Fractional distillation cyclohexane-toluene

Prelab Exercise Predict what a plot of temperature vs. volume of distillate will look like for the simple distillation and the fractional distillation of (a) a cyclohexane-toluene mixture, (b) an ethanol-water mixture. 

At 100°C cyclohexane has a partial pressure of433 mm and toluene a partial pressure of 327 mm the sum of the partial pressures is 760 mm and so the liquid boils. If some of the liquid in equilibrium with this boiling mixture were condensed and analyzed, it would be found to be 433/760 or 57 mole percent cyclohexane (pointB, Fig. 2). This is the best separation that can be achieved on simple distillation of this mixture. As the simple distillation proceeds, the boiling point of the mixture moves toward 110°C along the line from A, and the vapor composition becomes richer in toluene as it moves from B to 110°C. In order to obtain pure cyclohexane, it would be necessary to condense the liquid at B and redistill it. When this is done it is found that the liquid boils at 90°C (point C) and the vapor equilibrium with this liquid is about 85 mole percent cyclohexane (point D). So to separate a mixture of cyclohexane and toluene, a series of fractions would be collected and each of these partially redistilled. If this fractional distillation were done enough times the two components could be separated. 

B) Fractional Distillation of an Ethanol-Water Mixture. Place the 50 mL of distillate from the simple distillation experiment in a 100-mL round-bottomed flask, add one or two boiling chips, and assemble the apparatus for fractional distillation. Follow the procedure (above) for the fractional distillation of a cyclohexane-toluene mixture. Repeat the ignition test. Is any difference noted ... 

From the boiling point versus volume of distillate plot in the fractional distillation of the cyclohexane-toluene mixture (3), what conclusion can you draw about the homogeneity of the distillate ... 

Extractive distillation is not limited to the separation of binary mixtures, but is also capable of removing particular classes of substances from multicomponent inixtiire.s, as for instance benzene from mineral oil fractions. Mixtures of saturated and imsaturated hydrocarbons having closely similar boiling points can be separated by extractive distillation with ketoesters [73]. Recently, the sei)aration of lower hydrocarbons CyCa has been gaining ground [74]. Garner et al. [75] studied the efficiency of packed columns in the extractive distillation of the system iiictliyl cyclohexane-toluene with derived equations for this process. 

Frequent impurities in ben2 ne are thiophene, cyclohexane and sometimes toluene. Removal of the thiophene content is of particular importance and can be effected by shaking with concentrated sulphuric acid. Benzene is then freed from sulphuric acid by washing with dilute sodium hydroxide solution, and the residual alkali is removed by washing with water. The solvent is dried by treatment on a molecular sieve, and the purification process is completed by fractional distillation. 

In the fractional distillation of your mixture of cyclohexane and toluene, what can be learned about the efficiency of the separation on the basis of the relative volumes of fractions A, B, and C ... 

Refer to the GLC traces given in Figure 6.16. These are analyses of the various fractions collected during the fractional distillation of the mixture of cyclohexane and toluene. The weight and mole correction factors (flame ionization detector) for cyclohexane are 0.84 and 0.78, respectively, and those for toluene are given in Table 6.2. Accurately determine both the weight percent and the mole percent compositions of the distillation fractions A, B, and C. 

Medium Boiling Esters. Esterificatioa of ethyl and propyl alcohols, ethylene glycol, and glycerol with various acids, eg, chloro- or bromoacetic, or pymvic, by the use of a third component such as bensene, toluene, hexane, cyclohexane, or carbon tetrachloride to remove the water produced is quite common. Bensene has been used as a co-solvent ia the preparatioa of methyl pymvate from pymvic acid (101). The preparatioa of ethyl lactate is described as an example of the general procedure (102). A mixture of 1 mol 80% lactic acid and 2.3 mol 95% ethyl alcohol is added to a volume of benzene equal to half that of the alcohol (ca 43 mL), and the resulting mixture is refluxed for several hours. When distilled, the overhead condensate separates iato layers. The lower layer is extracted to recover the benzene and alcohol, and the water is discarded. The upper layer is returned to the column for reflux. After all the water is removed from the reaction mixture, the excess of alcohol and benzene is removed by distillation, and the ester is fractionated to isolate the pure ester. 

The nanosecond pulse radiolysis technique has been described (8, 14). Carbon tetrachloride was purified as follows Matheson Research grade CC14 was dried over anhydrous potassium carbonate for several days, and subsequently distilled, discarding initial and final fractions. However, untreated research grade CCLj gave identical results to that treated as above. Zone refined naphthalene, anthracene, biphenyl, and N,N,N, N -tetramethyl-paraphenylenediamine (TMPD) were used pyrene, 1 2 benzanthracene were recrystallized from absolute alcohol, and aniline was purified as described in an earlier paper (6). Normal hexane, cyclohexane, 3-methylpentane, benzene, and toluene were Matheson research grade methanol and ethyl alcohol were analytical grade. 

Unless directed to do otherwise, pour the pot residue into the container for nonhalo-genated organic liquids and return the distillation fractions to a bottle marked "Recovered Cyclohexane and Toluene."... 

An example of the use of GLC as a qualitative, analytical tool is illustrated in Figure 6.16. These sets of peaks represent a gas chromatographic separation of the distillation fractions of a mixture of cyclohexane and toluene similar to those obtained in the distillation experiment described in Section 4.3. The notations A, B, and C refer to the three fractions taken in that experiment. The individual peaks... 

In the following set of experiments, we wiU examine the applications of a variety of distillation techniques to the purification of liquid mixtures. In Experiments [3A] and [3B] you will conduct simple distillations. In Experiment [3A] a volatile liquid component is separated from a nonvolatile solid. Experiment [3B] illustrates the use of the Hickman still in the separation of hexane and toluene, which have boiling points 42 °C apart. The composition of the fractions is analyzed by refractive index and boiling point. Experiments [3C] and [3D] introduce the use of micro spinning-band distillation columns for the separation of cyclohexane (bp 80.7 °C) and 2-methylpentane (bp 60.3 °Q. The composition of the distillate fractions are determined by gas chromatography. The number of theoretical plates is determined for the spinning-band column used. In Experiment [3D] you wiU be introduced to one of the simplest yet most efficient and powerful distillation techniques for the separation of liquid mixtures at the semimicroscale level, the Hickman-Hinkle stiU. 

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