WO2011004429A1

WO2011004429A1 - Method for refining crude terephthalic acid

Info

Publication number: WO2011004429A1
Application number: PCT/JP2009/003153
Authority: WO
Inventors: 原徳明; 豊嶋弘幸; 山▲崎▼初太郎
Original assignee: 株式会社日立プラントテクノロジー
Priority date: 2009-07-07
Filing date: 2009-07-07
Publication date: 2011-01-13
Also published as: CN102548947B; CN102548947A

Abstract

With current methods for manufacturing refined terephthalic acid by means of a hydrogenation reaction of a crude terephthalic acid aqueous solution by means of a precious-metal-supporting activated carbon catalyst, excessive condition settings and extra equipment are used for setting safely in order to ensure quality when setting the hydrogenation reaction conditions based on an increase in production, new equipment or other variations in the amount of production. Disclosed is a method for refining crude terephthalic acid having more economical reaction conditions and stable quality with good reproducibility. With the method for refining crude terephthalic acid, crude terephthalic acid is dissolved in water to form an aqueous solution that is then supplied together with hydrogen gas to the top of an activated carbon catalyst layer. Said aqueous reaction solution is supplied until it rises above the catalyst layer, and by means of a type of reaction vessel that forms/retains a hydrogen-containing gas phase portion above the surface of said aqueous solution, said aqueous solution dissolves (absorbs) hydrogen contained in the upper gas phase portion from the gas-liquid interface, after which the hydrogenation reaction occurs while said solution flows down through the catalyst layer. In addition, the hydrogenation reaction occurs while the hydrogen partial pressure of the gas phase portion at the upper part of the catalyst layer is maintained, based on its relationship with the downward superficial velocity of the respective reaction liquid, in a partial pressure range that is calculated based on the correlation of the hydrogen partial pressure (H2.PP) with the downward superficial velocity (LV), and with the superficial velocity of said aqueous reaction solution that flows down through the catalyst layer introduced as a determining condition.

Description

Method for purifying crude terephthalic acid

The present invention relates to a method for producing reproducible and stable purified terephthalic acid by a stable hydrogenation reaction when crude terephthalic acid is brought into contact with a noble metal-supported activated carbon catalyst as an aqueous solution and hydrorefined. In particular, it relates to the production of purified terephthalic acid with stable quality by supplying the optimum amount of hydrogen necessary for the purification reaction in a hydrogenation reactor at a stable rate. In response to the above, hydrogenation conditions for economically producing purified terephthalic acid of stable quality with a hydrogen partial pressure following the supply amount of the refined raw material are set.

Crude terephthalic acid produced by liquid phase oxidation using p-xylene as a starting material in an acetic acid solvent in the presence of an oxidation catalyst with an oxygen-containing gas is a reaction intermediate 4-carboxybenzaldehyde (4-CBA). ) And coloring side reaction products are contained in trace amounts, so after dissolving in water at high temperature and high pressure to form an aqueous solution, dissolve the hydrogen gas in a hydrogen gas atmosphere, Hydrogenation reaction is carried out by contact. Then, after the impurities in the solution are converted or decomposed into a substance soluble in water, the aqueous reaction solution is cooled to produce crystals of terephthalic acid, and after solid-liquid separation, the impurities are collected. Reduced purified terephthalic acid (powder) is produced industrially.
The purified terephthalic acid has been produced industrially on a large scale as a raw material for the production of polyethylene terephthalate (PET) as a polyester for a fiber or a container for a film or a container, as demand and applications expand.
For this reason, in order to increase production at refined terephthalic acid production equipment and production at new production facilities, the quality of the purified terephthalic acid produced will deviate from the target quality, which requires pressure equipment that exceeds the setting. Equipment modifications may be required. At the same time, the specific conditions for the hydrogenation reaction of crude terephthalic acid, which stably produces the target quality, have not been clarified against fluctuations in the amount of raw material supplied to the hydrogenation reactor.
Although the hydrogenation reactor for purifying crude terephthalic acid is a gas-liquid reaction on a catalyst layer packed with a noble metal-supported activated carbon catalyst, it passes through the catalyst layer as seen in the proposal below. This is thought to be the result of conducting a search for hydrorefining reaction conditions without clarifying the fluid flow state.

Incidentally, in gas-liquid contact reactions using a catalyst layer, the reaction liquid flows down as droplets (Trickling) in the reaction gas flow atmosphere (gas continuous phase) and the reaction liquid flow (liquid continuous phase). There are a system in which the reaction gas passes through the catalyst layer as a bubble (Bubbling), or a system in which the reaction gas and the reaction liquid are forcibly supplied to flow in the catalyst layer in a mixed phase flow.
According to Patent Document 1 (US Pat. No. 3,639,465), a method for purifying crude terephthalic acid is a method in which an aqueous solution of crude terephthalic acid is about 10 ° F. above the temperature at which the aqueous solution first precipitates crystals (about 440 ° It is said that the hydrorefining reaction is carried out by allowing the aqueous solution to pass through the catalyst layer together with hydrogen gas at a pressure at which the aqueous solution maintains the liquid phase.

The hydrorefining reaction is preferably a refining reaction in which the aqueous solution drops a catalyst layer in a hydrogen gas continuous atmosphere (Trickle), and the hydrotreating time of the aqueous solution in the catalyst layer (Hydrogenation treatment time) ) Or space velocity is about 0.001 to 10 hours, preferably 0.01 to 2 hours. The hydrogen partial pressure in the gas atmosphere is 14.7 to 150 psi or more.

On the other hand, in Patent Document 2 (US Pat. No. 4,405,809), the conditions of the reaction in hydrorefining are almost the same as the above proposal, but the dissolved hydrogen in the crude terephthalic acid aqueous solution is about 10 to 75% dissolved hydrogen with respect to saturation. Hydrogen gas is supplied so as to maintain the concentration, and the purification reaction is performed by a liquid single-phase flow (liquid continuous phase) method in which a gas phase (gas atmosphere phase) does not exist and the catalyst layer is filled with the aqueous solution.

According to the reaction mode, the amount of hydrogen gas used is reduced, and purified terephthalic acid having a reduced ΔY value (an index of the amount of carbon (black) particles in the purified terephthalic acid) is obtained.
However, as the inventors have stated, the saturation amount of dissolved hydrogen in the crude terephthalic acid aqueous solution varies depending on the temperature, pressure (hydrogen partial pressure) and terephthalic acid concentration, and is a difficult factor to measure as the reaction conditions.

The amount of hydrogen gas used in this purification process is described in Patent Document 3 (US Pat. No. 6,407,286) in the hydrogenation (reduction) of impurities (4-CBA, colored by-products, etc.) dissolved in the reaction aqueous solution. Suppose that more hydrogen is used than required, specifically one of the stoichiometrically required amounts of 4-CBA dissolved in crude terephthalic acid aqueous solution to p-toluic acid. It is said that up to 7 moles of hydrogen will be used.

