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  • Author or Editor: M. Dirand x
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Abstract  

The enthalpy variations of pure n-tricosane (n-C23H48), pure n-pentacosane (n-C25H52) and sixteen binary mixtures were determined from 282 to 360 K. The differential enthalpy analyses were carried out on the pure components on the four terminal solid solutions, denoted βo(C23), β′o(C23), β′o(C25), βo(C25) and on the three intermediate phases, called β″1, β′1, β″2of the binary system (C23:C25) using a calorimeter of the Tian Calvet type. These variations can be represented by an analytical expression, which is derived from Einstein‘s model. The two Rotator phases β-RI and α-RII were also studied.

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Abstract  

The solubility of two n-alkanes in commercial organic liquids, such as diesel fuel and jet fuel represent a problem to industry, because they precipitate in an unpredictable fashion. First we calculated the metastable enthalpy and entropy of fusion of the low temperature forms of the n-alkanes. We analyzed the solubility of alkanes n-C22H46, n-C23H48, n-C24H50 and n-C28H58 in ethylbenzene, m-xylene, n-heptane and gas oil. All systems seem to be close ideal, possibly with a slight positive deviation. We analyzed the solubility at constant temperature of the ternary system solvent C22H46-C24H50, C23H48-C24H50, C13H28-C16H34, C20H42-C22H46, C20H42-C24H50 and C20H42-C28H58, and looked at cloud points in various ternary systems. When the difference in the number of carbon atoms in the two alkanes is small, four or less, a metastable solid solution precipitates from the solvent. If the difference in the number of carbon atoms is six or more, the ‘equilibrium’ phases, or at least phases with low solubility precipitate.

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Abstract  

Differential enthalpy analyses were performed on the binaryn-alkane systemn-C24H50-n-C26H54 with a Setaram DSC111 calorimeter of Tian Calvet type. The measurements provided enthalpy data from 260 to 260 K onn-tetracosane,n-hexacosane and 19 binary mixtures. An analytical expression, derived from the Einstein model, is proposed for every pure phase in its temperature domain, to represent the variation in the enthalpy with temperature. A general expression for the enthalpy as a function of temperature and composition is also given.

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