PROCESS TO CONTINUOUSLY PREPARE A CYCLIC CARBONATE

Abstract

The invention is directed to a process to continuously prepare a cyclic carbonate product by reacting an epoxide compound with carbon dioxide in the presence of a supported dimeric aluminium salen complex. The process is performed in a reactor comprising a slurry of the supported dimeric aluminium salen complex and liquid cyclic carbonate product. The produced cyclic carbonate is discharged from the reactor while the supported dimeric aluminium salen complex remains in the reactor. The liquid carbonate product is purified by means of distillation. Between the reactor and the distillation one or more buffer vessels are present having a volume of between 5 and 50 m.sup.3 per kmol of dimeric aluminium salen complex as present in the reactor.

Claims

1. A process to continuously prepare a cyclic carbonate product by reacting an epoxide compound with carbon dioxide in the presence of a supported dimeric aluminium salen complex which catalyst is activated by a halide compound, wherein the process is performed in a reactor comprising a slurry of the supported dimeric aluminium salen complex and the cyclic carbonate product as present as a liquid and wherein to the reactor carbon dioxide and the epoxide compound is continuously supplied and a liquid cyclic carbonate product stream comprising part of the halide compound and dissolved epoxide compound is discharged while substantially all of the supported dimeric aluminium salen complex remains in the reactor, wherein the cyclic carbonate product as present in the liquid cyclic carbonate product stream is separated from the halide compound in a distillation step wherein a purified cyclic carbonate product is obtained as a bottom product of the distillation step and wherein between the reactor and the distillation step the liquid cyclic carbonate product stream passes one or more buffer vessels, wherein the total volume of the one or more buffer vessels expressed in m.sup.3 relative to the amount of dimeric aluminium salen complex as present in the reactor and expressed in kmol is between 5 and 50 m.sup.3/kmol.

2. The process according to claim 1, wherein the supported dimeric aluminium salen complex is represented by the following formula: ##STR00004## wherein S represents a solid support connected to the nitrogen atom via an alkylene group, wherein the supported dimeric aluminium salen complex is activated by a halide compound and wherein X.sup.1 is tertiary butyl and X.sup.2 is hydrogen and wherein Et is an alkyl group having 1 to 10 carbon atoms.

3. The process according to claim 2, wherein the support S is composed of particles having an average diameter of between 10 and 2000 μm.

4. The process according to claim 3, wherein the support S is a particle chosen from the group consisting of silica, alumina, titania, siliceous MCM-41 or siliceous MCM-48.

5. The process according to claim 1, wherein the halide compound is benzyl halide.

6. The process according to claim 5, wherein the benzyl halide is benzyl bromide.

7. The process according to claim 1, wherein the epoxide compound has 2 to 8 carbon atoms.

8. The process according to claim 7, wherein the epoxide compound is ethylene oxide, propylene oxide, butylene oxide, pentene oxide, glycidol or styrene oxide.

9. The process according to claim 1, wherein the temperature in the reactor is between 20 and 150° C. and the absolute pressure is between 0.1 and 0.5 MPa and wherein temperature is below the boiling temperature of the cyclic carbonate product at the chosen pressure.

10. The process according to claim 1, wherein the dissolved epoxide as present in the liquid cyclic carbonate product stream is stripped out by contacting the liquid cyclic carbonate product stream with carbon dioxide resulting in a cleaned product stream and a loaded carbon dioxide stream containing epoxide compound and wherein the loaded carbon dioxide stream is supplied to the reactor.

11. The process according to claim 1, wherein to the reactor halide compound is added in an amount sufficient to decrease deactivation of the supported dimeric aluminium salen complex.

12. The process according to claim 1, wherein a further reactor as a second reactor is positioned in series with the reactor which becomes a first reactor, wherein the second reactor comprises a slurry of the supported dimeric aluminium salen complex and the cyclic carbonate product as present as a liquid, and wherein a second liquid cyclic carbonate product stream comprising liquid cyclic carbonate product, part of the halide compound and dissolved epoxide compound is discharged while substantially all of the supported dimeric aluminium salen complex remains in the second reactor, wherein from the first reactor unreacted carbon dioxide and epoxide is discharged as a first gaseous effluent, which gaseous effluent is continuously supplied to the second reactor, and wherein the cyclic carbonate product as present in the second liquid cyclic carbonate product stream is separated from the halide compound in the distillation step and wherein between the second reactor and the distillation step the second liquid cyclic carbonate product stream passes one or more buffer vessels separately or in admixture with the first liquid cyclic carbonate product stream, wherein the total volume of the one or more buffer vessels expressed in m.sup.3 relative to the amount of dimeric aluminium salen complex as present in the first and second reactor and expressed in kmol is between 5 and 50 m.sup.3/kmol.

13. The process according to claim 12, wherein in a cycle step of the process a deactivated supported dimeric aluminium salen complex as present in a third reactor as a slurry of the supported dimeric aluminium salen complex and the cyclic carbonate product as present as a liquid is activated by adding halide compound and wherein in a next cycle step of the process the third reactor becomes the second reactor, the second reactor becomes the first reactor and the first reactor becomes the third reactor.

14. The process according to claim 13, wherein the time period of one cycle step of the process is between 1-30 days.

15. The process according to claim 11, wherein the added halide compound is obtained in the distillation step.

16. The process according to claim 12, wherein from the second reactor unreacted carbon dioxide and epoxide is discharged as a second gaseous effluent and wherein part of the second gaseous effluent is recycled to the first reactor and part of the second gaseous effluent is purged from the process.

Description

EXAMPLE

[0039] Reference is made to the process shown in FIG. 1. The concentration of benzyl bromide in stream (13) of FIG. 1 is calculated for a three reactor configuration as shown wherein the production of propylene carbonate is kept at a constant value. The total amount of dimeric aluminium salen complex as present in the operating reactors (A) and (B) is 0.22 kmol. During a step between 175 and 213 kg/hr of carbon dioxide is fed to first reactor (A) and between 154 and 187 kg/hr of propylene oxide is fed to first reactor (A). These values change due to the deactivation of the catalyst in reactors (A) and (B) and because the production of propylene carbonate is kept at the same level.

[0040] In a first simulation of the process no buffer vessel (F) is present. In a second simulation of the process a buffer vessel (F) is present having a volume of 2 m.sup.3. In a third simulation of the process a buffer vessel (F) is present having a volume of 5 m.sup.3. In a fourth simulation of the process a buffer vessel (F) is present having a volume of 10 m.sup.3. The effect of the presence of a buffer vessel (F) and its size is illustrated in FIG. 2. It is shown that by having a buffer vessel (F) the maximum and also minimum benzyl bromide contents in this stream (13) will be less extreme making it easier to perform the downstream distillation (H).