Therefore, the reaction in which 4-CBA is reduced to p-toluic acid is as follows:

The stoichiometric amount required to hydrogenate 4-CBA to p-toluic acid is 2 molar times that of 4-CBA, so to purify an aqueous solution of crude terephthalic acid, This is equivalent to using 3 to 9 mole times.

Therefore, Patent Document 3 (US Pat. No. 6,407,286) proposes a method for recovering and reusing hydrogen discharged as a surplus after the purification reaction. Furthermore, in Patent Document 4 (U.S. Pat. No. 4,626,598) in which influential factors for the hydrorefining reaction were examined in detail, the color level of the purified terephthalic acid (Color scale “ It is proposed to measure the b-value ") and adjust the hydrogen concentration (hydrogen gas flow rate, hydrogen partial pressure) of the aqueous reaction solution in order to maintain the color level.

In a liquid single-phase reaction system in which a hydrogenation reactor is filled with a crude terephthalic acid aqueous solution (Hydraulically full reactor), the hydrogen gas flow rate is adjusted, and the crude terephthalic acid is fed into the reactor. In the reaction mode in which the aqueous solution is not filled, it is proposed to adjust the color level of the purified terephthalic acid crystal to a predetermined value (predetermined color scale) by adjusting the hydrogen gas partial pressure. In other words, this is a method of adjusting the hydrogen partial pressure with respect to the change in the color level b-value and performing the purification result.

As described above, in the hydrorefining reaction of crude terephthalic acid, a range of conditions such as temperature, pressure, hydrogen / 4-CBA molar ratio, and hydrotreating time (Space velocity) as the reaction conditions have been proposed, It also proposes the control of reaction conditions to support the production of stable quality purified terephthalic acid.

U.S. Pat.No. 3,639,465 U.S. Pat.No. 4,405,809 U.S. Pat.No. 6,407,286 U.S. Pat.No. 4,626,598

However, it cannot be said that the range of these setting conditions alone is sufficient to economically produce purified terephthalic acid with stable quality in response to an increase in the supply of raw terephthalic acid, and the color of purified terephthalic acid. A feedback control method is used in which conditions are controlled based on monitoring results such as levels.

Therefore, the quality of the purified terephthalic acid cannot be guaranteed against the change in production volume (mainly increased production) in the existing equipment and the reaction conditions of the hydrorefining reactor in the new production facility. This could result in non-standard manufacturing. The current situation is that excessive conditions are set for safety setting, and there are excessive facilities.

Under the circumstances as described above, the present inventors based this hydrorefining reaction on the basis of a catalytic reaction between a gas phase and a liquid phase via a solid catalyst, and the reaction by the Langmuir-Hinshelwood mechanism proceeds. Assuming that the reaction substrate (4-CBA) and hydrogen are each adsorbed and activated on the catalyst and react, the dynamic conditions such as the flow and reactivity of the aqueous raw material solution are assumed. I realized that there was not enough knowledge about.

That is, under the conventional reaction conditions, hydrogen dissolves and diffuses in the reaction aqueous solution and reaches the catalyst, so the hydrogen partial pressure that is the driving force for dissolving hydrogen gas is regarded as one of the reaction factors. However, it does not capture the flow of the reaction aqueous solution on the catalyst which affects the diffusion in the solution. Similarly, there is no knowledge about the diffusion and adsorption of the reaction substrate (4-CBA) in the solution and the flow of the solution on the catalyst as an influence factor on the desorption and diffusion of the reaction product.

It is not limited to either the drop-down method (Trickling reactor gas continuous phase) or the liquid filling method (Hydraulically full reactor liquid continuous phase), and the hydrogenation time or space velocity of the reaction solution is about 0.001 to 10 hours. It is said that the contact reaction in the solid catalyst is preferably carried out between about 0.01 to 2 hours, and the apparent residence time in the relationship between the reaction liquid supply amount (volume) and the catalyst capacity, that is, space time (space This is because it is only prescribed by (speed).

Generally, the space velocity (Space velocity hr ^-1 ) in the catalyst layer (contact) reaction is obtained by dividing the reaction solution supply rate (m ³ / hr) by the catalyst layer capacity (m ³ ) as one index. The reciprocal space time (Space time hr) is treated as an apparent processing time.

Therefore, the setting of the hydrotreatment time (apparent residence time) in the catalytic reaction of about 0.001 to 10 hours, preferably about 0.01 to 2 hours is about 0.1 to 1000 (hr ^{− 1} ), preferably in a wide range corresponding to about 0.5 to 100 (hr ⁻¹ ). For this reason, no mention is made of the flow velocity which is an index of the reaction liquid flow as an influencing factor for diffusing in the liquid on the catalyst surface.

Incidentally, even in the same space velocity (same space time), the flow rate of the reaction liquid in the catalyst layer and the flow on the catalyst surface greatly differ depending on the cross section (diameter) of the reactor as well as the above different reaction methods.

Therefore, unless reproducibility of the flow of the reaction liquid is taken into consideration in the production increase or the new production which is the subject of the present invention, the economic production of the purified terephthalic acid having a stable reactivity and quality can be guaranteed. The present inventors have realized that this was not the case. Based on the assumed reaction mechanism of the hydrorefining reaction, the present inventors consider that the reaction substrate (4-CBA) and hydrogen are directly influencing the diffusion process of diffusion, adsorption, reaction, and desorption on the catalyst surface. The goal is to find the stricter hydrogenation reaction conditions corresponding to fluctuations in the feed rate and other conditions in the purification reaction of crude terephthalic acid, taking the liquid flow rate as one of the reaction conditions.

The present invention provides a method for purifying crude terephthalic acid, which enables economical production of purified terephthalic acid having stable and reproducible reactivity and quality.

For this reason, the inventors of the present hydrogenation reaction, which is a contact reaction between a gas phase and a liquid phase that have a complicated flow, have the reaction aqueous solution up to the catalyst layer as a reaction method in which the flow of the reaction aqueous solution is reproducibly and most stable. The hydrogen-containing gas phase is filled on the surfaces of the aqueous solution, and the reaction aqueous solution in which hydrogen is dissolved (absorbed) from the gas-liquid interface (liquid surface) continuously flows down in the catalyst layer to advance the purification reaction. The method is limited to

Then, a crude terephthalic acid aqueous solution and hydrogen gas are continuously supplied from the upper part of the reactor, and supplied to the upper part of the catalyst layer. A liquid surface of the aqueous solution and a hydrogen-containing gas phase part (gas phase part) are formed on the upper part of the liquid surface. By maintaining the solution, the stable supply of the aqueous solution ensures the stable flow rate of the catalyst layer, and the hydrogen corresponding to the hydrogen partial pressure is dissolved (absorbed) from the liquid surface constantly, resulting in a more stable purification reaction. Will progress.

The inventors of the present invention achieve the object of the present invention by pursuing the influence of the relationship between the flow rate of the catalyst layer of the aqueous reaction solution (the apparent superficial velocity of the reactor) and the hydrogen partial pressure on the purification reaction according to the above reaction method. I decided to find out the conditions.

