THE EFFECT OF THE ADDITION OF WATER, PROPANE, OR DOCOSANE ON THE VAPOR-LIQUID AND SOLID-FLUID EQUILIBRIA IN ASYMMETRIC BINARY N-ALKANE MIXTURES

In this paper experimental results on vapour-liquid and solid-fluid ph ase equilibria for three types of ternary mixtures are reported. The t ernary systems studied were methane + water + hexadecane, methane + pr opane + tetracosane, and methane + docosane + tetracosane. The influen ce of an excess water phase on the vapour-liquid critical curve of the methane + hexadecane system is determined and found to be negligible in a temperature range from 290 to 350 K. The effect of the addition o f propane on the phase behaviour of two mixtures of methane + tetracos ane was studied. On addition of propane (x(C3) = 0.15) a decrease of t he bubble-and dew-point pressures of up to 40 MPa was observed. Also a shift of the solid + fluid/fluid)boundary curve towards lower tempera tures at constant pressure of approximately 6 K was found. For 20 mixt ures of the ternary system methane + docosane + tetracosane, the solid -fluid and vapour-liquid equilibria were studied at temperatures up to 350 K and at pressures up to 200 MPa. The different isobaric solid-so lubility curves show discontinuities at a relative solute mole fractio n of tetracosane of 0.15 and 0.5. This most likely indicates the prese nce of different mixed crystal structures in the solid phases precipit ating from the ternary mixtures at high pressures. (C) 1998 Elsevier S cience B.V.