Method for producing polyester using terephthalic acid

Abstract

To efficiently transport terephthalic acid by air, thereby preventing a decrease in the polyester production rate and enabling efficient polyester manufacturing. [Solution] A method for producing polyester using terephthalic acid, comprising the step of transporting terephthalic acid from a first container to a second container by pneumatic transport using an inert gas, wherein the terephthalic acid has an angle of repose of 50 degrees or less and a degree of cohesion of 98% or less.

Description

[[Technical Field]]

[0001] The present invention relates to a method for producing polyester using terephthalic acid, and more particularly to a method for producing polyester using terephthalic acid, which includes a step of transporting terephthalic acid from a first container to a second container by pneumatic transport using an inert gas. [[Background Art]]

[0002] Terephthalic acid used for producing polyester is generally transported in bulk by tank trucks or tank wagons, and since there is a risk of dust explosion, it is pneumatically transported into a plant using an inert gas such as nitrogen or carbon dioxide gas.

[0003] Patent Document 1 describes that after performing aeration in a terephthalic acid transport tank, transporting terephthalic acid at a low speed and high concentration enables stable and efficient transport of terephthalic acid particles without crushing them. [[Prior Art Documents]] [[Patent Documents]]

[0004] [[Patent Document 1]] Japanese Patent Laid-Open Publication No. 54-107077 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0005] However, during pneumatic transport of terephthalic acid, large pressure fluctuations can lead to equipment failure, so it is necessary to reduce the transport amount. It has been found that reducing the transport amount of terephthalic acid lowers the production rate of polyester, resulting in the problem that efficient production cannot be achieved.

[0006] Therefore, the present invention aims to efficiently transport terephthalic acid using pneumatic energy, thereby enabling the efficient production of polyester without significantly reducing its production rate. [Means for solving the problem]

[0007] However, in light of these circumstances, the inventors conducted extensive research and found that the above problems can be solved by adjusting the powder properties of terephthalic acid used as a raw material for polyester to specific values.

[0008] In other words, the present invention has the following aspects. [1] A method for producing polyester using terephthalic acid, comprising the step of transporting terephthalic acid from a first container to a second container by pneumatic transport using an inert gas, A method for producing polyester, wherein the terephthalic acid has an angle of repose of 50 degrees or less and a degree of cohesion of 98% or less.

[0009] [2] The method for producing polyester according to [1] above, wherein the terephthalic acid is a mixture of two or more terephthalic acids having different angles of repose and / or degrees of cohesion. [Effects of the Invention]

[0010] According to the present invention, terephthalic acid can be efficiently transported, thereby preventing a decrease in the polyester production rate and enabling the efficient manufacture of polyester. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a block diagram showing the pneumatic transport of this embodiment. [Modes for carrying out the invention]

[0012] The present invention will be described below with reference to the drawings, based on examples of embodiments for carrying out the invention. However, the present invention is not limited to the embodiments described below.

[0013] [Air-powered transport using inert gas] Figure 1 is a block diagram illustrating the pneumatic transport of this embodiment, showing an example in which terephthalic acid, transported pneumatically to the primary receiving tank, is fed into the slurry preparation tank via the secondary receiving tank. In this embodiment, the primary receiving tank is exemplified as the first container and the secondary receiving tank as the second container, but the first and second containers do not have a superior-subordinate or hierarchical relationship with each other; they simply represent different containers. Furthermore, a tank truck is exemplified as a mobile container for pneumatically transporting terephthalic acid from the outside into the plant, but it is not limited to this, and tank cars or other types of containers may also be used.

[0014] Terephthalic acid, filled in a tank truck, is mixed with inert gas circulated by a first blower and supplied to a primary receiving tank. Unlike air, inert gas is expensive, making it economically disadvantageous to release it into the atmosphere. Furthermore, if some terephthalic acid is released along with the exhaust, it could cause environmental pollution. Therefore, it is preferable to recirculate and reuse the inert gas. The inert gas discharged from the primary receiving tank is recirculated to transport terephthalic acid in a mobile container using pneumatic energy, and a portion of it is also recirculated to transport terephthalic acid discharged from the primary receiving tank to a secondary receiving tank using pneumatic energy. An inert gas supply means may be provided within the system to replenish any small amount of inert gas that leaks outside the system.

