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 CO 2 from flue gas or natural gas is a promising method for mitigating CO 2 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 CO 2 /CH 4 and CO 2 /N 2 mixtures. Results show that MIP-202 had ultrahigh CO 2 /CH 4 (72.9 and 241.5 for CO 2 /CH 4  = 50/50 and 10/90, respectively) and CO 2 /N 2 (1,950,000 and 2129.1 for CO 2 /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 CO 2 with greater polarizability and quadruple moment tends to occupy the pore walls of large cages with higher polarity, while the less polar CH 4 or N 2 majorly being adsorbed in the pore walls of small cages with lower polarity, resulting in the ultrahigh CO 2 /CH 4 and CO 2 /N 2 separation selectivities. MIP-202 exhibits low CO 2 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 SO 2 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% CO 2 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 CO 2 /CH 4 and CO 2 /N 2 mixtures.