Ciba Specialty Chemicals Corporation

Jacek Malisz

Holger Lautenbach

Martina Hoffmann

Rainer Kaufel

Elke Polley

Adolf Käser

Adolf K&auml;ser

Rolf Lucas

Ernst Wagner

Kurt Huber

The present invention relates to a method of reducing the total organic carbon (TOC) content of waste water in the course of the preparation of concentrated solutions or suspensions of anionic organic compounds, which method comprises increasing the concentration of an aqueous solution or suspension of an anionic organic compound in the form of its free acid or its alkali metal salt, having a salt content of less than 5% of extraneous salt by weight based on the total solution or suspension, by microfiltration, ultrafiltration and/or nanofiltration, a) the membrane pore size being so selected that compounds having molecular weights in the range from 300 to 1000 Daltons or higher are retained, and b) the content of anionic compound in the concentrate being so adjusted to from 10 to 50% by weight that the total organic carbon (TOC) content of the permeate is less than 0.5% by weight, based on the total permeate, and c) optionally, after increasing the concentration of a suspension, dissolving the anionic organic compound by adding a suitable base. The invention relates also to the solutions and suspensions prepared by that means and to the use of such solutions or suspensions in dyeing or optically whitening paper or textile materials.

Method of reducing the organic carbon content of production waste water in the course of the preparation of concentrated solutions of anionic organic compounds

Described is a process for preparing concentrated solutions or suspensions of anionic organic compounds which comprises a) acidifying an aqueous solution or suspension of an anionic organic compound containing salts and/or impurities to a pH of 4.5 or less, if the pH is above this value, so that b) the anionic organic compound is water-insoluble and precipitates in the form of the free acid, c) bringing the suspension to a salt content below 2% by weight, based on the total weight of the retentate, by means of ultrafiltration with a membrane having pore diameters of from 0.001 to 0.02 &#x3bc;m, and d) optionally washing out the salts with water having a pH below 4,5, e) optionally carrying out acid-free washing with water thereafter, and then f) concentrating, so that the amount of anionic organic compound is 5-50% by weight, and g) if desired, bringing the anionic organic compound into solution by adding an appropriate base.

Process for preparing solutions of anionic organic compounds

Process for the preparation of solutions of anionic organic compounds

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Grenzach-Wyhlen, Germany

Jacek Malisz