IE59879B1 - Process for the purification of tetraacetylethylene diamine - Google Patents

Abstract

Crude tetraacetylethylenediamine (TAED), such as obtained in crystalline form during synthesis, is converted by successive washing with acetic acid and water and subsequent drying into a colourless and odourless form, such as is required for use in detergents and bleaching agents.

Description

This invention relates to the purification of Tetraacetylethy1ene diamine.

The compound N ,Ν , N' , N '-Tetraacetyl ethyl ene diamine, hereinafter more simply designated Tetraacetyl ethylene diamine or TAED, has recently aquired a practical significance as an activator in peroxide-containing bleach liquors and washing agents. The most important manufacturing process is the acetylation of , N '-D i acety 1 ethy 1 ene diamine (DAED), with the aid of acetic anhydride. This process was first used for producing TAED in the year 1911, and numerous variations have become known since then (eg DE 21 33 458, DE 21 18 281, DE 30 24 694, GB 2 096 133, EP 4 919, EP 51 739 and EP 79 671).

The reaction of DAED with acetic anhydride, which is usually carried out at temperatures between 120 and 170°C with excess acetic anhydride, yields TAED in an equilibrium reaction, so that the reaction mixtures, apart from the desired end product, still contain unreacted DAED and tri acetyl ethylene diamine. During the reaction, moreover, there are formed dark-coloured by-products whose nature is unknown. Crude TAED, as isolated from these reaction mixtures, for example by crystallization, always contains a - 3 certain proportion of by-products, and in this form cannot generally be directly further used, since for most fields ' of application there is required a product which is as pure, colourless and odourless as possible. The production of TAED has therefore to be combined with a purification process .

Numerous proposals have also been made for the purification of TAED, extending from a simple washing with acetic anhydride (DE 21 33 458, DE 21 18 281) through the use of adsorbents prior to crystal 1ization (EP 4 919) all the way to fractional distillation of the TAED (EP 8 369). A further suggestion (EP 70 432) is to disperse the crude TAED uniformly in a suspending agent, and after a longish standing time to isolate it again. None of these purifi15 cation procedures is free of disadvantages, whether of low efficiency or product losses or of high energy consumption and/or requirements as to equipment.

Early or late, the problem remained of developing a simple and efficient purification process for TAED. in particular the problem was to develop a purification process of that kind, which would yield a TAED suitable for use in washing agents.

This problem is solved in accordance with the invention by a purification process which comprises treating the crude crystalline TAED by first (a) washing it with acetic acid, then (b) washing it with water and finally (c) drying it. The material is for preference partially dried between the two washing steps. In particularly preferred variations of i the process several successive partial steps are carried out in the same apparatus and/or the drying is effected with the aid of gases, preferably air, which are blown through the product, in one or both drying steps. _ 4 The invented process surprisingly permits a colourless and odourless product to be obtained with extremely small amounts of washing liquids and without significant losses of valuable substances. The requirements as regards time, energy and apparatus are likewise small, so that the (- process permits more rapid and economic purification than other processes of the same efficiency, despite the necessity of three or four separate steps.

The purification process according to the invention is not restricted to a particular TAED manufacturing process. It is applied to particular advantage, however, after such manufacturing processes as have acetic acid for a component of the reaction mixture, since in that case the first washing liquid can be worked up without difficulty together with the mother liquors of the reaction and, if desired, recycled. Preferably therefore the purification process according to the invention is combined with a manufacturing process in which TAED is produced by acetylation by means of acetic anhydride.

The separate steps of the purification process of the invention can be carried out individually in separate apparatus, such as are known per se for filtration, washing and drying processes. It is preferred however to carry out several steps, or indeed all the steps, in the same apparatus. Examples of devices in which washing operations can be carried out as well as the drying, are single layer filters, such as suction filters and filter dryers, belt filters and drum filters.

Among such apparatus, moreover, those pressurized rotary f filters are preferred, which not only permit all steps of the purification process of the invention to be performed ί continuously in several successive working segments, but on which the above-mentioned final step of the preparation process, the filtration of the crystalline TAED, can be carried out. - 5 The design of the individual steps of the purification process is such as to accommodate both the quality of the crude TAED and the desired quality of the purified material. The process according to the invention can be adapted to both parameters within broad limits.

The first washing step (a) is preferably carried out at temperatures between 17 and 30 ° C , but can also be done if desired by using warm TAED and/or warmed acetic acid, at raised temperatures, but preferably not above 50°C. The starting quantities of acetic acid, which if necessary may also contain small amounts of water, lie for preference between 0.2 and 2 litres, especially between 0.5 and 1.2 litres per kg TAED (calculated as the pure substance). The washing can be encouraged by slurrying and agitation of the TAED in the acetic acid, but is preferably done on the more or less undisturbed filter cakes of the TAED. The contact times or flow times, from the addition of acetic acid to the end of the filtration, lie between about 0.001 and 6, preferably between 0.01 and 2 seconds.

