for polyester production, but high-purity dimethyl terephthalate has a high melting point, making the raw material melting process in polyester production time-consuming. In addition, the boiling point of methanol, a by-product of ester exchange during polyester production, is significantly lower than the process temperature for polyester production, which makes it prone to bumping within the system and makes it difficult to increase the scale of production.

[0003] Patent Document 1 proposes a dimethyl terephthalate composition that suppresses problems associated with by-products of dimethyl terephthalate obtained by the Witten-Hercules process, which involves air-oxidizing paraxylene and methyl p-toluate, esterifying the resulting oxidation reaction mixture with methanol under high-temperature and high-pressure conditions, and separating and purifying dimethyl terephthalate from the esterification reaction mixture. The proposed dimethyl terephthalate composition has improved properties as a polyester raw material, and is primarily composed of dimethyl terephthalate, 0.001 to 200 ppm of methyl 4-(1,3-dioxolan-2-yl)benzoate, and 0 to 1 ppm of dimethyl hydroxyterephthalate. However, this dimethyl terephthalate composition fails to solve the above-mentioned problems. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-220362 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a dimethyl terephthalate composition that enables polyester production in a short time and on a large scale by shortening the time required for melting raw materials during polyester production and by suppressing bumping during the reaction, and to provide a polyester using this dimethyl terephthalate composition. [Means for solving the problem]

[0006] As a result of intensive investigations to solve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by using a dimethyl terephthalate composition containing a trace amount of methyl alkyl terephthalate relative to dimethyl terephthalate, and have completed the present invention. That is, the present invention relates to the following inventions.

[0007] [1] A dimethyl terephthalate composition containing 0.0001% by mass or more and 1% by mass or less of a methyl alkyl terephthalate represented by the following formula (1) relative to dimethyl terephthalate:

[0008] [ka]

[0009] (In the above formula (1), R 1 represents a hydrocarbon group having 2 to 10 carbon atoms, which may be branched. [2] The dimethyl terephthalate composition according to [1], wherein the dimethyl terephthalate composition is obtained by chemical recycling. [3] A polyester obtained by reacting the dimethyl terephthalate composition according to [1] or [2] with a diol component. [4] The polyester according to [3], wherein 50 mol % or more of the diol component is 1,4-butanediol. [5] The polyester according to [3] or [4], wherein the diol component is derived from biomass. [6] The polyester according to [3] or [4], wherein the diol component is produced by depolymerizing a polyester. [Effects of the Invention]

[0010] The dimethyl terephthalate composition of the present invention shortens the time required for melting raw materials in polyester production and can suppress bumping during the reaction, thereby enabling efficient polyester production. The polyester obtained by reacting the dimethyl terephthalate composition of the present invention with a diol component can be preferably used for various applications, such as electric and electronic parts, automobile parts, films, sheets, filaments, etc. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes in detail an embodiment of the present invention. However, the description of the constituent elements described below is an example of an embodiment of the present invention, and the present invention is not limited to the following description as long as it does not go beyond the gist of the present invention. In this specification, when the expression "to" is used, it is intended to be used as an expression that includes the numerical values ​​or physical property values ​​before and after it. In the present invention, the "main component" of a dicarboxylic acid component refers to a component that accounts for 50 mol % or more of the dicarboxylic acid component. The same applies to the "main component" of a diol component.

[0012] [Dimethyl terephthalate composition] The dimethyl terephthalate composition according to an embodiment of the present invention contains dimethyl terephthalate and a predetermined amount of a methyl alkyl terephthalate represented by the following formula (1) (hereinafter, sometimes referred to as "compound (1)").

[0013] [ka]

[0014] In formula (1), R 1 represents a hydrocarbon group having 2 to 10 carbon atoms, which may be branched, i.e., a linear or branched hydrocarbon group. The hydrocarbon group having 2 to 10 carbon atoms, which may be branched, is preferably a hydrocarbon group having 2 to 8 carbon atoms.

[0015] R 1 Examples of the hydrocarbon group include an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, and a 2-ethylhexyl group, with an ethyl group or a 2-ethylhexyl group being preferred, and an ethyl group being particularly preferred. The compound (1) may be used alone or in combination of two or more kinds.

