Isopleth Sections of the Systems: Commercial Multi-alkane Product—n-Eicosane or n-Pentacontane

Abstract

This paper displays recent works relative to the effect on structural state and thermodynamic properties of n-alkanes added to a commercial multi-n-alkane product. The G.P.C. and X-ray diffraction analyses have shown on one hand that the n-alkanes molar concentration distribution is of “normal logarithmic” type and on the other hand that this wax forms a single solid solution of orthorhombic structure, isostructural to the intermediate phase previously characterized with the binary and ternary n-alkane mixtures. Pure components (n-eicosane or n-pentacontane) have been added to the wax and the molecular alloys resulting were examined by means of X-ray diffraction (at various temperatures) and by Differential Thermal Analysis. Compilation of the results led to the proposal of the isopleth sections of both the systems: n-eicosane/commercial product and commercial product/n-pentacontane. In the first system, the crystallization is of eutectic type while in the second, it is of peritectic type. Nevertheless, whatever the diagram, no intermediate solid solution was observed, in fact both the phases characteristic of the component coexist in a large concentration domain. Thus, several invariant transformation are proposed in order to respect the law of adjoining phase regions.