JPH11246476A - Method for producing aromatic carboxylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxidation reaction temperature of 140 to 190 which is relatively low.
In the production of aromatic carboxylic acids at ℃, the use of acetic acid separation method combining distillation and extraction can reduce the amount of heat consumed, efficiently separate the water produced by the oxidation reaction contained in the acetic acid solvent, To provide a very industrially advantageous method which can also reduce the acetic acid concentration of acetic acid. SOLUTION: The alkyl aromatic hydrocarbon is subjected to liquid phase oxidation with a molecular oxygen-containing gas in a lower aliphatic carboxylic acid in the presence of a catalyst, and water produced by the oxidation is mixed with the lower aliphatic carboxylic acid and the lower fatty acid ester. In a method for producing an aromatic carboxylic acid in which a mixture containing low-boiling by-products such as is separated and the lower aliphatic carboxylic acid is reused, the oxidation reaction is performed at 140 to 190 ° C., and heat generated in the reaction is recovered. A method for producing an aromatic carboxylic acid, wherein the method is used as a heat source for the separation, and a method for separating the lower aliphatic carboxylic acid is a combination of distillation and extraction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an aromatic carboxylic acid. More specifically, the present invention relates to a method for producing an aromatic carboxylic acid which is industrially advantageously carried out by recovering a reaction solvent in a liquid phase oxidation reaction of an alkyl aromatic hydrocarbon.

[0002]

2. Description of the Related Art As a method for producing an aromatic carboxylic acid such as terephthalic acid, industrially, an alkyl aromatic hydrocarbon such as para-xylene is industrially converted into a catalyst containing cobalt, manganese and bromine in an acetic acid solvent. The most common method is a liquid phase oxidation reaction with molecular oxygen in the presence.

Generally, the quality of terephthalic acid can be adjusted by selecting oxidation reaction conditions such as the reaction temperature of the oxidation reactor, the amount of catalyst used, and the residence time. However, in general, in order to produce high quality terephthalic acid, it is necessary to make the oxidation reaction conditions severe. Accompanying this, there is a problem that the acetic acid solvent burns or decomposes and the loss amount increases, thereby increasing the production cost of terephthalic acid.

Against this background, attention has been paid to a method in which an oxidation reaction is carried out at a low temperature in an attempt to prevent the loss of acetic acid from being reduced by combustion or decomposition, and an accelerator such as a co-oxidant is used as an example of this method. Improved technology to produce terephthalic acid of excellent quality even at low temperatures, such as the case where a reaction system was used, or the case where the reaction activity is enhanced by circulating and supplying a part of the oxidation exhaust gas to the liquid phase of the reactor. It has been reported.

[0005]

In the case of producing terephthalic acid by subjecting para-xylene to a liquid phase oxidation reaction by this low-temperature oxidation reaction method, the reaction after separating terephthalic acid from the oxidation reaction product in a slurry state. The acetic acid solvent, which is the main component of the mother liquor, must be recovered from the reaction mother liquor in order to be recycled, and a distillation method as generally proposed in JP-B-39-10119 has been industrially employed. . That is, a mixture of water and an acetic acid solvent generated by the oxidation reaction is separated by distillation, water is distilled off and discharged outside the system, and acetic acid recovered from the bottom of the column is reused for the oxidation reaction and / or for washing. I do. Further, heat generated by the oxidation reaction is recovered as steam, and a part of the heat is used as a heat source for the above-mentioned distillation separation. In the distillation separation of water and acetic acid, the bottom temperature is about 120 ° C. or higher even under operating conditions under atmospheric pressure,
Naturally, the temperature of steam as a heat source also needs to be higher. Higher steam temperatures are advantageous, but are limited by the oxidation reaction temperature. Therefore, 0.3-0.
It is common to use steam having a pressure of 6 MPa. Further, in this distillation separation, a large amount of steam is consumed since water having a large heat of evaporation is evaporated. In particular, when the oxidation reaction temperature is relatively low at 140 to 190 ° C,
As compared with the case where the temperature exceeds 190 ° C., there is a problem that the amount of by-product steam that can be recovered from the reaction heat and has a temperature higher than the required temperature is reduced, and the consumption of steam is restricted.

