Deriving osmotic pressures of draw solutes used in osmotically driven membrane processes

In osmotically driven membrane processes (ODMPs), such as forward osmosis (FO), the concentration of the draw solute and the related osmotic pressure play a critical role in mass transport and overall process performance. Search of the literature reveals that the concentration units used to describe draw solutes vary and the methods for deriving osmotic pressure from those concentrations are often unclear or not discussed. This paper recommends the use of molality and identifies the benefit of experimentally determined van’t Hoff indices when calculating osmotic pressures.

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► Critical comparison of concentration units for use in osmotic studies.
► Analysis of theoretical models for predicting osmotic pressure.
► Benefits of an experimentally determined van’t Hoff index.
► Influence of waters of hydration on osmotic pressure.
► Best practice recommendation for dealing with concentration and osmotic pressure.