First, the present inventors measured the terephthalic acid concentration of the reaction aqueous solution (terephthalic acid aqueous solution) and the vapor pressure (water vapor pressure) at each (reaction) temperature, which are the key to accurate measurement of the hydrogen partial pressure in the purification reaction. It was.

The hydrogen partial pressure in the hydrorefining reaction can be obtained as a pressure difference between the reactor pressure (reaction pressure) at each reactor temperature (reaction temperature) and the vapor pressure (Table 1) of the aqueous reaction solution (terephthalic acid aqueous solution). .

The reactor pressure at each reaction temperature consists of the sum of the vapor pressure and hydrogen partial pressure of the aqueous solution without using Raoult's law because the vapor pressure of the aqueous solution and the vapor pressure of hydrogen gas are far apart. ing.

Therefore, the inventors measured the vapor pressure of the crude aqueous terephthalic acid solution by changing the amount of dissolved terephthalic acid (concentrations: 23.1 wt%, 27.0 wt%, 30.0 wt%). The measurement results are as shown in Table 1.

Note that the vapor pressure of the crude terephthalic acid aqueous solution is lower than the vapor pressure of water due to the effect of increasing the boiling point by dissolution of terephthalic acid, and decreases as the amount of terephthalic acid dissolved increases. However, since terephthalic acid did not reach full dissolution up to 285 ° C like an aqueous solution with a terephthalic acid concentration of 30 wt%, the vapor pressure was measured by partial dissolution.

In this setting, it was assumed that the hydrogen gas was supplied with pure hydrogen without being diluted with an inert gas (N ₂ ), but if the gas was diluted with N 2 gas, the reaction pressure and the vapor of the aqueous solution The pressure difference from the pressure becomes the gas pressure, and the hydrogen partial pressure can be obtained as the product of the gas pressure and the hydrogen gas ratio in the gas.

Next, the present inventors regard the flow of the supplied crude terephthalic acid aqueous solution on the catalyst layer as the diffusion factor in the flow of dissolved hydrogen and the reaction substrate over the catalyst surface as the apparent linear velocity (reactor superficial velocity) of the reactor. The purification effect by the measured hydrogen partial pressure and reactor superficial velocity was analyzed. At the same time, the hydrogen supply amount, that is, the hydrogen absorption amount in this reaction method was measured and confirmed.

As a result, the reactor superficial velocity (LV = 41.1) was also obtained in hydrorefining reactions (Examples 1 and 2) with greatly different crude terephthalic acid aqueous solution supply amounts (slurry supply amounts) in facilities with different production scales of purified terephthalic acid. m / hr, 44.4m / hr) and hydrogen partial pressure (10.3Kg / cm ² , 10.9Kg / cm ² ) were made the same (closer), and the hydrogen gas absorption and purification effect could be reproduced. .

Also, the hydrogen gas absorption amount and the purification effect are maintained by changing the hydrogen partial pressure in response to the change in the supply amount (slurry supply amount) of the crude terephthalic acid aqueous solution, that is, in response to the reactor superficial velocity. Or could be reproduced (see FIG. 2). FIG. 2 is a plot of the 4-CBA content in the purified terephthalic acid according to the example in relation to the partial pressure of hydrogen (H2PP) with the superficial velocity (LV) as a parameter. In addition, the 4-CBA content of the purified terephthalic acid in the comparative example in which the 4-CBA content is out of product specifications was plotted as 27 ppm.

Based on the results of the production of purified terephthalic acid by the reaction method as described above (reaction liquid continuous flow method in which the gas phase part is held on the upper part of the catalyst layer), the present inventors have developed a gas phase on each surface of the reaction aqueous solution. It was confirmed that the amount of hydrogen gas absorbed and the reaction rate of hydrogenation were balanced by the partial pressure of hydrogen and the flow rate of the reaction aqueous solution (superficial velocity), and a stable purification effect was exhibited.

For this reason, the present inventors conducted a hydrogenation reaction on the results of the purification of a crude aqueous terephthalic acid solution, taking the superficial velocity (LV) and hydrogen partial pressure (H2.PP) of the reaction aqueous solution as reaction factors. Figure 3 shows the partial pressure plot of hydrogen partial pressure (H2.PP) at superficial velocity (LV), distinguishing differences in reactor, hydrogen gas absorption (hydrogen / 4-CBA molar ratio) and terephthalic acid concentration. It became as shown in. As a result, in the purification reaction of the crude aqueous terephthalic acid solution, a relational expression between the superficial velocity (LV) and the hydrogen partial pressure (H2.PP) under the catalyst laminar flow of the reaction aqueous solution was obtained as follows.

And, in a method of hydrorefining a crude terephthalic acid aqueous solution through a hydrogenation reactor packed with a precious metal-supported activated carbon catalyst,
Fill the catalyst layer with a crude aqueous terephthalic acid solution, hold the hydrogen-containing gas phase part above the aqueous solution,
The hydrogen partial pressure (H2.PP) in the gas phase is maintained in the following relationship with the superficial velocity (LV) at which the aqueous solution flows down the catalyst layer:
(H2PP) = -0.000550 x (LV) ² +0.299 x (LV)-1.48 (1)
It has been found that the hydrogenation reaction is preferably a purification of crude terephthalic acid.

That is, the hydrogen partial pressure (H2PP) in the upper gas phase is based on the above relational expression (1) corresponding to the flow velocity (superficial velocity LV) at which the crude aqueous terephthalic acid solution flows down the catalyst layer of the hydrogenation reactor. It has been found that there is a correlation in which a stable quality of purified terephthalic acid (4-CBA content approximately 15 ppm) can be obtained by maintaining the partial pressure (Claim 3).

Also, if the hydrogen partial pressure (H2PP) in the upper gas phase becomes the partial pressure according to the following relational expression (2), the hydrogen gas absorption amount will decrease (hydrogen / 4-CBA molar ratio about 3), and the purified terephthalic acid It was suggested that the quality deteriorated (4-CBA content about 20 ppm).
(H2PP) = -0.000413 x (LV) ² +0.224 x (LV)-1.11 (2)
Therefore, by performing the hydrogenation reaction at a hydrogen partial pressure that does not satisfy the above relational expression (2) (region F in FIG. 3), non-product specification (4-CBA content> 25 ppm Comparative Examples 1, 2, 3, 4 ) Of purified terephthalic acid may be produced, and since the reaction proceeds without absorbing the hydrogen required for the purification reaction, there is a possibility of generation of new impurities and catalyst deterioration due to lack of hydrogen. It has been suggested. This suggests that purified terephthalic acid within the product specification is produced by performing the hydrogenation reaction at a hydrogen partial pressure equal to or higher than the relational expression (2) (claim 1).

And the hydrogen partial pressure (H2.PP) in the hydrogen-containing gas phase part is maintained at the partial pressure of the following relational expression (3) with the superficial velocity (LV) under the flow of the crude terephthalic acid aqueous solution,
(H2.PP) = - 0.0020 × ( LV) 2 + 0.569 × (LV) -1.93 (3)
Hydrogen gas absorption by hydrogenation reaction increases (hydrogen / 4-CBA molar ratio about 9) and 4-CBA content in purified terephthalic acid tends to decrease (about 10ppm). If the partial pressure of (3) is exceeded (region E in Fig. 3), it is suggested that the hydrogen partial pressure produced by purified terephthalic acid with a low 4-CBA content but excessive quality is maintained. It was done.

