Balance Equations for Molecular Distillation

Abstract

We have derived balanced equations for continuous molecular (short-path) distillation of a binary mixture in a falling film evaporator. The relation of heat and mass transfer in liquid films on both the evaporating and condensing surfaces were taken into account, as well as the mass transfer in the vapor phase in the distillation gap. Individual balance equations were coupled by boundary conditions into a closed set of partial differential equations. By introducing the streams, we have transformed partial differential equations into the simple form of ordinary differential equations. These were solved numerically or approximately for some selected problems in isothermal (e.g., for turbulent film on evaporation surface) and nonisothermal regimes and for the influence of reevaporation from the condenser. These developed mathematical formulations can be used to model various operational situations in a molecular evaporator or to evaluate the influence of some parameters on the molecular distillation process.