High CO2 Selectivity of A Microporous Metal–Imidazolate Framework: A Molecular Simulation Study

Unusually large microporous HKUST-1 via polyethylene glycol-templated synthesis: enhanced CO2 uptake with high selectivity over CH4 and N2

Porous solids with highly microporous structures for effective carbon dioxide uptake and separation from mixed gases are highly desirable. Here we present the use of polyethylene glycol (20,000 g/mol) as a soft template for the simple and rapid synthesis of a highly microporous Cu-BTC (denoted as HKUST-1). The polyethylene glycol-templated HKUST-1 obtained at room temperature in 10 min exhibited a very high Brunauer-Emmett-Teller (BET) surface area of 1904 m2/g, pore volume of 0.87 cm3/g, and average micropore size of 0.84 nm. However, conventional HKUST-1 exhibits a BET surface area of 700-1700 m2/g confirming the advantages of using this method. X-ray powder diffraction and electron microscopy analysis confirm the formation of highly crystalline and uniform octahedral particles with sizes ranging from 100 nm to 120 µm. Adsorption isotherms recorded at temperatures between 273 and 353 K and pressures up to 40 bar revealed a more favorable adsorption capacity of HKUST-1 for CO2 vs. CH4 and N2 (708 mg (CO2)/g, 214 mg (CH4)/g and 177 mg (N2)/g at 298 K and 40 bar). The Langmuir, isotherm model, and isosteric heats of adsorption were evaluated. The CO2 interaction at PEG-templated HKUST-1 is physical, exothermic, and spontaneous with DH° =  - 6.52 kJ/mol, DS° =  - 13.72 J/mol, and DG° =  - 2.43 kJ/mol at 298 K at 40 bar. The selectivities in equimolar mixtures were determined as 53 and 24, respectively, for CO2 over N2 and CH4. CO2 adsorption-desorption tests reveal high adsorbent reusability. The cost-effective and quickly prepared PEG-templated HKUST-1 demonstrates high efficacy as a gas adsorbent, particularly in selectively capturing CO2.

Highly CO2 Selective Microporous Metal-Imidazolate Framework-Based Mixed Matrix Membranes

Microporous metal-imidazolate framework (MMIF), a highly CO₂ selective MOF, was incoporated into a polymeric membrane for separation of CO₂ from CH₄ and N₂ for the first time. MMIF nanoparticles of 50-200 nm were synthesized using the sonication method and dispersed into Matrimid, a commercial polyimide, with MOF loading of 10% and 20% by weight to fabricate mixed matrix membranes (MMMs). Morphology, thermal behavior, and glass transition temperature of the membranes were characterized, and single and mixed gas permeation measurements at 35 °C and 4 bar feed pressure were carried out to reveal their separation performance. Both 10% and 20% MMIF containing Matrimid membranes exhibited enhanced gas permeabilities for all three gases. Contrary to expectations, ideal selectivity of membranes was not improved possibly due to the flexible framework of MMIF. On the other hand, mixed gas permeability measurements showed significant improvement in CO₂/CH₄ separation factor by 130% and CO₂/N₂ separation factor by 79% due to competitive adsorption favoring CO₂.

CO2 Capture and Separations Using MOFs: Computational and Experimental Studies

This Review focuses on research oriented toward elucidation of the various aspects that determine adsorption of CO₂ in metal-organic frameworks and its separation from gas mixtures found in industrial processes. It includes theoretical, experimental, and combined approaches able to characterize the materials, investigate the adsorption/desorption/reaction properties of the adsorbates inside such environments, screen and design new materials, and analyze additional factors such as material regenerability, stability, effects of impurities, and cost among several factors that influence the effectiveness of the separations. CO₂ adsorption, separations, and membranes are reviewed followed by an analysis of the effects of stability, impurities, and process operation conditions on practical applications.