DE1618717A1 - Process for the production of aromatic carboxylic acids - Google Patents

Description

Process for the preparation of aromatic carboxylic acids The invention relates to an improvement in the liquid phase oxidation process of an aromatic Compound or aromatic compounds with at least one oxidizable aliphatic Substituents with molecular oxygen in the presence of a catalyst system under high temperature and elevated pressure conditions to generate the appropriate aromatic carboxylic acid or carboxylic acids, with the desired product under increased Reaction speed and with high yield is obtained. Also used as a side effect improves the smoothness of the response and allows regular operation of the reaction process 1 and furthermore, by the improved process itself aromatic starting compounds with a plurality of oxidizable aliphatic Substituents the corresponding aromatic carboxylic acids with industrial advantage getting produced.

In particular, the invention relates to the above method of manufacture aromatic carboxylic acids, the improvement being that in addition to the catalyst system at the same time silicones are present as promoters in the liquid phase reaction system.

So far, the liquid phase oxidation of an aromatic compound was with at least one oxidizable aliphatic substituent with molecular oxygen under the high temperature and elevated pressure conditions in the presence of a catalyst system such as for example a heavy metal, e.g. cobalt, manganese, nickel, or e.g. one Heavy metal and bromine, to produce the corresponding aromatic carboxylic acid known.

However, there are still a number of unsolved issues with this common approach Problems with reaction rate and yield occurred, and it was sought improvements to these points without any limitation as to of the starting material.

The yield could to some extent due to the simultaneous Use of heavy metal catalyst and bromine can be increased. However, were for the oxidation of aromatic starting compounds with a plurality of oxidizable ones aliphatic substituents, high reaction temperatures and long reaction times required before the complete oxidation of all substituents, and is therefore such a reaction method is not satisfactory.

-Furthermore, the above- process can produce a by-product, its Separation from the desired product is difficult, and also its control to achieve an even and regular course of the reaction is by no means simple. Accordingly, the introduction is higher: reaction temperature and / or longer Reaction times disadvantageous with regard to the purity of the product, although it it appears that with such a procedure high yields of the desired product are attainable.

For example, it is a typical example of the oxidation of p-xylene for the production of terephthalic acid is not very difficult, terephthalic acid Producing in apparently high purity with good yield, however, became common found when using such terephthalic acid as a material for polyester, that the polyester product is qualitatively uneven and inferior. There were hence further efforts to produce so-called fiber-grade terephthalic acid undertaken at the current state of technology.

The above is just an example. It was made after a Researched improvement in general of the usual method described above, and it was found that the reaction rate as well as the yield improved can be done by the liquid phase oxidation in the presence of a small amount a promoter or Accelerator is carried out. It was also found that without using high reaction temperatures or more specifically Limitation with regard to the starting material due to the method according to the invention the uniformity of the reaction is improved and regular reaction control is made possible and the quality of the aromatic carboxylic acid obtained is also satisfactory is.

It has also been found that silicone is particularly advantageous as a promoter is.

The exact mechanism by which the silicone works in an advantageous manner as a promoter for the reaction system in question according to the invention and Oxidation process works, has not yet been clarified, but its effectiveness is - as will be demonstrated later on the basis of comparisons with control examples - striking.

The object of the invention is therefore an improved method for the production of aromatic carboxylic acids by means of the liquid phases described above oxidation method.

The silicone, according to the invention, at the same time in the liquid phase reaction system should be present as a promoter in addition to the heavy metal and bromide as a catalyst, carries to increase the reaction speed.

The silicone can also be called siloxane and has the basic structure represented by the following formula: More specifically, in addition to low molecular weight compounds with a simple structure, such as hexamethyldisiloxane and octamethyltrisiloxane, the known silicones include polyslloxanes with higher molecular weights. Silicones having molecular weights which varied over a considerably wide range can be used in the practice of the invention. Substituents to be connected to the silicon atom are hydrogen, alkyl radicals such as methyl and ethyl radicals, phenyl radicals and halogenated alkyl radicals. Among the listed substituents are those which are relatively chemically stable, such as zß. the methyl group or phenyl group, particularly preferred, but the substituent is not critical.

