Basf Aktiengesellschaft

Gerhard Wickenhaeuser

Leopold Hupfer

Bernd Heida

Fritz Graser

Fritz Graf

Aqueous glyoxylic acid solutions, essentially free of other acids, are recovered from aqueous solutions which still contain other acids, by a method in which the aqueous solution is mixed with an organic nitrogen compound at as high as 50.degree. C., the phases are separated, and the glyoxylic acid is extracted from the organic phase with water, at a higher temperature.

Recovery of aqueous glyoxylic acid solutions

Aqueous solutions of glyoxal which contain acids are purified by treatment with a solution which contains from 20 to 60% by weight of a tertiary amine and from 80 to 40% by weight of an alcohol which is not infinitely miscible with water, the treatment being carried out by mixing the two solutions during a residence time of less than 5 minutes.

Purification of aqueous glyoxal solutions

A process for the preparation of deeply colored organic pigments by crystallizing finely divided crude organic pigments, whose primary particles have a size of .ltoreq.0.2 .mu.m, in C.sub.3 -C.sub.5 -alkanes, C.sub.3 -C.sub.5 -alkenes or C.sub.1 -C.sub.3 -chloroalkanes at from 40.degree. to 250.degree. C. to under atmospheric pressure or superatmospheric pressure, and isolating the pigment. The pigments obtained by the process give deep, brilliant colorations.

Conditioning of finely divided crude organic pigments

A process for drying finely divided pigments contained in a press cake or a suspension, wherein a mixture of the pigment and a liquid whose critical temperature is below the decomposition temperature of the pigment is heated under pressure to above the critical temperature of the liquid and is then released while keeping the temperature above the dew line of the liquid. The process gives fine pigments powders which are easily dispersible in the media in which pigments are used, and which produce deep, brilliant colorations.

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Birkenheide, Germany

Gerhard Wickenhaeuser