To remove CO2 from CH4, tetraethylenepentamine was grafted onto coordinatively unsaturated centers of MIL-101(Cr) by postsynthetic functionalization: wet impregnation at 298 K, followed by grafting, drying, and washing. Compared to MIL-101(Cr), TEPA MIL-101(Cr) showed 54% higher CO2 adsorption at 1 bar and 98% reduction of CH4 adsorption at 60 bar. The ideal adsorption solution theory (LAST) selectivity of CO2/CH4 for a binary gas mixture of 2% CO2 + 98% CH4 at 298 K and 60 bar predicted by the Toth equation was found to be 11 and 598 for ungrafted and grafted MIL-101(Cr), respectively. Single column breakthrough tests were performed for upgrading the 2% CO2 + 98% CH4 mixture to liquefied quality of natural gas (CO2 < 50 ppm) under various operating conditions including different temperatures and total amount of purge gas at the fixed pressure of 60 bar and temperature of 298 K At the feed flow rate of 1000 sccm, the TEPA-MIL-101(Cr) extrudates obtained 0.89 mmol/g CO2 adsorption capacity and nearly 83% of adsorbed CO2 can be removed by regenerating extrudates at 393 K with 79 cm(3)/gadsorbent of total amount of purge gas.