Gas Permeation Experiment Preparation

Pemeability and selectivity of membranes were detennined by using a constant volume system shown in Fig. 5.11. 

According to the method the permeability of a membrane is proportional to the rate of pressure rise and can be calculated by 

The time lag, 0, is obtained by extrapolating the p versus t straight line to the x axis. The time lag is related to the diffusion coefficient, (cm /s) of gas through the membrane by the following equation. 

Steady state permeation rate dp/dt is obtained from the slope of p versus t plot for i 10 0. Since the time lag is veiy short (0 1 min), it is difficult to determine precise diffusion coefficient. 

The cross-section of the test permeation cell used to measure the permeation rate is schematically shown in Fig. 5.12. The permeation cell consists of two stainless steel blocks (upstream side and down stream side) to sandwich a membrane in between. The two O-rings seal the gas leak through aity space between these two blocks. 

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