Vapor diagrams

Figure 6.1. Pressure-vapor diagram of a typical material (Reid 1976).

Temperature (7) versus atom percent (X) liquid-vapor diagram for ethanol-water mixtures, which follow Dalton s4 law for partial pressures in the vapor phase, and Raoult s5 law for ideal solutions, but only approximately. One theoretical plate is the segment LM + MN another is NQ + QR. At point R there is a constant-boiling mixture. This is a variation of Fig. 4.7... 

The upper curve in Fig. 15.16 is the liquidus curve the lower curve, the solidus curve. If a system represented by point a is cooled to b, a solid solution of composition c appears. At point d the system consists of liquid of composition b in equilibrium with solid solution of composition c. The interpretation of the diagram is similar to the interpretation of the liquid-vapor diagrams in Section 14.6. An experimental difficulty arises in working with this type of system. Suppose the system were chilled quickly from a to e. If the system managed to stay in equilibrium, then the last vestige of liquid b" would be in contact with a... 

This obvionsly results in signillcant differences, for example, in the liquid-vapor diagrams, and it seems that the activity coefficients obtained from the model are correct as shown in Figure 8.8 by the comparison between the curves obtained using the VTPR method using UNIFAC (Do) and those directly obtained with UNIFAC (Do) only for the liquid-vapor diagram of the propane-methanol binary compoimd. 

Tabulated below are vapor-liquid equilibrium data for nitric acid/water mixtures at 1.0 atm. Use these data to plot a phase diagram (suitable for analyzing a flash drum) and an x-y liquid-vapor diagram (suitable for McCabe-Thiele analysis). Label the axes and, where appropriate, label the regions of the plot (liquid, vapor, etc.). ... 

Discuss the dependence of the friction phase diagram on temperature, mono-layer density, velocity, load and solvent vapor. Explain why each of these variables will drive one to the right or left in Fig. XII-8. 

Phase transitions in binary systems, nomially measured at constant pressure and composition, usually do not take place entirely at a single temperature, but rather extend over a finite but nonzero temperature range. Figure A2.5.3 shows a temperature-mole fraction T, x) phase diagram for one of the simplest of such examples, vaporization of an ideal liquid mixture to an ideal gas mixture, all at a fixed pressure, (e.g. 1 atm). Because there is an additional composition variable, the sample path shown in tlie figure is not only at constant pressure, but also at a constant total mole fraction, here chosen to be v = 1/2. 

Schematic diagram of a thermospray ion. source. This source, of current design, also incorporates (a) a discharge electrode so that the source can be operated in plasmaspray mode and (h) a repeller electrode to induce fragmentation. The vaporizer itself can be used as a discharge electrode.

The freezing point diagram for the hydrazine—water system (Eig. 1) shows two low melting eutectics and a compound at 64 wt % hydrazine having a melting point of —51.6°C. The latter corresponds to hydrazine hydrate [7803-57-8] which has a 1 1 molar ratio of hydrazine to water. The anomalous behavior of certain physical properties such as viscosity and density at the hydrate composition indicates that the hydrate exists both in the Hquid as well as in the soHd phase. In the vapor phase, hydrazine hydrate partially dissociates. 

Fig. 3. Vapor—liquid-phase diagram for the HCl—H2 O system (5) where (-) represents the demarcation between the two-phase region and the gas...

Air is compressed to modest pressures, typically 100 to 200 kPa ( 15-30 psig) with either a centrifugal or radial compressor, and mixed with superheated vaporized butane. Static mixers are normally employed to ensure good mixing. Butane concentrations are often limited to less than 1.7 mol 1 to stay below the lower flammable limit of butane (144). Operation of the reactor at butane concentrations below the flammable limit does not eliminate the requirement for combustion venting, and consequendy most processes use mpture disks on both the inlet and exit reactor heads. A dow diagram of the Huntsman fixed-bed maleic anhydride process is shown in Figure 1. 

