Hoechst Aktiengesellschaft

Hans Schafer

Peter Herbrechtsmeier

Rudolf Steiner

Wolfgang Grunbein

Eberhard Ritter

Wolfgang Wendel

Martin Schottler

Gunter Greiner

Norbert Nix

Thomas Vollheim

Process for the preparation of 2,5-di(phenylamino)terephthalic acid and dialkyl esters thereof in high purity. The invention relates to a process for the preparation of dialkyl 2,5-di(phenylamino)terephthalates of the formula (I) ##STR1## in which R is a hydrogen atom or a methyl group and R' is a methyl group or ethyl group, by dehydrogenation (oxidation) of the corresponding dialkyl 2,5-di(phenylamino)-3,6-dihydroterephthalate with oxygen, which comprises blanketing with oxygen a solution or suspension of the dialkyl 2,5-di(phenylamino)-3,6-dihydroterephthalate in aromatic hydrocarbons in a stirred vessel, circulating this reaction mixture via a spraying device, so that the sprayed reaction mixture is distributed over the reaction mixture present in the stirred vessel, the sprayed reaction mixture being mixed with the circulating gas. The process has the advantage of a short reaction time, combined with favorable space-time yields and simplicity in terms of apparatus.

Process for the preparation of 2,5-di(phenylamino)terephthalic acid and

The invention provides a process for multistep gassing of liquids streaming downward in a gassing apparatus, which comprises using a gassing apparatus consisting of at least two superposed downstream parts, wherein the gas is fed in at the upper end of each downstream part, the gas bubbles are separated at the lower end of each downstream part and the separated gas bubbles are discharged to the outside. The invention provides furthermore a corresponding gassing apparatus.

Process and apparatus for gassing liquids

The invention provides a process for multistep gassing of liquids streaming downward in a gassing apparatus, which comprises using a gassing apparatus consisting of at least two superposed downstream parts, wherein the gas is fed in at the upper end of each downstream part and fresh gas is fed in exclusively at the upper end of the lowest downstream part, the gas bubbles are separated at the lower end of each downstream part and the separated gas bubbles are discharged to the outside and recycled to the next downstream part above. The invention provides furthermore a corresponding gassing apparatus.

The invention relates to a process for absorbing ozone in water by introducing an ozone-containing gas into a water current streaming downward in an absorber, wherein the ozone-containing gas is introduced into the water current in the form of bubbles at the upper end of the absorber and subsequently conveyed downward to the absorber outlet in a direction opposed to its ascending direction.

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Bad Soden am Taunus, Germany

Hans Schafer