JP3864609B2 - Method for producing terephthalic acid - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing terephthalic acid in which terephthalic acid obtained by liquid phase oxidation of para-xylene is subjected to solid-liquid separation and drying.
[0002]
[Prior art]
When paraxylene is oxidized in the liquid phase with a molecular oxygen-containing gas in the presence of an oxidation catalyst such as a catalyst containing cobalt, manganese and bromine in an acetic acid solvent under pressure, the main impurities are 4 in addition to terephthalic acid. -Crude terephthalic acid (CTA) containing carboxybenzaldehyde (hereinafter sometimes referred to as 4-CBA) is produced. However, since the production of polyester fibers and the like requires high-purity terephthalic acid (PTA) as a raw material, it is necessary to purify CTA.
Hydrogenation treatment is performed as a purification method of CTA. In this method, a slurry in which CTA is suspended in water is heated to form an aqueous solution, subjected to hydrogenation treatment in the presence of a hydrogenation catalyst, and the treatment liquid is crystallized and solid-liquid separated to produce PTA.
[0003]
The terephthalic acid produced in this way is dried to obtain a product after solid-liquid separation. As the solid-liquid separator, means for separating water from terephthalic acid crystals, such as a filter (for example, a rotary filter) and a centrifuge, is used. As the dryer, a general dryer in which the crystal and the heated gas are brought into contact with each other is used so that moisture adhering to the separated crystal is removed and dried.
[0004]
However, in such a method for producing terephthalic acid, the solid-liquid separator and the dryer are operated as separate systems. Done. Accordingly, separate drive systems and control systems are required, which increases the complexity and cost of the apparatus, and also causes problems such as accumulation of impurities, for example, accumulation of halogen and corrosion.
[0005]
[Problems to be solved by the invention]
The object of the present invention is to consolidate the separator / drying gas used in the solid-liquid separator and the dryer, simplify the configuration of the apparatus, enable the use of exhaust gas in the process, reduce costs, and concentrate impurities. It is to propose a method for producing terephthalic acid capable of preventing the corrosion of the apparatus.
[0006]
[Means for Solving the Problems]
The present invention is the following method for producing terephthalic acid.
(1) an oxidation reaction step for producing terephthalic acid by liquid phase oxidation of para-xylene in an oxidation reactor;
A solid-liquid separation step for solid-liquid separation of the crystalline terephthalic acid produced by a solid-liquid separator, and a drying step for drying the terephthalic acid separated by the solid-liquid separator,
Supplying at least part of the oxidation exhaust gas discharged from the oxidation reactor to the dryer from the first gas supply path;
Supplying the exhaust gas from the dryer to the solid-liquid separator from the second gas supply path;
A method for producing terephthalic acid in which the exhaust gas generated by the solid-liquid separator is taken out from the gas outlet.
(2) The method according to (1) above, wherein the solid-liquid separator is a rotary filter.
(3) The method according to (1) or (2) above, wherein the dryer is a rotary drum dryer.
(4) The method according to any one of the above (1) to (3), comprising a gas-liquid separator that gas-liquid separates the gas extracted from the solid-liquid separator.
[0007]
The terephthalic acid to be produced in the present invention is terephthalic acid produced by liquid phase oxidation of para-xylene, and may be CTA or PTA. In general, a method for producing terephthalic acid is preferred in which PTA is produced through a purification step such as hydrogenation after the production of CTA and a crystallization step.
[0008]
An oxidation reactor generally used for the production of terephthalic acid can be used. However, a raw material such as paraxylene, a catalyst and a solvent are accommodated in the lower part of the tank, and air is blown into the liquid phase while supplying these raw materials. Those that oxidize are preferred.
The liquid phase oxidation of para-xylene is performed using a solvent and a catalyst. Examples of the solvent in the liquid phase oxidation of para-xylene include aliphatic carboxylic acids such as acetic acid, propionic acid, n-butyric acid, isobutyric acid, n-valeric acid, trimethylacetic acid, caproic acid, and mixtures of these with water. .
[0009]
The liquid phase oxidation catalyst for para-xylene is generally a heavy metal compound and / or a bromine-containing compound, and the former is nickel, cobalt, iron, chromium, manganese, etc. Used in a form that dissolves in the reaction system. As a preferred embodiment, a cobalt compound, a manganese compound and a bromine compound are used, and the amount of the cobalt compound used is usually 10 to 10,000 ppm, preferably 100 to 3000 ppm as cobalt with respect to the solvent. Further, the manganese compound has an atomic ratio of manganese to cobalt of 0.001 to 10, and the bromine compound has an atomic ratio of bromine to cobalt of 0.1 to 10.
