Dynamics adsorption of the enhanced CH4 recovery by CO2 injection

The dynamic adsorption isotherms of CO2-EGR were measured by using an Intelligent Gravimetric Analysis system. In the initial CO2 injecting stage, all the injected CO2 enters into the adsorbent and the mole fraction of CH4 in the gas phase (yCH4) is maintained at 1.0. The CH4 recovery factor (RCH4) increases. The duration of this stage (t(CD)) depends on the selectivity of CO2 over CH4 (SCO2/CH4). An adsorbent with large SCO2/CH4 has long t(CD). In the second stage, the injected CO2 competes with CH4 for adsorption. The cumulative RCH4 of the second stage is much larger than that of the initial stage. However, yCH4 decreases sharply. pCH4 in the whole CO2 injection is always larger than that before CO2 injection, suggesting that CH4 desorption results from the displacement of CO2 rather than from pressure depletion.