Hybrid Postsynthetic Functionalization of Tetraethylenepentamine onto MIL-101(Cr) for Separation of CO₂ from CH₄

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 (IAST) 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 cm³/g_adsorbent of total amount of purge gas