KR800000077B1 - Continuous production method of terephthalic acid - Google Patents

Abstract

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Description

Continuous production method of terephthalic acid

In the present invention, when terephthalic acid is continuously produced by catalytic liquid phase oxidation of P-xylene, an aqueous solution containing a catalyst with good catalyst extraction efficiency and high preparation rate of undesired organic by-products by an easy operation from a mother liquor from which terephthalic acid has been separated The present invention relates to an improved process for continuously producing terephthalic acid industrially advantageously by recovering and recycling it to an oxidation reaction.

More specifically, the present invention provides a liquid phase oxidation of P-xylene to molecular oxygen in acetic acid in the presence of a heavy metal oxidation catalyst, isolating and recovering terephthalic acid from the obtained oxidation reaction mixture, part of the mother liquor as it is or concentrated Recirculating to the catalytic liquid phase oxidation zone, concentrating the remaining portion of the mother liquor, extracting the residue containing the heavy metal oxidation catalyst and organic by-products with water, and recycling the resulting catalyst-containing aqueous solution to the catalytic liquid phase oxidation zone. In the continuous production method of terephthalic acid composed of

(1) In the concentration, the amount of acetic acid in the residue is less than 5% based on the weight of the residue, and the amount of benzoic acid in the residue is less than 15% based on the weight of the residue. Until not,

(2) the residue is brought into contact with water of 2-5 times its weight in a hot molten state and then quenched to a temperature of 50 ° C. or less,

(3) Separating the catalyst-containing aqueous solution from the mixture of the above-mentioned organic by-product obtained in the form of granular solid and the catalyst-containing aqueous solution, and recycling the separated catalyst-containing aqueous solution to the catalytic liquid oxidation zone (concentration as required). Can be recycled).

In acetic acid solvents, P-xylene is prepared in the presence of a catalyst composed of a heavy metal compound such as cobalt or manganese and a bromine donor, or in the presence of an activator such as a ketone or an aldehyde in addition to such a heavy metal oxidation catalyst, which contains molecular oxygen. It is well known to produce a terephthalic acid by liquid phase oxidation with a title containing a gas). In this case, the mother liquor from which the resulting terephthalic acid is separated from the reaction mixture is composed of acetic acid used as a solvent, heavy metal compounds and bromine donors used as catalysts, and optionally ketones or aldehydes used as activators, and organic compounds of oxidizing intermediates or oxidative by-products. Consists of by-products.

Therefore, in order to effectively use such an expensive catalyst, it is appropriate to recycle the mother liquor all to the oxidation system. However, since the mother liquor contains by-products that inhibit or inhibit the oxidation of P-xylene, it is possible to recycle the entire amount of the mother liquor since the catalyst and the terephthalic acid may be contaminated. For this reason, in the case of the continuous production method of terephthalic acid in which the mother liquor is recycled to the catalytic liquid phase oxidation system, an amount of organic impurities in excess of the allowable amount must be removed from the mother liquor.

As for the method of treating the mother liquor with water, a proposal described in the US patent and Japanese Laid-Open Publicatien is known.

In the former proposal, the heavy metal oxidation catalyst is extracted from the steam residue comprising the dicatalyst and the tar-type antioxidant byproduct using water 3-50 times the volume of the distillation residue at a temperature of 50-150 ° C. The proposal states that the distillation residue can be extracted when it is a hot molten liquid or in the form of a solid powder or solid flakes. In this embodiment, the mother liquor is repeatedly distilled to completely distill off a solvent such as a volatile aromatic acid such as benzoic acid or phthalic anhydride or aliphatic monocarboxylic acid, which is easily dissolved in an aqueous phase upon contact with water. State, pulverize and extract the heavy metal oxidation catalyst from this residue. This method of extracting from the pulverized solid residue has the advantage that undesirable organic by-products are not extracted into the aqueous phase, while there is a lot of heat loss because the mother liquor is repeatedly distilled until the residue becomes water-insoluble. The disadvantage is that a step of grinding the residue is required. In order to extract the heavy metal oxidation catalyst from such a solid with good efficiency, very high extraction temperature and a long time are required, and the extraction effect is also low.

