Correlation for predicting the molecular weight of Brazilian petroleum residues and cuts: An application for the simulation of a molecular distillation process

In this work a correlation to predict the molecular weights of Brazilian heavy petroleum residues and cuts is developed. The residues were obtained from conventional distillation processes ASTM D 2892 (2005) and ASTM D 5236 (2003). The correlation was developed by adjusting experimental parameters of the API correlation (defined for light cuts). For the adjustment, molecular weight data of atmospheric residues (673.15 K+) of 14 heavy crude oils (API ≤ 25.5) obtained from a steady state refining process simulator (PETROX) were used. The adjusted correlation was validated with data from the molecular weights of atmospheric residues derived from 7 other heavy Brazilian crude oils and very good results were obtained, with an average absolute deviation of 2.20%. Furthermore, the predicted molecular weights and actual measured ones using Vapor Pressure Osmometry (VPO) of the 10 distillate cuts and 10 residues obtained by molecular distillation of atmospheric residues were compared. In general, improved results are provided by the developed correlation in relation to the conventional method, with a good correspondence between the predicted and experimental values for the cuts and residues studied here.

Research highlights
► Heavy residues are composed by macromolecules of difficult characterization.
► A correlation to predict molecular weights of heavy petroleum residues was adjusted.
► The equation is easy to use and useful in the absence of experimental data.
► The accuracy of prediction is good for cut and atmospheric residues 673.15 K+.
► The accuracy of prediction is worse for vacuum residues 810.15 K+.