Surface sieving carbon skins for propylene and propane separation

The adsorptive separation of olefin/paraffin mixtures requires the development of robust adsorbents with high selectivity and adsorption capacity. Here we introduce surface sieving carbon adsorbents for propylene/propane separations. The surface sieving carbon skins, with a thickness of approximately 5.0 nm, selectively sieve propylene through narrow slits centered at 3.6 Å. Underneath the carbon skin lies a pore reservoir centered at 4.9 Å, resulting in a high propylene adsorption capacity of ~2.0 mmol g⁻¹. Such carbon structures readily self-assemble into water-stable and robust monoliths with highly interconnected macropores for efficient mass transfer. These structural advantages collectively contribute to the high propylene/propane separation performance of the surface sieving carbon even after boiling in water for a week. Process simulations reveal that, using this adsorbent class, 99.5% and 99.9% purity of propylene with the according recovery of 82% and 79% can be obtained from an equimolar propylene/propane mixture through a two-bed six-step vacuum swing adsorption process.