Highly gas permeable, ultrathin Teflon AF2400/Γ-alumina composite hollow fiber membranes for dissolved gas analysis

Dissolved gas analysis (DGA) is a useful approach to monitor the electrical faults of transformers. For extraction of dissolved gases from transformer oil in the DGA process, membrane-based separation represents an appealing technology option since the use of an oil-resistant, stable and highly gas permeable dense membrane can greatly enhance the efficiency by shortening the extraction time. However, most membranes reported in the literature have a membrane thickness in the micrometer range, making these membrane devices not sufficiently effective in practical separation of dissolved gasses from transformer oil. To reduce the thickness of membranes, Teflon AF2400 composite membranes synthesized using three different types of alumina (Al₂O₃) supports were investigated, including macroporous α-Al₂O₃ disk support, macroporous α-Al₂O₃ hollow fiber support, and mesoporous γ-Al₂O₃/α-Al₂O₃ hollow fiber support. The result shows that the γ-Al₂O₃/α-Al₂O₃ supports with a mesoporous top-coating γ-Al₂O₃ layer prepared by the sol-gel method could provide a high-quality surface for synthesizing an ultrathin and defect-free Teflon AF2400 layer. For the ultrathin Teflon AF2400/γ-Al₂O₃ composite hollow fiber membranes prepared by coating with a 0.5 wt% Teflon AF2400 solution, the thickness of the Teflon AF2400 layer is about 270 nm, and the permeances of H₂, CH₄, CO₂ and C₂H₆ at room temperature can reach to 14,069, 2847, 11,901 and 2030 GPU, respectively, which are about 8 times higher than that of the α-Al₂O₃ disk or hollow fiber supported membranes. This result demonstrates the promise of the ultrathin Teflon AF2400/γ-Al₂O₃ composite hollow fiber membranes for extraction of dissolved gases from the transformer oil for DGA.