Observation of Olefin/Paraffin Selectivity in Azo Compound and Its Application into a Metal–Organic Framework

Abstract

Olefin/paraffin separation is an important and challenging issue because the two molecules have similar physicochemical properties. Although a couple of olefin adsorbents have been developed by introducing inorganic nanoparticles into metal-organic frameworks (MOFs), there has been no study on the development of an olefin adsorbent by introducing a certain organic functional group into a MOF. In this study, we posited that azo compounds could offer olefin/paraffin selectivity. We have revealed using first-principles calculations that the simplest aromatic azo compound (azobenzene, Azob) has an unusual propylene/propane selectivity due to special electrostatic interactions between Azob and propylene molecules. On the basis of this interesting discovery, we have synthesized a novel propylene adsorbent, MIL-101(Cr)_DAA, by grafting 4,4'-diaminoazobenzene (DAA) into open metal sites in a mesoporous MIL-101(Cr). Remarkably, MIL-101(Cr)_DAA exhibited enhanced propylene/propane selectivity as well as considerably higher propylene heat of adsorption compared to pristine MIL-101(Cr) while maintaining the high working capacity of MIL-101(Cr). This clearly indicates that azo compounds when introduced into MOFs can provide propylene selectivity. Moreover, MIL-101(Cr)_DAA showed good CH/CH separation and easy regeneration performances from packed-bed breakthrough experiments and retained its propylene adsorption capacity even after exposure to air for 12 h. As far as we know, this is the first study that improves the olefin selectivity of MOF by postsynthetically introducing an organic functional group.

Efficient Separation of Propene and Propane Using Anion-Pillared Metal–Organic Frameworks

“…To further evaluate the C 3 H 6 /C 3 H 8 separation selectivity of GeFSIX-2-Cu-i and SIFSIX-2-Cu-i, the calculation of the C 3 H 6 /C 3 H 8 uptake ratio, a significant index for industrial application, and the ideal adsorbed solution theory (IAST) calculation were performed at 298 K. − The value of the C 3 H 6 /C 3 H 8 uptake ratios on GeFSIX-2-Cu-i and SIFSIX-2-Cu-i are 1.49 and 1.59, respectively. These values are pretty competitive and higher than Cu(0.6)@MIL-100­(Fe), MOF-74 series, MAF-23-O, MIL-101­(Cr)-DAA, zeolite 13X, and CuBTC, the detailed comparison are presented in Figure C and Table S2. ,,,,− Additionally, the record-high C 3 H 6 /C 3 H 8 thermodynamic uptake ratio of 1.49 was obtained on GeFSIX-2-Cu-i, which is even higher than that of Co 2 (dobdc) (1.46) at 298 K . When the temperature is raised to 313 K, the uptake ratio increases to 1.95 for GeFSIX-2-Cu-i and even to 2.24 for SIFSIX-2-Cu-i.…”

Machine-Learning-Based Prediction of Methane Adsorption Isotherms at Varied Temperatures for Experimental Adsorbents

“…Metal–organic frameworks (MOFs) are a relatively new class of porous materials constructed from a combination of organic linkers and inorganic clusters. − MOFs can have thousands of structures by suitable selections of linkers and clusters, and many of them have high surface areas (SAs) and special functionalities resulting in promising adsorption properties for various gases and vapors. ,− ,− Because MOFs are crystalline materials whose microscopic structures can be fully revealed by X-ray diffraction, they can be considered as the optimal materials for large-scale GCMC simulation studies. Recently, large-scale GCMC simulation studies on MOFs have been performed to screen top performing materials and investigate the structure/property relationships for various adsorptive gas separations and storage. − ,− …”

Amino Acid Imprinted UiO-66s for Highly Recognized Adsorption of Small Angiotensin-Converting-Enzyme-Inhibitory Peptides

“…Recently, porous crystalline metal organic frameworks (MOFs) have attracted general interest in the fields of adsorption and separation − attributed to their high surface area, uniform structure, and tunable chemical functionality. − They are reported to have ultrahigh adsorption capacity and specific affinity toward many light molecules, such as CO 2 , olefin, alkane, and dutrex. − However, few MOFs are reported to adsorb or separate larger molecules because of their limited pore tuning in the mesoporous regime. , Design of defective pores with specific surface properties can create nanoregions in MOFs and endorse them with high affinity or recognition toward nanometer size specific molecules, such as some small peptides. In this regards, many studies have been reported on defect engineering to expand the application scope of MOFs. − For example, Ravon used 2-methyl-toluic acid as a modulator to engineering large defects in MOF-5, which open the door to the alkylation of very large polyaromatic compounds .…”