Therefore, it can be seen that maintaining the hydrogen partial pressure exceeding the partial pressure of the above relational expression (3) and hydrogenating is a hydrorefining reaction that consumes excess hydrogen for the purification of crude terephthalic acid. It was also suggested that it would cause severe hydrogenation due to excess hydrogen. This suggests that purified terephthalic acid within the product specification can be produced economically by carrying out the hydrogenation reaction at a hydrogen partial pressure equal to or lower than the relational expression (3) (Claim 2).

Therefore, the hydrogen partial pressure (H2.PP) in the hydrogen-containing gas phase part is in the range between the relational expression (2) and the relational expression (3) with respect to the superficial velocity (LV) under the flow of the crude aqueous terephthalic acid solution (in FIG. 3). A method for purifying crude terephthalic acid in which hydrogenation reaction is carried out while maintaining the hydrogen partial pressure in region C) can be a preferred method (claim 2). That is, the range is expressed as a relational expression as follows. −0.0020 × (LV) ² + 0.569 × (LV) −1.93 ≧ (H2.PP) ≧ −0.000413 × (LV) ² + 0.224 × (LV) −1.11
On the other hand, in the hydrorefining reaction of a crude terephthalic acid aqueous solution, the above relational expression (2) of the hydrogen partial pressure (H2PP), which is considered to be the limit for producing a purified terephthalic acid with a preferable quality (4-CBA content about 20 ppm), This corresponds to a relationship of approximately −25% of the partial pressure in the above relational expression (1), which is a hydrogen partial pressure (H2PP) preferable for the purification of terephthalic acid.

Therefore, the hydrogen partial pressure that produces a stable and reproducible quality of purified terephthalic acid is ± 25% of the relational expression (1) above with the flow rate (superficial velocity LV) of the catalyst layer of crude terephthalic acid. It is preferable to perform the hydrorefining by setting the hydrogen partial pressure (H2PP) within the range (region B in FIG. 3) (Claim 3). That is, the range is expressed as a relational expression as follows.
(−0.000550 × (LV) ² + 0.299 × (LV) −1.48) × 0.75 ≦ (H2.PP) ≦
(−0.000550 × (LV) ² + 0.299 × (LV) −1.48) × 1.25
Since the hydrogen partial pressure (H2PP) corresponding to + 25% of the relational expression (1) corresponds to the following relational expression (4), the right side of the inequality expression may be replaced with the following relational expression (4).
(H2PP) = − 0.000688 × (LV) ² + 0.374 × (LV) −1.85 (4)
Therefore, in the catalytic hydrogenation reaction of a crude terephthalic acid aqueous solution, the reaction system is limited (filled with the crude terephthalic acid aqueous solution up to the catalyst layer, and the hydrogen-containing gas phase part is held on the upper surface of the aqueous solution. The production volume of refined terephthalic acid can be increased or decreased by using the continuous flow of hydrogen and the apparent vacancy rate under the catalyst layer flow of the reaction aqueous solution, which was not previously considered as a reaction factor. It is possible to set stable and reproducible reaction conditions in response to changes in the conditions, and economical purification reaction conditions for crude terephthalic acid aqueous solution that does not cause excessive hydrogenation reaction using excess hydrogen gas. I was able to find it.

According to the present invention, in the production of purified terephthalic acid by hydrorefining method of a crude aqueous terephthalic acid solution, the above relational expressions (1), (2) and (3) with the flow-down superficial velocity (LV) of the reaction aqueous solution By setting the hydrogen partial pressure (H2.PP) and the range of the hydrogen partial pressure (H2.PP) in the above relational expressions (2) and (3), the quality can be stabilized in response to changes in various reaction conditions. The purified terephthalic acid thus produced can be produced, and it contributes to economical production without causing excessive hydrogenation reaction with excess hydrogen without producing a product having a non-standard property.

Therefore, even when increasing the amount of refining and installing new equipment, it will be modified or newly installed to the optimum equipment that does not set excessive conditions. In the subsequent manufacturing, it will contribute to economic production.

The systematic diagram of the refinement | purification process of the crude terephthalic acid of this invention embodiment. The figure which shows the relationship between 4-CBA content in refined terephthalic acid, and hydrogen partial pressure (H2PP) by using the superficial velocity (LV) as a parameter according to Examples. In addition, the 4-CBA content of the purified terephthalic acid in the comparative example in which the 4-CBA content is out of product specifications was plotted as 27 ppm. Based on the results of the examples, the hydrogen partial pressure (H2.PP) was determined by distinguishing differences such as hydrogenation reactor, hydrogen gas absorption (hydrogen (H2) / 4-CBA molar ratio) and terephthalic acid concentration. Plotted in relation to superficial velocity (LV).

An embodiment of a preferred method for purifying crude terephthalic acid according to the method of the present invention will be described below. As raw materials for producing purified terephthalic acid, crude terephthalic acid produced by liquid-phase oxidation with oxygen-containing gas in the presence of catalysts such as cobalt and manganese in acetic acid solvent is mainly used. Crude terephthalic acid containing about 2,000-3,500 ppm of 4-CBA is used.

The flow of the process of dissolving such crude terephthalic acid in high-temperature and high-pressure water, performing a hydrorefining reaction in a hydrogenation reactor, and producing purified terephthalic acid is as shown in FIG. An outline of these methods and conditions is described below.

The supply ratio of crude terephthalic acid and water supplied to the slurry preparation tank A is usually adjusted to a slurry of 23 to 30% by weight or 26 to 29% by weight in terms of terephthalic acid concentration, and then using a high pressure pump The prepared slurry is supplied to the heater C and the dissolution tank D at a pressure exceeding the hydrogenation reactor pressure (55 to 100 kg / cm ² G). The slurry is heated to a set temperature of 275 to 300 ° C. by the heater C, and then stays in the dissolution tank D to form an aqueous solution in which the entire amount of crude terephthalic acid is dissolved. Then, the slurry is supplied to the hydrogenation reactor F. The

In the hydrogenation reactor F, high-pressure hydrogen gas wetted with the aqueous solution and high-pressure (high-temperature) steam is supplied to the upper part of the catalyst layer F1, respectively, and is controlled and maintained at a predetermined reactor pressure and reaction temperature. In the upper space of the catalyst layer, a gas phase-liquid separation phase of upper and lower phases of a gas phase portion J containing hydrogen gas and a liquid phase portion by the reaction aqueous solution is formed.

