Measuring Carbon Dioxide Solubility in Ionic Liquids with IGA Analyzers

We are looking forward to the ILSEPT conference in Toronto which is co-chaired by customers from two key sites who have been using Hiden Isochema IGA instruments to measure gas solubilty in ionic liquids. The solubility of CO₂ in ionic liquids is of specific interest as ionic liquids are an extremely energy efficient green solvent with potential applications for CO₂ capture.

A paper [1] published recently in RSC Advances by our customers at University of Regina, Canada and their collaborators at Chulalongkorn University, Thailand describes the measurement of CO₂ solubilities in five room temperature ionic liquids using an IGA-003, and we thought it timely to comment on this paper in advance of ILSEPT.

After validation of the method and instrument by measuring CO₂ solubility in a well characterised imidazolium- based ionic liquid, [bmim][PF6], five ammonium- and sulfonium- based ionic liquids were studied [2]. Each ionic liquid sample was loaded into the IGA and degassed in situ. The IGA was programmed to measure equilibrium CO₂ solubility in each ionic liquid gravimetrically at thirteen pressures and three temperatures; with the IGA’s unique real-time processor used to determine the end point for each pressure / temperature point before automatically moving onto the next pressure / temperature point of the map.

A thermodynamic assessment including relevant equations of state for CO₂ and temperature- dependent densities of ionic liquids was used to additionally give enthalpies and entropies of adsorption, and Henry’s law constants for CO₂ solubility in the different ionic liquids.

This paper is a good demonstration of the ability of IGA instruments to accurately and reproducibly measure gas solubilities in ionic liquids at a range of temperatures and pressures, and has provided a significant addition to the literature of published gas solubilties in ionic liquids.

More generally, it is worth noting that the paper provides an excellent illustration of validation of measurements with peer reviewed data obtained using three different IGA instruments at three different laboratories over a period of more than 10 years.

[1] Densities and low pressure solubilities of carbon dioxide in five promising ionic liquids; Thanawat Nonthanasin, Amr Henni and Chintana Saiwana; RSC Adv., 2014, 4, 7566-7578.

[2] The ionic liquids studied were [S₂₂₂][Tf₂N], [deme][Tf₂N], [pmim][Tf₂N], [amim][[Tf₂N] and [4mbp][BF₄].111