Gas Transport Properties of Teflon AF2400/Ceramic Composite Hollow Fiber Membranes in Dissolved-Gas-in-Oil Extraction

Membrane-based dissolved gas extraction from transformer oil has been gaining importance in dissolved gas analysis (DGA). However, there lacks a systematic study on the transport of dissolved gases from oil. This paper reports an experimental study of dissolved-gas-in-oil extraction by Teflon AF2400 membranes on bare α-Al₂O₃ and modified γ-Al₂O₃/α-Al₂O₃ hollow fiber supports. Dense, ultrathin, and durable Teflon AF2400 top-coating layer can be synthesized on the modified γ-Al₂O₃/α-Al₂O₃ support but not the bare α-Al₂O₃ support. The long-term stability of the composite membranes strongly depends on the microstructure of the Teflon AF2400 top-coating layers. Mass transfer in the liquid phase is the rate-limiting step for extraction by the fresh membranes. The measured gas permeances in the extraction process are lower than that in the gas separation process. During extraction, the gas extraction rate decreases exponentially with on-stream time due to an increase in the membrane transport resistance caused by oil infiltration into the membrane. The overall mass transfer rate is determined by gas-in-oil solubility constant, mass transfer coefficient in the liquid phase, and the membrane permeance. The effects of these equilibrium and rate parameters on overall mass transport are sensitive to operating temperature due to the difference temperature dependence of these parameters.