Titanium catalyst solution, method for producing the same, and method for producing polybutylene terephthalate using the same

Abstract

In particular, this invention provides a titanium catalyst solution that can suppress the precipitation of the titanium catalyst without the need for continuous stirring, and that exhibits excellent storage stability and thermal stability. [Solution] A titanium catalyst solution comprising an organic titanium compound, 1,4-butanediol, and water, wherein the water concentration W (mass%) in the solution is 0.030

Description

Technical Field

[0001] The present invention relates to a titanium catalyst solution having excellent storage stability that can be suitably used when producing polybutylene terephthalate and a method for producing the same. The present invention also relates to a method for producing polybutylene terephthalate using this titanium catalyst solution.

Background Art

[0002] Among polyesters, taking advantage of its excellent physical and chemical properties, polybutylene terephthalate is widely industrially used in fields such as electrical and electronic parts and automotive connectors as a so-called engineering plastic.

[0003] Polybutylene terephthalate can be produced by subjecting terephthalic acid or its derivative and 1,4-butanediol to an esterification or transesterification reaction to form an oligomer, and then subjecting the oligomer to a polycondensation reaction. As a catalyst for this polycondensation reaction, various metal compounds such as titanium are mainly known. In particular, titanium catalysts are widely used because they are inexpensive and have excellent catalytic activity.

[0004] To supply a titanium catalyst to an esterification or transesterification reaction and a polycondensation step, a method of previously dissolving the titanium catalyst in 1,4-butanediol used in the reaction and supplying the solution is generally used. However, if the titanium catalyst is stored as a 1,4-butanediol solution for a long time, or if heat is generated during stirring or pump circulation during storage, a part of the titanium catalyst may precipitate. When using a titanium catalyst solution in which the titanium catalyst has precipitated, problems such as line blockage during charging and deterioration of charging accuracy occur. There is also a problem that the catalytic activity decreases and the polycondensation step takes a long time, which has an adverse effect on the quality and operability of the obtained polybutylene terephthalate.

[0005] In order to solve such problems, conventionally, the following methods have been proposed as methods for preparing a titanium catalyst solution and the like. (1) A method of adding 0.05 to 1.0% by weight of water to the entire tetraalkyl titanate catalyst solution (see Patent Document 1) (2) A method for preparing a titanium catalyst solution containing 0.1 to 10% by weight of tetraalkoxytitanium and 0.5 to 2.0 times the amount of water per mole of tetraalkoxytitanium (equivalent to approximately 1.3 to 5.3 titanium / water by weight ratio), wherein the tetraalkoxytitanium and 1,4-butanediol are mixed first, and then water is added and mixed (see Patent Document 2). (3) A titanium catalyst solution for polyester production comprising an organic titanium compound, an alkylene glycol, and water, wherein the titanium concentration Ti (weight%) and water concentration W (weight%) in the solution satisfy the following formulas (1) and (2) (see Patent Document 3). (1)0 <W≦0.9 (2) Ti / W ≤ 1.3 (4) A method for producing polybutylene terephthalate, comprising supplying a catalyst solution obtained by dissolving an organotitanium compound catalyst in a diol to the reaction system with a water content of 250 ppm or less (see Patent Document 4).

[0006] On the other hand, in recent years, in addition to conventional methods for producing 1,4-butanediol using fossil fuels such as petroleum as raw materials (hereinafter referred to as "petrochemical-derived"), methods for producing biomass-derived 1,4-butanediol using biomass resources as raw materials (hereinafter referred to as "biomass-derived" in this invention) have also been developed. For example, a method for obtaining 1,4-butanediol by hydrogenating succinic acid obtained by sugar fermentation (for example, Patent Document 5) and a method for directly obtaining 1,4-butanediol by fermenting biomass resources such as sugar have been proposed (for example, Patent Document 6). Furthermore, a method for producing 1,4-butanediol by depolymerizing polybutylene terephthalate has also been developed (for example, Patent Document 7). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Special Publication No. 3-72653 [Patent Document 2] Japanese Patent Publication No. 2001-72751 [Patent Document 3] Japanese Patent Publication No. 2004-189921 [Patent Document 4] Japanese Patent Publication No. 2009-235288 [Patent Document 5] Patent No. 4380654 [Patent Document 6] International Publication No. 2015 / 158716 [Patent Document 7] Japanese Patent Publication No. 2004-323378 [Overview of the project] [Problems that the invention aims to solve]

[0008] According to the results of a detailed investigation by the inventors into the conventional method of preparing the titanium catalyst solution described above, it was found that while adding a small amount of water to the titanium catalyst solution does indeed show some effect in suppressing the precipitation of the titanium catalyst compared to simply mixing the titanium catalyst with a diol such as 1,4-butanediol, continuous stirring is necessary to maintain the precipitation suppression effect over a long period of time. Therefore, the problem of increased utility costs for agitation, and above all, the problem of titanium catalyst deposition in dead spaces where agitation force is difficult to reach, such as in transfer piping, could not be avoided, leaving significant problems for long-term operation using titanium catalysts.

[0009] For example, Patent Document 3 describes a method for mixing ethylene glycol, water, and a titanium compound in a specific order of addition, and the effects regarding the water and titanium content, with respect to an ethylene glycol solution. However, when 1,4-butanediol was used instead of ethylene glycol, sufficient effects could not be obtained due to a significant difference in storage stability between the ethylene glycol solution and the 1,4-butanediol solution, and it was found that further improvements were necessary. Furthermore, it was found that the moisture content described in Patent Document 4 is not sufficient for long-term storage.

[0010] As mentioned above, in recent years, biomass-derived 1,4-butanediols and 1,4-butanediols obtained by the depolymerization of polybutylene terephthalate have been proposed. However, there has been no research into using 1,4-butanediols other than those derived from petrochemicals in the preparation of catalyst solutions, or using catalyst solutions prepared with these petrochemical-derived 1,4-butanediols, or even using these petrochemical-derived 1,4-butanediols as raw materials to produce polybutylene terephthalate.

[0011] The present invention aims to solve the problems of the above-mentioned prior art and to provide a titanium catalyst solution and a method for producing the same that have excellent storage stability and thermal stability, and that can suppress the precipitation of the titanium catalyst without continuous stirring or other operations. Furthermore, the present invention provides a method for producing polybutylene terephthalate using the titanium catalyst solution. [Means for solving the problem]

[0012] As a result of diligent research to solve the above problems, the inventors have found that the above objective can be achieved by setting the water content, the concentration ratio of titanium atoms to water, and the solution haze of a titanium catalyst solution containing an organotitanium compound, 1,4-butanediol, and water. Furthermore, they have found that such a titanium catalyst solution can be obtained by setting the mixing order of 1,4-butanediol, water, and the organotitanium compound.

[0013] This invention was completed based on these findings, and its gist is as follows.

