In the quest for ionic liquid entrainers for the recovery of R-32 and R-125 by extractive distillation under rate-based considerations

In line with the reduction targets imposed on the production of high global warming potential (GWP) hydrofluorocarbons by the Kigali Amendment to the Montreal Protocol, the recovery of refrigeration fluids at the endof-life of refrigeration and air-conditioning equipment and the selective separation of the most valuable refrigerants is sought for recycling purposes and climate change mitigation. To that end, extractive distillation (ED) processes using ionic liquids (ILs) as entrainers is considered a promising technology to solve the difficulty of separating the typical close boiling or azeotropic behaviour of fluorinated hydrocarbon mixtures. This work provides insight into the design of ED processes evaluating the influence of both mass transfer phenomena (ratebased models) and IL properties (absorption capacity, solubility selectivity and viscosity) on the critical process variables (e.g., solvent-to-feed ratio, reboiler temperature, packing height) to separate the components of the binary mixture R-410A (50 wt% difluoromethane (R-32) + 50 wt% pentafluoroethane (R-125)) with minimum energy consumption and purity greater than 99.5 wt% of the two products. Results point to the solubility selectivity as the most influential IL property, and to [C2C1im][SCN], among all ILs assessed, as a promising entrainer because of its high R-32/R-125 solubility selectivity and low viscosity, which enables to operate the ED process at lower temperatures. The recovered R-32 can be used as a greener alternative to the high-GWP R-410A, as well as a main component in the formulation of new low-GWP mixtures.

Automated summary

In this study, the design of extractive distillation (ED) processes for separating the components of the R-410A mixture was evaluated by considering the influence of mass transfer phenomena and ionic liquid (ILs) properties. The results showed that solubility selectivity was the most influential IL property, and [C2C1im][SCN] was identified as a promising entrainer due to its high solubility selectivity and low viscosity, which allowed for operation at lower temperatures. The recovered R-32 can serve as a greener alternative to high-GWP R-410A and as a main component in the formulation of new low-GWP mixtures.