[0006]

Means for Solving the Problems In view of the above circumstances, the present inventors have considered that the oxidation reaction temperature is relatively low at 140 to 190 ° C.,
Preferably 140 to 180 ° C, more preferably 150 to 180 ° C
In producing terephthalic acid in the range of 175 ° C., as a result of various studies on a method for efficiently separating the water produced by the oxidation reaction contained in the acetic acid solvent to be reused, the conventional method can be achieved by combining distillation and extraction. Thus, an industrially advantageous method for producing terephthalic acid has been provided.

[0007] That is, the gist of the present invention is that liquid aromatic oxidation of an alkyl aromatic hydrocarbon in a lower aliphatic carboxylic acid with a molecular oxygen-containing gas in the presence of a catalyst and water produced by the oxidation and the lower fatty acid In the method for producing an aromatic carboxylic acid in which a mixture with an aromatic carboxylic acid is separated and the lower aliphatic carboxylic acid is reused, the oxidation reaction is carried out at 140 to 19
A method for producing an aromatic carboxylic acid, wherein the method is carried out at 0 ° C., the heat generated by this reaction is recovered and used as a heat source for the above-mentioned separation, and distillation and extraction are used in combination as the above-mentioned separation method. Exists.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. In the present invention, an alkyl aromatic hydrocarbon used as a raw material is converted into an aromatic carboxylic acid such as an aromatic monocarboxylic acid, an aromatic dicarboxylic acid, or an aromatic tricarboxylic acid by liquid phase oxidation, such as mono-, di-, or trialkylbenzene. Alternatively, alkyl aromatic hydrocarbons such as mono-, di-, and trialkylnaphthalenes, including those in which some of the alkyl groups have been oxidized. Specifically, para-xylene, meta-xylene, ortho-xylene, trimethylbenzene, toluene, methylnaphthalene, dimethylnaphthalene and the like are exemplified. The aromatic carboxylic acids generated include terephthalic acid, isophthalic acid, orthophthalic acid,
Trimellitic acid, benzoic acid, naphthoic acid, naphthalenedicarboxylic acid, etc. are exemplified, but the method of the present invention is preferably applied to the production of terephthalic acid or isophthalic acid,
In these cases, the starting material, alkylbenzene,
Examples include para-xylene and meta-xylene. Particularly preferred is a method for producing terephthalic acid using para-xylene as a raw material.

The amount of the solvent comprising a lower aliphatic carboxylic acid, preferably acetic acid, is usually 2 to 6 times the weight of the alkyl aromatic hydrocarbon. The solvent may contain a small amount of water, for example, 10% by weight or less.
As the molecular oxygen-containing gas, air, oxygen diluted with an inert gas, oxygen-enriched air, or the like is used, but air is preferable from the viewpoint of facilities and operation costs.

As the catalyst, those containing a heavy metal are usually mentioned, and those containing cobalt, manganese and bromine are particularly preferable. Specific examples of these include:
Examples of the cobalt compound include cobalt acetate, cobalt naphthenate, and cobalt bromide. Examples of the manganese compound include manganese acetate, manganese naphthenate, and manganese bromide. Examples of the bromine compound include hydrogen bromide, sodium bromide, cobalt bromide, and manganese bromide. These compounds may be used in combination for each component.

As the catalyst component, a component other than the above-mentioned components of cobalt, manganese and bromine may be present. For example, in the case of producing terephthalic acid, when a sodium component is usually present at about 1 to 1000 ppm, effects such as prevention of precipitation of a manganese component and transmittance of the obtained terephthalic acid are recognized. The sodium component may be added at the time of adjusting the catalyst, or the sodium component accumulated in the system during the production process may be used as it is. Further, if necessary, a co-oxidizing agent may be used in combination to promote the reaction. As the co-oxidizing agent, an aldehyde compound such as acetaldehyde, a ketone compound such as methyl ethyl ketone, or the like is used.

