Various key gas/vapors separations are accomplished using energy intensive processes as exemplified by the olefin/paraffin separation, an essential separation in chemical industry.
Here we present our progress in the development of functional metal-organic frameworks (MOFs) to address some energy-intensive separations. Successful practice of reticular chemistry had afforded the fabrication of a chemically stable fluorinated MOF adsorbent materials (NbOFFIVE-1-Ni, also referred to as KAUST-7 and AlFFIVE-1-Ni, also referred to as KAUST-8).
KAUST-7 fully split propylene from propane. The bridging of Ni(II)-pyrazine square-grid layers with (NbOF5)2- pillars permitted the construction of a 3-dimensional MOF, enclosing a periodic array of fluoride anions in a contracted square-shaped channels. The judicious selection of the bulkier pillar (NbOF5)2- caused the looked-for hindrance of the previously free-rotating pyrazine moieties, delimiting the pore system and dictating the maximum opening of the pore aperture-size. The restricted MOF window resulted in the selective molecular exclusion of propane from propylene at atmospheric pressure, as evidenced by multiple cyclic mixed-gas adsorption and calorimetric studies. Remarkably, KAUST-7 maintains its distinctive separation properties in the presence of water as a result of its high chemical and hydrolytic stability.1
The development of suitable storage and refining processes makes natural gas an excellent alternative fuel, but before its transport and use, natural gas must first be dehydrated. Conventional dehydration agents are energy intensive. KAUST-8 selectively removes water and requires just 105°C for regeneration of the dehydrating agent.2
The deliberate control of the pore aperture-size of various selected MOFs and its impact on various separations will be discussed.
1. Cadiau, A.; Adil, K.; Bhatt, P. M.; Belmabkhout, Y.; Eddaoudi, M. “A metal-organic framework-based splitter for separating propylene from propane” Science, 2016, 353, 137-140.
2 Cadiau, A.; Belmabkhout, Y.; Adil, K.; Bhatt, P. M.; Pillai, R. S.; Shkurenko, A.; Martineau-Corcos, C.; Maurin, G.; Eddaoudi, M. “Hydrolytically stable fluorinated metal-organic frameworks for energy-efficient dehydration” Science, 2017, 356, 731-735.