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

Significance 

The continuous advancement in software and instrumentation technologies has significantly contributed to innovative and ground-breaking advancement in engineering and science. For example, developing novel materials with improved properties requires a thorough understanding of their chemical and physical properties. This has been successfully achieved via gravimetric analysis of the sorption behaviors. However, most of the sorption studies reply on single components utilizing either volumetric or gravimetric techniques. To overcome the limitations of single components under realistic operating conditions, multicomponent sorption measurements have been adopted.

Despite its potential benefits, multicomponent sorption measurements face two major challenges: (1) it is difficult to calculate the concentration of each species present in the sorbed phase, and (2) the process is laborious and time-consuming. The analytical and experimental difficulties associated with multicomponent absorption measurements present serious practical challenges for efficient and accurate multicomponent gas sorption measurement. This has directly contributed to the limited studies on multicomponent sorption and the lack of comprehensive kinetic data for real separation systems.

Recently, there has been a growing need to develop efficient instrumentation methods for characterizing materials using multitechnique approaches, mixed gas systems, dynamic conditions and small qualities by combining sorption measurements with other analytical tools. Among these methods is the Integral Mass Balance (IMB) method recently developed by Hiden Isochema. It has proved effective in designing a separation process for measuring the binary and multicomponent sorption of hydrofluorocarbon (HFCs) in ionic liquids (ILs), which is important in evaluating the potential of using ILs to separate refrigerant mixtures. This requires extensive studies on multicomponent HFC/IL systems, which is currently lacking.

Herein, University of Kansas researchers: PhD candidate Kalin Baca, Dr. Darren Broom, Dr. Mark Roper, Dr. Michael Benham and led by Professor Mark Shiflett investigated the mixture absorption of difluoromethane (HFC-32) and pentafluoroethane (HFC-125) in two different ILs (1-n-butyl-3-methylimidazolium hexafluorophosphate ([C4C1im][PF6]) and 1-n-butyl-3-methylimidazolium tetrafluoroborate) ([C4C1im][PF4]) at a temperature of 298.15 K. A combination of Intelligent Gravimetric Analyzer (IGA), XEMIS and IMB methods was used to measure the multicomponent gas absorption. Their main objective was to gain a deeper understanding of the interactions between HFC mixture and ILs. The research work is currently published in the peer-reviewed journal, Industrial and Chemistry Engineering Research.

The research team demonstrated that the state-of-the-art instruments were capable of measuring HFC binary gas mixtures in ILs with remarkably higher efficiency and accuracy. The obtained measurement results were comparable with those of the existing measurements of single gas solubility. The difference in the total absorption for ([C4C1im][PF6]) and ([C4C1im][PF4]) was significantly influenced by the solubility of HFC-32 in the individual ILs. In contrast, the solubility of HFC-125 had a minimal impact. The HFC-32 equilibrium selectivity in the two ILs was dependent on the inlet HFC-125 composition.

In summary, this is the first study to measure the simultaneous sorption of HFC-32 and HFC-125 gas mixture as a function of composition in two different ILs. The combination of IGA, XEMIS and IMB methods successfully overcome the inherent challenges of studying multicomponent absorption of gases in solids and low-volatility liquids. In a statement to Advances in Engineering, the lead and corresponding author distinguished Professor Mark Shiflett noted that their study provided valuable insights that would pioneer the design and development of extractive distillation processes using IL entrainers for efficient separation of azeotropic refrigerant mixtures.

About the author

Kalin Baca is a 2020-2024 Self Graduate Fellow pursuing a Ph.D. in chemical engineering at the University of Kansas in the Shiflett Research Group. She holds a M.S. in chemical engineering (2019), MBA with a concentration in organizational behavior (2019), and B.S. in chemical engineering with a concentration in bioengineering and a minor in business management (2018) from the University of New Mexico. Her doctoral research is focused on the separation of hydrofluorocarbon (HFC) refrigerant mixtures using ionic liquids. This research is part of Project EARTH (Environmentally Applied Research Toward Hydrofluorocarbons) that is focused on identifying sustainable processes for the selective separation of hydrofluorocarbon (HFC) refrigerant mixtures. Baca is the cofounder of Iconium Engineering Company that is commercializing the refrigerant separation process.

About the author

Mark B. Shiflett is a Distinguished Foundation Professor in the Department of Chemical Engineering and Director of the Institute for Sustainable Engineering at the University of Kansas (KU). Before joining KU, Professor Shiflett worked for DuPont for 28 years and was a Technical Fellow in the Central Research and Development organization. Professor Shiflett received his Ph.D. and M.S. degrees in chemical engineering from the University of Delaware (UD) in 2001 and 1998 and served as an adjunct professor at UD from 2011 – 2016. He received his B.S. degree in chemical engineering from N.C. State University in 1989. Professor Shiflett is an inventor on 45 U.S. patents and has published 125 articles. He was awarded the DuPont Bolton Carothers award in 2005, the ACS Hero of Chemistry award in 2006, the University of Delaware presidential citation in 2007, and the American Institute of Chemical Engineers Institute award for Industrial Research in 2016 for his development of hydrofluorocarbon refrigerant mixtures to replace chlorofluorocarbons which were linked to the depletion of the Earth’s ozone layer. Professor Shiflett leads Project EARTH (Environmentally Applied Research Toward Hydrofluorocarbons) that is developing new technologies for separating and recycling refrigerant mixtures. Professor Shiflett cofounded Iconium Engineering Company to commercialize the refrigerant separation technology and is a licensed professional engineer in the State of Delaware. To learn more about Professor Shiflett and his research group you can visit their website: www.shiflettresearch.com.

Reference

Baca, K. R., Broom, D. P., Roper, M. G., Benham, M. J., & Shiflett, M. B. (2022). First measurements for the simultaneous sorption of Difluoromethane and pentafluoroethane mixtures in ionic liquids using the integral mass balance method. Industrial & Engineering Chemistry Research, 61(27), 9774–9784.

Go To Industrial & Engineering Chemistry Research

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