A predictive model for ultrafiltration: Combination of osmotic pressure model and irreversible thermodynamics

An unsteady state model for ultrafiltration that describes transport within the pores of the ultrafiltration membrane is presented. The new, improved model combines the osmotic pressure model for transport in the polarization layer and the irreversible thermodynamics approach. The model is capable o f simultaneously predicting 1) the permeate flux, 2) the permeate concentra tion, and 3) the concentration at the membrane feed surface when all the tr ansport parameters are fixed. The model data are comparable to the experime ntal data cited in the literature. Model simulations conducted by varying 1 parameter while the others are kept constant show that the entire range of observed transmissions is a function of permeate flux. For certain paramet er values, the model predicts observed transmission greater than unity. Hen ce, in principle, an ultrafiltration system in which the product of interes t is concentrated in the permeate stream can be designed. The model also co rrectly predicts the experimental observation that the magnitude of observe d transmission that is greater than unity decreases as the feed concentrati on increases.