Computational Methods for MOF/Polymer Membranes

High-Throughput Screening of COF Membranes and COF/Polymer MMMs for Helium Separation and Hydrogen Purification

Hundreds of covalent organic frameworks (COFs) have been synthesized, and thousands of them have been computationally designed. However, it is impractical to experimentally test each material as a membrane for gas separations. In this work, we focused on the membrane-based gas separation performances of experimentally synthesized COFs and hypothetical COFs (hypoCOFs). Gas permeabilities of COFs were computed by combining the results of grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations, and many COF membranes were found to overcome the upper bound of polymeric membranes for He/H₂, N₂/CH₄, H₂/N₂, He/CH₄, H₂/CH₄, and He/N₂ separations. We then examined the structure-permeability relations of the COF membranes that are above the upper bound for each of the six gas separations, and based on these relations, we proposed an efficient approach for the selection of the best hypoCOFs from a very large database. Molecular simulations showed that 120 hypoCOFs that we identified to be promising based on these structure-performance relations exceed the upper bound for He/CH₄, He/N₂, H₂/CH₄, and H₂/N₂ separations. Both real and hypothetical COFs were then studied as fillers in 25 different polymers, leading to a total of 29 020 COF/polymer and hypoCOF/polymer mixed matrix membranes (MMMs), representing the largest number of COF-based MMMs investigated to date. Permeabilities and selectivities of COF/polymer MMMs were computed for six different gas separations, and results revealed that 18 of the 25 polymers can be carried above the upper bound when COFs were used as fillers. The comprehensive analysis of COFs provided in this work will fully unlock the potential of COF membranes and COF/polymer MMMs for helium separation and hydrogen purification.

Trends and Prospects in UiO-66 Metal-Organic Framework for CO2 Capture, Separation, and Conversion

Among thousands of known metal-organic frameworks (MOFs), the University of Oslo's MOF (UiO-66) exhibits unique structure topology, chemical and thermal stability, and intriguing tunable properties, that have gained incredible research interest. This paper summarizes the structural advancement of UiO-66 and its role in CO₂ capture, separation, and transformation into chemicals. The first part of the review summarizes the fast-growing literature related to the CO₂ capture reported by UiO-66 during the past ten years. The second part provides an overview of various advancements in UiO-66 membranes in CO₂ purification. The third part describes the role of UiO-66 and its composites as catalysts for CO₂ conversion into useful products. Despite many achievements, significant challenges associated with UiO-66 are addressed, and future perspectives are comprehensively presented to forecast how UiO-66 might be used further for CO₂ management.

Exploring the Potential Application of Matrimid® and ZIFs-Based Membranes for Hydrogen Recovery: A Review

Hydrogen recovery is at the center of the energy transition guidelines promoted by governments, owing to its applicability as an energy resource, but calls for energetically nonintensive recovery methods. The employment of polymeric membranes in selective gas separations has arisen as a potential alternative, as its established commercial availability demonstrates. However, enhanced features need to be developed to achieve adequate mechanical properties and the membrane performance that allows the obtention of hydrogen with the required industrial purity. Matrimid^®, as a polyimide, is an attractive material providing relatively good performance to selectively recover hydrogen. As a consequence, this review aims to study and summarize the main results, mechanisms involved and advances in the use of Matrimid^® as a selective material for hydrogen separation to date, delving into membrane fabrication procedures that increase the effectiveness of hydrogen recovery, i.e., the addition of fillers (within which ZIFs have acquired extraordinary importance), chemical crosslinking or polymeric blending, among others.

A Review on Computational Modeling Tools for MOF-Based Mixed Matrix Membranes

Computational modeling of membrane materials is a rapidly growing field to investigate the properties of membrane materials beyond the limits of experimental techniques and to complement the experimental membrane studies by providing insights at the atomic-level. In this study, we first reviewed the fundamental approaches employed to describe the gas permeability/selectivity trade-off of polymer membranes and then addressed the great promise of mixed matrix membranes (MMMs) to overcome this trade-off. We then reviewed the current approaches for predicting the gas permeation through MMMs and specifically focused on MMMs composed of metal organic frameworks (MOFs). Computational tools such as atomically-detailed molecular simulations that can predict the gas separation performances of MOF-based MMMs prior to experimental investigation have been reviewed and the new computational methods that can provide information about the compatibility between the MOF and the polymer of the MMM have been discussed. We finally addressed the opportunities and challenges of using computational studies to analyze the barriers that must be overcome to advance the application of MOF-based membranes.

