The concentration of molecules of a substance on the surface of a porous solid is called adsorption.All solid matter has an unsaturated field of force on its surface, and its range of action corresponds to the diameter of the molecule.Therefore, it has a certain adsorption effect on the gas molecules in contact with the solid surface.However, only porous materials with large internal surface area have significant adsorption effect.
It is not enough for adsorbent to have adsorption capacity only.Adsorbent must have selective adsorption ability to achieve the separation and purification of each component in the gas, that is to say, adsorbent must have different adsorption ability to each component in the gas.
The adsorbability of adsorbent to various gases depends on the composition and structure of the adsorbent, the size and polarity of the gas molecules, and the adsorption conditions (such as temperature, pressure, etc.).The pore sizes of different adsorbents are different. The effective pore sizes of several molecular sieves are listed in table 1.Therefore, only molecular sieves may use pore size effect to separate various gases.In order to separate the components in the gas, the adsorbent with proper pore diameter should be selected according to the molecular diameter of each component.
In addition to pore size effect, the selective adsorption capacity of molecular sieve also varies with the polarity and other properties of gas molecules.For example, the molecular size of CO and argon is similar. Since CO is a polar molecule and argon is a non-polar molecule, the equilibrium adsorption capacity of CO on 4A molecular sieve is much larger than that of argon.If CO and argon are mixed gases, CO will be preferentially adsorbed when passing through 4A adsorption bed.When selecting various components of the gas mixture for adsorption and separation, the appropriate molecular sieve should be selected according to the required adsorption sequence of each component.