Furthermore, both chain-like siloxanes and cyclic siloxanes can be used be used. The siloxane compounds used according to the invention are at room temperature liquid or cream-like, and hence vulcanized silicone rubber and silicone resin high molecular weight unsuitable for the purpose.

So that means that vulcanized silicone rubber and silicone resin are excluded from the scope of the "silicone" specified in the invention.

For the process according to the invention, silicones are those which are below the reaction temperature and pressure conditions are liquid, including those with molecular weights of normally 400 or above and those below the reaction temperature - and pressure conditions are liquid, are preferred.

Silicones that become gaseous under the conditions mentioned can can also be used if an additional means is provided to prevent the gaseous evaporated silicones to condense and the condensate in the reaction system traced back.

For specific examples of silicones useful in the invention include octamethyltrisiloxane, methylhydropolysiloxane, methylalkylpolysiloxane (where the alkyl group has 1-10 carbon atoms), methylphenylpolysiloxane, Diethylpolysiloxane and methylfluoroalkylpolysiloxane (where the fluoroalkyl group is 1-4 Has carbon atoms).

According to the invention, the silicone compound is left as described above - In the liquid reaction system simultaneously with the catalyst system in one Amount of about 0.0001-2% by weight, preferably 0.001-0.2% by weight, based on the aromatic Starting compound are present. At the amount below the lower limit above Promoter performance tends to drop and, on the other hand, use wears an amount greater than the upper limit in no way affects the reaction rate to increase. For these reasons, the silicone is used in amounts within that specified above Range applied with satisfactory results.

Since the silicone to increase the reaction rate in the according to the invention contemplated reaction system and method is used believed that it acts as a promoter for the reaction system and process, however the exact mechanism of its mode of action is not yet clear. However goes from a comparison of the results of the present method with those of reactions which were done in exactly the same way except that that was done at the same time present silicone has been omitted, with a view to converting within a predetermined length of time, the purity and hue of the product and the Reproducibility of the reaction indicates the improvement achievable by the invention from an industrial point of view, is extremely valuable.

The aromatic compounds suitable for the invention include, for example, the compounds with at least one, preferably 1-3, oxidizable aliphatic substituents. The aromatic ring can be either the benzene or the benzene Be naphthalene ring, compounds with a benzene ring are preferred.

As oxidizable aliphatic substituents, any alkyl, Aldehyde and alcohol residues are used in particular the compounds in which the substituent is an alkyl radical having 1-3 carbon atoms are preferred starting materials. Of course, the aromatic can Starting compound in addition to these oxidizable aliphatic substituents contain other substituents under the reaction conditions not take part in the oxidation. Such other substituents are e.g. B. carboxyl radicals, Nitro groups and halogen atoms.

As some of the specific examples of such starting aromatic compounds the following can be cited: alkylbenzene such as toluene, thylbenzene, cumene, Xylene, diisopropylbenzene and pseudocumene; aromatic alcohols and aldehydes such as e.g., benzyl alcohol, benzaldehyde, methylbenzyl alcohol, and terephthalaldehyde. Examples of compounds that simultaneously have other substituents that are not involved in the oxidation reaction are aromatic carboxylic acids such as toluic acid and alkylbenzene derivatives, such as B. chlorotoluene.

Among the compounds exemplified above are, for example Toluene, ethylbenzene, cumene, xylene, diisopropylbenzene, pseudocumene and toluic acid the preferred starting materials.

The starting materials listed above can either be used alone or can be used as a mixture of several specific compounds.

The invention can be particularly advantageous in the manufacture of the corresponding aromatic dicarboxylic acids, for example terephthalic acid from dialkyl-substituted aromatic compounds such as p-xylene can be used.

The reaction takes place according to the known liquid phase oxidation method, in the oxidation with the introduction of molecular oxygen into the liquid phase reaction system in the presence of the catalyst system under the high temperature and elevated Printing conditions progresses.

While a solvent is not always required if the to be generated acid is liquid under the reaction conditions, and as a solvent is used, it is usually preferred to use a solvent as the reaction medium.

The type of solvent is not critical as far as it is opposite the oxyadion reaction or the reaction conditions is stable or inert. Man can also use a plurality of, for example, two starting components in order to Allowing one of them to act as a solvent for the other, creating two types each of the corresponding carboxylic acid can be prepared.

