Preparation of highly graphitized porous carbon and its ethane/ethylene separation performance

Abstract

The efficient separation of ethane (C₂H₆) and ethylene (C₂H₄) is crucial for the preparation of polymer-grade C₂H₄, necessitating the development of highly selective and stable C₂H₆/C₂H₄ adsorbents. Highly graphitized porous carbon, denoted GC-800, was synthesized by polymerization at room temperature followed by carbonization at 800 °C using phenolic resin as the precursor and FeCl₃ as the iron source. Vienna Ab-initio Simulation Package (VASP) calculations confirmed a higher binding energy between C₂H₆ molecules and graphitized porous carbon surfaces, so that a high degree of graphitization increased the adsorption capacity of porous carbon for C₂H₆. However, catalytic graphitization using Fe at high temperatures disrupted the microporous structure of the carbon, thereby reducing its ability to separate C₂H₆/C₂H₄. By controlling the carbonization temperature, the degree of graphitization and pore structure of the porous carbon could be changed. Raman spectra and XPS spectra showed that the GC-800 had a high degree of graphitization, with a sp² C content as high as 73%. Low-temperature N₂ physical adsorption measurements estimated the specific surface area of GC-800 to be as high as 574 m²·g⁻¹. At 298 K and 1 bar, it had an equilibrium adsorption capacity of 2.16 mmol·g⁻¹ for C₂H₆, with the C₂H₆/C₂H₄ (1:1 and 1:9, v/v) ideal adsorbed solution theory selectivity respectively reaching 2.4 and 3.8, significantly higher than the values of most reported high-performance C₂H₆ selective adsorbents. Dynamic breakthrough experiments showed that GC-800 could produce high-purity C₂H₄ in a single step from a mixture of C₂H₆ and C₂H₄. Dynamic cycling tests confirmed its good cyclic stability, and that it could efficiently separate C₂H₆/C₂H₄ even under humid conditions.