[0010]
The liquid phase oxidation of para-xylene is performed using a molecular oxygen-containing gas. As such an oxygen-containing gas, oxygen diluted with an inert gas is usually used. For example, air or oxygen-enriched air is used. The temperature of the oxidation reaction is usually 150 to 270 ° C., preferably 170 to 220 ° C., and the pressure is at least the pressure at which the mixture can maintain a liquid phase at the reaction temperature, and usually 0.5 to 4 MPa (gauge pressure). . Furthermore, although reaction time is based on the magnitude | size of an apparatus etc., it is about 20 minutes-about 180 minutes as normal residence time. The water concentration in the reaction system is usually 3 to 30% by weight, preferably 5 to 15% by weight.
[0011]
When PTA is produced, PTA can be obtained by removing impurities such as 4-CBA by a purification step in which CTA obtained as described above is purified as a water slurry by hydrogenation treatment or the like.
In the hydrogenation, hydrogenation is performed in the presence of a hydrogenation catalyst such as palladium, ruthenium, rhodium, osmium, iridium, platinum, platinum black, palladium black, iron, cobalt-nickel, and the impurities are reduced.
[0012]
The solid-liquid separation step is a step of separating the terephthalic acid crystals produced by the oxidation reaction step or the crystallization step after hydrogenation from the mother liquor. The solid-liquid separator used here may be any as long as it can separate the crystal and the mother liquor, and a filter, a centrifuge, etc. can be used. In the present invention, a filter that introduces gas and pressurizes is preferable. A rotary filter in which the filter medium rotates is preferable.
[0013]
The drying step is a step of drying the terephthalic acid crystals separated in the solid-liquid separation step. Although the dryer used here should just be a dryer which contacts heating gas and dries, the rotary drum type dryer which rotates by rotating a drum is preferable.
[0014]
In the present invention, at least a part of the oxidation exhaust gas is supplied from the oxidation reactor to the dryer through the first gas supply path to perform drying. The exhaust gas from the dryer is supplied to the solid-liquid separator from the second gas supply path to perform solid-liquid separation. The exhaust gas of the solid-liquid separator is taken out from the gas outlet, and if necessary, gas / water separation or the like is performed, the gas is discharged out of the system, and the liquid is returned to the reactor.
[0015]
By forming such a gas flow path, the gas generated by the oxidation reaction can be passed through each device in a transient manner. For this reason, since there is no gas circulation, the occurrence of corrosion due to accumulation of impurities is prevented. Further, since the drive sources of the respective devices are unified, the configuration becomes simple and the operation becomes simple. Moreover, since exhaust gas is used, waste can be effectively used.
[0016]
【The invention's effect】
According to the present invention, since the exhaust gas of the oxidation reactor is supplied to the solid-liquid separator through the dryer, the configuration of the apparatus is simplified, the use of the exhaust gas of the process is enabled, and the cost is reduced. Therefore, it is possible to prevent the corrosion of the apparatus.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a flowchart of the terephthalic acid production apparatus of the embodiment.
[0018]
In FIG. 1, 1 is an oxidation reactor, 2 is a solid-liquid separator for CTA, 3 is a hydrogenation device, and 4 is a crystallizer, which are connected to the series via lines L1, L2, L3, and L4. Reference numeral 5 denotes a rotary filter as a solid-liquid separator for PTA, and reference numeral 6 denotes a dryer. A line L5 communicates from the crystallizer 4 to the lower part of the rotary filter 5. The oxidation reactor 1 communicates with an air line L6 at the bottom and an exhaust gas line L7 at the top. A line L8 communicates from the solid-liquid separator 2 to the oxidation reactor 1.
[0019]
The rotary filter 5 is provided with a cylindrical rotary filter medium 12 in a casing 11, and a lower part of the rotary filter 5 is immersed in a slurry 14 of a slurry tank 13, and the rotary filter 5 under pressure and the gas-liquid separator 7 under normal pressure. Due to the pressure difference, the filtrate flows through the line 9, and the cake 15 captured by the filter medium 12 is configured to be peeled off by gas blowing from the peeling gas passage 16.
Lines L10 and L11 communicate with the upper and lower portions of the gas-liquid separator 7.
[0020]
In the production method of terephthalic acid by the above apparatus, first, paraxylene, a catalyst, a solvent, etc. as raw materials are supplied from line L1, air is introduced from line L6, liquid phase oxidation is performed, and paraxylene is oxidized to terephthalic acid To do. Since terephthalic acid gradually precipitates to form a slurry, a part of the terephthalic acid is transferred from the line L2 to the solid-liquid separator 2 for solid-liquid separation, and the separated liquid is returned to the oxidation reactor 1 from the line L8. The solid-liquid separator 2 may be a rotary filter 5, a centrifuge, or another separator.
[0021]
The CTA separated by the solid-liquid separation is sent from the line L3 to the hydrogenation device 3, where water is sent from the line L12 to reslurry, and this is dissolved and hydrogenated to reduce 4-CBA. The hydrogenated liquid is sent from the line L4 to the crystallizer 4 for crystallization. The slurry crystallized by the crystallizer 4 and crystallized from terephthalic acid (PTA) is sent from the line L5 to the rotary filter 5 for solid-liquid separation.
