JP2004216331A - Method of and apparatus for crystallizing aromatic carboxylic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of and an apparatus for preventing solid adhesion to internal surfaces of condenser tubes and other pipes, which adhesion will otherwise be caused by crystalline solid substance mixed into a vapor in a process and an apparatus for producing aromatic carboxylic acid. <P>SOLUTION: The apparatus comprises: a first pipe 4 for supplying a vapor generated in a crystallization tank 1 to a first condenser 2; a second pipe 5 for circulating part of the vapor condensed in the first condenser 2 to the crystallization tank 1; a third pipe 6 for transporting a vapor not condensed in the first condenser 2 to a second condenser 3, a fourth pipe 7 for circulating part of vapor V condensed in the second condenser 3 to the crystallization tank 1; a washing liquid injection device 8 connected with the first pipe 4; a fifth pipe 12 for use in bypass to directly supply a vapor generated in the crystallization tank 1 to the second condenser 3; another washing liquid injection device 8; washing liquid discharge outlets 14 and 16 provided in the second pipe 5 and the fourth pipe 7 and each provided with a switchable valve. The crystallizing apparatus as a whole can be subjected to washing treatment without having to be stopped. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a crystallization method in a process for producing an industrially useful aromatic carboxylic acid such as terephthalic acid, which is a raw material of polyester, and a crystallization apparatus used in the method.
[0002]
[Prior art]
Generally, when an aromatic carboxylic acid such as terephthalic acid is industrially produced, an alkyl aromatic hydrocarbon such as paraxylene is used as a raw material in an acetic acid solvent in the presence of a catalyst containing cobalt, manganese, and bromine. Then, a liquid-phase oxidation reaction with molecular oxygen is performed to make the generated aromatic carboxylic acid such as terephthalic acid saturated in the slurry, which is evaporated under reduced pressure to precipitate crystals, and then subjected to a solid-liquid separation treatment to give a crude liquid. A method of obtaining terephthalic acid and a method of further dissolving a crude terephthalic acid crystal in water, purifying it by a hydrogenation reaction, and crystallizing the same in the same manner as described above to obtain high-purity terephthalic acid are known.
[0003]
In such a method for producing an aromatic carboxylic acid, solids entrained in a reaction exhaust gas discharged from an oxidation reactor adhere to a pipe wall of a pipe or an inner wall of equipment such as a condenser in a downstream region of a gas flow. Normal function may be impaired.
As a countermeasure, Patent Document 1 describes supplying a acetic acid-containing solvent to the inlet of a condenser (condenser) (see Patent Document 1).
[0004]
Then, in the crystallization step, as in the reaction step, the solvent is vaporized from the slurry containing the aromatic carboxylic acid in the solvent in a saturated state to precipitate the aromatic carboxylic acid crystals, and the vaporized vapor is condensed by the condenser. Then, the slurry is refluxed.
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-212133 (Claim 1 etc.)
[0006]
[Problems to be solved by the invention]
Even in the crystallization method and the crystallization apparatus in the above-described conventional aromatic carboxylic acid production process, solids such as crystals are mixed with the vapor of the volatilized solvent to enter the condenser and pipes before and after the condenser. Therefore, there is a problem that so-called entrainment is likely to occur.
[0007]
This problem of entrainment of solid matter into the equipment is addressed so that the superficial velocity and other factors are taken into consideration when designing the equipment, but the load on the equipment is increased when production needs to be increased. Inevitably occurs when it gets bigger.
[0008]
The problem of entrainment of solids in steam in such a crystallization step is specifically caused by a condenser (also called a condenser or a heat exchanger) downstream of the crystallization tank for heat exchange. This may result in blockage of a large number of tubes and poor distribution of other pipes, and decrease in production efficiency and purification efficiency of the aromatic carboxylic acid.
