RK-, SRK-, & SRK-PR-TYPE EQUATION OF STATE FOR HYDROCARBONS, BASED ON SIMPLE MOLECULAR PROPERTIES

A database made of 429 different hydrocarbons was utilized to fit their critical pressure and temperature as a function of molecular weight and carbon atomic fraction. The critical parameters, appearing in Redlich-Kwong, Soave-Redlich-Kwong and Redlich-Kwong-Peng-Robinson equation of state (EoS), were replaced by two curve-fitted equations. The afore-mentioned original equations were tested and contrasted versus their counterparts as far as predicting the molar volume of both liquid and vapor at a given pair of pressure and temperature for a given hydrocarbon. Using either an empirical or a reference datum for the estimated molar volume, it was found that the substituted equation did predict the volumetric properties with accuracy as good as the original equation. The replacement will ease the calculation of volumetric properties of liquid and vapor with a reasonable accuracy. It was found that, in general, all models, the original and the substituted/modified equations, predicted well , with a good accuracy (i.e., a percent relative error (PRE) < 10%). The predicted values almost coincided. Moreover, none of the models, neither the original nor its counterpart equation, would predict, with a good accuracy (i.e., PRE <10%), if the hydrocarbon molecular size was greater than C7. On the other hand, for a hydrocarbon molecular size less than C7, the best three models that predicted, with a good accuracy (i.e., PRE < 10%) were SRK-type, RK-type, and SRK. Finally, at the critical condition (i.e., Tr=1.0 and Pr=1.0), all models failed to predict the critical molar volume (); i.e., PRE values > 10%.