Using the above reaction materials, the oxidation reaction is carried out at a reaction temperature of 140 to 190 ° C., preferably 140 to 180 ° C., more preferably 150 to 175 ° C. If the temperature is lower than 140 ° C., the reaction rate decreases. The reaction pressure is at least a pressure at which the mixture can maintain a liquid phase at least at the reaction temperature, and is usually 0.2 to 5M.
Pa. The water concentration in the reaction system is usually 5 to 25% by weight, preferably 7 to 20% by weight. This water concentration is usually adjusted by extracting gas volatilized in the reactor and condensing the gas. This can be performed by discharging (purging) a part of the reflux liquid of the condensable component to the outside of the system.

The oxidized exhaust gas obtained by condensing and removing condensable components from the gas extracted from the reactor is branched into two streams, one of which is discharged out of the system, and the other of which is discharged to the liquid phase of the reactor. It is preferable to continuously circulate and supply. This method makes it possible to increase the reaction pressure and the oxygen partial pressure. In this case, the volume ratio of the stream circulated to the reactor to the stream discharged out of the system (the amount of exhaust gas circulated) is usually 0.1 to 10%.
10, preferably 0.3 to 5, particularly preferably 0.5 to
Set to 3. The oxidation reaction temperature in this case is 140 to 1
It is preferably performed at 80 ° C.

In the present invention, after the above oxidation reaction,
Crystallization may be performed immediately for recovery of the product, or crystallization may be performed after performing additional oxidation if necessary.
The additional oxidation treatment includes a method of performing the second oxidation treatment at a temperature of 140 to 190 ° C. without supplying the alkyl aromatic hydrocarbon, or a method of increasing the oxidation reaction temperature to 210 ° C. after the second oxidation treatment. A method in which the third oxidation treatment is performed at a temperature of 220C or higher, preferably 220 to 280C. The crystallization process is usually
It is preferable to perform the operation in multiple stages and gradually lower the temperature and pressure. The crystallized slurry solution is separated into the generated aromatic carboxylic acid crystals and the oxidation reaction mother liquor by a crystal separation means, for example, a rotary vacuum filter method, a centrifugation method, or another appropriate separation method. As a method for purifying the obtained aromatic carboxylic acid, a method of purifying impurities in crude aromatic carboxylic acid by hydrogen reduction or a method of removing the impurities by oxidation treatment is known. Among these, as a method for hydrogen reduction and purification of impurities in the aromatic carboxylic acid, an aromatic carboxylic acid is dissolved in water under high temperature and high pressure, brought into contact with a hydrogenation catalyst, and crystals of the aromatic carboxylic acid are recovered from the aqueous solution. (Japanese Patent Publication No. 41-16)
860).

In the above method for producing an aromatic carboxylic acid, after the aromatic carboxylic acid is separated from the resulting oxidation reaction product in the form of a slurry, the acetic acid solvent as the main component is recovered from the reaction mother liquor and recycled. That is, in the reaction mother liquor, in addition to the acetic acid solvent and the reaction product water, cobalt used as a catalyst, heavy metal compounds such as manganese and bromine compounds, and reaction intermediates such as p-toluic acid and 4-carboxybenzaldehyde, Further, it contains reaction by-products and the like. Then, the reaction mother liquor is first sent to a solvent flushing distillation column, where a mixture of acetic acid solvent and water distilled off from the top of the column and a distillation residue composed of a catalyst component, a reaction intermediate product and a reaction by-product obtained from the bottom of the column. Divided into things. Next, the distillate mixture and a part of the reflux liquid of the condensable component obtained by condensing the oxidation reaction exhaust gas are reused in the oxidation reaction after removing water by distillation and extraction.

