DE936568C - Process for the preparation of mixtures of aromatic polycarboxylic acids - Google Patents

Description

Process for the preparation of mixtures of aromatic polycarboxylic acids Addition to additional patent 892895 The invention relates to a further development of the method for the separation of low molecular weight, mainly aromatic carboxylic acids from crude Fuel oxidation products according to patents 864992 and 892895. The oxidation firm Fuels that z. E. with oxygen, air, nitrogen oxides or other oxidizing agents Gases made in the presence of strong acids or alkalis and also oil under increased pressure is known to lead to a carboxylic acid mixture which is made up of different acids Degree of degradation is composed. The separation of individual acids is extraordinary difficult, but it is possible to use the very valuable aromatic polycarboxylic acids to be separated in their entirety from the crude oxidation mixture, essentially higher molecular weight carboxylic acids remain.

It has already been proposed in the patent 864 992 that the Treatment of fuels with nitric acid with resulting oxidation products To digest a lot of water, with only the low molecular weight acids, which are predominant Partly consist of aromatic polycarboxylic acids, go into solution and won for themselves can be. The separation achieved by this process is very economical, but not so complete that it could fully satisfy. It was then suggested further in patent 892,895 instead of using water with acetone or a mixture of acetone and chlorinated hydrocarbons, e.g. chloroform, to digest, and one has a usable separation with the latter mixture or extraction achieved.

It has now been found that solvent mixtures from a low-boiling point Ketone, e.g. 3.

Acetone, and a low-boiling chlorinated hydrocarbon, e.g., chloroform, according to the method of the aforesaid patent in particular useful for the extraction of the low molecular weight, mainly aromatic carboxylic acids are and that such solvent mixtures are generally used for the extraction eminently suitable, which are composed of at least one solvent, one or more contains hydrophilic groups in the molecule, and one that is strongly hydrophobic, put together. These solvent mixtures show good dissolving power for the low molecular weight, mainly aromatic, acids and act at the same time sufficiently selective, i.e. higher molecular acids are not dissolved by them. While the hydrophilic solvents used according to the invention, the solution of the bring about the aromatic carboxylic acids in question, the effect of a hydrophobic one Solvent existing part of the solvent mixture used according to the invention ensure that the low molecular weight carboxylic acids are not dissolved and the extraction runs selectively.

The hydrophilic solvents used in the present invention include z. 3. Alcohols, ketones, aldehydes, esters, lactones, acetals, ethers, ketone alcohols or ether alcohols. The hydrophilic character can continue, for. B. by sulfur or the amount of nitrogen atoms in the molecule can be determined.

The hydrophobic solvents used according to the invention include z. B. aliphatic, aromatic and hydroaromatic hydrocarbons, furthermore their halogen derivatives.

Solvent mixtures consisting of a ketone and a liquid chlorinated Hydrocarbons exist, but are excluded.

The so far proposed uniform organic solvents are unsuitable because they are not sufficiently selective, i.e. not just the desired ones low molecular weight, mainly aromatic carboxylic acids, but also the higher molecular weight ones Solve by-products. Such an extraction is of little value. on the other hand the solvents used up to now may only have a low level Solvent power, so that they are generally very selective, but only to a small extent. The fraction of the desired low molecular weight, mainly aromatic, obtained in this way Acids is then irrelevant for a technical process.

It was therefore surprising that with mixtures of the two types the above-mentioned solvents can achieve useful results, so that you can use the cheapest solvent in each case Identify and apply mixtures.

The appropriate mixing ratio of the solvents used is different from case to case. When extracting with acetone-gasoline one chooses z. B. advantageous the ratio 2: 1 or 5: 3, while in the extraction with Propanol-toluene works better with a ratio of 1: 6.

So it depends a lot on the composition of the solvent mixture and above all on the dissolving power of the hydrophilic solvent used away. In addition, there is also the composition of the carboxylic acid mixture to be extracted of greater influence on the choice of the mixing ratio. You can z. 3. one Extract which, according to the process, is based on low molecular weight, mainly aromatic Carboxylic acids have been enriched again, but the extraction with the same mixture with a different mixing ratio, e.g. 3. Towards a more selective one Effect, extract. This results in a further enrichment of the desired cabonic acids and a division into several fractions is possible. But you can also do the repeated Use a different mixture for extraction.

Under certain circumstances, the extraction at elevated temperature can be special Offer advantages, because some extractants tend to work with that under certain circumstances to form emulsions in aqueous solution of the oxidation product, especially if if a strong mechanical mixing, which is necessary for the extraction, takes place. Such emulsions can simply be increased by increasing the Break the extraction temperature to temperatures above room temperature. In very many In some cases, a temperature increase to 30 to about 500 is sufficient.

