Aminosilane-Grafted Zirconia-Titiania-Silica Nanoparticles/Torlon Hollow Fiber Composites for CO2 Capture

Metal- and solvent-free synthesis of aminoalcohols under continuous flow conditions

Multifunctional organocatalysts were immobilized on porous hollow fiber polymer and used as intelligent and cooperative heterogeneous catalysts and continuous flow reactor for sustainable chemical transformation.

On the Morphological Characterization Procedures of Multilayer Hydrophobic Ceramic Membranes for Membrane Distillation Operations

The paper introduces some aspects of the characterization of hydrophobized multilayer ceramic membranes intended for use in membrane distillation (MD) operations. Four-layer hydrophobic carbon-based titania membranes, manufactured by the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS, Hermsdorf, Germany), were tested according to the gas permeation technique. Gas permeance data were elaborated following the premises of the dusty gas model, to calculate the average pore size and the porosity-tortuosity ratio of each layer. Membrane testing was the opportunity to discuss which characterization method is more appropriate to obtain the membrane parameters necessary for the simulation of membranes in MD processes. In the case of multilayer membranes, the calculation of the morphological parameters should be performed for each layer. The “layer-by-layer gas permeation” method, previously introduced by other authors and completed in this work, is more appropriate for obtaining representative parameters of the membrane. Conversely, the calculation of morphological parameters, averaged over the entire membrane, might lead to heavy underestimations of the total membrane resistance and then to a heavy error on the transmembrane flux simulation.

Ultrahigh Metal-Organic Framework Loading and Flexible Nanofibrous Membranes for Efficient CO2 Capture with Long-Term, Ultrastable Recyclability

In the global transition to a sustainable low-carbon economy, CO₂ capture and storage technology plays a key role in reducing emissions. Metal-organic frameworks (MOFs) are crystalline materials with ultrahigh porosity, tunable pore size, and rich functionalities, holding the promise for CO₂ capture. However, the intrinsic fragility and depressed processability of MOF crystals make the fabrication of the flexible MOF nanofibrous membrane (NFM) rather challenging. Herein, we demonstrate an effective strategy for the versatile preparation of self-supported and flexible HKUST-1 NFM with ultrahigh HKUST-1 loading (up to 82 wt %) and stable and uniform HKUST-1 growth through the combination of electrospinning, multistep seeded growth, and activation process. The loading rate of MOF is the highest level among the reported analogues. Significantly, the HKUST-1 NFM exhibits a prominent CO₂ adsorption capacity of 3.9 mmol g^-1, good CO₂/N₂ selectivity, and remarkable recyclability. The CO₂ capacity retains ∼95% (3.7 mmol g^-1) of the initial value after 100 adsorption-desorption cycles, indicating that the HKUST-1 NFM has long-term and ultrastable recyclability and a significant practical value. Thus, the low-cost and scalable production pathway is able to convert MOF particles into self-supported and flexible NFMs, and thereby, they are better applied to the efficient postcombustion CO₂ capture.

Novel Zeolite-5A@MOF-74 Composite Adsorbents with Core-Shell Structure for H2 Purification

Hydrogen is considered as one of the most important clean and renewable energy sources for a sustainable energy future. However, its efficient and cost-effective purification still remains challenging. In this work, we report the development of novel zeolite@metal-organic framework (MOF) composites comprised of MOF-74 and zeolite-5A with core-shell structure for efficient purification of H₂. The composites were synthesized hydrothermally through the addition of zeolite particles with and without carboxyl functional groups to the MOF synthesis solution. The zeolite/MOF weight ratio was varied systematically to find the optimum composition based on the adsorption performance. The formation of zeolite@MOF composites was confirmed by various characterization techniques. Single-component adsorption isotherms of CO₂, CO, CH₄, N₂, and H₂ over composites were measured at 25 °C to determine their equilibrium adsorption capacity. It was found that the zeolite-5A@MOF-74 with weight ratio of 5:95 exhibited a similar morphology to that of pristine MOF-74, but with higher surface area and total pore volume. Moreover, this composite showed 20-30% increase in CO₂, CO, CH₄, and N₂ uptake than the bare MOF, which could be attributed to the formation of new mesopores at the MOF-zeolite interface. The estimated selectivity values for CO₂/H₂, CO/H₂, CH₄/H₂, and N₂/H₂ were higher than those of the zeolite and/or MOF. Our results also indicated that surface modification of zeolite prior to composite formation does not enhance the adsorption capacities of the composites. Overall, the findings of this study suggest that the zeolite-5A@MOF-74 composites with core-shell structure are promising candidates for industrial H₂ purification processes.

