A study of Metal-organic Frameworks (MOF) as an effective platform for analysis and removal of malodorous sulfur compounds

Abstract

To effectively apply sorptive approaches to treat gaseous odorants, it is imperative to accurately assess the performance of the selected adsorbent under ambient conditions. A survey was conducted on the quantification of hydrogen sulfide (H2S) and other components in the air before starting work on the adsorption study. Then, the performance of various advanced functional materials against H2S was investigated thoroughly. In chapter 2, the characteristics of malodor released from piggery excreta samples were investigated by measuring their emission concentrations both before and after such treatments as composting or aeration from filed sites. These samples were then collected from field sites and brought into the lab for analysis with the aid of the dynamic flux chamber method. The dominating compounds in the emissions were reduced sulfur compounds, phenol, and indole. The results were examined in terms of two key odor intensity factors, odor intensity (OI) and odor activity values (OAVs), after being grouped by criteria. When the odor contribution in the composting facility was assessed by the OAV value, methanethiol (53.1%), trimethylamine (TMA) (25.5%), and skatole (10.1%) were dominant in the pre-treatment facilities, while skatole (64.7%) and p-cresol (27.9%) in the post-treatment specimens. Likewise, in the liquid treatment facility, hydrogen sulfide (47.4%), p-cresol (26.9%), and skatole (20.2%) were dominant in the pre-treatment, while only p-cresol (73.6%) in the post-treatment. In comparison to the composting facility, the liquid treatment facility proved to be more efficient in the treatment of diverse pigpen-related odorants. In chapter 3, the emphasis of this study was directed for the removal function of the adsorption concentrations against different MOFs. To effectively apply sorptive approaches to treat gaseous odorants, it is imperative to accurately assess the performance of the selected adsorbent under real-world conditions. In this respect, the performance of five functional materials against hydrogen sulfide (H2S) was investigated (i.e., three metal-organic frameworks (MOFs: MOF-199 [M199], MOF-5 [M5], and UiO-66-NH2 [U6N]) and two covalent-organic polymers (COPs: CBAP-1 (EDA) [CE] and CBAP-1 (DETA) [CD]). The sorptive performances of the tested sorbents at an inlet stream H2S partial pressure of 1 Pa (~10 ppm: e.g., near ambient conditions) were compared to two reference (commercial or conventional) sorbents (i.e., Carbopack-X [CX] and activated carbon [AC]). As such, the MOF-199 had the largest 100% breakthrough adsorption capacity of 69 mg g-1. The 10% breakthrough volume (BTV10: L g-1)/capacity (mg.g-1) were: M199 (3,040/42) > M5 (94/1.3) > AC > (3.5/0.049) > U6N (3.1/0.043) > CE (2.5/0.035) > CD (2/0.028) > CX (1.9/0.026). The partition coefficient (PC: mol.kg-1.Pa-1) values of M-199, when compared using our experimental data and density functional theory (DFT), were highly divergent (e.g., 11,400 (experimental) vs. 7.5E-05 (simulation)) to reflect at least partially the fact that the MOF’s geometry was frozen to simplify DFT or force-field simulations. Among the tested/surveyed materials, M199 and IRMOF-3 appear to have the largest capacities for H2S ascribable to the unsaturated Cu metal sites and amine functionalized ligand, respectively. The experimental results obtained in this and other studies clearly support that M199 is potentially one of the most excellent candidates to effectively capture H2S in raw natural gas. Based on our study, we propose a strategy to build upgraded forms of M-199 which can overcome its limitation (e.g., framework collapse) while maintaining its capturing capacity across varying partial pressures.