Ciba-Geigy Corporation

Alberto Rabassa

Beat Bruttel

Bruno Fortsch

Christiane Hartling

The invention describes a process for the preparation of formulations of water-insoluble to sparingly soluble azo dyes by simultaneous diazotization and coupling in a single step reaction, filtering the dye dispersion and, if desired, drying the dyestuff, which process comprises carrying out said simultaneous diazotization and coupling by intimately mixing the aqueous solution or suspension of the reactants, in the presence of one or more surface-active agents, concentrating the dilute dye dispersion by membrane separating methods, and at the same time at least partially removing salt and/or acid from the dispersion and converting it into a storage stable liquid formulation or, by drying, into a solid dye formulation.

Process for the manufacture of formulations of water-insoluble azo dyes

The continuous workup of aqueous crude dye suspensions is carried out in a multi-stage membrane separation unit by feeding into each membrane separation stage a dye suspension and also wash water, permeate from the subsequent membrane separation stage or a mixture consisting of wash water and permeate. A separation into retentate (concentrate) and permeate takes place, in which the degree of concentration and the degree of desalting in each membrane separation stage is controlled by means of a suitable variable, for example the conductivity or the volume of the permeate in each case or the concentration of the retentate. This control allows the reproducible preparation of dye formulations having constant properties and, due to the optimization of the volume streams, leads to a significant reduction in water pollution.

Process for the continuous workup of aqueous crude dye suspensions

A process for the preparation of formulations of water-soluble organic dyes starting from an aqueous salt-containing suspension of the untreated dye and using membrane separation methods, which process comprises substantially freeing the aqueous suspension of the untreated dye from by-products and reducing the salt concentration by more than half in a first membrane separation treatment, then diluting the dye suspension in a further optional step and effecting deionization and concentration in a second membrane separation treatment and converting the concentrate so obtained into a liquid or solid commercial formulation. This multi-step membrane separation process, e.g. ultrafiltration combined with hyperfiltration, results in a high rate of permeation through the membrane and avoids operating problems caused by membrane clogging.

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Oberwil, Switzerland

Alberto Rabassa