When the acetic acid solvent is separated from the reaction mother liquor only by a general distillation method, the boiling point of water and acetic acid (boiling point 1)
(17.8 ° C./standard pressure) are close to each other, so that a high-stage distillation column of 70 or more stages is required, and since the specific volatility of water with respect to acetic acid is small, it is necessary to increase the reflux ratio at the top of the column. Yes, inefficient. Further, a large amount of heat source consumption is required since a large amount of water having a large heat of evaporation must be evaporated.

In order to solve this problem, various proposals have hitherto been made. Among them, in the present invention, a combination of an extraction method using an organic solvent and a distillation method is employed. That is, JP-A-7-53443 proposes a method for recovering acetic acid by a combination of a distillation operation and an extraction operation in a process for producing terephthalic acid. This method has the advantage that the amount of heat required for distilling water can be reduced by reducing the reflux ratio at the top of the distillation column.

The extractant used in the above extraction is a known compound (lower fatty acid such as butyl formate, ethyl acetate, propyl acetate, ethyl propionate, ethyl butanoate, etc.) used for extraction of a mixed solution consisting mainly of acetic acid and water. Esters, ketones such as methyl ethyl ketone, methyl isobutyl ketone, diethyl ketone, methyl butyl ketone, alcohols such as butanol, tert-amyl alcohol, and 3-pentanol; phosphine oxide commercially available as Cyanex from Cytek; ) Can be used. Of these, lower fatty acid esters such as ethyl acetate are most preferred.

After the extraction, the steam or condensate sent to the solvent recovery step contains water produced by the oxidation reaction in addition to low-boiling by-products such as acetic acid and methyl acetate. In order to discharge to the outside, first, distillation separation is performed using a distillation column. The vapor or condensate sent to the distillation column is supplied to the middle stage of the distillation column, and acetic acid is obtained from the bottom of the column so that acetic acid is dehydrated to such an extent that it can be used for an oxidation reaction. At this time, the component concentration of the distillate obtained from the top of the distillation column is not particularly limited, but the acetic acid concentration is usually 1% by weight or more, preferably 5% by weight or more, particularly preferably 10% by weight or more based on the aqueous solution. % By weight is desirable. If the acetic acid concentration is too low, the reboiler load of the acetic acid distillation column increases, which is not preferable. On the other hand, the upper limit is usually 50% by weight or less, preferably 40% by weight or less, more preferably 30% by weight or less. If the acetic acid concentration is too high, the load on the extraction device increases, which is not preferable. The distillation column has a reflux ratio containing acetic acid in the above ratio and / or the conditions of the theoretical stage of the distillation column. This distillate is sent to the extraction tower. In order to efficiently separate acetic acid and an extraction solvent (extractant) after acetic acid extraction, it is preferable to use an extractant having a boiling point difference of at least 10 ° C. from acetic acid. As the extraction column, a commonly used type, for example, a mixer-settler type extraction column, a perforated plate type, a packed tower type, a baffle tower type, a vibrated perforated plate type, a stirring and mixing type, a pulsating packed type, etc. can be used. The extract phase mainly composed of the extractant obtained by the extraction is advantageously worked up by distillation. If there is a sufficient boiling point difference between acetic acid and the extractant, high-purity acetic acid can be easily recovered by a normal distillation operation.
Further, the extractant eluted in the raffinate phase containing water as a main component after the extraction is also recovered by the distillation operation. The used extractant is circulated again to the extraction column, but after removing low-boiling by-products contained in the extractant, such as methyl acetate, by distillation or the like,
It is preferable to circulate and supply to the extraction column. Alternatively, a method of removing methyl acetate or the like by distilling the distillate at the top of the distillation column before being sent to the extraction step is also effective. In the former case,
When trying to separate methyl acetate etc. by distillation etc. to avoid accumulation of methyl acetate etc. in the extractant, loss of the extractant occurs together, but the latter has less loss of extractant than the former This is advantageous. In either case, it is preferable to recycle methyl acetate and the like into the reaction system.