Lower fatty acids, aromatic carboxylic acids, aromatic hydrocarbons and halogenated hydrocarbons are used, ; among which the lower fatty acids are preferred. Lower fatty acids with 1 up to 8 carbon atoms in their molecule are particularly for use for the invention suitable. Among others are saturated fatty acids with 2 to 4 carbon atoms in their molecule, e.g. B. acetic acid, propionic acid and n-butyric acid, the most common preferred acids.

The amount of solvent is when an aliphatic Monocarboxylic acid is used, suitably in the range of 1 to 15 parts, preferably 3 to 10 parts Parts by weight, per part of the earth to be oxidized.

The reaction takes place under freely variable heating conditions, as far as such phenomena as charring of the desired product or formation tarry substances are avoided. Applicable temperatures are usually in the range from 150 to 3000C, preferably in the region from 180 to 2500C The reaction pressure is variable Depending on such factors as the starting material and the solvent, However, it can freely according to known means for liquid phase oxidation within the range at which the reaction system is maintained as a liquid phase will. Normally the pressure can be between atmospheric pressure and 100 kg / cm2 (overpressure: Unless otherwise stated, the pressure in the present description is a gauge pressure expressed), preferably 10 to 50 kg / cm2.

Catalysts known per se can be used as the catalyst, however, for the invention is the catalyst system consisting of heavy metal and Bromine, suitable.

As a heavy metal catalyst, for. B. nickel, cobalt, iron, chromium and manganese are listed, with cobalt and / or manganese being particularly preferred are. As already known, such heavy metals and bromine can be in any Form can be applied as an element, ion or compound.

However, it is preferred that their form be in the parent compound and or is soluble in the reaction medium.

For example, the following catalyst systems can be used with advantage can be used, that is, include examples of heavy metals as a catalyst Bromides or carboxylic acid salts of manganese or cobalt, such as bromide and acetate and naphthenate of magnesium or cobalt, whereas examples of bromine as Catalyst include ammonium bromide, ethane tetrabromide and benzyl bromide.

The reference in the description of the invention to 11 heavy metal and Bromine as a catalyst system thus includes all of these known forms.

As the amount of the catalyst, it is usually an amount in the range of about 0.005 to 5% by weight, preferably 0.02 to 2% by weight, of the heavy metal (in the case that the heavy metal is in the form of a compound, expressed as metal) based on the aromatic starting compound, normally sufficient. Possibly a greater amount can be used, but with no noticeable benefit, and consequently the amounts within the range given above are usually used. The amount of bromine can in turn vary depending on the amount of heavy metal catalyst.

The most commonly used ratio between metal and bromine is 0.1 to 10 g-atoms of bromine per g-atom of metal.

Of course, the foregoing is simply the description conventional quantitative conditions used and are not critical to the invention.

Air is also to be introduced into the liquid phase reaction system molecular oxygen is most practical, but pure oxygen gas, oxygen-enriched air or oxygen gas diluted with an inert gas, such as nitrogen or carbon dioxide can be used.

The term molecular oxygen used in the present process thus includes such molecular oxygen-containing gases.

The amount of oxygen to be introduced into the reaction system should be at least sufficient to convert the oxidizable substituent in the starting material to the carboxyl group to oxidize. For example, if the substituent is methyl, 1.5 molecules are oxygen required per methyl radical. However, the supply of an excess amount shortens in molecular oxygen - namely more than is necessary for oxidation - not alone the reaction time, but also reduces the formation of the in the oxidation reaction generated impurities and thus contributes to the production of aromatic carboxylic acids in high yield. Because of this, the addition will be more than the stoichiometric Amount of molecular oxygen preferred. For this purpose, molecular oxygen is used fed at such a rate that that discharged from the reaction zone Exhaust contains a certain amount of unused oxygen. However, if the Supply speed is too high, most of the oxygen is blown off, without what is needed for consumption Dwell time. With one of these The exhaust gas can be an explosive mixture with the reactant or a state Form part of the solvent withdrawn with the gas and make operation extremely dangerous design. In practice, it is therefore preferred to carry out the reaction in such a Execute condition in which the rate of oxygen supply in such -Excess occurs that the main amount of oxygen in the feed gas for the Reaction is consumed. The supply amount should also vary depending on the type of used Catalyst can be varied.

