JP2006143612A - Method for conveying slurry - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for continuously conveying slurry through suppressing crystallization and other solids deposition or the cloggings of slurry conveyance pipings associated with these phenomena as the most problematic points in the case of handling aqueous terephthalic acid slurry at high temperatures and pressures, thus keeping devices including the slurry conveyance pipings and valves in continuously operable conditions. <P>SOLUTION: The method comprises the following process: In terephthalic acid production equipment having such a structure that at least two continuous-type reaction vessels are connected to each other in series via the slurry conveyance pipings provided with openable pressure-reducing valves and washing water feed pipings and washing water flow control valves are connected to the slurry conveyance pipings on the upstream side of the pressure-reducing valves, slurry comprising water and terephthalic acid is conveyed at high temperatures and pressures from one of the continuous-type reaction vessels to another, wherein while continuously feeding the slurry, the washing water flow control valves at the washing water feed pipings connected to the slurry conveyance pipings connecting the continuous-type reaction vessels to each other are controlled to vary the flow of washing water while periodically feeding washing water. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for feeding a water slurry containing terephthalic acid in the production of terephthalic acid, which is a main raw material of polyester resin widely used for fibers, films, industrial members, general molded articles and the like. More specifically, the present invention relates to a method for operating a terephthalic acid crystallization tank, or a method for feeding an aqueous slurry containing terephthalic acid which is produced by a hydrolysis method of dimethyl terephthalate and is suitable as a polyester production raw material represented by polyethylene terephthalate. Is.

  There are several methods for supplying a solution or slurry under high temperature and high pressure to the crystallization tank or reaction tank, and the solution or slurry to be transported to one of them is under a lower pressure through a pressure reducing valve. There is a method of continuous transportation to the tank. For example, in the hydrorefining process of crude terephthalic acid, after passing through a noble metal catalyst bed at about 300 ° C. and hydrorefining, the terephthalic acid crystals can be precipitated by supplying to the crystallization tank and lowering the temperature due to water evaporation. Has been done. In this case, 3 to 6 crystallization tanks are connected in series, and a pressure reducing valve is installed in each supply pipe to each crystallization tank, so that crystals are precipitated by sequentially cooling between the crystallization tanks. It is supposed to be. In addition, when producing terephthalic acid by using dimethyl terephthalate as a raw material with water at high temperature and high pressure to produce terephthalic acid, the slurry produced using one or more continuous reaction tanks is subjected to a lower pressure through a pressure reducing valve. The purity is adjusted by improving the reaction rate while being supplied to a certain reaction vessel.

  However, in the transportation of a slurry mainly composed of terephthalic acid and water (hereinafter sometimes simply referred to as terephthalic acid slurry), if the transportation is continued for a long period of time, a part of the terephthalic acid in the terephthalic acid slurry is deposited on the inner surface of the supply pipe. There was a problem that the terephthalic acid slurry could not be transported due to adhesion and solidification. For this reason, it was necessary to scrape and remove the deposits periodically. In addition, when handling terephthalic acid slurry at high temperature and high pressure, crystal precipitation and adhesion to the pipes occur in the vicinity of the valves in the slurry transport pipe due to flash evaporation, etc. There was a problem of causing a drop and product loss. On the other hand, although a method has been reported in which the attached crystal is impacted and peeled off from the vessel wall by abruptly opening and closing a pressure reducing valve installed in the slurry transport pipe (see, for example, Patent Document 1). In this method, it is a cleaning effect only by the impact caused by abruptly flowing a slurry having no solubility with respect to the attached crystal using a large pressure difference, and is insufficient for remarkable crystal precipitation. In many cases, there was a problem that the downtime of the equipment was unavoidable and the operating rate was lowered and the product was lost. There is also a problem that the pressure fluctuation at the liquid delivery destination is large and a large equipment cost is required to cope with safety problems due to blow-through.

