In the present investigation, a molecular thermodynamic model is proposed to predict the asphaltene precipitation at live-oil conditions. The amount of the precipitated asphaltene can be calculated at various pressures, temperatures, and added solvent ratios. Asphaltene is assumed to be the only precipitated component and the crude oil heavy fraction is considered as a continuous family and asphaltene is assumed to be the heaviest subfraction of that family. This continuous family is represented by the Gamma function and it's parameters are calculated by utilizing the heavy fraction mean molecular weight. The Gamma function is then discreted by using collocation points chosen as the roots of a polynominal and the asphaltene's molecular weight is thus determined. The asphaltne deposition is assumed not interfering with the VLE calculation, therefore two sequential phase equilibrium calculations are performed, a VLE and subsequently a liquid–solid equilibrium calculation. The SRK equation of state is used for all calculations. The asphaltene's critical temperature has been taken as an adjustable parameter, while the critical pressure and the acentric factor are calculated by empirical correlations as for any other C 7+ fraction. A perturbation theory based equation is proposed for calculating the critical temperature by taking it to be the sum of two terms, i.e. a reference temperature and a perturbation term. This is in line with the experimental evidence that the amount and the properties of the precipitated asphaltene varies with varying the amount of the added solvent. The model parameters were calculated using the available data for the amount of the precipitated asphaltene and the compositions of four crude oil specimens contacted with four different solvents over temperatures varying from 100 to 107 o C and pressures varying from 205 to 341 atm. A satisfactory representation of the experimental data was obtained. The proposed model needs the crude oil and the solvent compositions as well as the temperature, pressure and the crude heavy fraction's molecular weight.
