A cubic equation of state for compounds with no critical point: Application to asphaltenes

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Many compounds of interest do not have critical properties, mostly because they decompose before reaching a critical state. Examples include polymers, ionic liquids, and asphaltenes. In this work, a novel numerical methodology for determining the glass transition temperature and boundary condition for the energy parameter in the Gibbs–Helmholtz Constrained (GHC) equation of state framework for compounds without critical properties is proposed. The glass temperature and boundary condition are then used in the multi-scale GHC equation to predict thermo-mechanical properties of a model asphaltene fluid proposed by Mullins (2010). Computational results for the GHC equation for the model asphaltene over the temperature range [263.15, 593.15 K] give mass densities that range from 1190.66 to 1064.37 kg/m3 and coefficients of thermal expansion in the range [9.04 × 10−5, 8.97 × 10−4 K−1] at 1 bar pressure. Multi-scale GHC-predicted isothermal compressibilities for the model asphaltene for pressures from 1 to 600 bar and temperatures of 380 and 480 K range from 7.43 to 1.56 × 10−5 bar−1. These results compare favorably with available experimental data for asphaltenes reported in the open literature and show that the GHC equation can accurately and reliably predict mass and molar densities, molar volumes, isothermal compressibilities, and coefficients of expansion over wide ranges of temperature and pressure. Advantages and disadvantages of the proposed approach are also given.

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Chemical Engineering Research and Design