Process for preparing isocyanates containing alkoxysilane groups
The invention relates to a process for preparing isocyanate containing alkoxysilane groups, in which, in the sequence of steps A) to D), A) alkoxysilano(cyclo)alkylamine is reacted with dialkyl carbonate in the presence of a basic catalyst to give alkoxysilano(cyclo)alkylurethane, B) simultaneously or successively, the catalyst is deactivated, and low boilers, solids, salt burdens and/or high boilers are removed, C) alkoxysilano(cyclo)alkylurethane obtained after B) is thermally cleaved to release isocyanate containing alkoxysilane groups and by-product, leaving bottoms material, and D) isocyanate containing alkoxysilane groups and by-product are separated from one another and from bottoms material and collected, wherein the process regime at least of steps C) to D) is continuous.
1. A process for preparing isocyanate containing alkoxysilane groups comprising the sequence of steps A) to D),
A) alkoxysilano(cyclo)alkylamine is reacted with dialkyl carbonate in the presence of a basic catalyst to give alkoxysilano(cyclo)alkylurethane,
B) successively
removing and/or deactivating the basic catalyst, and then
removing low boilers by distillation,
removing solids and salt burdens by filtration or centrifugation
removing high boilers by thin-film evaporation,
C) alkoxysilano(cyclo)alkylurethane obtained after B) is thermally cleaved to release isocyanate containing alkoxysilane groups and by-product, leaving bottoms material, and
D) isocyanate containing alkoxysilane groups and by-product are separated from one another and from bottoms material and collected,
wherein the process regime at least of steps C) to D) is continuous.
2. The process according to claim 1 , wherein in step
C) alkoxysilano(cyclo)alkylurethane obtained after B) is thermally cleaved to release isocyanate containing alkoxysilane groups and by-product, leaving bottoms material, while
i) the bottoms material is being wholly or partly discharged from the cleavage apparatus,
ii) subjected to thermal treatment and/or purification and/or an aftertreatment in the presence of alcohol and
iii) the material removed, after thermal treatment and/or purification and/or aftertreatment in A), B) or C), is fed back.
3. The process according to claim 2 , wherein the discharged bottoms material
is subjected to thermal treatment at a temperature of 150-250° C. over a period of 0.2 to 4 h and/or
is distilled under reduced pressure and at a temperature of 150-250° C. and/or
is converted in the presence of an alcohol of the formula R 2 OH with R 2 =linear, branched or cyclic hydrocarbyl radical having 1-6 carbon atoms at 25-100° C. in the presence or absence of a catalyst.
4. The process according to claim 3 , wherein no reaction with alcohol is conducted.
5. The process according to claim 4 , wherein the distillate obtained is sent to step B) or C).
6. The process according to claim 4 , wherein the isocyanate obtained by rectification is additionally purified and isolated by distillation.
7. The process according to claim 2 , wherein the alkoxysilano(cyclo)alkylamine has the formula (1)
R a m (OR 2 ) 3-m Si—R 1 —NH 2 (1)
where R 3 , R 2 and R 1 are each independently identical or different hydrocarbyl radicals having 1-6 carbon atoms, where these may be linear, branched or cyclic, and m is 0-2.
8. The process according to claim 2 , wherein the dialkyl carbonate used is selected from dimethyl, diethyl, dipropyl and dibutyl carbonate.
9. The process according to claim 2 , wherein, in step
B) in the sequence of steps i) to iv)
i) the catalyst is deactivated,
iii) solids and/or salt burdens are filtered off.
10. The process according to claim 2 , wherein the thermal cleavage C) is conducted without solvent and in the presence of a catalyst at a temperature of 150-280° C. and a pressure of 0.5-200 mbar.
11. The process according to claim 10 , wherein the catalyst concentration is 0.5-100 ppm.
12. The process according to claim 2 , wherein, in step C), an amount of bottoms material corresponding to 5-60% by weight based on the feed is discharged from the bottom and added again in step A), B) or C).
13. The process according to claim 1 , wherein the alkoxysilano(cyclo)alkylamine has the formula (1)
R a m (OR 2 ) 3-m Si—R 1 —NH 2 (1)
where R 3 , R 2 and R 1 are each independently identical or different hydrocarbyl radicals having 1-6 carbon atoms, where these may be linear, branched or cyclic, and m is 0-2.
14. The process according to claim 1 , wherein the dialkyl carbonate used is selected from dimethyl, diethyl, dipropyl and dibutyl carbonate.
15. The process according to claim 1 , wherein, in step
B) in the sequence of steps i) to iv)
i) the catalyst is deactivated,
iii)solids and/or salt burdens are filtered off.
16. The process according to claim 15 , wherein the residue from the thin-film evaporation is recycled into the urethane synthesis A) or into the filtration/centrifugation step B) iii).
17. The process according to claim 1 , wherein the thermal cleavage C) is conducted without solvent and in the presence of a catalyst at a temperature of 150-280° C. and a pressure of 0.5-200 mbar.
18. The process according to claim 17 , wherein the catalyst concentration is 0.5-100 ppm.
19. The process according to claim 1 , wherein, in step C), an amount of bottoms material corresponding to 1-90% by weight based on the feed is discharged from the bottom and added again in step A), B) or C).
20. The process according to claim 1 , wherein the separation in step D) is a rectification.