Asphaltene continued distributions

Kodera, Y., Kondo, T., Isaito, S. Y., and Ukegawa, K., Continuous-distribution kinetic analysis for asphaltene hydrocracking, Energy Fuels 16, 291-296 (2000). 

The history and fundamentals of continuous thermodynamics will be briefly presented here and has been discussed in detail elsewhere. Before the 1980 s many authors applied continuous distribution functions to specific cases of non-equilibrium thermodynamics, statistical thermodynamics, the VLE of petroleum fractions and the LLE of polydisperse polymer systems. Starting in 1980 a consistent version of chemical thermodynamics directly based on continuous distribution functions was developed and called continuous thermodynamics. The work of Kehlen and Ratzsch," " Gualtieri et al., Salacuse and Stell, Briano and Glandt," are to be mentioned as sources of information. In the following years several groups applied continuous thermodynamics to nearly all important types of polydisperse systems." Cotterman and Prausnitz reviewed the literature up until about 1990. In the 1980 s continuous modelling of phase equilibria was mostly focused on polymer systems, petroleum fractions and natural gases. In the last ten years, this has been expanded to also include problems with asphaltene precipitation from crude oils and wax precipitation from hydrocarbon mixtures. In section 9.4 the more recent papers are discussed. 

Figure 3. Molecular weight distributions of asphaltenes before and after flocculation predicted by our continuous mixture model.

Monteagudo et al characterized the asphaltenes as a continuous ensemble for which the distribution function was taken from the fractal aggregation theory. The asphaltene family was discretized in pseudo-components by the Gauss-Laguerre quadrature. Only the asphaltene polydispersity was taken into account. All other components were represented by as solvent whose properties (molar volume and solubility parameter) were calculated form a cubic equations of state. Aggregation of asphaltenes was considered to be a reversible process. And it was assumed the phase equilibrium was between a liquid phase and a pseudo-liquid phase containing only asphaltenes. 

Browarzik et al calculated asphaltenes flocculation at high pressures for methane + crude oil - - 2,2,4-trimethylpentane [i-octane] using continuous thermodynamics where 2,2,4-trimethylpentane acts as a precipitant. The asphaltene flocculation was considered to be a liquid -b liquid equilibrium. Browarzik et al applied the van der Waals equation of state. The polydispersity of the crude oil was considered to be described by the solubility parameter of the Scatchard-Hildebrand theory. Within this distribution the asphaltenes represent the species with the highest solubility parameters. The calculated results were compared to experimental data. For oils with a very low content of asphaltenes the model describes the experimental flocculation data reasonably well. However, on contrary to the experimental results, the model predicts the asphaltenes to show a higher flocculation tendency with increasing asphaltenes content of the crude oil. Based on these comparisons further work was undertaken by Browarzik et al and the associates formed... 

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