A three phase thermodynamic model for predicting wax formation in paraffinic hydrocarbon mixtures

This paper presents a thermodynamic prediction method for vapor-liquid-solid wax phase equilibria of paraffinic hydrocarbon mixtures. This paper uses a new modified regular solution theory for liquid-solid equilibrium and Soave-Redlich-Kwong equation of state (EOS) for vapor-liquid equilibrium and presents an algorithm forcalculation of three-phase thermodynamic equilibrium. The difference between the liquid and wax phase heat capacities, a term which has been neglected in the mostprevious wax prediction models, are taken into consideration. It is noted that the ajor part of the enthalpy change observed during the wax prediction process seems to originate from phase transitions taking place in the already formed wax. Experimentaldata of the wax appearance temperatures and the amount of wax precipitation are reported for 2 paraffinic hydrocarbon mixtures (Pauly, 1998). The values predicted by the new model are in very good agreement with the experimental data