The difference between charcoal and activated carbon: It is well known that charcoal is a porous carbonaceous material by isolating the air from the wood and strengthening the heat. It has a large surface area, can adsorb molecules of other substances, and has a strong adsorption function. If the high-temperature steam is continuously introduced during the production of charcoal, the oil adhering to the surface of the charcoal is removed, and the numerous internal pipes are smoothed, so the surface area of ​​the charcoal is inevitably larger, which becomes activated carbon, which is also a porous Sexual carbonaceous material, its highly developed pore structure makes it have a larger specific surface area than charcoal, so it is easier to adsorb toxic and harmful gases (impurities) in the air and purify the air.
The working principle of wood activated carbon:
The atoms of activated carbon have a large specific surface area, making them exhibit a strong attraction to the outside. These are called van der Waals forces that attract molecules around the gas or liquid. The combination of these attractive forces and the forces between the molecules in the surrounding medium gives the activated carbon a surface adsorption force. Some molecules have structures that make them easier to absorb than others, and we can separate different molecules based on this principle.
Physical adsorption occurs during the removal of contaminants from gas streams and liquid streams. The porous structure provides a large specific surface area for the activated carbon, making it easy for contaminants to accumulate in the activated carbon. This attraction exists among all the molecules. In this way, the surface molecules of the pore walls have a strong attraction and attract the molecules of the contaminants through the channels of the pores. It must be pointed out that the molecules of the adsorbed contaminants must be smaller than the size of the open pores so that they can pass through the pores and be accumulated. Now, you can understand why we use different raw materials and activation conditions to produce different types of activated carbon with different pore structures, the purpose is to make our products suitable for different purposes.
In addition to physical adsorption, chemical reactions also occur on the surface of carbon. Activated carbon contains not only carbon but also a small amount of hydrogen and oxygen on its surface. These components are in the form of various compounds and functional substances, including carbonyl, hydroxyl, phenol, esters, and benzoquinone. These oxidizing agents and complexes on the carbon surface are capable of chemically reacting with substances adsorbed by the activated carbon. Here is a typical example: in water treatment, activated carbon reacts with chlorine in water to convert chlorine to chloride. In this way, the chlorine is removed, and the unpleasant taste and odor in the water are gone.
Production process and properties of wood activated carbon:
1. The external form of charcoal: The high-quality charcoal section has a black luster, and it emits a loud and crisp metallic sound when struck. The charcoal fired at different temperatures has different external forms. Charcoal fired at less than 250 degrees Celsius, the surface is brown, not easy to break, there is a flame when burning; the surface of charcoal fired at 300-350 degrees Celsius is black, when the firing temperature reaches 500 degrees Celsius, when the tapping, charcoal is issued Loud metal sound.
2. Fixed carbon for charcoal: Fixed carbon is a hypothetical concept. It is ash-free charcoal at a specified high temperature, generally 850-950 degrees Celsius, without air being introduced for calcination. General charcoal may contain 70% to 80% of fixed carbon. As the calcination temperature increases, the relative amount of fixed carbon in the charcoal increases.
3. Volatile matter of charcoal: When charcoal is calcined at high temperature, gaseous products such as carbon monoxide, carbon dioxide, hydrogen, methane and other hydrocarbons are released as volatiles. When the temperature of firing charcoal is within 300-700 degrees Celsius, the composition of volatiles separated during charcoal calcination changes with the following changes: the content of carbon dioxide, carbon monoxide and methane gradually decreases, while the content of hydrogen gradually decreases. increase. When the temperature of the charcoal is increased, the calorific value of the charcoal is increased, and the calorific value of the gas is lowered.
4. Mechanical strength of charcoal: The mechanical strength of charcoal indicates its resistance to crushing and abrasion. It has great significance in the trans-construction and transportation of charcoal and in the application of metallurgical industry. The more the number of reloadings, the charcoal is strongly pressurized by the upper charge in the furnace of the molten iron furnace, and when it moves from top to bottom, it is strongly rubbed by the furnace block and the chest wall. If the charcoal becomes debris, the gas is difficult to pass. The charge and the operation of the molten iron furnace will malfunction. The charcoal strength is higher in the longitudinal direction, lower in the radial direction, and lowest in the chord direction. When the final temperature of the fired charcoal is the same, the charcoal strength increases as the charring time increases.
