Multicomponent systems boiling

The shape of the coohng and warming curves in coiled-tube heat exchangers is affected by the pressure drop in both the tube and shell-sides of the heat exchanger. This is particularly important for two-phase flows of multicomponent systems. For example, an increase in pressure drop on the shellside causes boiling to occur at a higher temperature, while an increase in pressure drop on the tubeside will cause condensation to occur at a lower temperature. The net result is both a decrease in the effective temperature difference between the two streams and a requirement for additional heat transfer area to compensate for these losses. 

For multicomponent systems with boiling range greater than 80°C, a single adiabatic flash calculation to 80 to 90 percent of the inlet pressure P0 yields the two-phase specific volume oI at pressure P1 and co is calculated from (Nazario and Leung, Sizing Pressure Relief Valves in Flashing and Two-Phase Service An Alternative Procedure, J. Loss Prev. Process lnd. 5(5), pp. 263-269, 1992)... 

In view of the complicated reaction kinetics of multicomponent systems, it was not clear whether or not the diffusional effects would also affect the relative rate of conversion of feed molecules in a mixture. To answer this question we studied the hydrocracking of three multicomponent systems. The first was a C5-C8 mixture, a C5 360° C boiling range midcontinent reformate which contained 12.5 wt % n-paraffins including 4.2% n-pentane, 4.3% n-hexane, 2.9% n-heptane, l.l%n-octane, and <1% C9+ n-paraffins, with the remainder isoparaffins and aromatics. The reaction was carried out at 400 psig, 2 H2/HC, 2 LHSV, and 800°F. Secondly, a Cg-Cie mixture... 

The maximum boiling point is that temperature corresponding to a definite composition of a Iwo-coinponenl or multicomponent system al which the boiling point of the system is a maximum. At this temperature the liquid and vapor have the same composition and the solution distills completely without change in temperature. Binary liquid systems that show negative deviations from Raoult s law have maximum boiling points. See Raoult s I xiw and Van t Hoff I,aw. 

The Non-Random, Two Liquid Equation was used in an attempt to develop a method for predicting isobaric vapor-liquid equilibrium data for multicomponent systems of water and simple alcohols—i.e., ethanol, 1-propanol, 2-methyl-l-propanol (2-butanol), and 3-methyl-l-butanol (isoamyl alcohol). Methods were developed to obtain binary equilibrium data indirectly from boiling point measurements. The binary data were used in the Non-Random, Two Liquid Equation to predict vapor-liquid equilibrium data for the ternary mixtures, water-ethanol-l-propanol, water-ethanol-2-methyl-1-propanol, and water-ethanol-3-methyl-l-butanol. Equilibrium data for these systems are reported. 

A complex system may be compared with a defined multicomponent system on the basis of a true boiling point curve (TBP) diagram as shown in Figure 12.18. The TBP curve is a close... 

FIGURE 12.18 True boiling point curve diagram for a complex system and a defined multicomponent system. 

Figure 12.18 shows how a complex system differs from a multicomponent system. The complex system exhibits a smooth TBP curve, because even the high separating power of the TBP apparams cannot resolve all the many close-boiling constiments. The multicomponent system, on the other hand, is easily resolved by the powerful TBP apparams, although any azeotropes will be distilled over as though they were pure (pseudo) components. 

Azeotropes occur in binary, ternary, and multicomponent systems. They can be homogeneous (single liquid phase) or heterogeneous (two liquid phases). They can be minimum boiling or maximum boiling. The ethanol/water azeotrope is a minimumboiling homogeneous azeotrope. 

Here po is the density of the sorptive medium in a reference liquid state which may be chosen as the density of the saturated boiling liquid at the chosen temperature, i. e. po = Ps (T), [7.5, 7.3]. The parameter a in the characteristic curve of the sorbent material (7.78) is the reciprocal of a specific energy the exponent N normally is limited to 2 < N < 6 and for zeolites and activated carbons often has numerical values about N = 3. Both parameters are characteristic for a sorbent material and the micropore spectrum included in it. Details of practical applications of (7.79) and a variety of generalizations to real gas adsorptives and multicomponent systems can be found in the (still growing) literature in this field [7.53 7.55, 7.58]. 

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