DE1072620B - Process for the production of hexahydroterephthalic acid - Google Patents

Description

GERMAN

The invention relates to a catalytic process for the hydrogenation of terephthalic acid to hexahydroterephthalic acid.

The hydrogenation of the aromatic ring of esters of terephthalic acid has already been described (see U.S. Patent 2,070,770). In one such known process, esters are used hydrogenated the terephthalic acid to esters of hexahydroterephthalic acid in good yield in that the hydrogenation in the molten state at elevated temperature and pressure in the presence of a metallic hydrogenation catalyst is carried out. Although the known method discloses that the metallic hydrogenation catalyst made of nickel, platinum or palladium or compounds of these May consist of metals, the preferred catalyst should be a nickel catalyst, e.g. B. Raney nickel or Be nickel on kieselguhr.

Although this known process is a tempting route to the preparation of esters of hexahydroterephthalic acid the free acid is often the ultimate desired product. Hexahydroterephthalic acid can of course be obtained by saponification of the esters prepared by the known process but this requires an additional step which also incurs additional costs. It would Of course, it would be much more convenient to use the acid directly by hydrogenating terephthalic acid but a practical method for such direct hydrogenation has not yet been known.

Obviously, there is a good reason why the technique has not been a suitable method for the hydrogenation of terephthalic acid, since it was found that this acid not hydrogenated satisfactorily by the methods used to hydrogenate their esters can be. It has now been found that the satisfactory hydrogenation of terephthalic acid Presence of an inert liquid medium requires containing terephthalic acid under reaction conditions is at least partially soluble, and that terephthalic acid in the presence of certain catalysts is not in can be satisfactorily hydrogenated. For example, it has been found that the acid does not turn into hydrogenated satisfactorily in the presence of a nickel catalyst, which is preferred Is a catalyst for the hydrogenation of the terephthalic acid ester. In the same way it was found that only low yields of hexahydroterephthalic acid in the presence of platinum, rhodium and other known ones Hydrogenation catalysts can be obtained. However, it was observed that one through the selective use of a palladium or process for the preparation of hexahydroterephthalic acid

Applicant:

Hercules Powder Company, Wilmington, Del. (V. St. A.)

Representative: Dr.-Ing. A. van der Werth, patent attorney, Hamburg-Harburg I ₁ Wilstorfer Str. 32

Claimed priority: V. St. v. America 9 September 1957

Henry Christopher Dehm _r Wilmington, Del.,

and Lucien Garnett Maury, Newark, Del. (V. St. A.),

have been named as inventors

Rutenium catalyst terephthalic acid can hydrogenate under moderate conditions and is almost quantitative Yields of the desired product of the hexahydroterephthalic acid obtained.

The invention is therefore a process for the hydrogenation of terephthalic acid to hexahydroterephthalic acid, which consists in that terephthalic acid is exposed to the action of hydrogen at elevated temperature and pressure in the presence of palladium or ruthenium and in the presence of an inert liquid medium, wherein terephthalic acid is at least partially soluble under the reaction conditions will.

The procedure is illustrated by the following examples. Parts and percentages in the examples refer to weights unless otherwise stated.

example 1

55 parts of terephthalic acid were placed in a stainless steel shaking autoclave with 5.5 parts of a commercially available catalyst containing 5% palladium on activated carbon and 200 parts of water. The air in the autoclave was displaced by nitrogen, the nitrogen by hydrogen, and the autoclave was then pressurized to 350 kg / cm ² with hydrogen. The autoclave was then let down to 175 kg / cm ² , and while stirring the re-

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action mixture, the temperature was brought to 180 ° C. over a period of 75 minutes and held at this value for 35 minutes. The autoclave was then cooled and the hydrogen vented. The product was taken up in aqueous sodium hydroxide, nitrated and the clear, colorless solution was diluted with water to a total weight of 1600 parts. Ultraviolet analysis indicated complete reduction of the aromatic nucleus. The titrimetric analysis indicated that the yield of hexahydroterephthalic acid was 98.5%. Then, the solution was added dropwise with stirring to a _pH value of 2 with concentrated hydrochloric acid to give an odorless, colorless suspension. Because the strongly characteristic odor of hexahydrobenzoic acid was completely absent, monodecarboxylation did not occur during the hydrogenation. The product was cooled to about 5 ° C, collected on a sintered funnel, washed four times with cold water and dried in a vacuum oven at 50 ° C to give 29.6 parts (51.8%) of colorless microcrystals (melting point 306-308 ° C) to result. This melting point was not lowered after mixing with a real sample of trans-hexahydroterephthalic acid. The filtrate and washings were combined and washed ten times with ¹ Ii. Volume of ether drawn out. The combined extracts were dried over anhydrous sodium sulfate and distilled to give 23.6 parts (41.3%) of colorless crystals (melting point 173-174 ° C.) which melting point was not lowered after mixing with true cis-hexahydroterephthalic acid. The total yield of cis- and trans-hexahydroterephthalic acid was thus brought to 93.1%. More exhaustive extraction of the cis isomer would likely have increased the yield.