[0015] For the first blower, for example, a Roots blower or a turbo blower is used, and for the inert gas, for example, nitrogen gas or carbon dioxide gas is used. The transport pressure is usually 0.4 to 1.4 kg / cm². 2 It's about G.

[0016] A nozzle may be provided below the primary receiving tank to intermittently inject inert gas into the tank, thereby aerating the terephthalic acid in the tank to fluidize it and facilitate discharge. The pressure of the inert gas used for aeration is typically 0.5 to 1.5 kg / cm².2 It is G level.

[0017] The terephthalic acid discharged from the primary receiving tank is mixed with an inert gas circulated by a second blower, and then supplied into the secondary receiving tank. It is preferable that the inert gas discharged from the secondary receiving tank is recirculated to pneumatically convey the terephthalic acid discharged from the primary receiving tank. Therefore, simply put, it is preferable that terephthalic acid is transported from the first container to the second container by closed-loop pneumatic transportation using an inert gas. In addition, an inert gas supply means may be provided in the system to replenish a trace amount of inert gas leaked out of the system.

[0018] The terephthalic acid supplied into the secondary receiving tank in this manner is charged into a slurry preparation tank and mixed with ethylene glycol to form a slurry. Similar to the primary receiving tank, a nozzle for aeration may be provided below the secondary receiving tank.

[0019] [Terephthalic Acid] In general, terephthalic acid is obtained by purifying crude terephthalic acid obtained by liquid-phase oxidation of para-xylene in an acetic acid solvent using a catalyst through hydrogenation or the like, followed by drying. The terephthalic acid used in the present invention is characterized by the physical properties of the powder. Hereinafter, the physical properties of the powder will be described. The physical properties of terephthalic acid powder can be measured using known measurement methods and powder property evaluation devices. For example, the measurement can be carried out using a multi-tester manufactured by Seishin Enterprise Co., Ltd., a powder tester manufactured by Hosokawa Micron Corporation, or the like as the device.

[0020] (Angle of Repose) The angle of repose of terephthalic acid powder is preferably 50° or less, more preferably 49° or less, and preferably 35° or more, more preferably 40° or more. The angle of repose is measured by a method in accordance with JIS-R-9301-2-2. Specifically, paraxylene powder as a measurement object is gently poured and deposited from an opening of a funnel onto a horizontal plate, and the angle formed between the generatrix of the formed conical deposit and the horizontal plane is measured as the angle of repose.

[0021] (Degree of Agglomeration) The degree of agglomeration of terephthalic acid powder is preferably 98% or less, more preferably 97% or less, and preferably 50% or more, more preferably 60% or more. When measuring the degree of agglomeration, terephthalic acid powder that has been left to stand for 100 hours in an environment at a temperature of 50°C and a humidity of 80 RH% is used. Using sieves of 150 µm, 75 µm, and 45 µm, stack the sieves in the order of 150 µm, 75 µm, and 45 µm from top to bottom, place 2 g of terephthalic acid powder on the topmost sieve, measure the mass of terephthalic acid powder remaining on each sieve after vibrating the sieves (with an amplitude of 1 mm and a vibration time of 65 seconds), and calculate the degree of agglomeration according to the following formula. Degree of agglomeration = (T / 2 + C / 2 × (3 / 5) + B / 2 × (1 / 5)) / 100 In the formula, T represents the mass of terephthalic acid powder remaining on the upper sieve, C represents the mass of terephthalic acid powder remaining on the middle sieve, and B represents the mass of terephthalic acid powder remaining on the lower sieve.

[0022] When at least the angle of repose and the degree of agglomeration among the physical properties of terephthalic acid powder fall within the above ranges, the powder has good fluidity, and polyester can be produced without reducing the production rate.