[0009]
Therefore, an object of the present invention is to solve the above-mentioned problems and to remove solid matter accompanied by vapor in a crystallization step or a crystallizer in a production step of an aromatic carboxylic acid, in a tube of a condenser, and in other pipes. It is an object of the present invention to provide a method or an apparatus which prevents the solid matter from adhering and does not reduce the production efficiency and purification efficiency of the aromatic carboxylic acid.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention, water or acetic acid is used as a solvent to vaporize the solvent from a slurry containing an aromatic carboxylic acid in a saturated state to precipitate an aromatic carboxylic acid crystal, which is vaporized. In the method for crystallizing an aromatic carboxylic acid in which vapor is condensed in a condenser and refluxed to the slurry, the vapor of the vaporized solvent is selectively supplied to one or more condensers, and a cleaning liquid is supplied to each of the vapor supply paths. , And a reflux path from the condenser to the slurry is provided with an openable and closable discharge port to selectively perform reflux and discharge of the washing liquid, thereby providing a method of crystallizing aromatic carboxylic acid.
[0011]
In the method for crystallizing an aromatic carboxylic acid according to the present invention comprising the above-described steps, a cleaning liquid is injected into a steam supply passage leading to at least one selected condenser from among a plurality of condensers, and the vapor supply passage and a connection therewith are connected. The inside of the condenser can be cleaned, and the unselected steam supply path and the inside of the condenser can be simultaneously operated in the crystallization and cleaning steps while continuing the normal operation.
[0012]
In this case, if a solvent composed of water or acetic acid (may be a mixture) is used as the cleaning solution, the production process of the aromatic carboxylic acid is not significantly affected, and thus the cleaning solution can be refluxed without discharging. In parallel with the normal manufacturing process, all the capacitors and the piping before and after the capacitors can be washed and manufactured to increase the efficiency.
[0013]
Therefore, adhesion of the solid matter in the narrow tube and other piping of the condenser due to the incorporation of the crystalline solid matter into the vapor in the crystallization step or the crystallization apparatus is prevented, and the production efficiency does not decrease.
[0014]
In addition, when an alkaline cleaning solution is used as the cleaning solution, the solvent is affected even on the downstream side of the crystallization step, so that the cleaning solution is preferably discharged. By injecting the washing liquid continuously or intermittently, the crystallization of the aromatic carboxylic acid can be efficiently performed.
[0015]
In particular, in the method for crystallizing an aromatic carboxylic acid using two or more condensers, the vaporized vapor is supplied from a first pipe to the first condenser, and one of the vapors condensed by the first condenser is supplied to the first condenser. Part is refluxed from the second pipe to the crystallization tank, the steam not condensed in the first condenser is sent from the third pipe to the second condenser, and a part of the vapor condensed in the second condenser is sent from the fourth pipe. Preferably, the method is a method for crystallizing an aromatic carboxylic acid, wherein the method comprises refluxing to a crystallization tank and allowing a cleaning liquid to be injected into the first pipe.
[0016]
With this configuration, the cleaning liquid continuously or intermittently injected into the first pipe during the operation of the aromatic carboxylic acid production plant provided with the crystallizer is supplied to the first pipe, the first condenser, and the second pipe. To reflux. Further, when cleaning the plant by stopping the operation of the plant, it is necessary to inject the cleaning liquid only into the first pipe by operating the valve for opening and closing the pipe provided at a key point, thereby simultaneously cleaning the two condensers and the pipe. I can do it.
[0017]
A crystallization apparatus applicable to the above-described method is provided with a crystallization tank for containing a slurry containing an aromatic carboxylic acid in a saturated state with water or acetic acid as a solvent and evaporating the solvent, and a capacitor is provided in the crystallization tank. In a crystallization apparatus for aromatic carboxylic acid capable of condensing and refluxing vaporized vapor by connecting, a first pipe for supplying vapor generated in the crystallization tank to a first condenser is provided, and the first condenser is condensed by the first condenser. A second pipe for refluxing a part of the evaporated steam to the crystallization tank, and a third pipe for sending steam not condensed by the first condenser to the second condenser, and the steam condensed by the second condenser. A fourth pipe for refluxing a part of the solution to the crystallization tank is provided, and a washing liquid injection device is connected to the first pipe.
[0018]
Further, in addition to the washing step in the above-mentioned crystallization method, the steam generated in the crystallization tank is directly supplied to the second condenser through the fifth pipe for bypass, and the second pipe is provided with a cleaning liquid discharge port that can be opened and closed. In addition, a cleaning liquid can be injected into the fifth pipe, and the following step A and step B are alternately carried out to provide an aromatic carboxylic acid crystallization method.