In the latter proposal, the terephthalic acid is separated and recovered from the reaction mixture, and the mother liquor is distilled until its acetic acid content is 10-50% by weight, and the concentrated acetic acid solution is kept at a temperature of 10-40 ° C. at 1-10 ° C. Pear water is added to precipitate the organic byproduct using the difference in solubility at low temperatures in water between the catalyst and the organic byproduct and the catalyst is extracted into the aqueous phase. In this proposed method, the heavy metal oxide catalyst can be extracted well, but since a large amount of acetic acid is present, an insignificant amount of organic by-products is dissolved in acetic acid, leaving organic by-products containing oxidation inhibitor by-products completely. Cannot be precipitated. In particular, when the content of water-soluble organic by-products increases, the amount of by-products dissolved in the water phase increases. In this case, an aqueous emulsion containing by-products is also formed, making separation of organic by-products more difficult. As a result, oxidation by-products accumulate in the catalytic liquid oxidation system.

To avoid this binding, either adverse pretreatment is performed to remove the non-aqueous organic by-product from the concentrated acetic acid solution by distillation or evaporation of the mother liquor, or undesirable by-products dissolved in aqueous solution accumulate in the oxidation system in substantial amounts. There is a need to perform an adverse post treatment to recycle a portion of the resulting catalyst-containing aqueous solution to prevent it from becoming.

The present inventors conducted a study to provide a continuous production method of terephthalic acid, which does not involve the disadvantages of the conventional method described above, and does not bind to it. As a result, the remaining mother liquor from which terephthalic acid was separated and recovered was concentrated by distillation or evaporation, The amount of acetic acid and benzoic acid in the mixture is adjusted to a specific range of amounts, and the hot molten residue containing the controlled amount of acetic acid and benzoic acid is brought into contact with a specific amount of water, and the residue is then heated to a temperature of 50 ° C. or lower. It was found that by quenching the furnace, the combination could be overcome. In addition, by contacting the residue in a hot molten state containing the adjusted amount of acetic acid and benzoic acid with a specific amount of water and then quenching the residue to a specific temperature, the heavy metal oxidation catalyst is evaporated into the aqueous phase with high selectivity, It has been found that organic byproducts, including oxidation inhibitor byproducts, are removed as a solid with a high degree of selectivity. As indicated by many comparative experiments next, if one or both of the above specific binding requirements are not met, either or both of the selective extraction of the heavy metal oxidation catalyst and the selective removal of undesirable organic by-products cannot be achieved.

The present inventors have found that organic by-products containing water-soluble oxidation-inhibiting by-products are only solidified into granular solids having a relatively hard surface without being associated with substantial amounts of heavy metal oxidation catalysts only when the binding requirements are met, and thus are difficult to dissolve again in the aqueous phase. Found to be a granular of state.

Accordingly, an object of the present invention is to combine a conventional method by recycling a part of the mother liquor from which terephthalic acid has been separated into a catalytic liquid oxidation zone, recovering the catalyst-containing aqueous solution from another part of the mother liquor, and recycling the recovered aqueous solution to the oxidation zone. It is to provide a continuous production method of terephthalic acid removed. If desired, it can be concentrated and recycled.

Many other objects and advantages of the present invention will become more apparent from the following description.

According to the process of the present invention, P-xylene is subjected to liquid phase oxidation in acetic acid with molecular oxygen such as, for example, air in the presence of a heavy metal oxidation catalyst according to a conventional method, and terephthalic acid is separated and recovered from the resulting oxidation reaction mixture. The terephthalic acid is separated and a portion of the remaining mother liquor is recycled to the oxidation zone as it is or concentrated after conventional methods. The remainder of the mother liquor is concentrated by distillation or evaporation and the residue containing the heavy metal oxidation catalyst and organic byproducts is extracted with water. The resulting catalyst-containing aqueous solution is recycled to the liquid phase oxidation zone.

According to the present invention, the remaining portion of the mother liquor has an acetic acid content in the residue of 5% by weight or less, preferably 2% by weight or less, more preferably 1% by weight or less, based on the weight of the residue. Concentrate until the content of benzoic acid formed by or by oxidation of monoalkylbenzenes present as impurities of P-xylene is at least 15% by weight, preferably at least 20% by weight, based on the weight of the residue. More preferably, it is carried out until the content of isophthalic acid in the concentrate residue is 3% by weight or less based on the weight of the residue, and the content of P-toluic acid is 3% by weight or more based on the weight of the residue. do. When the amount of acetic acid in the residue exceeds the above upper limit, a substantial amount of undesirable organic by-products are dissolved and / or dispersed in the resulting catalyst-containing aqueous solution, thereby containing a catalyst containing an optionally extracted heavy metal oxidation catalyst. No aqueous solution can be obtained.

