Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer–Emmett–Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro‐ and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already‐measured raw adsorption isotherms were provided to sixty‐one labs, who were asked to calculate the corresponding BET areas. This round‐robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called “BET surface identification” (BETSI), expands on the well‐known Rouquerol criteria and makes an unambiguous BET area assignment possible.

Recent advances in adsorptive gas separations have focused on the development of porous materials with high operating capacity and selectivity, useful parameters that provide early guidance during the development of new materials. Although this material-focused work is necessary to advance the state of the art in adsorption science and engineering, a substantial problem remains: how to integrate these materials into a fixed bed to efficiently utilize the separation. Structured sorbent contactors can help manage kinetic and engineering factors associated with the separation, including pressure drop, sorption enthalpy effects, and external heat integration (for temperature swing adsorption, or TSA). In this review, we discuss monoliths and fiber sorbents as the two main classes of structured sorbent contactors; recent developments in their manufacture; advantages and disadvantages of each structure relative to each other and to pellet packed beds; recent developments in system modeling; and finally, critical needs in this area of research.

Microencapsulated phase change materials (μPCM) are combined with the metal–organic framework (MOF) UiO-66 and a cellulose acetate fiber support to introduce thermal modulation into CO2 capture devices operating in subambient conditions. μPCM particles are incorporated into sorbent fibers during the fiber spin dope preparation step and are observed to withstand the spinning and subsequent solvent exchange steps with little to no loss of thermal modulating properties as determined by differential scanning calorimetry (DSC). The spinning of this novel sorbent-μPCM fiber sorbent is the first instance of single step spinning of sorbents with a thermal modulator. It was found that μPCM weight loading as high as 75 wt % was attainable while maintaining spinable fibers. Breakthrough adsorption experiments and subsequent temperature profile analysis were collected to compare CO2 breakthrough capacity and heat release for sorbent systems with and without phase change materials incorporated. In adsorption modules with a diameter of 0.455 cm, where heat dissipation through the module wall dominates the global thermal response of the system, modulated fibers showed a 20–25% increase in breakthrough capacity at short times (CO2 concentration C/C 0 = 0.05) as compared to their unmodulated counterparts. Higher breakthrough capacity indicates the phase change material would help manage the heat effects due to the local contact between the μPCM and the MOF. In larger diameter modules (0.7 cm) where wall heat dissipation effects are less dominant than the 0.455 cm diameter modules, fibers with “inactive” μPCM (i.e., 50 °C below their melting point) show larger sorption-induced thermal excursions and as much as 4× lower capacities at low adsorbate leakage as compared to fibers where the phase change material was active. Through the incorporation of phase change material, the sorbent in the system acts more efficiently, thus potentially driving down adsorption system cost.

Adsorption of CO 2 from post-combustion flue gas is one of the leading candidates for globally impactful carbon capture systems. This work focused on understanding the opportunities and limitations of sub-ambient CO 2 capture processes utilizing a multistage separation process. A hybrid process design using a combination of pressure-driven separation of CO 2 from flue gas (e.g., adsorption-or membrane-based separation) followed by CO 2 -rich product liquefaction to produce high-purity (>99%) CO 2 at pipeline conditions is considered. The operating pressure of the separation unit is a key cost parameter and also an important process variable that regulates the available heat removal necessary to reach the sub-ambient operating conditions. The economic viability of applying pressure swing adsorption (PSA) processes using fiber sorbent contactors with internal heat management was found to be most influenced by the productivity of the adsorption system, with productivities as high as 0.015 mol CO 2 /kg sorb À1 sec À1 being required to reduce costs of capture below $60/ ton CO 2 captured. This analysis was carried out using a simplified two-bed process, and thus there is opportunity for further cost reduction with exploration of more complex cycle designs. Three exemplar fiber sorbents (MIL-101(Cr), UiO-66, and zeolite 13X) were considered for application in the sub-ambient process of PSA unit.Among the considered sorbents, zeolite 13X fiber composites were found to perform better at ambient temperatures as compared to sub-ambient. MIL-101(Cr) and UiO-66 fiber composites had improved purity, recovery, and productivity at colder temperatures reducing costs of capture as low as $61/ton CO 2 . Future economic improvement could be achieved by reducing the required operating pressure of the PSA unit and pushing the Pareto frontier closer to the final pipeline requirement via a combination of PSA cycle design and material selection.

