Osmotic pressures. Diffusion coefficients

Membrane separation technologies (reverse osmosis, ultrafiltration, tangential microfiltration) have undergone significant development in recent years, both in laboratories and in industry. Knowledge of osmotic pressures and diffusion coefficients is essential for engineers designing or operating such processes. Osmotic pressure is essential for determining the operating pressure of a reverse osmosis unit: the choice of operating pressure will determine, on the one hand, the energy consumption of the process and, on the other, the membrane surface area and, consequently, the investment.

The diffusion coefficient can be used to calculate the flow of materials reaching the membrane, and the limiting concentrations at the membrane/solution interfaces. This makes it possible to control concentration polarization phenomena, which are often at the root of membrane clogging problems and, by the same token, plant malfunctions.

The numerical data in this article can be used to perform the calculations developed in the article Membrane separation techniques for various salt solutions. Theoretical considerations [J 2 790] of the Génie des procédés textbook.