Caractérisations thermodynamique et structurale de mélanges multiparaffiniques synthétiques et réels : aspects de leur cristallisation

Abstract : The crystallization of normal paraffin hydrocarbons in middle distillate fuels and petroleum cuts bas been shown to be at the origin of real problems for refiners and diesel-fuel consumers in very cold regions. Thermodynamic calculations of paraffinic crude oil crystallization are based on equations of solid/liquid equilibria and the ir capacity to fit and predict experimental data depend on the choice of the best model for each phase. To understand the behaviour of these solid deposits, the aim of this study is to determine and to compare the structural and thermodynamic properties of a great number of synthetic mixtures and wax es, whose n-alkane molar concentration distributions are similar to that observed in crude and diesel oils or in petroleum waxes. First, the crystallization study of synthetic mixtures, with decreasing distribution of alkanes (as in paraffinic crude oil) allows to detlne crystallization process and to underline the influence of parameters, like temperature, length and composition of the distribution, on the number of crystallized solid solutions. Secondly, n-alkanes calorimetrie studies lead to the determination of simple analytical expressions to represent thermodynamic properties (temperatures and enthalpies of phase change, heat capacities of solid and liquid phases) as a function of carbon atom number. These relations allow to bring out the existence of excess properties for paraffinic mixtures. For ail synthetic mixtures and waxes studied, the ordered solid phase shows a great deviation to ideality, and the liquid phase, an athermal behaviour. Finally, the measurement of solid solutions formation enthalpies of multicomponent paraffinic systems permit to test the predictive capacity of the Uniquac model, for the restitution of solid phases excess properties.
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Anne-Julie Briard. Caractérisations thermodynamique et structurale de mélanges multiparaffiniques synthétiques et réels : aspects de leur cristallisation. Autre. Institut National Polytechnique de Lorraine, 2002. Français. ⟨NNT : 2002INPL098N⟩. ⟨tel-01749827⟩

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