“… 1 Comparison of eq 1 with experimental data for alkanoic acids and Rosenthal et al are also shown. 2 Comparison of eq 1 with experimental data for 1-alkenes …”
Section: Further Validation Of the Methods Based On Recent
Experiment...mentioning
confidence: 88%
“…Comparison of eq 1 with experimental data for alkanoic acids. 7 For lower acids, the data by Ambrose et al 16 and Rosenthal et al 17 the experimental data in Figures 3 and 5 for the critical temperature and in Figures 4 and 6 for the critical pressure.…”
Section: Testing Of Literature Group-contribution Methodsmentioning
A simple theoretical-based correlation of the ratio of the critical temperature to the critical pressure (T c /p c ) as a function of the van der Waals surface area (Q w ) has been previously developed based on an extensive database of critical data published prior to 1996. The final equation was the following: T c /p c ) 9.0673 + 0.43309(Q w 1.3 + Q w 1.95 ) where T c is the critical temperature in kelvin and p c is the critical pressure in bar. This correlation is further validated here based on recent experimental data for various families of organic compounds, including some heavy ones (mono-and diacids, alkenes, cyclo/phenylalkanes, and squalane). This and previous validations verify that this correlation has a much broader application range, up to (T c /p c ) ratios of 200, than the data used in its development (compounds with ratios up to 100). It seems that most organic compounds, including the very heavy and complex ones, follow the trend suggested by this equation. This equation can be used for testing existing group-contribution estimation methods. It is shown here that direct comparison of the Joback and Constantinou-Gani methods for two families of compounds (alkenes and carboxylic acids) is in agreement with their validation via the proposed equation. Similar results have been obtained for other compounds. Both group-contribution methods are of equal accuracy for heavy alkenes and acids, provided that experimental boiling point temperatures are available for the Joback method. If such data are not available, e.g., for heavy compounds, the Constantinou-Gani method should be preferred. The proposed correlation does not offer an alternative to group-contribution methods as it only provides a single relationship of the two critical properties. Its universal character, though, and validation for many heavy compounds offer a way to test and compare existing group-contribution methods and, finally, to select the one that best conforms with the proposed correlation. It is recommended that the proposed correlation is indeed used for high molecular weight compounds for which experimental critical properties are typically not available.
“… 1 Comparison of eq 1 with experimental data for alkanoic acids and Rosenthal et al are also shown. 2 Comparison of eq 1 with experimental data for 1-alkenes …”
Section: Further Validation Of the Methods Based On Recent
Experiment...mentioning
confidence: 88%
“…Comparison of eq 1 with experimental data for alkanoic acids. 7 For lower acids, the data by Ambrose et al 16 and Rosenthal et al 17 the experimental data in Figures 3 and 5 for the critical temperature and in Figures 4 and 6 for the critical pressure.…”
Section: Testing Of Literature Group-contribution Methodsmentioning
A simple theoretical-based correlation of the ratio of the critical temperature to the critical pressure (T c /p c ) as a function of the van der Waals surface area (Q w ) has been previously developed based on an extensive database of critical data published prior to 1996. The final equation was the following: T c /p c ) 9.0673 + 0.43309(Q w 1.3 + Q w 1.95 ) where T c is the critical temperature in kelvin and p c is the critical pressure in bar. This correlation is further validated here based on recent experimental data for various families of organic compounds, including some heavy ones (mono-and diacids, alkenes, cyclo/phenylalkanes, and squalane). This and previous validations verify that this correlation has a much broader application range, up to (T c /p c ) ratios of 200, than the data used in its development (compounds with ratios up to 100). It seems that most organic compounds, including the very heavy and complex ones, follow the trend suggested by this equation. This equation can be used for testing existing group-contribution estimation methods. It is shown here that direct comparison of the Joback and Constantinou-Gani methods for two families of compounds (alkenes and carboxylic acids) is in agreement with their validation via the proposed equation. Similar results have been obtained for other compounds. Both group-contribution methods are of equal accuracy for heavy alkenes and acids, provided that experimental boiling point temperatures are available for the Joback method. If such data are not available, e.g., for heavy compounds, the Constantinou-Gani method should be preferred. The proposed correlation does not offer an alternative to group-contribution methods as it only provides a single relationship of the two critical properties. Its universal character, though, and validation for many heavy compounds offer a way to test and compare existing group-contribution methods and, finally, to select the one that best conforms with the proposed correlation. It is recommended that the proposed correlation is indeed used for high molecular weight compounds for which experimental critical properties are typically not available.
“…Apparatus. Different methods have been used to determine the critical points of pure substance or mixtures, such as observation of the appearance and/or disappearance of the meniscus at the vapor−liquid interface, flow methods, , acoustic methods, , a pulse heating method, and measurements of the vapor−liquid coexistence …”
Section: Methodsmentioning
confidence: 99%
“…To exploit the advantages of SCFs, the mixtures should be homogeneous and should be supercritical mixtures. Critical parameters are key criteria for identifying the supercritical state, and critical parameters of many pure compounds and binary mixtures have been reported. − However, the data for ternary mixtures or more complex mixtures are scarce. − …”
The critical parameters of hexane + carbon monoxide + hydrogen and hexane + methanol + carbon monoxide + hydrogen mixtures have been determined in the n-hexane-rich region. The critical temperature and the critical density of the hexane + carbon monoxide + hydrogen system decrease with increasing concentrations of carbon monoxide and hydrogen, whereas the critical pressure increases with the concentrations of the light gases. The critical density of the hexane + methanol + carbon monoxide + hydrogen mixture increases significantly with increasing concentration of methanol, and the critical pressure decreases with increasing methanol concentration.
“…The methods for measuring critical parameters of thermally unstable fluids or reactive compounds (flow method; transient pulse-heating thin wire probe) have been proposed by various authors (see, for example, Refs. [74][75][76][77][78][79]). These methods are capable of residence times between 0.01 ms and 30 s. Unfortunately, these methods have not been applied to the measurement of the critical parameters of methanol.…”
The isochoric heat capacity of pure methanol in the temperature range from 482 to 533 K, at near-critical densities between 274.87 and 331.59 kg · m −3 , has been measured by using a high-temperature and high-pressure nearly constant volume adiabatic calorimeter. The measurements were performed in the singleand two-phase regions including along the coexistence curve. Uncertainties of the isochoric heat capacity measurements are estimated to be within 2%. The single-and two-phase isochoric heat capacities, temperatures, and densities at saturation were extracted from experimental data for each measured isochore. The critical temperature (T c = 512.78 ± 0.02 K) and the critical density (ρ c = 277.49 ± 2 kg · m −3 ) for pure methanol were derived from the isochoric heat-capacity measurements by using the well-established method of quasi-static thermograms. The results of the C V V T measurements together with recent new experimental PVT data for pure methanol were used to develop a thermodynamically self-consistent Helmholtz free-energy parametric crossover model, CREOS97-04. The accuracy of the crossover model was confirmed by a comprehensive comparison with available experimental data for pure methanol and values calculated with various multiparameter equations of state and correlations. In the critical and supercritical regions at 0.98T c T 1.5T c and in the density range 0.35ρ c ρ 1.65ρ c , CREOS97-04 represents all available experimental thermodynamic data for pure methanol to within their experimental uncertainties.
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