Mass Transfer in Heterogeneous Distillation.

Abstract

An experimental study on mass transfer in heterogeneous distillation was made with wetted-wall columns of different lengths for an ethanol-benzene-water system under total reflux conditions. The observed local diffusion fluxes obtained from the data of shorter distillation paths agree well with the theoretical values of mass transfer in a tube, but the average diffusion fluxes of longer distillation paths deviate from the theoretical ones.Simulation of heterogeneous distillation with a wetted-wall column is carried out using the theoretical diffusion flux in a tube. The predicted concentrations and reflux flow rates at the top of the column showed good agreement with the observed data of longer distillation paths obtained by a longer column. The simulation results show that a large concentration driving force causes a longer distillation path and results in a large variation along the column. Also the deviation of the average diffusion flux from the theoretical value is demonstrated and explained by being made dimensionless with the average or non-local concentration driving force. Furthermore, the length of the distillation path is affected considerably by the bottom concentration and the vapor phase Reynolds number.