The adsorption function of activated carbon is well used in environmental protection industry, especially for those organic waste gas which is difficult to treat, activated carbon can also be selected for adsorption treatment, so as to reduce the possibility of substandard emissions. So what is the adsorption principle of activated carbon? Let's introduce it to you.
Adsorption mechanism of activated carbon
Adsorption and desorption are reversible processes. When fresh adsorbent is used to adsorb the adsorbate in the gas, there is no adsorbate on the surface of the adsorbent, so there is no desorption of the adsorbate. However, with the progress of adsorption, the amount of adsorbate on the surface of adsorbent increases gradually, and the desorption rate increases with time. However, from the macroscopic point of view, the adsorption capacity of the adsorbate is still greater than the desorption amount at the same time, so the general trend of the process is considered as adsorption. When the adsorption amount and desorption amount of adsorbate are equal at the same time, the adsorption and desorption reach dynamic equilibrium, which is called adsorption equilibrium. At equilibrium, the concentration of the adsorbate in the fluid and on the surface of the adsorbent does not change any more. The equilibrium concentration of adsorbate in the fluid is called the equilibrium concentration, and the concentration in the adsorbent is called the equilibrium adsorption capacity.
When the adsorbate contacts with the adsorbent for a long time, the adsorption equilibrium will be reached. Adsorption equilibrium capacity is the limit adsorption capacity of adsorbent to adsorbate, also known as static adsorption amount fraction or activated fraction, expressed by, dimensionless. It is a very important parameter in design and production. The concentration relationship of adsorbate in gas and solid phase is generally expressed by adsorption isotherm. The adsorption isotherms are usually drawn according to experimental data and expressed by various empirical equations.
Adsorption principle of activated carbon
1. Adsorption process
When two phases form a system, the composition is different at the interface and inside of the phase. The components at the interface of the two phases accumulate (condense), which is called adsorption. When treating waste gas by adsorption, the object of adsorption is gaseous pollutants. The adsorbed gas components are called adsorbents, and the substances adsorbing gas components are called adsorbents.
The operation of regenerating the adsorbed component from the saturated adsorbent is called desorption. That is, under certain conditions, the material adsorbed on the interface leaves the interface and re enters the bulk phase, which is also called desorption. However, after adsorption for a period of time, due to the concentration of adsorbate on the surface, the adsorption capacity of the adsorbent is obviously reduced, which can not meet the requirements of adsorption purification. At this time, some measures should be taken to desorb the adsorbed adsorbate on the adsorbent to restore the adsorption capacity of the adsorbent. This process becomes the regeneration of the adsorbent. Therefore, in practical work, the cycle process of adsorption regeneration adsorption of adsorbent is formally used to remove pollutants in waste gas and recover useful components in waste gas.
2. Desorption process
The desorption process is to remove the adsorbate from the pores of the adsorbent and restore its adsorption capacity when the structure of the adsorbent does not change or changes very little. Through recycling, the treatment cost can be reduced, the discharge of waste residue can be reduced, and the adsorbate can be recovered at the same time. The concentration of the released gas is higher than that of the original mixture.
The conditions for promoting desorption are as follows:
(1) Increase temperature (thermal regeneration;
(2) Vacuum to reduce pressure (PSA);
(3) Reduce the concentration of components around the adsorbent (air purge).
3. Adsorption capacity
Adsorption capacity refers to the amount of adsorbate adsorbed on unit mass adsorbent under certain conditions, usually expressed in kg adsorbent or mass fraction, which is a sign of adsorption capacity of adsorbent. In industry, the adsorption capacity is called the activity of adsorbent.