Mass transfer coefficient is an important parameter in the calculation and design of mass transfer processes. Many variables affect the value of mass transfer coefficient. Among which

the effect of concentration has not yet been paid due attention. In an experimental column containing 6 trays

two non-ideal binary mixtures are distilled under total reflux to study the relationship between mass transfer coefficient and concentration. Based on the experimental data and Maxwell-Stefan equation

a mathematical model for calculating mass transfer coefficient is presented. The results show that mass transfer coefficient depends not only on the concentration of the vapor and liquid on the tray

but also on the concentration of the vapor and liquid on the neighboring tray. For highly non-ideal alcohol-water systems

the difference between the maximum and the minimum values of mass transfer coefficients is about an order of magnitude

therefore

the assumption of constant mass transfer coefficient in common design practice for non-ideal systems may lead to considerable error.