Thermodynamic properties of the components of natural hydrocarbon systems. Methylcyclohexane
The demand for development of a fundamental equation of state for methylcyclohexane, which is a representative of naphthenic hydrocarbons, is shown. This specified equation of state is necessary both forcalculating the thermodynamic properties, and for modeling the phase equilibria of gas condensate systems containing methylcyclohexane.Published data on the thermodynamic properties of methylcyclohexane are collected and critically analyzed. Based on the analysis, it was found that only the liquid phase was experimentally investigated at temperatures up to 600 K. To increase stability of the equation in regions lacking the experimental data, the calculated data were included in the fitting process. In this case, well-tested generalized calculation methods developed in the framework of the theory of thermodynamic similarity were used. Based on a hybrid array of experimental and calculated data, the fundamental equation of state of methylcyclohexane was obtained by means of the random search method. The equation is applicable in the temperature range from a triple point to 700 K at pressures up to 100 MPa. The presented equation of state describes the reduced Helmholtz potential and takes the reduced density and reduced temperature as variables. The functional form of the equation contains five polynomial terms, five exponential terms and three Gauss terms. The proposed equation satisfies the critical conditions, the Maxwell rule, the rectilinear diameter rule, and physically correctly describes the ideal curves and the curvature of the thermodynamic potential derivatives. The average absolute deviations of properties are: ±0,4% for saturated vapor pressure; ±0,25 % for liquid phase density including saturation line; ±1,1% for gas phase density; ±0,9% for isobaric heat capacity in liquid phase including saturation line; ±2,0% for isobaric heat capacity in vapor phase; ±0,3% for speed of sound in liquid phase.