[0016] By including methyl alkyl terephthalate together with dimethyl terephthalate, the melting point can be lowered compared to that of highly pure dimethyl terephthalate. This reduces the time required to melt the raw materials during polyester production, thereby improving polyester production efficiency. In addition, the transesterification reaction during polyester production produces a monofunctional alcohol (R 1 The generation of OH) calms the boiling state in the system and suppresses bumping, which makes it easier to increase the scale of polyester production, thereby improving polyester production efficiency.

[0017] The content of the methyl alkyl terephthalate in the dimethyl terephthalate composition of the present invention is 0.0001% by mass or more and 1% by mass or less, preferably 0.0005% by mass or more and 0.7% by mass or less, and more preferably 0.001% by mass or more and 0.5% by mass or less, based on the dimethyl terephthalate. When the content of the methyl alkyl terephthalate is equal to or more than the lower limit, the above-mentioned effects of the present invention due to the inclusion of the methyl alkyl terephthalate can be sufficiently obtained. Furthermore, when the content is equal to or less than the upper limit, the reactivity in the transesterification reaction can be sufficiently ensured.

[0018] The dimethyl terephthalate composition of the present invention preferably consists essentially of dimethyl terephthalate and the above-mentioned methyl alkyl terephthalate. Here, "consisting essentially of dimethyl terephthalate and methyl alkyl terephthalate" means that the total content of dimethyl terephthalate and methyl alkyl terephthalate in the dimethyl terephthalate composition is preferably 98% by mass or more, more preferably 99% by mass or more, and particularly preferably 99.5 to 100% by mass.

[0019] The method for producing the dimethyl terephthalate composition of the present invention is not particularly limited, but examples thereof include a method in which a methyl alkyl terephthalate is added to and mixed with molten dimethyl terephthalate (a method in which dimethyl terephthalate and a methyl alkyl terephthalate are melt-mixed); and a method in which a methyl alkyl terephthalate is produced by a disproportionation transesterification reaction between dimethyl terephthalate and a dialkyl terephthalate and the content of the methyl alkyl terephthalate is adjusted. In order to fully obtain the effect of lowering the melting point of dimethyl terephthalate, it is preferred that the methyl alkyl terephthalate is uniformly mixed in the dimethyl terephthalate.

[0020] The dimethyl terephthalate or methyl alkyl terephthalate used in the production of the dimethyl terephthalate composition is not limited to those produced using fossil fuels as raw materials, but may also be those produced using biomass resources as raw materials, those produced by recycling waste products or defective products, or a mixture of two or more of these. For example, the dimethyl terephthalate composition used in the present invention, and the dimethyl terephthalate and methyl alkyl terephthalate in the dimethyl terephthalate composition may be obtained by chemical recycling of polyesters such as polyethylene terephthalate or polybutylene terephthalate, for example, by depolymerization of polyesters such as polyethylene terephthalate or polybutylene terephthalate.

[0021] [Polyester manufacturing method] Examples of a method for producing a polyester of the present invention using the dimethyl terephthalate composition of the present invention include a method in which the dimethyl terephthalate composition of the present invention and a diol component are subjected to a transesterification reaction in the presence of a transesterification catalyst.

[0022] Hereinafter, the method for producing a polyester of the present invention will be described mainly with reference to a method for producing polybutylene terephthalate (hereinafter sometimes abbreviated as "PBT") as a polyester, using a diol component containing 1,4-butanediol (hereinafter sometimes abbreviated as "BDO"). However, according to the method for producing a polyester of the present invention, it is also possible to produce polyesters other than PBT, such as polyethylene terephthalate (hereinafter sometimes abbreviated as "PET"), using a diol component other than 1,4-butanediol, in the same manner as the method described below.

[0023] Hereinafter, the polyester produced by the polyester production method of the present invention may be referred to as "the polyester of the present invention", and the PBT produced by the polyester production method of the present invention may be referred to as "the PBT of the present invention".

[0024] PBT refers to a polymer having a structure in which a dicarboxylic acid component and a diol component are ester-bonded, with 50 mol % or more of the dicarboxylic acid component being terephthalic acid and 50 mol % or more of the diol component being BDO. The proportion of the terephthalic acid component in all dicarboxylic acid components is preferably 70 mol % or more, more preferably 80 mol % or more, and even more preferably 95 mol % or more, and the proportion of BDO in all diol components is preferably 70 mol % or more, more preferably 80 mol % or more, and even more preferably 95 mol % or more. If the terephthalic acid component or BDO is less than 50 mol %, the crystallization rate of the PBT decreases, resulting in poor moldability.

