PROCESS FOR PREPARING ISOCYANATES CONTAINING ALKOXYSILANE GROUPS

Abstract

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, pa wherein the process regime at least of steps C) to D) is continuous.

Claims

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) 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.

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 1, wherein the alkoxysilano(cyclo)alkylamine has the formula (1)
R.sup.3.sub.m(OR.sup.2).sub.3-mSiR.sup.1NH.sub.2 (1) where R.sup.3, R.sup.2 and R.sup.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.

4. The process according to claim 1, wherein the dialkyl carbonate used is selected from dimethyl, diethyl, dipropyl and dibutyl carbonate.

5. The process according to claim 1, wherein, in step B) in the sequence of steps i) to iv) i) the catalyst is deactivated, ii) low boilers are removed by distillation, iii) solids and/or salt burdens are filtered or centrifuged off and iv) high boilers are removed via thin-film evaporation.

6. The process according to claim 5, wherein the residue from the thin-film evaporation is recycled into the urethane synthesis A) or into the filtration/centrifugation step B) iii).

7. 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.

8. The process according to claim 7, wherein the catalyst concentration is 0.5-100 ppm.

9. 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).

10. 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 s converted in the presence of an alcohol of the formula R.sup.2OH with R.sup.2=linear, branched or cyclic hydrocarbyl radical having 1-6 carbon atoms at 25-100 C. in the presence or absence of a catalyst.

11. The process according to claim 10, wherein no reaction with alcohol is conducted.

12. The process according to claim 11, wherein the distillate obtained is sent to step B) or C).

13. The process according to claim 1, wherein the separation in step D) is a rectification.

14. The process according to claim 11, wherein the isocyanate obtained by rectification is additionally purified and isolated by distillation.

15. The process according to claim 2, wherein the alkoxysilano(cyclo)alkylamine has the formula (1)
R.sup.3.sub.m(OR.sup.2).sub.3-mSiR.sup.1NH.sub.2 (1) where R.sup.3, R.sup.2 and R.sup.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.

16. The process according to claim 2, wherein the dialkyl carbonate used is selected from dimethyl, diethyl, dipropyl and dibutyl carbonate.

17. The process according to claim 2, wherein, in step B) in the sequence of steps i) to iv) i) the catalyst is deactivated, ii) low boilers are removed by distillation, iii) solids and/or salt burdens are filtered or centrifuged off and iv) high boilers are removed via thin-film evaporation.

18. 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.

19. The process according to claim 18, wherein the catalyst concentration is 0.5-100 ppm.

20. The process according to claim 2, 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).

Description

Example 1

Inventive Preparation of 3-(trimethoxysilyl)propyl isocyanateReurethanization of the Bottoms Discharge and Recycling into the Filtration

[0087] 11.50 kg of AMMO (aminopropyltrimethoxysilane) were reacted with 8.10 kg of DMC (dimethyl carbonate) in the presence of 0.12 kg of a 30% solution of sodium methoxide in methanol at 60 C. for 6 h, and then neutralized by addition of 0.08 kg of acetic acid. The reactor discharge was freed of the low boilers by thin-film evaporation at 140 C. and 250 mbar, the crude UPMS (methyl [3-(trimethoxysilyl)propyl]carbamate) was filtered through a cartridge filter at 50 C. and the filtrate stream was subjected to a further purification step by thin-film evaporation at 185 C. and 5 mbar. The TFE distillate (17.52 kg/h) was run continuously into the circulation of the cleavage column and rectification column, and the deblocking reaction was conducted at a temperature of 195 C. and a bottom pressure of 60 mbar in the presence of a steady-state concentration of tin dichloride of 50 ppm. The cleavage gases IPMS (3-(trimethoxysilyl)propyl isocyanate) and methanol were condensed out in two successive condensers that were operated at different temperature levels, it being possible to reuse the methanol obtained as the top product, after further distillation, as raw material, and the IPMS was withdrawn at the side draw with a purity of >98% in an amount of 11.04 kg/h, which corresponds to a continuous yield of 82%. To maintain the mass balance within the cleavage column and rectification column, and for avoidance of deposits and possibly blockage of the cleavage apparatus, and for regeneration of values, a substream was continuously discharged from the circuit, cooled down and combined with methanol, and the combined stream (8.0 kg/h) was converted in a tubular reactor at 65 C. until urethanization of all NCO groups was complete. The reurethanizate stream was recycled into the filtration stage.

