Bayer Aktiengesellschaft

Hermann Dallmeyer

Uwe J Zarnack

Berthold Keggenhoff

Bernd Weber

Heinz Sauer

Heiko Beckhaus

Harro Witt

Wilhelm Hagen

Dieter Becher

Heinrich Lokum

Harald Stein

Ove Nommensen

A process for the purification of toluenediisocyanate by fractionating a crude distillation feed containing toluenediisocyante, an organic solvent and less than 2% by weight of phosgene in a heat integrated system having an upstream distillation column, an interchanger and a downstream distillation column which are connected in series. The vapor which is recovered from the upstream distillation column is used to reboil the bottoms product of the downstream distillation column or the feed to the downstream distillation column in the interchanger. The crude distillation feed comprising less than 2% by weight of phosgene is fractionated into three product fractions P1-P3 and optionally a fourth fraction P4. P1 is a noncondensible gas stream enriched with phosgene and/or low-boilers. P2 is a solvent-enriched product. P3 is a high boiler enriched bottoms product comprising toluenediisocyanate, and P4 is a toluenediisocyanate enriched stream lean in highboilers and reaction residues.

Process for the purification of mixtures of toluenediisocyanate

With a view to improving the heat transfer in exothermic reactions and simplifying the construction of the cooling system of the reactor, in particular a stirrer reactor, vertical boiling tubes which are sealed at the bottom are provided, above which is arranged a condensate collecting and liquid distributing chamber in which a sufficient layer of cooling liquid is constantly maintained by means of a liquid level regulator. Cooling fluid and the vapor produced flow in direct contact with each other as they are carried in counter current through the boiling tubes which have only single walls. The vapor passes through the layer of cooling fluid and is continuously discharged and preferably recovered. The condensate is preferably returned to the cooling system.

Reactor for carrying out exothermic reactions

The present invention is directed to a mixer for mixing at least two free-flowing, reactive or unreactive substances comprising

Mixer for mixing at least two free-flowing substances, especially those

The present invention is directed to a process for the production of a mono- and/or polyisocyanate by the phosgenation of a mono- and/or polyamine in a mixer which comprises

Process for the production of isocyanates

An amine is separated from an aqueous solution of amine and volatile organic compounds by distillation in a column. The vapors generated during distillation are condensed. The condensed vapors are then passed into a separating device in which the volatile organic compounds are removed. The liquid remaining in the separating device is then fed to the head of the distillation column. Water is removed from the column in a sidestream and diamine is the residue. This process is particularly effective in recovering aromatic diamines from solutions which accumulate during hydrogenation of dinitro aromatic compounds.

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Odenthal, Germany

Hermann Dallmeyer