Preparation and permeability evaluation of carbon molecular sieve membrane for efficient separation of H₂/ CH₄ in hydrogen-doped pipeline

Abstract The problem of long-distance transportation and storage of hydrogen is solved in a short time by purifying the Hydrogen-doped pipeline. Membrane separation method is especially suitable for the purification of hydrogen-containing gas mixture with low H 2 content. Carbon Molecular Sieve Membranes (CMSMs) can achieve efficient separation of H 2 /CH 4 by molecular sieve separation principle, based on the significant difference in molecular dynamic diameters between H 2 and CH 4 . In this paper, the influence factors of pore structure evolution from microporous polyvinylidene fluoride-hexafluoropropylene (PHF) to ultramicroporous CMSMs were studied by experiments and characterization. Through precise regulation of membrane pore size, alumina-supported PHF-CMSMs suitable for hydrogen separation from hydrogen-doped natural gas were prepared, and the permeation performance of the H 2 /CH 4 membrane separation process was analyzed. Firstly, the study confirmed that the structural evolution from PHF to PHF-CMSMs were influenced by the polymer chain configuration and pyrolysis conditions. By adjusting the molecular weight of polymer and solution concentration, the free volume fraction can be adjusted, and the ultra-microporous structure of CMSMs after pyrolysis can be subsequently adjusted. The results showed that the higher the solution concentration of the polymer, the lower the gas permeability, but the higher the H 2 /CH 4 selectivity. Secondly, the addition of 2% PVP enhanced the thermostability of the membrane by 25%. Additionally, the graft of hydroxyl groups into PHF-CMSMs promotes the formation of an open and interconnected porous structure. Finally, based on the findings of the permeation experiments, it was observed that the selectivity of H 2 /CH 4 reached a maximum of 97.95 at 30°C. The research indicated that the supported PHF-CMSMs can efficiently purify hydrogen-doped natural gas in various pressure segments at ambient temperature, with low pressure drop losses. This study can provide theoretical basis and data guidance for H 2 /CH 4 separation in hydrogen-doped pipelines, and promote the development of hydrogen energy industry.