Determination of the number of trays in a distillation column by full reflux
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The laboratory has a glass distillation column that is about 1.5 meters tall and 3 cm in diameter, equipped with θ mesh ring packing. The manufacturer specifies a tray height of about 15 trays per meter, which means there are roughly 17 trays in total. Now I am preparing to determine the exact number of theoretical plates using a full reflux experiment (since my supervisor said that the data provided by the manufacturer is not convincing). At first, benzene and toluene were used as the substances for separation. However, since benzene and toluene are easy to separate, only 14 trays were needed to achieve 100% purity of benzene at the top of the column and 100% purity of toluene at the bottom (the boiling point of benzene is 80 degrees Celsius, while that of toluene is 110 degrees Celsius). As a result of their ease of separation, the number of trays in this column turned out to be excessive (around 27), making it impossible to determine the exact number of trays. I would like to ask everyone whether there are two substances for which the number of trays required for complete separation is around 30, and for which vapor-liquid equilibrium data are available.
p-Xylene and m-xylene are difficult to separate; you can give it a try. As for whether it’s thirty, that depends on the separation efficiency of your distillation column; it’s hard to determine which substance system it is.
The heptane-methylcyclohexane system can be used to determine the number of theoretical plates for 20 to 80 plates. The benzene-tetrachloroethylene system is used to determine the number of theoretical plates for less than 20 plates
You can try benzene and 1,2-dichloroethane
The acetic acid and butyl acetate system can be determined
This is a very practical question. Recently, our laboratory also has a distillation column for which we need to determine the number of theoretical plates; we were struggling with choosing an appropriate system for this purpose. After reading this post, I found it useful. Thank you
This is a specialized experiment in the field of chemical engineering; the chemistry department uses n-heptane-methylcyclohexane. The refractive index of various mixtures of n-heptane and methylcyclohexane can be found in relevant sources. The concentrations at the top and bottom of the column are measured using an Abbe refractometer, and finally, the Fenske equation is used to determine the minimum number of theoretical plates required.
0-8 theoretical plates: acetaldehyde and water; 0-12 theoretical plates: benzene and toluene; 0-15 theoretical plates: propanone and ethanol; 0-18 theoretical plates: chloroform and benzene; 0-18 theoretical plates: ethanol and water; 0-45 theoretical plates: acetic acid and butyl acetate; 0-90 theoretical plates: benzene and 1,2-dichloroethane; 0-100 theoretical plates: n-heptane and methylcyclohexane
When measuring 1# vitalshui, different known binary mixture systems can be selected based on the approximate theoretical number of theoretical plates in the distillation column. Commonly used combinations are: benzene–carbon tetrachloride when N≤25; benzene–1,2-dichloroethane when N≤60; n-heptane–methylcyclohexane when N≤90; n-heptane–isooctane when N≤300. Additionally, a few points should be noted for the poster: 1. In any system, the VLE values are generally quite similar overall – the values are farther apart in the middle and very close at the ends. Therefore, the concentrations at the bottom and top of the tower should fall within the middle range of these VLE values, which makes it easier to determine the number of tray levels; this can be done by performing calculations tray by tray based on the VLE data to find out where the bottom and top of the tower lie ； 2. When the reboiler is relatively large, the concentration at the bottom of the tower is close to the initial concentration of the system ； 3. The tower’s stabilization time should be at least 2 hours; adding the initial solution to the top of the tower to wet the packing helps to reduce the time required to reach equilibrium ； 4. Insulation of the tower is very important; otherwise, accurate measurements cannot be obtained ； 5. PRO/II and Aspen can simulate full reflux; these are theoretical results for comparison with experimental results
I was doing experiments recently, using tower plates worth over ten yuan each. I plan to use an ethanol-water system to try and determine the number of plates.