Separation of Sulfur Hexafluoride from a Nitrogen/Sulfur Hexafluoride Mixture Using a Polymer Hollow Fiber Membrane

Abstract

Sulfur hexafluoride (SF6) has been evaluated by the Intergovernmental Panel on Climate Change (IPCC) as the substance with the highest global warming index. Because of its superior insulating and arc clearing capacities, it is commonly used as an insulator in electrical machines. SF6 waste products form in the process of storing, maintaining, and repairing the machines. SF6 emitted into the atmosphere remains for 3,200 years, causing global warming. Release into the mesosphere leads to photolysis and creation of highly toxic and corrosive by-products. A review of the literature related to the retrieval and separation of SF6 using a separating membrane indicates that research on the permeability of the separating membrane material is lacking. Additionally, research on the concentrations of the SF6 waste products and the separation/retrieval with operating conditions with optimal energy efficiency is only in the initial stages. Therefore, this research assessed the permeability of commercialized separation membranes polysulfone (PSf), polycarbonate (PC), and polyimide (PI) using the gases SF6 and N-2. Using an SF6/N-2 mixture with the same concentration as the SF6 waste products, we studied the separation and retrieval capacities of PSf, PC, and PI separation membranes under varying operating conditions. The permeability tests showed that the selective permeability of N-2/SF6 is highest for the PI membrane and lowest for the PC membrane. When the concentrations of SF6 retrieved from the mixture separation process were compared, the PC membrane was found to be the highest, with 95.6 % at 0.5 MPa. The retrieval percentage of SF6 was highest for PSf, with 97.8 % at an operating pressure of 0.3 MPa and a waste production of 150 cm(3)/min. The retrieval rates and retrieval failure rates have an inverse relationship. In total, 99 % of the supply of SF6 was identified via the retrieval rates and retrieval failure rates, so it could be confirmed that the separation of the SF6/N-2 mixture using a macromolecular hollow fiber separation membrane works properly.