TH47159A - Separation of gases containing SF6. - Google Patents

Abstract

DC 60 (14/09/42) Gas mixtures of SF6 and N2, which are used, for example, as insulating filler gases for underground cables, for insulating gas window panes, or as filler gases for tires, and SF6-air mixtures used as shielding gases when casting magnesium, can be broken down if these mixtures are exposed to hydrophobic zeolites with some pores as the selective adsorbent for sulfur hexafluoride. For relatively high SF6 concentrations, the mixtures should be subjected to membrane separation first, and the permeate should be exposed to the adsorbent. The invention also concerns a complete instrument for carrying out the process. A process for separating SF6 from waste gases may also be used. Gas mixtures of SF6 and N2, which are used, for example, as insulating filler gases for underground cables, for insulating gas window panes, or as filler gases for tires, and SF6-air mixtures used as shielding gases when casting magnesium, can be broken down if these mixtures are exposed to hydrophobic zeolites with some pores as the selective adsorbent for sulfur hexafluoride. These mixtures are brought into contact with hydrophobic zeolites of a certain pore size, which are the selective adsorbents for sulfur hexafluoride. For relatively high SF6 concentrations, the mixtures should be subjected to membrane separation first, and then the permeate should be brought into contact with the adsorbent. The invention also concerns a complete instrument for carrying out the process. This process may also be used for separating SF6 from waste gas.

Claims (15)

1. A process for separating SF6/N2 mixtures or SF6-air mixtures, in which the mixture is subjected to at least one adsorption period with a hydrophobic zeolite with a SiO2/Al2O2 ratio of at least 80 and a pore diameter of 4 to 7 angstroms (0.4 to 0.7 nm) to adsorb SF6 and to recover the N2 or air from which the SF6 has been lost as appropriate. 2. The process described in claim 1, which is characterized by the use of hydrophobic zeolites with a pore diameter of 5 to 6.5 angstroms (0.5 to 0.65 nanometers). 3. The process specified in claim 1, which is characterized by the use of finely ground hydrophobic zeolites. 4. The process described in claim 1 is characterized by adsorption being performed at a maximum pressure of 5 atmospheres (absolute). 5. The procedure under claim 1, which is characterized by the use of a process for separating SF6 from gases containing SF6. 6. The process under claim 1, which is characterized by the use of exhaust air containing SF6 or exhaust gases, industrial exhaust gases, magnesium, insulating gases from window panes, or filler gases from tires. 7. The procedure under claim 1, characterized by the separation of the membrane separation mixture in at least one phase to obtain a retainate with increasing SF6 content and a permeate with decreasing SF6 content, and the subsequent permeate for further separation being subjected to at least one adsorption phase contact with a hydrophobic zeolite with a SiO2/Al2O3 ratio of at least 80 and a pore diameter of 4 to 7 angstroms (0.4 to 0.7 nm) for optimal SF6 adsorption. 8. A process pursuant to claim 1 or 7, characterized by an starting point of an SF6/N2 mixture with an SF6 content of 5 to 30% by volume, or an SF6/air mixture of 0.5 to 2%. 9. A procedure pursuant to claim 7 or 8, which is characterized by the provision of two or more membrane separation and two or more adsorption stages. 10. The procedure described in claim 9 is characterized by the provision of a two-stage membrane separation. The permeate of the first-stage membrane separation is fed to the second-stage membrane separation to obtain a mixture with an increased amount of SF6 retained from the second-stage separation. The permeate of the second-stage membrane separation is then returned to the first-stage membrane separation with an increased amount of N2 or air, and the permeate of the first-stage membrane separation with high N2 or air content is fed to one, two, or more absorbers to obtain N2 or air with significantly lost SF6. 11. The process pursuant to claim 10, which is characterized by the provision of a two-stage absorber to obtain N2 or air with less than 10 parts per million of SF6 at ambient pressure. 12. A complete apparatus for separating SF6/N2 mixtures, comprising a 1, 2, 3 or more stage membrane with N2 permeability and a 1, 2 or more stage absorber with a zeolite bed containing a SiO2Al2O2 ratio of at least 80 and a pore diameter of 4 to 7 Angstroms (10.4 to 0.7 nanometers). 13. The process under claim 12, involving two-stage membrane separation and two-stage absorbers, includes a pipe for feeding the gas mixture to be separated to the first-stage membrane separation; a connecting pipe for retaining the retaining material to the second-stage membrane separation; a connecting pipe between the first and second-stage membrane separations for transferring the permeate of the second-stage membrane separation to the first-stage membrane separation; a pipe for removing retaining material from the second-stage membrane separation containing high levels of SF6; a pipe for feeding the permeate of the first-stage membrane separation to the first-stage absorber; a pipe for feeding the gas exiting the first-stage absorber to the second-stage absorber; and a pipe for removing near-SF6-free nitrogen gas from the second-stage absorber. 14. The procedure under claim 13, which includes a third-stage membrane separation where a connecting tube for the permeate of the third-stage membrane separation is transferred to the absorber, a connecting tube for the transfer of the third-stage retainate to the first-stage membrane separation, a connecting tube for the transfer of the first-stage membrane separation permeate to the third-stage membrane separation, and a connecting tube for the transfer of the second-stage membrane separation permeate to the first-stage membrane separation. 15. Any of the processes under claims 12 through 14 in a movable form, for example, built on the board of a vehicle.