[0023] (Angle of Collapse · Difference Angle) The collapse angle of the terephthalic acid powder is preferably 30 degrees or less, more preferably 29 degrees or less, preferably 15 degrees or more, and more preferably 20 degrees or more. The conical deposit whose angle of repose has been measured is collapsed by applying a constant impact three times to a measuring table, and the base angle is calculated from the diameter and height of the conical deposit, and this base angle is taken as the collapse angle. Here, the constant impact is the impact adopted in the measuring device used, and is device-specific and constant. The difference angle is calculated by subtracting the collapse angle from the angle of repose, and is preferably 15 degrees or more, more preferably 16 degrees or more, preferably 27 degrees or less, and more preferably 26 degrees or less.

[0024] (Degree of compression) The compressibility of terephthalic acid powder is calculated from the loose bulk density and the compacted bulk density using the following formula, and the value is preferably 31% or less, more preferably 30% or less, preferably 20% or more, and more preferably 21% or more. Compression (%) = {(Compressed bulk density - Loose bulk density) / (Compressed bulk density)} × 100

[0025] The loose bulk density can be measured using a container (measuring cell). The volume and mass of the bulk density measuring cell are measured in advance, and terephthalic acid powder is filled into the measuring cell. After filling is complete, the top of the measuring cell is leveled, and the mass of the measuring cell after filling is measured using a balance. The value obtained by subtracting the mass of the measuring cell from the mass of the measuring cell after filling is the loose bulk density of terephthalic acid, and the loose bulk density is calculated by dividing this value by the volume of the measuring cell.

[0026] Similarly, the bulk density can also be measured using a container (measuring cell). The volume and mass of the bulk density measuring cell are measured in advance, a cell cap is attached to the measuring cell, and terephthalic acid powder is filled into it. After filling is complete, the cell is tapped 180 times, the cell cap is removed, the top of the measuring cell is leveled, and the mass of the measuring cell after filling is measured using a balance. The value obtained by subtracting the mass of the measuring cell from the mass of the measuring cell after filling is the mass of the bulk density of terephthalic acid, and the value calculated by dividing this by the volume of the measuring cell is the bulk density.

[0027] (Spatula corner) The spatula angle of the terephthalic acid powder is preferably 73 degrees or less, more preferably 72 degrees or less, preferably 30 degrees or more, and more preferably 35 degrees or more. The spatula angle can be measured according to the manual included with the tester being used. For example, 50g of terephthalic acid powder is placed on a tray in contact with the spatula. After confirming that the granules on the tray are at a uniform height, the tray is gently moved downwards to create a deposit of terephthalic acid powder on the spatula. The angle between the edge of the powder on the spatula and the bottom surface of the spatula is then measured.

[0028] (Dispersion degree) The dispersion of the terephthalic acid powder is preferably 10% or more, more preferably 11% or more, preferably 35% or less, and more preferably 30% or less. The degree of dispersion is calculated using the following formula based on the amount of powder that falls onto the watch glass when 10g of terephthalic acid powder is placed in the dispersion unit of the tester used. Dispersion (%) = (10(g) - Amount of powder that fell onto the watch glass (g)) / 10(g)

[0029] The above physical properties of terephthalic acid powder can be adjusted by crystallization conditions in terephthalic acid production, mechanical grinding using jet mills or hammer mills, control of particle size range by classification, and control of crystal morphology by using crystallization control agents or pH control. Even terephthalic acid powder that does not satisfy the above physical property conditions can be used as terephthalic acid in the present invention by mixing it in an appropriate proportion with terephthalic acid powder that does satisfy the above physical property conditions.

