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

• Mesoporous NIIC-20 is a superior material for separation of light alkanes. • The best combination of adsorption uptakes and selectivities for CH 4 /C 2 H 6 /C 3 H 8. • Efficient breakthrough separation of gas mixtures with remarkable productivity. • An influence of the alkyl substituent on the MOF adsorption properties was explored. 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, absorption 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 CH 4 , 55.0 ml(STP)⋅g –1 for C 2 H 6 and 125.4 ml(STP)⋅g –1 for C 3 H 8 . The IAST adsorption selectivities at ambient conditions (298 K, 1:1 gas mixture) reach 24.2 for C 2 H 6 /CH 4 , 29.0 for C 3 H 8 /C 2 H 6 and as high as 1110 for C 3 H 8 /CH 4 . 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 C 2 H 6 /CH 4 , and 4193 ml(STP)⋅g –1 (187.3 mol⋅kg –1 ) for C 3 H 8 /CH 4 equimolar gas mixtures, which greatly surpass earlier published data. The ethane productivity for an equimolar C 3 H 8 /C 2 H 6 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.