Process for preparing isocyanates by thermal dissociation of carbamates

US8680323B2 · kind B2 · utility

Assignee

• BASF SE

Inventors

• Michael Bock · Ruppertsberg, DE
• Axel Franzke · Goldkronach, DE
• Robert Baumann · Mannheim, DE
• Eckhard Stroefer · Mannheim, DE

Key dates

• Filing date: Jan 18, 2011
• Grant date: Mar 25, 2014
• Expiry date: Nov 16, 2031

Classification

• Technology area (CPC C): Chemistry; Metallurgy
• CPC primary: C07C263/04
• WIPO field: Organic fine chemistry
• WIPO sector: Chemistry

Abstract

The invention relates to a process for preparing isocyanates by thermal dissociation of carbamates and separation by distillation of the reaction mixture from the carbamate dissociation, comprising the corresponding isocyanate and the corresponding alcohol, by distillation in a column (K) having an enrichment section (V) and a stripping section (A), where the carbamate (1) is introduced between the enrichment section (V) and the stripping section (A) and the isocyanate is taken off as a constituent of the bottom stream (2) and the alcohol is taken off as a constituent of the overhead stream (3) from the column (K), in the presence of an inert solvent, wherein an intermediate boiler having a boiling point between the boiling point of the isocyanate and the boiling point of the alcohol under the operating conditions of the carbamate dissociation is used as inert solvent and is fed as external runback (4) in liquid form in a purity of >95% by weight, based on the total weight of the external runback (4), in the upper region of the enrichment section (V) and as gaseous, superheated stream (5) into the lower region of stripping section (A) at one or more points.