The drying step, which in the preferred embodiment of the process follows the acetic acid wash, is preferably carried out on the filter which was used for the preceeding step. Although this drying can also be achieved in the conventional manner under vacuum with optional warming, it has nevertheless proved more advantageous to blow inert gas, such as nitrogen or carbon dixoide, but preferably air under pressure, through the product, in order to dry it. Agitation of the product during this procedure can be useful, but is not necessary. Amounts of gas from 0.05 to 3 3 m , preferably 0.1 to 1 m per kg TAED are sufficient in general for the partial drying demanded by the invention. The entry temperatures of the gases are preferably about 10 to 100’C, but especially between 15 and 70C.

The second washing step (b) is carried out with water at preferably 5 to 50°C, especially 10 to 30°C, and can likewise be encouraged by slurrying and agitation of the TAED in the water. But here too, it is preferable to pass the wash liquid through the undisturbed filter cake. The quantities of wash water are preferably between 0.5 and 8 1, especially between 1 and 5 1 per kg TAED. They are principally determined by the acetic acid content of the TAED, as are the contact or flow times, which preferably lie between 0.001 and 6 seconds, especially between 0.01 and 2 seconds.

The final drying step (c) is generally carried out in a manner similar to the drying step after the washing with acetic acid. The conditions are chosen so that, in combination with the preceding washing process, the acetic acid is removed to the extent required, preferably to yield an odourless product, and so that the water content of the material corresponds to the given specification. In this drying step also, drying is carried out with the aid of gases, especially air, which are blown through the moist material at temperatures of preferably 10 to 100°C, especially between 15 and 70°C. The necessary quantities of gas, as in the first drying step, are preferably between 3 0.05 and 2 m „ especially between 0.1 and 1 m per kg TAED.

The purification process in accordance with the invention permits the TAED obtained to be passed on directly for further use, especially in washing, bleaching and disinfecting agents. As a rule, however, the finely crystalline TAED is first converted to a granulate, in an agglomeration process such as that of DE 30 11 998, in order to increase its storage stability in the presence of alkaline materials. The quantity of water necessary in this process can be previously provided for the purified TAED without difficulty, by suitable prosecution of the steps b and c of the purification process according to the invention.

Example 1 360 kg Di acetyl ethylene diamine was heated with 1275 kg acetic anhydride in a stirring vessel with reflux condenser and bottom outlet for three hours at reflux temperature.

The resulting brown solution was quickly cooled down to about 30°C with agitation, and TAED precipitated in crystalline form. The suspension of crystals was released onto a pressurized rotary filter with six segments, on which the following continuous processes were taking place in succession (the data refer to 1 kg TAED pure substance): - substantial separation of the mother liquor, - washing of crude TAED with 0.8 1 acetic acid (water content 0.6 % w/w, temperature 25°C, pressure 0.8 bar) with a contact time of about 0.05 seconds, - through blowing of 0.2 m air (temperature 20°C, pressure 1.5 bar), which was recycled via a liquid separator, - washing with 1.8 1 water (temperature 15’C, pressure 1 bar) with a contact time of about 0.05 seconds, - through blowing of 0.3 m air (temperature 20°C, pressure 1.8 bar), ~ mechanical discharge of the end product.

The total yield was 364 kg of a colourless and odourless TAED. The water content was about 5.4% w/w, referred to the dry weight, which in turn had a TAED content of 99.4%. The TAED, thus purified, was suitable for use in washing agents and could be introduced without difficulty into a granulation process. The losses in acetic acid discharged with the wash water were small (acetic acid content of the wash water 4%). - 8 Example 2 The procedure adopted was that of example 1, except that the intermediate drying after the acetic acid washing was dispensed with. In order to obtain an odourless product, the filter cake had to be washed with 5 1 water per kg TAED. The acetic acid losses, which arose by discharge with the wash water, were three times as great as in example 1. In addition the purified TAED was found to be equally good for use in washing agents as that obtained in example 1.

Example 3 This example was likewise conducted on the lines of example 1, except that acetic anhydride was used instead of acetic acid as the wash liquid in the first washing step. Despite an increase in the amount of water in the following washing process to over 8 1 per kg TAED, the end product contained more than 1 % acetic acid, so that it was not suitable for use in washing agents. The TAED had to be subjected to a further, intensive drying process in order to remove the acetic acid.

Claims (11)

Cl aims

1. Process for the purification of crystalline Ν,N,N',N 1 -Tetraacetylethevlene diamine (TAED), characterized by the following process steps: a) washing with acetic acid b) washing with water c) drying.

2. Process according to claim 1, in which a partial drying is carried out between the process steps a and b.

3. Process according to one of claims 1 and 2, in which one or both drying steps consist of blowing gases through the moist product.

4. Process according to claim 3, by which the gas used is air.

5. Process according to one of claims 1 to 4, in which several successive steps are carried out in the same apparatus .

6. Process according to claim 5, in which all the process steps are carried out continuously in a pressurized rotary filter.

7. Process according to one of claims 1 to 6, in which acetic acid is used as the washing liquid at the rate of 0.2 to 2 1 per kg TAED. - 10

8. Process according to one of claims 1 to 7, in which water is used as the washing liquid at the rate of 0.5 to 8 1 per kg TAED.

9. Process according to one of claims 1 to 8, in which 0.05 to 5 2 of air with an entry temperature of 10 to 100°C is used for drying.

10. Process according to claim 1 substantially as herein before described with reference to the examples.

11. Use of a TAED purified by one of the processes according to claims 1 to 10, in washing, bleaching or disinfecting agents.