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Toward the Recycling of Low-GWP Hydrofluorocarbon/Hydrofluoroolefin Refrigerant Mixtures Using Composite Ionic Liquid–Polymer Membranes

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journal contribution
posted on 07.05.2021, 21:04 by Fernando Pardo, Sergio V. Gutiérrez-Hernández, Gabriel Zarca, Ane Urtiaga
The restrictions imposed to the production of high-global warming potential refrigerant gases have boosted the search of novel separation processes for the selective recovery of hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFO) from exhausted refrigerant mixtures. Membrane materials functionalized with ionic liquids can offer an effective techno-economical response to the challenging separation of HFC/HFO blends. In this work, we provide for the first time a thorough characterization of the gas solubility and permeation properties of three of the most relevant compounds for the future of the refrigeration and air conditioning sector, that is, difluoromethane (HFC-R32), 1,1,1,2-tetrafluoroethane (HFC-R134a), and 2,3,3,3-tetrafluoropropene (HFO-R1234yf), through composite ionic liquid–polymer membranes (CILPMs) that were prepared combining the Pebax 1657 copolymer with several ILs, [C2mim]­[SCN], [C2mim]­[BF4], [C2mim]­[OTf], and [C2mim]­[Tf2N], varying the IL content in the range of 20–60 wt %. The CILPMs with the best separation performance and mechanical stability against feed pressure were those with 40 wt % of [C2mim]­[BF4] and [C2mim]­[SCN]. For the 40 wt % [C2mim]­[BF4] CILPM, the addition of IL promoted the permeability of the smallest molecules R32 and R134a and reduced the permeability of the largest molecule R1234yf, which resulted in 120 and 75% selectivity enhancement relative to that of the pristine polymer for R32/R1234yf and R134a/R1234yf mixtures, respectively. Finally, this CILPM was stable in the separation of two commercial HFC/HFO refrigerant blends (R513A and R454B) over a wide pressure range (up to 12 bar). These results indicate that CILPMs can be used for separating azeotropic and near-azeotropic exhausted HFC/HFO mixtures, which could stimulate the recovery and reuse of their components and thus avoid their emissions and pull down the demand for virgin refrigerants.