Elise Provost

Multicomponent paraffin waxes and petroleum solid deposits: structural and thermodynamic state

The X-ray diffraction analyses, carried out on eight commercial and industrial waxes and a heavy crude oil, show the following remarkable results: (i) each multicomponent paraffin wax (from 20 to 33 n-alkanes), which has a continuous distribution of consecutive n-alkanes (19 < n < 53), forms a single orthorhombic solid solution; (ii) the molecule packing identity period along the long c-axis of this solid solution corresponds to a chain length of a hypothetical orthorhombic n-alkane whose carbon atom number is equal to the average carbon atom number of n-alkanes contained in each multicomponent paraffin wax. This multicomponent phase, whose orthorhombic structure is analogous to one of the two intermediate solid solutions, β′n or β″n, of binary and ternary molecular alloys of consecutive n-alkanes, is also observed in the deposit of the heavy crude oil with the presence of an amorphous solid.

Phase diagram of n-heneicosane and n-tricosane molecular alloys

Abstract The phase diagram of the mixtures n-C21H44:n-C23H48 has been established by joint calorimetric and structural analyses. This study indicates the existence of nine solid single-phase domains of equilibrium: four terminal solid solutions, denoted βo(C21), β′o(C21), β′o(C23) and β′o(C23) with the n-heneicosane and n-tricosane structures, three orthorhombic intermediate solid phases, called β″1, β′1 and β″2 (β″1 and β″2 on both sides of β″1 are isostructural), with increasing temperature, a total miscibility field: β, with the orthorhombic structure Fmmm, above the intermediate solid solution regions (a second order transition which is characterized by the Rotator RI state is observed in this phase) and below the solidus line α-RII with the rhombohedral structure R3m. These results complete the literature diagrams which only presented two solid single-phase domains.

Structural evolutions of the n-heneicosane and n-tricosane molecular alloys at 293 K

Abstract A structural study of odd-numbered n -alkane (C n ) binary mixtures (C 21 : C 23 ) was carried out on powder samples using a Guinier-de Wolff camera with increasing concentration of n -C 23 at 293 K. Despite the reports in the literature, these molecular alloys do not form an orthorhombic continuous homogeneous solid solution to C 21 from C 23 at “low temperature”. Instead, as already observed in two even-numbered C n systems, X-ray diffraction results show the existence of seven solid solutions as the molar concentration of C 23 increases: four terminal solid solutions, denoted β 0 (C 21 ) β 0 (C 23 ), isostructural with the “low temperature” phase of pure C 21 and C 23 (Pbcm), β ′ 0 (C 21 ) and β ′ 0 (C 23 ), identical to the phase β ′ 0 which appears in pure C 23 above the δ transition, and three orthorhombic intermediate solid solutions, designated β ″ 1 , β ′ 1 and β ″ 2 . On the basis of powder X-ray photographs, the phases β ″ 1 and β ″ 2 (C 21 : C 23 ) are indistinguishable, and they are isostructural with the intermediate solid solution β″ of the even-numbered C n binary systems (C 22 : C 24 ) and (C 24 : C 26 ). The phase β ′ 1 (C 21 : C 23 ) is also isostructural with the two indistinguishable intermediate solid solutions β ′ 1 and β ′ 2 of the molecular alloys (C 22 : C 24 ) and ( 24 : C 26 ). From this study and our other laboratory results, the sequences of appearance of the solid solutions and the structural identities between these phases are established at “low temperature” for all the binary molecular alloys of consecutive C n (odd-odd, even-even or odd-even: 19 n

Variation in enthalpy of the systemn-tetracosane-n-hexacosane as functions of temperature and composition

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.

The solubility of n-alkanes C13H28 to C36H74 and of some binaries in various organic solvents

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.

Salt addition effect on partition coefficient of some phenolic compounds constituents of olive mill wastewater in 1-octanol-water system at 298.15 K

The 1-octanol-water partition coefficient is an important property to measure the hydrophobicity of organic compounds, which has been demonstrated to be a parameter in studying the conformation of biomolecules in aqueous solutions. For biological systems, electrolytes play an important role in thermodynamic properties. The salt addition effect on the distribution of phenolic compounds between water and 1-octanol at 298.15 K has been studied. The phenolic compounds used were vanillic acid, protocatechuic acid, vanillin, tyrosol, cathecol, caffeic acid and syringic acid, and the considered salts were potassium chloride, sodium chloride and lithium chloride. The influence of both the concentration and size of the added salt on the partition coefficient (Kow) have been considered. This study shows a salting in with the following decreasing order: LiCl > NaCl > KCl. The Gibbs energies of transfer of phenolic compounds (168–1) form chloride solutions to organic phase have been calculated using experimental 1-octanol-water partition coefficients.