PROCESS TO PREPARE A CYCLIC CARBONATE

Abstract

The invention is directed to a process to continuously react a gaseous mixture of an epoxide compound and carbon dioxide in the presence of a heterogeneous catalyst at a pressure of between 0.1 and 0.4 MPa in one or more reactors to a liquid cyclic carbonate product and a gaseous effluent stream comprising unreacted epoxide compound and carbon dioxide. Part of the gaseous effluent is purged from the process and another part of the gaseous effluent is fed to an ejector where the gaseous effluent mixes with gaseous mixture of epoxide compound and carbon dioxide having a pressure which is at least more than 0.3 MPa higher than the pressure of the gaseous effluent. The obtained ejector effluent is fed to the one or more reactors.

Claims

1. A process to continuously react a gaseous mixture of an epoxide compound and carbon dioxide in the presence of a heterogeneous catalyst at a pressure of between 0.1 and 0.4 MPa in one or more reactors to a liquid cyclic carbonate product and a gaseous effluent stream comprising unreacted epoxide compound and carbon dioxide; and wherein part of the gaseous effluent is purged from the process and another part of the gaseous effluent is fed to an ejector where the gaseous effluent mixes with a gaseous mixture of epoxide compound and carbon dioxide having a pressure which is at least more than 0.3 MPa higher than the pressure of the gaseous effluent to obtain an ejector effluent which ejector effluent is fed to the one or more reactors.

2. The process according to claim 1, wherein the gaseous effluent is increased in pressure by means of a blower before mixing the gaseous effluent in the injector.

3. The process according to claim 1, wherein the gaseous mixture of epoxide compound and carbon dioxide as supplied to the ejector is obtained by mixing gaseous epoxide obtained by evaporating liquid epoxide and gaseous carbon dioxide obtained by evaporating liquid carbon dioxide having a pressure of between 1.4 and 4 MPa.

4. The process according to claim 3, wherein a liquid cyclic carbonate product is discharged from the one or more reactors and wherein any epoxide compound present in the discharged liquid cyclic carbonate product is stripped out by contacting the liquid cyclic carbonate product with the gaseous carbon dioxide wherein a cleaned product stream is obtained.

5. The process according to claim 4, wherein the pressure of the gaseous carbon dioxide is between 0.5 and 0.8 MPa.

6. The process according to claim 1, wherein the one or more reactors are two or more reactors in series comprising a most upstream reactor and a most downstream reactor and optional intermediate reactors, wherein to the most upstream reactor the ejector effluent is fed, wherein a liquid cyclic carbonate product is discharged from every reactor and wherein an intermediate gaseous effluent comprising unreacted epoxide compound and carbon dioxide is routed from an upstream reactor to the next downstream reactor in the series of reactors and wherein from the most downstream reactor of the series the gaseous effluent stream comprising unreacted epoxide compound and carbon dioxide is discharged.

7. The process according to claim 6, wherein the catalyst of the most upstream reactor is regenerated by taking this reactor off line such the second reactor in the series becomes the most upstream reactor of the series of reactors and wherein a new reactor comprising regenerated catalyst is connected to the series of reactors as the most downstream reactor.

8. The process according to claim 6, wherein the heterogenous catalyst is present in the two or more reactors in series as a slurry and wherein the temperature in the two or more reactors is between 20 and 150° C. and below the boiling temperature of the cyclic carbonate product at the chosen pressure.

9. The process according to claim 1, wherein the heterogeneous catalyst comprises an organic compound containing one or more nucleophilic groups.

10. The process according to claim 9, wherein the nucleophilic group is a quaternary nitrogen halide.

11. The process according to claim 10, wherein the heterogeneous catalyst is a supported dimeric aluminium salen complex and the activating compound is a halide compound.

12. The process according to claim 11, wherein the supported dimeric aluminium salen complex is represented by the following formula: ##STR00003## 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.

13. The process according to claim 12, wherein the support S is composed of particles having an average diameter of between 10 and 2000 μm.

14. The process according to claim 13, wherein the support S is a particle chosen from the group consisting of silica, alumina, titania, siliceous MCM-41 or siliceous MCM-48.

15. The process according to claim 11, wherein the halide compound is benzyl halide.

16. The process according to claim 15, wherein the benzyl halide is benzyl bromide.

17. The process according to claim 1, wherein the epoxide compound is ethylene oxide, propylene oxide, butylene oxide or pentene oxide.

