Quasicritical behavior of dense‐gas solventsolute clusters at near‐infinite dilution

O'Brien, James A.; Randolph, Theodore W.; Carlier, Claude; Ganapathy, Shankar

doi:10.1002/aic.690390615

Cited by 57 publications

(100 citation statements)

References 43 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The L-J parameters for ethane are from Prausnitz (1969). The technique used to estimate the L-J parameters for DTBN is described by O'Brien et al (1993). Table 1 lists the L-J parameters that were used in the simulations (ethane = 1, DTBN = 2).…”

Section: Background and Methodologymentioning

confidence: 99%

Effect of solute‐solute correlations on rapid reactions in supercritical fluids

1995

Self Cite

View full text Add to dashboard Cite

Brownian and molecular dynamics simulations are used to study rapid bimolecular reactions at near-in finite dilution in near-critical and supercritical fluids. We probe the dynamics of both nonreactive and reactive collisions and measure rate constants f o r reaction and collision. Collision rate constants are nearly independent of bulk solvent density, but affected by local solute-solute density enhancements at a given density: their magnitudes depend on the length scale for molecular encounters (cybotactic radius) in the reaction through the equilibrium solute-solute radial distribution function. In contrast, reaction rate constants asymptotically approach the gas-kinetic limit at low densities and the IntroductionThere are certain classes of extremely rapid reactions where mass transfer is the rate-limiting step. Almost all free-radical reactions require so little activation energy that they are diffusion-controlled at liquid-like densities; examples of such reactions include atom recombinations, low molecular-weight free-radical reactions, and macroradical reactions such as freeradical polymerization (North, 1964). While these limitations could be relieved by carrying out these reactions in the gas phase, gas-phase reactant solubilities are often extremely low. The supercritical fluid phase provides a balance between the high solubilities provided by liquids and the high mass-transfer rate achievable in gases.Correspondence concerning this article should be addressed to J . A. O'Brien 346 February 1995The use of supercritical fluids (SCFs) as reaction media is an area of current technological development. Some of the unique features that characterize SCFs are liquid-like densities, gas-like viscosities, and diffusivities that are intermediate between typical gas and liquid values. Perhaps the most important feature is the ability to vary widely these properties of a SCF using small changes in temperature and pressure. Despite these potential advantages, fundamental understanding of the effect of supercritical fluid structure on reactivity is still incomplete, Reactivity of a solute in a supercritical solvent is strongly dependent on its local environment (Johnston and Haynes, 1987). Studies of reactions in supercritical fluid media have shown that local solvent structure has a substantial effect on reaction rate constants, which has been explained in terms of local density variations of the solvent in the environment sur- Vol. 41, No. 2 AIChE Journalrounding the solute (Johnston and Haynes, 1987). Local density augmentation of solvents around solute molecules has been measured in various spectroscopic studies (Kim and Johnston, 1987; Kajimito et al., 1988;Yonker and Smith, 1988;Johnston et al., 1989; Eckert, 1988, 1989;Betts et al., 1992;Carlier and Randolph, 1993). Computational approaches and integral equation theories have provided further evidence of these local density variations. Molecular dynamics (MD) simulations of Knutson et al. (1992) showed local density enhancements of supercritical carbon dioxid...

show abstract

Section: Background and Methodologymentioning

confidence: 99%

Effect of solute‐solute correlations on rapid reactions in supercritical fluids

1995

Self Cite

View full text Add to dashboard Cite

show abstract

“…While radical reactions have been studied in SCFS [13][14][15][16] for example], we are unaware of any ET reactions that have been studied in SCFS.…”

Section: Introductionmentioning

confidence: 99%

Solvent reorganization energies measured by an electron transfer reaction in supercritical ethane

Takahashi

Sawamura

Jonah

1998

The Journal of Supercritical Fluids

View full text Add to dashboard Cite

The intermolecular electron transfer reaction between a biphenyl anion and pyrene in supercntical ethane was studied using pulse radiolysis. Second-order electron trausfer rates were found to be of the order of 1011M-1 s-l. The rate constants appear to be approximately constant over the pressure range 55-133 bar. Two possibilities are discussed that could explain the present results: solvent clustering; or a dependence of the solvent reorganization energy on pressure. Reorganization energies Er of non-polar supercritical ethane were estimated from the observed rate constant using the modified Marcus equation. Er may be larger than normally expected for nonpolar solvents because of density fluctuations. .-Introduction It is well known that density fluctuations [1] and clustering of solvent molecules [2][3][4][5][6][7][8] are observed in supercritical fluids(SCFs). The local density of SCFS around a solute may be significantly greater than the bulk density of fluid not only in polar fluids [9] but also in non-polar fluids [ 10]. The number of molecules around a solute is sibtificantly changed near the critical pressure [11]. RecentIy,Matyushov and Schrnid[12] have theoretically studied solvent reorganization energy Er arising from charge separation and recombination reactions in non-polar fluids. According to their results, the Er in non-polar solvent is not zero but can be represented as the sum of two terms that arise from liquid polarization and density reorganization, with the latter component being of much greater importance.For this reason we felt that electron transfer (ET) reactions in non-polar SCFS might show a new aspect of the solvent reorganization energy in non-polar fluids. While radical reactions have been studied in SCFS[13-16 for example], we are unaware of any ET reactions that have been studied in SCFS.In this work we present the intermolecular ET reactions in non-polar SCFS. We chose to use ethane as a non-polar solvent because it was relatively unreactive to the ions formed and a supercritical fluid could be formed conveniently. Biphenyl anion and pyrene were used as au electron donor and acceptor, respectively. The solvent reorganization energies were estimated using the measured ET rates. Materials and MethodsHi~h messure eauir)ment Experiments were run with a cylindrical stainless-steel high pressure cell (Takagi equipment CO., LTD., 4 cm in O.D., 9.5 cm in length). The 1 cm thick supra.silwindows were mounted to the cell using Teflon o-rings. The optical path length is 6 cm and the cell capacity is 4.2 cm3. The temperature of the cell was maintained constant to~0.1'C at 35°C (A 0.5"C) using an Omega temperature controller (Model CNIOOIRTD), a cartridge heater and a platinum resistance thermometer. The thermometer was installed into the cell so that it is in contact with the fluid. Pressures were generated using a JASCO HPLC pump (Model PU-980, with a flow controller and pressure sensor). The fluid pressure was monitored with Cole-Parrner digital pressure meter (Model 7350-38) and pressu...

