Determination of vapour pressures of FAME industrial mixtures by ebullioscopic and thermogravimetric experimental methods

Abstract

Vapour pressure (VP) is a parameter that characterizes, by principle, only pure compounds. Nevertheless, it can refer also to mixtures in order to characterize their volatility or to be inserted in technical documents. The measurement of VP for mixtures is strongly dependent on the possible variation of the composition, during experiments, due to the different volatility of the constituent compounds. It is possible to calculate the VP of the mixture starting from its composition, but different thermodynamic scenarios must be considered. Moreover, for industrial samples, possible effects due to the presence of impurities must be considered. In this work, two different experimental methods have been employed to determine VP of some acetates esters and two industrial mixtures of fatty acid methyl esters (FAME). The first method is a direct ebullioscopic method, while the second is an indirect thermogravimetric analysis (TGA). An error function was calculated to compare the experimental results of VPs obtained with the two methodologies with the theoretical ones. Ebullioscopic measures resulted suitable only for acetates esters, as FAME mixtures are characterized by VPs too low to be quantified with this technique. On the contrary, TGA methodology is more accurate for FAME than acetates. It allows the collection of a great number of VP values with a very fast analysis. This method is less accurate than others, but it can be useful for a fast screening of the FAME mixtures, also contaminated with light impurities.