2.4 Transient breakthrough experiments
The breakthrough curves of MIL-120Al were obtained at 298–313 K at a CH4/N2 mixed gas flow rate of 10 mL/min. The adsorbent powders were first tableted under a pressure of 4 MPa using a tablet press and then sieved into particles with diameters of ~2 mm using a stainless-steel screen. The prepared MIL-120Al (3.40 g) particles were activated at 423 K and 1 × 10–5 mbar for 12 h and then filled in an adsorption column (Φ 9.0 × 150 mm) under an environment free from water. Prior to starting the test, the adsorption column was flushed with He gas at a flow rate of 15 mL/min and 373 K. The inlet gas was then switched to the CH4/N2 mixture to be tested at a total gas flow of 10 mL/min. The component concentrations in the effluent gas were monitored using an online mass spectrometer (HPR-20 EGA, Hiden, UK, detection limit 0.01%). After each separation test, the adsorption bed was regenerated under a flow of He (15 mL/min) for 20 min at ambient temperature.