Investigations in Supercritical Fluids

Niessen, Heiko G.; Woelk, Klaus

doi:10.1007/b135837

Cited by 17 publications

(8 citation statements)

References 148 publications

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“…At temperatures and pressures above its critical point, a substance exists in a state that exhibits the properties of both liquid and gas. − The properties of supercritical fluids (SCFs) such as compressibility, diffusivity, density, and solvation of different solutes can be modulated through minor variations of temperature and pressure when the system is very close to the its critical conditions. − These fascinating features of SCFs lead to their important potential as environmentally benign green alternatives to toxic organic solvents and there have been many industrial and technological applications using SCFs. Industrial separations using SCFs are well-known with the most famous example being decaffeination . In conditions of the high dilution that prevail in different processes, solute’s thermodynamic properties scale as the solvent isothermal compressibility.…”

Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulation of Na⁺–Cl^– Ion-Pair in Water–Methanol Mixtures under Supercritical and Ambient Conditions

2015

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Constrained molecular dynamics simulations have been performed to investigate the structure and thermodynamics of Na(+)-Cl(-) ion-pair association in water-methanol mixtures under supercritical and ambient conditions in dilute solutions. From the computed potentials of mean force (PMFs) we find that contact ion pairs (CIPs) are more stable than all other associated states of the ion pairs in both ambient and supercritical conditions. Stabilities of CIPs increase with increase in the mole fraction of methanol. In supercritical conditions, major changes in PMFs occur as we go from x(methanol) = 0.00 to x(methanol) = 0.50. The stable solvent shared ion pair (SShIP) which occurs in x(methanol) = 0.00 and 0.25, vanishes when x(methanol) is 0.50 or greater. The stabilities of these ion pairs increase with increasing temperature. Local structures around the ions are studied using the radial distribution functions, density profiles, angular distribution functions, running coordination numbers and excess coordination numbers. Preferential solvation analysis shows that both Na(+) and Cl(-) ions are preferentially solvated by water. From the calculation of enthalpies and entropies, we find that Na(+)-Cl(-) ion-pair association in water-methanol binary mixtures is endothermic and driven by entropy both in ambient as well as under supercritical conditions.

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Section: Introductionmentioning

confidence: 99%

Molecular Dynamics Simulation of Na⁺–Cl^– Ion-Pair in Water–Methanol Mixtures under Supercritical and Ambient Conditions

2015

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“…At the LGCP, the boiling curve (separating the liquid and gas phases) ends, and the two phases merge into a single phase of supercritical fluid (SCF). Understanding the SCF also has practical implications because the blend of liquid-like and gas-like traits renders it particularly useful in chemical engineering. − …”

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confidence: 99%

Widom Delta of Supercritical Gas–Liquid Coexistence

Yoon

Tlusty

et al. 2018

J. Phys. Chem. Lett.

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Density fluctuations and the Widom line are of great importance in understanding the critical phenomena and the behaviors of supercritical fluids (SCFs). We report on the direct classification of liquid-like and gas-like molecules coexisting in the SCF, identified by machine learning analysis on simulation data. The deltoid coexistence region encloses the Widom line and may therefore be termed the Widom delta. Number fractions of gas-like and liquid-like particles are found to undergo continuous transition across the delta, following a simplified two-state model. These fractions are closely related to the magnitude of supercritical anomaly, which originates from the fluctuation between the two types. This suggests a microscopic view of the SCF as a mixture of liquid-like and gas-like structures, providing an integrative explanation to the anomalous behaviors near the critical point and the Widom line.

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“…At densities around those of conventional organic solvents, scCO 2 exhibits similar solvent power than typical non-polar solvents such as hexane, benzene or toluene. Diffusivity in scCO 2 has been measured and compared with toluene (Niessen and Woelk 2007) showing that scCO 2 exhibits diffusivities about five or more times higher than those measured in toluene even if the dissolution capabilities of both solvents are similar. The low viscosity exhibited by scCO 2 is the result of the reduced solvent -solvent molecular interactions in CO 2 .…”

Section: Supercritical Comentioning

confidence: 99%

“…Indeed, this number has increased proportionally to the increase in environmentally motivated research and technology (Niessen and Woelk 2007).…”

Section: Scco 2 As a Green Process And Its Place In Sustainable Enginmentioning

confidence: 99%

Cellulosic materials as biopolymers and supercritical CO₂as a green process: chemistry and applications

Medina-González

Camy

Condoret

2012

International Journal of Sustainable Engineering

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao. In this review, we describe the use of supercritical CO 2 (scCO 2 ) in several cellulose applications. The focus is on different technologies that either exist or are expected to emerge in the near future. The applications are wide from the extraction of hazardous wastes to the cleaning and reuse of paper or production of glucose. To put this topic in context, cellulose chemistry and its interactions with scCO 2 are described. The aim of this study was to discuss the new emerging technologies and trends concerning cellulosic materials processed in scCO 2 such as cellulose drying to obtain aerogels, foams and other microporous materials, impregnation of cellulose, extraction of highly valuable compounds from plants and metallic residues from treated wood. Especially, in the bio-fuel production field, we address the pre-treatment of cellulose in scCO 2 to improve fermentation to ethanol by cellulase enzymes. Other reactions of cellulosic materials such as organic inorganic composites fabrication and de-polymerisation have been considered. Cellulose treatment by scCO 2 has been discussed as well. Finally, other applications like deacidification of paper and cellulosic membranes fabrication in scCO 2 have been reviewed. Examples of the discussed technologies are included as well.

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Investigations in Supercritical Fluids

Cited by 17 publications

References 148 publications

Molecular Dynamics Simulation of Na⁺–Cl^– Ion-Pair in Water–Methanol Mixtures under Supercritical and Ambient Conditions

Molecular Dynamics Simulation of Na⁺–Cl^– Ion-Pair in Water–Methanol Mixtures under Supercritical and Ambient Conditions

Widom Delta of Supercritical Gas–Liquid Coexistence

Cellulosic materials as biopolymers and supercritical CO₂as a green process: chemistry and applications

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Investigations in Supercritical Fluids

Cited by 17 publications

References 148 publications

Molecular Dynamics Simulation of Na+–Cl– Ion-Pair in Water–Methanol Mixtures under Supercritical and Ambient Conditions

Molecular Dynamics Simulation of Na+–Cl– Ion-Pair in Water–Methanol Mixtures under Supercritical and Ambient Conditions

Widom Delta of Supercritical Gas–Liquid Coexistence

Cellulosic materials as biopolymers and supercritical CO2as a green process: chemistry and applications

Contact Info

Product

Resources

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Molecular Dynamics Simulation of Na⁺–Cl^– Ion-Pair in Water–Methanol Mixtures under Supercritical and Ambient Conditions

Molecular Dynamics Simulation of Na⁺–Cl^– Ion-Pair in Water–Methanol Mixtures under Supercritical and Ambient Conditions

Cellulosic materials as biopolymers and supercritical CO₂as a green process: chemistry and applications