The adsorption and simulated separation of light hydrocarbons in isoreticular metal-organic frameworks based on dendritic ligands with different aliphatic side chains.

Three isoreticular metal-organic frameworks, JUC-100, JUC-103 and JUC-106, were synthesized by connecting six-node dendritic ligands to a [Zn4O(CO2)6] cluster. JUC-103 and JUC-106 have additional methyl and ethyl groups, respectively, in the pores with respect to JUC-100. The uptake measurements of the three MOFs for CH4, C2H4, C2H6 and C3H8 were carried out. At 298 K, 1 atm, JUC-103 has relatively high CH4 uptake, but JUC-100 is the best at 273 K, 1 atm. JUC-100 and JUC-103 have similar C2H4 absorption ability. In addition, JUC-100 has the best absorption capacity for C2H6 and C3H8. These results suggest that high surface area and appropriate pore size are important factors for gas uptake. Furthermore, ideal adsorbed solution theory (IAST) analyses show that all three MOFs have good C3H8/CH4 and C2H6/CH4 selectivities for an equimolar quaternary CH4/C2H4/C2H6/C3H8 gas mixture maintained at isothermal conditions at 298 K, and JUC-106 has the best C2H6/CH4 selectivity. The breakthrough simulations indicate that all three MOFs have good capability for separating C2 hydrocarbons from C3 hydrocarbons. The pulse chromatographic simulations also indicate that all three MOFs are able to separate CH4/C2 H4/C2H6/C3H8 mixture into three different fractions of C1, C2 and C3 hydrocarbons.