| dc.description.abstract | The objective of this work is to experimentally determine the thermophysical properties such as diffusion coefficients and excess volumes of mixing of some organic liquids, specifically of binary systems involving the homologous series of n-paraffinic alcohols. The systems chosen for the present study are: cyclohexane–alcohols and methylcyclohexane–alcohols. The alcohol series includes ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol, n-heptanol and n-octanol.
The diaphragm cell technique has been used to measure integral diffusion coefficients of the above binary systems at 25°C and at atmospheric pressure. The cell constant was determined by diffusing 0.1N KCl into water. The diaphragm cell was frequently recalibrated as the value of the cell constant slowly changes over a long period of usage due to rubbing of the stirrer on the diaphragm surface. The composition of liquid mixtures was read out from calibrated graphs of density versus composition for the corresponding systems. The density of the mixtures was measured using Anton-Paar DMA-55 densitometer, having an accuracy of 0.00001 g/cm³. The factors such as the cell volume, homogeneity of the solution, steady-state assumption, calibration of the cell etc., that affect the experimental results have also been considered and sufficient precautions have been taken to see that they did not bring in any systematic error in the experimental measurements. An error analysis of the experimental data shows that the integral diffusion coefficients were determined within a maximum experimental error of 4%.
The plots of diffusion coefficient vs. composition for all the binaries of the systems cyclohexane–n-alkyl alcohols and methylcyclohexane–n-alkyl alcohols, respectively, show distinctive features. Whereas the diffusion coefficient vs. composition curves for all the binaries of the cyclohexane–n-alkyl alcohol system show smooth regular catenaries running parallel to each other, as to be expected, those for the methylcyclohexane–n-alkyl alcohol system intersect each other within a small composition range around 35% methylcyclohexane, showing an unexpected behaviour.
Experimental values of integral diffusion coefficients for all the binary systems were expressed as a function of mole fraction of a component in the form of a second-order power series polynomial. A set of three constants was obtained for each of these equations. For a homologous series, each of the three constants was related to a property involving pure component properties such as molecular weight, viscosity and molar volume, yielding a correlation. The diffusion coefficients estimated with the correlation have been compared with experimental values and an agreement with the latter at an average of 3.5% deviation was obtained.
The excess volumes for the above binary systems were also determined using the density data. The excess volumes obtained in this work were compared with the data already reported in the literature for some of the binary systems studied. The agreement between the two sets was fairly satisfactory. | |
