Efficient separation of methane, ethane and propane on mesoporous metal-organic frameworks

Abstract

Adsorption and separation of light saturated hydrocarbons (methane, ethane and propane) as main components of natural gas on a series of isoreticular mesoporous metal–organic frameworks NIIC-20-G (G = ethyleneglycol, 1,2-propyleneglycol, 1,2-butyleneglycol, 1,2-pentylenglycol, glycerol) has been thoroughly investigated. An impact of the size and nature of the glycol moiety on fundamental parameters of the adsorption (gas uptakes, adsorption constants, enthalpy and entropy, adsorption selectivity factors) was revealed and rationalized. The highest gas uptakes at 1 bar and 298 K are 13.2 ml(STP)·g−1 for CH4, 55.0 ml(STP)·g−1 for C2H6 and 125.4 ml(STP)·g−1 for C3H8. The IAST adsorption selectivities at ambient conditions (298 K, 1:1 gas mixture) reach 24.2 for C2H6/CH4, 29.0 for C3H8/C2H6 and as high as 1110 for C3H8/CH4. A rare combination of high adsorption uptakes and superb adsorption selectivity values achieved for NIIC-20-G put those MOFs ahead of the most other materials for light saturated hydrocarbon adsorption and separation. Dynamic breakthrough gas separation experiments on NIIC-20-Pr fully confirm effective separation of lighter alkanes from the corresponding binary or ternary mixtures. The obtained methane productivities are 1182 ml(STP)·g−1 (52.8 mol·kg−1) for C2H6/CH4, and 4193 ml(STP)·g−1 (187.3 mol·kg−1) for C3H8/CH4 equimolar gas mixtures, which greatly surpass earlier published data. The ethane productivity for an equimolar C3H8/C2H6 gas mixture is 3009 ml(STP)·g−1 (134.4 mol·kg−1). The breakthrough separation experiments validate a remarkable performance of the studied MOFs in the practical separation of natural gas or other relevant mixtures of light alkanes to valuable individual components.