Abstract: This study advances the scale-up of recovering the refrigerant R-32 (difluoromethane), a hydrofluorocarbon with moderate global warming potential and high thermodynamic efficiency that is a major component in most next-generation low-GWP blends. In particular, R-32 recovery from R-410A (R-32/R-125: 69.7/30.3 vol%) is sought as R-410A is being phased-down and represents a substantial stockpile of recoverable R-32 from end-of-life refrigeration equipment. To that end, asymmetric hollow fiber membranes made of the highly selective 6FDA-TMPD polyimide were extruded via dry-jet wet spinning, and the spinning parameters and dope composition are reported. These membranes were used to assemble membrane modules with a surface area of 31 cm2 and their integrity was verified using CO2 and N2. The performance of the 6FDA-TMPD prototype for separating R-410A was assessed under relevant pressures up to 7bar, achieving exceptional R-32 product purity (99.5 vol%) together with high R-32 recovery (85.4%). Moreover, a mathematical model was developed incorporating local fugacity gradients along the fiber length and concentration-dependent permeance that captured the strong condensability effects of fluorinated hydrocarbons on membrane plasticization. Finally, this model was applied to optimize the membrane area and compressor duty of a two-stage membrane process designed to maximize R-32 recovery while meeting the product specifications of the virgin refrigerant, R-32 purity >99.5 wt%. The normalized total energy required was as low as 0.06 kWh kg-1 of R-410A treated, showing that membrane separation is an extremely energy efficient way of reclaiming R-32 from waste R-410A refrigerants. Overall, the results support improved resource efficiency and reduced uncontrolled emissions of potent greenhouse gases, thus contributing to more sustainable practices in the refrigeration sector.
