Influence of Pore Size on Hydrocarbon Transport in Isostructural Metal–Organic Framework Crystallites

Abstract

Hydrocarbon separations using porous materials such as metal–organic frameworks (MOFs) have been proposed to reduce the energy demands associated with current distillation-based methods. Despite the potential of these materials to distinguish hydrocarbons through thermodynamic or kinetic mechanisms, experimental data quantifying hydrocarbon transport in MOFs is lacking. Such mass transfer measurements are vital to elucidate structure–property relationships and design future high-performing separation materials. In this work, we aim to isolate the influence of pore size on hydrocarbon diffusion by studying a pair of isoreticular MOFs, Co2Cl2BBTA and Co2Cl2BTDD. We use a volumetric method to extract mass transport coefficients for six hydrocarbon probe molecules of varying size and chemical functionality. From these nonequilibrium mass transport measurements, we determine the rate-limiting diffusion mechanism and identify trends in hydrocarbon surface permeabilities in the MOFs based on pore size, hydrocarbon chain length, and temperature.

A Copper-Based Metal–Organic Framework for Selective Separation of C2 Hydrocarbons from Methane at Ambient Conditions: Experiment and Simulation

“…Though the BE values are higher for linker a than for the other linkers, the experimental C2 hydrocarbon uptake is lower for UNT-14a than that of the MOFs obtained from the corresponding linkers, UTSA-60 for linker c and ZJU-30 for linker b . We assume that this low uptake is due to the presence of larger pores in UNT-14a compared to UTSA-60 and ZJU-30 that have smaller micropores . Also, the experimental C 2 H 6 uptake is higher than that of C 2 H 4 and C 2 H 2 both at 273 and 298 K. We speculate that this finding is due to the larger kinetic diameter of the C 2 H 6 molecule (C 2 H 6 : 4.443 Å; C 2 H 4 : 4.163 Å; C 2 H 2 : 3.300 Å) as well as the stronger “agostic” interaction of the C–H bonds of the C 2 H 6 molecule with the unsaturated metal sites. − The highest uptake and Q st for ethane among C2 hydrocarbons are also desirable technologically, given the higher concentration of ethane than that of ethylene or acetylene in natural gas .…”

Isoreticular Contraction of Cage-like Metal–Organic Frameworks with Optimized Pore Space for Enhanced C2H2/CO2 and C2H2/C2H4 Separations

“…In light of the tunable pore size/shape/volume, − and functionable pore surface, − metal–organic frameworks (MOFs), emerging as a new class of porous solid materials, have attracted a lot of attention in the field of gas adsorption and separation. − The pore system involving pore size/shape/volume and pore space environment can be precisely regulated by substituting the organic linkers with the same symmetry or the inorganic metal nodes based on the isostructural principle and building block strategy, − which in turn endows MOFs with enormous potentials for selective gas separation via the integration of pore size/shape matching and preferential binding interactions toward specific gas molecules. − So far, tremendous endeavors have been devoted to improving the enrichment and separation performance for specific gas molecules, in which the construction of cage-like mixed-ligands MOFs without open metal sites (OMSs), featuring small pore window size, functional pore space, and appropriate pore volume, has represented one of the most effective approaches. − For instance, the pore-space-partition-based MOFs (PSP-MOFs), with cage-like cavities, have shown high performance for gas adsorption and separation, ,− attributed to the relocation of the pore system, stemming from the introduction of the second spacers, involving compartmentalized small pore, functionalized pore space, and reserved appropriate pore volume. The segmented small pore size and functionalized pore surface impart enhanced gas separation through providing dramatically increased adsorbent–adsorbate binding sites toward specific gas molecules, while the preserved appropriate pore volume bestows PSP-MOFs with high gas adsorption performance, thereby making the PSP-MOFs a prominent scaffold for gas adsorption and separation, including C 2 H 2 and CO 2 capture, , C 2 H 2 /CO 2 , − C 2 H 2 /C 2 H 4 /C 2 H 6 , and C 3 H 6 /C 3 H 8 separation. ,, Additionally, the cage-like MOFs without OMSs usually exhibit relatively low adsorption enthalpy compared with the MOFs with O...…”

Extraordinary Separation of Acetylene-Containing Mixtures in a Honeycomb Calcium-Based MOF with Multiple Active Sites

“…Current separation technologies mainly rely on low-temperature distillation and organic solvent extraction, which are unfavorable to the environment and consume a lot of energy, accompanied by potential safety risks. 9,10 In contrast, the implementation of adsorbent-based separation technology has been considered as a promising method to overcome these drawbacks associated with chemical separation. 11−13 The emerging metal−organic frameworks (MOFs) based on physical adsorption are promising sorbents for gas separation because of their potent predictability and tunability on pore shape/size and functionality.…”

“…Acetylene, (C 2 H 2 ), the simplest unsaturated hydrocarbon, is not only widely applied in metal welding or cutting but also extensively used as a petrochemical raw material to manufacture versatile chemical products. − However, during the process of C 2 H 2 manufacturing via natural gas combustion or hydrocarbon steam cracking, the limitation of production technology leads to inevitable mixing of CO 2 or other C 1 /C 2 light hydrocarbons that need to be removed for C 2 H 2 purification. − In addition, C 2 H 2 also coexists as a trace pollutant in the production process of ethylene (C 2 H 4 ), and this part of C 2 H 2 impurity can poison the catalyst in the C 2 H 4 polymerization process and reduce the quality of the final products. , Therefore, the separation of C 2 H 2 is of great industrial significance that plays a major role in the chemical and polymer industry. Current separation technologies mainly rely on low-temperature distillation and organic solvent extraction, which are unfavorable to the environment and consume a lot of energy, accompanied by potential safety risks. , In contrast, the implementation of adsorbent-based separation technology has been considered as a promising method to overcome these drawbacks associated with chemical separation. − …”