Résumé
Making hydrogen a reliable energy vector in future decades requires the implementation of complex technologies related namely to its production, storage or transport. Intensive research is also underway to optimize its use by increasing its purity and to ensure the safety of hydrogen facilities. Techniques such as cryogenic distillation, pressure swing adsorption (PSA) or membrane processes can be used to purify hydrogen. Both cryogenic distillation and PSA are used at commercial scale although these techniques are energy intensive. In comparison, membrane processes appear as a promising technology to separate H2 from gas mixtures, by consuming less energy and operating in a continuous way. They can be either dense or porous, and made of polymers, metals, carbon, ceramics, hybrids or composite materials. Different gas transport and separation mechanisms are involved depending on the type of membrane. In microporous membranes (pore sizes < 2 nm) the separation of gas molecules might occur by molecular sieving, difference in diffusivity and/or competitive adsorption. Molecular sieving is an efficient thermally activated separation mechanism, particularly attractive for gas mixtures with different kinetic diameters. A good compromise between selectivity and permeability values can be reached with a pore sizes smaller than the kinetic diameters of the gas to be retained. This work is dedicated to the development of a new type of alumina microporous membrane using the Molecular Layer Deposition (MLD) technique. As Atomic Layer Deposition (ALD), MLD allows to synthesize hybrid organic-inorganic materials by conformal coatings on various substrates using both organic and inorganic precursors. We developed a MLD process able to coat uniformly the pores (size~ 5-8 nm) of an alumina tubular support with alucone (aluminum alkoxide). Then, the film was calcined to transform the organic layer into a microporous alumina frame. Maximum pore sizes around 0.3 nm are targeted to obtain a molecular sieve membrane able to extract H2 from mixtures with larger gas. The MLD parameters have been optimized to obtain homogenous layers. Then, we investigated the influence of post-synthesis parameters to improve the membrane selectivity and permeability, as well as its stability. Single gas permeance measurements with He (H2 simulant) and N2 were used to validate the membrane quality and molecular sieving performance before testing them with a gas mixture under various temperature working conditions.