JP2004203864A - Method for supplying crude terephthalic acid solution to reaction vessel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To supply a crude terephthalic acid solution to a reaction vessel so as not to cause local thickness reduction or breakage phenomenon on the inner wall face of the vessel. <P>SOLUTION: A high purity terephthalic acid is produced by dissolving in water a crude terephthalic acid obtained by oxidizing p-xylene in an acetic acid solvent, reducing the resulting solution with hydrogen in the reaction vessel in the presence of a catalyst, and then crystallizing the reduction product followed by solid-liquid separation. In this production method, the inflow rate of the crude terephthalic acid solution to the vessel is regulated to be ≤1 m/s. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a method for supplying a crude terephthalic acid solution in a reactor in a process for producing high-purity terephthalic acid.

  In the process of producing high-purity terephthalic acid, which is a raw material for polyester, first, a crude terephthalic acid crystal is generated by dissolving para-xylene in an acetic acid solvent and oxidizing the same, and a crude terephthalic acid aqueous solution obtained by dissolving this in water is subjected to high temperature and high pressure The crude terephthalic acid is refined by passing through a packed tower reactor having a catalyst layer containing a platinum group metal under the hydrogenation reaction treatment in the reactor to obtain high-purity terephthalic acid.

  In the above step, hydrogen is supplied to the packed column reactor at a pressure higher than the reaction pressure, and a high temperature and high pressure crude terephthalic acid aqueous solution is supplied.

  In this step, if a crude terephthalic acid aqueous solution containing undissolved terephthalic acid crystals is supplied to the platinum group metal catalyst packed bed in the reactor, stable continuous operation becomes impossible. Is provided to completely dissolve the terephthalic acid crystals, and then the liquid is supplied into the reactor, or the following method is employed.

  That is, as shown in FIG. 4, a retention zone 4 partitioned by a cylindrical overflow wall 3 is provided at an upper portion of a packed tower type reactor 11, and a crude terephthalic acid aqueous solution is injected into the retention zone 4 from a supply port 12. Then, by overflowing the cylindrical overflow wall 3, only the liquid in which the terephthalic acid crystals are completely dissolved passes through the catalyst layer 2 (for example, see Patent Document 1). Reference numeral 5 in the figure is a hydrogen supply pipe connection port.

Japanese Patent No. 3232700 (Claims)

  However, in the above-described conventional method for supplying a crude terephthalic acid solution into a reactor, when a high flow rate of a crude terephthalic acid aqueous solution is supplied into the reactor, the inner wall surface of the reactor or an overflow wall in a vessel, etc. High-pressure crude terephthalic acid solution collides against the structure of the structure, and the mechanical action of erosion due to the pressure at that time and the chemical action of the high-temperature corrosive component act synergistically, resulting in so-called erosion. There is a problem that local thinning or destruction of the inner wall surface of the reactor due to corrosion (for example, a portion shown by a chain line in FIG. 4) is likely to occur.

  In practice, the operation of terephthalic acid production equipment for several months on stainless steel or other well-known corrosion-resistant alloys having a higher corrosion resistance (for example, titanium steel, Hastelloy steel, etc.) will cause such physicochemical effects. Often causes local deterioration of the inner wall of the reactor.

  Therefore, an object of the present invention is to solve the above-mentioned problems, and when a crude terephthalic acid aqueous solution is supplied to a reactor, local thinning or destruction of the inner wall surface of the reactor does not occur. Is to do so.

  In order to solve the above-mentioned problems, in the present invention, crude terephthalic acid obtained by oxidizing para-xylene in an acetic acid solvent is dissolved in water, and this liquid is reduced with hydrogen in the presence of a catalyst in a reactor. In the method of supplying the crude terephthalic acid solution into the reactor in the process of producing high-purity terephthalic acid for crystallization and solid-liquid separation of the reduced product, the flow of the crude terephthalic acid solution into the reactor This is a method for supplying a crude terephthalic acid solution into the reactor in the process of producing high-purity terephthalic acid, wherein the speed is set to 1 m / s or less.

  According to the method for supplying the crude terephthalic acid solution into the reactor configured as described above, the crude terephthalic acid solution contacts the inner wall surface of the reactor at a flow rate of 1 m / s or less. Therefore, the burden on the inner wall surface of the reactor due to the liquid pressure and the flow of the crude terephthalic acid solution, which is usually heated to 230 ° C. or higher, is reduced, and the local inner wall surface of the reactor is reduced by so-called erosion and corrosion. Meat or destruction phenomena are less likely to occur.

