Absorption of Fluorinated Greenhouse Gases Using Fluorinated Ionic Liquids

Abstract

The increasing awareness of the environmental impact of fluorinated gases (Fgases) used in refrigeration is instigating the development of technologies to recover and recycle them. With this goal in mind, single-component absorption equilibrium isotherms at 303.15 K of F-gases in different ionic liquids (ILs) were determined using a gravimetric method. The selected F-gases are the most used in domestic refrigeration (R-32: difluoromethane, R-125: pentafluoroethane, and R-134a: 1,1,1,2-tetrafluoroethane). The results show that ILs containing a fluorinated alkyl side chain with four carbon atoms, i.e., fluorinated ionic liquids (FILs), have higher gas absorption capacity than conventional fluoro-containing ILs. All studied ILs showed ideal selectivity towards R-134a. Conventional fluoro-containing ILs showed better selectivities for the separation of the binary mixtures R-134a/R-125 and R-32/R-125 and FILs showed better selectivities for the R-134a/R-32 mixture. These results provide fundamental knowledge of the behavior of these new alternative solvents and key information for their application in the separation of F-gases mixtures of commercial refrigerants.

Vapor–Liquid Equilibria and Diffusion Coefficients of Difluoromethane, 1,1,1,2-Tetrafluoroethane, and 2,3,3,3-Tetrafluoropropene in Low-Viscosity Ionic Liquids

“…Ionic liquids (ILs) are a family of compounds that has attracted attention in several fields because of their interesting properties, namely, extremely low vapor pressure, chemical and thermal stability, wide liquid temperature range or non-flammability, among others. [8][9][10] The use of ILs as entrainers has been proposed to allow for the separation of azeotropic or close-boiling point blends of refrigerant gases, [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] and as working fluids in absorption refrigeration systems. [25][26][27][28][29][30][31][32][33][34] The efficient separation of refrigerant blends would promote a more circular economy in the RAC sector, whereby HFCs and HFOs recovered from end-of-life equipment are used to formulate novel low GWP blends.…”

Fluorinated Ionic Liquids as Task-Specific Materials: An Overview of Current Research

“…This behaviour is similar to what is observed when the size of the hydrogenated alkyl chain in the cation of fluoro-containing imidazolium-based ILs increases, [86,88,92,93] and can be explained by the entropic contribution of the accommodation of gas molecules in the cavities of absorbents with higher molar volume. Moreover, when the absorption of R-125 and R-134a in the abovementioned ILs was studied, a higher solubility capacity of FILs in comparison to mere fluoro-containing ILs was observed [83]. This demonstrates the relevance of the FILs nanosegregated domains for gas solubility, either by increasing the free volume for the accommodation of gas molecules or by increasing the number of possible gas-absorbent interactions.…”

“…R-410A is widely used in the refrigeration sector but has a high GWP. Therefore, this refrigerant is one of the focus of the EU HFC phase-down [83]. This blend is a near-azeotropic system of R-32 and R-125 and therefore the separation of its individual components is hampered [83].…”

“…Therefore, this refrigerant is one of the focus of the EU HFC phase-down [83]. This blend is a near-azeotropic system of R-32 and R-125 and therefore the separation of its individual components is hampered [83]. Consequently, there is a growing interest in the search for new efficient, low-energy, and sustainable separation processes.…”

“…The increased solubility of F-gases in FILs supports the use of these absorbent as an alternative to conventional ILs with longer hydrogenated chains, which present higher toxicity [83]. Other study focused on evaluating the viability and costs of an absorption technology in near-industrial conditions for the capture of R-32 and R-134a (with HFC recoveries above 90%) from a dilute gas stream, using FILs or mere fluoro-containing ILs as absorbents.…”