Mixed matrix carbon stainless steel (MMCSS) hollow fibres for gas separation

Abstract

This work reports the preparation and investigation of novel mixed matrix carbon stainless steel (MMCSS) membranes. The study involves the production of MMCSS hollow fibres using SS particles of 6, 10, 16 and 45 μm in diameter, polyetherimide as a polymeric binder and pyrolysis using a N2 inert atmosphere. As a result, the binder pyrolysed to carbon was retained in the hollow fibre structure, filling the voids between the SS particles. Smaller SS particles (6 μm) yielded a bi-modal pore size distribution and superior mechanical properties. An interesting morphological feature was the formation of honeycomb-like carbon structures between the SS particles, attributed to the densification of the hollow fibre during pyrolysis at 1050 °C. The MMCSS hollow fibres (6 μm) delivered almost pure N2 for the separation of a synthetic flue gas composition (13% CO2 and 87% N2). It was found that CO2 had a strong affinity to the surface of the MMCSS materials (isosteric heat of adsorption of 38 kJ mol−1) whilst N2 was a non-absorbing gas. Therefore, CO2 permeation was controlled by surface diffusion whilst N2 was controlled by the faster Knudsen diffusion mechanism. For CO2 feed concentrations in excess of 13%, the CO2 diffusion increased as the excess CO2 could not adsorb on the fully saturated surface of the MMCSS hollow fibres, thus slightly reducing the N2 purity in the permeate stream.