Process for the preparation of 3,3,3-trifluoropropene

Abstract

The present invention provides a process for preparing 3,3,3-trifluoropropene (1243zf), the process comprising: (a) fluorinating CCl.sub.3CH.sub.2CH.sub.2Cl (250fb) to produce a reaction product comprising CF.sub.3CH.sub.2CH.sub.2Cl (253fb) in the liquid phase in a first reactor, using HF as the fluorinating agent; and (b) (i) dehydrohalogenating 253fb to produce 1243zf in the vapour phase in the present of a catalyst in a second reactor; or (b)(ii) dehydrohalogenating 253fb to produce 1243zf in a second reactor, wherein the reaction product comprising 253fb produced in step (a) has subjected to one or more purification steps before step (b). The present invention also provides an azeotropic or near-azeotropic composition comprising HF and 253fb.

Claims

1. A process for preparing 3,3,3-trifluoropropene (1243zf), the process comprising: (a) fluorinating CCl.sub.3CH.sub.2CH.sub.2Cl (250fb) to produce a reaction product comprising CF.sub.3CH.sub.2CH.sub.2Cl (253fb) in the liquid phase in a first reactor, conducted at a temperature of from 20° C. to 100° C., using HF as a fluorinating agent; and (b) dehydrohalogenating 253fb to produce 1243zf in the vapour phase, conducted at a temperature of from 250° C. to 350° C., in the presence of a catalyst in a second reactor; wherein the product stream exiting the second reactor is subjected to one or more separation and/or purification steps and any unreacted 253fb is recycled back into the second reactor.

2. The process according to claim 1, wherein the catalyst used in step (b) comprises activated carbon, alumina and/or chromia or zinc/chromia.

3. The process according to claim 2, wherein the catalyst used in step (b) comprises an additional metal or compound thereof.

4. The process according to claim 3, wherein the catalyst used in step (b) is Pd/carbon, Pt/carbon, Au/carbon, Pd/alumina, Ni/alumina, Pt/alumina, Cr/alumina or Zn/chromia.

5. The process according to claim 3, wherein the catalyst used in step (b) is pre-fluorinated.

6. The process according to claim 3, wherein the catalyst used in step (b) comprises activated carbon and the process of step (b) is conducted at a temperature of from about 250° C. to about 300° C.

7. The process according to claim 5, wherein the catalyst used in step (b) is a prefluorinated Zn/chromia catalyst.

8. The process according to claim 1, wherein in step (b) HF is co-fed with 253fb.

9. The process according to claim 1, wherein the reaction product comprising 253fb produced in step (a) is subjected to one or more purification steps before step (b).

10. The process according to claim 1, wherein the 1243zf product is stored for future use or is passed directly into a further reactor.

11. A process for preparing 3,3,3-trifluoropropene (1243zf), the process comprising: (a) fluorinating CCl.sub.3CH.sub.2CH.sub.2Cl (250fb) to produce a reaction product comprising CF.sub.3CH.sub.2CH.sub.2Cl (253fb) in the liquid phase, conducted at a temperature of from 20° C. to 100° C., using HF as a fluorinating agent; and (b) dehydrohalogenating 253fb to produce 1243zf in the vapour phase, conducted at a temperature of from 250° C. to 350° C., in the presence of a catalyst.

12. The process according to claim 11, wherein the catalyst used in step (b) comprises activated carbon, alumina and/or chromia or zinc/chromia.

13. The process according to claim 12, wherein the catalyst used in step (b) comprises an additional metal or compound thereof.

14. The process according to claim 13, wherein the catalyst used in step (b) is Pd/carbon, Pt/carbon, Au/carbon, Pd/alumina, Ni/alumina, Pt/alumina, Cr/alumina or Zn/chromia.

15. The process according to claim 13, wherein the catalyst used in step (b) is pre-fluorinated.

16. The process according to claim 11, wherein step (b) is conducted at a temperature of from about 250° C. to about 300° C.

17. The process according to claim 11, wherein the catalyst used in step (b) comprises activated carbon and the process of step (b) is conducted at a temperature from about 250° C. to about 300° C.

18. The process according to claim 15, wherein the catalyst used in step (b) is a pre-fluorinated Zn/chromia catalyst.

19. The process according to claim 11, wherein the process is a single-step process.

20. The process according to claim 11, wherein the fluorinating is performed in a single reactor.

21. The process according to claim 11, wherein the fluorinating is a single-step process.

22. The process according to claim 11, wherein in step (b) HF is co-fed with 253fb.

23. The process according to claim 11, wherein the reaction product comprising 253fb produced in step (a) is subjected to one or more purification steps before step (b).

