Abstract: A mixture of isomeric diisocyanatodiphenylmethanes composed of at least 2,2?-diisocyanato-diphenylmethane, 2,4?-diisocyanatodiphenylmethane and 4,4?-diisocyanatodiphenyl-methane is distilled in at least one stage and a divided-wall column is used in at least one distillation stage.

Abstract: 2,4?-MDI which contains very little 2,2?-MDI is prepared by distilling an isomeric starting mixture of diisocyanatodiphenylmethanes which includes 2,2?-diisocyanato-diphenylmethane, 2,4?-diisocyanatodiphenylmethane and 4,4?-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?-diisocyanatodiphenylmethane, up to 15 wt. % of 4,4?-diisocyanatodiphenyl-methane and no more than 0.2 wt. % of 2,2?-diisocyanatodiphenylmethane.

Abstract: 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–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.

Abstract: 2,4?-MDI which contains very little 2,2?-MDI is prepared by distilling an isomeric starting mixture of diisocyanatodiphenylmethanes which includes 2,2?-diisocyanato-diphenylmethane, 2,4?-diisocyanatodiphenylmethane and 4,4?-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?-diisocyanatodiphenylmethane, up to 15 wt. % of 4,4?-diisocyanatodiphenyl-methane and no more than 0.2 wt. % of 2,2?-diisocyanatodiphenylmethane.

Abstract: 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° 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° C. and the solid precipitate obtained is washed with water, and 1,5-dinitronaphthalene is isolated from the washed precipitate by washing with acetone.

Abstract: 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° 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° C. and the solid precipitate obtained is washed with water, and 1,5-dinitronaphthalene is isolated from the washed precipitate by washing with acetone.

Abstract: A mixture of isomeric diisocyanatodiphenylmethanes composed of at least 2,2′-diisocyanato-diphenylmethane, 2,4′-diisocyanatodiphenylmethane and 4,4′-diisocyanatodiphenyl-methane is distilled in at least one stage and a divided-wall column is used in at least one distillation stage.

Abstract: Toluene diisocyanate is recovered from a crude distillation feed comprising less than 2% by weight of phosgene by

Abstract: 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° C.

Abstract: 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.

Abstract: 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.