Design and preparation of polytetrafluoroethylene/carbon (PTFE/C) composite membrane-equivalent foam for gravity-driven emulsion separation

Herein, the concept of a membrane-equivalent foam (MEF) with equivalent characteristics to a separated multilayer membrane is proposed and elaborated to mitigate the conflict between efficiency and selectivity in emulsion separation. Porous polytetrafluoroethylene/carbon (PTFE/C) composite MEF with a two-level microporous structure (bubble pores and ice-templated pores) was prepared successfully, derived from a PTFE/glutaraldehyde crosslinked polyvinyl alcohol (PVAG) composite foam green body. The PVAG-based in situ carbon was analyzed as composed mainly of amorphous carbon. The bubble pores were observed to be interconnected by ice-templated pores. The porosity of the porous PTFE/C composite MEF reached a remarkable value of 73.35%. Corresponding to m(PTFE)/m(PVA) values of 14/1, 12/1, 10/1 and 8/1, the average pore sizes of the bubble pores were 32.99, 44.31, 47.33 and 48.01 μm, and the average sizes of the ice-templated pores were about 2.24, 2.77, 3.02 and 3.47 μm, respectively. Meanwhile, the porous PTFE/C composite MEF exhibited near superhydrophobicity in air and superhydrophobicity under oil. In gravity-driven water−oil emulsion separation tests, the oil flux was up to 3541 L h⁻¹ m⁻² and the separation efficiency reached more than 99.52%. After 20 cycles of testing, the oil flux and separation efficiency remained stable. The membrane-equivalent thickness of the samples from PTFE/C-m1 to PTFE/C-m4 were below 3.47, 4.26, 0.58 and 0.30 nm, respectively, which is about 10⁻⁷–10⁻⁶ times lower than the height of porous PTFE/C composite MEF. It is reasonable to believe that porous PTFE/C composite MEF could effectively mitigate the ‘trade-off’ effect. © 2023 Society of Industrial Chemistry.