From the Correlation of Binary Systems Involving Supercritical CO₂ and Fatty Acid Esters to the Prediction of (CO₂−Fish Oils) Phase Behavior

Abstract

In this paper, a purely predictive model for the phase equilibria computation of mixtures involving fatty acid esters (FAE) and supercritical carbon dioxide is proposed. In a first step, the phase equilibria modeling of FAE/CO2 binary systems were performed using the Peng−Robinson equation of state. To obtain a purely predictive model, the critical properties (T c, P c) and the acentric factor (ω) of the FAE were estimated with specific correlations. Moreover, the group contribution method developed by Abdoul et al., which allows the prediction of binary interaction parameters (k ij ), was extended to ester compounds and an additional group (the ester function) was defined. Such an approach allowed us to correlate with quite good accuracy all the binary FAE/CO2 systems. In a second step, dew points of (CO2/fish oil) systems were measured and the previous model was used to check its capability in predicting these data. The fish oil under study contained 30 different fatty acid ethyl esters, and the model was able to predict with very good accuracy the measured saturation pressures.

High pressure phase behaviour of the CO2+1-decanol+n-dodecane system

“…At the critical point the first and second derivatives of pressure with respect to volume are zero, complicating calculations near the critical point of the solvent. Consequently many EOSs have difficulty M a n u s c r i p t 8 in accurately predicting phase behaviour in the critical region [7,10,16]. Even more sophisticated models, such as the statistical associating fluid theory (SAFT) family of equations struggle, to predict phase behaviour in the mixture critical region [16].…”

“…However, good experimental data is required to improve the predictive capabilities of these models and to verify their applicability [5][6][7].…”

Relationship between the binary interaction parameters (kij) of the Peng–Robinson and those of the Soave–Redlich–Kwong equations of state: Application to the definition of the PR2SRK model

“…As recently shown [11], such a model is perfectly able to predict the behavior of petroleum fluids. A GCM has been chosen to estimate the BIPs because we were aware that the group contribution concept could be useful to model complex processes like those involving supercritical fluids [25][26][27] and because the number of binary systems for which phase equilibrium data are available is at most several thousands while the number of the compounds used now by industry is estimated at around 100,000. …”

Predicting the phase equilibria of synthetic petroleum fluids with the PPR78 approach

“…A cubic EoS has been chosen because in process design, due to their low complexity and their high accuracy for nonpolar compounds, such EoS allow for fast screening of a large number of design alternatives and preselection of the most favorable candidate structures. A GCM has been chosen to estimate the binary interaction parameters because we were aware that the group contribution concept could be useful to model complex processes like those involving supercritical fluids [15][16][17] and because the number of binary systems for which phase equilibrium data are available is at most several thousands while the number of the compounds used now by industry is estimated at around 100,000. It is thus necessary to be able to predict the binary interactions from the mere knowledge of the molecular structure.…”