JP2011178684A - Method for producing terephthalic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing terephthalic acid in high production efficiency, which inhibits foaming of a reaction liquid containing DMT, MMT and terephthalic acid and sublimation of DMT in a hydrolysis reaction tank, prevents clogging in a vent line in a method for producing terephthalic acid from DMT by hydrolysis. <P>SOLUTION: In the method for producing terephthalic acid by hydrolyzing dimethyl terephthalate in a hydrolysis reaction tank, a gas containing methanol generated from the hydrolysis reaction tank is removed by piping connected to a part above the reaction liquid level of the hydrolysis reaction tank and pure water in an amount of ≥1 pt.wt. based on 10 pts.wt. of dimethyl terephthalate supplied to the hydrolysis reaction tank or water containing impurities equal to or lower than solubility at a hydrolysis reaction temperature is supplied from a part above the reaction liquid level of the hydrolysis reaction tank to the hydrolysis reaction tank. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a production method by hydrolysis of terephthalic acid from dimethyl terephthalate.

  Various methods for industrially producing terephthalic acid are known, and one of them is a DMT hydrolysis method using dimethyl terephthalate (hereinafter abbreviated as DMT) as a starting material. In the terephthalic acid produced by the hydrolysis method of DMT, unreacted DMT and terephthalic acid monomethyl ester (hereinafter abbreviated as MMT), which is a reaction intermediate, are contained as impurities. Therefore, a reaction temperature of 150 ° C. or higher was required as a hydrolysis reaction condition (for example, see Patent Document 1). Furthermore, in order to promote the hydrolysis reaction, it is known that methanol and dimethyl ether generated in the reaction need to be removed from a pipe (hereinafter abbreviated as a vent line) installed at the top of the hydrolysis reaction tank. In order to accelerate the reaction, there is a method of introducing water vapor for stripping methanol and dimethyl ether into the hydrolysis reaction tank (for example, see Patent Document 2). Here, the removed methanol contains a large amount of moisture, and is generally purified by a distillation column and used separately.

  However, under the hydrolysis reaction conditions as described above, there is a problem that the reaction solution is vigorously formed, and DMT, MMT, and terephthalic acid adhere to the vent line and the vent line is blocked. In addition, a large amount of DMT is mixed into a methanol distillation column for purifying methanol that is removed by sublimation of DMT, and DMT is deposited in a normal atmospheric distillation column to close the shelf and tray. When the blockage of these vent lines and methanol distillation towers worsens, it becomes necessary to temporarily stop the hydrolysis reaction, and there is a problem that the production efficiency of terephthalic acid decreases.

JP 60-202848 A Japanese Patent Laid-Open No. 08-231464

  Accordingly, the object of the present invention is to prevent the formation of DMT, MMT and terephthalic acid in the hydrolysis reaction tank and the sublimation of DMT in the production method by hydrolysis of terephthalic acid from DMT, and blockage in the vent line. Is to provide a method for producing terephthalic acid with high production efficiency.

As a result of intensive studies, the present inventors have
In a method for producing terephthalic acid by hydrolyzing dimethyl terephthalate in a hydrolysis reaction tank, a gas containing methanol generated from the hydrolysis reaction tank is connected to the upper part from the reaction liquid level of the hydrolysis reaction tank. The reaction liquid in the hydrolysis reaction tank contains 1 part by weight or more of pure water or water containing impurities not more than the solubility at the hydrolysis reaction temperature with respect to 10 parts by weight of dimethyl terephthalate to be removed from the pipe and supplied to the hydrolysis reaction tank. It has been found that the above-mentioned object can be achieved because it is possible to prevent clogging in the process by the method for producing terephthalic acid, which is characterized by being fed into the hydrolysis reaction tank from above the surface.

  According to the present invention, terephthalic acid can be efficiently produced from DMT by hydrolysis reaction, and its industrial significance is great.