[0025] <Dicarboxylic acid component> In the method for producing a polyester of the present invention, the dimethyl terephthalate composition of the present invention is used as the dicarboxylic acid component.

[0026] As the dicarboxylic acid component, a dicarboxylic acid component other than dimethyl terephthalate can also be used as long as the proportion of the terephthalic acid component satisfies the above-mentioned preferred proportion. Examples of dicarboxylic acid components other than dimethyl terephthalate include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-benzophenonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid; and dialkyl esters of aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. The alkyl group of these dicarboxylic acid dialkyl esters preferably has 1 to 6 carbon atoms. These dicarboxylic acid components other than dimethyl terephthalate may be used alone or in combination of two or more. Furthermore, as for these dicarboxylic acid components other than dimethyl terephthalate, any of those produced using fossil fuels as raw materials, those produced using biomass resources as raw materials, and those produced by recycling waste products or defective products may be used.

[0027] <Diol ingredient> The diol components other than BDO to be subjected to the transesterification reaction are not particularly limited, and examples thereof include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, and dibutylene glycol; alicyclic diols such as 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethylol, and 1,4-cyclohexanedimethylol; polyalkylene glycols such as xylylene glycol, polyethylene glycol, polytrimethylene glycol, and polytetramethylene ether glycol; and aromatic diols such as 4,4'-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone. These diol components other than BDO may be used alone or in combination of two or more.

[0028] The diol component such as BDO may be any of a petroleum-derived diol component produced using fossil fuel as a raw material, a diol component produced using biomass resources as a raw material, a chemically recycled diol component produced by recycling waste products or defective products, or a mixture thereof. The use of a diol component produced using biomass resources as a raw material or a diol component produced by recycling waste products or defective products is preferable from the viewpoint of building a recycling-oriented society.

[0029] For example, as a diol component such as BDO produced using a biomass resource as a raw material, a diol component produced by fermentation is preferred, and examples thereof include a diol component produced by direct fermentation of sugar, and a biomass-derived diol component produced by hydrogenating succinic acid or a succinic acid derivative produced using a biomass resource, such as succinic anhydride or a succinate ester such as a dialkyl succinate (more specifically, a dialkyl succinate having an alkyl group with 1 to 4 carbon atoms, preferably 1 to 3, more preferably 1 to 2, and most preferably a methyl group with 1 carbon atom). In addition, examples of chemically recycled diol components produced by depolymerization of waste polyester include chemically recycled BDO obtained by depolymerizing polybutylene terephthalate and chemically recycled ethylene glycol obtained by depolymerizing polyethylene terephthalate.

[0030] <Other Monomers> In the present invention, one or more copolymerization components can be used in the production of PBT. These include hydroxycarboxylic acids such as lactic acid, glycolic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 6-hydroxy-2-naphthalenecarboxylic acid, and p-β-hydroxyethoxybenzoic acid; alkoxycarboxylic acids; monofunctional components such as stearyl alcohol, benzyl alcohol, stearic acid, benzoic acid, t-butylbenzoic acid, and benzoylbenzoic acid; and trifunctional or higher polyfunctional components such as tricarballylic acid, trimellitic acid, trimesic acid, pyromelic acid, gallic acid, trimethylolethane, trimethylolpropane, glycerol, and pentaerythritol.

[0031] The polyester of the present invention may also be a PTMG copolymerized PBT in which crystalline PBT is used as a hard segment and polytetramethylene ether glycol (hereinafter, sometimes referred to as "PTMG") is used as a soft segment.

[0032] The PTMG copolymerized PBT can be obtained by subjecting the dimethyl terephthalate composition of the present invention to an ester exchange reaction with a diol component containing BDO and PTMG, and further with other components used as needed, followed by a polycondensation reaction, and preferably further a solid-state polycondensation reaction.

[0033] In this case, the number average molecular weight of the PTMG used is preferably 650 to 2000, more preferably 800 to 1500. When the molecular weight is within this range, the reactivity during production of the PTMG copolymerized PBT is good, the degree of melting point depression due to copolymerization is small, and a PTMG copolymerized PBT with good mechanical properties can be obtained. The molecular weight of the PTMG is controlled by the reaction temperature, reaction time, catalyst amount, etc. during production of the PTMG.

