Further results on the performance of present-day osmotic membranes in various osmotic regions

Abstract Laboratory experiments were conducted to investigate the performance of present-day osmotic membranes in osmosis, reverse osmosis (RO), and pressure-retarded osmosis (PRO). Flat-sheet membranes were tested in osmosis and RO, spiral-wound and hollow fiber minimodules were tested in RO and PRO. p]Fourteen different flat-sheet membranes from eight different manufacturers were tested to assess their relative performance in osmosis, both with and without osmotic pressure on the porous substructure side, compared to that in RO. It was found that the water permeation coefficient in osmosis is generally lower than that in RO by a factor of about 1.2 to 3.0. While there was no permanent damage to the membrane, the water permeation coefficient in osmosis decreased at high osmotic pressures with osmotic pressure on the porous substructure side. p]To determine whether a present-day spiral-wound RO module will work in PRO, tests with UOP four-port spiral-wound cellulose acetate minimodules were conducted. The experimental results show that these modules can be used in PRO; but their performance will have to be improved by about one order of magnitude for economical power generation using a salinity gradient system. p]Experiments were conducted to determine the permeation characteristics of DuPont B-9 commercial RO hollow fibers in PRO at higher temperatures with potassium alum as the solute. The water permeation coefficient in PRO with potassium alum at 50°C was only about 18% of that in RO with NaCl solution at the same temperature.