Metrics for Evaluation and Screening of Metal–Organic Frameworks for Applications in Mixture Separations

Abstract

For mixture separations, metal–organic frameworks (MOFs) are of practical interest. Such separations are carried out in fixed bed adsorption devices that are commonly operated in a transient mode, utilizing the pressure swing adsorption (PSA) technology, consisting of adsorption and desorption cycles. The primary objective of this article is to provide an assessment of the variety of metrics that are appropriate for screening and ranking MOFs for use in fixed bed adsorbers. By detailed analysis of several mixture separations of industrial significance, it is demonstrated that besides the adsorption selectivity, the performance of a specific MOF in PSA separation technologies is also dictated by a number of factors that include uptake capacities, intracrystalline diffusion influences, and regenerability. Low uptake capacities often reduce the efficacy of separations of MOFs with high selectivities. A combined selectivity–capacity metric, Δ q , termed as the separation potential and calculable from ideal adsorbed solution theory, quantifies the maximum productivity of a component that can be recovered in either the adsorption or desorption cycle of transient fixed bed operations. As a result of intracrystalline diffusion limitations, the transient breakthroughs have distended characteristics, leading to diminished productivities in a number of cases. This article also highlights the possibility of harnessing intracrystalline diffusion limitations to reverse the adsorption selectivity; this strategy is useful for selective capture of nitrogen from natural gas.

Tailoring a robust Al-MOF for trapping C2H6 and C2H2 towards efficient C2H4 purification from quaternary mixtures

“…, enabling the preferential sorption of C 2 H 6 over C 2 H 4 is non-trivial, which can simplify the separation process by selectively releasing pure C 2 H 4 from the downstream outlet. 5,55 On a similar note, separating C 2 H 2 /CO 2 is equally complex as a consequence of cognate molecular dimensions (C 2 H 2 : 3.32 × 3.34 × 5.7 Å 3 and CO 2 : 3.18 × 3.33 × 5.36 Å 3 ) and boiling points (C 2 H 2 , 189.3 K; CO 2 , 194.7 K). The higher uptake ratio of C 2 H 6 over C 2 H 4 and C 2 H 2 over CO 2 in Al-MOFM 15 motivated us to study the nature of hydrocarbon binding interaction in its pore channels.…”

Selective capture of carbon dioxide from hydrocarbons using a metal-organic framework

“…Crucially, the larger C 2 H 6 and C 3 H 8 components do not diminish the CO 2 capture capabilities of MUF-16. This is an important observation for the removal of CO 2 from natural gas, where mixed-gas separations involving these hydrocarbons are often required yet the pool of competent materials is limited 19,63 . To further probe the applicability of MUF-16 to natural gas sweeting, we conducted breakthrough measurements at a higher pressure of 9 bar.…”

Using Molecular Simulations for Elucidation of Thermodynamic Nonidealities in Adsorption of CO2-Containing Mixtures in NaX Zeolite

“…In current industrial practice, amine absorption technologies, which are energy intensive, are used for capture of CO 2 from a variety of gaseous mixtures. Potential reduction in the energy consumption is achievable using pressure swing adsorption (PSA) processes, 1 − 4 which are normally conducted in fixed-bed adsorbers. 4 − 7 A variety of microporous crystalline adsorbents such as zeolites and metal–organic frameworks (MOFs) can be employed in fixed-bed devices.…”

“…Potential reduction in the energy consumption is achievable using pressure swing adsorption (PSA) processes, 1 − 4 which are normally conducted in fixed-bed adsorbers. 4 − 7 A variety of microporous crystalline adsorbents such as zeolites and metal–organic frameworks (MOFs) can be employed in fixed-bed devices. 8 − 10 For postcombustion CO 2 capture, 13X zeolite is considered to be the benchmark adsorbent, with the ability to meet the U.S. Department of Energy (US-DOE) targets for CO 2 purity and recovery.…”