Highly efficient ethylene/ethane separation via molecular sieving using chitosan-derived ultramicroporous carbon

The selective separation of C2H4/C2H6 pair is of paramount importance in the petrochemical industry, which is yet challenged by their similar polarities, shapes, and kinetic diameters. The use of carbonaceous adsorbents with molecular sieving capability holds great promise in achieving the desired selectivity and economically feasibility. However, such progress has been hindered by the typically wide pore size distribution observed in traditional carbons. Herein, we report a series of chitosan-based ultramicroporous carbons with C2H4/C2H6 molecular sieving performance through an activating reagents-free method. The hydrothermal process of chitosan was initially employed to prepare condensed carbonaceous hydrochar rich in heteroatoms. The subsequent thermal etching led to the formation of sieving-based ultramicropores, stemming from the decomposition of heteroatoms and hot-shrinkage of pores at high temperature. The as-synthesized optimal CNC-700 sample achieved a high C2H4 uptake of 32.3 cm3 (STP) g−1 and negligible C2H6 adsorption at 298 K and 1.0 bar. The isosteric heat of C2H4 on CNC-700 reached 34.5 kJ mol−1, significantly lower than other thermodynamically driven carbonaceous adsorbents. The fixed-bed breakthrough experiments further validated the efficient separation of equimolar C2H4/C2H6 mixture under dynamic conditions. This work provides an important guideline to fabricate carbons with adjustable ultramicropore size derived from biomass for the highly effective separation of light hydrocarbons via molecular sieving.