In the present invention, the heat generated by the oxidation reaction is recovered as steam and used as the heat source for the separation. Examples of the object of the separation heat source include an acetic acid dehydration tower, a methyl acetate recovery tower, an acetic acid recovery tower, and an extractant recovery tower, and one or several of them may be used. Since the above separation is generally performed under normal pressure and the heat source temperature needs to be 120 ° C. or more, steam having a pressure corresponding to this temperature is by-produced from the heat of the oxidation reaction. The higher the by-product steam temperature, the better, but it is limited by the oxidation reaction temperature.
It is common to produce by-product steam having a pressure of 3 to 0.6 MPa. In particular, the oxidation reaction temperature is 1 as in the present invention.
When the temperature is relatively low at 40 to 190 ° C, the reaction temperature is 1
Compared to the case where the temperature exceeds 90 ° C., the amount of steam by-product having this pressure is inevitably reduced, and it is necessary to suppress the amount of steam consumed in the distillation column and the like.

As described above, in the production of aromatic carboxylic acids, when the water produced by the oxidation reaction contained in the oxidation reaction mother liquor is removed by separation, the combination of distillation and extraction has the advantage that the amount of heat consumed is reduced. There is. In particular, as in the present invention, in a process for producing an aromatic carboxylic acid at a relatively low temperature of 140 to 190 ° C. in the oxidation reaction temperature, when the amount of by-product steam utilizing the reaction heat of the oxidation reaction decreases, the oxidation The use of a combination of distillation and extraction for the separation of the reaction solvent to significantly reduce the consumption of steam, which is the heat source for the separation, is a highly advantageous and industrially very advantageous process.

[0022]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples unless it departs from the gist. In Examples, “parts” means “parts by weight”.

Embodiment 1 A description will be given below with reference to FIG. Stirrer (no number), heating device (no number), supply line 4 of catalyst solvent slurry and para-xylene, air introduction line 5, reaction slurry extraction line 8, reflux liquid extraction line 9, circulating oxidizing exhaust gas to reactor 30.6 parts / hr of para-xylene, 154.4 parts / hr of acetic acid containing 9% of water, and cobalt from line 4 of the pressure-resistant main oxidation reactor 1 made of titanium having a blower 3 for circulating and a circulation line 7 therefor. And a mixture containing manganese and bromine as catalyst components,
More air is used as the oxidizing gas and the oxygen concentration in the oxidizing exhaust gas is 6
Supply so as to be% by volume. The oxidizing exhaust gas is purged from the titanium condenser 2 also serving as the steam by-product from the line 6 and the volume ratio of the circulating gas amount based on the non-condensable component to the oxidizing exhaust gas amount purged out of the system is 1.0. The oxidation exhaust gas is circulated by the blower 3 through the line 7 to the liquid phase portion of the main oxidation reactor 1 such that Also, 100.2 parts / hr of reflux liquid was withdrawn from line 9,
The water concentration in the reaction system was adjusted to about 10%, and the residence time was 10
The oxidation reaction of para-xylene is performed under the conditions of 0 minute, a pressure of 1.36 MPa and a reaction temperature of 175 ° C.

In the condenser 2, steam having a pressure of 0.35 MPa is recovered by utilizing heat of the oxidation reaction. Most of the recovery heat referred to here is the heat of oxidation reaction generation, and if the terephthalic acid production is the same, the heat of oxidation reaction generation is almost constant, and the recovered heat itself is independent of the set oxidation reaction temperature. It can be interpreted that there is not much difference.

