Nitrogen-doped carbon particles with distinctive ethylene adsorption selectivity for efficient ethylene/acetylene separation

Separation of ethylene/acetylene (C2H4/C2H2) mixtures with C2H4-selective adsorbents is of economics and energy efficiency to purify crude C2H2 from methane pyrolysis or partial oxidation (POX) process. Herein, a systematic study was carried out to investigate the structural properties and C2H4/C2H2 separation performance of novel nitrogen-doped carbon particles, as well as the mechanism of preferentially adsorbing C2H4 over C2H2 through the Grand Canonical Monte Carlo (GCMC) simulations. The nitrogen-doped carbon particles derived from coconut shell and metronidazole present regular particle sizes centering at 710 μm and excellent crushing strength of 89 N. Well-developed microporosity with pore dimension mainly ranging in 0.54–0.68 nm, and fine-tuning surface chemistry with abundant nitrogen-containing species (pyridinic N, pyrrolic N and graphitic N) were observed in nitrogen-doped carbon particles. Interestingly, nitrogen-doped carbon particles exhibit preferential adsorption of C2H4 over C2H2, and the IAST-predicted selectivity of 1.5-N-CP reaches as high as 5.2 for C2H4/C2H2 (1/9) mixture at 1.0 bar and 25 °C. Remarkably, the separation stability and recyclability with complete separation for C2H4/C2H2 were well maintained during cyclic dynamic breakthrough experiments. GCMC simulation results demonstrate that the graphitic N with great binding energy (−22.61 kJ/mol for C2H4 and −19.87 kJ/mol for C2H2) favors the adsorption of both C2H4 and C2H2. The pore dimension ranging 0.54–0.68 nm, together with pyridinic N and pyrrolic N species significantly enhance the separation of C2H4/C2H2 through the large difference in adsorption interactions between C2H4 and C2H2. Therefore, the nitrogen-doped carbon particles have the excellent application accessibility in purifying C2H2 from C2H4/C2H2 mixture.