[0014] [1] A titanium catalyst solution comprising an organotitanium compound, 1,4-butanediol, and water, The water concentration W (mass%) in the titanium catalyst solution is 0.030 <W≦0.90で、 The ratio of titanium concentration Ti (mass %) to water concentration W (mass %) is 1.3 < Ti / W ≤ 10.0, and the titanium catalyst solution is characterized in that the solution haze (%) is 8.0 or less.

[0015] [2] The titanium catalyst solution according to [1], wherein the titanium concentration Ti (mass %) is more than 0.1 and 1.5 or less.

[0016] [3] The titanium catalyst solution according to [1] or [2], wherein the 1,4-butanediol is 1,4-butanediol derived from biomass resources or 1,4-butanediol derived from the depolymerization of polybutylene terephthalate.

[0017] [4] A method for producing a titanium catalyst solution containing an organic titanium compound, 1,4-butanediol and water, where the water concentration W (mass %) is 0.030 < W ≤ 0.90, and the ratio of titanium concentration Ti (mass %) to water concentration W (mass %) is 1.3 < Ti / W ≤ 10.0, characterized in that after mixing 1,4-butanediol and water, an organic titanium compound is added to the obtained mixture. A method for producing a titanium catalyst solution.

[0018] [5] The method for producing a titanium catalyst solution according to [4], wherein the titanium concentration Ti (mass %) of the titanium catalyst solution is more than 0.1 and 1.5 or less.

[0019] [6] The method for producing a titanium catalyst solution according to [4] or [5], wherein the 1,4-butanediol is 1,4-butanediol produced by direct fermentation of sugar or produced by hydrogen reduction of succinic acid or dialkyl succinate produced using biomass resources or 1,4-butanediol produced by depolymerization of polybutylene terephthalate.

[0020] [7] A method for producing polybutylene terephthalate using the titanium catalyst solution according to any one of [1] to [3].

[0021] A method for producing polybutylene terephthalate using a titanium catalyst solution produced by any of the methods for producing a titanium catalyst solution described in [8] [4] to [6].

[0022] [9] A method for producing polybutylene terephthalate according to [7] or [8], wherein the 1,4-butanediol used as a raw material for polybutylene terephthalate is 1,4-butanediol produced by direct fermentation of sugar, succinic acid produced using biomass resources or 1,4-butanediol produced by hydrogen reduction of dialkyl succinate, or 1,4-butanediol produced by depolymerization of polybutylene terephthalate.

[0023]

[10] A method for producing polybutylene terephthalate according to any one of [7] to [9], wherein the terephthalic acid component of the polybutylene terephthalate is terephthalic acid produced by chemical recycling of polyester or dimethyl terephthalate, or terephthalic acid produced using biomass resources. [Effects of the Invention]

[0024] The titanium catalyst solution of the present invention exhibits excellent inhibition of titanium catalyst precipitation, does not become cloudy even without stirring during storage or handling, has excellent long-term storage stability, and can maintain the activity of the titanium catalyst over a long period. When a polymerization reaction is carried out using such a titanium catalyst solution of the present invention, a high degree of polymerization can be achieved even with a short reaction time, and polybutylene terephthalate can be produced stably and productively over a long period of time. According to the present invention, the above effects can be effectively obtained even when using biomass-derived 1,4-butanediol or 1,4-butanediol obtained by the depolymerization of polybutylene terephthalate as the 1,4-butanediol used in the preparation of a titanium catalyst solution, or as the raw material 1,4-butanediol used in the production of polybutylene terephthalate. [Modes for carrying out the invention]

[0025] The present invention will be described in detail below, but the following descriptions of constituent elements are representative examples of embodiments of the present invention, and the present invention is not limited to these contents. In this invention, the "main component" in a dicarboxylic acid component refers to the component present in the component at a concentration of 50 mol% or more. The same applies to the "main component" in a diol component.

[0026] [Titanium catalyst solution] The titanium catalyst solution of the present invention is a titanium catalyst solution comprising an organotitanium compound, 1,4-butanediol, and water. The water concentration W (mass%) in the titanium catalyst solution is 0.030 <W≦0.90で、 The ratio of titanium concentration Ti (mass%) to water concentration W (mass%) is 1.3 <Ti / W≦10.0であり、 The solution haze (%) is characterized by being 8.0 or less.

[0027] <Organic Titanium Compounds> Examples of organotitanium compounds in the present invention include titanium alkoxides, acetates, and oxalates. Specifically, examples include titanium alkoxides such as tetra-n-propyl titanate, tetra-i-propyl titanate, tetra-n-butyl titanate, tetra-n-butyl titanate tetramer, tetra-t-butyl titanate, tetracyclohexyl titanate, tetraphenyl titanate, tetrabenzyl titanate, and tetramethyl titanate, as well as titanium acetate, titanium oxalate, and potassium titanium oxalate. Among these, titanium alkoxides such as tetra-n-propyl titanate, tetra-iso-propyl titanate, and tetra-n-butyl titanate, titanium acetate, and titanium oxalate are preferred, tetraalkyl titanates are more preferred, and tetra-n-butyl titanate is preferred. These organotitanium compounds may be used individually or in combination of two or more.

[0028] <1,4-Butanediol> In the present invention, as the 1,4-butanediol constituting the titanium catalyst solution, usually, 1,4-butanediol which is a raw material of polybutylene terephthalate produced using the titanium catalyst solution of the present invention is used. Therefore, when using biomass-derived 1,4-butanediol as the 1,4-butanediol which is a raw material for producing polybutylene terephthalate, it is preferable that the 1,4-butanediol in the titanium catalyst solution is also biomass-derived 1,4-butanediol. Alternatively, when using 1,4-butanediol obtained by depolymerizing polybutylene terephthalate as the 1,4-butanediol which is a raw material for producing polybutylene terephthalate, it is preferable that the 1,4-butanediol in the titanium catalyst solution is also 1,4-butanediol obtained by depolymerizing polybutylene terephthalate.

[0029] <W·Ti / W·Solution haze> The titanium catalyst solution of the present invention needs to satisfy the following formulas (1), (2) and (3) in terms of the water concentration W (mass %), the ratio of the titanium concentration Ti (mass %) in the solution to the water concentration W (mass %), and the solution haze (%). (1) 0.030 < W ≤ 0.90 (2) 1.3 < Ti / W ≤ 10.0 (3) Solution haze ≤ 8.0

[0030] When the catalyst solution is stored for a long time, white precipitate will precipitate when the water concentration W is 0.030 mass % or less. On the other hand, when the water concentration W exceeds 0.90 mass %, the time until the titanium catalyst solution becomes cloudy during warm storage becomes shorter, so white insoluble matter precipitates during the storage of the catalyst solution, and this precipitate causes problems such as blockage of the charging line, deterioration of the charging accuracy, and decrease in the catalyst activity. From these viewpoints, the water concentration W is preferably 0.040 to 0.80 mass %, and more preferably 0.050 to 0.70 mass %.