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

Several thousands of metal organic frameworks (MOFs) have been reported to date, but the information on H₂/N₂ separation performances of MOF membranes is currently very limited in the literature. We report the first large-scale computational screening study that combines state-of-the-art molecular simulations, grand canonical Monte Carlo (GCMC) and molecular dynamics (MD), to predict H₂ permeability and H₂/N₂ selectivity of 3765 different types of MOF membranes. Results showed that MOF membranes offer very high H₂ permeabilities, 2.5 × 10³ to 1.7 × 10⁶ Barrer, and moderate H₂/N₂ membrane selectivities up to 7. The top 20 MOF membranes that exceed the polymeric membranes' upper bound for H₂/N₂ separation were identified based on the results of initial screening performed at infinite dilution condition. Molecular simulations were then carried out considering binary H₂/N₂ and quaternary H₂/N₂/CO₂/CO mixtures to evaluate the separation performance of MOF membranes under industrial operating conditions. Lower H₂ permeabilities and higher N₂ permeabilities were obtained at binary mixture conditions compared to the ones obtained at infinite dilution due to the absence of multicomponent mixture effects in the latter. Structure-performance relations of MOFs were also explored to provide molecular-level insights into the development of new MOF membranes that can offer both high H₂ permeability and high H₂/N₂ selectivity. Results showed that the most promising MOF membranes generally have large pore sizes (>6 Å) as well as high surface areas (>3500 m²/g) and high pore volumes (>1 cm³/g). We finally examined H₂/N₂ separation potentials of the mixed matrix membranes (MMMs) in which the best MOF materials identified from our high-throughput screening were used as fillers in various polymers. Results showed that incorporation of MOFs into polymers almost doubles H₂ permeabilities and slightly enhances H₂/N₂ selectivities of polymer membranes, which can advance the current membrane technology for efficient H₂ purification.

Modeling Permeation through Mixed-Matrix Membranes: A Review

Over the past three decades, mixed-matrix membranes (MMMs), comprising an inorganic filler phase embedded in a polymer matrix, have emerged as a promising alternative to overcome limitations of conventional polymer and inorganic membranes. However, while much effort has been devoted to MMMs in practice, their modeling is largely based on early theories for transport in composites. These theories consider uniform transport properties and driving force, and thus models for the permeability in MMMs often perform unsatisfactorily when compared to experimental permeation data. In this work, we review existing theories for permeation in MMMs and discuss their fundamental assumptions and limitations with the aim of providing future directions permitting new models to consider realistic MMM operating conditions. Furthermore, we compare predictions of popular permeation models against available experimental and simulation-based permeation data, and discuss the suitability of these models for predicting MMM permeability under typical operating conditions.

Engineered Transport in Microporous Materials and Membranes for Clean Energy Technologies

Many forward-looking clean-energy technologies hinge on the development of scalable and efficient membrane-based separations. Ongoing investment in the basic research of microporous materials is beginning to pay dividends in membrane technology maturation. Specifically, improvements in membrane selectivity, permeability, and durability are being leveraged for more efficient carbon capture, desalination, and energy storage, and the market adoption of membranes in those areas appears to be on the horizon. Herein, an overview of the microporous materials chemistry driving advanced membrane development, the clean-energy separations employing them, and the theoretical underpinnings tying membrane performance to membrane structure across multiple length scales is provided. The interplay of pore architecture and chemistry for a given set of analytes emerges as a critical design consideration dictating mass transport outcomes. Opportunities and outstanding challenges in the field are also discussed, including high-flux 2D molecular-sieving membranes, phase-change adsorbents as performance-enhancing components in composite membranes, and the need for quantitative metrologies for understanding mass transport in heterophasic materials and in micropores with unusual chemical interactions with analytes of interest.