The technical implementation of the new process takes place z. 3. in in such a way that the dry product is mixed with the organic solvent mixture vigorously with a good stirrer or with a suitable shaker messed up special value is with the one below. cited use of moist product to be placed on good mixing, using a suitable mixer must be used, since a simple stirrer or shaker is insufficient is.

In general, the low molecular weight, mainly aromatic ones Carboxylic acids can be processed on esters, since the esters are distillable and the Acids can therefore be easily cleaned by esterification and saponification. In the given Case is used for the extraction with advantage a solvent mixture, its The hydrophilic component consists of the alcohol with which the acids are esterified should be. The extraction is then carried out by heating to the esterification temperature, optionally under increased pressure, the hydrophobic part of the Solvent mixture in the case of propanol-benzene, e.g. 3. Benzene, as an entrainer can serve to remove the water released during the reaction. Another- aside the esterification can also be carried out after the hydrophobic solvent component has been separated off make.

Sometimes the applied hydrophilic solvents are at the same time applied hydrophobic solvents not infinitely miscible, as z. B. is the case with methanol and gasoline.

Often times, too, small amounts of moisture cause that either from the product to be extracted or from the solvents used for the extraction originate, segregation or lead to clumping of the extraction material. It was found that it is expedient to add a further solvent in such cases, in a methanol-gasoline mixture z. B. Benzene, which again makes it completely miscible produced, prevents the extraction material from clumping together and a suitable one Formed solvent mixture of great selectivity in the context of the invention will. It is also possible to use several hydrophilic solvents instead of just one use, i.e., the solvent mixtures to be prepared according to the invention can on the other hand, several solvents with hydrophilic groups and, on the other hand, several with hydrophobic groups contained in the molecule.

The crude oxidation product contains, in so far as the oxidation with nitric acid was carried out, always picric acid, which is in the extraction according to the invention located in the extracts. This can be prevented by using the crude oxidation product before extraction with the solvent mixture with a suitable solvent, like benzene, the picric acid, but not the mainly aromatic carboxylic acids solves, extracted. But you can also extract according to the invention and the picric acid subsequently remove from the extracts available. If necessary, you turn a mixture of gasoline, benzene and chloroform is used to extract the raw products or contains other picric acid solvents as a hydrophobic component. To the extraction can be the hydrophobic solvent by adding water which contains dissolved picric acid, separate easily. Small amounts of moisture disturb generally not. One can even more frequently with particular benefit from a damp one Run out of product if you adjust the moisture content like this - which is very easy it is possible - that after the addition of the organic solvent a mushy soil body and the extract which can be produced according to the process is produced.

One often comes up with a minimal amount of organic in these cases Solvents, as shown in Example 5.

When working up the extracts by evaporating the organic Solvents can be added to water, on the one hand to encrust the carboxylic acids on the wall of the evaporator, on the other hand to prevent condensation reactions to prevent organic solvents.

For these reasons, too, it is advisable to use the raw carbonic acid mixture not to be used completely dry. It is then of particular advantage to have such Use solvent mixtures that evaporate with the existing water form ternary mixtures, e.g. B. 112 0-butanone-benzene.

You can then use the resulting distillate again as such for extraction, If necessary with the addition of one or the other component, use it again immediately.

Is the extract available after the first extraction not yet for further processing, e.g. B. on paints, so it is, as already at the beginning was carried out, possible to extract several times according to the invention, with both the ratio of the solvent components as well as their composition changed can be.

It was further found that it is necessary for a clean separation of the Low molecular weight, mainly aromatic carboxylic acids is important that the raw oxidation product is as free as possible from natural ash. It is therefore It is advisable to start from a low-ash coal when digesting coal, and to do this carefully care must be taken that there are no corresponding impurities in the course of the oxidation be introduced into the digestion mixture.

The presence of salts such as sodium chloride interferes with the process not. Digestion products from alkaline oxidation can therefore also be used easily work up according to the method of the invention. Neutralized here the alkaline digestion solution is sufficiently acidic, evaporated and can do that Then extract the raw oxidation product.

Example I 100 parts of a dry crude carboxylic acid mixture which by oxidation of deashed coal (0.7% ash) with ENT, after extraction of the picric acid with benzene and evaporation of the digestion solution are in a vessel, which is provided with a stirrer and a reflux condenser, with 400 parts of one Solvent mixture of butanone (methyl ethyl ketone) and gasoline (bp = go up to I40 °) Heated in a ratio of 1: 1 1/4 hour to 80 ". The undissolved part is separated and the extract evaporated.

42 parts of a pale yellow carbonic acid mixture (extract 1).

The portion not dissolved in the first extraction is again extracted with 200 parts of the same mixture as above and after separating the Evaporated residue. Another 10 parts of a light yellow carboxylic acid mixture are obtained (Extract II).