Since hydrogen gas dissolves (absorbs) in the reaction aqueous solution from the two-phase separation liquid surface corresponding to the hydrogen partial pressure of the gas phase part J, it is dissolved by maintaining and controlling the reactor pressure (PIC). (Absorption) A considerable amount of hydrogen gas is replenished and supplied. Therefore, hydrogen gas is supplied directly from the supply line 6 (line 6 in FIG. 1) above the hydrogenation reactor F, and the pressure in the gas phase portion J of the reactor F is maintained. Although the reactor pressure can be maintained by supplying the reaction solution to the reaction aqueous solution supply line 4 and thereafter, a method of stably supplying the reactor pressure at a fast response speed is preferable.

Then, the level of the aqueous solution at the upper and lower gas-liquid separation interface at the upper part of the catalyst layer is controlled and maintained (LIC), and the supply equivalent amount of the reaction aqueous solution flows down in the catalyst layer and dissolves in the presence of the catalyst ( Absorption) After performing a hydrogenation reaction with hydrogen, it is extracted from the lower part of the catalyst layer to the first crystallization tank G via the line 9. In the first crystallization tank G, the reaction pressure is kept at a set pressure of about 30 to 55 kg / cm ² G, and the reaction aqueous solution at high temperature (275 to 300 ° C.) and high pressure (55 to 100 kgg.cm ² G) is flushed ( (Relief pressure) and cooling, some crystals are precipitated, producing a purified terephthalic acid slurry at about 230-270 ° C.

The reaction temperature when flowing down the catalyst layer is a temperature exceeding the temperature at which the terephthalic acid crystals of the supplied crude terephthalic acid slurry are completely dissolved (the temperature at which crystals are precipitated in the supplied crude terephthalic acid aqueous solution). Preferably, the reaction is carried out at a temperature exceeding the respective dissolution temperature (about 275 to 300 ° C.) with respect to a reaction aqueous solution having a crude terephthalic acid concentration of 23 to 30% by weight. For example, Patent Document 1 (US Pat. No. 3,639,465) states that the purification reaction is performed at a temperature of about 10 ° F. (about 5.6 ° C.) exceeding the temperature of the terephthalic acid crystal precipitation point.

And the pressure of the reactor F is the above-mentioned relational expression between the vapor pressure of the aqueous terephthalic acid solution (Table 1) corresponding to the terephthalic acid concentration and temperature of the aqueous reaction solution (Table 1) 1), the hydrogen partial pressure (H2.PP) obtained from (2) and (3), and the hydrogen partial pressure (H2PP) obtained from the relational expression (2), or the relational expressions (2) and (3) The hydrogenation reaction is carried out with the pressure obtained by adding the hydrogen partial pressure in the pressure range (C in FIG. 3) between the hydrogen partial pressures (H2.PP) obtained from (1). Hydrogenation that sets the pressure obtained by adding the hydrogen partial pressure in the range of about ± 25% of the hydrogen partial pressure (H2PP) obtained from the relational expression (1) (B in FIG. 3) to the vapor pressure of the reaction aqueous solution. The reaction is a more preferred purification reaction. Therefore, it is usually carried out at a pressure of about 55-100 kg / cm ² G.

FIG. 3 shows the difference between hydrogen partial pressure (H2.PP) and hydrogenation reactor, hydrogen gas absorption (hydrogen / 4-CBA molar ratio) and terephthalic acid concentration, etc. It is the figure plotted in relation to the superficial velocity (LV), and at the same time, the approximate relationship line where the 4-CBA content is the same and the relationship were expressed by a formula. The relational expression is as follows.
4-CBA content about 15ppm
(H2.PP) = - 0.000550 × ( LV) 2 + 0.299 × (LV) -1.48 (1)
4-CBA content about 20ppm
(H2.PP) = -0.000413 x (LV) ² +0.224 x (LV)-1.11 (2)
4-CBA content about 10ppm
(H2.PP) = -0.0020 x (LV) ² +0.569 x (LV)-1.93 (3)
The relational expression (2) corresponds to the relation of −25% of the relational expression (1), and the hydrogen partial pressure corresponding to + 25% of the relational expression (1) is the following relational expression (4). Become.
(H2.PP) = -0.000688 x (LV) ² +0.374 x (LV)-1.85 (4)
Relational expressions corresponding to the approximate relation lines in FIG. 3 are indicated by (1) to (4). Regions partitioned by the relationship lines are indicated by (A) to (F), (A) is a region below Equation (3), and (B) is Equations (2) and (4) centering on Equation 1. (C) is a region surrounded by equations (2) and (3), (D) is a region above equation (2), (E) is a region above equation (3), and (F) is an equation (2) The following areas are shown.

The catalyst used for filling the hydrogenation reactor F is a catalyst of an activated carbon carrier supporting a Group VIII noble metal such as palladium, platinum or ruthenium, and a palladium-supported activated carbon catalyst is most commonly used. Yes. The amount of each precious metal supported is in the range of 0.1 to 3% by weight, but an active catalyst supporting 0.5% by weight of palladium is usually used. In addition, about the catalyst layer F1 in the hydrogenation reactor F, and the upper and lower two-phase separated phases on the upper part of the catalyst layer and the reaction aqueous solution, the dimensions of the hydrogenation reactor used in this embodiment are shown in FIG. Although schematically shown in the hydrogenation reactor F, there is no particular limitation as long as the hydrogen-containing gas phase portion J and the reaction aqueous solution can be stably formed and held on the upper part of the catalyst layer.

Next, the crystallization slurry extracted from the first crystallization tank G is flash-cooled through a plurality of crystallization tanks (not shown) whose pressure is lowered stepwise, and then about 2 to 5 kg / cm ^2. Flush into the final crystallization vessel H held in G to obtain a purified terephthalic acid crystallization slurry at a temperature of about 130-160 ° C.

As for the method of flash cooling stepwise using a plurality of crystallization tanks including the first crystallization tank G, US Pat. No. 3,931,305, Japanese Patent Laid-Open No. 8-208561, Japanese Patent No. 3848372, Japanese Patent Laid-Open No. Any method proposed in 2006-96710 can be used.

The crystallization slurry in the final crystallization tank H is separated and washed with a solid-liquid separator I while maintaining the temperature, and a wet cake of purified terephthalic acid is recovered. The collected wet cake is dried by a dryer (not shown) to obtain a product of purified terephthalic acid.

In addition, the purified terephthalic acid cake, which is not washed in the solid-liquid separator I and is recovered only by solid-liquid separation of the crystallization slurry in the final crystallization tank H, is heated with high-temperature (about 100 to 160 ° C.) water. After re-slurry, a method of solid-liquid separation using a solid-liquid separator again and recovery with a wet cake of purified terephthalic acid is also carried out, followed by drying to obtain a product of purified terephthalic acid.

In order to describe the present embodiment in detail, a specific example will be described and described below. However, the method of the present invention is not limited to the examples described below.

Hereinafter, in the description of the examples, a system diagram of the process of FIG. 1 of a purified terephthalic acid production apparatus in which the above crude terephthalic acid is dissolved in water and hydrorefined is used. The outline and reaction conditions in the hydrogenation reactor are specifically described in each example.

