Gas separation membranes are very fine hollow fibers through

which different mixtures of gases are fed. As the gases travel

through the tubes, a process called selective permeation

(Diffusion-Sorption) allows us to separate gases using.

At a closer look, gas separation membrane, the wall of each of

these micro-thin hollow fibers, is an asymmetric filter made of

various types of polymers. As different gases travel through

the fiber, they come into contact with the membrane and

permeate through it.

The permeation rate of each gas is determined by its solubility

in the membrane material and its diffusion rate. Gases with

higher solubility and smaller molecules (fast gases) can pass

through the membrane faster than other less soluble gases with generally larger molecules (slow gases). Gases which

permeate faster and more are collected outside of the hollow

fiber as permeates while gases which do not permeate so well

and stay inside of the fiber until they reach the other end are

separated out as retentates. Depending on the properties of

the desired gas, either or both of permeates and retentates can

be used.

For instance, if we want to separate methane from carbon

dioxide for biogas upgrading, we feed biogas through the

membrane filter.Since carbon dioxide (CO2) permeates through

the membrane much faster than the heavier methane (CH4),

we get carbon dioxide concentrated out of the membrane

fiber as permeate and methane staying inside the hollow

fiber as retentate; methane is then collected at the end of the

membrane.