Experimental data for the crossover process in a model supercritical system

Kelley, F.D.; Chimowitz, Eldred H.

doi:10.1002/aic.690350611

Cited by 18 publications

(14 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In the near-critical region of a supercritical fluid in contact with a solute, one interesting property of the system is the existence of retrograde behavior. This has been the subject of a number of our recent papers and those of others, (Chimowitz et al, 1988;Kelley and Chimowitz, 1989;Debenedetti and Kumar, 1988;Johnston et al, 1987;Schaeffer et al, 1988). The allied crossover effect phenomenon, a situation in which certain components in the system are retrograde while others are not, was proposed by Chimowitz and Pennisi (1986) as the basis for novel molecular separation techniques using a staged processing concept.…”

Section: Introductionmentioning

confidence: 79%

Near‐critical phenomena and resolution in supercritical fluid chromatography

Kelley

Chimowitz

1990

AIChE Journal

Self Cite

View full text Add to dashboard Cite

The analysis in this paper shows the relationship between molecular resolution in supercritical fluid chromatography (SFC), and certain divergent thermodynamic properties of solutes dissolved in near-critical fluids. This divergence is most pronounced in the near-critical regime, leading to the hypothesis that this region provides most promise for heightened molecular resolution, which lies at the heart of analytical and separation technologies.A thermodynamic model for representing capacity factor data in SFC is proposed, spanning a wide density range. The model uses a perturbed hard sphere equation for the fluid phase and lattice concepts for the stationary phase. In addition, data are presented for a number of systems and discussed in terms of the analysis provided. For an isomeric system, the data shows that resolution between species increases with the onset of retrograde behavior, resulting in a distinct maximum point.

show abstract

Section: Introductionmentioning

confidence: 79%

Near‐critical phenomena and resolution in supercritical fluid chromatography

Kelley

Chimowitz

1990

AIChE Journal

Self Cite

View full text Add to dashboard Cite

show abstract

“…This phenomenon and its significance in separation technology have been explored by Chimowitz and Pennisi [4]. Schaeffer et al [5], Johnston et al [6], Kelly and Chimowitz [7] and Tai et al [8]. Esmaeilzadeh, and Goodarznia [9] also undertook some experimental research on this region.…”

Section: Crossover Pressurementioning

confidence: 95%

Two New Thermodynamic Constraints for a Solid/Supercritical Fluid System

Esmaeilzadeh

Bozorgi

2008

Chem Eng & Technol

View full text Add to dashboard Cite

One of the phenomenological observations in any supercritical system is the common pressure where all the solubility isotherms intersect. Thus, this crossover pressure addresses a thermodynamic constraint or a key set of conditions for supercritical mixtures. In this paper, a phase stability analysis has been performed for the formulation and estimation of the crossover pressure. This absolute theoretical approach includes two subsequent steps. At the first step, it has been formulated in terms of an abstract quantity, i.e., Gibbs free energy. However, the system should be treated more quantitatively in order to estimate the crossover pressure. Therefore, at the second step, which is based on the solute behavior at the infinite dilution limit, the equations formerly used have been further manipulated, which ultimately leads to two equations that are given in terms of estimable properties. They are actually two thermodynamic constraints for solid/SCF mixtures. One of them has been used to predict the crossover pressure of certain mixtures. The other one has not been used for this task due to a theoretical restriction. However, the successfully prediction of the crossover pressure by using either of the equations confirms the other one since they are subsequent and related equations. Crossover PressureAccording to Foster et al. [1], the crossover pressure is a phenomenological observation. In other words, researchers who measure the solubility of solids in supercritical fluids (SCFs), observe that there is a common pressure where all the solubility isotherms intersect [1-10]. As a result, this point can be assumed to be a thermodynamic constraint over the supercritical mixtures. This common pressure is mathematically represented by Eq. (1) 1) :The schematic intersection of the solubility isotherms is shown in Fig. 1. According to Fig. 1, at pressures below the crossover pressure, an increase in temperature induces a decrease in solubility of the solid in the SCF phase while the opposite effect occurs above the upper crossover pressure. This behavior can be explained by the reasoning that at pressures below the crossover pressure, the density of the SCF phase is more sensitive to temperature changes than that at higher pressures. A temperature increase in this region affects the sol- -1) List of symbols at the end of the paper.