[0034] Furthermore, the lower limit of the copolymerization amount of the PTMG component in the PTMG copolymerized PBT is preferably 8 mass%, more preferably 10 mass%, and even more preferably 15 mass%, and the upper limit is preferably 35 mass%, more preferably 30 mass%, and even more preferably 25 mass%. Here, the copolymerization amount (content) of PTMG refers to the proportion of PTMG units as a diol component in the PTMG-copolymerized PBT, i.e., the proportion of the amount of the component obtained by subtracting the amount of water molecules resulting from ester bond formation from PTMG, relative to the PTMG-copolymerized PBT, expressed in mass %. By ensuring that the copolymerization ratio of PTMG is within this range, a PTMG copolymerized PBT with a good balance of flexibility and impact strength can be obtained. The amount of PTMG copolymerized can be controlled by the amount of PTMG charged during the production of the copolymerized PBT.

[0035] <Polyester manufacturing method> The method for producing the polyester of the present invention is not particularly limited, and the production method may be a continuous method or a batch method. One example is a method for producing the polyester through the following transesterification reaction step and polycondensation reaction step.

[0036] (Transesterification reaction process) An example of the process for converting the dimethyl terephthalate composition of the present invention and a diol component into an oligomer through a transesterification reaction is a method in which a single transesterification reaction tank or a multistage reaction apparatus in which a plurality of transesterification reaction tanks are connected in series is used to perform the transesterification reaction under normal or reduced pressure with or without a catalyst until the transesterification reaction rate (the proportion of ester groups in the raw dicarboxylic acid component that have reacted with the diol component and undergone a transesterification reaction) reaches typically 90% or more, while removing the alcohol produced in the reaction and the excess diol component from the system, to obtain an oligomer. Generally, the temperature of the transesterification reaction is about 210 to 230°C, the pressure is about 10 to 133 kPa, and the residence time in the reaction tank, which corresponds to the reaction time, is about 1 to 4 hours.

[0037] (Polycondensation reaction step) An example of the polycondensation reaction step is a method in which a single melt polycondensation tank or a multistage reaction apparatus in which a plurality of melt polycondensation tanks are connected in series, for example, a first-stage reactor is a complete mixing type reactor equipped with stirring blades, and second-stage and third-stage reactors are horizontal plug flow type reactors equipped with stirring blades, is used, and the diol produced is distilled out of the system while heating under reduced pressure in the presence of a catalyst. Generally, the polycondensation reaction is carried out at a temperature of 210 to 280°C, preferably about 220 to 250°C, under reduced pressure of 27 kPa or less, preferably 13 kPa or less.

[0038] The reaction tank may be a single tank or multiple tanks. However, in order to prevent coloration and deterioration and to suppress an increase in terminal groups such as vinyl groups, it is advisable to carry out the reaction in at least one reaction tank under a high vacuum of usually 1.3 kPa or less, preferably 0.3 kPa or less.

[0039] The polyester obtained by the polycondensation reaction is usually withdrawn in the form of a strand or sheet from a withdrawal port provided at the bottom of the polycondensation reaction tank, and then cut with a cutter while or after water cooling to form granular bodies such as pellets or chips (for example, lengths of about 3 to 10 mm). Alternatively, the molten resin is released from the polycondensation reaction tank through a pipe into cold water adjusted to a predetermined temperature, and then cut with a cutter to form spheres (diameters of about 2 to 10 mm).

[0040] <Polycondensation catalyst> When the oligomer obtained by the transesterification reaction between the diol component and the dicarboxylic acid component is polycondensed, a titanium compound and preferably a compound of a metal of Group 2A of the Periodic Table are usually used as catalysts. These catalyst components may be used in the transesterification reaction and then directly subjected to the polycondensation reaction, or they may not be used in the transesterification reaction, or only the titanium catalyst may be used, with the remaining catalyst components added at the polycondensation stage. Furthermore, a portion of the catalyst amount ultimately used in the transesterification reaction may be used, and then appropriately added as the polycondensation reaction proceeds. In any case, in the present invention, the polyester finally obtained necessarily contains titanium and, preferably, also a metal of Group 2A of the Periodic Table. The content thereof will be described later.