Next, a reaction slurry is withdrawn from the main oxidation reactor 1 through a line 8, and this slurry is continuously sent to the additional oxidation reactor, where the residence time is 45 minutes and the pressure is 1.22M.
Under the conditions of Pa and a reaction temperature of 174 ° C., air is supplied so that the oxygen concentration in the oxidation exhaust gas becomes 6% by volume, and additional oxidation is performed. The post-oxidation reaction slurry was subsequently sent to a titanium cooling crystallizer equipped with an inlet and an outlet for the reaction slurry to be crystallized and then separated into a solid and a liquid.The obtained solid was dried to obtain terephthalic acid crystals. obtain. 50% of the reaction mother liquor obtained by solid-liquid separation is recycled to the oxidation reaction system.

On the other hand, from the line 9, 100.2 parts / hr of condensate of the oxidation reaction exhaust gas (acetic acid = 81% by weight, water = 18.
0% by weight) and 60.8 parts / h of mixed steam from line 10.
r (acetic acid = 50.5% by weight, water = 49.3% by weight) at a top of 100 ° C. and a bottom of 120 ° C., actual stage = 70 stages, reflux ratio =
It is introduced into the acetic acid dehydration distillation column 11 equipped with a reboiler 17, which is 1.7. Acetic acid containing 7.2% by weight of water is recovered from the lower part of the tower 11 (line 16), and treated with a condenser 12 and a decanter 13 from the upper part of the tower 11 to obtain a distillate mainly composed of water (line 15). 4 parts / hr (acetic acid = 15.3% by weight, methyl acetate = 2.6% by weight) are obtained. Further, the distillate was introduced into a methyl acetate recovery column 18 equipped with a reboiler 25 having a top of 50 ° C., a bottom of 103 ° C., an actual stage of 17, and a reflux ratio of 5, and a condenser 20 through a line 19 from the top. , Treated with a decanter 21, and a distillate containing methyl acetate as a main component (line 23) 0.6 part / h
While recovering r, 19.8 parts / hr (15.8% by weight of acetic acid) mainly containing water (line 26) are obtained from the bottom of the column. Liquid containing methyl acetate as the main component (line 2)
3) is recycled to the reaction system.

The distillate 24 from the methyl acetate recovery column 18 is passed through a line 26 to an RDC type extraction column 27 (actual stage = 55).
Supply continuously from the top. Ethyl acetate as an extractant is continuously supplied from the bottom of the extraction column 27. At this time, the extractant / the aqueous solution is set to 1.5. Water containing ethyl acetate corresponding to the solubility is obtained from the bottom of the extraction column 27, and an ethyl acetate phase obtained by extracting acetic acid is obtained from the top of the extraction column 27 (line 2).
8). The liquid obtained from the lowermost part of the extraction column 27 is extracted at the top 71 ° C., the bottom 100 ° C., the actual stage = 10, and the extraction agent recovery column 3 having a reflux ratio = 1.1.
9 is introduced. The extractant is recovered from the upper part of the extractant recovery tower 39 (line 40), and 14.9 parts of treated water (line 43) / hr (acetic acid = 560 pp) from the lower part of the extractant recovery tower 39.
m). The liquid obtained from the uppermost part of the extraction column 27 is introduced through a line 28 into an acetic acid distillation column 29 having a top of 71 ° C., a bottom of 103 ° C., and a reflux ratio of 0.1. The extractant is recovered from the upper part of the acetic acid distillation tower 29 (line 30), and the acetic acid recovered from the lower part of the acetic acid distillation tower 29 (line 36).
4.8 parts / hr (acetic acid = 64.7% by weight) are recovered.
The extractant components (line 30 and line 40) containing water extracted from the acetic acid distillation column 29 and the extractant recovery column 39, respectively, are cooled by condensers 31 and 41, respectively, and then combined into a liquid-liquid separator 32. It is separated into a component mainly composed of the recovered extractant and a component mainly composed of water. The component mainly composed of water is sent to the extractant recovery column 39 as a reflux liquid (line 42) and is subjected to distillation separation. The water component is purged as treated water. Further, the recovered extractant is circulated to the acetic acid recovery tower 29 via the lines 33 and 35 and the extraction tower 27 via the lines 33 and 34 and is reused.

