Membranes for Energy-Efficient Hydrocarbon Separation from Refrigerants

Refrigeration is crucial in modern society, particularly for storing perishable foods, medicines, and other temperature sensitive products. Refrigerant mixtures, such as R-422B, are commonly used in a variety of industrial applications. R-422B is composed of 55 wt.% HFC-125 (CHF₂CF₃), 42 wt.% HFC-134a (CH₂FCF₃), and 3 wt.% isobutane. The separation of these components is desired because of the high global warming potentials for HFC-125 (GWP₁₀₀ = 3500) and HFC-134a (GWP₁₀₀ = 1430) and isobutane’s high flammability. Separation of these components would allow for proper handling and recycling. However, current recycling approaches are incapable of separating these components, so there is an increased demand for sustainable and energy-efficient refrigerant recycling processes. Membrane-based separations offer a low-energy approach to separate hydrocarbons and hydrofluorocarbons (HFCs) from refrigerant mixtures to facilitate recovery, repurposing, and recycling. This study investigates the synthesis of polyimide membranes via chemical imidization for separation of hydrocarbons from HFCs in refrigerant mixtures. Polyimides are high-performance polymers with excellent thermal stability, chemical resistance, and tunable free volume that make them ideal for gas separation applications. Permeability and selectivity data were obtained to determine the membrane’s separation performance, with initial testing conducted using flat sheet membranes; and the potential to develop hollow fiber membranes in the future.