Solubility Measurements and Data Correlation of Carbon Dioxide in Pentaerythritol Tetrahexanoate (PEC6)

Abstract

The compatibility of carbon dioxide with synthetic oils, employed as lubricants for compressors in the refrigeration and air conditioning plants, is a fundamental and still unsolved problem. Mutual solubility with the refrigerant is one of the properties that influences the choice of a particular lubricant for a specific application. A systematic study of the solubility of carbon dioxide in polyolester oils (POE) has been started at our laboratories with the aim to investigate the dependence of this property on various parameters, such as pressure, temperature, and oil chemical structure. In this paper, experimental measurements of solubility of carbon dioxide in pentaerythritol hexanoate (PEC6), which is a precursor of polyol ester based lubricants, are presented in a temperature range of (243 to 343) K and pressures up to about 10 MPa. The uncertainty in the liquid composition measurements was estimated to be from 0.002 (high CO 2 molar fraction) to 0.02 (low CO 2 molar fraction). The experimental data were correlated by means of the Peng-Robinson equation of state with the Huron Vidal mixing rules in which the excess Gibbs energy at infinite pressures was represented by the UNIQUAC equation.

Solubility of Carbon Dioxide in Pentaerythritol Tetrabutyrate (PEC4) and Comparison with Other Linear Chained Pentaerythritol Tetraalkyl Esters

“…This work completes a series of solubility measurements and data correlation for binary systems composed of carbon dioxide and linear chained precursors of POE lubricants (PECs), after previous studies of CO 2 + PEC6 [13] and CO 2 + PEC8 [14] systems, and preliminary results on CO 2 + PEC4, which have been reported already [12]. Here, complete experimental results for the solubility of CO 2 + PEC4, with modeling with the Peng-Robinson equation of state with Huron-Vidal mixing rules, are presented.…”

“…The solubility measurements were performed with an apparatus that has already been extensively described [8,13], so here only its main features will be noted. The equilibrium between the two substances was reached in a stainless steel cell with a calibrated volume of 180 cm 3 , equipped with glass windows to observe the mixture.…”

“…1, while for the other systems the available experimental data were 91 and 56 points for PEC6 + CO 2 [13] and for PEC8 + CO 2 [14], respectively.…”

“…The complete model was already described in [13], in which the following expression was used for the PR EoS a 22 temperature dependence, …”

“…Unfortunately, in the literature there is a lack of such information, except for few systematic works, as [1][2][3][4][5][6][7]. For this reason, our group is involved in a research program to provide experimental measurements and the development of a general predictive model focused on the phase behavior of lubricant + refrigerant blends, with particular attention to systems of POE precursors and CO 2 [8][9][10][11][12][13][14].…”