Prediction of asphaltene precipitation by the extended Flory–Huggins model using the modified Esmaeilzadeh–Roshanfekr equation of state

Asphaltene precipitation is caused by a number of factors, such as the variation of pressure and temperature, the change in composition and the mixing of oil with diluting solvents. The deposition of asphaltene precipitation is one of the main problems with the oil industries, appearing in the well bore, the well tubing and the refining processes. This causes an increase in the operating costs and imposes the costs of cleaning and washing well tubing as well. Therefore, it would be economically beneficial to know under what conditions and to what amount the asphaltene precipitates.In this paper, a model is presented based on the Flory–Huggins theory of polymeric solutions. Because the interaction parameter term plays a key role in the asphaltene precipitation, a correlation is proposed to account for the effect of the solvent ratio in addition to molecular weight. Several adjustable parameters in terms of the interaction parameter are determined in this work using a series of experimental precipitation data from a crude oil sample of a field located in the southwest of Iran (oil sample 1), and applying a robust optimization method (the differential evolution). Regarding the influence of the solubility parameter on the accuracy of the final results, a comparison is made between the m-ER, PR and the SRK EOSs. Finally, the obtained results from the comparison between the asphaltene precipitation amounts of various solvents and the existing experimental values for another group of data from oil sample 1, and two other oil samples verify the accuracy of the presented model.

► A modified F–H model is presented for investigation of asphaltene precipitation.
► The effects of SR and Mw on interaction parameter of the F–H theory are considered.
► Selection of EoS to evaluate the solubility parameter is of drastic significance.
► The results using the m-ER EoS better coincide with the precipitation data.