Development of ionic liquids tethered to coconut shell activated carbon for biogas upgrading in a packed bed.

Ionic liquids (ILs) were prepared insitu successfully on coconut shell activated carbon (AC) granules for biogas upgrading in a packed bed. In biogas upgrading, the saturated CO2 capture capacities of AC-tethered 1-butyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (AC-[BPIM][Tf2N]) and AC-tethered 1-aminoethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (AC-[EPIM-NH2][Tf2N]) were 2.58 and 2.95mmolg(-1) at 20 degrees C and 0.5MPa, respectively. The heat of adsorption was 23-28kJmol(-1) for AC-[BPIM]-based adsorbents and 65-71kJmol(-1) for AC-[EPIM-NH2]-based ones. As a CO2 concentration of less than 3% is required for biogas to be used in a vehicle, an adsorption capacity at which 3% of CO2 is reached in the upgraded gas could be more important. If the flow rate of the inlet gas was 50mLmin(-1), the adsorption capacity at which 3% of CO2 is reached in the upgraded gas was 1.44mmolg(-1) for AC-[BPIM][Tf2N] and 1.95mmolg(-1) for AC-[EPIM-NH2][Tf2N] at 20 degrees C and 0.2MPa. The adsorption selectivities of CO2 over CH4 were approximate to 92 and 95% for AC-[BPIM][Tf2N] and AC-[EPIM-NH2][Tf2N], respectively. The immobilized ILs exhibited a relatively stable cyclability in a packed bed.