Solubility of carbon dioxide in pentaerythritol tetrabutyrate (PEC4) and comparison with other linear chained pentaerythritol tetraalkyl esters

Carbon dioxide (CO2) is one of the most promising natural refrigerants that can be employed as an alternative to hydrofluorocarbons (HFC), due to its low global warming potential (GWP). Nevertheless, CO2 presents several technical problems when employed as a working fluid in refrigeration systems. In particular, the selection of the most suitable lubricant for each application is far from being resolved. The thermodynamic behavior of a CO2+lubricant system must be well-known for a correct oil selection. This work is part of a research project to study the solubility of CO2 in commercial oils and their precursors. Here, solubility measurements of CO2 in pure pentaerythritol tetrabutyrate (PEC4) between 243 K and 343 K are presented and compared with miscibility data of CO2 in pentaerythritol tetrahexanoate (PEC6) and pentaerythritol tetraoctanoate (PEC8). The experimental data were correlated with a thermodynamic model based on a cubic equation of state with Huron-Vidal mixing rules and the UNIQUAC equation for the excess Gibbs energy at infinite pressure.