Process for preparing methylenediphenyl diisocyanates

US8318971B2 · kind B2 · utility

Assignee

• Bayer MaterialScience AG · DE

Inventors

• Fritz Pohl · Wittmund, DE
• Andreas Bulan · Langenfeld, DE
• Rainer Weber · Leverkusen, DE
• Richard Adamson · Leichlingen, DE
• Matthias Böhm · Leverkusen, DE
• Christian Six · Neuss, DE

Key dates

• Filing date: Feb 27, 2009
• Grant date: Nov 27, 2012
• Expiry date: Apr 22, 2030

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C25B1/26
• WIPO field: Organic fine chemistry
• WIPO sector: Chemistry

Abstract

The invention relates to a process for preparing methylenediphenyl diisocyanates which comprises at least the steps: A) reaction of aniline with formaldehyde in the presence of hydrochloric acid as catalyst to give a mixture of diamines and polyamines of the diphenylmethane series (MDA) and subsequent at least partial neutralization of the hydrochloric acid by means of alkali metal hydroxide, B) reaction of the mixture of diamines and polyamines of the diphenylmethane series obtained in step A) with phosgene to give a mixture of diisocyanates and polyisocyanates of the diphenylmethane series (MDI) and hydrogen chloride, wherein C) the hydrochloric acid which has been neutralized in step A) is separated off in the form of a solution containing alkali metal chloride and is subsequently at least partly fed to an electrochemical oxidation to form chlorine, alkali metal hydroxide and optionally hydrogen and D) at least part of the chlorine produced in step C) is used for preparing the phosgene used in step B).