Example 2

Inventive Preparation of 3-(trimethoxysilyl)propyl isocyanateThermal Aftertreatment and Separation of the Bottoms Discharge, Reurethanization and Recycling into the Urethane Preparation

[0088] 12.10 kg of AMMO (aminopropyltrimethoxysilane) were reacted with 7.60 kg of DMC (dimethyl carbonate) in the presence of 0.12 kg of a 30% solution of sodium methoxide in methanol at 60 C. for 6 h, and then neutralized by addition of 0.08 kg of acetic acid. The reactor discharge was freed of the low boilers by thin-film evaporation at 140 C. and 250 mbar, the crude UPMS (methyl [3-(trimethoxysilyl)propyl]carbamate) was filtered through a cartridge filter at 50 C. and the filtrate stream was subjected to a further purification step by thin-film evaporation at 185 C. and 5 mbar. The residue was recycled into the next urethane preparation. The TFE distillate (18.85 kg/h) was run continuously into the circulation of the cleavage column and rectification column, and the deblocking reaction was conducted at a temperature of 195 C. and a bottom pressure of 60 mbar in the presence of a steady-state concentration of tin dichloride of 30 ppm. The cleavage gases IPMS (3-(trimethoxysilyl)propyl isocyanate) and methanol were condensed out in two successive condensers that were operated at different temperature levels, it being possible to reuse the methanol obtained as the top product, after further distillation, as raw material, and the IPMS (3-(trimethoxysilyl)propyl isocyanate) was withdrawn at the side draw with a purity of >98% in an amount of 12.16 kg/h, which corresponds to a continuous yield of 86%. To maintain the mass balance within the cleavage column and rectification column, and for avoidance of deposits and possibly blockage of the cleavage apparatus, and for regeneration of values, a substream was continuously discharged from the circuit and run through a thin film evaporator at 215 C. and 5 mbar. The distillate stream was combined with methanol, and the combined stream (8.8 kg/h) was converted in a tubular reactor at 65 C. until urethanization of all NCO groups was complete. The reurethanizate stream was recycled into the urethane preparation.

Example 3

Inventive Preparation of 3-(trimethoxysilyl)propyl isocyanate (IPMS)Thermal Aftertreatment and Separation of the Bottoms Discharge and Recycling into the Urethane Cleavage

[0089] 14.29 kg of AMMO (aminopropyltrimethoxysilane) were reacted with 9.34 kg of DMC (dimethyl carbonate) in the presence of 0.17 kg of a 30% solution of sodium methoxide in methanol at 60 C. for 6 h, and then neutralized by addition of 0.09 kg of acetic acid. The reactor discharge was freed of the low boilers by thin-film evaporation at 140 C. and 250 mbar, the crude UPMS (methyl [3-(trimethoxysilyl)propyl]carbamate) was filtered through a cartridge filter at 50 C. and the filtrate stream (18.63 kg/h) was subjected to a further purification step by thin-film evaporation at 185 C. and 5 mbar. The residue was recycled into the next urethane preparation. The TFE distillate was run continuously into the circulation of the cleavage column and rectification column, and the deblocking reaction was conducted at a temperature of 195 C. and a bottom pressure of 60 mbar in the presence of a steady-state concentration of tin dichloride of 25 ppm. The cleavage gases IPMS (3-(trimethoxysilyl)propyl isocyanate) and methanol were condensed out in two successive condensers that were operated at different temperature levels, it being possible to reuse the methanol obtained as the top product, after further distillation, as raw material, and the IPMS (3-(trimethoxysilyl)propyl isocyanate) was withdrawn at the side draw with a purity of >98% in an amount of 14.89 kg/h, which corresponds to a continuous yield of 89%. To maintain the mass balance within the cleavage column and rectification column, and for avoidance of deposits and possibly blockage of the cleavage apparatus, and for regeneration of values, a substream was continuously discharged from the circuit, subjected to thermal aftertreatment at 220 C. with a residence time of 1 h, and then run through a thin film evaporator at 5 mbar. The distillate stream was recycled into the circuit.