Description

[0028] The invention shall be illustrated making use of FIGS. 1 and 2.

[0029] FIG. 1 shows a possible line-up for a process not according to the invention to prepare a cyclic carbonate from an epoxide compound and carbon dioxide wherein use is made of a compressor (2) to increase the pressure to the pressure in reactor (10) of a gaseous epoxide compound (1). The epoxide with the increased pressure (8) is mixed with carbon dioxide (5) having about the same pressure. The carbon dioxide (5) contains some epoxide compound which is obtained in stripper (4) by contacting a liquid cyclic carbonate product (6) with gaseous carbon dioxide (3) and wherein a cleaned cyclic carbonate (7) is obtained. The combined epoxide compound and carbon dioxide gaseous mixture (9) is fed to an upstream reactor (10) containing a slurry of a heterogenous catalyst which is activated by a halide compound. From this upstream reactor vessel (10) a first cyclic carbonate product (12) is discharged and an intermediate gaseous effluent (11). The intermediate gaseous effluent (11) is fed to a downstream reactor (13) containing a slurry of the heterogenous catalyst. This reactor (13) is operated at a lower pressure than reactor (10). From this downstream reactor vessel (13) a second cyclic carbonate product (14) is discharged and a gaseous effluent (15). Part of the gaseous effluent (15) is purged as purge (16) and the remaining part of the gaseous effluent (15) is recycled to be combined with the gaseous epoxide compound (1) upstream the compressor (2). The first (12) and second (14) cyclic carbonate streams are collected in a buffer vessel (18). From this vessel a combined liquid cyclic carbonate product (6) is fed to stripper (4). Also shown is a third reactor (19) containing a slurry of the heterogenous catalyst which is regenerated in an off line mode by addition of halide compound (20).

[0030] FIG. 2 shows an embodiment according to the invention which does not make use of a large compressor (2) as in FIG. 1. A liquid propylene oxide stored at 16° C. and at 0.2 MPa is increased in pressure by pump (21a) to be mixed with a return flow (26a) of liquid propylene oxide having a temperature of 94° C. and a pressure of 1.3 MPa. The resulting mixture is increased in temperature in heat exchanger (22) to 130 C and reduced in pressure and temperature in throttle valve (23) to a gas (27) and liquid (25) having a pressure of 0.6 MPa and temperature of 95° C. The liquid (25) is recycled via pump (26) to become pressurised return flow (26a).

[0031] Liquid carbon dioxide (28) stored at a pressure of 1.9 MPa is regassed in vaporiser (29) and increased in temperature in heat exchanger (30) to a carbon dioxide gas (31) having a temperature of 100° C. and a pressure of 0.6 MPa. In stripper (32) a cleaned propylene carbonate (34) is obtained by contacting a liquid propylene carbonate product (33) with the gaseous carbon dioxide (31). The carbon dioxide (35) as discharged from the stripper (32) contains some reclaimed propylene oxide. This carbon dioxide (35) is combined with the gaseous propylene oxide (27) obtained in the gas liquid separator (24) and the resultant mixture is fed to ejector (36) as the high pressure feed of the ejector having a pressure of 0.6 MPa. To the ejector (36) also a pressurised gaseous effluent (37) having a pressure of 0.23 MPa is fed resulting in an ejector effluent (38) having a pressure of 0.26 MPa. The ejector effluent (38) is fed to the upstream reactor (39) containing a slurry of a heterogenous catalyst which is activated by a halide compound. From this upstream reactor vessel (39) a first propylene carbonate product (40) is discharged and an intermediate gaseous effluent (41). The intermediate gaseous effluent (41) is fed to a downstream reactor (42) containing a slurry of the heterogenous catalyst. This reactor (42) is operated at 0.17 MPa. From this downstream reactor vessel (42) a second propylene carbonate product (43) is discharged and a gaseous effluent (44). Part of the gaseous effluent (44) is purged as purge (45) and the remaining part of the gaseous effluent (46) is increased in pressure in blower (47) to 0.23 MPa to become pressurised gaseous effluent (37). Blower (47) may be considered to be a compressor and will be much smaller than compressor (2) of FIG. 1.