In such a process, the heat sources of the acetic acid dehydration distillation column 11, the methyl acetate recovery tower 18, the acetic acid recovery tower 29, and the extractant recovery tower 39 are obtained by recovering the heat of oxidation reaction.
Steam with a pressure of 40 MPa is used. At this time, the oxidation reactor 1, the acetic acid dehydration distillation column 11, the methyl acetate recovery column 18, the extraction column 27, the acetic acid recovery column 29, and the extractant recovery column 39
Table 1 shows the operating conditions and equipment specifications.

Comparative Example 1 The reaction and distillation were carried out in the same manner as in Example 1 except that the distillation separation was carried out only by the general distillation method (see FIG. 2). The acetic acid dehydration distillation column 11 has 70 theoretical stages, and the reflux ratio (reflux amount / distillate amount) is 3.4. The results are shown in Table 1.

[0030]

[Table 1]

The meanings of * 1 to * 4 in Table 1 are as follows. * 1 Exhaust gas circulation amount: Indicates the volume ratio of the circulating gas amount based on the non-condensable component to the oxidizing exhaust gas amount purged out of the system. * 2 Condenser heat transfer area ratio: The heat transfer area of the condenser 2 that recovers heat generated by the oxidation reaction as steam having a pressure of 0.40 MPa is a relative value based on the value of Example 1.

* 3 Reboiler consumption calorie ratio: The calorie consumed in the acetic acid dehydration distillation system is a relative value based on the value in Example 1. The target here is the reboiler 17 of the acetic acid dehydration distillation column 11 and the methyl acetate recovery column 18.
Reboiler 25, reboiler 37 of acetic acid recovery tower 29,
This is the amount of heat consumed by the reboiler 44 of the extractant recovery tower 39. * 4 Reboiler heat transfer area ratio: The heat transfer area of the reboiler 17 of the acetic acid dehydration distillation column 11 is a relative value based on the value of Example 1.

From the above results, in Comparative Example 1 in which only the general distillation method was employed, in comparison with Example 1 in which distillation and extraction were combined with dehydration and separation of acetic acid, the required heat consumption was as large as 1.2 times. As a result, 0. 0 recovered from the exhaust gas of the oxidation reaction.
It can be seen that it is necessary to increase the heat transfer area of the condenser 2 by 1.6 times in order to increase the amount of by-produced steam having a pressure of 40 MPa (* 2). On the other hand, the heat transfer area of the reboiler 17 of the acetic acid dehydration distillation column 11 also needs to be increased by 1.6 times as the heat consumption increases (*
4).

The reason why the heat transfer area of the condenser 2 and the reboiler 17 in Comparative Example 1 is larger than that in Example 1 is that the required steam temperature is relatively low at 175 ° C. A major factor is that there is a restriction in maintaining the amount of by-products. Therefore, it is not a problem when the oxidation reaction temperature exceeds 190 ° C., but can be said to be a problem peculiar to the reaction at a relatively low temperature in the present invention.

Further, since the material of the condenser 2 and the reboiler 17 is used in an environment where the acetic acid concentration is high, a high-grade metal such as titanium or an alloy is generally used in consideration of corrosion resistance. Therefore, in the case where the oxidation reaction temperature is relatively low at 140 to 190 ° C., the use of the extractive distillation method for the dehydration distillation of acetic acid has a large effect on the reduction of the equipment cost. Therefore, it can be said that the method of the present invention is industrially extremely advantageous.

