Bayer Aktiengesellschaft

Bayer Materialscience Ag

Covestro Deutschland Ag

Hans-Peter Schal

Hartmut Knofel

Michael Brockelt

Marcel Petinaux

Rudolf Uchdorf

Ulrich Wolf

Berthold Keggenhoff

Gerhard Wegener

Hartmut Hetzel

Dieter Grenner

Bernd Thelen

Kai Verkerk

Vera Yakovlevna Popkova

Bill Brady, Jr

Boris Mikhaylovitch Laskin

Alexander Sergeevitch Malin

Sofia Borisovna Volkova

R&uuml;diger Drope

Marcus Paul Grün

Boris Mikhaylovitch Prof Laskin

Vera Yakovelevna Prof Popkova

A mixture of isomeric diisocyanatodiphenylmethanes composed of at least 2,2'-diisocyanato-diphenylmethane, 2,4&#x2032;-diisocyanatodiphenylmethane and 4,4&#x2032;-diisocyanatodiphenyl-methane is distilled in at least one stage and a divided-wall column is used in at least one distillation stage.

Process for the distillation of a mixture of isomeric diisocyanatodiphenylmethanes

2,4'-MDI which contains very little 2,2&#x2032;-MDI is prepared by distilling an isomeric starting mixture of diisocyanatodiphenylmethanes which includes 2,2&#x2032;-diisocyanato-diphenylmethane, 2,4&#x2032;-diisocyanatodiphenylmethane and 4,4&#x2032;-diisocyanatodiphenyl-methane in at least one stage in a separating wall column. This distillation produces at least one mixture which contains 85 to 99 wt. % of 2,4&#x2032;-diisocyanatodiphenylmethane, up to 15 wt. % of 4,4&#x2032;-diisocyanatodiphenyl-methane and no more than 0.2 wt. % of 2,2&#x2032;-diisocyanatodiphenylmethane.

Process for the distillation of a mixture of isomeric diisocyanatodiphenyl-methanes

Toluene diisocyanate is recovered from a crude distillation feed containing less than 2% by weight of phosgene by (a) fractionating the crude distillation feed containing less than 2% by weight of phosgene to remove the solvent and optionally the reaction residues to produce a crude toluene diisocyanate feed containing less than 20% by weight of solvent and (b) separating the crude toluene diisocyanate feed containing less than 20% by weight of solvent in a divided-wall distillation column into four product fractions P1&#x2013;P4. P1 is a vapor phase low-boiler and solvent-enriched gas stream, P2 is a low-boiler and solvent-enriched product, P3 is a high boiler-enriched bottoms product containing toluene diisocyanate and P4 is a toluene diisocyanate product stream lean in low-boilers, high-boilers and reaction residues.

Process for the purification of toluene diisocyanate incorporating a dividing-wall distillation column for the final purification

The invention is directed to a process for the production of 1,5-dinitronaphthalene wherein naphthalene is nitrated by nitric acid in the absence of sulfuric acid at temperatures of from 30 to 80&#xb0; C., wherein the nitric acid has a concentration of from 72 to 87 wt.-%, the reaction mixture obtained is filtered at temperatures of from 5 to 20&#xb0; C. and the solid precipitate obtained is washed with water, and 1,5-dinitronaphthalene is isolated from the washed precipitate by washing with acetone.

Process for the production of 1,5-dinitronaphthalene

A process is described for obtaining pure isocyanate isomers from a mixture of isocyanate isomers by suspension crystallization and the isolation of isomerically pure crystals, which is characterized in that, prior to the isolation of the crystals, 5 to 40% by weight of the crystals produced are remelted while simultaneously increasing the temperature of the crystal slurry by 4.5 to 9&deg; C.

Process for the isomeric separation of isocyanates

The invention relates to an improved process for the production of polynuclear aromatic polyamines by condensation of aniline with formaldehyde in the presence of water and acidic catalysts and working up of the reaction mixture by extraction with a hydrophobic solvent, the acid catalyst accumulating in the aqueous phase of the extraction step being reused.

Process for the production of polynuclear aromatic polyamines

Growing community of inventors

Dormagen, Germany

Hans-Peter Schal