Further, when the concentration is excessively performed so that the amount of benzoic acid is below the lower limit, it solidifies too rapidly upon cooling of the molten residue to form a large mass. As a result, the catalyst cannot be extracted into the aqueous solution with good efficiency.

The object of the present invention is not to achieve simply by concentrating the residue with a certain amount of acetic acid and benzoic acid (Requirement (1)), and contacting the residue with two to two times the weight of water when it is a hot molten liquid. Thereafter, it is necessary to quench the residue to a temperature of 50 ° C. or lower, preferably 20-50 ° C. or lower (requirement (2)).

This requirement (2) is important as a coupling condition with the above requirement (1), and if any one of them is not satisfied, the object of the present invention cannot be achieved. It is not clear why the combination of requirements (1) and (2) is important in the process of the present invention. However, organic by-products containing water-soluble or several emulsions and antioxidant inhibitory by-products are extracted with an aqueous phase in a heavy metal oxidation catalyst. It can be easily understood from the experimental results of the comparative example described below that the combination of the above requirements (1) and (2) plays a great role in solidifying into particles having a size and surface state suitable for the following.

When carrying out the process of the invention, keeping the residue in a hot melt is carried out by heating the residue to a temperature above the melting point of benzoic acid. Contact of the hot melt residue with water can be carried out by adding water to the residue with stirring. Desired quenching can be performed by appropriately adjusting the temperature and amount of water or the stirring conditions. If necessary, other cooling means may be used in combination. The quenching is preferably carried out by adding the molten residue and water to the tank while maintaining the temperature of the extraction tank mixing the molten residue and water to 50 ° C or less. The temperature of the extraction tank is maintained by a common method such as using a cooler such as a jacket or by introducing the mixture into the cooler to cool and then circulate.

When the temperature of the extraction tank is not below 50 ° C, the organic by-products do not solidify into granular solids but become an emulsion and are incorporated into the catalyst-containing aqueous solution. However, if the residue is quenched at too low a temperature, the solidified particles of the organic by-products become lumps, which prevents the incorporation of organic by-products into the aqueous solution containing the catalyst, but the extraction of the catalyst is insufficient. Therefore, it is preferable to make quenching into the temperature of 20-50 degreeC. Solidification of the organic by-products is carried out instantaneously, but in order to improve the extract of the catalyst, it is preferable to stir the mixture at a temperature of 50 ° C. or lower for 10-30 minutes.

There is a limit to the amount of water used to cool the residue below 50 ° C, using 2-5 times the amount of water based on the weight of the residue. If the amount of water is insufficient, the organic by-products tend to become large agglomerates and the catalyst extraction rate does not increase. On the other hand, when the amount of water is excessive, an emulsion of organic by-products is formed, and the organic by-products including oxidation inhibitor by-products are incorporated into the catalyst-containing aqueous solution. Therefore, it is necessary to adjust the amount of water within the above specific range.

The aqueous solution is separated from the mixture of the organic by-product in the form of particulate solid and the catalyst-containing aqueous solution formed as described above, and the separated catalyst-containing aqueous solution is recycled to the catalytic liquid phase oxidation zone. Separation can be performed by any liquid-solid separation method, for example by centrifugation. The separated catalyst-containing aqueous solution may be partially or wholly recycled to the catalytic liquid phase oxidation zone. If desired, it can be concentrated and recycled.

The following examples and comparative examples further illustrate the method of the present invention.

Example 1

To the oxidation reactor, 100 kg / hr of P-xylene, 900 kg / hr of acetic acid and catalyst (3.4 kg / hr of cobalt acetate, 3.4 kg / hr of manganese acetate and 1.7 kg / hr of sodium bromide) were continuously fed and P-xylene was oxidized while continuously introducing air at a rate of 400 m 3 / hr (standard state) at a temperature and a pressure of 10 kg / cm 2 -G to remove water produced as a by-product. After 1 hour, the oxidation product was continuously discharged from the oxidation reactor, and 148 kg / hr of terephthalic acid was separated from the reaction product by centrifugation. 95% by weight of the obtained mother liquor was circulated directly to the oxidation reactor, and the remainder of the mother liquor was concentrated by evaporation to give a residue in a molten state (0.5 wt% acetic acid, 32 wt% benzoic acid, 19 wt% isophthalic acid, P-tol). 14 kg by weight of rumic acid, 2% by weight of P-formbenzoic acid, 25.5% by weight of other organic impurities, and 2% by weight of catalyst) 1.5 kg / hr.

