How Do Trays in a Fractionating Column Create Temperature Differences?

[Godwin Kessy]

Liquid mixture boils at the same temperature, and on the fractionating column are series of trays with bubble caps and overflow pipes, that circulates the liquid mixture. Then how comes the column contains trays at diferent temperatures?

 

[Borek]

Mixture composition is not contant, it changes when you go up/down. The higher you are, the higher the fraction of the substance with lower boiling point.

 

[quicknote]

Fractional distillation is a process used to separate a mixture of liquids based on their boiling points. In this process, the liquid mixture is heated, causing it to vaporize. The vapor then travels up a fractionating column, which contains a series of trays with bubble caps and overflow pipes. These trays help to circulate the vapor and liquid mixture, allowing for more efficient separation.

The trays in the fractionating column are designed to create temperature differences within the column. As the vapor rises, it encounters cooler temperatures near the top of the column. This causes some of the vapor to condense back into a liquid, which then falls back down to the lower trays. As the liquid passes through each tray, it becomes increasingly enriched in the component with the lower boiling point, while the vapor becomes enriched in the component with the higher boiling point.

The temperature differences between the trays are crucial for the separation process. As the liquid and vapor mixture moves up the column, it gradually becomes more and more enriched in the component with the lower boiling point. This is because the vapor that rises to the next tray is slightly richer in the lower boiling point component than the vapor that entered the tray. This process continues until the vapor reaches the top of the column, where it is collected and condensed back into a liquid.

In summary, the trays in a fractionating column are designed to create temperature differences, which are essential for the efficient separation of a liquid mixture based on their boiling points. The trays allow for multiple stages of vapor-liquid contact, which results in a more effective separation of the components.