Adsorption principle of activated carbon
活性炭是一种主要由含碳材料制成的外观呈黑色，内部空隙结构发达、比表面积大、吸附能力强的一类微晶质碳素材料。 活性炭材料中有大量肉眼看不见的微孔，1克活性炭材料中微孔，将其展开后表面积可高达 800-1500平方米，特殊的更高。也就是说，在一个米粒大小的活性炭颗粒中，微孔的内表面积可能相当于一个客厅面积的大小。正是这些高度发达，如人体毛细血管般的空隙结构，使活性炭拥有了优良的吸附性能。
Activated carbon is a kind of microcrystalline carbon material which is mainly made of carbon containing materials with black appearance, developed internal void structure, large specific surface area and strong adsorption capacity. There are a lot of micro holes in the activated carbon materials which are invisible to the naked eye. The surface area of the activated carbon material can reach 800-1500 square meters after expansion, especially higher. That is, in a rice size activated carbon particle, the inner surface area of the microporous may be equivalent to the size of a living room area. It is these highly developed, such as capillary like pore structure, so that activated carbon has excellent adsorption performance.
The interaction force between molecules is the van der Waals force. Although the molecular velocity is affected by temperature and material, it is always moving in micro environment. Because of the mutual attraction force between molecules, when a molecule is captured into the space in the activated carbon by the inner hole of activated carbon, more molecules will be attracted until the inner space of activated carbon is filled.
Method of desorption of activated carbon
When the void inside the activated carbon is filled with organic waste gas, the adsorbed substance is filled and saturated, the pollutants are released, which is called penetration. The adsorption bed of saturated activated carbon needs to be regenerated. Generally, the heated gas is used to desorption the adsorption bed. On the one hand, the regeneration of the adsorption bed is reactivated, on the one hand, the pollutants are released for recovery or decomposition treatment. This desorption method is called the temperature rising desorption. The adsorption capacity of the substance decreases with the increase of temperature. The temperature of the adsorbent can be increased to remove the adsorbed components. This method is also called variable temperature desorption. The temperature in the whole process is periodic.
对无机废气采用液体吸取法，其吸取效率可达90%以上。液体吸取法是无机气体净化的常用处理工艺，工艺技术相当成熟，且稳定可靠。以液体为吸取剂，通过洗涤收集装置使废气中的有害成分被液体吸取，从而达到净化的目的。该吸取系统属于气膜控制吸取过程，采用液相分散型装置，即喷淋填料塔。其工作时吸取液通 过填料塔顶部的喷淋装置被均匀的喷洒在填料层顶部，并沿着填料层自上而下呈膜状流动，而废气则自塔下部进入，穿过填料层从塔顶排出。在此过程中，废气被迫多次改变方向、速度与吸取液不断碰撞、接触，使废气与吸取液在填料层中有充分接触反应时间，令废气中有害成分能够被吸取液充分吸取净化。 净化后的气体经塔内除雾后可达标排放。
The absorption efficiency of inorganic waste gas can reach more than 90% by liquid absorption method. Liquid absorption is a common process for inorganic gas purification, and the technology is mature and stable. The harmful components in the waste gas are absorbed by the liquid through the washing and collecting device, so as to achieve the purpose of purification. The absorption system belongs to the process of gas film control absorption, and adopts liquid-phase dispersion device, namely spray packing tower. During its operation, the absorbing liquid is evenly sprayed on the top of the packing layer through the spray device at the top of the packing tower, and flows in membrane form from top to bottom along the packing layer, while the exhaust gas enters from the lower part of the tower and is discharged from the top of the tower through the packing layer. In this process, the exhaust gas is forced to change the direction, speed and absorption liquid repeatedly, which makes the waste gas and the absorption liquid have full contact reaction time in the filler layer, so that the harmful components in the exhaust gas can be fully absorbed and purified by the absorption liquid. The purified gas can be discharged up to standard after being defogged in the tower.
According to the types of waste gas produced in this laboratory, the treatment scheme adopts the method of activated carbon adsorption and combination. The organic pollutants were adsorbed by activated carbon and then absorbed by the packing spray tower.
The reason is:
In the inorganic waste gas of laboratory, the acid waste gas is the main one, and the alkaline waste gas generally exists in industrial production. The influence of pH on the adsorption efficiency of activated carbon generally decreases with the increase of pH value of solution. When the pH value is higher than 9.0, it is not easy to absorb, and the better the effect is when the pH value is lower. So the combination of active carbon adsorption and packing spray is adopted.