Separation of Azeotropic Refrigerant Mixtures: R‑450A, R‑456A, R‑515B, and R-516A Using Phosphonium- and Imidazolium-Based Ionic Liquids

Hydrofluorocarbon (HFC) refrigerants are currently being phased down by 85% over the next two decades due to their high global warming potential (GWP). Hydrofluoroolefin (HFO) refrigerants are being commercialized as replacements for HFCs and have significantly lower GWP and zero ozone depletion potential (ODP). A challenge in the transition to HFO refrigerants is compatibility with the existing equipment. One solution is blending HFO and HFC refrigerants to match equipment performance. Several azeotropic refrigerant mixtures, such as R-450A, R-456A, R-515B, and R-516A, have lower GWP and provide similar thermophysical properties to replace HFCs in existing systems. HFO/HFC blends are excellent alternatives that enable the reduction of HFCs while still maintaining the lifespan of existing equipment. Many HFO/HFC refrigerant mixtures are designed to be azeotropic or near-azeotropic so that if the refrigerant leaks from the system, only a minimal change in composition will occur, which makes servicing the equipment easier. However, this poses a challenge when recycling the refrigerant because conventional distillation cannot be used to separate the HFO/HFC components back into pure products. A proposed solution for separating azeotropic mixtures uses extractive distillation with an ionic liquid (IL) as the entrainer. This novel method offers an efficient means of separating azeotropic refrigerant mixtures. The efficacy of ILs as entrainers is contingent upon their selectivity and strong affinity toward one or more components of the mixture. In addition, the limited availability of solubility data for HFOs and HFCs in ILs constrains the process of selection. This work has identified phosphonium- and imidazolium-based ILs for the separation of four commercial HFO/HFC refrigerant mixtures based on ASPEN Plus simulations

Carbon Dioxide Capture Using Ionic Liquid 1-Butyl-3-methylimidazolium Acetate

Carbon dioxide (CO₂) capture using aqueous amine scrubbing is currently considered the most feasible option for separating CO₂ from post-combustion flue gas. Using simple absorption and stripping configurations, monoethanolamine has been commercially demonstrated to effectively scrub CO₂ from post-combustion flue gas. However, the current capital and operating costs are high and do not meet the target of the Department of Energy to remove 90% of CO₂ from post-combustion flue gas with no more than a 35% increase in the cost of electricity. The evaluation of advanced absorbents, adsorbents, and membranes is under way to find the most energy-efficient CO₂-capture technology. We have modeled an ionic liquid that can reduce the energy losses by 16% compared to a commercial monoethanolamine process. The choice of the ionic liquid, 1-butyl-3-methylimidazolium acetate, has not been optimized but was chosen based on chemical absorption behavior and the desire to understand performance. Engineering design estimates indicate that the investment for the ionic liquid process will be 11% lower than the amine-based process and provide a 12% reduction in equipment footprint. A parametric study examined four improvements in the ionic liquid technology, which may reduce even further the energy and cost required for CO₂ capture

Creating Nanoparticle Stability in Ionic Liquid [C₄mim][BF₄] by Inducing Solvation Layering

The critical role of solvation forces in dispersing and stabilizing nanoparticles and colloids in 1-butyl-3-methylimidazolium tetrafluoroborate [C₄mim][BF₄] is demonstrated. Stable silica nanoparticle suspensions over 60 wt % solids are achieved by particle surface chemical functionalization with a fluorinated alcohol. A combination of techniques including rheology, dynamic light scattering (DLS), transmission electron microscopy (TEM), and small angle neutron scattering (SANS) are employed to determine the mechanism of colloidal stability. Solvation layers of ∼5 nm at room temperature are measured by multiple techniques and are thought to be initiated by hydrogen bonds between the anion [BF₄]⁻ and the fluorinated group on the surface coating. Inducing structured solvation layering at particle surfaces through hydrogen bonding is demonstrated as a method to stabilize particles in ionic liquids

Synthesis and Characterization of Fluorinated Ionic Liquids and Their Application in Hydrofluorocarbon Gas Uptake

This study reports the synthesis and comprehensive characterization of five fluorinated ionic liquids (FILs), each composed of an imidazolium cation of varied fluoroalkyl chain lengths paired with a fluorinated anion: a newly developed aromatic sulfonamide, bistriflimide (Tf2N), or iodide. The relationship between molecular structure and physical properties, including thermal behavior, density, and viscosity, is reported. The identity of the anion has the strongest effect on both thermal stability and thermal behavior, whereas elongation of the fluorinated alkyl chain of the cation more strongly influences density and viscosity. These observations suggest nanosegregation within the liquid and the formation of three microphases (polar, nonpolar, and fluorous). We then evaluate the solubilities of commonly used hydrofluorocarbon refrigerant gases, HFC-32 (difluoromethane) and HFC-125 (pentafluoroethane), in the neat and encapsulated FILs, comparing their performance against commercially available ionic liquids (ILs). We find higher solubilities of HFC-32 in the FILs relative to nonfluorinated commercial ILs that exhibited greater solubility of HFC-125, highlighting selective gas absorption. Additionally, we observe that encapsulated FILs exhibit trends in gas uptake analogous to those of neat FILs. This work not only contributes to a deeper understanding of the structure–property relationships in FILs but also presents promising avenues for their utilization in HFC gas uptake and separation processes, emphasizing the potential of encapsulated FILs as a viable technology to overcome challenges associated with high viscosities of ILs in bulk processing