Adsorption- and Membrane-Based CH₄/N₂ Separation Performances of MOFs

Abstract

Metal organic frameworks (MOFs) have been widely studied as adsorbents and membranes for gas separation applications. Considering the large number of available MOFs, it is not possible to fabricate and test the gas separation performance of every single MOF using purely experimental methods. In this study, we used molecular simulations to assess both adsorption-based and membrane-based CH4/N2 separation performances of 102 different MOFs. This is the largest number of MOF adsorbents and membranes studied to date for separation of CH4/N2 mixtures. Several adsorbent evaluation metrics such as adsorption selectivity, working capacity, and regenerability were predicted, and the top performing adsorbents were identified. Several MOFs were predicted to exhibit higher adsorption selectivities than the traditional adsorbents such as zeolites and activated carbons. Relation between adsorption-based separation performances of MOFs and their structural properties were also investigated. Results showed that MOFs having the largest cavity diameters in the range of 4.6–5.4 Å, pore limiting diameters in the range of 2.4–3.7 Å, surface areas less than 2000 m2/g, and porosities less than 0.5 are promising adsorbents for CH4/N2 separations. We then combined adsorption and diffusion data obtained from molecular simulations and predicted both membrane selectivities and gas permeabilities of MOFs for separation of CH4/N2 mixtures. A significant number of MOF membranes were identified to be CH4 selective in contrast to the traditional membrane materials which are generally N2 selective. Several MOFs exceeded the upper bound established for the polymeric membranes, and many MOFs exhibited higher gas permeabilities than zeolites. The results of this study will be useful to guide the experiments to the most promising MOF adsorbents and membranes for efficient separation of CH4/N2 mixtures.

Large-Scale Computational Screening of Metal Organic Framework (MOF) Membranes and MOF-Based Polymer Membranes for H2/N2 Separations

“…In our previous studies, 29,60 we validated the accuracy of our computational approach by comparing the experimentally reported single-component H 2 and N 2 permeabilities of various types of MOF membranes with the predictions of molecular simulations. In this work, we additionally compared results of our molecular simulations for H 2 /N 2 mixture permeances of several MOF membranes with the available experimental data under the same conditions.…”

Gas permeation through single-crystal ZIF-8 membranes

“…These light gases constitute industrially relevant separations. Carbon dioxide and nitrogen are the main impurities in natural gas [47], which is also an important source of the increasingly demanded helium [26,48]. Separating CO2 from N2, the largest component of flue gas, is essential to curbing CO2 emission [49].…”

Metal Organic Framework Based Polymer Mixed Matrix Membranes: Review on Applications in Water Purification

“…These unique properties include adjustable pore size, internal surface areas, enormous porosity [43], regularity, rigidity/flexibility, and versatile structures [44]. These exceptional and unique properties attracted the interest for MOFs utilization in applications such as high capacity adsorbents [45,46,47,48,49], organic contaminants removal [50,51], environmental protection [52], heavy metals removal [53,54,55], H 2 storage [56,57,58,59,60] and purification [61], CO 2 adsorption [62,63] and capture [64,65,66,67,68,69,70], drug delivery [71,72,73,74,75,76,77,78], gas/liquid separation [79,80,81,82], membrane fuel cell [83], organic solvent nanofiltration [84,85,86,87] and storage media [88,89,90,91].…”