Asymmetric polysilazane-derived ceramic structures with multiscalar porosity for membrane applications

摘要

Novel ceramic structures with multi-scalar porosity were developed using a single preceramic poly(vinyl)silazane to generate asymmetric Si-C-N-based membranes through pyrolytic conversion. Macro porous supports in planar-disc configuration were prepared through a sacrificial filler approach, intermediate structures and microporous layers were deposited via dip-coating. Microporosity in the selective layer was generated through a controlled thermal decomposition of the precursor component in nitrogen atmosphere at temperatures up to 600 degrees C, resulting in micropores with average pore sizes of 0.8 nm, as investigated by nitrogen adsorption and small-angle X-ray scattering (SAXS). The general feasibility of the single-precursor approach towards selective permeation of gaseous species was demonstrated by the investigation of gas permeances of the generated structures using single-gas permeance testing of He, N-2, Ar, C2H6, and CO2. By variation of the deposition sequence during preparation of the selective layer by dip-coating, asymmetric structures with ideal permselectivities exceeding predicted Knudsen values were obtained. At 500 degrees C, He/N-2 and He/CO2 permselectivities of up to 3.1 and 4.1 were found, respectively, at He permeances up to 3 x 10(-8) mol m(-2) Pa-1 s(-1). The new single-material system is a first step towards the potential establishment of new, alternative membrane materials systems, circumventing thermal and chemical incompatibilities between constituents, and increasing material performance due to the applicability under extreme operating conditions. (C) 2016 The Author(s). Published by Elsevier Inc.