Separation of ternary salt/acid aqueous solutions using hollow fiber reverse osmosis

Abstract

A hollow fiber reverse osmosis system was used to separate ternary mixtures of sodium chloride and acetic acid aqueous solutions to investigate interactions between an inorganic salt and a weak organic acid which does not ionize extensively. Acetic acid rejection is enhanced and permeability is decreased by adding NaCl to the solution. Conversely, the separation of NaCl is decreased and permeability increased as the concentration of acetic acid in the mixture is increased. Furthermore, the permeability of acetic acid in the polyamide hollow fiber membrane is approximately one order of magnitude larger than that of the salt. The results suggest that it may be possible to purify etching solutions of weak acids by passing water and unionized acid through the membrane and rejecting ionized and particulate constituents. The linear relationship between the inverse of salt rejection and the inverse of solvent flux, as developed by Pusch (1977) for flat membranes and later applied by Soltanieh and Gill (1981, 1982, 1984) to hollow fiber systems on the basis of the completely-mixed model, also is valid in this case which involves ternary solutions. The coupling between the components of mixtures shown in this study may be useful in understanding better applications as diverse as treatment by the reverse osmosis of etching solutions of microelectronic industries to wastewaters from oil shale retorting, metal finishing industries and other wastes streams involving organic/inorganic mixtures.