[0031] The lower limit of the ratio Ti / W, which is the ratio of titanium concentration Ti (mass%) to water concentration W (mass%), is usually greater than 1.3, preferably 1.6 or higher, and more preferably 2.1 or higher. If Ti / W is greater than 1.3, no white precipitate will precipitate in the catalyst solution. On the other hand, if Ti / W is excessively high, a white precipitate will precipitate in the catalyst solution, so Ti / W is usually 10.0 or less, and preferably 9.0 or less.

[0032] The content of the organotitanium compound in the titanium catalyst solution of the present invention is not particularly limited, as long as it satisfies the above Ti / W ratio with respect to the above water concentration W (mass%). However, it is preferable that the titanium concentration Ti be higher than 0.1 mass%, more preferably 0.3 mass% or higher, and even more preferably 0.4 mass% or higher. If the titanium concentration Ti is higher than the above lower limit, the amount of titanium catalyst solution required during the production of polybutylene terephthalate will not be excessively large, and the amount of BDO consumed in the solution can also be reduced. In addition, a large titanium catalyst solution storage tank is not required, which is preferable. On the other hand, the upper limit of the titanium concentration Ti is preferably 1.5% by mass or less, more preferably 1.3% by mass or less, and even more preferably 1.2% by mass or less. If the titanium concentration Ti is below the above upper limit, a certain amount of titanium catalyst solution will be added as the amount of titanium catalyst solution necessary for the production of polybutylene terephthalate, which improves the accuracy of controlling the amount added and makes it easier to suppress the deposition of the titanium catalyst, and is therefore preferable.

[0033] The solution haze of the organic titanium solution of the present invention immediately after uniform stirring is typically 8% or less, preferably 5% or less, and more preferably 3% or less. Furthermore, even after standing at 60°C for 7 days, the solution haze is preferably 8% or less, particularly 5% or less, and especially 3% or less. When titanium catalyst solutions with a solution haze content exceeding 8% are used to produce polybutylene terephthalate, the polymerization reaction tends to slow down and impurities increase, significantly reducing the product's value.

[0034] In this invention, a solution haze of 8% or less, preferably 5% or less, and more preferably 3% or less of the titanium catalyst solution means that, preferably, after homogeneously stirring the organotitanium compound, water, and 1,4-butanediol by the method described later, the solution haze measured within one day is 8% or less, preferably 5% or less, and more preferably 3% or less. There is no particular limit to the lower limit of the solution haze of the titanium catalyst solution; a lower value is preferable, but typically, the lower limit is 0.1%.

[0035] The solution haze of the titanium catalyst solution can be determined by the method described in the Examples section below.

[0036] [Method for producing titanium catalyst solution] There are no particular limitations on the method for producing the titanium catalyst solution of the present invention, but preferably, according to the method for producing the titanium catalyst solution of the present invention, an organotitanium compound, 1,4-butanediol, and water are used to satisfy the aforementioned water concentration W (mass%) and Ti / W (mass%) ratio, and it is preferable to first mix the 1,4-butanediol and water, and then add the organotitanium compound to the resulting mixture and mix.

[0037] In the present invention, the mixing order of water, 1,4-butanediol, and organotitanium compound is an important requirement for producing the titanium catalyst solution of the present invention. Even if the aforementioned water concentration W (mass%) and Ti / W (mass%) ratio are met, if water, organotitanium compound, and 1,4-butanediol are added and mixed in that order, that is, if 1,4-butanediol is added and mixed to a mixture of water and organotitanium compound, the oxidation reaction of the organotitanium compound, particularly tetraalkyl titanate, by water proceeds rapidly, resulting in turbidity and precipitation. Furthermore, if 1,4-butanediol and organotitanium compound, particularly tetraalkyl titanate, are mixed first, and then water is added, turbidity occurs immediately after stirring, and the precipitation stability of the organotitanium compound is poor when stored without stirring.

[0038] In particular, to fill the aforementioned solution haze, it is necessary to mix the required amount of 1,4-butanediol with water, and then add a predetermined amount of organotitanium compound, especially tetraalkyl titanate, and stir to obtain a titanium catalyst solution of a predetermined concentration. The temperature at which 1,4-butanediol and water are mixed, and the temperature at which the organotitanium compound is added to the resulting mixture and mixed, can be room temperature (25-70°C).

[0039] [Storage method for titanium catalyst solution] When storing the titanium catalyst solution of the present invention, the storage temperature is not particularly limited, but is preferably 25 to 90°C, more preferably 40 to 70°C. If this temperature is above the lower limit, 1,4-butanediol will not freeze, and if it is below the upper limit, water will not volatilize.

[0040] [Method for producing polybutylene terephthalate] Next, a method for producing polybutylene terephthalate (hereinafter sometimes abbreviated as "PBT") using the titanium catalyst solution of the present invention will be described. The present invention's method for producing PBT is characterized by using the titanium catalyst solution of the present invention as a catalyst. The production of PBT is carried out in accordance with conventional methods by polycondensing a dicarboxylic acid component mainly composed of terephthalic acid, i.e., terephthalic acid and / or its ester-forming derivative, and a diol component containing 1,4-butanediol (hereinafter sometimes abbreviated as "BDO"), via an esterification reaction or transesterification reaction (hereinafter sometimes referred to as "esterification (transesterification) reaction"). Basically, it is carried out by conventional production methods. Hereinafter, PBT manufactured by the PBT manufacturing method of the present invention may be referred to as "PBT of the present invention."

[0041] <Raw material: Dicarboxylic acid component, diol component, copolymer component> In the present invention, PBT refers to a polymer having a structure in which a terephthalic acid component and a 1,4-butanediol (BDO) component are ester-bonded, wherein 50 mol% or more of the dicarboxylic acid component consists of the terephthalic acid component, and 50 mol% or more of the diol component consists of BDO. The proportion of the terephthalic acid component in the total dicarboxylic acid component is preferably 70 mol% or more, more preferably 80 mol% or more, and particularly preferably 95 mol% or more. The proportion of BDO in the total diol component 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 PBT decreases, leading to a deterioration in moldability.

[0042] (Dicarboxylic acid component) In the present invention, the dicarboxylic acid component includes dicarboxylic acids and dicarboxylic acid derivatives.

[0043] <Terephthalic acid> Terephthalic acid (hereinafter sometimes abbreviated as "TPA") can be terephthalic acid synthesized by oxidation of the petrochemical product paraxylene (petrochemical-derived terephthalic acid), chemically recycled terephthalic acid obtained by recovering waste polyester and depolymerizing the recovered polyester, or biomass-derived terephthalic acid obtained using isobutanol produced from plant-derived raw materials such as corn and sugarcane, or paraxylene produced from ethanol. From the perspective of aiming for a sustainable society for the sake of the global environment and future generations, it is preferable to use terephthalic acid produced by chemical recycling of polyesters such as polyethylene terephthalate or polybutylene terephthalate. For example, terephthalic acid produced directly by the depolymerization of polyester is preferable because it reduces the number of chemical recycling steps. However, since it is difficult to increase the purity of terephthalic acid produced directly by the depolymerization of polyester by distillation, it is also preferable to produce dimethyl terephthalate by depolymerization of polyester, as in Production Examples 1 to 3 described in the Examples section below, and then hydrolyze it to produce high-purity terephthalic acid, as in Production Examples 4 to 6.