24. The process according to claim 11, wherein the 1234zf product is stored for future use or is passed directly into a further reactor.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIGS. 1 to 3 show the results obtained when measuring the vapour pressure of varying compositions of HF and 253fb over a temperature range of −25° C. to +70° C. The invention will now be illustrated with the following non-limiting examples.

(2) The invention will now be illustrated by the following non-limiting Examples.

Example 1—Catalytic (Activated Carbon) Dehydrochlorination of 253fb

(3) The carbon-based catalysts in Table 1 were ground to 0.5-1.4 mm and 2 mL charged to an Inconel 625 reactor (0.5″ OD×32 cm) supported by Inconel mesh. The catalysts were pre-dried at 200° C. for at least 2 hours under a flow of N.sub.2 (60 ml/min) at atmospheric pressure then the reactor temperature was increased to 250° C. and the nitrogen reduced to 30 ml/min and diverted to the reactor exit. A flow of 253fb (3-chloro-1,1,1-trifluoropropane, 99.09%) was fed over the carbon catalysts by sparging liquid 253fb at 10° C. with 4-6 ml/min nitrogen, yielding 253fb vapour flows of 1-2.5 ml/min. After allowing the reaction to run for 30 min, reactor off-gases were sampled into deionised water and analysed by GC, to give the conversion of 253fb and selectivity to 1243zf results shown in Table 1. The experiment was also repeated at 300 and 350° C. for selected catalysts.

(4) TABLE-US-00001 TABLE 1 Results for 253fb dehydrochlorination to 1243zf with activated carbon catalysts 250° C. 300° C. 350° C. TR 253fb 1243zf 253fb 1243zf 253fb 1243zf Ref Conversion Selectivity Conversion Selectivity Conversion Selectivity Catalyst # % % % % % % Act. Carbon 2367 9.82 100.00 37.23 100.00 Act. Carbon 2091 17.12 100.00 64.24 100.00 Act. Carbon 2032 26.10 100.00 73.01 100.00 Act. Carbon 1968 55.37 100.00 96.87 100.00 Act. Carbon 2019 20.03 100.00 66.12 100.00 Act. Carbon 2366 64.60 100.00 93.25 100.00 96.99 99.55 1.5% 2630 14.06 100.00 17.87 97.79 36.62 33.77 Pd/Carbon 0.8% 2629 48.53 100.00 93.08 100.00 88.69 97.23 Pd/Carbon 0.3% 2634 47.09 100.00 94.60 99.40 Au/Carbon

Example 2—Catalytic Dehydrochlorination of 253fb Investigating the Effect of Pre-Fluorination, with/without HF Co-Feed on ZnO/Cr.SUB.2.O.SUB.3

(5) A ZnO/Cr.sub.2O.sub.3 catalyst was ground to 0.5-1.4 mm and 2 mL charged to an Inconel 625 reactor (0.5″ OD×32 cm) supported by Inconel mesh. The catalyst was pre-dried at 200° C. for at least 2 hours under a flow of N.sub.2 (60 ml/min) at atmospheric pressure. Three experiments carried out in duplicate were as follows:

(6) Without Pre-Fluorination:

(7) The nitrogen flow was reduced to 30 ml/min and diverted to the reactor exit and the reactor temperature increased to 250° C. A flow of 253fb (3-chloro-1,1,1-trifluoropropane, 99.09%) was fed over the catalyst by sparging liquid 253fb at 10° C. with 10-12 ml/min nitrogen, yielding 253fb vapour flows of 4-5 ml/min. After allowing the reaction to run for 30 min, reactor off-gases were sampled into deionised water and analysed by GC, to give the conversion of 253fb and selectivity to 1243zf results shown in Table 2. The experiment was also repeated at 300 and 350° C.

(8) Pre-Fluorinated:

(9) HF at 30 ml/min was passed over the catalyst along with 60 ml/min nitrogen at 300° C. for one hour. The nitrogen flow was then directed to the reactor exit leaving neat HF passing over the catalyst. The temperature was slowly ramped to 360° C. and held for 10 hours. After this time the temperature was reduced to 300° C. and the flow of HF stopped and replaced with 30 ml/min nitrogen, for 1 h. The flow of nitrogen was then diverted to the reactor exit then a flow of 253fb (3-chloro-1,1,1-trifluoropropane, 99.09%) was fed over the catalyst by sparging liquid 253fb at 10° C. with 10-12 ml/min nitrogen, yielding 253fb vapour flows of 4-5 ml/min. After allowing the reaction to run for 30 min, reactor off-gases were sampled into deionised water and analysed by GC, to give the conversion of 253fb and selectivity to 1243zf results shown in Table 2.