[0032] The first (40) and second (43) propylene carbonate streams are collected in a buffer vessel (48). From this vessel a combined liquid propylene carbonate product (33) is fed to stripper (4). Also shown is a third reactor (50) containing a slurry of the heterogenous catalyst which is regenerated in an off line mode by addition of halide compound (51).

[0033] FIG. 3 shows the same embodiment according to the invention as in FIG. 2 except in that the blower is now present downstream of ejector (36). In blower (52) ejector effluent (38) is further increased in pressure before being fed as stream (53) to the upstream reactor (39).

Comparative Example A

[0034] A heat and mass balance is calculated for the process of FIG. 1. The gaseous epoxide is fed at 4.5 kg/s (1 in FIG. 1), the fresh carbon dioxide is fed at 3.5 kg/s (5 in FIG. 1) and the recycle flow is set at 2 kg/s (17 in FIG. 1). The gaseous epoxide and the recycle flow and their resulting mixture upflow compressor (2) has a pressure of 0.7 barg. The energy input for heating feedstock A from 16° C. to 55° C. is calculated. No energy input for CO2 feedstock pressurization (stored at 10+ barg) is taken into account. The required compression duty of compressor (2) of FIG. 1 for compressing the mixture of gaseous epoxide and the recycle from 0.7 barg to the specified reactor inlet pressure 2.1 barg is calculated. For calculation of compression duty, the polytropic compression energy is calculated using a compression efficiency of 65%. The calculated energy consumptions are presented in Table 1.

Example 1 According to Invention

[0035] A heat and mass balance is calculated for the process of FIG. 3. The gaseous epoxide is fed at 4.5 kg/s (27 in FIG. 3), the fresh carbon dioxide is fed at 3.5 kg/s (35 in FIG. 3) and the recycle flow is set at 2 kg/s (46 in FIG. 3). In the energy calculations the energy input for heating the epoxide feedstock from 16° C. to 110° C. (at 100° C., feedstock A vapor pressure is 5 barg) and an additional superheating to 110° C. to prevent unwanted condensation in downstream piping is taken into account. No energy input for CO2 feedstock pressurization (will be supplied and stored at 10+ barg) is taken into account. In static ejector (36 in FIG. 3) stream (46) is pressurized to a resulting discharge pressure. The discharge pressure is calculated based on the pre-defined ratio between flows (27), (35) and (46) and using the figures provided by the supplier of static ejector equipment. The remaining required compression duty for a compressor/blower (52) between elector (36) and upstream reactor (39) is calculated to achieve the same pressure as in the Comparative Example. For calculation of compression duty for (52), the polytropic compression energy is calculated using a compression efficiency of 65%.

[0036] Both energy balances are calculated and compared in Table 1.

TABLE-US-00001 TABLE 1 Example 1 Comparative According to Energy consumption Example A invention Heating liquid Feedstock A to boiling 346.8 904.8 point [kW] Evaporation duty at boiling point [kW] 2103.6 1820.4 Heating gas to discharge temperature [kW] 29.2 68.5 Total heating duty for evaporator unit [kW] 2479.6 2793.7 Possible heat integration [kW] −230.3 −662.6 Gas compressor duty [kW] 491.0 197.7 Discharge heater to reactor inlet 73.1 386.0 temperature [kW] Total energy duty [kW] 2813.4 2714.8 Net energy gain [kW] 0 98.7 Thermal energy duty [kW] 2322.5 2517.1 Electrical energy duty [kW] 491.0 197.7

[0037] The presented energy consumptions of Table 1 show that the overall, the energy profit when using the static ejector to boost the recycle flow is equal to 3,7% in this calculation example. Also, the CAPEX costs will be reduced due to the downsizing of the required gas compressor, which is replaced by a relatively cheap static component such as the ejector. And moreover, when applying further heat integration to the total plant, which is overall requiring net cooling duty (exothermic process), the thermal energy duty can be further reduced. In which case the net energy benefit, when using the static ejector, further increases, because the amount of electrical energy duty (which cannot be replaced) is larger in the conventional process.

[0038] Applicants found that the process of FIG. 2 consumes less energy. The loss in carbon dioxide caused by operating the stripper at a higher pressure in the process of FIG. 3 has been found to be low and fully compensated by the advantage of not having to use the complex compressor and by the lower energy requirement.