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In the laboratory, it can be activated and dehydrated by drying in a muffle furnace at a temperature of 350°C and drying under normal pressure for 8 hours (if there is a vacuum pump, it can be dried at 150°C for 5 hours). The activated molecular sieve is cooled in the air to about 200°C (about 2 minutes) and stored in a desiccator immediately. If possible, use dry nitrogen for maintenance during the cooling and storage process to avoid re-adsorption of water vapor in the air. The old molecular sieve after use has pollutants. It does not only need to be as high as 450°C for activation, but also water vapor or inert gas (nitrogen, etc.) must be introduced to replace other substances in the molecular sieve. 4A molecular sieve avoids oil and liquid water. Avoid contact with oil and liquid water when using it.
1. Change the temperature, that is, "change temperature". It removes adsorbed substances by heating 4A molecular sieve. In industry, it is generally heated by preheated regas to sweep the molecular sieve to about 200°C and take away the desorbed adsorbate.
2. Change the relative pressure, that is, "variable pressure". Generally used in gas phase adsorption process. The basic method is to keep the temperature of the adsorbent constant, and remove the adsorbate by reducing the pressure and blowing back with inert gas.
"Molecular sieve", if it is a "molecular sieve" used for drying, adsorption separation, and catalytic cracking, that is, "aluminosilicate type desiccant", then it only needs to be sealed and stored to prevent it from adsorbing other substances that can be adsorbed. . Of course, don't be contaminated by other substances.
Molecular sieve has a wide range of uses. It is not only a new type of high-performance selective microporous adsorbent, but also a type of catalyst and catalyst carrier with excellent functions. As a desiccant, 4A molecular sieve has a strong desiccation effect and can be used for desiccation of many gases and liquids. Because molecular sieves have a stronger adsorption effect on unsaturation, polar molecules and easily polarized molecules, molecular sieves cannot be used to dry unsaturated compounds. Molecular sieve has a small water absorption capacity. If the dry substance contains too much water, other desiccants should be used to remove water first, and then molecular sieve should be used for drying.
Because the useful pore size of 4A molecular sieve is 0.4nm, it is called 4A molecular sieve. It can adsorb water, methanol, ethanol, hydrogen sulfide, sulfur dioxide, carbon dioxide, ethylene, propylene and other low-molecular compounds. It does not adsorb any molecules with a diameter greater than 4A (including propane). ), the ability to select and adsorb water is higher than that of any other molecule, and it is one of the most used molecular sieves in the industry.
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