[0030] [Polyester manufacturing] Terephthalic acid, introduced from the secondary receiving tank into the slurry tank, is mixed with diol components, along with other dicarboxylic acid components as needed, under stirring to prepare the raw material slurry. The resulting raw material slurry is subjected to an esterification reaction in an esterification reaction tank under atmospheric pressure to pressurized conditions and heating, or to transesterification in the presence of a transesterification catalyst. Subsequently, the resulting esterification reaction product or transesterification reaction product, a low molecular weight polyester polymer, is transferred to a polycondensation tank and melt-polymerized under reduced pressure (gradually reduced from atmospheric pressure) and heating. Further solid-phase polymerization can be carried out as needed to produce high molecular weight polyester. The reaction can be carried out by batch or continuous method, but the continuous method is preferred in terms of production efficiency. The molar ratio of the diol component to terephthalic acid (dicarboxylic acid component) is usually in the range of 1.0 to 2.2, preferably 1.03 or higher, and more preferably 1.05 or higher. The upper limit is preferably 1.7 or lower, and more preferably 1.5 or lower. When the molar ratio is within the above range, the energy cost is low, the esterification reaction proceeds sufficiently, and the amount of diethylene glycol produced as a by-product is small, which is therefore preferable.

[0031] Other dicarboxylic acid components besides terephthalic acid include, for example, aromatic dicarboxylic acids such as isophthalic acid, orthophthalic acid, sodium sulfisoisophthalate, phenylenedioxydicarboxylic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-diphenylketonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, and franciocarboxylic acid; alicyclic dicarboxylic acids such as hexahydroterephthalic acid and hexahydroisophthalic acid; aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecadicarboxylic acid, and dodecadicarboxylic acid; esters of these dicarboxylic acids having alkyl groups with approximately 1 to 4 carbon atoms, and halides. These other dicarboxylic acid components may be used individually or in combination of two or more.

[0032] Examples of diol components include aliphatic diols such as ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, octamethylene glycol, decamethylene glycol, neopentyl glycol, 2-ethyl-2-butyl-1,3-propanediol, polyethylene glycol, and polytetramethylene ether glycol; 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethylol, and 1,4-cyclohexanediol. Examples include alicyclic diols such as methylol and 2,5-norbornane dimethylol; aromatic diols such as xylylene glycol, 4,4'-dihydroxybiphenyl, 2,2-bis(4'-hydroxyphenyl)propane, 2,2-bis(4'-β-hydroxyethoxyphenyl)propane, bis(4-hydroxyphenyl)sulfone, and bis(4-β-hydroxyethoxyphenyl)sulfonic acid; and ethylene oxide adducts or propylene oxide adducts of 2,2-bis(4'-hydroxyphenyl)propane, dimerols, etc. One of these diol components may be used, or two or more may be used.

[0033] (Esterification process) The esterification step involves esterifying a dicarboxylic acid component containing terephthalic acid with a diol component to obtain an oligomer. The esterification reaction is carried out in a single esterification tank or a multi-stage reactor with multiple esterification tanks connected in series, under reflux of the diol component, while removing the water and excess diol component produced in the reaction from the system. The reaction is carried out until the esterification reaction rate (the percentage of all carboxyl groups of the starting material dicarboxylic acid component that react with the diol component and are esterified) reaches 90% or more, preferably 93% or more. Furthermore, the number-average molecular weight of the oligomer obtained as the esterification reaction product is preferably 500 to 5000.

[0034] For esterification reactions, the reaction conditions are as follows: in the case of a single esterification reactor, the temperature is usually around 240-280°C, the pressure is usually around 0-400 kPaG (where kPaG indicates relative pressure to atmospheric pressure), and the reaction time is 1-10 hours under stirring. In the case of multiple esterification reactors, the reaction temperature in the first esterification reactor is usually 240-270°C, the reaction temperature in the final stage is usually 250-280°C, preferably 255-257°C, and the relative pressure to atmospheric pressure is usually 0-150 kPaG, preferably 0-130 kPaG.

[0035] In the transesterification reaction, the reaction conditions are as follows: In the case of multiple transesterification reactors, the reaction temperature in the first stage of the transesterification reactor is usually 180°C to 230°C, preferably 180°C to 220°C, and the pressure is usually 0kPaG to 300kPaG, preferably 0kPaG to 200kPaG. In the final stage, the reaction temperature is usually 220°C to 260°C, preferably 225°C to 240°C, and the pressure is usually 0kPaG to 200kPaG, preferably 0kPaG to 150kPaG. When the reaction is carried out in a single transesterification reactor, the reaction temperature of the transesterification reactor is 150°C to 280°C, preferably 150°C to 250°C, and the pressure is 0kPaG to 200kPaG, preferably 0kPaG to 150kPaG.

