Multicomponent Mass Transfer In Nonideal System

In this dissertation three problems are studied, the first one is the study about the relation between concentration and mass transfer coefficients, the second one is the study of multicomponent mass transfer in non-ideal systems, the last one is the study of multiple steady states in distillation processes.Many factors influence mass transfer, current practice is to lump the effects of most of variables into mass transfer coefficients. Concentration is one of variables that influence mass transfer coefficients. In this dissertation, the study about the effects of concentration on mass transfer coefficients first is developed. The non-ideal binary and multicomponent distillation experiments are carried out in a sieve tray column. Basing on the experiment data and Maxwell-Stefan(MS) equations, this dissertation set up a mathematical model used to calculate the mass transfer coefficients. The calculative results show mass transfer coefficients depends on the concentration of the vapor and liquid on the trays, therefore, it is not suitable to take the mass transfer coefficients as constancy in the design practice for non-ideal systems.In this dissertation a mathematics model used to the simulation calculation of concentration profiles in the column is set up .The model is based on MS equations, the solution of MS equations is simplified. The model set up a function used to calculate overall mass transfer coefficients, the function takes the mass transfer coefficients of the binary pair of components in systems as independent variables, and the effects of concentration on mass transfer coefficients are considered. The model includes the calculation of material balance, the vapor and liquid equilibrium compositions, the interfacial area of mass transfer, mass transfer rate. The composition values predicted by the model agree well with the experimental values in the column. Theory and experiment show that mass transfer rate of a component not only relates to the concentration gradient itself, but also relates to the concentration gradients of other components. Due to the interaction effects of components, the concentration profiles of some components in a column appear complex change.Simple distillation columns may display multiple steady states that can have different sources. In this paper, multiple steady states in input transformations have been studied. As the nonlinear transformations between refluxes, there are three steady states for output variables. The area of multiple steady states is different for different systems. When a column is operated in multiple steady state area, a small upset may bring the column to move from a normal steady state to a abnormal steady state, as a result, the outputs of the column will jump to totally different values.