Process for purifying (hydro)fluoropropenes contaminated with halogenated ethane

Abstract

A process for treating a composition comprising one or more desired (hydro)fluoroolefins and one or more undesired halogenated ethanes, halogenated methanes or mixtures thereof so as to reduce the concentration of at least one undesired halogenated ethane or halogenated methane, the process comprising contacting the composition with an adsorbent comprising pores having openings which have a size across their largest dimension of about 6 Å or less.

Claims

1. A process of purifying a tetrafluoropropene composition comprising: contacting a composition with an adsorbent, the composition comprising at least one tetrafluoropropene and an impurity comprising a halogenated ethane, the adsorbent comprising pores having openings which have a size across their largest dimension of about 6 Å or less, so as to remove at least a portion of the halogenated ethane from the composition.

2. The process according to claim 1 wherein the at least one tetrafluoropropene comprises at least 10 wt % of the composition to be treated.

3. The process according to claim 1 wherein the adsorbent comprises pores having openings which have a size across their largest dimension of from about 4 Å to about 6 Å.

4. The process according to claim 1 wherein the adsorbent is a molecular sieve.

5. The process according to claim 1 wherein the adsorbent comprises a zeolite.

6. The process according to claim 1 wherein the tetrafluoropropene is 2,3,3,3-tetrafluoropropene (1234yf).

7. The process according to claim 1 wherein the halogenated ethane is a fluorinated ethane.

8. The process according to claim 7 wherein the fluorinated ethane is tetrafluoroethane.

9. The process according to claim 8 wherein the tetrafluoroethane is 1,1,1,2-tetrafluoroethane (134a).

10. The process according to claim 1 wherein the contacting step is performed, at least in part, at a temperature of from about 0° C. to about 200° C.

11. The process according to claim 1 wherein the contacting step is conducted at a pressure of from about 0.1 MPa to the saturation pressure.

12. The process according to claim 11 wherein the adsorbent treatment step comprises an exposure step comprising exposing the adsorbent to one or more inert gases.

13. The process according to claim 1 further comprising an adsorbent treatment step prior to the contacting step.

14. The process according to claim 13 wherein the adsorbent treatment step comprises a heat treatment step comprising heating the adsorbent to a maximum temperature of at least 150° C.

15. The process according to claim 14 wherein the heat treatment step comprises heating the adsorbent to the maximum temperature at a rate of from 1° C./minute to 100° C./minute.

16. The process according to claim 14 wherein the heat treatment step comprises maintaining the adsorbent at or around the maximum temperature for a time of from 1 second to 1 hour.

17. The process according to claim 1 wherein the process removes at least 50% by weight of the halogenated ethane.

18. The process according to claim 17 wherein the process reduces the concentration of the halogenated ethane to levels at, around or below the limit of detection by gas chromatography.

19. The process according to claim 1 wherein the adsorbent is dried before use.

20. The process according to claim 1 further comprising a step of regenerating the adsorbent after it has been contacted with the composition.

21. The process according to claim 20 wherein the regenerating step comprises contacting the adsorbent with a heated stream of inert gas and/or heating the adsorbent whilst the or an inert gas is passed over it.

22. The process according to claim 20 wherein the regenerating step comprises subjecting the adsorbent to a change in pressure.

23. The process according to claim 1 further comprising one or more additional purifying steps, which may be conducted before and/or after the contacting step.

24. The process according to claim 1 which is carried out, at least in part, in the gas or liquid phase.

25. A process for treating a composition comprising one or more desired tetrafluoropropenes and one or more undesired halogenated ethanes, so as to reduce the concentration of at least one undesired halogenated ethane, the process comprising contacting the composition with an adsorbent comprising pores having openings which have a size across their largest dimension of about 6 Å or less, wherein the moisture content of the adsorbent is less than about 1.5% by weight.

26. A method for recovering a desired component of a spent refrigerant, the method comprising removing a spent refrigerant comprising a desired component and an undesired component from a refrigerant system and contacting the spent refrigerant with an adsorbent comprising pores having a size opening across their largest dimension of 6 Å or less to remove or reduce the concentration of one or more undesired components, the desired component comprising a tetrafluoropropene, the undesired component comprising a halogenated ethane.

