Zeotropic mixture
[1] For example, nitrogen, methane, ethane, propane, and isobutane constitute a zeotropic mixture.
[5] Zeotropic mixtures have different characteristics in nucleate and convective boiling, as well as in the organic Rankine cycle.
As shown in Figure 1, the mole fraction of component 1 decreases from 0.4 to around 0.15 as the liquid mixture boils to the gas phase.
[4] However, with any zeotropic mixture, the temperature glide decreases when the mass fraction of a component approaches 1 or 0 (i.e. when the mixture is almost separated into its pure components) because the boiling and dew curves get closer near these mass fractions.
[4] A larger difference in boiling points between the substances also affects the dew and bubble curves of the graph.
[4] Azeotropic and zeotropic mixtures have different dew and bubble curves characteristics in a temperature-composition graph.
[11] For example, the minimum superheating needed to achieve this boiling is greater for zeotropic mixtures than for pure liquids because of the different proportions of individual substances in the liquid versus gas phases of the zeotropic mixture.
[11] From low cryogenic to room temperatures, the heat transfer coefficients of zeotropic mixtures are sensitive to the mixture's composition, the diameter of the boiling tube, heat and mass fluxes, and the roughness of the surface.
[15] The component with the intermediate boiling point has a max concentration in the middle of the distillation column.
[14] On the other hand, the mixture ABC could first be separated into AB and BC, and lastly split into A, B, and C in the same column.
[14] This is a non-sharp split configuration in which the substance with the intermediate boiling point is present in different mixtures after a separation step.
[16] In addition, other methods can be used to lower the energy or equipment costs required to distill zeotropic mixtures.
[16] Combining main and side columns saves equipment costs by reducing the number of heat exchangers in the system.
[16] Thus, using waste heat requires changing the pressure inside evaporators and condensers of the distillation system in order to control the temperatures needed.
[14] Crude oil is separated into five components with main and side columns in a sharp split configuration.
[14] In addition, ethylene is separated from methane and ethane for industrial purposes using multi-component distillation.
[14] Zeotropic mixtures that are used in refrigeration are assigned a number in the 400 series to help identify its component and their proportions as a part of nomenclature.
[18] Research has proposed using zeotropic mixtures as substitutes to halogenated refrigerants due to the harmful effects that hydrochlorofluorocarbons (HCFC) and chlorofluorocarbons (CFC) have on the ozone layer and global warming.
[3] For example, researchers found that zeotropic mixture R-404A can replace R-12, a CFC, in household refrigerators.
[3] In the Organic Rankine Cycle (ORC), zeotropic mixtures are more thermally efficient than pure fluids.
[20] The changing temperature of the zeotropic working fluid can be matched to that of the fluid being heated or cooled to save waste heat because the mixture's evaporation process occurs at a temperature glide[20][21] (see Pinch Analysis).
R21/R245fa and R152a/R245fa are two examples of zeotropic working fluids that can absorb more heat than pure R245fa due to their increased boiling points.
[22] In a cosolvent system, two miscible fluids with different boiling points are mixed to create a zeotropic mixture.
[22] Cosolvent systems are used for heavy oils, waxes, greases and fingerprints,[22][23] and can remove heavier soils than processes that use pure or azeotropic solvents.