[0044] <Dimethyl terephthalate> Dimethyl terephthalate (hereinafter sometimes abbreviated as "DMT") can be terephthalic acid synthesized by oxidation of the petrochemical product paraxylene (petrochemical-derived terephthalic acid), chemically recycled terephthalic acid obtained by recovering waste polyester and depolymerizing the recovered polyester, or biomass-derived terephthalic acid obtained using isobutanol produced from plant-derived raw materials such as corn and sugarcane, or paraxylene produced from ethanol, which can be methyl-esterified. From the perspective of aiming for a sustainable society for the sake of the global environment and future generations, it is preferable to use materials produced by chemical recycling of polyesters such as polyethylene terephthalate or polybutylene terephthalate. In particular, dimethyl terephthalate produced directly by depolymerization of polyester, as shown in Production Examples 1 to 3 below, is preferable because it can reduce the number of chemical recycling steps.

[0045] In the present invention, terephthalic acid or dimethyl terephthalate can be derived from terephthalic acid or dimethyl terephthalate, respectively, and two or more of these can be mixed and used. In addition, dialkyl terephthalates other than dimethyl terephthalate can also be used.

[0046] <Dicarboxylic acid components other than terephthalic acid or dimethyl terephthalate> There are no particular restrictions on the dicarboxylic acid component other than terephthalic acid or dimethyl terephthalate that can be subjected to the esterification (exchange) reaction. Examples 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 aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. Examples of dicarboxylic acid derivatives include ester-forming derivatives of these dicarboxylic acids, such as esters and dicarboxylic acid halides. These dicarboxylic acid components may be used individually or as a mixture of two or more. Furthermore, dicarboxylic acid components such as succinic acid may be derived from biomass.

[0047] (Diol component) <1,4-butanediol> The 1,4-butanediol in this invention may be petrochemical-derived 1,4-butanediol, biomass-derived 1,4-butanediol, or 1,4-butanediol obtained by depolymerization of PBT. Furthermore, 1,4-butanediol may be produced by fermentation from substrates containing various carbohydrates and carbon monoxide. Biomass-derived 1,4-butanediol may be produced by direct fermentation of sugars, or by hydrogen reduction (hydrogenation reaction) after producing succinic acid or dialkyl succinates such as dimethyl succinate from biomass resources. Furthermore, 1,4-butanediol may be recycled from product waste or defective products. For example, as the 1,4-butanediol, 1,4-butanediol produced by depolymerization of PBT can be used, as shown in Production Example 8 described in the Examples section below. The 1,4-butanediol in this invention may be a mixture of two or more types of 1,4-butanediol obtained from petrochemicals, 1,4-butanediol obtained by fermentation, 1,4-butanediol obtained from biomass, and recycled 1,4-butanediol obtained by depolymerization of PBT, etc.

[0048] <Other diol components> There are no particular restrictions on diol components other than BDO. Examples include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 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; and aromatic diols such as xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone. These diol components other than BDO may be used individually or in combination of two or more.

[0049] Furthermore, biomass-derived diol components other than BDO may also be used.

[0050] (Other ingredients) In the present invention, for the production of PBT, further, hydroxycarboxylic acids such as lactic acid, glycolic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, p-β-hydroxyethoxybenzoic acid, alkoxycarboxylic acids, monofunctional components such as stearyl alcohol, benzyl alcohol, stearic acid, benzoic acid, t-butylbenzoic acid, benzoylbenzoic acid, trifunctional or higher polyfunctional components such as tricarballylic acid, trimellitic acid, trimesic acid, pyromellitic acid, gallic acid, trimethylolethane, trimethylolpropane, glycerol, pentaerythritol, etc. can be used as one or more copolymer components.

[0051] < Intrinsic viscosity of PBT > The intrinsic viscosity of the PBT of the present invention is preferably 0.6 to 1.3 dL / g. If the intrinsic viscosity is 0.6 dL / g or more, the mechanical strength of the obtained molded product will be excellent, and if it is 1.3 dL / g or less, the melt viscosity will be low, the fluidity will be excellent, and the moldability will tend to be good. The intrinsic viscosity of the PBT of the present invention is more preferably 0.65 to 1.26 dL / g, and still more preferably 0.7 to 1.2 dL / g. The intrinsic viscosity of PBT can be determined by the method described in the section of Examples below.

[0052] < Catalyst > When polycondensing an oligomer obtained by an esterification reaction of a diol component and a dicarboxylic acid component or a transesterification reaction of a diol component and an ester-forming derivative of a dicarboxylic acid such as a dicarboxylic acid diester, usually, a titanium compound is used as a catalyst, and preferably, a Group 2A metal compound of the periodic table is further used. These catalyst components may be used in the esterification (exchange) reaction and then proceed directly to the polycondensation reaction, or they may not be used in the esterification (exchange) reaction, or only the titanium catalyst may be used, with the remaining catalyst components added at the polycondensation stage. Furthermore, a portion of the final amount of catalyst to be used may be used in the esterification (exchange) reaction, and additional catalysts may be added as appropriate as the polycondensation reaction progresses. In any case, in this invention, the final PBT will inevitably contain titanium and preferably a Group 2A metal of the periodic table, the amount of which will be described later. In the following, titanium compounds may be referred to as titanium catalysts, and Group 2A metal compounds may be referred to as Group 2A metal catalysts. In the production of PBT according to the present invention, the titanium catalyst solution of the present invention is used as the titanium catalyst.

[0053] The titanium content in the PBT of the present invention is preferably 5 to 120 ppm by mass ratio of titanium atoms to PBT. More preferably 10 ppm or more, even more preferably 20 ppm or more, and most preferably 25 ppm or more. Furthermore, it is preferably 110 ppm or less, and more preferably 100 ppm or less. In particular, in direct polymerization methods that involve esterification reactions, a concentration of 50 ppm or less is more preferable, and 45 ppm or less is most preferable. If the titanium content is too high, the color and hydrolysis resistance will deteriorate, while if it is too low, the polymerization properties will deteriorate.

[0054] Specific examples of Group 2A metal compounds in the present invention include various compounds of beryllium, magnesium, calcium, strontium, and barium. However, magnesium compounds and / or calcium compounds are preferred in terms of ease of handling and availability, as well as catalytic effect, and magnesium compounds with excellent catalytic effect are particularly preferred. Specific examples of magnesium compounds include magnesium acetate, magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium alkoxide, and magnesium hydrogen phosphate. Specific examples of calcium compounds include calcium acetate, calcium hydroxide, calcium carbonate, calcium oxide, calcium alkoxide, and calcium hydrogen phosphate. These Group 2A metal compounds may be used individually or in combination of two or more. Of these, magnesium acetate is the most preferred.