[0036]

According to the present invention, in the production of aromatic carboxylic acid at a relatively low oxidation temperature of 140 to 190 ° C., the amount of heat consumed can be reduced by employing an acetic acid separation method combining distillation and extraction. It can efficiently separate water produced by the oxidation reaction contained in the acetic acid solvent, which is extremely industrially advantageous. This effect cannot be attained by simply setting the oxidation temperature to a specific oxidation reaction or independently performing the acetic acid separation method combining distillation and extraction in the production of aromatic carboxylic acids. This is unexpectedly efficient and a special effect obtained for the first time. Furthermore, it became possible to reduce the acetic acid concentration in the wastewater as compared with the case of only the distillation method.

[Brief description of the drawings]

FIG. 1 is a diagram showing the steps of a main oxidation reaction system and an acetic acid dehydration separation system by a combination of distillation and extraction used in Example 1 of the present invention.

FIG. 2 is a diagram showing steps of a main oxidation reaction system and a acetic acid dehydration distillation system by a general distillation method used in Comparative Example 1 of the present invention.

[Explanation of symbols]

1: Main oxidation reactor 2: Condenser 3: Blower 4: Supply line for catalyst acetic acid solvent slurry and para-xylene 5: Air introduction line 6: Oxidation exhaust gas purge line 7: Oxidation exhaust gas recycling line 8: Reaction slurry Extraction line 9: Extraction line for reflux liquid 10: Distillation vapor line from which reaction by-products have been removed 11: Acetic acid dehydration distillation column 12: Condenser 13: Decanter 17: Reboiler 18: Methyl acetate recovery column 20: Condenser 21:
Decanter 25: Reboiler 27: Extraction tower 29: Acetic acid recovery tower 31: Condenser 32: Liquid-liquid separator 37: Reboiler 39: Extractant recovery tower 41: Condenser 44: Reboiler Others 14, 15, 16, 19, 22, 23, 24, 2
6, 28, 30, 33, 34, 35, 36, 38, 4
0, 42, 43 and 45 are pipes.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI // C07B 61/00 300 C07B 61/00 300 (72) Inventor Hirotetsu Azumi 1-1 Kurosaki Castle Stone, Yawata Nishi-ku, Kitakyushu-shi, Fukuoka Prefecture Mitsubishi Chemical Corporation Kurosaki Office

Claims (5)

[Claims] An alkyl aromatic hydrocarbon is subjected to liquid phase oxidation with a molecular oxygen-containing gas in a lower aliphatic carboxylic acid in the presence of a catalyst, and water produced by said oxidation is mixed with said lower aliphatic carboxylic acid and lower fatty acid. In a method for producing an aromatic carboxylic acid in which a mixture containing low-boiling by-products such as esters is separated and the lower aliphatic carboxylic acid is reused, the above oxidation reaction is performed at 140 to 190 ° C., and the heat generated by this reaction is A method for producing an aromatic carboxylic acid, comprising recovering and using this as a heat source for the separation, and using a combination of distillation and extraction as a method for separating the lower aliphatic carboxylic acid. 2. A method according to claim 1, wherein a gas is extracted from a reactor for performing an oxidation reaction, and a part of the oxidized exhaust gas obtained by condensing and removing condensable components from the gas is circulated and supplied to a liquid phase portion of the reactor.
The method for producing an aromatic carboxylic acid according to the above. 3. An alkyl aromatic hydrocarbon is subjected to liquid phase oxidation with a molecular oxygen-containing gas in a lower aliphatic carboxylic acid in the presence of a catalyst, and water produced by said oxidation is mixed with said lower aliphatic carboxylic acid and lower fatty acid. The method for producing an aromatic carboxylic acid according to claim 1 or 2, wherein a low-boiling by-product such as an ester is removed from the mixture containing the low-boiling by-product by distillation, and then subjected to extraction. 4. The method for producing an aromatic carboxylic acid according to claim 1, wherein the low-boiling by-product contained in the extractant is removed by distillation when the extractant used in the extraction is recycled. 5. The method for producing an aromatic carboxylic acid according to claim 1, wherein the alkyl aromatic carboxylic acid is para-xylene.