27. The method according to claim 26 wherein the tetrafluoropropene comprises at least 10 wt % of the spent refrigerant.

28. A kit for recovering a desired component of a spent refrigerant, the kit comprising an apparatus comprising an adsorbent comprising pores having a size opening across their largest dimension of 6 Å or less and instructions for removing a spent refrigerant comprising a desired component and an undesired component from a refrigerant system and contacting the spent refrigerant with the apparatus to remove or reduce the concentration of one or more undesired components, the desired component comprising a tetrafluoropropene, the undesired component comprising a halogenated ethane.

Description

(1) The present invention is now illustrated, but not limited by, the following description and Examples, with reference to the following drawings:

(2) FIG. 1 shows a chart representing the 2 hour absorption capacity of a range of absorbent materials for each of the refrigerants R-134a, 1234yf and E-1234ze;

(3) FIG. 2 shows a chart representing the heat of absorption for a range of absorbent materials for each of the refrigerants R-134a, 1234yf and E-1234ze.

(4) As described above, the invention provides a method for the separation of one or more undesired halogenated ethanes and/or methanes from a composition comprising one or more desired (hydro)fluoroolefins as a major component. Such a method serves to reduce the concentration of at least one undesired halogenated ethane or halogenated methane through the retention by the absorbent of at least a portion of the halogenated ethanes and/or methanes. The process comprises contacting the composition with an adsorbent comprising pores having openings across their largest dimension of about 6 Å or less, preferably between 4 Å and 6 Å, (also referred to as ‘nominal pore diameter’).

(5) A particularly preferred variety of adsorbent is a zeolite molecular sieve material preferably having a pore size across its largest dimension of approximately 5 Å, however alternative molecular sieve materials having similar pore dimensions may also be effective.

(6) The use of such an adsorbent is unexpectedly selective in retaining, within the adsorbent, undesired halogenated ethanes and/or methanes from a composition comprising desired (hydro)fluoroolefins as a major component.

(7) A composition to be treated may be contacted with a granulated solid sorbent bed comprising the adsorbent. Such a contacting step may be conducted as part of a “once through” process, wherein the product composition is recovered after being contacted with the adsorbent.

(8) Alternatively, the composition to be treated may be contacted with a single granulated solid sorbent bed, comprising the adsorbent, multiple times as part of a cyclic process. In which case the sorbent may be regenerated through a change in temperature or pressure as described above, prior to the composition being re-contacted.

(9) Twin or multi sorbent bed schemes may also be adopted in order to work the process. In two or multi bed schemes, one or more temperature changes as described above may be employed in order to regenerate the sorbent after each time the composition has been contacted with the sorbent bed. Such processes are known also as “temperature-swing processes”. For example, in a two bed temperature swing process, the second bed becomes operational while the first is regenerated, and vice-versa. It will be appreciated that for the process to be continuous, the regeneration time will be equal to the adsorption time so that the composition feed stream can be switched between the beds.

(10) Alternatively, in a two or multi bed scheme, one or more pressure changes, as described above, may be employed to regenerate the sorbent after each contacting step, known also as “pressure-swing” processes. Similarly to temperature swing processes, the composition feed may be switched between beds. As pressure changes can typically be effected more quickly than temperature changes, cycle times can be significantly quicker than temperature swing processes.

(11) The process of the invention may be used in preparative chromatographic separation processes.

(12) The processes of invention may be used in numerous applications.

(13) The invention may be employed as part of the synthesis and/or purification of desired (hydro)fluoroolefins, in order to remove unwanted by-products or impurities, such as halogenated ethanes and/or halogenated methanes that could be present in the final product.

(14) Alternatively, the invention may be employed in order to recover and/or purify a refrigerant that has been used in a system to replace an undesired halogenated ethane or methane refrigerant.

(15) Where the invention is used to recover and/or purify a refrigerant as previously discussed, the invention may be used in situ in the refrigeration apparatus, e.g. a mobile air-conditioning unit. Alternatively, the invention may be operated in a separate apparatus in which the composition to be treated is introduced to the apparatus.

(16) The invention may also form part of a kit for recovering a desired component of a spent refrigerant in which the kit comprises an apparatus comprising an adsorbent comprising pores having a size opening across their largest dimension of 6 Å or less, and instructions for removing the refrigerant from the refrigerant system and contacting the refrigerant with the apparatus to remove or reduce the concentration of one or more undesired components.

