Bayer Aktiengesellschaft

Ludwig Deibele

Oswald Wilmes

Kaspar Hallenberger

Heinz-Ulrich Blank

Bernd-Ulrich Kaiser

Hans-Walter Brandt

Harry Danziger

Jurgen Dahmer

Heinrich Steude

Heinz-Jurgen Alpers

Gerhard Ruffert

Karl-Heinz Steinacker

Gunther Rauchschwalbe

Kurt Toepffer

Siegfried Taurat

Low-boiling by-products are removed from diurethanes prepared by a phosgene-free process by carrier vapor distillation using alcohol vapor, preferably the vapor of the basic alcohol found in the diurethane, as the carrier vapor. The diurethanes freed of low-boiling by-products in this manner may be thermally decomposed to produce diisocyanates.

Process for removing by-products from diurethanes

In a distillation column with vaporous sidestream removal, the vaporous product removed is condensed in a condenser. The vapor pipe provided for the removal of product opens into a dip tank of which the upper end is connected to the condenser while its lower end is connected to a discharge pump. Inert gas present in the condensate is returned to the column above the sidestream removal through an inert gas pipe arranged at the upper end of the condenser.

Distillation column with vaporous sidestream removal

Pure or substantially enriched 2,4- and 2,6-dinitrotoluene can be isolated from a mixture containing these isomers if such a mixture is distilled under a pressure of 0.5 to 20 mbar at a temperature of 80.degree. to 200.degree. C. with exclusion of reducing conditions.

Process for the isolation of pure dinitrotoluenes

A thin layer evaporator which has a vapor lock above the solvent inlet is used for the preparation of distillate-free sump product which is obtained as solid from the concentration of solutions of water, organic substances and non-volatile constituents and dissolved in solvents.

Process for the preparation of sump product

Process for the removal of residues of solvent from crystallized .epsilon.-caprolactam, wherein the major quantity of solvent is removed in a first stage by distillation in the presence of water in an amount so that the water content of the residue of the first stage is from 0.5 to 6% by weight, and in a second stage by distilling water and any residues of solvent still present.

Process for the purification of epsilon-caprolactam

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Koln, Germany

Ludwig Deibele