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.
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.