The adsorbent adsorbs VOCs in the gas, then the purified gas is discharged into the atmosphere. Activated carbon has good adsorption performance and reasonable cost advantage, it is the most commonly used adsorbent. The study shows that activated carbon has a good purification effect on VOCs with a mass concentration of about 100 mg/m3, and the lifetime is more than 1000h. Using specific chemical substances impregnated to make activated carbon, which has a good adsorption effect to sulfur, hydrogen sulfide, benzene, acetone, octane steam and other specific gas, and it has been widely used in specific places and specific industry.
In addition, activated carbon fiber (ACF) has more excellent adsorption behavior than activated carbon, it’s with large adsorption capacity, fast adsorption and desorption speed, good adsorption selectivity, compared with ordinary activated carbon has better adsorption effect in the adsorbent concentration is low condition, so activated carbon fiber adsorption has been widely used in the gas phase.
The activated carbon adsorbent is modified to make it have a better adsorption and desorption performance. Commonly used adsorbent modifications include surface structure modification and surface chemical modification. The modified activated carbon generally has a larger specific surface area, a richer pore structure, a more uniform pore size distribution, and an improved adsorption performance for different polar substances. The adsorption effect of certain substances is enhanced and other properties. Therefore, it is more suitable for the adsorption and purification of different pollutants. The activated carbon is impregnated and modified with HNO3, H2SO4, HCl, H3PO4, CH3COOH, KOH, and NaOH solutions to purify mixed waste gas of benzene, toluene, xylene, methanol, ethanol, isopropanol, and butanone. The study found that the adsorption capacity of activated carbon after alkali solution modification was reduced, among the acid-modified samples, the performance of activated carbon impregnated with H3PO4 increased the most. Except for the decrease of the adsorption capacity of m-xylene and butanone, the adsorption capacity of other pollutants has been greatly improved. This is because the decrease in the adsorption capacity of the two substances is due to the modification of phosphoric acid, which reduces the ability of activated carbon to adsorb macromolecular organic substances. At the same time, although phosphoric acid narrows the micropores of activated carbon, it changes its surface, which makes the chemical properties of the modified activated carbon increase the adsorption capacity of other organic substances.
When the organic waste gas contains flammable gas, there is a safety hazard due to the heat generated during the adsorption process. The solution is to limit the VOCs content of the inlet airflow to less than 25%, and air dilution is one of the feasible methods. When the molecular weight of VOCs is greater than 130 and has low volatility (boiling point greater than 240 ℃), the adsorbent will strongly adsorb it, which will cause difficulty in desorption. On the contrary, when the molecular weight of VOCs is less than 45, the adsorption is not strong, and For mixed-type organic waste gas, when the molecular weight of the organic matter in the waste gas differs too much, the adsorption effect is not good. Therefore, the adsorption method should be adopted reasonably according to the nature of the organic waste gas.
