Working capacities and selectivity characteristics of CO2 capture using a single-ligand ultra-microporous MOF

DOI: 10.1126/sciadv.150042

“To more thoroughly explore the potential of 1 for precombustion CO₂ capture, binary mixtures of CO₂ and H₂ were simulated at 313 K from 1 to 40 bar at two relevant gas compositions: 80H₂/20CO₂ and 60H₂/40CO₂. Figure 4 (A and B) compares the simulated PSA working capacities of 1 (using a desorption pressure of 1 bar) to the working capacities of the recently reported industrial benchmarks zeolite 13X and activated carbon JX101, and two of the top-performing MOFs identified for this application, MgMOF-74 and Cu-BTTri (23). A similar comparison of the CO₂/H₂ selectivities is given in Fig. 4 (C and D) at the two H₂/CO₂ ratios (table S7). At low CO₂ concentrations (80% H₂ and 20% CO₂), 1 has the largest working capacity of up to an adsorption pressure of 15 bar but remains among the top performers in this respect throughout the pressure range (51). Only the MOF Cu-BTTri has a significantly higher working capacity at pressures greater than 25 bar. However, Cu-BTTri has a very poor H₂/CO₂ selectivity, the lowest of all the materials compared, making it unsuitable for practical use (23). At higher CO₂ concentrations (60% H₂ and 40% CO₂), the working capacity of 1 is less competitive. Nonetheless, when compared to zeolite 13X, which is used industrially for PSA-based CO₂ scrubbing of natural gas, 1 has an almost identical selectivity but roughly double the working capacity throughout the pressure range. Compared to the high-performance activated carbon JX101, 1 has a higher working capacity for the 80:20 gas mixture and a comparable working capacity for the 60:40 gas mixture throughout the whole pressure range. However, 1 has a CO₂/H₂ selectivity that is at least 2.5 times better than JX101 for both gas compositions. Figure 4 shows that MgMOF-74 has one of the highest working capacities at all pressures and both gas compositions. Moreover, in all cases, it also has the highest CO₂/H₂ selectivity, outperforming Ni-4PyC by at least 50% in this respect. Despite the favorable adsorption properties, MgMOF-74 is not hydrolytically stable due to the presence of open metal sites, which limits its practical use. We note that 1 has one of the highest reported CO₂/H₂ selectivities of MOFs reported in the literature (see table S11 in the Supplementary Materials).”

“Fig. 4 Working capacities and selectivity characteristics.