Membrane Process Introduction

All membrane processes have the common feature that separation is achieved via a  membrane. The membrane can be considered to be a permselective barrier existing between two homogeneous phases. Transport through the membrane takes place when a driving force is applied to the components in the feed. In most the membrane processes the driving force is a pressure difference or a concentration (or activity) difference across the membrane. Parameters such as pressure, concentration (or activity) and even temperature may be included in one parameter, the chemical potential.

Various pressure-driven membrane processes can be used to concentrate or purity a dilute (aqueous or non-aqueous) solution. The characteristic of these processes is that the solvent is the continueous phase and that the concentration of the solute is relatively low. The particle or molecular size and chemical properties of the solute determine the structure,i.e. pore size and pore size distribution, necessary for the membrane employed. Various processes can be distinguished related to the particle size of the solute and consequently to membrane structure. These processes are microfiltration, ultrafiltration, nanofiltration and reverse osmosis.