DE965230C - Process for the recovery of catalysts and by-products from the mother liquors of the production of adipic acid - Google Patents

Description

ISSUED JUNE 6, 1957

19130 IVb / 12 ο

The invention relates to a process for the recovery of the catalysts and of By-products from the mother liquors, which are used in the production of adipic acid by nitric acid oxidation of cyclohexanol and / or cyclohexanone arise.

There have already been a wide variety of catalysts for use with nitric acid ^ Oxidation of cyclohexanol and / or cyclohexanone proposed. For example proposed in British patent specification 572260, Vanadium and copper either in pure form or in the form of their oxides or salts use. The mother liquors obtained after the adipic acid has been separated off by filtration contain valuable amounts of catalyst salts and organic acids as a by-product, like glutaric and succinic acid. When the recovery of these catalyst salts and By-products is tried by evaporation of the mother liquor to dryness, takes place violently Oxidation reaction takes place, which is a rapid one

709 5S2 / 265

Increase in temperature and therefore the intended recovery dangerous power.

It has now been found that this difficulty this can be overcome by evaporating the mother liquors to dryness before they are a little volatile mineral acid, for example sulfuric acid, is added.

The method according to the invention now consists in giving the mother liquors such an amount a little volatile mineral acid added, which is somewhat larger than that of the existing nitrates corresponding, whereupon the liquid is evaporated until the main amount of water and salt-pitric acid is removed, whereupon you get the catalyst and by-products from the residue isolated.

The mineral acid added to the mother liquors must be able to remove the nitric acid from their To displace ao salts with the formation of corresponding new salts. Suitable for this purpose Mineral acids are sulfuric acid and phosphoric acid.

The mother liquors containing the added mineral acid are preferably evaporated to dryness under reduced pressure. The evaporation can take place rapidly at a temperature up to about 150 ⁰ , provided that a violent reaction and decomposition are prevented in the orphan that one preferably introduces water vapor at a temperature of 100 to 170 ⁰ into the liquid or by constantly introducing it fresh or partially concentrated mother liquor, preferably at a temperature of 40 to 90 ⁰ , is added. The rate at which steam or fresh mother liquor is added is adjusted so that an undesired increase in temperature or the formation of nitrous gases above about 95 ° is prevented. It is also useful to blow air through the hot, molten evaporation residue in order to remove any small amounts of nitric acid that may have been retained. As a result of the presence of the added mineral acid, the entire amount of salicic acid, both free and salt-bound, is removed, and the resulting carboxylic acid / catalyst salt mixture can then be conveniently further processed, for example by using an alcohol to form an ester and the like, without the risk of exothermic reactions occurring, which is the case when a nitrate-carboxylic acid mixture is present.

The catalyst salt can be obtained from the evaporation residue separate in a known manner. The residue can also with an organic Solvent, such as ethylene dichloride or benzene, treated and the catalyst salt through Filtration can be separated from the solution. But you can also use an alcohol to remove the residue treat to esterify the carboxylic acid and recover the catalyst salt by filtration. Finally, the organic can be obtained from the residue by distillation. Remove acids.

The organic acids still contained in the residue, which to a large extent Glutaric acid with a certain amount of adipic and succinic acid can be used as such Production of mixed esters or other products can be used. The individual acids but can also be isolated, for example by esterification or fractionation of the crude esters and subsequent hydrolysis of the pure esters.

The process according to the invention is illustrated in more detail by the following examples.

example 1

20 parts by weight of concentrated sulfuric acid are added to 1150 parts by weight of an adipic acid mother liquor, as is obtained when carrying out the process of British patent specification 572 260, and which contains the salts of vanadium and copper, and the mixture is added with stirring at 20 to 150 mm of mercury and a liquid temperature evaporated from 35 to 70 ^0. As evaporation progresses, the temperature gradually rises and a final temperature of 95 to 100 ° at 20 to 150 mm of mercury is maintained until the distillation is complete. Due to the semi-molten residue air is 1 to 5 hours blown at a temperature of 95 to ioo ° until the residue was completely free from nitric acid, whereupon the mixture is heated above 130 ⁰ and the insoluble catalyst salts are filtered off on a heated pressure filter . If desired, a filter aid, for example kieselguhr, can be added to aid the filtration. The catalyst salts are obtained essentially free of organic constituents, and after they have been redissolved in nitric acid, they can be reused directly for the oxidation of cyclohexanol etc. to adipic acid.

The filtered organic acids can in a known manner either on the pure constituents or technically useful mixtures are further processed.

Example 2

To 500 parts by weight of an adipic acid mother liquor, as used when carrying out the process British Patent 572 260 and which the salts of vanadium and copper contain, - 4.6 parts by weight of syrupy phosphoric acid are added and the resulting solution worked up under the same conditions as in Example 1.

Example 3

190 parts by weight of an adipic acid mother liquor, as used in the implementation of the subject the British patent 572 260 forming process is obtained and the about 16 parts by weight of nitric acid, 48 parts of dicarboxylic acids and Contains dissolved catalysts, 3.2 parts by weight Added sulfuric acid and

evaporate under a pressure of 100 mm of mercury at 95 °. Concentration is then continued under a pressure of 100 to 150 mm of mercury to a temperature of 148 ^° C., with vapor being introduced below the surface of the liquid at a rate sufficient to cause the formation of brown nitrous vapors suppress. The catalyst salts are then separated from the molten dicarboxylic acids by filtering them on a heated pressure filter.

Example 4

82.5 parts by weight of an adipic acid mother liquor, which contains about 8 parts by weight of nitric acid, 28 Ge. contains parts weight dicarboxylic acids and dissolved catalysts, are mixed with 2.2 parts by weight of sulfuric acid and concentrated by evaporation at 96 ⁰

ao and a pressure of 145 mm of mercury. Evaporation is continued with the addition of more mother liquor sufficient to prevent the formation of brown vapors that are produced during decomposition. At a temperature of over 132 ⁰ the addition of mother liquor is slowed down and when the temperature has risen to 141 ° it is completely interrupted. During the heating from 96 to 141 ° a total of 22.5 parts of liquid are added.

The mixture is under a pressure of 90 mm

The mercury column was further ^{heated to 150 0} and the residue was worked up in the manner described above.

Claims (3)

PATENT CLAIMS: 1. Process for the recovery of catalysts and by-products from the mother liquors of the production of adipic acid by nitric acid oxidation of cyclohexanol and or or cyclohexanone, characterized in that the mother liquors a little volatile mineral acid is added in an amount slightly greater than that of the dissolved amount Nitrate equivalent amount, whereupon the main amount of water and by evaporation Removed nitric acid and eventually the catalyst salt and by-products from the Separates off residue in a known manner. 2. The method according to claim 1, characterized in that that the evaporation of the mother liquors mixed with mineral acid takes place under reduced pressure. 3. The method according to claim 1 or 2, characterized in that the evaporation of the liquids takes place rapidly at a temperature of up to 150 ⁰ , either introducing water vapor from 100 to 170 ⁰ or continuously fresh or partially concentrated mother liquors, preferably at 40 to 90 ⁰ , adds. © 609 710/357 11.56 (709 532/265 5. 57)