High Pressure Phase Equilibria of the CO₂/Saturated Ethyl Esters Homologous Series

Abstract

A systematic study on the phase behavior of saturated ethyl esters with supercritical CO2 is presented. High pressure phase behavior measurements for the systems CO2/ethyl decanoate, CO2/ethyl dodecanoate, CO2/ethyl tetradecanoate, and CO2/ethyl hexadecanoate were conducted in a static synthetic view cell in the temperature range 308–358 K. Phase transition pressures were measured in the range 5.86–23.01 MPa for ethyl ester mass fractions in the range 0.0174–0.657 and complement existing literature data. Throughout the temperature and compositional range measured, which encompassed the liquid phase, mixture critical region, and vapor phase, an increase in temperature leads to an increase in phase transition pressure with no temperature inversions or three phase regions observed. Additionally, an increase in hydrocarbon backbone length leads to an ever-increasing phase-transition pressure, suggesting fractionation of ethyl esters according to molecular mass with supercritical CO2 is possible. Finally, the measured and previously published CO2/ethyl ester data were successfully correlated with a modified Chrastil models and the MT model. While these models cannot easily be used predictively and depend on the data sets used for correlation, these are simple and easy methods that can be used to interpolate data.

Influence of Unsaturation on the High-Pressure Phase Behavior of C18 Fatty Acid Methyl Esters + CO2

“…This would explain the increasing gradient trend observed in Figure . A similar trend in the phase transition pressure was observed by Schwarz for the C 10 to C 16 ethyl esters at higher temperatures.…”

“…A given mixture of M18:0 and M18:1 cannot have a higher solubility (lower phase transition pressure) than pure M18:1, since the presence of M18:1 cannot reduce the packing density of the mixture beyond the case of there being only M18:1. This is in agreement with the 34 Hwu et al, 35 Schwarz, 36 Crampon et al, 8 and Bharath et al, 37 with consultation of the data review collections by Dohrn and coworkers. 38−40 The uncertainty u(P) was calculated for each phase transition pressure at each temperature, but the effect of the uncertainty in the temperature on u(P) was not significant and, thus, all pressures at a given composition have the same value of u(P), regardless of the measurement temperature.…”

“…The dashed line represents a straight line between the two data points with the lowest N C . Data from Borges et al, Hwu et al, Schwarz, Crampon et al, and Bharath et al, with consultation of the data review collections by Dohrn and co-workers. − …”

High-Pressure Phase Behavior of CO2 + (C12/C14 n-Alkane and/or C8/C10 Carboxylic Acid and/or C12/C14 Methyl Ester) Systems

“…Although the experimental setup and procedure have been extensively verified, − ,,,,− it is prudent to ensure that any new operator is able to produce reliable data by using the equipment. To this end a verification system, CO 2 + 1-octanol, was measured by the present authors and compared to a multitude of literature sources.…”