[0041] (Example of titanium compound) Specific examples of titanium compounds used as catalysts include inorganic titanium compounds such as titanium oxide and titanium tetrachloride, tetraalkyl titanates such as tetramethyl titanate, tetraisopropyl titanate and tetrabutyl titanate, and tetraaryl titanates such as tetraphenyl titanate. These may be used alone or in combination of two or more. Of these, tetraalkyl titanates are preferred, and among these, tetrabutyl titanate is preferred.

[0042] (titanium catalyst amount) The content of the titanium catalyst in the polyester of the present invention is preferably 5 to 200 ppm by mass of titanium atoms relative to the polyester. This amount is more preferably 10 ppm or more, even more preferably 20 ppm or more, and most preferably 25 ppm or more. This amount is more preferably 190 ppm or less, even more preferably 180 ppm or less, particularly preferably 170 ppm or less, particularly preferably 160 ppm or less, and most preferably 150 ppm or less. If the titanium content is too high, problems arise such as deterioration in color tone, hydrolysis resistance, and solution haze, and an increase in fish eyes in the resulting molded product, while if the titanium content is too low, polymerization properties deteriorate.

[0043] (Group 2A metal compound) Specific examples of the Group 2A metal compound of the periodic table used as a catalyst include various compounds of beryllium, magnesium, calcium, strontium, and barium. From the viewpoints of ease of handling and availability, and catalytic effect, magnesium compounds and / or calcium compounds are preferred, and magnesium compounds, which have excellent catalytic effect, are particularly preferred. Specific examples of magnesium compounds include magnesium acetate, magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium alkoxide, magnesium hydrogen phosphate, and the like. Specific examples of calcium compounds include calcium acetate, calcium hydroxide, calcium carbonate, calcium oxide, calcium alkoxide, and calcium hydrogen phosphate.

[0044] These Group 2A metal compounds of the periodic table may be used alone or in combination of two or more. Of these, magnesium acetate is preferred.

[0045] (Group 2A metal catalyst amount) The content of the Group 2A metal catalyst in the polyester of the present invention is not particularly limited, but is preferably 3 to 150 ppm by mass relative to the polyester in terms of Group 2A metal atoms. This amount is more preferably 5 ppm or more, and even more preferably 10 ppm or more. This amount is more preferably 140 ppm or less, even more preferably 130 ppm or less, and particularly preferably 100 ppm or less. If the content of the Group 2A metal is too high, color tone and hydrolysis resistance will deteriorate, while if it is too low, polymerization will deteriorate.

[0046] When an acetate of a metal of Group 2A of the Periodic Table is used, the amount of the metal of Group 2A of the Periodic Table in the polyester is preferably 100 ppm or less, since the acetic acid source enters the reaction system.

[0047] (M / Ti ratio) The molar ratio of titanium atoms to Group 2A metal atoms of the periodic table (Group 2A metal atoms of the periodic table / titanium) contained in the polyester of the present invention is usually 0.01 to 100, preferably 0.1 to 10, more preferably 0.3 to 3, and even more preferably 0.3 to 1.5.

[0048] (Metal analysis method) The content of metals such as titanium atoms in polyester can be measured using methods such as atomic emission, atomic absorption, and ICP emission after recovering the metals in the polymer by a method such as wet ashing.

[0049] (Other catalysts) In producing the polyester of the present invention, in addition to the titanium compound and the compound of a metal of Group 2A of the Periodic Table, reaction aids such as antimony compounds such as antimony trioxide, germanium compounds such as germanium dioxide and germanium tetroxide, manganese compounds, zinc compounds, zirconium compounds, cobalt compounds, phosphorus compounds such as orthophosphoric acid, phosphorous acid, hypophosphorous acid, polyphosphoric acid, esters or metal salts thereof, sodium hydroxide, sodium benzoate, etc. may be used.

[0050] [Intrinsic viscosity of PBT] When the PBT of the present invention is used for compounding or injection molding, the intrinsic viscosity of the PBT is preferably 0.6 to 1.3 dL / g. If the intrinsic viscosity is less than 0.6 dL / g, the mechanical strength of the molded product tends to be insufficient, while if it exceeds 1.3 dL / g, the melt viscosity tends to be high, which deteriorates the flowability and moldability. The intrinsic viscosity of the PBT of the present invention is more preferably 0.65 to 1.26 dL / g, and even more preferably 0.7 to 1.2 dL / g.

