Process for the preparation of concentrated stable liquid dye solutions of CI Direct Yellow 11 utilizing an extended surface silica filter aid during a desalting procedure

Abstract

A process is disclosed for the preparation of concentrated stable liquid dye solutions of CI Direct Yellow 11 starting with the tetrasodium complex of the stilbeneazo(xy) based-catalyzed condensation of 4-nitro-toluene-2-sulfonic acid, the wet-cake or the dried technical grade of the condensed tetrasodium complex. The process comprises the steps of forming an aqueous suspension of the starting materials which are admixed with the extended surface silica filter aid and the resulting slurry is acidified with a strong inorganic acid to pH below about 2.5; the slurry is heated to promote the metathetical reaction forming the free acid complex of the yellow chromophore and sodium sulfate or sodium chloride; the salt remains in water-soluble form while the insoluble free acid complex is absorbed on the filter aid; the resulting acidified slurry is filtered through a filter, pre-coated with an aqueous slurry of the filter aid; the resulting filter-cake, containing the free acid complex, is washed with water until all the salt is removed; the washed filter cake is reslurried with an alkanolamine/water mixture; the alkanolamine is present in an amount sufficient to provide an aqueous phase in the pH range 6.5 to 7.5; the free acid complex is converted to the liquid alkanolamine stilbeneazo(xy) complex of the Direct Yellow 11 which is desorbed from the filter aid; the neutralized slurry is filtered; the filtrate contains the alkanolamine-complexed Direct Yellow chromophore, which is concentrated by removing the contained water until the stable liquid Paper Yellow 11 complex dyestuff results.

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