Membrane-based separations offer energy-efficient solutions for various applications, but commercial polymer membranes show limited performance and stability. Mixed-matrix membranes (MMMs), incorporating nanoporous inorganic materials in polymer matrices, have been of great interest to circumvent these polymer-specific issues. However, reaching the percolation threshold is crucial to leverage high-performing inorganic phases fully, yet the traditional sphere-like nanofillers require high loadings that easily result in agglomerations and non-selective defects. Here, a branch-shaped zeolitic imidazole framework-8 (ZIF-8) nanoparticle is synthesized where its unique morphology automatically interconnects, readily forming percolated networks within the polymer matrix at loadings as low as 20 wt.%. Because of the high surface-area-to-volume ratios of branched ZIF-8 (BZ), strong polymer-particle interactions suppress polymer chain dynamics and the rotation of the ZIF-8 ligand. This interphase confinement results in enhanced membrane stability and a smaller diffusion cut-off than traditional ZIF-8. With pre-connected diffusion pathways and confined ZIF pores, BZ MMMs significantly outperformed MMMs with sphere-like ZIF-8 for H 2 -based separations. Overall, the findings provide a novel approach to enhance filler effects in MMMs even at low loadings without any alignment, which can enable the development of advanced membranes in fields where percolation is desired, including separations, sensors, conductors, and batteries.

The synthesis and functionalization of porous organic cages (POCs) for separation have attracted growing interest over the past decade. However, the potential of solid-phase POCs for practical, large-scale separations will require incorporation into appropriate gas–solid or liquid–solid contactors. Contactors with more effective mass transfer properties and lower pressure drops than pelletized systems are preferred. Here, we prepared and characterized fiber sorbents with POCs throughout a cellulose acetate (CA) polymer matrix, which were then deployed in model separations. The POC CC3 was shown to be stable after exposure to spinning solvents, as confirmed by NMR, powder X-ray diffraction, and gas sorption experiments. CC3-CA fibers were spun using the dry-jet wet-quench spinning method. Spun fibers retained the adsorptive properties of CC3 powders, as confirmed by CO2 and N2 physisorption and TGA, reaching upward of 60 wt % adsorbent loading, whereas the pelletized CC3 counterparts suffered significant losses in textural properties. The separation capabilities of the CC3-CA fibers are tested with both simulated postcombustion flue gas and with Xe/Kr mixtures. Fixed bed breakthrough experiments performed on fibers samples show that CC3 embedded in polymeric fibers can effectively perform these proof-of-concept gas separations. The development of fiber sorbents embedded with POCs provides an alternative to traditional pelletization for the incorporation of these materials into adsorptive separation systems.

Effective thermal modulation and storage are important aspects of efforts to improve energy efficiency across all sectors. Phase change materials (PCMs) can act as effective heat reservoirs due to the high latent heat associated with the phase change process (typically a solid−liquid transition). PCMs have been developed and integrated into various platforms such as building materials, gas sorbents/separators, and consumer products. Polymer fibers offer distinct benefits over other structures since they can be solution-processed and produced at enormous scales. In this work, we fabricate polymer fibers that possess high loadings (up to 80 wt %) of microencapsulated PCMs (μPCMs) to provide sufficient heat storage capacity. We focus on the solution spinning of cellulose due to its eco-friendly characteristics, low cost, and superior mechanical stability. We incorporate μPCMs into polymer dopes (e.g., cellulose acetate, polyethersulfone, cellulose), and μPCM-polymer fibers are then spun via solution-spinning processes. The thermal response behaviors of μPCM-polymer fibers were analyzed using differential scanning calorimetry (DSC), and no damage to μPCMs during the fiber spinning was observed. Additionally, no degradation of the PCM was observed after several freeze/melt cycles. The loading amount of μPCMs in fibers can be obtained up to 80 wt %, and around 95% of thermal storage capacities are retained in the fiber after the fabrication process. Dynamic mechanical analysis (DMA) reveals that there is a trade-off between the mechanical stability of μPCM-polymer fibers and loading amount of μPCMs; thus, optimization of the μPCM loading is required to meet application-specific mechanical stability. We expect that our engineered μPCM-polymer fibers can be applied to a smart thermal energy storage material that enables effective heat management.

Porosity and surface area analysis play a prominent role in modern materials science, where 123 their determination spans the fields of natural sciences, engineering, geology and medical 124 research. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory,[1] which has been 125 a remarkably successful contribution to the field of materials science. The BET method was 126 developed in the 1930s and is now the most widely used metric for the estimation of surface 127 areas of porous materials.[2] Since the BET method was first developed, there has been an 128 explosion in the field of nanoporous materials with the discovery of synthetic zeolites,[3] 129 nanostructured silicas,[4–6] metal-organic frameworks (MOFs),[7] and others. Despite its 130 widespread use, the manual calculation of BET surface areas causes a significant spread in 131 reported areas, resulting in reproducibility problems in both academia and industry. To probe 132 this, we have brought together 60 labs with strong track records in the study of nanoporous 133 materials. We provided eighteen adsorption isotherms and asked these researchers to 134 calculate the corresponding BET areas, resulting in a wide range of values for each one. We 135 show here that the reproducibility of BET area determination from identical isotherms is a 136 largely ignored issue, raising critical concerns over the reliability of reported BET areas in 137 the literature. To solve this major issue, we have developed a new computational approach 138 to accurately and systematically determine the BET area of nanoporous materials. Our 139 software, called BET Surface Identification (BETSI), expands on the well-known Rouquerol 140 criteria and makes, for the first time, an unambiguous BET area assignment possible.