Integration of Stable Ionic Liquid-Based Nanofluids into Polymer Membranes. Part II: Gas Separation Properties toward Fluorinated Greenhouse Gases

Abstract

Membrane technology can play a very influential role in the separation of the constituents of HFC refrigerant gas mixtures, which usually exhibit azeotropic or near-azeotropic behavior, with the goal of promoting the reuse of value-added compounds in the manufacture of new low-global warming potential (GWP) refrigerant mixtures that abide by the current F-gases regulations. In this context, the selective recovery of difluorometane (R32, GWP = 677) from the commercial blend R410A (GWP = 1924), an equimass mixture of R32 and pentafluoroethane (R125, GWP = 3170), is sought. To that end, this work explores for the first time the separation performance of novel mixed-matrix membranes (MMMs) functionalized with ioNanofluids (IoNFs) consisting in a stable suspension of exfoliated graphene nanoplatelets (xGnP) into a fluorinated ionic liquid (FIL), 1-ethyl-3-methylpyridinium perfluorobutanesulfonate ([C2C1py][C4F9SO3]). The results show that the presence of IoNF in the MMMs significantly enhances gas permeation, yet at the expense of slightly decreasing the selectivity of the base polymer. The best results were obtained with the MMM containing 40 wt% IoNF, which led to an improved permeability of the gas of interest (PR32 = 496 barrer) with respect to that of the neat polymer (PR32= 279 barrer) with a mixed-gas separation factor of 3.0 at the highest feed R410A pressure tested. Overall, the newly fabricated IoNF-MMMs allowed the separation of the near-azeotropic R410A mixture to recover the low-GWP R32 gas, which is of great interest for the circular economy of the refrigeration sector.

Overview of Membrane Science and Technology in Portugal

“…Constantino et al [236] presented pervaporation data for multicomponent mixtures in the absence of reaction for the compounds involved in the esterification of acrylic acid with n-butanol at different temperatures. This experimental data is very useful for designing and optimising pervaporation-based hybrid processes for butyl acrylate synthesis [213].…”

“…Remarkable CO 2 solubility and tunability are essential features of this unique platform. The potential of ionic liquid materials to improve membranebased CO 2 separation processes has been demonstrated, either through the preparation of supported ionic liquid membranes (SILMs) [45,[187][188][189][190][191][192][193][194][195][196][197][198], the blending of ionic liquids with poly(ionic liquid)s [199][200][201][202][203][204][205][206][207][208] or, more recently, through the development of mixed matrix membranes [209][210][211][212][213][214].…”

“…Considerable improvements in CO 2 , N 2, and H 2 permeabilities were achieved for irradiated PIL/IL membranes, while their CO 2 /N 2 and CO 2 /H 2 selectivities were almost unchanged. Mixed matrix membranes combining metal-organic frameworks (MOFs) [209][210][211][212] or graphene [213,214] have also been investigated. As an example, Nabais et al [209] incorporated different MOFs (MIL-53(Al), Cu 3 (BTC) 2 , and ZIF-8) into a pyrrolidinium-based PIL/IL (60/40 wt.%).…”

“…Pervaporation is a membrane separation process with unique and adequate features to remove volatile compounds present in liquid mixtures at trace levels [223]. Pervaporation has been used by Portuguese researchers for the dehydration of organic solvents (such as ethanol [224][225][226][227], isopropanol [50] or n-butanol [228]), aroma recovery [49,87,[229][230][231][232][233][234], and process intensification of ethyl lactate [235] or butyl acrylate [213,236].…”

Understanding the phase and solvation behavior of fluorinated ionic liquids

“…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]. Furthermore, Pebax membranes were functionalized with the so-called ioNanofluids, a suspension of exfoliated graphene nanoplatelets in the FIL [C 2 C 1 py][C 4 F 9 SO 3 ], and used for the separation of the R-410A refrigerant, showing enhanced gas permeation relative to the neat membranes [113].…”