Storage-stable iminodisuccinate solutions

Abstract

The present invention relates to a process for the preparation of storage-stable iminodisuccinate solutions, by subjecting an aqueous solution of iminodisuccinate having an ammonia content of less than 20 ppm to thermal treatment at 40 to 120° C. for 5 hours up to 300 days and subsequent distillation at <120° C.

Description

The present invention relates to a process for the preparation of storage-stable iminodisuccinate solutions, by subjecting an aqueous solution of iminodisuccinate having an ammonia content of less than 20 ppm to thermal treatment at 40 to 120° C. for 5 hours up to 300 days and subsequent distillation at <120° C.

The preparation of iminodisuccinate or iminodisuccinic acid and salts thereof belong to the prior art.

According to GB-A 130 6 331, iminodisuccinate is obtained by reacting the starting materials maleic acid and ammonia at 60 to 155° C.

According to SU-A 0639863, iminodisuccinate is obtained by reacting the same starting materials in the presence of alkali metals at 110-130° C.

WO-A 98/45251, finally, discloses the synthesis of iminodisuccinic acid alkali metal salts by reaction of maleic anhydride, alkali metal hydroxide, NH₃ and water, the reaction mixture being admixed with further water and, if appropriate, methanol, and being freed from NH₃ by distillation at 50 to 170° C. and 0.1 to 50 bar.

A disadvantage of the processes of the prior art is the fact that the product comprises considerable amounts of ammonia due to the process. Even the distillation in WO-A 98/45251, which has complex apparatus requirements, is not able to reduce the ammonia in the long term, so that the use of iminodisuccinates have hitherto been possible only under restrictions.

However, applications such as textile cleaning, domestic cleaning and cosmetics require a storage-stable iminodisuccinate free from emissions of NH₃ gas which originate from decomposition of the iminodisuccinate or of NH₃ production residues.

It is an object of the present invention, therefore, to find a process for the preparation of storage-stable iminodisuccinate solutions which makes it possible to store iminodisuccinate solutions for a long period without formation of ammonia and as a result makes possible the application in the abovementioned sectors.

Surprisingly, it has now been found that an iminodisuccinate solution which has been heated for a plurality of hours then forms significantly less ammonia than a correspondingly solution which has not been thermally treated. At the same time, an iminodisuccinate solution, after the heating, has a higher content of iminodisuccinate, than before the heating. It is possible as a result to obtain a product of significantly higher purity and better odour properties. Although iminodisuccinate is temperature-sensitive and heating the solution leads to chemical decomposition with the formation of ammonia, in the context of the present invention, it has been found that, by specifically metered supply of heat, higher product quality can be achieved with respect to stability of the iminodisuccinate solution against progressive decomposition and ammonia formation.

The solution, and thus object of the present invention, is a process for the preparation of a storage-stable solution of iminodisuccinate having an ammonia content <50 ppm, characterized in that an iminodisuccinate solution having an elevated ammonia content is thermally treated at 40 to 120° C. for 5 hours up to 300 days and is then subjected to a distillation at temperatures <120° C.

Thermal treatment in the context of the present invention means heating a substance, here an iminodisuccinate solution having elevated ammonia content, for a relatively long period. An elevated ammonia content in the context of the present invention and as is present in the product as a result of the iminodisuccinate syntheses of the abovedescribed prior art, means 50 to 500 ppm. In particular as a result of storage of iminodisuccinate solutions, as are obtained according to the processes described in the prior art, an increase of the ammonia concentration continuously up to values up to 150 ppm in the course of 200 days may be observed (FIG. 1).

An iminodisuccinate solution which has been, according to the invention, thermally treated at 90° C. and then subjected to a distillation, prepared by the abovementioned processes of the prior art, has formed only 35 ppm of ammonia after 200 days (FIG. 1).

The finding that a thermal treatment of the iminodisuccinate solution leads to better product properties is surprisingly in contrast to the observation that an iminodisuccinate solution loses concentration when it is heated.

Iminodisuccinate solutions in the context of the present invention are aqueous solutions of iminodisuccinate, preferably 0.1 to 40% strength by weight aqueous solutions, but also mixtures of these aqueous solutions with organic solvents, for example alcohols. Alcohols which may be mentioned by way of example are methanol, ethanol, propanols, butanols.

The invention preferably relates to a process for the preparation of storage-stable solutions of iminodisuccinate having an ammonia content <50 ppm, characterized in that an iminodisuccinate solution having elevated ammonia content is thermally treated at 40 to 120° C., particularly preferably at 80 to 115° C., for 10 to 100 hours, particularly preferably 15 to 70 hours, and is then subjected to a distillation at temperatures of 40 to 130° C., particularly preferably at 60 to 120° C.

A procedure is followed in such a manner that, after preparation of the iminodisuccinate solution, this is heated to temperatures of 80 to 120° C. and kept at these temperatures for 5 to 200 h, with mixing of the solution. This can be performed continuously or batchwise. In the case of the continuous procedure, suitable apparatuses can be selected and connected so that the said residence times at the said temperatures are achieved. For this, in chemical and thermal process engineering, a number of advantageous apparatuses and apparatus connections, for example the kettle cascade, the tubular reactor, heat exchangers equipped with internals or the cascaded column are known.

In a subsequent step, the ammonia distillation is then carried out continuously or batchwise. To carry out this distillation step, appropriate apparatuses and distillation designs are known to those skilled in the art.

By means of this procedure, iminodisuccinate solutions can be obtained, the ammonia content of which does not exceed 35 ppm without further post-treatment, even after a time period of several hundred days (FIG. 1).

In accordance with the inventive process, storage-stable iminodisuccinate solutions are obtained having an ammonia content less than 50 ppm, preferably less than 40 ppm, particularly preferably less than 20 ppm, even less than 5 ppm!

Such low ammonia concentration over a period of up to 200 days now allows the use of the storage-stable iminodisuccinate solutions in cosmetics, laundry detergents, cleaning compositions, in domestic cleaning, in paper manufacture, in bleaching processes and in textile treatment.

EXAMPLE

After preparation of the iminodisuccinate solution (obtained in accordance with WO-A 98/45251) this was heated in the reaction kettle to 102° C. and kept at this temperature for 20 hours with stirring. Ammonia and water were then distilled off overhead from the solution in a distillation column at atmospheric pressure. In the course of this, temperatures resulted in the bottom of 105 to 106° C. At the top of the column a temperature of 99° C. was established.

After the end of the experiment, the ammonia content in the distilled iminodisuccinate solution was below the limit of detection of 2 ppm. After 8 weeks, the ammonia content had increased to 16 ppm.

Claims

1. Process for the preparation of storage-stable solutions of iminodisuccinate having an ammonia content of <50 ppm, characterized in that iminodisuccinate solutions having an ammonia content greater than 50 ppm are thermally treated at 40 to 120° C. for 5 hours up to 300 days and are then subjected to a distillation at temperatures <120° C.

2. Process according to claim 1, characterized in that the thermal treatment is carried out at 80 to 115° C.

3. Use of the storage-stable iminodisuccinate solutions prepared according to claim 1 for cosmetics, laundry detergents, cleaning compositions, domestic cleaning, in paper manufacture, in bleaching processes and in textile treatment.