[0019]
(A) The fifth pipe is closed, vapor of the vaporized solvent is supplied from the first pipe to the first condenser, and a part of the vapor condensed by the first condenser is returned from the second pipe to the crystallization tank. Supplying the steam not condensed by the first condenser to the second condenser from the third pipe, and refluxing a part of the vapor condensed by the second condenser to the crystallization tank from the fourth pipe (B). The fifth pipe is opened to close the first pipe, the second pipe is closed downstream of the cleaning liquid discharge port, and the third pipe is closed upstream of the connection with the fifth pipe. In this state, steam is removed from the fifth pipe. A step of supplying a part of the vapor to the condenser, refluxing a part of the vapor from the fourth pipe to the crystallization tank, injecting the cleaning liquid into the first pipe, and opening and discharging the cleaning liquid outlet of the second pipe.
When the step A is selected, the solvent evaporated from the slurry containing the aromatic carboxylic acid can be surely refluxed by the two condensers.
[0021]
Further, when the step B is selected, even when only the first condenser is clogged or the liquid remains stagnant, the second condenser can be operated while the first condenser is stopped and washed.
[0022]
When the step A and the step B are alternately performed, the first pipe and the first condenser to which solid matter is likely to adhere are washed, and at that time, the second condenser is used alternately, and the entire crystallization apparatus is completely stopped. The device can be operated efficiently without the need for cleaning.
[0023]
When an alkaline cleaning liquid such as an aqueous solution of caustic soda is used as the cleaning liquid, the first pipe, the first condenser, and the cleaning liquid discharge port of the second pipe can be quickly discharged independently as a closed path. Alkaline cleaning does not affect the route.
[0024]
Further, the first pipe, the first condenser and the second pipe are independently cleaned up to the cleaning liquid discharge port, a solvent is injected as a cleaning liquid into the fifth pipe which is a bypass, and the second condenser and the fourth pipe are refluxed. Can also be washed.
[0025]
The crystallization apparatus applicable to the above method is a crystallization apparatus for the aromatic carboxylic acid described above, wherein a fifth pipe for bypass which directly supplies the steam generated in the crystallization tank to the second condenser is provided. Is a crystallizer of aromatic carboxylic acid provided with a cleaning liquid outlet that can be opened and closed, and a crystallizer of aromatic carboxylic acid provided with a cleaning liquid injection device in a fifth pipe.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of the present invention will be described below with reference to the accompanying drawings.
The apparatus for crystallizing an aromatic carboxylic acid according to the first embodiment shown in the apparatus system diagram of FIG. 1 uses a slurry S containing a saturated state of an aromatic carboxylic acid with water or acetic acid as a solvent. Has a crystallization tank 1 for evaporating the solvent and sending the concentrated slurry S 'to the next step. The first condenser 2 and the second condenser 3 are connected to the crystallization tank 1 to condense the vaporized vapor. It is a device that can be refluxed.
[0027]
The crystallization apparatus is provided with a first pipe 4 for supplying the vapor generated in the crystallization tank 1 to the first condenser 2, and a part of the vapor condensed in the first condenser 2 is returned to the crystallization tank 1. A second pipe 5 is provided, and a third pipe 6 for sending vapor not condensed by the first condenser 2 to the second condenser 3 is provided. A part of the vapor V condensed by the second condenser 3 is supplied to the crystallization tank 1. The first pipe 4 is connected to a cleaning liquid injection device 8.
[0028]
The first, second, and third pipes (4, 5, 6) are provided with valves 9, 10, and 11 that can be opened and closed appropriately, and each pipe is selectively opened and closed to variously change the processing path. I can do it.
[0029]
The structure of the cleaning liquid injection device 8 is not particularly limited, and a well-known injector having a cylinder or a pump capable of injecting or press-fitting a liquid additive into a liquid or slurry can be employed.
[0030]
In crystallizing the aromatic carboxylic acid using the above-mentioned crystallization apparatus, the apparatus can be washed either during operation or while the apparatus is stopped.
That is, in order to carry out the cleaning process concurrently with the operation of the crystallizer, the valves 9, 10, 11 and the valves 17, 18 provided downstream of the second condenser 3 are all opened, and the cleaning liquid is injected. A cleaning liquid composed of a solvent component such as an acetic acid aqueous solution is supplied from the apparatus 8 continuously or intermittently. The solvent vapor is condensed by the first condenser 2 and is returned to the crystallization tank 1 from the second pipe 5 together with the cleaning liquid. The solvent not condensed in the first condenser 2 is sent to the second condenser 3 via the third pipe 6, and the solvent condensed here is returned to the crystallization tank 1 from the fourth pipe 7.
