(525c) Design and Environmental Assessment of an Ionic-Liquid-Based R407F Refrigerant Separation Process

Within the battle against climate change and following the recommendations of the Kigali Amendment, all country regulations are tightening the emission reduction goals of high global warming potential (GWP) fluorinated gases. In particular, the European Union has proposed to cut their emissions by two thirds within the next decade respect to their 2014 levels.¹ Accordingly, some of the currently most employed hydrofluorocarbons (HFC) blends used in refrigeration, e.g. R404a (GWP = 3922), or even mid-term alternatives such as R410A (GWP = 2088) or R407F (GWP = 1824), will have to be soon replaced by more environmentally-friendly and energy-efficient refrigerants.

The new stricter regulation represents a challenge for the industrial sector, as very few developments are nowadays available for the treatment of F-gases. In fact, there is not a developed and standardized technology available to recover HFCs and, consequently, once the life cycle of the refrigeration equipment has ended, most of these gases are incinerated, generating harmful emissions to the atmosphere. One of the feasible approaches to meet both, the legal and technical requirements, is the formulation of new refrigerants by combining a low GWP compound (e.g., hydrofluoroolefins) with small amounts of one of the well-known working HFCs, such as difluoromethane (R32) or 1,1,1,2-tetrafluoroethane, R134a. This will also allow moving towards a more circular economy, as far as those gases can be reused. However, the current HFCs blends are characterized for behaving as near-azeotropic mixtures, with virtually no variation of composition between the vapor and liquid phase, making their separation an arduous task when using traditional distillation techniques or cryogenic separation. However, very recent studies have shown some alternatives, which seem to be efficient and cost-effective, including absorption in fluorinated ionic liquids (FILs) and Deep Eutectic Solvents (DES), adsorption on activated carbons, and membrane separation.^2-4 In spite of all these recent efforts toward the development of separation technologies, there is no information on the environmental cost of these alternatives. In this regard, it is necessary to ensure, through a careful life cycle analysis (LCA), the possible benefits of these new separation units, quantifying these environmental benefits with respect to the impacts generated during the production of fresh F-gas.

In this work, a methodology based on the COSMO-RS thermodynamic package integrated into an Aspen Plus process simulator was used to evaluate the performance of selected [C₂mim][C₄F₉CO₂] FIL to recover difluoromethane (R-32) from the commercial blend R-407F. The environmental sustainability of the recovery process (circular economy scenario) has been analyzed with a life cycle assessment (LCA) approach, comparing the obtained results with the conventional R-32 production (benchmark scenario). The results reveal a 30% recovery of 98 wt % R-32 suitable for further reuse with environmental load reduction in the 86−99% range compared to the R-32 production.⁵ This study can guide the development of new F-gas recovery technologies to improve the environmental impacts of these compounds from a circular economy perspective.

Acknowledgements

This publication is part of the R+D+I project STOP-F-Gas (ref: PID2019-108014RB-C21), funded by MCIN/AEI/10.13039/501100011033/.

Bibliography

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