On Enthalpies of Solution of Athabasca Pentane Asphaltenes and Asphaltene Fractions

摘要

The analysis and prediction of asphaltene precipitation behaviors and asphaltene-diluent interactions are typically treated from either a solution thermodynamics or a colloid perspective. The poh/dispersity and multiphase nature of asphaltenes allows for portions of these materials to exhibit both behaviors concurrently at fixed global composition. In the current work, this duality is explored using solution calorimetry. Measurements were performed for Athabasca pentane asphaltenes and asphaltene fractions in pure diluents (toluene, tetrahydrofiiran, quinoline, 1-methylnaphthalene) and in diluents where impurities were intentionally added. Reported values for the enthalpy of solution in the data set range from-16 to +10 J/g of asphaltenes. The observed changes in both the magnitude and sign of the enthalpy of solution values with global composition at fixed temperature and with temperature at fixed composition are interpreted qualitatively based on enthalpies of sorption (negative), enthalpies of phase transition (positive), and enthalpies of mixing (negative or positive). Quantitation of the asphaltene fractions potentially present as colloidal particles, as an asphaltene-rich liquid or as dissolved species in a diluent remains a subject for future study.