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

Abstract

High-pressure bubble point and dew point data were measured for several C18 fatty acid methyl ester (FAME) + CO2 systems. The supplementary data for the binary systems methyl stearate + CO2, methyl oleate + CO2, and methyl linoleate + CO2, as well as the new data for the methyl stearate + methyl oleate + CO2 ternary system for solvent-free methyl stearate mass fractions of 0.237–0.772 (g methyl stearate)·(g–1 total FAME), were measured. The reported data were measured in the ranges of temperature T = 308–348 K, pressure P = 7.22–22.22 MPa, and FAME fraction z = 0.0097–0.6234 g·g–1. The results indicate that at a constant hydrocarbon backbone length, saturated FAMEs have higher phase transition pressures in supercritical CO2 than unsaturated FAMEs, but there is no significant difference in phase transition pressure between the monounsaturated and polyunsaturated FAMEs. This phase transition pressure difference decreases with the increasing temperature. Additionally, for FAME mixtures, the phase transition pressures increase linearly with the increasing content of the saturated component. This indicates an absence of complex molecular interactions in these systems. Prediction of the data with the predictive Peng–Robinson equation of state failed to describe the experimental observations of the influence of unsaturation on the phase behavior.

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.…”

High-Pressure Phase Equilibria Measurements of the Carbon Dioxide + Cycloheptane Binary System

“…The isothermal curves (P, 𝑥 𝐶𝑂 2 ) thus cannot be graphed directly from the measured data presented in Table 2. Interpolated values were calculated using second order polynomials to describe the pressuretemperature relationship of the raw experimental data at constant composition, following the reliable method previously described in detail by Schwarz et al 6,[19][20][21] The following second order polynomial was used…”

“…1,3 Due to the important role of carbon dioxide in the chemical, pharmaceutical and petrochemical industries, phase equilibrium data of mixtures containing CO2 remain crucial. [4][5][6][7][8] In our previous works 3,9 , a lack of data for two kinds of binary systems containing carbon dioxide + a naphthenic compound was noticed; they are CO2 + branched naphthenes and CO2 + naphthenes that contains more than 6 carbon atoms in ring (cycloheptane, cyclooctane, etc.). Indeed, the binary systems CO2 + cyclopentane and CO2 + cyclohexane were widely investigated in the past and more details about the different studies related to these two systems can be found elsewhere.…”

“…However, experimental data are still needed for many application areas. , Even in the oil and gas sector, high-pressure phase equilibrium data as well as thermodynamic data regarding uncommon molecules (such as naphthenic components with more than six carbon atoms in the ring or with multiple aromatic rings) are welcomed. , Due to the important role of carbon dioxide in the chemical, pharmaceutical, and petrochemical industries, phase equilibrium data of mixtures containing CO 2 remain crucial. − …”