Mass Transport in Zeolite Membranes

Transport properties e.g. flux and selectivity) require single and mixture separation tests also for evaluating the presence of defects in the membrane structure. The permeance of a single gas through a zeolite membrane depends not only on the characteristics of the gas molecules and membrane, but also on the temperature and pressure. 

In the part A-B, the permeance increases because the mobility of the gas molecules increases. However, at a higher temperature the coverage degree of the inner surface of the membrane pores by gas molecules decreases and consequently 

The permeation follows the Knudsen diffusion and viscous flow in the mesoporous and macroporous defects, eventually present, respectively. The Knudsen mechanism is present when the pore size is smaller than the mean free path of the diffusing molecules and the collisions among molecules of gaseous species are less frequent than their collisions with the pore wall. Equation 17.1 describes the permeance when the Knudsen diffusion takes place  

The viscous flow occurs when gas molecules collide exclusively with each-another. In this case no separation can be obtained. Equation 17.2 describes the gas permeance in presence of the viscous flow  

The permeating flux (/j) is the product of permeance and driving force (APj) acting on the two membrane surface for each single chemical species  

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