show abstract

“…[24][25][26][27] Evidence shows that crystals reject impurities during normal growth when they are present in the solution. 28 To clarify the herein proposed process, the process developed by Chimowitz and co-workers 5,8 is briefly described first. Their process is operated in a oncethrough mode and consists mainly of three parts: the extractor where the solid mixture is charged, the condenser where the desired product nucleates without seeding, and the collection vessel where the residual solutes are precipitated by depressurization.…”

Section: Process Conceptsmentioning

confidence: 99%

“…The product purity of 2,3dimethylnaphthalene, 79 wt %,, is apparently lower than that of benzoic acid, 99.6 wt %, in the work done by Kelly and Chimowitz. 8 It is believed that the narrower crossover region of the 2,3-/2,6-dimethylnaphthalene system, 6 bar compared to 20 bar for the benzoic acid/1,10-decanediol system, causes the lower purity of product, because fluctuation in pressure may bring the operating pressure in the condenser out of the crossover region. In addition, the yield of 2,3-dimethylnaphthalene is limited, because the crossover region does not extend to the near-critical region, where the solubility is more sensitive to temperature change.…”

Section: Process Conceptsmentioning

confidence: 99%

“…In this pressure range (119-140 bar), one of the substances becomes supersaturated, and the other becomes undersaturated when the system shifts away from an equilibrium state by a change in temperature from 308 to 318 K. The phenomenon of the crossover region has been discussed in detail elsewhere. [10][11][12][13] In 1989, Kelly and Chimowitz 8 successfully separated benzoic acid and 1,10-decanediol from a mixture of these two substances by taking advantage of the crossover region. First, the supercritical carbon dioxide passed through an extractor to become saturated with benzoic acid and 1,10-decanediol, and then the mixture flowed into a condenser where the pure crystals of benzoic acid precipitated without seeding at a temperature higher than that of extractor.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Modified Retrograde Crystallization Process for Separation of Binary Solid Mixtures Exploiting the Crossover Region of Supercritical Carbon Dioxide

Tai

You

Wang

2000

Ind. Eng. Chem. Res.

View full text Add to dashboard Cite

A modified retrograde crystallization process with the circulation of supercritical carbon dioxide has been designed and tested for the separation of a mixture containing two solids. The apparatus consists of an extractor and a crystallizer, which are kept at different temperatures but at a fixed pressure within the crossover region. The metastable zone within the crossover region of the ternary system is first determined. Separation experiments are then conducted under various conditions with the crystallizer temperatures within or slightly above the metastable zone. The benzoic acid/1,10-decanediol/CO 2 system with a wide crossover region represents an ideal example of the modified process, and the results show that it is possible to obtain essentially pure products of both components (>97 wt %) from a 50/50 wt % mixture of benzoic acid and 1,10-decanediol. The average recovery is 49.3% for benzoic acid and 85.8% for 1,10-decanediol. The other system of 2,3-/2,6-dimethylnaphthalene/CO 2 with a narrow crossover region is then analyzed to demonstrate the possibility for the separation of organic isomers, and the results show that the modified process can produce the 2,6-dimethylnaphthalene of almost 100 wt % purity with a recovery of 37.1% starting from a mixture of 50/50 wt % isomers.

show abstract

Experimental data for the crossover process in a model supercritical system

Cited by 18 publications

References 5 publications

Near‐critical phenomena and resolution in supercritical fluid chromatography

Near‐critical phenomena and resolution in supercritical fluid chromatography

Two New Thermodynamic Constraints for a Solid/Supercritical Fluid System

Modified Retrograde Crystallization Process for Separation of Binary Solid Mixtures Exploiting the Crossover Region of Supercritical Carbon Dioxide

Contact Info

Product

Resources

About