Why can boiling agents be added during distillation to prevent overboiling?

The boiling point is the chemical formula of the liquid and the temperature above the liquid surface 1 atmosphere vapor chemical formula the same.

Burst boiling is caused by overheating of a liquid.

The surface on which the bubbles are formed is the concave surface.

due to the action of surface tension.

The chemical formula of steam is high and it is not easy to form.

Higher temperatures must be reached.

Once this temperature is reached.

A large number of small bubbles gather into large bubbles.

The curvature of the concave surface decreases.

The chemical formula is lowered, making it easier to form.

Produces a boil. Add a void substance such as zeolite.

There is air in the voids.

Keep the gas-liquid interface close to the flat liquid level.

So it boils directly when it reaches the boiling point.

To put it simply, the addition of anti-boiling agent or zeolite prevents the uneven discharge of air in the water during the boiling process, so that the boiling process can be carried out smoothly, thereby preventing overboiling.

Pure liquids lack a vaporizing core, and the thermal hysteresis phenomenon of heating beyond the boiling point and still not boiling - after adding a little impurity (essentially bringing in tiny bubbles), the boiling hysteresis is broken and boiling is produced. The bubbles in the liquid play the role of vaporizing the nucleus during boiling, and when there is a lack of bubbles in the liquid, it does not boil even if the temperature reaches and exceeds the boiling point, forming a superheated liquid. Superheated liquids are unstable, and if the external ambient temperature of superheated liquids drops sharply or invades bubbles, it will form a violent boiling accompanied by a popping sound, a phenomenon called overboiling

Because when heating the beaker.

The liquid in the liquid will rush upwards without grinding, and the anti-riot agent can effectively prevent the upward rush of the liquid, so that the liquid can remain stable when heating; If it is found that no anti-riot agent is added after heating, the liquid should be cooled to the boiling point before adding anti-riot agent; Because the addition of anti-riot agent when the liquid is boiling will cause a violent boil.

Liquids gushing out of the bottle, raising safety concerns.

Vacuum distillation using zeolite does not work、Can only be heated slowly、

I also encountered this situation when I was concentrating the bacterial solution, and I unscrewed the sealing valve a little bit to reduce the vacuum level inside a little bit, so as to prevent boiling.

If it is to rectify some solvents with high boiling points, you can add some zeolite to the distillation flask;

Usually vacuum distillation is done to remove excess solvent, and the last thing is the residue after distillation, and the zeolite is easy to contaminate the target product.

When decompressing, don't lower the air pressure too low to prevent overboiling. The addition of zeolite in the distillation process can prevent overboiling, but in the process of vacuum distillation, its anti-detonation effect is very small.

This is because anti-riot agents can reduce the filial piety of liquid surfaces.

Anti-riot agent is a porous substance, the small bubbles in the anti-riot agent become the vaporization center of liquid molecules, reduce the surface tension of the liquid, thereby reducing the fluctuation of the liquid level, so that the gas produced by liquid boiling can smoothly get out of the night surface, avoid the imbalance between gas and liquid, so as to prevent the occurrence of overboiling phenomenon.

During the distillation process, the liquid is heated to produce vapor gases, which will hit the liquid level upwards, producing large vibrations and unstable fluctuations. When the liquid level fluctuates too much, it can lead to an imbalance between the gas and the liquid, resulting in a burst of boiling. Due to the violent vibration of the liquid during boiling, it is easy to cause the glass instrument to break, and after adding the anti-riot agent, the liquid boiling can be avoided at the same time, and the risk of damage to the glass template glass instrument can also be reduced.

When the pressure in the system decreases, the distillation that takes place is vacuum distillation. Prevent the solution from overheating and produce overboiling, so that the boiling is kept stable.

The influence of external pressure on the boiling point of the substance is used, because the greater the external pressure, the higher the boiling point of the substance, and the smaller the external pressure, the lower the boiling point of the substance, so as to achieve the purpose of fractionation under reduced pressure through this method. Therefore, two liquids with similar boiling points can only be separated by fractions under reduced pressure, but they cannot be separated (with similar boiling points).