[0031]
When the crystallizer is stopped and the cleaning process is performed, all of the valves 9, 10 and 11 are closed, and an alkaline cleaning solution such as caustic soda or a cleaning solution containing a solvent component is supplied from the cleaning solution injection device 8. The first condenser 2 and the second pipe 5 are washed, and the contaminated liquid after the cleaning is discarded from the cleaning liquid outlet 14 with a valve. Further, when the valve 11 is opened as required, the cleaning liquid flows to the third pipe 6 and the second condenser 3. At this time, the valves 17 and 18 are closed, and the two condensers are simultaneously subjected to the cleaning treatment. Can be discarded from the cleaning liquid outlet 16 with a valve. Incidentally, the use of the alkaline cleaning solution can reliably clean the dirt that could not be dissolved and removed with only the acetic acid-based solvent.
[0032]
The apparatus for crystallizing aromatic carboxylic acid according to the second embodiment shown in the apparatus system diagram of FIG. 2 is similar to the apparatus for crystallizing aromatic carboxylic acid according to the first embodiment. This is a crystallization apparatus in which a fifth pipe 12 for bypass directly supplied to the two condensers 3 is provided and a cleaning liquid injection device 13 is provided.
[0033]
In the crystallization method using the above-described apparatus, as the step A, the valve 15 of the fifth pipe 12 is closed, and the vapor of the vaporized solvent is supplied from the first pipe 4 to the first condenser 2 and condensed by the first condenser 2. A part of the solvent thus obtained is refluxed from the second pipe 5 to the crystallization tank 1, and the solvent not condensed by the first condenser 2 is supplied to the second condenser 3 from the third pipe 6 and condensed by the second condenser 3. A part of the solvent thus obtained is refluxed from the fourth pipe 7 to the crystallization tank 1. In this case, the valves 17 and 18 are in an open state, and the cleaning liquid outlet 16 with a valve is in a closed state.
[0034]
Further, as a B step instead of the A step, the valve 9 is closed, the valve-equipped cleaning liquid outlet 14 of the second pipe 5 and the downstream valve 10 thereof are closed, and the valve 11 is closed in the third pipe 6, and the path in this state is closed. The steam is supplied from the fifth pipe 12 to the second condenser 3, the condensed solvent is returned to the crystallization tank 1 from the fourth pipe 7, and the cleaning liquid is injected into the first pipe 4 from the cleaning liquid injection device 8. The closed path is surely washed while opening and draining the washing liquid outlet 14 with a valve of the second pipe 5. In this case, since the slurry containing the aromatic carboxylic acid does not enter the first condenser 2 and the closed path of the pipes before and after the first condenser 2, a cleaning liquid having excellent cleaning properties (for example, a solvent which is not a solvent like an alkaline cleaning liquid) However, the cleaning process can be performed more reliably.
[0035]
When the step A and the step B are performed alternately, the first condenser 2 to which solid matter is likely to adhere and the pipes before and after the first condenser 2 are intensively washed. In that case, the first condenser 2 is replaced with the first condenser 2 in the B step. Since the two condensers 3 are used instead, the cleaning operation can be performed without completely stopping the entire crystallization apparatus, and the downtime of the aromatic carboxylic acid production apparatus for repair can be reduced.
[0036]
【The invention's effect】
As described above, according to the present invention, in a method for crystallizing an aromatic carboxylic acid, vapor of a vaporized solvent is selectively supplied to one or more condensers, and a cleaning liquid is injected into each of the vapor supply paths. An openable discharge port is provided in the return path to selectively perform return and discharge of the cleaning liquid, so that the steam supply path and the condenser in the selected path can be cleaned. A crystallization method or crystallization device that removes and prevents solids adhering to the inside of condensers and other pipes, and that does not reduce productivity because the steam supply path and condenser that have not been cleaned can be operated without cleaning. There is an advantage that it becomes.
[Brief description of the drawings]
FIG. 1 is a system diagram showing a manufacturing process according to a first embodiment. FIG. 2 is a system diagram showing a manufacturing process according to a second embodiment.
