Phase Behavior Modeling of Asymmetric n-Alkane + Aromatic and Naphthenic Hydrocarbon Mixtures

• Author / Creator

  Ahitan, Sourabh

• Global phase behavior calculations based on 150 n-alkane + aromatic and n-alkane + naphthenic hydrocarbon binary mixtures were performed. These calculations were compared with experimental measurements whenever possible, and additional measurements were made as part of this work. The widely used Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) equations of state are shown to predict non-physical liquid-liquid phase behavior for long chain n-alkane + aromatic and long chain n-alkane + naphthenic hydrocarbon binary mixtures with standard pure component parameters (Tc, Pc, ω). Incorrect global phase behavior prediction is shown to be insensitive to the selection of correlations for estimating pure component properties for n-alkanes that are not available from experimental data. For cubic equations of state, correct phase behaviors are only obtained if negative binary interaction parameter (kij) values are used. For PC-SAFT, a non-cubic equation of state (with standard parameter values defining molecules and with binary interaction parameters set to zero), phase behaviors that are consistent with observed phase behaviors are obtained. However, below the melting temperature of at least one of the components, liquid-liquid phase behavior is predicted for some binary mixtures. At higher temperatures (above the L1=L2 critical locus) correct phase behaviors (L, LV, V, L=V) are predicted by both cubic and PC-SAFT equations of state. To assess the quality of liquid/vapor phase equilibrium predictions in the miscible region, bubble pressures and L=V critical loci are evaluated for 13 binary n-alkane + benzene mixtures, including benzene + n-C20, n-C24, n-C28 and n-C36 binary mixtures for which new experimental bubble pressure data is obtained in this work. Computed bubble pressures for the Peng-Robinson (PR), Soave-Redlich-Kwong (SRK) and Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) equations of state are compared with one another and with experimental measurements. The PC-SAFT EOS, with pure component parameters rescaled to conform with critical temperatures and pressures, and interaction parameter values set to zero, yield accurate bubble pressures and critical loci for all benzene + n-alkane mixtures. By contrast, the PR and SRK EOS require mixture specific kij values in order to provide quantitative bubble pressure and critical loci estimates, and best-fit kij values exhibit significant temperature dependence. In the absence of experimental bubble pressures, options for estimating interaction parameters for cubic EOS for binary benzene + n-alkane mixtures, and for aromatic or naphthenic + alkane mixtures more broadly are discussed. While subject to further testing, selection of interaction paramater values for cubic EOS such that computed bubble pressures closely mimic bubble pressures predicted by the scaled PC-SAFT EOS is recommended.

• Subjects / Keywords

  • Bubble pressure
  • Phase behavior
  • SRK
  • PC-SAFT
  • Binary interaction parameter
  • PR
  • Equation of state

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3ZP3W78B

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.