Ultrahigh CO2/CH4 and CO2/N2 adsorption selectivities on a cost-effectively L-aspartic acid based metal-organic framework

Using porous materials to selectively adsorb CO2 from flue gas or natural gas is a promising method for mitigating CO2 emission and purifying methane. Here, we synthesized an L-aspartic acid based microporous metal-organic framework (MIP-202) and studied its adsorptive separation performance for CO2/CH4 and CO2/N-2 mixtures. Results show that MIP-202 had ultrahigh CO2/CH4 (72.9 and 241.5 for CO2/CH4 = 50/50 and 10/90, respectively) and CO2/N-2 (1,950,000 and 2129.1 for CO2/N-2=50/50 and 15/85, respectively) IAST selectivities at 298 K and 100 kPa. The high selectivity was verified by the calculations of Henery's law selectivity and breakthrough experiments. Metropolis Monte Carlo simulation calculations show that CO2 with greater polarizability and quadruple moment tends to occupy the pore walls of large cages with higher polarity, while the less polar CH4 or N-2 majorly being adsorbed in the pore walls of small cages with lower polarity, resulting in the ultrahigh CO2/CH4 and CO2/N-2 separation selectivities. MIP-202 exhibits low CO2 adsorption enthalpy (17.2-30.7 kJ/mol), superior persistent reusability after five cyclic adsorption experiments, easy desorption performance at 298 K, moderate water and moisture stability, good stability under dry and humid SO2 atmosphere, and low ligand cost ($36/kg). MIP-202 extrudates were prepared by an extrusion molding method using hydroxypropyl cellulose (HPC) as the binder and they retained 97.35% CO2 uptake of MIP-202 powder at room temperature and pressure. This work shows that MIP-202 is an industrially promising material for the separation of CO2/CH4 and CO2/N-2 mixtures.