Definition: A residue curve is a graphical representation used in chemical engineering and thermodynamics to depict the evolution of the liquid-phase composition during the continuous vaporization of a multicomponent mixture under equilibrium conditions, assuming no vapor is removed.
Overview: Residue curves are primarily used in the analysis of distillation processes, especially for understanding the feasibility and design of separation sequences in multicomponent mixtures. They are instrumental in constructing residue curve maps (RCMs), which are phase diagrams showing the trajectories of liquid composition changes over time as vaporization proceeds. These maps are particularly valuable in identifying distillation boundaries, azeotropes, and stable node, unstable node, and saddle points in phase behavior.
Etymology/Origin: The term "residue" refers to the portion of the mixture that remains after vaporization, while "curve" denotes the path traced by the changing composition. The concept originated in the early 20th century with the development of distillation theory and phase equilibrium thermodynamics, notably advanced by researchers such as Rayleigh and later systematized in the framework of geometric theory of distillation by researchers like Moritz Rosenthal and later Kenneth Doherty.
Characteristics:
- Residue curves start at an initial liquid composition and proceed toward a compositionally stable endpoint (typically a pure component or azeotropic mixture).
- They are derived by solving a set of ordinary differential equations based on the relationship between liquid and vapor compositions governed by vapor-liquid equilibrium (VLE).
- In ternary mixtures, residue curve maps can be plotted on triangular diagrams, showing trajectories that help identify regions of separability.
- The direction of the curve indicates the change in composition of the residual liquid as lighter components are preferentially vaporized.
- Residue curves do not cross distillation boundaries, which separate regions with different distillation outcomes.
Related Topics:
- Vapor-liquid equilibrium (VLE)
- Azeotrope
- Distillation
- Phase diagram
- Ternary diagram
- Relative volatility
- Rayleigh distillation
- Residue curve map (RCM)
- Continuous distillation
- Batch distillation