I. Product descriptions:
History:
Silica gel, namely the gel of silicon dioxide, is a highly active adsorbing material with micro-pore structure that is usually formed through the reaction between sodium silicate and sulfuric acid, polymerization and gelatinized, depurated and drying. Silica gel is a non-crystalline state substance that is mainly composed of silicon dioxide and has a certain amount of constitution water. Due to its chemical and physical structural characteristics, silica gel has many superior qualities that other similar materials can never replace, such as the adsorbability, selective absorption, and thermal stability, chemical stability, abrasion proof, dynamic resistance and so on.
Silica gel was generated in 1881 and was only used as a military material till the First World War with small-scale preparation. At the beginning of 20th century, its semi-industrialized production started. After the Second World War, as the rapid development of the modernized industries, all the industrialized countries gained impressive advances in the research and development of silica gel products. As an absorbent, dispersant, reinforcing agent, catalyzer and catalyzer carrier, silica gel has been used in many fields like the chemistry, rubber, plastic, petrol-chemistry, heavy industry, medicine and foodstuffs..
The production of silica gel started in China since 1955, after half century, from the single lump silica gel product into dozens kinds of products for various uses, such as spherical-shaped silica gel, micro-spherical shaped silica gel, activated silica gel, color-changing silica gel, big-pore silica gel, high-efficiency desiccant and so on. At present, the total domestic silica gel production capacity has reached about 100,000 tons annually, 70% of which are sold to the overseas market.
Characteristics:
Silica gel is a kind of high-active absorbing material, which is generally obtained by reaction of sodium silicate and sulfuric acid together with aging, acidic soaking and other series of post-processing. Silica gel belongs to amorphous substance and its chemical formula is mSiO2 . H2O. With stable chemical property, it won't burn and won't dissolve in any solvent except for alkali and hydrofluoric acid. Silica gels of various models form different fined-pore structures owing to different manufacturing methods. Additionally, the chemical components and physical structure of silica gel determine that silica gel owns many characteristics which can't be substituted by other materials of same kind, such as high absorption performance, excellent thermal stability, stable chemistry, high mechanical strength and others.
According to the size of pore diameter, silica gel can be classified into m acro -pored silica gel, coarse-pored silica gel, B-type silica gel and fine-pored silica gel. Owing to different pore structures, their absorption performances are various and own different characteristics. Coarse-pored silica gel owns higher absorbing capacity under high relative humidity, fine-pored silica gel owns higher absorbing capacity than coarse-pored silica gel under lower relative humidity, and B-type silica gel owns absorbing capacity which is between coarse-pored and fine-pored silica gel owing to its pore structure is between coarse-pored and fine-pored silica gel. In addition, m acro -pored silica gel is generally used as catalytic agent carrier, delustering agent, toothpaste abrasive. Therefore, we should select different varieties according to different purposes.
Adsorbability:
Silica gel’s absorptive action includes two processes: the absorption and the coacervation. The absorption is connected with the surface and the coacervation with the diameter of the pore. They both depend on the relative pressure of the adsorbate. Take the water vapor as an example.
Silica gel’s adsorptive capacity for the water vapor will reinforce along with the air relative humidity enhances, but the adsorptive capacity of different pore-sized silica gels have different changing rules. Under the same relative humidity, their absorptive capacity performances are variable. This kind of regular changes are usually described with the curve of adsorption isotherm, as shown below:
We can see that fine-pore silica gel has a higher adsorptive capacity under the low relative humidity; whereas the wide-pore silica gel has a relatively high adsorptive capacity under the high relative humidity. So we may choose the appropriate silica gel products according to different environments and conditions to gain the best effect.
Safety Performance:
The main component of silica gel is silicon dioxide, which owns stable chemistry and won't burn. As silica gel is a kind of amorphous substance, the dust content in workshop should be controlled below 10mg/sq.m. In addition, the ventilation should be enhanced and the operators should wear when operating.
Owning powerful absorbing capacity, silica gel has drying effect on human's skin. Therefore, the operators should wear working clothes when operating. If silica gel accidentally enters into eyes, please wash with a great of water and then go to hospital as soon as possible.
Owing to containing a little cobalt chloride, blue silica gel is poisonous. Therefore, it should avoid to contacting food and being sucked into mouth. If poisoning event occurs, please go to hospital for treatment immediately.
