Shaping of gallate-based metal-organic frameworks for adsorption separation of ethylene from acetylene and ethane

Hierarchically porous MOF@COF structures with ultrafast gas diffusion rate for C2H6/C2H4 separation

For ethylene purification, C2H6-selective metal-organic frameworks (MOFs) show great potential to directly produce polymer-grade C2H4 from C2H6/C2H4 mixtures. Most C2H6-traping MOFs are ultra-microporous structures so as to strengthen multiple supramolecular interactions with C2H6. However, the narrowed pore channels of C2H6-traping MOFs cause large guest diffusion barriers, greatly hampering their practical applications. Herein, we present a feasible strategy by precisely constructing hierarchically porous MOF@COF core-shell structures to address this issue. Additional mesoporous diffusion channels were incorporated between MOF crystals through the construction of the COF shell, thereby enhancing the gas adsorption kinetics. Notably, designing a core-shell MOF@COF structure with an optimal coating amount of mesoporous COF shell will further improve the gas diffusion rate. Breakthrough experiments reveal that the tailored MOF@COF composites can effectively achieve C2H6/C2H4 separation and maintain its separation performance over five continuous measurement cycles. This investigation opens up a new avenue to solve the diffusion/transfer issues and provides more opportunities and potentials for MOF@COF composites in practical separation applications.

Pore chemistry and geometry control in a metal azolate framework for one-step ethylene purification from quinary gas mixture

In the petrochemical industry, obtaining polymer-grade ethylene from complex light-hydrocarbon mixtures by one-step separation is important and challenging. Here, we successfully prepared the Metal-Azolate Framework 7 (MAF-7) with pore chemistry and geometry control to realize the one-step separation of ethylene from cracking gas with up to quinary gas mixtures (propane/propylene/ethane/ethylene/acetylene). Based on the tailor-made pore environment, MAF-7 exhibited better selective adsorption of propane, propylene, ethane and acetylene than ethylene, and the adsorption ratios of ethane/ethylene and propylene/ethylene are as high as 1.49 and 2.81, respectively. The pore geometry design of MAF-7 leads to the unique weak binding affinity and adsorption site for ethylene molecules, which is clearly proved by Grand Canonical Monte Carlo theoretical calculations. The breakthrough experiments show that ethylene can be directly obtained from binary, ternary, and quinary gas mixtures. These comprehensive properties show that MAF-7 is expected to achieve one-step purification of ethylene in complex light hydrocarbon mixtures.

Binding Materials for MOF Monolith Shaping Processes: A Review towards Real Life Application

Metal–organic frameworks (MOFs) could be utilized for a wide range of applications such as sorption, catalysis, chromatography, energy storage, sensors, drug delivery, and nonlinear optics. However, to date, there are very few examples of MOFs exploited on a commercial scale. Nevertheless, progress in MOF-related research is currently paving the way to new industrial opportunities, fostering applications and processes interconnecting fundamental chemistry with engineering and relevant sectors. Yet, the fabrication of porous MOF materials within resistant structures is a key challenge impeding their wide commercial use for processes such as adsorptive separation. In fact, the integration of nano-scale MOF crystallic structures into bulk components that can maintain the desired characteristics, i.e., size, shape, and mechanical stability, is a prerequisite for their wide practical use in many applications. At the same time, it requires sophisticated shaping techniques that can structure nano/micro-crystalline fine powders of MOFs into diverse types of macroscopic bodies such as monoliths. Under this framework, this review aims to bridge the gap between research advances and industrial necessities for fostering MOF applications into real life. Therefore, it critically explores recent advances in the shaping and production of MOF macro structures with regard to the binding materials that have received little attention to date, but have the potential to give new perspectives in the industrial applicability of MOFs. Moreover, it proposes future paths that can be adopted from both academy and industry and can further boost MOF exploitation.

Deep Desulfurization with Record SO2 Adsorption on the Metal-Organic Frameworks

Selective elimination of sulfur dioxide is significant in flue gas desulfurization and natural gas purification, yet developing adsorbents with high capture capacity especially at low partial pressure as well as excellent cycling stability remains a challenge. Herein, a family of isostructural gallate-based MOFs with abundant hydrogen bond donors decorating the pore channel was reported for selective recognition and dense packing of sulfur dioxide via multiple hydrogen bonding interactions. Multiple O···H-O hydrogen bonds and O···H-C hydrogen bonds guarantee SO₂ molecules are firmly grasped within the framework, and appropriate pore apertures afford dense packing of SO₂ with high uptake and density up to 1.86 g cm^-3, which is evidenced by dispersion-corrected density functional theory calculations and X-ray diffraction resolution of a SO₂-loaded single crystal. Ultrahigh adsorption uptake of SO₂ at extremely low pressure (0.002 bar) was achieved on Co-gallate (6.13 mmol cm^-3), outperforming all reported state-of-the-art MOFs. Record-high IAST selectivity of SO₂/CO₂ (325 for Mg-gallate) and ultrahigh selectivity of SO₂/N₂ (>1.0 × 10⁴) and SO₂/CH₄ (>1.0 × 10⁴) were also realized. Breakthrough experiments further demonstrate the excellent removal performance of trace amounts of SO₂ in a deep desulfurization process. More importantly, M-gallate shows almost unchanged breakthrough performance after five cycles, indicating the robust cycling stability of these MOFs.

Efficient Purification of Ethylene from C2 Hydrocarbons with an C2H6/C2H2-Selective Metal-Organic Framework

The separation of ethylene (C₂H₄) from C₂ hydrocarbons is considered as one of the most difficult and important processes in the petrochemical industry. Heat-driven cryogenic distillation is still widely used in the C₂ hydrocarbons separation realms, which is an energy intensive process and takes up immense space. In response to a greener, more energy-efficient sustainable development, we successfully synthesized a multifunction microporous Mg-based MOF [Mg₂(TCPE)(μ₂-OH₂)(DMA)₂]·solvents (NUM-9) with C₂H₆/C₂H₂ selectivity based on a physical adsorption mechanism, and with outstanding stability; especially, it is stable up to 500 °C under an air atmosphere. NUM-9a (activated NUM-9) shows good performances in the separation of C₂H₆/C₂H₂ from raw ethylene gases. In addition, its actual separation potential is also examined by IAST and dynamic column breakthrough experiments. GCMC calculation results indicate that the unique structure of NUM-9a is primarily conducive to the selective adsorption of C₂H₆ and C₂H₂. More importantly, compared with C₂H₄, NUM-9a prefers to selectively adsorb C₂H₆ and C₂H₂ simultaneously, which makes NUM-9a as a sorbent have the capacity to separate C₂H₄ from C₂ hydrocarbon mixtures under mild conditions through a greener and energy-efficient separation strategy.