X-ray scattering study of carbon dioxide at supercritical states

Nishikawa, Keiko; Takematsu, Masakazu

doi:10.1016/0009-2614(94)00728-4

Cited by 39 publications

(32 citation statements)

References 9 publications

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“…Due to the typical anisotropic behaviors of carbon dioxide molecules, the structural properties of carbon dioxide have been studied through neutron-diffraction experiments [50][51][52][53][54][55] or x-ray diffraction measurements. 56 However, the measured radial distribution functions by different authors are not always consistent with each other for the uncertainties and statistical fluctuations involved in these experiments. 51,52 Ricci and co-workers continuously and systematically carried out neutron-diffraction measurements on fluid carbon dioxide over wide temperature and density ranges.…”

Section: Structural Propertiesmentioning

confidence: 86%

An optimized molecular potential for carbon dioxide

Zhang

Duan

2005

The Journal of Chemical Physics

212

172

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An optimized molecular potential model for carbon dioxide is presented in this paper. Utilizing the established techniques of molecular-dynamics and histogram reweighting grand canonical Monte Carlo simulations, this model is demonstrated to show excellent predictability for thermodynamic, transport, and liquid structural properties in a wide temperature-pressure range with remarkable accuracies. The average deviations of this new model from experimental data for the saturated liquid densities, vapor densities, vapor pressures, and heats of vaporization are around 0.1%, 2.3%, 0.7%, and 1.9%, respectively. The calculated critical point is almost pinpointed by the new model. The experimental radial distribution functions ranging from 240.0 to 473.0 K are well reproduced as compared to neutron-diffraction measurements. The predicted self-diffusion coefficients are in good agreement with the nuclear-magnetic-resonance measurements. The previously published potential models for CO2 are also systematically evaluated, and our proposed new model is found to be superior to the previous models in general.

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Section: Structural Propertiesmentioning

confidence: 86%

An optimized molecular potential for carbon dioxide

Zhang

Duan

2005

The Journal of Chemical Physics

212

172

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“…Therefore, the correlation length ξ is related to the density fluctuations as ( N ) 2 /N ∝ ξ γ /ν . On the higher-order phase transition curve, the variety in the cluster size becomes extreme, and in the gas-like region, the clusters become smaller in size (see also Nishikawa and Tanaka [56] and Nishikawa and Takematsu [57]). Since all thermodynamic functions are directly related with K T , and thus with the correlation length ξ , isochoric heat capacities and other thermodynamic properties exhibit critical anomalies in the supercritical region.…”

Section: Isochoric Heat Capacity Of Supercritical Dee Isothermal Denmentioning

confidence: 96%

“…The ridge where the correlation length (density fluctuations) and also C V are maxima is the extension curve, which corresponds to the critical isochore. Therefore, this curve determines the higher-order supercritical phase-transitions curve, i.e., the extension curve to the supercritical region is the boundary of the phase transition with higher order [56,57]. Isochoric heat-capacity measurements are very helpful in understanding the changes in structure (phase transition phenomena) of fluids in the supercritical region.…”

Section: Isochoric Heat Capacity Of Supercritical Dee Isothermal Denmentioning

confidence: 99%

Experimental Study of the Isochoric Heat Capacity of Diethyl Ether (DEE) in the Critical and Supercritical Regions

et al. 2012

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Two-and one-phase liquid and vapor isochoric heat capacities (C V ρT relationship) of diethyl ether (DEE) in the critical and supercritical regions have been measured with a high-temperature and high-pressure nearly constant-volume adiabatic calorimeter. The measurements were carried out in the temperature range from 347 K to 575 K for 12 liquid and 5 vapor densities from 212.6 kg· m −3 to 534.6 kg· m −3 . The expanded uncertainties (coverage factor k = 2, two-standard deviation estimate) for values of the heat capacity were 2 % to 3 % in the near-critical region, 1.0 % to 1.5 % for the liquid isochores, and 3 % to 4 % for the vapor isochores. The uncertainties of density (ρ) and temperature (T ) measurements were 0.02 % and 15 mK, respectively. The values of the internal energy, U (T, V ), and second temperature derivative of pressure, ∂ 2 P/∂ T 2 ρ , were derived using the measured C V data near the critical 123 186 Int J Thermophys (2012) 33:185-219 point. The critical anomaly of the measured C V and derived values of U (T, V ) and ∂ 2 P/∂ T 2 ρ in the critical and supercritical regions were interpreted in terms of the scaling theory of critical phenomena. The asymptotic critical amplitudes ( A + 0 and A − 0 ) of the scaling power laws along the critical isochore for one-and two-phase C V were calculated from the measured values of C V . Experimentally derived values of the critical amplitude ratio for C V A + 0 /A − 0 = 0.521 are in good agreement with the values predicted by scaling theory. The measured C V data for DEE were analyzed to study the behavior of loci of isothermal and isochoric C V maxima and minima in the critical and supercritical regions.

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“…6 For example, the solubility, 7-9 separation, 10-12 diffusion coefficient, 13 and adsorption behavior 14 were successfully studied. The microstructure of supercritical CO2 has been actively investigated from a diffraction study, 15,16 and UV-vis, IR, [17][18] Raman spectra measurements. 19 However little information is available in the literature regarding supercritical fluid extraction of metal ions, except for a few reports.…”

Section: Introductionmentioning

confidence: 99%

Supercritical fluid extraction of toxic metals from woods containing preservatives

Takeshita¹,

Satō²,

Nishi³

1999

Proceedings First International Symposium on Environmentally Conscious Design and Inverse Manufacturing

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Although woods containing preservatives have been widely used for many years, some of these preservatives contain heavy metal compounds, so when the woods are incinerated, heavy metals remain in the ashes, creating a disposal problem. Supercritical fluid extraction is a promising technology for turning these hazardous wastes into harmless substances that can be safely recovered. Carbon dioxide is a suitable solvent for such extraction due to its moderate critical constants (Tc = 304.2 K and Pc = 7.38 MPa ), inertness, and ready availability in purified form. We tested the use of supercritical carbon dioxide and found that regardless of their amount, chromium, copper, and arsenic ions could definitely be extracted. Using acetylacetone as a reagent significantly improved the extraction efficiency. Supercritical carbon dioxide is thus a strong candidate as a solvent for extracting metals from woods safely and economically.

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X-ray scattering study of carbon dioxide at supercritical states

Cited by 39 publications

References 9 publications

An optimized molecular potential for carbon dioxide

An optimized molecular potential for carbon dioxide

Experimental Study of the Isochoric Heat Capacity of Diethyl Ether (DEE) in the Critical and Supercritical Regions

Supercritical fluid extraction of toxic metals from woods containing preservatives

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