Abstract
Efficient separation of acetylene (C2H2) from CO2 and CH4 is important to meet the requirement of high-purity acetylene in various industrial applications. Metal organic frameworks (MOFs) are great candidates for adsorption-based C2H2/CO2 and C2H2/CH4 separations due to their unique properties such as wide range of pore sizes and tunable chemistries. Experimental studies on the limited number of MOFs revealed that MOFs offer remarkable C2H2/CO2 and C2H2/CH4 selectivities based on single-component adsorption data. We performed the first large-scale molecular simulation study to investigate separation performances of 174 different MOF structures for C2H2/CO2 and C2H2/CH4 mixtures. Using the results of molecular simulations, several adsorbent performance evaluation metrics, such as selectivity, working capacity, adsorbent performance score, sorbent selection parameter, and regenerability were computed for each MOF. Based on these metrics, the best adsorbent candidates were identified for both separations. Results showed that the top three most promising MOF adsorbents exhibit C2H2/CO2 selectivities of 49, 47, 24 and C2H2/CH4 selectivities of 824, 684, 638 at 1 bar, 298 K and these are the highest C2H2 selectivities reported to date in the literature. Structure-performance analysis revealed that the best MOF adsorbents have pore sizes between 4 and 11 Å, surface areas in the range of 600–1,200 m2/g and porosities between 0.4 and 0.6 for selective separation of C2H2 from CO2 and CH4. These results will guide the future studies for the design of new MOFs with high C2H2 separation potentials.
Highlights
Metal organic frameworks (MOFs), nanoporous materials that are composed of metal clusters connected with organic linkers, have attracted significant interest in the last decade
We examined the relations between structural properties of MOFs such as pore sizes, porosities, surface areas and their C2H2 selectivities to provide the structure-performance relationships that can serve as a map for experimental synthesis of new MOFs with better C2H2 separation performances
Adsorption selectivity (Sads) is the most widely used metric to evaluate adsorbents and it is defined as the ratio of compositions of the adsorbed gases (x) in the adsorbent normalized by the ratio of bulk phase compositions (y)
Summary
Metal organic frameworks (MOFs), nanoporous materials that are composed of metal clusters connected with organic linkers, have attracted significant interest in the last decade. The most important characteristic of MOFs is that their physical, chemical and structural properties can be tuned during synthesis. This controllable synthesis leads to a large diversity of materials having different geometry, pore size, and chemical functionality (Mondloch et al, 2013). Due to these advantageous physical and chemical properties, MOFs have emerged as strong alternatives to traditional nanoporous materials in various gas separation applications. C2H2/CO2 separation is challenging because both gas molecules have similar molecular sizes (3.4 × 3.4 × 5.5 and 3.4 × 3.4 × 5.3 Å)
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