[0051] Furthermore, when the PBT pellets of the present invention are used for extrusion applications such as film, sheet, or filament, the intrinsic viscosity of the PBT is usually 1.00 to 1.60 dL / g, preferably 1.03 to 1.50 dL / g, more preferably 1.05 to 1.55 dL / g, particularly preferably 1.10 to 1.50 dL / g, and particularly preferably 1.15 to 1.35 dL / g. If the intrinsic viscosity is less than 1.00 dL / g, extrusion moldability deteriorates, leading to drawdown of the resin and molding defects, resulting in insufficient mechanical strength of extrusion-molded products such as films, or the melt viscosity decreases, resulting in excessively high fluidity and thus poor extrusion moldability. On the other hand, if the intrinsic viscosity exceeds 1.60 dL / g, the melt viscosity increases, resulting in poor fluidity and thus poor extrusion moldability.

[0052] [Compound] The polyester of the present invention can be produced with good productivity using the dimethyl terephthalate composition of the present invention with excellent reaction efficiency and production stability, and is also excellent in quality such as color tone. The polyester of the present invention can be compounded into a compound product by adding various additives or compounding materials as required during or after the polyester production stage. [Example]

[0053] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0054] [Raw materials and reagents] Dimethyl terephthalate and tetrabutyl titanate were reagents manufactured by Tokyo Chemical Industry Co., Ltd. The petrochemically derived 1,4-butanediol used was a product of Mitsubishi Chemical Corporation. The biomass-derived 1,4-butanediol used was 1,4-butanediol produced by hydrogenation of succinic acid, manufactured by Zhejiang Boju New Materials Co., Ltd. As the methyl alkyl terephthalate (compound (1)), ethyl methyl terephthalate and 2-ethylhexyl methyl terephthalate, reagents manufactured by Merck were used. Furthermore, "ADEKA STAB AO-60" manufactured by ADEKA Corporation was used as a phenolic antioxidant.

[0055] [Measurement and evaluation method] <Analysis of Dimethyl Terephthalate Composition> The dimethyl terephthalate composition was analyzed by gas chromatography using the following apparatus and conditions. Equipment: Shimadzu GC-2014 Column: Agilent Technologies "DB-1" (inner diameter 0.53 mm, column length 30 m, film thickness 1 μm) Carrier gas: Helium Carrier gas flow rate: 5.58 cm per minute 3 Linear speed: 47.4 cm per second ·Inlet temperature: 250℃ Detector temperature: 280℃ Column temperature rise pattern: First, hold at 150°C for 5 minutes, then raise the temperature at 13°C per minute to 295°C, and hold at 295°C for 15 minutes for analysis.

[0056] <Raw material melting time> In the transesterification reaction, the reaction vessel was immersed in an oil bath at 150°C, and the time until the raw materials were completely melted without stirring was confirmed visually.

[0057] <Interesterification time> In the transesterification reaction, the time required for 90% or more of the theoretical amount of alcohol to be produced as a by-product when the dimethyl terephthalate composition was completely reacted was defined as the transesterification time.

[0058] <Bumping suppression effect> The reaction system was visually observed, and the maximum flying distance of the droplets from the liquid surface when foaming occurred was used as an index and evaluated as follows. S: No foaming observed. A: Droplet reach distance: less than 1 cm B: Droplet reach distance: 1cm or more and less than 3cm C: Droplet reach distance: 3cm or more

[0059] <Intrinsic viscosity of polybutylene terephthalate> The viscosity was measured using a fully automatic viscosity measuring device (model DT553, capillary type) manufactured by Sentec Co., Ltd. in the following manner. A mixed solution of phenol and 1,1,2,2-tetrachloroethane (1 / 1 mass ratio mixture) was used as the solvent. The number of seconds it took for a 1.0 g / dL PBT sample solution and the solvent alone to fall at 30°C was measured and calculated using the following formula. Intrinsic viscosity (dL / g)=((1+4K H η sp ) 0.5 -1) / (2K H C) (However, η sp =η / η0-1, where η is the time it takes for the sample solution to fall, η0 is the time it takes for the solvent to fall, C is the PBT concentration of the sample solution (g / dL), and K H is Huggins' constant. K H The value used was 0.33.)

