Membrane Research for Salinity Gradient Energy Production. Final Report.

摘要

The results of an initial feasibility study of pressure retarded osmosis (PRO) as a power generation technique from various salinity gradient resources are presented. A number of flat sheet reverse osmosis membranes were evaluated including cellulose acetates, polyamide, polybenzimidazolone, and composite membranes. Reverse osmosis (RO) and direct osmosis (DO) experiments were used to predict the performance of the membranes under PRO conditions. The conclusions are: (1) concentration polarization is a major problem in PRO; (2) internal concentration polarization cannot be overcome by using brines of highly rejected salts such as magnesium sulfate; (3) useful PRO membranes do not require the ultrahigh permselectivity necessary in reverse osmosis, and a trade-off between flux and salt rejection is possible; (4) hollow fiber membranes are likely the most promising membrane geometry for two reasons: they allow control of external concentration polarization by circulation of solution on both sides of the membrane, and they are the cheapest form of membrane currently available; (5) the flux through a direct osmosis membrane using concentrated brine as the salt solution and seawater as the dilute solution is approximately half of the flux obtained when fresh water is used on the dilute side of the membrane; (6) because the operating pressures of PRO systems are lower than those used in RO, compaction of porous membranes due to hydrostatic pressure gradients is reduced; and (7) it appears that PRO is an economically viable power generation technique, provided that asymmetric (Loeb-Sourirajan-type) hollow fibers can be prepared with membrane fluxes comparable to flat sheet membranes. (ERA citation 06:007212)