(10) Pre-Fluorinated and HF Co-Feed:

(11) Pre-fluorination as described above. After this time the temperature was reduced to 250° C. and the flow of HF maintained over the catalyst. A flow of 253fb (3-chloro-1,1,1-trifluoropropane, 99.09%) was fed over the catalyst by sparging liquid 253fb at 10° C. with 10-12 ml/min nitrogen, yielding 253fb vapour flows of 4-5 ml/min. After allowing the reaction to run for 30 min, reactor off-gases were sampled into deionised water and analysed by GC, to give the conversion of 253fb and selectivity to 1243zf results shown in Table 2. The experiment was also repeated at 300 and 350° C.

(12) TABLE-US-00002 TABLE 2 Results for 253fb dehydrochlorination to 1243zf with ZnO/Cr.sub.2O.sub.3 catalyst 250° C. 300° C. 350° C. HF 253fb 253fb 1243zf 253fb 1243zf 253fb 1243zf Pre- flow flow Conversion Selectivity Conversion Selectivity Conversion Selectivity fluorinated ml/min ml/min % % % % % % Yes 31 5.3 41.20 85.15 93.50 99.47 93.57 99.29 Yes 31 5.1 40.19 85.00 87.96 99.01 98.02 99.79 No 0 4.1 6.93 93.30 8.74 90.32 5.53 77.57 No 0 4.7 1.94 83.70 6.01 86.08 7.34 82.15 Yes 0 5.1 22.00 98.03 Yes 0 4.9 19.57 97.57

(13) Overall there was an improvement in the conversion and slightly higher selectivity to 1243zf when the catalyst was pre-fluorinated and 253fb co-fed with HF.

Example 3—Azeotrope Identification

(14) A binary azeotrope between HF and 253fb was identified by a study of the vapour-liquid equilibrium of binary mixtures over a temperature range of −25° C. to +70° C. using a constant volume apparatus.

(15) The experimental data were measured in a static constant volume apparatus consisting of a vessel of precisely known internal volume (32.57 ml) located in a temperature-controlled metal block. A magnetic stirring device was located inside the vessel. Refrigerated fluid was passed through the block to allow precise control of temperature inside the vessel. The cell was evacuated then known amounts of compositions of HF and 253fb were charged to the cell. The cell was then varied stepwise from about −25° C. to +70° C. At each step the cell temperatures and pressure were logged and recorded when stable conditions were reached.

(16) The compositions studied are given in Table 3 below. The phase behaviour of these compositions at three exemplary temperatures, being −25° C., +30° C. and +70° C. is illustrated in FIGS. 1 to 3. The graphs in FIGS. 1 to 3 show that a constant vapour pressure is reached at compositions wherein HF is present in an amount of from about 55 mol % to about 95 mol % and 253fb is present in an amount of from about 45 mol % to about 5 mol %, which is consistent with what would be expected of azeotropic compositions. This trend is evidenced across all temperature ranges tested.

(17) TABLE-US-00003 TABLE 3 Mole fraction Mole fraction % w/w R253fb HF HF 1.000 0.000 0.000 0.971 0.029 0.452 0.952 0.048 0.752 0.906 0.094 1.546 0.855 0.145 2.488 0.766 0.234 4.417 0.708 0.292 5.867 0.638 0.362 7.902 0.558 0.442 10.696 0.558 0.442 10.696 0.434 0.566 16.442 0.335 0.665 23.058 0.253 0.747 30.790 0.150 0.850 46.130 0.126 0.874 51.102 0.100 0.900 57.743 0.073 0.927 65.671 0.052 0.948 73.330 0.016 0.984 90.390 0.000 1.000 100.000

Example 4

(18) A feed composition of HF and 253fb was charged to a whitey bomb, agitated, and placed in a chilled bath at constant temperature. The system was left overnight to achieve thermal and phase equilibrium. Consecutive samples were withdrawn from the base of the whitey bomb, slowly, every half an hour over a total period of 4 hours so as not to disturb the phase equilibrium in the bomb, and analysed to determine HF concentration. The results shown in Table 4 demonstrate the separation of HF and 253fb into two liquid phases.

(19) TABLE-US-00004 Initial charge 99.7 g Feed composition 81.91 mol % HF Temp −25° C.

(20) TABLE-US-00005 TABLE 4 Sample Sample mass (g) Mol Frac HF 1 8.2 33.91* 2 7.2 16.64 3 25.9 17.53 4 8.2 15.06 5 12.3 96.11 6 8.5 97.53 7 7.8 97.47 8 10.4 97.01 9 Residual mass Not analysed *Note, the geometry of the offtake line at the base of the bomb means that the initial contents of the offtake line do not reach phase equilibrium with the bulk contents within the bomb. This results in an initial sample which contains high levels of HF.