  In order to more reliably perform such an operation, a dispersing device for the liquid flow is provided in the reactor, and the flow rate of the crude terephthalic acid solution by the above-described production process in which the inflow speed of the crude terephthalic acid solution is reduced. It is preferable to adopt a method of supplying the solution into the reactor, whereby the burden on the inner wall surface of the reactor is surely reduced.

Further, the dispersing apparatus has a supply port to which a supply pipe for the crude terephthalic acid solution is connected, and a plurality of dispersion ports opened in the reactor, and has an area S of the supply port and a plurality of dispersion ports. More preferably, the method is a method of supplying a crude terephthalic acid solution, which is a dispersing device, designed to have a ratio to the total area S _{A of the} mouth (S _A / S) exceeding 1, into the reactor.

By doing so, the flow velocity at the dispersion port is surely slower than the flow velocity at the supply port, and by adjusting the ratio (S _A / S), the crude terephthalic acid solution that has passed through the dispersion apparatus is surely removed. The flow velocity can be reduced.

  Further, as a preferable structure of the dispersing device, a dispersing device in which a supply pipe is connected to an annular pipe and a plurality of dispersing ports are formed by penetrating through the peripheral wall surface of the annular pipe may be adopted. According to the method for supplying the crude terephthalic acid solution into the reactor employing such a dispersing device, the crude terephthalic acid solution can be supplied from the peripheral wall surface of the annular tube toward various directions of the reactor inner wall, At this time, the inflow pressure can be dispersed and supplied at a low inflow speed.

  As described above, in the present invention, the supply of the crude terephthalic acid solution in the production process of high-purity terephthalic acid is performed at a flow rate of 1 m / s or less into the reactor. The burden on the inner wall of the reactor due to the liquid pressure and liquid flow of the high temperature crude terephthalic acid solution is reduced, and there is an advantage that local wall thinning or destruction phenomenon is less likely to occur on the inner wall of the reactor. .

  In addition, the above effects can be more reliably achieved by providing a liquid flow dispersing device in the reactor to reduce the inflow speed of the crude terephthalic acid solution.

Further, a dispersing device for a liquid stream is provided in the reactor to reduce the inflow rate of the crude terephthalic acid solution, and the ratio of the area S of the supply port of the dispersing apparatus to the total area S _A of the plurality of dispersing ports ( By designing S _A / S) to exceed 1, the burden on the inner wall surface of the reactor is surely reduced.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
In the step of producing high-purity terephthalic acid, first, crude terephthalic acid obtained by oxidizing para-xylene in a liquid phase is dissolved in water, and this crude terephthalic acid aqueous solution is subjected to a catalyst layer in the reactor 1 at high temperature and high pressure. 2 to reduce with hydrogen. The supply of the crude terephthalic acid solution in the process of producing high-purity terephthalic acid for crystallization and solid-liquid separation of the reduced product is performed at a flow rate of 1 m / s or less into the reactor 1. . A preferred inflow velocity is 0.9 m / s or less, and a more preferred inflow velocity is 0.8 m / s. On the other hand, if the inflow velocity is too low, the dispersion apparatus itself becomes too large. Therefore, the lower limit of the inflow velocity is preferably 0.1 m / s, more preferably 0.2 m / s.

  The oxidation reaction of para-xylene is usually performed by reacting para-xylene with molecular oxygen in an acetic acid solvent, for example, in the presence of a catalyst containing cobalt, manganese, and bromine, usually at a temperature of 170 to 230 ° C. The SD method can be adopted. The crude terephthalic acid obtained by this reaction is a crystalline terephthalic acid which generally contains 4-carboxybenzaldehyde (hereinafter referred to as “4CBA”) as an impurity in an amount of 1000 to 5000 ppm by weight.

  Terephthalic acid has low solubility at normal temperature and pressure, and it is necessary to raise the temperature and pressure to increase the solubility of terephthalic acid.A general method for obtaining an aqueous solution of crude terephthalic acid includes the following method. Can be illustrated.

  First, crude terephthalic acid is mixed with water at a ratio of 10 to 40% by weight to form a slurry. Next, this slurry is pressurized to the reaction pressure plus α pressure (plus α is a pressure in consideration of the pressure loss until reaching the reactor) by a pressurizing pump, and heated by a combination of a multi-tube heat exchanger. Supply to dissolution process. The temperature rise by heating is carried out stepwise up to a predetermined reaction temperature, preferably by a plurality of heat exchanger groups, and the temperature of the crude terephthalic acid solution becomes 230 ° C. or higher.

  The crude terephthalic acid aqueous solution obtained as described above is passed through a packed tower type reactor 1 in which a catalyst layer 2 containing a platinum group metal is accommodated, and the crude terephthalic acid is subjected to a hydrogenation reaction treatment in the reactor 1. Purify the acid. Here, 4CBA in the crude terephthalic acid aqueous solution is reduced with hydrogen to paratoluic acid.

