The membrane technology is applied for separation of different mixtures. Here it should be noted that there are no universal polymers, and respectively no universal membranes applicable for efficient separation of various mixtures. Manufactures produce several types of membranes depending on composition of treated mixtures, their applications and parameters (pressure, flow rate and temperature). Each manufacturer engineers its own membranes and methods in production of membrane elements and modules. Modules from the same manufacturer may differ by the type of membrane, composition and thickness of the separation layer, and this is translated into gas separation properties of the whole membrane module.