Enhanced Separation of Butane Isomers via Defect Control in a Fumarate/Zirconium-Based Metal Organic Framework

Abstract

The discovery of appropriate synthetic reaction conditions for fabricating a stable zirconium-based molecular sieve (Zr-fum-fcu-MOF) with minimal defects and its utilization in the challenging separation of linear paraffins from branched paraffins is reported. The crystallinity and structural defects were modulated and adjusted at the molecular level by controlling the synthetic reaction conditions (i.e., amounts of modulators and ligands). The impact of molecular defects on the separation of n-butane from iso-butane was studied through the preparation, fine characterization, and performance evaluation of Zr-fum-fcu-MOFs with varying degrees of defects. Defect-rich Zr-fum-fcu-MOFs were found to have poor n-butane/iso-butane separation, mainly driven by thermodynamics, while Zr-fum-fcu-MOFs with fewer or minimal defects showed efficient separation, driven mainly by kinetics and full molecular exclusion mechanisms. The impact of intrinsic defects (i.e., missing organic or inorganic blocks) on the associated mechanisms involved in the separation of n-butane/iso-butane was evidenced through single-gas adsorption, mixed-gas column breakthrough experiments, and calorimetric studies. This investigation demonstrates, for the first time, the importance of controlling intrinsic defects to maintain the selective exclusion behavior of hydrocarbon isomers when using molecular sieves.

Highly efficient separation of linear and branched C4 isomers with a tailor‐made metal–organic framework

“…The n −/ iso ‐C 4 H 8 uptake ratio on ZU‐36‐Co is the highest reported to date (Figure 4a). The uptake ratio for n −/ iso ‐C 4 H 10 (18.3) on ZU‐36‐Co is also significantly higher than that on TIFSIX‐3‐Ni (8.1), TIFSIX‐2‐Cu‐i (6.4), MIL‐120 (1.2, Figure S6A), and the state‐of‐the‐art materials (Figure 4a), such as Zr‐fum‐100 (10.10), 9 Zr‐fum‐200 (2.13), 9 CMS‐PMOF‐1(1.33), 8 and SBA‐800 (11.0) 42 . Therefore, ZU‐36‐Co exhibits exceptionally greater potential for n ‐C 4 H 8 / iso ‐C 4 H 8 and n −/ iso ‐C 4 H 10 separation in industrial applications.…”

“…Pure compounds obtained from the mono‐olefin fraction can be used as starting materials for the production of polymers (rubbers, lubricants, etc.). For example, high‐purity n ‐butene ( n ‐C 4 H 8 ) is needed in the production of linear low‐density polyethylene 7‐10 . Furthermore, to obtain gasoline with a high‐octane number, the separation of normal paraffins from their branched paraffins has been extensively investigated.…”

“…Furthermore, to obtain gasoline with a high‐octane number, the separation of normal paraffins from their branched paraffins has been extensively investigated. Meanwhile, purified n ‐paraffin is an important raw material for the production of ethylene 1‐11 . However, due to the similar chemical and physical properties of linear and branched isomers (boiling point, vapor pressure, etc.…”

A Stable Amine‐Functionalized Microporous Metal–Organic Framework for Thermodynamically and Kinetically Selective Gas Separations

“…For example, the nominal pore aperture of ZIF‐8 is only ∼3.4 Å, while there is convincing evidence that the pore cages of ZIF‐8 are accessible to hydrocarbon molecules with significantly larger kinetic diameters (4.3‐5.85 Å) . In addition, some nonsieving behaviors are also ascribed to the presence of defects in crystal structures . Besides, noting the very close diameters between isobutene molecules (∼5.0 Å) and pore apertures of Co 2 (abim)(im) 3 (∼4.9 Å), it is thus reasonable for the small adsorption for iso‐C 4 H 10 .…”

Green Synthesis of a Functionalized Zirconium-Based Metal–Organic Framework for Water and Ethanol Adsorption

“…Metal-organic frameworks (MOFs) [1][2][3][4][5] are a promising class of crystalline porous materials with a wide range of applications including but not limited to heterogeneous catalysis [6][7][8][9][10], enzyme and nanoparticle encapsulation [11][12][13][14], water capture [15][16][17][18][19], gas storage, and separation [20][21][22][23][24][25]. Importantly, physical and chemical properties of MOFs can be fine-tuned with the help of reticular chemistry, where pre-selected molecular building blocks are combined to yield pre-designed frameworks for targeted applications [26][27][28][29][30].…”