Liquid benzene and toluene

FIGURE 8.38 Some of the steps that represent fractional distillation of a mixture of two volatile liquids (benzene and toluene). The original mixture boils at A and its vapor has composition B. After condensation of the vapor, the resulting liquid boils at C and the vapor has composition D, and so on. 

FIGURE 11.11 The vapor pressure of a solution of the two volatile liquids benzene and toluene at 25°C is the sum of the two individual contributions, each calculated by Raoult s law. 

A liquid mixture of benzene and toluene containing 50.0 wt% benzene at 90 C and pressure Po is fed at a rale of 32.5 m /h into a flash evaporator, a heated tank maintained at a pressure P,ank Po-When the feed is exposed to the reduced pressure in this unit, a portion of it evaporates. The liquid and vapor product streams are in equilibrium at 75 C and P,ank- liquid product contains 43.9 mole% benzene. When carrying out the requested calculations, assume volume additivity of liquid benzene and toluene, use Raoult s law and the Antoine equation where necessary, and neglect the effect of pressure on enthalpy. 

The heat capacities of liquid benzene and toluene have been taken to be 0.138 kI(mol- Cl and 0.165 kJ/(mol °C). respectively, and the vapor heat capacities and heats of vaporization of both species are those given in Appendix B. 

Huang, S.S.-S., and Freeman, G.R., 1980, Electron transport in gaseous, critical and liquid benzene and toluene, J. Chem. Phys., 72 2849. 

Physical Properties. Benzene, C H, toluene, C Hj-CH, and petrol (a mixture of aliphatic hydrocarbons, e.g., pentane, hexane, etc.) are colourless liquids, insoluble in and lighter than water. Benzene and toluene, which have similar odours, are not readily distinguishable chemically, and their physical constants should therefore be carefully noted benzene, m.p. 5 (solidifies when a few ml. in a dry test-tube are chilled in ice-water), b.p. 8i toluene, m.p. —93°, b.p. 110°. Petroleum has a characteristic odour. 

Prepare a benzene-toluene mixture by placing 0.05 mL of each liquid in a 25 mL graduated flask and making up to the mark with methanol. Take 1.5 mL of this solution, place in a lOmL graduated flask and dilute to the mark with methanol this solution contains benzene at the same concentration as solution 5, and toluene at the same concentration as solution 5. Measure the absorbances of this solution at the two wavelengths selected for the Beer s Law plots of both benzene and toluene. Then use the procedure detailed in Section 17.48 to evaluate the composition of the solution and compare the result with that calculated from the amounts of benzene and toluene taken. 

A simple rectifying column consists of a tube arranged vertically and supplied at the bottom with a mixture of benzene and toluene as vapour. At the top a condenser returns some of the product as a reflux which flows in a thin film down the inner wall of the tube. The tube is insulated and heat losses can be neglected. At one point in the column the vapour contains 70 mol% benzene and the adjacent liquid reflux contains 59 moi% benzene. The temperature at this point is 365 K. Assuming the diffusional resistance to vaponr transfer to be equivalent to the diffusional resistance of a stagnant vapour layer 0.2 mm thick, calculate the rate of interchange of benzene and toluene between vapour and liquid. The molar latent heats of the two materials can be taken as equal. The vapour pressure of toluene at 365 K is 54.0 kN/nt2 and the diffusivity of the vapours is 0.051 cm2/s... 

What is the vapor pressure of each component at 25°C and the total vapor pressure of a mixture in which one-third of the molecules are benzene (so Xben/ene,liquid = 3 and xtoiuene,iiqUid = ) The vapor pressures of benzene and toluene at 25°C are 94.6 and 29.1 Torr, respectively. 

This expression relates the composition of the vapor (in terms of the mole fraction of A in the vapor) in a binary mixture to the composition of the liquid (in terms of the mole fraction of A in the liquid, remembering that xB = 1 — xA). It is plotted for benzene and toluene in Fig. 8.36, and we see that xben,ene vapor > Xbenzenejiquid just as we anticipated. 

FIGURE 8.36 The composition of the vapor in equilibrium with a mixture of two volatile liquids (here, benzene and toluene) and its variation with the composition of the liquid. Note that the vapor is richer in benzene than the liquid mixture for each composition of the mixture. For instance, when the mole fraction of benzene is 0.133 in the liquid, in the vapor it is 0.619. 

FIGURE 8.37 A temperature-composition diagram for benzene and toluene. The lower, blue curve shows the boiling point of the mixture as a function of composition. The upper, orange curve shows the composition of the vapor in equilibrium with the liquid at each boiling point. Thus, point B shows the vapor composition for a mixture that boils at point A. 

