Regulating the aqueous phase monomer balance for flux improvement in polyamide thin film composite membranes

• Published in: Journal of membrane science 2015-08, Vol.487, p.74-82
• Main Authors: Perera, D.H.N., Song, Q., Qiblawey, H., Sivaniah, E.
• Format: Article
• Language: English
• Subjects: Desalination; Interfacial polymerization; Reverse osmosis
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2015.03.038

Polyamide thin film composite (PA TFC) membranes are synthesized from interfacial polymerization using two amines in the aqueous phase. The conventional monomer, m-phenelynediamine (MPD), is partially replaced by a linear monomer, 1,3–diamino-2-hydroxypropane (DAHP). The water permeability of the membranes improves by around 22% (to 2.67±0.09Lm−2h−1bar−1) while keeping the same high salt rejection (96–98%) at an optimum DAHP/MPD ratio of 12.8%. While developing the control PA TFC membrane we introduce a washing step and show that the support surface should be free from surface protective coatings to achieve high water flux (2.18±0.08Lm−2h−1bar−1). Incorporating DAHP units into the polyamide network improves the water flux through the membranes fabricated on both original and washed supports. The surface morphologies of polyamide films change significantly with introduction of DAHP, from large ridge-and-valley structure to enlarged nodular structures. High resolution SEM images show an ultrathin polyamide thin film with a thickness that is reduced with addition of DAHP. These influences of DAHP, namely a reduction in the selective layer thickness, an alteration in surface morphology, changes in internal molecular packing and hydrophilicity, are suggested as factors behind the improved water permeability. [Display omitted] •We develop thin film composite (TFC) RO membranes via interfacial polymerization.•We use a blend of two aqueous phase monomers, one containing an aliphatic moiety.•Tuning the reactant blend conditions enhances water permeability.•The structural causality for the enhanced permeability is explored.•Improvement of support conditions significantly enhances TFC performances.