Do silicone- based membranes permeate or reject salts?

• Salt retention of a silicone-based membrane is up to 86% using CaCl2.
• A silicone based membrane differs from a commercial PA-based membrane with respect to solvent fluxes and NaCl retentions.
• Retentions differ between NaCl, LiCl and CaCl2 and correlate with ion pair formation.

Very little is known about the transport of aqueous ionic solutions through hydrophobic non-porous nanofiltration membranes. The comparison of well-established aqueous desalination nanofiltration phenomena to silicone-based hydrophobic nanofiltration has not been addressed until now. We investigate the salt permeation and retention in water/methanol mixtures permeating through a silicone-based composite membrane. Its retention behavior is rigorously analyzed and for some aspects compared with a hydrophilic, polyamide-based (Desal DK) membrane. In particular, the retention of NaCl, LiCl and CaCl2 in different MeOH/H2O solutions was investigated. Retentions vary between 10% and 80% depending on the composition from aqueous to methanol solutions. Ion pair formation, i.e. prohibited ion dissociation in the alcoholic solution, correlates with an increase of salt retention.

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