A mathematical model for the concentric-tube square-off continuous-contact countercurrent separation process with recycles at both ends is developed to predict the concentrations of product. An analytical solution is obtained by means of the orthogonal expansion method. It has been found that only the positive eigenvalues for the enriching section and the negative eigenvalues for the stripping section are required during the calculation of the concentrations of product. Numerical results are presented for the separation of a benzene-n-heptane mixture in a concentric-tube thermal diffusion column.
Separation science and technology 21(4), pp.403-419