THE EXPERIMENTAL-DETERMINATION AND MODELING OF VLE FOR BINARY SUBSYSTEMS OF THE QUATERNARY SYSTEM N2 + CH4 + C4H10 + C14H30 UP TO 1000-BAR AND 440-K

As a part of a laboratory study on nitrogen displacement in light-oil reservoirs, in which a mixture of methane, butane and tetradecane is used as a model oil, the phase behaviour of the binary subsystems of the quaternary system nitrogen + methane + butane + tetradecane is investigated in the temperature and pressure range of interest. The phase behaviour of the binary systems nitrogen + methane and methane + butane is known from literature. VLE of the binary systems nitrogen +tetradecane and methane + tetradecane were determined experimentally at 320 - 440 K according to the synthetic method using a high pressure cell with sapphire windows. VLE of the binary system butane + tetradecane were determined experimentally in the same temperature range according to the same method but now using the so-called Cailletet equipment. The experimental data were fitted using several equations of state in combination with a number of mixing rules. It is found that local composition mixing rules of the Huron-Vidal type and density dependent mixing rules as used by Mohammed and Holder and a new density dependent mixing rule, are superior to the conventional mixing rules with one or two binary interaction parameters. With these improved mixing rules a satisfactory description of the experimental data, even at pressures as high as 1200 bar can be realized.