Collaborative Research: Development and Application of a Molecular and Process Design Framework for the Separation of Hydrofluorocarbon Mixtures

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Refrigerators and heat pumps use a substance called a refrigerant to move heat between two spaces. Prior to the late 1980s, refrigerants often contained chlorfluorocarbons, but these materials were phased out because of their high ozone depletion potential. Mixtures of hydrofluorocarbons appeared on the market as replacement refrigerants. Hydrofluorocarbons (HFC) do not deplete the Earth's ozone layer, but they to do tend to trap greenhouse gases in the atmosphere, measured as global warming potential, prompting a concerted effort to phase out the use of high global warming potential HFCs. The phase out of these materials is complicated by the fact that there are thousands of tons of refrigerant mixtures that contain both low and high global warming potential compounds, and there is no viable method for separating and reclaiming the components. The separation of low and high global warming HFCs is complex because they are azeotropic or near-azeotropic materials, meaning they are chemically similar and behave like a single (pure) fluid. The goal of the project is to develop tools and processes that enable the separation of high and low global warming potential HFCs, allowing the recovery and reuse of the low global warming potential HFCs. To accomplish this goal, an integrated molecular and chemical process design framework will be developed to engineer novel ionic liquid-based HFC separation technologies. The approach will unify "top-down" computer-aided molecular design with "bottom-up" experimentally-driven approaches to more efficiently identify new separation agents for HFC azeotropic mixtures. The engineering framework will be widely applicable to other chemical separation processes, including that of next-generation refrigerants such as hydrofluoro-olefins and hydrochlorofluoro-olefins. The physical property data and computational tools will be disseminated through national data repositories and open source agreements, respectively. The project also provides experiential training opportunities for two graduate students who will interface with industrial partners. It is hypothesized that ionic liquids can be designed to achieve unprecedented separation efficiency for azeotropic HFC mixtures. However, there are millions of potential ionic liquids, making a trial-and-error search infeasible. The overall goals of this project are: i) to establish a unified framework for ionic liquid molecular design and separation process configuration optimization and ii) to engineer new technologies to enable recycling of HFC refrigerants. The collaborative project integrates state-of-the-art methods in pure and mixed gas solubility measurements, high throughput molecular simulations, and superstructure optimization into a single, unified framework. Both experimental physical property measurements and laboratory-scale demonstrations will be used to validate the multiscale computational models. The proposed framework offers a systematic approach to rapidly engineer ionic liquid solvent and separation processes. The framework is general purpose and has the potential to enable dramatically faster discovery of novel separation solvents and systems well beyond the HFC domain.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.