[0060] <Color tone of polybutylene terephthalate> The color tone of the polybutylene terephthalate was evaluated using a color difference meter "Z-300A" manufactured by Nippon Denshoku Co., Ltd., in the L, a, b color system.

[0061] <Production Example 1: Production of BDO by depolymerization of polybutylene terephthalate> 1,4-butanediol obtained by chemical recycling was produced in accordance with Example 3 of JP-A-2004-323378. An autoclave equipped with a stirring blade was charged with 1,030 parts by mass of polyethylene terephthalate, 3,200 parts by mass of methanol, and 13 parts by mass of sodium carbonate. The autoclave was immersed in an oil bath at 200°C, and the mixture was reacted for 8 hours with stirring at a pressure of 1.3 MPa. The autoclave was removed from the oil bath and cooled to below 10°C with ice water to obtain a slurry. The obtained slurry was separated into solid and liquid using filter paper to obtain a filtrate. The obtained filtrate was placed in a distillation apparatus equipped with a thermometer, a pressure reduction control device, a stirring blade, a condenser, and a distillate receiver. After recovering methanol and tetrahydrofuran as the initial distillate, the mixture was distilled under reduced pressure to obtain a main distillate. A portion of the obtained main fraction was extracted and analyzed by gas chromatography, which revealed that the 1,4-butanediol content was 99 mass % or more. This main fraction was used as chemically recycled 1,4-butanediol.

[0062] [Example 1] <Production of Dimethyl Terephthalate Composition> A 5 L separable flask reactor was charged with 2000 parts by mass of dimethyl terephthalate and 0.04 parts by mass of ethyl methyl terephthalate, and the system was purged with nitrogen. The system was then heated to 160°C and maintained at 160°C, and stirred in a molten state for 30 minutes. The molten contents were then removed and cooled, yielding dimethyl terephthalate composition 1. The content of compound (1) (ethyl methyl terephthalate) relative to dimethyl terephthalate in this dimethyl terephthalate composition 1 was 0.002% by mass.

[0063] <Transesterification reaction> 132 parts by mass of dimethyl terephthalate composition 1 and 74 parts by mass of petrochemical-derived 1,4-butanediol were fed into a glass reactor equipped with a stirrer and a distillation tube. The pressure in the glass reactor was reduced to approximately 100 Pa, and then the pressure was returned to atmospheric pressure with nitrogen. This operation was repeated three times to replace the inside of the reactor with nitrogen. The reactor was then immersed in an oil bath at 150°C. The time from immersion of the reactor in the oil bath until the raw materials were completely melted (raw material melting time) was 40 minutes. After confirming that the contents had melted, the rotation speed was increased to 150 rpm. Next, a butanediol mixture containing 94% by mass of petrochemical-derived 1,4-butanediol and 6% by mass of tetrabutyl titanate was added so that the titanium atom content was 33 ppm by mass relative to the resulting polybutylene terephthalate. The oil bath temperature was then raised from 150°C to 210°C over 105 minutes to obtain a transesterification reaction liquid. A distillate of 40 parts by mass (91% of the theoretical amount of alcohol by-product) was obtained in the receiver at the end of the distillation column. The time required for the transesterification reaction from the addition of the BDO solution of tetrabutyl titanate until 40 parts by mass of a distillate was obtained (transesterification time) was 128 minutes.

[0064] <Polycondensation reaction> A butanediol mixture containing 70% by mass of petroleum-derived 1,4-butanediol, 10% by mass of magnesium acetate tetrahydrate, and 20% by mass of water was fed to the resulting transesterification reaction solution so that the magnesium atom content was 48 ppm by mass relative to the resulting polybutylene terephthalate. A butanediol mixture containing 94% by mass of petroleum-derived 1,4-butanediol and 6% by mass of AO-60 was fed to the resulting polybutylene terephthalate so that the AO-60 content was 530 ppm by mass relative to the resulting polybutylene terephthalate. A butanediol mixture containing 94% by mass of petroleum-derived 1,4-butanediol and 6% by mass of tetrabutyl titanate was fed to the resulting polybutylene terephthalate so that the titanium atom content was 61 ppm by mass relative to the resulting polybutylene terephthalate. The oil bath was heated from 210°C to 240°C over 45 minutes, and the internal pressure of the glass reactor was reduced from 101 KPa to 133 Pa over 85 minutes to carry out a polycondensation reaction. The internal pressure was then fully evacuated, and the polymerization reaction was terminated when the agitator in the reactor reached a predetermined stirring power. The time required for the polycondensation reaction from the start of pressure application to the stop of the stirrer (polycondensation time) was 170 minutes.

