Process for the preparation of diisocyanates

A process for the preparation of diisocyanates and triisocyanates of the general formula (I)

• R(NCO)n (I),
• in which
• R represents a (cyclo)aliphatic or aromatic hydrocarbon radical having up to 15 carbon atoms with the proviso that at least 2 carbon atoms are arranged between two NCO groups, and
• n represents the number 2 or 3,
• the process comprising gas phase phosgenating the corresponding diamines and/or triamines of the general formula (II)
• R(NH2)n (II),
• in which
• R represents a (cyclo)aliphatic or aromatic hydrocarbon radical having up to 15 with the proviso that at least two carbon atoms are arranged between two amino groups, and
• n represents the number 2 or 3,
• by providing a tubular reactor which has a double-walled guide tube extending centrally in the direction of the axis of rotation of the tubular reactor, a concentric annular gap being formed between the inner and the outer wall of the double walled guide tube, and the ratio of the cross-sectional area of the tubular reactor, which area is bounded by the inner wall of the double-walled guide tube, to the cross-sectional area of the tubular reactor, which area is bounded by the wall of the tubular reactor and the outer wall of the double-walled guide tube, being 1:0.5 to 1:4,
• heating the diamines and/or triamines in vapour form and phosgene separately from one another to temperatures of 200° C. to 600° C.,
• feeding the diamines and/or triamines in vapour form to the tubular reactor via the concentric annular gap at a mean flow velocity of 20–150 m/s, and
• feeding the phosgene to the tubular reactor over the remaining cross-sectional areas of the tubular reactor at a mean flow velocity of at least 1 m/s.