[0036] (Melting polycondensation process) Following the esterification step, a polycondensation step is performed to obtain a polyester prepolymer by melt polycondensation of the oligomer. The melt polycondensation is carried out under reduced pressure using a single melt polycondensation tank or a multi-stage reactor consisting of multiple melt polycondensation tanks connected in series, while distilling off the ethylene glycol produced. An example of such a multi-stage reactor is one in which the first stage is a fully mixed reactor equipped with stirring blades, and the second and third stages are horizontal plug-flow type reactors equipped with stirring blades.

[0037] For melt polycondensation, the reaction conditions are as follows: in the case of a single polymerization tank, the temperature is usually around 250-290°C, the pressure is gradually reduced from atmospheric pressure to a final pressure of usually around 1.3-0.0013 kPa, and the reaction time is 1-20 hours under stirring. In the case of multiple polycondensation tanks, the reaction temperature in the first stage polycondensation tank is usually 250-290°C, preferably 260-280°C, and the pressure is usually 65-1.3 kPa, preferably 26-2 kPa. In the final stage, the reaction temperature is usually 265-300°C, preferably 270-295°C, and the pressure is usually 1.3-0.013 kPa, preferably 0.65-0.065 kPa. Intermediate reaction conditions are selected from those intermediate conditions. For example, in a three-stage reactor, the reaction temperature in the second stage is usually 265 to 295°C, preferably 270 to 285°C, and the pressure is usually 6.5 to 0.13 kPa, preferably 4 to 0.26 kPa.

[0038] The PET obtained by the melt polycondensation reaction can usually be extracted in strand form from an outlet at the bottom of the polycondensation tank, and then cut with a cutter while or after water cooling to form pellets or other granular material. Furthermore, this granular material after melt polycondensation can be used as a prepolymer and subjected to solid-phase polycondensation by heating it at a temperature of 190 to 230°C, preferably 195 to 225°C, for about 1 to 20 hours under reduced pressure, usually 6.5 to 0.013 kPa, preferably 1.3 to 0.065 kPa, in an inert gas atmosphere such as nitrogen, carbon dioxide, or argon. [Examples]

[0039] 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 gist of the invention.

[0040] Terephthalic acid was transported using the aerial transport system shown in Figure 1. The primary receiving tank had a capacity of 1300 m³. 3 The silo, which will be used as a secondary receiving tank, has a capacity of 29 m³. 3 Roots blowers were used as the silos and the first and second blowers. The distance from the primary to the secondary receiving tank was 37m horizontally and 29m vertically, and the inner diameter of the transport piping was 65mm. Nitrogen gas was used as the inert gas, and the pneumatic transport system was closed-loop as much as possible to recycle the nitrogen gas. The outlet pressure of the Roots blower was set to 1.2 kg / cm². 2 G, nitrogen gas flow rate 70m 3 Assuming a transport rate of terephthalic acid of 6 tons per hour.

[0041] [Measurement and evaluation methods] The physical properties of various terephthalic acid powders shown in Table 1 were measured. The powder properties were measured using a multi-functional powder property analyzer, the Multi-Tester MT-02, manufactured by Seishin Corporation. In cases where two types of terephthalic acid were used, powder measurements were performed on the terephthalic acid mixture prepared in the proportions shown in Table 1. These terephthalic acid powders were transported using pneumatic energy, and the state of pneumatic transport within the manufacturing plant was confirmed. At that time, it was confirmed whether or not nitrogen gas recycling could be continued, and whether or not the production rate was reduced. The overall evaluation was "○" when nitrogen gas recycling could be continued and the production rate was not reduced, "×" when nitrogen gas recycling was difficult and the production rate was reduced, and "△" for all other overall evaluations.