The normal boiling point of a binary liquid mixture is the temperature at which the total vapor pressure is equal to 1 atm. If we were to heat a sample of pure benzene at a constant pressure of 1 atm, it would boil at 80.1°C. Similarly, pure toluene boils at 110.6°C. Because, at a given temperature, the vapor pressure of a mixture of benzene and toluene is intermediate between that of toluene and benzene, the boiling point of the mixture will be intermediate between that of the two pure liquids. In Fig. 8.37, which is called a temperature-composition diagram, the lower curve shows how the normal boiling point of the mixture varies with the composition. 

Figure 4.3 Vapor-liquid equilibrium for a binary mixture of benzene and toluene at a pressure of 1 atm. (From Smith R and Jobson M, 2000, Distillation, Encyclopedia of Separation Science, Academic Press reproduced by permission).

Benzene and toluene form an ideal liquid mixture. A mixture composed of 50 mol % benzene is used in a chemical plant. The temperature is 80°F, and the pressure is 1 atm. 

A distillation column is fed with a mixture of benzene and toluene, in which the mole fraction of benzene is 0.35. The column is to yield a product in which the mole fraction of benzene is 0.95, when working with a reflux ratio of 3.2, and the waste from the column is not to exceed 0.05 mole fraction of benzene. If the plate efficiency is 60 per cent, estimate the number of plates required and the position of the feed point. The relation between the mole fraction of benzene in liquid and in vapour is given by ... 

Because these two liquids, when mixed, obey Raoult s law, we say they form an ideal mixture. In fact, relatively few pairs of liquids form ideal mixtures a few examples include benzene and bromobenzene, benzene and toluene, bromobenzene and chlorobenzene, n-pen lane and i-pentane. Note how each set represents a pair of liquids showing a significant extent of similarity. 

SAQ 5.8 Benzene and toluene form an ideal mixture, i.e. they obey Raoult s law. At 20 °C, the pressure of benzene and toluene are 0.747 x p° and 0.223 xp respectively. What is the pressure above a mixture of these two liquids that contains 12 mol% of benzene ... 

If a mixture of benzene and toluene is heated in a vessel, closed in such a way that the pressure remains atmospheric and no material can escape and the mole fraction of the more volatile component in the liquid, that is benzene, is plotted as abscissa, and the temperature at which the mixture boils as ordinate, then the boiling curve is obtained as shown by ABCJ in Figure 11.5. The corresponding dew point curve ADEJ shows the temperature at which a vapour of composition y starts to condense. 

An equimolar mixture of benzene and toluene is subjected to flash distillation at 100 kN/m2 in the separator. Using the equilibrium data given in Figure 11.9, determine the composition of the liquid... 

Cumene is a colorless liquid, soluble in benzene and toluene and insoluble in water. It can be shipped in tank cars, tank trucks, barges, and drums. The flash point is high enough that it is not considered a hazardous material, and no DOT red shipping label is required. 

The production ofp-xylene begins with petroleum naphtha, as does the production of the other mixed xylene components, benzene and toluene. Naphtha is chemically transformed to the desired petrochemical components and the individual components are recovered at required purity in what is known in the industry as an aromatics complex [12]. A generic aromatics complex flow scheme is shown in Figure 7.2. It is useful to briefly review the general flow scheme of this complex for subsequent discussion of the liquid adsorptive processes. The process blocks... 

Consider two liquid substances that are rather similar, such as benzene and toluene or water and ethylene glycol. When moles of the one are mixed with B moles of the other, the composition of the liquid mixture is given by specification of the mole fraction of one of them [e.g., Xa, according to Eq. (2.2)]. The energy or heat of the mutual interactions between the molecules of the components is similar to that of their self interactions, because of the similarity of the two liquids, and the molecules of A and B are distributed completely randomly in the mixture. In such mixtures, the entropy of mixing, which is a measure of the change in the molecular disorder of the system caused by the process of mixing the specified quantities of A and B, attains its maximal value ... 

Pale yellow or colorless liquid corrosive refractive index 1.651 at 20°C density 2.42 g/mL at 22°C freezes at 8.5°C boils at 176.4°C decomposes at 176.4°C decomposes in water forming hydrochloric acid and selenious acid soluble in carbon disulfide, carbon tetrachloride, chloroform, benzene, and toluene. 

As in the case of hexafluorobenzene solvent anion, EPR and ODMR spectroscopies suggests that no dimerization of monomer radical anions of benzene and toluene occur in liquid benzene and/or in alkane solutions of benzene (whereas the radical cation of benzene is known to dimerize rapidly). The conductivity studies also indicate that there is no volume change associated with the dimerization [45]. 

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