  In addition, a method of using a pipe having a jacket made of a porous material and preventing solid crystals from adhering to the inner surface of the slurry transport pipe by a bubbling effect by blowing nitrogen gas has been reported (for example, see Patent Document 2). However, when handling terephthalic acid slurry at high temperature and high pressure, not only high pressure nitrogen (N2) is required, but also crystal precipitation and adhesion to the pipe occur in the vicinity of the valve in the slurry transport pipe due to flash evaporation, etc. The N2 bubbling effect is insufficient. On the other hand, methods have been reported to prevent clogging by applying vibration to the clogging site using a vibration generator (see, for example, Patent Document 3), but in the case of terephthalic acid, adhesion to the inner surface is severe, and these methods It is insufficient. Further, the method of alternately taking out the terephthalic acid slurry and flowing a gas component such as a cleaning liquid or pressurized air (for example, refer to Patent Document 4) is an intermittent extrusion method, in which the liquid feeding of the terephthalic acid slurry is intermittent and the cleaning is performed. Since the amount of the liquid is large and the solid concentration in the extracted liquid is remarkably reduced, there is a high possibility that the particle diameter of the product terephthalic acid will be adversely affected when used in a terephthalic acid production facility.

JP-A-8-89706 JP-A-8-12624 JP 2001-278449 A JP-A-11-226385

  Therefore, the present invention is a slurry transport which is the biggest problem of a method of supplying a terephthalic acid aqueous solution or a terephthalic acid slurry to a tank under a lower pressure through a pressure reducing valve or the like when the terephthalic acid slurry is handled at a high temperature and a high pressure. Proposed solution to solid deposition at piping, outlet of each tank or receiving port of each tank, crystal precipitation from solution or terephthalic acid slurry immediately after passing through pressure reducing valve, etc., and clogging of slurry transport piping accompanying this Is. That is, it is intended to provide a continuous slurry feeding method by preventing solid deposition and crystal precipitation by a simple and reliable method.

  In order to achieve the above object, the present inventors have conducted intensive studies, and as a result, at least two or more continuous tank reactors are connected in series via a slurry transport pipe having an openable / closable pressure reducing valve. In a terephthalic acid production facility having a structure in which a washing water supply pipe and a washing water flow rate regulating valve are connected to a slurry transport pipe upstream of the pressure reducing valve, a slurry of water and terephthalic acid is When transporting from a continuous tank type reaction tank to another continuous tank type reaction tank, the washing water supply pipe connected to the slurry transport pipe connecting the continuous tank type reaction tanks while continuously supplying the slurry. It was found that the above problem can be solved by a slurry feeding method characterized in that the washing water flow rate adjustment valve is adjusted and the washing water flow rate is changed while periodically supplying the washing water.

  The slurry feeding method of the present invention includes a slurry transporting pipe connected between a plurality of continuous tank-type stirred reaction tanks, a pressure reducing valve installed in this, a cleaning water supply pipe connected to the upstream side of the valve, and a cleaning By devising equipment consisting of a water flow control valve and supplying slurry continuously while supplying the washing water periodically and while changing the flow rate, crystals adhere to the slurry transport piping and pressure reducing valve. To prevent. Moreover, by using the adhering crystals mixed with washing water having a sufficient solubility, the slurry can be fed not only by impact but also without stopping the slurry transportation due to the washing effect by dissolution. At the same time, it is possible to suppress the blockage of the slurry transport pipe while suppressing the pressure fluctuation of the downstream liquid supply destination, and to continuously feed the slurry. In addition, by using pure water not containing terephthalic acid concentration or terephthalic acid at a concentration lower than the solubility of terephthalic acid whose temperature is controlled as washing water, the crystals precipitated in the slurry transport pipe can be dissolved and removed by washing, The effect of suppressing occlusion is great.

  Embodiments of the present invention will be described below with reference to the drawings. In the figure, FIG. 1 is a schematic view showing a slurry feeding method according to an embodiment of the present invention. When producing terephthalic acid by hydrolyzing dimethyl terephthalate under high temperature and high pressure in one or more continuous tank type reaction tanks, the terephthalic acid slurry in the continuous tank type reaction tanks is subjected to pressure difference or a pump. Lead to the next reactor through terephthalic acid slurry transport pipe. In the terephthalic acid production method using a hydrolysis method using dimethyl terephthalate as a raw material, the temperature in each reaction tank is usually 180 to 300 ° C., and the pressure is hydrolyzed within a range of 1.0 to 10 MPa to convert terephthalic acid. To manufacture. As shown in FIG. 1, the liquid feeding of the present invention is level-controlled so that the terephthalic acid slurry has a constant liquid holding amount in the reaction tank with respect to the amount of terephthalic acid slurry supplied. The terephthalic acid slurry transport pipe 6 has a pressure reducing valve 4 for adjusting the flow rate of the terephthalic acid slurry, and a washing water supply pipe 5 having a valve for controlling the flow rate upstream of the pressure reducing valve. Any type of pressure reducing valve may be installed in the slurry transport pipe. Furthermore, the terephthalic acid production facility is a crystallization facility in which a multistage continuous stirring tank is used, and after terephthalic acid is water-treated at 100 ° C. or higher and 0.1013 MPa or higher, a recrystallization operation is performed while gradually reducing the pressure. The case is more preferred.