Example 1
A hydrogenation catalyst (0.5 wt% Pd-supported activated carbon) was added to the hydrogenation reactor F (Fig. 1, hydrogenation reactor F schematic diagram) consisting of a cylindrical part with an inner diameter of 740 mmφ and a length of 7,000 mm and upper and lower mirror parts (hemisphere). Catalyst) A hydrogenation reactor packed with 2.56 m ³ , the catalyst layer packed to a height of about 5,710 mm (about 1,290 mm from the top end of the cylinder), and fixed on the catalyst layer with a 20-mesh metal mesh catalyst holder Using.

First, crude terephthalic acid (4-CBA content 2800 ppm) is supplied from a powder supply hopper B to a slurry preparation tank A from a line 1 to prepare a slurry having a terephthalic acid concentration of 26% by weight. The prepared slurry is supplied to the heater C through the line 3 at a rate of 14,500 kg / hr with a high-pressure pump, heated to about 283 ° C., and supplied to the hydrogenation reactor F through the dissolution tank D and the line 4.

The aqueous solution obtained by heating and dissolving crude terephthalic acid is dispersedly supplied onto a liquid surface held at a position of about 650 mm on the catalyst layer through a branched porous supply pipe attached to the upper part of the reactor F. On the other hand, for hydrogen gas, high-pressure hydrogen (about 120 kg / cm ² G) is heated from line 7 through the steam saturator E, and then the pressure is controlled from the top of reactor F to a reactor pressure of about 73 kg / cm ² G (PIC Pressure regulator) to replenish dissolved (absorbed) hydrogen gas.

The supplied aqueous solution flows downward in the catalyst layer by liquid level control (LIC liquid level controller), and after catalytic hydrogenation with dissolved hydrogen from the liquid level, the first crystal is formed from the bottom of the reactor F. Extracted into the analysis tank G. A cylindrical liquid collection part with a 0.8 mm mesh is attached to the lower part of the catalyst layer, and the hydrotreating liquid is drawn through the liquid collection part. In the hydrogenation reactor F, the temperature (TI temperature indicator) is maintained at approximately 282 ° C., and the reactor pressure is maintained at 73.2 kg / cm ² G. At this time, the vapor pressure of the 26 wt% aqueous terephthalic acid solution is 62.9 kg / cm ² G (282 ° C.), and the hydrogen partial pressure is 10.3 kg / cm ² . The average amount of hydrogen supplied (absorbed) during the reaction was 8.2 Nm ³ / hr.

Therefore, when the hydrogen absorption amount is calculated as a ratio to the 4-CBA supply amount (hydrogen / 4-CBA ratio), it is 5.2 (molar ratio). In the hydrogenation reactor F, the supply amount of the crude terephthalic acid aqueous solution was hydrotreated at an apparent superficial velocity (LV) of 41.1 m / hr.

The hydrotreated aqueous solution is flushed through line 9 to the first crystallization tank G of high pressure (about 48 kg / cm ² G), and then sequentially flushed using a plurality of crystallization tanks (not shown) in series. After that, it is produced as a purified terephthalic acid slurry cooled to about 150 ° C. in the final crystallization tank H. The produced slurry is separated and washed by the solid-liquid separator I via the line 13 to collect a wet cake of purified terephthalic acid crystals. By drying the cake with a drier (not shown), purified terephthalic acid is recovered and produced.

When the stable operation was carried out for about 24 hours under the above hydrotreatment conditions, the 4-CBA content of the purified terephthalic acid crystals recovered during that period was about 15 ppm, and the p-toluic acid content was about 125 ppm.

(Example 2)
Using an apparatus system (schematic diagram FIG. 1) similar to that of Example 1 equipped with a hydrogenation reactor having an inner diameter of 3,900 mmφ, a length of 14,000 mm, and a mirror part (hemisphere) at the top and bottom, it is described below. Under the same conditions and the same conditions and methods as in Example 1, crude terephthalic acid was dissolved in water and subjected to a hydrorefining reaction to produce purified terephthalic acid. The hydrogenation reactor F was filled with 159 m ³ of a hydrogenation catalyst (the same catalyst as in Example 1), and the cylinder portion was filled with a catalyst layer height of about 12,000 mm. A slurry of crude terephthalic acid (4-CBA content 2700ppm) and pure water with a terephthalic acid concentration of 26.5% by weight was prepared, and the prepared slurry was supplied at a rate of 435ton / hr with a high-pressure pump. The hydrogenation reactor F is supplied in the same manner as in 1.

In the hydrogenation reactor F, with the liquid level control (LIC liquid level controller) that keeps the reaction liquid level at 1,000 mm above the catalyst layer, the reaction liquid is extracted from the lower part of the catalyst layer, and from the upper part of the reactor. Hydrogen gas supply by pressure control (PIC pressure controller) was performed in the same manner as in Example 1. In the hydrorefining reaction, the temperature of the hydrogenation reactor F (TI temperature indicator) was controlled to 282 ° C., the pressure was controlled to 73.6 kg / cm ² G, and the hydrogen gas supply (absorption) amount was 239 Nm ³ / hr.

The hydrogen partial pressure at this time was 10.8 kg / cm ² (aqueous solution vapor pressure 62.8 kg / cm ² G), and the amount of hydrogen absorbed with respect to 4-CBA supply was 5.1 (molar ratio). The apparent velocity (Linear velocity LV) in supplying the crude aqueous terephthalic acid solution was 44.4 m / hr. As a result, the recovered purified terephthalic acid crystal had a 4-CBA content of about 15 ppm and a p-toluic acid of about 125 ppm. Table 2 summarizes the reaction conditions of Examples 1 and 2 and the properties of purified terephthalic acid.

Therefore, even if the feed rate of the hydrogenation reactor and the crude terephthalic acid slurry changes greatly, and the space velocity (SVhr ⁻¹ ) changes, the apparent superficial velocity and hydrogen partial pressure of the aqueous solution are made equal. It was confirmed that the amount of gas absorbed (vs. 4-CBA molar ratio) and the properties of purified terephthalic acid were equivalent.

(Examples 3, 4, 5, 6)
Using the same apparatus as in Example 1, a slurry of crude terephthalic acid (4-CBA content 2800 ppm) prepared in slurry preparation tank A to a concentration of 26% by weight was passed through line 3 with a high-pressure pump, and 25,000 kg / hr. 35,000 kg / hr, 41,000 kg / hr and 7,500 kg / hr were supplied to the heater C, and a hydrogenation reaction was carried out in the same manner as in Example 1 to produce purified terephthalic acid. The reactor temperature was maintained at 282 ° C and the reactor pressure was maintained at 79.8Kg / cm ² G, 85.8Kg / cm ² G, 88.8Kg / cm ² G and 67.3Kg / cm ² G, respectively. Went.

As a result, the hydrogen absorption was 5.2 (molar ratio) with respect to the supplied 4-CBA, and all the purified terephthalic acid crystals produced had a 4-CBA content of about 15 ppm and a p-toluic acid content of about 125 ppm. Met. The calculated hydrogen partial pressure and apparent superficial velocity are 16.9 kg / cm ² , 22.9 kg / cm ² , 25.9 kg / cm ² , 4.4 kg / cm ² , and 70.9 m / mm, as shown in Table 3. hr, 99.3 m / hr, 116 m / hr, 21.3 m / hr. Therefore, it is necessary to maintain the hydrogen gas absorption amount (hydrogen (H2) / 4-CBA molar ratio) by increasing the reactor pressure (increasing hydrogen partial pressure) even when the slurry supply amount is increased. is there.

