Polymer/ionic liquid pilot scale membrane prototype for the recovery of difluoromethane (R-32) from refrigerant mixtures

Difluoromethane (R-32) is a hydrofluorocarbon (HFC) that has been massively used over the last 30 years in refrigeration and air conditioning as a primary component of azeotropic or close boiling refrigerant mixtures. Despite environmental directives commanded to drastically reduce the use of HFCs, R-32 has excellent ther-modynamic properties and moderate GWP, thus its recovery from depleted mixtures collected from end-of-life equipment is sought to synthesize alternative low-GWP refrigerant blends. Membrane separation using com-posite polymer/ionic liquid membranes based on poly-ether-block-amide have shown potential to separate R-32 from other fluorinated hydrocarbons, yet the development of this type of composite membranes still remains at laboratory scale. In this work, a spray coating technique was successfully applied to create defect-free thin se-lective layers of neat Pebax (R) 1657, Pebax (R) 1657/40 wt% [C2C1im][BF4] and Pebax (R) 1657/40 wt% [C2C1im] [SCN] coated on porous PVDF substrates. This methodology was transferred from the lab-scale tests (12.6 cm2) to a custom pilot set-up (300 cm2). The pilot results confirmed the superior performance and stability of [C2C1im] [SCN]-based membranes, which allowed the recovery of up to 64.3% and 67.1% R-32 from the refrigerant mixtures R-410A (69.8 mol % R-32 and 30.2 mol % R-125) and R-454B (82.1 mol % R-32 and 17.9 mol % R-1234yf) at 6 bar, increasing the R-32 permeate concentration up to 89.6 and 95.9 mol %, respectively. These results highlight the need to expand the knowledge of this type of gas separation membranes towards thinner and defect-free selective dense layers with the purpose of approaching their real applications.

Automated summary

Difluoromethane (R-32), a hydrofluorocarbon (HFC), has been widely used as a primary component of refrigerant mixtures in refrigeration and air conditioning. The recovery of R-32 from depleted mixtures collected from end-of-life equipment is sought for synthesizing low-GWP refrigerant blends. Composite polymer/ionic liquid membranes based on poly-ether-block-amide have shown potential for separating R-32 from other fluorinated hydrocarbons. In this study, a spray coating technique was successfully applied to create defect-free thin selective layers of different coatings. The pilot results confirmed the superior performance and stability of [C2C1im] [SCN]-based membranes in recovering R-32 from refrigerant mixtures.