Growing concerns about the global warming potential of hydrofluorocarbons (HFCs) has led to increasing interest in developing technologies to effectively recover and recycle these refrigerants. Ionic liquids (ILs) have shown great potential to selectively separate azeotropic HFC gas mixtures, such as R-410A composed of HFC-32 (CH2F2) and HFC-125 (CHF2CF3), based on solubility differences between the refrigerant gases in the respective IL. Isothermal vapor–liquid equilibrium (VLE) data for HFC-32 and HFC-125 were measured in ILs containing fluorinated and nonfluorinated anions using a gravimetric microbalance at pressures ranging from 0.05 to 1.0 MPa and a temperature of 298.15 K. The van der Waals equation of state (EoS) model was applied to correlate the experimental solubility data of each HFC refrigerant/IL mixture. The solubility differences between HFC-32 and HFC-125 vary significantly depending on the choice of IL. The diffusion coefficients for both HFC refrigerants in each IL were calculated by fitting Fick’s law to time-dependent absorption data. HFC-32 has a higher diffusivity in most ILs tested because of its smaller molecular radius relative to HFC-125. Based on the calculated Henry’s law constants and the mass uptake for each system, [C6C1im]­[Cl] was found to have the highest selectivity difference for separating R-410A at 298.15 K.

Current legislation calling for the phase out of hydrofluorocarbon (HFC) refrigerants is driving a global market shift that has prompted industry and research institutions to investigate new refrigerant mixtures and sustainable separation techniques for recycling refrigerants. The recent American Innovation and Manufacturing (AIM) Act of 2020 requires an 85% phase down of HFC production over the next 15 years. To achieve this goal, azeotropic refrigerant mixtures, such as R-410A composed of 50 wt % HFC-32 (difluoromethane, CH 2 F 2 ) and 50 wt % HFC-125 (pentafluoroethane, CHF 2 CF 3 ), will have to be separated to recycle the lower global warming HFC-32 component. The present work investigates the solubility of HFC-32 and HFC-125 in six ionic liquids (ILs) with halogen anions for the purpose of developing the thermophysical property data required for designing extractive distillation recycling processes and understanding the choice of cation and anion type. A gravimetric microbalance was used to collect isothermal vapor liquid equilibrium data for each of the ILs at 298.15 K and pressures from 0.05 to 1.0 MPa. The Peng−Robinson equation of state was used to model the solubility of the HFCs in the ILs. The solubility of HFC-32 in the ILs showed small differences, while the solubility of HFC-125 had significant variations with respect to the anion type and the cation alkyl chain length. Fick's law was applied to calculate diffusion coefficients for each HFC/IL system. HFC-32 has a greater diffusivity than HFC-125 based on smaller molecular size. The 1-n-hexyl-3-methylimidazolium chloride and the trihexyl(tetradecyl)phosphonium chloride ILs have the highest HFC-125/HFC-32 selectivity at 298.15 K. Based on both the mass uptake and selectivity ratio, these two ILs are potential entrainers for the separation of R-410A using extractive distillation.

Multicomponent absorption measurements are notoriously difficult both experimentally and analytically, which is why the literature is lacking information, even though the results are important for understanding real separation systems. In the case of designing a separation process for hydrofluorocarbon (HFC) refrigerant mixtures using an ionic liquid (IL), it is important to understand multicomponent effects; however, almost all published results are for single component HFC/IL systems. To address this challenge, new gravimetric microbalances utilizing the Integral Mass Balance (IMB) method have been designed by Hiden Isochema to efficiently and accurately measure multicomponent gas sorption in liquids with low volatility (e.g., ILs) and solids. The present work investigates the mixture absorption of difluoromethane (HFC-32) and pentafluoroethane (HFC-125) in two ILs (1-n-butyl-3-methylimidazolium tetrafluoroborate and 1-n-butyl-3methylimidazolium hexafluorophosphate) at 298.15 K for the purpose of understanding HFC mixture/IL interactions. For the first time, these state-of-the-art instruments have allowed for the measurement of an HFC binary gas mixture in ILs that can be compared with existing single gas solubility measurements.

Project EARTH (Environmentally Applied Research Toward Hydrofluorocarbons) is focused on developing sustainable processes for selectively separating refrigerant mixtures with high global warming potentials. The initial focus of the project is R-410A which is widely used in both commercial refrigeration systems and residential air conditioning. It is an azeotropic mixture containing 50 wt.% HFC-32 (CH2F2) and 50 wt.% HFC-125 (CHF2CF3). The separation approaches being investigated include membranes, porous media, and the use of ionic liquids as entrainers for extractive distillation. This poster will describe the work being conducted using ionic liquids and will specifically focus on the impact of phase changes of imidazolium based ionic liquids that are solid at room temperature on the solubility of HFC-32 and HFC-125. The poster will include an overview of how we use specialized equipment including a High-Pressure View Cell and Hiden Isochema IGA gravimetric microbalance to build a comprehensive understanding of these solubility differences.

Refrigeration and air-conditioning systems are widespread throughout modern society, from the refrigerated cold chain that provides fresh foods and storage of medicines to the air conditioning of homes and buildings. Refrigeration is viewed as one of the most transformative engineering achievements of the 20th century and the demand for cooling will continue to increase as economic conditions improve and the climate continues to warm; however, refrigerants do come with an environmental cost. In 1987, the Montreal Protocol phased out chlorofluorocarbon (CFC) refrigerants because of their high ozone depletion potential (ODP). The replacements, typically mixtures of hydrofluorocarbons (HFCs), are safe for the Earth's ozone layer, but most have high global warming potentials (GWPs). HFCs account for 7.8% of total global greenhouse gas emissions, with 63% of that from “indirect” emissions (i.e., energy for running the system). As a result, 197 countries signed the Kigali agreement in 2016 to phase out high-GWP HFCs, with the goal of reducing emissions by 80% in the next 20 years. Millions of metric tons (mts) of high-GWP refrigerants will need to be reclaimed, but there are no good methods for separating and recycling the individual components, given that many are azeotropic mixtures. Currently, there is no means of separating azeotropic HFC mixtures, and the refrigerants will ultimately have to be incinerated. The commercial HFC mixture R-410A containing 50 wt.% HFC-32 (GWP = 675) and 50 wt.% HFC-125 (GWP = 3500) is a prime example. The HFC-32 can be reused when separated in new low-GWP products such as R-454B (69 wt% HFC-32 and 31 wt% HFO-1234yf) with a 75% lower GWP than R-410A. Ionic liquids are being developed that can separate azeotropic HFC mixtures based on differences in solubility and used as entrainers in extractive distillation. This presentation will provide experimental data on the solubility of HFCs in ionic liquids that have been measured using gravimetric microbalances and modeling using the Peng-Robinson equation of state. ASPEN Plus simulations will show how a pilot process has been designed that can continuously separate azeotropic refrigerant mixtures such as R-410A.