Crossing of boundaries in ternary azeotropic distillation: influence of interphase mass transfer

Abstract

This paper examines the influence of mass transfer on the composition trajectories in multicomponent azeotropic distillation. Simulations were carried out for five different ternary systems: methanol — isopropanol — water, water — ethanol — acetone, acetone — chloroform — methanol, acetone — chloroform — ethanol, and water — cyclohexane — ethanol. Two different models were used to calculate the composition trajectories in a tray column: an equilibrium (EQ) stage model and a rigorous nonequilibrium (NEQ) stage model based on the Maxwell-Stefan diffusion equations. The simulations show that the EQ and NEQ model trajectories could follow different composition paths and could end up in completely different corners of the composition triangular space. Futhermore, in some of the case studies the NEQ model trajectory was found to cross the distillation boundary even with the feed on the convex side or when the boundary is a straight line. The study has implications for the development of improved separation possibilities.