  The catalyst containing a platinum group metal is selected from palladium, ruthenium, rhodium, osmium, iridium, platinum and the like, or a metal oxide thereof. These metals or metal oxides can be used directly as a catalyst, but those supported on a carrier such as activated carbon at about 0.2 to 10% by weight are particularly effective. The temperature as the reaction condition is 200 to 400 ° C., preferably 230 to 350 ° C., and the pressure may be a pressure that can be maintained as a liquid, and is 1.6 MPa or more, preferably 2.8 to 16.5 MPa. . Hydrogen is pressurized above the reaction pressure and supplied into the reactor.

  As shown in FIGS. 1 to 3, the packed tower type reactor 1 of the embodiment has a retention zone 4 of a crude terephthalic acid aqueous solution partitioned by an overflow wall 3 at an upper inlet portion. 4 has a catalyst layer 2 serving as a reaction zone below.

  As shown in FIGS. 2 and 3, the upper inlet portion of the packed tower type reactor 1 will be described in detail. The dome-shaped upper space of the reactor 1 having the hydrogen supply pipe connection port 5 at the top is a disk. The stagnation zone 4 and the reaction zone 10 below the stagnation zone 4 are partitioned by a mold partition plate 6, and the cylindrical overflow wall 3 stands upright in the center of the partition plate 6.

  A solution supply pipe 7 for crude terephthalic acid penetrates the side wall of the retention zone 4 and is connected to an annular pipe 8 of the dispersing device. The annular pipe 8 is shown as having a small number of holes 9 formed in the peripheral wall surface of a cylindrical pipe, but other shapes such as a cylindrical or polygonal cylindrical pipe are connected in a polygonal shape. It may be a known ring shape.

The ratio (S _A / S) of the area S of the inner diameter of the supply pipe 7 to the total area S _A of the plurality of small holes 9 of the annular pipe 8 is designed to exceed 1. When the flow rate of the crude terephthalic acid solution in the pipe 7 is 1.1 m / s or more, the flow rate flowing out of the small holes 9 is designed to be 1 m / s or less. _A preferred value of S _A / S is 1.1 or more, and a more preferred value is 1.5 or more. Further, if S _A / S is too large, the dispersion apparatus itself becomes too large. Therefore, the upper limit of S _A / S is preferably 10 and more preferably 5.

  Due to such an upper structure of the reactor 1, the solution supplied into the retention zone 4 rises along the overflow wall 3 and finally overflows and is supplied to the reaction zone 10 below the partition plate 6. At this time, even if there are undissolved crystal particles, the particles settle and stay at the lower part of the stay zone 4, are mixed and dissolved by the solution flow supplied thereto, and do not overflow as they are.

  As described above, the flow rate of the crude terephthalic acid solution flowing out of the small holes 9 of the annular tube 8 is 1 m / s or less, and the overflow terephthalic acid solution contacts the overflow wall 3 and the upper side wall of the reactor 1 at the flow rate or less. The burden on the inner wall surface of the reactor due to the liquid pressure and liquid flow of the high-temperature crude terephthalic acid solution is reduced, and local wall thinning or destruction of the inner wall surface of the reactor 1 is unlikely to occur.

  The terephthalic acid solution that has normally overflowed in this way is purified through the reaction zone 10, specifically, the catalyst layer 2, and flows out of the system from the lower outlet of the reactor. This effluent is usually recovered through further crystallization, solid-liquid separation and drying steps as purified terephthalic acid crystals.

[Example 1]
A slurry of raw terephthalic acid as a raw material in an aqueous solution concentration of 30% by weight was raised to a pressure of 9 MPa, heated to 285 ° C. by a multitubular heat exchanger, and this slurry was filled with the structure shown in FIGS. The solution was supplied to a tower type solution supply pipe. The reactor had a tower diameter of 1.26 m, a height of 10 m, and a height of the catalyst layer of 7 m. The structure of the retention zone was such that the height of the overflow wall was 0.7 m and the diameter of the downcomer was 0.3 m. The material of the reactor body is clad steel in which SUS304 of 7 mm is laminated on carbon steel, and the material of the overflow wall is titanium steel.

