Oil-Tea Shell Derived N-Doped Porous Carbon for Selective Separation of CO2, CH4, and N2

Nitrogen-doped porous activated carbon samples were successfully synthesized using oil-tea shells. The resulted N-doped carbons were analyzed for their physical and chemical properties with XRD, SEM, TEM, Raman spectroscopy, and nitrogen adsorption/desorption at 77 K. The high BET specific surface area (1641 m(2)/g), uniform pore-size distribution with a median pore size of 2.85 nm, and a large pore volume (1.47 cm(3)/g) enable the porous carbon as an ideal adsorbent for gas separation and purification applications. Pure component adsorption isotherms of CO2, N-2, and CH4 were determined at 273, 283, and 298 K and gas pressures up to 1 atm. The ideal adsorbed solution theory (IAST) model was applied for calculating the adsorption selectivity for CO2/N-2, CO2/CH4, and CH4/N-2 binary mixtures at equimolar compositions and pressures. At 298 K and 1 atm, the predicted selectivities for equimolar CO2/N-2, CH4/N-2, and CO2/CH4 were 55.0, 3.6, and 5.2, respectively; and the adsorption capacities for CO2, N-2 and CH4 were 1.92, 0.12, and 0.62 mmol g(-1), respectively. Combining excellent adsorption separation properties and relative low heats of adsorption, the N-doped carbons fabricated in this work appear to be very promising for separating CO2 CH4, CH4/N-2, and CO2/N-2 gas mixture pairs.