During using process, silica gel absorbs water vapor or other organic substance in medium and its absorbing capacity decreases accordingly. However, it can be repeatedly used after being regenerated.
I Regeneration after silica gel absorbing water vapor
After silica gel absorbing moisture, the moisture can be removed through thermal desorption . The heating methods are various, such as electrothermal furnace , flue waste heat heating and hot air drying, etc.
The temperature of desorption heating is controlled between 120 ℃ and 180 ℃ . For blue gel indicator, allochroic silica gel and DL type blue silica gel, the temperature should be controlled between 100 ℃ and 120 ℃. During the regeneration of industrial silica gel of various kinds, the maximum temperature should not be higher than below limit:
For coarse-pored silica gel, it should not be higher than 600 ℃;
For fined-pored silica gel, it should not be higher than 200 ℃ ;
For blue gel indicator (or allochroic silica gel), it should not be higher than 120 ℃ ;
For alumina silica gel, it should not be higher than 350 ℃ .
For silica gel after being regenerated, its moisture should be controlled below 2% for repeated operation.
II Regeneration after silica gel absorbing organic impurities
• Baking Method: For coarse-pored silica gel, it can be placed in baking furnace to rise to 500 ℃ to 600 ℃ and the gel granules will take on white or yellow brown after 6 to 8 hours. For fine-pored silica gel, the baking temperature should not be over 200 ℃.
• Bleaching Method: After silica gel's absorption in saturated water vapor reaching to saturation level, put silica gel into hot water for soaking and bleaching. Additionally, remove waste oil or other organic impurities in combination with detergent.
• Solvent Washing Method: According to the variety of organic substance absorbed by silica gel, please select appropriate solvent to dissolve the organic substances absorbed in silica gel and then heat the silica gel to remove the solvent.
III Notices on Regeneration of Silica Gel
• When drying and regenerating, please note that the temperature should be gradually raised, in order not to cause breaking of gel granule and recycle rate reduction owing to drastic drying.
• When baking silica gel for regeneration, too higher temperature will lead to change of pore structure of silica gel and reduce its absorbing effect obviously and affect its usage value accordingly. For blue gel indicator or allochroic silica gel, the temperature of desorption regeneration should not be higher than 120 ℃ , otherwise, the coloration effect will be lost owing to oxidation of coloring agent.
• For regenerated silica gel, it is generally to screen the fine granules to make the granules equal and even.
Storage and Packing
Silica gel owns excellent moisture absorption capacity, so it should be stored in dry place, and a rack is required between packing materials and the ground. The packing materials include steel bucket, paper bucket, paper carton, plastic bottle, polyethylene plastic composite bag, flexible container, etc. Concrete packing specification refers to classified production introduction.
II.Guide to buy:
Silica gels used as desiccant and moisture resisting agent
Fine porous silica gel, B-type silica gel, C-type silica gel, macro-porous silica gel, Alusil, blue silica gel, DL blue silica gel, high effective desiccant, tablet form of silica gel desiccant, small packed silica gel, and FNG silica gel.
mainly used in:
Static drying
Moisture-proof packaging: cameras and photosensitive materials, precision instruments/electric appliances, foodstuffs, medicines, shoes, clothes, leather products, weapons, communications apparatus and materials, etc. Air dehumidifying: closets, wardrobes, floor boards, , musical instruments, etc.
Dynamic drying
Drying of air: warehouses, ship's holds, pharmaceutical factories, precision machinery factories, electronic instruments and materials manufacturing factories, compressed air and ambient air about instruments. Dehydration and refinery of industrial gases: hydrogen, oxygen, nitrogen, chlorine, CO 2 , acetylene, ethene, methane, ethane, propane, SO 3 , SO 2 , natural gas, city gas.
Dehydration of liquids
Dehydration of organic solvents: methanol, ethanol, benzene, toluene, chloromethane, kerosene, gasoline, liquefied petroleum gas, hydrogen halide, liquid wax, acetone, etc.
dehydration of refrigerants: liquid ammonia, freon, dichloromethane, etc.
dehydration of transformer oil and inverter oil.
Features of these products are listed in the following table:
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Fine porous silica gel
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higher adsorption capacity at low relative humidity, its dew-point temperature: - 40℃ ~ - 70℃
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B-type silica gel
C-type silica gel
Macro-porous silica gel
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higher adsorption capacity at high relative humidity, suitable for use in those packages where humidity needs to be controlled or dew forming must be prevented.
