Co3(HCOO)6 Microporous Metal-Organic Framework Membrane for Separation of CO2/CH4 Mixtures

Continuous metal-organic framework-type Co-3(HCOO)(6) inter-grown films with a one-dimensional zigzag channel system and pore aperture of 5.5 angstrom are prepared by secondary growth on preseeded macroporous glass-frit disks and silicon wafers. The adsorption behavior of CO2 or CH4 single gases on the Co-3(HCOO)(6) membrane is investigated by in situ IR spectroscopy. It is shown that the isosteric heats of adsorption for CO2 (17.7 kJ mol(-1)) and CH4 (14.4 kJ mol(-1)) do not vary with increasing amount of adsorbed gases. The higher value of isosteric heat for CO2 is an indication of the stronger interaction between the CO2 and the Co-3(HCOO)(6) membrane. The Co-3(HCOO)(6) membrane is studied by binary gas permeation of CO2 and CH4 at different temperatures (0, 25, and 60 degrees C). The membrane has CO2/CH4 selectivity with a separation factor higher than 10, which is due to the unique structure and molecular sieving effect. Upon increasing the temperature from 0 to 60 degrees C, the preferred permeance of CO2 over CH4 is increased from 1.70x10(-6) to 2.09x10(-6) mol m(-2)s(-1)Pa(-1), while the separation factor for CO2/CH4 shows a corresponding decrease from 15.95 to 10.37. The effective pore size of the Co-3(HCOO)(6) material combined with the pore shape do not allow the two molecules to pass simultaneously, and once the CO2 molecules are diffused in the micropores, the CH4 is blocked. The supported Co-3(HCOO)(6) membrane retains high mechanical stability after a number of thermal cycles.