Boiling temperature-composition relationships

Figure 10 shows the relationship between yx and xx for different values of an calculated from Eq. (8). When two components have close boiling points, by implication they have similar vapor pressures, so that an is close to unity. Separation of mixtures by distillation becomes more difficult as an approaches unity. Figure 11 indicates some of the x, y diagrams that can be obtained for distillation systems. Also shown are corresponding temperature-composition diagrams. The saturated vapor or dewpoint curve is determined by finding the temperature at which liquid starts to condense from a vapor mixture. Similarly, the saturated liquid or bubble-point curve corresponds to the temperature at which a liquid mixture starts to boil. For ideal mixtures, the dewpoint and bubble-point curves can be calculated as follows. From Eq. (3), at the dew point, since... 

Temperature-composition (f-x) diagrams (Fig. 1.5). Curve ABC shows the composition-temperature relationship for the saturated liquid. At temperature T, and liquid composition xlt point B is the condition at which the liquid is ready to start boiling. Point B is termed the bubble... 

Give a fully labeDed diagram showing the relationship between boiling temperature and composition for mixtures of methanol and ethanol. Give full practical details for the fractional distillation in the laboratory of a mixture of methanol and ethanol in which die mole fraction of methanol is 0.2 and. hy reference to your temperature-conipoadon diagram, explain the principles of the process. 

These equations fix the equilibrium compositions of the three phases. As a consequence of these relationships, and as long as both liquid phases are present, the system boils as an azeotrope the boiling temperature and the composition of all phases remain constant and the only change is that the vapor phase increases at the expense of the liquid. When one of the two liquids boils off completely, the system consists of a single liquid and a vapor and behaves as usual, namely, its boiling temperature and the composition of the two phases vary continuously as more liquid is converted into vapor. 

Figure 8-54 shows a depropanizer controlled by reflux and boil-up ratios. The actual mechanism through which these ratios are manipulated is as D/(L + D) and B/(V + B), where L is reflux flow and V is vapor boil-up, which decouples the temperature loops from the liquid-level loops. Column pressure here is controlled by flooding both the condenser and accumulator however, there is no level controller on the accumulator, so this arrangement will not function with an overloaded condenser. Temperatures are used as indications of composition in this column because of the substantial difference in boiling points between propane and butanes. However, off-key components such as ethane do affect the accuracy of the relationship, so that an analyzer controller is used to set the top temperature controller (TC) in cascade. 

At a given composition, the higher the saturation temperature, the higher the saturation pressure. For this reason, the effect of saturation temperature discussed above can be considered as the effect of saturation pressure. A study of boiling point data in the pressure range of 1 to 10 atmospheres and a wide temperature range (28) led to a simple and rough approximation of the relationship between saturation pressure and saturation temperature for common substances ... 

Crude petroleum is a mixture of compounds boiling at different temperatures that can be separated into a variety of different generic fractions by distillation (Speight, 1999a, Speight, 2001). The terminology of these fractions has been bound by utility and often bears little relationship to composition. 

Tlie relationship between boiling point and vapor composition for the mixture of X (bp 80°C) and y (bp 110°C), both at 1 atm, is shown in Rgure 1.3, where the lower curve presents the boiling point of the liquid mixture at any temperature between 80 and 110°C, and the upper curve corresponds to the vapor composition as calculated from Equations 1.2 and 1.3. 

Consider first a typical section at constant pressure (Fig. 9.2a). The intersection of the double surface of Fig. 9.1 with the constant-pressure plane produces a looped curve without maxima or minima extending from the boiling point of pure B to that of pure A at the pressure in question. The upper curve provides the temperature-vapor composition (/-y ) relationship, the lower that of the temperature-liquid composition (/-x). Liquid and vapor mixtures at equilibrium are at the same temperature and pressure throughout, so that horizontal /ie lines... 

Pour point and viscosity determinations of crude oils are performed principally to ascertain their handling characteristics at low temperatures. There are, however, some general relationships about crude oil composition that can be derived from pour point and viscosity data. Commonly, the lower the pour point of a crude oil the more aromatic it is, and the higher the pour point, the more paraffinic it is. There are numerous exceptions to this rule-of-thumb, and other data must be used to verify a crude oil s character. Probably the most widely used index is the Characterization or K Factor [75 ], which was originally defined as the cube root of the average molal boiling point in °F absolute (Rankine) tempera-... 

---