Complete-Mixing Model for Gas Separation by Membranes

In Fig. 13.4-1 a detailed process flow diagram is shown for complete mixing. When a separator element is operated at a low recovery (i.e., where the permeate flow rate is a small fraction of the entering feed rate), there is a minimal change in composition. Then the results derived using the complete-mixing model provide reasonable estimates of permeate purity. This case was derived by Weller and Steiner (W4). 

The rate of diffusion or permeation of species A (in a binary of A and 5) is given below by an equation similar to Eq. (6.5-8) but which uses cm (STP)/s as rate of permeation rather than flux in kg mol/s cm . 

This equation relates yp, the permeate composition, to x , the reject composition, and the ideal separation factor a is defined as 

4B Solution of Equations for Design of Complete-Mixing Case 

For design of a system there are seven variables in the complete-mixing model (Hi), Xf, Xp, yp, 0, a, Pi/Ph, and A , four of which are independent variables. Two commonly occurring cases are considered here. 

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