MXPA99006740A - Method for separating an imine from a mixture containing an amine and an imine - Google Patents

Abstract

The invention relates to a method for separating by distillation all or part of an imine (III) from a mixture (II) containing an amine (I) and an imine (III). Said method is characterized in that a compound (IV) which under distillation conditions is inert in relation to the amine (I) and whose boiling point under distillation conditions lies above the boiling point of the amine, is added to the distillation mixture, and that distillation yields a mixture (VI) which essentially contains a compound (IV).

Description

SEPARATION OF AN IMINE FROM A MIXTURE THAT CONTAINS AN AMINA AND AN IMINA The present invention relates to a process for the separation by distillation of part of all of an imine (III) from a mixture (II) containing an amine (I) and the amine (III), which consists in adding to the distillation mixture a compound (IV) which is inert to the amine (I) under the distillation conditions and whose boiling point is above the boiling point of the amine (I) under the distillation conditions to obtain, after distillation, a mixture (VI) containing practically the compound (IV). Mixtures containing an amine and an imine are commonly obtained in the hydrogenation of nitriles to amines. The complete hydrogenation of adiponitrile to hexamethyl amine, also the partial hydrogenation with co-production of hexamethylenediamine and 6-aminocapronitrile, in the presence of a catalyst based on a metal such as nickel, cobalt, iron, rhodium or ruthenium is generally known, for example from : K. Weisser, H. - J. Arpe, Industrielle Organische Chemie, 3a. Emission, VCH Verlagsgesellschaft mbH, Weinhei, 1988, page 266, US-A 4 601 859, US-A 2 762 835, US-A 2 208 598, DE-A 848 654, DE-A 954 416, DE- A 42 35 466, US-A 3 696 153, DE-A 19500222, WO 92/21650 and German Application 19548289.1. The products include imines such as aminohexylideneimine and tetrahei roazepine. These imines, which, like their color and detrimental effects on the property, are the product, are undesirable impurities in the amines, which are not usually used to produce synthetic fibers, are difficult to separate from the amines. For example, GB-A-893 709 describes the installation of a container with time delay in the reflux line of a distillation column used to purify hexamethylenediamine. GB-A-1 238 351 describes the separation of hexamethylenediamine from mixtures containing hexamethylenediamine and imines by the addition of mixtures of alkali metal hydroxide. GB-A-1 041 442 discloses the passage of dioxy? E carbon to a distillation column used to separate hexamethylenediamine from mixtures containing hexamethylenediamine and imines, during distillation. The disadvantages with the aforementioned processes are the use of large containers, which allow a reduced control of the columns, the styling, and the solid formation, which causes blockages.

An object of the present invention is to provide a process for separating an imine from mixtures containing an amine and an imine in a technically simple and inexpensive manner. We have found that this goal is achieved through the process defined at the beginning. Suitable amines I include aromatic amines such as benzylamine, aliphatic amines such as cyclic amines, for example isophorone, or preferably acyclic amines, for example, 1,4-diaminobutane, especially hexamethylene diamine or 6-aminocapronitrile, and also mixes them. These amines can be prepared in a conventional manner. For example, hexamethylenediamine can be obtained by partial or complete catalytic hydrogenation, with a gas containing a molecular hydrogen, of adiponitrile to form hexamethylenediamine, or mixtures containing hexamethylenediamine and 6-aminocapronitrile. Suitable catalysts for this hydrogenation are, for convenience, those based on a metal selected from the group consisting of ruthenium, rhodium, nickel, cobalt and preferably iron, and the catalysts may contain other elements as promoters. In the case of iron-based catalysts, suitable promoters especially include one or more, such as 2,3,4 or 5 elements selected from the group consisting of aluminum, silicon, zirconium, titanium and vanadium. These catalysts and the process conditions for the reaction mentioned are described, for example in W0-A-96/20166, the German Application 16 636 768.9 and the German application 19 646 436.6. The products obtained by the mentioned processes can subsequently be post-hydrogenated with gases containing molecular hydrogen, advantageously in the presence of catalysts based on noble metals such as platinum, palladium or mixtures thereof. Suitable imines III include aromatic imines, aliphatic imines such as acyclic imines, in particular to inohexyli eni ina, or cyclic imines, especially tetrahyloazepine of the formula: and also mixtures thereof Imines (III) may be present in the mixture (II) as individual compounds or as byproducts and addition, for example, with an amine (I), in which case these products of addition must, for the purposes of the present invention, in the same manner be called imines (III). These imines and the processes for their preparation are generally known. For example, aminohixylideneimine and tetrahydroazepine can generally be obtained in quantities from 1 to 10,000 ppm, based on mixing, in mixtures (II) in the partial catalytic hydrogenation of adiponitrile with gas containing molecular hydrogen to form hexamethylenediamine. or mixtures containing hexamethylenediamine and 6-aminocapronitrile according to the processes described for the production of amines (I). The invention provides that a compound (IV) which is inert to the amine (I) under the conditions of the distillation and whose boiling point is above the boiling point of the amine (I) under the conditions of the distillation is added to the the distillation mixture. Suitable compounds (IV) include aromatic compounds, aliphatics such as acyclic and cyclic aliphatics, and aliphatic-aromatics. These compounds can carry substituents, such as a hydroxyl, keto, ester, alkyl, aryl, cycloalkyl or arylalkyl group, preferably a nitrile or amino group, or a plurality of these identical or identical groups.

