what is the purpose of having glass beads during fractional distillation?

Answer 1

The glass beads serve as "theoretical plates" on which reflux can occur. Remember that simple distillation only allows for a single cycle of evaporation (of the solution) and condensation (of the product). Simple distillation is effective at separating components whose boiling points differ by >50 degrees Celsius.

But solutions composed of components with close boiling points will boil at nearly the same time, so a single evaporation-condensation cycle is not enough to separate the components of such a solution with good yield. Let's say you have a 50%:50% solution of two components with nearly similar boiling points. The vapor phase will consist of a mixture of the two components, but as long as the boiling points aren't exactly the same, there still should be a higher concentration of the more volatile component than of the component with the higher boiling point. Condensation of these vapors would produce a new solution that had a slightly higher concentration of the more volatile component. If multiple simple distillations were performed successively, you would eventually reach a sufficiently good separation of your two components.

Unfortunately, this could take a long time. So a shortcut was invented. Packing a column with glass beads gives the solution multiple sites ("theoretical plates") upon which evaporation-condensation can occur. As vapors rise up the column, some of the vapor will condense on the glass bead producing a solution that is higher in concentration in the more volatile component of the mixture. As the condensed liquid is heated by surrounding vapors, it re-evaporates to form vapors that are even higher in concentration in the more volatile component. The vapor then travels a little farther up your column where it encounters another glass bead, re-condenses, and then re-evaporates, and so on and so forth until it reaches the top of the column. Each time that vapor condenses on a bead and re-evaporates is nearly equivalent to performing another simple distillation on the solution. Therefore, the more packed your column, the more theoretical plates your column has, the more sites for recondensation-reevaporation, and the more effective your column will be at separating liquids with similar boiling points. You could also make your column longer (the petroleum industry uses fractional distillation columns several stories tall in order to distill components from raw oil).

Glass beads act as theoretical plates upon which condensation-reevaporation can occur.

Answer 2

We used glass beads, wool or a fractional distillation column that had indentations on the inside glass walls for fractional distilation. The purpose for these is as follows:

When boiling a mixture of liquids the vapour has a partial pressure for all liquid components i.e. there is always a percentage of each component in the vapour. As it rises in the fractional distillation column (again be they glass beads, wool etc) there will be some condensation. This condensation will contain a higher percentage of the higher boiling point components (i.e. lower boiling point components remain preferencially in the vapour phase and go higher up in the fractionation column).

This condensate then flows back into your distillation flask. With this method the distillate that comes over has a higher purity than if fractional distillation was not used.

Answer 3

Glass Distillation Column

Answer 4

They give a large area of contact between rising vapour and falling liquid and, as some liquid condenses higher up the column, it runs back down over the beads as internal Reflux that controls the degree of separation of the components giving purer bottom and top products.

Answer 5

In even simpler terms, it helps to knock the liquid back down so it doesn't rush up the column to fast (like when the pot foams over when you cook spaghetti too hot).

It helps to get a cleaner separation.

Answer 6

to prevent superheating of solvent.

Answer 7

even heat distribution and over-boiling