Nanofiltration thin-film-composite polyesteramide membranes based on bulky diols

Polyesteramide thin-film-composite (TFC) membranes have promise for diafiltration applications due to their relatively good oxidative resistance coupled with the ability to tailor the membrane rejection profile by varying the ester/amide ratio. The incorporation of ester linkages in interfacially prepared polyesteramide TFC membranes has been previously shown to increase the oxidation resistance of the membrane. It was also found that polyesteramide TFC membranes incorporating hydroquinone (HQ) or bisphenol-A (Bis-A) had high rejection for monovalent salts, i.e.,their rejection profiles matched those of reverse osmosis rather than nanofiltration membranes. We report the properties of polyesteramide TFC membranes incorporating bulky diols such as phenolphthalein (Phe) and terabromobisphenol-A (TBrBis-A). The data were used to correlate the influence of different ester functionalities on membrane flux and rejection characteristics. Membranes incorporating TBrBis-A had relatively high rejections for monovalent salts coupled with low water permeance. By contrast, membranes incorporating Phe showed 10 times higher flux and a rejection profile which appears to be of interest for diafiltration applications involving the separation of organics with molecular weight >400 gmol(-1) from low-molecular-weight organics and salts. The Phe-based membranes show rejection characteristics for monovalent and multivalent salts typical of negatively charged membranes.