DE1950080A1 - Process for the preparation of terephthalic acid - Google Patents

Description

EGG. DU PONT DE NEMOURS AND COMPANY 10th and Market Streets, Wilmington / Delaware 19 898, V.St.A,

Process for the production of terephthalic acid

The invention relates to the production, in particular, to the purification of terephthalic acid (hereinafter also referred to as TPA for short).

The TPA represents a technical chemical «which is today im Large scale is generated, mainly for use. in the production of polyesters for which the TPA or a derivative such as dimethyl terephthalate, in a high purity State must be available. Any improvement in such a process represents a significant economic advantage and is of considerable importance.

U.S. Patent 2,952,704 provides mixtures of Isophthalic and terephthalic acid by washing the mixed acids with acetone or similar ketone and thus dissolving them Refining the Impurities Without Dissolving the Acids · Temperatures of up to about 200 C and preferably not above about 150 ° C (400 or 300 ° F) should be suitable

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. be. The patent also states that sin modifying »solvents, such as water« are used for this purpose . can * reduce the dissolving power of the ketone for the phthalic acids and which are in the decolorizing agent to reduce the dissolving amount of phthalic acids, but that the use of water is not a condition and is satisfactory. Results in many cases can be achieved without any water. Nowhere in the patent is there any another mention of a single use of water »and the examples work old acetone without water,

In younger tent is old the British patent specification 1 069 856 has been provided, raw TPA in la essential anhydrous ketone at elevated temperatures, χ, B. 250 ° C » and to dissolve at overpressure and then to crystallize out purified TPA. The solvent ketone is preferred a cyclic "ketone" such as cyclohexanone, but can also be acetone. The ketone should be essentially anhydrous but contain up to 10 Qew. £ of water, taking into account that the ketone must dissolve the TPA.

It has now been found that when acetone is used under conditions alone, meeityloxide is formed "which means a loss of acetone" and can lead to contamination of the TPA. According to the invention, however, it has also been shown that washing the crude TPA with aqueous acetone * dee predominant amounts of water «d» h * at least 50 ow. % and preferably higher amounts, e.g. B. at least 80 dew. % up to 95 oew. $ As a action of the acetone as a solvent to prevent "contains" as well at relatively high temperatures moderately »223-275 ° C and preferably up to 250 ° C, advantageous 1st. Without restricting the invention to any particular theory, "it is assumed * that at lower temperatures, such as those used in US Pat. No. 2,952,704," any Bxtrak-

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tion of impurities takes place mainly physically, while at the higher temperatures used in accordance with the present invention some chemical reaction between the acetone and at least some of the impurities is likely to occur and the resulting reaction products are easier to detect. In any case, by increasing the ^{value of the 1} Tesiperatv: · In contrast to the method according to the USA patent document 2 952 7Q ^ a significant difference in effect is achieved. Furthermore, the use of such large amounts of water reduces the likelihood that the acetone will react with the TPA to form undesirable by-products. The ra * ächverhl * Xtni8 @@ kömierx 5: 1 to I t 5 »preferably 2 :: to I : S, calculated as the weight of the asetone to the one on? raw TPA, betregen and hangers * from the WascfobedlHgwng ^ &&> wes autsli applies to the required time, however usually between 20 minutes and 2 Sfcd., see B. I hours to 80! Sin., genilger ,. The process can be carried out in one or more stages and discontinuously or continuously. If there is enough Druct you should: work * to keep the laundry in the liquid phase, e.g. B. up to about 15 to 65 atm., Preferably about 25 to 40 <> tm. (250 to 900 or 40C to 600 poundff / square inch overpuek). The resulting TPA can be separated off in a conventional manner, such as by filtering or centrifuging. Likewise, the TPA is preferably cooled prior to performing the separation, e.g. B. to '100 to 150 ° C. The pure; Treatment treatment can, if desired, be combined with any other such pre- or post-treatment.

Raw TPA for use in the process is by oxidation an aromatic hydrocarbon such as p-xylene, with molecular oxygen, especially air, in the presence a heavy metal catalyst, such as cobalt naphthenate,

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ζ. B. geroäss USA patent J 299 125 available. the The main impurities are generally partially oxidized Intermediate compounds, such as p ~ toluic acid (hereinafter for short: PTA) and ρ-PoCTuy! Benzoic acid (hereinafter for short: PFBA) and perhaps p-toluylaldehyde (hereinafter abbreviated to PTL) and benzoic acid · The hollow lugs used in the examples are in such a typical process at about 2.90 ° c has been manufactured.

The following examples are all parts and percentages information * unless otherwise stated, refer to the weight, serve to further explain the invention *

B is ρ i, s I ₁ Q

1. One 81.9 % TPA, 12.9 % PTA, 5Λ% PffBA and 0.2 % PTL around! The benzoic acid-containing mixture was agitated with an equal amount of acetone and four times the amount of water and heated to 250 ° C for about 40 minutes under autogenous pressure and then allowed to settle and filtered at 150 ° C. This treatment was repeated, yielding a TPA with a PFBA content of only about 0.2 % and FTA of $ 0.1, which was essentially free of meeityloxide and other impurities attributed to acetone treatment.

2. By using aqueous acetone with a water content of 95 % , a result comparable to that of Example 1 was obtained.

The method according to the invention can thus be used to obtain TPA with a degree of purity of over 99.5 % .

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In a first test, samples of the same crude mixture as above were used. In each case it was the sample a single wash treatment at autogenous pressure with a corresponding, agitated mixture (containing the same Amount of acetone like a 20 # mixture, with water) subject to the temperature mentioned below * allowed to settle and filtered at 100 ° C, with the exception of those in Table I. mentioned the same conditions as above were used.

T a b le I Washing temperature, ° C Remaining soiling

200 1.2 % PFBA, 0.6 % PTA

Example J5 250 0.2 % PFBA, 0.6 % PTA

The second test corresponded to the above, with the modification that a Rohraischung was used, the 85.6% TPA, 9 * 4 $ PTA, 4.4% and 0.3% PFBA PTL and benzoic acid contained, and the filtration temperature 150 ⁰ C. fraud; Results:

TaJ el le II Sample washing temperature, ° C Remaining impurities

Example 4 250 tracks 0.2 %

In a further series of tests, raw samples (containing about 3 % FFBA and 2 % PIA) were washed in a corresponding manner at 250.degree. C. with aqueous media containing various proportions of acetone, and then filtered at 150.degree. Without the use of acetone (with 100 % water), a washed TPA with a substantial content of PPBA is obtained, while

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the use of 10 or 20 # strength acetone solutions results in much smaller amounts of PFBA. When the acetone concentration is increased to 40 %, however, traces of mesityl oxide appear, which lead to a small loss of acetone of perhaps up to 5 % . Such small losses may sometimes be tolerable, but higher losses, such as those easily resulting from the use of essentially anhydrous acetone, are undesirable.

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Claims (1)

Cook 4 χ}. October 1969 Claim Process for the production of terephthalic acid by oxidation of an aromatic hydrocarbon, such as p-xylene, in the presence of a Sohwemetalcatalyst, such as cobalt naphthenet, while washing the crude terephthalic acid at elevated temperatures and at excess pressures with aqueous acetone, characterized in that nan at a temperature of 225 to 275 ° C works and aqueous acetone with a water content of at least 50 oew. % starts. -T- 009815/1890