Calculation of vapor pressure curves for hydroxy benzoic acid derivatives using thermogravimetry

This study aims at providing a simple thermogravimetric method in estimating the vapor pressure characteristics using the Antoine equation as the analytical tool. The heat treatment for the majority of benzoic acid derivatives follows zero order rate processes that are in good correlation with their evaporation process. The optimum conditions for the rising temperature experiments were found when the heating rate was 10 degreesC/min in an atmosphere of dry nitrogen (100 ml/min). Methyl paraben was taken as the calibration compound since its Antoine constants are reported in literature and its selected thermodynamic parameters were evaluated using the Langmuir equation. The coefficient of vaporization k was determined to be 124525 +/- 0.8, with units being reported in the SI system. The corresponding vapor pressure plots were obtained for the remaining compounds that followed a zero order evaporation process and their Antoine constants were calculated using the Levenberg-Marquardt least square curve fit method. (C) 2002 Elsevier Science B.V. All rights reserved.