The compound (IV) can consist of a compound or mixtures of these compounds. It is advantageous to use the compounds (IV) which are simple to convert, as by hydrogenation, for example, with a gas containing molecular hydrogen in the presence of a catalyst, into a mixture (V) containing an amine (I) and an imine (III) or especially a mixture (II). The products obtained in this reaction can advantageously be used again in the process of the invention. The difference in boiling points between the amine (I) and the compound (IV) should be from 1 to 200 ° C, preferably from 5 to 100 ° C, under the conditions of the distillation. If hexamethylenediamine is used as the amine (I) and aminohexylideneimine, tetrahydroazepine or mixtures thereof as the imine (III), then the use of adiponitrile, 6-aminocapronitrile or mixtures thereof is particularly advantageous. If 6-aminocapronitrile is used as the amine (I) and aminohexylideneimine, tetrahydroazepine or mixtures thereof as imine (III), then the use of adiponitrile or mixtures containing mainly adiponitrile is particularly advantageous. The compound (IV) can be admixed to the mixture (II) before or during the distillation.

The addition of the compound (IV) to the mixture (II) before the distillation can be carried out in a conventional manner in customary mixing apparatuses. The addition of the compound (IV) to the mixture (II) during the distillation can be carried out by feeding the compound (IV) into the distillation apparatus, preferably in the lower region. The suitable apparatus for the styling is any apparatus customary as described for example in Kirk-Othmer, Encyclopedia of Chemical Technology, 3a. Ed. Vol. 7, John Wiley & Sons, New York, 1979, pages 870-881, such as columns, sieve plates, bubble cap columns or columns packed with cushioned or cushioned packaging. The distillation can be carried out in a plurality of columns, such as 2 or 3, but it is advantageously carried out in a single column. The distillation produces, preferably as residual product, a mixture (VI) essentially containing a compound (IV). If the mixture (VI) also contains amine (I), it is conveniently possible to reduce the lower temperature of the distillation. The compound (IV) can be recovered from the mixture (VI) in a conventional manner, for example, by physical processes, such as distillation or extraction, or chemical processes, such as chemosorption or hydrogenation. This compound (IV) obtained from the mixture (VI) can advantageously be recycled to the distillation of the invention. Hexamethylenediamine can be processed with dicarboxylic acids as adipic acid to form industrially important polymers.

Claims (1)

1. CLAIMS A process for the distillative separation of part, or all, of an imine (III) from a mixture (II) containing an amine (I) and imine (III), which consists of adding to the distillation mixture a compound (IV) which is inert to the amine (I) under the conditions of the distillation and whose boiling point is above the boiling point of the amine (I) under the distillation conditions to obtain, after distillation, a mixture (VI) essentially containing the compound (IV). The process, as mentioned in claim 1, wherein the compound (IV) is added to the mixture (II) before the stylation. The process, as mentioned in claim 1, wherein the compound (IV) is added to the mixture (II) during the distillation. The compound, as mentioned in any of claims 1 to 3, wherein the compound (IV) is a compound from which a mixture (V) containing an amine (I) and a imine (III) or a mixture (II). The process, as mentioned in claim 4, wherein, after distillation, the compound (IV) is converted into a mixture (V) which essentially contains an amine (I) and an imine (III). The process, as mentioned in any of claims 1 to 5, wherein the amine (I) is hexamethylenediamine. The process, as mentioned in any of claims 1 to 6, wherein the amine (III) is selected from the group consisting of aminohexylideneimine, tetrahydroazepine, hexylhexahydroazepine and amino hexylhexahydroazepine. The process, as mentioned in any of claims 1 to 7, wherein the compound (IV) is α-iponitrile, 6-aminocapronitrile or a mixture thereof. The process, as mentioned in any one of claims 1 to 8, wherein the compound (IV) is recovered from the mixture (VI). The process, as mentioned in any of claims 1 to 8, wherein a compound (IV) is recovered from the mixture (VI) and recycled to the distillation.