Process simulation of desalination by electrodialysis of an aqueous solution containing a neutral solute

A model was developed to describe the desalination process of an aqueous solution consisting of a salt and a neutral solute using electrodialysis (ED). Under the assumption of plug flow in compartments, the ED process was analyzed in two-dimensional directions of the electric field and flow to get the differential equations of mass balance in the flow length. Then the transport equations of solutes and water through the membrane were deduced by the irreversible thermodynamics approach. Under the limited condition of uniform current density, the model composed of a first-order differential equation set was developed. While the model parameters such as transport coefficients, dimensions of ED equipment, operation conditions and characteristics of solutes are given, the model was solved by the numerical method. The variations of current density, concentrations of solutes and velocities in dilute and concentrated compartments vs. flow length can be simulated by the model. While there was no neutral solute, the model was used to simulate the desalination process of a salt solution. By comparing the ED experiments to the simulations, it is shown that the model is well suited to describe the actual desalination process. The effects of the initial values of variables in the model on the desalination process were simulated to attempt to construct the actual ED process; and the general simulation of desalination process can be realized by the model. While the effect of concentration polarization on the desalination process is reflected by the variation of membrane conductivity, the model was verified to describe the ED process successfully under low velocity.

A more universal model was developed to describe the desalination process of an aqueous solution consisting of a salt and a neutral solute by the ED method. Based on the analysis of the ED process in two-dimensional directions of electric field and flow, the differential equations of mass balance and volume variation with the flow length were obtained. Then the transport equations of solutes and water through the membrane were deduced by the irreversible thermodynamics approach. Under the limited condition of uniform current density, a model composed of a first-order differential equation set was deduced. While the values of model parameters, the initial values of variables and the target value of the model were set, the equation set was solved. The variations of the concentrations of solutes and the current density in the ED process can be simulated by the model. Comparisons of the simulations with experiments show the validity of the model to simulate ED processes. Then the effects of the initial value of variables in the model on the desalination process of an aqueous solution without a neutral solute is discussed to construct the actual production. Through the model, the actual ED process in continuous and batch modes can be described. Finally, the model was verified under low velocities while considering the phenomena of concentration polarization.