Optimizing gas transport for C3H6/C3H8 size sieving separation via fine pore engineering of carbon microspheres

For the adsorptive separation of propylene/propane (C3H6/C3H8) with high similarities in physiochemical properties, size-exclusive effect is highly attractive that can realize the superior selectivity. Nevertheless, the required narrow pores would unavoidably resist mass transfer of C3H6 molecules. To minimize the hindered diffusion, we report a systematic pore-engineering study in a family of carbon microspheres with fine-tuning pore sizes by exceptional activation-free method. The manipulation of pores was realized by varied temperature during glucose hydrothermal synthesis with acid additive as catalysis. Among as-obtained carbon analogs, GC -190 with optimal pore size closing to the kinetic diameter of C3H8 (5.11 angstrom), exhibited outstanding C3H6/C3H8 size-sieving property as well as fast C3H6 kinetics plausibly. However, GC-230 with smaller pores closing to the size of C3H6 (4.68 angstrom) showed sluggish C3H6 diffusion despite retaining size-sieving effect. The C3H6 diffusion constant rate (D') of 1.21 x 10-2 min-1 on GC-190 is about two orders of magnitude higher than GC-230 of 2.29 x 10-4 min-1. DFT simulation further supports the remarkably reduced diffusion energy barrier of C3H6 by sub -angstrom level increased pore size. This study may deepen the understanding of gas diffusion in confined narrow pores and provides a general design concept.