[0055] The content of Group 2A metals in the PBT of the present invention is not particularly limited, but is preferably 3 to 150 ppm by mass ratio of Group 2A metal atoms to PBT. More preferably 5 ppm or more, and even more preferably 10 ppm or more. Furthermore, this amount is more preferably 50 ppm or less, even more preferably 40 ppm or less, particularly preferably 30 ppm or less, and most preferably 15 ppm or less. If the content of Group 2A metals in the periodic table is too high, the color and hydrolysis resistance will deteriorate, while if it is too low, the polymerization properties will deteriorate.

[0056] The molar ratio (group 2A metal / titanium) of titanium atoms to group 2A metal atoms in the PBT of the present invention is usually 0.01 to 100, preferably 0.1 to 10, more preferably 0.3 to 3, and particularly preferably 0.3 to 1.5.

[0057] The metal content, such as titanium atoms, in PBT can be measured using methods such as atomic emission, atomic absorption, or inductively coupled plasma (ICP) after recovering the metal from the polymer using methods such as wet ashing.

[0058] In the production of PBT of the present invention, apart from the above-mentioned titanium compounds and Group 2A metal compounds of the periodic table, antimony compounds such as antimony trioxide, germanium compounds such as germanium dioxide and germanium tetraoxide, manganese compounds, zinc compounds, zirconium compounds, cobalt compounds, orthophosphoric acid, phosphorous acid, hypophosphorous acid, polyphosphoric acid, phosphorus compounds such as their esters and metal salts, reaction aids such as sodium hydroxide and sodium benzoate may also be used.

[0059] <Production method of PBT> Next, the production method of PBT of the present invention will be described. The production method of PBT of the present invention is roughly classified into a so-called direct polymerization method using dicarboxylic acid as the main raw material and a transesterification method using an ester-forming derivative of dicarboxylic acid such as dialkyl dicarboxylate as the main raw material from the raw material aspect. The former mainly generates water in the initial esterification reaction, and the latter mainly generates alcohol in the initial transesterification reaction.

[0060] Also, the production method of PBT is roughly classified into a batch method and a continuous method from the aspect of raw material supply or polymer discharge form. There is also a method in which the initial ester (exchange) reaction is carried out by continuous operation, followed by polycondensation by batch operation, or conversely, the initial ester (exchange) reaction is carried out by batch operation, followed by polycondensation by continuous operation.

[0061] For the production of PBT, ordinary methods can be applied. For example, PBT is produced through a process of mixing a dicarboxylic acid component mainly composed of terephthalic acid or its ester-forming derivative and a diol component mainly composed of 1,4-butanediol in a predetermined ratio under stirring to form a raw material slurry, then heating the raw material slurry under normal pressure or pressure to carry out an ester (exchange) reaction to obtain a PBT low polymer, and then gradually reducing the pressure of the obtained low polymer while heating to carry out a melt polycondensation reaction to obtain PBT granular bodies through a melt polycondensation process. After air classification and sieving of the PBT granular bodies and mixing as necessary, the PBT of the present invention can be obtained.

[0062] An example of a process for producing a low PBT polymer is to use a single esterification (exchange) reactor or a multi-stage reactor with multiple esterification (exchange) reactors connected in series, and carry out the esterification (exchange) reaction until the esterification (exchange) reaction rate (the proportion of all carboxyl groups or ester groups of the starting material dicarboxylic acid that have reacted with the diol component) reaches 90% or more, while removing the water, methanol, and excess diol components produced in the reaction from the system, thereby obtaining a low PBT polymer.

[0063] An example of a melt polycondensation process is a method using a single melt polycondensation tank, or multiple melt polycondensation tanks connected in series, for example, a multi-stage reactor consisting of a fully mixed reactor with a stirring blade in the first stage, and horizontal plug-flow reactors with stirring blades in the second and third stages, while distilling the diol produced out of the system under reduced pressure.

[0064] The PBT polycondensation catalyst may be added to the reaction system at any stage of the mixing and preparation of the dicarboxylic acid component and the diol component, at any stage of the process of forming the PBT low polymer, or at an early stage of the melt polycondensation process. At least the titanium catalyst solution of the present invention is used as the PBT polycondensation catalyst in this case.

[0065] Furthermore, antioxidants and basic compounds can be added in the process of forming a low-molecular-weight PBT or in the melt polycondensation process to suppress side reactions such as thermal decomposition and dimerization of diols. Specifically, examples of antioxidants include Irganox 1330 (manufactured by BASF) and Irganox 1010 (manufactured by BASF), while examples of basic compounds include tertiary amines such as triethylamine, tri-n-butylamine, and benzyldimethylamine; quaternary ammonium hydroxides such as tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide, and trimethylbenzylammonium hydroxide; lithium carbonate, sodium carbonate, potassium carbonate, and sodium acetate.

[0066] The PBT obtained by the melt polycondensation process is usually extracted in strand form from an outlet at the bottom of the polycondensation tank, and then, while water-cooling or after water-cooling, is cut with a cutter to form pellets or chips or other granular PBT material. [Examples]

[0067] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the essence of the invention.

[0068] The solution haze and intrinsic viscosity of PBT in the titanium catalyst solution were measured by the following method.

[0069] (1) Solution haze of titanium catalyst solution Measurements were taken using a NDH-300A turbidimeter manufactured by Nippon Denshoku Co., Ltd., with a cell length of 10 mm. Lower values ​​indicate better transparency.

[0070] (2) Intrinsic viscosity of PBT (IV) The following procedure was used with an Ubbelohde viscometer: Specifically, using a phenol / tetrachloroethane (mass ratio 1 / 1) mixed solvent, the number of seconds for dropping a 1.0 g / dL polymer solution and the solvent alone was measured at 30°C, and the viscosity was calculated using the following formula. IV = ((1 + 4K H η sp ) 0.5 -1) / (2K H ·C) (However, η sp =η0-1, where η is the number of seconds the polymer solution falls, η0 is the number of seconds the solvent falls, C is the polymer solution concentration (g / dL), and K H (This is Huggins' constant, and we adopted 0.33.)

[0071] [Example of dimethyl terephthalate production through chemical recycling] <Manufacturing Example 1: Chemical Recycling Dimethyl Terephthalate 1> Referencing the method described in Japanese Patent Publication No. 2001-151934, chemically recycled dimethyl terephthalate 1 was obtained as follows. A flask equipped with a fraction recovery receiver, a stirrer, and a thermometer contained 100 parts by mass of waste fiber made of polyethylene terephthalate, 100 parts by mass of ethylene glycol, and 1.5 parts by mass of sodium carbonate. This flask was immersed in an oil bath at 210°C and reacted for 10 hours while removing the light-boiling components to obtain depolymerization reaction solution 1. The obtained depolymerization reaction solution 1 was filtered hot through a glass filter to obtain filtrate 1. To the obtained filtrate 1, 200 parts by mass of methanol and 0.5 parts by mass of sodium carbonate were added and reacted at 65°C for 1 hour to obtain reaction solution 2. The obtained reaction solution 2 was placed in a vacuum distillation apparatus equipped with a fraction recovery receiver, Liebig condenser, stirrer, thermometer, and pressure controller. The distillation apparatus was immersed in an oil bath, and the temperature and pressure of the oil bath were controlled while observing the distillate. The initial fraction, main fraction, and stock residue were obtained in the order of distillation. The obtained main fraction and xylene were placed in a round-bottom flask, heated to a homogeneous solution, and then cooled to room temperature for crystallization to obtain a slurry. The obtained slurry was filtered through a glass filter to obtain a cake. The obtained cake was placed in a round-bottom flask and attached to an evaporator equipped with an oil bath, and xylene was removed from the cake under reduced pressure to obtain a white solid. A portion of the obtained white solid was extracted and analyzed by gas chromatography, and the dimethyl terephthalate content was found to be 99% by mass or more.

