Polydispersity and backmixing effects in diffusion controlled mass transfer with irreversible chemical reaction: An analysis of liquid emulsion membrane processes

Abstract

The effects of polydispersity and backmixing on diffusion-controlled mass transfer with irreversible chemical reaction in liquid emulsion membrane processes have been analysed in terms of the “Advancing Front” model. Separation-of-variables is used to decouple the drop size and axial dependence effects to reduce the problem to a numerically-manageable form. In column-type contactors, it is shown that for constant Sauter mean radius, polydispersity effects arise primarily through the changes in dispersed phase hold-up caused by the distribution in globule rise velocities. For constant hold-up, an increase in Sauter mean radius causes an increase in performance despite a lowered total interfacial area, which can be attributed to the non-linear interaction between the fractional utilization of the internal reagent, the diffusional resistance to transport, and bypassing and segregation phenomena associated with the larger globules. The nonlinear dependence of the transport processes on fractional utilization of internal reagent is also responsible for the development of characteristically convex, rather than concave, concentration profiles in countercurrent operations. Polydispersity effects are evident in batch and mixer-settler operations only at large residence times, although even then they are not significant.