What are the characteristics of homogeneous membranes or how do they differ from porous membranes?

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There are two types of separation membranes: porous and homogeneous.

NAGASEP is a homogeneous membrane separation module filled up with silicone rubber hollow fibers.

Porous membranes are permeable. They separate various components by sorting them according to the size of the pores in the membrane. Therefore, membrane fouling, a phenomenon in which membrane performance deteriorates during operation due to clogging of the pores, is likely to occur and requiremaintenance.

Homogeneous membranes, on the other hand, have no pores, so there is no need to worry about membrane fouling. Gase moleculars have a  diameter of only a few Å (10-10 m), so small that they can permeate through a homogeneous membrane without pores by the thermal motion of the polymer chains.

Permeation through a homogeneous membrane happenrs in three steps:

①dissolution of molecules at the high pressure side of the membrane

② diffusion of molecules within the membrane

③ desorption of molecules at the low pressure side of the membrane.

Solubility in the membrane increases in proportion to the size of the molecule. Thus, the larger the molecule, the greater its condensability, and this effect makes it easier to dissolve into the membrane.

Conversely, diffusivity in the membrane is generally smaller because the larger the molecules, the greater the resistance. However, silicone rubber membranes have large gaps in the polymer chains, so even gases with large molecules are not affected by diffusion velocity. The permeation rate is determined by the difference in solubility.