Comparative Example 1

Preparation of 3-(trimethoxysilyl)propyl isocyanateNo Bottoms Discharge and Recycling into the Process (Noninventive)

[0090] 12.22 kg of AMMO (aminopropyltrimethoxysilane) were reacted with 7.91 kg of DMC (dimethyl carbonate) in the presence of 0.14 kg of a 30% solution of sodium methoxide in methanol at 60 C. for 6 h, and then neutralized by addition of 0.08 kg of acetic acid. The reactor discharge was freed of the low boilers by thin-film evaporation at 140 C. and 250 mbar, the crude UPMS (methyl [3-(trimethoxysilyl)propyl]carbamate) was filtered through a cartridge filter at 50 C. and the filtrate stream was subjected to a further purification step by thin-film evaporation at 185 C. and 5 mbar. The TFE distillate was run continuously into the circulation of the cleavage column and rectification column, and the deblocking reaction was conducted at a temperature of 195 C. and a bottom pressure of 60 mbar in the presence of a steady-state concentration of tin dichloride of 110 ppm. The cleavage gases IPMS (3-(trimethoxysilyl)propyl isocyanate) and methanol were condensed out in two successive condensers.

[0091] It was not possible to maintain a continuous mode of operation since it was found to be impossible to maintain the mass balance between the cleavage column and rectification column. It was not possible to balance the input (TFE distillate stream) and output (cleavage gas stream) over a prolonged period, and so, over the course of time, either too much material collected in the cleavage equipment and there was overflow or the discharge stream of IPMS (3-(trimethoxysilyl)propyl isocyanate) gradually came to a stop.

Comparative Example 2

Batchwise Preparation of 3-(trimethoxysilyl)propyl isocyanateBatchwise Deblocking (Noninventive)

[0092] 13.39 kg of AMMO (aminopropyltrimethoxysilane) were reacted with 8.69 kg of DMC (dimethyl carbonate) in the presence of 0.16 kg of a 30% solution of sodium methoxide in methanol at 60 C. for 6 h, and then neutralized by addition of 0.09 kg of acetic acid. The reactor discharge was freed of the low boilers by thin-film evaporation at 140 C. and 250 mbar, the crude UPMS (methyl [3-(trimethoxysilyl)propyl]carbamate) was filtered through a cartridge filter at 50 C. and the filtrate stream was subjected to a further purification step by thin-film evaporation at 185 C. and 5 mbar. 350 g of the TFE distillate were heated to a temperature of 195 C. in a 3 l round-bottom flask with distillation apparatus, stirrer and thermometer in the presence of 110 ppm of tin dichloride and at a pressure of 60 mbar. The cleavage gases formed were separated by distillation and condensed out. After 6.5 h, the experiment was stopped after no product stream was obtained any longer in the distillation. A total of 209.1 g of IPMS (3-(trimethoxysilyl)propyl isocyanate) were obtained with a purity of 97.4% (about 67% yield); 95.2 g of high boilers remained in the round-bottom flask.

Comparative Example 3

Preparation of 3-(trimethoxysilyl)propyl isocyanatewith Bottoms Discharge and without Recycling into the Process (Noninventive)

[0093] 12.90 kg of AMMO (aminopropyltrimethoxysilane) were reacted with 8.05 kg of DMC (dimethyl carbonate) in the presence of 0.15 kg of a 30% solution of sodium methoxide in methanol at 60 C. for 6 h, and then neutralized by addition of 0.08 kg of acetic acid. The reactor discharge was freed of the low boilers by thin-film evaporation at 140 C. and 250 mbar, the crude UPMS (methyl [3-(trimethoxysilyl)propyl]carbamate) was filtered through a cartridge filter at 50 C. and the filtrate stream was subjected to a further purification step by thin-film evaporation at 185 C. and 5 mbar. The TFE distillate (16.15 kg/h) was run continuously into the circulation of the cleavage column and rectification column, and the deblocking reaction was conducted at a temperature of 195 C. and a bottom pressure of 60 mbar in the presence of a steady-state concentration of tin dichloride of 110 ppm. The cleavage gases IPMS (3-(trimethoxysilyl)propyl isocyanate) and methanol were condensed out in two successive condensers that were operated at different temperature levels, it being possible to reuse the methanol obtained as the top product, after further distillation, as raw material, and the IPMS (3-(trimethoxysilyl)propyl isocyanate) was withdrawn at the side draw with a purity of >98% in an amount of 9.00 kg/h, which corresponds to a continuous yield of 61%. To maintain the mass balance within the cleavage column and rectification column, and for avoidance of deposits and possibly blockage of the cleavage apparatus, a substream was continuously discharged from the circuit.