PFB1023_W10-C6

Chapter 6: Phase Stability and Azeotropes

Overview

  • Focuses on the stability of phases in mixtures.

  • University Technology Malaysia, September 2024 semester, taught by Dr. Dzetifarhah Mohshim.

Key Questions

  • How to identify the volatility of a component in a mixture?

Course Learning Outcomes

  • Calculate the composition of a mixture (bubble and dew point).

  • Sketch P-xy and T-xy diagrams of a mixture.

  • Define azeotrope.

  • Differentiate between minimum and maximum boiling points of azeotropic mixtures.

Bubble Point and Dew Point

  • Bubble Point: First drop of liquid mixture vaporizes.

  • Dew Point: First drop of gaseous mixture condenses.

P-xy and T-xy Diagrams

  • Represent liquid and vapor equilibrium in binary mixtures.

  • Key characteristics:

    • Most volatile component is plotted.

    • X-axis shows mole fractions; Y-axis shows temperature (T-xy) or pressure (P-xy).

  • Useful for predicting phase compositions based on temperature and pressure.

Bubble Point Calculation

  • Method 1: Using Dalton’s & Raoult’s Law to calculate bubble pressure.

  • Method 2: Calculation of bubble composition using total pressure.

Dew Point Calculation

  • Method 1: Calculate dew point pressure using Dalton's & Raoult's Law.

  • Method 2: Determine dew point composition from total pressure.

Azeotropes

  • Definition: Mixture with a constant boiling point where vapor composition equals liquid composition.

  • Azeotropes cannot be separated by simple distillation.

Minimum Boiling Azeotropes

  • Boiling point lower than any component; requires less energy to vaporize.

  • Exhibits positive deviations from Raoult's Law.

Maximum Boiling Azeotropes

  • Boiling point higher than any component; requires more energy to vaporize.

  • Exhibits negative deviations from Raoult's Law.

Example Problems

  • P-xy diagram of ethanol/ethyl acetate; calculate liquid/vapor compositions at given pressures.

  • In-class exercises involving T-xy diagrams of the same mixture under different conditions.

Recap Questions

  • Identify the correct regions of bubble and dew point lines in diagrams.

Additional Learning Outcomes

  1. Explain thermodynamic system concepts.

  2. Apply the laws of thermodynamics to open/closed systems.

  3. Utilize phase equilibrium concepts in hydrocarbon systems.

Conclusion

  • Institutional rights and QR code for the latest updates.