The success of the extraction is based on a comparison of the available Amounts of methyl esters that one z. B. obtained by esterification with diazomethane. There are from the extract 1 (42 parts) 40 parts of methyl ester (b. 0.1 mm Hg distilled) obtained, which corresponds to 80,000 pure aliphatic and benzene carboxylic acids. Of the Extract II (10 parts) provides 9 parts of methyl ester, which corresponds to 75% pure aliphatic and benzene carboxylic acids. The amount of according to the procedural Extraction available methyl ester, namely 49 parts, J corresponds almost to the amount of methyl esters, which, according to analytical investigations, actually come from the crude carboxylic acid mixture is available.

Example 2 100 parts of the raw caorbon used in Example 1, acid mixture are three times with 200 parts of a solvent mixture of aoetone-benzene (1: 5) extracted. The combined extracts are evaporated and give 55 parts of a light yellow carboxylic acid mixture.

By esterification with diazomethane and comparison of the distillable Methyl ester (b. O, 1 mm Hg distilled) can be used to characterize the enrichment effect. From the 55 parts of extract obtained, 50 parts of methyl ester are obtained, which corresponds to a yield as in example I.

Example 3 100 parts of the crude carboxylic acid mixture used in Example 1 are treated with a mixture of 660 parts of ether and 340 parts of naphtha gasoline (bp = go to I40 °) refluxed for 1/2 hour. The extract becomes from the undissolved separated off and gives 35 parts of light yellow carboxylic acids on evaporation. The unsolved one The residue is taken under the same amount of solvent mixture for another 1/2 hour Heated to reflux. Another 13 parts of pale yellow acids are obtained.

Instead of naphtha gasoline, all other gasoline fractions can also be used can be used with equal success. Using higher boiling than ether Fractions has the advantage that the extracts cannot be obtained to dryness must be evaporated, because the ether first boils out of the mixture and that remaining gasoline no longer dissolves the carboxylic acids. You can do it by simply Separate decanting.

Example 4 100 parts of the crude carboxylic acid mixture used in Example 1 are with a solvent mixture of 425 parts of toluene and 75 parts of n-propyl alcohol extracted. There are 48 parts of light yellow extract or, when it is esterified and subsequent distillation of the ester at 0.1 mm Hg, 45 parts of propyl ester were obtained. The residue is extracted again in the same way and delivers after Esterification of another 20 parts of propyl ester.

Example 5 100 parts of a crude carboxylic acid mixture which still contains 50 parts Contains water are mixed with 40 parts of butanone to form a homogeneous paste. These Mixture is mixed well with 100 parts of benzene. One lets sit down and kicks a separation into a lower aqueous and an upper organic solvent layer a. The organic layer is separated and the solvent mixture is evaporated.

The evaporated solvent mixture is repeated several times used in extraction. Extracting three times gives 56 parts of one pale yellow acid mixture of the properties given in Examples I and 2.

Sometimes this holds as well as that obtained in Examples I and 2 Acid mixture stubbornly small amounts of black smear solid that are not im Are soluble in water. This simply separates them from the pale yellow components from the fact that the dry residue is digested again with a little water and the aqueous Solution evaporated after separating the grease.

Claims (7)

PATENT CLAIMS: I. Process for the preparation of mixtures of aromatic substances Polycarboxylic acids, which are also aliphatic polycarboxylic acids in minor amounts contained by treating fossil fuels or recent fuels or their Distillation residues, possibly after pre-oxidation with oxidizing agents Gases, with nitric acid, evaporation of the remaining acid from the reaction mixture and digesting or extracting the residue obtained with organic solvents, preferably ketones, evaporation of the extract and, if necessary, final purification by esterification and distillation or fractionation of the ester mixture obtained according to patent 892 895, characterized in that after evaporation of the Acid obtained residue extracted with organic solvent mixtures, the at least one hydrophilic and at least one strongly hydrophobic solvent component contain, but with the exception of solvent mixtures that contain a ketone and a contain liquid chlorinated hydrocarbon, and the extract evaporates, whereby any picric acid present before or after extraction with the solvent mixture is removed by extraction. 2. The method according to claim I, characterized in that at elevated temperature, preferably at 30 to ion ", extracted. 3. The method according to claim I and 2, characterized in that one the resulting residues and / or the resulting extracts repeatedly with the same solvent mixture with a change in the ratio of the solvent components or extracted with another solvent mixture of a different composition. 4. The method according to claim I to 3, characterized in that one extracted with solvent mixtures that are used as a hydrophilic solvent for one. Contain alcohol required for esterification. 5. The method according to claim I to 4, characterized in that one the received return initially stood in the hydrophilic solvent dissolves and then the higher molecular weight by adding the hydrophobic agent By-products precipitates. 6 The method according to claim I to 5, characterized in that one Low-ash and / or moist oxidation products extracted. 7. The method according to claim I to 6, characterized in that one Solvent mixtures forming azeotropic mixtures with the moisture of the oxidation product used.