Detailed explanation of the manufacturing method of activated carbon
When the toxic and harmful gas molecules hit the micropores on the carbon particles on the surface of the product, they are combined by the van der Waals force (gravitational force) between the toxic and harmful gases and the carbon molecules. The greater the collision probability, the better the adsorption effect. The probability of collision is related to gas temperature, pressure, flow rate, toxic gas concentration, molar mass, molecular size, and pore structure of activated carbon. The toxic and harmful gas is adsorbed by the activated carbon from the outside to the third level, firmly locking the toxic and harmful gas, and has no side effects. Main adsorbed substances:
Formaldehyde (CH2O), benzene (C6H6), toluene (C6H5CH3), xylene (C8H10), ammonia (NH3), cyanogen sulfide (H2S), methane (CH4), sulfur dioxide (SO2), carbon monoxide (CO), smoke, odor Wait. Such as gas masks and some efficient air purifiers are designed and manufactured using this principle.
1. General manufacturing method of activated carbon by chemical activation method
(1) The first step, raw material preparation
The carbonaceous material is pretreated, and the treatment may include one or more of drying, decontamination, crushing, milling, and even pre-oxidation.
At the same time, prepare chemicals that meet the quality requirements. If it is a direct use of solid chemicals (such as potassium hydroxide, sodium hydroxide, etc.), it is only necessary to crush the raw materials to a certain degree. If used in solution, it is necessary. Chemical agents and solvents (using distilled water or deionized water) are formulated into a certain concentration of chemical solution, sometimes not only to control the concentration of the solution, but also to control the specific gravity of the solution or even the ionization coefficient.
(2) The second step, raw material mixing
The carbonaceous raw materials and chemical agents (solid or solution) are mixed in proportion. For some raw materials, a grinding process may be added after mixing to make the raw materials more fully contacted to facilitate the subsequent chemical reaction.
(3) The third step, heating and heating to carry out chemical reactions such as hydrolysis or oxidation, dehydrogenation, etc.
It is usually carried out in the temperature range of 400 to 1000 Â° C, and is usually carried out by using an inert gas (using nitrogen gas) or mechanically insulating the air. Sometimes a temperature-programming process is used to obtain a special function of the activated carbon product. After the completion of the process, a product in which a carbon skeleton having a fixed carbon content of 80 to 95% and a conversion product (reaction product) of a raw material chemical agent and an unreacted chemical agent are mixed together can be obtained. Generally, the mixed product is extremely It is flammable and may even deflagrate. It needs to be immediately processed into subsequent processes to reduce this danger.
(4) The fourth step, leaching, removal of activator and its reaction products
After the above mixed product is cooled, it is generally repeatedly immersed in tap water (sometimes after adding several times of water washing to increase the purity of the activated carbon) to completely remove the activated agent and its reaction product to obtain a wet activated carbon product.
(5) The fifth step, the post-processing process
Possible post-treatment processes are: drying, screening; pickling and purification; molding processing.
2. General manufacturing method of activated carbon for gas activation method
(1) Raw material preparation process
Possible raw material preparations include one or more of the following processes: drying, decontamination, crushing, screening, oxidation (chemical wet oxidation, or thermal oxidation with air or oxygen-enriched air or even pure oxygen) ), milling, wind selection and so on.
(2) Forming process
Possible molding methods include: extrusion, rolling ball, heavy liquid into a ball, tableting, briquetting, pelleting, honeycomb molding, spinning, hollow molding, and the like.
(3) Molding process oxidation
The hot air forced oxidation method is often used, and the purpose may be: swelling, breaking, increasing the reactivity of the activation process, modification or surface modification.
(4) Carbonization process
It can take a one-step carbonization method or a multi-pass (such as two-way, different carbonization temperature) carbonization process. The carbonization temperature is generally between 350 and 1200 Â° C depending on the raw material and the target product. In particular, when manufacturing asphalt microsphere carbon or molecular sieve activated carbon, a temperature-programmed carbonization process is also required.
(5) Post-treatment process of carbonized material
Sometimes, in order to obtain some special functions of activated carbon products, carbonized materials may be further processed by one or more of the following processes: purification, addition of chemicals, forced oxidation, forced dehydrogenation, and the like.
(6) Activation process
The carbonized material is gasified with an activating gas (steam, carbon dioxide, oxygen or air) in the range of 700 to 1500 Â° C, and part of the amorphous carbon is ablated into the gas phase to form a pore structure.
(7) Post-treatment of the activated material
Typical post-treatment processes include: crushing, screening, milling, decontamination, overmolding, drying, grading, packaging, and the like.
How to identify activated carbon:
Activated carbon is a porous carbonaceous material, its developed void structure gives it a large surface area, and there are finer pores in the carbon particles - the capillary, which has a strong adsorption capacity due to the surface area of â€‹â€‹the carbon particles. It is very large, so it can fully contact with gas (impurities). When the toxic gas in the air is in contact with the activated carbon, the strong adsorption field around the activated carbon hole will immediately inhale the toxic gas molecules into the pores, so the activated carbon has a strong adsorption capacity.
The material is not the key to determine the quality of activated carbon. The key to determining the adsorption capacity of activated carbon is the production process of activated carbon. The production process of different manufacturers is often different. Therefore, the specific surface area and pore diameter of activated carbon produced are different. Generally, the gas phase adsorption index is four. The adsorption of carbon chloride CTC is not a professional company that can not produce good activated carbon, so the key to selecting activated carbon is to look at the technical content of the production enterprise, not the material. For example, coconut shell charcoal (specific surface area 300-500 square / g), only 2.5 yuan per kilogram, you can say that it is a good activated carbon, it is worth noting that 90% of the domestic bamboo charcoal is only carbonized charcoal. Instead of activated activated carbon.
Not all activated carbons have gas adsorption capacity. Only a large amount of activated carbon with a pore diameter slightly larger than the molecular diameter of toxic and harmful gases has a strong adsorption capacity. To meet this requirement, the material selection and processing supply requirements for activated carbon are extremely high. strict. Only the selection of high-quality fruit-shell activated carbon has a better adsorption effect on home decoration pollution. At present, the ideal air purification activity is coconut shell activated carbon. The coconut shell iodine value required for air purification requirements should be above 900, and the shape is 20-40 mesh.
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