Fluid mixtures at high pressures II. Phase separation and critical phenomena of (ethane + an n-alkanol) and of (ethene + methanol) and (propane + methanol)

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To study various effects on the critical phase behaviour of fluid mixtures, the critical p( T) curves and liquid-liquid-gas (llg) three-phase lines of the six mixtures (ethane + an n-alkanol) with methanol, ethanol, n-propanol, n-butanol, n-pentanol, and n-octanol, and of (ethene + methanol) and (propane + methanol) have been investigated. All mixtures apart from (propane + methanol) exhibit an interrupted critical curve and show ll phase separation. The two branches of the critical curve end at an upper critical end point (UCEP) and at a lower critical end point (LCEP). These are connected by an llg three-phase line. Among the mixtures exhibiting an interrupted critical curve, (ethane + methanol) is the only one which does not have an LCEP. Quasi-binary mixtures of ethane with three different { xCH 3OH + (1 − x)C 2H 5OH} mixtures, where x is 0.50, 0.75, and 0.90, are used to demonstrate the transition from a mixture having only a UCEP, such as (ethane + methanol), to a mixture possessing a UCEP and an LCEP, such as (ethane + ethanol).