DE2051320C3 - Process for the purification of aliphatic dicarboxylic acid mixtures - Google Patents

Description

Example I.

350 kg of a crude dicarboxylic acid shell, which is obtained after distilling off nitric acid and water an oxidation mixture obtained and 31 percent by weight of adipic acid, 20 percent by weight consists of succinic acid and 47 percent by weight of glutaric acid and another 0.36 percent by weight Contains copper and 0.11 percent by weight vanadium in addition to small amounts of impurities per hour a Sambay evaporator with an evaporator area of 2.4 m - fed via a pump. At a temperature of 182 ° C and a pressure of 10 torr distill over 335 kg of the dicarboxylic acid mixture per hour, with the composition adjusts as follows: 31 percent by weight adipic acid. 21 percent by weight succinic acid and 48 percent by weight Glutaric acid. This corresponds to a yield of 95.5% of pure dicarboxylic acids, based on on the oxydassons mixture before separation of nitric acid and water. A residue is obtained which contains the total amount of the catalyst substance and which is very fluid.

Example 2

370 kg of a crude dicarboxylic acid melt, consisting from 29 percent by weight adipic acid, 49 percent by weight glutaric acid and 20 percent by weight succinic acid and 0.41 percent by weight of copper and 0.12 percent by weight of vanadium as well as minor ones Amounts of impurities are fed to a Sambay vaporizer per hour via an ε · "ε pump. At a temperature of 184 "C and a pressure of 5 Torr distilled over 355 kg of the dicar ^ onic acid mixture, which corresponds to a yield of 96.1 percent by weight of pure dicarboxylic acids.

The Sanibay residue, which is 10.1% copper and 2.9% Vanadium, along with traces of iron and cobalt, is added to a combustion chamber with natural gas Burned 1200C. The smoke gases are at 200 C cool and then pass through an electrostatic precipitator, on which the oxides are deposited. In this way, 95 percent by weight of the copper and Vanadins regained.

The critical importance of using a thin film evaporator ^ when performing the Procedure results from the following comparison examples:

Comparison example 1

In the same Samb.i> VLrddinpLr as in ücispicl 1. with an evaporator area of 2.4 in ', will be at 195 C under vacuum 335 kg / h succinic acid distilled over. The distillate contains 217 kg of succinic acid and 100 kg of succinic anhydride. In addition, in a deep freezing 18 kg of water condensed. During the distillation, 32.5% of the succinic acid becomes converted to succinic anhydride.

Comparative example 2

In a round bottom flask with a Claisen attachment, 25 g melted dicarboxylic acid filled. With a continuous supply of 250 g dicarboxylic acid mixture / h 237 g of Dcsüiiat are continuously over 237 g of Dcsüiiat under oil bath heating at a temperature of Ί84 C in vacuo The top is removed and 1 3 g / h of bottom product is continuously withdrawn. The distillation is 4 hours operated continuously. During this time, the initial level in the flask is kept, so that the average Dwell is 6 min. Bu using a dicarboxylic acid mixture as in Example 1 obtained a distillate of the following composition:

Succinic acid

Succinic anhydride

Glutaric acid

Glutaric anhydride

Adipic acid

J b

32.V

It can be seen from the examples and the comparative examples that only the distillation of the crude nn., Ir ₍ i ₍ > n acid mixture in a thin-film evaporator / ti leads to a distillate which consists of the unchanged dicarboxylic acids. Distillation incorporates., Components ( Succinic acid) or slight changes in the distillation system lead to desililins which no longer consist of mixtures of pure dicarboxylic acids.

Claims (1)

