Characterization and membrane stability study for the switchable polarity solvent N,N-dimethylcyclohexylamine as a draw solute in forward osmosis

• Published in: Journal of membrane science 2016-03, Vol.501 (C), p.93-99
• Main Authors: Reimund, Kevin K., Coscia, Benjamin J., Arena, Jason T., Wilson, Aaron D., McCutcheon, Jeffrey R.
• Format: Article
• Language: English
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2015.10.039

Commercially available reverse osmosis and forward osmosis thin-film composite membranes were assessed for long-term chemical stability when immersed in 10 molal N,N-dimethylcyclohexylammonium hydrogen carbonate draw solution, a model switchable polarity solvent draw solute for forward osmosis. Membrane performance was monitored with reverse osmosis testing, including rejection of 2000ppm sodium chloride (NaCl), for three commercial reverse osmosis membranes—Dow BW30, SW30HR, and SW30HR with polyester backing layer removed—and a commercial forward osmosis membrane (HTI TFC). The RO membranes were observed to be largely unaffected by exposures up to 90 days while the HTI TFC suffered a sharp increase in both water permeance and sodium chloride permeability, manifesting itself as a reduction in intrinsic rejection of NaCl from 95% to 82%. The as-received HTI TFC membrane was characterized for osmotic water flux, where it was found the water flux was very insensitive to draw solute concentration in both the pressure-retarded osmosis and forward osmosis operating modes. Reverse permeation of the draw solute was highly variable, despite lower variability in the forward water flux. Forward osmosis desalination of a 0.5 molal sodium chloride feed with the HTI TFC membrane and 10 molal draw solution indicated higher rejection (ca. 98.7) than under reverse osmosis testing, albeit with lower flux and the presence of reverse permeation of the draw solute. The overall results imply that a forward osmosis membrane with acceptable tolerance to switchable polarity solvent draw solutions can be developed within the existing framework of polyamide-on-polysulfone membrane chemistry. [Display omitted] •We show the compatibility of TFC membranes with a switchable polarity draw solute.•Seawater membranes are not degraded while a forward osmosis membrane is.•The draw solute generates ~7.5l/m2h flux against a 0.5 molal NaCl feed.•FO desalination of 0.5 molal NaCl feed generates 99% rejection of NaCl.