[0065] The reactor was then restored to 101 KPa with nitrogen, and the pressure was then increased to a predetermined level, and strands of polybutylene terephthalate were extracted from the bottom of the reactor. The strands were then pelletized using a rotary cutter to obtain pellets of polybutylene terephthalate. The resulting pelletized polybutylene terephthalate had an intrinsic viscosity of 0.966 dL / g, and its color was L=86.5, a=-0.7, and b=-0.2.

[0066] [Examples 2 to 5, Comparative Examples 1 and 2] The same procedure as in Example 1 was carried out, except that the dimethyl terephthalate compositions shown in Table 1 were prepared and used. In Examples 1 to 4 and Comparative Examples 1 and 2, the raw material melting time, transesterification time, bumping suppression effect, and polycondensation time, as well as the intrinsic viscosity, L value, a value, and b value of color tone of the obtained polybutylene terephthalate are summarized in Table 1. In Table 1 and Table 2 below, "R 1 " is R in formula (1) representing methyl alkyl terephthalate in the dimethyl terephthalate composition. 1 The "content of compound (1)" indicates the content of compound (1) relative to dimethyl terephthalate in the dimethyl terephthalate composition.

[0067] [Table 1]

[0068] [Example 5] The same procedure as in Example 2 was carried out, except that 1,4-butanediol derived from biomass resources was used instead of petrochemically derived 1,4-butanediol.

[0069] [Example 6] Example 2 was carried out in the same manner as in Example 2, except that the chemically recycled 1,4-butanediol produced in Production Example 1 was used instead of the petrochemically derived 1,4-butanediol.

[0070] In Examples 5 and 6, the raw material melting time, transesterification time, bumping suppression effect, and polycondensation time, as well as the intrinsic viscosity, L value, a value, and b value of color tone of the resulting polybutylene terephthalate, are summarized in Table 2.

[0071] [Table 2]

[0072] Tables 1 and 2 show that a dimethyl terephthalate composition containing 0.0001% by mass or more and 1% by mass or less of a methyl alkyl terephthalate represented by formula (1) relative to dimethyl terephthalate can shorten the melting time of the raw materials and suppress bumping in the system, thereby improving polyester production efficiency, without impairing the transesterification reactivity or affecting the quality of the resulting polyester. Furthermore, it can be seen that this effect is not limited to petrochemically derived 1,4-butanediol, but is similarly achieved when biomass-derived 1,4-butanediol or chemically recycled 1,4-butanediol is used as the 1,4-butanediol.

[0073] In contrast, in Comparative Example 1, which does not contain methyl alkyl terephthalate and uses only dimethyl terephthalate, it takes a long time to melt the raw materials and there is also the problem of bumping in the system. In Comparative Example 2, in which the content of methyl alkyl terephthalate in the dimethyl terephthalate composition was too high, the melting time of the raw materials was short and bumping in the system was suppressed, but the reactivity in the transesterification reaction was poor, and the transesterification time and the subsequent polycondensation time were long.

Claims

1. A dimethyl terephthalate composition comprising 0.0001 mass % or more and 1 mass % or less of a methyl alkyl terephthalate represented by the following formula (1) relative to dimethyl terephthalate: 【Chemistry 1】 (In the above formula (1), R １ represents a hydrocarbon group having 2 to 10 carbon atoms, which may be branched.

2. The dimethyl terephthalate composition according to claim 1, wherein the dimethyl terephthalate composition is obtained by chemical recycling.

3. A polyester obtained by reacting the dimethyl terephthalate composition according to claim 1 or 2 with a diol component.

4. The polyester according to claim 3, wherein 50 mol % or more of the diol component is 1,4-butanediol.

5. The polyester of claim 3 , wherein the diol component is derived from biomass.

6. The polyester of claim 3, wherein the diol component is produced by depolymerization of the polyester.

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