Claim: Process for the purification of aliphatic dicarboxylic acid mixtures which contain adipic acid, glutaric acid and succinic acid and are obtained by oxidation of cyclohexanol / cyeluhexanone mixtures or by direct oxidation of cyclohexane with nitric acid at elevated temperature and in the presence of copper and vanadium catalysts, characterized in that, that after the nitric acid and water have been distilled off, the mixture is passed ^{through a thin-film evaporator at a temperature of 170 to 240 °} C. and a pressure of 1 to 20 Torr In the production of adipic acid from a mixture of cyclohexanol and cyclohexanone by Oxidation with nitric acid in the presence of Vi nadium- and copper-containing catalysts is obtained Mixtures containing larger amounts of glutaric acid and succinic acid, besides adipic acid. One is endeavors to keep the proportion of glutaric and succinic acid as low as possible. A well-known method consists in subtracting a certain amount from the circuit of the oxidation product in order to / u “Reach that the level of by-products remains low. When working up this share will be First, nitric acid and water are distilled off in a known manner by a two-stage distillation. Possibly becomes / ur destruction of Nilro connections The sump was kept at a temperature of 180 ° C. for a further 2 hours. Ks remains a dark colored Schmel / c back, the adipic acid. Glutaric acid. Bernsic Acid and Copper and Vanadium Catalysts besides containing some impurities. The separation of the mixture of pure acids from this distillation residue must be carried out gently in order to avoid further losses. French Patent 15 55 151, for example, knows that this can be achieved by steam distillation. The process is, however, technically complex The other possibility is a clone demillion at a temperature of about 2Ί0 (. At this temperature the presence of copper and vanadium has a catalytic effect on the carboxy components, especially the adipic acid to form cyclopentanone. It leads to a partial anhydration of glitaric and succinic acid. This process worsens the howling considerably if the harmful finned catalytic converters are not switched off by treatment with ion exchangers prior to the desilication. For this, however, the silicon / c of the dicarboxylic acids must be in water be solved, which according to the Katioilcrtaiislaii sch "wiedcrulu; ib / ti (les (iHiefcn ist.- This results from the process engineering point of view energy disadvantage. Even the attempt to exaggerate the dicarboxylic acids by means of a carrier did not result in a technically useful solution, since in this way, as a result of excessive growth, very large numbers of cheeses are formed. It has now been found that a pure ash-free and anhydride-free mixture of adipic acid, Glutaric acid and succinic acid are obtained, with only small amounts of these compounds as residue, ■ 5 but the entire catalyst proportions remain if the crude catalyst-containing dicarboxylic acid mixture, after distilling off the nitric acid and the Water, at a temperature of 170 to 240C and at a pressure of t to 20 Torr over a ι »Thin film evaporator leads. According to the process according to the invention, oxidation mixtures that are obtained during the treatment are purified of cyclohexanol and cyclohexanone with high percentage nitric acid, e.g. B. a nitric acid of i> about 55 to 58%, at 75 to 80 ⁰ C in the presence of copper and vanadium catalysts. In a conventional two-stage distillation process, nitric acid and water are separated off. If appropriate, a bottom treatment at! 80 ⁰ C to the destruction of the nitro compounds may be preceded irn residue after removal of nitric acid and water. This distillation residue then contains, in addition to the adipic acid, glutaric acid and succinic acid, the total amount of copper and vanadium cata- 2Ί lysator partly in the form of oxides. In addition, there are small amounts of impurities in the mixture. The distillation in the thin film evaporator, z. B. in a Sambay vaporizer. is advantageous for a «Ι temperature carried out from 180 to 200X. At a Pressure of 1 to 20 Torr succeeds. 94 to 96 percent by weight of the feed in a gentle manner and to distill over with very short residence times. Compared to the known processes, the reverse Ji stand proportion to 4 and less weight percent lowered. Another advantage of the process is that you can get from the evaporation residue Can fully recover catalyst. When recovering the catalyst from the residues the thin film evaporation is obtained z. B. by leaching the residue nut water the catalyst in the form of salts up to 40% recyclable Shape back. But you can also burn the rucksack with natural gas, with copper and vanadium in 4Ί I orm of oxides can be precipitated from the flue gases by means of an electric filter or a cloth filter. Here, too, the catalyst is obtained in an amount of from 70 to QO ¹ Vn. The precipitate can be recovered after being dissolved in nitric acid > n can be used directly for the oxidation. In the process of cleaning the Dicirhonsaurc gcmischs is / u note that only through Finh.illiine a low dwell time as well as the specified temperature range the gcn.inr.tcn good weeping • Ί can be ascertained. Wild, on the other hand, the Temper.itiu exceeded, or the expiry date. so begins the Decomposition of adipic acid / cyclopentanone and the anhydration of Ciliitars.iiire and Bernsicins.iuie and thus a side reaction. the · zur I rnicdriguiii! the M yield führl If, however, set the Tcmper.iiiir too low - so the lUickslandsantcil is at 10% and raised it. The purified by the effirulungsgcinäßdii method Dicarboxylic acid can be used as an output fabric for the manufacture of plasticizers or as Use acidic agents in the textile and leather industry. But you can also use the mixture in the Separate pure acids.