(Comparative Example 1)
Using the same apparatus as in Example 1, a prepared slurry having a terephthalic acid concentration of 26% by weight was fed at a rate of 14,500 kg / hr, the reactor pressure was maintained at 69.3 Kg / cm ² G, and the temperature was maintained at 282 ° C. Purified terephthalic acid was produced in the same manner as in Example 1. Hydrogen gas supply (absorption) amounted to 3.1 Nm ³ / hr. As a result, the 4-CBA content in the purified terephthalic acid crystal started to rise about 15 hours after setting the reactor pressure at 69.3 Kg / cm ² G, and after 25 hours it exceeded 25 ppm, and the 4-CBA content was Production of purified terephthalic acid outside the product standards.

The hydrogen partial pressure at that time is 6.4 kg / cm2, the hydrogen gas absorption (hydrogen / 4-CBA molar ratio) is 1.9, and the superficial velocity is 41.1 m / hr, as shown in Table 3. Therefore, by reducing the reactor pressure in Example 1 (73.2 → 69.3 Kg / cm ² G), the hydrogen partial pressure is reduced (10.3 → 6.4 Kg / cm ² ) and the hydrogen gas absorption is reduced. It was found that the 4-CBA content of the acid was out of specification (4-CBA specification 25 ppm).

(Comparative Example 2)
Using the same apparatus as in Example 1, a prepared slurry having a terephthalic acid concentration of 26% by weight was fed at a rate of 35,000 kg / hr, the reactor pressure was maintained at 74.9 Kg / cm ² G, and the temperature was maintained at 282 ° C. Purified terephthalic acid was produced in the same manner as in Example 1. Hydrogen gas supply (absorption) amounted to 7.1 Nm ³ / hr.
As a result, the 4-CBA content in the purified terephthalic acid crystal started to rise about 15 hours after setting the reactor pressure to 74.9 Kg / cm ² G, and after 25 hours it exceeded 25 ppm, and the 4-CBA content was Production of purified terephthalic acid outside the product standards. As shown in Table 3, the hydrogen partial pressure at that time is 12.0 kg / cm2, the hydrogen gas absorption (hydrogen / 4-CBA molar ratio) is 1.9, and the superficial velocity is 99.3 m / hr. Therefore, despite the fact that the pressure (73.2 → 74.9 kg / cm ² G) higher than the reactor pressure of Example 1 is maintained, the increase in the slurry feed rate (14.500 → 35,000 kg / hr) It can be seen that the 4-CBA content is out of product specifications.

(Examples 7, 8, and 11)
Using the same apparatus as in Example 1, as shown in Table 4, the supply of 26% by weight of the adjusted slurry was supplied at the same rate of 14,500 kg / hr as in Example 1, and the reactor pressure was 75.0 kg / cm, respectively. Purified terephthalic acid was produced in the same manner as in Example 1 while maintaining ² G, 70.6 Kg / cm ² G and 81.0 Kg / cm ² G. Hydrogen gas supply (absorption) amount became respectively 9.1Nm ^³ /hr,4.8Nm ³ / hr and 14.0 nm ³ / hr.
As a result, it was possible to produce purified terephthalic acid having a 4-CBA content of about 15 ppm, about 20 ppm and about 10 ppm, and a p-toluic acid content of about 125 ppm.

The hydrogen partial pressures at that time are 12.1 kg / cm ² , 7.7 kg / cm ² , 18.1 kg / cm ² , and the hydrogen gas absorption (hydrogen / 4-CBA molar ratio) is 5.7, 3.0, and 8.9, respectively. All superficial velocities are 41.1m / hr. Therefore, in the same slurry supply amount (including Example 1), the reactor pressure fluctuation (hydrogen partial pressure fluctuation) directly corresponds to the hydrogen gas supply (absorption) amount, which also affects the purification effect. I found out. It was suggested that Example 11 supplied (absorbed) excess hydrogen in the production of purified terephthalic acid.

(Examples 9 and 10)
Using the same apparatus as in Example 1, as shown in Table 5, the 26% by weight of the prepared slurry was the same rate of 25,000 kg / hr as in Example 3 (the apparent superficial velocity was 70.9 m / hr), and the reactor pressure was maintained at 91.4 Kg / cm ² G and 75.1 Kg / cm ² G, respectively, and purified terephthalic acid was produced in the same manner as in Example 3. As a result, it was possible to produce purified terephthalic acid products with 4-CBA content of 10 ppm and 20 ppm, respectively, and p-toluic acid content of 125 ppm. The hydrogen partial pressures at that time are 28.5 kg / cm ² and 12.2 kg / cm ² , hydrogen gas absorption (hydrogen / 4-CBA molar ratio) is 8.8, 3.1, space velocity and superficial velocity are shown in Table 5. As shown.

Therefore, in the same slurry supply amount (including Example 3), the reactor pressure fluctuation (hydrogen partial pressure fluctuation) directly corresponds to the hydrogen gas supply (absorption) amount, which also affects the purification effect. You can see that It was suggested that Example 9 supplied (absorbed) excess hydrogen in the production of purified terephthalic acid.

(Comparative Example 3)
Using the same apparatus as in Example 1, 26 wt% of the prepared slurry was supplied at the same rate of 25,000 kg / hr as in Example 3 (apparent superficial velocity was 70.9 m / hr as in Example 3). Purified terephthalic acid was produced in the same manner as in Example 3 while maintaining the reactor pressure at 72.3 kg / cm ² G. Hydrogen gas supply (absorption) amount became 5.3 nm ³ / hr. As a result, after setting the reactor pressure to 72.3 Kg / cm2G, about 20 hours later, the 4-CBA content exceeded 25 ppm, and the production of purified terephthalic acid with a 4-CBA content outside the product standard was achieved. The hydrogen partial pressure at that time was 9.4 kg / cm ² , the hydrogen gas absorption (hydrogen / 4-CBA molar ratio) was 2.0, the space velocity and the superficial velocity were as shown in Table 5.

Therefore, by reducing the reactor pressure of Example 3 (79.8 → 72.3 kg / cm ² G), the hydrogen partial pressure (16.9 → 9.4 kg / cm ² ) and the hydrogen gas supply (absorption) amount are reduced. As a result, it was found that the 4-CBA content of purified terephthalic acid was out of the product standard (4-CBA standard 25 ppm).

