DE1668837B - Process for purifying adipic dinitrile - Google Patents

Description

to purify less than 250 ppm of ring compounds.

The reaction time can be shortened further by adding organic mono- and / or dicarboxylic acids be achieved. In practice, this has been the case with the oxidation of cyclohexane with nitric acid System used for adipic acid copper nitrate— Ammonium vanadate — iron, which together with oxaline, Succinic and glutaric acid accumulates as residue, very reliable.

The duration of the oxidation is thereby shortened to about 1 1/2 hours

Finally, an even further reduction in the time and temperature can be achieved by carrying out the above-described oxidations under pressure, expediently at 100 to 170 ^° C. and a pressure of 2 to 25 atmospheres. In this form, the oxidation of the by-products proceeds so rapidly that additional heating can be dispensed with and, moreover, continuous operation is possible even with large throughputs.

As the oxygen-containing gas, it is expedient to use Air used. Pure oxygen can also be used, but should be used for better utilization returned in the circuit, with a reaction temperature 180 ° should not be exceeded for safety reasons.

All of the above-described oxidations with oxygen-containing gases are expediently apparatus-based designed so that the heat exchanger located at the gas outlet is kept at one temperature which condenses the high-boiling (300 ° / 760 mm Hg) adipic acid dinitrile, but other lower-boiling ones Impurities, such as cyclopentanone, which is also constantly present, through the Gas flow removed.

The products obtained in the ways described above have a low consumption of permanganate, that they to achieve the highest purity - below 10 ppm or-Cyancyclopentanylimin- or «-Cyancyclopentanonealtehalt - either as such, but better after the high-boiling tar-like impurities have been separated off in an economical way, for example, post-cleaning by perraanganate oxidation can be subjected. This kind of final removal by permanganate is made easier by that the originally present a-CyancycIopentanylimin is not only largely destroyed, but also the remaining residual imine content to 70 to 75% converted into α-Cyancyclcpentanon by hydrolysis which is already oxidized by neutral permanganate, while c-Cyancylopentanylimin acidic ίο must be oxidized.

Examples

1. 1 kg of crude adipic acid dinitrile with a content of 1.8% cyanocyclopentanylimine, 2.2% cyclopentanone, 0.2% water and 5.1% higher-boiling impurities are at 170 ° by means of a Intensive stirrer with an air stream preheated to 150 ° of 5001 per hour at a height of 68 cm fumigated. The content ·> η Cyancyclopentanylimin after 1 hour 1.65%, after 3 hours 1.24%, after 6 hours 0.49% and after 8 hours 0.058%. The brown-black material yields 872 g of pure overhead after distillation Dinitrile. The residue weighs 143 g.

2. 1 kg of adipic dinitrile of the same composition as in example 1 is gassed with 0.1 g of copper nitrate, 0.03 g of ammonium vanadate and 2 g of ammonium nitrate at 120 ° with 100 l of air as in example 1. After 4 hours the black reaction product is distilled. 881 g of dinitrile with a cyanocyclopentanone content of less than 100 ppm (0.0%) are obtained along with 140 g of residue.
3. 1 kg of adipic dinitrile of the composition as in Examples 1 and 2 is mixed with 35 g of a catalyst mixture which is obtained as a mother liquor residue in the manufacture of the adipic acid. In addition to the dicarboxylic acids, the catalyst system contains at least 0.6% copper nitrate.

The gassing with air is carried out as in Example 2. After ₂ hours, the mixture is distilled. 876 g of dinitrile are obtained with a «-cyanocyclopentanone content of 70 ppm.

Claims (4)

