Thermodynamic modeling for petroleum fluids - I. Equation of state and group contribution for the estimation of thermodynamic parameters of heavy hydrocarbons

A group contribution method is proposed for estimating the critical properties and acentric factors of paraffins, naphtenes and aromatics with emphasis on extrapolating to very heavy compounds. Group contributions for sulfurized compounds were added to improve further applications in petroleum engineering or in any other domain, From the experimental normal boiling point, critical temperatures were correlated with a 0.6% average deviation on a set of 268 data and critical pressures with a 2.6% deviation on a 222 data set. The normal boiling points can be estimated without any experimental values, With this method, it was possible to correlate the normal boiling points of 641 hydrocarbons and sulfurized compounds with a deviation of less than 0.9%. From these estimated values, a 1% deviation was obtained at the critical temperatures and 2.8% at the critical pressures. The acentric factors of 160 compounds were correlated with a 6.5% deviation. With the proposed method, experimental vapor pressures were predicted using the Peng-Robinson equation of state for 125 compounds with a deviation of less than 5%, The results are compared with those obtained using other methods. (C) 1997 Elsevier Science B.V.