Metal–Organic Frameworks Polyurethane Composite Foams for the Capture of Volatile Organic Compounds

Composites of metal–organic frameworks (MOFs) in polyurethane foams (PUF) are reported to adsorb polar or apolar volatile organic compounds (VOCs), avoiding the problems usually found when handling MOFs in the powder form. MOF/PUF composites were prepared using MIL-160(Al) and UiO-66(Zr)-(CF3)2 via one step process where the MOFs particles are incorporated during the foam matrix formation. Under adjusted conditions, the composite materials maintained the shape and characteristics of the MOF material, good mechanical stability, and good accessibility to the pores without significantly compromising the VOCs adsorption capacity for hexane, acetone, methanol, toluene, and acetic acid. This methodology proved the possibility of incorporating high amounts of shaped MOF particles, reaching 200% (w/w) of foam, upon maintaining a considerable open-cell volume percentage (32%). As an application perspective, we demonstrate that the composites can overcome the challenge of acetic acid capture in the presence of ambient moisture with a similar performance to the pure MOF. Thus, VOCs capture through MOF/polyurethane foam composites is a promising environmental technology to eliminate air pollutants

Separation of CO₂/N₂ onto Shaped MOF MIL-160(Al) Using the Pressure Swing Adsorption Process for Post-combustion Application

Adsorption processes have already been considered as an appealing technology for carbon capture and climate change mitigation. Accordingly, this work investigated the capacity of shaped MIL-160(Al) as a water stable bioderived Al dicarboxylate microporous metal–organic framework for separation of carbon dioxide and nitrogen concerning postcombustion application. First, breakthrough experiments of carbon dioxide and nitrogen were accomplished at 313 K and 4.0 bar. Then, a set of equations/relations were considered to model the dynamic fixed-bed tests, in which the outcomes proved the capacity of the developed model for such a purpose. Next, a pressure swing adsorption (PSA) process with five steps, including pressurization, feed, rinse, blowdown, and purge, was planned and validated using performed experiments in a laboratory-scale PSA setup. In the end, an industrial PSA process was designed to attain a better grasp of the capacity of MIL-160(Al) for postcombustion application. The results indicated an exciting potential of this adsorbent for postcombustion carbon capture, with the purity and recovery of carbon dioxide around 67.3 and 99.1%, respectively

Impact of the Flexible Character of MIL-88 Iron(III) Dicarboxylates on the Adsorption of <i>n</i>‑Alkanes

Adsorption of <i>n</i>-alkane vapors was performed to probe the unusual highly flexible character of a series of iron­(III) dicarboxylate materials of the MIL-88 structure type. In agreement with the presence of strong intraframework interactions within the dried closed pores form of MIL-88, it appears first that an increase of the size and aromaticity of the spacer makes it more difficult to adsorb alkanes at room temperature. Thus, this led to a high level of adsorption in the iron fumarate MIL-88A and poor levels in the terephthalate and naphthalenedicarboxylate based MIL-88­(B and C, respectively). Second, upon increase in the length of the alkane, diffusion limitations of the guest occur within the very narrow pores, also illustrated through kinetics of adsorption measurements, which result in an overall decrease in the adsorption capacity. Noteworthy, the swelling of the flexible non modified MIL-88 solids occurs only for the MIL-88A sample, because of the number and orientation of aromatic rings that are arranged in trimers within the MIL-88 structures and, therefore, making those more difficult to open than those where the rings are arranged in dimers such as the metal terephthalate MIL-53 structures. Interestingly, modification of the organic linkers by grafting several bulky functional groups (2CF₃, 4CH₃) makes the adsorption of <i>n-</i>alkanes easier because of a strong decrease in interactions within these trimers associated with a lower pore contraction upon drying, while the substitution of a hydrogen atom by a bromine one on the spacer proved to be not sufficient for an improvement of the adsorbed amounts