What is the principle of boiling? Zeolite prevents boiling principle

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

When there is a lack of bubbles or impurities 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 suddenly and sharply or invades bubbles or impurities, violent boiling will be formed, accompanied by a popping sound, this phenomenon is called overboiling.

There are many occasions and types that are easy to cause boiling, and there are two kinds of rough classification:

1) "Burst boiling" caused by heat of dissolution + heat of vaporization: If water is poured into concentrated sulfuric acid during misoperation, the heat released when the two are miscible meets the heat of vaporization of the water, but it is not evenly exported, resulting in "burst boiling";

2) "Burst boiling" caused by the heat of vaporization: such as "burst boiling" caused by cold water dripping into hot oil;

The main cause of boiling is that a large number of bubbles are formed in the liquid during the boiling process, which swell and rise to the liquid level and burst. Normally, this boiling process is harmlessBut the problem is that this gasification process requires a "core"., which is the initial bubble. If there are no small bubbles, the water molecules that are thermally moving enough to break free from the intermolecular forces are still individual and do not become gases escaping from the liquid surface (unless there are water molecules on the surface of the liquid), which forms a "superheated liquid".

It's like a spring outing for elementary school students, and when they want to get on the bus, the teacher will make the elementary school students line up. If all the students in a class are running around on the playground, then honestly, wouldn't they just be able to stand at the door of the bus and catch one passing by and get on the bus? 】

However, there are still many water molecules gathered together in the superheated liquid occasionally, and the vapor pressure inside the bubble is very low, but because the liquid temperature is now higher than the boiling point, the vapor pressure of the bubble will rise rapidly, and the bubble will also increase sharply, and there will be violent boiling, that is, the phenomenon of boiling. In severe cases, the vessel bursts, or the unlided container is sprayed, or the catheter is sprayed into the next stage.

You can imagine that more than a dozen elementary school students on the playground suddenly gathered in a group, rushed to the door of the bus, and rushed to get on the bus. 】

The zeolite prevents the boiling because the surface of the zeolite is loose and porous, and when you put it in the water, you will see that its surface will be full of large and small bubbles. These bubbles then provide a vaporizing core when boiling, preventing the liquid from overheating and eliminating the overboiling.

That is, the teacher draws the line on the playground, and each class has its own concentration point, and then gets on the bus in an orderly manner. 】

But does anyone still use zeolite today? Generally, you use a stirrer. At the same time, zeolite cannot be used continuously.

By the way, it is generally difficult to boil boiling water at home, because the containers at home are not clean in the first place, and gasification centers can be found everywhere.

Hazards: The solution splashes, flushes out of the container, and is easy to burn people.

Treatment: 1. In the micro-test Mengming (no more than 50ml), a sturdy long-necked flask can be used as a reaction vessel to resist overboiling.

2. Add capillaries, broken porcelain pieces, zeolite and other porous substances to the reaction system.

Zeolite. 3. Stir. Usually reactions use magnetic stirring, and reactions that are very prone to overboiling and reactions that are exothermic require more intense mechanical stirring.

4. Add a large number of glass fibers to the reaction system.

5. Carefully control the temperature and feeding speed, or replace it with indirect heating.

For example, in the ethanol to ethylene experiment, in order to prevent the catalyst absorbent concentrated sulfuric acid from boiling and splashing, it is necessary to put broken porcelain pieces or zeolite.

In the experiment of water distillation, because the glass surface of the distillation flask is very smooth and lacks the vaporization nucleus, it is easy to boil, and it is necessary to add zeolite or broken porcelain chips to the distillation flask during the experiment to prevent overboiling.

3. All boiling: due to the sudden drop in pressure, the saturated liquid that was originally in equilibrium is overheated under atmospheric pressure and rapidly boils and evaporates, and the volume expands sharply and shows a phenomenon called detonation or steam (water vapor for high-temperature saturated water), which is very prone to scalding accidents.

When a pressure vessel ruptures, the gas inside the vessel first expands rapidly, causing the pressure in the vessel to drop to atmospheric pressure instantaneously. At this point, the saturated liquid of the container is in a superheated state, that is, its temperature is higher than its boiling point at atmospheric pressure. As a result, the gas-liquid phase loses its equilibrium, the liquid rapidly evaporates and vaporizes in large quantities, the volume expands sharply, and the container shell is subjected to a high pressure impact, causing it to further rupture.

Surfaces such as zeolite and broken porcelain tiles have tiny pores, and when the liquid is heated, steam is generated in the liquid. This is the same principle as when you usually see bubbles rising up when boiling water. The surface pores such as zeolite have the effect of temporarily storing gases, reducing the pressure in the liquid, thereby preventing overboiling.

Zeolite History

In 1932, McBain proposed the concept of "molecular sieves". Indicates a porous material that can sieve substances at the molecular level. Although zeolite is only one type of molecular sieve, zeolite is the most representative of it, so the terms "zeolite" and "zeolite" are often used interchangeably.

Artificial zeolites are: sulfonated polystyrene; Natural zeolite: sodium aluminosilicate.

Zeolite group minerals are commonly found in the pores of ejecta rocks, especially basalts, but also in sedimentary, metamorphic and hydrothermal deposits, and in some modern thermal deposits. Weichang County, Hebei Province is the area with the highest zeolite reserves found in China, with more than 2 billion tons of zeolite reserves.