Enhancement in the selectivity of O/N via ZIF-8/CA mixed-matrix membranes and the development of a thermodynamic model to predict the permeability of gases.

Zeolitic imidazolate framework-8 (ZIF-8) has a sodalite topology. ZIF-8 is composed of zinc ion coordinated by four imidazolate rings. The pore aperture of ZIF-8 is 3.4 Å, which readily retains large gas molecules like N. In this work, mixed-matrix membranes (MMMs) have been fabricated by utilizing ZIF-8 and pristine cellulose acetate (CA) for O/N separation. Membranes of pristine CA and MMMs of ZIF-8/CA at various ZIF-8 concentrations were prepared in tetrahydrofuran (THF). Permeation results of the fabricated membranes revealed increasing selectivity for O/N with increasing pressure as well as ZIF-8/CA concentration up to 5% (w/w). The selectivity of O/N increased 4 times for MMMs containing 5% (w/w) of ZIF-8/CA as compared with the pristine CA membrane. A thermodynamic model has also been developed to predict the permeability of gases through polymeric membranes. The results were compared with literature data as well as the pristine CA membrane produced in this work for model validation.