Activated carbon adsorption

1、 Overview
The activated carbon filter uses highly adsorptive and overactive carbon particles as the filter material, with a highly developed microporous structure, large adsorption capacity, fast adsorption and desorption speed, and good purification effect. Used for removing odors and high-density gas-phase pollutants.
Application of Activated Carbon Air Filters:
◎ Electronic components and odors from food processing plants;
The putrid odor and other unpleasant odors in hospitals and museums;
◎ Odors generated by rubber, lubricating oil, and plastic product factories;
◎ Kitchen and bathroom odors;
◎ Paint smell in paint spray workshop;
2、 Principle of Activated Carbon Adsorption
Activated carbon selectively adsorbs gases instead of mechanically "filtering" impurities.
There are numerous micropores on the surface of activated carbon, with the vast majority having pore sizes less than 500 Å (1 Å=10-10m). The total internal surface area of unit material micropores is called the "specific surface area", which can be as high as 700-2300m2/g.
When it comes to adsorption, harmful gases in the air are called "adsorbates", and activated carbon is called "adsorbents". Due to the intermolecular attraction, the adsorbate adheres to the inner surface of the micropores. If accompanied by a chemical reaction, it is called chemical adsorption, otherwise it is physical adsorption.
At the same time as the adsorbate is adsorbed by the adsorbent, some of the adsorbate will also detach from the adsorbent, known as "desorption". During use, the adsorption capacity will continuously weaken, desorption will increase, and when it reaches a certain level, activated carbon will be scrapped.
Sometimes, heating or steam fumigation can cause the adsorbate to detach from the adsorbent and regenerate the activated carbon.
● Activated carbon materials
Activated carbon materials are divided into granular carbon and fibrous carbon.
Traditional granular activated carbon includes coal charcoal, wood charcoal, coconut shell charcoal, and bone charcoal. Sometimes, granular charcoal is made into powder, adhered to other porous materials, and then processed into shapes.
Fiber activated carbon is made from organic fibers containing carbon. It has a small pore size (<50 Å), large adsorption capacity, fast adsorption, and fast regeneration. Common fiber substrates include phenolic, plant fibers, polyacrylonitrile, and asphalt.
● Adsorption performance of activated carbon
Adsorption capacity - The maximum amount that a unit of activated carbon can adsorb for a certain gas is called "adsorption capacity". Different materials or gases have different adsorption capacities.
Retention time - The time during which the airflow passes through the activated carbon layer is called "retention time". The longer the retention time, the more sufficient the adsorption. To maintain sufficient retention time, the carbon layer should be thick enough and the filtration wind speed should not be too high.
Service life - The new activated carbon has high adsorption efficiency, but the efficiency continuously decreases during use. When the concentration of harmful substances downstream of the filter approaches the allowable range, the filter is scrapped. The usage time before scrapping is the service life, also known as the "penetration time".
Selectivity - Generally speaking, gases with high molecular weight or boiling point are easily adsorbed; Volatile organic gases are more easily adsorbed than inorganic small molecule gases; Chemical adsorption has stronger selectivity than physical adsorption. After chemical impregnation, activated carbon increases its adsorption capacity for specific gases.
3、 Selection of Activated Air Carbon Filters
The main factors affecting the adsorption efficiency and service life of activated carbon filters are: the type and concentration of pollutants, the temperature, pressure, relative humidity, and retention time of the airflow.
When selecting, the type of activated carbon and filter form should be determined based on the type, concentration, and treatment air volume of pollutants.
By monitoring the changes in pollutant concentration before and after the filter, it can be determined whether the activated carbon should be replaced. However, there is currently no convenient and practical monitoring method in China, so users can only determine the service life of activated carbon filters according to prescribed cycles or based on experience.
During use, the resistance of the activated carbon filter remains unchanged, but its weight increases. Experienced professionals can determine the service life of the filter based on weight changes.
Both upstream and downstream of the activated carbon filter should have good dust removal filters to prevent dust from clogging the activated carbon material; The downstream filter removes dust from the activated carbon itself.
4、 Structure and working principle of activated carbon exhaust gas filter
The device consists of multiple fixed beds and air inlet and outlet ports. The fixed bed has air inlet and outlet ports at both ends, and a multi-layer adsorption bed is set up in the central part, filled with paint mist filter material and high-performance activated carbon. During work, the organic gas containing paint mist is fully purified through multiple fixed bed paint mist and organic waste gas, and the purified gas is discharged through the fan outlet. Using imported specialized dry paint mist filtering materials as the core component, spray paint exhaust gas is filtered through multiple activated carbon filtering materials. Paint mist particles are contained in the material through interception, collision, absorption, etc., and gradually weathered into powder form, thereby achieving the purpose of purifying paint mist. Activated carbon can be regenerated after saturation, and the treated activated carbon can continue to be used without reducing its adsorption effect.
5、 Operating Procedures for Activated Carbon Filters
To ensure the purification effect of exhaust gas, the first layer of saturated adsorption filter should be removed from the equipment after a certain period of use, and the remaining filter layers in the equipment should be moved forward in sequence. At the same time, a new filter layer should be placed at the end of the equipment. If all filter layers have reached saturation adsorption, all filter layers need to be replaced.
The replaced filter layer activated carbon can be placed centrally and delivered to the activated carbon manufacturer for regeneration after reaching a certain amount.