Nickel-Based Metal-Organic Frameworks to Improve the CO2/CH4 Separation Capability of Thin-Film Pebax Membranes

Incorporating metal-organic frameworks (MOFs) into the thin layer of thin-film composite (TFC) membranes is an effective way of improving the CO2/CH4 separation performance. In this study, porous polyethersulfone (PES) membranes were surface-coated with a novel CO2-permeable layer consisting of CO2-philic Pebax and nickel-based MOF particles. The MOF particles were synthesized using nickel(II) acetate tetrahydrate as a metal source and 2-amino-1,4-dicarboxybenzene (NH2-BDC) as an organic linker. The properties and performance of the MOFs and synthesized membranes were assessed using analytical techniques including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), field-emission scanning electron microscopy (FE-SEM), and dynamic light scattering (DLS). DLS analysis showed that the MOF particle size range was in a range of 350-650 nm. Moreover, cross-sectional FE-SEM images depicted that a uniform and dense Pebax layer was shaped on top of the PES substrate. Well dispersion of the particles was demonstrated by surface FE-SEM imaging. DSC analysis showed that embedding Ni-NH2-BDC MOF particles into the Pebax-1657 film increased the crystallinity degree and the glass-transition temperature (T-g) of resulted membranes. To evaluate the membrane's separation performance, permeation experiments were performed with CO2, CH4, and CO2/CH4 mixtures at ambient temperature. Embedding 5 wt % Ni-based MOF particles improved the CO2 permeability and CO2/CH4 selectivity from 19.05 Barrer and 32.2 to 31.55 Barrer and 94, respectively, compared to MOF-free membranes. Loading MOF particles into the Pebax matrix also improved the real gas separation factor. The obtained results demonstrate the great potential of the fabricated TFC membranes for gas separation.