  Hereinafter, embodiments of the present invention will be described in detail. In the production method of the present invention, a hydrolysis reaction is carried out using DMT as a raw material to produce terephthalic acid. Here, as the reaction conditions for the hydrolysis reaction, any known technique may be adopted as long as the reaction proceeds, but it is preferably performed without a catalyst from the viewpoint of suppressing mixing of foreign materials into the reaction system. . Further, from the viewpoint of avoiding the formation (foaming phenomenon) of the hydrolysis reaction tank, the amount of water of the liquid charged into the hydrolysis reaction tank should be 0.6 parts by weight or more and 2 parts by weight or less with respect to 1 part by weight of DMT. The amount is particularly preferably 0.8 parts by weight or more and 1.5 parts by weight or less. If the amount of water in the liquid is reduced, the concentration of the slurry composed of terephthalic acid and water obtained after the hydrolysis reaction is increased, and the operability of the slurry is deteriorated. Further, when the amount of liquid water increases, forming is accelerated, which is not preferable. From the viewpoint of defoaming, it is necessary to supply water or pure water containing impurities having a solubility equal to or less than the solubility at the hydrolysis reaction temperature into the hydrolysis reaction tank from above the reaction liquid surface of the hydrolysis reaction tank.

  The amount of water or impurities containing impurities below the solubility is preferably 1 part by weight or more, preferably 1 part by weight or more and 20 parts by weight with respect to 10 parts by weight of DMT supplied to the hydrolysis reaction. It is more preferable that the amount is not more than parts. More preferably, it is 2 parts by weight or more and 15 parts by weight or less. By setting the amount within this range, it is possible to suitably prevent the clogging of the piping and to prevent unnecessary addition of excessive water or the like in the hydrolysis reaction tank.

  Here, the impurities contained in water containing impurities having a solubility equal to or lower than the hydrolysis reaction temperature are specifically gases such as oxygen, nitrogen, carbon dioxide, and various argon gases, sodium chloride, potassium chloride, and magnesium chloride. , Calcium chloride, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, sodium acetate, potassium acetate, magnesium acetate, calcium acetate, disodium terephthalate, dipotassium terephthalate, magnesium terephthalate, calcium terephthalate, MMT sodium salt And various inorganic salts and organic salts such as MMT potassium salt. Here, if the water to be used contains impurities that are higher than the solubility at the hydrolysis reaction temperature, the impurities will precipitate in the vent line and promote the blockage in the pipe connected to the hydrolysis reaction tank. It is not preferable. In order to avoid the precipitation of impurities in the vent line, water containing impurities below the solubility or pure water is used. In addition to water, for example, an organic solvent can be used to wash away DMT and terephthalic acid. However, the addition of an organic solvent unrelated to the hydrolysis reaction has the effect of generating side reactions, and is preferable. Absent.

  The term “above the reaction liquid surface of the hydrolysis reaction tank” means a portion above the reaction liquid surface. Specifically, when a distillation tower or the like is installed in the upper part of the hydrolysis reaction tank and not filled with the reaction solution (gas phase part) or above the hydrolysis tank, the distillation tower May be the lower part of the column (provided that the upper part of the hydrolysis tank is required), the middle part of the distillation column, or the upper part of the distillation column. Piping of the piping can be prevented by introducing the above-described water or the like from this place.

  It is preferable to supply DMT thrown into a hydrolysis reaction tank in a reaction liquid. By supplying DMT into the reaction solution, there is little scattering of DMT to the vent line, and blockage of the vent line can be prevented. By removing methanol and dimethyl ether generated in the hydrolysis reaction of DMT, the reaction equilibrium is shifted in the direction in which terephthalic acid is generated, and a gas containing methanol generated from the hydrolysis reaction tank is used to improve the hydrolysis reaction rate. It removes from the piping connected to the upper part from the reaction liquid level of a hydrolysis reaction tank. Preferably, water vapor for stripping methanol and dimethyl ether is introduced into the hydrolysis reaction tank.

  Either a batch type or a continuous type can be adopted as the hydrolysis reaction tank, and the hydrolysis reaction of DMT is performed at a temperature of 150 to 280 ° C., a pressure of 0.3 to 6.3 MPa (gauge pressure), preferably 150. -260 degreeC and the pressure of 0.3-4.6 MPa (gauge pressure) are good. At this time, the temperature of the gas containing methanol is also preferably 150 ° C. or higher. If the temperature of the gas is lower than 150 ° C., the DMT scattered with the gas becomes below the melting point, and solidifies in the vent line and becomes clogged by adhering, so that the hydrolysis reaction cannot be carried out efficiently.