Example 2

The procedure of Example 1 was repeated with the modification that the autoclave was charged with 100 parts of terephthalic acid and 10 parts of catalyst, the reaction pressure was 210 kg / cm ² , the temperature was 200 ° C. and the reaction time was 2 hours. Analysis of the product showed that the yield of cis- and trans-hexahydroterephthalic acid was greater than 83.5% with a terephthalic acid conversion of 100%.

Example 3

The procedure of Example 2 was repeated except that the reaction pressure was 350 kg / cm ² , the reaction temperature was 180 ° C. and the reaction time was 35 minutes. The yield of hexahydroterephthalic acid (mixture of cis and trans isomers) was greater than 93% with a 100% conversion of the terephthalic acid.

Example 4

The procedure of Example 2 was repeated except that the reaction pressure was 350 kg / cm ² and the reaction temperature was 160 ° C. The yield of hexahydroterephthalic acid (mixture of cis and trans isomers) was about 92% with 100% conversion of the terephthalic acid.

Example 5

The procedure of Example 2 was repeated except that the reaction pressure was 350 kg / cm ² , the reaction temperature was 250 ° C. and the reaction time was 30 minutes. The yield of hexahydroterephthalic acid (mixture of cis and trans isomers) was about 92% with 100% conversion of the terephthalic acid.
5

Example 6

The process of Example 2 was repeated with the modification that the reaction ^{pressure was 350 kg / cm 2} , the reaction temperature was 195 ° C. and the reaction time was 2 hours. The yield of hexahydroterephthalic acid (mixture of cis and trans isomers) was about 98.5% with 100% conversion of the terephthalic acid.

Example7

100 parts of terephthalic acid were placed in a stainless steel shaking autoclave with 2 parts of a commercially available 5% palladium catalyst on silica (grain size 0.84 to 0.234 mm) and 200 parts of water. The autoclave was flushed twice with nitrogen and twice with hydrogen and then brought to a pressure of 210 kg / cm ² with hydrogen. The autoclave was then heated to 240 ° C. for 1 to 1.5 hours. When the temperature reached 240 ° C, the pressure ^{had risen to 350 kg / cm 2} and was held at 350 + 14 kg / cm ^{2 for} 1.8 hours. Work-up and analysis of the product showed that 100% of the terephthalic acid had been converted and the yield of mixed cis- and trans-hexahydroterephthalic acids was greater than 92.5%.

Example 8

According to Example 2, 75 parts of terephthalic acid were added at 140 ° C. and a pressure of 350 kg / cm ² in

Presence of 300 parts of water and 10 parts of a powdered catalyst composed of 1.25% ruthenium hydrogenated on activated charcoal for 9 hours. The yield of hexahydroterephthalic acid (mixture of trans and cis isomers) was about 98% with 100% conversion of the terephthalic acid. Essentially the same Results were obtained by repeating this example with the temperature increased to 200 ° C and the reaction time was reduced to 4.5 hours.

In order to explain the selectivity of palladium and ruthenium catalysts, comparative experiments were carried out using Raney nickel, nickel on kieselguhr, platinum on animal charcoal and rhodium on animal charcoal as catalysts. With Raney nickel at a reaction pressure of 420 kg / cm ² and a reaction temperature of 160 ° C., only about 10% of the terephthalic acid was converted after 8 hours. When using 5% nickel on kieselguhr, a reaction pressure of 350 kg / cm ² and one

At a reaction temperature of 200 ° C., there was no detectable yield after 6 hours. In the presence of 5% platinum on activated carbon at a reaction temperature of 270 ° C. and a reaction pressure of 420 kg / cm ² , the hydrogenation gave a conversion of terephthalic acid of 62% and a yield of hexahydroterephthalic acid of only 70% after 6 hours. Conversion and yield were significantly lower under less severe reaction conditions in the presence of the same platinum catalyst. When the reaction was carried out in the presence of 5% rhodium on activated carbon as a catalyst at 300 ° C. and 350 kg / cm ² , a conversion of 100% was obtained after 4.5 hours, but only a yield of 38%. The yield was even lower under less severe conditions.

