The Adsorption and Simulated Separation of Light Hydrocarbons in Isoreticular Metal-Organic Frameworks Based on Dendritic Ligands with Different Aliphatic Side Chains

摘要

Three isoreticular metal-organic frameworks, JUC-100, JUC-103 and JUC-106, were synthesized by connecting six-node dendritic ligands to a [Zn_4O(CO_2)_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 CH_4, C_2H_4, C_2H_6 and C_3H_8 were carried out. At 298 K, 1 atm, JUC-103 has relatively high CH_4 uptake, but JUC-100 is the best at 273 K, 1 atm. JUC-100 and JUC-103 have similar C_2H_4 absorption ability. In addition, JUC-100 has the best absorption capacity for C_2H_6 and C_3H_8. 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 C_3H_8/CH_4 and C_2H_6/CH_4 selectivities for an equimolar quaternary CH_4/C_2H_4/C_2H_6/C_3H_8 gas mixture maintained at isothermal conditions at 298 K, and JUC-106 has the best C_2H_6/CH_4 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 CH_4/C_2H_4/C_2H_6/C_3H_8 mixture into three different fractions of C1, C2 and C3 hydrocarbons.