I 668 837 ι 2 The method according to the invention is also patent claims: "Can be carried out without a great deal of equipment and work. 1. A process for purifying adipic acid- The invention is a process for dinitrile, characterized in that 5 purification of adipic dinitrile, which is characterized in that the adipic dinitrile to be purified is characterized in that there is a catalyst to be purified 120 to 220 ⁰ C in the absence of a catalyst at 120 to 220 ⁰ C or in the presence of a salt of a heavy or in the presence of a heavy metal salt of a metal with an atomic number between 23 and 29 atomic number between 23 and 29 and optionally and optionally of ammonium nitrate and / or io of ammonium nitrate and / or an organic one organic mono- and / or dicarboxylic mono and / or dicarboxylic acid as a catalyst in acid as a catalyst at 85 to 180 ^0C with oxygen temperatures of 85-180 ⁰ C with oxygen or material or treats an oxygen-containing gas with an oxygen-containing gas and optionally acts and optionally the thus purified adipic dinitrile with potassium per-adipic dinitrile with potassium permanganate in 15 manganate in neutral or acidic medium after neutral or acidic medium. cleans. 2. Method according to claim 1, characterized in that Unexpectedly, adipic acid dinitrile is below draws that the treatment under the increased reaction conditions of oxygen not in Printing. attacked to a significant extent. It is therefore 3. The method according to claim 1 or 2, characterized 20 possible, characterized by treatment with oxygen or acid that one is a crude adipic dinitrile as oxygen-containing substance-containing gases Gas used air. of the unwanted impurities «-Cyancy- 4. The method according to any one of claims 1 to 3, to free clopentanylimine and or-cyanocyclopentanone, characterized in that it is difficult to attack without the dinitrile. The inventive metal salts which uses nitrates. The method also has the advantage that other interfering compounds, such as cyclopentanone and others, are removed in the process. The inventive treatment of the contaminated adiponitrile with oxygen containing 30 gases can be produced without the presence of catalysts Made from adipic acid and ammonia can be carried out; through catalysts, each Adipic acid dinitrile contains, among other impurities, but the oxidation time is shortened and the treatment the α-cyano temperature produced by cyclization is lowered, cyclopentanylimine. The temperature of such a fumigation is While almost all other by-products behave between 120 and 220 ⁰ C. At lower temperatures moderately easy - for example, by distillation, the oxidation takes too long for practical purposes. via columns with few bottoms - are separated sam. The upper limit is around 220 ° C, because at is the removal of a quantity of certain materials used in the plant about 1 to 2 percent of cyclization is present, if this temperature is exceeded, new formation Product can be made because of the very adipic dinitrile 40 of «-Cyancyclopentanylimin. As op- Similar vapor pressure with a much larger timal has been found when working without catalysts for Effort involved. the air oxidation a temperature of 160 to 170 "C The previous attempts to remedy this evil have proven to be bad. Under these conditions the original The aim was to add the Cyancyclopentanylimin so Hch in Adipinsäuredinitril in an amount of 1 to implement that the resulting substances in the 45 2% present «-Cyancyclopentanylimin after about subsequent fractionation because of its stronger from 8 hours down to ^ 00 to 600 ppm (0.04 to 0.06%) Adipic acid dinitrile with a different boiling point is not removed. disturb more. For example, when using catalysts, the effect can be created of acids α-cyanocyclopentanone, the action of which with gases containing oxygen has an advantageous boiling point that of the dinitrile can be carried out more strongly than that of the 50 at a lower temperature. Imins differs. The salts of are suitable as catalysts According to further known processes, α-cyancy heavy metals with the atomic number 23 to 29 are insclopentanylimin treatment of the raw product specializes its nitrates. A particularly good katalymit Hydroxylamine, bisulfites, bisulfates, formaldehyde show the effects of the salts of the divalent or isocyanates reacted. It is also known to 55 copper; the nitrate anion also influences the oxydadas cyclic imine and the cyclic ketone favorable by ion. Oxidation with potassium permanganate or hydrogen - A mixed catalyst made from copper nitrate and ammoperoxide to dismantle. nium nitrate and ammonium vanadate in proportion These known processes have a common disadvantage of 1500/1500/200 ppm, based on the crude nitrile an addition of interfering reagents, 60 stands, allows the oxidative removal of a-cyandie lead to further contamination of the mixture, cyclopentanylimine even at temperatures above and they require additional equipment. of 65 ° C. It has been shown that the optimal temperature A process has now been found which allows temperature for the oxidation in the presence of catalysis is both a-Cyancyclopentanylimin as well as its hydro- factors in the range of 110 to 14O ⁰ C. at Oxidation product of a-cyanocyclopentanone without a temperature of 125 to 130 ° and more intensely the mixture to be cleaned by at least gassing with 100 liters of air per kg and hour, it is possible equimolar amounts corresponding to impurities of Hch, a crude adipine containing 1.6% of the imine Contaminate reagent. acid nitrile to a content within 4 hours