High-pressure separation of CH4/CO2 using activated carbon

Abstract

Activated carbon was evaluated as selective adsorbent for separation of CO2 from CO2/CH4 mixtures with special focus on high pressure applications. Adsorption equilibrium of pure gases was recorded at three different temperatures up to 8000kPa for CH4 and 5000kPa for CO2. Multi-site Langmuir, Virial and Sips models were used to fit the equilibrium data and predict multi-component equilibrium. Binary adsorption equilibrium measurements and binary breakthrough curves with mixtures of 10 and 20% CO2 balanced with CH4 were carried out at three different pressures: 500, 2500 and 5000kPa. A 1D mathematical model including mass, energy and momentum transport was used to describe the curves using a non-ideal gas behaviour equation.CO2 is more selectively adsorbed than CH4 in the activated carbon used in this study. The binary adsorption capacity obtained from binary breakthrough curves could only be well described by the Sips model. In all breakthrough curves, a small effect of the film mass transfer could be observed, particularly at higher pressures where this effect is more pronounced. The significant adsorption of CH4 may limit the application of this adsorbent for natural gas upgrading.