[0022]
The rotary filter 5 corresponds to a solid-liquid separator used in the solid-liquid separation process of the present invention, and is under pressure. The slurry 14 entering from the line L5 accumulates in the lower part of the slurry tank 13. In this state, when the rotary filter medium 12 is rotated and connected to the gas-liquid separator 7 under normal pressure by the line L9, the inside of the filter medium 12 becomes low pressure, the liquid in the slurry enters the filter medium 12, and the terephthalic acid crystals in the slurry are It is trapped on the filter medium 12 to form a cake 15. The flow of the liquid in the filter medium 12 enters the drainage chamber 18 from the suction path 17 and is sent to the gas-liquid separator 7 from the line L9.
[0023]
Corresponding to this suction, pressurization is performed by introducing a gas from the dryer 6, which will be described later.
When the cake 15 rises due to the rotation of the rotary filter medium 12, the cake is washed by supplying water from the line L13 and blowing the washing water from the washing water nozzle 19. Thereafter, gas is introduced into the air supply chamber 20 from the line L14, and the cake 15 is peeled off by being blown onto the cake 15 from the peeling gas passage 16. The peeled cake 15 enters the dryer 6 through the communication path 21.
[0024]
The dryer 6 is a rotary drum type dryer. The hollow drum is arranged in the horizontal direction (however, the outlet side is slightly lower) and is rotatable, and a line L15 branched from the line L7 is connected to the terminal side. The oxidation exhaust gas from the oxidation reactor 1 is supplied. Oxidation exhaust gas is a gas mainly composed of a non-condensable gas after the catalyst and solvent are recovered by a distillation tower and the vapor is removed by a condenser.
[0025]
The cake 15 is sequentially supplied while rotating the drum in the dryer 6, and the oxidized exhaust gas is sent from the opposite side and brought into countercurrent contact, whereby the terephthalic acid is dried and dry PTA is obtained from the line L 16. In the dryer 6, heating is performed as necessary. Steam generated by the drying enters the rotary filter 5 from the communication path 21 together with the exhaust gas.
[0026]
The exhaust gas entering the rotary filter 5 is used as a pressure source for the rotary filter 5. The steam contained in the exhaust gas is mixed with the filtrate together with the steam generated by the rotary filter 5 and absorbed, and is extracted from the line L9. The mixture of exhaust gas and liquid entering the gas-liquid separator 7 from the line L9 is separated into a gas phase and a liquid phase by stationary separation. The liquid phase is returned from the line L11 to the hydrogenation device 3 and other parts. The gas phase can be discharged from the line L10 to the atmosphere, but it may be sent to the processing apparatus together with the exhaust gas of L17.
[0027]
By forming such a gas flow path, the gas generated by the oxidation reaction can be passed through each device in a transient manner. Thereby, since there is no gas circulation, the occurrence of corrosion due to accumulation of impurities is prevented. In addition, the configuration of each device is simplified and the operation is simplified. Moreover, since exhaust gas is used, waste can be effectively used.
[0028]
For this reason, according to the above method, the exhaust gas of the oxidation reactor is supplied to the solid-liquid separator through the dryer, thereby simplifying the configuration of the apparatus, enabling the use of the exhaust gas of the process, and reducing the cost. It is possible to prevent the concentration of impurities and the corrosion of the apparatus.
[Brief description of the drawings]
FIG. 1 is a flow diagram of an apparatus for producing terephthalic acid according to an embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Oxidation reactor 2 Solid-liquid separator 3 Hydrogenation apparatus 4 Crystallizer 5 Rotary filter 6 Dryer 7 Gas-liquid separator 11 Casing 12 Rotating filter medium 13 Slurry tank 14 Slurry 15 Cake 16 Stripping gas path 17 Suction path 18 Drain Chamber 19 Washing water nozzle 20 Air supply chamber 21 Communication path

Claims (4)

An oxidation reaction step for producing terephthalic acid by liquid phase oxidation of para-xylene in an oxidation reactor;
A solid-liquid separation step for solid-liquid separation of the crystalline terephthalic acid produced by a solid-liquid separator, and a drying step for drying the terephthalic acid separated by the solid-liquid separator,
Supplying at least part of the oxidation exhaust gas discharged from the oxidation reactor to the dryer from the first gas supply path;
Supplying the exhaust gas from the dryer to the solid-liquid separator from the second gas supply path;
A method for producing terephthalic acid in which the exhaust gas generated by the solid-liquid separator is taken out from the gas outlet. The method according to claim 1, wherein the solid-liquid separator is a rotary filter. The method according to claim 1 or 2, wherein the dryer is a rotary drum dryer. The method according to any one of claims 1 to 3, further comprising a gas-liquid separator that gas-liquid separates the gas extracted from the solid-liquid separator.

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