Enhancing carbon dioxide separation from natural gas in dynamic adsorption by a new type of bimetallic MOF; MIL-101(Cr-Al)

This study explores the use of a high surface area nano-adsorbent for selective adsorption and separation of very low concentrations of carbon dioxide from methane. The adsorbent, MIL-101(Cr-Al) with unsaturated metal sites, was prepared by one pot facile hydrothermal method and it was compared with MIL-101(Cr). Characterizations of the synthesized samples were conducted using XRD, FESEM, EDAX, elemental mapping, and BET analyses. Static adsorption experiments were carried out at pressures ranging from close to 1 bar up to 50 bar and at temperatures of 25 and 35 °C. The ideal selectivity of carbon dioxide relative to methane and the isosteric heat of adsorption were also calculated. Results indicated that with the bimetallic modification method, the CO2/CH4 selectivity increased from 5.2 to 5.7 at the pressure of 1 bar and from 8.2 to 8.3 at the pressure of 50 bar and temperature of 35 °C. Dynamic adsorption experiments were conducted for the mixture of CH4, CO2 and He (85 %-5% −10 % mol%). The dynamic selectivity of CO2/CH4 at the pressure of 15 bar with the space time of 1.12 min was increased from 1.82 to 4.2 using bimetallic MIL-101(Cr-Al).