Molecular simulation of osmosis, reverse osmosis, and electro-osmosis in aqueous and methanolic electrolyte solutions

Abstract

Computer simulations of aqueous and methanolic electrolyte (NaCl, LiCl, NaBr, LiBr) solutions undergoing osmosis, reverse osmosis, and electro-osmosis have been carried out using semi-permeable membranes. These studies used a novel technique developed by the present authors in which the atomic roughness of the membrane is preserved. In addition, the molecules that constitute the membrane are, allowed to vibrate. The effect of the important driving forces in these separations, viz., pressure, concentration, temperature and electric field strength, has been investigated. These results show that the water and methanol molecules cluster strongly around the ions in these simulations, and this plays a significant role in membrane based separations in both aqueous and methanolic solutions-an effect of which the importance was not previously recognized. In addition, studies have been made of the self-diffusion coefficients and density profiles in these systems. It has been found that external electric fields usually lead to a large measurable increase in the rate of reverse osmosis separations.