5. Specific gravity and porosity of charcoal: The specific gravity of charcoal varies with tree species, quality of wood, final temperature of carbonization, and rate of temperature increase. Generally, the proportion of charcoal fired from wood is also large. Charcoal porosity determines most of the properties of charcoal, such as reactivity, thermal conductivity, and adsorption.
6. Calorific value of charcoal: The calorific value of charcoal is related to the carbonization temperature, the carbonization temperature is high, the carbon content of charcoal is large, and the calorific value is also high.
7. Charcoal ash: A substance that becomes white or reddish after charcoal is burned is called ash. The ash content in charcoal varies with firing temperature, tree species, proportion of charred wood and bark, site conditions of trees, deforestation season, transportation materials, and firing methods. Generally, the higher the firing temperature and the higher the ash content, the higher the ash content of the charcoal fired from the hardwood material than the softwood; the bark is higher than the wood.
The principle of adsorption of wood activated carbon:
Activated carbon is an environmentally friendly field. Many people know that he is a good sucking agent. With the recent development, activated carbon is widely used in various industries. Activated carbon cloth is manufactured by the unique microporous adsorption principle of activated carbon. The odor and harmful gases in the air are removed by adsorption. Its characteristics are: large surface area, strong adsorption capacity, and can quickly absorb a variety of harmful gases such as benzene, formaldehyde, ammonia. At the same time, the photocatalytic material can be loaded to achieve a better purification effect.
Several methods of regeneration of activated carbon:
Chemical method for drug elution:
For high-concentration, low-boiling organic matter adsorbates, chemical regeneration should be considered first.
Biological regeneration method:
The domesticated activated carbon is used to treat the spent activated carbon, and the organic matter adsorbed on the activated carbon is degraded and oxidatively decomposed into CO 2 and H 20 to restore its adsorption performance. The method for regenerating saturated carbon by using microorganisms is only suitable for adsorbing susceptible microorganisms. The carbon of the decomposed organic matter is saturated, and the decomposition reaction must be thorough, that is, the organic matter is finally decomposed into CO 2 and H 20 , otherwise there is a possibility of being adsorbed by the activated carbon. If the treated water contains organic matter that is difficult to degrade or hard to desorb, the biological regeneration effect will be affected.
Wet oxidation method:
This regeneration process is commonly used to regenerate powdered activated carbon, such as powdered charcoal added to enhance aeration tank processing capabilities. The adsorbed saturated carbon slurry is heated to 200-250 ° C, and pressurized with air to (300-700) X104P, and the organic matter adsorbed by the activated carbon in the reaction tower is oxidatively decomposed under high temperature and high pressure to regenerate the activated carbon. The regenerated carbon is cooled by a heat exchanger and sent to a carbon storage tank for reuse. The ash after carbonization of the organic matter is periodically discharged after being accumulated at the bottom of the reactor.
The wet oxidation method is suitable for treating adsorbent substances with high toxicity and biodegradability. The temperature and pressure must be determined according to the characteristics of the adsorbate, as this directly affects the recovery rate of carbon adsorption performance and the loss of carbon. The regeneration system of this regeneration method has many auxiliary facilities, so the operation is troublesome.
Electrolytic oxidation method:
The organic matter adsorbed by the activated carbon is oxidatively decomposed by using a strong oxidant such as [O], [C1], which is generated during electrolysis. However, in actual operation, there are problems such as corrosion, passivation, and clogging of metal electrodes. Insoluble electrode--Graphite has the disadvantages of large volume, high electrical resistance, high power consumption, etc., so it has not been applied in practice.
Heating regeneration method:
According to the temperature at which the organic matter decomposes and desorbs during heating, the heating regeneration is classified into low-temperature heating regeneration and high-temperature heating regeneration.
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