  In the method of the present invention, the top temperature of the distillation column for distilling the gas containing methanol generated from the hydrolysis reaction tank described above is preferably 142 ° C. or higher. If it is less than 142 degreeC, since DMT does not melt | dissolve, obstruction | occlusion of a distillation column will arise. The bottom temperature of the distillation column is preferably not higher than the hydrolysis reaction temperature. If the temperature exceeds the hydrolysis reaction temperature, energy for distillation is required separately, which is inefficient. From the viewpoint of avoiding troubles in which DMT is precipitated from methanol, the distillate at the top of the distillation column containing methanol as a main component has a DMT concentration of 0.1 wt% or less.

  The installation position of the distillation tower for carrying out the step of distilling the gas containing methanol generated from the hydrolysis tank is a structure in which the lower part of the distillation tower and the upper part of the hydrolysis reaction tank are directly connected. Is preferably supplied to the hydrolysis reaction tank because DMT, MMT, and terephthalic acid adhering to the vent line can be removed by forming the reaction solution after the hydrolysis reaction.

  The contents of the present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto.

[Example 1]
DMT 4100-4200 kg / h, pure water 3200-3300 kg / h, steam 4100-4200 kg / h are continuously supplied from separate lines to the hydrolysis reaction tank, under conditions of a reaction temperature of 250 ° C. and a reaction pressure of 4.2 MPa. A terephthalic acid was produced from DMT by carrying out a hydrolysis reaction. During this hydrolysis reaction, a gas containing methanol generated at 4800 to 4900 kg / h is supplied to the distillation column from the pipe at the top of the hydrolysis reaction tank, and has 10 theoretical plates and the same pressure as the hydrolysis tank. Distillation was performed under the conditions, and methanol and water were fractionated. While performing the distillation, pure water at 200 ° C. was supplied at 900 kg / h from the top of the hydrolysis reaction tank above the reaction liquid surface, and further supplied to the hydrolysis reaction tank to continue the hydrolysis reaction. As a result, no blockage in the piping occurred. The methanol condensate obtained from the tower top gas was sampled and measured by gas chromatography. As a result, DMT was less than the detection limit and less than 0.01 wt%.

[Comparative Example 1]
In Example 1, the hydrolysis reaction was carried out under the same conditions except that pure water was not supplied into the pipe at the top of the hydrolysis reaction tank leading to the distillation tower. As a result, the pressure increased in the piping at the upper part of the hydrolysis reaction tank where DMT led to the distillation tower, and the hydrolysis reaction was stopped because clogging occurred.

[Comparative Example 2]
In Example 1, the pressure of the distillation column was normal pressure, 99 wt% methanol was extracted from the top of the column, and water containing 0.5 wt% or less of methanol and DMT were supplied from the bottom of the column to the hydrolysis reaction tank as a bottoms. . As a result, DMT adhered to the distillation column, the pressure in the distillation column increased, and clogging occurred, so the hydrolysis reaction was stopped.

  According to the present invention, terephthalic acid can be efficiently produced from DMT by hydrolysis reaction, and its industrial significance is great.

Claims (3)

  In a method for producing terephthalic acid by hydrolyzing dimethyl terephthalate in a hydrolysis reaction tank, a gas containing methanol generated from the hydrolysis reaction tank is connected to the upper part from the reaction liquid level of the hydrolysis reaction tank. The reaction liquid in the hydrolysis reaction tank contains 1 part by weight or more of pure water or water containing impurities not more than the solubility at the hydrolysis reaction temperature with respect to 10 parts by weight of dimethyl terephthalate to be removed from the pipe and supplied to the hydrolysis reaction tank. A method for producing terephthalic acid, wherein the terephthalic acid is supplied into the hydrolysis reaction tank from above the surface.   The gas containing methanol generated from the hydrolysis reaction tank is distilled under pressure at a temperature at which the top temperature of the distillation column is 142 ° C. or higher, and the concentration of dimethyl terephthalate in the distillate of methanol from the distillation column is 0.1 wt. The manufacturing method of the terephthalic acid of Claim 1 including the process made into% or less.   In the process of distilling the gas containing methanol generated from the hydrolysis reaction tank, the distillation column lower part and the hydrolysis reaction tank upper part are directly connected, and the distillation column bottoms are supplied to the hydrolysis reaction tank. The method for producing terephthalic acid according to claim 1 or 2, wherein: