Henry's law constants of propane, propene, butane, and 2-methylpropane in methanol at 374–490 K

doi:10.1016/j.fluid.2005.12.001

Fluid Phase Equilibria

Volume 240, Issue 1, 10 February 2006, Pages 56-62

https://doi.org/10.1016/j.fluid.2005.12.001 Get rights and content

Abstract

Henry's law constants of propane, propene, butane, and 2-methylpropane in methanol in the temperature range of 374–490 K are experimentally obtained. A similar method to a gas stripping method is applied to measure the Henry's law constants at high temperatures up to the critical point of methanol. The rigorous formula for evaluating the Henry's law constants from these measurements is applied to the data reduction for these highly volatile mixtures. By using this formula, the effect of the vapor space of the cell is discussed. The plot of Henry's law constants versus temperature goes through a maximum and approaches an unique point at the critical temperature of methanol. The fugacity coefficient of the solute in the vapor phase at infinite dilution and the infinite dilution activity coefficient of the solute in liquid phase are evaluated from these experimental data.

Introduction

The study of gas solubilities is useful in providing design data for absorption processes, as well as, indirectly, in aiding the analysis of molecular interactions in solutions. For practical use, much attention has been given to the thermodynamic properties near the critical point of mixtures. High temperature data are rarely available and are difficult to measure. Hayduk and Buckley [1] observed that all gas solubilities in a solvent tend towards a common value as the solvent critical temperature is approached. Beutier and Renon [2] and Schotte [3] showed that this is due to the thermodynamic relationship for the solute (g) at the solvent (s) critical point. ${(\frac{H_{g}}{φ_{g}^{V}})}_{T_{c, s}} = P_{c, s}$ ${(\frac{d ln H_{g}}{d T})}_{T_{c, s}} = - \infty, {(\frac{d (H_{g} / φ_{g}^{V})}{d T})}_{T_{c, s}} = - \infty$ where H_g is the Henry's law constant of the solute, $φ_{g}^{V}$ the fugacity coefficients of the solute in the vapor phase, P_c,s the critical pressure of the solvent, T_c,s the critical temperature of the solvent, and T is the absolute temperature.

Oxygenates such as ethers and alcohols have been used widely as fuel additives to increase the octane number, improve the combustion process, and reduce emissions, and solubility data of gases in alcohols are needed in the design of these production facilities.

To develop a molecular theory, on the other hand, an accurate intermolecular potential is necessary. Henry's law constant is directly related to the residual chemical potential of the solute at infinite dilution that is evaluated from the intermolecular potential between a solute molecule and a solvent molecule. Therefore, Henry's law constant is a suitable macroscopic property for correlating the intermolecular potential between different kinds of molecules.

The gas stripping method that was originally proposed by Leroi et al. [4] is usually used to measure the activity coefficients at infinite dilution of solutes in nonvolatile solvents, when the total pressures are negligibly small.

In a previous paper [5], Henry's law constants of carbon dioxide in methanol in the temperature range of 250–500 K were measured by a similar method to the gas stripping method. In this work, the Henry's law constants of propane, propene, butane, and 2-methylpropane in methanol at high temperatures and high-pressures are measured by the same method and the activity coefficients and the fugacity coefficients of the solute at infinite dilution are evaluated from these experimental data.

In the literature, we have found the following experimental data of the mixtures studied in this work. The solubilities of 2-methylpropane in methanol were measured at 298.15 K and pressures less than 102 kPa by Miyano and Hayduk [6]. The solubilities of propane, butane, and 2-methylpropane were measured by Kretschmer and Wiebe [7]. The Henry's law constants of propane, propene, butane, and 2-methylpropane at 255–320 K were measured by Miyano et al. [8], [9]. The vapor–liquid equilibria were measured for propane + methanol system by Leu et al. [10], and for propene + methanol system by Ohgaki et al. [11].

Section snippets

Experimental

The gas stripping method originally proposed by Leroi et al. [4] is based on the variation of vapor phase composition when the highly diluted solute in a liquid mixture in an equilibrium cell is stripped from the solution by a flow of inert gas (helium). The composition of the gas leaving the cell is periodically sampled and analyzed by means of gas chromatography. The peak area, S, of the solute decreases exponentially with the volume of inert gas flowing out of the cell. This rigorous

Results and discussion

As indicated in Eq. (3), $H_{g} / φ_{g}^{V}$ can be obtained directly from this experiment. Fig. 2 shows the temperature dependencies of $H_{g} / φ_{g}^{V}$ of propane, propene, butane, and 2-methylpropane in methanol in the temperature range of 250–490 K. As shown in this figure, the values of $H_{g} / φ_{g}^{V}$ obtained in this work are smoothly combined with those obtained by using the gas stripping method at lower temperatures [8], [9]. The smoothed lines are the calculated results from the Soave equation of state with

Conclusion

Henry's law constants for propane, propene, butane, and 2-methylpropane in the methanol divided by the fugacity coefficient, $H_{g} / φ_{g}^{V}$ , have been directly measured by a method similar to the gas stripping method in a very wide temperature range of 374–490 K. The value of $H_{g} / φ_{g}^{V}$ increases with the temperature, goes through a maximum around at 450 K, and approaches the critical point of the solvent with a slope of −∞. The plot of the Henry's law constants versus temperature also goes through a maximum

Acknowledgements

This paper reports part of the work supported by Grant-in-Aid for Scientific Research from Japan Society for the Promotion of Science (16560663), which is gratefully acknowledged.

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Henry's law constants of propane, propene, butane, and 2-methylpropane in methanol at 374–490 K

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusion

Acknowledgements

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

J. Chem. Thermodyn.

Chem. Eng. Sci.