Regular Solution Theories Are Not Appropriate for Model Compounds for Petroleum Asphaltenes

The solubility, melting point temperature, and enthalpy of fusion of a series of model compounds for heavy petroleum fractions were measured experimentally in n -heptane, toluene, dichloromethane, and mixtures thereof. Two porphyrins ( meso -tetraphenylporphyrin and octaethylporphyrin), the vanadyl analogues of the same two porphyrins, and one model asphaltene (4,4′-bis-(2-pyren-1-yl-ethyl)-[2,2′]bipyridinyl) were selected to test the efficacy of the regular solution and the Flory−Huggins theories in predicting the solubility behavior of these complex polyaromatic molecules in organic solvents. These simple solubility models were not capable of qualitatively or quantitatively describing the solubility behavior of these high-melting solid compounds, even with the solubility parameter as an adjustable parameter. Various different methods of estimating the differential heat capacity, Δ C P, improved the fits in certain cases, although no universally acceptable method was identified. Several group contribution theories were also tested on the current measurements, and none of the methods tested was able to quantitatively match the measured solubility parameters or the melting point properties of these compounds.