Controlling phase behaviour on gas expansion of fluid mixtures

Abstract

The application of moderate pressures (50 bar) of CO 2 to binary liquid solvent mixtures at room temperature can induce changes in phase behaviour; both inducing miscibility and splitting miscible mixtures. The cause of this phase change behaviour was found to be due to the balance between enthalpic and entropic terms that define the Gibbs energy of mixing and, hence, the partition coefficient. In the majority of binary solvent mixtures, the solvents were miscible at ambient pressure with two phases forming upon application of CO 2 . For some mixtures, the phase behaviour was found to be very composition dependent and in only five systems did no phase change occur.

Phase equilibrium of the CO2/glycerol system: Experimental data by in situ FT-IR spectroscopy and thermodynamic modeling

“…Also, understanding the effects of dissolved CO 2 on the physicochemical properties of the glycerol-rich phase is important for reaction design [13,14]. Indeed, CO 2 modifies the polarity of the solvent and, for instance, from this effect, initially miscible compounds are likely to become immiscible when the solvent is pressurized with CO 2 , even at moderate pressures (5.0 MPa) [15]. So, CO 2 can then act as a switch to control the polarity and solvating properties of the partner solvent, allowing recovery of catalysts, products, byproducts, and so on.…”

Sustainable Synthesis of Dimethyl- and Diethyl Carbonate from CO2in Batch and Continuous Flow─Lessons from Thermodynamics and the Importance of Catalyst Stability

“… 71 In addition, the option of tunable phase behavior by modulation of temperature and pressure offers interesting possibilities for separations of the product mixture obtained. 72 − 74 We thus investigated the performance of the CeO 2 catalyst for DAC formation as a fixed bed in a continuous flow reactor 53 using neat, dry alcohol dissolved in scCO 2 (for experimental details, see the Supporting Information ).…”

“…For the synthesis of DACs from short-chain alcohols and CO 2 , the use of compressed (near- or supercritical) CO 2 as the carrier in a flow system is particularly appealing, as such media are known to combine gas-like diffusivity with solution-like solubility . In addition, the option of tunable phase behavior by modulation of temperature and pressure offers interesting possibilities for separations of the product mixture obtained. − We thus investigated the performance of the CeO 2 catalyst for DAC formation as a fixed bed in a continuous flow reactor using neat, dry alcohol dissolved in scCO 2 (for experimental details, see the Supporting Information).…”

“…A variety of separation technologies may be evaluated to achieve this task, including CO 2 -induced phase splits, ,, supercritical extraction, or pervaporation membranes. The latter have been used successfully for DMC/MeOH separations as well as two-step distillation–pervaporation separations in DEC synthesis from EtOH .…”

Ternary System CO2/2-MTHF/Water—Experimental Study and Thermodynamic Modeling

“…Upon addition of CO 2 to biphasic solvent systems, the diffusivities, partition coefficients, and extensive volumes typically increase in the organic phase. − These CO 2 -expanded liquids (CXL) have been intensively studied in the past decade. − The change in volume of the organic phase at moderate pressures (<5 MPa) is an established way to characterize a CXL system. To understand and exploit the possibilities of tailoring the properties of liquid/liquid solvent systems by adding CO 2 , knowledge of pressure- and temperature-dependent equilibrium compositions as well as molar densities is necessary .…”