The molten residue was continuously supplied to an extraction tank equipped with a stirrer, contacted with water three times (weight) at room temperature, passed through a jacket of water and quenched to 40 ° C. to solidify the organic byproduct into a granular solid form. did. At the same time, the granular solid is held at 40 ° C. for 20 minutes to extract the catalyst. The effluent from the extraction tank was separated by centrifugation into organic solid by-products (1.65 kg / hr) and aqueous solution containing catalyst (4.35 kg / hr). The catalyst containing aqueous solution was concentrated and recycled to the oxidation reactor. Continuous operation was performed for 2000 hours, but no abnormality occurred.

The organic by-product content in the catalyst-containing aqueous solution was 0.5% by weight, and the extract contained 90.6% by weight of cobalt, 91.8% by weight of manganese, and 80.6% by weight of bromine. Moreover, the removal rate of the granular organic by-product from the residue was 98 weight%.

Comparative Example 1

In Example 1, the molten residue (10 wt% acetic acid, 29 wt% benzoic acid, 17 wt% isophthalic acid, 12.7 wt% P-toluic acid, P-formbenzoic acid obtained by relaxing the concentration of the remaining portion of the mother liquor) The same treatment was carried out except that 1.8% by weight, 4.5% by weight of terephthalic acid, 23.2% by weight of other impurities, and 1.8% by weight of catalyst) were used. An emulsion was formed, and as a result, the content of organic by-products in the catalyst-containing aqueous solution was high as 5.7 wt%, while the removal rate of organic by-products from the residue was low as 74 wt%, making it impossible to operate continuously for a long time.

Comparative Example 2

In Example 1, the same extraction was carried out except that the residue in the molten state and the water at room temperature were contacted without being quenched, but were heated for 20 minutes at 60 ° C. by steam through the jacket. An emulsion was formed, and as a result, the removal rate of organic by-products from the residue was as low as 77% by weight, while the content of organic by-products in the aqueous solution containing catalyst was as high as 5% by weight, making it impossible to operate continuously for a long time.

[Comparative Examples 3, 4 and 5]

In Example 1, when contacting the molten residue with water, the amount of water was changed to 1 (weight), 6 and 10 times, respectively, based on the residue, and the jacket was passed through cooling water or water vapor to The same treatment was performed except that the temperature was maintained at about 40 ° C. When the amount of water was 1 times, it was found that the organic by-products became agglomerates and the proportion of extracted cobalt was as low as 62.3%. When the amount of water was 10 times, an emulsion was formed and the removal rate of organic by-products was low as 69% by weight. In either case, it was impossible to operate continuously for a long time.

[Examples 2, 3 and 4 and Comparative Examples 6, 7 and 8]

In Example 1, it carried out similarly to Example 1 except having changed the amount of acetic acid and benzoic acid in a residue within the range of this invention.

This result was shown in Table 1 with the result of Example 1 and the comparative example 1-5. Comparative Example 6 was carried out in the same manner as in Comparative Example 1 except that the concentrated residue contained 6% by weight of acetic acid. Comparative Example 7 was carried out in the same manner as in Comparative Example 1 except that the residue was cooled, solidified, pulverized, extracted with hot water for 20 minutes, and then cooled to room temperature to obtain an aqueous solution containing catalyst. Comparative Example 8 was carried out in the same manner as in Example 1, except that the residue was distilled to 13 wt% of benzoic acid.

TABLE 1

Claims (1)

As described in the text, P-xylene is liquid-oxidized to molecular oxygen in acetic acid in the presence of a heavy metal oxidation catalyst, and terephthalic acid is separated and recovered from the obtained reaction mixture, and part of the mother liquor is concentrated or concentrated, followed by catalytic liquid oxidation zone. In the continuous preparation of terephthalic acid consisting of the step of recycling the residue of the mother liquor and the residue containing the heavy metal oxidation catalyst and organic by-products with water and recycling the resulting aqueous solution containing the catalyst to the oxidation zone, (1) In the concentration, the amount of acetic acid in the residue is less than 5% based on the weight of the residue, and the amount of benzoic acid in the residue is less than 15% based on the weight of the residue. Until not, (2) the residue is brought into contact with water of 2-5 times its weight in a hot molten state and then quenched to a temperature of 50 ° C. or less, (3) The catalyst-containing aqueous solution is separated from the mixture of the above-mentioned organic by-product and the catalyst-containing aqueous solution in the form of granular solid, and the separated catalyst-containing aqueous solution is recycled to the catalytic liquid phase oxidation zone. Manufacturing method.