Eigure 3 is a flow diagram which gives an example of the commercial practice of the Dynamit Nobel process (73). -Xylene, air, and catalyst are fed continuously to the oxidation reactor where they are joined with recycle methyl -toluate. Typically, the catalyst is a cobalt salt, but cobalt and manganese are also used in combination. Titanium or other expensive metallurgy is not required because bromine and acetic acid are not used. The oxidation reactor is maintained at 140—180°C and 500—800 kPa (5—8 atm). The heat of reaction is removed by vaporization of water and excess -xylene these are condensed, water is separated, and -xylene is returned continuously (72,74). Cooling coils can also be used (70). 

Another representation of the stabiUty relations of the siUca minerals is shown in Figure 4. This diagram, developed in the classical studies early in the twentieth century (51), illustrates the relationship of vapor pressure to temperature. It is assumed that vapor pressure increases with temperature and that the form having the lowest vapor pressure is the most stable. The actual values of the vapor pressures are largely unknown. Therefore, the ordinate must be considered only as an indication of relative stabiUties. This diagram does not show all the various forms of tridymite that have been identified. 

For systems other than air—water vapor or for total system pressures different from 101.3 kPa (1 atm), humidity diagrams can be constmcted if basic phase-equihbria data are available. The simplest of these relations is Raoult s law, apphcable at small solute concentrations ... 

The integration can be carried out graphically or numerically using a computer. For illustrative purposes the graphical procedure is shown in Figure 5. In this plot of vapor enthalpy or FQ vs Hquid temperature (T or T, the curved line is the equiHbtium curve for the system. For the air—water system, it is the 100% saturation line taken direcdy from the humidity diagram (see Fig. 3). 

A.mmonium C/j/oride. Work on the distribution of ammonium chloride [12125-02-9] between the vapor andhquid phases (8) suggests that the Ray diagram is sometimes an oversimplification. In most steam systems, there is much more ammonia than any other impurity. In particular, there is more ammonia than hydrogen chloride. The volatiUty of ammonium chloride is therefore expressed by the following chemical equation ... 

Processes involving oxygen and nitrogen oxides as catalysts have been operated commercially using either vapor- or Hquid-phase reactors. The vapor-phase reactors require particularly close control because of the wide explosive limit of dimethyl sulfide in oxygen (1—83.5 vol %) plants in operation use Hquid-phase reactions. Figure 2 is a schematic diagram for the Hquid-phase process. The product stream from the reactor is neutralized with aqueous caustic and is vacuum-evaporated, and the DMSO is dried in a distillation column to obtain the product. 

Fig. 1. Flow diagram of production of sulfur dioxide from oleum 1, 30% oleum exchanger 2, SO vaporizer 3, reactor 4, coolant surge tank 5, coolant ckculatkig pump 6, coolant exchangers 7, sludge and acid pump 8, scmbber 9, SO2 cooler 10, gas cleaner 11, SO2 compressor 12, pulsation damper and 13, SO2 condenser. CM is the condensate FRC, flow recording controller PIC, pressure kidicatkig controller SM, steam TC, temperature recorder ...

Phase Behavior. One of the pioneering works detailing the phase behavior of ternary systems of carbon dioxide was presented ia the early 1950s (12) and consists of a compendium of the solubiHties of over 260 compounds ia Hquid (21—26°C) carbon dioxide. This work contains 268 phase diagrams for ternary systems. Although the data reported are for Hquid CO2 at its vapor pressure, they yield a first approximation to solubiHties that may be encountered ia the supercritical region. Various additional sources of data are also available (1,4,7,13). 

The Class I binary diagram is the simplest case (see Fig. 6a). The P—T diagram consists of a vapor—pressure curve (soHd line) for each pure component, ending at the pure component critical point. The loci of critical points for the binary mixtures (shown by the dashed curve) are continuous from the critical point of component one, C , to the critical point of component two,Cp . Additional binary mixtures that exhibit Class I behavior are CO2—/ -hexane and CO2—benzene. More compHcated behavior exists for other classes, including the appearance of upper critical solution temperature (UCST) lines, two-phase (Hquid—Hquid) immiscihility lines, and even three-phase (Hquid—Hquid—gas) immiscihility lines. More complete discussions are available (1,4,22). Additional simple binary system examples for Class III include CO2—hexadecane and CO2—H2O Class IV, CO2—nitrobenzene Class V, ethane—/ -propanol and Class VI, H2O—/ -butanol. 

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