HIGH-PRESSURE PHASE-BEHAVIOR OF BINARY-SYSTEMS OF HEPTADECANE AND OCTADECANE WITH CARBON-DIOXIDE OR ETHANE

Phase behavior of four binary systems of heptadecane and octadecane with CO2 and ethane was investigated in the temperature range from 270 to 320 K and pressures up to 30 MPa. The observed phase boundaries correspond to the three-phase coexisting lines with some nonvariant points of quadruple points and critical endpoints. Phase density inversion between two liquid phase was also observed in the n-alkanes with CO2 systems. The phase density inversion points form a straight line in the pressure-temperature diagram regardless of the carbon number of the n-alkanes. In the homologous series of n-alkane + CO2 systems, the ''odd-even effect'' of carbon numbers of n-alkanes has been observed in the relation of the triple point of n-alkane and the quadruple point.