azeotropelike

Azeotropelike describes a property of certain liquid mixtures whose phase behavior resembles that of an azeotrope without meeting the formal criterion of a true azeotrope. In a true azeotrope at a given pressure, the liquid and vapor phases have the same composition, so the mixture boils at a constant temperature and cannot be separated into pure components by simple distillation at that pressure. Azeotropelike behavior, by contrast, refers to systems where the liquid and vapor compositions are very close, or the boiling point curve is particularly flat over a range of compositions, giving the appearance of nearly constant-boiling behavior but not an exact equality at any single composition and pressure.

Causes and implications: Azeotropelike behavior arises from non-ideal interactions in the mixture, which are described by activity coefficients and the excess Gibbs energy. These interactions cause deviations from Raoult’s law and can produce near-equal liquid and vapor compositions or a flattened boiling-point region. In practice, such systems present challenges for separation by conventional distillation, since the achievable separation near the azeotropelike region is limited. To achieve further separation, engineers may employ techniques like azeotropic distillation with entrainers, extractive distillation, or changes in pressure that shift the system away from the azeotropelike behavior. Some binary and multicomponent mixtures exhibit near-azeotropic characteristics under certain temperatures and pressures, making their separation more difficult than for ideal, regularly behaving mixtures.