Comparison of models for ternary mass transfer

Abstract

Methods for predicting ternary mass transport behaviour from information on the transport parameters of the constituent binary pairs are discussed. Experimental data obtained by Modine in a wettedwall column for mass transfer between a falling film of a binary liquid mixture containing acetone and benzene and a downward flowing vapour-gas mixture containing acetone, benzene and either nitrogen or helium are used to test three predictive transport models: 1. Model I : a multicomponent ‘film’ model based on an exact matrix method of solution to the Maxwell-Stefan equations, 2. Model II : a model utilizing the linearized theory of multicomponent mass transfer and 3. Model III : a model which assumes that acetone and benzene transfer independently of each other. For measured inlet conditions at the top of the wetted-wall column, the outlet conditions (temperatures, compositions, flows) and overall rates of transfer predicted by the three models are compared with the experimentally obtained values. It is seen that the predictions of Models I and II are reasonably close to the experimental values whereas Model III shows large deviations. The differences between the predictions of Models I and II are not found to be significant. It is concluded that for the system studied, diffusional interactions are significant and that a general treatment of multicomponent mass transfer must proceed via non-diagonal matrices of mass transfer coefficients, calculable reasonably accurately my multicomponent ‘film’ models.