WISE Researcher Advances Reliable Process Design for Ionic-Liquid-Based Refrigerant Separation

Modern cooling systems rely on complex refrigerant mixtures that must be carefully separated, reused, or recycled to reduce environmental impact. A new study from the University of Kansas helps engineers better understand how advanced materials called ionic liquids behave at high temperatures—knowledge that supports more efficient, reliable, and sustainable cooling technologies. 

Highlights 

• Ionic liquids remain effectively non-volatile under industrial conditions. 
  Experimental measurements confirm negligible vapor pressure at typical reboiler and flash tank temperatures, validating their use in high-temperature extractive distillation. 
• Common simulation tools overestimate vapor pressure. 
  Widely used thermodynamic models and group contribution methods significantly overpredict ionic liquid volatility, which can lead to conservative or inaccurate process designs. 
• Thermal stability—not evaporation—is the primary design constraint. 
  Within normal operating ranges, ionic liquid performance is limited by thermal degradation rather than vaporization, shifting design priorities toward stability analysis. 

Arishi Abdulrhman, a researcher with the Shiflett Research Group at the Wonderful Institute for Sustainable Engineering (WISE), has published a peer-reviewed article titled “Vapor Pressure Estimation of Imidazolium-Based Ionic Liquids via Non-Isothermal Thermogravimetric Analysis (TGA) and Its Implications for Process Design” in Industrial & Engineering Chemistry Research. 

Ionic liquids are promising entrainers for the separation of hydrofluorocarbon (HFC) and HFC/HFO refrigerant mixtures due to their high thermal stability and extremely low volatility. However, property estimation methods and equations of state commonly used in process simulation software often overestimate ionic liquid vapor pressure at elevated temperatures, leading to conservative or inaccurate predictions in extractive distillation and flash operations. 

In this study, Abdulrhman employed non-isothermal thermogravimetric analysis (TGA) to experimentally estimate the vapor pressure and heat of vaporization of three imidazolium-based ionic liquids relevant to industrial separation processes. The results demonstrate that these ionic liquids maintain negligible vapor pressure under typical reboiler and flash tank operating conditions, even where simulation tools predict measurable evaporation. 

The findings improve the accuracy of rate-based modeling and process design, strengthening confidence in simulations used for refrigerant recovery, recycling, and low-global-warming-potential cooling technologies.  

This work contributes to ongoing efforts within the NSF Engineering Research Center for Environmentally Applied Refrigerant Technology (EARTH) by supporting scalable, energy-efficient, and environmentally responsible separation solutions. EARTH operates within WISE, bringing together interdisciplinary teams to advance breakthrough technologies in refrigerant chemistry and sustainable systems engineering. 

Read the full publication below:
Vapor Pressure Estimation of Imidazolium-Based Ionic Liquids via Non-Isothermal Thermogravimetric Analysis (TGA) and Its Implications for Process Design
https://pubs.acs.org/doi/10.1021/acs.iecr.5c03459

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