  Usually, the first stage continuous tank type stirred reaction tank 1 is continuously supplied with dimethyl terephthalate and water as raw materials, and the liquid holding amount in the first stage continuous tank type stirred reaction tank 1 is constant. In this way, it is supplied to the second-stage continuous tank type stirred reaction tank 2 through the pressure reducing valve 4. At this time, a small amount of cleaning water is constantly supplied from the cleaning water supply pipe 5 connected to the upstream side of the pressure reducing valve 4 while adjusting the cleaning water flow rate adjusting valve 3. It opens for a short time, increases the supply amount of washing water, and removes the crystal adhesion to the pressure reducing valve 4 and the slurry transport pipe 6 without stopping the transport of the slurry. The time for opening the washing water flow rate adjusting valve 3 is preferably about several seconds to 60 seconds. In addition, the larger the washing water flow rate used for washing, the greater the washing effect, but the amount of washing water supplied to the second-stage continuous tank-type stirred reaction tank 2 is remarkably increased. It becomes difficult to manage the liquid holding amount and pressure of the continuous tank type stirring reaction tank 2. In addition, when the amount is small, there is no cleaning effect, and the normal flow rate of the slurry is 0.01 to 0.1 times the flow rate other than cleaning, and 0.5 to 1 times the flow rate for cleaning. It is preferable to supply washing water. Normal water is used as the washing water, and if the solubility of terephthalic acid is not exceeded, water containing terephthalic acid, for example, water in which the solute is dissolved within the range not exceeding the solubility or liquid having a lower solid concentration than terephthalic acid slurry For example, in-process circulating water may be used, and the temperature of the washing water is preferably equal to or higher than the temperature of the slurry to be fed. The purity of water is not particularly limited, and it can be sufficiently used with industrial water. By using the washing water under the above conditions, it is possible to suppress a rapid temperature change of the slurry and to efficiently prevent the clogging of the slurry transport pipe and the like. Further, when supplying the cleaning water periodically, it is also preferable to perform an operation of opening and closing the cleaning water flow rate adjusting valve at regular intervals. By repeating this operation periodically, it is possible to stably produce terephthalic acid without causing blockage accompanied by operation stop.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

[Example 1]
In a terephthalic acid production facility using a hydrolysis reaction of dimethyl terephthalate, the hydrolysis reaction is carried out in a four-stage continuous tank type reactor having a plurality of cleaning facilities as shown in FIG. A terephthalic acid slurry having a temperature of about 250 ° C., a pressure of 4 MPa, and a slurry concentration of about 50% in the reaction vessel is continuously passed through a pressure reducing valve to a second-stage reaction vessel maintained at a temperature of about 235 ° C. and a pressure of 3 MPa. Liquid was sent. Subsequently, the terephthalic acid slurry in the second-stage continuous tank-type stirred reaction tank is continuously fed to the third-stage continuous tank-type stirred reaction tank that is maintained at a temperature of about 235 ° C. and a pressure of 3 MPa by a pump. Liquid was sent. Subsequently, the terephthalic acid slurry in the third-stage continuous tank-type stirred reaction tank is passed through a pressure reducing valve, and is maintained at a temperature of about 220 ° C. and a pressure of 2.2 MPa. The solution was continuously fed. During this time, crystals of terephthalic acid gradually precipitated by recrystallization due to reduced pressure and temperature drop. Subsequently, the terephthalic acid slurry in the fourth-stage continuous tank-type stirred reaction tank was continuously fed through a pressure reducing valve to a slurry storage tank maintained at a temperature of about 100 ° C. and atmospheric pressure.

  At that time, water heated to 260 ° C. supplied from a pressure reducing valve installed in the slurry transport pipe and a wash water supply pipe connected to the upstream side of the valve is used as the wash water for each slurry transport pipe. While supplying the slurry continuously, usually the cleaning water is continuously supplied at a flow rate of 0.05 times the slurry transport flow rate, and the wash water at a flow rate of 0.5 times the slurry transport flow rate once every 20 minutes. Was fed for 20 seconds. Here, the washing water is water supplied to the terephthalic acid production facility, and the pure water does not include solutes exceeding the solubility, and the solid content contained in the slurry compared to the water in the terephthalic acid slurry. The solubility in was great. By performing this operation, it was possible to prevent terephthalic acid from adhering to the pressure reducing valve or the like without stopping the transportation of the terephthalic acid slurry, and to maintain a stable operation for a long time.

