Gavin F. Shilstone

Solubilities of solids and liquids of low volatility in supercritical carbon dioxide

A table is given of the compounds of low volatility, whose experimental solubilities in supercritical carbon dioxide have been published up to the end of 1989, with the temperature and pressure ranges of the experimental measurements, the experimental method, and references to the source of data. The data for pure compounds, which were presented in tabular form in the original publications, are shown in a series of figures along with correlation lines for each isotherm. The method of correlation was to fit the experimental data for each isotherm, in the form of the natural logarithm of the product of mole fraction and pressure, to a linear function of density above a pressure of 100 bars. The constants obtained from the fitting procedures are given in a table. Procedures for estimating, from these constants, the solubilities of the compounds at temperatures and pressures different from those of the experimental data are suggested.

Estimation of solubilities in supercritical carbon dioxide: A correlation for the peng-robinson interaction parameters☆

Abstract The isotherms of published solubilities of 19 compounds of varied chemical type in pure C0 2 have been fitted to the Peng-Robinson equation-of-state using the binary interaction parameter as an adjustable variable. The parameters thus obtained at temperatures close to 308 K are found to be approximately correlated to a particular function of some of the physical properties of the solute and solvent. This allows rough estimates to be made of solubilities of compounds in supercritical C0 2 , where there are no published experimental measurements.

Effect of pressure drop across the column on average densities and capacity factors in supercritical fluid chromatography

Abstract Calculations have been carried out of the average densities and capacity factors in supercritical fluid chromatographic (SFC) columns, taking into account the effect of the pressure drop along the column using, as examples, carbon dioxide as the mobile phase and phenanthrene as the solute. The values obtained were compared with those predicted for the mean pressure in the column. Differences are found which can be substantial for both the density and the capacity factor. Maximum deviations are found to move to higher pressures as the temperature rises. The effect of pressure drop needs to be taken into account by those using SFC to make quantitative measurements.

Use of chromatographic retention measurements to obtain solubilities in a liquid or supercritical fluid mobile phase

Abstract A thermodynamic analysis is given of the relationship between the capacity factor in high-performance liquid chromatography (HPLC) and supercritical fluid chromatography (SFC) and the solubility of the solute in the mobile phase. The analysis shows that in certain circumstances, where particular assumptions are valid, there is a simple inverse relationship between the two quantities. In these circumstances the proportionality constant has a fixed value for a particular column, temperature and solute, and is independent of the mobile phase. Furthermore, the logarithm of the constant is approximately linearly related to the inverse of the absolute temperature over a limited temperature range. Some experimental studies are then described which show that practical conditions exist where these relationships are valid. It is shown that the same equation-of-state, with the same parameters, can be used to predict quantitatively both supercritical fluid solubilities and the temperature dependence of retention in SFC. Experimental results illustrate the inverse relationship between solubility and retention where the same column was used in both SFC and HPLC. Results are also given for the variation of the proportionality constant with temperature. The various ways in which these relationships could be used to measure solubilities are discussed and examples of experimental measurements are given for some methods.

Prediction of the conditions for supercritical fluid extraction of atrazine from soil

Samples of soil were spiked with known concentrations of atrazine and extracted with supercritical carbon dioxide. Quantitative analysis of the extracts was carried out by capillary gas chromatography and the kinetics of extraction were fitted to the ‘hot-ball’ model. The conditions for extraction were predicted from calculated solubilities using the Peng–Robinson equation of state, and were in satisfactory agreement with experiment.

Prediction of solubilities for tar extraction by supercritical carbon dioxide

Abstract Predictions are given for the solubilities of four compounds (naphthalene, phenanthrene, phenol, and 2-naphthol) in carbon dioxide at six temperatures between 40 °C and 100 °C and pressures up to 240 bar. The data are intended to be relevant to the extraction of coal-gasification tars. The Peng-Robinson equation-of-state was used for predictions. Temperature-dependent interaction parameters were obtained using, where possible, the published solubility data.

Supercritical fluid chromatography of coal-derived polycyclic aromatic hydrocarbons on packed columns

The supercritical fluid chromatographic behaviour of coal-derived polycyclic aromatic hydrocarbons using modified HPLC equipment with carbon dioxide (CO2) and methanol-CO2 as the mobile phases is described. Factors affecting the separation and retention of these compounds are considered.

Studies of the temperature dependence of retention in supercritical fluid chromatography

The capacity factors for the chromatographic retention of naphthalene, fluorene, phenanthrene and pyrene in supercritical carbon dioxide using an octadecyl silate bonded-phase column have been measured between 300 and 400 K. The results, which go through a maximum as a function of temperature, are quantitatively explained using the Peng–Robinson equation of state to calculate fugacity coefficients in the supercritical phase. Values of the enthalpies of solution of the compounds in the stationary phase from the vapour phase are obtained which are approximately equal and opposite to published values of the enthalpies of sublimation of the compounds.

Coupled Supercritical Fluid Extraction/Chromatography of Polycyclic Aromatic Hydrocarbons: Correlation with Solubility Calculations

Abstract The solubility of: naphthalene, fluorene, phenanthrene, pyrene, and chrysene in supercritical CO2 at two temperatures and pressures up to 200 atm were calculated from fugacities derived via the Peng-Robinson equation of state. The calculated solubilities were correlated with the results of experiments in which polycyclic aromatic hydrocarbons (PAH) in fuel mixtures were extracted with supercritical CO2 and analysed by supercritical fluid chromatography and by gas chromatography.

Separation of compounds from gasifier tars by extraction with supercritical carbon dioxide

Abstract Coal gasification tars were extracted with supercritical carbon dioxide at different temperatures and pressures, and the properties of the extraction residues (pitches) were determined by elemental analysis, size-exclusion chromatography and simulated distillation. Extract fractions were analysed by supercritical fluid chromatography. The pitches generally had softening points near the temperature of extraction. Raising the extraction temperature at constant pressure reduces the solvent density, and hence reduces the solubility of tar constituents. Extraction is optimized by extracting at low flow rates, initially at low temperature (high density) to remove low molecular mass compounds, and then increasing the temperature to ensure good contact with molten pitch and increasing the pressure to increase the density. Contact with powdered pitch is preferable. In agreement with calculated solubilities, polycyclic aromatic hydrocarbons, especially naphthalene, fluorene and phenanthrene, are the principal constituents of the extracts. More polar compounds remain in the pitch.