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1、Thermodynamics of Separation Operations,Chapter2,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
2、 the Liquid Phase,Purpose and Requirements: Know the importance and mechanism of separation Learn to select feasible separation process,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
3、PROPERTIES 2.5 NONIDEAL THERMODYNAMIC PROPERTY MODELS 2.6 Activity Coefficient Models for the Liquid Phase,2.1ENERGY, ENTROPY, AND AVAILABILITY -BALANCES,Gas Mixture (Solutes or Absorbate) Liquid (Solvent or Absorbent) Separate Gas Mixtures Remove Impurities, Contaminants, Pollutants, or Catalyst Po
4、isons from a Gas(H2S/Natural Gas) Recover Valuable Chemicals,2.2 PHASE EQUILIBRIA,A = L/KV Component A = L/KV K-valueWater 1.7 0.031Acetone 1.38 2.0Oxygen 0.00006 45,000Nitrogen 0.00003 90,000Argon 0.00008 35,000,Larger the value of A，Fewer the number of stages required 1.25 to 2.0 ，1.4 being a freq
5、uently recommended value,2.3 IDEAL GAS, IDEAL LIQUID SOLUTION MODEL,Stripping DistillationStripping Factor (S解吸因子) S = 1/ A= KV/L,High temperature Low pressure is desirableOptimum stripping factor ：1.4.,6.1 EQUIPMENT,Figure 6.2 Industrial Equipment for Absorption and Stripping,trayed tower,packed co
6、lumn,spray tower,bubble column,centrifugal contactor,Figure 6.3 Details of a contacting tray in a trayed tower,Trayed Tower (Plate Clolumns板式塔),Figure 6.4 Three types of tray openings forpassage of vapor up into liquid,(d) Tray with valve caps,(b) valve cap,(c) bubble cap,(a) perforation,Figure 6.5
7、Possible vapor-liquid flow regimes for a contacting tray,(a) Spray(b) Froth(c) Emulsion(d) Bubble(e)Cellular Foam,Froth,Liquid carries no vapor bubblesto the tray below Vapor carries no liquid dropletsto the tray above No weeping of liquid through theopenings of the trayEquilibrium between the exiti
8、ng vapor and liquid phases is approached on each tray.,Packed Columns,Figure 6.6 Details of internalsused in a packed column,Figure 6.7 Typical materials used in a packed column,Packing Materails,(a) Random PackingMaterials,(b) Structured PackingMaterials,More surface area for mass transfer Higher f
9、low capacity Lower pressure drop,ExpensiveFar less pressure drop Higher efficiency and capacity,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 se
10、cond 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
11、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.,4. Graphical correlations of pure-component thermodynamic proper
12、ties 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-7equation-of-state models such as S-R-K, P-R, and L-K-P can be used to estimate density, en
13、thalpy, 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, e
14、xcess entropy of mixing, and k-values.,REFERENCES,1. Mix, T.W., J.S. Pweck, M. Weinhcrg, and R.C. Armstrong, AlChESymp. Ser., No. 192, Vol. 76, 15-23 (1980). 2. Pettier, R.M., and R.W. Rousseau, Elementary Principles of Chemical Prucr.v.vtv. 2nd ed John Wiley & Sons, New York (1986). 3. de Nevers, N
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