As the examples have shown, the hydrogenation of terephthalic acid can be carried out under variable reaction conditions be carried out to give high yields of hexahydroterephthalic acid in the form of a mixture of cis and trans isomers, provided that a palladium or ruthenium catalyst is used and the reaction in one inert liquid medium is carried out, wherein terephthalic acid is at least partially under the reaction conditions is soluble. ίο

While this reaction is specific to palladium and ruthenium catalysts, the physical structure and composition of the catalyst can be varied widely without affecting the feasibility of the process. A catalyst, wherein metallic palladium or ruthenium is distributed on a carrier having a high surface area is S ¹ are most preferred. The catalysts of this type are well known in the art and include palladium on carbon, palladium on kieselguhr, palladium on alumina, palladium on rutile, and the corresponding ruthenium catalysts. These supported catalysts are equally effective, regardless of the form in which they are used, e.g. B. as beads or powder. Unsupported catalysts are also useful, such as powdered palladium or ruthenium, although as a general rule the effectiveness of the catalyst, based on terephthalic acid, is proportional to the exposed surface area of the palladium or ruthenium, which explains the preference for supported catalysts.

The amount of catalyst to be used varies considerably. It was found that fast conversions and good yields are available when the amount of palladium or ruthenium is only 0.003 parts per 100 parts of terephthalic acid, although practically speaking it is desirable to be at least apply about 0.025 parts palladium or ruthenium to 100 parts terephthalic acid. Naturally there is no upper limit in the ratio of catalyst to terephthalic acid, so this is only is an economic consideration.

The conditions of temperature and pressure can also be varied widely in practicing the invention, but in general temperatures between 150 and 300 ° C, most preferably 200 to 300 ° C, are preferred as they result in the most desirable reaction rates. There does not seem to be an upper limit in the pressure which can be used according to the invention, but a minimum pressure of about 70 kg / cm ² represents a practical lower pressure limit below which the reaction rate is too slow for industrial operation. More preferably, however, the process of the invention is carried out at a pressure of at least 210 kg / cm ^{2 in} order to obtain the best reaction rates.

In choosing the reaction medium, there are many liquids which meet the requirement To be inert under the reaction conditions, and to have the ability to at least terephthalic acid partially to solve. Water is by far the preferred inert liquid for economic reasons Medium, but other liquids, such as dimethyl sulfoxide, dimethylformamide and hydrogenated esters of Terephthalic acid, are also useful.

The initial reaction mixture is made simply by charging terephthalic acid and the inert liquid medium into the reaction vessel either separately or in admixture with one another. In most cases, especially in continuous operation, it is desirable to fill the reactor with a slurry of terephthalic acid and to feed the inert liquid medium. This is practically the lower limit of the given minimum amount of solvent required for hydrogenation. In general, the Amount of inert liquid medium about 2 to 5 times the weight of the terephthalic acid used. A larger amount of the inert liquid medium can of course be used without disadvantage of the process, but to avoid excessive dilution of a reaction mixture, is preferred, no more than about 20 parts of the inert liquid medium per part of terephthalic acid apply.

Depending on the amount of inert liquid medium used and the reaction temperature a varying amount of terephthalic acid is dissolved in the process during the reaction. With a suitable choice of the medium, it is possible to carry out the reaction essentially with the total amount on terephthalic acid in solution, although this is by no means critical and the The reaction also proceeds satisfactorily when only part of the terephthalic acid is dissolved.

Claims (2)

Patent claims: 1. A process for the preparation of hexahydroterephthalic acid, characterized in that terephthalic acid in a known manner with hydrogen advantageously at 150 to 300 ° C and at least 210 kg / cm ² in the presence of palladium and ruthenium and in the presence of an inert liquid medium in which terephthalic acid at least is partially soluble under the reaction conditions, is hydrogenated. 2. The method according to claim 1, characterized in that the inert liquid medium is water. Considered publications:
U.S. Patent No. 2,070,770;
Ber. German Chem. Ges., Vol. 44, 1911, pp. 2310, 2311. © 909 708/342 12.59