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

Abstract

The restrictions imposed to the production of highglobal 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, [C 2 mim][SCN], [C 2 mim][BF 4 ], [C 2 mim][OTf], and [C 2 mim][Tf 2 N], 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 [C 2 mim][BF 4 ] and [C 2 mim][SCN]. For the 40 wt % [C 2 mim][BF 4] 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 nearazeotropic 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.

Understanding the phase and solvation behavior of fluorinated ionic liquids

“…Pebax membranes functionalized with the ILs [C 2 C 1 Im][SCN] and [C 2 C 1 Im][BF 4 ] were tested for the separation of the refrigerant R-410A (a near-azeotropic system of the HFCs R-32 and R-125), showing improvement in the permeability towards R-32 and of the R-32/R-125 selectivity, relatively to the neat polymer membranes [111]. Additionally, CILPMs were prepared by functionalizing Pebax membranes with SO 3 ], and [C 2 C 1 Im][N(CF 3 SO 2 ) 2 ] and were tested for the solubility and permeation of R-32, R-134a, and the HFO R-1234yf [112]. In this study, the CILPM based on [C 2 C 1 Im][BF 4 ] showed higher permeability towards the HFCs R-32 and R-134a compared to the HFO R-1234yf, demonstrating to be useful for the separation of HFC/HFO blends [112].…”

Data‐driven approximation of thermodynamic phase equilibria

“…HFCs are commonly used as refrigerants in domestic and commercial cooling systems. These compounds account for 2%–3% of the global greenhouse gas (GHG) emissions 46 which prompted the Kigali Amendment to the Montreal Protocol to recommend cutting the global HFC emissions by 80%–85% by 2047 47 . Therefore, it is desirable for these HFCs to be recycled so that the amount of newly manufactured HFC molecules can be minimized.…”

“…These compounds account for 2%-3% of the global greenhouse gas (GHG) emissions 46 which prompted the Kigali Amendment to the Montreal Protocol to recommend cutting the global HFC emissions by 80%-85% by 2047. 47 Therefore, it is desirable for these HFCs to be recycled so that the amount of newly manufactured HFC molecules can be minimized. However, recycling through separation of HFCs pose a significant challenge as these are azeotropic or closeboiling mixtures that often behave as single fluids.…”

“…However, recycling through separation of HFCs pose a significant challenge as these are azeotropic or close‐boiling mixtures that often behave as single fluids. Consequently, conventional separation techniques, such as cryogenic distillation, when used for HFC separation are not a viable option as they are very energy and cost‐intensive and pose significant operational challenges 47 . To that end, ILs have garnered significant attention as potential solvents for extractive distillation based separation of these azeotropic mixtures.…”

Preparation ofAl2O3/PDA/Pebax membrane modified by (C3NH2MIm)(PF6) for improvingCO2separation performance

“…4,5 In recent years, researchers have prepared mixed matrix membranes (MMMs) by filling dopants into polymer substrates, and tried to overcome the trade-off effect by taking advantage of the respective performance advantages of dopants materials and polymer materials. 6 Up to now, the commonly used dopants mainly include nano metal oxides (Al 2 O 3 , SiO 2 , TiO 2 ), 7 carbon nanotubes (CNTs), 8 graphene oxide (GO), 9,10 MOFs, 11,12 ionic liquids, 13,14 etc. Pebax, as a common membrane matrix, has often been used to prepare MMMs due to its special properties.…”