[0072] <Manufacturing Example 2: Chemical Recycling Dimethyl Terephthalate II> Referencing the method described in Japanese Patent Publication No. 2004-323378, chemically recycled dimethyl terephthalate 2 was obtained as follows. In an autoclave equipped with a stirrer and thermometer, 100 parts by mass of waste polyethylene terephthalate fiber, 300 parts by mass of methanol, and 1.5 parts by mass of sodium carbonate were placed. This autoclave was immersed in an oil bath at 150°C and reacted at 1.3 MPa for 10 hours. After that, a distillation tube was attached to the autoclave, and the pressure was slowly reduced to atmospheric pressure to distill off the light-boiling components to obtain depolymerization reaction solution 1. After lowering the temperature of the obtained depolymerization reaction solution 1 to room temperature, xylene was added and the mixture was immersed in an oil bath at 120°C to obtain slurry 1. The obtained slurry 1 was filtered through a glass filter, cooled to room temperature, and crystallized to obtain slurry 2. The obtained slurry 2 was separated into solid and liquid components using a centrifuge to obtain a cake. The obtained cake was placed in a flask equipped with a fraction recovery receiver, stirrer, and thermometer, and then immersed in an oil bath. While monitoring the distillate, the temperature and pressure of the oil bath were controlled, and the initial fraction, main fraction, and residue were obtained in the order of distillation. A portion of the obtained main fraction was extracted and analyzed by gas chromatography, and the dimethyl terephthalate content was found to be 99% by mass or more.

[0073] <Manufacturing Example 3: Chemical Recycling of Dimethyl Terephthalate-3> Referencing the method described in Japanese Patent Publication No. 2001-151934, chemically recycled dimethyl terephthalate 3 was obtained as follows. 100 parts by mass of polybutylene terephthalate containing glass filler and 200 parts by mass of methanol were placed in an autoclave equipped with a stirrer and thermometer. This autoclave was immersed in an oil bath at 170°C and reacted at 5.5 MPa for 5 hours. After that, the autoclave was removed from the oil bath and allowed to cool to room temperature to obtain depolymerization reaction solution 1. The obtained depolymerization reaction solution 1 was filtered through a glass filter to obtain the solids. Tetrahydrofuran was added to the obtained solids to dissolve the white solids contained in the solids, and the glass filler was removed as a filtrate by filtration to obtain solution 1. The obtained solution 1 was placed in a flask equipped with a fraction recovery receiver, stirrer and thermometer, and then immersed in an oil bath. While observing the distillate, the temperature and pressure of the oil bath were controlled, and the light-boiling component containing tetrahydrofuran, the initial distillate, the main distillate, and the residue were obtained in the order of distillation. A portion of the obtained main distillate was extracted and analyzed by gas chromatography, and the dimethyl terephthalate content was found to be 99% by mass or more.

[0074] [Example of terephthalic acid production through chemical recycling] <Manufacturing Example 4: Chemical Recycling of Terephthalic Acid 1> A white solid of dimethyl terephthalate with a dimethyl terephthalate content of 99% by mass or more (chemically recycled dimethyl terephthalate 1) was obtained in the same manner as in Production Example 1. The obtained white solid of dimethyl terephthalate was dissolved in methylene chloride, and a methanol solution of potassium hydroxide was added to hydrolyze it to obtain reaction solution 1. 60% by mass of sulfuric acid was added to the obtained reaction solution 1 to neutralize it and obtain slurry 2. Slurry 2 was filtered using a centrifuge to obtain cake 2. Cake 2 was supplied to pure water and mixed to obtain slurry 3. Slurry 3 was filtered using a centrifuge to obtain cake 3. Cake 3 was again supplied to pure water and mixed to obtain slurry 4. Slurry 4 was filtered using a centrifuge to obtain cake 4. Cake 4 was placed in a round-bottom flask and attached to an evaporator equipped with an oil bath. Light-boiling components were removed from cake 4 under reduced pressure to obtain white solid terephthalic acid 1. Analysis of a portion of the obtained white solid by liquid chromatography revealed that the terephthalic acid content was 99% by mass or more.

[0075] <Manufacturing Example 5: Chemically Recycled Terephthalic Acid 2> A main fraction containing 99% by mass or more of dimethyl terephthalate was obtained in the same manner as in Production Example 2. Instead of the white solid dimethyl terephthalate, this main fraction of dimethyl terephthalate (chemically recycled dimethyl terephthalate 2) was used and hydrolysis and purification were performed in the same manner as in Production Example 4 to obtain terephthalic acid 2 as a white solid containing 99% by mass or more of terephthalic acid.

[0076] <Manufacturing Example 6: Chemically Recycled Terephthalic Acid 3> A main fraction containing 99% by mass or more of dimethyl terephthalate was obtained in the same manner as in Production Example 3. Instead of the white solid dimethyl terephthalate, the main fraction of this dimethyl terephthalate (chemically recycled dimethyl terephthalate 3) was used, and hydrolysis and purification were carried out in the same manner as in Production Example 4 to obtain terephthalic acid 3, a white solid with a terephthalic acid content of 99% by mass or more.

[0077] [Example of 1,4-butanediol production from biomass] <Production Example 7: 1,4-Butanediol produced by hydrogenation of biomass-derived succinate ester> BDO manufactured by Yuanli Chemical Group and BDO manufactured by Zhejiang Boju New Materials Co., Ltd. were mixed to obtain a mixture. The resulting mixture was subjected to vacuum distillation, and the primary, main, and secondary fractions were obtained in the order of distillation. A portion of the obtained main fraction was extracted and analyzed by gas chromatography, and the 1,4-butaneziel content was found to be 99% by mass or more.

[0078] [Example of chemical recycling for the production of 1,4-butanediol] <Production Example 8: 1,4-butanediol produced by depolymerization of PBT> Chemically recycled 1,4-butanediol was produced following Example 3 of Japanese Patent Publication No. 2004-323378. 1030 parts by mass of polybutylene terephthalate, 3200 parts by mass of methanol, and 13 parts by mass of sodium carbonate were supplied to an autoclave equipped with a stirring blade. The autoclave was immersed in an oil bath at 200°C and the reaction was carried out with stirring at a pressure of 1.3 MPa for 8 hours. The autoclave was removed from the oil bath and cooled to below 10°C in ice water to obtain a slurry. The obtained slurry was separated into solid and liquid components using filter paper to obtain the filtrate. The obtained filtrate was placed in a distillation apparatus equipped with a thermometer, vacuum control device, stirring blade, condenser, and fractionation receiver. Methanol and tetrahydrofuran were recovered as the initial fraction, and then the mixture was distilled under reduced pressure to obtain the primary fraction, main fraction, and secondary fraction in the order in which they were distilled. A portion of the obtained main fraction was extracted and analyzed by gas chromatography, revealing that the 1,4-butanediol content was 99% by mass or more.

