Chemisorption of hydrogen sulfide by metal-organic frameworks and covalent-organic polymers based on experimental/theoretical evaluation

Abstract

The rapid expansion of modern industrial productivity has led to the ever-increasing emissions of various hazardous gaseous pollutants. In order to efficiently treat gaseous odorants like hydrogen sulfide (H2S), it is important to accurately assess the sorptive performance under near ambient conditions [<1 Pa at 298 K]. To this end, the performance of H2S sorption was investigated at 1 Pa (∼10 ppm at 298 K) inlet stream partial pressure of H2S in 1 bar of N2 using three metal-organic frameworks (MOFs: MOF-199, MOF-5, and UiO-66-NH2), two covalent-organic polymers (COPs: CBAP-1 (EDA) and CBAP-1 (DETA)), and two commercial sorbents (Carbopack-X and activated carbon [AC]). The 10% breakthrough volume (BTV10: L g−1)/corresponding adsorption capacity (mg g−1) confirmed a noticeable advantage of MOF-199 (3040/42) over all other tested materials (i.e., MOF-5 (94/1.3) >AC (3.5/0.049) > UiO-66-NH2 (3.1/0.043) > CBAP-1 (EDA) (2.5/0.035) > CBAP-1 (DETA) (2/0.028) > Carbopack-X (1.9/0.026)). The overall results clearly confirm that MOF-199 is an excellent chemisorbent to effectively capture gaseous H2S via the formation of irreversible chemical bonds with Cu–Cu site bridge (i.e., Cu–S). However, a comparison between previous (theoretical) and present (experimental) data indicates substantial divergence in the partition coefficient (PC: mol kg−1 Pa−1) data of MOF-199 (e.g., PC (at BTV5) = 16.0 (experiment) vs. PC = 7.5E-05 (simulation)). These divergences with the computed PC values are attributed to the fact that the crystal lattice of MOF-199 relaxes to a more thermodynamically stable structure under real-experimental conditions. In contrast, the assumption of frozen geometry of MOF-199 crystal lattice used for the theoretical simulation (by density functional theory) unrealistically underestimated the H2S adsorption capacity.