show abstract

“…The results represent ideals of molecular interactions which do not capture all of the structural and dynamics effects associated with the complex molecules in supercritical fluids. The "molecular charisma" is thought to be a dynamic exchange process with bulk molecule, at a frequency of about one of a picosecond [47], and may persist for 100 picoseconds [43]. The addition of a small amount of a volatile cosolvent to a supercritical fluid may dramatically increase the solute solubility.…”

Section: Solute Solubilitymentioning

confidence: 99%

“…These experimental studies are based on the solubility of solids and on partial molar properties of dilute solutes in near-critical solvents [32,40,49,51,52] and also on spectroscopic techniques which provide information on solvation (short ranged interactions) and solvent structure [43,45,53,54,55,56,57,58,59].…”

Section: Solute Solubilitymentioning

confidence: 99%

“…Solutes with a same size but a different polarity present an equivalent factor E. Finally, E factor is very sensitive to the nature of the solvent and may vary to 8 orders of magnitude as a function of density [38]. The classical description takes into account short-range effects in relation to solvation phenomena, and long-range correlations due to local quasicriticality, that leads to large partial molar properties in the vicinity of the critical point [40,41,42,43].…”

Section: Solute Solubilitymentioning

confidence: 99%

See 1 more Smart Citation

Thermodynamic Aspects of Supercritical Fluids Processing: Applications of Polymers and Wastes Treatment

Cansell

Rey

Beslin

1998

Rev. Inst. Fr. Pét.

View full text Add to dashboard Cite

La mise en Ïuvre des fluides supercritiques est d'un intŽr•t croissant dans de nombreux domaines : pour la sŽparation (sŽparation et purification en pŽtrochimie, industrie alimentaire) et la chromatographie par fluides supercritiques (sŽparation analytique et prŽ-paratoire, dŽtermination des propriŽtŽs physicochimiques), comme milieux rŽactifs aux propriŽtŽs continžment ajustables allant du gaz au liquide (polyŽthyl•ne de faible densitŽ, Žlimination des dŽchets, recyclage des polym•res), en gŽologie et en minŽralogie (volcanologie, Žnergie gŽothermique, synth•se hydrothermique), dans la formation des particules, fibres et substrats (produits pharmaceutiques, explosifs, rev•tements), pour le sŽchage des matŽriaux (gels).Cet article prŽsente les propriŽtŽs physicochimiques exceptionnelles des fluides supercritiques en rapport avec leurs applications en ingŽnierie. Apr•s un bref rappel des concepts fondamentaux relatifs au comportement critique des fluides purs, nous dŽvelop-pons d'une mani•re plus dŽtaillŽe les propriŽtŽs physicochimiques ajustables des fluides dans le domaine supercritique. La deuxi•me partie de lÕarticle dŽcrit les applications en ingŽnierie des fluides supercritiques relatives aux rŽactions chimiques et au traitement des polym•res. Chaque prŽsentation d'application est divisŽe en deux parties : la premi•re rappelle les concepts de base et le contexte gŽnŽral ainsi que les propriŽtŽs physicochimiques, la seconde dŽveloppe les applications en ingŽnierie se rapportant au domaine concernŽ. THERMODYNAMIC ASPECTS OF SUPERCRITICAL FLUIDS PROCESSING: APPLICATIONS TO POLYMERS AND WASTES TREATMENTSupercritical fluid processes are of increasing interest for many fields: in supercritical fluid separation (petroleum-chemistry separation and purification, food industry) and supercritical fluid chromatography (analytical and preparative separation, determination of physicochemical properties); as reaction media with continuously adjustable properties from gas to liquid (lowdensity polyethylene, waste destruction, polymer recycling); in This paper presents the unusual physicochemical properties of supercritical fluids in relation to their engineering applications. After a short report of fundamental concepts of critical behavior in pure fluids, we develop in more details the tunable physicochemical properties of fluid in the supercritical domain. The second part of this paper describes the engineering applications of supercritical fluids relevant of chemical reactions and polymer processing. Each application presentation is divided in two parts: the first one recalls the basic concepts including general background, physicochemical properties and the second one develops the engineering applications relevant of the advocated domain. ASPECTOS TERMODINçMICOS DEL TRATAMIENTO DE LOS FLUIDOS SUPERCRêTICOS : APLICACIONES PARA LOS TRATAMIENTOS DE LOS POLêMEROS Y DE LOS RESIDUOSLa implementaci-n de los fluidos supercr'ticos presenta un interŽs cada vez mayor en numerosos campos : para la separaci-n (separaci-n y purific...

show abstract

Quasicritical behavior of dense‐gas solventsolute clusters at near‐infinite dilution

Cited by 57 publications

References 43 publications

Effect of solute‐solute correlations on rapid reactions in supercritical fluids

Effect of solute‐solute correlations on rapid reactions in supercritical fluids

Solvent reorganization energies measured by an electron transfer reaction in supercritical ethane

Thermodynamic Aspects of Supercritical Fluids Processing: Applications of Polymers and Wastes Treatment

Contact Info

Product

Resources

About