[0079] [Preparation of titanium catalyst solution and production of PBT by direct polymerization] <Example 1-1> (Preparation of titanium catalyst solution) At room temperature, 96.8g of petrochemical-derived BDO from Mitsubishi Chemical was placed in a glass container, followed by 0.2g of distilled water. After stirring until homogenized, 3.0g of tetra-n-butyl titanate was added and completely dissolved, at which point stirring was stopped. After 10 minutes of homogenized stirring, the solution haze was 0.7%. Furthermore, this titanium catalyst solution was left to stand at 60°C. After 21 days of standing, the solution remained colorless and transparent with no turbidity, and the solution haze was 0.8%.

[0080] (Direct polymerization method for PBT production) PBT was manufactured using the titanium catalyst solution described above by the method shown below. The titanium catalyst solution used was prepared as described above and stored for 21 days. A slurry prepared by mixing 1.00 mole of petrochemical-derived terephthalic acid from Toray Industries with 1.80 moles of petrochemical-derived BDO from Mitsubishi Chemical Industries was continuously supplied to an esterification reactor equipped with a screw-type stirrer packed with PBT oligomers with a 99% esterification rate to carry out the esterification reaction. A titanium catalyst solution was supplied to the esterification reactor in an amount that resulted in a titanium concentration of 40 ppm relative to the PBT. Additional BDO was supplied to the esterification reactor so that the molar ratio of BDO to terephthalic acid was 3.2. The reaction vessel temperature was 226°C, the pressure was 60 kPa, and the average residence time was 180 minutes.

[0081] Next, the PBT oligomer with an esterification rate of 96.5% was continuously transferred to the first polycondensation reactor. In the first polycondensation reactor, the polycondensation reaction was carried out continuously. The reaction temperature was 230°C, the pressure was 3.9 kPa, and the average residence time was 120 minutes. Next, this product was transferred to the second polycondensation reactor, where the polycondensation reaction was carried out continuously. The reaction temperature was 240°C, the pressure was 130 Pa, and the average residence time was 80 minutes.

[0082] The obtained polymer was extracted via an extraction gear pump through an extraction line, filtered, and continuously extracted in strand form from a die head. It was then cut with a rotary cutter to obtain PBT pellets (approximately 3 mm in major diameter, 2 mm in minor diameter, and 4 mm in length).

[0083] <Examples 1-2 to 1-4, Example 2, Example 3-1, Example 4, Example 5, Examples 6-1 to 6-4, Examples 8-1 to 8-4, Comparative Examples 1 to 4> (Preparation of titanium catalyst solution) The procedure was carried out in the same manner as in Example 1-1, except that the type of BDO used, the amounts of tetra-n-butyl titanate and water, their mixing order, and the number of days for standing were as shown in Tables 1 to 4. However, in Comparative Example 1, BDO and tetra-n-butyl titanate were mixed and then water was added in accordance with the method described in Example 7 of Japanese Patent Publication No. 2001-72751. Comparative Example 2 was prepared by mixing BDO and tetra-n-butyl titanate in accordance with Table-1 No. 4 of Example 2 in Japanese Patent Publication No. 3-72653, and then mixing with water. In Comparative Examples 3 and 5, no water was added.

[0084] (Direct polymerization method for PBT production) The procedure was carried out in the same manner as in Example 1-1, using the BDOs and titanium catalyst solutions using those BDOs listed in Tables 1-4, and the terephthalic acid listed in Tables 1-4. Furthermore, in the PBT manufacturing process, the titanium catalyst solutions used were all those that had undergone a set standing period (number of days / hours) for stability testing of the titanium catalyst solutions.

[0085] [Preparation of titanium catalyst solution and production of PBT by DMT method] <Example 3-2> (Preparation of titanium catalyst solution) A titanium catalyst solution was prepared in the same manner as in Example 1-1, except that the amounts of tetra-n-butyl titanate and water were shown in Table 1.

[0086] (Manufacturing of PBT using the DMT method) PBT was manufactured using the titanium catalyst solution described above by the method shown below. The titanium catalyst solution used was prepared as described above and stored for 21 days. In a transesterification reactor, 1.20 moles of petrochemical-derived BDO from Mitsubishi Chemical were added to 1.00 mole of petrochemical-derived dimethyl terephthalate from SK Petrochemical. As a catalyst, the above titanium catalyst solution was added at a concentration of 33 ppm by mass relative to the polymer to be produced, in terms of metallic titanium. Next, the temperature of the liquid in the reactor was maintained at 150°C for 60 minutes, then raised to 210°C over 90 minutes and held at 210°C for 30 minutes. During this time, the methanol produced was distilled off, and the transesterification reaction was carried out for a total of 180 minutes.

[0087] Fifteen minutes before the end of the transesterification reaction, magnesium acetate tetrahydrate was dissolved in petroleum-derived BDO manufactured by Mitsubishi Chemical Corporation and added to the polymer at a concentration of 48 ppm by mass relative to the magnesium metal to be produced. Then, 0.15 parts by mass of a hindered phenol antioxidant (ADEKA Corporation, AO-60: pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]) was added in the BDO slurry form relative to the polymer to be produced. Subsequently, the above titanium catalyst solution was added in an amount equivalent to 25 ppm by mass relative to the polymer to be produced in terms of titanium metal. After that, the mixture was transferred to a polycondensation reactor equipped with a stirrer, nitrogen inlet, heater, thermometer, distillation tube, and vacuum exhaust port, and the polycondensation reaction was carried out under reduced pressure.

[0088] The polycondensation reaction was carried out by gradually reducing the pressure inside the tank from atmospheric pressure to 0.4 kPa over 85 minutes, and then continuing at a pressure of 0.4 kPa or less. The reaction temperature was maintained at 210°C for 15 minutes from the start of the reduced pressure, and then raised to 240°C over 45 minutes and maintained at this temperature. The reaction was terminated when the predetermined stirring torque was reached. The total time required for the polycondensation reaction was 150 minutes.

[0089] Next, the tank was repressurized with nitrogen after being under reduced pressure, and then pressurized for polymer extraction. The heat transfer medium temperature at the nozzle was set to 235°C for extraction, and the polymer was extruded from the nozzle in the form of strands. After cooling the strands in a cooling water tank, they were cut with a strand cutter to form pellets (approximately 3 mm in length, 2 mm in width, and 4 mm in length).

