1. Thermodynamics of Separation Operations
Chapter2
Thermodynamics of Separation Operations

2. Key and Difficult Points:
Purpose and Requirements:
Know the importance and mechanism of separation
Learn to select feasible separation process
Key and Difficult Points:
Key Points
Phase Equilibria: Fugacities and activity Coefficients
Graphical Correlations of Thermodynamic Properties
Calculation of K-value
Difficult Points
Nonidea Thermodynamic Property Modes
Activity Coefficient Models for the Liquid Phase

3. Outline 2.1 ENERGY, ENTROPY, AND AVAILABILITY -BALANCES
2.2 PHASE EQUILIBRIA
2.3 IDEAL GAS, IDEAL LIQUID SOLUTION MODEL
2.4 GRAPHICAL CORRELATIONS OF THERMODYNAMIC PROPERTIES
2.5 NONIDEAL THERMODYNAMIC PROPERTY MODELS
2.6 Activity Coefficient Models for the Liquid Phase

4. 2.1ENERGY, ENTROPY, AND AVAILABILITY -BALANCES
Gas Mixture (Solutes or Absorbate)
Liquid (Solvent or Absorbent)
Separate Gas Mixtures
Remove Impurities, Contaminants, Pollutants, or Catalyst Poisons from a Gas(H2S/Natural Gas)
Recover Valuable Chemicals

5. 2.2 PHASE EQUILIBRIA A = L/KV Component A = L/KV K-value
Water
Acetone
Oxygen ,000
Nitrogen ,000
Argon ,000
Larger the value of A，Fewer the number of stages required
1.25 to 2.0 ，1.4 being a frequently recommended value

6. 2.3 IDEAL GAS, IDEAL LIQUID SOLUTION MODEL
Stripping
Distillation
Stripping Factor (S解吸因子)
S = 1/ A= KV/L
High temperature
Low pressure is desirable
Optimum stripping factor ：1.4.

7. 6.1 EQUIPMENT
trayed tower
packed column
bubble column
spray tower
centrifugal contactor
Figure 6.2 Industrial Equipment for Absorption and Stripping

8. Trayed Tower (Plate Clolumns板式塔)
Figure 6.3 Details of a contacting tray in a trayed tower

9. (d) Tray with valve caps
(a) perforation
(b) valve cap
(c) bubble cap
(d) Tray with valve caps
Figure 6.4 Three types of tray openings for
passage of vapor up into liquid

10. Froth (a) Spray(b) Froth(c) Emulsion(d) Bubble(e)Cellular Foam
Liquid carries no vapor bubbles
to the tray below
Vapor carries no liquid droplets
to the tray above
No weeping of liquid through the
openings of the tray
Equilibrium between the exiting
vapor and liquid phases
is approached on each tray.
(a) Spray(b) Froth(c) Emulsion(d) Bubble(e)Cellular Foam
Figure 6.5 Possible vapor-liquid flow regimes for a contacting tray

11. Packed Columns
Figure 6.6 Details of internals
used in a packed column

12. Packing Materails (a) Random Packing Materials (b) Structured Packing
More surface area for mass transfer
Higher flow capacity
Lower pressure drop
Packing Materails
(a) Random Packing
Materials
(b) Structured Packing
Materials
Expensive
Far less pressure drop
Higher efficiency and capacity
Figure 6.7 Typical materials used in a packed column

13. SUMMARY
1. Separation processes are often energy-intensive. Energy requirements are determined by applying the first law of thermodynamics. Estimates of minimum energy needs can be made by applying the second law of thermodynamics with an entropy balance or an availability balance.
2. Phase equilibrium is expressed in terms of vapor-liquid and liquid-liquid AT-values, which are formulated in terms of fugacity and activity coefficients.
3. For separation systems involving an ideal gas mixture and an ideal liquid solution, all necessary thermodynamic properties can be estimated from just the ideal gas law, a vapor heat capacity equation, a vapor pressure equation, and an equation for the liquid density as a function of temperature.

14. 4. Graphical correlations of pure-component thermodynamic properties are widely avail­able and useful for making rapid, manual calculations at near-ambient pressure for an ideal solution.
5. For nonideal vapor and liquid mixtures containing nonpolar components, certain P-u-7'equation-of-state models such as S-R-K, P-R, and L-K-P can be used to estimate density, enthalpy, entropy, fugacity coefficients, and k-values.
6. For nonideal liquid solutions containing nonpolar and/or polar components, certain free-energy models such as Margules, van Laar, Wilson, NRTL, UNIQUAC, and UNIFAC can be used to estimate activity coefficients, volume and enthalpy of mixing, excess entropy of mixing, and k-values.

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