Distillation hints

Why must the alkyl halide product be dried carefully with anhydrous sodium sulfate before the distillation (Hint See Technique 15, Section 15.7.)... 

J. E. Troyan s series of articles on plant startup has a cause/effect table on instrumentation in Part II. This article also has troubleshooting hints for distillation, vacuum systems, heat transfer, and filtration. Here is the table on instrumentation. 

HINT. When you set up a heating mantle to heat any flask, usually for distillation or reflux, put the mantle on an iron ring and keep it clamped a few inches above the desktop (Fig. 61). Then clamp the flask at the neck, in case you have to remove the heat quickly. You can just unscrew the lower clamp and drop the mantle and iron ring. 

When citral (Problem 26, p. 652) is refluxed with aqueous potassium carbonate, acetaldehyde distills from the mixture and 6>methyl-5-hepten-2-one is obtained in high yield. Show all steps in a likely mechanism. Hint See Sec. 21.5.)... 

Evaluating methods K it was important to use very cold water to wash the KNO3, why was the salt-and-ice-water mixture from the bath not used After all, it had a lower temperature than the ice and distilled water from beaker 2 did. (Hint Consider what is contained in rock salt.)... 

Explain why it was important to rinse the burets with KMn04 or FeS04 before adding the solutions. (Hint Consider what would happen to the concentration of each solution if it were added to a buret that had been rinsed only with distilled water.)... 

Class 3. Fractional Distillation A Hint from Dalton Dalton and Raoult A Little Algebra... 

The following stream comes out of a distillation tower (described in detail in Chapter 6). It is at 138 psia and 197.5°F. If the pressure is reduced (adiabatically) to 51 psia, what will be the vapor fraction and temperature (Hint In Aspen Plus, put a valve before the Flash2 unit, and reduce the pressure with the valve block.)... 

Model column B2 in Figure 6.8 using a detailed model, RadFrac. (Hint Use the results from Problem 6.1 to choose key operating parameters.) Prepare a report comparing the output when using DSTWU and RadFrac to model the distillation column. What information was needed for each How do the results compare ... 

Distillation is one method that can he used to separate a specific metal from a mixture of other elements. Distillation involves raising the temperature of a mixture until one of its components turns into a gas and then cooling the gas to recover that component as a liquid or solid. If there were a mixture containing all of the period 4 transition metals, which metal would be easiest to separate by distillation Explain your reasoning. (Hint Use a reference such as the CRC Handbook of Chemistry and Physics to find the boiling points of these metals.)... 

Figure 20.20 shows a process for the isothermal production of C from A and B (A + B - C). The two reagents are fed to a CSTR, R-lOO, where complete conversion of B is assumed. The reactor effluent stream, consisting of C and unreacted A is separated in a distillation column, T-lOO, where the more volatile A is withdrawn in the distillate and recycled, and the product C is withdrawn in the bottoms stream. Your task is to devise a conceptual plantwide control system for the process. Hint It may be helpful to reposition the feed stream of A. 

Prepare unknown mixtures consisting of the following pairs of liquids hexane-heptane, hexane-toluene, and cyclohexane-toluene. For each mixture, use an equal volume of both liquids. Distillation of these mixtures should provide a good contrast between the two distillation methods. It is important that you read the Instructor s Manual for helpful hints about these mixtures. 

In a steam distillation, the amount of water actually distilled is usually greater than the amount calculated, assuming that both water and organic substance exert the same vapor pressure when they are mixed that they exert when each is pure. Why does one recover more water in the steam distillation than was calculated (Hint Are the organic compound and water truly immiscible )... 

Notice that the details of vacuum distillation are left for you to figure out on your own. However, here are two hints. First, all of the products boil between 100°C and 150°C at 20-mm pressure. Second, if your chosen substrate is anisole, the product will be a solid with a low melting point and will solidify soon after vacuum distillation is completed. The solid can be distilled, but you should not run any cooling water through the condenser. It will also be worthwhile to preweigh the receiving flask, because it will be difficult to transfer the entire solidified product to another container to determine a yield. 

In Figure 4.68 are shown phase-equilibrium maps for benzene mixed with other chemicals (not toluene). What is the volatility of the second component, compared to benzene Compared to toluene (Hint Use the maps in Figures 4.67 and 4.68 to determine the composition of the vapor above a 50/50 liquid mixture.) Which benzene mixture will be easier to separate by distillation ... 

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