# FRACTIONATION AND PURIFICATION OF AROMATIC POLYAMINE MIXTURES AND THE USE THEREOF 

## BACKGROUND OF THE INVENITON 

The present invention relates to a process for the frac› tionation and purification of aromatic polyamine mixtures and to the use thereof. 

The preparation of aromatic polyamines and polyamine mixtures, particularly of the diphenylmethane series, is described in numerous patent applications and patents, as is the use of these products. Outstanding importance is attached to the use of these products as raw materials for the preparation of isocyanates, usually by reaction of the polyamine mixtures with phosgene according to the gener› ally conventional and well known methods. 

In many cases, however, the resulting isocyanates and isocyanate mixtures are not obtained in the form and com› position subsequently preferably used in the isocyanate stage but have to be converted beforehand to the appropriate form for use by means of sometimes elaborate working-up and separation processes. Suitable polyamine precursors which may be converted in a less elaborate manner to the isocyanate use forms are in many cases difficult to produce or unobtainable in terms of process technology, or economi› cally unattractive. 

An example is the production of 4,4’› diisocyanatodiphenylmethane which is important for the preparation of valuable polyurethane materials, the amine precursor of which may be obtained usually from aniline and formaldehyde only together with isomers, particularly the 2,4’ isomers and more highly functional polyamines. Although these constituents are the basis for isocyanates which are also sought after, the separation of the crude isocyanates into the isocyanates and isocyanate mixtures suitable for subsequent use is not easy. 

Initially, a proportion of the binuclear compounds is usually separated from the remainder. The 4,4’› diisocyanatodiphenylmethane from the binuclear fraction is then separated from the other isomers in a second distillation stage requiring many separation stages. 

Even in recent times, the 2,4’ isomer in the enriched form has gained increasing importance as a polyurethane raw material, but may be enriched compared with the 4,4’ isomer and separated from the 2,2’ isomer possibly present only by an elaborate distillation procedure. 

Isomer separation methods or enrichment methods within the fraction of polynuclear homologues, or of polyfunctional amine constituents, and of isocyanates of the diphenyl› methane series, are virtually unknown. 

4,4’-Diaminodiphenylmethane is also attracting increas› ing interest as a raw material for di-(4- isocyanatocyclohexyl)methane, the form of 4,4’- diisocyanatodiphenylmethane hydrogenated on the nucleus, wherein the provision of suitable aromatic polyamine mix› tures for the hydrogenation stage with the highest, possible content of 4,4’-diarninodiphenylmethane with simulta› neously the smallest possible proportion of 2,4’- diaminodiphenylmethane is very expensive. 

It is well known that amines may be separated in certain cases by partial conversion to their salts, wherein use may be made inter alia of the different base strengths. These are usually monoamines with very different base strengths. 

Such disproportionation effects in two-phase systems have also already been described for aromatic polyamine 

mixtures, particularly of the diphenylmethane series (German Auslegeschriften 2,238,319 and 2,528,694). 

As a result of the numerous components present in such a mixture, the amino groups of which hardly differ at all in terms of type (virtually all of them are arylamino groups), the effects are not particularly great and pronounced to be of interest for direct use with simple means. 

The object was thus to provide a process which allows the pwposeful production of aromatic polyamine mixtures of a purer, novel composition in an economic manner under mild conditions. 

## BRIEF DESCRIPTION OF THE DRAWINGS 

FIGS. 1 through 4 are flow diagrams of various embodi› ments of the present invention. 

## DESCRIPTION OF THE INVENITON 

The above object could be achieved by the process according to the invention which achieves a surprisingly good separating efficiency during the fractionation of aro› matic polyamine mixtures, particularly of the diphenyl› methane series, and in terms of its effect thereby far exceeds the known effects of the prior art. 

Other polyamine mixtures of varying composition are obtained during the fractionation of aromatic polyamine mixtures according to the invention. These derived polyamine mixtures may be those that are obtainable only at great expense by known synthesis routes. They may also be polyamine mixtures which are more suitable for a simplified preparation of isocyanates than the well known polyamine mixtures that are technically easy to prepare in that they, for example, anticipate in the amine stage the isomer separa› tions that are difficult to perform in the isocyanate stage. Such mixtures may also be completely novel polyamine mixtures, because they cannot be prepared according to the prior art, which lead to completely new types of isocyanates. 

On the other hand, the process according to the invention may be used to obtain product fractions conforming with the standard or the starting polyamines from any, i.e. also from recovered polyamine mixtures that differ from the originally used polyamines or isocyanates in terms of contamination or non-random, i.e. selective losses in the case of individual components during recovery from the originally used polyamines or isocyanates. 

Finally, the process according to the invention may be used to co-fractionate synthesis-dependent secondary prod› ucts and intermediates unwanted in the end product and to deplete them in one product fraction and enrich them accordingly in another, and optionally to expel them in an individual fraction. 

The present invention is a broadly applicable process, by means of which the object of fractionating and purifying aromatic di- and polyamine mixtures, in particular of the diphenylmethane series, may be achieved. 

The present invention provides a process for the fraction› ation and purification of aromatic polyarnine mixtures, par› ticularly polyamine mixtures of the diphenylmethane series, which is characterized in that 

a) the polyamine starting mixture (A) is distributed in a two-phase system comprising (i) a hydrophobic solvent phase (B) which is composed substantially of hydro› phobic solvent and optionally an aromatic auxiliary amine that is virtually insoluble in water and under normal pressure has a boiling point at least 20° C. below the boiling point of the lowest boiling compo- 

