Example 3 Flowing Sweep Gas with Pervaporation

This example illustrates the distillation of a binary mixture in an open-batch distillery with flowing sweep gas and pervaporation by having a porous plate floating on top of the liquid hold up, as shown in Fig. 4.20. The porous plate was made from inert sintered metal with various pore sizes between 100 and 1 mfi, and had a thickness of 1 mm. The porosity was 40 % and the tortuosity factor was about 2. This results in an effective liquid phase mass transfer coefficient of about hiq = 2 X 10-7 m s-i, which results in Kiiq = 1.9 X 10 22. Therefore, one would expect the distillation process to be nonselective - that is, Si = xi - xi = 0. 

4 Thermodynamic and Kinetic Effects on the Feasible Products of Reactive Distillation 

On the left-hand side of Fig. 4.21, iso-propanol escapes preferentially. Therefore, water accumulates at the surface of the plate. This causes a two-fold instability  

Both types of convection stimulate a vivid internal fluid circulation within the porous plate, thereby reducing the liquid phase mass transfer resistance almost down to zero. This circulation becomes suppressed by friction force if the pore 

On the right-hand side of Fig. 4.21 the situation is just the opposite density and surface tension gradients are stable so that there is no internal fluid circulation. A mathematical analysis of this phenomenon has been provided in Ref. [31]. 

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