[Example 2]
In Example 1, in the slurry transport piping from the fourth-stage continuous tank-type stirred reaction tank to the slurry storage tank maintained at atmospheric pressure, the internal temperature of the fourth-stage continuous tank-type stirred reaction tank is 220. Using pure water at 225 ° C., which is higher than ℃, as the washing water, the washing water is normally supplied continuously at a flow rate 0.05 times the slurry conveyance flow rate as in Example 1, and the slurry is conveyed once every 20 minutes. By supplying cleaning water at a flow rate of 0.5 times the flow rate for 20 seconds, it was possible to prevent terephthalic acid from adhering to the pressure reducing valve, etc. without stopping slurry transportation, and to continue stable operation for a long time. .

[Comparative Example 1]
In Example 1, when the supply of cleaning water was not performed, the shutoff valve and the pressure reducing valve were blocked by a lump of slurry in which the deposits inside the device were thought to have peeled off, and long-term stable operation was not possible.

  As mentioned above, although the Example considered to be typical of this invention was described, this invention can be applied not only to the production of terephthalic acid by the hydrolysis method but also to the crystallization equipment for terephthalic acid, and only the structure of this example. However, the present invention is not limited to the above-described configuration, and can be implemented with appropriate modifications within the scope having the above-described constituent requirements according to the present invention, achieving the object according to the present invention, and having the following effects. is there.

  A method of producing terephthalic acid by hydrolysis using at least one continuous type reactor in which dimethyl terephthalate is connected in series, or terephthalic acid obtained by oxidation of para-xylene is subjected to high-temperature hydrogenation treatment to produce multistage crystals. In the method of crystallization in the precipitation tank, a pipe for supplying water with a low terephthalic acid concentration or pure water and a flow control valve are installed upstream of the flow control pressure reducing valve installed in the slurry feed pipe and washed. By periodically changing the water flow rate, the terephthalic acid slurry can be continuously fed while preventing clogging.

It is an example of the equipment used in the case of implementation of this invention.

Explanation of symbols

1 First-stage continuous tank-type stirred reaction tank (liquid source)
2 Second-stage continuous tank reaction tank (destination)
3 Flow rate adjustment valve 4 Valve on the destination side (pressure reducing valve)
5 Cleaning water supply piping 6 Slurry transportation piping

Claims (8)

  At least two or more continuous tank type reaction tanks are connected in series via a slurry transport pipe having a pressure-reducing valve that can be opened and closed for feeding liquid, and a washing water supply pipe and a wash are connected to the slurry transport pipe upstream of the pressure-reducing valve. In a terephthalic acid production facility with a structure connected to a water flow control valve, the slurry of water and terephthalic acid is transported from one continuous tank reactor to another continuous tank reactor under high temperature and pressure. While continuously supplying, adjusting the cleaning water flow rate adjusting valve in the cleaning water supply pipe connected to the slurry transport pipe connecting the continuous tank type reaction tanks, and supplying the cleaning water periodically A method for feeding a slurry, wherein the flow rate of washing water is changed.   2. The method according to claim 1, wherein the washing water uses a liquid having a lower solid concentration than the slurry of water and terephthalic acid.   The method according to claim 1 or 2, wherein the washing temperature of the washing water is equal to or higher than the temperature of the slurry comprising the water and terephthalic acid.   The method according to any one of claims 1 to 3, wherein the washing water does not contain a solute exceeding the solubility.   The method according to any one of claims 1 to 4, wherein the washing water is circulating water used in the terephthalic acid production facility or water for replenishing the production facility.   The method according to any one of claims 1 to 5, wherein the cleaning water flow rate adjustment valve is opened and closed at regular intervals when the cleaning water is supplied periodically.   The method according to any one of claims 1 to 6, wherein the terephthalic acid production facility is a facility for producing terephthalic acid by hydrolysis using dimethyl terephthalate as a raw material.   The terephthalic acid production facility is a crystallization facility in which a multistage continuous stirring tank is used, and terephthalic acid is subjected to water treatment at 100 ° C. or higher and 0.1013 MPa or higher, and then the recrystallization operation is performed while gradually reducing the pressure. The method of any one of Claims 1-6.

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