MEMBRANE TECHNOLOGY

Membranes can be seen as filters that divide a feed stream into two streams: a retentate and a permeate stream (see Fig. 1 below). Depending on which of these two is needed, both can be seen as the 'product' of the separation process.

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The actual performance of a membrane is determined by two different factors, namely its permeability and selectivity. Permeability is defined as the volume of gas flowing through the membrane per unit of area and time. The selectivity, also known as the separation factor, is determined by the difference in permeability of the components of interest (see Fig. 2 below). If, for instance, the permeability of component A is three times higher than component B, the permeate stream contains three times more of component A and the selectivity from A over B is 3.

Fig. 1: The working principle of membranes	Fig. 2: Selectivity of membranes

The permeability of gases and therefore selectivity between different gasses depends strongly on the gas and type of material used for the membrane. Membranes can be constructed from different starting materials. The two main classes in membrane science are organic membranes (e.g. plastics, carbon) and inorganic membranes (ceramics). Both classes of material have been subject of investigation in NanoGLOWA.

Out of five types of membranes, two types proved to have the most promising performance: Diffusion Transport Membranes and Fixed Site Carrier Membranes. These two types have been integrated into modules and have been used in industrial tests.