[0042] [Table 1]

[0043] In Examples 1, 2, 4-8, where the angle of repose was 50 degrees or less and the degree of cohesion was 98% or less, there was no decrease in the production rate due to pressure fluctuations in the pneumatic transport system. In contrast, in Example 3, where the angle of repose exceeded 50 degrees and the degree of cohesion exceeded 98%, the production rate decreased as a result of the reduced transport rate of terephthalic acid due to pressure fluctuations.

[0044] Furthermore, in examples 1, 2, 5, and 6, where the compressibility was 28% or less, nitrogen gas recycling was possible. However, in examples 3, 4, 7, and 8, where the compressibility exceeded 28%, nitrogen gas recycling became difficult during transport due to pressure fluctuations in the pneumatic transport system, and therefore recycling was stopped.

[0045] Examples 5-8 are terephthalic acid mixtures obtained by mixing two types of terephthalic acid A, C, and D, which have different angles of repose and / or degrees of cohesion, in the proportions shown in Table 1. Even with terephthalic acid C in Example 3, which has an angle of repose exceeding 50 degrees and a degree of cohesion exceeding 98%, mixing it in a predetermined proportion with terephthalic acid A in Example 1, which has an angle of repose of 50 degrees or less and a degree of cohesion of 98% or less, results in a terephthalic acid mixture with an angle of repose of 50 degrees or less and a degree of cohesion of 98% or less (Examples 6-8), thus preventing a decrease in production rate due to pressure fluctuations. Furthermore, even with terephthalic acid D in Example 4, which has a compressibility exceeding 28%, mixing it with terephthalic acid A in Example 1, which has a compressibility of 28% or less, in a predetermined ratio results in a terephthalic acid mixture with a compressibility of 28% or less (Example 5), thus enabling the recycling of nitrogen gas.

[0046] [PET manufacturing] A continuous polymerization apparatus was used, consisting of a slurry preparation tank, two esterification reaction tanks connected in series thereto, and a third melt polycondensation tank connected in series to the second esterification reaction tank. Terephthalic acid and ethylene glycol were continuously supplied to the slurry preparation tank in a mass ratio of 865:485, and an ethylene glycol solution of ethyl acid phosphate was continuously added in an amount that resulted in a phosphorus atom content of 17 ppm by mass relative to the resulting PET. The mixture was then stirred and mixed to prepare the slurry.

[0047] This slurry was continuously transferred to a first-stage esterification reactor set to 260°C, 50 kPaG relative pressure, and 4 hours average residence time under a nitrogen atmosphere, and then to a second-stage esterification reactor set to 260°C, 5 kPaG relative pressure, and 1.5 hours average residence time under a nitrogen atmosphere, to carry out the esterification reaction. In the second-stage reactor, an ethylene glycol solution of magnesium acetate tetrahydrate was continuously added through piping installed at the top of the reactor in an amount equal to 26 ppm by mass of magnesium atoms relative to the resulting PET. Subsequently, when the oligomer obtained above was continuously transferred to a melt polycondensation tank, antimony trioxide was continuously added to the oligomer in the transfer piping in an amount equal to 238 ppm by mass of antimony atoms relative to the resulting PET. The oligomer or the molten polycondensed oligomer was continuously transferred to a first-stage molten polycondensation tank set to 270°C and 2.6kPa, a second-stage molten polycondensation tank set to 278°C and 0.5kPa, and a third-stage molten polycondensation tank set to 280°C and 0.3kPa for melt polymerization. After the reaction was complete, the material was extracted in strand form, cut while being cooled with water, and pelletized PET was obtained. Furthermore, the residence times in each polycondensation tank were set to 70 minutes for the first stage, 70 minutes for the second stage, and 80 minutes for the third stage, resulting in a total residence time of 220 minutes.

Claims

1. A method for producing polyester using terephthalic acid, comprising the step of transporting terephthalic acid from a first container to a second container by pneumatic transport using an inert gas, A method for producing polyester, wherein the terephthalic acid has an angle of repose of 50 degrees or less and a degree of cohesion of 98% or less.

2. The method for producing polyester according to claim 1, wherein the terephthalic acid is a mixture of two or more terephthalic acids having different angles of repose and / or degrees of cohesion.

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