Fractionation of aqueous organic mixtures by reverse osmosis

Modern synthetic polymer membranes for reverse osmosis, although primarily developed for seawater desalination, are remarkably selective and chemically resistant in the case of organic solvents. Accordingly, reverse osmosis is increasingly employed for the treatment of industrial effluents such as solvent-contaminated waste water. In this case flux and selectivity can no longer be calculated with the simple relationships valid for seawater desalination. Semi-empirical relationships are presented, capable of quantitatively describing the local partial fluxes of organic-aqueous solutions. The relationships are based on the solution diffusion model but contain less stringent simplifying assumptions than in the case of dilute salt solutions.

Compared to empirical relationships, very few experiments are required to determine the model parameters. In combination with the differential mass and material balances, these equations are sufficient for process design. This is illustrated by a comparison of calculated results and experiments on a pilot plant scale and is even valid for quasi-binary systems.