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Metal–organic frameworks with potential for energy-efficient adsorptive separation of light hydrocarbons
Summary:
The authors from University of Texas at San Antonio & University of Amsterdam developed M-MOF-74 (Mg, Co, Fe) adsorbents with open-metal sites, achieving energy-efficient one-step fractionation of C1–C3 hydrocarbons to polymer-grade purity.
Background:
1. Cryogenic distillation for CH4/C2H2/C2H4/C2H6/C3H6/C3H8 separation is energy-intensive; earlier zeolites or ZIFs show either low selectivity or low capacity.
2. The authors proposed exploiting open-metal sites in M-MOF-74 to create strong, selective π-complexation with alkynes/alkenes, obtaining record combined selectivity & uptake.
Research Content:
1. Synthesis: Solvothermal self-assembly of H4dobdc with M(NO3)2·xH2O (M = Mg, Co, Fe) followed by methanol exchange & 250 °C activation.
2. Characterizations:
1) BET 1 200–1 700 m² g⁻¹; narrow 1D ~11 Å channels.
2) SEM 200–500 nm rod-like crystallites; PXRD confirms phase purity.
3) Qst (alkene) –45 kJ mol⁻¹ vs –30 kJ mol⁻¹ (alkane); IAST Sads(C2H4/C2H6) up to 11; breakthrough validates <40 ppm C2H2 in C2H4.
3. Application: Six-component gas-mixture PSA gives 99.5 % C2H4, 99 % C2H6, 99.5 % C3H6 in a single column; productivity 5 mol L⁻¹ bed.
4. Mechanism: DFT + IAST show side-on η²-binding of C=C/C≡C to unsaturated M²⁺ lowers adsorption energy; Maxwell–Stefan modelling confirms diffusion negligible for 50–200 µm crystals.
Outlook:
M-MOF-74 series provides universal, high-capacity adsorbents ready for industrial PSA replacement of cryogenic trains, cutting energy use >50 %.
Metal–organic frameworks with potential for energy-efficient adsorptive separation of light hydrocarbons
Authors: Yabing He, Rajamani Krishna, Banglin Chen
DOI: 10.1039/C2EE22858K
Link: https://pubs.rsc.org/en/content/articlelanding/2012/ee/c2ee22858k
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