Physical properties of adsorbents - Huaqiang Electronic Network

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The good adsorption properties of the adsorbent are due to its dense pore structure. The physical properties associated with the pores of the adsorbent are:

a. pore volume (VP): the volume of micropores in the adsorbent is called pore volume, usually expressed as the volume of the adsorbent micropores per unit weight of adsorbent (cm3 / g). The pore volume is the effective volume of the adsorbent, It is a value calculated from the saturated adsorption amount, that is, the volume at which the adsorbent can accommodate the adsorbate, so the pore volume is large. The pore volume (Vk) of the adsorbent is not necessarily equal to the pore volume (VP), and the micropores in the adsorbent have adsorption, so the coarse pores are not included in the VP. Vk includes the volume of all holes, which is generally larger than VP.

b. Specific surface area: that is, the surface area per unit weight of the adsorbent, the common unit is m2 / g. The surface area of ​​the adsorbent ranges from hundreds to thousands of square meters per gram. The surface area of ​​the adsorbent is mainly the surface of the microporous wall, and the outer surface of the adsorbent is small.

c. Pore size and pore size distribution: In the adsorbent, the shape of the pores is extremely irregular and the pore size is also different. A hole having a diameter of several angstroms (A0) to several tens of angstroms is called a fine hole, and a hole having a diameter of several hundred angstroms or more is called a coarse hole. The more pores, the larger the pore volume and the larger the surface area, which is beneficial to the adsorption of the adsorbate. The role of the coarse pores is to provide access to the adsorbate molecules. The relationship between the coarse hole and the fine hole is like that of the street and the alley. The foreign molecules can pass through the coarse hole to reach the depth of the adsorbent quickly. Therefore, the coarse holes should also occupy an appropriate ratio. Coarse pores and pores in adsorbents such as activated carbon and silica gel are formed during the manufacturing process. Zeolite molecular sieves form crystals of several micrometers in diameter during synthesis, in which only uniform pores are formed, and coarse pores between crystals and crystals are formed during molding.

The pore size distribution is a relationship indicating the pore size corresponding to the pore volume. This characterizes the pore properties of the adsorbent.

d. apparent gravity (dl): also known as visual gravity.

The volume (Vl) of the sorbent particles consists of two parts: the volume of the solid skeleton (Vg) and the pore volume (Vk), ie: Vl = Vg + Vk

The apparent gravity is the ratio of the weight (D) of the adsorbed particles to the volume (Vl) they occupy.

The pore volume (Vk) of the adsorbent is not necessarily equal to the pore volume (VP), and the micropores in the adsorbent are effective, so the coarse pores are not included in the VP. Vk includes the volume of all holes, which is generally larger than VP.

e. True severity (dg): Also known as the severity or the weight of the adsorbent solids, ie the ratio of the weight of the adsorbent particles (D) to the volume Vg of the solid backbone.

Assume that the weight of the adsorbed particles is based on one gram, based on the definition of apparent gravity and true gravity:

Dl==l/Vl; dg=l/Vg

Then the pore volume of the adsorbent is: Vk = l / dl - l / dg

f. Stacking gravity (db): Also known as the filling weight, that is, the weight of the adsorbent filled in a unit volume. This volume also includes the gap between the adsorbed particles, which is an important parameter for calculating the volume of the adsorbent bed.

The above heavy units are usually expressed in g/cm3, kg/l, and kg/m3.

g. Porosity (εk): the ratio of the pore volume in the adsorbed particles to the volume of the particles.

Εk=Vk/(Vg+Vk)=(dg-dl)/ dg=1-dl/dg

h. Void ratio (ε): the ratio of the void between the adsorbed particles to the bulk of the adsorbent.

ε=(Vb-Vl)/Vb=(dl-db)/dl=1-db/dl