The present process can be batchwise or discontinuous or be carried out in a continuous system.

For example, isophthalic acid from metmaxylene, terephthalic acid from paraxylene, benzoic acid from toluene and trimelitic acid from pseudocumene with economical Advantage can be produced.

Some embodiments of the invention are illustrated below of working examples given together with control examples for Verdbichszwecken.

Examples 1 to 6 and Comparative Examples 1 to 2 In one with one A titanium autoclave equipped with a stirrer, a reflux condenser and an air inlet tube Xylene, acetic acid, the catalyst system and silicone as a promoter given. The reaction takes place with air being blown as molecular oxygen into the Liquid phase zone, while the above materials are kept under heating.

During the reaction, the exhaust gas was drawn off through the cooler-2, in order to keep the pressure of the reaction zone constant at 25 kg / cm. By analyzing the Oxygen concentration in the withdrawn gas could stop the reaction be determined.

After the reaction had ended, the air supply was cut off, and the reaction system was cooled and filtered to separate the solid reaction product.

The results are shown in Table I below, in which the results of the comparative tests, which were carried out in exactly the same way as in the examples with the exception that no silicone was used are listed.

Table 1 Reaction example p-xylene acetic catalyst temp.

(g) acid (g) promoter (g3 (° C) (g) 1 40 300 manganese acetate methyl poly- 220 (0.30) siloxane cobalt acetate (0.04) (0.15) ammonium bromide (0.20) 2 40 300 "methylethyl 220 polysiloxane m (0.04) 3 40 300 "methylphenyl- 220 polysiloxane (0.04) 4 40 300 "Octamethyl- 220 trisiloxane (0.04) Comparative Ex. 1 40 300" - 220 Ex. 5 50 200 Manganese naphtho diethyl 190 nat (1.0) polysil-cobalt naphtheoxane (0.08) nat (0.50) Tetrabromoethane (0.30) Ex. 6 50 200 "methylfluoroethyl poly- 210 siloxane (0.06) Comparative example 2 50 20 "- 210 Table 1 Port setting APIiA air supply Time b. Yield pure color value example speed. for unity d. he (l'h) end. d. Tere- d.- preserved reactiphthal. stop. Tereon wt .-% tere- phthal- (min) phthalic acid 1 350 30 92 99.9 30 2 350 29 91 99.9 33 3 350 30 91 99.9 30 4 350 31 90 99.8 34 Comparative ex. 1 350 38 86 99.0 70 Ex. 5 350 36 89 99.2 50 ex. 6 35 33 91 99.6 40 comparative ex. 2,350 42 85 98.5 80 at The table values were the purity of the terephthalic acid by weighing the terephthalic acid determined as the barium salt. The APHA color value of terephthalic acid is determined by 2.5 g of terephthalic acid were dissolved in 100 ml of ln sodium hydroxide solution and then the color of the solution obtained with the APA standard value (American Public Health Associaton) was compared.

Examples 7 to 13 and Comparative Examples 3 to 6 Example 1 was used repeatedly except that the kind of the starting aromatic compound is changed became.

The results are given in Table II.

Table II -Reakt.-Example aromat. Vinegar catalyst temp.