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Alusil
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adsorption capacity at low relative humidity similar to fine porous silica gel, and that at high relative humidity better than fine porous silica gel; thermal stability is 150° C higher than fine porous silica gel
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Blue silica gel
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ambient relative humidity can be indicated by the change of its colour so as to judge whether the ambient humidity meets the set requirement and whether it is ineffective.
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Silica gel desiccant
tablet
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mainly used to prevent moisture for bottled medicines and foodstuffs.
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DL blue silica gel
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its colour begins to change when it has absorbed a certain amount of moisture and the change of colour will finish when the moisture absorbed reaches a prescribed amount ? a feature of colour change with quantitative adsorption.
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High effective
desiccant
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mainly used to dehumidify for precision instruments and apparatuses, higher adsorption capacity and having the ability to decrease the dew point to lower than - 70° C at normal temperature
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FNG silica gel
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not cracking when meeting with water, mainly used for air dehumidifying in air separation facilities and used as a buffer desiccant in ordinary silica gel protective bed
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Silica gels used as adsorbent and separating agent
Fine porous silica gel, B-type silica gel, C-type silica gel, pressure swing adsorptive silica gel, siliceous silt, FNG silica gel, beer silica gel, macro-porous silica gel, macro-porous micro-pellet silica gel, Alusil and column chromatographic silica gel are mainly used for the adsorption or separation of impurities in petrochemical industry, synthetic chemical industry, electric power stations and the refining process of organic chemicals. Their respective features are listed in the following table:
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Macro-porous silica gel
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used for removing acids from transformer oil and as a decolorizing agent for
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Pressure swing
adsorptive silica gel
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fast-acting adsorption and desorption, mainly used in recovery and preparation of CO 2 in synthetic chemicals, foodstuffs and beverage industries.
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FNG silica gel
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mainly used as a liquid adsorbent in petrochemical, electrical and brewing industries, and for adsorbing acetylene in liquid oxygen preparation process.
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Siliceous silt
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mainly used as a padding material for cats, dogs and other small animals, featuring deodorization, cleanliness, money-saving and small quantity of garbage.
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Beer silica gel
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mainly used to adsorb high molecular proteins from industrial fermented goods
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Alusil
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mainly used as a temperature swing adsorbent to remove low molecular hydrocarbons
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Column chromatogra-
phic silica gel
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mainly used for removing aromatic hydrocarbons in petroleum refining, or separation and purification of effective constituents in traditional Chinese medicinal herbs
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Practical examples of applications:
adsorption of vapors of ethanol, ether, acetone, benzene, gasoline and other organic solvents
adsorption, recovery or removal of SO2, H2O, N2O4, CO2, CO, acetylene, carbonyl chloride and other gases
separation of hydrocarbons from natural gas and its devulcanization
separation of aromatic hydrocarbons from paraffin
Silica gels used as catalyst or catalyst carrier
In this category there are macro-porous silica gel, B-type silica gel, macro-porous micro-pellet silica gel, C-type silica gel, fine porous silica gel, pressure swing adsorptive silica gel, FNG silica gel and Alusil, mainly used as catalyst carrier or catalyst in industries of petrochemicals, organic chemicals and synthetic chemicals. Two of this category are listed below:
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Macro-porous
Micro-pellet
silica gel
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mainly used in the synthesis of melamine, benzoic anhydride, maleic anhydride, cis-polybutadiene rubber, vinyl cyanide, etc.
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Macro-porous blocky silica gel
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used as a catalyst in manufacturing benzoic anhydride, etc.
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Silica gels used in chemical analysis and test
In this category there are thin layer chromatographic silica gel, column chromatographic silica gel, liquid chromatographic stationary phase silica gel, silica gel plate, silicic acid, activated silica gel, mainly used in the analysis and separation of natural and synthetic organic matters, the qualitative and quantitative analysis of major constituents or impurities contained in medicines, pesticides, traditional Chinese herbal medicinal materials, cereals, foodstuffs and organic chemicals, or the separation and refining of some substances. Some of these silica gels are listed below:
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Thin layer chromatographic
silica gel
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used as the stationary phase in thin layer chromatograph
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Silicic acid
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mainly used as a flux for chemical reagents and in the production of tungsten wire
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Activated silica gel
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used as a carrier in the identification of harmful and poisonous gasses in the atmosphere and in the monitoring of flammable and explosive gasses
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