Development of Ionic Liquids Tethered to Coconut Shell Activated Carbon for Biogas Upgrading in a Packed Bed

Ionic liquids (ILs) were prepared in situ successfully on coconut shell activated carbon (AC) granules for biogas upgrading in a packed bed. In biogas upgrading, the saturated CO 2 capture capacities of AC-tethered 1-butyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (AC-[BPIM][Tf 2 N]) and AC-tethered 1-aminoethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (AC-[EPIM-NH 2 ][Tf 2 N]) were 2.58 and 2.95 mmol g −1 at 20 °C and 0.5 MPa, respectively. The heat of adsorption was 23–28 kJ mol −1 for AC-[BPIM]-based adsorbents and 65–71 kJ mol −1 for AC-[EPIM-NH 2 ]-based ones. As a CO 2 concentration of less than 3 % is required for biogas to be used in a vehicle, an adsorption capacity at which 3 % of CO 2 is reached in the upgraded gas could be more important. If the flow rate of the inlet gas was 50 mL min −1 , the adsorption capacity at which 3 % of CO 2 is reached in the upgraded gas was 1.44 mmol g −1 for AC-[BPIM][Tf 2 N] and 1.95 mmol g −1 for AC-[EPIM-NH 2 ][Tf 2 N] at 20 °C and 0.2 MPa. The adsorption selectivities of CO 2 over CH 4 were ∼92 and 95 % for AC-[BPIM][Tf 2 N] and AC-[EPIM-NH 2 ][Tf 2 N], respectively. The immobilized ILs exhibited a relatively stable cyclability in a packed bed.