Osmotic and mean activity coefficients of LiBr and LiC in methanol at 25, 35, and 45 degrees C
Date of Award
Master of Science in Chemical Engineering - (M.S.)
Chemical Engineering and Chemistry
Dimitrios P. Tassios
Mahmoud F. Abd-El-Bary
R. P. T. Tomkins
Vapor pressure depression data of LiBr and LiCl in methanol at temperatures of 25,35, and 45°C were measured in the molality range 0.1-4.4m using a static method, where the difference in vapor pressure of the electrolytic solution is compared to that of pure methanol.
Osmotic coefficients were calculated from the vapor pressure data. This data was then correlated with both the one parameter Bromley equation and the three parameter Pitzer equation. For all systems at all temperatures, the data were better correlated by the Pitzer equation than with the Bromley equation. Mean activity coefficients of the two salts at the three temperatures were calculated based on the parameters obtained by regression of the experimental osmotic coefficient data. They were also calculated using a graphical procedure. However, it was shown that if data are not available at low concentrations with which to extrapolate the data to infinite dilution, the mean activity coefficients determined graphically can be in error by 20%.
Although the Pitzer equation fit the experimental osmotic coefficient data better than the Bromley equation, it appears that the constants of both equations that reflect an aqueous media must be modified to reflect the properties of the nonaqueous methanol.
The temperature dependency of B in the Bromley equation was investigated using a two parameter equation for both the LiBr and LiCl systems. Since the fit is good, the equation can be used to estimate the value of B in the range of 25-45 °C.
The temperature dependency of the parameters in the Pitzer equation was also studied. However, no relation ship between the parameters and temperature could be found.
Since the temperature dependency of the parameter B in the Bromley equation can easily be expressed with a two parameter equation, it appears that this equation is more useful in the correlation of salt-solvent data over many temperatures than is Pitzer's equation.
Tomasula, Peggy, "Osmotic and mean activity coefficients of LiBr and LiC in methanol at 25, 35, and 45 degrees C" (1980). Theses. 2158.