Then, the crude terephthalic acid solution stays in the upper part of the reactor at a rate of 0.5 to 0.7 m / s through a number of small holes formed on the peripheral wall surface of the annular disperser made of titanium (S _A /S=1.8). The hydrogen gas was supplied while being dispersed in the zone, overflowed, and hydrogen gas was supplied from the space inside to the reaction zone.
The reaction conditions were a pressure of 8.0 MPa, a temperature of 285 ° C., a hydrogen partial pressure of 0.8 MPa, and 0.5% palladium / carbon as a catalyst.
Under these conditions, the continuous operation was performed for about 150 days. However, there was no local thinning or destruction of the inner wall of the reactor due to erosion and corrosion in the reactor, and high-quality purified terephthalic acid was obtained.

[Example 2]
The hydrogenation reaction was carried out in the same manner as in Example 1, except that the annular pipe of the dispersion device was changed to a hexagonal pipe as shown in FIG. 5 (S _A /S=1.6). The crude terephthalic acid solution was supplied at a rate of about 0.7 m / s to a retention zone above the reactor.
After continuous operation for 150 days, no local wall thinning or destruction of the inner wall of the reactor due to erosion and corrosion in the reactor was observed, and high-quality purified terephthalic acid was obtained.

[Comparative Example 1]
In the examples, continuous operation was performed for about 90 days under exactly the same conditions except that the crude terephthalic acid solution was directly supplied to the reactor at 1.1 m / s from the solution supply port without using the annular tube of the dispersion apparatus. went.
As a result, there was a local wall thinning phenomenon due to erosion and corrosion at the overflow wall portion in the reactor, and a 7 mm thick SUS304 layer was cut off at a part of the wall.

[Comparative Example 2]
In Example 1, except that the crude terephthalic acid solution was supplied to the reaction device from the tangential direction at 1.1 m / s from the solution supply port as shown in FIG. 6 without using the annular tube of the dispersion device. Carried out a hydrogenation reaction in the same manner.
After 150 days of continuous operation, a local wall thinning phenomenon due to erosion and corrosion was observed on the inner wall of the reactor near the solution supply port, and a 7 mm thick SUS304 layer was formed on a part of the inner wall of the reactor. Had been shaved off.

[Comparative Example 3]
A hydrogenation reaction was carried out in the same manner as in Comparative Example 2, except that the material of the reactor was changed to clad steel in which 5 mm of SUS304 and 2 mm of titanium were laminated in this order on carbon steel.
After continuous operation for 150 days, a local wall thinning phenomenon due to erosion and corrosion was observed on the inner wall of the reactor near the solution supply port, and a part of the inner wall of the reactor was a 2 mm titanium layer and 5 mm SUS304 layer was scraped off.

Schematic diagram for explaining the structure of the reactor of the embodiment Longitudinal sectional view showing the upper structure of the reactor of the embodiment FIG. 2 is a sectional view taken along line III-III in FIG. 2. Schematic diagram illustrating the structure of a conventional reactor Cross-sectional view showing a superstructure of a reactor according to another embodiment Cross-sectional view showing the upper structure of another conventional reactor

Explanation of reference numerals

Reference numerals 1 and 11 Reactor 2 Catalyst layer 3 Overflow wall 4 Retention zone 5 Hydrogen supply pipe connection port 6 Partition plate 7 Solution supply pipe 8 Annular pipe 9 Small hole 10 Reaction zone 12 Supply port

Claims (6)

Crude terephthalic acid obtained by oxidizing para-xylene in acetic acid solvent is dissolved in water, this liquid is reduced in a reactor with hydrogen in the presence of a catalyst, and the reduced product is crystallized and solid-liquid separated. In a method for supplying a crude terephthalic acid solution in a reactor in a process of producing high-purity terephthalic acid,
A method for supplying a crude terephthalic acid solution into a reactor in a process for producing high-purity terephthalic acid, wherein the flow rate of the crude terephthalic acid solution into the reactor is 1 m / s or less.   The method according to claim 1, wherein the crude terephthalic acid solution is a crude terephthalic acid solution heated to 230 ° C or higher.   The method for supplying a crude terephthalic acid solution into a reactor according to claim 1 or 2, wherein a liquid flow dispersing device is provided in the reactor to reduce the inflow rate of the crude terephthalic acid solution. The dispersing apparatus has a supply port to which a supply pipe for the crude terephthalic acid solution is connected, and a plurality of dispersion ports that open into the reactor, and the area S of the supply port and the total area of the plurality of dispersion ports S ratio of _a (S _a / S) is, the method of supplying into the reactor crude terephthalic acid solution according to 1, which is a dispersing device which is designed to exceed the claims 3.   The supply of the crude terephthalic acid solution into the reactor according to claim 4, wherein the dispersing device is a dispersing device in which a supply pipe is connected to an annular pipe and a number of dispersion ports penetrating through the peripheral wall surface of the annular pipe are formed. Method.   A method for producing terephthalic acid using the method for feeding into a reactor according to claim 1.

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