(431e) Bubble Pressure Measurement and Prediction for n-Alkane + Naphthenic Hydrocarbon Binary Mixtures

Cubic equations of state are widely used for phase equilibrium calculations due to their simplicity and reliability, especially for hydrocarbon mixtures. Unfortunately, common choices such as the Peng-Robinson and Soave-Redlich-Kwong equations of state systematically predict both qualitatively and quantitatively incorrect phase behaviors for long chain n-alkane + aromatic and naphthenic mixtures unless negative binary interaction parameter (k_ij) values are used [1, 2]. Binary interaction parameters are typically obtained by fitting vapour-liquid equilibrium (VLE) data for binary mixtures. Experimental VLE data for these mixtures are scarce. In this study, VLE data for representative binary mixtures of naphthenes with long chain n-alkanes are presented. The selected n-alkanes range from n-C₂₀ to n-C₂₈. These compounds are paired with naphthenes including cyclohexane, alkyl-cyclohexanes and decahydronaphthalene. These experimental data are compared with computed bubble pressures using the Peng-Robinson, Soave-Redlich-Kwong and PC-SAFT equations of state in order to evaluate the accuracy of predictions and to obtain custom k_ij values. In a parallel companion works, bubble pressure data and the corresponding fitted k_ij values for 15 representative long chain n-alkanes + aromatic binary mixtures are reported [3] and strategies for estimating k_ijin the absence of experimental data are discussed [4]. Expected applications of these contributions include improved phase behavior model accuracy for hydrocarbon production, transport and refining environments, and improved corresponding state based transport property predictions, particularly for viscosity, that require accurate phase behaviors and phase compositions as inputs.

References: [1] Ahitan, S., Satyro, M. A., Shaw, J. M. Systematic misprediction of n-alkane + aromatic and naphthenic hydrocarbon phase behavior using common equations of state. J. Chem. Eng. Data 2015, 60, 3300-3318.

[2] Ahitan, S., Shaw, J. M. Quantitative comparison between predicted and experimental binary n-alkane+ benzene phase behaviors using cubic and PC-SAFT EOS. Fluid Phase Equilib. 2016, 428, 4-17.

[3] Liu, Q. MSc. Thesis, University of Alberta (in progress 2017).

[4] Ahitan, S., Luo, M., McLaughlin, J., Shaw, J. M. On cubic eos interaction parameter estimation for long chain n-alkane + aromatic binary mixtures (in preparation).