Critical Comparison of Structured Contactors for Adsorption-Based Gas Separations

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.

Engineering Porous Polymer Hollow Fiber Microfluidic Reactors for Sustainable C-H Functionalization

Highly hydrophilic and solvent-stable porous polyamide-imide (PAI) hollow fibers were created by cross-linking of bare PAI hollow fibers with 3-aminopropyl trimethoxysilane (APS). The APS-grafted PAI hollow fibers were then functionalized with salicylic aldehyde for binding catalytically active Pd(II) ions through a covalent postmodification method. The catalytic activity of the composite hollow fiber microfluidic reactors (Pd(II) immobilized APS-grafted PAI hollow fibers) was tested via heterogeneous Heck coupling reaction of aryl halides under both batch and continuous-flow reactions in polar aprotic solvents at high temperature (120 °C) and low operating pressure. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) analyses of the starting and recycled composite hollow fibers indicated that the fibers contain very similar loadings of Pd(II), implying no degree of catalyst leaching from the hollow fibers during reaction. The composite hollow fiber microfluidic reactors showed long-term stability and strong control over the leaching of Pd species.

Formulation of Aminosilica Adsorbents into 3D-Printed Monoliths and Evaluation of Their CO2 Capture Performance

Amine-based materials have represented themselves as a promising class of CO₂ adsorbents; however, their large-scale implementation requires their formulation into suitable structures. In this study, we report formulation of aminosilica adsorbents into monolithic structures through a three-dimensional (3D) printing technique. In particular, 3D-printed monoliths were fabricated using presynthesized silica-supported tetraethylenepentamine (TEPA) and poly(ethylenimine) (PEI) adsorbents using three different approaches. In addition, a 3D-printed bare silica monolith was prepared and post-functionalized with 3-aminopropyltrimethoxysilane (APS). Characterization of the obtained monoliths indicated that aminosilica materials retained their characteristics after being extruded into 3D-printed configurations. Adsorptive performance of amine-based structured adsorbents was also investigated in CO₂ capture. Our results indicated that aminosilica materials retain their structural, physical, and chemical properties in the monoliths. In addition, the aminosilica monoliths exhibited adsorptive characteristics comparable to their corresponding powders. This work highlights the importance of adsorbent materials formulations into practical contactors such as monoliths, as the scalabale technology platform, that could facilitate rapid deployment of adsorption-based CO₂ capture processes on commercial scales.

3D-Printed Zeolite Monoliths for CO2 Removal from Enclosed Environments

Structured adsorbents, especially in the form of monolithic contactors, offer an excellent gas-solid contacting strategy for the development of practical and scalable CO₂ capture technologies. In this study, the fabrication of three-dimensional (3D)-printed 13X and 5A zeolite monoliths with novel structures and their use in CO₂ removal from air are reported. The physical and structural properties of these printed monoliths are evaluated and compared with their powder counterparts. Our results indicate that 3D-printed monoliths with zeolite loadings as high as 90 wt % exhibit adsorption uptake that is comparable to that of powder sorbents. The adsorption capacities of 5A and 13X monoliths were found to be 1.59 and 1.60 mmol/g, respectively, using 5000 ppm (0.5%) CO₂ in nitrogen at room temperature. The dynamic CO₂/N₂ breakthrough experiments show relatively fast dynamics for monolithic structures. In addition, the printed zeolite monoliths show reasonably good mechanical stability that can eventually prevent attrition and dusting issues commonly encountered in traditional pellets and beads packing systems. The 3D printing technique offers an alternative, cost-effective, and facile approach to fabricate structured adsorbents with tunable structural, chemical, and mechanical properties for use in gas separation processes.