What is the difference between zeotropic and near-azeotropic?

Answer 1

zeotrope is a liquid mixture that shows no local maximum or minimum when vapour pressure is plotted as a function of composition.[1] Such a mixture is separable into its component parts by fractional distillation

azeotropic distillation[1] is any of a range of techniques used to break an azeotrope in distillation. In chemical engineering, azeotropic distillation usually refers to the specific technique of adding another component to generate a new, lower-boiling azeotrope that is heterogeneous (e.g. producing two, immiscible liquid phases), such as the example below with the addition of benzene to water and ethanol. This practice of adding an entrainer which forms a separate phase is a specific sub-set of (industrial) azeotropic distillation methods, or combination thereof. In some senses, adding an entrainer is similar to extractive distillation.

Answer 2

Zeotropic refrigerant blends have varying boiling points, resulting in a varying composition as they evaporate or condense. Near-azeotropic refrigerant blends have components with very similar boiling points, so their composition remains relatively stable during phase changes. This difference affects their performance and behavior in refrigeration systems.