Solubilities of Phthalic Acid and o-Toluic Acid in Eight Alcohol Solvents: Experimental Measurement and Thermodynamic Modeling

In this study, the solubilities of phthalic acid (PA) and o-toluic acid (o-TA) in methanol, ethanol, n-propanol, isopropanol, n-butanol, iso-butanol, sec-butanol, and tert-butanol were measured by the laser dynamic method at atmospheric pressure (101.3 kPa) in the range of 292.25-353.35 K. The experimental results show that the solubilities of PA and o-TA in eight alcohols are positively correlated with temperature. In the four solvents methanol, ethanol, n-propanol, and n-butanol, the solubilities of PA and o-TA decrease with the increase of the number of carbon atoms in the main chain, and the order of solubility of PA and o-TA in butanol isomers from high to low is tert-butanol, sec-butanol, n-butanol, and iso-butanol. The solubility ratio of o-TA and PA in iso-butanol is the largest, indicating that iso-butanol could best separate the two. The experimental data were correlated by using the Apelblat model, the Buchowski- Ksiazczak lambda h model, and the modified no n-random two liquid activity coefficient model. The calculated solubilities were in good fit with the measured results. The Akaike information criterion was used to evaluate the selected model. The thermodynamic properties were calculated, and the main contributor of standard molar Gibbs energy of PA and o-TA in eight alcohols is enthalpy, about 54.66 to 68.34%.