What is Adsorption?

When a fluid comes into contact with a porous solid, a component or components in the fluid accumulate at the solid surface. This phenomenon is called adsorption. Adsorption also refers to the phenomenon that the surface of a substance (mainly solid substance) attracts molecules or ions in the surrounding medium (liquid or gas).

Adsorption is the adsorption of gas or solute on a solid or liquid surface. Adsorption due to the action of chemical bonds is chemisorption. For example, the nickel catalyst adsorbs hydrogen, and the chemical adsorption process has the formation and destruction of chemical bonds. The absorption heat released or released is relatively large, the required activation energy is also large, and it needs to be performed under high heat and selective. Physical adsorption is the adsorption produced by the interaction of forces between molecules. Such as activated carbon adsorption of gas, physical adsorption is generally carried out at low temperature, fast adsorption speed, small adsorption heat, non-selective adsorption. ^[2]

When the liquid or gas mixture is in full contact with the adsorbent for a long time, the system reaches equilibrium, and the equilibrium adsorption capacity of the adsorbent (the adsorption mass absorbed by the unit mass of the adsorbent when it reaches the adsorption equilibrium) depends first on the chemical composition and Physical structure, both with the temperature and pressure of the system and the concentration of this and other components or

The method of using some porous solids to selectively adsorb one or several components in a fluid to separate the mixture is called an adsorption operation, which is one of the important unit operations for separating and purifying gas and liquid mixtures.

Examples of adsorption separation:

(1) Dehydration and deep drying of gas or liquid, such as removing moisture from ethylene gas to a trace amount, and then polymerizing.

(2) Deodorization, decolorization of gas or solution, and recovery of solvent vapors, such as in the spray paint industry, there are often a large number of

(1) Adsorption tank. Stirring tanks for adsorption operations, such as refining oil or sugar liquid with activated white clay in adsorption tanks.

(2) Fixed bed adsorption equipment. The most widely used fixed bed mass transfer equipment for adsorption operations.

(3) Fluidized bed adsorption equipment. The adsorbent performs adsorption in a fluidized state, such as removing nitrogen oxides from the tail gas of a nitric acid plant using a fluidized bed. When the recovery of adsorbate is required, multi-layer fluidization equipment can be used. Fluidized bed adsorption is easy to operate continuously, but the material is mixed back and the adsorbent is worn seriously.

(4) Moving bed adsorption column. Also called super-adsorption column, it is used for moving bed mass transfer equipment in adsorption. It was used in the intermediate plant for separating olefins.