Starting acid (g) promoter (g) (° C) Comp. (g) (g) 7 toluene --a) Cobalt naphtho-methylphe- 200 (100) nat (1.0) nylpolysi-manganese naphtheloxane (0.08) nat (2.0) benzyl bromide (0.5) 8. cumene 200 manganese acetate methyl ethyl 190 (50) (0.50) polysiloxane ammonium bromide (0.04) mid (0.40) 9 m-xylene 200 nanganbro-methylphenyl-220 (40) mid (0.40) polysiloxane cobalt acetate (0.04) (0.15) comp. ex. 3 "200 ft n 220 Ex. 10 p-diiso- 300 manganese bromethylpoly- 210 propyl- mid (0.80) siloxane benzene (0.05) (40) Comp. ex. 4 "300" - 210 ex. 1t pseudo-250 cobalt naph-methylcumene thenat (0.50) polysiloxane 210 (40) manganese naph- (0.06) thenate (1.0) tetrabromoethane (0.40) Table II continued APHA air supply time b. yield Pure color value example speed. for unity d. er (l / h) end. d. Carbon d.- retained reactive acid. Carboxylic acid% w / w carboxylic acid (min) 7 400 35 Benzoic 99.8 - c) acid # (96) 8 400 110 Benzoic 98.1 100 acid (90) 9 350 27 Iso- 100 @@ phthalic acid (95) cf. ex. 3 350 34 isophthalic 99.1 70 acid (88) E.g. 10 400 45 tere- 96.6 200 phthalic acid (75) cf. - Terex. 4 400 54 phthal- 92.3 350 acid (67) ex. 11 350 40 trimetalit- 98.6 160 acid (92) continuation Table II Example aromat. Vinegar catalyst promoter (g) reactant starting acid (g) temp.

Connection (g) ° C (s) comparative- pseudo- 250 cobalt naph- - 210 example cumol thenate (0.50) 5 (40) manganese naphthenate (1.0) tetrabromoethane (0.40) Ex. 12 p-toluene 250 cobalt naphmethyl poly 200 ylic acid thenate (0.30) siloxane (40) manganese acetate (0.04) (0.30) ammonium- ~~~~~~ bromide (0.20) comparative example "250" - 200 6 Example 13 p-methyl-200 cobalt methyl 210 benzyl naphthenate phenyl alcohol (1,3) polysi- (40) ammonium broloxane mid (0.30) (0.05) Continuation table II Continuation of example air-to-time b. Yield purity APHA-derived z. Be an d. Receive color fast. Carbon- tenan Car value d. Recyclic acid d. er (l / h) action (wt .-%) (%) hold.

(min.) carboxylic acid b) comparative 350 48 trimellite 93.7 300 example acid 5 (84) Ex. 12 300 24 tert- 99.8 45 phthalic acid (94) comparative tertiary example 300 29 phthalic 98.8 80 6 acid (89) Ex. 13 350 38 tere 97.8 160 phthalic acid (80) Table II footnotes: a) To shorten the lead-in period 5 g of benzoic acid was added. b) The APHA color value of the carboxylic acid obtained is determined by adding 2.5 g of the carboxylic acid in 100 ml of aqueous solution, the equivalent Amount of sodium hydroxide contained, were dissolved and then the color of the obtained Solution were compared with APHA (American Public Health Association) standard values. c) No APHA color value was obtained due to the mixture of the catalyst residue.

Claims (11)

Claims 1. Process for the production of aromatic carboxylic acids by liquid phase oxidation of aromatic compounds with at least one oxidizable aliphatic substituents with molecular oxygen in the presence of a heavy metal and bromine-containing catalyst system under high temperature and elevated pressure conditions, characterized in that in the liquid phase reaction system together with the Catalyst at the same time silicone is present as a promoter. 2. The method according to claim 1, characterized in that the aromatic Compound has 1 to 3 substituents. 3. The method according to claim 1 to 2, characterized in that the Substituent is an alkyl, aldehyde or alcohol radical. 4. The method according to claim 3, characterized in that the substituent is an alkyl radical having 1 to 3 carbon atoms. 5o method according to claim 4, characterized in that the aromatic Compound toluene, ethylbenzene, cumene, xylene, diisopropylbenzene, pseudocumene or Is toluic acid. 6. The method according to claim 1, characterized in that the as Promoter applied silicone has a molecular weight of not less than 400 and is liquid under the reaction temperature and pressure conditions. 7. The method according to claim 1, characterized in that the as Promoter used silicone under the reaction temperature and pressure conditions forms a gas that is condensable and can be returned to the reaction system can. 8. The method according to claim 1, characterized in that the as Promoter used silicone in a length of 0.0001 to 2 wt .-%, based on the aromatic starting compound presented. 9. The method according to claim 1, characterized in that the heavy metal in the catalyst there is manganese and / or cobalt. 10. The method according to claims 1, characterized in that the oxidation reaction in the presence of a lower fatty acid with 2 to I carbon atoms in the molecule is carried out. 11. The method according to claim 10, characterized in that the lower Fatty acid is acetic acid.