Limiting Cases of the Maxwell-Stefan Equations

Let us now consider some limiting cases of Eqs. 2.2.10. The first important special case is that of diffusion in a two-component mixture. In this case the n - 1 dimensional matrices reduce to scalar quantities and we have 

For ideal mixtures the activity and fugacity coefficients are unity, = 1, = 1, and, 

In many chemical engineering problems we are interested in calculating the transfer rates of a component that is present in a liquid mixture in very low concentrations. Let us identify the trace component by the subscript 1 Xj 0. This means that the coefficients Bi2 Bi3,- of [B] all reduce to zero (see Eqs. 2.1.21 and 2.1.22). Also, the matrix 

The D°j VLTe the Maxwell-Stefan diffusivities of the i-j pair where species i is present in infinitely dilute concentrations. 

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