DESCRIPTION OF SYMBOLS 1 Crystallization tank 2 1st condenser 3 2nd condenser 4 1st piping 5 2nd piping 6 3rd piping 7 4th piping 8, 13 Cleaning liquid injection apparatus 9, 10, 11, 15, 17, 18 Valve 12 5th piping 14, 16 Cleaning liquid outlet with valve

Claims (7)

Water or acetic acid is used as a solvent to vaporize the solvent from a slurry containing an aromatic carboxylic acid in a saturated state to precipitate crystals of the aromatic carboxylic acid. In the method for crystallizing a carboxylic acid,
The vaporized solvent vapor is selectively supplied to one or more condensers, and a cleaning liquid can be injected into each of these vapor supply paths, and a return path from the condenser to the slurry is provided with an openable / closable outlet. A method for crystallizing an aromatic carboxylic acid, comprising selectively refluxing and discharging a washing solution. 2. The method for crystallizing an aromatic carboxylic acid according to claim 1, wherein the cleaning liquid comprises a solvent or an alkaline cleaning liquid, and the cleaning liquid is continuously or intermittently injected. Water or acetic acid is used as a solvent to vaporize the solvent from a slurry containing an aromatic carboxylic acid in a saturated state to precipitate aromatic carboxylic acid crystals, and the vaporized vapor is condensed by a plurality of condensers and returned to the slurry. In the method for crystallizing an aromatic carboxylic acid,
The vaporized vapor is supplied to the first condenser from the first pipe, and a part of the vapor condensed in the first condenser is returned to the crystallization tank from the second pipe, and the vapor not condensed in the first condenser is A third pipe is sent to a second condenser, a part of the vapor condensed in the second condenser is returned from a fourth pipe to a crystallization tank, and a cleaning liquid can be injected into the first pipe. For crystallization of aromatic carboxylic acids. The method for crystallizing an aromatic carboxylic acid according to claim 3,
The vapor generated in the crystallization tank is directly supplied to the second condenser through a fifth pipe, and the second pipe is provided with an opening and closing of a cleaning liquid that can be opened and closed, and the fifth pipe is capable of injecting the cleaning liquid. A method for crystallizing an aromatic carboxylic acid, wherein the step and the step B are performed alternately.
(A) The fifth pipe is closed, vapor of the vaporized solvent is supplied from the first pipe to the first condenser, and a part of the vapor condensed by the first condenser is returned from the second pipe to the crystallization tank. Supplying the steam not condensed by the first condenser to the second condenser from the third pipe, and refluxing a part of the vapor condensed by the second condenser to the crystallization tank from the fourth pipe (B). The fifth pipe is opened to close the first pipe, the second pipe is closed downstream of the cleaning liquid discharge port, and the third pipe is closed upstream of the connection with the fifth pipe. In this state, steam is removed from the fifth pipe. (2) a step of supplying a part of the vapor to the condenser, refluxing a part of the vapor from the fourth pipe to the crystallization tank, injecting the cleaning liquid into the first pipe, and opening and discharging the cleaning liquid outlet of the second pipe; A crystallization tank for containing a slurry containing an aromatic carboxylic acid in a saturated state with water or acetic acid as a solvent is provided and a crystallization tank for evaporating the solvent is provided, and a condenser is connected to the crystallization tank to condense and return the vaporized vapor. In a possible crystallizer of aromatic carboxylic acids,
A first pipe for supplying the vapor generated in the crystallization tank to a first condenser; a second pipe for returning a part of the vapor condensed in the first condenser to the crystallization tank; A third pipe for sending steam not condensed by the second condenser to the second condenser, a fourth pipe for returning a part of the vapor condensed by the second condenser to the crystallization tank, and a cleaning liquid for the first pipe. A crystallizer for aromatic carboxylic acid, characterized by being connected to an injector of (1). 6. The aromatic carboxylic acid crystallization apparatus according to claim 5, further comprising: a fifth pipe for bypass for directly supplying steam generated in the crystallization tank to the second condenser, wherein the second pipe is capable of opening and closing a cleaning liquid. An apparatus for crystallizing an aromatic carboxylic acid, comprising an outlet. 7. The apparatus for crystallizing aromatic carboxylic acid according to claim 6, wherein a cleaning liquid injection device is provided in the fifth pipe.

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