Let me talk about the problem of silica gel regeneration: after silica gel absorbs water, it can be removed by thermal desorption. There are many heating methods, such as electric furnace, flue waste heat heating and hot air drying. The temperature for removing the additional heat should be controlled at 120-180℃. For blue gel indicator, discoloration silica gel, and DL-type blue silica gel, the temperature should be controlled at 100-120℃. The maximum temperature during regeneration of various industrial silica gels should not exceed the following limits:

       The coarse-pored silica gel shall not be higher than 600℃;

       The fine-pored silica gel shall not be higher than 200℃;

       Blue glue indicator (or discoloration silica gel) shall not be higher than 120℃;

       Silica-alumina glue shall not be higher than 350℃.

       After the regenerated silica gel, its moisture content is generally controlled below 2% before being put into use again.

       Problems that should be paid attention to in the regeneration of silica gel:

       1. When drying and regenerating, pay attention to gradually increasing the temperature, so as to avoid violent drying causing the rubber particles to burst and reduce the recovery rate.

       2. When the silica gel is calcined and regenerated, too high temperature will cause changes in the pore structure of the silica gel, which will significantly reduce its adsorption effect and affect its use value. For blue gel indicator or color-changing silica gel, the temperature of desorption and regeneration should not exceed 120℃, otherwise the color development effect will be lost due to the gradual oxidation of the color developer.

       3. Generally, the regenerated silica gel should be sieved to remove fine particles to make the particles uniform.

 

Uses of inorganic silica gel:

       Macroporous silica gel is generally used as a catalyst carrier, matting agent, toothpaste abrasive and so on. Therefore, different varieties should be selected according to different uses. Silica gel can be used as a desiccant and can be reused. Silica gel is a porous material with different particle sizes formed by proper dehydration of silicic acid gel mSiO2·nH2O. It has an open porous structure with a large specific surface (surface area per unit mass) and can adsorb many substances. It is a good desiccant, adsorbent and catalyst carrier.

       The adsorption of silica gel is mainly physical adsorption, which can be regenerated and reused. Add acid to the alkali metal silicate (such as sodium silicate) solution to acidify it, and then add a certain amount of electrolyte to stir to form a silicic acid gel; or add acid or Ammonium salts can also generate silica gel. Let the silicic acid gel stand for a few hours to age it, then wash it with hot water to remove the soluble salts, dry it at 60-70℃ and activate it at about 300℃ to obtain silica gel.

       The silicic acid gel is soaked in the cobalt chloride solution and then dried and activated to obtain the color-changing silica gel. When it is used as a desiccant, it is blue before absorbing water, and turns red after absorbing water. From the change of color, we can see the degree of water absorption and whether it needs regeneration treatment. Silica gel is also widely used in steam recovery, petroleum refining and catalyst preparation.

 

Performance of organic silica gel:

       The basic structural unit of organic silica gel products is composed of silicon-oxygen chain links, and the side chains are connected to various other organic groups through silicon atoms. Therefore, the structure of organic silicon products contains both "organic groups" and "inorganic structures". This special composition and molecular structure make it integrate the characteristics of organic substances and the functions of inorganic substances. Compared with other polymer materials, the most outstanding properties of silicone products are:

       1. Temperature resistance characteristics. Silicone products are based on the silicon-oxygen (Si-O) bond as the main chain structure. The bond energy of C-C bond is 82.6 kcal/mole. The bond energy of Si-O bond is 121 kcal in silicone /Mole, so the thermal stability of organic silicon products is high, and the chemical bonds of molecules will not be broken or decomposed under high temperature (or radiation exposure). Silicone is not only resistant to high temperatures, but also resistant to low temperatures, and can be used in a wide temperature range. Whether it is chemical properties or physical mechanical properties, the change with temperature is very small.

       2. Weather resistance. The main chain of organic silicon products is -Si-O-, there is no double bond, so it is not easy to be decomposed by ultraviolet light and ozone. Silicone has better thermal stability, radiation resistance and weather resistance than other polymer materials. The service life of silicone in natural environment can reach several decades.

       3. Electrical insulation performance. Silicone products have good electrical insulation properties. Their dielectric loss, voltage resistance, arc resistance, corona resistance, volume resistivity and surface resistivity are among the best in insulating materials, and their electrical properties are affected by temperature and frequency. The impact is very small. Therefore, they are a kind of stable electrical insulating materials and are widely used in the electronics and electrical industries. In addition to excellent heat resistance, silicone also has excellent water repellency, which is a guarantee for high reliability of electrical equipment used in wet conditions.

       4. Physiological inertia. Polysiloxane compounds are among the most inactive compounds known. They are very resistant to biological aging, have no rejection reaction with animal bodies, and have good anticoagulant properties.

       5. Low surface tension and low surface energy. The main chain of organosilicon is very flexible, and its intermolecular force is much weaker than that of hydrocarbons. Therefore, it has lower viscosity than hydrocarbons of the same molecular weight, weak surface tension, low surface energy, and strong film-forming ability. This low surface tension and low surface energy are the main reasons for its many applications: hydrophobic, defoaming, foam stability, anti-sticking, lubrication, glazing and other excellent properties.