(Comparative Example 4)
Using the same apparatus as in Example 1, 26% by weight of the prepared slurry was fed at the same rate of 41,000 kg / hr as in Example 5 (the apparent superficial velocity was 116 m / hr as in Example 5), and the reaction Purified terephthalic acid was produced in the same manner as in Example 5 while maintaining the vessel pressure at 77.0 kg / cm ² G. Hydrogen gas supply (absorption) amounted to 8.7 Nm ³ / hr. As a result, after about 20 hours after setting the reactor pressure to 77.0 kg / cm ² G, the 4-CBA content exceeded 25 ppm, and the production of purified terephthalic acid with a 4-CBA content outside the product standard was achieved. The hydrogen partial pressure at that time was 14.1 kg / cm ² , the hydrogen gas absorption (hydrogen / 4-CBA molar ratio) was 2.0, the space velocity and the superficial velocity were as shown in Table 5.

Therefore, by reducing the reactor pressure in Example 5 (88.8 → 77.0 kg / cm ² G), the hydrogen partial pressure is lowered (25.9 → 14.1 kg / cm ² ) and the hydrogen gas supply (absorption) amount is reduced. As a result, it was found that the 4-CBA content of purified terephthalic acid was out of the product standard (4-CBA standard 25 ppm).

(Example 12)
Using the same apparatus as in Example 1, as shown in Table 6, a slurry having a crude terephthalic acid (4-CBA content 2,800 ppm) concentration of 29 wt% was prepared in a slurry preparation tank A, and the prepared slurry was 14,500 kg / hr. The hydrogenation reaction was carried out in the same manner as in Example 1 while maintaining the reactor pressure at 76.4 Kg / cm ² G and the reactor temperature at 287 ° C. Manufactured. The apparent superficial velocity of the slurry supply at that time is 41.1m / hr, the hydrogen gas supply (absorption) amount was 9.0 nm ³ / hr.

The vapor pressure of 29 wt% terephthalic acid solution is ^{66.9Kg / cm 2 G (287 ℃} ), hydrogen partial pressure becomes 9.5 kg / cm ^2. As a result, it was possible to produce purified terephthalic acid having a 4-CBA content of about 15 ppm and a p-toluic acid content of about 125 ppm. The hydrogen gas absorption (hydrogen / 4-CBA molar ratio) at that time is calculated as 5.1, and the space velocity and superficial velocity are as shown in Table 6. Therefore, it was found that the same purified terephthalic acid as in Example 1 can be produced by responding to changes in the terephthalic acid concentration and the reactor temperature with the reactor pressure (hydrogen partial pressure).

(Example 13, Comparative Example 5)
Using the same hydrorefining apparatus as in Example 2, as shown in Table 6, the ratio of crude terephthalic acid (4-CBA content 2700 ppm) concentration 26.5 wt% water slurry to 220,000 kg / hr and 435.000 kg / hr The reactor pressure was maintained at 67.7 Kg / cm ² G and 68.8 Kg / cm ² G, and a hydrogenation reaction was performed in the same manner as in Example 2 to produce purified terephthalic acid. The hydrogenation reaction temperature was maintained at 282 ° C. The vapor pressure of 26.5 wt% of terephthalic acid solution was ^{62.8Kg / cm 2 G (282 ℃} ), hydrogen partial pressure, respectively 4.9 kg / cm ² and 6.0 kg / cm ^2, and the hydrogen gas supply (absorption) amount 124Nm ³ / hr and 54 Nm ³ / hr.

As a result, in Example 13, the 4-CBA content was 15 ppm, but in Comparative Example 5, the 4-CBA content exceeded 25 ppm after about 20 hours after setting the reactor pressure to 68.8 kg / cm ² G. The production of purified terephthalic acid with a 4-CBA content outside the product standards was achieved. The apparent superficial velocity at that time is 22.4 m / hr and 44.4 m / hr, the hydrogen gas absorption (hydrogen / 4-CBA molar ratio) is 5.2 and 1.2, and the others are as shown in Table 6.

Therefore, Comparative Example 5 responded to the increase in the slurry supply amount (220 → 435 ton / hr) without increasing the reactor pressure to 73.6 Kg / cm ² G (Example 2 reactor pressure). Due to the lack of absorption (124 → 54Nm ³ / hr), the production of purified terephthalic acid out of product specifications was made.

A ... Slurry adjustment layer, B ... Powder supply hopper, C ... Heater, D ... Dissolution tank, E ... Heating / steam saturator, F ... Hydrogenation reactor, F1 ... Catalyst layer, G ... First crystallization tank , H ... Final crystallization tank, I ... Solid-liquid separator, J ... Gas phase part (hydrogen-containing gas phase part), FIC ... Flow controller, PIC ... Pressure controller, LIC ... Liquid level controller, FI ... Flow rate Indicator, TI ... Temperature indicator.

Claims

In a method in which crude terephthalic acid is dissolved in water to form an aqueous solution and then hydrorefined through an activated carbon catalyst layer supporting a noble metal,
Fill the catalyst layer with the crude aqueous terephthalic acid solution, hold the hydrogen-containing gas phase part above the aqueous solution,
The hydrogen partial pressure (H2.PP) in the gas phase is maintained at a partial pressure equal to or higher than the following relational expression with the superficial velocity (LV) at which the aqueous solution flows down the catalyst layer, and the aqueous solution continues the catalyst layer. A method for purifying crude terephthalic acid, characterized in that a hydrogenation reaction is carried out by flowing downward.
(H2.PP) = -0.000413 x (LV) 2 +0.224 x (LV)-1.11
2. The method for purifying crude terephthalic acid according to claim 1, wherein the surface of the crude terephthalic acid aqueous solution is held on the catalyst layer, and the hydrogen partial pressure (H2.PP) in the hydrogen-containing gas phase portion above the liquid surface is changed to A method for purifying crude terephthalic acid, wherein the hydrogenation reaction is carried out while maintaining a partial pressure equal to or less than the following relational expression with the superficial velocity (LV) flowing down the catalyst layer of the aqueous solution.
(H2.PP) = -0.0020 x (LV) 2 +0.569 x (LV)-1.93
3. The method for purifying crude terephthalic acid according to claim 1, wherein the surface of the crude terephthalic acid aqueous solution is held on the catalyst layer, and the hydrogen partial pressure (H2.PP) in the hydrogen-containing gas phase portion above the liquid surface is set. A method for purifying crude terephthalic acid, wherein the hydrogenation reaction is carried out while maintaining a partial pressure range of ± about 25% of the following relational expression with the superficial velocity (LV) flowing down the catalyst layer of the aqueous solution: .
(H2.PP) = -0.000550 x (LV) 2 +0.299 x (LV)-1.48
4. The method for purifying crude terephthalic acid according to claim 1, wherein 4-CBA is produced by liquid phase oxidation with oxygen-containing gas in the presence of a catalyst using p-xylene as a raw material and acetic acid as a solvent. A method for purifying crude terephthalic acid, comprising performing a hydrogenation reaction using crude terephthalic acid having a content of 2,000 to 3,500 ppm.
5. The method for purifying crude terephthalic acid according to claim 1, wherein a hydrogenation reaction is performed through a catalyst layer of a crude terephthalic acid aqueous solution having a terephthalic acid concentration of 23 to 30% by weight and a temperature of 275 to 300 ° C. A method for purifying crude terephthalic acid.