(74k) Prediction of Asphaltenes Solubility in Organic Solvents Via NRTL-SAC and COSMO-SAC

Asphaltenes are polyaromatics with hetero atoms (N, O, and S) that contribute to the polar characteristics of hydrocarbon mixture, i.e., crude oil. Solubility of asphaltenes reflecting the characteristic nature of mixture of compounds collectively, i.e., hydrophobicity, polarity, and hydrophilicity, greatly affects the production and transportation of hydrocarbon mixture, and causes fouling in unit operations. Current solubility models are based on the Scatchard–Hildebrand concept, and further extended with the Flory–Huggins correlation. These model require molecular weight and molar volume as input parameters. However, asphaltenes are solubility class rather than pure components, and the uncertainty of distribution of pure components within asphaltenes hampers the efficacy of these models. In the present work, ‘like dissolves like’ phenomena and solvation thermodynamics are used to calculate the activity coefficient of asphaltenes and solubility subsequently. Also, the conceptual segments of NRTL-SAC model for asphaltenes from published solubility data in mixed solvents is identified to generate the apparent sigma profile, i.e., a histogram of charge density distribution over the molecular surface  of asphaltene. The sigma profile is then used in COSMO-SAC model to calculate activity coefficient and solubiliy. By comparison, the sigma profiles of asphaltenes is also obtained from quantum chemistry calculation, i.e., density functional theory, with molecular structure for asphaltene molecules as input collected from literature proposed by different authors. Furthermore, various entropy models are investigated since both Flory-Huggins and Staverman-Guggenheim models have been found with issues.