First Measurements for the Simultaneous Sorption of Difluoromethane and Pentafluoroethane Mixtures in Ionic liquids Using the Integral Mass Balance Method

Abstract

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.

Separation of Azeotropic Hydrofluorocarbon Refrigerant Mixtures: Thermodynamic and Kinetic Modeling for Binary Adsorption of HFC-32 and HFC-125 on Zeolite 5A

“…eq is used by the HIsorp software to calculate the moles of species i adsorbed by the adsorbent. The full development of the IMB method was described by Broom et al and has also been discussed by Baca et al…”

“…eq 46 is used by the HIsorp software to calculate the moles of species i adsorbed by the adsorbent. The full development of the IMB method was described by Broom et al 19 and has also been discussed by Baca et al 45 XEMIS Gravimetric Microbalance. A separate Hiden Isochema XEMIS gravimetric microbalance was used to measure pure gas adsorption isotherms for HFC-125 and HFC-32 with zeolite 5A.…”

Multicomponent Refrigerant Separation Using Extractive Distillation with Ionic Liquids

“…Developing a separation process to purify HFCs from refrigerant mixtures can be challenging since many of these mixtures are azeotropic or near azeotropic, making separation difficult to impossible using conventional distillation methods. Only advanced separation processes provide an alternative for recovering refrigerant blends, such as absorption in liquid entrainers, , adsorption on materials such as zeolites, and membrane separation technologies . Project EARTH (Environmentally Applied Research Towards Hydrofluorocarbons) is developing environmentally responsible materials and technology to separate azeotropic HFC mixtures and recycle the pure component refrigerants.…”

Understanding the Molecular Features Controlling the Solubility Differences of R-134a, R-1234ze(E), and R-1234yf in 1-Alkyl-3-methylimidazolium Tricyanomethanide Ionic Liquids

“…Our extensive analysis of the information available on F-gas absorption in ILs showed that the solubility selectivity for separation of HFC and HFO mixtures could be enhanced using ILs with low molar volume (which is linked to higher charge density in the ions) . Using this knowledge, we previously studied the absorption of HFCs and HFOs in ILs with thiocyanate and dicyanamide anions and obtained the highest selectivity values to date for the separation of R-32 (difluoromethane) and R-134a from R-125 (pentafluoroethane) and R-1234yf, calculated in terms of the ratio of Henry’s law constants at infinite dilution and equilibrium flash separations at 5 bar based on NRTL model calculations. ,, These statements should be validated by means of experimental ternary data as in the recent article by Baca et al , However, the separation of R-134a from R-1234ze­(E) was still found to be difficult because the HFO R-1234ze­(E) is more soluble than its isomer R-1234yf. The rationale behind this difference in solubility is not completely clear because of their very similar physical properties.…”