Bars

At pressures to a few bars, the vapor phase is at a relatively low density, i.e., on the average, the molecules interact with one another less strongly than do the molecules in the much denser liquid phase. It is therefore a common simplification to assume that all the nonideality in vapor-liquid systems exist in the liquid phase and that the vapor phase can be treated as an ideal gas. This leads to the simple result that the fugacity of component i is given by its partial pressure, i.e. the product of y, the mole fraction of i in the vapor, and P, the total pressure. A somewhat less restrictive simplification is the Lewis fugacity rule which sets the fugacity of i in the vapor mixture proportional to its mole fraction in the vapor phase the constant of proportionality is the fugacity of pure i vapor at the temperature and pressure of the mixture. These simplifications are attractive because they make the calculation of vapor-liquid equilibria much easier the K factors = i i ... 

If the vapor mixture contains only ideal gases, the integrals in Equations (3) and (6) are zero, z is unity for all compositions, and ()i equals 1 for each component i. At low pressures, typically less than 1 bar, it is frequently a good assumption to set ( ) = 1, but even at moderately low pressures, say in the vicinity of 1 to 10 bars, (f) is often significantly different from unity, especially if i is a polar component. 

Figure 4-12. Vapor-liquid equilibria for ethane-n-heptane at 6.9 bars. Ethane is treated as a condensable component even though its critical temperature is 305.4 K.

Figure 5-1. Enthalpy concentration diagram for ethanol-water at 1.013 bar.

Enthalpies are referred to zero enthalpies of the pure liquids. at 1.013 bars and 273.2 K. 

Case Flash Number Type Components Mole Fraction Pressure (bar) Temperature (K) Pressure (bar) Temperature V (K) F Mole Fractions Liquid Vapor No. of Iterations... 

TC = critical temperature, K PC = critical pressure, bars VC = critical volume, cm /g-vol... 

TEMPERATURE T(K), PRESSURE P(BAR)t AND VAPOR PHASE COMPOSITION Y. PHIS... 

Output FIP(I) vector (length 20) of standard-state fugacity (bars) (I = 1,N)... 

The reaction is carried out in the gas phase sind normally operates at around 700°C and 40 bar. Some of the benzene formed undergoes a secondary reversible reaction to an unwanted byproduct, diphenyl, according to the reaction... 

Heat flow required from the turbine exhaust = 21.9 MW From steam tables, inlet conditions at T, = 300°C and Pi = 41 bar are /ii = 2959kJkg ... 

---