[0090] <Examples 3-3 to 3-5, Examples 7-1 to 7-4, Examples 9-1 to 9-4, Comparative Example 5> (Preparation of titanium catalyst solution) The procedure was carried out in the same manner as in Example 3-2, except that the type of BDO used, the amounts of tetra-n-butyl titanate and water, their mixing order, and the number of days for standing were as shown in Tables 1-4.

[0091] (Manufacturing of PBT using the DMT method) The procedure was carried out in the same manner as in Example 3-2, using the BDOs listed in Tables 1-4, the titanium catalyst solutions using those BDOs, and the dimethyl terephthalate listed in Tables 1-4. Furthermore, in the PBT manufacturing process, the titanium catalyst solutions used were all those that had undergone a set standing period (number of days / hours) for stability testing of the titanium catalyst solutions.

[0092] Tables 1-4 show the stability of the titanium catalyst solution (solution haze and visual evaluation) and the intrinsic viscosity of the manufactured PBT in the above examples and comparative examples, along with the composition of the titanium catalyst solution, preparation method, number of days (hours) the tung catalyst solution was left to stand during PBT production, and the type of PBT raw material for each example.

[0093] In Tables 1-4, the symbols for the preparation procedure of the titanium catalyst solution are as follows: A: After mixing BDO with water, an organotitanium compound was added. B: After mixing BDO and an organotitanium compound, water was added. C: BDO with added organotitanium compounds (water-free)

[0094] Furthermore, regarding the stability of the titanium catalyst solution, the titanium catalyst solution was visually observed every 7 days after storage, and the number of storage days at which a transparent state was confirmed, as well as the solution haze at that time, were measured. The number of storage days was evaluated according to the following criteria. However, for the comparative examples, the solution haze was measured when turbidity or white precipitate formed. A: Clear after 21 days of storage. B: Clear after 14 days of storage. C: Clear after 7 days of storage. D: Cloudiness or white precipitate precipitation occurs before 6 days of storage.

[0095] [Table 1]

[0096] [Table 2]

[0097] [Table 3]

[0098] [Table 4]

[0099] From Tables 1-4, the following can be seen. The titanium catalyst solution of the present invention exhibits low solution haze not only immediately after production but also after long-term storage, and there are no problems with the precipitation of organotitanium compounds. Therefore, the desired PBT can be stably and efficiently produced using this titanium catalyst solution. Furthermore, such a highly stable titanium catalyst solution can be prepared by mixing BDO and water, followed by the addition and mixing of an organotitanium compound. However, as in Comparative Examples 1 and 2, when BDO and an organotitanium compound are mixed, followed by the addition and mixing of water, the solution haze is poor immediately after preparation due to the precipitation of the organotitanium compound, and further turbidity occurs after storage due to the precipitation of the organotitanium compound. As shown in Comparative Examples 3 and 5, when water is not used, although the solution haze is relatively low immediately after preparation, turbidity and white precipitate occur in a short time of 4 hours, and the stability is significantly poor. Even when an organotitanium compound is added and mixed after mixing BDO with water, as in Comparative Example 4, if the water concentration is low and the Ti / W ratio is too high, the stability is poor, although it is an improvement over Comparative Examples 3 and 5 where no water is used, and turbidity and white precipitate form within 3 days. As shown in Comparative Examples 1-5, in titanium catalyst solutions with poor stability, the problem of precipitation of organotitanium compounds in the reaction system during the PBT manufacturing process cannot be avoided. For this reason, the PBT produced in Comparative Examples 1-5 has a lower intrinsic viscosity than the PBT produced in the Examples, and in particular, in Comparative Examples 3 and 5, which have significantly poor stability, the intrinsic viscosity of the produced PBT is very low compared to the PBT in the other examples.

[0100] Furthermore, in the titanium catalyst solution of the present invention, the solution haze within one day after preparing the titanium catalyst solution by uniform stirring is specified to be 8.0% or less. However, in Examples 1-1 to 9-4, whether using petroleum-derived BDO, biomass-derived BDO, or BDO derived from the depolymerization of PBT, the solution haze remained 1.8% or less even after storage for 7 days or more, indicating that the provisions of the present invention are fully satisfied. Furthermore, it has been shown that by using the titanium catalyst solution of the present invention, the target polybutylene terephthalate can be stably produced even when using biomass-derived BDO or BDO obtained by depolymerization of PBT as the raw material BDO, and even when using chemically recycled terephthalic acid or chemically recycled dimethyl terephthalate as the raw material terephthalic acid component.

Claims

1. A titanium catalyst solution comprising an organotitanium compound, 1,4-butanediol, and water, The water concentration W (mass%) in the titanium catalyst solution is 0.030 < W ≤ 0.

90. The ratio of titanium concentration Ti (mass%) to water concentration W (mass%) is 1.3 < Ti / W ≤ 10.

0. A titanium catalyst solution characterized by having a solution haze (%) of 8.0 or less.

2. The titanium catalyst solution according to claim 1, wherein the titanium concentration Ti (mass%) is greater than 0.1 and less than or equal to 1.

5.

3. The titanium catalyst solution according to claim 1 or 2, wherein the 1,4-butanediol is a 1,4-butanediol derived from biomass resources or a 1,4-butanediol derived from the depolymerization of polybutylene terephthalate.

4. It contains an organotitanium compound, 1,4-butanediol, and water. If the water concentration W (mass%) is 0.030 < W ≤ 0.90, A method for producing a titanium catalyst solution in which the ratio of titanium concentration Ti (mass%) to water concentration W (mass%) is 1.3 < Ti / W ≤ 10.0, A method for producing a titanium catalyst solution, characterized by mixing 1,4-butanediol with water, and then adding an organotitanium compound to the resulting mixture.

5. The method for producing a titanium catalyst solution according to claim 4, wherein the titanium concentration Ti (mass%) of the titanium catalyst solution is greater than 0.1 and less than or equal to 1.

5.

6. The method for producing a titanium catalyst solution according to claim 4 or 5, wherein the 1,4-butanediol is a 1,4-butanediol produced by hydrogen reduction of succinic acid or dialkyl succinate produced by direct fermentation of sugar or using biomass resources, or a 1,4-butanediol produced by depolymerization of polybutylene terephthalate.

7. A method for producing polybutylene terephthalate using the titanium catalyst solution described in claim 1.

8. A method for producing polybutylene terephthalate using a titanium catalyst solution produced by the method for producing a titanium catalyst solution described in claim 4.

9. The method for producing polybutylene terephthalate according to claim 7 or 8, wherein the 1,4-butanediol used as a raw material for polybutylene terephthalate is 1,4-butanediol produced by direct fermentation of sugar, succinic acid produced using biomass resources or 1,4-butanediol produced by hydrogen reduction of dialkyl succinate, or 1,4-butanediol produced by depolymerization of polybutylene terephthalate.

10. A method for producing polybutylene terephthalate according to claim 7 or 8, wherein the terephthalic acid component of the polybutylene terephthalate is terephthalic acid produced by chemical recycling of polyester or dimethyl terephthalate, or terephthalic acid produced using biomass resources or dimethyl terephthalate.

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