Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 149881

149881 - Interfacial Tension Measurements of Diflouromethane (Hfc-32), Pentafluoroethane (Hfc-125), and Ionic Liquid [C2c1im][tf2n] Systems at Elevated Pressures and Temperatures 

 

Introduction

The world is transitioning to the “fourth generation” of refrigerants, hydrofluoroolefins (HFOs), as many current hydrofluorocarbons (HFCs) have high Global Warming Potential (GWP).  The American Innovation Manufacturing (AIM) Act mandates the phasedown of the high GWP HFCs by 85% by 2036. Many of the current HFC refrigerants are azeotropic mixtures containing both low and high GWP HFCs.  For instance, the common R-410A is a 50/50 wt% mixture of difluoromethane HFC-32 (CH₂F₂, GWP₁₀₀ = 675), which has a low enough GWP that it can be blended with HFOs for continued use; and pentafluoroethane HFC-125 (C₂HF₅, GWP₁₀₀ = 3500) which must be phased out. As R-410A is an azeotrope, conventional separation methods are not effective for separating and recovering low-GWP components such as HFC-32. Extractive distillation using ionic liquids (ILs) may be an effective solution for separating azeotropic HFC-based refrigerants. The modeling and design of extractive distillation systems requires transport properties to accurately calculate mass transfer phenomena. This investigation presents the experimental and modeling study of the interfacial tension (IFT) of HFC-32, HFC-125, and IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C₂C₁im][Tf₂N] at elevated pressures and temperatures. The results will provide the data necessary for developing a rate-based process simulation of a pilot-scale extractive distillation system.

 

Contribution/Application/Significance

This experimental work is the first attempt to measure and model HFC-32, HFC-125, and [C₁C₂im][Tf₂N] systems at high-pressures and high-temperatures found in an extractive distillation system. Likewise, results from this effort will be used for developing a rate-based model that will allow the process optimization using ILs as entrainers. The extractive distillation system located at the University of Kansas aims to separate recycled HFC refrigerants such as R-410A, reusing low-GWP components such as HFC-32 and repurposing high-GWP components such as HFC-125. Results from this work support the design and scale-up of the extractive distillation process for separating recycled HFC refrigerants.

 

Methods/Procedures/Process

The IFT of two refrigerants, HFC-32 and HFC-125 with [C₁C₂im][Tf₂N] in binary mixtures has been measured as a function of temperature and pressure. The measurements were conducted under equilibrium conditions between the liquid and its saturated vapor phase. The pendant drop method used a high-pressure, high-temperature (HPHT) cell with an internal volume of 25 cc. Experiments were conducted over a temperature range  from 283.15 to 373.15 K and a pressure range from 1 to 14 bar. The accuracy of IFT measurements was estimated to be within ±0.2 mNm⁻¹. Temperatures and pressures are accurate to within ± 2.0 K and ± 0.1 bar, respectively. Available surface tension data for pure compounds are compared with the present data. No reported data for experimental interfacial tension has been previously published for HFC-32 and HFC-125 in a mixture with IL [C₁C₂im][Tf₂N] at high-pressure, high-temperature conditions.  The resultant IFT experimental data was modeled using various methods.

 

Results/Observations/Conclusion

Results show that an increase in temperature decreases IFT for the binary systems (e.g., HFC-32//[C₂C₁im][Tf₂N] and HFC-125/[C₂C₁im][Tf₂N]). Likewise, the addition of HFC-32 or HFC-125 reduces the IFT between the droplet and the continous phases. In particular, the influence of HFC-32 have been found to be less pronounced than HFC-125. With respect to predictions from an ideal mixing rule, increase in HFC-32 composition leads to a larger IFT value compared with the ideal mixing rule. In contrast, increase in HFC-125 composition leads to a smaller IFT value compared with the ideal mixing rule. In both cases, the IFT deviations with respect to the ideal mixing rule predictions increases with temperature.

 

Keywords: interfacial tension, ionic liquids, refrigerants.

Presenting Author: Julia Espinoza Mejia University of Kansas

Presenting Author Biography: Julia Espinoza is an international, first-gen, and nontraditional graduate student from Peru. After receiving her bachelor’s degree in Chemical Engineering from the National University of Engineering, Lima, Peru, in 2010, she joined the National Petroleum Company of Peru (PETROPERU), where she has worked for eight years. At work, she performed different positions such as process engineer, design engineer, and lastly, as leader of the process engineering unit in 2018. In 2019, she earned the Fulbright-CAREC scholarship, which allowed her to train in English and graduated with M.Sc. in Petroleum Engineering at KU (2022). In her investigation, she studied the phase behavior of Oil-CO2 systems under various pressure and temperature conditions to predict asphaltene precipitation using HPHT PVT and SDS techniques. From this research, she has published 02 scientific papers. She also graduated with a Master in Process Engineering from the National University of Engineering, Lima, Peru (2013). She is currently pursuing a Ph.D. in Chemical and Petroleum Engineering at KU under the advice of Dr. Scurto and Dr. Shiflett as part of the NSF-funded project, Project EARTH (Environmentally Applied Research Toward Hydrofluorocarbons). Her research focuses on the separation of azeotropic hydrofluorocarbon (HFC) mixtures from refrigerants using ionic liquids as solvents. Julia’s work occurs mainly in the lab where a state-of-the-art pilot-scale extractive distillation tower is commissioning and starting up for the first time. She has also been a partial Teaching Assistant (TA) for some C&PE courses, including Thermodynamics I and II and Reservoir Engineering I, serves as a vice president of the Graduate Engineering Association, and is the adviser for the Peruvian Student Association at KU. Outside the lab, her interests include learning languages, learning about cultures, swimming, and practicing zumba.

Authors:

Julia Espinoza Mejia University of Kansas
Aaron M. Scurto University of Kansas
Mark B. Shiflett University of Kansas