Forward Osmosis as a Chemical Capacitance at Dynamic Equilibrium

The current models that describe mass transfer in Forward Osmosis (FO) process are limited, but because the process shares many similarities with pressure-driven membrane processes, e.g. reverse osmosis, models developed in that area are used. This paper presents a new approach to describe the FO process as a chemical capacitance operating under dynamic equilibrium conditions. A mechanistic model is suggested, called the Dynamic-Equilibrium Chemical-Capacitance (DECC), explains the effects of the membrane microstructure, the solution physical properties, and the solute molecular parameters, on water flux and permeability across the membranes. The theory is experimentally validated using different aqueous solutions of sodium chloride, magnesium sulphate, and glycerol. The experiments were carried out at a constant temperature (25 oC) using a cellulosic membrane. The model, which is found to be in good agreement with the experimental results, may be useful for design applications and further process development.