(17) In a further aspect, the invention provides a heat transfer fluid comprising at least one desired (hydro)fluoroolefin as described above and being substantially free of any undesired halogenated methanes or ethanes, the at least one (hydro)fluoroolefin having been purified by a method as described above.

(18) In another aspect, the invention provides a heat transfer device comprising a heat transfer fluid comprising one or more desired (hydro)fluoroolefins and an adsorbent comprising pores having openings which have a size across their largest dimension of about 6 Å or less. Preferably, the heat transfer device is a refrigeration system.

EXAMPLES

(19) In the following Examples, industrial grade R-1234yf and R-134a was obtained from Apollo Scientific limited and Mexichem. The adsorbents were obtained from Aldrich and Chemviron.

Examples 1 to 10

(20) The uptake of gas phase adsorbates by adsorbents in real time was measured by TGA analyser. The following adsorbents were tested: Molecular sieve 3A—pores having openings which have a size across their largest dimension of about 3 Å; Molecular sieve 4A—pores having openings which have a size across their largest dimension of about 4 Å; Molecular sieve 5A—pores having openings which have a size across their largest dimension of about 5 Å; Molecular sieve 13X—pores having openings which have a size across their largest dimension of about 10 Å;
and Chemviron 207ea activated charcoal.

(21) A small sample (approximately 50 mg) of each adsorbent was accurately weighed into a 100 μL aluminium crucible before being loaded into the TGA furnace.

(22) The adsorbent was first pre-treated by being equilibrated at 30° C. under nitrogen (75 mL/min) for 5 minutes, before being heated to 450° C. at 30° C./minute under flowing nitrogen (75 mL/min). The sample was held at 450° C. for 5 minutes, before being cooled to 40° C. at a rate of 30° C./minute, and being equilibrated at 40° C. for 5 minutes, all under a flow of nitrogen (75 mL/min).

(23) The adsorbents were then exposed to 3.3% v/v refrigerant (R-1234yf or R-134a) in nitrogen (75 mL/min), at 40° C. for 120 minutes.

(24) The results are shown in Table 1, with FIGS. 1 and 2 illustrating the capacity of the adsorbents and the heat of adsorption in each case.

(25) As can be seen from the Table and Figures, adsorbents comprising pores having openings which have a size across their largest dimension of below about 6 Å, particularly between 4 Å and 6 Å, show surprising selectivity for the halogenated ethane over the (hydro)fluoroolefin. This indicates the proficiency of such adsorbents for separating halogenated ethanes from (hydro)fluoroolefins.

(26) TABLE-US-00001 TABLE 1 Reference Wt Conc Drying wt loss Dry wt Wt gain Capacity Capacity Exotherm ΔH.sub.(ads) Example Adsorbent Adsorbate (mg) (v/v) (mg) (mg) (mg) (% wt) (mol/Kg) Equilibrium (mj) (kj/mol) 1 3A 134a 58.6 3.3 9.1937 49.4063 1.6507 3.34 0.33 No 137.65 8.5 2 4A 134a 55.8 3.3 5.3326 50.4674 2.2154 4.39 0.43 No 239.68 11 3 5A 134a 54.2 3.3 8.1745 46.0255 5.1451 11.18 1.1 No 330.82 6.6 4 13X 134a 49.7 3.3 12.2144 37.4856 12.8923 34.39 3.37 Yes 3447.79 27.3 5 207ea 134a 34.2 3.3 0.9434 33.2566 2.5564 7.69 0.75 Yes 339.64 13.6 6 3A 1234yf 56.3 3.3 9.8521 46.4479 1.9397 4.18 0.37 No 62.18 3.3 7 4A 1234yf 53.3 3.3 10.873 42.427 2.1945 5.17 0.45 No 72.99 3.4 8 5A 1234yf 59.7 3.3 11.0719 48.6281 2.3742 4.88 0.43 No 88.19 3.8 9 13X 1234yf 47.1 3.3 11.726 35.374 10.4077 29.42 2.58 Yes 1821.33 17.8 10 207ea 1234yf 31.8 3.3 0.9976 30.8024 4.6035 14.95 1.31 Yes 699.24 15.5

(27) Preferences and options for a given aspect, feature or parameter of the invention should, unless the context indicates otherwise, be regarded as having been disclosed in combination with any and all preferences and options for all other aspects, features and parameters of the invention.

(28) The listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.