Process for the preparation of diisocyanates
View Patent ↗The invention relates to a process for the preparation of isocyanates in the gas phase, in which the possibilities for back-mixing and byproduct formation are reduced by improving the mixing of the starting materials in a tubular reactor.
1. 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(NH 2 ) 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.
2. The process according to claim 1 , in which the mean flow velocity of the diamines and/or triamines in vapour form is 40 to 100 m/s.
3. The process according to claim 1 , in which the mean flow velocity of the phosgene is 5 to 15 m/s.
4. The process according claim 1 , in which isophoronediamine, hexamethylenediamine or bis(p-aminocyclohexyl)methane are used as diamines.
5. The process according to claim 1 , in which 1,8-diamino-4-(aminomethyl)octane or triaminononane are used as triamines.
6. The process according to claim 1 , wherein the phosgenating is carried out in a tubular reactor in which 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, is 1:1 to 1:3.
7. The process according to claim 2 , in which the mean flow velocity of the phosgene is 5 to 15 m/s.
8. The process according claim 2 , in which isophoronediamine, hexamethylenediamine or bis(p-aminocyclohexyl)methane are used as diamines.
9. The process according claim 3 , in which isophoronediamine, hexamethylenediamine or bis(p-aminocyclohexyl)methane are used as diamines.
10. The process according to claim 2 , in which 1,8-diamino-4-(aminomethyl)octane or triaminononane are used as triamines.
11. The process according to claim 3 , in which 1,8-diamino-4-(aminomethyl)octane or triaminononane are used as triamines.
12. The process according to claim 2 , wherein the phosgenating is carried out in a tubular reactor in which 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, is 1:1 to 1:3.
13. The process according to claim 3 , wherein the phosgenating is carried out in a tubular reactor in which 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, is 1:1 to 1:3.
14. The process according to claim 1 , wherein the phosgenating is carried out in a tubular reactor in which 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, is 1:1 to 1:3.
15. The process according to claim 1 , wherein R is from 4 to 13 carbon atoms.