TETRAACETYLETHYLENEDIAMINE (TAED) currently commercially consititutes the most important activator of the sodium perborate which is present in washing-machine detergents. It is generally produced from ethylenediamine (EDA) and acetic acid in two reaction stages: initially ethylenediamine is caused to react with acetic acid so as to form diacetylethylenediamine (DAED), through the intermediate double-salt stage; then DAED is converted into TAED by reaction with acetic anhydride by means of the intermediate stage of triacetylethylenediamine (TRIAED). Once the acetylation reaction has been exhausted, the reaction mixture is cooled, causing the crystallization of the TAED, which is isolated from the mother liquor by filtration. However, the TAED thus obtained still has, despite its high titer, traces of by-products and colored impurities and thus is not suitable for direct use in detergents, for which a perfectly colorless, odorless and controlled-granulometry product is expressly required. The TAED production cycle must therefore be completed with additional purification and granulometry-correction processes. Various proposals have been made, such as: exhaustive washings of the crystals with acetic acid and water (DE 3 609 735) or dispersion of the crude TAED in an appropriate suspension medium prior to filtration (EP 70432). However, these purification systems are not free from disadvantages, such as mainly the loss of substance and limited effectiveness.
Better results are obtained by adopting the recrystallization process which consists in hot-resolubilizing the crude TAED into acetic anhydride, in subsequently cooling the solution and then in separating the crystals from the mother liquor, which is recycled in order to avoid product losses. However, the crystals obtained with the above mentioned crystallization method are generally coarse and have wide granulometric ranges. Usually, in order to provide finer powders with well-defined and constant granulometric ranges, it is necessary to resort to additional grinding methods (EP 301 722-EP 63512).
USPTO Backgrounds
USPTO Backgrounds