Gas separation membrane

(1) Principle of gas separation membrane

The gas membrane separation process is a process in which the gas to be separated is separated by the selective osmosis of the membrane under pressure driving (see Figure 10-29)

Figure 10-29 Schematic diagram of gas membrane separation process

Figure 10-30 Relative permeation rate of gas through membrane

People usually call the gas with faster permeation "fast gas" because it preferentially permeates through the membrane and obtains enriched permeate gas, while the gas with slower permeation is called "slow gas" because it is more retained in the raw material.

Gas permeation membrane is a relatively complicated process

Figure 10-31 Schematic diagram of the gas separation mechanism between porous membranes and non-porous membranes

Figure 10-32 Separation mechanism of polymer homogeneous membrane

Therefore, people can adjust the size and distribution of the freely generated channels by changing the chemical properties of the polymer, so as to delay the movement of one component, and allow another component to pass more, thereby achieving the purpose of separation

It can be seen from Figure 10-31 and Figure 10-32 that the separation mechanism of gas in porous membranes is mainly restricted by the pore size, while the permeation through non-porous membranes is based on the dissolution-diffusion mechanism and double absorption and double migration The mechanism proceeds

①Permeation theory of gas in porous membrane As can be seen from Figure 10-33, when gas passes through the porous membrane, its separation performance is related to the type of gas and the size of the pore size of the membrane

If the membrane pore size is smaller than the mean free path of gas molecules, convection is replaced by molecular flow (Knudsen diffusion)

As it can be seen from the above description, when the gas permeable porous membrane transfer mechanism can be divided into a molecular flow, viscous flow, surface diffusion flow, the molecular sieve screening mechanism, mechanism of capillary condensation

②Permeation theory of gas in non-porous membranes For non-porous membrane materials, there are mainly rubbery polymers and glassy polymers

③The gas permeation in the composite membrane The composite membrane is a kind of non-porous membrane, its structure is asymmetrical, and its permeation mechanism should conform to the mechanism of the non-porous membrane.

Figure 10-34 Schematic diagram of composite membrane for gas separation

Supported porous bottom membrane: This type of membrane is mainly composed of two parts.

Film forming methods mainly include thin lamination, solution casting, interfacial polymerization and plasma polymerization

Resistance type composite membrane: The resistance type composite membrane is a complete epidermal asymmetric membrane, which consists of an asymmetric base membrane and a coating

Multilayer composite type: This type of film can be regarded as an improvement of the first-type and second-type composite film